Layered CDC-polyamide membrane and its make and use

Abstract

New carbon nanomaterials, preferably titanium carbide-derived carbon (CDC) nanoparticles, were embedded into a polyamide film to give CDC/polyamide mixed matrix membranes by the interfacial polymerization reaction of an aliphatic diamine, e.g., piperazine, and an activated aromatic dicarboxylate, e.g., isophthaloyl chloride, supported on a sulfone-containing polymer, e.g., polysulfone (PSF), layer, which is preferably previously prepared by dry/wet phase inversion. The inventive membranes can separate CO.sub.2 (or other gases) from mixtures of CO.sub.2 and further gases, esp. CH.sub.4, based upon the generally selective nanocomposite layer(s) of CDC/polyamide.

Claims

1. A multilayered membrane, comprising: a first layer, comprising at least 50 wt. % of one or more sulfone-containing polymers; a second layer, comprising at least 50 wt. % of one or more polyamides comprising, in condensation polymerized form, an aliphatic diamine and an aromatic dicarboxylate; and at least one carbide-derived carbon (CDC) nanoparticles selected from the group consisting of SiC, Fe.sub.3C, WC, Ti.sub.3SiC.sub.2, ZrC, B.sub.4C, TaC, Mo.sub.2C, and TiC-derived nanoparticles, wherein the CDC nanoparticles are embedded in the second layer in an amount of from 0.005 to 0.5 wt. %, based on a total weight of the second layer, wherein the first layer directly contacts the second layer.

2. The membrane of claim 1, wherein the second layer comprises the CDC nanoparticles in a range of from 0.01 to 0.5 wt. %, and wherein the CDC nanoparticles in the second layer comprise TiC-derived CDC nanoparticles.

3. The membrane of claim 1, further comprising: at least one additional polyamides-comprising layer comprising the CDC nanoparticles.

4. The membrane of claim 2, wherein the CDC nanoparticles are prepared by a method comprising: heating titanium carbide and chlorine gas at temperature in a range of from 600 to 1000° C. for a time period in a range of from 2 to 6 hours; replacing the chlorine gas with hydrogen gas at within 100° C. of the heating in (i); and replacing the hydrogen gas with inert gas and cooling.

5. The membrane of claim 1, wherein the aliphatic diamine is a cyclic diamine.

6. The membrane of claim 1, wherein the aliphatic diamine comprises at least one selected from the group consisting of a piperazine, 4-aminopiperidine, 3-aminopyrrolidine, 1,4-diaminocyclohexane, 1,4-diaminomethylene-cyclohexane, 1,4-diazacycloheptane, 1,5-diazocane, hexahydropyrrolo[3,4-c]pyrrole, hexahydropyrrolo[3,4-b]pyrrole, 3,7-diaza-bicyclo[3.3.1]nonane, 2,5-diazabicyclo[2.2.2]octane, 3,8-diazabicyclo[3.2.1]octane, 2,5-diazabicyclo[2.2.1]heptane, ethylenediamine, 1,3-diaminopropane, 1,4-butanediamine, and 1,5-pentanediamine.

7. The membrane of claim 1, wherein the aliphatic diamine comprises piperazine and a content of the piperazine is at least 75 wt. % relative to total aliphatic diamine.

8. The membrane of claim 1, wherein the dicarboxylate comprises at least one selected from the group consisting of 1,3-benzenedicarboxylate (isophthalate), 1,4-benzenedicarboxylate (terephthalate), 1,2-benzenedicarboxylate (phthalate), 2,6-naphthalenedicarboxylate, 2,3-naphthalenedicarboxylate, 1,4-naphthalenedicarboxylate, 1,5-naphthalenedicarboxylate, 1,7-naphthalenedicarboxylate, 1,2,3,4-tetrahydro-1,4-naphthalenedicarboxylate, 2,6-pyridinedicarboxylate (dipicolinic acid), 2,5-pyridinedicarboxylate (isocinchomeronic acid), and 1H-pyrrole-2,4-dicarboxylate.

9. The membrane of claim 1, wherein the dicarboxylate comprises 1,3-benzenedicarboxylate and a content of the 1,3-benzenedicarboxylate is at least 75 wt. %, relative to total dicarboxylate.

10. The membrane of claim 1, wherein the sulfone-containing polymer is of formulae (I), (II), (III), (IV) or (V): ##STR00005## wherein Ar, Ar′, and Ar″ are independently aromatic residues, Y and Z are independently aliphatic, cycloaliphatic, aromatic, or heterocyclic residues, and n is in a range of from 100 to 100,000.

11. The membrane of claim 10, wherein the sulfone-containing polymer comprises at least one selected from the group consisting of ##STR00006##

12. The membrane of claim 11, wherein the sulfone-containing polymer is PSF having a M.sub.w from 10,000 to 50,000.

13. A gas filter or gas treatment apparatus, comprising the membrane of claim 1.

14. A method, comprising: passing a gas mixture, comprising CO.sub.2 and at least one additional gas, through the membrane of claim 1, to obtain a permeate that is enriched in CO.sub.2 content.

15. The method of claim 14, wherein the at least one additional gas is methane.

16. A method of preparing the multilayered membrane of claim 1, comprising: combining a sulfone-containing polymer with a polar aprotic solvent, to obtain a first mixture; mixing an alcohol with the first mixture, to obtain a second mixture; casting the second mixture onto a surface to create a layer with a thickness in a range of from 100 to 400 μm; drying the layer, to obtain a dried sulfone-containing polymer layer; polymerizing, on the dried sulfone-containing polymer layer, a composition comprising an aliphatic diamine and an aromatic dicarboxylate, wherein the composition further comprises at least one CDC nanoparticle selected from the group consisting of SiC, Fe.sub.3C, WC, Ti.sub.3SiC.sub.2, ZrC, B.sub.4C, TaC, Mo.sub.2C, and TiC-derived carbon CDC nanoparticles, to obtain the CDC-doped polyimide layer comprising the CDC nanoparticles in an amount of from 0.005 to 0.5 wt. % in direct contact with the sulfone-containing polymer layer.

17. The method of claim 16, wherein the CDC nanoparticles comprise TiC-based CDC nanoparticles.

18. The method of claim 16, further comprising: repeating the polymerization to obtain two or more polyamide layers on the membrane.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) A more complete appreciation of the invention and many of the attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein:

(2) FIG. 1 shows a flow sheet of the setup used in the permeation experiments described herein;

(3) FIG. 2A-D show scanning electron microscope (SEM) images of (a) a porous polysulfone (PSF) surface, (b) a dense PSF membrane surface, (c) a pure polyamide surface, and (d) a 0.5 wt. % CDC polyamide membrane surface within the scope of the invention;

(4) FIG. 3 shows the effect of CDC nanoparticle loading on gas permeance for a mixture of CO.sub.2 and CH.sub.4;

(5) FIG. 4 shows the effect of CDC nanoparticle loading on CO.sub.2/CH.sub.4 selectivity;

(6) FIG. 5 shows the effect of the number of polyamide layers on gas permeance for a mixture of CO.sub.2 and CH.sub.4; and

(7) FIG. 6 shows the effect of the number of polyamide layers on CO.sub.2/CH.sub.4 selectivity.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

(8) Aspects of the invention provide multilayered membrane(s), comprising: a first layer, comprising at least 50, 75, 85, 90, 95, 97.5, 99, 99.9, 99.99 wt. % or even exclusively, relative to the polymers in the first layer, one or more sulfone-containing polymers; a second layer, comprising at least 50, 60, 65, 75, 85, 90, 95, 97.5, 99, 99.9, 99.99 wt. % or even exclusively, relative to the polymers in the second layer, one or more polyamide polymers comprising, in condensation polymerized form, an aliphatic diamine and an aromatic dicarboxylate; and SiC, Fe.sub.3C, WC, Ti.sub.3SiC.sub.2, ZrC, B.sub.4C, TaC, Mo.sub.2C, and/or TiC-derived carbon (CDC) nanoparticles, preferably TiC-derived nanoparticles, embedded in the second layer in an amount in a range of from, e.g., 0.001 to 1.0, 0.005 to 0.9, 0.01 to 0.8, or 0.025 to 0.75 wt. %, based on a total weight of the second layer, wherein the first layer directly contacts the second layer.

(9) As referred to herein, carbide-derived carbon (CDC) materials are generally tunable nanoporous carbons derived from carbides. A large family of CDC materials can be prepared from any metal carbide, such as SiC, TiC, B.sub.4C, Ti.sub.3SiC.sub.2, WC, Mo.sub.2C, Fe.sub.3C, etc., or mixtures thereof, by selective removal of the metal atom using a halogen gas at elevated temperature (200 to 1200° C.). For example, the synthesis of CDC from TiC powder can be explained by the chemical reaction shown in Equation 1, below:
2TiC(s)+3Cl.sub.2(g).fwdarw.2TiCl.sub.3(g)+2C(s)  Eq. 1.

(10) CDC particles generally have a surface area per unit mass, i.e., specific surface area (SSA), in a range from 1000 to 3000 m.sup.2/g, and have a tunable pore size (0.5 to 3 nm), pore shape, surface chemistry, and SSA, e.g., by changing the synthetic conditions, composition, and structure of the carbide precursor. Relevant SSAs could be at least 800, 900, 1000, 1200, 1250, 1300, 1500, 1750, 2000, or 2500 m.sup.2/g and/or up to 4500, 4000, 3500, 3250, 3000, 2750, 2500, 2250, 2000, or 1800 m.sup.2/g.

(11) The CDC nanoparticles may preferably be TiC-derived for particular applications, e.g., gas treatment, and/or may preferably be present in the second layer at any of the previously discussed endpoints, and/or at least 0.0001, 0.0005, 0.0025, 0.0033, 0.0067, 0.0125, 0.015, 0.0175, 0.02, 0.03, 0.033, 0.04, 0.06, 0.075, 0.1, 0.125, 0.15, 0.175, 0.2, 0.225, 0.25, 0.275, 0.3, 0.325, 0.333, 0.35, 0.375, or 0.4 wt. %, and/or no more than 1.2, 1.1, 1.05, 0.975, 0.95, 0.925, 0.9, 0.875, 0.85, 0.825, 0.8, 0.775, 0.75, 0.725, 0.7, 0.675, or 0.667 wt. % CDC nanoparticles, whereby any of these endpoints may be upper or lower ends of ranges depending upon the circumstances

(12) For certain gas separation/enriching applications, as disclosed herein, unexpectedly superior membrane performance may be obtained with ranges of CDC nanoparticles in a polyamide layer, e.g., the second layer, in a range of from 0.01 to 0.9, 0.02 to 0.875, 0.05 to 0.85, 0.1 to 0.825, or even 0.2 to 0.8 wt. %, based on a total weight of the second (or polyamide-comprising) layer. Additionally or alternatively, the CDC nanoparticles in the second layer may comprise at least 75, 80, 85, 90, 91, 92, 92.5, 93, 94, 95, 96, 97, 97.5, 98, 99, 99.1, 99.5, or 99.9 wt. % of TiC-derived CDC nanoparticles, relative to a total weight of the CDC nanoparticles in the layer. In the event of several polyamide layers, the CDC nanoparticles embedded may be the same from layer to layer, or may vary randomly, or may vary in a pattern, e.g., (a) CDC.sub.1 (e.g., TiC-derived), CDC.sub.2 (e.g., WC-derived), CDC.sub.1, CDC.sub.2, CDC.sub.1, CDC.sub.2, . . . ; (b) CDC.sub.1, CDC.sub.2, CDC.sub.3 (e.g., SiC-derived), . . . ; (c) CDC.sub.1, CDC.sub.2, CDC.sub.3, CDC.sub.1, CDC.sub.2, CDC.sub.3, CDC.sub.1, CDC.sub.2, CDC.sub.3, . . . ; (d) CDC.sub.1, CDC.sub.2, CDC.sub.1 , CDC.sub.3, CDC.sub.1, CDC.sub.2, . . . ; (e) CDC.sub.1, CDC.sub.2, CDC.sub.1, CDC.sub.3, CDC.sub.1, CDC.sub.4, . . . ; (f) CDC.sub.1, CDC.sub.2, CDC.sub.3, CDC.sub.2, CDC.sub.3, CDC.sub.4, CDC.sub.3, CDC.sub.4, CDC.sub.5, . . . ; (g) CDC.sub.1, CDC.sub.2, CDC.sub.3, . . . CDC.sub.3, CDC.sub.2, CDC.sub.1, or the like.

(13) The inventive membrane may comprise a further polyamide-comprising layer comprising the CDC nanoparticles, for example membranes may contain 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 15, 20 or more polyamide-containing layers. The membranes may contain 1, 2, 3 or more sulfone-containing polymer layers, though generally no more than the polyamide layer(s).

(14) The CDC nanoparticles may be prepared by a method comprising: (i) heating titanium carbide, or any other carbide or combination of carbides used, and chlorine gas at temperature in a range of from 600 to 1000° C. for a time period in a range of from 2 to 6 hours; (ii) replacing the chlorine gas with hydrogen gas at within 100° C. of the heating in (i); and (iii) replacing the hydrogen gas with inert gas and cooling. In place of, or in addition to, the Cl.sub.2 gas, a further halogen gas or gas mixture may be used, e.g., F.sub.2, vaporized and/or liquid Br.sub.2, and/or vaporized, solid, and/or liquid I.sub.2. The temperature may vary, e.g., based on a gradient, or may be fixed, e.g., around 600, 650, 675, 700, 725, 750, 775, 800, 825, 850, 875, or 900° C. The time period of heat treatment may be at least 1 hour and over a range of 1, 2, 3, 4, 5, 6, or 7 hours, although the heat treatment may be limited to 5, 4, 3.5, or 3 hours.

(15) The diamine may be a cyclic diamine. For example, the diamine may comprise a piperazine, 4-aminopiperidine, 3-aminopyrrolidine, 1,4-diaminocyclohexane, 1,4-diaminomethylene-cyclohexane, 1,4-diazacycloheptane, 1,5-diazocane, hexahydropyrrolo[3,4-c]pyrrole, hexahydropyrrolo[3,4-b]pyrrole, 3,7-diaza-bicyclo[3.3.1]nonane, 2,5-diazabicyclo[2.2.2]octane, 3,8-diazabicyclo[3.2.1]octane, 2,5-diazabicyclo[2.2.1]heptane, ethylenediamine, 1,3-diaminopropane, 1,4-butanediamine, 1,5-pentanediamine, or a mixture of two or more of these. The diamine may comprise at least 75, 80, 85, 90, 92.5, 95, 97.5, 98, 99, 99.9, or 99.99 wt. %, relative to total diamine, unsubstituted piperazine. The polyamide may contain, in polymerized form, no further monomers than the sole diamine (or diamines) and/or sole dicarbonyl compound (or dicarbonyls) than 7.5, 7, 6, 5, 4, 3, 2.5, 2, 1, or 0.5 wt. %.

(16) The dicarboxylate may comprise a 1,3-benzenedicarboxylate (isophthalate), 1,4-benzenedicarboxylate (terephthalate), 1,2-benzenedicarboxylate (phthalate), 2,6-naphthalenedicarboxylate, 2,3-naphthalenedicarboxylate, 1,4-naphthalenedicarboxylate, 1,5-naphthalenedicarboxylate, 1,7-naphthalenedicarboxylate, 1,2,3,4-tetrahydro-1,4-naphthalenedicarboxylate, 2,6-pyridinedicarboxylate (dipicolinic acid), 2,5-pyridinedicarboxylate (isocinchomeronic acid), 1H-pyrrole-2,4-dicarboxylate, or a mixture of two or more of any of these. The dicarboxylate may comprise at least 75, 80, 85, 90, 92.5, 95, 97.5, 98, 99, 99.9, or 99.99 wt. %, relative to total dicarboxylate, 1,3-benzenedicarboxylate with no further substituents. The dicarboxylate may have no more than 25, 20, 15, 10, 5, 4, 3, 2, 1, 0.5, 0.1, 0.001, or 0.0001 wt. % or no more than trace detectable amounts of tricarboxylate compound(s), such as triacid halides or tri-anhydrides.

(17) The sulfone-containing polymer may have a structure (I), (II), (III), (IV), and/or (V), as follows: -(—Ar—SO.sub.2-).sub.n- (I), -(—Ar′—SO.sub.2—Ar″—O—).sub.n- (II), -(—YAr—SO.sub.2-).sub.n- (III),

(18) ##STR00003##
wherein Ar, Ar′, and Ar″ are independently substituted or unsubstituted aromatic residues, such as phenylene, naphthylene, anthracenyl, biphenylene, or the like, Y and Z are independently aliphatic, such as methylene, ethylene, propylene, or other C4-C8 alkyl residues, etc., cycloaliphatic, such as 5, 6, 7, 8 and 10-membered rings, substituted or unsubstituted aromatic groups, such as phenylene, naphthylene, biphenylene, or the like, or heterocyclic residues, such as 5, 6, 7, 8 and 10-membered rings, including substituents such as such as methylene, ethylene, propylene, or other C4-C8 alkyl residues, etc., and/or heteroatoms such as nitrogen, sulfur, and/or oxygen, and n is in a range of from 100 to 100,000, 150 to 75,000, 200 to 50,000, 250 to 40,000, 300 to 30,000, 400 to 20,000, 500 to 10,000, 750 to 7,500, or 1,000 to 5,000. Examples of useful sulfone-containing polymers can be found in Parodi, Fabrizio, “Polysulfones,” Ch. 33 in Comprehensive Polymer Science and Supplements, Vol. 5, 1989, pp 561-591, which is incorporated by reference herein in its entirety.

(19) The sulfone-containing polymer may have one or more repeating units of structure PSU, PES, PAS, PPSU, and/or PSF:

(20) ##STR00004##
The sulfone-containing polymer may preferably be PSF and/or may preferably have an M.sub.w in a range of from 10,000 to 50,000, 15,000 to 45,000, 20,000 to 40,000, 25,000 to 35,000, or 27,500 to 32,500. The sulfone-containing polymer may alternatively or further have an M.sub.n in a range of from 10,000 to 25,000, 12,000 to 20,000, or 14,000 to 18,000, and/or the PDI may be in a range of 1.5 to 10, 1.6 to 8, 1.75 to 6, or 1.9 to 4.

(21) Aspects of the invention may provide gas filter(s) and/or gas treatment apparatus(es), comprising any permutation of the inventive membrane(s) as described herein. Such filters or apparatuses may contain 1, 2, 3, 5, 10, 20, 50, 100, 250, 500, or more such inventive membranes. The surface area covered by the filters may vary by application, but may be at least 0.01, 0.05, 0.075, 0.1, 0.25, 0.5, 1, 2.5, 5, 7.5, 10, 15, 25, 50, 100, or 250 m.sup.2, and/or no more than 1000, 500, 250, 125, 75, 40, 20, 10, 5, 1, 0.1, or 0.01 m.sup.2.

(22) Aspects of the invention may provide method(s), comprising: passing a gas mixture, comprising CO.sub.2 and a further gas, through any permutation of the inventive membrane(s) as described herein, thereby enriching a CO.sub.2 in an effluent gas mixture from the membrane. The further gas may be methane, ethane, ethylene, ethylene oxide, acetylene, propane, propylene, isobutene, isobutene, 1-butene, 2-butene, butane, and/or butadiene. The gas mixture may comprise 2, 3, 4, 5, 6, 7, 10 or more gases. The gas mixture may be an exhaust or syngas or PSA by-product. The gas mixture may be a refined and/or purified gas mixture.

(23) Aspects of the invention may provide method(s) of preparing a mixed matrix membrane, e.g., any permutation of the inventive membrane(s) as described above, the method(s) comprising: (a) combining a sulfone-containing polymer with a polar aprotic solvent, to obtain a first mixture; (b) mixing an alcohol with the first mixture, to obtain a second mixture; (c) casting the second mixture onto a surface to create a layer with a thickness in a range of from 100 to 400 μm; (d) drying the layer, to obtain a dried layer; (e) polymerizing, on the dried layer, a composition comprising an aliphatic diamine, an aromatic dicarboxylate, and SiC, Fe.sub.3C, WC, Ti.sub.3SiC.sub.2, ZrC, B.sub.4C, TaC, Mo.sub.2C, and/or TiC-derived carbon (CDC) nanoparticles, to obtain the mixed matrix membrane comprising a CDC-doped polyamide layer upon a sulfone-containing polymer layer. Inventive methods may further comprise: (f) repeating the polymerization so as to obtain two or more polyamide layers on the membrane. Sulfone-containing polymer layers within the scope of the invention may have a thickness in a range of from 50 to 1000, 100 to 500, 125 to 400, 150 to 300, or 175 to 250 μm, and/or the polyamide containing layer(s) may have thicknesses of no more than 500, 400, 300, 250, 225, 200, 175, 150, 125, 100, 75, 50, or 25 μm. The polyamide containing layers may generally be thinner than the sulfone-containing polymer layer.

(24) The polar aprotic solvent may comprise dimethyl formamide, dimethyl acetamide, N-methylpyrrolidone, tetrahydrofuran, dimethyl sulfoxide, ethyl acetate, 1,4-dioxane, nitromethane, dichloromethane, chloroform, acetonitrile, and/or acetone. The polar, aprotic solvent may preferably include dimethyl acetamide and THF.

(25) The polymerization (e) may comprise: (i) contacting the dried layer with a third mixture (preferably aqueous) comprising the diamine, to give an amine-treated layer; and (ii) agitating or contacting the amine-treated layer with a fourth mixture (preferably in an organic solvent such as hexane) comprising the aromatic dicarboxylate and the CDC nanoparticles.

(26) In the inventive methods, the third mixture may comprise from 0.5 to 5.0, 1.0 to 4.0, 1.5 to 3.5, 1.75 to 3.0, or 2 to 2.5% (w/v) diamine, e.g., piperazine, and water or similar polar solvent, and/or the fourth mixture may comprises from 0.05 to 0.5, 0.1 to 0.4, 0.15 to 0.3, or 1.75 to 0.25% (w/v) dicarbonyl compound, e.g., isophthaloyl chloride or isophthaloyl anhydride, and hexane or similar solvent(s), and/or the CDC nanoparticles may be present in an amount of from 0.001 to 1.0 wt. % (or any percentage range discussed above). Hexane, as a solvent, may be substituted by, or supplemented with butane, pentane, cyclohexane, heptane(s), octane(s), decalin, diethyl ether, diisopropyl ether, and/or additive-free gasoline. The diamine may be in water and/or methanol in varying proportions or any solvent to create a phase separation with the solvent of the carbonyl compound and sufficient to dissolve the diamine.

(27) Inventive membranes need not, but may as desired, exclude polyester layers and/or contain no more than 25, 20, 15, 10, 5, 4, 3, 2, 1, 0.5, 0.1, 0.001, or 0.0001 wt. %, relative to total weight, or no more than trace detectable amounts of polyesters. The second (polyamide-containing) layer generally contain less than 15, 10, 7.5, 5, 2.5, 2, 1, 0.1, 0.01, 0.001, or 0.0001 wt. %, relative to polymer content of each layer, vinylidene fluoride (VDF), tetrafluoroethylene (TFE), ethylenetetrafluoroethylene (ETFE), perfluoroalkoxyalkane to (PFA), vinylfluoride (VF), chlorotrifluoroethylene (CTFE), fluorinated ethylene propylene (FEP), hexafluoropropylene (HFP), perfluoro (propyl vinylether), polyethylene, polypropylene, polysulfone, polyketone, polyethersulfone, cellulose, cellulose acetate, cellulose triacetate, regenerative cellulose, acryl resin, epoxy, and/or polyimide-based (co)polymers. Inventive membranes generally contain less than 15, 10, 7.5, 5, 2.5, 2, 1, 0.1, 0.01, 0.001, or 0.0001 wt. % polyimide. Additionally, or separately, the doped layers may contain no more than 25, 20, 15, 10, 5, 4, 3, 2, 1, 0.5, 0.1, 0.001, or 0.0001 wt. % or no more than trace detectable amounts of zeolites, titanium oxide, (fumed) silica, silicon carbide, silicon nitride, spinel, silicon oxycarbide, glass powder, glass fiber, carbon fiber, graphene, nanotubes, gold microparticles, silver microparticles, alumina, magnesia, silicon nitride, zirconia, zirconium carbide, sialon, nasicon, silceram, mullite, aluminum, copper, nickel, steel, titanium, titanium carbide, and titanium diborate, SiC, WC, Fe.sub.3C, ZrC, B4C, TaC, Mo.sub.2C, and/or Ti.sub.3SiC.sub.2. Inventive polyamides may contain no more than 25, 20, 15, 10, 5, 4, 3, 2, 1, 0.5, 0.1, 0.001, or 0.0001 wt. % or no more than trace detectable amounts of tricarbonyl and/or tetracarbonyl compounds. Inventive polyamides may contain no more than 25, 20, 15, 10, 5, 4, 3, 2, 1, 0.5, 0.1, 0.001, or 0.0001 wt. % or no more than trace detectable amounts of triamine and/or tetraamine compounds.

EXAMPLES

(28) Carbide-derived carbon (CDC)/polyamide film(s) on top of a polysulfone (PSF) support were prepared to study the merits of such membranes for CO.sub.2 separation from CH.sub.4. The membranes produced, as well as CDCs nanoparticles, were characterized by SEM, FT-IR, TGA, and XRD. CO.sub.2 and CH.sub.4 permeation were tested for the membranes using the established constant volume/variable pressure method. Gas permeation measurements of the membranes demonstrated 88.14% enhancement in CO.sub.2 permeance and 49.35% improved CO.sub.2/CH.sub.4 selectivity compared to pure polyamide on PSF membranes. A Netzsch model STA 449 F345 Jupiter® TGA device was used to check the thermal stability/degradation behavior of the membranes and components.

(29) Titanium carbide nano-powder (cubic TiC, 99+%, 40-60 nm) was purchased from US Research nanomaterials, Inc., USA. Polysulfone (average MW˜35,000) and dimethyl acetamide (DMAc) were purchased from Sigma-Aldrich, USA, and n-hexane was purchased from Fisher Scientific Canada.

(30) Synthesis of CDC nanoparticles: titanium carbide (which may be substituted by, or supplemented with, any metal carbide described herein or otherwise known in the art) in quartz boat was inserted in a quartz tubular furnace and heated at a rate of 10° C./min to the desired temperature while continuously purging with argon to create air-free and oxygen-free, closed system. The atmosphere may desirably contain less than 15, 10, 7.5, 5, 2.5, 2, 1, 0.1, 0.01, 0.001, 0.0001, or 0.00001 vol. % O.sub.2, based on the amount of all gases in the atmosphere. The heating rate may be anywhere in a range of from 1 to 50, 2 to 40, 3 to 30, 5 to 25, 7.5 to 15, or 8 to 12° C./min. When the furnace temperature reached the desired set point of 700, 800, or 900° C., pure chlorine gas was introduced at a flow rate of 10 to 13 cm.sup.3/min for 3 hours. After chlorination, a post-treatment was carried out with hydrogen gas at the same final temperature, i.e., 700, 800, or 900° C., for one hour to remove the remaining chlorine from the CDC which will enhance the SSA and micro-pore volume of the nanoparticles. Useful temperatures may be in a range of from 200 to 1200, 400 to 1100, 500 to 1000, or 600 to 900° C., e.g., any of these endpoints or at least 300, 450, 550, 650, 675, 725, 750, 775, 825, or 850° C., and/or no more than 1150, 1050, 1025, 975, 950, 925, 875, 850, or 825° C. Then the furnace was purged with argon gas to cool it down to ambient temperature.

(31) Membranes Preparation—Polysulfone Support: a polysulfone (PSF) support was fabricated by dry/wet phase inversion technique. Prior to membrane preparation, commercially available PSF polymer pellets were dried overnight at 100° C. in a vacuum oven in order to completely remove the moisture from the polymer. Dry PSF pellets were dissolved in a mixture of DMAC and THF, then ethanol was added and the solution, which was stirred for 24 hours at 25° C. using a magnetic stirrer. The polymeric solution, having a composition shown in Table 1, below, was then degassed at room temperature for 24 hours to remove dissolved gases/air bubbles. After that, the solution was cast on a clean glass plate to a thickness of 200 μm using a casting knife. The membrane was left in air for 60 seconds under ambient condition and subsequently immersed in a deionized (DI) water bath for 24 hours. The membranes were immersed in methanol for 2 hours for solvent-exchange and treated with polydimethylsiloxane (3% in hexane) to eliminate infinitesimal defects or pinholes in the membrane and then finally dried in vacuum oven at100° C. for 48 hours.

(32) TABLE-US-00001 TABLE 1 Composition and amount of the dope solution Amount Concentration Component (g) (%) PSF Pellets 4.00 23.03 DMAC 5.81 33.45 THF 5.81 33.45 Ethanol 1.75 10.07

(33) Membranes Preparation—Preparation of Polyamide (PA) and CDC/PA Mixed Matrix Membranes (MMMs): a polyamide membrane was prepared by interfacial polymerization, whereby polymerization occurs between a diamine—here piperazine in deionized water—and an activated carbonyl compound (e.g., acid halide, such as acid chloride or acid bromide, or acid anhydride)—here isophthaloyl chloride in hexane. The previously prepared PSF layer was saturated with the 2% (w/v) piperazine solution for 10 minutes, then a rubber roller was used to remove the excess piperazine solution. Subsequently, the PSF support layer was immersed in the 0.2% (w/v) isophthaloyl chloride solution for 3 minutes, then the excess unreacted isophthaloyl chloride was removed using pure hexane. Finally, the membranes were cured/dried at 80° C. for 10 min, and the polyamide-polysulfone membranes were kept in DI water. For thin film nanocomposite (TFN) membranes, CDCs nanoparticles were incorporated into the polyamide layer during interfacial polymerization reaction by adding the desired amount of nanoparticles, shown in Table 2, to 100 mL of the isophthaloyl chloride solution, then the CDC-doped isophthaloyl chloride solution was sonicated for 15 minutes using probe sonicator for 1 hour in a bath sonicator.

(34) TABLE-US-00002 TABLE 2 List of membrane Codes and Composition of the prepared TFN membranes Membrane code Description MMM0 Pure polyamide membrane without CDC (Control PA) nanoparticles. This membrane was used as the control sample with which, the performance of other membranes were compared MMM1 Mixed matrix membrane comprises polyamide and 0.0005% CDC nanoparticles MMM2 Mixed matrix membrane comprises polyamide and 0.002% CDC nanoparticles MMM3 Mixed matrix membrane comprises polyamide and 0.1% CDC nanoparticles MMM4 Mixed matrix membrane comprises polyamide and 0.5% CDC nanoparticles MMM5 Mixed matrix membrane comprises polyamide and 1% CDC nanoparticles

(35) After sonication, the interfacial polymerization was conducted as above. To synthesize a layer-by-layer membrane structure, the interfacial polymerization can be repeated with multiple reactions between the same monomers, each time after drying/curing. For each complete cycle of interfacial polymerization and curing/drying, the membrane can be considered to include one additional deposited (optionally doped polyamide) layer. It is also possible to vary doped and undoped layers in any pattern as discussed above.

(36) Gas Permeation Measurements: The permeance of the fabricated membranes was examined using pure CO.sub.2 and CH.sub.4 gases. The membranes were tested at different feed pressures from 1 to 5 bar and temperatures from 300 to 323K. Gas permeation experiments were conducted using the well-known constant volume/variable pressure (time-lag) method.

(37) Referring now to the drawings, wherein like reference numerals designate identical or corresponding parts throughout the several views.

(38) As shown in FIG. 1, the gas permeation setup was built to work in two modes, constant volume/variable pressure and constant pressure/variable volume. The system contains three Bronkhorst Coriolis mass flow controllers, a membrane module (M), a permeation volume, a vacuum pump (V) that is connected to the permeate volume (V2 to V5), and pressure transducers (P1, P2, P3, P4) to detect the feed and permeate pressures. The process is controlled by software and the data is collected by LabVIEW. A membrane sample with an effective area of 4.91 cm.sup.2 was cut and fixed inside the membrane cell, and both sides of the membrane module were evacuated to a pressure of less than 1 mbar. The gas was then fed into the module at a constant pressure. To determine the gas permeation, the valve (V4) used for the evacuation was closed and the pressure change in the permeate side was monitored with time. The leak rate was measured at the start of each experiment to get accurate permeation rate and the data reported here is the average of at least two independent measurements. The permeance (p) was calculated in gas permeation units (1 GPU=10.sup.−6 cm.sup.3 (STP)/(s cm.sup.2 cm-Hg)) using Eq. (1):

(39) $\begin{array}{cc}p=\frac{273.15\times {10}^6{V}_d}{760\left(P_2\times \frac{76}{1407}\right)AT}\left[{\left(\frac{{\mathrm{dP}}_1}{\mathrm{dt}}\right)}_{\mathrm{ss}}-{\left(\frac{{\mathrm{dP}}_1}{\mathrm{dt}}\right)}_{\mathrm{leak}}\right],& \left(1\right)\end{array}$

(40) where V.sub.d is the downstream volume (cm.sup.3), A is the effective membrane area (cm.sup.2), P.sub.2 is the upstream pressure (mm Hg), and (dP.sub.1/dt).sub.ss is the rate of pressure change in the downstream chamber at the steady state in (mm Hg/s), and (dP.sub.1/dt).sub.leak is the leak rate in (mm Hg/s), T is the cell temperature in K. The selectivity of gas i to j (α.sub.ij) can be estimated by Eq. (2):

(41) $\begin{array}{cc}{\alpha }_{\mathrm{ij}}=\frac{p_i}{p_j}.& \left(2\right)\end{array}$

(42) SEM images of polysulfone membrane are shown in FIG. 2. The images were made using a MIRA3 Field Emission Scanning Electron microscope (FE-SEM) from TESCAN, with an increasing electron voltage of 15 KV. A gold layer of 10 nm thickness was used for samples coating using Ion Sputter Q 150R S (Quorum Technologies). The highly porous PSF surface, seen in FIG. 2A, was observed for membranes prepared by a conventional wet phase inversion method. These membranes showed very low gas selectivity. Therefore, a convective air evaporation period was applied to the membranes before coagulation in a DI water bath, which resulted in an asymmetric PSF structure with a top dense layer, as can be seen in FIG. 2B.

(43) The micrograph SEM images of the polyamide surface (FIG. 2C) and CDC/polyamide MMM surface (FIG. 2D) indicate the formation of a thin layer of composite polyamide and CDC/PA layers on top of PSF support membrane. SEM images show that a defect-free polyamide layer (FIG. 2C) and CDC/polyamide layer (FIG. 2D) were built on top of the PSF support, and the smooth PSF surface (FIG. 2B) was totally covered by a rough and nodular polyamide structure. The polyamide and CDC-polyamide layers were formed as a result of interfacial polymerization reaction between the diamine (here, piperazine) and the dicarboxylate (here, isophthaloyl chloride).

(44) The gas separation performance of the multi-layer membranes, including polysulfone support, and (optionally CDC-doped) polyamide layer(s), fabricated according to the above procedure, was evaluated using pure carbon dioxide (CO.sub.2) and methane (CH.sub.4) gases at a temperature of 300.15 K (27° C.) and 5 bar feed pressure are shown in Table 3, below.

(45) TABLE-US-00003 TABLE 3 Gas separation performance of the fabricated polysulfone support, thin film polyamide membranes, and (CDCs)/polyamide MMMs at 300.15 K and 5 bar. Membrane Loading % CO.sub.2 CH.sub.4 CO.sub.2/CH.sub.4 PSF 0 2.41 0.556 4.33 PA 0 2.16 0.162 13.33 MMM.sub.4 0.5 4.07 0.204 19.92

(46) From Table 3, overall experimental results indicate that CDC/polyamide mixed matrix membranes, e.g., MMM.sub.4, can provide higher gas permeance and selectivity in comparison with the reference pure polyamide and polysulfone membranes. Without wishing to be bound to any theory, enhanced gas permeation and selectivity were may be attributed to the addition of carbide-derived carbon (CDC) nanoparticles, which can allow faster gas flow through the membrane by disrupting the polymer chain matrix. As indicated by SEM images in FIG. 2D, CDC nanoparticles can disperse well in the polyamide layer. Higher gas permeance may be due to well-dispersed CDC forming channels in polyamide matrix to transport gas molecules more effectively. Furthermore, the gas selectivity of a PSF membrane may be enhanced by including a thin polyamide layer upon the PSF layer, while the gas permeance may decrease as a result of the increased mass transfer resistance.

(47) FIG. 3 shows the change in CO.sub.2 and CH.sub.4 gas permeance by varying CDCs loading from 0.0005% to 1% in the polyamide-comprising layer for the respective membranes (MMM.sub.1-MMM.sub.5). The permeation rate of both CO.sub.2 and CH.sub.4 gas molecules may be enhanced by increasing the CDC nanoparticles content in the polyamide layer(s). This may be attributed to a beneficial interaction between polyamide matrix and nanofiller surface, implying good adhesion of the CDC to the polyamide chain. Moreover, high surface areas and/or porosities of CDC may offer more surface and volume for gases to diffuse through the membrane matrix.

(48) As seen in FIG. 3, even though both CO.sub.2 and CH.sub.4 gas permeation increased with increasing CDC content in the polyamide layer, the increments were not the same for the two gasses. From FIG. 3, CO.sub.2 permeance initially increased from 2.16 GPU for pure polyamide to 2.44 GPU for MMM.sub.2 with 0.002 wt. % CDC-loading and continued to increase to 3.13 GPU for 0.1 wt. % CDC-loading, while the maximum CO.sub.2 permeance was recorded at 1 wt. % CDC-loading with a value of 5.00 GPU. On the other hand, when CDC concentration was increased to 0.1 wt. %, the permeation of CH.sub.4 increased by only 14.8%, with a maximum value of 0.375 GPU observed at 1 wt. % CDC-loading. The unexpectedly higher increase in CO.sub.2 permeation relative to CH.sub.4 provides improved CO.sub.2-versus-CH.sub.4 selectivity.

(49) From FIG. 4, possibly as a result of the good dispersion of CDC nanoparticles in the polyamide layer(s), the CO.sub.2-versus-CH.sub.4 selectivity improved by increasing CDC loading up to a concentration of 0.5 wt. %, then the gas selectivity unexpectedly declined to 13.31 with 1.0 wt. % TiC-derived CDC-loading. The diminished selectivity of the 1.0 wt. % TiC-derived CDC-loading may arise from nanoparticle agglomeration, which can be observed in SEM images. CDC agglomeration indicates the creation of defects in the membrane surface, possibly resulting in higher CH.sub.4 permeance compared to CO.sub.2. FIG. 4 shows that when CDC loading increased from 0.5% to 1%, the CO.sub.2 permeance increased by 22.8% while the CH.sub.4 permeance increased 83.82%, resulting in lower CO.sub.2-versus-CH.sub.4 selectively.

(50) The best-performing loading amount selected from MMM.sub.0 to MMM.sub.5, i.e., 0.5 wt. % CDC-loaded polyamide (MMM.sub.4), was then chosen to fabricate CDC/polyamide MMMs including multiple 0.5 wt. % CDC-loaded polyamide layers as follows: M.sub.1(1 layer), M.sub.2 (2 layers), M.sub.3 (6 layers), and M.sub.4 (10 layers). FIG. 5 shows the permeance of CO.sub.2 and CH.sub.4 as a function of the number of 0.5 wt. % CDC-loaded polyamide layers. Both CO.sub.2 and CH.sub.4 gas permeance were reduced as the number of the layers increased, likely due to higher mass transfer resistance for gas permeation.

(51) FIG. 5 shows that CO.sub.2 permeance in 10 CDC-loaded (0.5 wt. %) polyamide layer membrane (M.sub.4) reduced from 4.07 GPU to 2.32 GPU. While CH.sub.4 permeation decreased from 0.204 GPU to 0.096 GPU. Reduced gas permeance was accompanied by a moderate enhancement in CO.sub.2-versus-CH.sub.4 selectivity, which is shown in FIG. 6, wherein the selectivity improved by 21% for 10 selective layers. The higher selectivity for CO.sub.2 over CH.sub.4 with increased layer count may be attributed to functional groups in the CDC/polyamide layer and/or to the presence of larger amount of CDC, which may enhance CDC structural properties, e.g., porosity, to allow higher permeation of CO.sub.2 relative to CH.sub.4.

(52) Numerous modifications and variations of the present invention are possible in light of the above teachings. It is therefore to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described herein.