CO2-SELECTIVE MEMBRANE PROCESS AND SYSTEM FOR REFORMING A FUEL TO HYDROGEN FOR A FUEL CELL

Abstract: The present invention provides a CO2-selective membrane process that is useful for the purification and/or water gas shift reaction of a reformed gas, generated from on-board reforming of a fuel, e.g., hydrocarbon, gasoline, diesel, methanol or natural gas, to hydrogen for fuel cell vehicles. Another embodiment of the present invention is directed toward a composition comprising a hydrophylic polymer and at least one ammonium halide salt, the ammonium halide salt being present in an amount ranging from about 10 to 80 wt. % based on the total weight of the composition. The composition is suitable in formation of a membrane useful for separating CO2 from a CO2-containing gas, particularly from an on-board reformed gas for the CO2-selective membrane process.

Description: C0 2 -SELECTIVE MEMBRANE PROCESS AND SYSTEM FOR REFORMING A FUEL TO HYDROGEN FOR A FUEL CELL Field of the Invention The present invention relates to a membrane process and system for the purification of a fuel, e.g., hydrocarbon, gasoline, diesel, methanol, ethanol or natural gas, to hydrogen for fuel cells. The purification process selectively removes C0 from the reformed product thereby enriching the reformed product in H 2 and increasing the H 2 /C0 2 ratio. This invention also relates to a polymer composition suitable for forming a membrane that is useful for separating C0 2 from a C0 2 -containing gas stream in the purification process. The present invention is particularly useful when the process is carried-out onboard a vehicle using a fuel cell for transportation. Background of the Invention Reforming of a fuel, e.g., hydrocarbon, gasoline, diesel, methanol, ethanol or natural gas, to hydrogen is generally proceeded with the formation of the synthesis gas of CO and H2 first. For example, steam reforming of methanol with a NiO / AI2O3 catalyst at 300-400°C (T. B. Su and M. H. Rei, J. Chin. Chem. Soc. (Taipei), 8, 535 (1991)) gives the synthesis gas: CH 3 OH → CO +2H 2 (1) Steam reforming of CH4 with a nickel-based catalyst at 800°C is: CH4 + H 2 O -> CO + 3H 2 (2) Partial oxidation of CH4 is: CH 4 + -O 2 - CO + 2H 2 (3) Similarly, partial oxidation of other hydrocarbons, e.g., gasoline and diesel, produces the synthesis gas: C n H n+2 + °2 → n CO + (n+l) H 2 (4) where n is an integer. In the partial oxidation, the synthesis gas produced does not contain N2 when O2 is used. If air is used instead of O2, the synthesis gas produced contains N2. The synthesis gas is then sent conventionally to two-stage water gas shifters, in which CO is converted to CO2 via the water gas shift reaction: CO + H 2 O → CO 2 + H 2 (5) Typically, the first-stage shifter operates at higher temperature than the second- stage shift, e.g., 373°C for the first stage and 225°C for the second stage. For the water gas shift reaction, CuO / ZnO / AI2O3 catalysts can be used. The product gas from steam reforming of methanol under the optimum conditions at 1 arm and 227°C with a water rich feed (water / methanol = 1.5) contains approximately 66% H 2 , 21% C0 2 , 1% CO, and 12% H 2 0 (J. C. Amphlett, M. J. Evans, R. A. Jones, R. F. Mann, and R. D. Weir, Can. J. Chem. Eng.. 59, 720 (1981)). In some reforming cases, such as the steam reforming of methanol with a CuO / ZnO / AI2O3 catalyst, methanol is converted directly and predominantly to CO2 and H2: CH 3 OH + H 2 O CatalySt > CO 2 + 3H 2 (6) This reaction operates at temperatures lower than 260°C with methanol conversion as high as 90%; however, trace CO appears at temperatures above 300°C and high methanol conversions of about 90% (C. J. Jiang, D. L. Trimm, and M. S. Wainwright, Appl. Catal. A, 93, 245 (1993)). Japanese Patents 04,321,502 and 04,325,402 claim processes employing H2~selective membranes, which selectively pass H2 and reject other gases, for hydrogen manufacture for fuel cells. However, these processes suffer from a low pressure for the H2 product gas which is much lower than the pressure for the feed gas. Thus, a compressor is needed to compress the product gas to the pressure of the feed gas. In addition, these processes also usually have other shortcomings, such as low H2 recoveiy, large membrane areas, and a high CO2 concentration in the product gas. It is an object of the present invention to provide a Cθ2-selective membrane process that selectively passes CO2 over H2 and other gases and that is useful for the purification and/or water gas shift reaction of a reformed gas, generated from refonning of a fuel, e.g., hydrocarbon, gasoline, diesel, methanol, ethanol or natural gas, to hydrogen for fuel cells. This Cθ2-selective membrane process can be more advantageous than ^-selective membrane processes in terms of H2 product pressure (to avoid the need of a compressor for the product gas), H2 recovery, membrane area, and CO2 concentration. Another object of the present invention is to provide a novel polymer composition that is suitable in formation of a membrane useful for the Cθ2-selective membrane process. Membranes disclosed in U.S. 5,611,843 may also be used for the C0 2 selective membrane process. Summary of the Invention The present invention is a process and system to purify a fuel feedstream so that the feedstrean is enriched in H 2 . In general, the process includes the steps of reforming the feedstream, and separating C0 2 with a membrane that selectively removes C0 from the feedstream. For most fuel feedstreams, a step of water gas shift reaction is also included in the process. The C0 2 selectively permeable membrane may also be used to perform both steps of enhancing water gas shift reaction and separating C0 . The process further comprises the step of methanating the H 2 -enriched feedstream. If the fuel feedstream is methanol, then a water gas shift reaction step is not necessaiy. In this embodiment, the C0 2 selectively permeable membrane may be used to perform both steps of refonning and separating. In a prefeιτed embodiment, the process is carried-out on board a vehicle that uses a fuel cell for transportation. Another embodiment of the present invention is directed toward a composition comprising a hydrophilic polymer and at least one ammonium halide salt, the ammonium halide salt being present in an amount ranging from about 10 to about 80 wt% based on the total weight of the composition. The composition is suitable in formation of a membrane useful for separating CO2 from a Cθ2-containing gas, particularly from an on-board reformed gas for the Cθ2-selective membrane process. The embodiments of the present invention will become apparent upon a reading of the brief description of the drawings and the detailed description of the invention which follow. Brief Description of the Drawings Figure 1 shows the flow diagram for the first case of the CO2- selective membrane process of the present invention, in which a Cθ2-selective membrane is incorporated into the water gas shifter to become the water gas shifter and Cθ2-selective membrane reactor for enhancing the conversion of the water gas shift reaction and for purifying the H2 product via CO2 removal. Figure 2 illustrates the flow diagram for the second case of the Cθ2-selective membrane process of the present invention, in which a CO2- selective membrane separator is used to purify the H2 product from the water gas shift converter. Figure 3 exhibits the flow diagram for the third case of the CO2- selective membrane process of the present invention, in which a Cθ2-selective membrane is incorporated into the steam reformer for methanol to become the reformer and Cθ2-selective membrane reactor for increasing the conversion of the methanol steam refonning reaction and for purifying the H2 product via CO2 removal. Figure 4 shows the flow diagram for the fourth case of the CO2- selective membrane process of the present invention, in which a Cθ2-selective membrane separator is used to purify the H2 product from the steam reforming of methanol. Detailed Description of the Invention The present invention provides a Cθ2-selective membrane process that is useful for the purification of a fuel, e.g., hydrocarbon, gasoline, diesel, methanol, ethanol or natural gas, to hydrogen for fuel cells. This process includes reforming the fuel feedstream and separating C0 from the feedstream. The C0 2 is removed by contacting a C0 2 -containing gas steam with one side of a nonporous, CO2 selectively peπneable membrane whereby CO2 is selectively transported over other gases through the membrane and withdrawing from the other side of the membrane a permeate containing CO2 whereby CO2 is selectively removed from the gaseous stream. The permeate comprises the CO2 in increased concentration relative to the feed stream. By "permeate" is meant that portion of the feed stream which is withdrawn at the second side of the membrane, exclusive of other fluids such as sweep gas or liquid which may be present at the second side of the membrane. Air or nitrogen may be used as the sweep gas. There are four embodiments of the process and the system for performing the process. In the first case of the present invention, a Cθ2-selective membrane is incorporated into the water gas shifter to become the water gas shifter and Cθ2-selective membrane reactor for enhancing the conversion of the water gas shift reaction (Eq.(5)) and for purifying the H2 product via CO2 removal. Figure 1 shows the flow diagram for the Cθ2-selective membrane process of the present invention, consisting of a refonner, a water gas shifter and Cθ2-selective membrane reactor, a methanator, and a fuel cell. As shown in this figure, the H2 product with low CO2 and CO concentrations is sent to the methanator, in which CO2 and CO are converted to CH4 via the methanator reactions: CO 2 + 4H 2 → CH 4 + 2H 2 O (7) CO + 3H 2 - CH 4 + H 2 O (8) For enhancing the methanation reactions (Eqs. (7) and (8)), a catalyst of Ru supported on ΗO2 may be used. Finally, the high-purity H2 product with CH4 is fed to the fuel cell to drive the electric vehicle. The H2 product without CO and CO2 is the most desirable fuel for the fuel cell since CO is a poison for the fuel cell and CO2 produces CO via the reverse reaction of Eq.(5). To speed up the removal of CO2 from the permeate side of the Cθ2-selective membrane process, a sweep gas, such as air, may be used. The exit stream of the sweep gas may be combined with the anode exhaust stieam of the fuel cell to be burned for supplying heat, for example, to the steam refonner or for other heat integration. The second case of the present invention involves the use of a Cθ2-selective membrane separator to purify the H2 product from the water gas shifter converter. Figure 2 gives the flow diagram for the Cθ2-selective membrane process, consisting of a refonner, a water gas shifter, a Cθ2-selective membrane separator, a methanator. and a fuel cell. As mentioned earlier, in some refonning cases, such as the steam reforming of methanol with a CuO / ZnO / AI2O3 catalyst, methanol is converted directly and predominantly to CO2 and H2 The third case of the present invention is to incorporate a Cθ2~selective membrane into the methanol steam reformer to become the reformer and Cθ2-selective membrane reactor for increasing the conversion of the steam refonning reaction (Eq.(6)) and for purifying the H2 product via CO2 removal. Figure 3 shows the flow diagram for the Cθ2-selective membrane process of this invention, consisting of a reformer and Cθ2-selective membrane reactor, a methanator, and a fuel cell. The fourth case of the present invention uses a Cθ2-selective membrane separator to purify the H2 product from the steam reforming of methanol shown in Eq.(6). Figure 4 illustrates the flow diagram for the CO2- selective membrane process, consisting of a refonner, a Cθ2-selective membrane separator, a methanator, and a fuel cell. Another embodiment of the present invention is directed toward a composition comprising a hydrophilic polymer and at least an ammonium halide salt, the ammonium halide salt being present in an amount ranging from about 10 to about 80 wt% based on the total weight of the composition and preferably about 40 to about 65 wt%. The hydrophilic polymers suitable in the practice of the present invention include polyvinylalcohol, polyvinylpyιτolidone, polyethyleneoxide, polypropyleneoxide, polyaciylamide, polyvinylacetate, blends and copolymers thereof. In general, these polymers will have weight average molecular weights in the range of about 30,000 to 2,000,000 and preferably in the range from about 50,000 to 200,000. Particularly preferred polymers useful in the present invention are polyvinylalcohols having molecular weights in the range from about 50,000 to 150,000. The ammonium halide salts in the compositions of the present invention are selected from salts having the formulae and mixtures thereof: (R) 4 N + X- wherein R is hydrogen or an alkyl group having from 1 to 4 carbon atoms and X is a halide, the halide being selected from the group consisting of fluoride, chloride, bromide, iodide, and mixtures thereof. As previously stated, the amount of ammonium halide salt to be present in the composition is in the range from about 10 to 80 wt% based on the total weight of the composition, and preferably about 40 to about 65 wt%. The compositions of the present invention are prepared by first forming a solution of the polymer and the ammonium halide salt in a suitable solvent such as water. Generally, the amount of water employed will be in the range from about 70%> to 95%o. The composition can then be recovered from the solution by removing the solvent, for example, by allowing the solvent to evaporate; however, it is preferred to use the solution in forming a nonporous membrane. Thus, the resulting solution is formed into a nonporous membrane by techniques well known in the art. For example, the polymer solution can be cast onto a solid support with techniques such as "knife casting" or "dip casting". Knife casting, of course, is a process in which a knife is used to draw a polymer solution across a flat surface to form a thin film of the polymer solution of uniform thickness after which the solvent of the polymer solution is evaporated, at ambient or temperatures up to about 200°C, to yield the fabricated membrane. When, for example, a glass plate is used as the flat surface, the membrane can then be removed from the support providing a free standing polymer membrane. When, alternatively, the flat surface used is a non-selective porous support such as porous polytetrafluoroethylene, the resulting membrane is a composite membrane comprising the selective membrane polymer and the support. Dip casting is the process in which the polymer solution is contacted with a non- selective porous support. Then excess solution is permitted to drain from the support, and the solvent of the polymer solution is evaporated at ambient or elevated temperatures as above. The membrane comprises both the polymer and the porous support. The membranes of the present invention also may be shaped in the form of hollow fibers, tubes, films, sheets and the like. In an alternate embodiment of the present invention, a cross- linking agent is added to the polymer and ammonium halide salt solution before forming a membrane from it. Suitable cross-linking agents include formaldehyde, divinyl sulfone, toluene diisocyanate, glyoxyal, glutaraldehyde, trimethylol melamine, terephthalatealdehyde, epichlorohydrin, vinyl acrylate, and maleic anhyride. Formaldehyde, divinyl sulfone and toluene dissocyanate are particularly preferred. The amount of cross-linking agent employed will be in the range of about 1 to about 20 wt% based on the total weight of the solid composition formed from the solution. Membranes formed from the solution containing a cross-linking agent typically are heated at a temperature and for a time sufficient for cross- linking to occur. Generally, cross-linking temperatures in the range from about 80°C to about 200°C are employed. Cross-linking will occur in from about 1 to 72 hours. As indicated previously, the compositions of the present invention are suitable for use as a nonporous membrane for separating CO2 from a CO2- containing gas stieam, particularly from an on-board reformed gas for the CO2- selective membrane process of the present invention. The present invention will be better understood by reference to the following examples which are offered by way of illustration not limitation. Examples In the examples which follow, the separation factor (selectivity) for CO2 vs. H2 is expressed as follows: CO- / H- concentration ratio in the permeate , n . SeparationFactor = (9) CO 2 / H 2 concentration ratio in the retentate The retentate refers to the mixture on the feed side of the membrane which is rejected by the membrane under the operating conditions. Permeability is expressed in Barrer (1 Barrer = 10 - 1 ^ cm3(STP)-cm/(cm2-s-cm Hg)). The permeability is determined by the use of the relationship between the permeability P and the permeation rate Q (cm^(STP)/s) as follows: where A is the membrane area, p j and p 2 are the CO2 partial pressures in the retentate and permeate streams, respectively, and L is the membrane thickness. P/L is called the permeance with a typical unit of GPU (gas permeation unit, 1 GPU = 10"6 cm3(STP)/(cm2-s-cm Hg)). The partial pressures are determined based on concentiation measurements by gas chromatography and total pressure measurements by pressure gauges. The peπneation rate is determined based on concentration measurements obtained by gas chromatography and permeate stream flow rate measurements by a flow meter. Example 1: Cθ2-Selective Membrane Process for Purification of a Reformed Gas Containing N2 at 3 atm The Cθ2-selective membrane process of the present invention is used to purify a reformed gas to supply H2 to a 10 KW fuel cell with a flow diagram shown in Figure 2 or 4. It should be noted that a fuel cell vehicle may require several 10 KW fuel cells, e.g., 5 (50 KW total). The 10 KW fuel cell requires a hydrogen feed rate of 0.07 mole H2/S. The reformed gas contains 40%) H 2 , 19% C0 2 , 1%) CO, and 40% N 2 (on a water-free basis) at a total pressure of 3 atm. The Cθ2-selective membrane used has a CO2 permeance of 600 GPU, a CO2 / H 2 selectivity of 75, a C0 2 / CO selectivity of 100, and a CO2/N2 selectivity of 100. Air is used as the sweep gas for the permeate to have H2, CO2, CO and N2 partial pressures in the permeate to be insignificant in comparison with their partial pressures in the retentate. By the use of Eq. (10), the membrane area, H2, CO and N2 concentrations in the retentate, and H2 recoveiy are calculated for a CO2 concentration of 0.5% in the retentate. The membrane area is 92.5 ft2, the retentate, i.e., the product gas, has 49.0% H2, 0.5% CO2, 1.2% CO, and 49.3% N 2 at a total pressure of 3 atm, and the H recoveiy is 97.2% of the H2 available in the reformed gas. The retentate is then treated in a methanator to convert CO2 and CO to CH4, resulting in a desirable fuel without containing CO2 and CO for the fuel cell. Example 2: Cθ2-Selective Membrane Process for Purification of a Reformed Gas Containing N2 at 10 atm The Cθ2-Selective Membrane Process of the present invention for purification of a reformed gas containing 40% H2, 19%o CO2, 1%) CO, and 40% N2 (on a water-free basis) at a total pressure of 10 atm is the same as that described in Example 1 except the total pressure. The higher the total pressure (at the same gas composition), the smaller the membrane area. Again, Eq. (10) is used to calculate the membrane area, H2, CO and N2 concentrations in the retentate, and H2 recoveiy for a CO2 concentiation of 0.5% in the retentate. The membrane area is 27 ft 2 , the retentate (product gas) has 49.0%> H2, 0.5%> CO2, 1.2% CO, and 49.3%o N2 at a total pressure of 10 atm, and the H2 recovery is 97.2% of the H2 available in the reformed gas. Similarly, the retentate is then treated in a methanator to convert CO2 and CO to CH4, yielding a desirable fuel cell fuel without containing CO2 and CO. Example 3 : H2 -Selective Membrane Process for Purification of a Reformed Gas Containing N2 at 10 atm (for comparison) For comparison, the membrane area and H2, CO2, CO and N2 concentrations in the permeate, i.e., the product gas, for an ^-selective membrane process with 80% H2 recoveiy from the same reformed gas described in Example 2 are calculated in the same way as in Example 2 via Eq. (10) for the 10 KW fuel cell. The membrane process uses a state-of-the-art, commercially available ^-selective membrane (polyimide) with a H2 permeance of 100 GPU, a H2 / CO2 selectivity of 10, a H 2 / CO selectivity of 100, and a H2 /N2 selectivity of 170 (W. S. Winston Ho and Kamalesh K. Sirkar, Membrane Handbook, p. 44, Chapman & Hall, New York (1992)), and this process gives the product gas (permeate) at 1 atm (without the use of a sweep gas). The membrane area is 126 ft 2 , and the product gas (permeate) contains 88.3% of H2 , 10.1% CO2 , 0.06% CO, and 1.5% N 2 . Table 1 shows the comparison of the Cθ2-selective membrane process of the present invention (Example 2) with the H2-selective membrane process (Example 3). As shown in this table, the membrane process of this invention gives much higher product gas pressure (10 atm vs. 1 atm), greater H2 recoveiy (97.2% vs. 80%), and less membrane area required (27 ft 2 vs. 126 ft 2 ) than the ^-selective membrane process. In addition, the former process gives a lower combined concentration of carbon oxides in the product gas (0.5% CO2 and 1.2% CO vs. 10.1%o CO2 and 0.06%o CO) than the latter process. The product gas of the former process is suitable for methanation to yield a desirable fuel cell fuel without carbon oxides, whereas the product gas of the latter process has too much CO2 to be practically suitable for methanation. Therefore, the process of this invention is more effective and advantageous than the H2-selective membrane process. Table 1 Comparison of the C0 2 -Selective Membrane Process with a H -Selective Membrane Process for Purification of a Reformed Gas Containing N 2 * Product Gas Composition Total Product H 2 Membrane (mole %) Gas Pressure Recovery Area Process H 2 C0 2 CO N 2 (atm) (%) (ft 2 ) C0 2 -Selective Membrane Process, 49.0 0.5 1.2 49.3 10 97.2 27 This Invention (Example 1) H 2 -Selective Membrane Process 88.3 10.1 0.06 1.5 1 80 126 (Example 3) ♦ The reformed gas contains 40% H 2 , 19% C0 2 , 1% CO, and 40% N 2 at total pressure of 10 atm. Example 4: CO2 -Selective Membrane Process for Purification of a Reformed Gas without Containing N2 at 10 atm Similar to the process described in Example 1, the Cθ2-selective membrane process of the present invention is employed to purify a reformed gas to supply H2 to a 10 KW fuel cell with a flow diagram shown in Figure 2 or 4. As mentioned earlier, a fuel cell vehicle may require several 10 KW fuel cell, e.g., 5 (50 KW total). The 10 KW fuel cell requires a hydrogen feed rate of 0.07 mole H2/S. The reformed gas does not contain N2, and it has a composition of 74.9%) H2, 24%o CO2, and 1.1% CO (on a water-free basis) at a total pressure of 10 atm. The Cθ2-selective membrane used, which has a composition of 50 wt% tetramethylammonium fluoride salt and 50 wt% polyvinylalcohol described in Examples 6 and 7, has a CO2 permeance of 600 GPU and a CO2 H2 selectivity of 19. Air is used as the sweep gas for the permeate to have H2, CO2 and CO partial pressures in the permeate to be insignificant in comparison with their partial pressures in the retentate. Again, Eq. (10) is used to calculate the membrane area, H2 and CO concentrations in the retentate, and H2 recovery for a CO2 concentration of 1.2% in the retentate and a CO2/CO selectivity of 100. The membrane area is 17 ft 2 , the retentate (product gas) has 97.1% H2, 1.2% CO2, and 1.7% CO at a total pressure of 10 atm, and the H2 recovery is 83% of the H2 available in the reformed gas. Again, the retentate is then treated in a methanator to convert CO2 and CO to CH4, giving a desirable fuel without containing CO2 and CO for the fuel cell. Example 5: ^-Selective Membrane Process for Purification of a Reformed Gas without Containing N2 at 10 atm (for comparison) For comparison, the membrane area and H2, CO2 and CO concentrations in the permeate, i.e., the product gas, for a ^-selective membrane process with 80% H2 recoveiy from the same reformed gas described in Example 4 (without containing N2) are calculated in the same way as in Example 4 via Eq. (10) for the 10 KW fuel cell. The membrane process employs the state-of-the-art ^-selective membrane (polyimide) described in Example 3 with a H2 permeance of 100 GPU, a H2/CO2 selectivity of 10, and a H2/CO selectivity of 100, and this process yields the product gas (permeate) at 1 atm (without the use of a sweep gas). The membrane area is 45 ft 2 , and the product gas (permeate) contains 92.7%o H 2 , 7.3% CO2, and 0.04%> CO. Table 2 shows the comparison of the Cθ2-selective membrane process of the present invention (Example 4 ) with the ^-selective membrane process (Example 5). As shown in this table, the membrane process of this invention gives higher H2 concentration (97.1% vs. 92.7%), i.e., lower combined concentration of carbon oxides (1.2% CO2 and 1.7% CO vs. 7.3%o CO2 and 0.04% CO), much higher product gas pressure (10 atm vs. 1 atm), greater H2 recovery (83%o vs. 80%), and less membrane area required (17 ft 2 vs. 45 ft 2 ) than the ^-selective membrane process. In addition, the product gas of the former process with a lower combined concentration of carbon oxides is suitable for methanation to yield a desirable fuel cell fuel without carbon oxides, whereas the product gas of the latter process has too much CO2 to be practically suitable for methanation. Thus, the process of this invention is again more effective and advantageous than the H2-selective membrane process. Table 2 Comparison of the C0 2 -Selective Membrane Process with a H 2 -Selective Membrane Process for Purification of a Reformed Gas without Containing N 2 * Product Gas Compo; sition Total Product H 2 Membrane (mole %) Gas Pressure Recovery Area Process H 3 CO, CO (atm) (%) (ft 2 ) C0 2 -Selective Membrane Process, 97.1 1.2 17 10 83 17 This Invention (Example 1) H 2 -Selective Membrane Process 92.7 7.3 0.04 1 80 45 (Example 3) *The reformed gas contains 74.9% H 2 , 24% CO : , and 1.1 % CO at total pressure of 10 atm. Example 6: Synthesis of 50 wt%> Tetramethylammonium Fluoride Salt and 50 wt% Polyvinylalcohol Membrane To 18.65 g of water was added 3.0 g of polyvinylalcohol (PVA) with stining and heating at about 75°C until a clear solution of the polymer was obtained. Separately, 5.32 g of a tetramethylammonium fluoride salt with 4 H2O ((CH3)4NF-4 H2O), which contained 3.0 g of tetiamethylammonium fluoride salt, was dissolved in 5 g of water. This solution was added to the PVA solution with stirring for about 15 minutes to otain a clear, homogeneous solution. The resulting solution was then centiifuged while cooling for about 30 minutes. Following centrifugation, a membrane was knife-cast with a gap setting of 8 mils onto a support of microporous polytetrafluoroethylene. Water was allowed to evaporate from the membrane overnight in a nitrogen box at ambient conditions. The membrane was then heated in an oven at 90°C for 5 hours. The resulting membrane comprised about 60 wt% tetiamethylammonium fluoride salt and 50 wt% polyvinylaclohol on the microporous polytetrafluoroethylene support, and had a thickness of 49 microns (exclusive of the support). Example 7: Peπneation Measurement of Membrane of Example 6 In the permeation measurement to evaluate the separation factor (selectivity) of CO2 vs. H2 and the permeability of CO2, the membrane was placed in a peπneation cell comprising the first compartment for contacting a feed stream against the upstream side of the membrane and the second compartment for withdrawing the permeate from the downstream side of the membrane. The active membrane area in the cell was 63.62 cm 2 . A feed gas comprising 75% H2 and 25%) CO2 under a total pressure of about 3 atm at ambient temperature (23 °C) was contacted against the membrane at a flow rate of 120 cm^/min. The permeate was swept by nitrogen under a pressure of about 1 atm and a total flow rate of 50.9 cm-Vmin for the permeate/nitrogen stream. Both the feed and the sweep streams were humidified by bubbling through deionized water prior to contacting the membrane. For the membrane of Example 6 comprising 50 wt% tetramethylammonmm fluoride salt and 50 wt%> polyvinylalcohol, the CO2 H2 selectivity result obtained was 19, and the C2 permeability was 348 Barrers. As shown in Example 7, the membrane of this invention may be employed for removal of CO2 from a Cθ2-containing gas, e.g., a reformed gas. The use of the membrane composition in the Cθ2-selective membrane process of the present invention for the purification of a reformed gas for a fuel cell vehicle has been described in Example 4.

Claims: CLAIMS: 1. A process to purify a fuel feedstream comprising: (a) refonning said fuel feedstream (b) separating C0 2 from the fuel feedstream with a nonporous, CO2 selectively permeable membrane so that CO2 is selectively removed from the fuel feedstream leaving an enriched feedstream in hydrogen. 2. The process of claim 1 further comprising the step of water gas shift reaction for the fuel feedstream. 3. The process of claim 1 wherein the refonning step and the separating step are perfoπned concuπently. 4. The process of claim 1 wherein refonning step and the separating step are performed sequentially. 5. The process of claim 2 wherein the water gas shift reaction step and the separating step are perfoπned concmτently. 6. The process of claim 2 wherein the water gas shift reaction step and the separating step are perfoπned sequentially. 7. The process of claim 1 further comprising the step of methanating said enriched feedstream. 8. The process of claim 2 further comprising the step of methanating said enriched feedstream. 9. A system for converting a fuel feedstream to a hydrogen rich and COχ (C0 2 and CO) deficient feedstream comprising a reformer, a water gas shifter and Cθ2-selective membrane reactor, and a methanator. 10. A system for converting a fuel feedstream to a hydrogen rich and CO x deficient feedstieam comprising a refonner, a water gas shifter, a CO2- selective membrane separator, and a methanator. 11. A system for converting a fuel feedstream to a hydrogen rich and CO x deficient feedstream comprising a refonner and Cθ2-selective membrane reactor, and a methanator. 12. A system for converting a carbon fuel feedstieam to a hydrogen rich and Co deficient feedstieam comprising of a refonner, a Cθ2-selective membrane separator, and a methanator. 13. The system of claim 9 further comprising a fuel cell. 14. The system of claim 10 further comprising a fuel cell. 15. The system of claim 11 further comprising a fuel cell. 16. The system of claim 12 further comprising a fuel cell. 17. The system of claim 13 wherein said system is on-board a vehicle that is driven by said fuel cell. 18. The system of claim 14 wherein said system is on-board a vehicle that is driven by said fuel cell. 19. The system of claim 15 wherein said system is on-board a vehicle that is driven by said fuel cell. 20. The system of claim 16 wherein said system is on-board a vehicle that is driven by said fuel cell. 21. A composition comprising: a hydrophilic polymer and at least one ammonium halide salt, the ammonium halide salt being present in an amount ranging from about 10 to about 80 wt% based on the total weight of the composition, wherein the ammonium halide salt is selected from ammonium halide salts having the formulae and mixtures thereof: (R) 4 N + X wherein R is hydrogen or an alkyl group having from 1 to 4 carbon atoms and X is a halide, the halide being selected from the group consisting of fluoride, chloride, bromide, iodide, and mixtures thereof. 22. The composition of claim 17 wherein the hydrophilic polymer is selected from the group consisting of polyvinylalcohol, polyvinylpyrrolidone, polyethyleneoxide, polypropyleneoxide, polyacrylamide, polyvinylacetate, blends and copoloymers thereof. 23. The composition of claim 21 wherein the polymer is polyvinylalcohol. 24. The composition of claim 21 including from about 1 to about 20 wt% of a cross-linking agent based on the total weight of composition. 25. The composition of claim 22 wherein the cross-linking agent is selected from the group consisting of formaldehyde, divinyl sulfone, toluene disocyanate, glyoxal, glutaraldehyde, trimethylol melamine, terephthaladehyde, epichlorohydrin, vinyl aciylate, and maleic anhydride. 26. The composition of claim 21 wherein the ammonium halide salt is tetramethylammonmm fluoride salt. 27. A nonporous membrane formed from the composition of claim 21. 28. A method for producing a nonporous membrane having properties sufficient to enable separation of CO2 from a gaseous stream containing CO2, the method comprising: forming a casting solution of a solvent, a hydrophylic polymer and at least one ammonium halide salt, the ammonium halide salt being present in an amount ranging from about 10 to about 80 wt% based on the total weight of polymer and salt; casting the solution on a substrate; and evaporating the solvent whereby a nonporous membrane is formed. 29. The method of claim 28 including adding a cross-linking agent to the polymer solution. 30. The process of claim 1 wherein the membrane of claim 27 is used. 31. The process of claim 2 wherein the membrane of claim 27 is employed. 32. The process of claim 3 wherein the membrane of claim 27 is utilized. 33. The process of claim 4 wherein the membrane of claim 27 is used. 34. The process of claim 5 wherein the membrane of claim 27 is employed. 35. The process of claim 6 wherein the membrane of claim 27 is utilized. 36. The process of claim 7 wherein the membrane of claim 27 is used. 37. The process of claim 8 wherein the membrane of claim 27 is employed.

Inventors: HO WIN-SOW WINSTON, HO, WIN-SOW, WINSTON
Applicants: EXXON RESEARCH ENGINEERING CO, EXXON RESEARCH AND ENGINEERING COMPANY
Application year: 1998
Main classification: B01D53
IPC codes: B01D53, B01D67, B01D69, B01D71, C01B3, C08K5, C08L101, C10K3, H01M8