MEMBRANE ENHANCED REACTOR

REACTEUR A MEMBRANE AMELIORE

English Abstract

A hydrogen producing reactor is disclosed. The hydrogen producing reactor has
a reaction chamber containing a catalyst bed adapted to produce reaction
products containing hydrogen from a hydrogen-producing feedstock. The reaction
chamber also includes a hydrogen-selective, hydrogen-permeable gas separation
module adapted to receive the reaction products from the catalyst bed and to
separate a product stream containing hydrogen from the reaction products. The
gas separation module comprises a porous substrate, an intermediate layer
located at the porous substrate, and a hydrogen-selective membrane overlying
the intermediate layer. The intermediate layer comprises particles and a
binder metal, where the binder metal is distributed through out the
intermediate layer. A steam reforming process is also disclosed using the
disclosed reactor.

French Abstract

La présente invention concerne un réacteur produisant de l'hydrogène. Ce réacteur produisant de l'hydrogène possède une chambre de réaction contenant un lit de catalyseur conçu pour produire des produits de réaction contenant de l'hydrogène à partir d'une alimentation produisant de l'hydrogène. Cette chambre de réaction comprend aussi un module de séparation de gaz perméable à l'hydrogène et sélectif d'hydrogène conçu pour recevoir les produits de réaction du lit de catalyseur et pour séparer un flux de produits contenant de l'hydrogène des produits de réaction. Le module de séparation de gaz comprend un substrat poreux, une couche intermédiaire située au niveau du substrat poreux et, une membrane sélective d'hydrogène recouvrant la couche intermédiaire. Cette couche intermédiaire comprend des particules et un métal lieur, ce métal lieur étant distribué à travers la couche intermédiaire. Cette invention concerne aussi un processus de reformage de flux utilisant le réacteur de l'invention.

Claims

CLAIMS

1. A reactor, comprising:
a) ~a reaction chamber comprising:
a catalyst bed adapted to produce reaction products comprising
hydrogen gas from a hydrogen-producing feedstock; and
b) ~at least one hydrogen-selective, hydrogen-permeable gas separation module
adapted to receive the reaction products from the catalyst bed and to
separate the reaction products into (1) a product stream comprising
hydrogen and (2) a byproduct stream, wherein the gas separation module

comprises:
(i) ~a porous substrate;
(ii) ~an intermediate layer at the porous substrate that comprises
particles and a binder metal, wherein the binder metal is distributed
throughout the intermediate layer; and
(iii) ~a hydrogen-selective membrane, wherein the hydrogen-selective
membrane overlies the intermediate layer.

2. A steam reforming process for the production of hydrogen, comprising:
(a) ~reacting steam with a hydrogen-producing feedstock at a temperature of
from
200°C to 700°C and at a pressure of from O.1MPa to about 20.0
MPa in a steam reforming
reaction chamber containing a reforming catalyst to produce a mixture of
primarily
hydrogen and carbon dioxide, with a lesser amount of carbon monoxide; and
(b) ~separating hydrogen from the mixture produced by the reforming reaction
with
a hydrogen-selective, hydrogen-permeable gas separation module; wherein the
gas
separation module comprises:
(i) ~a porous substrate;
(ii) ~an intermediate layer at the porous substrate that
comprises particles and a binder metal, wherein the binder metal is
distributed throughout the intermediate layer; and
(iii) ~a hydrogen-selective membrane, wherein the hydrogen-selective
membrane overlies the intermediate layer.

3. The reactor of claim 1 or process of claim 2 wherein the intermediate layer
of the gas
separation module comprises at least two sub-layers of particles and binder
metal.



53




4. The reactor or process of any of claims 1-3 wherein at least one
distributed combustion
chamber is in a heat transferring relationship with said catalyst bed.

5. The reactor or process of any of claims 1-4 wherein the gas separation
module is a tube.

6. The reactor or process of any of claims 1-5 wherein the intermediate layer
of said gas
separation module comprises a gradient of particle size from a surface of the
intermediate
layer proximate to the porous substrate to a surface of the intermediate layer
distal to the
porous substrate.

7. The reactor or process of any of claims 1-6 wherein a metal hydride
precursor is
separated from said reaction chamber by said gas separation module, said metal
hydride
precursor being in gaseous fluid communication with said gas separation
module, where
said metal hydride precursor is located to react with hydrogen permeating said
gas
separation module to form a metal hydride.

8. The reactor or process of any of claims 1-7 wherein the hydrogen-selective
membrane is
formed of palladium or an alloy thereof with at least one of the metals
selected from the
group consisting of copper, silver, gold, platinum, ruthenium, rhodium,
yttrium, cerium and
indium; and the porous substrate is a porous ceramic substrate or a porous
metal substrate
selected from the group consisting of stainless steel, an alloy comprising
chromium and
nickel, a nickel based alloy, and an alloy comprising chromium, nickel, and
molybdenum.

9. The reactor or process of any of claims 1-8 wherein the binder metal is a
hydrogen-
selective hydrogen-permeable metal or an alloy thereof.

10. The reactor or process of any of claims 1-9 wherein the particles of the
intermediate
layer are selected from the group consisting of metal particles, metal oxide
particles
including aluminum oxide particles, ceramic particles, zeolite particles, and
combinations
thereof.

11. The reactor or process of any of claims 1-10 wherein the particles of the
intermediate
layer are a preactivated powder.

12. The reactor or process of any of claims 1-11 wherein the intermediate
layer has an
average thickness of from 0.3 micrometers to 3 micrometers.

13. The reactor or process of any of claims 1-12 further comprising additional
particles
deposited over the particles and binder metal and additional binder metal
deposited onto
the additional particles.

14. The reactor of claim 1 wherein the reactor is a steam reforming reactor
and the catalyst
bed is a steam reforming catalyst bed.



54




15. The reactor of claim 1 wherein the reactor is a dehydrogenation reactor
and the
catalyst bed is a dehydrogenation catalyst bed.

16. An integrated steam reforming reactor-hydrogen fuel cell comprising the
reactor of
claim 1 wherein the product stream containing hydrogen is delivered from the
reactor to an
anode compartment of a hydrogen fuel cell and the byproduct stream from the
reactor is
delivered to a cathode compartment of the hydrogen fuel cell.

Description

CA 02580580 2007-03-13
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MEMBRANE ENHANCED REACTOR

Field of the Invention
This invention relates to reactor containing a high temperature gas separation
membrane suitable for high temperature production and separation of product
gases. The
invention further relates to a process for producing a high purity gaseous
product using said
reactor.
Background of the Invention
Purified hydrogen is an important fuel source for many energy conversion
devices.
For example, fuel cells use highly purified hydrogen to produce electricity.
Chemical
processes, such as steam reforming, are usually operated at high temperature
and produce
hydrogen as well as certain by-products and impurities. Subsequent
purification processes
are required to remove the undesirable impurities to provide hydrogen
sufficiently purified
for certain applications, such as a fuel cell.
A majority of the hydrogen-producing chemical processes and subsequent
processes of hydrogen purification occur in separate apparatus. It is
advantageous to have
a single, compact and more economical apparatus which combines a hydrogen-
production
reactor, such as a steam reformer, with a hydrogen separation and purification
device
which is operable at high temperature.
U.S. 5,997,594, issued December 7, 1999, discloses a steam reformer which
contains a hydrogen purification palladium metal membrane module.
Typical hydrogen-selective metal membranes used in hydrogen gas separation
modules must be free of defects and/or pinholes that breach the metal layer to
prevent the
migration of undesired gases through the metal membrane. Thick hydrogen-
selective
metal membranes, e.g., palladium membranes, generally are very expensive.
Porous
substrates used in the fabrication of composite gas separation modules can
have broad pore
size distributions and/or rough surfaces such that thick gas-selective
membranes can be
needed to effectively separate gases. Generally, as the thickness of the gas-
selective
membrane increases, gas flux through the gas separation module decreases.
However, in
ordinary metal membranes operated at high temperature, intermetallic diffusion
between
the porous substrate and metal membrane will occur. This diffusion will cause
deterioration of the hydrogen flux. Therefore, a need exists for a hydrogen
gas separation

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module which is durable for a high temperature operation by preventing
intermetallic
diffusion while being thin enough to provide sufficiently high fluxes of
hydrogen gas.
Typical reactors operated at high temperatures usually are made of metals
which
would withstand high temperature for producing hydrogen and high pressure and
which are
relatively expensive. It would be desirable if lower temperatures could be
used so that
lower-cost metallurgy can be utilized for the reactor. Therefore, there is a
need for
providing for the reactors with more uniform heating and having more control
over
temperatures at various points to avoid hot spots.
Furthermore, it would be desirable in the art to provide an integrated
hydrogen-
production and purification reactor design for producing high purity hydrogen
having
carbon and carbon oxides separated while having minimal production of NOX
within the
integrated reactor. It would also be desirable to provide the modularity
needed at bulk-
hydrogen production scales so that a producer can match the desired capacity
by installing
multiple reactor units of the specific design. This is more cost-effective
than either trying
to scale up or down the existing large box furnace reactor designs or building
several
thousand single-tube reactors. It would also be desirable to employ less
volume than
conventional processes by intensifying the process and using less catalyst and
smaller
heater space. Furthermore, if the process produced CO2 in higher
concentrations and
greater purity than other processes in the art, and the CO2 could be
sequestered for other
uses, it would be extremely desirable: Such an integrated system would
demonstrate far
greater efficiency than any power generating system currently available.

SummarYof the Invention
In one embodiment, the present invention is directed to a reactor, comprising:
a) a reaction chamber comprising:
a catalyst bed adapted to produce reaction products comprising hydrogen
gas from a hydrogen-producing feedstock; and
b) at least one hydrogen-selective, hydrogen-permeable gas separation module
adapted to receive the reaction products from the catalyst bed and to
separate the reaction products into (1) a product stream comprising
hydrogen and (2) a byproduct stream, wherein the gas separation module
comprises:
(i) a porous substrate;
(ii) an intermediate layer at the porous sub
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strate that comprises particles and a binder metal, wherein the binder metal
is distributed
throughout the intermediate layer; and
(iii) a hydrogen-selective membrane, wherein
the hydrogen-selective membrane overlies the
intermediate layer.
In another embodiment, the present invention is directed to a steam reforming
process for the production of hydrogen, comprising:
(a) reacting steam with a hydrogen-producing feedstock at a temperature of
from
200 C to 700 C and at a pressure of from 0.1MPa to about 20.0 MPa in a steam
reforming
reaction chamber containing a reforming catalyst to produce a mixture of
primarily
hydrogen and carbon dioxide, with a lesser amount of carbon monoxide; and
(b) separating hydrogen from the mixture produced by the reforming reaction
with
a hydrogen-selective, hydrogen-permeable gas separation module; wherein the
gas
separation module comprises:
(i) a porous substrate;
(ii) an intermediate layer at the porous substrate that comprises particles
and a binder metal, wherein the binder metal is
distributed throughout the intermediate layer; and
(iii) a hydrogen-selective membrane, wherein
the hydrogen-selective membrane overlies the intermediate layer.
Brief Description of the Drawings
Figure 1 is a schematic diagram of the novel hydrogen producing reactor with
catalyst section, and a hydrogen gas separation tube placed in order from the
outside in.
Figure 2 is a schematic diagram of one of the configurations of the hydrogen
gas
separation tubes useful for the present hydrogen-producing reactor and
process.
Figure 3A, EB, 3C, 3D, and 3E are cross-section representations of various
composite hydrogen gas separation modules in the present reactor.
Figure 4 is schematic diagram of a multi-tubular, distributed combustion
heated,
radial flow, membrane, steam reforming reactor in accordance with the
invention. Some of
the inlet and outlet streams of the membrane and distributed combustion tubes
have been
omitted for simplicity.

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Figure 5 is a cross section of the shell of the multi-tubular, distributed
combustion
heated, radial flow, membrane reactor shown in Figure 4.
Figures 6A and 6B are schematic diagrams of a "closed ended" and of an "open
ended" distributed combustion ("DC") tubular chamber used to drive the
reforming
reactions in the process and apparatus of the present invention.
Figure 7 is a schematic diagram of a multi-tubular, DC heated, axial flow,
membrane steam reÃorming reactor in accordance with the invention.
Figures 8 is a cross section of the shell of the multi-tubular, distributed
combustion
heated, axial flow, membrane reactor shown in Figure 7.
Figures 9A & 9B and 9C & 9D are schematic diagrams of two baffle
configurations
which can be employed to increase the contact of the reactant gases with the
catalyst in a
multi-tubular, distributed combustion-heated, axial flow, membrane reactor in
accordance
with the invention.
Figures 10, 11, 12, and 13 are top cross section views of the shells of other
embodiments of the multi-tubular, distributed combustion heated, axial flow,
membrane,
steam reforming reactors of the invention.
Figure 14 is a simplified flow diagram of the distributed combustion membrane
steam reformer fuel hybrid power system.
Detailed Description of the Invention
The invention relates to a membrane-enhanced reactor which comprises a
reaction
chamber and a gas separation module. The present invention provides a new
apparatus and
process for producing high purity hydrogen from a hydrogen producing
feedstock, said
process being accomplished in one reactor, constantly removing pure hydrogen,
and
optionally using distributed combustion as a heat source which provides great
improvements in heat exchange efficiency and load-following capabilities to
drive the
steam reforming reaction. The hydrogen-selective gas separation module has a
thinner
dense gas-selective membrane producing higher rates of gas flux, e.g. hydrogen
flux, while
durability (such as with reduced diffusion of substrate components), hydrogen
permeation
as well as selectivity are maintained or improved. In another embodiment, the
invention is
also a zero emission hybrid power system wherein the produced hydrogen is used
to power
a high-pressure internally or externally manifold fuel cell, such as a molten
carbonate fuel
cell. The design can be a membrane steam reforming reactor (MSR) fueled'hybrid
system
that makes it possible to capture high concentrations of CO2 for sequestration
or use in

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other processes. Finally, the design of the system may be scaled down to a
mobile,
lightweight unit.
Moreover, at bulk-hydrogen production scales, a multi-tubular (multiple
distributed
combustion tubes and/or multiple hydrogen selective and permeable membrane
tubes)
containing reactor disclosed herein provides the modularity needed. A producer
can match
the desired capacity by installing multiple reactor units of the specific
design or having
multiple distributed combustion tubes and/or multiple hydrogen selective and
permeable
membrane units in a large steam reformer. This is more cost-effective than
either trying to
scale up or down the existing large box furnace reactor designs or building
several
thousand single-tube reactors.
The hydrogen-producing reactor of the present invention comprises a) reaction
chamber comprising:(i) an inlet adapted to receive a hydrogen-producing
feedstock, and
(ii)a catalyst bed for producing reaction products comprising hydrogen gas
from the
hydrogen-producing feedstock; and b)at least one hydrogen selective, hydrogen
permeable
composite gas separation module adapted to receive the reaction products from
the catalyst
bed and to separate the reaction products into (1) a product stream comprising
a major
amount of hydrogen and (2) a by-product stream; wherein the composite gas
separation
module comprises: (i) a porous substrate, (ii) an intermediate layer at the
porous substrate
that comprises particles and a binder metal, wherein the binder metal is
uniformly
distributed throughout the intermediate layer; and (iii) a dense gas-selective
membrane,
wherein the dense gas-selective membrane overlies the interrnediate layer. In
one
particular embodiment, the composite gas separation module is made by a
process
comprising the steps of.= 1) depositing a preactivated powder over a porous
substrate; 2)
depositing a binder metal onto the preactivated powder; and 3) depositing a
dense gas-
selective membrane to overlie the preactivated powder and binder metal,
thereby forming
the composite gas separation module. In a particular embodiment, the
intermediate layer
comprises a gradient of particle size from a surface of the intermediate layer
proximate to
the porous substrate to a surface of the intermediate layer distal to the
porous substrate.
Non-limiting illustrative examples of the hydrogen-producing feedstock include
natural gas, methane, ethyl benzene, methanol, ethane, ethanol, propane,
butane, light
hydrocarbons having 1-4 carbon atoms in each molecule, light petroleum
fractions
including naphtha, diesel, kerosene, jet fuel or gas oil, and hydrogen, carbon
monoxide and
mixtures thereof.

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In a particular embodiment, the catalyst bed contains baffles in a form
selected
from the group consisting of (i) washers and disks, and (ii) truncated disks.
In a particular embodiment, the reactor is suitable for a dehydrogenation
reaction
and has a dehydrogenation chamber containing a dehydrogenation catalyst bed
with a
dehydrogenation catalyst such as an iron-oxdide-containing catalyst. The
invention also
relates to a process for the dehydrogenation of ethylbenzene comprising the
steps of
feeding ethylbenzene into the reactor as described above to produce styrene
and hydrogen.
The reactor can be a steam-reforming reactor wherein the reaction chamber is a
steam reforming reaction chamber comprising a catalyst bed comprising a steam
reforming
catalyst. In another embodiment, the present invention also relates to a steam
reforming
process comprises the steps of reacting a hydrogen-producing feedstock and
steam in a
reactor as described above. The steam reforming process for the production of
hydrogen
can comprise the steps of a) reacting steam with a hydrogen-producing
feedstock at a
temperature of from about 200 C to about 700 C and at a pressure of from about
1 bara
(absolute) to about 200 bara (absolute) in a steam reforming reaction chamber
containing a
reforming catalyst to produce a mixture of primarily hydrogen and carbon
dioxide, with a
lesser amount of carbon monoxide; and b) conducting said reaction in the
vicinity of at
least one hydrogen-permeable, hydrogen-selective membrane tube, whereby
hydrogen
formed in said reaction zone permeates through said hydrogen selective
membrane tube
and is separated from said carbon dioxide and carbon monoxide; wherein the
hydrogen
selective, hydrogen permeable membrane tube is made of a composite gas
separation
module as described herein. In a particular embodiment, the carbon dioxide
produced from
said steam reforming chamber may have a pressure of from about 0.1 to about 20
MPa,
particularly from about 1 to about 5 MPa, and the carbon dioxide produced from
the steam
reforming chamber has a concentration of from about 80% to about 99% molar dry
basis,
or of from about 90% to about 95% molar dry basis. In a particular embodiment,
the
carbon dioxide produced from the steam reforming chamber is used at least in
part for
enhanced recovery of oil in oil wells or enhanced recovery of methane in coal
bed methane
formations.
In some embodiments, the afore-mentioned hydrogen-producing reactors,
including
the steam reformer and dehydrogenation reactor, further comprise at least one
heater
comprising a distributed combustion chamber in a heat transferring
relationship with the
catalyst bed. The distributed combustion chamber comprises an inlet and a flow
path for

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an oxidant, an outlet for combustion gas, and a fuel conduit having an inlet
for fuel and a
plurality of fuel nozzles or openings which provide fluid communication from
within the
fuel conduit to the flow path of said oxidant. The plurality of fuel nozzles
or openings are
sized and spaced along the length of said fuel conduit to avoid hot spot
formation when the
fuel is mixed with said oxidant in said distributed combustion chamber. In one
embodiment, the distributed combustion does not form any flame when the fuel
is mixed
with said oxidant in said distributed combustion chamber and during its
heating operation.
The distributed combustion heater(s) may also have a preheater capable of
preheating the
oxidant, such as air or oxygen, to a temperature that when said fuel and said
oxidant are
mixed in the distributed combustion chamber, the temperature of the resulting
mixture of
said oxidant and fuel exceeds the autoignition temperature of said mixture. In
some other
embodiments, the ratio of the surface area of said distributed combustion
chambers to the
surface area of said membrane tubes is from about 0.1 to about 20.0,
particularly from
about 0.2 to about 5.0, more particularly from about 0.5 to about 5.0, and
still more
particularly from about 0.3 to about 3.0 and even more particularly from about
1.0 to about
3Ø In still some other embodiments, the distributed combustion chamber may
have an
external tubular dimension such that the length to diameter ratio is higher
than 4, or higher
than 10.
As a particular embodiment, the hydrogen-selective, hydrogen-permeable
composite gas separation module is connected to a section containing a metal
hydride
precursor, and the hydrogen formed in the reforming chamber permeates through
the gas
separation module to the section containing the metal hydride precursor which
reacts with
the permeated hydrogen to form hydride. This reaction reduces the effective
partial
pressure of hydrogen in the permeate stream and drives the equilibrium within
the reaction
chamber to produce more hydrogen from the feedstock.
In some embodiments, the reactor may contain multiple distributed combustion
chambers and/or multiple hydrogen separation tubes. In some embodiments, the
products
produced are separated by hydrogen-selective, hydrogen-permeable hydrogen
separation
membrane tube(s) having a ratio of length to diameter of less than about 500,
wherein gaps
between the membrane tubes are from about 1/4 inch (about 0.64 cm) to about 2
inches
(about 5.08 cm), and gaps between the membrane and distributed combustion
("DC") tubes
are from about'/4 inch (about 0.64 cm) to about 2 inches (about 5.08 cm); or
the hydrogen-
selective and hydrogen-permeable membrane tube(s) have a ratio of length to
diameter of

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less than about 250, wherein gaps between the membrane tubes are from about %a
inch
(about 1.27 cm) to about 1 inch (about 2.54 cm), and gap between the membrane
and DC
tubes is from about %z inch (about 1.27 cm) to about 1 inch (about 2.54 cm).
In some embodiments, a sweep gas is used to promote the diffusion of hydrogen
through the hydrogen separation module. The sweep gas can be, but is not
limited to,
steam, carbon dioxide, nitrogen and condensable hydrocarbon.
In some embodiments, the hydrogen-selective membrane is palladium or an alloy
thereof and the porous substrate is a porous metal substrate or a porous
ceramic substrate.
Non-limiting illustrative examples of the palladium alloy include alloys of
palladium with
least one of the metals selected from the group consisting of copper, silver,
gold, platinum,
ruthenium, rhodium, yttrium, cerium and indium. Illustrative non-limiting
examples of the
porous metal substrate include (i) stainless steel, (ii) an alloy comprising
chromium and
nickel, (iii) a nickel-based alloy, (iv) an alloy comprising chromium, nickel
and
molybdenum, (v) porous Hastelloy , and (vi) porous Inconel.
In a particular embodiment, the composite gas separation module is made by a
process further comprising the step of treating the composite gas separation
module with
hydrogen gas at a temperature of up to about 250 C.
In another particular embodiment, the particles or the preactivated powder
have an
average diameter ranging from about 0.01 to about 5 micrometers. As used
herein, the

term micron(s) means micrometer(s).
In some embodiments, the binder metal is a hydrogen selective metal or an
alloy
thereof. In some embodiments, the particles are selected from the group
consisting of metal
particles, metal oxide particles, ceramic particles, zeolite particles, and
combinations
thereof; and the preactivated powder is selected from the group consisting of
preactivated
metal powders, preactivated metal oxide powders, preactivated ceramic powders,
preactivated zeolite powders, and combinations thereof. In a particular
embodiment, the
particles comprise aluminum oxide particles and the preactivated powders
comprise
preactivated alumiinum oxide particles. In certain embodiments, the
intermediate layer has
an average thickness of at least about 0.01 micrometers or from about 1 to
about 3
micrometers. In a particular embodiment, the composite gas separation module
is made by
a process further comprising the step of: a) depositing an additional
preactivated powder
over the deposited preactivated powder and binder metal; and b) depositing an
additional
binder metal onto the additional preactivated powder; wherein the dense gas-
selective

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membrane is deposited to overlie the additional preactivated powder and the
additional
binder metal. In a particular embodiment, the additional preactivated powder
has an
average particle size that is smaller than the average particle size of the
preactivated
powder. In some embodiments, the preactivated powder has an average particle -
diameter
ranging from about 0.3 to about 3 micrometers, and the additional preactivated
powder has
an average particle diameter ranging from about 0.01 to about 1 micrometer. In
a
particular embodiment, the powder is surface activated by seeding the powder
with nuclei
of a hydrogen-selective metal to form the preactivated powder.
In some embodiments, the composite gas separation module is made by a process
further comprising the step of (i) oxidizing the surface of the porous metal
substrate prior
to depositing the preactivated powder, (ii) depositing a powder over the
porous substrate
prior to depositing the preactivated powder, (iii) exposing porous substrate
anchoring sites
following deposition of the preactivated powder over the porous substrate,
(iv) exposing
porous substrate anchoring sites prior to applying the dense gas-selective
membrane, (v)
surface activating the deposited preactivated powder and binder metal prior to
depositing
the dense gas-selective membrane, or (iii) the combination thereof. In a
particular
embodiment, the gas separation module or membrane tube further comprises a
layer of
particles underlying the intermediate layer wherein a binder metal is not
uniformly
distributed.
In some embodiments, the hydrogen flux through the module is at least about 4
Nm3/ma-hr, particularly at least about 10 Nm3/m2-hr, and more particularly at
least about
28 Nm3/mz-hr at about 350 C and with a hydrogen partial pressure difference of
about 1
bara (absolute)(0. 1 MPa (absolute)) in the permeate side and 2 bara
(absolute) (0.2 MPa
(absolute)) in the process side.
In one embodiment, the present invention relates to a distributed combustion
heated, membrane, dehydrogenation reactor comprising:
a) a dehydrogenation chamber containing a catalyst bed, said dehydrogenation
chamber having an inlet for vaporizable hydrocarbon, a flow path for
hydrogen and product gases resulting from the dehydrogenation reactions
taking place in said dehydrogenation chamber and an outlet for said product
gases,
b) at least one distributed combustion chamber in a heat transferring
relationship with said catalyst bed whereby a distributed, controlled heat
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flux is provided by said distributed combustion chamber to said catalyst
bed, said distributed combustion chamber comprising an inlet and a flow
path for an oxidant, an outlet for combustion gas and further comprising a
fuel conduit having an inlet for fuel and a plurality of fuel nozzles which
provide fluid communication from within the fuel conduit to the flow path
of said oxidant, said plurality of fuel nozzles being sized and spaced along
the length of said fuel conduit so that no flame results when said fuel is
mixed with said oxidant in said distributed combustion chamber;
c) a preheater capable of preheating said oxidant to a temperature that when
said fuel and said oxidant are mixed in said distributed combustion
chamber, the temperature of the resulting mixture of said oxidant and fuel
exceeds the autoignition temperature of said mixture; and
d) at least one hydrogen-selective, hydrogen-permeable, membrane tube in
contact with said catalyst bed, said membrane tube having an outlet
whereby hydrogen formed in the dehydrogenation chamber permeates into
said membrane tube and passes through said outlet.
In the present invention, heat transfer limitations are overcome by the
innovative
use of distributed combustion (distributed combustion) as the primary heat
source.
Distributed combustion is used to distribute heat throughout the reactor at
high heat fluxes
without high temperature flames and with low NOX production. This is achieved
by
injecting small quantities of fuel into a preheated air stream and reaching
autoignition
conditions. Fuel quantity is controlled by nozzle size, the -temperature rise
is very small,
and there is much reduced or substantially no hot spots such as flame
associated with the
combustion (combustion is kinetically limited, rather than mass-transfer
limited).
Distributed combustion is disclosed in U.S. 5,255,742, U.S. 5,862,858,
U.S. 5,899,269, U.S. 6,019,172, and EP 1 021 682 B1.
An important feature of the distributed combustion is that heat is removed
along the
length of the combustion chamber so that a temperature is maintained that is
significantly
below what an adiabatic combustion temperature would be. This almost
eliminates
formation of NOX, and also significantly reduces metallurgical requirements,
thus
permitting the use of less expensive materials in construction of equipment.
Generally, distributed combustion involves employing a fuel conduit having an
inlet for fuel and a plurality of fuel nozzles or openings which provide fluid



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communication from within the fuel conduit to the flow path of said oxidant.
The plurality
of fuel nozzles or openings are sized and spaced along the length of said fuel
conduit to
avoid hot spot formation when the fuel is mixed with said oxidant in said
distributed
combustion chamber. It also involves preheating combustion air and fuel gas
(e.g.,
methane, methanol, hydrogen and the like) sufficiently such that when the two
streams are
combined the temperature of the mixture exceeds the autoignition temperature
of the
mixture, but to a temperature less than that which would result in the
oxidation upon
mixing, being limited by the rate of mixing. Preheating of the combustion air
and fuel
streams to a temperature between about 1500 F (about 815 C) and about 2300 F
(about

1260 C) and then mixing the streams in relatively small increments will result
in
distributed combustion to avoid hot spots, such as flames. For some fuels such
as
methanol, preheating to a temperature above about 1000 F about (about 537 C)
is
sufficient. The increments in which the fuel gas is mixed with the combustion
gas stream

preferably result in about a 20 (about 11 C) to about 200 F (about 111 C)
temperature rise
in the combustion gas stream due to the combustion of the fuel.
With most hydrogen-producing, such as steam methane reforming, controlling the
temperature in the catalyst bed is a problem. The advantages of the
distributed combustion
as a heat source in the present process and apparatus can be summarized as
follows:

= DC helps maintain a more uniform temperature, but simultaneously controls
heat flux
to match the local heat needed for the material left to be reacted. At the
highest heat
flux there is as much heat present as can be accommodated by the reaction and
as the
process progresses less and less heat is required to drive the reaction.

= DC has a lower maximum-temperature combustion gas.
= DC does not have hot spots which might damage the hydrogen-selective,
hydrogen-
permeable membrane.

= DC has a negligible NOX production.
= DC makes it easier to tailor axial heat flux distribution to minimize
entropy production
or energy loss and, thus, making it more efficient.

= DC permits a more compact reactor design that is less expensive to build.
= DC permits a modular reactor design, at a wide range of sizes and heat
duties.
= DC provides a tapered heat flux profile.

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Thus, the distributed combustion (DC) used to drive the steam reforming
reactions
in the present invention can be described as comprising:
a) preheating either a fuel gas or oxidant or both to a temperature that
exceeds the
autoignition temperature of the mixture of the fuel gas and oxidant when they

are mixed;
b) passing said fuel gas and oxidant in into a heating zone which is in heat
transferring contact along a substantial portion of the reaction zone (i.e.,
the
zone in which said reforming reactions take place); and
c) mixing the fuel gas and oxidant in said heating zone in a manner that
autoignition occurs, resulting in combustion without high temperature hot
spots
such as flames, thereby providing uniform, controllable heat to said reaction
zone.
In the practice of the invention, some degree of sulfur removal will probably
be
necessary to protect the palladium material making up the hydrogen-permeable
separation
membrane and the Ni reforming catalyst. Sulfur is a temporary poison to such
catalysts, but
the catalyst activity can be regenerated by removing the source of sulfur. The
sulfur
tolerance of commercial reforming catalysts is dependent upon process
conditions. On
average, sulfur must be reduced to below 10 ppb to allow the catalyst to
function properly.
Feed clean up with ZnO beds or by other means known in the art may be used to
remove impurities such as H2S and other sulfur containing compounds in the
feed that
could contribute to membrane degradation. For heavier hydrocarbons, like
naphtha, some
hydrotreating may be necessary to convert organic sulfur to H2S, as known in
the art.
Heavy oil, solids carried by liquid water, oxygen, amines, halides, and
ammonia are also
known poisons for palladium membranes. Carbon monoxide competes with hydrogen
for
active surface sites, thus reducing the hydrogen permeability by 10% at 3-5
Bar (0.3-0.5
MPa). Thus, the partial pressure needs to stay low for best performance, as is
the case in
our preferred design.
In another embodiment of the present invention the pure hydrogen generated by
the
present reactor and process is used in an integrated design to power a fuel
cell such as high
pressure molten carbonate fuel cell, PEM (proton exchange membrane) fuel cells
or SOFC
(solid oxide fuel cells) and the like. This embodiment of the present
invention has the
potential for about 71% or greater efficiency in the generation of electricity
from starting
fuel. In addition, due to the unique integration of the system, CO2 is
produced in high

12


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concentrations from about 80% to about 95% molar dry basis, and high pressure
of from
about 0.1 to about 20 MPa, particularly from about 1 to about 5 MPa, and is
easier to
separate from nitrogen, which makes the system even more efficient.
Referring now to Figure 14, a hydrogen-producing feedstock such as vaporizable
hydrocarbon and steam 5 are fed into the catalyst section 4 of a DC-membrane
reactor of
the type described in Figure 1, while preheated air 7 and fuel 14 are fed into
the DC
heating section 2 of the reactor containing fuel tubes 10. A sweep gas (in
this case steam)
is fed into the DC-membrane reactor at 6. The produced high purity hydrogen
stream 12,
is directed to the anode compartment of the molten carbonate fuel cell, 20,
operating at

about 650 C and 5 Bar (0.5 MPa). The reactor effluent 13 containing the
unreacted steam,
CO2 and low quantities of methane, hydrogen and CO, and the flue gas 11 from
the DC
heater and air, 16 are fed to the cathode compartment of the same fuel cell,
17. The CO2
reacts with the 02 to form C03 anions that transport through the molten
carbonate
membrane.
The C03 anions are constantly renewed. The reactions with indicated transport
are
described as follows:

CO2 cathode + 1/2 02 cathode + 2e'cathode -> C03 cathode R. 1
C 3 cathode -> C03 anode R. 2
CO3 anode --> CO2 + 1/2 02 anode + 2e anode R. 3

H2 anode + 1/2 02 anode -> H2Oanode -242 kJ/gmol-H2 R. 4
Net: H2 anode + 1/2 02 cathode + CO2 cathode + 2e cathode

H2Oanode + CO2 anode + 2e anode -242 kJ/g11101-H2 R. 5

Electricity generated by the fuel cell is shown as electrical output 21. The
stream
from the anode, 22, now contains the permeated CO2 and steam but no hydrogen,
nitrogen,
methane or oxygen, if hydrogen and oxygen are fed in exactly 2:1
stoichiometry. A
portion of stream 22 may recycled to the cathode compartment 17 of the fuel
cell. The CO2
recycle stream is shown as 23 on Figure 6. A portion of streams 22 and/or 13
also may be
put through a turbine expander to generate electrical or mechanical work 30
and 24,
respectively. In the present invention CO2 is separated from nitrogen
essentially for free
while electricity is simultaneously generated. Furthermore the CO2 capture
leverage is
high. As shown above, each mole of methane is converted to 4 moles of H2.
Therefore 4
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moles of COz per mole of converted methane are required to transport the
oxygen in the
fuel cell and are therefore separated from the nitrogen. Thus, this process
can also be used
to separate CO2 from an external COa containing stream. The high concentration
CO2
stream, 29, is now a prime candidate for sequestration after the steam is
condensed. The
CO2 can be used for oil recovery, or injected into subterranean formations, or
converted to
a thermodynamically stable solid. Also, since the present process can be
operated to
produce high purity hydrogen and nitrogen as well as concentrated C02, it can
be used to
facilitate the production of chemicals such as urea, which can be made from
these three
raw materials. Other chemicals which can be manufactured using the products
and by-
products of the present process include ammonia and ammonium sulfate. Other
uses for
the concentrated stream of COZ and the high purity hydrogen and nitrogen
streams will be
apparent to those skilled in the art.
The stream from the cathode, stream 18, contains all the nitrogen, unreacted
oxygen, a little unpermeated CO2, and trace amounts of the methane, hydrogen
and CO
from the MSR effluent. All or part of this stream can be put through a turbine
expander
(not shown) to generate work (electrical or mechanical), 19. The trace
components of
stream 18 may be oxidized in a catalytic converter, 26, and emitted in the
atmosphere as a
low CO2 concentration containing stream, 27, containing less than 10% CO2,
preferably
less than 1% COZ. The trace components may also be oxidized inside the fuel
cell if the
appropriate catalyst is placed in the cathode compartment. A stream, 28,
containing water
and steam exits condenser 25 and is recycled to the DC-MSR reactor, and
reheated to
between about 250 to 500 C.
The zero emission hybrid system of the present invention is extremely
efficient.
Byproduct compounds are separated, the steam and hydrogen are reheated
efficiently, and
electricity is produced. Furthermore, water is separated from purified CO2
which is
produced in concentrations large enough to be easily sequestered. Advantages
include
using waste heat to raise steam and using water collected for recycling to
support
additional steam reforming or other beneficial uses. The system is a totally
integrated,
extremely efficient design having the potential for greater than 71%
generation efficiency
as mentioned above. The 71% is approximately a 20% fractional improvement over
the
best results we are aware of in the art, the 60% figure mentioned above that
is possible
under laboratory conditions. In addition to the great improvement in
efficiency, the

14


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WO 2006/034086 PCT/US2005/033267
integrated design provides a concentrated source of CO2 for capture and
sequestration as
well.
Fuel cells which would be suitable for use in the present invention are those
that
could function in a highly pressurized system. Most fuel cells run at
atmospheric
conditions. For this reason, a high pressure molten carbonate fuel cell is
preferred.
However, other types of fuel cells, such as PEM fuel cells and SOFC, can also
be
effectively combined with the DC-MSR reactor of the present invention.
Another very attractive feature is that the DC powered MSR hydrogen generator
produces very low NOX, especially compared with the combined processes known
in the
art. Due to the use of distributed combustion very little NOX is generated in
this system.
Furthermore, other steam reforming reactors used to generate hydrogen known in
the art
could not feed to the MCFC the flue gas from the furnace as in the present
design, because
they produce high NO,,, which would poison the molten carbonate membrane.
In a particular embodiment of the invention, the aforesaid distributed
combustion
heated, membrane hydrogen-producing reactor such as a steam reforming reactor
contains
multiple distributed combustion charnbers (preferably, but not necessarily, in
the form of
tubes) and multiple hydrogen-selective, hydrogen-permeable membrane tubes
disposed in,
or otherwise in contact with, the reforming catalyst bed in the reforming
chamber.
Examples of multi-tubular reactors in accordance with the invention are shown
in Figures
4-5, 7-8 and 10-13.
The multi-tubular, distributed combustion heated, membrane hydrogen-producing
reactor such as steam reforming reactor in accordance with the invention may
be either of
the radial flow type as shown in Figures 4 and 5, or may be of the axial flow
type as shown
in Figures 7-8 and 12-13. In a radial flow reactor the gases generally flow
through the
reforming catalyst bed radically from outside to inside (or from inside to
outside), while in
an axial flow reactor the gases generally flow through the reforming catalyst
bed in the
same direction as the axis of the reactor. In the case of a vertical reactor,
the flow would
be from the top of the reactor to the bottom, or the bottom of the reactor to
the top.
The multi-tubular, distributed combustion heated, membrane reactor such as a
steam reforming reactor in accordance with the present invention may contain
from as few
as 2 distributed combustion tubes up to 100 or more, particularly 3 to 19,
depending the
size of the distributed combustion tubes, the size of the catalyst bed and the
level of heat
flux desired in the catalyst bed. The size of the distributed combustion tube
can vary from



CA 02580580 2007-03-13
WO 2006/034086 PCT/US2005/033267
about 1 inch outer diameter up to about 40 inches or more outer diameter. The
number of
hydrogen-selective membrane tubes may also vary from as few as 2 up to 400 or
more,
particularly 3 to 90. The outer diameter size of the membrane tubes may vary
from about 1
inch up to about 10 inches or more. In general, the ratio of distributed
combustion tube
surface area to membrane tube surface area will be in the range of about 0.1
to about 20.0,
particularly from about 0.2 to about 5.0, more particularly from about 0.5 to
about 5.0, still
more particularly from about 0.3 to about 3.0 and even more particularly from
about 1.0 to
about 3Ø The term "surface area" when used in reference to the above ratios,
means the
external (circumferential) area of the distributed combustion tubes and the
membrane
tubes. For instance, a 1 inch outer diameter tube of 12 inches length would
have an
external surface area of 37.6 square inches.
Each distributed combustion tube or chamber will have at least one fuel
conduit
disposed therein. Large distributed combustion chambers generally will have
multiple fuel
conduits. The distributed combustion chambers or tubes employed in the multi-
tubular
reactors of the invention may be "open ended" or "closed ended" as discussed
below in
connection with Figures 6A and 6B.
A sweep gas may be used to promote the .diffusion of hydrogen through the
hydrogen-selective, hydrogen-permeable membrane. In case a sweep gas is
employed, the
membrane tube may contain an inlet and flow path for sweep gas feed and a flow
path and
outlet for the return of sweep gas and permeated hydrogen.
Baffles and/or screens may also be employed in the multi-tubular reactors of
the
present invention to improve contact of the reactive gases with the catalyst
and to improve
flow distribution. The distributed combustion tubes and/or membrane tubes may
also be
surrounded by cylindrical screens to protect the tubes from direct contact
with the catalyst.
In a further embodiment of the invention the reforming chamber of a reactor in
accordance with the invention is in communication with a high pressure molten
carbonate
fuel cell, wherein the outlet for hydrogen from the reformer is in
communication with the
anode of said fuel cell and the outlet for by-product compounds is in
communication with
the cathode of said fuel cell.
In one embodiment, the present reactor is an integrated distributed combustion-

steam reformer, and the present process or apparatus of is capable of
producing high purity
hydrogen with minimal production of CO, particularly less than about 5 molar%,
more
particularly less than 3 molar %, and still more particularly less than 2
molar% on a molar

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WO 2006/034086 PCT/US2005/033267
dry basis of the total products, and with less than 1000 ppm of CO and
particularly less
than 10 ppm of CO on a dry basis, more particularly virtually no CO in the
hydrogen
stream produced. By practice of the present invention it is possible to
produce high purity
hydrogen e.g., hydrogen having a purity on a dry basis of greater than 95%.
The present
invention can be used to produce hydrogen having purities as high as 97%, 99%,
or under
optimum conditions 99+%. The effluent (by product) stream from the MSR reactor
will
typically contain more than 80% CO2 on a dry basis, e.g., 90% CO2, 95% COz or
99%
COz, and less than about 10% CO on a dry basis, e.g., less than about 5% CO,
preferably
less than 1% CO.
Total heat management and turbines may be included in the system to increase
the
efficiency and produce additional electricity or to do useful work such as
compress gases
or vapors.
One aspect of the present invention is a distributed combustion heated
membrane
steam reformer hydrogen generator. In the design of the invention there are
disclosed
distinct improvements in overall efficiency, particularly size, scalability
and heat exchange.
The present invention typically employs only one reactor to produce the
hydrogen versus
typically four reactors used in conventional processes, and part of the heat
load is supplied
by the water-gas-shift reaction. The design of the invention captures
essentially all of the
heat in the reaction chamber since heat exchange occurs on a molecular level,
which
reduces the overall energy requirements.
Chemical equilibrium and heat transfer limitations are the two factors that
govern
the production of hydrogen from hydrogen-producing feedstock in conventional
reactors.
These factors lead to the construction of large reactors fabricated from
expensive high
temperature tolerant materials. They are enclosed in high temperature furnaces
that are
needed to supply the high heat fluxes.
In the present invention the two major limitations of chemical equilibrium and
heat
transfer are overcome by the innovative combination of an in-situ membrane
separation of
hydrogen in combination with a heat source comprising distributed combustion
("DC")
that makes it possible to more efficiently use all the energy in the system,
as well as
provide load following capabilities.
The reformer of the present invention reduces the operating temperature of the
steam reforming reactor close to the lower temperature used in a shift
reactor. With the
temperatures for the steam reforming and shift closer, both operations are
combined into
17


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WO 2006/034086 PCT/US2005/033267
one reactor. With both reactions occurring in the same reactor the exothermic
heat of
reaction of the shift reaction is completely captured to drive the endothermic
steam
reforming reaction. This reduces the total energy input for the sum of the
reactions by
20%. The lower temperature reduces stress and corrosion and allows the reactor
to be
constructed from much less expensive materials. Combining the operations also
reduces
the capital and operating cost since only one reactor, instead of two or
three, are required.
Moreover, the reaction is not kinetics-limited even at the lower temperature,
thus, the same
or even less catalyst can be used.
The general description for steam reformers, including but not limited to the
reactions, enthalpies, values of equilibrium constants, advantages of
integrated distributed
combustion-SMR reactor, as well as the advantages of the use of the membrane
in the
reactor can be found in US 2003/0068269.
The in-situ membrane separation of hydrogen employs a membrane fabricated,
particularly from an appropriate metal or metal alloy, on a porous ceramic or
porous metal
support, as described below, to drive the equilibrium to high conversions.
With constant
removal of the hydrogen through the membrane, the reactor can be run at much
lower than
the commercially practiced temperatures of 700-900+ C. A temperature of 500 C
is
sufficient to drive the kinetics to high conversions when the equilibrium is
shifted using the
hydrogen separation membrane. At this temperature the selectivity to CO2 is
almost 100%,
while higher temperatures favor the formation of CO as a major product.
The term "reforming catalyst" as used herein means any catalyst suitable for
catalyzing a steam reforming reaction, which includes any steam reforming
catalyst known
to one skilled in the art, as well as any "pre-reforming catalyst" which is
suitable for
catalyzing steam reforming reactions in addition to being suitable for
processing heavier
hydrocarbons prior to a steam reforming reaction.
Figure 1 shows a schematic diagram of a hydrogen-producing reactor with
catalyst
section, and permeate section. The reactor 1 shown in Figure 1 consists of two
concentric
sections. The inner concentric section 3 is the permeate section. The annulus,
4, in
between is the catalyst section. A hydrogen-producing catalyst, such as a
reforming
catalyst, is loaded into the annulus section 4 wherein the above-described
reactions take
place. (section 4 is also variously referred as the catalyst section, the
reaction section or the
reaction zone). The membrane, 8, is represented on the inside of the small
section, 3, (the
permeate section) in Figure 1.

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The feed stream containing hydrogen-producing feedstock, such as a mixture of
vaporizable hydrocarbon-containing compounds (e.g. naphtha, methane or
methanol) and
H20 with a minimum overall 0: C ratio of 2:1 when a steam reforming reaction
is carried
out, enters catalyst section 4 at 5. If used, sweep gas for promoting the
diffusion of
hydrogen through the membrane enters the top of the permeate section 3 at 6.
Alternatively, sweep gas can be introduced into the permeate section by means
of a stinger
pipe fitted to bottom of the permeate section. In case of this alternative,
hydrogen in sweep
gas would exit the permeate zone at the bottom of the permeate section.
Optionally, the
stinger pipe to introduce the sweep gas may be connected at the top of the
permeate section
in which case the hydrogen and sweep gas would exit at the top of this
section. Hydrogen
(pure or in sweep gas) exits at 12. Unreacted products and by-products (e.g.,
C02, H2O,
H2, CH4, and CO) exit catalyst section 4 at 13. It is also possible to remove
the produced
hydrogen using a vacuum instead of a sweep gas.
The catalyst beds, 4, can be heated by any suitable heating method known to
one
skilled in the art, such as a by a traditional burner, an electric heating
means, a microwave
heating means, etc.'
Any hydrogen-producing, particularly vaporizable, feedstock such as an
(optionally
oxygenated) hydrocarbon-containing compound(s) can be used in the present
process and
apparatus, including, but not limited to, methane, methanol, ethane, ethanol,
propane,
butane, light hydrocarbons having 1-4 carbon atoms in each molecule, and light
petroleum
fractions like naphtha at boiling point range of 120-400 F, which is a typical
feed for
commercial steam reformers. Petroleum fractions heavier than naphtha can also
be
employed like diesel or kerosene or jet fuel at boiling point range of 350-500
F (about 177-

253 C) or gas oil at boiling point range of 450-800 F. Hydrogen, carbon
monoxide and

mixtures thereof, e.g., syngas, may also be used in the process and apparatus
of the present
invention, and are included in the definition of "hydrogen-producing
feedstock" or
"vaporizable hydrocarbon". Methane was used in the examples to demonstrate the
process.
The catalyst bed can be heated 107 by any suitable means 107, such as electric
heating,
microwave, conventional combustion, distributed combustion, etc.
In some embodiments, with the distributed combustion-steam reforming process
and apparatus of the present invention it is possible to use 0: C ratios as
low as 2.8, down
to 2.6, without coking problems, with the minimum 0: C ratio being about 2:1.
This
results lower energy costs if methane is used as the feed in the present
invention, since

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lower steam to methane ratios can be used thus requiring less energy to
vaporize water.
Because of the ability to operate at lower O:C ratios, it is also possible to
use heavier, less
expensive feeds in the distributed combustion-MSR reactor of the present
invention than
can be used in conventional steam methane reformers.
In another embodiment of the invention, the integrated hydrogen-producing
process
and apparatus of the invention can be used to perform water-gas-shift
reactions on syngas
mixtures (i.e., mixtures of hydrogen and carbon monoxide) produced from
conventional
processes like Catalytic Partial Oxidation (CPO), Steam Methane Reforming
(SMR) and
Autothermal Reforming (ATR). The integrated distributed combustion-MSR reactor
is
well suited for this since it produces high purity hydrogen and converts
carbon monoxide
to carbon dioxide and more hydrogen. Thus, the versatile hydrogen-producing
reactor of
the invention is capable of replacing high temperature shift, low temperature
shift and
methanation reactors and a hydrogen purification section. A mixture of syngas
and
vaporizable hydrocarbon can also be used to yield a net reaction which may be
either
endothermic, thermally neutral or slightly exothermic.
The reactor annulus is packed with steam reforming catalyst and equipped with
a
perm-selective (i.e., hydrogen selective) membrane that separates hydrogen
from the
remaining gases as they pass through the catalyst bed. The steam reforming
catalyst can be
any known in the art. Typically steam reforming catalysts which can be used
include, but
are not limited to, Group VIII transition metals, particularly nickel. It is
often desirable to
support the reforming catalysts on a refractory substrate (or support). The
support is
preferably an inert compound. Suitable compounds contain elements of Group III
and IV
of the Periodic Table, such as, for example the oxides or carbides of Al, Si,
Ti, Mg, Ce and
Zr. The preferred support composition for the reforming catalyst is alumina.
The catalyst used in the examples to demonstrate the present invention was
nickel
on porous alumina. As the hydrogen is formed in the catalyst bed, it is
transported out
through the hydrogen-permeable separation membrane filter. Advantages of this
technology include the capacity to separate essentially pure hydrogen from any
poisons
that may also be present, including CO and H2S, and from other fuel diluents.
The poisons
do not pass through the separation membrane, which is fabricated from one of a
variety of
hydrogen-permeable and hydrogen-selective materials including ceramics.
Illustrative, but non-limiting examples of materials suitable for use as a
support for
the membranes which may be used in the apparatus and process of the present
invention


CA 02580580 2007-03-13
WO 2006/034086 PCT/US2005/033267
include an inorganic porous material such as palladium, platinum, palladium
alloys, porous
stainless steel, porous silver, porous copper, porous nickel, porous Ni-based
alloys, metal
mesh, sintered metal powder, refractory metals, metal oxides, ceramics, porous
refractory
solids, honeycomb alumina, aluminate, silica, porous plates, zirconia,
cordierite, mullite,
magnesia, silica matrix, silica alumina, porous Vycar, carbon, glasses, and
the like.
The composite gas separation modules described herein include a dense gas-
selective membrane such as, for example, a dense hydrogen-selective membrane.
The
dense hydrogen-selective membrane can include, for example, palladium or an
alloy
thereof. A "dense gas-selective membrane," as that term is used herein, refers
to a
component of a composite gas separation module that has one or more layers of
a gas-
selective material, i.e., a material that is selectively permeable to a gas,
and that is not
materially breached by regions or points which impair the separation of the
gas by allowing
the passage of an undesired gas. For instance, in one embodiment, the dense
gas-selective
membrane is not materially breached by regions or points which do not have the
desired
gas selectivity properties of the gas-selective material. An example of a
dense gas-
selective membrane is a dense hydrogen-selective membrane that is
substantially free of
defects such as open pores, holes, cracks and other physical conditions that
impair the gas-
selectivity of the composite gas separation module by allowing the passage of
an undesired
gas.
The term "support," as used herein, includes a substrate, a surface treated
substrate,
a substrate upon which a material (e.g., a gas-selective material) has been
deposited, a
substrate with an intermediate layer, or a subsequently plated substrate upon
which a dense
gas-selective membrane has been or will be formed. Serving as a support
structure, the
substrate can enhance the durability and strength of the composite gas
separation module.
"Gas-selective material," as used herein, refers to those materials which,
when
formed into dense gas-selective membranes, allow the passage of a select gas,
or select
gases, through the dense gas-selective membrane. Suitable gas-selective
materials include
metals, ceramics (e.g., perovskite and perovskite-like materials) and zeolites
(e.g., MFI and
Zeolites A, X, etc.). In one embodiment, the gas-selective material is a
hydrogen-selective
metal such as palladium or an alloy thereof. Examples of suitable palladium
alloys include
palladium alloyed with at least one of the metals selected from the group
consisting of
copper, silver, gold, platinum, ruthenium, rhodium, yttrium, cerium and
indium. For
example, palladium/silver and palladium/copper alloys can be used to form
dense

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hydrogen-selective membranes. In one embodiment, the gas-selective material is
a
ceramic such as oxygen gas-selective perovskite.
The side of the support upon which the dense gas-selective membrane is formed
is
referred to herein as the "outside" or "membrane-side" and the opposite side
of the support
is called the "inside" or "substrate-side" surface. However, it should be
noted that the
dense gas-selective membrane can be formed on the exterior surface and/or the
interior
surface of the substrate. For example, the dense gas-selective membrane can be
formed on
either or both surfaces of a planar substrate or can be formed on the exterior
and/or interior
surfaces of a substrate tube. Preferably, the dense gas-selective membrane is
formed on
only one surface of the substrate, for example, on either the exterior or the
interior surface
of a substrate tube.
In one embodiment, the gas-selective material can include a combination of
substances, for example, a combination of a hydrogen-selective metal and a
zeolite. In one
embodiment, the zeolite used in a combination of substances is gas-selective.
In an
alternative embodiment, the zeolite used in a combination of substances is not
gas-
selective, for example, the zeolite used in a combination of substances is not
hydrogen-
selective.
The composite gas separation module includes an intermediate layer at a porous
substrate. In one embodiment, for example, the intermediate layer has a top
side and a
bottom side and the intermediate layer is adjacent to the porous substrate on
the bottom
side and is adjacent to the dense gas-selective membrane on the top side. The
intermediate
layer can be a continuous or a discontinuous layer. In one embodiment, at
least part of the
intermediate layer is in pores of the porous substrate and/or covers pores of
the porous
substrate. In some embodiments, the intermediate layer is a discontinuous
layer in the
pores of the porous substrate, covering the pores of the substrate, and/or
proximate to the
pores of the substrate. Alternatively, the intermediate layer is a continuous
layer that
overlies the surface of the porous substrate including portions of the surface
that do not
contain pores.
The intermediate layer includes particles and a binder metal. The binder metal
is
uniformly distributed throughout the intermediate layer. The term "uniformly
distributed,"
as used herein, refers to a uniform distribution of binder metal across the
surface area of
the particles of the intermediate layer. In one embodiment, the binder metal
is a hydrogen-
selective metal or an alloy thereof. "Hydrogen-selective metals" include, but
are not

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limited to, niobium (Nb), tantalum (Ta), vanadium (V), palladium (Pd),
platinum (Pt),
zirconium (Zr) and hydrogen-selective alloys thereof. Palladium and alloys of
palladium
are preferred.
In some embodiments, the intermediate layer includes particles substantially
uniform in size, e.g., of substantially uniform diameter. Alternatively, the
intermediate
layer can include particles of varying sizes and/or size distributions. The
intermediate
layer can include blends and/or layering of different particles including
particles of
differing sizes. The intermediate layer can include a gradient of particle
size from a
surface of the intermediate layer proximate to the porous substrate to a
surface of the
intermediate layer distal to the porous substrate. In one embodiment,
particles having a
smaller average size overlie particles having a larger average size. For
example, particles
having a larger average size are located proximate to the porous substrate
(e.g., inside the
pores of the porous substrate) and particles having a smaller average size are
located distal
to the porous substrate (e.g., inside the pores of the porous substrate but
closer to the

membrane-side surface of the porous substrate).
In one embodiment, the particles can have an average particle diameter of at
least
about 0.01 micron such as at least about 0.1, 0.5, 1, or at least about 5
microns. The
particles can include particles capable of fitting into pores of the porous
substrate. In some
embodiments, the particles can have an average particle diameter of less than
5 microns
such as less than 1, 0.5, 0.1, or less than 0.01 microns. In one embodiment,
the particles
have an average diameter ranging from about 0.01 to about 5 microns. For
example, the
particles can have an average diameter ranging from about 0.01 to about 3
microns or
about 0.3 to about 1 micron. As used herein, micron or microns mean micrometer
or
micrometers.
In one embodiment, the intermediate layer includes sublayers of particles and
binder metal, e.g., at least two sublayers of particles and binder metal. For
example, the
sublayers of particles and binder metal can include a first sublayer of a
first population of
particles and a first binder metal and a second sublayer of a second
population of particles
and a second binder metal, wherein the first population of particles has a
larger average
diameter than the average diameter of the second population of particles and
wherein the
second sublayer overlies the first sublayer. Thus, in one embodiment, the
intermediate
layer includes a sublayer of particles having a larger average diameter and an
overlying
sublayer of particles having a smaller average diameter. For example, the
intermediate
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layer can include a sublayer of particles having an average diameter of about
0.3 to about 3
microns and an overlying sublayer of particles having an average diameter of
about 0.1 to
about 1 micron. Sublayers of particles and binder metal are not necessarily
distinct
sublayers. For example, the intermediate layer can include a gradient of
particle sizes in a
binder metal. In one embodiment, the intermediate layer includes a gradient of
particle
sizes ranging from generally larger particles at a point proximate to the
porous substrate to
generally smaller particles at a point distal to the porous substrate.
The particles of the intermediate layer can include metal particles, metal
oxide
particles, ceramic particles, zeolite particles, and combinations thereof,
among others. For
example, the particles can include such materials as tungsten, silver, copper
oxide,
aluminum oxide, zirconia, titania, silicon carbide, chromium oxide, and
combinations
thereof. Suitable metal oxide particles include, but are not limited to,
aluminum oxide,
titanium oxide, yttrium oxide, and chromium oxide. In some embodiments, the
particles
include aluminum oxide particles, e.g., alpha-alumina particles and/or gamma-
alumina
particles. The particles can include a blend or a layering of different
particles including
particles of differing compositions and/or sizes. The particles of the
intermediate layer can
have various morphologies and shapes. For example, the particles can be
ordered or
amorphous (e.g., crystalline). In one embodiment, the particles include
spherical or mostly
spherical particles.
In some embodiments, the particles can have a melting point temperature higher
than the melting point temperature of the porous substrate, e.g., a porous
metal substrate.
The intermediate layer can include particles having a melting point
temperature higher than
the melting point temperature of the dense gas-selective membrane. For
example, in one
embodiment, the intermediate layer includes particles having a melting point
temperature
higher than both the melting point temperature of the porous metal substrate
and the
melting point temperature of the dense gas-selective membrane.
In one embodiment, the intermediate layer is at least about 0.01, 0.1, 1, 2,
3, 4, or at
least about 5 microns thick. For example, the intermediate layer can range
from about 0.01
to about 5 microns thick, such as from about 0.1 to about 3 or from about 1 to
about 3
microns thick. In one embodiment, the intermediate layer is not significantly
less porous to
helium gas flux than the porous substrate. The intermediate layer can have an
average pore
size that is less than the average pore size of the porous substrate. In one
embodiment, the
largest pore of the intermediate layer is smaller than the largest pore of the
porous

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substrate. Maximum (largest) pore size can be measured by a typical "Bubble
Point" test
such as per ISO standard 4003 or per ASTM E-128
In another embodiment, the composite gas separation module can further include
a
layer of particles underlying the intermediate layer. In one particular
embodiment, the
composite gas separation module includes a layer of particles underlying the
intermediate
layer wherein a binder metal is not uniformly, distributed throughout the
layer of particles
underlying the intermediate layer. For example, the binder material is not
uniformly
distributed across the surface area of this layer of particles underlying the
intermediate
layer. The layer of particles underlying the intermediate layer can include
any of the
particles described herein, e.g., aluminum oxide particles.
The composite gas separation module used herein includes a porous metal
substrate. The porous metal substrate can be formed from any of a variety of
components
known to those of ordinary skill in the art. Examples of suitable substrate
components
include, but are not limited to, iron, nickel, palladium, platinum, titanium,
chromium,
porous silver, porous copper, aluminum, and alloys thereof, e.g., steel,
stainless steel,
porous stainless steel, HASTELLOY alloys (e.g., HASTELLOY C-22 ) (trademarks
of
Haynes International, Inc., Kokomo, IN) and INCONEL alloys (e.g., INCONEL
alloy
625) (INCONEL is a trademark of Huntington Alloys Corp., Huntington WV). In
one
embodiment, the porous metal substrate is an alloy containing chromium and
nickel (e.g.,
INCONEL alloy 625). In an additional embodiment, the alloy contains chromium,
nickel
and molybdenum such as, for example, HASTELLOY C-22 or INCONEL alloy 625.
The porous metal substrate can be porous stainless steel. Cylinders of porous
stainless
steel that are suitable for use as substrates are available from Mott
Metallurgical
Corporation (Farmington, CT) and from Pall Corporation (East Hills, NY), for
example.
The substrate can also be metal mesh, sintered metal powder, refractory
metals, metal
oxides, ceramics, porous refractory solids, honeycomb alumina, aluminate,
silica, porous
plates, zirconia, cordierite, mullite, magnesia, silica matrix, silica
alumina, porous Vycar,
carbon, glasses, and the like.
One of ordinary skill in the art can select substrate thickness, porosity, and
pore size
distribution using techniques known in the art. Desired substrate thickness,
porosity and
pore size distribution can be selected based on, among other factors, the
operating
conditions of the final composite gas separation module such as operating
pressure.
Substrates having generally higher porosities and generally smaller pore sizes
are



CA 02580580 2007-03-13
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particularly suited for producing composite gas separation modules. In some
embodiments, the substrate can have a porosity in a range of about 5 to about
75% or about
15 to about 50%. While the pore size distribution of a substrate can vary, the
substrate can
have pore diameters that range from about 0.1 microns or less to about 15
microns or more.
Generally, smaller pore sizes are preferred. However, in some embodiments, a
substrate
having larger pores is used and an intermediate layer having generally smaller
pore sizes is
formed at the porous substrate (e.g., a graded support is formed).
In some embodiments, the mean or median pore size of the substrate can range
from about 0.1 to about 15 microns, e.g., from about 0.1 micron to about 1, 3,
5, 7 or about
10 microns. For example, the substrate can be an about 0.1 micron grade
substrate to an
about 0.5 micron grade substrate, e.g., 0.1 micron, 0.2 micron, and 0.5 micron
grades of
stainless steel substrates can be used. In one embodiment, the substrate is
0.1 micron grade
HASTELLOY alloy.
The composite gas separation module can further include a substrate surface
treatment. For example, a layer of a ceramic can be bonded to a porous metal
substrate.
The ceramic can include oxides, nitrides, and/or carbides, for example, iron
oxide, iron
nitride, iron carbide and/or aluminum oxide.
The composite gas separation module can also further comprise a layer of a
metal
selected from the group consisting of palladium, gold and platinum, wherein
the layer of
metal overlies the porous substrate and/or a substrate surface treatment.
The composite gas separation module includes a dense gas-selective membrane,
wherein the dense gas-selective membrane overlies the intermediate layer. In
one
embodiment, the dense gas-selective membrane is selectively permeable to
hydrogen, e.g.,
the dense gas-selective membrane is a dense hydrogen-selective membrane and
can include
one or more hydrogen-selective metals or alloys thereof. As described above,
hydrogen-
selective metals include, but are not limited to, niobium (Nb), tantalum (Ta),
vanadium
(V), palladium (Pd), platinum (Pt), zirconium (Zr) and hydrogen-selective
alloys thereof.
Palladium and alloys of palladium are preferred. For example, palladium can be
alloyed
with at least one of the metals selected from the group consisting of copper,
silver, gold,
platinum, ruthenium, rhodium, yttrium, cerium and indium.
Where the gas separation module is to be used at temperatures below about 300
C,
the dense gas-selective membrane can be formed of a palladium alloy such as,
for example,
an alloy of about 75,to about 77 weight percent palladium and about 25 to
about 23 weight
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percent silver. An alloy is typically preferred at low temperatures because
pure palladium
can undergo a phase change in the presence of hydrogen at or below about 300 C
and this
phase change can lead to embrittlement and cracking of the membrane after
repeated

cycling in the presence of hydrogen.
In one embodiment, the dense gas-separation membrane can include one or more
non-metallic components. In an additional embodiment, the dense gas-separation
membrane can include one or more components that are not gas-selective
materials, e.g.,
components that are not hydrogen-selective materials.
In one embodiment, the thickness of the dense gas-selective membrane is less
than
about 3 times the diameter of the largest pore of the porous substrate. For
example, the
thickness of the dense gas-selective membrane can be less than about 2.5, 2,
or less than
about 1.5 times the diameter of the largest pore of the porous substrate.
While the
thickness of the dense gas-selective membrane can depend, among other factors,
on the
size of the largest pores in the porous substrate, in some embodiments the
dense gas-
selective membrane is less than about 25, 20, 15, 12 or less than about 10
microns in
thickness. For example, in one embodiment, the thickness of the dense gas-
selective
membrane is less than about 14 microns such as about 3 to 14 microns. In one
particular
embodiment, the dense gas-selective membrane is of substantially uniform
thickness.
In one aspect, performance of the composite gas separation modules described
herein can be assessed by measuring hydrogen flux through the module during
operation.
For example, hydrogen flux through the composite gas separation modules, in
some
embodiments, is at least about 4, 10, 20, or at least about 30 (m3/m2-hr)sTP
at about 350 C
and with a hydrogen partial pressure difference of about 1 bar (0.1 MPa). In
at least one
embodiment, hydrogen flux through the composite gas separation module is'at
least about
33.6 (m3/m2-hr)sTP at about 350 C and with a hydrogen partial pressure
difference of about =
1 bar (0.1 MPa).
As an illustration of one embodiment of the present invention, FIG. 3A shows a
partial cross-section of a composite gas separation module. Porous substrate
110 can
include, for example, a porous metal substrate such as porous stainless steel.
Intermediate
layer 112 includes particles and a binder metal. Intermediate layer 112 is
shown in FIG.
3A as a continuous layer at porous substrate 110. The are two sublayers of
particles. The
first layer has a larger average diameter than the average diameter of the
second layer. The
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second sublayer overlies the first sublayer. Dense gas-selective membrane 114
overlies the
intermediate layer.
FIG. 3B shows a partial cross-section of a composite gas separation module.
Porous substrate 110 can include, for example, a porous metal substrate such
as porous
stainless steel. Intermediate layer 112 includes particles and a binder metal,
wherein the
binder metal is uniformly distributed throughout the intermediate layer.
Intermediate layer
112 is shown in FIG. 3B as a continuous layer at porous substrate. Dense gas-
selective
membrane 114 overlies the intermediate layer.
FIG. 3C shows a magnified partial cross-section of one embodiment of a
composite
gas separation module described by the present invention. Porous substrate 110
includes
pores 116. Intermediate layer 112 includes particles and a binder metal,
wherein the binder
metal is uniformly distributed throughout the intermediate layer. Intermediate
layer 112 is
shown in FIG. 3 C as a discontinuous layer at porous substrate 110 wherein
intermediate
layer is contained within pores 116. Dense gas-selective membrane 114 overlies

intermediate layer 112.
FIG. 3D shows a magnified partial cross-section of one embodiment of a
composite
gas separation module described by the present invention. Porous substrate 110
includes
pores 116. Intermediate layer 112 includes particles and a binder metal,
wherein the binder
metal is uniformly distributed throughout the intermediate layer. Intermediate
layer 112 is
shown in FIG. 3D as a discontinuous layer at porous substrate 110 wherein the
intermediate layer is both within and covering pores 116. In some embodiments,
the
intermediate layer only covers the pores of the porous substrate. Dense gas-
selective
membrane 114 overlies intermediate layer 112.
FIG. 3E shows a magnified partial cross-section of one embodiment of a
composite
gas separation module described by the present invention. Porous substrate 110
includes
pores 116. Intermediate layer 112 includes particles and a binder metal,
wherein the binder
metal is uniformly distributed throughout the intermediate layer. Intermediate
layer 112 is
shown in FIG. 3E as a continuous layer at porous substrate 110 but in other
embodiments
the intermediate layer is a discontinuous layer. Dense gas-selective membrane
14 overlies
the intermediate layer.
While FIGS. 3A to 3E illustrate planar cross-sections of composite gas
separation
modules, composite gas separation modules of the present invention can include
planar and
cylindrical composite gas separation modules such as those having flat porous
substrates
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and tubular porous substrates. In addition, the composite gas separation
modules
illustrated in FIGS. 3A to 3E can also include a layer of particles (not
illustrated)
underlying intermediate layer 112 wherein a binder metal is not uniformly
distributed
throughout the layer of particles underlying the intermediate layer.
In one aspect, the invention includes a method for fabricating a composite gas
separation module, comprising the steps of: (a) depositing a preactivated
powder over a
porous substrate; (b) depositing a binder metal onto the preactivated powder;
and (c)
depositing a dense gas-selective membrane to overlie the preactivated powder
and binder
metal, thereby forming the composite gas separation module. Suitable porous
substrates,
binder metals, and dense gas-selective membranes are described above.
In a particular fabrication method, any contaminants are initially cleaned
from the
substrate, for example, by treating the substrate with an alkaline solution
such as by
soaking the substrate in an approximately 60 C ultrasonic bath for about half
an hour.
Cleaning is typically followed by rinsing such as, for example, wherein the
substrate is
sequentially rinsed with tap water, deionized water and isopropanol or wherein
the
substrate is sequentially washed with deionized water and acetone. Preparation
of the
porous substrate can also include surface treatment; formation of an
intermetallic diffusion
barrier such as by oxidizing the substrate; surface activation, described
infra; and/or
deposition of a metal such as palladium, gold or platinum, described infra,
prior to
depositing the preactivated powder over the porous substrate.
An intermediate layer is generally formed at the porous substrate prior to
deposition
of a dense gas-selective membrane (e.g., a hydrogen selective membrane).
Generally,
forming the herein-described intermediate layer includes depositing a
preactivated powder
over a porous substrate and depositing a binder metal onto the preactivated
powder. An
intermediate layer can be formed by depositing one or more sublayers that
include powder
and binder metal wherein at least one sublayer contains a preactivated powder.
In some
embodiments, one or more non-surface activated powders may be deposited over
the
porous substrate, over deposited preactivated powder, or over deposited
preactivated
powder and binder metal.
"Preactivated powder," as used herein, refers to a powder that has been
surface
activated by depositing metal nuclei on the surface of the powder. In one
embodiment, the
metal nuclei are nuclei of hydrogen-selective metals, e.g., palladium nuclei.

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The method for fabricating a composite gas separation module includes the step
of
depositing a preactivated powder over a porous substrate. In one embodiment,
depositing
the preactivated powder over the porous substrate includes depositing the
preactivated
powder into the pores of the porous substrate. The preactivated powder can
include
preactivated metal powder, preactivated metal oxide powder, preactivated
ceramic powder,
preactivated zeolite powder, and combinations thereof, among others. For
example, the
preactivated powder can include preactivated tungsten, silver, copper oxide,
aluminum
oxide, zirconia, titania, silicon carbide, chromium oxide, and combinations
thereof.
Suitable preactivated metal oxide particles include, but are not limited to,
preactivated
aluminum oxide, preactivated titanium oxide, preactivated yttrium oxide, and
preactivated
chromium oxide. In some embodiments, the preactivated powder includes
preactivated
aluminum oxide particles, e.g., preactivated alpha-alumina powder and/or
preactivated
gamma-alumina powder. The deposited powder can include a blend or a layering
of
different powders including powders of differing compositions and/or sizes.
The powder
can include particles of various morphologies and shapes. For example, the
particles can
be ordered (e.g., crystalline) or amorphous. In one embodiment, the powders
include
spherical or mostly spherical particles. In some embodiments, the powder can
have a
melting point temperature higher than the melting point temperature of the
porous
substrate, e.g., a porous metal substrate, and/or higher than the melting
point temperature
of the dense gas-selective membrane.
In one embodiment, the preactivated powder can have an average particle
diameter
of at least about 0.01 micron such as at least about 0.1, 0.5, 1, or at least
about 5 microns.
The preactivated powder can include particles capable of fitting into pores of
the porous
substrate. In some embodiments, the preactivated powder can have an average
particle
diameter of less than 5 microns such as less than 1, 0.5, 0.1, or less than
0.01 microns. In
one embodiment, the preactivated powder has an average diameter ranging from
about 0.01
to about 5 microns. For example, the particles can have an average diameter
ranging from
about 0.01 to about 3 microns or about 0.3 to about 1 micron.
In one embodiment, the present invention includes the further step of surface
activating a powder to thereby form the preactivated powder. For example,
surface
activating the powder to form the preactivated powder can include seeding the
powder with
nuclei of a hydrogen-selective metal, e.g., palladium nuclei. In one
embodiment, the


CA 02580580 2007-03-13
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powder is seeded with nuclei of a hydrogen-selective metal using an aqueous
activation
solution.
One technique for surface activating a powder to thereby form the preactivated
powder includes placing the powder in an'aqueous stannous chloride (SnC12)
solution (e.g.,
1 g/L, pH=2) for sensitization and filtering the powder from the solution
shortly after.
Then, the filter cake can be placed in an aqueous palladium chloride (PdCI2)
(e.g., 0.1g/L,
pH=2) activation solution. Shortly after, the resulting mixture can be
filtered and washed
to recover the preactivated powder.
Another technique for surface activating a powder to thereby form the
preactivated
powder includes placing the powder in an aqueous SnC12 solution (e.g., 1 g/L,
pH=2).
Shortly after, aqueous PdC12 solution (e.g., 0.1 g/L, pH=2) can be added. The
resulting
mixture can be filtered and washed to recover the preactivated powder.
The preactivated powder can be deposited using any of a number of techniques
for
applying a powder to a porous surface. For example, the preactivated powder
can be
deposited after transport to the support by a gas (e.g., a gas stream). In
other embodiments,
the powder particles are pressed and/or rubbed onto the support. In one
embodiment, the
preactivated powder is deposited from a slurry or suspension. For example, in
one
embodiment, the preactivated powder can be deposited from a liquid-based
(e.g., water-
based) slurry or suspension. In some embodiments, the preactivated powder can
be
deposited from a composition of several powders of varying compositions and/or
particle
size, e.g., from a slurry or suspension containing several different
materials. For example,
in one embodiment, a water-based slurry is prepared by mixing water with a
preactivated
powder selected from the group consisting of preactivated metal powders,
preactivated
metal oxide powders, preactivated ceramic powders, preactivated zeolite
powders, and

combinations thereof.
The slurry can contain, e.g., about 0.1 to about 30 g/L preactivated powder.
For
example, the slurry can contain about 0.1 to about 20, about 1 to about 15,
about 1 to about
10, about 1 to about 5, or about 1 to about 3 g/L preactivated powder. For
example, in one
embodiment, the slurry can contain about 0.1 to about 10 g/L preactivated
alumina powder
such as about 1 to about 3 g/L preactivated alumina powder.
The preactivated powder can be deposited from a slurry or suspension by
filtering
the slurry or suspension througli a porous support. For example, in one
embodiment, the
preactivated powder is deposited on a porous support as a filter cake after a
slurry is

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filtered through the porous support. In some embodiments, a vacuum is applied
to one side
of a porous support and a slurry is applied to the opposite side of the porous
support. Thus,
a filter cake can accumulate on the side of the support to which the slurry is
applied and
filtrate can be collected on the side of the support to which the vacuum is
applied. In one
embodiment, a vacuum is applied to the tube side of a tubular support and a
slurry is
applied to the membrane side of the tubular support.
In some embodiments, the preactivated powder is deposited using a liquid-based
composition such as a water-based slurry. Following deposition of the
preactivated
powder, the liquid-wetted preactivated powder can be dried. In other
embodiments, the
preactivated powder can be kept wet.
In one embodiment, the method further includes the step of exposing porous
substrate anchoring sites following deposition of the preactivated powder over
the porous
substrate. Porous substrate anchoring sites include, for example, the tips of
porous
substrate constituent particles. Porous substrate anchoring sites can be
exposed, for
example, by mechanically treating the surface of the support. In one
embodiment, porous
substrate anchoring sites are exposed by brushing or abrading the surface
following
deposition of the preactivated powder over the porous substrate.
The method for fabricating a composite gas separation module includes the step
of
depositing a binder metal onto the preactivated powder. The binder metal can
be deposited
onto the preactivated powder, for example, by electrolessly plating the binder
metal onto
the preactivated powder. Without wishing to be held to any particular theory,
it is believed
that by depositing a binder metal (e.g., a hydrogen-selective metal or alloy
thereof) onto
the preactivated powder, the preactivated powder can be mechanically
stabilized. It is
thought that by depositing a binder metal onto a preactivated powder, a more
unifonm
binder metal distribution results as compared to when a powder layer is
applied to a
support, the powder layer is surface activated, and then metal is deposited
over the powder
layer.
In one embodiment, the method for fabricating a composite gas separation
module
includes the further steps of: (a) depositing an additional preactivated
powder over the
deposited preactivated powder and binder metal; and (b) depositing an
additional binder
metal onto the additional preactivated powder; wherein the dense gas-selective
membrane
is deposited to overlie the additional preactivated powder and the additional
binder metal.
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In one embodiment, the additional preactivated powder has an average particle
size
that is smaller than the average particle size of the preactivated powder
(i.e., a prior
deposited preactivated powder). For example, the preactivated powder can have
an average
particle diameter ranging, e.g., from about 0.3 to about 3 microns and the
additional
preactivated powder can have an average particle diameter ranging, e.g., from
about 0.01 to
about 1 micron. In some embodiments, the inventive method can include
depositing
multiple successive layers of powder and binder metal over the porous
substrate wherein at
least one of the successive layers contains a preactivated powder.
The present inventive method can also further include the step of depositing a
powder over the porous substrate prior to depositing the preactivated powder.
The powder
deposited over the porous substrate can be preactivated or not preactivated.
In one
embodiment, this powder has an average particle size ranging from about 1 to
about 5
microns. The powder can include any of the powders described herein, for
example,
aluminum oxide particles. This powder can be deposited using any of the
techniques
described herein for depositing a powder on a porous support, e.g., the powder
can be
deposited from a slurry.
After deposition of a preactivated powder over a porous substrate and
deposition of
a binder metal onto the preactivated powder, a dense gas-selective membrane is
deposited
to overlie the preactivated powder and binder metal. For example, a dense gas-
selective
membrane can be deposited by depositing a gas-selective metal, e.g., a
hydrogen-selective
metal, to overlie the preactivated powder and binder metal. In one embodiment,
the
method further includes the step of exposing porous substrate anchoring sites
prior to
applying the dense gas-selective membrane. Porous substrate anchoring sites
include, for
example, the tips of porous substrate constituent particles. Porous substrate
anchoring sites
can be exposed, for example, by mechanically treating the surface of the
support. In one
embodiment, porous substrate anchoring sites are exposed by brushing or
abrading the
surface of the support prior to depositing a dense gas-selective membrane.
In one embodiment, palladium or an alloy thereof is deposited, e.g.,
electrolessly
plated, to overlie the preactivated powder and binder metal, thereby forming a
dense gas-
selective membrane. Application of the dense gas-selective membrane can
include surface
activating the preactivated powder and binder metal prior to depositing dense
gas-selective
membrane components. In some embodiments, a vacuum is applied to one side of a
porous support and an activation composition is applied to the opposite side
of the porous

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support. In one embodiment, a vacuum is applied to the tube side of a tubular
support and
an activation composition is applied to the membrane side of the tubular
support.
Components of the dense gas-selective membrane, e.g., a hydrogen-selective
metal
or an alloy thereof, can be deposited to overlie the preactivated powder and
binder metal
using any of the techniques known in the art for depositing such materials on
a support.
For example, a component of the dense gas-selective membrane can be deposited
on the
support using electroless plating, thermal deposition, chemical vapor
deposition,
electroplating, spray deposition, sputter coating, e-beam evaporation, ion
beam evaporation
or spray pyrolysis. In some embodiments, a vacuum is applied to one side of a
porous
support and an plating composition, such as an electroless plating solution,
is applied to the
opposite side of the porous support. In one embodiment, a vacuum is applied to
the tube
side of a tubular support and a plating composition is applied to the membrane
side of the
tubular support.
An alloy of a gas-selective metal can be deposited over the deposited
preactivated
powder and binder metal as a component of the dense gas-selective membrane. In
one
embodiment, a palladium/silver alloy is formed by first depositing palladium
onto the
support by electroless deposition and then depositing silver, also by
electroless deposition,
onto the support. An alloy membrane layer can then be formed by heating the
silver and
palladium layers, for example, to about 500 C to about 1000 C in an inert or
hydrogen
atmosphere. In one embodiment, metal components can be co-deposited onto the
support
to form a layer of a finely divided mixture of small regions of the pure metal
components.
In another embodiment, a technique such as sputtering or chemical vapor
deposition is
used to simultaneously deposit two or more metals to form an alloy layer on
the support.
In one embodiment, the present inventive method can further include the step
of
depositing a gas-selective material to overlie the preactivated powder and
binder metal,
thereby forming a coated substrate and abrading the surface of the coated
substrate, thereby
forming a polished substrate, prior to formation of the dense gas-selective
membrane (e.g.,
a dense hydrogen-selective membrane) over the intermediate layer.
The composite gas-separation module can be treated with hydrogen gas at a
temperature of up to about 250 C. In one embodiment, the pressure of the
hydrogen gas
can range up to about 8 bar (0.8 MPa). Typically, the treatment with hydrogen
gas lasts for
at least about 1 hour, for example, about 1 hour to about 4 hours or about 3
to about 4
hours. Without wishing to be held to any particular theory, it is believed
that by exposing

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newly formed palladium-containing membranes to hydrogen at a low temperature
(e.g., up
to about 250 C such as about 200 C to about 250 C) and at a low pressure
(e.g., up to
about 8 bar (0.8 MPa) such as up to about 2 or 3 bar (0.2 to 0.3 MPa)),
palladium grain
growth is slowed and membrane cracking is slowed or prevented. It is believed
that
suitable hydrogen temperatures and pressures for this treatment are those that
lie outside
the two phase region on a palladium-hydrogen phase diagram.
The composite can be treated by a method that comprises the step of treating a
composite gas separation module with hydrogen gas at a temperature of up to
about 250 C.
The composite gas separation module may be formed using any technique known in
the
art. In one embodiment, the composite gas separation module is formed as
described
herein. Preferably, the composite gas separation module includes palladium or
an alloy
thereof.
In one embodiment, the temperature of the hydrogen gas is at least about 200
C.
The pressure of the hydrogen gas can range up to about 8 bar (0.8 MPa). For
example, the
pressure of the hydrogen gas can be in the range from about 2 to about 3 bar
(0.2 to 0.3
MPa). The composite gas-separation module can be treated with hydrogen gas,
for
example, for at least about 1 hour such as about 1 hour to about 4 hours or
about 3 to about
4 hours. It is believed that by exposing newly formed palladium-containing
membranes to
hydrogen at a low temperature (e.g., up to about 250 C such as about 200 C to
about
250 C) and at a low pressure (e.g., up to about 8 bar (0.8 MPa) such as up to
about 2 or 3
bar (0.2 to 0.3 MPa)), palladium grain growth is slowed and membrane cracking
is slowed
or prevented. It is believed that suitable hydrogen temperatures and pressures
for this
treatment are those that lie outside the two phase region on a palladium-
hydrogen phase
diagram.
In one embodiment, a small quantity of the metal, sufficient to cover the pore
walls
of the substrate, for example less than about 10, 7, 5, 3 or 1 percent of the
ultimate
thickness of the dense gaseous membrane, is deposited on the porous substrate
without a
significant reduction of the substrate porosity. Typically, the deposition of
palladium, gold
and/or platinum on the porous substrate is made by surface activating and
plating on the
side of the substrate opposite to the side on which a gas-selective membrane
will be
formed. For example, in one embodiment, a deposit of palladium, gold and/or
platinum is
formed from the inside of a substrate tube (e.g., using an electroless plating
solution) and a
dense gas-selective membrane is subsequently formed on the outside of the
substrate tube.


CA 02580580 2007-03-13
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The gas separation modules can also be fabricated by selectively surface
activating
a support proximate to a defect and preferentially depositing a material on
the selectively
surface activated portion of the support. The method is discussed in "Method
for Curing
Defects in the Fabrication of a Composite Gas Separation Module," U.S.
Application
Serial No. 10/804,848 filed March 19, 2004.
In one embodiment, the invention includes removing residual metal chlorides,
for
example, by treatment with an aqueous phosphoric acid solution, e.g., 10%
phosphoric acid
solution. For example, the treatment can include application of 10% phosphoric
acid
solution at room temperature for a time sufficient to convert residual metal
chlorides to
metal phosphates, e.g., about 30 minutes, followed by appropriate rinsing and
drying, e.g.,
rinsing with deionized water for about 30 minutes and drying at about 120 C
for at least
about 2 hours.
In some embodiments, the composite gas separation modules are made by one or
more of the following steps:(i) substrate surface treatments by oxidizing the
surface of the
substrate or by forming a nitride layer, (ii) intermetallic diffusion barrier
formation, (iii)
surface activation of the support,,e.g. with aqueous stannous chloride and
palladium
chloride prior to deposition of metal membrane, or (iv) metal deposition over
the support
or the intermediate layer, which steps are described in U.S. Patent No.
6,152,98, and also in
U.S. Patent Application No.10/804,848, 10/804,846; U.S. Patent Application No.
10/804,847, entitled "Method for Fabricating Composite Gas Separation
Modules," filed
on March 19, 2004;-and U.S. Patent Application No. 10/836,088, entitled "High
Tamman
Temperature Intermediate Layer", filed on Apri130, 2004.
The following illustrative embodiments will serve to illustrate the invention
disclosed herein. The examples are intended only as a means of illustration
and should not
be construed as limiting the scope of the invention in any way. Those skilled
in the art will
recognize many variations that may be made without departing from the spirit
of the
disclosed invention.
ILLUSTRATIVE EMBODIMENT 1
Figure 4 shows a schematic diagram of a multi-tubular, DC heated, radial flow,
membrane, steam reforming reactor in accordance with the present invention. In
the reactor
shown in Figure 4, a vaporizable hydrocarbon and steam enter the reactor at
inlet 69 and
flow through the reforming catalyst bed 70 (which is in the form of an
annulus) containing
multiple membrane tubes 71 (made by a process as described in Illustrative
Embodiment

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11 or Illustrative Embodiment 12) and multiple DC tubes 72 surrounded by the
catalyst
bed. In this embodiment the feed gases and reaction gases flow through the
catalyst bed
radially from outside to inside. The multiple hydrogen-selective, hydrogen-
permeable,
membrane tubes 71 are disposed axially in concentric rows in the reforming
catalyst bed
and serve to remove hydrogen, which is produced by the reforming reactions.
The multiple
DC tubes (i.e., chambers) 72 are also disposed axially in concentric rows in
the reforming
catalyst bed (for example, in a ratio of 1:2 or other number of DC tubes to
the number of
membrane tubes). The multiple DC tubes are in contact with the reforming
catalyst bed
and provide a controlled, distributed heat flux to the catalyst bed sufficient
to drive the
reforming reactions. While the membrane tubes and the DC tubes are shown to be
in
concentric rows in Figure 4, other geometric arrangements of these tubes can
be suitably
employed, and are within the scope of the present invention.
The DC tubes 72 generally comprise a fuel conduit disposed within a larger
tube
with an inlet and flow path for a preheated oxidant (e.g., preheated air) and
an outlet for
combustion (flue) gas. The DC tubes may be closed ended with a fuel conduit,
oxidant
inlet and flow path, and flue gas outlet arranged as shown in Figure 6A, or
may open ended
with the fuel conduit, oxidant inlet and flow path arranged as shown in Figure
6B.
High purity hydrogen is removed from the multi-tubular, radial flow, reactor
shown
in Figure 8 via outlets 73, with the aid of vacuum. Optionally, a sweep gas
may be used to
promote the diffusion of hydrogen through the membranes of the membrane tubes
71. If a
sweep gas is employed, the membrane tubes 71 may contain an outer sweep gas
feed tube
and an inner return tube for sweep gas and hydrogen as discussed in Figure 12.
By-product
gases, including unpermeated hydrogen, if not further used internally for heat
production,
e.g., combustion or heat exchange, exit the multi-tubular, radial flow,
reactor via outlet 74.
A hollow tube or cylinder 75 may optionally be used for flow distribution.

ILLUSTRATIVE EMBODIMENT 2
Figure 5 is a top cross-section view of the shell of the multi-tubular, DC
heated,
radial flow, membrane, steam reforming reactor of Figure 4. The cross
sectional view of
the reactor shows multiple membrane tubes 71 (made by a process as described
in
Illustrative Embodiment 11 or Illustrative Embodiment 12 and multiple DC tubes
72
dispersed in catalyst bed 70 with optional hollow tube or cylinder 75 being in
the center of
the reactor. In the example shown, the membrane tubes 71 have outside
diameters (OD) of
about one inch (2.54 cm) while DC tubes have an OD of approximately two inches
(about
37


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5.08 cm), although other sizes of these tubes can be suitably employed. If a
sweep gas is
employed, the membrane tubes 71 may contain an outer sweep gas feed tube and
an inner
return tube for sweep gas and hydrogen as shown in Figures 8 and 13. A larger
shell
containing more tubes duplicating this pattern can also be used.

ILLUSTRATIVE EMBODIMENT 3
. Figures 6A and 6B are schematic diagrams showing an example of a "closed
ended" and of an "open ended" distributed combustion tubular chamber which are
used to
drive the reforming reactions in various embodiments of the present invention.
Referring
to Fig. 6A, an oxidant (in this case preheated air) enters the DC tube at
inlet 76 and mixes
with fuel which enters the DC tube at inlet 77 and passes into fuel conduit 78
through
nozzles 79 spaced along the length of the fuel conduit, whereupon it mixes
with the air
which has been preheated to a temperature such that the temperature of the
resulting
mixture of fuel and air is above the autoignition temperature of the mixture.
The reaction
of the fuel passing through the nozzles and mixing with the flowing preheated
air at a
temperature above the autoignition temperature of the mixture, results in
distributed
combustion which releases controlled heat along the length of the DC tube as
shown, with
no flames or hot spots. The combustion gases, (i.e., flue gas) exit the DC
tube at outlet 80.
In the "open ended" DC tubular chamber shown in Fig. 6B, preheated air enters
the
DC tube at inlet 76 and the fuel at inlet 77, and the fuel passes through
conduit 78 and
nozzles 79, similar to "closed end" DC tube in Fig. 6A. However, in the case
of the "open
ended" DC tube, the flue gas exits the DC tube at open end 81, instead of
outlet 80 as
shown in Fig.6A.
ILLUSTRATIVE EMBODIMENT 4
Figure 7 is a schematic drawing of a multi-tubular, DC heated, axial flow,
membrane, steam reforming reactor in accordance with the present invention. In
the
reactor shown in Figure 7, a vaporizable hydrocarbon and steam enter the
reactor at inlet
69 and flow through the reforming catalyst bed 70 containing multiple hydrogen-
selective
membrane tubes 71 (made by a process as described in Illustrative Embodiment
11 or
Illustrative Embodiment 12) and multiple DC tubes 72. In this embodiment the
feed gases
and reaction gases flow through the catalyst bed axially from the top of the
catalyst bed to
the bottom. The multiple hydrogen-selective membrane tubes 71 are disposed
axially in
the reforming catalyst bed and serve to remove hydrogen which is produced by
the
reforming reactions. In the embodiment shown the membrane tubes are closed at
the top

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and a sweep gas (e.g. steam) is employed, which enters the reactor at inlet 85
into the
bottom of the membrane tubes where it flows upward in the outer part of the
membrane
tube, counter-current to the hydrocarbon and steam feed. A stinger pipe fitted
to the
bottom of the permeate section may be used to distribute the sweep gas in the
membrane
tube. The permeated hydrogen and sweep gas flow downward in a return tube
located in
the center of the membrane tube and exit the reactor via outlet 86. The
pressure drop in the
permeate pipe section is significant when the length of the pipe relative to
the diameter
exceeds a given limit. Actually, the volumetric amount of hydrogen crossing
the
membrane is proportional to the membrane area, ~*D*L and the multiplier is the
velocity,
which is fixed as a function relating to Sievert's law, the description of
which can be found
in US2003/0068269. The same hydrogen amount has to flow across the pipe cross
section
which is equal to ri*D2/4. The ratio of hydrogen velocities through the pipe
and through
the membrane respectively is proportional to (ri *D*L)/(tt *D2/4) or to L/D.
Pressure drop
increases with gas velocity. If this ratio exceeds a limit, then the velocity
in the permeate
pipe exceeds a limit too, since the velocity through the membrane is fixed.
Then the
pressure drop in the permeate pipe becomes high and it reduces the hydrogen
flux by
creating back pressure in the permeate section. In such a case, the reactor
design has to
accommodate either a higher membrane diameter, or a reduced length.
There are also multiple DC tubes (i.e., chambers) 72 disposed axially in the
reforming catalyst bed. In the embodiment shown the DC tubes are "closed
ended" tubes
with preheated air entering at inlet 76, fuel entering at 77 and combustion
gas (i.e., flue
gas) exiting the reactor at outlet 80. The multiple DC tubes are in heat
transferring contact
with the reforming catalyst bed 70 and provide a controlled, distributed heat
flux to the
catalyst bed sufficient to drive the reforming reactions. While the membrane
tubes and the
DC tubes are shown to be in a particular geometric pattern in Figure 11, it is
understood
that other geometric arrangements of these tubes may be used and are within
the scope of
the invention. While "closed ended" DC tubes are employed in the particular
reactor
shown in Figure 7, "open ended" DC tubes may be suitably employed as well.
Also, the
DC tubes and/or the membrane tubes may be surrounded by cylindrical screens
(not
shown) to protect them from getting in direct contact with the catalyst, and
to allow
insertion of these tubes even after the catalyst is loaded into the reactor.
The DC chamber must be free of obstructions and have a tubular dimension for
the
external or exterior tube of the DC chamber such that the length to diameter
ratio is higher
39


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than a given limit, preferably more than 4. This ratio ensures that the air
velocity in the
chamber becomes higher than the flame velocity of the fuel and that turbulence
is induced
to improve heat transfer. In such a condition, no flames are created or
stabilized. Any
obstructions (like baffles) would create stagnation points where flames would
form and

stabilize.
High purity hydrogen, which diffuses through the membrane into the membrane
tubes, is removed from the reactor via outlet(s) 86 together with the sweep
gas (in this case
steam). While outlet 86 is shown in Figure 7 to be located on the side of the
reactor, this
outlet may optionally be located at the bottom of the reactor thereby avoiding
a bottom side
exit manifold. A further option involves the use of a vacuum instead of a
sweep gas to
facilitate diffusion of the hydrogen through the membrane into the membrane
tubes.
Vacuum can be induced either mechanically with a pump or chemically with a
metal
hydride precursor which reacts away the hydrogen to form metal hydride. The
hydride is
on-line for a given period of time and when it is saturated, a parallel
compartment can be
put on-line, while the original compartment is isolated and heated to desorb
and produce
the hydrogen. This is advantageous in cases where the hydrogen needs to be
stored and/or
shipped to a customer or in cases where the cost of electrical energy for
running a pump is
higher than using waste energy to desorb the hydrogen from the hydride.
Detailed
economics will dictate the right choice.
In another embodiment of the reactor in Figure 7, the sweep gas inlet 85 and
the
hydrogen, sweep gas outlet 86 and their associated plenums, may be placed on
the top of
the reactor allowing easy access to the bottom of the reactor. In a further
embodiment of
the reactor of Figure 11, the preheated air inlet 76, the fuel inlet 77 and
the flue gas outlet
80 and their associated plenums may be placed on the bottom of the reactor
allowing easy
access to the top of the reactor.
By-product gases, including carbon dioxide, steam, and minor amounts of carbon
monoxide and unpermeated hydrogen, if not further used internally for heat
production,
e.g., combustion or heat exchange, exit the multi-tubular, axial flow, reactor
via outlet 74.
The reactor shown in Fig. 11 may be equipped with baffles and/or screens such
as the
baffles shown in Figures 13A and 13B or 13C and 13D.
ILLUSTRATIVE EMBODIMENT 5
Figure 8 is a top cross-section view of the shell of the multi-tubular, DC
heated,
axial flow, membrane reactor shown in Figure 7. In the embodiment shown
multiple


CA 02580580 2007-03-13
WO 2006/034086 PCT/US2005/033267
membrane tubes 71 (made by a process as described in Illustrative Embodiment
11 or
Illustrative Embodiment 12) and multiple DC tubes 72 are dispersed in
reforming catalyst
bed 70. The multiple DC tubes employed in this embodiment are "closed ended"
DC tubes
as discussed above in connection with Figure 7. The membrane tubes are
equipped with an
outer sweep gas feed tube and an inner hydrogen, sweep gas return tube as
discussed in
connection with Figure 7. A typical reactor of the type shown in this Figure 8
may
comprise, for example, 19 DC tubes of 5.5" outer diameter and 90 membrane
tubes of 2"
outer diameter enclosed in a shell of 3.5 ft diameter containing catalyst in
the void spaces.
Other shell sizes and numbers of tubes can be suitably employed depending on
the capacity
needed. The design parameter which is of utmost importance is the optimum gap
between
the membrane and the DC tubes. If a high gap is assumed, then heat transfer
limitations
occur since the flow of enthalpy from DC to the reforming reaction is slow.
The
membranes may not operate isothermally and cold spots may develop, thus
reducing the
reactor efficiency. If a small gap is assumed, then there may be problems with
insufficient
catalyst penetration in the gap, overheating of the membrane, or even touching
of the hot
DC tube with the membrane in conditions where the tubes are not perfectly
straight. A
narrow gap limitation will make reactor fabrication more expensive, since
clearances are
hard to achieve. Thus, an intermediate gap is more preferable. As a particular
non-limiting
example, the gap between the membrane and the DC tubes is from about'/4 inch
(about
0.64 cm) to about 2 inches (about 5.08 cm), particularly from about %2 inch
(about 1.27 cm)
to about 1 inch (about 2.54 cm). The gap between the membrane tubes may be
from about
%4 inch (about 0.62 cm) to about 2 inches (about 5.08 cm), particularly from
about % inch
to about 1 inch and this has to be also optimized. The hydrogen-permeable
membrane tube
has a ratio of length to diameter of less than about 500.

ILLUSTRATIVE EMBODIMENT 6
Figures 9A and 9B and 9C and 9D show two different configurations of baffles
which may be employed in the multi-tubular, DC heated, axial flow, membrane
steam
reforming reactors of the invention to increase contact of the reactant gases
with the
catalyst in the catalyst beds. The baffle configuration shown in Figures 9A
and 9B
comprises a washer shaped baffle 87 and a disk shaped baffle 88 arranged in an
alternating
pattern. This baffle arrangement causes the feed and reactant gases to flow
through the
hole in the washer shaped baffle and be deflected by the disk shaped baffle
thereby

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enhancing the contact of the reactant gases with the catalyst (not shown)
which is packed
in the area between the baffles.
The baffle arrangement shown in Figures 9C and 9D comprises truncated disks 89
which are placed in an alternating pattern (truncated left and truncated
right) in the reactor
thereby causing the feed and reactant gases to "zigzag" as they flow through
the catalyst
(not shown) which is packed in the area between the baffles.
The baffles in Figures 9A&B and 9C&D will have openings (not shown) to allow
the DC tubes and membrane tubes to pass through them. Screens positioned in
vertical
alignment (not shown) may also be used to support the baffles and in some
cases hold the
catalyst away from the shell wall or from the center of the shell for better
gas flow
distribution.
ILLUSTRATIVE EMBODIMENT 7
Figure 13 is a top cross-section view of the shell of a multi-tubular reactor
in
accordance with one embodiment of the invention in which four membrane tubes
71 (made
by a process as described in Illustrative Embodiment 11 or Illustrative
Embodiment 12) are
dispersed in the reforming catalyst bed 70 which is packed into reactor tube
82, while the
DC chamber is in the form of an annulus surrounding the reforming catalyst
bed. The
tubular DC chamber (which is defined by outer wal183 and the wall of the
reactor tube 82)
contains multiple fuel conduits 78 having nozzles (not shown) through which
fuel flows
and mixes with preheated air flowing in the DC chamber whereupon combustion
occurs. If
a sweep gas is employed, the membrane tubes 71 may contain an outer sweep gas
feed tube
and an inner return tube for sweep gas and hydrogen as shown in Figure 13. In
one
embodiment of the invention, the membrane tubes have an outer diameter of 2
inches,
while the outer DC tube has an inner diameter (ID) of approximately 8.6
inches. However,
other sizes can be suitably employed.
ILLUSTRATIVE EMBODIMENT 8
Figure 10 is a top cross-section view of the shell of another embodiment of
the
multi-tubular, axial flow, reactor of the invention in which multiple reactor
tubes 82
packed with reforming catalyst are employed. In this example each of the six
reactor tubes
82 contains a catalyst bed 70 and a membrane tube 71 (made by a process as
described in
Illustrative Embodiment 11 or Illustrative Embodiment 12) containing an outer
sweep gas
feed tube and an inner hydrogen, sweep gas return tube. Heat is provided to
the reforming
catalyst beds by the tubular DC chamber defined by outer wall 83 and inner
wall 84. The
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DC chamber contains multiple fuel conduits 78 dispersed at various intervals
in the DC
chamber. A hollow tube or cylinder defined by inner wall 84 may optionally be
used for
flow distribution.
ILLUSTRATIVE EMBODIMENT 9
Figure 12 is a top cross-section view of the shell of further embodiment of
the
multi-tubular, axial flow, reactor of the invention in which four membrane
tubes are
dispersed in each of six reactor tubes 82 containing catalyst beds 70. Heat is
provided to
the catalyst beds by DC chamber defined by outer wall 83 and inner wall 84.
The DC
chamber contains multiple fuel conduits 78 having nozzles 79 (not shown). If a
sweep gas
is employed, the membrane tubes 71 (made by a process as described in
Illustrative
Embodiment 11 or Illustrative Embodiment 12 ) may contain an outer sweep gas
feed tube
and an inner return tube for sweep gas and hydrogen as discussed shown and
discussed
above in connection with Figures 8 and 13. The hollow cylinder or tube defined
by inner
wall 84 may optionally be used for flow distribution.
ILLUSTRATIVE EMBODIMENT 10
Figure 12 is a top cross-section view of the shell of further embodiment of
the
multi-tubular, axial flow, reactor of the invention in which six membrane
tubes 71 (made
by a process as described in Illustrative Embodiment 11 or Illustrative
Embodiment 12) are
dispersed in each of the six reactor tubes 82 packed with reforming catalyst.
Heat is
provided to the reforming catalyst beds by the DC chamber defined by outer
wall 83 and
inner wa1184. The DC chamber contains multiple fuel conduits 78. Additional
heat may be
provided to the catalyst beds by employing a DC tube 72 in the center of each
of the
reactor tubes 82 as shown in Figure 12. The hollow tube or cylinder defined by
inner wall
84 may optionally be used for flow distribution.
If a sweep gas is employed, the membrane tubes 71 may contain an outer sweep
gas
feed tube and an inner return tube for sweep gas and hydrogen as discussed in
Figure 12.
ILLUSTRATIVE EMBODIMENT 11
This embodiment describes the fabrication of a composite structure which can
be
used for making the hydrogen selective and hydrogen-permeable membrane tubes
for the
reactors of Illustrative embodiments 1-10. It had a dense hydrogen-selective
membrane, an
intermediate layer that included a preactivated aluminum oxide (A12O3) powder
and a
palladium binder, and a nomina10.1 media grade porous 316L stainless steel
("PSS")
support.

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A 2.5 inch (6.35 centimeter (cm)) long, 0.5 inch (1.27 cm) outside diameter
(O.D.)
section of PSS tube, welded to a section of non-porous 316L stainless steel
tube on one end
and a non-porous cap on the other end, was obtained from Mott Metallurgical
Corporation.
Contaminants were removed by cleaning the tube in an ultrasonic bath with
alkaline
solution at 60 C for one hour. Tap water was flushed on both the inside and
the outside of
the tube for 5 hours to remove all the alkaline solution from the PSS pore
system. The tube
was then washed with distilled water 2 or 3 times in an ultrasonic bath (10
minutes each
wash). Finally, the tube was rinsed with acetone for 10 minutes. The support
was then
dried at 120 C overnight. The tube was then oxidized in air at 500 C for 10
hours. After
oxidation, the color of the porous substrate had changed from silver to gray-
green and did
not appear uniform. A second oxidation at 500 C for 10 hours was performed and
the
color of the support changed from gray-green to red and uniform.
Preactivated aluminum oxide (alumina) powder was formed by surface activating
aluminum oxide powder using the following method. 5 grams (g) of A1203 powder
with an
average particle size of 5 microns (Buehler, Ltd., Lake Bluff, IL), 2.5 g of
A1203 powder
with a mean particle size of 3 microns (Buehler, Ltd.) and 1 g of A1203 powder
with a
mean particle size of 0.01-0.02 microns (Alfa Aesar; Ward Hill, MA) were
cleaned in 200
milliliters (mL) of water solution with pH adjusted to 2 using 10 M HCI. The
cleaning step
was performed in an ultrasonic bath at 60 C for 1 hour. The cleaned alumina
powder
mixture was filtered using glass microfiber filter paper (WHATMAN GF/F type,
Whatman, Inc; Clifton, NJ) and an aspirator. The filter cake with the glass
microfiber filter
was then put in 200 mL of aqueous stannous chloride (SnC12) solution (1 g/L,
pH=2) for
sensitization. The sensitizing step was performed in an ultrasonic bath at 60
C for 10
minutes. The GF/F filter was removed from the solution using a glass rod and
the
sensitized powder mixture was filtered. The filter cake with the glass
microfiber filter was
placed in 200 mL aqueous palladium chloride (PdC12) (0.1g/L, pH=2) activation
solution.
The activation step was performed in an ultrasonic bath at 60 C for 10
minutes. Finally,
the activated powder mixture was filtered, washed with distilled water, and
dried overnight
at 120 C. At the end of the activation procedure, a thin yellowish cake of
preactivated
aluminum oxide was formed on the glass microfiber filter.
0.5 g of the pre-activated mixture was mixed in 200 ml of water at pH 2 to
form a
slurry which was placed in ultrasonic bath for homogenization. The oxidized
support was
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then placed in the slurry and a vacuum was pulled (using an aspirator) from
the inside of
the tube. After 30 seconds, a gray, deposit formed on the porous section of
the support.
Palladium adhesion to the support was increased by the presence of anchoring
sites.
Anchoring sites, such as the tips of the substrate particles (e.g., the tips
of PSS grains
forming the PSS support), were not covered by the alumina powder to produce
good
adhesion between the palladium membrane and the support. To expose the
anchoring sites,
extra alumina cake was removed by gloved hand while gently rinsing with
distilled water.
The vacuum in the tube side was maintained during removal of the extra
alumina.
Alumina remained inside the pore mouths of the porous support.
The support was then palladium plated for 20-30 minutes while applying a
vacuum
to the tube side using the following procedure. The tube was immersed in a
plating
solution at room temperature. The plating solution was composed of 4 grams
Pd(NH3)4C12
' H20/liter, 198 milliliters NH4OH (28 weight percent)/liter, 40.1 grams
NaZEDTA/liter,
and 6 milliliters aqueous H2NNH2 (1 M)/liter. The plating solution and tube
were placed in
a water bath at 60 C. During plating, the level of plating solution was kept
constant by
adding a small quantity of plating solution for loss of solution to the
vacuum. After the
palladium in the plating solution was depleted, the tube was removed and
placed in
deionized water at 60 C until the water temperature reached room temperature.
The tube
was rinsed with cold water 4 to 5 times. Then, the support was dried at 120 C
overnight.
After the powder deposition, the support was surface activated by sequentially
immersing the exterior of the support in aqueous baths of SnCl2 and PdC12. The
exterior of
the tube was immersed in 140 mL of aqueous SnCl2 (1 g/L) at 20 C for about 5
minutes
and was subsequently rinsed with deionized water. The exterior of the tube was
then
immersed in 140 mL of aqueous PdC12 (0.1 g/L) at 20 C for about 5 minutes
followed by
rinsing first with 0.01 molar hydrochloric acid and then with deionized water.
The above-
described surface activation cycle was performed a total of three times.
The surface activated support was then plated with palladium for 3 hours (2
cycles
of palladium plating, as described above). After the first cycle of palladium
plating, a
slight mechanical treatment was preformed on the palladium layer with 600 grit
silicon
carbide paper to smooth the palladium layer. A dense palladium film, 14.8
microns thick
(determined gravimetrically), was achieved after a total plating time of 9
hours. This
composite palladium membrane showed a hydrogen permeance of 22.7 [m3/(m2 hour
bar 'S)]sTP at 500 C. The hydrogen permeance was stable during the total time
of the



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experiment (70 hours) at 500 C. The selectivity (H2/He) of this membrane at
500 C was
260.
ILLUSTRATIVE EMBODIMENT 12
This embodiment describes the fabrication of a composite structure which can
be
used for making the hydrogen selective and hydrogen-permeable membrane tubes
for the
reactors oflllustrative embodiments 1-10. It had a dense hydrogen-selective
membrane, an
intermediate layer that included preactivated aluminum oxide (A12O3) powders
and a
palladium binder, and a nomina10.1 media grade porous 316L stainless steel
("PSS")
support.
A 2.5 inch (6.35 cm) long, 0.5 inch (1.27 cm) outer diameter section of PSS
tube,
welded to a section of non-porous 316L stainless steel tube on one end and a
non-porous
cap on the other end, was obtained from Mott Metallurgical Corporation. The
support was
cleaned and dried following the same procedure described in Example 1. The
support was
then oxidized at 500 C in air for 10 hours.
Three different mixtures of powders were prepared as described below.
Powder Mixture 1 included 65 wt% A1203 with an average particle size of 1
micron
(Alfa Aesar); 30 wt% A1203 with an average particle size of 5 microns
(Buehler, Ltd.), and
5 wt% A1203 with an average particle size of 3 microns (Buehler, Ltd.).
Powder Mixture 2 included 60 wt% A12O3 with an average particle size of 0.3
micron (Alfa Aesar); 30 wt% A1203 with an average particle size of 3 microns
(Buehler,
Ltd.), and 10 wt% A1203 with an average particle size of 1 micron (Alfa
Aesar).
Powder Mixture 3 included 60 wt% A1203 with an average particle size of 0.01-
0.02 micron (Alfa Aesar); 30 wt% A1203 with an average particle size of 1
micron (Alfa
Aesar), and 10 wt% A12O3 with an average particle size of 0.3 micron (Alfa
Aesar).
The fine and very fine mixtures of alumina powders (i.e., Powder Mixtures 2
and 3)
were activated separately following the procedure described in Example 1. The
coarse
powder (i.e., Powder Mixture 1) was not activated to avoid subsequent
deposition of
palladium too deep into the pore system of the PSS support.
The oxidized PSS support was placed for 1 minute in a 200 mL water slurry at
pH 2
that contained 0.5 g of Powder Mixture 1. A vacuum was applied to the tube
side of the
support and an alumina cake easily formed on the support. Extra alumina cake
was
removed by gloved hand while gently rinsing with distilled water while vacuum
on the
tube side was maintained. Alumina powder only remained in the pore mouths of
the

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support. Following the deposition of Powder Mixture 1, the support was
immersed for 1
minute in a 200 mL water slurry that contained 0.5 g of pre-activated
Powder Mixture 2 while a vacuum was applied to the tube side of the support.
Again,
extra alumina cake was removed carefully by gloved hand as described above.
After
deposition of the pre-activated Powder Mixture 2, the support was placed in
140 mL of
palladium plating solution (described in Example 1) for 5 minutes of palladium
plating
(with no vacuum applied to the tube side) to glue the alumina particles.
Following
deposition of Powder Mixture 2, the support was immersed in a 200 mL water
slurry that
contained 0.5 g of pre-activated Powder Mixture 3 for 1 minute while a vacuum
was
applied to the tube side of the support. Again, extra alumina cake was removed
carefully
by gloved hand. After deposition of pre-activated Powder Mixture 3, the
support was
immersed in 140 mL of palladium plating solution for 5 minutes of palladium
plating (with
no vacuum applied to the tube side). This process produced a graded support.
The graded support was then surface activated by performing two times the
surface
activation cycle described in Example 1. The surface activated support was
then plated
with palladium for 3 hours (2 cycles of palladium plating, as described in
Example 1 with
no vacuum applied). After the first cycle of palladium plating a slight
mechanical
treatment was preformed on the palladium layer with 600 grit silicon carbide
paper to
smooth the palladium layer. After the first two palladium plating cycles, the
support was
surface activated using one cycle without a vacuum applied and then two
surface activation
cycles with a vacuum applied to the tube side of the support. Following
surface activation,
palladium was plated for 3 hours while pulling a vacuum on the tube side of
the support.
The support was then surface activated again using 3 surface activation cycles
and then
plated with palladium for an additional 3 hours, both steps performed without
vacuum.
After a total plating time of 9 hours, the membrane was 14 microns thick
(determined
gravimetrically).
The permeance of this membrane reached 16 [m3/(m2 hour bar 'S)]sTP after 50
hours
at 250 C, which was extremely high compared to the membrane of Example 1. The
selectivity of this membrane at 250 C was measured to be 84. The low
selectivity was
likely due to an imperfection in the PSS support that could not be covered by
palladium.
ILLUSTRATIVE EMBODIMENT 13
This embodiment describes the fabrication of a composite structure which can
be
used for making the hydrogen selective and hydrogen-permeable membrane tubes
for the
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reactors of Illustrative embodiments 1-10. It had a dense hydrogen-selective
membrane, an
intermediate layer that included preactivated aluminum oxide (A1203) powders
and a
palladium binder, and a nominal 0.1 media grade porous HASTELLOY C-22
support.
(HASTELLOY C-22 is a nickel-chromium-molybdenum-iron-tungsten alloy.)
A 6 inch (15.24 cm) long, 1 inch (2.54 cm) outer diameter section of
HASTELLOY tube, welded to a section of non-porous 316L stainless steel tube
on one
end and a non-porous cap on the other end, was obtained from Mott
Metallurgical
Corporation. The support was cleaned and dried following the same procedure
described
in Example 1. The support was then oxidized at 700 C in air for 12 hours. A
graded
support was then produced using the same procedures and the same alumina
powder
mixtures as described in Example 2.
The graded support was then surface activated by performing two times the
surface
activation cycle described in Example 1. The surface activated support was
then plated
with palladium for 3 hours (2 cycles of palladium plating, as described in
Example 1 with
no vacuum applied). A third cycle of palladium plating was performed without
vacuum for
the first 40 minutes and pulling a vacuum in the tube side during the last 50
minutes.
After the last plating and rinsing with DI water, the membrane was dried for 2
hours at 120 C. The thickness of the palladium layer after these steps was 7.7
microns
(determined gravimetrically). The helium leak of the membrane after the total
of 4.5 hours
of palladium plating was 8.9x104 m3/(m2 hour bar) and the membrane was
considered
dense.
The permeability of this membrane reached 21.5 [m3/(m2 hour bar 'S)]sTP at 250
C
after 150 hours in hydrogen. The selectivity (H2/He) at 250 C was 2016. The
membrane
showed hydrogen permeance of 28.5 [m3/(m2 hour bar '5)]sTP at 300 C, 33.6
[m3/(m2 hour
bar0.5)]sTP at 350 C, 38.3 [m3/(m2 hour bar '5)]sTP at 400 C, 43.5 [m3/(m2
hour bar '5)]sTP at
450 C, and 50 [m3/(m2 hour bar0'S)]sTp at 500 C. The selectivity of the
membrane
decreased from 2016 at 250 C to 42 at 500 C. However, the large helium leak
was likely
due to a blister in the welding between the porous part of the support and the
non-porous
part. The module was repaired as described in Example 14, below.
ILLUSTRATIVE EMBODIMENT 14
After hydrogen characterization (which lasted 743 hours), the membrane
produced
as described in Illustrative Embodiment 13 was repaired. The surface of the
membrane
was examined and large blisters were found at the interface between the porous
parts and

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the non-porous parts of the support. The surface of the membrane was masked
using
polytetrafluoroethylene tape, and palladium was plated for 6 hours locally on
the welds
between the porous HASTELLOY C-22 support and the non-porous parts. After
local
palladium plating of the two welds, the helium leak dropped to 0:006 [m3/(m2
hour bar)]sTp
at room temperature. Finally, the support was unmasked and the total surface
was
activated with three surface activation cycles using the procedure described
in Example 1
while applying a vacuum to the tube side of the support and a last palladium
plating cycle
(1.5 hours) was performed. The thickness of the membrane after repair was
about 10
microns and the helium leak was undetectable.
The permeability of this membrane reached 14.8 [m3/(m2 hour bar 'S)]sTP at 250
C
after 47 hours in hydrogen. The membrane was then slowly heated (0.5 C/min) to
500 C
and the hydrogen permeance was measured to be 40.6 [m3/(m2 hour bar 'S)]sTp at
500 C.
After 200 hours in hydrogen at 500 C, helium was introduced in the reactor to
measure the
helium leak. The helium leak was 0.00064 [m3/(m2 hour bar)]sTp so that the
selectivity
(H2/He) was 27000. Hydrogen was then reintroduced for another 270 hours. After
the 270
hours, the permeance was 41.2 [m3/(m2 hour bar0*5)]sTp and the selectivity
(after switching
to helium) was 2400. After another 285 extra hours in hydrogen (with 4 changes
H2-He-
H2), the membrane had a permeance of 42.5 [m3/(m2 hour bar 'S)]sTp and a
selectivity of
600. To conclude, the repaired module was stable at 500 C for 755 hours and
the final
permeance was 42.5 [m3/(m2 hour bar '5)]sTP with a selectivity of 600.
ILLUSTRATIVE EMBODIMENT 15
This embodiment describes the fabrication of a composite structure which can
be
used for making the hydrogen selective and hydrogen-permeable membrane tubes
for the
reactors of Illustrative embodiments 1-10. It had a dense hydrogen-selective
membrane, an
intermediate layer that included preactivated aluminum oxide (A1203) powders
and a
palladium binder, and a nomina10.1 media grade porous HASTELLOY C-22
support.
A 6 inch (15.24 cm) long, 1 inch (2.54 cm) outer diameter section of
HASTELLOY tube, welded to a section of non-porous 316L stainless steel tube
on one
end and a non-porous cap on the other end, was obtained from Mott
Metallurgical
Corporation. The support was cleaned and dried following the same procedure
described
in Example 1. The support was then oxidized at 700 C in air for 12 hours.
Three different powders were prepared as described below.

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Powder No. 1(coarse powder) was y-alumina powder with an average particle size
of 3 microns (SPA-Gamma-AF CERALOX high purity aluminum oxide, Sasol North
America, Inc., Houston, TX). Powder No. 2 (fine powder) was A1203 with an
average
particle size of 0.3 micron (10-20 y(gamma) phase, Alfa Aesar). Powder No. 3
(very fine
powder) was A1203 with an average particle size of 0.01-0.02 micron (80-95
y(gamma)
phase, Alfa Aesar).
g of the coarse powder, 10 g of the fine powder, and 5 g of the very fine
powder
were separately surface activated using the following procedure. Each powder
was placed
in a separate 500 mL cylinder containing 250 mL of aqueous SnC12 solution (1
g/L, pH=2).
10 This step of sensitizing the powder was performed in an ultrasonic bath at
60 C for 10
minutes. After 10 minutes, 250 mL of aqueous PdCl2 solution (0.1 g/L, pH=2)
were added
into the cylinder already containing the aqueous SnC12 solution and alumina
powder. The
resulting slurry, with a total volume of about 500 mL, became brown instantly.
The slurry
was placed in an ultrasonic bath at 60 C for 10 minutes. The resulting surface
activated
powder was then filtered from the slurry by using one filter paper (WHATMAN
GF/F
type) for every 50 mL of slurry. Therefore, each filter paper contained about
1 g of
preactivated coarse powder, about 1 g of preactivated fine powder, or about
0.5 g of
preactivated very fine powder. The filter cakes, 30 in number, were dried at
120 C for 2
hours.
1 g of the pre-activated coarse powder (i.e., 1 filter paper with its cake)
was mixed
with 450 mL of water at pH 2 to form a slurry which was then placed in
ultrasonic bath to
homogenize the alumina suspension. After 1 minute, the filter paper was
removed from
the slurry using a glass rod. The oxidized support was then placed into the
slurry and a
vacuum was pulled (using an aspirator) from the inside of the tube. After 30
seconds, a
gray deposit formed on the porous section of the support. Extra alumina cake
was removed
by gloved hand while gently rinsing with distilled water while the tube side
vacuum was
maintained. The support was then dipped for 4 additional seconds in the
slurry. Then, the
support was plated with palladium for 15 minutes using a procedure similar to
that
described in Example 1 using 400 mL of plating solution and with no vacuum
applied to
the support.
Following deposition and plating of the preactivated coarse powder, the
support
was immersed for 20 to 30 seconds in a 450 mL water slurry containing 1 g of
the
preactivated fine powder while a vacuum was applied to the inside of the
support. An



CA 02580580 2007-03-13
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alumina cake formed on the support. Extra alumina cake was removed by gloved
hand
while gently rinsing with distilled water while a vacuum was applied to the
inside of the
support. The support was then dipped for 5 additional seconds in the slurry.
Then, the
support was again plated with palladium, as described above, for 10 minutes.
Following the deposition and plating of the preactivated fine powder, the
support
was immersed for 30 seconds in a 450 mL water slurry containing 0.5 g of the
preactivated
very fine powder while a vacuum was applied to the inside of the support. No
extra
alumina cake seemed to form using the preactivated very fine powder. The
support was
again plated with palladium, as described above, for 10 minutes. The support
became
black in color. Underneath the black layer, shiny gray palladium could be
seen. This black
powdery layer was readily removed. With gloved hands the very fine black
powder was
used to polish the surface of the support. After 5-10 minutes of rubbing the
surface, the
support was rinsed with deionized water to remove the black particles. Once
the shiny
gray surface was visible, the support was plated with palladium for another 10
minutes.

Finally, the support was dried at 120 C for 4 hours.
The support was then masked with polytetrafluoroethylene tape, letting only
2 mm of the porous section of the tube and 5 mm of the non-porous section of
the tube
visible. To increase the adhesion between palladium and the tube, the oxide
layer on the
tube weld was removed by dipping the masked support in 400 mL of 1 M HCI. The
surface was gently rubbed with gloved hands to ease the oxide removal. The
support was
surface activated using with 2 activation cycles and palladium was plated to
the welding
zones for 1.5 hours using a procedure similar to that described in Example 1
under
vacuum. Then, the support was dried at 120 C for 4 hours.
Finally, the support was unmasked and the surface was activated with two
surface
activation cycles using the procedure described in Example 1. Then, the
support was
palladium plated for 3 hours (2 cycles of 1.5 hours) wherein 400 mL of plating
solution
was used for each cycle. A third palladium plating cycle, lasting 1 hour, was
performed
while a vacuum was applied to the tube side of the support. A palladium layer
formed that
was only 3.9 microns thick (determined gravimetrically). The helium leak was
measured
to be 0.0024 [m3/(m2 hour bar)]sTP. The membrane was considered to be dense.
The ranges and limitations provided in the instant specification and claims
are
those, which are believed to particularly point out and distinctly claim the
instant
invention. It is, however, understood that other ranges and limitations that
perform

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substantially the same function in substantially the same manner to obtain the
same or
substantially the same result are intended to be within the scope of the
instant inventions
defined by the instant specification and claim

52

Representative Drawing