Note: Descriptions are shown in the official language in which they were submitted.
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HOLLOW FIBER CONTACTOR AND PROCESS
BACKGROUND OF THE INVENTION
This invention relates to a hollow fiber contactor and process having forced
circulation with entry of fluid to be treated through the open ended lumen of
a porous input
hollow fiber having its opposite end closed and exit of treated fluid through
the open ended
lumen of an adjacent or nearby porous output hollow fiber having its opposite
end closed.
In the contactor of this invention fluid to be treated passes through the
porous wall of an
input hollow fiber, passes in contact with a treatment medium forming treated
fluid which
passes through the porous wall of an output hollow fiber, and exits the
contactor. The
contactor of this invention provides high contact with a treatment medium
between the
hollow fibers providing effective treatment at unexpectedly high flow rates
resulting in
contacting apparatus of greatly reduced size than prior contactors for the
same fluid
treatment. Hollow fiber contactors of this invention are especially suited for
selective
sorption, such as gas purification or separation, and for conduct of catalytic
reactions.
DESCRIPTION OF RELATED ART
A number of prior patents teach hollow fiber membranes for fluid treatment.
U.S. Patent Number 3,956,112 teaches hollow fiber non-porous membrane solvent
extraction
by passing a first liquid solvent through lumen of hollow fiber membranes and
a solute in
a second solvent, which is immiscible with the first solvent, through the
space surrounding
the hollow fiber membranes, the solute diffusing across the solvent swollen
membrane to the
first solvent without intermixing the two liquids. U.S. Patent Number
4,268,279 teaches
microporous hollow fibers with a liquid in the lumen and a fluid outside the
fiber allowing
gaseous components to transfer through the microporous fiber to the inside or
outside of the
fiber. U.S. Patent Number 4,966,699 teaches a hollow fiber membrane fluid
processor
providing counter current flow of fluid in the fiber lumen and the fluid
surrounding the
outside of the fibers from one end of the fiber bundle to the other. U.S.
Patent Number
5,041,220 teaches hollow fiber filter cartridges wherein one end of the
encapsulated potted
fibers is opened and the other end of the encapsulated potted fibers may be
opened or left
potted. U.S. Patent Number 5,198,110 teaches a bundle of permselective hollow
fibers
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having a plurality of filaments extending substantially lengthwise over the
length of the
exterior of each hollow fiber.
Spiral wound hollow fiber membrane fabric-like cartridges for phase contact
applications having a turbulence promoting web in which the hollow fibers in
the array are
arranged in a single mutually parallel layer facing one side of and at least
intermittently
bonded across their full lengths to the web which is co-extensive with the
entire layer of
hollow fibers are taught by U. S. Patent Number 5,186,832. U. S. Patent Number
5,264,171
teaches spiral wound hollow fiber membrane fabric-like cartridges for phase
contact
applications having baffles that induce radial feed flow in the shell side of
the hollow fiber
membrane bundle. U. S. Patent Number 5,284,584 teaches hollow fiber membrane
fabric-
like cartridges and modules for phase contact applications having tube sheets,
isolating the
lumen-side and shell-side portions of the cartridge or module, providing
improved solvent
resistance and mechanical durability by simultaneously with winding of the
array of hollow
fibers extruding a molten, high strength, solvent resistant thermoplastic
resin onto each of
the bundle ends to pot each of the bundle ends in the resin.
Various flow patterns through bundles of hollow fiber systems have been
suggested. U. S. Patent Number S,OI3,437 teaches a bundle of hollow fiber
membranes
partitioned into multiple stages of concentric annular regions, each providing
counter current
flow of a feed and a nonpermeate with a permeate. U.S. Patent Number 5,139,668
teaches
a hollow fiber bundle having two sets of passageways, the lamina of the fibers
and the space
between the fibers, wherein one set of passageways is filled with solid
particles in sealed
fashion except for the microporous walls, and the second set of passageways is
open for
passage of the process streams. U.S. Patent Number 5,221,474 teaches a
transfusion filter
for removal of gas bubbles having centrally located closed ended hydrophilic
porous hollow
fibers in a chamber of inlet process fluid with the opposite ends of the
hydrophilic porous
hollow fibers serving as the treated fluid output and having outer annularly
arranged closed
ended hydrophobic porous hollow fibers surrounding the hydrophilic fibers in
the chamber
with the opposite open ends of hydrophobic fibers open to the atmosphere for
discharge of
gas. U.S. Patent Number 5,282,964 teaches hollow fiber bundles having improved
counter
current flow of fluids in the fiber lamina and outside the fiber by parallel
flow of feed fluid
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mixture through a plurality of fiber bundles, each bundle enclosed in a
separate enclosure and
having a radial Peclet number of less than about 30.
SUMMARY OF THE INVENTION
The hollow fiber contactor and process of the present invention provides more
effective contacting, therefore, allowing higher rates of fluid flow, enabling
purification of
a mixture of gases, such as natural gas, at many times the rate of the same
size presently used
apparatus. Alternatively, the same rate of fluid flow may be processed in a
significantly
smaller apparatus.
The fluid flow system of this invention provides entry of fluid to be treated
through the lumen of input hollow porous wall fibers and exit of treated fluid
through the
lumen of adjacent or close output hollow porous wall fibers. The apparatus of
this invention
comprises a plurality of input hollow fibers closed at one end and a plurality
of output hollow
fibers closed at one end, the input hollow fibers and the output hollow fibers
being spaced
within a treatment medium, such as sorbent or catalyst particles. The inlet
for fluid to be
treated is in communication with the open end of the input hollow fibers while
the treated
fluid outlet is in communication with the open end of the output hollow
fibers. The input
hollow fibers have walls within the treatment medium porous to the fluid to be
treated and
the output hollow fibers have walls within the treatment media porous to
treated fluid. The
input and output hollow fibers are spaced within the treatment medium such
that the fluid
to be treated passes through the porous walls of the input hollow fibers to
contact the
treatment medium forming treated fluid which passes through the porous walls
of the output
hollow fibers for discharge from the contactor.
BRIEF DESCRIPTION OF THE DRAWINGS
The above and further objects and advantages of the invention will become
apparent upon reading the preferred embodiments together with reference to the
drawings,
wherein:
Fig. 1 shows fluid flow patterns in prior art hollow fiber contactors;
Fig. 2 shows fluid flow patterns in hollow fiber contactors according to one
embodiment of this invention;
Fig. 3 is a schematic showing of a woven structure of hollow fibers and solid
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fibers according to one embodiment of this invention;
Fig. 4 is a schematic showing of a woven structure of hollow fibers and solid
fibers according to another embodiment of this invention;
Fig. 5 is a schematic showing of fluid flow through a contactor containing a
woven structure as shown in Fig. 3;
Fig. 6 is a schematic showing of fluid flow through a contactor containing a
woven structure as shown in Fig 4;
Fig. 7 is a cross sectional view of a woven structure of hollow fibers and
solid
fibers according to one embodiment of this invention;
Fig. 8 is a cross sectional view of a spiral structure of rolled woven hollow
fibers and solid fibers according to one embodiment of this invention; and
Fig. 9 is a plot of treated fluid butane concentration showing separation from
a mixture of methane and butane, as described in the Example.
DESCRIPTION OF PREFERRED EMBODIMENTS
Fig. 1 illustrates fluid flow during the high pressure flow step of a typical
pressure swing adsorption cycle in conventional prior art hollow fiber sorbent
contactors.
Such devices are used to treat a fluid flowing through lumen passageways with
a sorbent
outside the hollow fibers. Hollow fibers 10 extend in spaced relation through
sorbent bed
12. Lumen 11 of all hollow fibers 10 are open on both ends with fluid to be
treated entering
the lumen as shown by arrows 14 and treated fluid leaving the lumen at their
opposite ends
as shown by arrows 15. The fluid being treated flows into and out of all of
the lumen
passageways of all the hollow fibers 10. The material to be sorbed out of the
fluid to be
treated is transported through the walls of microporous hollow fibers 10 and
contacts sorbent
in sorbent bed 12 by molecular diffusion as shown by arrows 13.
Fig. 2 illustrates fluid flow during the high pressure flow step of a high
pressure swing adsorption cycle according to one embodiment of this invention.
Input
hollow porous wall fibers 20 have closed ends 22 and opposite open ends 21.
Output hollow
porous wall fibers 23 have closed ends 25 and open ends 24. Input hollow
fibers 20 and
output hollow fibers 23 extend in alternate spaced relation through a
treatment medium bed
26, such as a sorbent bed. Open ends 21 of lumen of input hollow fibers 20 are
all located
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at one end of sorbent bed 26 to receive fluid to be treated as shown by arrows
28 with
opposite closed ends 22 of the lumen. Open ends 24 of lumen of output hollow
fibers 23 are
all located at the opposite end of sorbent bed 26 for the exit of treated
fluid as shown by
arrows 29 with opposite closed ends 25 of the lumen. Fluid to be treated flows
into lumen
passageways of only input hollow fibers 20, as shown by arrows 28, and out of
lumen
passageways of only output hollow fibers 23, as shown by arrows 29. The fluid,
with the
material to be treated, such as by selective sorption, passes through the
microporous walls
of the input hollow fibers 20, through treatment medium bed 26, where
separated material
is selectively sorbed from the fluid that had contained it, and the treated
fluid then passes
through the microporous walls of the output hollow fibers 23, as shown by
arrows 19. The
fluid flow paths obtained in the process and apparatus of this invention
provide forced flow
of the fluid being treated from the lumen of the input hollow fibers, through
the treatment
medium, and into the lumen of the output hollow fibers, thereby providing
better and more
positive contact between the material to be treated and the treatment medium.
Use of the fluid flow patterns according to this invention, as shown in Fig.
2,
provides unexpectedly high sorption efficiency. For example, it can be
calculated that
purification of natural gas using the contactor of this invention may be
effected in the order
of 100 times the rate obtained by use of the contactor shown in Fig. 1. The
very high sorption
efficiency of the contactor, as shown in Fig. 2, allows use of small sized
contactors while
achieving high efficiency selective sorption.
Hollow fiber contactors according to this invention may be arranged in
different configurations, an important feature being that all of the hollow
fibers have one end
closed. Using hollow fibers with one end closed provides forced fluid flow
through the
contactor by the fluid to be treated entering through an input hollow fiber,
passing over a
treatment medium forming treated fluid, and discharging treated fluid through
an output
hollow fiber. A plurality of input and output hollow fibers having closed ends
are spaced
within a treatment medium. A hollow fiber contactor for treatment of fluid
according to this
invention comprises a plurality of input hollow fibers closed at one end and a
plurality of
output hollow fibers closed at one end. The input hollow fibers and the output
hollow fibers
are spaced within a treatment medium, the input hollow fibers having walls
within the
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treatment medium porous to fluid to be treated for passage of such fluid to be
treated to the
treatment medium and the output hollow fibers having walls within the
treatment medium
porous to treated fluid for discharge of treated fluid. The input and output
hollow fibers are
spaced within the treatment medium such that the fluid to be treated passes
through porous
walls of the input hollow fibers to contact the treatment medium, forming
treated fluid and
the treated fluid passes through porous walls of the output hollow fibers for
discharge from
the contactor. While the input hollow fibers and the output hollow fibers may
be placed
randomly, or in many other placements with respect to each other, in preferred
embodiments
the input hollow fibers and output hollow fibers that are in flow
communication are placed
alternately, as is disclosed in further detail herein.
A process for treatment of fluid according to this invention comprises passing
fluid to be treated into the open end of lumen of a plurality of input hollow
fibers having the
lumen closed their opposite ends and having walls porous to the fluid to be
treated within a
treatment medium. 'The fluid to be treated is passed through the porous walls
of input hollow
fibers and contacts the treatment medium forming treated fluid which is passed
through the
walls of a plurality of output hollow fibers having one closed end and spaced
within the
treatment medium from the input hollow fibers. The output hollow fibers have
an opposite
open end for exit of the treated fluid and walls porous to the treated fluid
within the treatment
medium.
Suitable hollow fibers for use in this invention have side walls with a
viscosity normalized permeance of at least 1 x 10-' liter cp/cmz min bar,
preferably greater
than about 1 X 10-2 liter cp/cmz min bar, and most preferably greater than
about 1 X 10-1 liter
cp/cm2 min bar, and in all cases having pores small enough to prevent passage
of treatment
particles through the walls. Generally, the thickness of the porous walls of
the hollow fibers
is about 5 to about 25 percent of their outside diameters. The hollow fibers
may be made of
any suitable material which is not chemically reactive with the fluid flowing
through the
lumen or the particles surrounding the outside of the hollow fiber, such as,
polypropylene,
polysulfone, Teflon, and sintered powdered metal such as stainless steel. Such
hollow fibers
are known and available and the choice will be apparent to one skilled in the
art dependent
upon the particular application and size of the contactor. The hollow fibers
may be
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appropriately sized for specific applications and contactor sizes, as will be
apparent to one
skilled in the art.
The treatment medium for use in this invention may be a single material or
a plurality of materials used in fluid contact processes, such as sorbents and
catalysts for
chemical reactions. For example, suitable sorbents may be used, such as, for
purification of
natural gas activated carbon may be used to remove high carbon number
components (natural
gas liquids); silica gel may be used to remove acid gases (HzS and COZ)
natural gas liquids,
water, and water plus natural gas liquids; Zeolite molecular sieves may be
used to remove
acid gases, water, and natural gas liquids. For treatment of air, sorbents
such as Zeolite
molecular sieves may be used to remove nitrogen and carbon molecular sieves
may be used
to remove oxygen. Other sorbents, as will be apparent to one skilled in the
art, may be used
for other sorption separation processes. The treatment medium may be a
catalytic material
which catalyzes reaction between components of a mixed input fluid. The
apparatus and
process of this invention is particularly useful when it is desired to use
small catalyst
particles, such as to avoid slow diffusion into large porous catalyst
particles. Such catalytic
reactions include reactions such as, for example, hydrogenation of petroleum
fractions or
animal or vegetable fats using catalyst particles having largest dimensions of
less than about
1 mm and the Friedel-Craft ketone synthesis, for example, the reaction
catalyzed by
heterogeneous aluminum chloride catalyst starting with aryl halides and an
aromatic to form
mono aryl ketones or starting with aroyl halides to form diaryl ketones.
Suitable spacing of the hollow fibers in the treatment medium is from about
the outside diameter of the hollow fiber to about 100 times this diameter,
preferably about
1 to about 30 times the outside hollow fiber diameter.
One embodiment of assembly of input hollow fibers having one closed end
and output hollow fibers having one closed end is in a woven sheet structure
as shown in Fig.
3. Input hollow fibers 20 are configured with their open ends 21 facing in a
first direction
(downward) and their closed ends 22 facing in an opposite second direction
(upward) with
alternate output hollow fibers 23 oppositely configured with their open ends
24 f acing in the
second direction (upward) and their closed ends 25 facing in the first
direction {downward).
A woven sheet structure is formed by weaving fibers or filaments 31 in woven
relationship
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with alternating input hollow fibers 20 and output hollow fibers 23.
Preferably, the weaving
fibers are substantially smaller diameter than the hollow fibers. While the
weaving fibers are
preferably single solid fibers, weaving fibers of conventional formed thread
may also be
used. Weaving fibers 31 may be of any material which is non-reactive with the
treatment
medium and the walls of the input and output hollow fibers and may be the warp
or the woof
of the weave with the hollow fibers being the opposite. Exemplary materials
for the weaving
fibers are plastic or metallic materials inert to the fluids being treated and
to the treatment
medium, such as, polypropylene, steel, and stainless steel. It is preferably
that the hollow
fibers be maintained in an equal spacing which may be accomplished by coating
the weaving
fibers with an adhesive so that the hollow fibers will adhere to the weaving
fibers where they
intersect and contact. Alternatively, the woven assembly can be heated to
soften the fibers
enough so that they adhere at the contact points. Fig. S schematically shows
the input and
output flow in one embodiment of an alternate side flow type contactor
suitable for a woven
sheet structure as shown in Fig. 3, having all input lumen open to one side
and all output
lumina open to the opposite side. The input hollow fibers pass through a seal
in the input
end seal 33 and the output hollow fibers pass through a seal in the output end
seal 34. The
enclosed space between the hollow fibers, input end seal 33, output end seal
34, and
containment vessel 35 is packed with a desired treatment medium. Fluid to be
treated passes
into the input manifold section of containment vessel 35 as indicated by arrow
28, passes into
the lumen of input hollow fibers 20, through the porous walls of input hollow
fibers 20,
passes in contact with treatment medium between the hollow fibers forming
treated fluid, the
treated fluid passes through the porous walls of output hollow fibers 23 and
is transported
through their lumen to treated fluid output manifold section of containment
vessel 35, and
exits containment vessel 35 as indicated by arrow 29.
In another embodiment of assembly of input and output hollow fibers having
one closed end according to this invention, all open ends may be faced in the
same direction,
as shown in Fig. 4 schematically showing input and output fluid flow. Fig. 4
shows input
hollow fibers 20 configured with their open ends 21 facing in one direction
and alternate
output hollow fibers 23 configured with their open ends 24 facing in the same
direction. In
similar manner as described above, a woven sheet structure is formed by
weaving fibers or
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filaments 31 in woven relationship with alternating input hollow fibers 20 and
output hollow
fibers 23. For assembly into a cantactor, as shown in Fig. 6, the open ends of
the hollow
fibers extend beyond the woven structure to be directed to a suitable
manifold. The open
ends of the hollow fibers extending beyond the woven structure, as shown
schematically in
Fig. 6, pass through a seal in end seal 36 to form separated intake and output
manifolds. The
enclosed volume between the hollow fibers, end seal 36, and containment vessel
35 is packed
with a desired treatment medium. Fluid to be treated passes into the input
manifold as
indicated by arrow 28, passes into the lumen of input hollow fibers 20,
through the porous
walls of input hollow fibers 20, passes in contact with treatment medium
between the hollow
fibers forming treated fluid, the treated fluid passes through the porous
walls of output
hollow fibers 23 and is transported through their lumen to treated fluid
output manifold
section of the containment vessel 35, and exists containment vessel 35 as
indicated by arrow
29.
The woven structure of input and output hollow fibers, as shown
schematically in Figs. 3 and 4, is preferably assembled into a composite sheet
structure,
including a layer of treatment medium on a barner sheet which is non-permeable
to fluid to
be treated and treated fluid, as shown in cross section in Fig. 7. Barrier
sheet 37, which is
non-permeable to the fluid to be treated and the treated fluid, is coated on
one side with a
layer of treatment medium and the woven structure with alternating input
hollow fibers 20
and output hollow fibers 23 woven with weaving fibers 31 is embedded in the
central portion
of the thickness of treatment medium 26. The adjacent hollow fibers in this
structure are in
flow communication through the medium because the barrier sheet does not pass
between
them. This structure may be rolled into a spiral where the non-permeable
barrier sheet
prevents undesired flow communication between fibers in different layers of
the spiral. The
woven structure may be embedded in a sheet of treatment medium which is then
laid over
the barrier sheet. In another embodiment, particles of a porous treating
material may be
poured over the woven structure lying on the barrier sheet in a horizontal
plane and the
particles then spread into a layer of uniform thickness. When fabricating the
contactor using
some types of porous particles, it is possible to form the spiral structure by
keeping the
unrolled portion of the layers in a horizontal plane and rolling the spiral
portion of the device
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over the horizontal layer into the spiral structure, analogous to rolling up a
rug while it is
lying on the floor. Other types of particles will tend to fall off the edges
of the horizontal
layer to an excessive degree. This can be avoided by adding a sufficient
quantity of liquid
to just fill the interparticle voids resulting in a mixture of particles and
liquid in a paste form
which does not flow. The liquid selected must wet the surfaces of the
particles, such as water
or an organic solvent, depending upon the particles, and must have a
significant vapor
pressure so that after the spiral device is formed by rolling up the layers,
the liquid can be
removed by evaporation. This procedure leaves only particles of the treating
material and
the woven structure in the space between layers of the barrier sheet. For some
applications,
it is desirable to have the particles of treating material in fixed, locked
positions relative to
each other. For such applications, the external surfaces of the particles can
be coated with
an adhesive, such as, for example, epoxy or cyano-acrylic, that will allow
sufficient time for
fabrication of the device before locking the particles into a fixed position.
Such an adhesive
must not significantly block the pore structure of the sorbent or catalyst.
The treatment medium comprises solid particles larger than the pores in the
input or output hollow fibers. Preferably, the solid particles are porous to
provide a high
surface area for fluid contact to result in high efficiency chemical
reactions. The treatment
medium may comprise a single or plurality of materials suitable for the
desired contact
treatment. For example, selective sorbents may be used to selective sorb one
or more
materials from a fluid, such as purifying natural gas, separation of oxygen
from air, and other
known sorption processes. Likewise, the contactor of this invention may
advantageously be
used to promote catalytic reactions by use of a catalyst as the treatment
medium. The
distance between adjacent hollow fibers, that is, the thickness of the layer
of treatment
medium, is suitably about 1 to about 100 fiber outside diameters, preferably
about 3 to about
30 fiber diameters.
In one embodiment of this invention, the composite sheet of a barrier sheet
and treatment medium with embedded woven structure of alternating input and
output
hollow fibers is rolled into a spiral, as shown in the schematic cross section
of Fig. 8. Solid
core 38, non-permeable to the gas to be treated and treated gas and
substantially non-reactive
with any of the components, may be used as an aid in forming the spiral. It
also may be
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advantageous to wet. the treatment medium to hold particles of treatment media
in a stable
interposition to each other as the spiral is being formed. The wetting fluid
and the binding
material may be removed, such as by vaporization or solution, before the
device is used. The
formed spiral of the composite sheet structure of barrier sheet 37, treatment
media 26, and
embedded woven sheet of alternating input hollow tubes 20 and output hollow
tubes 23
woven with solid fibers 31 may be placed in containment vessel 35 with the
excess space
between the exterior of the spiral and the containment vessel filled with
shell seal 39 to
prevent flow in this space. Shell seal 39 should be non-pervious to gas to be
treated and
treated gas, as well as substantially non-reactive with any components of the
system.
Suitable materials for the seal are any poured or cast sealing materials inert
to the fluids
being processed, such as, for example, butyl rubber and epoxy resin. The solid
core may be
any plastic or metallic material inert to the fluids being processed, such as
polypropylene,
steel or stainless steel. It is seen that with the configuration shown in Fig.
8, fluid flow paths
will be established through treatment medium 26 between adjacent input and
output hollow
fibers to promote good contact with the treatment medium for high reaction
rates and provide
very high pass through flow rates.
Either the alternate side communication contactor configuration, as shown in
Figs. 3 and 5, or the single side communication configuration, as shown in
Figs. 4 and 6, may
be used in the spiral sheet configuration, as shown in Fig. $. Generally, when
the flow path
through the lumen of the hollow fiber is greater than about 100 times the
inside diameter of
the hollow fiber the alternate side communication contactor will provide
better performance,
and when that flow path is less than about 100 the single side communication
contactor
provides better performance.
Many specific parameters of the process of this invention, using the improved
contactor, are determined by the particular application, such as, for example,
pressure swing
adsorption and catalytic processes. The temperature, pressure, specific
treatment material,
flow rates per unit mass of treatment material, cycle times, and the like, for
specific
applications are quite different and can be ascertained by one skilled in the
art. Optimum
cycle times can be ascertained by progressively reducing the cycle time for
the process, while
keeping all other parameters substantially constant, until a substantial
decrease in
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performance is measured. The cycle time of the process of this invention will
be reduced by
a factor of about 2 to 200, as compared with the cycle time using a
conventional contactor
as shown in Fig. 1, and usually by a factor of about 4 to about 50. It should
be noted that the
rate of production of treated product per unit of treatment material is
directly proportional
to the reduction in cycle time factor.
EXAMPLE
Good separation of butane from a mixture of methane and butane was
achieved using the flow paths according to this invention by assembling in a
reactor vessel
ten hollow fibers in the configuration as shown in Fig. 3. The hollow fibers
were spaced in
an active treatment zone which was 0.1 inch deep, approximately the outside
diameter of the
hollow fibers. The hollow fibers were held at a distance of 0.42 inch between
the fibers by
sealing devices at each end of the active treatment zone. An input fiber was
at one outside
edge of the active zone and an output fiber at the other outside edge of the
active zone,
making the total active treatment zone 4.78 inches wide. Each of the hollow
fibers had a
length of 6.25 inches in the active treatment zone. The hollow fibers were
porous
polypropylene with an outside diameter of 1.6 mm and a 0.4 mm wall thickness
available
from Akzo under the registered trademark Accurel. The viscosity normalized
permeance for
the walls of these hollow fibers was measured, using methane at 30 psig and
ambient
temperature, and found to be 5.60 x 10-3 liters cp/cm2 min bar. Five of the
hollow f bets were
input fibers used to introduce gas to be treated and the other five
alternately arranged hollow
fibers were output fibers used to withdraw treated gas. The ten hollow fibers
thus defined
9 interior subzones with input gas flow going into the lumens of the input
fibers and exiting
through the walls of these fibers, then passing through the treatment medium
in the subzones,
and then passing through the walls of the output fibers and removed from the
lumens of the
output fibers, as shown in Fig. 2. This treatment zone represents one layer of
a contactor that
could be rolled up as shown in Figs. 7 and 8 to form a contactor as shown in
Fig. 5.
Treatment medium particles were poured between the hollow fibers which
also limited fiber movement. The treatment medium was 18.7 gms of activated
carbon
having a mean particle diameter of 0.44 mm available as 267-R-95 from Westvaco
Corp.,
Covington, VA 24426. The carbon was first equilibrated by passing an input of
pure
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methane through the apparatus at ambient temperature while maintaining the
outlet pressure
at 30 psig. The input gas was then switched to 2 mole percent butane in
methane and flowed
through the apparatus at a rate of 4.75 liters at STP/minute at ambient
temperature with the
outlet pressure maintained at 30 psig. The composition of the output gas was
continuously
monitored using a thermal conductivity instrument.
The ideal result of flow through any subzone of the contactor, assuming
perfect flow distribution and infinite rates of transport and infinitely
strong adsorption of the
butane on the activated carbon, would be zero concentration of butane in the
output gas as
progressively more input gas was processed until the carbon was saturated with
butane. At
that point, the butane concentration in the output gas would instantaneously
increase to 100
percent of the input gas butane concentration. The apparatus used in this
Example had nine
subzones. The flow rates throughout the different subzones, that were all
exposed to the
same differential pressure of the total treatment zone, could be controlled by
the resistance
to flow through the walls of the hollow fibers or by the resistance to flow
through the bed of
particles of activated carbon. If the flow were controlled by resistance of
flow through the
bed of carbon particles, the flow through each of the subzones would be the
same, because
the geometry of the carbon particles in each of the subzones was identical.
However, if the
flow rates were controlled by the resistance of flowing through the walls of
the hollow fibers,
the flows through the two outer subzones would be greater since they each have
one hollow
fiber which has its total peripheral area available for flow, while each of
the interior hollow
fibers have flow into or out of two subzones, and thus, have only one half of
their peripheral
area available for flow into or out of each of these subzones. The increased
hollow fiber
peripheral area in the outer subzones results in higher flow rate through
these subzones.
Thus, the carbon in the outer two subzones is exposed to butane more rapidly
and that carbon
would reach saturation sooner than the carbon in the interior subzones.
Therefore, the output
flow from the outside subzones would contain 100 percent concentration of
butane after they
were saturated, while the butane concentration in the output from the interior
hollow fibers
would still be zero, causing an increase in the butane concentration of the
combined outputs
leaving the apparatus. Using the apparatus, as described above in this
Example, resistance
to flow measurements were made with and without the carbon particle bed in the
apparatus
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WO 99/21644 ~ PCT/US97/19664
and clearly showed that the flows were controlled by resistance to flow
through the walls of
the hollow fibers. Thus, 2 of the 9 subzones would have a high butane
concentration causing
a significant increase in the combined butane output concentration. However,
in a
commercial size apparatus with more than 1000 subzones, the 2 outside subzones
would
produce an insignificant increase in the combined output concentration.
The removal of butane from a mixture of methane and butane using the
apparatus and process conditions as described in this Example is shown in Fig.
9. Fig. 9
shows the projected theoretical ideal removal, assuming perfect flow
distribution and infinite
rates, showing the stepped increase of the concentration of butane leaving the
apparatus. Fig.
9 also shows a plot of the actual butane removal obtained using the apparatus
of this
invention under the conditions set forth above in this Example. The measured
performance
comes as close to the theoretical ideal performance as could be expected using
a real
adsorbent with actual transport rates, rather than infinite. This clearly
demonstrates that the
flow path of fluid obtained by this invention provides extremely effective
contacting and
treatment of a fluid stream flowing through an apparatus of this invention.
Also shown in
Fig. 9 is the much lower performance which we would project to be adequate for
practical,
economic commercial use.
While in the foregoing specification this invention has been described in
relation to certain preferred embodiments thereof, and many details have been
set forth for
purpose of illustration it will be apparent to those skilled in the art that
the invention is
susceptible to additional embodiments and that certain of the details
described herein can be
varied considerably without departing from the basic principles of the
invention.
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