HIGH SELECTIVITY CHEMICALLY CROSS-LINKED RUBBERY MEMBRANES AND THEIR USE FOR SEPARATIONS

Abstract

A novel chemically cross-linked rubbery polymeric thin film composite (TFC) membrane comprising a selective layer of a chemically cross-linked rubbery polymer supported by a porous support membrane formed from a glassy polymer has been developed. The chemically cross-linked rubbery polymeric thin film composite (TFC) membrane comprising a selective layer of a chemically cross-linked rubbery polymer supported by a porous support membrane formed from a glassy polymer may be used to separate at least one component from another.

Claims

1. A chemically cross-linked rubbery polymeric thin film composite (TFC) membrane comprising a selective layer of a chemically cross-linked rubbery polymer supported by a porous support membrane formed from a glassy polymer.

2. The chemically cross-linked rubbery polymeric thin film composite (TFC) membrane of claim 1 wherein the glassy polymer is polyethersulfone (PES), polysulfone (PSF), polyimide (PI), a blend of PES and PI, a blend of PSF and PI, or a blend of cellulose acetate (CA) and cellulose triacetate (CTA).

3. The chemically cross-linked rubbery polymeric thin film composite (TFC) membrane of claim 1 wherein the chemically cross-linked rubbery polymer is formed from chemical cross-linking between (a) an isocyanate functional polysiloxane and an amino functional cross-linking agent, or (b) an epoxy functional polysiloxane and an amino functional cross-linking agent, or (c) an amino functional polysiloxane and an isocyanate functional cross-linking agent.

4. The chemically cross-linked rubbery polymeric thin film composite (TFC) membrane of claim 1 wherein (a) the isocyanate functional polysiloxane is an isocyanate-terminated polyorganosiloxanes; (b) the amine functional polysiloxane is an amine-terminated polyorganosiloxane, or an aminoorganomethylsiloxane-dimethylsiloxane copolymer, or a mixture thereof; (c) the epoxy functional polysiloxane is an epoxy-terminated polyorganosiloxane, or an epoxycyclohexylmethylsiloxane-dimethylsiloxane copolymer, or a mixture thereof; (d) the amino functional cross-linking agent is an amine functional polysiloxane; or diamino organo silicone; and (e) the isocyanate functional cross-linking agent is isocyanate-terminated polydimethylsiloxane, tolylene-2,4-diisothiocyanate, tolylene-2,6-diisothiocyanate, tolylene-2,4-diisocyanate, tolylene-2,5-diisocyanate, tolylene-2,6-diisocyanate, tolylene-?,4-diisocyanate, 4,4-methylenebis(phenyl isocyanate), 1,3-phenylene diisocyanate, hexamethylene diisocyanate, 1,4-phenylene diisocyanate, or mixtures thereof.

5. The chemically cross-linked rubbery polymeric thin film composite (TFC) membrane of claim 1 wherein the porous support membrane is a flat sheet support membrane or a hollow fiber support membrane.

6. The chemically cross-linked rubbery polymeric thin film composite (TFC) membrane of claim 1 wherein the selective layer of a chemically cross-linked rubbery polymer is a flat sheet having a thickness from about 30 nm to about 40 ?m.

7. The chemically cross-linked rubbery polymeric thin film composite (TFC) membrane of claim 1 wherein the membrane is selective to olefins and ethane, propane, n-butane, and heavier than n-butane hydrocarbons over methane and inert gases.

8. The chemically cross-linked rubbery polymeric thin film composite (TFC) membrane of claim 1 wherein the membrane has a higher permeance for ethane, propane, n-butane, propylene, n-butene, and ethylene than for N.sub.2, H.sub.2, and CH.sub.4.

9. The chemically cross-linked rubbery polymeric thin film composite (TFC) membrane of claim 1 wherein the chemically cross-linked rubbery polymeric thin film composite (TFC) membrane is in the form of hollow fibers, flat sheets, tubes.

10. A method of making a chemically cross-linked rubbery polymeric thin film composite (TFC) membrane comprising a selective layer of a chemically cross-linked rubbery polymer supported by a porous support membrane formed from a glassy polymer, said method comprising: (a) preparing the porous support membrane using a phase inversion process by casting a glassy polymer solution using a casting knife; (b) forming the chemically cross-linked rubbery polymer on the porous support membrane by (i) applying a dilute hydrocarbon solution of a mixture of a solvent, an isocyanate functional polysiloxane and an amino functional cross-linking agent, or a mixture of a solvent, an epoxy functional polysiloxane and an amino functional cross-linking agent, or a mixture of a solvent, an amino functional polysiloxane and an isocyanate functional cross-linking agent to the top surface of the porous support membrane; (ii) evaporating the solvent; and (iii) heating at 70-150? C. for a period of time.

11. The method of claim 10 wherein the solvent is selected from the group consisting of n-heptane, n-hexane, n-octane, and mixtures thereof.

12. The method of claim 10 wherein: (a) the isocyanate functional polysiloxane is an isocyanate-terminated polyorganosiloxanes; (b) the amine functional polysiloxane is an amine-terminated polyorganosiloxane, or an aminoorganomethylsiloxane-dimethylsiloxane copolymer, or a mixture thereof; (c) the epoxy functional polysiloxane is an epoxy-terminated polyorganosiloxane, or an epoxycyclohexylmethylsiloxane-dimethylsiloxane copolymer, or a mixture thereof; (d) the amino functional cross-linking agent is an amine functional polysiloxane; or diamino organo silicone; and (e) the isocyanate functional cross-linking agent is isocyanate-terminated polydimethylsiloxane, tolylene-2,4-diisothiocyanate, tolylene-2,6-diisothiocyanate, tolylene-2,4-diisocyanate, tolylene-2,5-diisocyanate, tolylene-2,6-diisocyanate, tolylene-?,4-diisocyanate, 4,4-methylenebis(phenyl isocyanate), 1,3-phenylene diisocyanate, hexamethylene diisocyanate, 1,4-phenylene diisocyanate, or mixtures thereof.

13. The method of claim 10 wherein the isocyanate functional polysiloxane, the amino functional cross-linking agent, the epoxy functional polysiloxane, the amino functional polysiloxane, and the isocyanate functional cross-linking agent are diluted in a hydrocarbon organic solvent in a concentration of from about 1 to about 20 wt. %.

14. The method of claim 10 wherein the glassy polymer solution comprises NMP, 1,3-dioxolane, glycerol, and n-decane.

15. The method of claim 10 wherein the applying the dilute hydrocarbon solution to the top surface of the porous support membrane is by dip-coating, spin coating, casting, soaking, spraying, or painting.

16. The method of claim 10 wherein the heating at 70-150? C. is for 2 min to 120 min.

17. A process for removing at least one component from a stream comprising contracting the stream with a chemically cross-linked rubbery polymeric thin film composite (TFC) membrane comprising a selective layer of a chemically cross-linked rubbery polymer supported by a porous support membrane formed from a glassy polymer.

18. The process of claim 17 wherein the at least one component is nitrogen, or hydrogen, or methane.

19. The process of claim 17 wherein the stream is natural gas, fuel gas, an olefin recovery stream from a polyolefin production process, LPG, and a natural gas dew point control stream.

20. The process of claim 17 wherein the process is a step of an olefin recovery operation, a nitrogen recovery operation, an LPG recovery operation, a fuel gas conditioning operation, or a nitrogen removal from natural gas operation.

21. The process of claim 17 wherein the process is a two-stage process further comprising a glassy polymeric membrane.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0017] Membrane technology has been of great interest for the separation of gas, vapor, and liquid mixtures. However, despite significant research effort on separations by membrane technology, relatively low selectivity is still a remaining issue for rubbery polymeric membranes for separations such as for olefin recovery, LPG recovery, fuel gas conditioning, natural gas dew point control, and nitrogen removal from natural gas.

[0018] This invention discloses a new type of chemically cross-linked rubbery polymeric thin film composite (TFC) membrane comprising a thin selective layer of a chemically cross-linked rubbery polymer on top of a porous support membrane formed from a glassy polymer such as polyethersulfone (PES), polysulfone (PSF), polyimide (PI), a blend of PES and PI, a blend of PSF and PI, and a blend of cellulose acetate (CA) and cellulose triacetate (CTA), wherein said chemically cross-linked rubbery polymer is formed from chemical cross-linking between an isocyanate functional polysiloxane and an amino functional cross-linking agent, an epoxy functional polysiloxane and an amino functional cross-linking agent, or an amino functional polysiloxane and an isocyanate functional cross-linking agent. The present invention also discloses a method of making such a new type of chemically cross-linked rubbery polymeric thin film composite (TFC) membrane, and the use of such a membrane for olefin recovery from polyolefin production process, LPG recovery, fuel gas conditioning, natural gas dew point control, and nitrogen removal from natural gas.

[0019] Different from glassy polymeric membranes that are highly selective to gases with smaller kinetic diameters over larger diameter gases, the new chemically cross-linked rubbery polymeric TFC membrane comprising a thin selective layer of a chemically cross-linked rubbery polymer on top of a porous support membrane formed from a glassy polymer disclosed in the present invention is highly selective to olefins and heavier hydrocarbons over methane and inert gases such as N.sub.2 and H.sub.2. In addition, opposite from glassy polymeric membranes, the new chemically cross-linked rubbery polymeric TFC membrane described in the current invention has improved permeance and selectivity with the increase of operating time due to the increase of plasticization of condensable olefins on the membrane or with the decrease of operating temperature.

[0020] The porous support membrane can be formed from any glassy polymer that has good film forming properties such as PES, PSF, PI, a blend of PES and PI, a blend of PSF and PI, and a blend of CA and CTA. The porous support membrane used for the preparation of the new chemically cross-linked rubbery polymeric TFC membrane disclosed in the present invention is fabricated using a phase inversion process by casting the glassy polymer solution using a casting knife. The porous support membrane described in the current invention can be either asymmetric integrally skinned membrane or TFC membrane with either flat sheet (spiral wound) or hollow fiber geometry.

[0021] The current invention discloses the use of a porous support membrane for the preparation of the new chemically cross-linked rubbery polymeric TFC membrane by coating a thin selective layer of a chemically cross-linked rubbery polymer on top of the porous support membrane. The porous support membrane for the preparation of the new chemically cross-linked rubbery polymeric TFC membrane described in the present invention has a carbon dioxide permeance of at least 100 GPU and no carbon dioxide/methane selectivity at 50? C. under 30-100 psig 10% CO.sub.2/90% CH.sub.4 mixed gas feed pressure.

[0022] The solvents used for dissolving the glassy polymer material for the preparation of the porous support membrane are chosen primarily for their ability to completely dissolve the polymers, ease of solvent removal in the membrane formation steps, and their function for the formation of small pores on the skin layer of the support membrane. 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 porous support membrane, such as N-methylpyrrolidone (NMP) and N,N-dimethyl acetamide (DMAc), methylene chloride, tetrahydrofuran (THF), acetone, methyl acetate, isopropanol, n-octane, n-hexane, n-decane, methanol, ethanol, N,N-dimethylformamide (DMF), dimethyl sulfoxide (DMSO), lactic acid, citric acid, dioxanes, 1,3-dioxolane, glycerol, mixtures thereof, others known to those skilled in the art and mixtures thereof. Preferably, the solvents used for dissolving the glassy polymer material for the preparation of the porous support membrane in the current invention include NMP, 1,3-dioxolane, glycerol, and n-decane.

[0023] The thin selective layer of the chemically cross-linked rubbery polymer described in the present invention is formed on top of the porous support membrane by applying a dilute solution of a mixture of an isocyanate functional polysiloxane and an amino functional cross-linking agent, or an epoxy functional polysiloxane and an amino functional cross-linking agent, or an amino functional polysiloxane and an isocyanate functional cross-linking agent to the top surface of the porous support membrane by dip-coating, spin coating, casting, soaking, spraying, painting, and other known conventional solution coating technologies. The thin selective layer of the chemically cross-linked rubbery polymer is formed by chemical cross-linking between the isocyanate functional polysiloxane and the amino functional cross-linking agent, or the epoxy functional polysiloxane and the amino functional cross-linking agent, or the amino functional polysiloxane and the isocyanate functional cross-linking agent after evaporating the hydrocarbon organic solvent(s) and heating at 70-150? C. for a certain time.

[0024] The isocyanate functional polysiloxane used for the preparation of the new chemically cross-linked rubbery polymeric TFC membrane in the present invention is isocyanate-terminated polyorganosiloxanes such as isocyanate-terminated polydimethylsiloxane.

[0025] The amine functional polysiloxane used for the preparation of the new chemically cross-linked rubbery polymeric TFC membrane in the present invention can be selected from amine-terminated polyorganosiloxane, aminoorganomethylsiloxane-dimethylsiloxane copolymer, or a mixture thereof. An example of the amine-terminated polyorganosiloxane is aminopropyl-terminated polydimethylsiloxane as shown in formula (I)

##STR00001##

wherein n is an integer from 10 to 1000. The aminoorganomethylsiloxane-dimethylsiloxane copolymer comprises a plurality of a repeating units of formula (II)

##STR00002##

wherein R is H or CH.sub.2CH.sub.2NH.sub.2, wherein n and m are independent integers from 2 to 1000 and the molar ratio of n to m is in a range of 1:500 to 1:5.

[0026] The epoxy functional polysiloxane used for the preparation of the new chemically cross-linked rubbery polymeric TFC membrane in the present invention can be selected from epoxy-terminated polyorganosiloxane, epoxycyclohexylmethylsiloxane-dimethylsiloxane copolymer, or a mixture thereof. An example of the epoxy-terminated polyorganosiloxane is epoxypropoxypropyl-terminated polydimethylsiloxane as shown in formula (III)

##STR00003##

wherein n is an integer from 0 to 500. The epoxycyclohexylmethylsiloxane-dimethylsiloxane copolymer comprises a plurality of a repeating units of formula (IV)

##STR00004##

wherein n and m are independent integers from 2 to 1000 and the molar ratio of n to m is in a range of 1:500 to 1:5.

[0027] The amino functional cross-linking agent that will chemically cross-link with either the epoxy functional polysiloxane or the isocyanate functional polysiloxane for the formation of the new chemically cross-linked rubbery polymeric TFC membrane in the present invention is selected from said amine functional polysiloxanes or diamino organo silicone such as bis(3-aminopropyl)-tetramethyldisiloxane.

[0028] The isocyanate functional cross-linking agent that will chemically cross-link with amine functional polysiloxane for the formation of the new chemically cross-linked rubbery polymeric TFC membrane in the present invention can be selected from said isocyanate-terminated polyorganosiloxanes such as isocyanate-terminated polydimethylsiloxane, tolylene-2,4-diisothiocyanate, tolylene-2,6-diisothiocyanate, tolylene-2,4-diisocyanate, tolylene-2,5-diisocyanate, tolylene-2,6-diisocyanate, tolylene-?,4-diisocyanate, 4,4-methylenebis(phenyl isocyanate), 1,3-phenylene diisocyanate, hexamethylene diisocyanate, 1,4-phenylene diisocyanate, or mixtures thereof.

[0029] The organic solvents that can be used for dissolving the isocyanate functional polysiloxane, the amino functional cross-linking agent, the epoxy functional polysiloxane, the amino functional polysiloxane and the isocyanate functional cross-linking agent in the present invention are essentially hydrocarbons such as n-heptane, n-hexane, n-octane, or mixtures thereof. It is preferred that these polyorganosiloxanes and cross-linking agents are diluted in the hydrocarbon organic solvent or mixtures thereof in a concentration of from about 1 to about 20 wt % to provide a defect-free thin chemically cross-linked rubbery polymer selective layer.

[0030] The present invention also discloses a method of making the new chemically cross-linked rubbery polymeric TFC membrane comprising a thin selective layer of a chemically cross-linked rubbery polymer on top of a porous support membrane comprising: a) preparation of a porous support membrane from a glassy polymer such as polyethersulfone (PES), polysulfone (PSF), polyimide (PI), a blend of PES and PI, a blend of PSF and PI, and a blend of cellulose acetate (CA) and cellulose triacetate (CTA) via a phase inversion membrane fabrication process; b) coating a thin layer of a dilute hydrocarbon solution of a mixture of an isocyanate functional polysiloxane and an amino functional cross-linking agent, or a mixture of an epoxy functional polysiloxane and an amino functional cross-linking agent, or a mixture of an amino functional polysiloxane and an isocyanate functional cross-linking agent to the top surface of the porous support membrane by dip-coating, spin coating, casting, soaking, spraying, painting, and other known conventional solution coating technologies; c) evaporating the hydrocarbon organic solvents on said membrane and heating the coated membrane at 70-150? C. for a certain time, and the thin selective layer of the chemically cross-linked rubbery polymer is formed by chemical cross-linking between the isocyanate functional polysiloxane and the amino functional cross-linking agent, or between the epoxy functional polysiloxane and the amino functional cross-linking agent, or between the amino functional polysiloxane and the isocyanate functional cross-linking agent.

[0031] The new type of chemically cross-linked rubbery polymeric TFC membrane comprising a thin selective layer of a chemically cross-linked rubbery polymer on top of a porous support membrane described in the present invention can be fabricated into any convenient form suitable for a desired separation application. For example, the membranes can be in the form of hollow fibers, tubes, flat sheets, and the like. The new chemically cross-linked rubbery polymeric TFC membrane comprising a thin selective layer of a chemically cross-linked rubbery polymer on top of a porous support membrane in the present invention can be assembled in a separator in any suitable configuration for the form of the membrane and the separator may provide for co-current, counter-current, or cross-current flows of the feed on the retentate and permeate sides of the membrane. In one exemplary embodiment, the new chemically cross-linked rubbery polymeric TFC membrane comprising a thin selective layer of a chemically cross-linked rubbery polymer on top of a porous support membrane described in the present invention is in a spiral wound module that is in the form of flat sheet having a thickness from about 30 to about 400 ?m. In another exemplary embodiment, the new chemically cross-linked rubbery polymeric TFC membrane comprising a thin selective layer of a chemically cross-linked rubbery polymer on top of a porous support membrane described in the present invention is in a hollow fiber module that is in the form of thousands, tens of thousands, hundreds of thousands, or more, of parallel, closely-packed hollow fibers or tubes. In one embodiment, each fiber has an outside diameter of from about 200 micrometers (?m) to about 700 millimeters (mm) and a wall thickness of from about 30 to about 200 ?m. In operation, a feed contacts a first surface of said chemically cross-linked rubbery polymeric TFC membrane comprising a thin selective layer of a chemically cross-linked rubbery polymer on top of a porous support membrane described in the present invention, a permeate permeates said membrane described in the present invention and is removed therefrom, and a retentate, not having permeated said membrane described in the present invention, also is removed therefrom. In another embodiment, the chemically cross-linked rubbery polymeric TFC membrane comprising a thin selective layer of a chemically cross-linked rubbery polymer on top of a porous support membrane described in the present invention can be in the form of flat sheet having a thickness in the range of from about 30 to about 400 ?m.

[0032] The new chemically cross-linked rubbery polymeric TFC membrane comprising a thin selective layer of a chemically cross-linked rubbery polymer on top of a porous support membrane disclosed in the present invention has higher permeance for paraffins such as ethane, propane, n-butane, and olefins such as propylene, n-butene, ethylene than inert gases such as N.sub.2 and H.sub.2 as well as CH.sub.4 and has significantly higher selectivities for olefin/nitrogen, hydrocarbon/nitrogen, olefin/hydrogen, hydrocarbon/hydrogen, and C2+ hydrocarbon/methane than thermally cross-linked RTV615A/B silicone rubber membrane and UV cross-linked epoxysilicone rubbery membrane for olefin and N.sub.2 recovery, LPG recovery, and fuel gas conditioning applications (see Tables 1, 2, 3).

[0033] This invention discloses the use of single stage or multi-stage new chemically cross-linked rubbery polymeric TFC membrane comprising a thin selective layer of a chemically cross-linked rubbery polymer on top of a porous support membrane described in the current invention for olefin recovery, LPG recovery, fuel gas conditioning, natural gas dew point control, nitrogen removal from natural gas, etc. This invention also discloses the use of new chemically cross-linked rubbery polymeric TFC membrane comprising a thin selective layer of a chemically cross-linked rubbery polymer on top of a porous support membrane described in the current invention together with a high performance Separex glassy polymeric membrane in a multi-stage membrane system for olefin recovery, LPG recovery, fuel gas conditioning, natural gas dew point control, nitrogen removal from natural gas, etc.

EXAMPLES

[0034] 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.

Comparative Example 1

Preparation of 5RTVSi/PES-a TFC Membrane

[0035] A porous, asymmetric polyethersulfone (PES) gas separation support membrane was prepared via the phase-inversion process. A PES-a membrane casting dope comprising PES 18-25 wt %, NMP 60-65 wt %, 1,3-dioxolane 10-15 wt %, glycerol 1-10 wt % and n-decane 0.5-2 wt % was cast on a nylon fabric then gelled by immersion in a 1? C. water bath for about 10 minutes, and then annealed in a hot water bath at 85? C. for about 5 minutes. The wet membrane was dried at 70? C. The dried PES-a porous support membrane was coated with an RTVSi silicone rubber precursor polymer solution comprising RTV615A, RTV615B, and hexane (RTV615A:RTV615B=9:1 (weight ratio), 5 wt % of RTV615A+RTV615B in hexane) and then thermally cross-linked at 85? C. for 1 h to form a thin, nonporous, dense RTVSi selective layer on the surface of the PES-a support membrane (abbreviated as 5RTVSi/PES-a). The 5RTVSi/PES-a TFC membrane was tested with a fuel gas mixture of 70% C1, 15% C2, 10% C3 and 5% CO.sub.2 at 3549 kPa (500 psig) and 25? C. The membrane was also tested with N.sub.2, H.sub.2, CH.sub.4, propylene, and propane single gases at 791 kPa (100 psig) and 25? C.

Example 1

Preparation of 5DMS-TDI/PES-a TFC Membrane

[0036] A porous, asymmetric PES gas separation support membrane was prepared via the phase-inversion process. A PES-a membrane casting dope comprising PES 18-25 wt %, NMP 60-65 wt %, 1,3-dioxolane 10-15 wt %, glycerol 1-10 wt % and n-decane 0.5-2 wt % was cast on a nylon fabric then gelled by immersion in a 1? C. water bath for about 10 minutes, and then annealed in a hot water bath at 85? C. for about 5 minutes. The wet membrane was dried at 70? C. A 5 wt % DMS-TDI pre-cross-linked rubbery polymer solution was prepared by dissolving 6.0 g of an aminopropyl-terminated polydimethylsiloxane (Gelest catalog number: DMS-A21) and 0.25 g of 2,4-toluene diisocyanate (TDI) in 118.8 g of hexane at room temperature for about 10 min. The dried PES-a porous support membrane was coated with the 5 wt % DMS-TDI pre-cross-linked rubbery polymer solution, dried at room temperature for about 5 min, and then heated at 85? C. for 2 h to form a thin, nonporous, dense, chemically cross-linked DMS-TDI selective layer on the surface of the PES-a support membrane (abbreviated as 5DMS-TDI/PES-a). The 5DMS-TDI/PES-a TFC membrane was tested with a fuel gas mixture of 70% C1, 15% C2, 10% C3 and 5% CO.sub.2 at 3549 kPa (500 psig) and 25? C. The membrane was also tested with N.sub.2, H.sub.2, CH.sub.4, propylene, and propane single gases at 791 kPa (100 psig) and 25? C. The membrane permeances (P/L) and selectivities (?) are shown in Tables 1, 2, and 3.

Example 2

Preparation of 6.5DMS-TDI/PES-a TFC Membrane

[0037] A 6.5DMS-TDI/PES-a TFC membrane was prepared using the procedure described in Example 1 except that the PES-a support membrane was coated with a 6.5 wt % DMS-TDI pre-cross-linked rubbery polymer solution comprising 6.0 g of DMS-A21 and 0.25 g of 2,4-toluene diisocyanate (TDI) in 89.9 g of hexane at room temperature for about 10 min. The coated membrane was dried at room temperature for about 5 min, and then heated at 85? C. for 2 h to form a thin, nonporous, dense, chemically cross-linked DMS-TDI selective layer on the surface of the PES-a support membrane (abbreviated as 6.5DMS-TDI/PES-a). The 6.5DMS-TDI/PES-a TFC membrane was tested with a fuel gas mixture of 70% C1, 15% C2, 10% C3 and 5% CO.sub.2 at 3549 kPa (500 psig) and 25? C. The membrane was also tested with N.sub.2, H.sub.2, CH.sub.4, propylene, and propane single gases at 791 kPa (100 psig) and 25? C. The membrane permeances (P/L) and selectivities (?) are shown in Tables 1 and 2.

Example 3

Preparation of 5DMS-TDI/5DMS-TDI/PES-a Dual-Coated TFC Membrane

[0038] A 5DMS-TDI/5DMS-TDI/PES-a dual-coated TFC membrane was prepared using the procedure described in Example 1 except that the PES-a support membrane was first coated with a 5 wt % DMS-TDI pre-cross-linked rubbery polymer solution comprising 6.0 g of DMS-A21 and 0.25 g of 2,4-toluene diisocyanate (TDI) in 118.8 g of hexane at room temperature for about 10 min. The coated membrane was dried at room temperature for about 5 min, and then heated at 85? C. for 2 h to form the first layer of thin, nonporous, dense, chemically cross-linked DMS-TDI on the surface of the PES-a support membrane. The DMS-TDI-coated PES-a TFC membrane was then coated with a 5 wt % DMS-TDI pre-cross-linked rubbery polymer solution again, dried at room temperature for about 5 min, and then heated at 85? C. for 2 h to form the second layer of thin, nonporous, dense, chemically cross-linked DMS-TDI on the surface of the DMS-TDI-coated PES-a TFC membrane (abbreviated as 5DMS-TDI/5DMS-TDI/PES-a). The 5DMS-TDI/5DMS-TDI/PES-a dual-coated TFC membrane was tested with a fuel gas mixture of 70% C1, 15% C2, 10% C3 and 5% CO.sub.2 at 3549 kPa (500 psig) and 25? C. The membrane was also tested with N.sub.2, H.sub.2, CH.sub.4, propylene, and propane single gases at 791 kPa (100 psig) and 25? C. The membrane permeances (P/L) and selectivities (?) are shown in Tables 1, 2, and 3.

Example 4

Preparation of 5DMS-A-DMS-E/PES-a TFC Membrane

[0039] A 5DMS-A-DMS-E/PES-a TFC membrane was prepared using the PES-a support membrane same as that was used in Example 1. A 5 wt % DMS-A-DMS-E pre-cross-linked rubbery polymer solution was prepared by dissolving 3.0 g of an aminopropyl-terminated polydimethylsiloxane (Gelest catalog number: DMS-A21) and 4.5 g of epoxypropoxypropyl-terminated polydimethylsiloxane (Gelest catalog number: DMS-E21) in 142.5 g of hexane at room temperature for about 10 min. The dried PES-a porous support membrane was coated with the 5 wt % 5DMS-A-DMS-E pre-cross-linked rubbery polymer solution, dried at room temperature for about 5 min, and then heated at 85? C. for 2 h to form a thin, nonporous, dense, chemically cross-linked DMS-A-DMS-E selective layer on the surface of the PES-a support membrane (abbreviated as 5DMS-A-DMS-E/PES-a). The 5DMS-A-DMS-E/PES-a TFC membrane was tested with a fuel gas mixture of 70% C1, 15% C2, 10% C3 and 5% CO.sub.2 at 3549 kPa (500 psig) and 25? C. The membrane was also tested with N.sub.2, H.sub.2, CH.sub.4, propylene, and propane single gases at 791 kPa (100 psig) and 25? C. The membrane permeances (P/L) and selectivities (?) are shown in Tables 1 and 2.

TABLE-US-00001 TABLE 1 Pure gas permeation results for 5RTVSi/PES-a, 5DMS-TDI/PES-a, 6.5DMS-TDI/PES-a, and 5DMS-TDI/5DMS-TDI/PES-a TFC membranes for propylene recovery (propylene (C.sub.3?)/N.sub.2 and C.sub.3?/H.sub.2 separations)* Membrane P.sub.C3?/L (GPU) ?.sub.C3?/N2 ?.sub.C3?/H2 5RTVSi/PES-a 2881 31.8 10.3 5DMS-TDI/PES-a 1370 44.7 18.7 6.5DMS-TDI/PES-a 1069 48.7 21.3 5DMS-TDI/5DMS-TDI/PES-a 635 51.0 21.4 5DMS-A-DMS-E/PES-a 2794 41.9 15.8 *Tested at room temperature and 791 kPa (100 psig); 1 GPU = 10.sup.?6 cm.sup.3(STP)/cm.sup.2 .Math. sec .Math. cmHg

TABLE-US-00002 TABLE 2 Pure gas permeation results for 5RTVSi/PES-a, 5DMS-TDI/ PES-a, 6.5DMS-TDI/PES-a, and 5DMS-TDI/5DMS-TDI/PES-a TFC membranes for liquid petroleum gas (LPG) recovery (propane (C.sub.3)/N.sub.2 and C.sub.3/H.sub.2 separations)* Membrane P.sub.C3/L (GPU) ?.sub.C3/N2 ?.sub.C3/H2 5RTVSi/PES-a 3093 34.2 11.1 5DMS-TDI/PES-a 1588 51.8 21.7 6.5DMS-TDI/PES-a 1180 53.7 23.5 5DMS-TDI/5DMS-TDI/PES-a 740 59.5 25.0 5DMS-A-DMS-E/PES-a 3380 50.7 19.2 *Tested at room temperature and 791 kPa (100 psig); 1 GPU = 10.sup.?6 cm.sup.3(STP)/cm.sup.2 .Math. sec .Math. cmHg

TABLE-US-00003 TABLE 3 5DMS-TDI/PES-a and 5DMS-TDI/5DMS-TDI/PES-a TFC membranes for fuel gas conditioning (separation of methane (CH.sub.4) from ethane (C.sub.2), C.sub.3, and C.sub.3+)* Membrane P.sub.CH4/L (GPU) ?.sub.C2/CH4 ?.sub.C3/CH4 5RTVSi/PES-a 265 1.6 1.9 5DMS-TDI/PES-a 170 2.2 3.1 5DMS-TDI/5DMS-TDI/PES-a 69 2.5 3.9 *Tested at room temperature and 3549 kPa (500 psig) mixed gas comprising 70% CH.sub.4, 15% C.sub.2, 10% C.sub.3, and 5% CO.sub.2; 1 GPU = 10.sup.?6 cm.sup.3(STP)/cm.sup.2 .Math. sec .Math. cmHg

SPECIFIC EMBODIMENTS

[0040] 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.

[0041] A first embodiment of the invention is a chemically cross-linked rubbery polymeric thin film composite (TFC) membrane comprising a selective layer of a chemically cross-linked rubbery polymer supported by a porous support membrane formed from a glassy polymer. 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 glassy polymer is polyethersulfone (PES), polysulfone (PSF), polyimide (PI), a blend of PES and PI, a blend of PSF and PI, or a blend of cellulose acetate (CA) and cellulose triacetate (CTA). 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 chemically cross-linked rubbery polymer is formed from chemical cross-linking between (a) an isocyanate functional polysiloxane and an amino functional cross-linking agent, or (b) an epoxy functional polysiloxane and an amino functional cross-linking agent, or (c) an amino functional polysiloxane and an isocyanate functional cross-linking agent. 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 (a) the isocyanate functional polysiloxane is an isocyanate-terminated polyorganosiloxanes; (b) the amine functional polysiloxane is an amine-terminated polyorganosiloxane, or an aminoorganomethylsiloxane-dimethylsiloxane copolymer, or a mixture thereof, (c) the epoxy functional polysiloxane is an epoxy-terminated polyorganosiloxane, or an epoxycyclohexylmethylsiloxane-dimethylsiloxane copolymer, or a mixture thereof; (d) the amino functional cross-linking agent is an amine functional polysiloxane; or diamino organo silicone; and (e) the isocyanate functional cross-linking agent is isocyanate-terminated polydimethylsiloxane, tolylene-2,4-diisothiocyanate, tolylene-2,6-diisothiocyanate, tolylene-2,4-diisocyanate, tolylene-2,5-diisocyanate, tolylene-2,6-diisocyanate, tolylene-?,4-diisocyanate, 4,4-methylenebis(phenyl isocyanate), 1,3-phenylene diisocyanate, hexamethylene diisocyanate, 1,4-phenylene diisocyanate, or 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 porous support membrane is a flat sheet support membrane or a hollow fiber 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 selective layer of a chemically cross-linked rubbery polymer is a flat sheet having a thickness from about 30 nm to about 40 ?m. 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 membrane is selective to olefins and ethane, propane, n-butane, and heavier than n-butane hydrocarbons over methane and inert gases. 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 membrane has a higher permeance for ethane, propane, n-butane, propylene, n-butene, and ethylene than for N.sub.2, H.sub.2, and CH.sub.4. 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 chemically cross-linked rubbery polymeric thin film composite (TFC) membrane is in the form of hollow fibers, flat sheets, tubes.

[0042] A second embodiment of the invention is a method of making a chemically cross-linked rubbery polymeric thin film composite (TFC) membrane comprising a selective layer of a chemically cross-linked rubbery polymer supported by a porous support membrane formed from a glassy polymer, the method comprising (a) preparing the porous support membrane using a phase inversion process by casting a glassy polymer solution using a casting knife; (b) forming the chemically cross-linked rubbery polymer on the porous support membrane by (i) applying a dilute hydrocarbon solution of a mixture of a solvent, an isocyanate functional polysiloxane and an amino functional cross-linking agent, or a mixture of a solvent, an epoxy functional polysiloxane and an amino functional cross-linking agent, or a mixture of a solvent, an amino functional polysiloxane and an isocyanate functional cross-linking agent to the top surface of the porous support membrane; (ii) evaporating the solvent; and (iii) heating at 70-150? C. for a period of time. 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 solvent is selected from the group consisting of n-heptane, n-hexane, n-octane, and mixtures thereof. 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) the isocyanate functional polysiloxane is an isocyanate-terminated polyorganosiloxanes; (b) the amine functional polysiloxane is an amine-terminated polyorganosiloxane, or an aminoorganomethylsiloxane-dimethylsiloxane copolymer, or a mixture thereof; (c) the epoxy functional polysiloxane is an epoxy-terminated polyorganosiloxane, or an epoxycyclohexylmethylsiloxane-dimethylsiloxane copolymer, or a mixture thereof; (d) the amino functional cross-linking agent is an amine functional polysiloxane; or diamino organo silicone; and (e) the isocyanate functional cross-linking agent is isocyanate-terminated polydimethylsiloxane, tolylene-2,4-diisothiocyanate, tolylene-2,6-diisothiocyanate, tolylene-2,4-diisocyanate, tolylene-2,5-diisocyanate, tolylene-2,6-diisocyanate, tolylene-?,4-diisocyanate, 4,4-methylenebis(phenyl isocyanate), 1,3-phenylene diisocyanate, hexamethylene diisocyanate, 1,4-phenylene diisocyanate, or mixtures thereof. 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 isocyanate functional polysiloxane, the amino functional cross-linking agent, the epoxy functional polysiloxane, the amino functional polysiloxane, and the isocyanate functional cross-linking agent are diluted in a hydrocarbon organic solvent in a concentration of from about 1 to about 20 wt. %. 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 glassy polymer solution comprises NMP, 1,3-dioxolane, glycerol, and n-decane. 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 applying the dilute hydrocarbon solution to the top surface of the porous support membrane is by dip-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 second embodiment in this paragraph wherein the heating at 70-150? C. is for 2 min to 120 min.

[0043] A third embodiment of the invention is a process for removing at least one component from a stream comprising contracting the stream with a chemically cross-linked rubbery polymeric thin film composite (TFC) membrane comprising a selective layer of a chemically cross-linked rubbery polymer supported by a porous support membrane formed from a glassy polymer. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the third embodiment in this paragraph wherein the at least one component is nitrogen, or hydrogen, or methane. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the third embodiment in this paragraph wherein the stream is natural gas, fuel gas, an olefin recovery stream from a polyolefin production process, LPG, and a natural gas dew point control stream. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the third embodiment in this paragraph wherein the process is a step of an olefin recovery operation, a nitrogen recovery operation, an LPG recovery operation, a fuel gas conditioning operation, or a nitrogen removal from natural gas operation. An embodiment of the invention is one, any or all of prior embodiments in this paragraph up through the third embodiment in this paragraph wherein the process is a two-stage process further comprising a glassy polymeric membrane.

[0044] 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.

[0045] In the foregoing, all temperatures are set forth in degrees Celsius and, all parts and percentages are by weight, unless otherwise indicated.