Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
CA 02249126 1998-10-02
PALLADIUM COATED HIGH-FLUX TUBULAR MEMBRANES
FIELD OF THE INVENTION
The present invention relates to palladium coated high-flux tubular membranes
for hydrogen separation.
BACKGROUND OF THE INVENTION
Membrane reactors may utilize membranes for product separation or
purification in conjunction with chemical reactions. Such reactors are
particular suited for
reactions which are equilibrium limited, as significant enhancement over the
equilibrium
conversion may be achieved by selectively removing one or more reaction
products through
the membrane wall. It is well-known to use palladium and its alloys to form
such membranes
due to their high permeability, chemical compatibility with many hydrocarbon-
containing gas
streams and infinite hydrogen selectivity. Known palladium based membrane
applications
include steam reforming of methane, water gas shift, dehydrogenation of
various compounds
including hydrocarbons such as cyclohexane, ethylbenzene, ethane, propane and
butane.
Theoretically, there are several metals such as niobium, tantalum, zirconium
and vanadium which are more permeable to hydrogen than palladium. These metals
are also
much stronger than palladium. Therefore, even thin-walled membranes of these
metals may
provide the necessary thermal and mechanical strength to withstand hi~h
temperatures and
differential pressures. Furthermore, as flux is inversely proportional to
membrane thickness, it
is possible that thin-walled membranes of these metals have theoretical fluxes
that are orders
of magnitude greater than that of palladium alone.
However, these metals are not used for hydrogen separation because the
measured transport fluxes for these metals are much less than those predicted.
It is believed
that these metals have an inherent surface resistance or have a tightly held
oxide film which
CA 02249126 1998-10-02
impedes absorption. It is known to provide a very thin layer of palladium
coated on the
surface. This palladium coat serves two purposes - it catalyzes the molecular
hydrogen
dissociation and recombination reactions on the surface, and decreases the
transport barrier for
hydrogen atom absorption into the refractory metal. In addition, the palladium
layer protects
the refractory metal from oxidation. These palladium coated refractory metal
membranes
show the greatest promise for membrane separators for hydrogen separation.
Hydrogen flux through a composite membrane is inversely proportional to
membrane thickness and increases with pressure differential. Therefore, there
is a need in the
art for a thin-walled composite membrane which is strong enough to withstand
very high
pressure differentials at the high temperatures which may be encountered in
membrane
hydrogen separation reactors.
SUMMARY OF THE INVENTION
In one aspect of the invention and in general terms, the invention comprises a
composite tubular membrane having an outer surface and an inner surface
defining a
cylindrical bore, said membrane comprising:
a) a refractory metal chosen from the group of niobium, tantalum or vanadium;
b) a palladium coating on both the inner and outer surfaces; and
c) structural support means within the bore.
The structural support means preferably comprises a stainless steel spring
closely engaging the
inner surface of the tubular membrane. It is preferable if the spring is
compactly coiled
within the bore. Further, it is preferable if the thickness of the palladium
coating is greater
than about 3.0 pm and more preferably greater than about 4.0 Vim.
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CA 02249126 1998-10-02
The tubular membrane may be a straight tube or may be U-shaped. In either
embodiment, one end of the membrane is sealed and the other end is adapted to
connect with
a separation reactor.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention may be described with reference to the following the drawings:
Figure 1 - Permeation and abrasion test assembly.
Figure 1 a - Cross-sectional view of a tubular membrane of the present
invention.
Figure 1 b - An alternative tubular membrane of the present invention.
Figure 1 c - Is a U-shaped tubular membrane of the present invention.
Figure 2 - Effect of superficial velocity on permeation.
Figure 3 - Effect of temperature on permeation rate with pressure as a
parameter.
Figure 4 - Permeability variation with temperature for different membrane
tubes.
Figure 5 - Effect of hydrogen partial pressure on permeate flux.
Figure 6 - Effect of palladium coating thickness on overall transport
temperatures.
_,_
CA 02249126 1998-10-02
Figure 7 - Effect of hydrogen partial pressure on molar flux at different
temperatures.
Figure 8 - Variation of hydrogen flux with partial pressure for different feet
mixtures.
Figure 9 - Variation of permeation rate with partial pressure for different
membranes.
Figure 10 - Permeability variation with temperaWre for different membranes.
DETAILED DESCRIPTION OF THE INVENTION
It is generally accepted that hydrogen permeates through dense metallic
membranes by a "solution-diffusion" mechanism. The essential steps were
described by
Barrer ( 1951 ) and Athayde et al. ( 1994). The flux of hydrogen through a
metal membrane
can be estimated by (Collins and Way, 1993; Uemiya et al., 1991b; Hurlbert and
Konecny,
1961 ):
~, ""_,, p ""_, ( 1 )
J~~, - Pn-r( )
t
The relationship can be derived from Ficl<'s first law. According to Fick's
law, the flux of
hydrogen atoms through a homogeneous metal phase can be calculated from:
C~rr, - Cfn (2)
.l« - Dpi( t )
When diffusion through the metal is the rate limiting step (i.e. dissolved
hydrogen atoms are
in rapid equilibrium with the hydrogen molecules in the gas phase) and
hydrogen atoms from
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CA 02249126 1998-10-02
an ideal solution in the metal, C,~ is related to the partial pressure of
hydrogen in equilibrium
with the metal via Sieverts thermodynamic equation:
C'H - KS,( p 0.5,r) .J
Combining Equations 1 and 2, the value obtained for n is equial to 0.5
(Buxbaum and
Kinney, 1996; Buxbaum and Marker, 1993; Collins and Way, 1993; Hurlbert and
Konecny,
1961).
If the surface adsorption of hydrogen on palladium is the rate determining,
step,
the concentration of hydrogen at the interface of the membrane can be written
as (Wijmans
and Baker, 1995):
(4)
CHh Klt'pH?
Combining Equations 2 and 4, the value obtained for n is equal to 1.0 (Wijmans
and Baker,
1995).
When the rate of permeation is governed by both surface adsorption of
hydrogen molecules and diffusion of hydrogen atoms through the bulk of the
metal, the value
of 'n' is between 0.5 to 1.0 (Hurlbert and Konecny, 1961; Collins and Way,
1993; Yan et al.,
1994).
Deviation from ideal solution behavior (Sieverts law, Equation 3) also
influences the valuie of the pressure exponent 'n'. At low concentrations,
hydrogen atoms
form an ideal solution in the metal and there is no interaction between the
hydrogen atoms as
they diffuse through the metal. When the partial pressure of hydrogen in the
gas phase is
high, the atomic hydrogen concentration in the metal also increases and the
adsorbed
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CA 02249126 1998-10-02
hydrogen atoms attract each other. Therefore at high hydrogen partial
pressures, the atomic
hydrogen concentration in the metal (CH) is more than the value predicted by
Sieverts Law
(Equation 3) (Buxbaum and Kinney, 1996). If KS is taken as constant, this
effect increases
the value of the pressure exponent from 0.5 in Equation 3. The deviation from
ideal behavior
(i.e. deviation from n=0.5 behavior) is more pronounced in metals that form
hydrides (e.g.
palladium) with hydrogen atoms (Le Claire, 1983). In these metals, the
deviation is
encountered even at comparatively low pressures.
Another factor which influences with value of 'n' is the leakage of gas
through
metal film or membrane seals (Collins and Way, 1993). Since flow through any
leak is
hydrodynamic, the flow rate depends on the absolute pressure difference and
not on the .
difference in hydrogen partial pressures.
The value of 'n' may also depend on temperature since it is affected by the
Sieverts constant (KS), diffusivity (DM) and ratio of the rates of surface
processes and bulk
diffusion which all depend on temperature.
Hydrogen permeation experiments conducted with palladium have yielded n
values of 0.5 (Buxbaum and Kinney, 1996; Buxbaum and Marker, 1993; Uemiya et
al. 1991 b;
Holleck, 1970), 0.68 (Hurlbert and Konecny, 1961 ), 0.76 (Uemiya et al., 1991
a), 0.80 (De
Rosset, 1960), 0.53-0.62 (Collins and Way, 1993) and 1.0 (Yan et al., 1994).
All these
experiments were conducted at temperatures ranging from 340~C to 460~C and
hydrogen feed
pressures ranging from 101 to 4926 kPa.
Since both the diffusivity and Sieverts constant vary in an Arrhenius mamer
with temperature, the permeation constant can be expressed in terms of a pre-
exponential
factor, PMO, and an activation energy, EP, by:
(5)
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CA 02249126 1998-10-02
DNr~s
pnr' 2 -pnioexp( R T)
x
Two other quantities, "permeance" and "total resistance to transport" can be
derived from
Equation 1. "Permeance" , ~, is defined as the flux divided by the pressure
driving force:
JH, pm
p ~~":,, p ~r":, t
(6)
The inverse of permeance is the "total resistance to transport",
1 ( p ~~":,, p a"z,) t
Rr,~r- - -
JH, pm
For the High-flux membranes used for this study, the total resistance to
transport will be the
sum of the resistance offered by the palladium coating, and the constant
resistance (R~) which
accounts for the resistance offered by the substrate plus interfacial
resistances between the
coatings and the substrate:
t (g)
Rr"r p ~ mn Rc
~41
The diffusion rates reported by different authors for palladium membranes
differ by orders of magnitude. For example, the rates reported for a 50 ~m
palladium
membrane at 300~C by Jost and Widman (1940), Silberg and Bachman (1958),
Barrer (1940)
and Hurlbert and Konecny ( 19G 1 ) are in the ratio of 0.005:01:0.3 :1. Also
the reported
activation energy (EP) for permeation of hydrogen through palladium differs
considerably.
For example, Holleck ( 1970) reported an activation energy (E~,) of 43.97~0.42
kJ/mol whereas
Katsuta et al. ( 1979) determined EP to be 20.5~1.4 kJ/mol.
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CA 02249126 1998-10-02
As the data given by others has variability which is probably a result of the
purity of the palladium and the state of the palladium surface, the
permeability per-
exponential factor (PMO), the activation energy (EP) and the pressure exponent
(n) were
determined for our membranes from experimentally obtained permeation rates. At
a particular
termperature, the effective permeability of the high flux membrane tube, PM,
and pressure
exponent, n, were determined from nonlinear regression analysis of Equation 1.
From
experiments performed at different temperatures, the permeation pre-
exponential factor and
the activation energy were estimated using linear regression analysis of the
following
Equation:
1nP 1nP
~ti ;uo R T
x
The total resistance was determined from Equation 7. The resistance and
permeability of the
palladium coating and the constant resistance were determined by linear
regression analysis of
Equation 8.
Apparatus and procedure
Permeabilities and selectivities of membrane tubes were studied using the
permation and abrasion test assembly shown in Figure 1. The permeation and
abrasion unit
consisted of a cylindrical vessel flanged at both ends with a distributor
plate at the bottom.
As the feed gas (mixture of N, and H,) flowed up the catalyst bed, a small
fraction of
hydrogen permeated through the membrane and the retentate exited from the top
of the vessel.
The flow rate of the permeate was measured by water displacement method and
it's
composition was analyzed at regular intervals by a Shimadzu GC-8A IT
Chromatograph. At
each temperature and pressure, steady state was assumed when two successive
flow rate
measurements were within 4%. The pressure in the permeation unit was
maintained at the set
point by a back pressure regulator, whereas the pressure at the permeate side
was always
atmospheric. The membrane tubes used for permeation studies were 6.0 to 9.0 cm
long.
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CA 02249126 1998-10-02
Sufficient reforming catalyst, which is essentially Ni supported on alumina (A
1,0;) was used
to ensure that all of the membrane tube remain submerged in the fluidized bed.
The substrate
metal (alloy) thickness of all the high flux tubes was 76.1 ~,m and the
palladium coating
varied from approximately 3 to 9 ~,m on the inside and outside of the tubes.
The top ends of
S the tubes were brazed to 316 SS (stainless steel) tubes of slightly larger
diameter using a
commercially available high temperature braze UTP 6 (Bohler UTP Welding
Canada, Ltd.)
and the bottom ends were sealed using 316 SS plugs brazed with UTP 6. The 316
SS tube
was sealed to the permeation unit by Swagelok fittings. The retentate gas
passed through a
catalyst bed and the permeation unit were preheated to 400~C with nitrogen
flow. This was
performed to prevent damage to the palladium layer, because pinholes or cracks
could be
formed by phase transformation of palladium hydride from the a to the (3-phase
on exposure
to hydrogen at temperatures below 300~C.
For the first set of experiments, each of the two membrane tubes had an
outside
diameter of 1.98 mm and a substrate metal alloy thickness of 38 ~cm. One end
of each
membrane tube was first brazed to a 3.34 mm ID 316 SS tube which was then
brazed to a
4.93 mm ID 316 SS tube while the other end was plugged by brazing. The brazed
tubes,
supplied by REB Research, had palladium coating of 4 and 6 ~cm on both the
inside and
outside. Both of the tubes collapsed and resembled thin sheets at an operating
temperature of
600~C. This collapse caused stress in the braze and a leak developed at the
point where the
membrane was brazed to the stainless steel tube. Normally these tubes have
pressure in the
inside, and the thickness was computed to more than contain the pressure at
700~C. However
computations for tubes with pressure on the outside are approximate, as much
depends on
tubes being perfectly round.
New membranes with greater wall thickness (64 ~cm) were used for a second
set of experiments. The outside diameter of the membrane tubes were 1.98 mm
and they
were brazed to 3.18 mm OD 316 SS tubes. The tubes had a palladium coating
thickness of
4.2 and 6.2 ~,m, respectively. These membrane tubes were also crushed into the
shape of thin
sheets, although there was no leak (i.e. no nitrogen peals was detected in the
permeate gas) as
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CA 02249126 1998-10-02
the brazing remained intact. Surprisingly, the permeate continued to flow
through the
continuous channels of the crushed tube.
Results and discussion
From the initial experiments it was clear that the alloy tubes were unable to
maintain their mechanical structure at high temperature. It was decided to
reinforce the
membranes by inserting springs inside the tubes. Two spring reinforced
membranes were
tested for permeation and high temperature and presure resistance. The
membrane tubes had
an outside diameter of 3.18 mm and a substrate metal thickness of 7G ~,m. EAch
tube was
first brazed to a 3.34 mm ID tube which was subsequently brazed to another
1.75 mm ID SS
tube. Both of the tubes started leaking at approximately 600~C and 1378 kPa.
The leak
occurred due to the inability of the braze (performed by REB Research using
Braze 505) to
withstand this high temperature. But the spring reinforcement prevented the
tubes from
collapsing. The brazing of all the tubes tested afterwards was carried out
using a high
temperature braze called UTP 6 (49.0% Cu, 10.G% Ni, 1.0% Ag and the balance Zn
& other
traces).
The High-flux membrane tubes used for the next set of experiments had outside
diameters of 3.18 mm and substrate metal thickness of 76 ~cm. The palladium
coating
thickness of these tubes was 1.94, 4.05, 6.33 and 7.8 ~,m. Because of the very
thin palladium
layer, it was not possible to brazez the 1.94 ~,m membrane to a stainless
steel tube, so it was
not used. Permeation studies were performed with the G.33 and 4.05 ~,m
membranes at
different temperatures and differential pressure. For the 6.33 ~,m membrane,
nitrogen was
detected in the permeating gas at 625~C and 1330.3 kPa. Since, the spring
inside the tube
was not compact, the high outside pressure at this high temperature caused
both the spring
and the tube to collapse. For the same reason, the 4.05 ~m tube collapsed at
1330.3 kPa and
GOO~C.
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The following conclusions were drawn from all the experimentation up to this
point.
i) Spring reinforcement is preferable to provide strength at these high
temperatures and differential presssures. Moreover, the spring needs to be
packed compactly
although it may decrease the surface area for desorption.
ii) Brazing becomes very difficult if the palladium coating thickness is very
low.
The coating should be more than 3.0 ~,m and preferably above 4.0 p,m.
iii) UTP 6 can withstand the high temperatures and differential pressures used
in
the present investigation. For proper brazing, dust, oil and other surface
contaminants have to
be removed from the stainless steel surface.
PERMEATION CHARACTERISTICS
All the tubes tested for permeation characteristics had an outside diameter of
1.98 mm and substrate metal thickness of 76 Vim. One end of each tube was
plu~~ged with
brazing and the other end was brazed to a 3.34 mm ID 316 SS tube.
Figure 2 shows the effect of change in superficial velocity on the
permeabilities
of pure palladium and High-flux membrane tubes. Each data point in this figure
and all the
figures used afterwards represent the average of three readings. The maximum
percentage
deviation from the mean value was ~5%. From the results of Figure 2, it can be
concluded
that the permeation rate was independent of superficial velocity i.e. there is
no diffusional
resistance in the catalyst bed.
Figure 3 and 4 show the temperature effects on the flux and permeabilities of
different High-flux membrane tubes. Although, there is considerable scatter in
the date of
Figure 3, the trend follows Arrhenius behavior. Experimentally, the scatter
might be due to
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CA 02249126 1998-10-02
difficulties in controlling the temperature and pressure inside the permeation
unit. The
temperature varied by as much as 10~C from the mean whereas the pressure
varied from the
mean value by ~35 kPa.
The pre-exponential factors (Ph~o) in Equation 9 for the 3.8, 5.4 and 8.25 ~,m
membranes were determined to be 9.95 x 10-9 and 5.48 x 10-9
mol/(m.s.Pa°'''), respectively
and the corresponding activation energies (EP) were 12.7, 11.5 and 9.6 kJ/mol.
The above
mentioned PMO and EP values account for the combined effect of the palladium
coating and
the alloy substrate. Activation energy is positive (i.e. permeation increases
with increasing
temperature) for palladium while it is negative for niobium and tantalum. As
diffusion
through the palladium coating is the rate limiting step, it dominates the
overall activation
energy of the High-flux membrane. The EP for pure palladium is 10.5~1.4 kJ/mol
(Katsuta et
al., 1979). For High-flux membranes this value is clearly reduced because of
the opposing
effect of exothermic absorption in the substrate alloy.
The effect of hydrogen partial pressure on the permeation flux for different
membrane tubes is shown in Fi~~ure 5. The pressure exponent 'n = 0.72' was
determined
from nonlinear regression analysis using the combined permeation data from
three different
membrane tubes in Equation 1. One of the reasons for the high value of n is
that all the
experiments were performed at high hydrogen concentration (40% H~ in the
feed), which
causes deviations from ideal solution behavior and thus Sievert's law.
The reciprocal of the slopes of the best fit lines in Figure 5 are the
transport
resistances of different membrane tubes at 600~C. These resistances are
plotted against the
palladium coating thickness in Figure 6. The intercept of the line with the
resistance axis,
which was about 48700 m'.s.Pa°''/mol, represents the constant
resistance offered by the
substrate alloy plus the metal-metal interfaces. The slope of the best fit
line represents the
resistance offered per 1 ~m palladium coating and was about 1450
m'.s.Pa°''/mol. For a
single membrane tube, the variation of permeation rate with hydrogen partial
pressure at three
different temperatures is plotted in Figure 7. From this plot it can be
concluded that for the
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CA 02249126 1998-10-02
temperature range 400 to 600~C, the pressure exponent 0.72 satisfactorily
describes the
permeation characteristic of the membrane.
In most of the runs the composition of the feed mixture was 40% H, and 60%
N2. The high concentration of nitrogen was used so that even a small leak
could be detected
by analyzing the permeate. Experiments were also conducted using a 27.1 % CHI
and 72.9%
HZ feed mixture. Figure 8 shows the variation of hydrogen flux with pressure
fro the two
feed gas mixtures. The slopes of the best fit straight lines for the two sets
of data are almost
equal which means that the permeability is independenmt of the concentration
of hydrogen
and the choice of the non-permeating component.
For comparison purposes, a permeation study was performed using palladium
tubes supplied by Johnson Matthey Ltd. which were used by Adris (1994). Figure
9 shows
that the permeation rate was more than three times higher for the High-flux
tubes. The
permeability variation with temperature for the two membrane tubes is plotted
in Figure 10.
The permeation activation energies (EP), calculated from the slopes of the
lines, were 9.580
kJ/mol for the High-flux tube and 20.559 kJ/mol for the palladium tube. The EP
value for the
palladium tube was close to the value (20.5~1.4 kJ/mol) reported by Katsuta et
al. (1979).
The brazing with UTP 6 was not perfect as it failed in some occasions below a
temperature of 650~C. As a result of this uncertainty, a different method was
used to join the
membrane tube and the stainless steel tube. A ConaxT~'I PG gland with Grafoil
sealant was
used to connect the membrane tube to the 316 SS tube. A 3.18 mm OD SS tube was
first
machined to decrease its outer diameter so that it fit snugly inside the
spring reinforced
membrane tube. A Grafoil sealant was crushed on to the contacting/overlapping
surface of
the two tubes. Membrane tubes with ConaxTM fitting at the top and braze at the
bottom were
tested successfully (without any leak) up to a temperature of 670~C and a
differential pressure
of 1410 kPa.
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CA 02249126 1998-10-02
Conclusions
The spring reinforced High-flux membrane tubes were tested for permeation
over the temperature range of 400-700~C and at differential pressures up to
1480 kPa. This is
a significant improvement as this type of membranes were earlier tested only
up to a
temperature of 425 and a differential pressure of 110.3 kPa. Also the abrasion
resistance of
the palladium coating was tested in the fluidized bed of catalyst particles
and found to be
satisfactory. Due to their stability at high temperatures, differential
pressures and a fluidized
bed environment, the spring reinforced High-flux membrane tubes are the
preferred membrane
in membrane reactors including fluidized bed membrane reformers which require
operation at
relatively high temperatures and transmembrane pressure difference.
The dimensions of the tubular membranes may be scaled up to accomodate
existing fluidized bed membrane reformers as is well known in the art.
However, the
1 S thickness of the palladium coating should remain the same. Such tubular
membranes are well
suited to large scale hydrogen extractors using well-known shell and tube heat
exchanger
designs.
As shown in Figure 1 a and 1 b, a tubular membrane ( 10) is fitted with an
internal coil spring (12) which reinforces the membrane (10) and resists
deformation of the
membrane under high transmembrane pressure differentials. The coil spring (12)
is preferably
made of stainless steel. As shown in Figure lc, the tubular membrane (10) may
be bent into
a U-shaped membrane to increase membrane surface area in a reactor with
limited permeate
discharge connectors. The internal spring ( 12) is not shown in Figure 1 c.
In either the straight or U-shaped membranes, one end (14) is plugged while
the other end ( 16) is open as a permeate discharge opening. The open end (
16) may be
connected to a stainless steel connecting tube (not shown) by brazing as
described above or
more preferably to CornaxT'~' stainless steel connectors available from Cornax
Buffalo Inc.,
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CA 02249126 1998-10-02
Buffalo, New York with an appropriate sealant such as GrafoylT"'' available
from Union
Carbide.
In one application, the U-shaped tubular membranes are approximately 45 cm
in height (90 cm in total length), have an outside diameter of approximately
3.2 mm, a wall
thickness of approximately 76 ~m and a palladium coating thickness of
approximately 4ym.
These specific dimensions are not critical to the invention but are exemplary
of a preferred
embodiment.
As will be apparent to those skilled in the art, various modifications,
adaptations and variations of the foregoing specific disclosure can be made
without depat-ting
from the teachings of the present invention.
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CA 02249126 1998-10-02
Nomenclature
Cue, = concentration of hydrogen atoms at the high pressure side, mol/m3
C~ = concentration ofhydrogen atoms at the low pressure side, mol/m3
DM = diffusivity of atomic hydrogen, m2/sec
EP = activation energy for permeation, J/mol
JH = flux of hydrogen atoms, mol/(m2. sec)
J~ = molar flux ofhydrogen, mol/(mz.sec)
KR = sorption coefficient for hydrogen, mol/(m3.Pa)
= Sieverts constant, moll of atomic hydrogen/(m3.Pa°~s)
PH2h = partial pressure of hydrogen in the feed or high pressure side, Pa
Pm = partial pressure ofhydrogen in the permeate or low pressure side, Pa
PM = effective permeability in terms of molar flow,
mol/(msec.Pa°''2)
PMO = permeation pre-exponential factor, mol/(m.sec.Pa°'z)
R = resistance to transport, m2.sec.Pa°-'2/mol
R° = constant resistance, mz.sec.Pa°'2/mol
R~~ = total transport resistance through composite metal membrane,
m2.sec.Pa°~'2/mol
t = thickness of the metal membrane, p.m
t~o~ = total thiclmess of the membrane tube, p.m
T = temperature in the permeation unit, °C
Greek letter
= permeance, mol/(m2.sec.Pa°''2)
Superscript
n = exponent showing the dependency ofpartial pressure of hydrogen on
permeation rate
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CA 02249126 1998-10-02
Subscripts
h = feed or high pressure side
= permeate or low pressure side
M = metal
H2 = hydrogen
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CA 02249126 1998-10-02
References
Adris, A. M., "A Fluidized Bed Membrane Reactor for Steam Methane Reforming:
Experimental
Verification and Model Validation", Ph.D. Thesis, University of British
Columbia, April
1994.
Amano, M., M. Komaski and C. Nishimura, "Hydrogen Permeation Characteristics
of Palladium
Plated V-Ni Alloy Membranes", J. Less-Common Met., 172-174, 727-731 (1991).
Athayde, A. L., R W. Baker and P. Nguyen, "Metal Composite Membranes for
Hydrogen
Separation", J. Membr. Sci., 94, 299-311 (1994).
Barrer, R M., Traps. Faraday Soc., 36, 1235 (1940). -
Barrer, R M., "Di$usion in and through Solids", Cambridge University Press,
London, 1951.
Brown, C. C. and R E. Buxbaum, "Kinetics of Hydrogen Absorption in Alpha
Titanium", Metal.
Traps. A, 19A, 1425-1427 (1988).
Buxbaum, R E. and P. C. Hsu, "Method for Plating Palladium", US Patent
5,149,420, 1992.
Buxbaum, R E. and A. B. Kinney, "Hydrogen Transport through Tubular Membranes
of
Palladium-Coated Tantalum and Niobium", Ind. Eng. Chem Res., 35(2), 530-537
(1996).
Buxbaum, R E. and T. L. Marker, "Hydrogen Transport through Non-Porous
Membranes of
Palladium-Coated Niobium, Tantalum and Vanadium", J. Membr. Sci., 85, 29-38
(1993).
Cotlins, J. P. and J. D. Way, "Preparation and Characterization of a Composite
Palladium
Ceramic Membrane", Ind. Eng. Chem Res., 32, 3006-3013 (1993).
De Rosset, A. J., "Diffusion of Hydrogen through Palladium Membranes", Ind.
Eng. Chem Res.,
52, 525-528 ( 1960).
Hill, E. F., "Feasibility study: Removal of Tritium from Sodium During the
MDEC Process by
Oxidative Diffusion, Argonne West, DOE N707T1830035, 1982.
Holleck, G. L., '~i$usion and Solubility of Hydrogen in Palladium and
Palladium-Silver Alloys",
J. Phys. Chem, 74, 503-511 (1970).
Hurlbert, R C. and J. O. Konecny, "Diffusion of Hydrogen Through Palladium",
J. Chem Phys.,
34, 655-668 (1961).
Jost, W. and A. Widman, Z. Physik. Chem (Leipzig), B45, 285 ( 1940).
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CA 02249126 1998-10-02
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