Composite Perfluorohydrocarbon Membranes, Their Preparation and Use

Abstract

Composite porous hydrophobic membranes are prepared by forming a perfluorohydrocarbon layer on the surface of a preformed porous polymeric substrate. The substrate can be formed from poly(aryl ether ketone) and a perfluorohydrocarbon layer can be chemically grafted to the surface of the substrate. The membranes can be utilized for a broad range of fluid separations, such as microfiltration, nanofiltration, ultrafiltration as membrane contactors for membrane distillation and for degassing and dewatering of fluids. The membranes can further contain a dense ultra-thin perfluorohydrocarbon layer superimposed on the porous poly(aryl ether ketone) substrate and can be utilized as membrane contactors or as gas separation membranes for natural gas treatment and gas dehydration.

1 . A composite membrane comprising a perfluorohydrocarbon layer on a porous poly(aryl ether ketone) substrate. 
     
     
         2 . The membrane of  claim 1 , wherein said membrane is porous, having an average pore size below 1 micron. 
     
     
         3 . The membrane of  claim 2 , wherein the perfluorohydrocarbon layer is attached to the porous poly(aryl ether ketone) substrate by chemical grafting. 
     
     
         4 . The membrane of  claim 3 , wherein a surface of said substrate has been functionalized with reactive groups prior to chemical grafting. 
     
     
         5 . The membrane of  claim 4 , wherein the perfluorohydrocarbon layer is attached to said substrate by reacting a functional perfluorohydrocarbon that contains epoxy groups, primary, secondary or tertiary amino groups, isocyanate groups, silane groups or triazine groups with said reactive groups. 
     
     
         6 . The membrane of  claim 4 , wherein said reactive groups are formed by reacting ketone groups with a primary amine reagent. 
     
     
         7 . The membrane of  claim 6 , wherein the primary amine reagent is monoethanolamine. 
     
     
         8 . The membrane of  claim 4 , wherein said reactive groups are hydroxyl groups. 
     
     
         9 . The membrane of  claim 8 , wherein the hydroxyl groups are formed by selective reduction of ketone groups on the surface of said substrate. 
     
     
         10 . The membrane of  claim 8 , wherein the perfluorohydrocarbon layer is attached to said substrate by reacting a perfluorohydrocarbon containing functional epoxy groups with said hydroxyl groups. 
     
     
         11 . The membrane of  claim 2 , wherein the perfluorohydrocarbon is an oligomer with a molecular weight below 10,000 Dalton. 
     
     
         12 . The membrane of  claim 2 , wherein the perfluorohydrocarbon contains primary amino groups. 
     
     
         13 . The membrane of  claim 2 , wherein the perfluorohydrocarbon is a mixture of perfluorohydrocarbons. 
     
     
         14 . The membrane of  claim 13 , wherein at least one of the perfluorohydrocarbons is a polymer. 
     
     
         15 . The membrane of  claim 13 , wherein the perfluorohydrocarbon is a mixture of a functional oligomer with a non functional perfluoropolymer. 
     
     
         16 . The membrane of  claim 2 , wherein the average pore size is below 100 nanometers. 
     
     
         17 . The membrane of  claim 16 , wherein the membrane has a surface region with an average pore size below 20 nanometers. 
     
     
         18 . The membrane of  claim 2 , further comprising a dense perfluoropolymer layer at an exterior surface of the membrane. 
     
     
         19 . The membrane of  claim 1 , wherein the perfluorohydrocarbon layer is dense. 
     
     
         20 . The membrane of  claim 19 , wherein the perfluorohydrocarbon is a mixture of perfluorohydrocarbons. 
     
     
         21 . The membrane of  claim 21 , wherein at least one of the perfluorohydrocarbons is a polymer. 
     
     
         22 . The membrane of  claim 19 , wherein the perfluorohydrocarbon is a mixture of a functional oligomer with a non functional perfluoropolymer. 
     
     
         23 . The membrane of  claim 19 , wherein said perfluorohydrocarbon is a copolymer of 2,2-bis(trifluoromethyl)-4,5-difluoro-1,3-dioxole and tetrafluoroethylene, 2,2,4-trifluoro-5-trifluoromethoxy-1,3-dioxide based polymer or poly(perfluorobutenyl vinyl ether). 
     
     
         24 . The membrane of  claim 2 , wherein the membrane includes at least two regions that differ in average pore size. 
     
     
         25 . The membrane of  claim 1 , wherein the poly(aryl ether ketone) is a poly(ether ether ketone), a poly(ether ketone) or a poly(ether ketone ketone). 
     
     
         26 . The membrane of  claim 1 , wherein said membrane is a flat sheet, a tube or a hollow fiber. 
     
     
         27 . The membrane of  claim 1 , wherein said membrane is a fluid separation membrane, or a membrane contactor. 
     
     
         28 . A process for preparing the membrane of  claim 1 , the process comprising:
 a. forming a blend of poly(aryl ether ketone) polymer with a polyimide;   b. shaping the blend to form a shaped substrate;   c. optionally annealing the shaped substrate;   d. bringing the shaped substrate into contact with a primary amine to decompose the polyimide into low molecular weight fragments while functionalizing the poly(aryl ether ketone) with the primary amine;   e. removing the low molecular weight fragments from the substrate to form a porous poly(aryl ether ketone);   f. washing the porous poly(aryl ether ketone) substrate;   g. drying the porous poly(aryl ether ketone) substrate; and   h. grafting the porous poly(aryl ether ketone) substrate with a perfluorohydrocarbon,   
       thereby forming the composite membrane. 
     
     
         29 . A process for preparing the membrane of  claim 1 , the process comprising:
 a. forming a blend of poly(aryl ether ketone) polymer with a polyimide;   b. shaping the blend to form a shaped substrate;   c. optionally annealing the shaped substrate;   d. bringing the shaped substrate into contact with a primary amine to decompose the polyimide into low molecular weight fragments without functionalizing of the poly(aryl ether ketone) with the primary amine;   e. removing the low molecular weight fragments from the substrate to form a porous poly(aryl ether ketone);   f. washing the porous poly(aryl ether ketone) substrate;   g. drying the porous poly(aryl ether ketone) substrate; and   h. functionalizing the surface of the porous poly(aryl ether ketone) substrate with reactive functional groups to form a modified poly(aryl ether ketone) substrate; and   i. grafting the modified poly(aryl ether ketone) substrate with a perfluorohydrocarbon,   
       thereby forming the composite membrane. 
     
     
         30 . The process of  claim 29 , wherein the blend is shaped by extrusion, casting or molding. 
     
     
         31 . The process of  claim 29 , wherein the primary amine is present in a solvent. 
     
     
         32 . The process of  claim 31 , wherein the solvent contains water. 
     
     
         33 . The process of  claim 29 , wherein said blend of poly(aryl ether ketone) with polyimide further contains a polymeric porogen or an additive. 
     
     
         34 . The composite membrane of  claim 1 , wherein said porous poly(aryl ether ketone) substrate is formed by a process comprising:
 a. forming a blend of poly(aryl ether ketone) polymer with a porogen;   b. forming the blend into a shaped substrate;   c. optionally annealing the shaped substrate; and   d. removing porogen to form said shaped substrate.   
     
     
         35 . A method for separating a fluid mixture into a fraction enriched in a first component and a fraction depleted in the first component, comprising the step of contacting said fluid mixture with a fluid separation membrane while maintaining partial pressure differential across the membrane, said membrane having been prepared by a process which includes forming a peprfluorohydrocarbon layer on a surface of a porous poly(aryl ether ketone) substrate, whereby said fraction enriched in the first component and said fraction depleted in the first component are generated by preferentially permeating a portion of said fluid mixture through said fluid separation membrane. 
     
     
         36 . The method of  claim 35 , wherein the membrane is porous. 
     
     
         37 . The method of  claim 36 , wherein the membrane has at least one layer having an average pore size below 100 nm. 
     
     
         38 . The method of  claim 37 , wherein said fluid mixture contains at least one alcohol dissolved in water and wherein said permeating fraction is enriched with said alcohol. 
     
     
         39 . The method of  claim 37 , wherein said alcohol is methanol, ethanol, isopropyl alcohol or butanol. 
     
     
         40 . The method of  claim 35 , wherein said partial pressure differential is generated through the application of vacuum or a sweep gas. 
     
     
         41 . The method of  claim 35 , wherein the fluid mixture contains dissolved or suspended water as the first component and wherein said fraction depleted in the first component is a dry fluid and the fraction enriched in the first component contains water vapor. 
     
     
         42 . The method of  claim 35 , wherein the perfluorohydrocarbon layer is formed only on an exterior surface of said porous poly(aryl ether ketone) membrane. 
     
     
         43 . The method of  claim 35 , wherein the fluid separation membrane is a composite membrane having a dense perfluorohydrocarbon layer. 
     
     
         44 . The method of  claim 43 , wherein said fluid mixture is a gas or a vapor. 
     
     
         45 . The method of  claim 44 , wherein the first component is water vapor, carbon dioxide, hydrogen or oxygen gas. 
     
     
         46 . The method of  claim 35 , wherein said fluid mixture is a hydraulic fluid, a jet fuel, a bio-diesel fluid or a transformer oil. 
     
     
         47 . The method of  claim 46 , wherein the first component is water vapor or oxygen. 
     
     
         48 . The method of  claim 35 , wherein said fluid mixture is a solution of one or more components and the first component is a solute dissolved in said solution. 
     
     
         49 . The method of  claim 35 , wherein said method for separating said fluid mixture is a micro filtration, an ultrafiltration, a nanofiltration, a membrane distillation or a gas separation process. 
     
     
         50 . A porous composite membrane with an average pore size below 1 micron comprising a perfluorohydrocarbon layer chemically grafted to a surface of a porous polymeric substrate. 
     
     
         51 . The membrane of  claim 50 , wherein the surface of said substrate has been functionalized with reactive groups prior to chemical grafting. 
     
     
         52 . The membrane of  claim 51 , wherein the perfluorohydrocarbon layer is attached to said substrate by reacting a functional perfluorohydrocarbon that contains epoxy groups, primary, secondary or tertiary amino groups, isocyanate groups, silane groups or triazine groups with said reactive groups. 
     
     
         53 . The membrane of  claim 51 , wherein said reactive groups are hydroxyl groups. 
     
     
         54 . The membrane of  claim 53 , wherein the perfluorohydrocarbon layer is attached to said substrate by reacting a perfluorohydrocarbon containing functional epoxy groups with said hydroxyl groups. 
     
     
         55 . The membrane of  claim 54 , wherein the perfluorohydrocarbon is an oligomer with a molecular weight below 10,000 Dalton. 
     
     
         56 . The membrane of  claim 50 , wherein said substrate is formed from a cellulose based polymer. 
     
     
         57 . The membrane of  claim 50 , wherein said substrate is formed from poly(aryl ether ketone).