CA2023054C - Hollow fiber bundle element for an adsorber - Google Patents

Abstract

An adsorber is provided comprising a bundle of microporous hollow fibers disposed in a cylindrical impermeable casing. With respect to each fiber, its wall is selected to provide a permeability in the microfiltration range (0.05 to 5 micrometers). The bundle forms two longitudinal passageways, being the lumina of the fibers and the other being the void space between the fibers. A first of these passageways is densely and uniformly packed with minute adsorbent particles. No binder is used to fix the particles - they maintain their distribution in the passageway as a result of having been densely packed under pressure. The ends of the first passageway are sealed and the fiber wall pores are smaller than the particles, whereby the adsorbent particles are immobilized therein. A fluid mixture, comprising a carrier and an adsorbate, is introduced into the second passageway. The adsorbate diffuses through the fiber walls and is collected by the adsorbent particles. By way of result, the particles used in this adsorber can be of much smaller size than those used in a conventional fixed bed column.
The use of small adsorbent particles enhances adsorption rate, and availability of a separate longitudinal flow passageway reduces pressure drop across the adsorber.

Description

FIELD OF THE INV~;N~l~lON

2 This invention relates to a hollow fiber bundle element

3 for use in an adsorber to separate at least one adsorbable

4 component from a ~ixture of fluid components.

BACKGROUND OF THE INVENTI~N
6 Adsorption processes are widely used in industry for 7 separation of fluid mixtures ~gas or liquid). The separation is 8 based on preferential adsorption of selective components on the 9 surface of solid adsorbents. For efficient separation, the adsorbent material must have large surface areas to provide 11 reasonable adsorptive capacities. The commonly used adsorbents, 12 such as molecular sieve zeolites, activated carhon, alumina and 13 silica gel, have surface areas of at least 200 m2/g.
14 Most industrial adsorption processes are carried out in fixed-bed type columns. ~he adsorbent granules are packed and 16 immobilized in a cylindrical vessel. As the fluid mixture to be 17 separated is passed through the packing via the void spaces among 18 the granules, the adsorbable components in the mixture are taken 19 up and retained by the adsorbent.
Since the adsorbent has a limited adsorption capacity, 21 it will become gradually saturated with adsorbate, and periodic 22 adsorbent regeneration is required. For continuoua processing 23 of a feed mixture, a multi-bed system is used in which each bed 24 goes through the adsorption/regeneration cycle in sequence.
Several different regeneration methods have been used 1 commercially. Chief a~ong them are the thermal swing adsorption 2 (TSA) and pressure swing adsorption (PSA) processes. In the TSA
3 process, the saturated adsorbent is regenerated by purging with 4 a hot gas. Each heating/cooling cycle usually requires a few hours to over a day. In the PSA process, the adsorbent 6 regeneration is effected by purging with a portion of the 7 purified product gas at reduced pressure. The throughput is 8 higher than that of the TSA since faster cycles, usually in 9 minutes, are possible.
Apart from the adsorptive capacity of the adsorbent, 11 the adsorption rate and pressure drop are two important factors 12 that must be considered in adsorber design.
13 Pressure drop through the adsorber column should be 14 ;nl~ized, because high fluid pressure drop can cause movement or fluidization of the adsorbent particles, resulting in serious 16 attrition and loss of the adsorbent.
17 The adsorption rate has a significant bearing on the 18 efficiency of the adsorption process. This rate is usually 19 determined by the mass transfer resistance to adsorbate transport from the bulk fluid phase to the internal surfaces of the 21 adsorbent particles. Slow adsorption rate due to large mass 22 transfer resistance will result in a long mass transfer zone 23 (MTZ~ within which the adsorbent is only partially saturated with 24 adsorbate. The adsorbent in the region upstream of the MTZ is substantially saturated with adsorbate, while that downstream of 26 the MTZ is essentially free of adsorbate. As the fluid continues 27 to flow, the MTZ advances through the adsorber column in the 28 direction of the fluid stream. The adsorption step must be 29 terminated before the MTZ reaches the adsorber outlet in order 1 to avoid the breakthrough of adsorbate in the effluent stream.
2 A long mass transfer zone, which contains a large quantity of 3 partially utilized adsorbent, will, therefore, result in a short 4 adsorption step and inefficient use of the adsorb~nt capacity.
These effects are especially serious for the pressure swing 6 adsorption process.
7 Both the pressure drop and the mass transfer resistance 8 are strongly influenced by the size of the adsorbent particles.
9 Changing the particle size, unfortunately, has opposite effects on these two important factors. This is elaborated below:
11 (1) The pore sizes of the void spaces among the 12 adsorbent particles in the fixed-bed are 13 proportional to the size of the particles. Since 14 the resistance to the fluid flow through the lS adsorber is inversely proportional to the pore 16 size of the packed bed, the use of small adsorbent 17 partic'e will cause high pressure drop. For this 18 reason, the SiZ8S of commercial adsorbents for 19 fixed-bed operation are generally larger than 2 mm in equivalent diameter. Adsorbent of smaller 21 particle sizes, such as zeolite crystals (less 22 than 10 microns), are pelletized using binding 23 material to suitable sizes.
24 (2) Almost all the surface areas of commercial adsorbents are located at the interior of the 26 adsorbent particle. For adsorption to occur, the 27 adsorbate needs to be transported from the 28 external fluid phase to the interior surface of 29 the particle. The transport rate is dominated by 2~

1 two mass transfer mechanisms in series: (a) 2 interfacial mass transfer - diffusion through the 3 fluid boundary layer surrounding the external 4 surface of the adsorbent particle; and (b) intraparticle mass transfer -- diffusion through 6 the internal pore space (micropores and 7 macropores) of the particle to its interior 8 surface where adsorption takes place. The size 9 of the particle has significant effects on the rates of these two diffusion processes. Small 11 particles offer large fluid/solid contact areas 12 in the fixed bed for interfacial mass transfer and 13 reduce the path length for the intraparticle 1~ diffusion. Hence, small adsorbent particles will increase adsorption rate and result in a narrow 16 mass transfer zone for fast and efficient 17 operation of adsorption/desorption cycles.
18 The above discussions and analysis show that small 19 adsorbent particles are desirable for efficient adsorption processes, but the minimum particle size is limited by acceptable 2I hydrodynamic operating conditions of the fixed bed adsorber.
22 That is, one wants to avoid fluidization and excessive pressure 23 ~drop.
24 It would there~ore be desirable to provide an adsorber containing adsorbent characterized by a relatively small particle 26 size and yet still able to operate with an acceptable pressure 27 drop.
28 At this point, it is appropriate to shortly describe 29 the structure and operation of a known separation device used for 2 ~ J ~

1 permeation and absorption and referred to as a hollow fiber 2 module. As will become clear below, this module is similar in 3 many respects to a shell and tube heat exchanger. The device is 4 used to separate at least one component (e.g. CO2) from a second S 'carrier' component (e.g. natural gas) with which it forms a feed 6 mixture. A typical module comprises a cylindrical vessel 7 encapsulating a bundle of small-diameter, elongate~, hollow 8 fibers. The fibers are formed of a material having a 9 permeability which, in the case of a permeation module, is selected to allow the component to be extracted to diffuse 11 therethrough but to substantially reject the carrier component.
12 In the case of an absorption module, the entire feed mixture may 13 readily diffuse through the fiber wall. The fibers are "po-tted"
14 at their ends in closure means, such as epoxy tube sheets, so that the ends of the fibers project therethrough, leaving their 16 bores or "lumina" open. The tube sheets function to seal the 17 void space between the fibers at the two ends. The tube sheets 18 further seal or are sealed by means, such as an O-ring~ against l9 the inside surface of the vessel. The vessel is provided with a first inlet and first outlet communicating with the ends of the 21 fiber lumina. It further has a second inlet and second outlet 22 communicating with the ends of the void space. In operation, the 23 feed mixture of gases is fed through the second inlet into the 24 void space. In the case of an absorption module, absorbent fluid is fed into the lumina. The absorbate (CO2) diffuses through the 26 fiber walls from the void space, is collected by the absorbent 27 fluid, and exi~s through the first outlet. The carrier gas, 28 reduced in CO2, leaves through the second outlet.

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1 With this background in mind, it i6 now appropriate to 2 describe the present invention.

4 The present invention involves use of a known article, namely a module comprising a bundle of hollow fibers contained 6 in an impermeable casing. The fibers each have a microporous 7 permeable wall having pore openings in the range of about 0.05 -8 5 micrometers ~known as the "microfiltration range"). Minute 9 adsorbent solid particles are emplaced in a first of two passageways, either the lumina of the fibers or the void space 11 between the fibers. The particles are sufficiently densely 12 packed substantially throughout the length and breadth of the 13 passageway, so as to have a density equal to or greater than the 14 free-standing bulk density of the particles. The particles are sufficiently small or minute so as to provide fast mass transfer 16 of adsorbate to the interior surface of the adsorbent particles 17 where adsorption takes place. They are "free" particles, not 18 being bonded together by binder or the like. The first 19 passageway containing the particles is sealed at its ends, for example by an epoxy tube sheet. The pore openings of the fiber 21 wall are smaller than the adsorbent particles involved. These 22 openings, however, are large enough to permit the fluid to 23 diffuse therethrough.
24 The particles are emplaced in the module in a unique fashion. More particularly, a suspension of the particles in a 26 liquid or gas carrier is pumped under pressure into one of the 27 passageways. The carrier filters through the fiber walls into 28 the other passageway and exits the module, leaving the particles ~ 3 1 trapped in the original passageway. By this process, a dense 2 uniform dispersion of particles is emplaced in the original 3 passageway throughout its length. The particles are individually 4 free but are collectively immobilized in the original passageway due to the completeness of the packing.
6 The final product, comprising the casing, the hollow 7 fibers, the end closures, and the charge of adsorbent particles, 8 is hereafter referred to as the "element".
9 As a result of assembling the foregoing, minute iO adsorbent solid particles having fast mass transfer rate are 11 immobilized in the sealed first passageway of the element. Yet 12 an adsorbate component (e.g. C~2 ) of a fluid mixture (e.g.
13 natural gas containing CO2), that is introduced into the other or 14 second passageway, can still reach the adsorbent by diffusing through a fiber wall to enter the first passageway, wherein it 16 is collected and retained by the adsorbent.
17 The pore openings of the fiber wall are sufficiently 18 large to enable the carrier liquid or gas to filter readily 19 therethrough during the fabrication step of emplacing the packing of particles in one of the passageways.
21 In this fashion, it is feasible to fabricate the 22 element without high expense and it is possible to use very small 23 adsorbent particles having a very high mass transfer rate, in 24 connection with a pressure-driven fluid mixture to be processed, without having fluidization occur. And the availability of the 26 second passageway, for the passage therethrough of the fluid 27 mixture, has ensured that only a relatively low pressure drop 28 will occur across the element.

~ 3 2 Figure 1 is a schematic showing the arrangement used 3 to emplace adsorbent particles in the lumina of an element;
4 Figure 2 ls a sahematic showing the arrangement used to emplace adsorbent particles in the void space between the 6 fibers;
7 Figure 3 is a schematic showing an element, having the 8 adsorbent particles in the lumina, being used as an adsorber; and 9 Figure ~ is a schematic showin~ an element, having the adsorbent particles in the void space between the fibers, being 11 used in conjunction with a vessel as an adsorber.

12 DESCRIPTION OF THE PREFERRED EMBODIM~NT
13 The adsorber A can take one of two forms, shown in 14 Figures 3 and 4 (which are not~to scale).
In Figure 3 the adsorber A is the element itself and 1~ comprises a bundle o~ fibers 1, each fiber having a bore or lumen 17 2. The plurality of fibers form a void space 3 between them.
18 An impermeable cylindrical casing 4 contains the bundle. The 19 bundle has top and bottom closures 5, 6 which seal the lumina 2 and void space 3. An inlet 7 is provided at one end of the 21 casing 4, for introducing the feed mixture, comprising a carrier 22 ~luid and an adsorbate fluid, and an outlet 8 is provided at the 23 opposite end of the casing for exhausting a stream comprising the 24 carrier fluid reduced in adsorbate fluid. Particles 9 of adsorbent are packed in the lumina 2. The fiber walls have sub-26 micron sized pores which enable the adsorbate to diffuse readily 27 therethrough but the pores are smaller than the adsorbent 2~ particles 9. As a result of providing fiber walls that prevent ~ ~3 3 ~

1 the particles 9 from movin~ therethrough and sealing the ends of 2 the lumina 2 with the closures 5,6, the particles 9 are 3 immobilized in the lumina 2.
4 In Figure 4, the adsorber B has the particles 9 S disposed in the void space 3 between the fibers 1. ~losures 5a, 6 6a are provided and leave the ends of the lumina 2 open but seal 7 the ends of the void space 3. The element 10 of Figure ~, 8 comprising the bundle of fibers 1, closures Sa, 6a and casing 4, 9 is positioned in a vessel 11 having a top inlet 12 and bottom outlet 13. The inlet 12 and outlet 13 communicate with the ends 11 of the lumina 2. The element 10, as described, combines with the 12 vessel 11 to form the adsorber B.
13 From the foregoing, it will be noted that each of the 14 adsorbers provides a continuous longitudinal flow passageway.
In the case of the adsorber A, the passageway is the void space 16 3. In the case of the adsorber B, the passageway i5 provided by 17 the lumina 2. For separation of fluid mixtures, the feed is 18 directed to flow through the flow passageway. Since the thin and 19 porous fiber wall has negligible mass transfer resistance, the fluid is always in intimate and substantially uniform contact 21 with the aasorbent particles 9. The adsorbers A, B are adapted 22 for use with PSA and TSA systems in accordance with known 23 technology.
24 Typically the hollow fibers will have a lumen diameter less than 2 mm. The fiber wall will typically have pore openings 26 of about 0.5 micrometer in equivalent diameter.
27 The adsorbent particles preferably will be selected 28 from the group consisting of molecular sieve zeolites, silica 29 gel, activated alumina, carbon black, and activated carbon. The 1 particle size preferably will be less than 30 microns, most 2 preferably 1 - 30 microns. The surface area preferably should 3 be at least about 200 m2/g.
4 The solid adsorbent particles or crystals (referred to collectively as "particles") can be packed into the lumina 2 or 6 void space 3 using one of several techniques. More particularly, 7 in the case of non-soluble particles, they are first suspended 8 by agitation in a liquid or gas carrier, such as alcohol, water 9 or air. The suspension is then pumped into the lumina 2 or void space 3, as shown in Figures 1 or 2. The li~uid or gas carrier 11 is able to permeate readily through the microporous ~iber wall.
12 In the case of pumping the slurry into the lumina 2 (Figure 1), 13 the top ends of the lumina are open, to receive the feed and the 14 bottom ends are sealed. The adsorbent particles 9 become trapped in the lumina while the carrier diffuses through the fiber walls 16 and exits through an outlet 8 in the casing ~. In this fashion, 17 a charge of densely packed particles may be accumulated to fill 18 the lumina substantially throughout its length. The top ends of 19 the lumina can then be sealed to immobilize the particles.
Similarly, in the case of pumping the slurry into the void space 21 3 (Figure 2), the top ends of the lumina 2 and the void space 3 22 are closed and the bottom ends of the lumina are left open. The 23 slurry enters the void space, the carrier passes through the 24 fiber walls and exits out the bottom of the lumina, and the particles 9 remain trapped in the void space 3. In bo-th cases, 26 adsorbent loading may be facilitated by vibration by immersing 27 the module in an ultrasonic bath.
2~ In the case of soluble adsorbent materials, the 29 adsorber, having fibers that will not be wetted by the solvent, 2~

1 can be packed by filling a first passageway of the module with 2 the solution and then drying or leaching out the solvent by 3 circulating air or non-solvent through the second passageway of 4 the module.
Still another class of materials that can be used as 6 the adsorbent are those that can be cast in-situ to form a 7 microporous structure by the sol-gel phase inversion techniques.
8 (See Example 2 and Robert E. Kesting, "Synthetic Polymeric 9 Membrane", 2nd Edition, John Wiley, N.Y., 1985). A typical sol-gel process ~or forming porous structure comprises: preparing 11 a solution of polymeric material, solvent, non-solvent and 12 swelling agent; evaporating or leaching ~he solvent with non-13 solvent; and drying the non-solvent.
14 The present hollow fiber adsorber has certain advantages over conventional packed bed adsorbers, namely:
16 (1) In the hollow fiber adsorber, the fluid pressure 17 drop through the adsorber is independent of the 18 particle size of the adsorbent, because the fluid 19 flow path is separated from the particles by the microporous fiber walls;
21 (2) The hollow fiber adsorber can use very fine 22 adsorbent particles, such as micron sized crystals 23 of molecular sieve zeolites. This will reduce 24 mass transfer resistance, because the use of small particles increases the fluid/solid interfacial 26 mass trans~er areas and reduces the intraparticle 27 diffusion path length. In addition, the binder 2~ materials contained in the larger pelletized 29 adsorbents used in conventional adsorbers is C~ ~3 ~
1 eliminated, resulting in higher adsorptivs 2 capacities;
3 (3) The hollow fiber adsorber broadens the choice of 4 adsorbent materials for the adsorption proaess.
It can use a wide range of powder materials that 6 have adsorptive properties. If the particle size 7 is small enough, the adsorbent need not be of 8 porous material, because small particles have 9 large external surface areas;
(4) ~he hollow fiber adsorber can use microporous and 11 adsorptive structure that can be cast into either 12 the lumina or void space of the module. Many 13 plastic materials can be converted to microporous 14 matrices by the so-called phase inversion techni~ue (see Example 2). The fiber wall 16 provides a partition between the matrix and the 17 flow passageway in the fiber module;
18 (5) The microporous hollow fibers provide efficient 19 and uniform contact between the adsorbent particles and the fluid mixture for a wide range 21 ~ of flow rates, thereby avoiding the channelling 22 problems that can affect the conventional 23 adsorber, 24 (6) The fast mass transfer and low pressure drop of the hollow fiber adsorber enables the PSA process 26 to be operated efficiently at fast cycle and high 27 feed rates.
28 The invention is illustrated by the following examples:

1 Example I
2 This example sets forth in detail an embodiment of the 3 best mode presently known to applicants for packing one of the 4 passageways with a charge of particles. It further describes the character of the charge so emplaced.
6 Two hollow fiber modules were made using microporous 7 polypropylene Celgardl hollow fibers manufactured by the Hoechst 8 Celanese Corporation (Charlotte, N.C.). The physical parameters 9 of these modules are given in the following Table. Element 1 was packed with molecular sieve zeolite crystals in -the fiber lumina 11 (see Figure 1) using cyclohexane as the carrier fluid. Element 12 2 was packed with activated carbon powder in the void space 13 between fibers (see Figure 2) using methanol as the carrier 14 fluid. Both elements were packed using 20 psi slurry solution of adsorbent particles suspended in the carrier fluid, driven by 16 a diaphragm pump. The slurry pumping operation was then followed 17 by dry nitrogen circulation to dry out the carrier fluid from 18 adsorbent partiales. As shown in the ~able, the resulting hollow 19 fiber elements have adsorbent particle packing density considerably greater than the free standing particle bulk 21 density. The packing was uniform throughout the length and 22 breadth of the packing space.

23 ITrade-Mark ~ ~ 2 6~ ~ ~r;~ ~

2Physical Parameters of Hollow Fiber Adsorher Elements 3 ~ollow Fiber ModuleElement 1 Element 2 4 casing, ID, cm .48 .45 fiber typeCelgard2 X20-400 Celgard3 X20-200 6 fibsr number 60 132 7 active fiber length, cm 65 64 8 fiber ID/ m.icrometer400 200 9 fiber OD, micrometer460 260 fiber wall porosity, %40 40 11 fiber wall pore opening 12 microme-ter 13 (width x length).065 x .19 .065 x .19 14 Adsorbent Packings packing locationfiber lumina outside fibers 16 adsorbent type Union Carbide 5A Darco4 KB carbon 17 particle size, micrometer <10 <30 18 par-ticle bulk density, g/cc 19 (free standing) .49 .25 packing density, g/cc.53 .40 21 total packing weight, g 2.6 2.3 22 2Trade-Mark 23 3Trade-Mark 24 4Trade-Mark 1 Example II
2 This example illustrates the use of very fine, non-3 soluble adsorbent particles in a hollow fiber adsorber for gas 4 separation.
Two hollow fiber modules were made containing 6 microporous polypropylene Celgards X10-400 hollow fibers. The 7 fiber had a 400 micron internal diameter lumen and 30 micron 8 thick wall. The fiber wall had 30% porosity provided by .065 x 9 .19 microns pore openings. Each of the test modules had 30 open-ended fibers of 50 cm length encased in a 3/16 inch OD stainless 11 steel tube (.375 cm ID) with both ends of the fiber bundle potted 12 in 3 cm long polyurethane tube sheets.
13 The previously described filtration technique was used 14 to pack a type Y zeolite powder (less than 10 micron size) in-to the modules. One module was packed with 1.3 g of powder in the 16 fiber lumen, and the other was loaded with 1.7 g of the same 17 powder in the void space between the fibers. The different modes 18 of adsorbent loading were chosen only to demonstrate the 19 workability of each version of the process.
The two modules were plumbed and instrumented to 21 operate as a cyclic pressure swing adsorption (PSA) system in 22 accordance with C. W. Skarstrom, U.S. patent 2,944,627. The 23 cyclic operation was automated with an 8 port valve directing 24 the gas to and from the inlets and outlets of the two adsorbers.
The valve was, in turn, driven by a solenoid controlled by a 26 programmable timer.
27 The PSA system was used to purify a feed stream 28 consisting of helium gas containing 1% CO2. In the first step of 29 5 Trade-Mark ~ ~ ~.J C~
1 the PSA cycle, the feed gas, at 200 psig and 23~C, was fed to the 2 first adsorber for CO2-removal at a rate of 200cc (STP)/min.
3 Simultaneously a portion (25cc/min.) of the purified helium was 4 throttled down to about 6 psig and supplied to the second adsorber to pur~e previously adsorbed CO2. The remainder, still 6 at high pressure, was taken off as purified helium product.
7 After 3.5 minutes, the timer switched the system into 8 the second step of operation. At the beginning of this step, the 9 Eirst adsorber was de-pressurized to atmospheric pressure and the 10 second adsorber was pressurized with feed gas. It then started 11 the adsorption and purging operations for the second and first 12 adsorbers, respectively. The duration of the second step was the 13 same as the first step, and the system was alternated between 14 these two steps in cyclic fashion. The gas flow direction in 15 each adsorber Eor adsorption and pressuri~ation cycles was 16 countercurrent to that for purging and de-pressurization cycles.
17 ~ thermal conductivity gas analyzer was used to measure 18 the CO2 concentration in helium. ~he test results showed that 19 the microporous hollow fiber module, packed with minute adsorbent 20 particles, in both versions, was effective for gas purification ~1 by pressure swing adsorption, because no C~2 could be detected in 22 the purified effluent helium.

23 Example III
24 This example illustrates the use oE the sol-gel phase 25 inversion techni~ue for casting a microporous matrix into the 26 hollow fiber module for use as an adsorbent.
27 A hollow fiber module was made using microporous 28 polypropylene Celgard hollow fibers of 2~0 micron ID and 30 ~ 3 1micron wall thickness. The fiber wall had 30% porosity with .065 2x .19 micron pore openings. The module had 60 50-cm long fibers 3encased in a 3/16 inch OD nylon tube, with both ends of the fiber 4bundle potted in 3 cm long polyurethane tube sheets.
5A microporous cellulose acetate matrix structure was 6cast into the void space between the fibers by first filling it 7with a cellulose acetate solution (made of 22 g cellulose 8acetate, 132 g acetone, 30 g water and 10 g ZnCl2), and then 9circulating water through the fiber lumina to leach out the 10acetone, followed by dry air circulation to remove water.
11The element was tested for gas dehydration. The water 12content in the gas was measured using a hygrometer. An air 13containing .04% water vapour at 80 psig and 23~C was fed to the 14module through the lumina at a rate of about 400 cc (STP)/min and 15dry air, containing only 20 ppm of water, was obtained from the 16element outlet.
17The moist air started to break through the element 18outlet only after about 20 minutes of operation. The water 19saturated cellulose acetate was able to be regenerated by purging 20the element with 6 psig dry air at 100 cc/min for about 20 2Iminutes.

22Example IV
23This example illustrates the use of non-porous soluble 24particles as an adsorbent in the hollow fiber adsorber. A hollow 25fiber module similar to the one described in Example 2 was packed 26with CuCl2 powder by filling the void space between the fibers 27with a 60~C concentrated aqueous CuCl2 solution (67% CuCl2 by 28weight) followed by dry air circulation through the fiber lumina 2 ~

1 to remove water. The module was tested for air dehydration, as 2 described in Example 2. An alr containing .052% water vapour was 3 fed to the module through the fiber lumina at 80 psig, 23~C, and 4 500cc(STP)/min. Dry air containing 110 ppm of water was obtained from the outlet of the element. The moist air started to break 6 through the element outlet after about 24 hours of operation.
7 The water-saturated CuCl2 was regenerated hy purging the element 8 with 100 cc/min. dry air at 100~C for 12 hours.

9 Example V
This example illustrates the efficiency of the hollow 11 fiber adsorber in the fast-cycle pressure swing adsorption 12 process for high feed gas flow rates.
13 A hollow fiber module was made containing polypropylene 14 Celgard hollow fibers. The fiber had a 200 micron ID and 30 micron thick wall. The fiber wall had 40% porosity provided by 16 about .065 x .19 micron pore openings. ~he module had 132 open-17 ended fibers of about 70 cm length encased in a 1/4 inch OD nylon 18 tube (0.44 cm ID) with both ends of the fiber bundle potted in 19 3 cm long epoxy tube sheets.
The previously described filtration technique, with 21 the aid of ultrasonic vibration, was used to pack 2.3 g Darco KB6 22 activated carbon powder (particle size less than 30 microns~ into 23 the void space between the fibers.

24 6 Trade-Mark 1 The element was plumbed and instrumented as a pressure 2 swing adsorber operating according to the following sequential 3 steps in cycle:
4 (1) Adsorbing adsorbate from a high pressure feed gas for a predetermined time period to obtain purified 6 gas from the adsorber outlet;
7 (2) Depressurizing the gas remaining in the adsorber 8 (after the adsorption step) through its outlet and 9 into a first gas storage vessel having an internal volume approximately equal to the internal void 11 volume of the adsorber;
12 (3) Further depressurizing the gas in the adsorber 13 into a second gas storage vessel having the same 14 internal volume;
(4) Venting the remaining gas in the adsorber through 16 its inlet;
17 (5~ Purging the adsorber using the gas stored in the 18 second storage vessel; the purge gas flow 19 direction being countercurrent to the feed gas direction in the adsorption step;
21 (6) Pressurizing the adsorber using the gas stored in 22 the first storage vessel; the remaining gas in the 23 storaye vessel is then removed as low pressure 24 product;
(7) Further pressurizing the adsorber to feed gas 26 pressure using a portion of the purified high 27 pressure product gas, and thus readying the 28 adsorber for the next adsorption cycle.

1 The aforementioned hollow fiber adsorber containing 2 2.3g of minute activated carbon particles was used to purify a 3 314 psia hydrogen gas containing about 10% C~2 using the above 4 pressure swing adsorption steps. In the tests, we varied the feed gas flow rate and determined the corresponding maximum 6 permissible adsorption step time without any CO2 breakth~ough 7 from the adsorber outlet. The following results were obtained:
8 Maximum Permissible 9 Feed Rate (Without 10Adsorption Step TimeC~2 Breakthrough) 11Seconds cc (STP)/min.

14 72 ~00 36 1,000 16 17 2,000 17 10 3,600 18 It is seen that the maximum permissible feed gas rate 19 is inversely proportional to the adsorption step time. The corresponding hydrogen recovery for each of these flow rates is 21 virtually identical and e~ual to about 76%.
22 ~hese test results clearly indicate that the feed gas 23 throughput of a hollow fiber adsorber can be effectively 24 increa~ed without loss of separation efficiency by simply shortening the PSA cycle time. The high adsorption efficiency 26 at short adsorption c~cle time and high feed rate is made 27 possible by the fast mass transfer rate and low gas pressure drop 2~ in the hollow fiber adsorber using minute adsorbent particles.
29 The scope of the invention is defined by the claims now following.

Claims (8)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN
EXCLUSIVE PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS
FOLLOWS:

1. A hollow fiber element for use in an adsorber adapted to separate adsorbate from a fluid mixture stream comprising a carrier fluid and the adsorbate, comprising:
a bundle of hollow fibers, each fiber having a microporous wall that is permeable relative to the adsorbate, the fiber wall having pore openings whose effective pore diameters are in the range of about 0.05 to 5 micrometers, each fiber forming a lumen, said lumina and the void space between the fibers providing two longitudinal passageways extending through the bundle, said bundle having means at each end for sealing a first of the passageways;
an impermeable casing sealing the side periphery of the bundle; and a charge of individually free, minute, solid, adsorbent particles packing the first passageway substantially throughout its length and breadth, said charge having a density substantially equal to or greater than the free-standing bulk density of the particles;
the pores of each fiber wall being smaller than the particles;
said particles being immobilized in the first passageway but being accessible to adsorbate introduced into the other passageway in the fluid mixture.

2. A hollow fiber adsorber adapted to separate adsorbate from a fluid mixture stream comprising a carrier fluid and the adsorbate, comprising:
a bundle of hollow fibers, each fiber having a microporous wall that is permeable relative to the adsorbate, the fiber wall having pore openings whose effective pore diameters are in the range of about 0.05 to 5 micrometers, each fiber forming a lumen, said lumina and the void space between the fibers providing two longitudinal passageways extending through the bundle, said bundle having means at each end for sealing a first of the passageways;
an impermeable casing sealing the side periphery of the bundle;
a vessel encapsulating the bundle;
means sealing the casing against the inside surface of the vessel;
first means for introducing the fluid mixture stream into one end of the first passageway and second means for removing the stream from the other end of the passageway;
a charge of individually free, minute, solid, adsorbent particles, packing the first passageway substantially throughout its length and breadth, said charge having a density substantially equal to or greater than the free-standing bulk density of the particles;
the pores of each fiber wall being smaller than the particles;
said particles being immobilized in the first passageway but being accessible to the adsorbate introduced into the other passageway.

3. The element as set forth in claim 1 wherein:
the surface area of the particles is at least about 200 m2/g; and the particle size is less than about 30 microns.

4. The adsorber as set forth in claim 2 wherein:
the surface area of the particles is at least about 200 m2/g; and the particle size is less than about 30 microns.

5. The element as set forth in claim 1 wherein:
the particles are selected from the group consisting of molecular sieve zeolites, silica gel, activated alumina, carbon black and activated carbon;
the surface area of the particles is at least about 200 m2/g; and the particle size is less than about 30 microns.

6. The adsorber as set forth in claim 2 wherein:
the particles are selected from the group consisting of molecular sieve zeolites, silica gel, activated alumina, carbon black and activated carbon;
the surface area of the particles is at least about 200 m2/g; and the particle size is less than about 30 microns.

7. A process for packing a hollow fiber element used to provide interaction between minute solid adsorbent particles and an adsorbate forming part of a feed mixture stream, comprising:
providing a bundle of hollow fibers, each fiber having a wall having pore openings whose effective diameters are in the range of about 0.05 to 5 micrometers, said openings being permeable relative to the adsorbate but not to the particles, each fiber forming a lumen, said lumina and the void space between the fibers providing two longitudinal passageways extending through the bundle, each passageway having corresponding first and second ends, said bundle having means at the second end of one of the passageways for sealing said passageway, said bundle having means at the first end of the other passageway for sealing said other passageway, said bundle having an impermeable casing sealing its side periphery;
pumping a suspension or solution of the minute solid particles in a carrier fluid, formed of liquid or gas, under pressure into the first end of the one passageway, said fiber walls being permeable to the carrier fluid, whereby the carrier fluid filters through the fiber walls into the other passageway and exits the element and the particles are retained in the one passageway and accumulate to form a dense, substantially uniform packing of individually free particles, said packing having a density substantially equal to or greater than the free-standing bulk density of the particles; and sealing the first end of the one passageway to immobilize the particles and opening the first end of the other passageway to remove the filtrate.

8. The process as set forth in claim 7 wherein it is a suspension of solid particles in a carrier fluid that is pumped under pressure into the first end of the one passageway.