Aromatic alkyl-substituted polyethersulfone and UV-cross-linked aromatic alkyl-substituted polyethersulfone membranes for gas sepratations

Abstract

The present invention provides high flux aromatic alkyl-substituted polyethersulfone membranes and methods for making and using these membranes for gas separations. The membranes may be fabricated into any known membrane configuration including a flat sheet or a hollow fiber. The present invention also provides high selectivity UV cross-linked aromatic alkyl-substituted polyethersulfone membranes and methods for making and using these membranes for gas separations.

Claims

1. A high flux aromatic alkyl-substituted polyethersulfone membrane formed from an aromatic alkyl-substituted polyethersulfone copolymer comprising a plurality of repeating units of formula (I) ##STR00005## wherein R.sub.1, R.sub.2, R.sub.3 and R.sub.4 are independently alkyl groups having 1 to 12 carbon atoms wherein m and n are independent integers and m is an integer from 1 to 500 and n is an integer from 2 to 500; and the molar ratio of m/n is in a range of 1:10 to 5:1.

2. The aromatic alkyl-substituted polyethersulfone membrane of claim 1 wherein R.sub.1, R.sub.2, R.sub.3 and R.sub.4 are selected from the group consisting of methyl and tertiary butyl groups and mixtures thereof.

3. The aromatic alkyl-substituted polyethersulfone membrane of claim 1 wherein R.sub.1, R.sub.2, R.sub.3 and R.sub.4 are methyl groups.

4. The aromatic alkyl-substituted polyethersulfone membrane of claim 1 wherein said aromatic alkyl-substituted polyethersulfone copolymer is selected a random copolymer derived from polycondensation reaction of bis(4-chlorophenyl) sulfone with a mixture of bis(4-hydroxyphenyl) sulfone and bis(4-hydroxy-3,5-dimethylphenyl) sulfone wherein the molar ratio of bis(4-hydroxyphenyl) sulfone to bis(4-hydroxy-3,5-dimethylphenyl) sulfone is in a range of 1:10 to 5:1.

5. The aromatic alkyl-substituted polyethersulfone membrane of claim 1 wherein said aromatic alkyl-substituted polyethersulfone copolymer has been crosslinked.

6. The aromatic alkyl-substituted polyethersulfone membrane of claim 1 further comprising a species that adsorbs strongly to a particular gas.

7. A process for separating at least one gas from a mixture of gases comprising providing a high flux aromatic alkyl-substituted polyethersulfone membrane formed from an aromatic alkyl-substituted polyethersulfone copolymer comprising a plurality of repeating units of formula (I) ##STR00006## wherein R.sub.1, R.sub.2, R.sub.3 and R.sub.4 are independently alkyl groups having 1 to 12 carbon atoms wherein m and n are independent integers and m is an integer from 1 to 500 and n is an integer from 2 to 500; and the molar ratio of m/n is in a range of 1:10 to 5:1 or an UV cross-linked said aromatic alkyl-substituted polyethersulfone membrane; contacting the mixture of gases to one side of said aromatic alkyl-substituted polyethersulfone membrane or the UV cross-linked said aromatic alkyl-substituted polyethersulfone membrane to cause at least one gas to permeate said membrane; and removing from an opposite side of said aromatic alkyl-substituted polyethersulfone membrane or the UV cross-linked said aromatic alkyl-substituted polyethersulfone membrane a permeate gas composition comprising a portion of said at least one gas that permeated said membrane.

8. The process of claim 7 wherein said mixture comprises a paraffin/olefin stream.

9. The process of claim 7 wherein said mixture comprises isoparaffins and normal paraffins.

10. The process of claim 7 wherein said mixture comprises carbon dioxide in natural gas.

11. The process of claim 7 wherein said mixture comprises hydrocarbon vapors and hydrogen.

12. The process of claim 7 wherein said mixture comprises volatile organic compounds.

13. The process of claim 7 wherein said mixture of gases comprises hydrogen, nitrogen, methane and argon or hydrogen from a refinery stream.

14. The process of claim 7 wherein said mixture of gases comprises olefin/paraffin separations selected from the group consisting of propylene/propane separations, xylene separations, and iso/normal paraffin separations.

15. The process of claim 7 wherein said mixture of gases is selected from the group consisting of nitrogen and oxygen, carbon dioxide and methane, hydrogen and methane or carbon monoxide, helium and methane.

16. The process of claim 7 wherein said mixture of gases is selected from the group consisting of carbon dioxide, oxygen, nitrogen, water vapor, hydrogen sulfide, helium, and other trace gases in a raw natural gas feed.

17. The process of claim 7 wherein said membrane is in a single stage membrane or in a first or second stage membrane of a two stage membrane system.

18. The process of claim 7 wherein said membrane is further used in separation of liquid mixtures by pervaporation.

19. The process of claim 18 wherein said liquid mixtures are selected from the group consisting of organic compounds in water; sulfur compounds in gasoline or diesel fuels; or mixtures of organic compounds selected from the group consisting of ethylacetate-ethanol, diethylether-ethanol, acetic acid-ethanol, benzene-ethanol, chloroform-ethanol, chloroform-methanol, acetone-isopropylether, allylalcohol-allyl ether, allylalcohol-cyclohexane, butanol-butylacetate, butanol-1-butylether, ethanol-ethylbutylether, propylacetate-propanol, isopropylether-isopropanol, methanol-ethanol-isopropanol, and ethylacetate-ethanol-acetic acid.

Description

DETAILED DESCRIPTION OF THE INVENTION

(1) The present invention is for high flux aromatic alkyl-substituted polyethersulfone membranes and methods for making and using these membranes for gas separations.

(2) An embodiment of the present invention is for high flux aromatic alkyl-substituted polyethersulfone membranes and UV cross-linked high selectivity aromatic alkyl-substituted polyethersulfone membranes prepared from the high flux aromatic alkyl-substituted polyethersulfone membranes via UV radiation.

(3) The present invention describes a high flux aromatic alkyl-substituted polyethersulfone membrane formed from an aromatic alkyl-substituted polyethersulfone polymer comprising a plurality of repeating units of formula (I)

(4) ##STR00004##
wherein R.sub.1, R.sub.2, R.sub.3 and R.sub.4 are independently alkyl groups having 1 to 12 carbon atoms; Preferably R.sub.1, R.sub.2, R.sub.3 and R.sub.4 are selected from the group consisting of methyl and tertiary butyl groups and mixtures thereof; Most preferably R.sub.1, R.sub.2, R.sub.3 and R.sub.4 are the same methyl groups; wherein m and n are independent integers and m is an integer from 0 to 500 and n is an integer from 2 to 500; and the molar ratio of m/n is in a range of 0:1 to 5:1.

(5) The aromatic alkyl-substituted polyethersulfone polymer described in the present invention has a weight average molecular weight in the range of 10,000 to 1,000,000 Daltons, preferably between 20,000 to 500,000 Daltons. The aromatic alkyl-substituted polyethersulfone polymer described in the present invention can be an alkyl-substituted homopolyethersulfone synthesized via a polycondensation reaction of bis(4-chlorophenyl)sulfone with an alkyl-substituted aromatic diphenol such as bis(4-hydroxy-3,5-dimethylphenyl)sulfone. The aromatic alkyl-substituted polyethersulfone polymer described in the present invention can also be a random copolyethersulfone synthesized via a polycondensation reaction of bis(4-chlorophenyl) sulfone with a mixture of bis(4-hydroxyphenyl)sulfone and an alkyl-substituted aromatic diphenol such as bis(4-hydroxy-3,5-dimethylphenyl)sulfone.

(6) The current invention further comprises a high flux aromatic alkyl-substituted polyethersulfone polymer membrane formed from an aromatic alkyl-substituted polyethersulfone polymer with formula (I) and a process for preparing the aromatic alkyl-substituted polyethersulfone polymer membrane. The process for preparing the high flux aromatic alkyl-substituted polyethersulfone polymer membrane comprises (a) making an aromatic alkyl-substituted polyethersulfone membrane dope solution comprising the aromatic alkyl-substituted polyethersulfone polymer, solvents which are miscible with water and can dissolve the alkyl-substituted polyethersulfone polymer, and non-solvents which cannot dissolve the aromatic alkyl-substituted polyethersulfone polymer; (b) fabricating the aromatic alkyl-substituted polyethersulfone membrane in either flat sheet or hollow fiber geometry by casting a thin layer of said aromatic alkyl-substituted polyethersulfone membrane dope solution onto a supporting substrate or by spinning said aromatic alkyl-substituted polyethersulfone membrane dope solution and a bore fluid simultaneously from an annular spinneret followed by solvent and non-solvent evaporating, coagulating, washing, and drying; and in some cases, (c) coating a high permeability material such as a fluoropolymer, a thermally curable silicone rubber, or a UV radiation curable epoxy silicone onto said aromatic alkyl-substituted polyethersulfone membrane.

(7) The membrane dope formulation for the preparation of high flux aromatic alkyl-substituted polyethersulfone membranes for gas separations in the present invention comprises good solvents for the aromatic alkyl-substituted polyethersulfone polymer that can completely dissolve the polymer. Representative good solvents for use in this invention include N-methylpyrrolidone (NMP), N,N-dimethyl acetamide (DMAC), methylene chloride, N,N-dimethylformamide (DMF), dimethyl sulfoxide (DMSO), dioxanes, 1,3-dioxolane, mixtures thereof, others known to those skilled in the art and mixtures thereof. In some cases, the membrane dope formulation for the preparation of the aromatic alkyl-substituted polyethersulfone membranes for gas separations in the present invention also comprises poor solvents for the aromatic alkyl-substituted polyethersulfone polymer that cannot dissolve the polymer such as acetone, methanol, ethanol, tetrahydrofuran (THF), toluene, n-octane, n-decane, lactic acid, citric acid, isopropanol, and mixtures thereof. It is believed that the proper weight ratio of the solvents used in the present invention provides asymmetric aromatic alkyl-substituted polyethersulfone membranes with <200 nm super thin nonporous selective skin layer which results in high flux.

(8) The invention further comprises a UV cross-linked aromatic alkyl-substituted polyethersulfone membrane formed from an aromatic alkyl-substituted polyethersulfone membrane described in the present invention. The UV cross-linked aromatic alkyl-substituted polyethersulfone membrane is prepared by UV cross-linking of the aromatic alkyl-substituted polyethersulfone membrane via UV radiation. The aromatic alkyl-substituted polyethersulfone polymers used for the preparation of the aromatic alkyl-substituted polyethersulfone membranes described in the current invention have UV cross-linkable sulfonyl and alkyl functional groups. The UV cross-linked aromatic alkyl-substituted polyethersulfone membranes comprise polyethersulfone polymer chain segments where at least part of these polymer chain segments are cross-linked to each other through possible direct covalent bonds by exposure to UV radiation. The cross-linking of the aromatic alkyl-substituted polyethersulfone membranes provides the membranes with improved selectivities and slightly decreased permeances compared to the corresponding uncross-linked aromatic alkyl-substituted polyethersulfone membranes.

(9) The aromatic alkyl-substituted polyethersulfone membranes and the UV cross-linked aromatic alkyl-substituted polyethersulfone membranes of the invention may be fabricated into any known membrane configuration or form such as flat sheet or hollow fiber.

(10) Some preferred examples of the aromatic alkyl-substituted polyethersulfone polymers used for the fabrication of the aromatic alkyl-substituted polyethersulfone membranes and the UV cross-linked aromatic alkyl-substituted polyethersulfone membranes of the present invention may be selected from the group consisting of poly(bis(4-chlorophenyl)sulfone-bis(4-hydroxy-3,5-dimethylphenyl) sulfone) homopolymer derived from polycondensation reaction of bis(4-chlorophenyl) sulfone with bis(4-hydroxy-3,5-dimethylphenyl)sulfone, poly(bis(4-chlorophenyl)sulfone-bis(4-hydroxyphenyl)sulfone-bis(4-hydroxy-3,5-dimethylphenyl) sulfone) random copolymer derived from polycondensation reaction of bis(4-chlorophenyl) sulfone with a mixture of bis(4-hydroxyphenyl)sulfone and bis(4-hydroxy-3,5-dimethylphenyl)sulfone wherein the molar ratio of bis(4-hydroxyphenyl) sulfone to bis(4-hydroxy-3,5-dimethylphenyl) sulfone is in a range of 1:10 to 5:1.

(11) The UV cross-linked aromatic alkyl-substituted polyethersulfone membrane described in the present invention showed high selectivity and good permeability for a variety of gas separation applications such as CO.sub.2/CH.sub.4 and H.sub.2/CH.sub.4 separations. For example, the UV cross-linked aromatic poly(bis(4-chlorophenyl) sulfone-bis(4-hydroxy-3,5-dimethylphenyl)sulfone)homopolyethersulfone dense film (abbreviated as poly(DCDPS-TMDHDPS)) formed from aromatic poly(bis(4-chlorophenyl) sulfone-bis(4-hydroxy-3,5-dimethylphenyl)sulfone)homopolyethersulfone that was produced from a polycondensation reaction of bis(4-chlorophenyl) sulfone with bis(4-hydroxy-3,5-dimethylphenyl) sulfone has CO.sub.2 permeability of 9.4 Barrers and high CO.sub.2/CH.sub.4 selectivity of 41 for CO.sub.2/CH.sub.4 separation. This UV cross-linked poly(DCDPS-TMDHDPS) dense film also has H.sub.2 permeability of 39.8 Barrers and high H.sub.2/CH.sub.4 selectivity of 171 for H.sub.2/CH.sub.4 separation.

(12) The invention also involves a process for separating at least one gas from a mixture of gases comprising providing the aromatic alkyl-substituted polyethersulfone membrane or the UV cross-linked aromatic alkyl-substituted polyethersulfone membrane described in the present invention; contacting the mixture of gases to one side of the aromatic alkyl-substituted polyethersulfone membrane or the UV cross-linked aromatic alkyl-substituted polyethersulfone membrane to cause at least one gas to permeate said membrane; and removing from an opposite side of said aromatic alkyl-substituted polyethersulfone membrane or the UV cross-linked aromatic alkyl-substituted polyethersulfone membrane a permeate gas composition comprising a portion of said at least one gas that permeated said membrane.

(13) The aromatic alkyl-substituted polyethersulfone membrane or the UV cross-linked aromatic alkyl-substituted polyethersulfone membrane described in the present invention is especially useful in the purification, separation or adsorption of a particular species in the liquid or gas phase. In addition to separation of pairs of gases, the aromatic alkyl-substituted polyethersulfone membrane or the UV cross-linked aromatic alkyl-substituted polyethersulfone membrane described in the present invention may, for example, be used for the desalination of water by reverse osmosis or for the separation of proteins or other thermally unstable compounds, e.g. in the pharmaceutical and biotechnology industries. The aromatic alkyl-substituted polyethersulfone membrane or the UV cross-linked aromatic alkyl-substituted polyethersulfone membrane described in the present invention may also be used in fermenters and bioreactors to transport gases into the reaction vessel and transfer cell culture medium out of the vessel. Additionally, the aromatic alkyl-substituted polyethersulfone membrane or the UV cross-linked aromatic alkyl-substituted polyethersulfone membrane described in the present invention may be used for the removal of microorganisms from air or water streams, water purification, ethanol production in a continuous fermentation/membrane pervaporation system, and in detection or removal of trace compounds or metal salts in air or water streams.

(14) The aromatic alkyl-substituted polyethersulfone membrane or the UV cross-linked aromatic alkyl-substituted polyethersulfone membrane described in the present invention is especially useful in gas separation processes in air purification, petrochemical, refinery, and natural gas industries. Examples of such separations include separation of volatile organic compounds (such as toluene, xylene, and acetone) from an atmospheric gas, such as nitrogen or oxygen and nitrogen recovery from air. Further examples of such separations are for the separation of He, CO.sub.2 or H.sub.2S from natural gas, H.sub.2 from N.sub.2, CH.sub.4, and Ar in ammonia purge gas streams, H.sub.2 recovery in refineries, olefin/paraffin separations such as propylene/propane separation, xylene separations, iso/normal paraffin separations, liquid natural gas separations, C.sub.2+ hydrocarbon recovery. Any given pair or group of gases that differ in molecular size, for example nitrogen and oxygen, carbon dioxide and methane, hydrogen and methane or carbon monoxide, helium and methane, can be separated using the aromatic alkyl-substituted polyethersulfone membrane or the UV cross-linked aromatic alkyl-substituted polyethersulfone membrane described in the present invention. More than two gases can be removed from a third gas. For example, some of the gas components which can be selectively removed from a raw natural gas using the aromatic alkyl-substituted polyethersulfone membrane or the UV cross-linked aromatic alkyl-substituted polyethersulfone membrane described herein include carbon dioxide, oxygen, nitrogen, water vapor, hydrogen sulfide, helium, and other trace gases. Some of the gas components that can be selectively retained include hydrocarbon gases. When permeable components are acid components selected from the group consisting of carbon dioxide, hydrogen sulfide, and mixtures thereof and are removed from a hydrocarbon mixture such as natural gas, one module, or at least two in parallel service, or a series of modules may be utilized to remove the acid components. For example, when one module is utilized, the pressure of the feed gas may vary from 275 kPa to about 2.6 MPa (25 to 4000 psi). The differential pressure across the membrane can be as low as about 70 kPa or as high as 14.5 MPa (about 10 psi or as high as about 2100 psi) depending on many factors such as the particular membrane used, the flow rate of the inlet stream and the availability of a compressor to compress the permeate stream if such compression is desired. Differential pressure greater than about 14.5 MPa (2100 psi) may rupture the membrane. A differential pressure of at least 0.7 MPa (100 psi) is preferred since lower differential pressures may require more modules, more time and compression of intermediate product streams. The operating temperature of the process may vary depending upon the temperature of the feed stream and upon ambient temperature conditions. Preferably, the effective operating temperature of the membranes of the present invention will range from about 50 to about 150 C. More preferably, the effective operating temperature of the aromatic alkyl-substituted polyethersulfone membrane or the UV cross-linked aromatic alkyl-substituted polyethersulfone membrane of the present invention will range from about 20 to about 100 C., and most preferably, the effective operating temperature of the membranes of the present invention will range from about 25 to about 100 C.

(15) The aromatic alkyl-substituted polyethersulfone membrane or the UV cross-linked aromatic alkyl-substituted polyethersulfone membrane described in the present invention are also especially useful in gas/vapor separation processes in chemical, petrochemical, pharmaceutical and allied industries for removing organic vapors from gas streams, e.g. in off-gas treatment for recovery of volatile organic compounds to meet clean air regulations, or within process streams in production plants so that valuable compounds (e.g., vinylchloride monomer, propylene) may be recovered. Further examples of gas/vapor separation processes in which the aromatic alkyl-substituted polyethersulfone membrane or the UV cross-linked aromatic alkyl-substituted polyethersulfone membrane described in the present invention may be used are hydrocarbon vapor separation from hydrogen in oil and gas refineries, for hydrocarbon dew pointing of natural gas (i.e. to decrease the hydrocarbon dew point to below the lowest possible export pipeline temperature so that liquid hydrocarbons do not separate in the pipeline), for control of methane number in fuel gas for gas engines and gas turbines, and for gasoline recovery. The aromatic alkyl-substituted polyethersulfone membrane or the UV cross-linked aromatic alkyl-substituted polyethersulfone membrane described in the present invention may incorporate a species that adsorbs strongly to certain gases (e.g. cobalt porphyrins or phthalocyanines for O.sub.2 or silver (I) for ethane) to facilitate their transport across the membrane.

(16) The aromatic alkyl-substituted polyethersulfone membrane or the UV cross-linked aromatic alkyl-substituted polyethersulfone membrane described in the present invention also has immediate application to concentrate olefin in a paraffin/olefin stream for olefin cracking application. For example, the aromatic alkyl-substituted polyethersulfone membrane or the UV cross-linked aromatic alkyl-substituted polyethersulfone membrane described in the present invention can be used for propylene/propane separation to increase the concentration of the effluent in a catalytic dehydrogenation reaction for the production of propylene from propane and isobutylene from isobutane. Therefore, the number of stages of a propylene/propane splitter that is required to get polymer grade propylene can be reduced. Another application for the aromatic alkyl-substituted polyethersulfone membrane or the UV cross-linked aromatic alkyl-substituted polyethersulfone membrane described in the present invention is for separating isoparaffin and normal paraffin in light paraffin isomerization and MaxEne, a process from UOP LLC, Des Plaines, Ill., for enhancing the concentration of normal paraffin (n-paraffin) in the naphtha cracker feedstock, which can be then converted to ethylene.

(17) The aromatic alkyl-substituted polyethersulfone membrane or the UV cross-linked aromatic alkyl-substituted polyethersulfone membrane described in the present invention can also be operated at high temperature to provide the sufficient dew point margin for natural gas upgrading (e.g, CO.sub.2 removal from natural gas). The aromatic alkyl-substituted polyethersulfone membrane or the UV cross-linked aromatic alkyl-substituted polyethersulfone membrane described in the present invention can be used in either a single stage membrane or as the first or/and second stage membrane in a two stage membrane system for natural gas upgrading.

(18) The aromatic alkyl-substituted polyethersulfone membrane or the UV cross-linked aromatic alkyl-substituted polyethersulfone membrane described in the present invention may also be used in the separation of liquid mixtures by pervaporation, such as in the removal of organic compounds (e. g., alcohols, phenols, chlorinated hydrocarbons, pyridines, ketones) from water such as aqueous effluents or process fluids. A membrane which is ethanol-selective would be used to increase the ethanol concentration in relatively dilute ethanol solutions (5-10% ethanol) obtained by fermentation processes. Another liquid phase separation example using the aromatic alkyl-substituted polyethersulfone membrane or the UV cross-linked aromatic alkyl-substituted polyethersulfone membrane described in the present invention is the deep desulfurization of gasoline and diesel fuels by a pervaporation membrane process similar to the process described in U.S. Pat. No. 7,048,846, incorporated by reference herein in its entirety. The aromatic alkyl-substituted polyethersulfone membrane or the UV cross-linked aromatic alkyl-substituted polyethersulfone membrane described in the present invention that are selective to sulfur-containing molecules would be used to selectively remove sulfur-containing molecules from fluid catalytic cracking (FCC) and other naphtha hydrocarbon streams. Further liquid phase examples include the separation of one organic component from another organic component, e.g. to separate isomers of organic compounds. Mixtures of organic compounds which may be separated using the aromatic alkyl-substituted polyethersulfone membrane or the UV cross-linked aromatic alkyl-substituted polyethersulfone membrane described in the present invention include: ethylacetate-ethanol, diethylether-ethanol, acetic acid-ethanol, benzene-ethanol, chloroform-ethanol, chloroform-methanol, acetone-isopropylether, allylalcohol-allylether, allylalcohol-cyclohexane, butanol-butylacetate, butanol-1-butylether, ethanol-ethylbutylether, propylacetate-propanol, isopropylether-isopropanol, methanol-ethanol-isopropanol, and ethylacetate-ethanol-acetic acid.

EXAMPLES

(19) The following examples are provided to illustrate one or more preferred embodiments of the invention, but are not limited embodiments thereof. Numerous variations can be made to the following examples that lie within the scope of the invention.

Example 1

Preparation of poly(bis(4-chlorophenyl) sulfone-bis(4-hydroxy-3,5-dimethylphenyl)sulfone)homopolyethersulfone (abbreviated as poly(DCDPS-TMDHDPS)) Dense Film Membrane

(20) Poly(bis(4-chlorophenyl) sulfone-bis(4-hydroxy-3,5-dimethylphenyl)sulfone)methyl-substituted homopolyethersulfone (abbreviated as poly(DCDPS-TMDHDPS)) was synthesized from the polycondensation reaction of bis(4-chlorophenyl) sulfone (DCDPS) with bis(4-hydroxy-3,5-dimethylphenyl) sulfone (TMDHDPS). 5.0 g of poly(DCDPS-TMDHDPS) was dissolved in 20.0 g of NMP solvent. The mixture was mechanically stirred for 2 hours to form a homogeneous casting dope. The resulting homogeneous casting dope was allowed to degas overnight. The poly(DCDPS-TMDHDPS) dense film membrane was prepared from the bubble free casting dope on a clean glass plate using a doctor knife with a 20-mil gap. The membrane together with the glass plate was then put into a vacuum oven. The solvents were removed by slowly increasing the vacuum and the temperature of the vacuum oven. Finally, the membrane was heated at 150 C. under vacuum for 48 hours to completely remove the residual solvents.

Example 2

Preparation of UV Cross-Linked Poly(DCDPS-TMDHDPS) Dense Film Membrane

(21) The methyl-substituted homopolyethersulfone poly(DCDPS-TMDHDPS) dense film membrane prepared in Example 1 was further UV cross-linked by exposure to UV radiation using 254 nm wavelength UV light generated from a UV lamp for a radiation time of 10 min.

Example 3

Evaluation of Gas Separation Performance of Poly(DCDPS-TMDHDPS) Dense Film Membrane and UV Cross-Linked Poly(DCDPS-TMDHDPS) Dense Film Membrane

(22) The poly(DCDPS-TMDHDPS) dense film membrane and UV cross-linked poly(DCDPS-TMDHDPS) dense film membrane were tested for CO.sub.2/CH.sub.4 and H.sub.2/CH.sub.4 separations at 50 C. under 791 kPa (100 psig) pure single feed gas pressure. The results show that the poly(DCDPS-TMDHDPS) dense film membrane has high CO.sub.2 permeability of 19.6 Barrers and CO.sub.2/CH.sub.4 selectivity of 22.3 for CO.sub.2/CH.sub.4 separation and the UV cross-linked poly(DCDPS-TMDHDPS) dense film membrane shows significantly improved CO.sub.2/CH.sub.4 selectivity of 40.1 and good CO.sub.2 permeability of 9.35 Barrers for CO.sub.2/CH.sub.4 separation. The UV cross-linked poly(DCDPS-TMDHDPS) dense film membrane also has H.sub.2 permeability of 39.8 Barrers and high H.sub.2/CH.sub.4 selectivity of 170.8 for H.sub.2/CH.sub.4 separation.

Example 4

Preparation of poly(bis(4-chlorophenyl) sulfone-bis(4-hydroxyphenyl) sulfone-bis(4-hydroxy-3,5-dimethylphenyl)sulfone) random copolyethersulfone (abbreviated as poly(DCDPS-DHDPS-TMDHDPS-2-1)) Dense Film Membrane and Gas Separation Performance Evaluation

(23) Poly(bis(4-chlorophenyl) sulfone-bis(4-hydroxyphenyl) sulfone-bis(4-hydroxy-3,5-dimethylphenyl) sulfone) random copolyethersulfone (abbreviated as poly(DCDPS-DHDPS-TMDHDPS-2-1)) was synthesized from the polycondensation reaction of bis(4-chlorophenyl)sulfone (DCDPS) with a mixture of bis(4-hydroxyphenyl) sulfone (DHDPS) and bis(4-hydroxy-3,5-dimethylphenyl) sulfone (TMDHDPS), wherein the molar ratio of DHDPS to TMDHDPS is 2:1. 5.0 g of poly(DCDPS-DHDPS-TMDHDPS-2-1) was dissolved in 20.0 g of NMP solvent. The mixture was mechanically stirred for 2 hours to form a homogeneous casting dope. The resulting homogeneous casting dope was allowed to degas overnight. The poly(DCDPS-DHDPS-TMDHDPS-2-1) dense film membrane was prepared from the bubble free casting dope on a clean glass plate using a doctor knife with a 20-mil gap. The membrane together with the glass plate was then put into a vacuum oven. The solvents were removed by slowly increasing the vacuum and the temperature of the vacuum oven. Finally, the membrane was heated at 150 C. under vacuum for 48 hours to completely remove the residual solvents.

(24) The poly(DCDPS-DHDPS-TMDHDPS-2-1) dense film membrane was tested for CO.sub.2/CH.sub.4 and H.sub.2/CH.sub.4 separations at 50 C. under 791 kPa (100 psig) pure single feed gas pressure. The results show that the poly(DCDPS-DHDPS-TMDHDPS-2-1) dense film membrane has CO.sub.2 permeability of 7.65 Barrers and CO.sub.2/CH.sub.4 selectivity of 24.9 for CO.sub.2/CH.sub.4 separation and has H.sub.2 permeability of 18.7 Barrers and H.sub.2/CH.sub.4 selectivity of 60.8 for H.sub.2/CH.sub.4 separation.

Example 5

Fabrication of Poly(DCDPS-TMDHDPS) Asymmetric Flat Sheet Membrane

(25) A poly(DCDPS-TMDHDPS) asymmetric flat sheet membrane was prepared from a casting dope comprising 38.5 g of poly(DCDPS-TMDHDPS), 38.0 g of 1,3-dioxolane, 74.5 g of NMP, and 3.0 g of n-decane. A film was cast on a Nylon cloth then gelled by immersion in a 0 C. water bath for about 10 minutes, and then annealed in a hot water bath at 86 C. for 10-15 minutes. The resulting wet membrane was dried in at a temperature between 70 and 90 C. to remove water. The dried asymmetric poly(DCDPS-TMDHDPS) flat sheet membrane was coated with an epoxy silicone solution containing 2-5 wt-% epoxy silicone in hexane. The epoxy silicone coating was exposed to a UV source for a period of 5 to 10 minutes at ambient temperature to cure the coating while the silicone solvent evaporated to produce the epoxy silicone coated poly(DCDPS-TMDHDPS) membrane of the present invention.

Example 6

Fabrication of Poly(DCDPS-TMDHDPS) Asymmetric Hollow Fiber Membrane

(26) A poly(DCDPS-TMDHDPS) asymmetric hollow fiber membrane was prepared from a spinning dope comprising 25.5 g of poly(DCDPS-TMDHDPS), 8.5 g of 1,3-dioxolane and 63.0 g of NMP. The poly(DCDPS-TMDHDPS) spinning dope was extruded from the annulus of a hollow fiber membrane spinneret at a flow rate ranging from 0.7 to 3.0 mL/min. At the same time, a bore solution of 20 wt % H.sub.2O/80 wt % NMP flowed from the inner passage of the spinneret at 1.2 to 3.8 mL/min to keep the nascent fiber from collapsing on itself. During extrusion, the dope and spinneret were controlled at 50 C. The nascent fiber passed through an air gap of 3 to 10 cm and then entered a water coagulation bath at approximately 3 C. Finally, the solidified hollow fiber membrane was wound on a take-up drum partially submersed in room temperature water at 8 to 30 m/min. The resulting poly(DCDPS-TMDHDPS) asymmetric hollow fiber membranes had a dense selective layer on the outside surface of the fibers.