High selectivity membranes for hydrogen sulfide and carbon dioxide removal from natural gas

Abstract

A thin film composite gas separation membrane comprising a polyether block amide copolymer coating layer and a nanoporous asymmetric support membrane with nanopores on the skin layer surface of the support membrane and gelatin polymers inside the nanopores on the skin layer surface of the support membrane. A method for making the thin film composite gas separation membrane is provided as well as the use of the membrane for a variety of separations such as separations of hydrogen sulfide and carbon dioxide from natural gas, carbon dioxide removal from flue gas, fuel gas conditioning, hydrogen/methane, polar molecules, and ammonia mixtures with methane, nitrogen or hydrogen and other light gases separations, but also for natural gas liquids recovery and hydrogen sulfide and carbon dioxide removal from natural gas in a single step.

Claims

1. A thin film composite gas separation membrane comprising a polyether block amide copolymer coating layer and a nanoporous asymmetric polyacrylonitrile support membrane with nanopores on a skin layer surface of the support membrane and gelatin polymers inside nanopores on the skin layer surface of the support membrane.

2. The thin film composite gas separation membrane of claim 1 wherein said gelatin polymer is a Type A gelatin derived from acid-cured tissue or a Type B gelatin derived from lime-cured tissue.

3. The thin film composite gas separation membrane of claim 1 wherein said polyether block amide copolymer comprises a polyamide segment and a polyether segment.

4. The thin film composite gas separation membrane of claim 3 wherein said polyamide segment is a saturated aliphatic polyamide segment.

Description

DETAILED DESCRIPTION OF THE INVENTION

(1) The use of membranes for separation of both gases and liquids is a growing technological area with potentially high economic reward due to the low energy requirements and the potential for scaling up of modular membrane designs. Advances in membrane technology, with the continuing development of new membrane materials will make this technology even more competitive with traditional, high-energy intensive and costly processes such as distillation. Among the applications for large scale gas separation membrane systems are nitrogen enrichment, oxygen enrichment, hydrogen recovery, removal of hydrogen sulfide and carbon dioxide from natural gas and dehydration of air and natural gas. Also, various hydrocarbon separations are potential applications for the appropriate membrane system. The membranes that are used in these applications must have high selectivity, durability, and productivity in processing large volumes of gas or liquid to be economically successful. Membranes for gas separations have evolved rapidly in the past 25 years due to their easy processability for scale-up and low energy requirements. Membrane gas separation is of special interest to petroleum producers and refiners, chemical companies, and industrial gas suppliers. Several applications of membrane gas separation have achieved commercial success, including carbon dioxide removal from natural gas and biogas and in enhanced oil recovery.

(2) The membranes most commonly used in commercial gas separation applications are polymeric membranes comprising a thin, dense, selectively semipermeable layer and a less dense porous, void-containing, non-selective support layer. Gas separation by these membranes is based on a solution-diffusion mechanism. This mechanism involves molecular-scale interactions of the permeating gas with the membrane polymer. This mechanism assumes that each component is sorbed by the membrane at one interface, transported by diffusion across the membrane through the voids between the polymeric chains (or called free volume), and desorbed at the other interface. According to the solution-diffusion model, the membrane performance for a given pair of gases (e.g., CO.sub.2/CH.sub.4, H.sub.2S/CH.sub.4, O.sub.2/N.sub.2, H.sub.2/CH.sub.4) is determined by two parameters: permeability coefficient (P.sub.A) and the selectivity (α.sub.A/B). The P.sub.A is the product of the gas flux and the membrane selective layer thickness, divided by the pressure difference across the membrane. The α.sub.A/B is the ratio of the permeability coefficients of the two gases (α.sub.A/B=P.sub.A/P.sub.B) where P.sub.A is the permeability of the more permeable gas and P.sub.B is the permeability of the less permeable gas. Gases can have high permeability coefficient because of a high solubility coefficient, a high diffusion coefficient, or both. The diffusion coefficient decreases, and the solubility coefficient increases with the increase in the molecular size of the gas. For high-performance polymer membranes, both high permeability and selectivity are desirable because higher permeability decreases the size of the membrane area required to treat a given amount of gas, thereby decreasing the capital cost of membrane units, and because higher selectivity results in a higher purity product gas with increased efficiency. However, polymeric gas separation membrane materials still have the issues of high cost, low selectivity, low permeance, poor hydrocarbon contaminant resistance, poor plasticization resistance, low chemical and thermal stability, unstable permeance (or flux) and selectivity over time, and poor processability to form a defect-free thin selective skin layer.

(3) This invention relates to a TFC gas separation membrane comprising a polyether block amide copolymer coating layer and a nanoporous asymmetric support membrane with nanopores on the skin layer surface of the support membrane and gelatin polymers inside the nanopores on the skin layer surface of the support membrane. In addition, this invention relates to a method for making the TFC gas separation membrane as well as the application of the membrane for a variety of gas separations such as separations of H.sub.2S and CO.sub.2 from natural gas, CO.sub.2 removal from flue gas, fuel gas conditioning, H.sub.2/CH.sub.4, polar molecules such as H.sub.2O, H.sub.2S, and NH.sub.3/mixtures with CH.sub.4, N.sub.2, H.sub.2, and other light gases separations, but also for NGL recovery and H.sub.2S and CO.sub.2 removal from natural gas in a single step.

(4) The TFC gas separation membrane described in the present invention comprises a polyether block amide copolymer coating layer and a nanoporous asymmetric support membrane with nanopores on the skin layer surface of the support membrane and gelatin polymers inside the nanopores on the skin layer surface of the support membrane. The gelatin polymers with super high intrinsic H.sub.2S/CH.sub.4 selectivity inside the nanopores on the skin layer surface of the support membrane not only further improve H.sub.2S/CH.sub.4 selectivity of the TFC gas separation membrane, but also further reduce the pore sizes of the nanopores on the skin layer surface of the support membrane, which prevents the penetration of the polyether block amide copolymer into the nanopores during coating. Therefore, a thin coating layer of the polyether block amide copolymer on the surface of the nanoporous asymmetric support membrane with gelatin polymers inside the nanopores on the skin layer surface of the support membrane can be formed and the resulting new TFC gas separation membrane shows high permeance. The incorporation of the gelatin polymer with super high intrinsic H.sub.2S/CH.sub.4 selectivity but super low H.sub.2S permeability into the nanopores on the skin layer surface of the support membrane rather than forming a continuous gelatin coating layer on the surface of the support membrane improves the H.sub.2S/CH.sub.4 selectivity of the resulting TFC membrane without significant reduction of H.sub.2S permeance. The thin polyether block amide copolymer coating layer provides the TFC gas separation membrane high permeance and high selectivity and can be formed from any polyether block amide copolymer that is soluble in organic solvent or a mixture of organic solvent and water.

(5) The new TFC gas separation membrane with either flat sheet or hollow fiber geometry described in the current invention provides low cost, high permeances (or fluxes) for both H.sub.2S and CO.sub.2, and high selectivities for both H.sub.2S/CH.sub.4 and CO.sub.2/CH.sub.4. The new TFC gas separation membrane described in the current invention also provides essentially no loss in selectivity or no loss in flux rates over a typical operating period in the presence of H.sub.2S and CO.sub.2. The term “essentially no loss in flux rates” means that the flux declines less than about 30%, and more particularly the flux rate declines less than 20% over a typical operating period of about 3 years.

(6) The nanoporous asymmetric support membrane with nanopores on the skin layer surface of the support membrane and gelatin polymers inside the nanopores on the skin layer surface of the support membrane described in the current invention has an average pore diameter of less than 50 nm on the membrane skin layer surface. The nanoporous asymmetric support membrane described in the current invention can have either flat sheet (spiral wound) or hollow fiber geometry. The nanoporous asymmetric support membrane described in the current invention can be formed by phase inversion followed by gelatin nipping and direct air drying or can be formed by phase inversion followed by gelatin nipping and solvent exchange. Design of the nanoporous asymmetric support membrane is based on the desired properties such as heat resistance, solvent resistance, and mechanical strength of the support membrane, as well as other factors dictated by the operating conditions for selective permeation. The polyether block amide copolymer coating and the nanoporous asymmetric support membrane with gelatin polymers nipped inside the nanopores on the skin layer surface of the support membrane need to have the prerequisite relative separation factors in accordance with the invention for at least one pair of gases. The nanoporous asymmetric support membrane with gelatin polymers nipped inside the nanopores on the skin layer surface of the support membrane not only provides essentially all the structural support for the membrane which can provide little, if any, resistance to the passage of gases, but also prevents the penetration of the polyether block amide copolymer into the nanopores during coating. In addition, the gelatin polymer with super high intrinsic H.sub.2S/CH.sub.4 selectivity but super low H.sub.2S permeability in the nanopores on the skin layer surface of the support membrane improves the H.sub.2S/CH.sub.4 selectivity of the resulting TFC membrane without significant reduction of H.sub.2S permeance.

(7) Generally, the nanoporous asymmetric support membrane described in the current invention can be made from any polymeric membrane materials such as polysulfone, polyethersulfone, polyacrylonitrile, polyimide, polyetherimide, polyether ether ketone, cellulose acetate, cellulose triacetate, and mixtures thereof. These polymers provide a range of properties such as low cost, high permeance, good mechanical stability, and ease of processability that are important for gas separations. Typical polymers that are used can be substituted or unsubstituted polymers and may be selected from but is not limited to, polysulfones; sulfonated polysulfones; polyethersulfones; sulfonated polyethersulfones; polyethers; polyacrylonitrile; polyetherimides; polycarbonates; cellulosic polymers such as cellulose acetate, cellulose triacetate, cellulose acetate-butyrate, cellulose propionate, ethyl cellulose, methyl cellulose, nitrocellulose; polyether ether ketone; polyimides; polyamide/imides; polyketones, polyether ketones; poly(arylene oxides) such as poly(phenylene oxide) and poly(xylene oxide); polyurethanes; poly(benzobenzimidazole)s; polybenzoxazoles; and mixtures of thereof. Some preferred polymers that are suitable for the preparation of the nanoporous asymmetric support membrane described in the current invention include, but are not limited to polyethersulfones, polyacrylonitrile, polyetherimides, cellulosic polymers such as cellulose acetate and cellulose triacetate, polyimides, and mixtures thereof.

(8) The solvents used for dissolving the polymer material for the preparation of the nanoporous asymmetric support membrane described in the current invention are chosen primarily for their ability to completely dissolve the polymers and for ease of solvent removal in the membrane formation steps. Other considerations in the selection of solvents include low toxicity, low corrosive activity, low environmental hazard potential, availability and cost. Representative solvents include most amide solvents that are typically used for the formation of the nanoporous asymmetric support membrane described in the current invention, such as N-methylpyrrolidone (NMP) and N,N-dimethyl acetamide (DMAc), N,N-dimethylformamide (DMF), dimethyl sulfoxide (DMSO), methylene chloride, tetrahydrofuran (THF), acetone, methyl acetate, isopropanol, n-octane, n-hexane, n-decane, methanol, ethanol, glycerol, lactic acid, citric acid, dioxanes, 1,3-dioxolane, mixtures thereof, others known to those skilled in the art and mixtures thereof.

(9) Gelatin polymer was selected as the “nipping” polymer inside the nanopores on the skin layer surface of the support membrane mainly because it has super high intrinsic H.sub.2S/CH.sub.4 selectivity. The incorporation of the gelatin polymer into the nanopores on the skin layer surface of the support membrane is accomplished by nipping of an aqueous solution of gelatin with a concentration in a range of 0.01 wt % to 1 wt % at the end of the membrane casting or spinning fabrication process or via the addition of gelatin polymer to the gelation water tank during the membrane casting or spinning fabrication process. The incorporation of the gelatin polymer with super high intrinsic H.sub.2S/CH.sub.4 selectivity but super low H.sub.2S permeability into the nanopores on the skin layer surface of the support membrane rather than forming a continuous gelatin coating layer on the surface of the support membrane improves the H.sub.2S/CH.sub.4 selectivity of the resulting TFC membrane without significant reduction of H.sub.2S permeance. The gelatin polymer inside the nanopores on the skin layer surface of the support membrane not only further improves H.sub.2S/CH.sub.4 selectivity of the TFC gas separation membrane, but also further reduces the pore sizes of the nanopores on the skin layer surface of the support membrane, which prevents the penetration of the polyether block amide copolymer into the nanopores during coating. Gelatin is a heterogeneous mixture of water-soluble proteins. The proteins are extracted by boiling skin, tendons, ligaments, bones, etc. in water. There are two types of gelatins, type A and type B. Type A gelatin is derived from acid-cured tissue and Type B gelatin is derived from lime-cured tissue. Either type A or type B gelatin can be used in the present invention and preferably type A gelatin is used for the preparation of the nanoporous asymmetric support membrane with gelatin inside the nanopores on the skin layer surface of the support membrane.

(10) The polyether block amide copolymer thin coating on the surface of the nanoporous asymmetric support membrane with gelatin polymers inside the nanopores on the skin layer surface of the support membrane described in the present invention can be formed from any polyether block amide copolymer that is soluble in organic solvent or a mixture of organic solvent and water. The polyether block amide copolymer used in the present invention comprises a polyamide segment and a polyether segment. Preferably, the polyamide segment in the polyether block amide copolymer is a saturated aliphatic polyamide segment. More preferably, the polyether block amide copolymer used in the current invention is a thermoplastic elastomer selected from Pebax® manufactured by Arkema such as Pebax 2533, 3533, 4033, 5533, 6333, Pebax MEI 1657, or Pebax MV 1074 and VESTAMID® E manufactured by Evonik Industries. The polyether block amide copolymer is synthesized by polycondensation of a carboxylic acid terminated polyamide such as nylon 6, nylon 12 or nylon 11 and an alcohol terminated polyether such as polytetramethylene glycol or polyethylene oxide. The polyether block amide copolymer used in the current invention has high intrinsic H.sub.2S/CH.sub.4 selectivity and H.sub.2S permeability. The solvents that can be used for dissolving the polyether block amide copolymer in the present invention are essentially alcohols such as ethanol, n-propanol, iso-propanol, n-butanol, 2-butanol, iso-butanol, tert-butanol or a mixture of water and the alcohol. It is preferred that the polyether block amide copolymer is dissolved in n-butanol at 50-100° C. with a concentration of from about 0.2 to about 5 wt % to provide an effective polyether block amide copolymer coating.

(11) The present invention also discloses a method of making the TFC gas separation membrane comprising a polyether block amide copolymer coating layer and a nanoporous asymmetric support membrane with nanopores on the skin layer surface of the support membrane and gelatin polymers inside the nanopores on the skin layer surface of the support membrane. The method involves the design and fabrication of a nanoporous asymmetric support membrane with nanopores on the skin layer surface of the support membrane and gelatin polymers inside the nanopores on the skin layer surface of the support membrane to improve the H.sub.2S/CH.sub.4 selectivity of the resulting TFC membrane. Gelatin polymer was incorporated into the nanopores on the skin layer surface of the support membrane via nipping of an aqueous solution of gelatin with a concentration in a range of 0.01 wt % to 1 wt % at the end of the membrane casting or spinning fabrication process or via the addition of gelatin polymer to the gelation water tank during the membrane casting or spinning fabrication process. The polyether block amide copolymer was then coated on the skin layer surface of the nanoporous asymmetric support membrane.

(12) The present invention discloses a new method of making the nanoporous asymmetric support membrane with nanopores on the skin layer surface of the support membrane and gelatin polymers inside the nanopores on the skin layer surface of the support membrane either in a flat sheet form or a hollow fiber form. The method comprises: a) casting or spinning a membrane casting or spinning dope to form a wet nanoporous asymmetric flat sheet or hollow fiber support membrane via a phase inversion membrane casting or spinning fabrication process, wherein the membrane casting dope was cast on a highly porous non-selective fabric backing such as a highly porous non-selective symmetric woven Nylon 6,6 fabric backing to form the wet nanoporous asymmetric flat sheet support membrane; b) nipping an aqueous solution of gelatin with a concentration in a range of 0.01 wt % to 1 wt % at the end of the membrane casting or spinning fabrication process or via the addition of gelatin polymer to the gelation water tank during the membrane casting or spinning fabrication process to incorporate high H.sub.2S/CH.sub.4 selectivity gelatin polymers into the nanopores on the skin layer surface of the support membrane; c) drying the wet nanoporous asymmetric support membrane with gelatin inside the nanopores the skin layer surface of the support membrane through a direct air drying method or through a solvent exchange method to form a dried nanoporous asymmetric support membrane with gelatin inside the nanopores the skin layer surface of the support membrane; d) coating a thin, nonporous, polyether block amide copolymer continuous layer on the skin layer surface of the dried nanoporous asymmetric support membrane via dip-coating, meniscus coating, spin coating, casting, soaking, spraying, painting, or other known conventional solution coating technologies using a solution of the polyether block amide copolymer comprising about 0.2 to about 5 wt % of polyether block amide copolymer and an alcohol solvent or a solvent mixture of an alcohol and water; e) drying the polyether block amide copolymer coated nanoporous asymmetric support membrane at about 50 to 100° C. to form the thin film composite (TFC) gas separation membrane comprising a polyether block amide copolymer coating layer and a nanoporous asymmetric support membrane with nanopores on the skin layer surface of the support membrane and gelatin polymers inside the nanopores on the skin layer surface of the support membrane.

(13) The membrane casting or spinning dope in the present invention comprises a polymer dissolved in a mixture of organic solvents or two or more blend polymers dissolved in a mixture of organic solvents. For example, the nanoporous asymmetric support membrane can be a thin nanoporous asymmetric polyethersulfone or polyacrylonitrile support membrane having a skin layer thickness of less than about 10,000 angstroms. Preferably, the thin nanoporous asymmetric polyethersulfone or polyacrylonitrile support membrane has a skin layer thickness between about 200 and about 1000 angstroms, and more preferably, the thin nanoporous asymmetric polyethersulfone or polyacrylonitrile support membrane has a skin layer thickness between about 300 and about 500 angstroms. The concentration of the aqueous gelatin solution in the current invention is dependent upon the initial porosity of the nanoporous asymmetric support membrane. The dried nanoporous asymmetric support membrane with gelatin inside the nanopores the skin layer surface of the support membrane has an average pore diameter of less than 50 nm on the membrane skin layer surface. The dried nanoporous asymmetric support membrane with nanopores on the skin layer surface of the support membrane and gelatin polymers inside the nanopores on the skin layer surface described in the present invention can have a CO.sub.2 permeance (P.sub.CO2/L) of ≥2,000 GPU and a CO.sub.2/CH.sub.4 selectivity (α.sub.CO2/CH4) of ≤1 at 50° C. under 50 psig, 10% CO.sub.2/90% CH.sub.4 mixed gas feed pressure. The TFC gas separation membrane comprising a polyether block amide copolymer coating layer and a nanoporous asymmetric support membrane with nanopores on the skin layer surface of the support membrane and gelatin polymers inside the nanopores on the skin layer surface of the support membrane can have a H.sub.2S permeance (P.sub.H2S/L) of 100-1,500 GPU, a P.sub.CO2/L of 50-350 GPU, a H.sub.2S/CH.sub.4 selectivity (α.sub.H2S/CH4) of 15-70, and a α.sub.CO2/CH4 of 5-30, and at 50° C. under 1000 psig, 50 ppm-35% H.sub.2S/10% CO.sub.2/balanced CH.sub.4 mixed gas feed pressure.

(14) The invention also provides a process for separating at least one gas from a mixture of gases using the TFC gas separation membrane comprising a polyether block amide copolymer coating layer and a nanoporous asymmetric support membrane with nanopores on the skin layer surface of the support membrane and gelatin polymers inside the nanopores on the skin layer surface of the support membrane, the process comprising: (a) providing the TFC gas separation membrane which is permeable to the at least one gas; (b) contacting the mixture on one side of the membrane to cause the at least one gas to permeate the membrane; and (c) removing from the opposite side of the membrane a permeate gas composition comprising a portion of the at least one gas which permeated said membrane.

(15) The simplest membrane processing scheme for the TFC gas separation membrane comprising a polyether block amide copolymer coating layer and a nanoporous asymmetric support membrane with nanopores on the skin layer surface of the support membrane and gelatin polymers inside the nanopores on the skin layer surface of the support membrane described in the present invention is a one-stage flow scheme. For the one-stage flow scheme, a natural gas feed comprising CO.sub.2 and H.sub.2S impurities is separated into a hydrocarbon-rich, low CO.sub.2 and H.sub.2S residual product stream and a CO.sub.2 and H.sub.2S rich permeate stream by the TFC gas separation membrane in the present invention. High hydrocarbon recovery (>95%) can be achieved using a two-stage or multi-stage flow scheme where the low pressure, first-stage permeate is compressed and processed in a second-stage membrane. The TFC gas separation membrane in the present invention can be used for the first stage membrane, the second stage membrane, or both the first stage and the second stage membranes. Another membrane processing scheme is a two-step flow scheme where the residue from the first membrane comprising low H.sub.2S content is sent to the second membrane to further remove CO.sub.2 and the permeate from the second membrane can be compressed and sent back to the first membrane feed. For the two-step membrane process, the TFC gas separation membrane in the present invention can be used as the first step membrane and a high CO.sub.2 permeance and high CO.sub.2/CH.sub.4 selectivity glassy polymer membrane can be used as the second step membrane.

(16) The TFC gas separation membrane comprising a polyether block amide copolymer coating layer and a nanoporous asymmetric support membrane with nanopores on the skin layer surface of the support membrane and gelatin polymers inside the nanopores on the skin layer surface of the support membrane are especially useful in the purification, separation or adsorption of species in the liquid or gas phase. In addition to separation of pairs of gases, these new TFC gas separation membranes may, for example, be used for natural gas liquid (NGL) recovery and CO.sub.2 removal from natural gas in one-step, fuel gas conditioning to separate methane from C2 and C2+ hydrocarbons, as well as natural gas upgrading applications to remove H.sub.2S and CO.sub.2 from natural gas such as FLNG and FPSO applications.

(17) The TFC gas separation membrane of the present invention are 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 CO.sub.2 and 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, fuel gas conditioning, and iso/normal paraffin separations. 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 TFC gas separation membrane described herein. 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 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 0.7 bar or as high as 145 bar (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 145 bar (2100 psi) may rupture the membrane. A differential pressure of at least 7 bar (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 TFC gas separation membrane of the present invention will range from about −50° to about 100° C. More preferably, the effective operating temperature of the TFC gas separation membrane of the present invention will range from about −20° to about 70° C., and most preferably, the effective operating temperature of the TFC gas separation membrane of the present invention will be less than about 70° C.

EXAMPLES

(18) 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 Gelatin-Nipped and then Pebax MV 1074-Coated PES TFC Membrane (Abbreviated as “G500-P1074-PES”)

(19) A nanoporous asymmetric polyethersulfone (PES) support membrane with nanopores on the skin layer surface of the support membrane and gelatin polymers inside the nanopores on the skin layer surface having a CO.sub.2/CH.sub.4 selectivity of <1 and a CO.sub.2 permeance of about 3950 GPU (50° C., 50 psig, 10% CO.sub.2/90% CH.sub.4) was prepared from a PES casting dope comprising PES polymer, N-methyl pyrrolidone and 1,3-dioxolane solvents, and a mixture of glycerol and n-decane non-solvents. A film was cast on a highly porous non-selective symmetric woven Nylon 6,6 fabric backing then gelled by immersion in a 1° C. water bath for about 10 minutes, and then annealed in a hot water bath at 80° to 90° C. for about 15 minutes to form a wet nanoporous asymmetric PES-32 support membrane. A 500-ppm aqueous gelatin nipping solution was dripped onto the skin layer surface of the wet nanoporous asymmetric PES support membrane on the winder under tension at the end of the membrane casting to form a wet nanoporous asymmetric PES flat sheet support membrane with nanopores on the skin layer surface of the support membrane and gelatin polymers inside the nanopores on the skin layer surface. The wet nanoporous asymmetric PES flat sheet support membrane was dried with a continuous drying machine at 70° C. at 1.3 fpm. The dried nanoporous asymmetric PES support membrane with nanopores on the skin layer surface of the support membrane and gelatin polymers inside the nanopores on the skin layer surface was dip coated with a 1 wt % Pebax MV 1074 polymer solution in n-butanol solvent and dried at 85° C. for 1 h to form the dried gelatin-nipped and then Pebax MV 1074-coated PES TFC membrane (abbreviated as “G500-P1074-PES”).

Example 2

Preparation of Gelatin-Nipped and then Pebax MV 1074-Coated PES TFC Membrane (Abbreviated as “G1000-P1074-PES”)

(20) A gelatin-nipped and then Pebax MV 1074-coated PES TFC membrane (abbreviated as “G1000-P1074-PES”) was prepared using the procedure same as that in Example 1 except that a 1000 ppm aqueous gelatin nipping solution instead of a 500-ppm aqueous gelatin nipping solution was used.

Example 3

Preparation of Gelatin-Nipped and then Pebax MV 1074-Coated PES TFC Membrane (Abbreviated as “G2000-P1074-PES”)

(21) A gelatin-nipped and then Pebax MV 1074-coated PES TFC membrane (abbreviated as “G2000-P1074-PES”) was prepared using the procedure same as that in Example 1 except that a 2000 ppm aqueous gelatin nipping solution instead of a 500-ppm aqueous gelatin nipping solution was used.

Example 4

Preparation of Gelatin-Nipped and then Pebax MV 1074-Coated PAN TFC Membrane (Abbreviated as “G1000-P1074-PAN”)

(22) A nanoporous asymmetric polyacrylonitrile (PAN) flat sheet support membrane with nanopores on the skin layer surface of the support membrane and gelatin polymers inside the nanopores on the skin layer surface having a N.sub.2 permeance of about 17,780 GPU (50° C., 50 psig, single gas N.sub.2) was prepared from a PAN casting dope comprising PAN polymer, dimethylformamide (DMF) solvent, and n-decane non-solvent. A film was cast on a highly porous non-selective symmetric woven Nylon 6,6 fabric backing then gelled by immersion in a 20° to 25° C. water bath for about 10 minutes, and then annealed in a hot water bath at 70° to 75° C. for about 15 minutes to form a wet nanoporous asymmetric PAN support membrane. A 1000-ppm aqueous gelatin nipping solution was dripped onto the skin layer surface of the wet nanoporous asymmetric PAN support membrane on the winder under tension at the end of the membrane casting to form a wet nanoporous asymmetric PAN flat sheet support membrane with nanopores on the skin layer surface of the support membrane and gelatin polymers inside the nanopores on the skin layer surface. The wet nanoporous asymmetric PAN flat sheet support membrane was dried with a continuous drying machine at 70° C. at 1.2 fpm. The dried nanoporous asymmetric PAN support membrane with nanopores on the skin layer surface of the support membrane and gelatin polymers inside the nanopores on the skin layer surface was meniscus coated continuously with a 1.5 wt % Pebax MV 1074 polymer solution in n-butanol solvent and dried at 70° to 80° C. to form the dried gelatin-nipped and then Pebax MV 1074-coated PAN TFC membrane (abbreviated as “G1000-P1074-PAN”).

Comparative Example 1

Preparation of Pebax MV 1074-Coated PES TFC Membrane (Abbreviated as “P1074-PES”)

(23) A Pebax MV 1074-coated PES TFC membrane (abbreviated as “P1074-PES”) was prepared using a procedure like that described in Example 1 except that no aqueous gelatin nipping solution was used for nipping and the nanoporous PES support membrane has no gelatin polymer inside the nanopores on the skin layer surface of the support membrane.

Comparative Example 2

Preparation of Hyaluronic Acid-Nipped and then Pebax MV 1074-Coated PES TFC Membrane (Abbreviated as “HA1000-P1074-PES”)

(24) A hyaluronic acid-nipped and then Pebax MV 1074-coated PES TFC membrane (abbreviated as “HA1000-P1074-PES”) was prepared using a procedure like that described in Example 1 except that a 1000-ppm aqueous hyaluronic acid nipping solution was dripped onto the skin layer surface of the wet nanoporous asymmetric PES support membrane on the winder under tension at the end of the membrane casting to form a wet nanoporous asymmetric PES support membrane with nanopores on the skin layer surface of the support membrane and hyaluronic acid polymers inside the nanopores on the skin layer surface of the support membrane.

Comparative Example 3

Preparation of Sodium Alginate-Nipped and then Pebax MV 1074-Coated PES TFC Membrane (Abbreviated as “Na-A1000-P1074-PES”)

(25) A sodium alginate-nipped and then Pebax MV 1074-coated PES TFC membrane (abbreviated as “Na-A1000-P1074-PES”) was prepared using a procedure like that described in Example 1 except that a 1000-ppm aqueous sodium alginate nipping solution was dripped onto the skin layer surface of the wet nanoporous asymmetric PES support membrane on the winder under tension at the end of the membrane casting to form a wet nanoporous asymmetric PES support membrane with nanopores on the skin layer surface of the support membrane and sodium alginate polymers inside the nanopores on the skin layer surface of the support membrane.

Example 5

H.SUB.2.S/CH.SUB.4 .and CO.SUB.2./CH.SUB.4 .Separation Performances of G500-P1074-PES, G1000-P1074-PES, G2000-P1074-PES, G1000-P1074-PAN, P1074-PES, HA1000-P1074-PES, Na-A1000-P1074-PES membranes

(26) 76 mm (3 inch) diameter circles of G500-P1074-PES membrane prepared in Example 1, G1000-P1074-PES membrane prepared in Example 2, G2000-P1074-PES prepared in Example 3, G1000-P1074-PAN prepared in Example 4, P1074-PES prepared in comparative Example 1, HA1000-P1074-PES prepared in comparative Example 2, and Na-A1000-P1074-PES membrane prepared in comparative Example 3 in the present invention were evaluated for gas transport properties using a natural gas feed containing 300 ppm H.sub.2S, 10% CO.sub.2 and balanced with CH.sub.4 at a feed pressure of 6996 kPa (1000 psig) at 50° C. as shown in Table 1. The results in Table 1 show that all the gelatin-nipped and then Pebax MV 1074-coated PES or gelatin-nipped and then Pebax MV 1074-coated PAN TFC membranes (G500-P1074-PES, G1000-P1074-PES, G2000-P1074-PES, and G1000-P1074-PAN) showed much higher H.sub.2S permeances and much higher H.sub.2S/CH.sub.4 selectivities than those of the comparative membranes without gelatin nipping (P1074-PES) or with hyaluronic acid or sodium alginate water soluble polymer-nipped and then Pebax MV 1074-coated PES TFC membranes (HA1000-P1074-PES and Na-A1000-P1074-PES), demonstrating that gelatin polymers with super high intrinsic H.sub.2S/CH.sub.4 selectivity inside the nanopores on the skin layer surface of the PES support membranes enhanced H.sub.2S/CH.sub.4 selectivity of the Pebax MV 1074-coated PES TFC gas separation membranes. The results in Table 1 also show that G1000-P1074-PAN TFC membrane has lower H.sub.2S/CH.sub.4 selectivity but much higher H.sub.2S permeance than G1000-P1074-PES TFC membrane.

(27) TABLE-US-00001 TABLE 1 H.sub.2S/CH.sub.4 and CO.sub.2/CH.sub.4 separation performance of G500-P1074- PES, G1000-P1074-PES, G2000-P1074-PES, G1000-P1074-PAN, P1074- PES, HA1000-P1074-PES, Na-A1000-P1074-PESmembranes .sup.a P.sub.H2S/ P.sub.CO2/ TFC Membrane L (GPU) .sup.b α.sub.H2S/CH4 L (GPU) .sup.b α.sub.CO2/CH4 G500-P1074-PES 162.1 49.2 52.4 15.9 G1000-P1074-PES 181.1 56.6 60.8 19.0 G2000-P1074-PES 191.7 65.9 57.3 19.7 G1000-P1074-PAN 762.8 32.5 194.8 8.27 P1074-PES 111.2 27.8 54.8 13.7 HA1000-P1074-PES 74.4 28.9 45.8 17.8 Na-A1000-P1074-PES 82.1 28.5 52.4 18.2 .sup.a Tested at 50° C. under 6996 kPa (1000 psig), 300 ppmH.sub.2S/10% CO.sub.2/balanced with CH.sub.4 mixed gas pressure. .sup.b 1 GPU = 2.7 × 10.sup.−5 m.sup.3 (STP)/m.sup.2 .Math. h .Math. kPa.

Example 6

CO.SUB.2./CH.SUB.4 .Separation Performance Stability of G1000-P1074-PES Membrane

(28) A 76 mm (3 inch) diameter circle of G1000-P1074-PES membrane of Example 2 was evaluated for gas transport properties for 24 h of continuous testing using a natural gas feed containing 10% CO.sub.2 and 90% CH.sub.4 at a feed pressure of 6996 kPa (1000 psig) at 50° C. Table 2 shows P.sub.CO2/L and α.sub.CO2/CH4 of G1000-P1074-PES membrane of the present invention for a 24 h of permeation test. It can be seen from Table 2 that G1000-P1074-PES membrane has P.sub.CO2/L of 61.4 GPU and α.sub.CO2/CH4 of 19.1 after 1 h of permeation in the presence of 10% CO.sub.2/90% CH.sub.4 feed under 1000 psig feed pressure. The membrane showed very stable performance with <5% drop in CO.sub.2 permeance and no drop in CO.sub.2/CH.sub.4 selectivity after 24 h of permeation testing.

(29) TABLE-US-00002 TABLE 2 Summary of CO.sub.2/CH.sub.4 separation performance stability tests on G1000-P1074-PES membrane .sup.a G1000-P1074-PES Membrane P.sub.CO2/L (GPU) .sup.b α.sub.CO2/CH4 1 h performance 61.4 19.1 2 h performance 61.2 19.1 5 h performance 60.6 19.1 20 h performance 58.7 19.2 22 h performance 58.8 19.2 24 h performance 58.8 19.2 .sup.a Tested at 50° C. under 6996 kPa (1000 psig), 10% CO.sub.2/90% CH.sub.4 mixed gas pressure. .sup.b 1 GPU = 2.7 × 10.sup.−5 m.sup.3 (STP)/m.sup.2 .Math. h .Math. kPa.

Example 7

CO.SUB.2./CH.SUB.4 .Separation Performance Stability of G1000-P1074-PAN Membrane

(30) A 76 mm (3 inch) diameter circle of G1000-P1074-PAN membrane of Example 4 was evaluated for gas transport properties for 52 h of continuous testing using a natural gas feed containing 10% CO.sub.2 and 90% CH.sub.4 at a feed pressure of 6996 kPa (1000 psig) at 50° C. Table 3 shows P.sub.CO2/L and α.sub.CO2/CH4 of G1000-P1074-PAN membrane of the present invention for a 52 h of permeation test. It can be seen from Table 3 that G1000-P1074-PAN membrane has P.sub.CO2/L of 194.8 GPU and α.sub.CO2/CH4 of 8.27 after 1 h of permeation in the presence of 10% CO.sub.2/90% CH.sub.4 feed under 1000 psig feed pressure. The membrane showed very stable performance without CO.sub.2 permeance and CO.sub.2/CH.sub.4 selectivity drop after 52 h of permeation testing.

(31) TABLE-US-00003 TABLE 3 Summary of CO.sub.2/CH.sub.4 separation performance stability tests on G1000-P1074-PAN membrane .sup.a G1000-P1074-PAN Membrane P.sub.CO2/L (GPU) .sup.b α.sub.CO2/CH4 1 h performance 194.8 8.27 2.2 h performance 196.4 8.26 4 h performance 196.4 8.26 24.2 h performance 196.4 8.26 52 h performance 196.4 8.26 .sup.a Tested at 50° C. under 6996 kPa (1000 psig), 10% CO.sub.2/90% CH.sub.4 mixed gas pressure. .sup.b 1 GPU = 2.7 × 10.sup.−5 m.sup.3 (STP)/m.sup.2 .Math. h .Math. kPa.

Specific Embodiments

(32) While the following is described in conjunction with specific embodiments, it will be understood that this description is intended to illustrate and not limit the scope of the preceding description and the appended claims.

(33) A first embodiment of the invention is a thin film composite gas separation membrane comprising a polyether block amide polymer coating layer and a nanoporous asymmetric support membrane with nanopores on a skin layer surface of the support membrane and gelatin polymers inside nanopores on the skin layer surface of the support membrane. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the first embodiment in this paragraph wherein the nanoporous asymmetric support membrane comprises a polymeric membrane material selected from polysulfone, polyethersulfone, polyacrylonitrile, polyimide, polyetherimide, cellulose acetate, cellulose triacetate, and mixtures thereof. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the first embodiment in this paragraph wherein the gelatin polymer is a Type A gelatin derived from acid-cured tissue or a Type B gelatin derived from lime-cured tissue. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the first embodiment in this paragraph wherein the polyether block amide copolymer comprises a polyamide segment and a polyether segment. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the first embodiment in this paragraph wherein the polyamide segment is a saturated aliphatic polyamide segment.

(34) A second embodiment of the invention is a method of making a thin film composite gas separation membrane comprising a polyether block amide copolymer coating layer and a nanoporous asymmetric support membrane with nanopores on a skin layer surface of the support membrane and gelatin polymers inside nanopores on the skin layer surface of the support membrane comprising a) casting or spinning a membrane casting or a spinning dope to form a wet nanoporous asymmetric flat sheet or hollow fiber support membrane via a phase inversion membrane casting or spinning fabrication process; b) nipping an aqueous solution of gelatin with a concentration in a range of 0.01 wt % to 1 wt % at the end of the membrane casting or spinning fabrication process or via the addition of gelatin polymer to a gelation water tank during the membrane casting or spinning fabrication process to incorporate high H.sub.2S/CH.sub.4 selectivity gelatin polymers into the nanopores on the skin layer surface of the support membrane; c) drying the wet nanoporous asymmetric flat sheet or hollow fiber support membrane with gelatin inside the nanopores on the skin layer surface of the support membrane through a direct air drying method or through a solvent exchange method to form a dried nanoporous asymmetric support membrane with gelatin inside the nanopores on the skin layer surface of the support membrane; d) coating a thin, nonporous, polyether block amide copolymer layer on the skin layer surface of the dried nanoporous asymmetric support membrane via using a solution of the polyether block amide copolymer comprising about 0.2 to about 5 wt % of polyether block amide copolymer and an alcohol solvent or a solvent mixture of an alcohol and water; and e) drying the polyether block amide copolymer coated nanoporous asymmetric support membrane at about 50 to 100° C. to form the thin film composite gas separation membrane. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the first embodiment in this paragraph wherein the polyether block amide copolymer layer is deposited on the dried nanoporous asymmetric support membrane via dip-coating, meniscus coating, spin coating, casting, soaking, spraying, or painting. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the first embodiment in this paragraph wherein the nanoporous asymmetric support flat sheet or hollow fiber membrane comprises a polymeric membrane material selected from polysulfone, polyethersulfone, polyacrylonitrile, polyimide, polyetherimide, cellulose acetate, cellulose triacetate, and mixtures thereof. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the first embodiment in this paragraph wherein the gelatin polymer is a Type A gelatin derived from acid-cured tissue or a Type B gelatin derived from lime-cured tissue.

(35) A third embodiment of the invention is a process for separating at least one gas from a mixture of gases using a thin film composite gas separation membrane, the process comprising (a) providing the thin film composite gas separation membrane which is permeable to the at least one gas; (b) contacting the mixture on one side of the membrane to cause the at least one gas to permeate the membrane; and (c) removing from the opposite side of the membrane a permeate gas composition comprising a portion of the at least one gas which permeated the membrane, wherein the thin film composite gas separation membrane comprises a polyether block amide copolymer coating layer on a nanoporous asymmetric support membrane with nanopores on a skin layer surface of the support membrane and gelatin polymers inside nanopores on the skin layer surface of the support membrane. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the second embodiment in this paragraph wherein the process is a one-stage flow scheme. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the second embodiment in this paragraph wherein the process is a two-step process wherein a residue stream from a first membrane containing a low hydrogen sulfide content is sent to a second membrane to further remove carbon dioxide. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the second embodiment in this paragraph wherein a permeate from the second membrane is compressed and sent back to a first membrane feed to the first membrane. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the second embodiment in this paragraph wherein the first membrane is the thin film composite gas separation membrane and the second membrane is a high CO2/CH4 selectivity glassy polymer membrane. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the second embodiment in this paragraph wherein the gases comprise methane, C2 and C2+ hydrocarbons. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the second embodiment in this paragraph wherein the gases comprise hydrogen sulfide and carbon dioxide in natural gas. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the second embodiment in this paragraph wherein the process is a two-stage process wherein the low pressure, first-stage permeate is compressed and processed in a second-stage membrane. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the second embodiment in this paragraph wherein the first stage membrane, the second stage membrane, or both the first stage and the second stage membranes are the thin film composite gas separation membrane.

(36) Without further elaboration, it is believed that using the preceding description that one skilled in the art can utilize the present invention to its fullest extent and easily ascertain the essential characteristics of this invention, without departing from the spirit and scope thereof, to make various changes and modifications of the invention and to adapt it to various usages and conditions. The preceding preferred specific embodiments are, therefore, to be construed as merely illustrative, and not limiting the remainder of the disclosure in any way whatsoever, and that it is intended to cover various modifications and equivalent arrangements included within the scope of the appended claims.

(37) In the foregoing, all temperatures are set forth in degrees Celsius and, all parts and percentages are by weight, unless otherwise indicated.