WO2022145637A1 - Method of producing solvent-resistant nanofiltration separation membrane - Google Patents
Method of producing solvent-resistant nanofiltration separation membrane Download PDFInfo
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- WO2022145637A1 WO2022145637A1 PCT/KR2021/013417 KR2021013417W WO2022145637A1 WO 2022145637 A1 WO2022145637 A1 WO 2022145637A1 KR 2021013417 W KR2021013417 W KR 2021013417W WO 2022145637 A1 WO2022145637 A1 WO 2022145637A1
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- separation membrane
- solvent
- resistant nanofiltration
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- nanofiltration separation
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- 238000000926 separation method Methods 0.000 title claims abstract description 213
- 239000012528 membrane Substances 0.000 title claims abstract description 212
- 238000000034 method Methods 0.000 title claims abstract description 76
- 238000003849 solvent resist ant nanofiltration Methods 0.000 title claims abstract description 73
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- ZMXDDKWLCZADIW-UHFFFAOYSA-N N,N-Dimethylformamide Chemical compound CN(C)C=O ZMXDDKWLCZADIW-UHFFFAOYSA-N 0.000 claims description 54
- 230000035699 permeability Effects 0.000 claims description 36
- KFZMGEQAYNKOFK-UHFFFAOYSA-N Isopropanol Chemical compound CC(C)O KFZMGEQAYNKOFK-UHFFFAOYSA-N 0.000 claims description 33
- 239000004693 Polybenzimidazole Substances 0.000 claims description 33
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- 238000004132 cross linking Methods 0.000 claims description 32
- YXFVVABEGXRONW-UHFFFAOYSA-N Toluene Chemical compound CC1=CC=CC=C1 YXFVVABEGXRONW-UHFFFAOYSA-N 0.000 claims description 24
- 229920001451 polypropylene glycol Polymers 0.000 claims description 18
- FXHOOIRPVKKKFG-UHFFFAOYSA-N N,N-Dimethylacetamide Chemical compound CN(C)C(C)=O FXHOOIRPVKKKFG-UHFFFAOYSA-N 0.000 claims description 13
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- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims description 11
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- 230000008023 solidification Effects 0.000 claims description 7
- 238000000576 coating method Methods 0.000 claims description 6
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- 150000003384 small molecules Chemical class 0.000 claims description 6
- YLQBMQCUIZJEEH-UHFFFAOYSA-N tetrahydrofuran Natural products C=1C=COC=1 YLQBMQCUIZJEEH-UHFFFAOYSA-N 0.000 claims description 6
- 239000011248 coating agent Substances 0.000 claims description 5
- 150000001875 compounds Chemical class 0.000 claims description 5
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- 125000004435 hydrogen atom Chemical group [H]* 0.000 claims description 5
- 239000000203 mixture Substances 0.000 claims description 5
- 125000000008 (C1-C10) alkyl group Chemical group 0.000 claims description 3
- HYZJCKYKOHLVJF-UHFFFAOYSA-N 1H-benzimidazole Chemical compound C1=CC=C2NC=NC2=C1 HYZJCKYKOHLVJF-UHFFFAOYSA-N 0.000 claims description 3
- 230000008569 process Effects 0.000 abstract description 27
- 238000001728 nano-filtration Methods 0.000 abstract description 19
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- WEVYAHXRMPXWCK-UHFFFAOYSA-N Acetonitrile Chemical compound CC#N WEVYAHXRMPXWCK-UHFFFAOYSA-N 0.000 description 21
- 230000000052 comparative effect Effects 0.000 description 19
- 230000006872 improvement Effects 0.000 description 12
- 238000005516 engineering process Methods 0.000 description 7
- IAZDPXIOMUYVGZ-UHFFFAOYSA-N Dimethylsulphoxide Chemical compound CS(C)=O IAZDPXIOMUYVGZ-UHFFFAOYSA-N 0.000 description 6
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- SECXISVLQFMRJM-UHFFFAOYSA-N N-Methylpyrrolidone Chemical compound CN1CCCC1=O SECXISVLQFMRJM-UHFFFAOYSA-N 0.000 description 4
- -1 and nonwoven Substances 0.000 description 4
- ZWEHNKRNPOVVGH-UHFFFAOYSA-N 2-Butanone Chemical compound CCC(C)=O ZWEHNKRNPOVVGH-UHFFFAOYSA-N 0.000 description 3
- UHOVQNZJYSORNB-UHFFFAOYSA-N Benzene Chemical compound C1=CC=CC=C1 UHOVQNZJYSORNB-UHFFFAOYSA-N 0.000 description 3
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- OKKJLVBELUTLKV-UHFFFAOYSA-N Methanol Chemical compound OC OKKJLVBELUTLKV-UHFFFAOYSA-N 0.000 description 3
- SUAKHGWARZSWIH-UHFFFAOYSA-N N,N‐diethylformamide Chemical compound CCN(CC)C=O SUAKHGWARZSWIH-UHFFFAOYSA-N 0.000 description 3
- 238000005259 measurement Methods 0.000 description 3
- VLKZOEOYAKHREP-UHFFFAOYSA-N n-Hexane Chemical compound CCCCCC VLKZOEOYAKHREP-UHFFFAOYSA-N 0.000 description 3
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- CYSGHNMQYZDMIA-UHFFFAOYSA-N 1,3-Dimethyl-2-imidazolidinon Chemical compound CN1CCN(C)C1=O CYSGHNMQYZDMIA-UHFFFAOYSA-N 0.000 description 2
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- CTQNGGLPUBDAKN-UHFFFAOYSA-N O-Xylene Chemical compound CC1=CC=CC=C1C CTQNGGLPUBDAKN-UHFFFAOYSA-N 0.000 description 1
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Images
Classifications
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D69/00—Semi-permeable membranes for separation processes or apparatus characterised by their form, structure or properties; Manufacturing processes specially adapted therefor
- B01D69/10—Supported membranes; Membrane supports
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D67/00—Processes specially adapted for manufacturing semi-permeable membranes for separation processes or apparatus
- B01D67/0002—Organic membrane manufacture
- B01D67/0006—Organic membrane manufacture by chemical reactions
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
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- B01D67/00—Processes specially adapted for manufacturing semi-permeable membranes for separation processes or apparatus
- B01D67/0002—Organic membrane manufacture
- B01D67/0009—Organic membrane manufacture by phase separation, sol-gel transition, evaporation or solvent quenching
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- B01D67/0009—Organic membrane manufacture by phase separation, sol-gel transition, evaporation or solvent quenching
- B01D67/0013—Casting processes
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- B01D67/00—Processes specially adapted for manufacturing semi-permeable membranes for separation processes or apparatus
- B01D67/0081—After-treatment of organic or inorganic membranes
- B01D67/0093—Chemical modification
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- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D69/00—Semi-permeable membranes for separation processes or apparatus characterised by their form, structure or properties; Manufacturing processes specially adapted therefor
- B01D69/02—Semi-permeable membranes for separation processes or apparatus characterised by their form, structure or properties; Manufacturing processes specially adapted therefor characterised by their properties
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- B—PERFORMING OPERATIONS; TRANSPORTING
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- B01D69/10—Supported membranes; Membrane supports
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- B01D69/1071—Woven, non-woven or net mesh
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- B—PERFORMING OPERATIONS; TRANSPORTING
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- B01D69/1213—Laminated layers
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- B—PERFORMING OPERATIONS; TRANSPORTING
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- B01D69/12—Composite membranes; Ultra-thin membranes
- B01D69/1214—Chemically bonded layers, e.g. cross-linking
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- B—PERFORMING OPERATIONS; TRANSPORTING
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- B01D71/00—Semi-permeable membranes for separation processes or apparatus characterised by the material; Manufacturing processes specially adapted therefor
- B01D71/06—Organic material
- B01D71/58—Other polymers having nitrogen in the main chain, with or without oxygen or carbon only
- B01D71/62—Polycondensates having nitrogen-containing heterocyclic rings in the main chain
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- B—PERFORMING OPERATIONS; TRANSPORTING
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- B01D61/00—Processes of separation using semi-permeable membranes, e.g. dialysis, osmosis or ultrafiltration; Apparatus, accessories or auxiliary operations specially adapted therefor
- B01D61/02—Reverse osmosis; Hyperfiltration ; Nanofiltration
- B01D61/027—Nanofiltration
Definitions
- the present invention relates to a method of producing a solvent-resistant nanofiltration separation membrane. Specifically, the present invention relates to a novel method of producing a solvent-resistant nanofiltration separation membrane which improves both permeation performance and a rejection rate, by producing a nanofiltration separation membrane having solvent resistance enhanced by crosslinking and then performing a post-treatment using a good solvent.
- a polymer separation membrane is widely applied in various industrial fields such as water treatment, gas separation, cosmetics, pharmaceuticals, petrochemicals, and electronic materials together with manufacturing and recovery industries of high-purity and high-functional materials, as a core separation/purification technology.
- a nanofiltration separation membrane having excellent solvent resistance is used in the fields using an organic solvent, thereby separating various solutes present in an organic solvent.
- an organic solvent nanofiltration separation membrane which may be applied to a separation/purification process in a fine chemical industry, a pharmaceutical industry, and the like is actively in progress.
- the organic solvent nanofiltration separation membrane technology may allow separation of materials ranging in molecular weights of 100 to 1000 Daltons using a separation membrane having high chemical stability, and unlike the conventional technology, this technology may be operated at room temperature without heating, thereby greatly reducing energy use in a product manufacturing process, and thus, being easily used for separation and purification of raw materials, intermediate by-products, and final products.
- a polymer which is mainly used for production of an organic solvent nanofiltration separation membrane requires fractionation performance and solvent resistance, and a material having solvent resistance is used to produce a separation membrane or a polymer separation membrane is crosslinked or modified for use.
- subsidiary materials such as a subsidiary support, a spacer in a module, and a housing should also secure solvent resistance and pressure resistance.
- the organic solvent nanofiltration separation membrane as such should have better chemical resistance and stability in an organic solvent than a conventionally used separation membrane, and also, should have a precise molecular weight cut-off (MWCO), and thus, requires a technology to improve a removal rate (rejection rate).
- MWCO molecular weight cut-off
- polymer materials having excellent chemical resistance such as polyimide, polybenzimidazole, and polyamide are used, but a technology to produce a separation membrane having precise molecular weight cut-off (MWCO)and permeability by a phase transition method is very important, and a technology of producing an organic solvent nanofiltration separation membrane which may improve both a permeability and a rejection rate which conflict with each other is demanded.
- MWCO molecular weight cut-off
- An object of the present invention is to provide a method of producing a solvent-resistant nanofiltration separation membrane having improved solvent resistance, permeation performance, and rejection performance, in comparison with a solvent-resistant nanofiltration separation membrane produced by a conventional phase transition and crosslinking method.
- Another object of the present invention is to provide a solvent-resistant nanofiltration separation membrane which may improve a rejection rate of a solute having a number average molecular weight of 100 g/mol or more by increasing the denseness of a pore structure of a nanofiltration separation membrane, and a method of producing the same.
- the present inventors constantly studied a solvent-resistant nanofiltration separation membrane which may improve both permeation performance and rejection performance, and as a result, found that when a post-treatment process using a good solvent is applied, the above physical properties are achieved, thereby completing the present invention.
- a method of producing a solvent-resistant nanofiltration separation membrane includes: (a) coating a polybenzimidazole dope solution on a porous support; (b) immersing the support coated with the dope solution in water to produce a separation membrane having a selective layer formed by solidification by interdiffusion of a solvent and a non-solvent; (c) immersing the separation membrane having a selective layer formed in a crosslinking solution to perform crosslinking; and (d) allowing a post-treatment solvent in which polybenzimidazole is soluble to permeate the separation membrane having a crosslinked selective layer to rearrange the crosslinked separation membrane, thereby, when a solvent-resistant nanofiltration separation membrane is produced, effectively improving all of solvent resistance, permeation performance, and rejection performance.
- the allowing of the solvent to permeate in step (d) may use cross-flow filtration with pressure applied or dead-end filtration.
- the allowing of the solvent to permeate in step (d) may be allowing the post-treatment solvent to permeate at a flow velocity of 1 to 200 L/h using cross-flow filtration under a pressure of 1 to 50 bar for 10 minutes to 10 hours.
- the crosslinking solution in step (d) may include a compound represented by the following Chemical Formula 1:
- R 1 to R 4 are C 1-10 alkyl halide and the rest is hydrogen.
- the post-treatment solvent in step (d) may be a good solvent in which polybenzimidazole is soluble.
- the good solvent may be any one or a mixture of two or more selected from the group consisting of toluene, isopropyl alcohol, dimethylformamide, dimethylacetamide, and tetrahydrofuran.
- step (c) may be performed by immersion under reflux conditions and under a temperature condition of 50 to 100°C for 1 to 60 hours.
- the separation membrane in step (c) may have an average thickness of 10 to 300 ⁇ m.
- the solvent-resistant nanofiltration separation membrane may be a separation membrane for separating a low-molecular weight compound having a number average molecular weight of 100 to 1200 g/mol which is mixed with a solvent.
- the low-molecular weight compound may be polypropylene glycol having a number average molecular weight of 100 to 1200 g/mol.
- the solvent-resistant nanofiltration separation membrane may satisfy the following Equation 1:
- P 1 is an acetone permeability of a separation membrane before step (d)
- P 2 is an acetone permeability of the separation membrane after step (d)
- R 1 is a rejection rate of the separation membrane for polypropylene glycol having a number average molecular weight of 100 to 1200 g/mol before step (d)
- R 2 is a rejection rate of the separation membrane after step (d) under the same condition.
- a solvent-resistant nanofiltration separation membrane produced by the production method according to an exemplary embodiment of the present invention is provided.
- a solvent-resistant nanofiltration separation membrane includes: a porous support layer and a crosslinked benzimidazole selective layer formed on the porous support layer, wherein the solvent-resistant nanofiltration separation membrane satisfies the following Equation 1:
- P 1 is a permeability of a separation membrane before post-treatment solvent permeation
- P 2 is a permeability of the separation membrane after post-treatment solvent permeation
- R 1 is a rejection rate of the separation membrane for polypropylene glycol having a number average molecular weight of 100 to 1200 g/mol before post-treatment solvent permeation
- R 2 is a rejection rate of the separation membrane after post-treatment solvent permeation under the same condition.
- the post-treatment solvent may be a good solvent in which polybenzimidazole is soluble.
- the good solvent may be any one or a mixture of two or more selected from the group consisting of toluene, isopropyl alcohol, dimethylformamide, dimethylacetamide, and tetrahydrofuran.
- the solvent-resistant nanofiltration separation membrane may have an average thickness of 20 to 500 ⁇ m.
- the solvent-resistant nanofiltration separation membrane may satisfy both the following Equations 1 and 2:
- Equation 1 P 1 , P 2 , R 1 , and R 2 are as defined in Equation 1.
- the solvent-resistant nanofiltration separation membrane of the present invention goes through a post-treatment process using a good solvent, so that the separation membrane performance may be effectively improved by rearrangement of size and structure of separation membrane pores.
- the solvent-resistant nanofiltration separation membrane has excellent chemical resistance, and also may improve both permeation performance and rejection performance which conventionally conflict with each other.
- the nanofiltration separation membrane produced by the production method of the present invention may be applied to a nanofiltration system to effectively filter solutes having a number average molecular weight of 100 g/mol or more and also provide a system having high efficiency.
- FIG. 1 shows a change in a molecular weight cut-off(MWCO) of a separation membrane before crosslinking, after crosslinking, and after a post-treatment process in Example 1.
- FIG. 2 is a graph of acetone permeability results of separation membranes according to Examples 1 to 4 and Comparative Examples 1 and 2.
- FIG. 3 is a graph of ethanol permeability results of separation membranes according to Examples 5 to 7 and Comparative Examples 1 and 3 to 5.
- good solvent in the present specifically refers to a solvent capable of dissolving polybenzimidazole.
- the present invention relates to a method of producing a solvent-resistant nanofiltration separation membrane, which is a novel method of producing a solvent-resistant nanofiltration separation membrane for overcoming a conflicting relation between permeation performance and rejection performance by applying a post-treatment process.
- the present invention provides a method of producing a solvent-resistant nanofiltration separation membrane, the method comprising:
- the porous support may be used for complementing mechanical strength of the separation membrane, and nonwoven, fabric, long fiber, sheets, and the like which are mainly used in the separation membrane field requiring precise filtration may be used without limitation.
- the porous support is preferably coated with a polybenzimidazole dope solution uniformly, so that it can be closely adhered without peeling off even after solidification and crosslinking of the selective layer, and since there is no protruding fiber on the surface of the porous support, it is preferred that the surface properties and permeability of the finally produced separation membrane are uniform.
- porous support may be any one selected from the group consisting of polyethylene, polypropylene, polyester, polyamide, polysulfone, polyethersulfone, polyimide, polyvinylidene fluoride, polyacrylonitrile, polyamideimide, and the like, but is not particularly limited thereto as long as a polybenzimidazole selective layer is formed.
- the polybenzimidazole dope solution in step (a) may include 5 to 35 wt%, preferably 15 to 25 wt%, or 20 to 25 wt% of polybenzimidazole in an organic solvent.
- the dope solution is prepared by including polybenzimidazole within the range, polybenzimidazole is evenly dissolved at an appropriate concentration, so that the separation membrane may be formed at a uniform thickness.
- the organic solvent may be used without limitation as long as it dissolves polybenzimidazole, and as a non-limiting example, acetonitrile, dimethyl sulfoxide, N-methylpyrrolidone, N,N-dimethylacetamide, 1,3-dimethyl-2-imidazolidinone, dimethylformamide, and the like may be used.
- the polybenzimidazole dope solution may be prepared by diluting polybenzimidazole in an organic solvent, stirring the solution at room temperature for 1 to 15 hours, preferably 5 to 10 hours, and then defoaming the solution at room temperature for 10 to 30 hours, preferably 15 to 25 hours.
- the dope solution When the thus-prepared dope solution is applied on the porous support at room temperature, the dope solution may be coated at a thickness of 50 to 500 ⁇ m, preferably 100 to 400 ⁇ m, and though a coating method is not particularly limited, as an example, the dope solution may be coated on the porous support at a certain thickness using a casting knife.
- the separation membrane may be produced by a non-solvent induced phase separation method, in which a porous support coated with a dope solution is immersed in water to induce solidification by interdiffusion of a solvent and a non-solvent.
- the non-solvent induced phase separation method is a method in which after the dope solution is coated, the porous support is immersed in a water bath containing water at 5 to 40°C, preferably 15 to 30°C for 0.5 to 3 hours, preferably 1 to 2 hours to induce solidification of polybenzimidazole by interdiffusion of a solvent and a non-solvent to produce a separation membrane having a selective layer formed thereon.
- the selective layer is a polybenzimidazole layer formed by solidifying the polybenzimidazole dope solution in step (a), and the polybenzimidazole separation membrane may be produced by step (b).
- the separation membrane produced may be immersed in purified distilled water for 0.5 to 3 hours, preferably 1 to 2 hours, and then stored in an alcohol-based non-solvent, for example, though is not particularly limited thereto, isopropyl alcohol and the like.
- the crosslinking solution may include a compound represented by the following Chemical Formula 1.
- a crosslinking network between polybenzimidazole polymer chains may be densely formed by step (c), thereby further improving solvent resistance of the separation membrane, which is thus preferred.
- R 1 to R 4 are C 1-10 alkyl halide and the rest is hydrogen.
- R 1 and R 4 may be -(CH 3 ) n Br and R 2 and R 3 may be hydrogen, or R 1 and R 3 may be -(CH 3 ) n Br and R 2 and R 4 may be hydrogen, and n may be 1 to 5.
- An example of the compound represented by Chemical Formula 1 may include para-dibromoxylene, meta-dibromoxylene, ortho-dibromoxylene, and the like, and in particular, when para-dibromoxylene is used, an interface of the separation membrane having the polybenzimidazole selective layer is effectively crosslinked to form a solid network, and thus, chemical resistance, stability, and durability of the separation membrane are improved and a pore form of the separation membrane becomes dense, thereby effectively improving the rejection rate of a solute having a number average molecular weight of 100 g/mol or more.
- the crosslinking solution may include the compound represented by Chemical Formula 1 at a concentration of 0.01 to 1 M, preferably 0.05 to 0.5 M, and more preferably 0.05 to 0.25 M in a polar aprotic solvent.
- the polar aprotic solvent is not particularly limited, but acetonitrile, dimethyl sulfoxide, N-methylpyrrolidone, N,N-dimethylacetamide, 1,3-dimethyl-2-imidazolidinone, dimethylformamide, and the like may be used, and in particular, when acetonitrile is used, not only a crosslinking reaction of the separation membrane but also a crosslinking reaction inside and outside the separation membrane occurs efficiently, and thus, chemical resistance and stability are excellent in the organic solvent and the pore structure of the separation membrane becomes dense, thereby significantly improving the rejection rate of the solute having a number average molecular weight of 100 g/mol or more.
- step (c) the separation membrane is crosslinked by being immersed in the crosslinking solution at 50 to 100°C, preferably 60 to 90°C, and more preferably 75 to 85°C under reflux condition for 1 to 60 hours, preferably 10 to 40 hours, and more preferably 20 to 30 hours, and after the crosslinking reaction, unreacted materials are removed by the polar aprotic solvent.
- the crosslinking is performed under the above conditions, the pore structure of the separation membrane becomes denser to improve the rejection rate of the solute having a number average molecular weight of 100 g/mol or more, which is thus preferred.
- the crosslinked polybenzimidazole separation membrane may be formed by step (c), and the separation membrane may have an average thickness of 10 to 300 ⁇ m.
- the separation membrane may be formed at a thickness of 10 to 300 ⁇ m, preferably 20 to 200 ⁇ m before crosslinking, and after crosslinking, it becomes thicker and may be formed at a thickness of 20 to 500 ⁇ m, preferably 60 to 400 ⁇ m, and more preferably 70 to 300 ⁇ m, excluding the thickness of the porous support.
- the separation membrane has a thickness within the above range, it may have high chemical resistance and stability in an organic solvent and the rejection rate of the solute having a number average molecular weight of 100 g/mol or more may be increased.
- step (d) of allowing the post-treatment solvent in which polybenzimidazole is soluble to permeate the separation membrane having the crosslinked selective layer (hereinafter, referred to as a crosslinked separation membrane) to rearrange the crosslinked separation membrane the post-treatment solvent permeates from one surface to the other surface of the crosslinked separation membrane, not using the method of immersing the crosslinked separation membrane in a reaction bath containing the post-treatment solvent, thereby removing an uncrosslinked selective layer and also rearranging a surface polymer chain of the crosslinked selective layer to uniformly adjust the size and structure of the separation membrane pores.
- the uncrosslinked selective layer is dissolved to improve permeation performance, and the polymer chain of the crosslinked separation membrane is rearranged so that pores become dense to improve rejection performance, which is thus preferred.
- step (d) is not performed, the form and structure of the pores of the crosslinked separation membrane are not adjusted uniformly, so that it is difficult to improve both permeation performance and rejection performance, which is thus not preferred.
- a method of allowing the solvent to permeate in step (d) may use cross-flow filtration with pressure applied or dead-end filtration.
- the method of solvent permeation in step (d) may be post-treatment solvent permeation under a pressure of 1 to 50 bar, more specifically 10 to 30 bar, using cross-flow filtration, at a flow velocity of 1 to 200 L/g, more specifically 50 to 200 L/g for 10 minutes to 10 hours, more preferably 1 to 6 hours.
- a process of washing using pure ethanol and the like may be further included after the post-treatment.
- the post-treatment solvent in step (d) may be a good solvent in which polybenzimidazole is soluble.
- the good solvent may be any one or a mixture of two or more selected from the group consisting of toluene, isopropyl alcohol, dimethylformamide, dimethylacetamide, and tetrahydrofuran.
- the separation method of a solution includes bringing a solution including an organic solvent and a solute having a number average molecular weight of 100 g/mol into contact with a separation membrane, and separating the organic solvent and the solute through the separation membrane, and the separation membrane is the solvent-resistant nanofiltration separation membrane as described above.
- the solvent-resistant nanofiltration separation membrane may be used for an organic solvent nanofiltration process, and specifically, the solution may be separated by bringing the organic solvent and the solute having a number average molecular weight of 100 g/mol or more into contact with the separation membrane, using, though is not particularly limited to, cross-flow filtration which is a filtration method of allowing a solution permeating the separation membrane to flow in a vertical direction to a supplied solution.
- cross-flow filtration is a filtration method of allowing a solution permeating the separation membrane to flow in a vertical direction to a supplied solution.
- the low-molecular weight compound may be polypropylene glycol, but is not limited thereto.
- any organic solvent may be used without limitation as long as the solvent is a known organic solvent, and as a non-limiting example, may be one or more selected from the group consisting of methanol, ethanol, isopropyl alcohol, acetone, tetrahydrofuran, dimethylformamide, dichloromethane, toluene, methylethylketone, formaldehyde, diethylformamide, dimethylacetamide, 1-methyl-2-pyrrolidone, dimethyl sulfoxide, diethylether, xylene, benzene, and N,N-dimethylacetamide, and the like.
- the solvent-resistant nanofiltration separation membrane (hereinafter, referred to as a separation membrane) may satisfy the following Equation 1:
- P 1 is an acetone permeability of a separation membrane before step (d)
- P 2 is an acetone permeability of the separation membrane after step (d)
- R 1 is a rejection rate of the separation membrane for polypropylene glycol (PPG) having a number average molecular weight of 100 to 1200 g/mol before step (d)
- R 2 is a rejection rate of the separation membrane after step (d) under the same condition.
- Equation 1 refers to the product of an acetone permeability improvement multiple of the separation membrane (P 2 /P 1 ) and a PPG rejection rate improvement multiple of the separation membrane (R 2 /R 1 ), and the value of the product may be 1.2 or more, preferably 1.5 or more, and more preferably 2 or more.
- P 2 /P 1 acetone permeability improvement multiple of the separation membrane
- R 2 /R 1 PPG rejection rate improvement multiple of the separation membrane
- the solvent-resistant nanofiltration separation membrane may satisfy both the following Equations 2 and 3:
- Equation 1 P 1 , P 2 , R 1 , and R 2 are as defined in Equation 1.
- Equation 2 refers to a permeability improvement multiple of the separation membrane depending on step (d) and Equation 3 refers to a rejection rate improvement multiple of the separation membrane depending on step (d), and satisfying both Equations 2 and 3 means improving both permeation performance and rejection performance of the separation membrane by performing step (d).
- the value of P 2 /P 1 in Equation 2 may be 1.1 or more, preferably 1.5 or more, and more specifically 5 or more
- the value of R 2 /R 1 in Equation 3 may be 1.01 or more, preferably 1.05 or more, and more specifically 1.1 or more.
- a solvent-resistant nanofiltration separation membrane produced by the production method according to an exemplary embodiment of the present invention may be provided.
- the solvent-resistant nanofiltration separation membrane goes through a post-treatment process using a good solvent, so that the separation membrane performance may be effectively improved by rearrangement of an uncrosslinked selective layer, and pore size and structure of the separation membrane.
- the solvent-resistant nanofiltration separation membrane has excellent chemical resistance, and also may improve both permeation performance and rejection performance which conventionally conflict with each other.
- the solvent-resistant nanofiltration separation membrane produced by the production method of the present invention may be applied to a nanofiltration system to effectively filter solutes having a number average molecular weight of 100 g/mol or more and also provide a system having high efficiency.
- the present invention may provide a solvent-resistant nanofiltration separation membrane includes: a porous support layer and a crosslinked benzimidazole selective layer formed on the porous support layer, wherein the solvent-resistant nanofiltration separation membrane satisfies the following Equation 1:
- P 1 is a permeability of a separation membrane before post-treatment solvent permeation
- P 2 is a permeability of the separation membrane after post-treatment solvent permeation
- R 1 is a rejection rate of the separation membrane for polypropylene glycol having a number average molecular weight of 100 to 1200 g/mol before post-treatment solvent permeation
- R 2 is a rejection rate of the separation membrane after post-treatment solvent permeation under the same condition.
- porous support In addition, detailed description and examples of the porous support, the selective layer, the separation membrane, and the post-treatment solvent are as described in the production method above.
- Pure solvent permeability was measured in a manner of cross-flow filtration, and evaluated under conditions of an effective area of a measured separation membrane of 14.8 cm 2 , an operation pressure of 15 bar, a temperature of 30°C, and a flow velocity of 100 L/h. Before measuring the pure solvent permeability, stabilization with pure ethanol was performed for 3 hours under the same conditions as the above, and then the experiment was performed.
- a pure solvent permeability was measured after 3 hours, 1.6 L of a 1000 ppm solution of polypropylene glycol (PPG) added to an organic solvent (N,N-methylpyrrolidone, N,N-dimethylacetamide, dimethylformamide, acetonitrile, acetone, ethanol, toluene, or hexane) was used to measure the permeability and the rejection rate.
- PPG polypropylene glycol
- three commercialized products having a number average molecular weight (Mn) of 425 g/mol or less, 700 g/mol or less, and 1000 g/mol or less were used, and used after being prepared to have a selectivity in a wide range of 300 to 1200 g/mol.
- Mn number average molecular weight
- Each polypropylene glycol was introduced to each organic solvent to prepare a test solution, and 1 hour after permeation, the obtained sample was analyzed by liquid chromatography to calculate the rejection rate.
- Ethanol containing 1000 ppm of polypropylene glycol was used to measure permeability and rejection rate of a separation membrane produced.
- a post-treatment solvent was used to perform permeation for 4 hours.
- Ethanol containing 1000 ppm of polypropylene glycol was used to measure permeability and rejection rate of the post-treated separation membrane.
- a solution including 20 wt% of polybenzimidazole (Celazole S26) was prepared using N,N-dimethylacetamide (DMAc), stirred at room temperature for 6 hours, and allowed to stand for 24 hours to defoam a dope solution.
- the thus-prepared dope solution was coated at a thickness of 200 ⁇ m on a polypropylene nonwoven porous support at room temperature.
- the porous support having the dope solution coated was immersed in a water bath containing water at 20°C to induce solidification of polybenzimidazole by interdiffusion of a solvent and a non-solvent to produce a separation membrane having a selective layer formed. Thereafter, the separation membrane produced was immersed in distilled water for 1 hour, and then stored in isopropyl alcohol (IPA).
- IPA isopropyl alcohol
- the thus-produced separation membrane was immersed in an acetonitrile solvent to remove isopropyl alcohol.
- the membrane was immersed in a crosslinking solution of 60 g of an acetonitrile solvent including 0.12 M para-dibromoxylene (DBX) and a crosslinking reaction was performed at 80°C for 24 hours under reflux conditions. Thereafter, unreacted materials were removed with the acetonitrile solvent.
- DBX para-dibromoxylene
- the crosslinked separation membrane was installed in a cross-flow filtration system, and the permeability and the rejection rate of the separation membrane in acetone were measured before a post-treatment process. Then, a post-treatment solvent permeated by a filtration process to perform a post-treatment process.
- the post-treatment solvent used was diethylformamide as described in Table 1, the solvent permeated for 4 hours under the conditions of an effective membrane area of 14.8 ⁇ 0.1 cm 2 , a temperature of 30 ⁇ 1°C, a pressure of 15 ⁇ 0.1 bar, and a flow velocity of 100 ⁇ 1 L/h.
- the permeability and the rejection rate of the separation membrane were measured in acetone, and the results are shown in Table 1.
- a separation membrane was produced in the same manner as in Example 1, except that the post-treatment process was performed for 8 hours and 24 hours as shown in Table 1, and then the permeability and the rejection rate of the separation membrane in ethanol were measured under the same conditions. The results are shown in Table 2.
- Example 1 The experiment was performed in the same manner as in Example 1, except that (d) the post-treatment process was performed not by cross-flow filtration but by immersing the membrane in a diethylformamide solvent for 4 hours, and the results are shown in Table 1.
- Table 1 shows the permeability improvement multiple and the rejection rate improvement multiple in the case of performing the post-treatment process in Examples 1 to 4, in comparison with the case in which the post-treatment was not performed as in Comparative Example 1.
- acetone was used as a solvent for permeability/rejection rate measurement.
- Table 2 shows the permeability improvement multiple and the rejection rate improvement multiple in the case of performing the post-treatment process in Examples 5 to 7 and Comparative Examples 3 to 5, in comparison with the case in which the post-treatment was not performed as in Comparative 1.
- a solvent for permeability/rejection rate measurement ethanol was used.
- Example 1 in which dimethylformamide was used as the post-treatment solvent, better effects were shown than other Examples, and considering that Example 5 using ethanol also showed excellent separation membrane performance, it is confirmed that when the nanofiltration separation membrane is produced by including the post-treatment process in a permeation manner, better separation membrane performance may be expressed.
- FIG. 1 shows a change in a molecular weight cut-off (MWCO) before crosslinking, after crosslinking, and after a post-treatment process in Example 1.
- MWCO molecular weight cut-off
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Abstract
Provided is a solvent-resistant nanofiltration separation membrane which goes through a post-treatment process using a good solvent, so that the separation membrane performance may be effectively improved by an uncrosslinked selective layer and rearrangement of size and structure of separation membrane pores. Specifically, the solvent-resistant nanofiltration separation membrane has excellent chemical resistance, and also may improve both permeation performance and rejection performance which conventionally conflict with each other. The nanofiltration separation membrane produced by the production method of the present invention may be applied to a nanofiltration system to effectively filter solutes having a number average molecular weight of 100 g/mol or more and also provide a system having high efficiency.
Description
The present invention relates to a method of producing a solvent-resistant nanofiltration separation membrane. Specifically, the present invention relates to a novel method of producing a solvent-resistant nanofiltration separation membrane which improves both permeation performance and a rejection rate, by producing a nanofiltration separation membrane having solvent resistance enhanced by crosslinking and then performing a post-treatment using a good solvent.
A polymer separation membrane is widely applied in various industrial fields such as water treatment, gas separation, cosmetics, pharmaceuticals, petrochemicals, and electronic materials together with manufacturing and recovery industries of high-purity and high-functional materials, as a core separation/purification technology.
In particular, a nanofiltration separation membrane having excellent solvent resistance is used in the fields using an organic solvent, thereby separating various solutes present in an organic solvent. With the merits, research on an organic solvent nanofiltration separation membrane which may be applied to a separation/purification process in a fine chemical industry, a pharmaceutical industry, and the like is actively in progress.
The organic solvent nanofiltration separation membrane technology may allow separation of materials ranging in molecular weights of 100 to 1000 Daltons using a separation membrane having high chemical stability, and unlike the conventional technology, this technology may be operated at room temperature without heating, thereby greatly reducing energy use in a product manufacturing process, and thus, being easily used for separation and purification of raw materials, intermediate by-products, and final products.
A polymer which is mainly used for production of an organic solvent nanofiltration separation membrane requires fractionation performance and solvent resistance, and a material having solvent resistance is used to produce a separation membrane or a polymer separation membrane is crosslinked or modified for use. In a flat membrane made of a flat type or spiral wound type module, subsidiary materials such as a subsidiary support, a spacer in a module, and a housing should also secure solvent resistance and pressure resistance.
The organic solvent nanofiltration separation membrane as such should have better chemical resistance and stability in an organic solvent than a conventionally used separation membrane, and also, should have a precise molecular weight cut-off (MWCO), and thus, requires a technology to improve a removal rate (rejection rate).
Usually, polymer materials having excellent chemical resistance such as polyimide, polybenzimidazole, and polyamide are used, but a technology to produce a separation membrane having precise molecular weight cut-off (MWCO)and permeability by a phase transition method is very important, and a technology of producing an organic solvent nanofiltration separation membrane which may improve both a permeability and a rejection rate which conflict with each other is demanded.
An object of the present invention is to provide a method of producing a solvent-resistant nanofiltration separation membrane having improved solvent resistance, permeation performance, and rejection performance, in comparison with a solvent-resistant nanofiltration separation membrane produced by a conventional phase transition and crosslinking method.
Another object of the present invention is to provide a solvent-resistant nanofiltration separation membrane which may improve a rejection rate of a solute having a number average molecular weight of 100 g/mol or more by increasing the denseness of a pore structure of a nanofiltration separation membrane, and a method of producing the same.
In order to achieve the above objects, the present inventors constantly studied a solvent-resistant nanofiltration separation membrane which may improve both permeation performance and rejection performance, and as a result, found that when a post-treatment process using a good solvent is applied, the above physical properties are achieved, thereby completing the present invention. In one general aspect, a method of producing a solvent-resistant nanofiltration separation membrane includes: (a) coating a polybenzimidazole dope solution on a porous support; (b) immersing the support coated with the dope solution in water to produce a separation membrane having a selective layer formed by solidification by interdiffusion of a solvent and a non-solvent; (c) immersing the separation membrane having a selective layer formed in a crosslinking solution to perform crosslinking; and (d) allowing a post-treatment solvent in which polybenzimidazole is soluble to permeate the separation membrane having a crosslinked selective layer to rearrange the crosslinked separation membrane, thereby, when a solvent-resistant nanofiltration separation membrane is produced, effectively improving all of solvent resistance, permeation performance, and rejection performance.
In the method of producing a solvent-resistant nanofiltration separation membrane according to an exemplary embodiment of the present invention, the allowing of the solvent to permeate in step (d) may use cross-flow filtration with pressure applied or dead-end filtration.
In the method of producing a solvent-resistant nanofiltration separation membrane according to an exemplary embodiment of the present invention, the allowing of the solvent to permeate in step (d) may be allowing the post-treatment solvent to permeate at a flow velocity of 1 to 200 L/h using cross-flow filtration under a pressure of 1 to 50 bar for 10 minutes to 10 hours.
In the method of producing a solvent-resistant nanofiltration separation membrane according to an exemplary embodiment of the present invention, the crosslinking solution in step (d) may include a compound represented by the following Chemical Formula 1:
[Chemical Formula 1]
wherein two or more of R1 to R4 are C1-10 alkyl halide and the rest is hydrogen.
In the method of producing a solvent-resistant nanofiltration separation membrane according to an exemplary embodiment of the present invention, the post-treatment solvent in step (d) may be a good solvent in which polybenzimidazole is soluble.
In the method of producing a solvent-resistant nanofiltration separation membrane according to an exemplary embodiment of the present invention, the good solvent may be any one or a mixture of two or more selected from the group consisting of toluene, isopropyl alcohol, dimethylformamide, dimethylacetamide, and tetrahydrofuran.
In the method of producing a solvent-resistant nanofiltration separation membrane according to an exemplary embodiment of the present invention, step (c) may be performed by immersion under reflux conditions and under a temperature condition of 50 to 100°C for 1 to 60 hours.
In the method of producing a solvent-resistant nanofiltration separation membrane according to an exemplary embodiment of the present invention, the separation membrane in step (c) may have an average thickness of 10 to 300 ㎛.
In the method of producing a solvent-resistant nanofiltration separation membrane according to an exemplary embodiment of the present invention, the solvent-resistant nanofiltration separation membrane may be a separation membrane for separating a low-molecular weight compound having a number average molecular weight of 100 to 1200 g/mol which is mixed with a solvent.
In the method of producing a solvent-resistant nanofiltration separation membrane according to an exemplary embodiment of the present invention, the low-molecular weight compound may be polypropylene glycol having a number average molecular weight of 100 to 1200 g/mol.
In the method of producing a solvent-resistant nanofiltration separation membrane according to an exemplary embodiment of the present invention, the solvent-resistant nanofiltration separation membrane may satisfy the following Equation 1:
[Equation 1] (P2/P1) × (R2/R1) ≥ 1.2
wherein P1 is an acetone permeability of a separation membrane before step (d), P2 is an acetone permeability of the separation membrane after step (d), R1 is a rejection rate of the separation membrane for polypropylene glycol having a number average molecular weight of 100 to 1200 g/mol before step (d), and R2 is a rejection rate of the separation membrane after step (d) under the same condition.
In another general aspect, a solvent-resistant nanofiltration separation membrane produced by the production method according to an exemplary embodiment of the present invention is provided.
In still another general aspect, a solvent-resistant nanofiltration separation membrane includes: a porous support layer and a crosslinked benzimidazole selective layer formed on the porous support layer, wherein the solvent-resistant nanofiltration separation membrane satisfies the following Equation 1:
[Equation 1] (P2/P1) × (R2/R1) ≥ 1.2
wherein P1 is a permeability of a separation membrane before post-treatment solvent permeation, P2 is a permeability of the separation membrane after post-treatment solvent permeation, R1 is a rejection rate of the separation membrane for polypropylene glycol having a number average molecular weight of 100 to 1200 g/mol before post-treatment solvent permeation, and R2 is a rejection rate of the separation membrane after post-treatment solvent permeation under the same condition.
According to an exemplary embodiment of the present invention, the post-treatment solvent may be a good solvent in which polybenzimidazole is soluble. Preferably, the good solvent may be any one or a mixture of two or more selected from the group consisting of toluene, isopropyl alcohol, dimethylformamide, dimethylacetamide, and tetrahydrofuran.
According to an embodiment of the present invention, the solvent-resistant nanofiltration separation membrane may have an average thickness of 20 to 500 ㎛.
According to an embodiment of the present invention, the solvent-resistant nanofiltration separation membrane may satisfy both the following Equations 1 and 2:
[Equation 2] P2/P1 ≥ 1.1
[Equation 3] R2/R1 ≥ 1.01
wherein P1, P2, R1, and R2 are as defined in Equation 1.
The solvent-resistant nanofiltration separation membrane of the present invention goes through a post-treatment process using a good solvent, so that the separation membrane performance may be effectively improved by rearrangement of size and structure of separation membrane pores. Specifically, the solvent-resistant nanofiltration separation membrane has excellent chemical resistance, and also may improve both permeation performance and rejection performance which conventionally conflict with each other. The nanofiltration separation membrane produced by the production method of the present invention may be applied to a nanofiltration system to effectively filter solutes having a number average molecular weight of 100 g/mol or more and also provide a system having high efficiency.
FIG. 1 shows a change in a molecular weight cut-off(MWCO) of a separation membrane before crosslinking, after crosslinking, and after a post-treatment process in Example 1.
FIG. 2 is a graph of acetone permeability results of separation membranes according to Examples 1 to 4 and Comparative Examples 1 and 2.
FIG. 3 is a graph of ethanol permeability results of separation membranes according to Examples 5 to 7 and Comparative Examples 1 and 3 to 5.
Hereinafter, the present invention will be described in more detail. However, the following specific examples or exemplary embodiments are only a reference for describing the present invention in detail, and the present invention is not limited thereto, and may be implemented in various forms.
In addition, unless otherwise defined, all technical terms and scientific terms have the same meanings as those commonly understood by one of those skilled in the art to which the present invention pertains. The terms used herein are only for effectively describing a certain specific example, and are not intended to limit the present invention.
In addition, the singular form used in the specification and claims appended thereto may be intended to also include a plural form, unless otherwise indicated in the context.
In addition, unless particularly described to the contrary, "comprising" any elements will be understood to imply further inclusion of other elements rather than the exclusion of any other elements.
The term "good solvent" in the present specifically refers to a solvent capable of dissolving polybenzimidazole.
The present invention relates to a method of producing a solvent-resistant nanofiltration separation membrane, which is a novel method of producing a solvent-resistant nanofiltration separation membrane for overcoming a conflicting relation between permeation performance and rejection performance by applying a post-treatment process.
The present invention provides a method of producing a solvent-resistant nanofiltration separation membrane, the method comprising:
(a) coating a polybenzimidazole dope solution on a porous support;
(b) immersing the support coated with the dope solution in water to produce a separation membrane having a selective layer formed by solidification by interdiffusion of a solvent and a non-solvent;
(c) immersing the separation membrane having a selective layer formed in a crosslinking solution to perform crosslinking; and
(d) allowing a post-treatment solvent in which polybenzimidazole is soluble to permeate the separation membrane having a crosslinked selective layer to rearrange the crosslinked separation membrane. When the nanofiltration separation membrane is produced by including the above steps, solvent resistance, permeation performance, and rejection performance may be effectively improved at the same time, which is thus preferred.
In step (a) of coating a polybenzimidazole dope solution on a porous support, the porous support may be used for complementing mechanical strength of the separation membrane, and nonwoven, fabric, long fiber, sheets, and the like which are mainly used in the separation membrane field requiring precise filtration may be used without limitation. Specifically, the porous support is preferably coated with a polybenzimidazole dope solution uniformly, so that it can be closely adhered without peeling off even after solidification and crosslinking of the selective layer, and since there is no protruding fiber on the surface of the porous support, it is preferred that the surface properties and permeability of the finally produced separation membrane are uniform. A non-limiting example of the porous support may be any one selected from the group consisting of polyethylene, polypropylene, polyester, polyamide, polysulfone, polyethersulfone, polyimide, polyvinylidene fluoride, polyacrylonitrile, polyamideimide, and the like, but is not particularly limited thereto as long as a polybenzimidazole selective layer is formed.
The polybenzimidazole dope solution in step (a) may include 5 to 35 wt%, preferably 15 to 25 wt%, or 20 to 25 wt% of polybenzimidazole in an organic solvent. When the dope solution is prepared by including polybenzimidazole within the range, polybenzimidazole is evenly dissolved at an appropriate concentration, so that the separation membrane may be formed at a uniform thickness.
In addition, the organic solvent may be used without limitation as long as it dissolves polybenzimidazole, and as a non-limiting example, acetonitrile, dimethyl sulfoxide, N-methylpyrrolidone, N,N-dimethylacetamide, 1,3-dimethyl-2-imidazolidinone, dimethylformamide, and the like may be used.
The polybenzimidazole dope solution may be prepared by diluting polybenzimidazole in an organic solvent, stirring the solution at room temperature for 1 to 15 hours, preferably 5 to 10 hours, and then defoaming the solution at room temperature for 10 to 30 hours, preferably 15 to 25 hours.
When the thus-prepared dope solution is applied on the porous support at room temperature, the dope solution may be coated at a thickness of 50 to 500 ㎛, preferably 100 to 400 ㎛, and though a coating method is not particularly limited, as an example, the dope solution may be coated on the porous support at a certain thickness using a casting knife.
Step (b) is described in detail: the separation membrane may be produced by a non-solvent induced phase separation method, in which a porous support coated with a dope solution is immersed in water to induce solidification by interdiffusion of a solvent and a non-solvent. Specifically, the non-solvent induced phase separation method is a method in which after the dope solution is coated, the porous support is immersed in a water bath containing water at 5 to 40°C, preferably 15 to 30°C for 0.5 to 3 hours, preferably 1 to 2 hours to induce solidification of polybenzimidazole by interdiffusion of a solvent and a non-solvent to produce a separation membrane having a selective layer formed thereon. The selective layer is a polybenzimidazole layer formed by solidifying the polybenzimidazole dope solution in step (a), and the polybenzimidazole separation membrane may be produced by step (b). The separation membrane produced may be immersed in purified distilled water for 0.5 to 3 hours, preferably 1 to 2 hours, and then stored in an alcohol-based non-solvent, for example, though is not particularly limited thereto, isopropyl alcohol and the like.
In step (c) of immersing the separation membrane having a selective layer formed in a crosslinking solution to perform crosslinking, the crosslinking solution may include a compound represented by the following Chemical Formula 1. A crosslinking network between polybenzimidazole polymer chains may be densely formed by step (c), thereby further improving solvent resistance of the separation membrane, which is thus preferred.
[Chemical Formula 1]
wherein two or more of R1 to R4 are C1-10 alkyl halide and the rest is hydrogen. Preferably, in Chemical Formula 1, R1 and R4 may be -(CH3)nBr and R2 and R3 may be hydrogen, or R1 and R3 may be -(CH3)nBr and R2 and R4 may be hydrogen, and n may be 1 to 5.
An example of the compound represented by Chemical Formula 1 may include para-dibromoxylene, meta-dibromoxylene, ortho-dibromoxylene, and the like, and in particular, when para-dibromoxylene is used, an interface of the separation membrane having the polybenzimidazole selective layer is effectively crosslinked to form a solid network, and thus, chemical resistance, stability, and durability of the separation membrane are improved and a pore form of the separation membrane becomes dense, thereby effectively improving the rejection rate of a solute having a number average molecular weight of 100 g/mol or more.
In the method of producing a solvent-resistant nanofiltration separation membrane according to an exemplary embodiment of the present invention, the crosslinking solution may include the compound represented by Chemical Formula 1 at a concentration of 0.01 to 1 M, preferably 0.05 to 0.5 M, and more preferably 0.05 to 0.25 M in a polar aprotic solvent. The polar aprotic solvent is not particularly limited, but acetonitrile, dimethyl sulfoxide, N-methylpyrrolidone, N,N-dimethylacetamide, 1,3-dimethyl-2-imidazolidinone, dimethylformamide, and the like may be used, and in particular, when acetonitrile is used, not only a crosslinking reaction of the separation membrane but also a crosslinking reaction inside and outside the separation membrane occurs efficiently, and thus, chemical resistance and stability are excellent in the organic solvent and the pore structure of the separation membrane becomes dense, thereby significantly improving the rejection rate of the solute having a number average molecular weight of 100 g/mol or more.
In the method of producing a solvent-resistant nanofiltration separation membrane according to an exemplary embodiment of the present invention, in step (c), the separation membrane is crosslinked by being immersed in the crosslinking solution at 50 to 100°C, preferably 60 to 90°C, and more preferably 75 to 85°C under reflux condition for 1 to 60 hours, preferably 10 to 40 hours, and more preferably 20 to 30 hours, and after the crosslinking reaction, unreacted materials are removed by the polar aprotic solvent. When the crosslinking is performed under the above conditions, the pore structure of the separation membrane becomes denser to improve the rejection rate of the solute having a number average molecular weight of 100 g/mol or more, which is thus preferred.
In the method of producing a solvent-resistant nanofiltration separation membrane according to an exemplary embodiment of the present invention, the crosslinked polybenzimidazole separation membrane may be formed by step (c), and the separation membrane may have an average thickness of 10 to 300 ㎛. The separation membrane may be formed at a thickness of 10 to 300 ㎛, preferably 20 to 200 ㎛ before crosslinking, and after crosslinking, it becomes thicker and may be formed at a thickness of 20 to 500 ㎛, preferably 60 to 400 ㎛, and more preferably 70 to 300 ㎛, excluding the thickness of the porous support. When the separation membrane has a thickness within the above range, it may have high chemical resistance and stability in an organic solvent and the rejection rate of the solute having a number average molecular weight of 100 g/mol or more may be increased.
In step (d) of allowing the post-treatment solvent in which polybenzimidazole is soluble to permeate the separation membrane having the crosslinked selective layer (hereinafter, referred to as a crosslinked separation membrane) to rearrange the crosslinked separation membrane, the post-treatment solvent permeates from one surface to the other surface of the crosslinked separation membrane, not using the method of immersing the crosslinked separation membrane in a reaction bath containing the post-treatment solvent, thereby removing an uncrosslinked selective layer and also rearranging a surface polymer chain of the crosslinked selective layer to uniformly adjust the size and structure of the separation membrane pores. Specifically, when the post-treatment process is performed, the uncrosslinked selective layer is dissolved to improve permeation performance, and the polymer chain of the crosslinked separation membrane is rearranged so that pores become dense to improve rejection performance, which is thus preferred. When step (d) is not performed, the form and structure of the pores of the crosslinked separation membrane are not adjusted uniformly, so that it is difficult to improve both permeation performance and rejection performance, which is thus not preferred.
In the method of producing a solvent-resistant nanofiltration separation membrane according to an exemplary embodiment of the present invention, a method of allowing the solvent to permeate in step (d) may use cross-flow filtration with pressure applied or dead-end filtration. Specifically, the method of solvent permeation in step (d) may be post-treatment solvent permeation under a pressure of 1 to 50 bar, more specifically 10 to 30 bar, using cross-flow filtration, at a flow velocity of 1 to 200 L/g, more specifically 50 to 200 L/g for 10 minutes to 10 hours, more preferably 1 to 6 hours. In addition, a process of washing using pure ethanol and the like may be further included after the post-treatment.
In the method of producing a solvent-resistant nanofiltration separation membrane according to an exemplary embodiment of the present invention, the post-treatment solvent in step (d) may be a good solvent in which polybenzimidazole is soluble. Preferably, the good solvent may be any one or a mixture of two or more selected from the group consisting of toluene, isopropyl alcohol, dimethylformamide, dimethylacetamide, and tetrahydrofuran. When the good solvent is used, an uncrosslinked selective layer is effectively removed to appropriately rearrange the size and structure of the separation membrane pores, thereby improving both permeation performance and rejection performance, which is thus preferred.
Hereinafter, a separation method of a solution using the separation membrane according to the present invention will be described in detail.
The separation method of a solution includes bringing a solution including an organic solvent and a solute having a number average molecular weight of 100 g/mol into contact with a separation membrane, and separating the organic solvent and the solute through the separation membrane, and the separation membrane is the solvent-resistant nanofiltration separation membrane as described above.
The solvent-resistant nanofiltration separation membrane may be used for an organic solvent nanofiltration process, and specifically, the solution may be separated by bringing the organic solvent and the solute having a number average molecular weight of 100 g/mol or more into contact with the separation membrane, using, though is not particularly limited to, cross-flow filtration which is a filtration method of allowing a solution permeating the separation membrane to flow in a vertical direction to a supplied solution. When the solute is separated by the separation method of a solution using the solvent-resistant nanofiltration separation membrane, chemical resistance, stability, and durability of it in the solution are excellent and also the rejection performance of the solute having a number average molecular weight of 100 g/mol or more may be improved, which is thus preferred.
The solvent-resistant nanofiltration separation membrane may be used as a separation membrane for separating a low-molecular weight compound mixed with the organic solvent, and the low-molecular weight compound may have a number average molecular weight of 100 to 1200 g/mol(=Da), 300 to 1000 g/mol, 300 to 600 g/mol, 300 to 500 g/mol, 300 to 450 g/mol, or 300 to 400 g/mol. As a non-limiting example, the low-molecular weight compound may be polypropylene glycol, but is not limited thereto.
In addition, any organic solvent may be used without limitation as long as the solvent is a known organic solvent, and as a non-limiting example, may be one or more selected from the group consisting of methanol, ethanol, isopropyl alcohol, acetone, tetrahydrofuran, dimethylformamide, dichloromethane, toluene, methylethylketone, formaldehyde, diethylformamide, dimethylacetamide, 1-methyl-2-pyrrolidone, dimethyl sulfoxide, diethylether, xylene, benzene, and N,N-dimethylacetamide, and the like.
In the method of producing a solvent-resistant nanofiltration separation membrane according to an exemplary embodiment of the present invention, the solvent-resistant nanofiltration separation membrane (hereinafter, referred to as a separation membrane) may satisfy the following Equation 1:
[Equation 1] (P2/P1) × (R2/R1) ≥ 1.2
wherein P1 is an acetone permeability of a separation membrane before step (d), P2 is an acetone permeability of the separation membrane after step (d), R1 is a rejection rate of the separation membrane for polypropylene glycol (PPG) having a number average molecular weight of 100 to 1200 g/mol before step (d), and R2 is a rejection rate of the separation membrane after step (d) under the same condition.
Equation 1 refers to the product of an acetone permeability improvement multiple of the separation membrane (P2/P1) and a PPG rejection rate improvement multiple of the separation membrane (R2/R1), and the value of the product may be 1.2 or more, preferably 1.5 or more, and more preferably 2 or more. When Equation 1 is satisfied, permeation performance and rejection performance of the separation membrane are very effectively improved, and high efficiency may be expressed when the separation membrane is applied to a nanofiltration system, which is thus preferred.
Specifically, the solvent-resistant nanofiltration separation membrane may satisfy both the following Equations 2 and 3:
[Equation 2] P2/P1 ≥ 1.1
[Equation 3] R2/R1 ≥ 1.01
wherein P1, P2, R1, and R2 are as defined in Equation 1.
Equation 2 refers to a permeability improvement multiple of the separation membrane depending on step (d) and Equation 3 refers to a rejection rate improvement multiple of the separation membrane depending on step (d), and satisfying both Equations 2 and 3 means improving both permeation performance and rejection performance of the separation membrane by performing step (d). The value of P2/P1 in Equation 2 may be 1.1 or more, preferably 1.5 or more, and more specifically 5 or more, The value of R2/R1 in Equation 3 may be 1.01 or more, preferably 1.05 or more, and more specifically 1.1 or more. When both Equations 2 and 3 are satisfied, permeation performance and rejection performance are improved very effectively to provide a nanofiltration system having high efficiency, which is thus preferred.
A solvent-resistant nanofiltration separation membrane produced by the production method according to an exemplary embodiment of the present invention may be provided. The solvent-resistant nanofiltration separation membrane goes through a post-treatment process using a good solvent, so that the separation membrane performance may be effectively improved by rearrangement of an uncrosslinked selective layer, and pore size and structure of the separation membrane. Specifically, the solvent-resistant nanofiltration separation membrane has excellent chemical resistance, and also may improve both permeation performance and rejection performance which conventionally conflict with each other. The solvent-resistant nanofiltration separation membrane produced by the production method of the present invention may be applied to a nanofiltration system to effectively filter solutes having a number average molecular weight of 100 g/mol or more and also provide a system having high efficiency.
The present invention may provide a solvent-resistant nanofiltration separation membrane includes: a porous support layer and a crosslinked benzimidazole selective layer formed on the porous support layer, wherein the solvent-resistant nanofiltration separation membrane satisfies the following Equation 1:
[Equation 1] (P2/P1) × (R2/R1) ≥ 1.2
wherein P1 is a permeability of a separation membrane before post-treatment solvent permeation, P2 is a permeability of the separation membrane after post-treatment solvent permeation, R1 is a rejection rate of the separation membrane for polypropylene glycol having a number average molecular weight of 100 to 1200 g/mol before post-treatment solvent permeation, and R2 is a rejection rate of the separation membrane after post-treatment solvent permeation under the same condition.
[Equation 2] P2/P1 ≥ 1.1
[Equation 3] R2/R1 ≥ 1.01
In addition, detailed description and examples of the porous support, the selective layer, the separation membrane, and the post-treatment solvent are as described in the production method above.
Hereinafter, the present invention will be described in more detail with reference to the Examples and Comparative Examples. However, the following Examples and Comparative Examples are only an example for describing the present invention in more detail, and do not limit the present invention in any way.
[Method of measuring physical properties]
1. Pure solvent permeability (flux) and rejection rate
Pure solvent permeability was measured in a manner of cross-flow filtration, and evaluated under conditions of an effective area of a measured separation membrane of 14.8 cm2, an operation pressure of 15 bar, a temperature of 30°C, and a flow velocity of 100 L/h. Before measuring the pure solvent permeability, stabilization with pure ethanol was performed for 3 hours under the same conditions as the above, and then the experiment was performed.
Thereafter, a pure solvent permeability was measured after 3 hours, 1.6 L of a 1000 ppm solution of polypropylene glycol (PPG) added to an organic solvent (N,N-methylpyrrolidone, N,N-dimethylacetamide, dimethylformamide, acetonitrile, acetone, ethanol, toluene, or hexane) was used to measure the permeability and the rejection rate. As polypropylene glycol, three commercialized products having a number average molecular weight (Mn) of 425 g/mol or less, 700 g/mol or less, and 1000 g/mol or less were used, and used after being prepared to have a selectivity in a wide range of 300 to 1200 g/mol. Each polypropylene glycol was introduced to each organic solvent to prepare a test solution, and 1 hour after permeation, the obtained sample was analyzed by liquid chromatography to calculate the rejection rate.
[Total measurement order]
1. A membrane was stabilized using pure ethanol for 3 hours.
2. Ethanol containing 1000 ppm of polypropylene glycol was used to measure permeability and rejection rate of a separation membrane produced.
3. A post-treatment solvent was used to perform permeation for 4 hours.
4. The post-treatment solvent was removed with pure ethanol.
5. The membrane was stabilized using pure ethanol for 3 hours.
6. Ethanol containing 1000 ppm of polypropylene glycol was used to measure permeability and rejection rate of the post-treated separation membrane.
[Example 1] Production of solvent-resistant nanofiltration separation membrane
(a) Dope solution coating
A solution including 20 wt% of polybenzimidazole (Celazole S26) was prepared using N,N-dimethylacetamide (DMAc), stirred at room temperature for 6 hours, and allowed to stand for 24 hours to defoam a dope solution. The thus-prepared dope solution was coated at a thickness of 200 ㎛ on a polypropylene nonwoven porous support at room temperature.
(b) Production of separation membrane by non-solvent induced phase separation method
The porous support having the dope solution coated was immersed in a water bath containing water at 20°C to induce solidification of polybenzimidazole by interdiffusion of a solvent and a non-solvent to produce a separation membrane having a selective layer formed. Thereafter, the separation membrane produced was immersed in distilled water for 1 hour, and then stored in isopropyl alcohol (IPA).
(c) Crosslinking process
The thus-produced separation membrane was immersed in an acetonitrile solvent to remove isopropyl alcohol. The membrane was immersed in a crosslinking solution of 60 g of an acetonitrile solvent including 0.12 M para-dibromoxylene (DBX) and a crosslinking reaction was performed at 80°C for 24 hours under reflux conditions. Thereafter, unreacted materials were removed with the acetonitrile solvent.
(d) Post-treatment process
The crosslinked separation membrane was installed in a cross-flow filtration system, and the permeability and the rejection rate of the separation membrane in acetone were measured before a post-treatment process. Then, a post-treatment solvent permeated by a filtration process to perform a post-treatment process. The post-treatment solvent used was diethylformamide as described in Table 1, the solvent permeated for 4 hours under the conditions of an effective membrane area of 14.8±0.1 cm2, a temperature of 30±1°C, a pressure of 15±0.1 bar, and a flow velocity of 100±1 L/h. After the post-treatment process, the permeability and the rejection rate of the separation membrane were measured in acetone, and the results are shown in Table 1.
[Examples 2 to 4]
The experiment was performed in the same manner as in Example 1, except that the type of post-treatment solvent was changed as shown in Table 1. The results are shown in Table 1.
[Examples 5 to 7]
A separation membrane was produced in the same manner as in Example 1, except that the post-treatment process was performed for 8 hours and 24 hours as shown in Table 1, and then the permeability and the rejection rate of the separation membrane in ethanol were measured under the same conditions. The results are shown in Table 2.
[Comparative Example 1]
The experiment was performed in the same manner as in Example 1, except that (d) the post-treatment process was not performed, and the results are shown in Table 1.
[Comparative Example 2]
The experiment was performed in the same manner as in Example 1, except that (d) the post-treatment process was performed not by cross-flow filtration but by immersing the membrane in a diethylformamide solvent for 4 hours, and the results are shown in Table 1.
[Comparative Examples 3 to 5]
The experiment was performed in the same manner as in Comparative Example 2, except that (d) the post-treatment process was performed by immersing the membrane for 4 hours, 24 hours, and 168 hours, and the permeability and the rejection rate of the separation membrane were measured in ethanol, not in acetone. The results are shown in Table 2.
The following Table 1 shows the permeability improvement multiple and the rejection rate improvement multiple in the case of performing the post-treatment process in Examples 1 to 4, in comparison with the case in which the post-treatment was not performed as in Comparative Example 1. As a solvent for permeability/rejection rate measurement, acetone was used.
| Post-treatment process | Acetone permeability improvement multiple |
PPG rejection rate improvement multiple |
||
| Post-treatment solvent | Treatment method/time | |||
| Comparative Example 1 | - | - | 1.0 | 1.0 |
| Comparative Example 2 | Dimethylformamide | Immersion/4 hours | 1.01 | 1.00 |
| Example 1 | Dimethylformamide | Permeation/4 hours | 6.99 | 1.21 |
| Example 2 | Dimethylacetamide | Permeation/4 hours | 6.34 | 1.20 |
| Example 3 | Toluene | Permeation/4 hours | 1.53 | 1.08 |
| Example 4 | Isopropyl alcohol | Permeation/4 hours | 1.97 | 1.02 |
The following Table 2 shows the permeability improvement multiple and the rejection rate improvement multiple in the case of performing the post-treatment process in Examples 5 to 7 and Comparative Examples 3 to 5, in comparison with the case in which the post-treatment was not performed as in Comparative 1. As a solvent for permeability/rejection rate measurement, ethanol was used.
| Post-treatment process | Ethanol permeability improvement multiple |
PPG rejection rate improvement multiple |
||
| Post-treatment solvent | Treatment method/time | |||
| Comparative Example 1 | - | - | 1.0 | 1.0 |
| Example 5 | Dimethylformamide | Permeation/4 hours | 1.20 | 1.10 |
| Example 6 | Dimethylformamide | Permeation/8 hours | 1.22 | 1.10 |
| Example 7 | Dimethylformamide | Permeation/24 hours | 1.22 | 1.10 |
| Comparative Example 3 | Dimethylformamide | Immersion/4 hours | 1.00 | 1.01 |
| Comparative Example 4 | Dimethylformamide | Immersion/24 hours | 1.01 | 1.00 |
| Comparative Example 5 | Dimethylformamide | Immersion/168 hours | 1.09 | 1.07 |
As seen in Table 1, in Examples 1 to 4 in which the post-treatment process in a permeation manner was performed to produce the nanofiltration separation membrane, significantly excellent permeation performance and rejection performance were shown, in comparison with Comparative Example 1 in which the post-treatment process was not performed and Comparative Example 2 in which the post-treatment process was performed in an immersion manner, and thus, the excellent performance of the solvent-resistant nanofiltration separation membrane according to the present invention was confirmed. In addition, in Example 1 in which dimethylformamide was used as the post-treatment solvent, better effects were shown than other Examples, and considering that Example 5 using ethanol also showed excellent separation membrane performance, it is confirmed that when the nanofiltration separation membrane is produced by including the post-treatment process in a permeation manner, better separation membrane performance may be expressed.
FIG. 1 shows a change in a molecular weight cut-off (MWCO) before crosslinking, after crosslinking, and after a post-treatment process in Example 1. As seen in FIG. 1, the rejection rate of the separation membrane after crosslinking (indicated as "after Xlink") was improved as compared with the separation membrane before crosslinking (indicated as "before Xlink"), and the rejection rate was further improved after post-treatment (indicated as "after treatment").
Hereinabove, although the present invention has been described by specified matters and specific exemplary embodiments, they have been provided only for assisting in the entire understanding of the present invention. Therefore, the present invention is not by the specific matters limited to the exemplary embodiments. Various modifications and changes may be made by those skilled in the art to which the present invention pertains from this description.
Therefore, the spirit of the present invention should not be limited to the above-described exemplary embodiments, and the following claims as well as all modified equally or equivalently to the claims are intended to fall within the scope and spirit of the invention.
Claims (14)
- A method of producing a solvent-resistant nanofiltration separation membrane, the method comprising:(a) coating a polybenzimidazole dope solution on a porous support;(b) immersing the porous support coated with the dope solution in water to produce a separation membrane having a selective layer formed by solidification by interdiffusion of a solvent and a non-solvent;(c) immersing the separation membrane having a selective layer formed in a crosslinking solution to perform crosslinking; and(d) allowing a post-treatment solvent in which polybenzimidazole is soluble to permeate the separation membrane having a crosslinked selective layer to rearrange the crosslinked separation membrane.
- The method of producing a solvent-resistant nanofiltration separation membrane of claim 1, wherein the allowing of the solvent to permeate in (d) uses cross-flow filtration with pressure applied or dead-end filtration.
- The method of producing a solvent-resistant nanofiltration separation membrane of claim 2, wherein the allowing of the solvent to permeate in (d) is to allow the post-treatment solvent to permeate at a flow velocity of 1 to 200 L/h using cross-flow filtration under a pressure of 1 to 50 bar for 10 minutes to 10 hours.
- The method of producing a solvent-resistant nanofiltration separation membrane of claim 1, wherein the crosslinking solution in (c) includes a compound represented by the following Chemical Formula 1:[Chemical Formula 1]
Wherein two or more of R1 to R4 are C1-10 alkyl halide, and the rest is hydrogen. - The method of producing a solvent-resistant nanofiltration separation membrane of claim 1, wherein the post-treatment solvent in (d) is a good solvent in which polybenzimidazole is soluble.
- The method of producing a solvent-resistant nanofiltration separation membrane of claim 5, wherein the good solvent is any one or a mixture of two or more selected from the group consisting of toluene, isopropyl alcohol, dimethylformamide, dimethylacetamide, and tetrahydrofuran.
- The method of producing a solvent-resistant nanofiltration separation membrane of claim 1, wherein the separation membrane in (c) has an average thickness of 10 to 300 ㎛.
- The method of producing a solvent-resistant nanofiltration separation membrane of claim 1, wherein the solvent-resistant nanofiltration separation membrane is a separation membrane for separating a low-molecular weight compound having a number average molecular weight of 100 to 1200 g/mol which is mixed with a solvent.
- The method of producing a solvent-resistant nanofiltration separation membrane of claim 1, wherein the solvent-resistant nanofiltration separation membrane satisfies the following Equation 1:[Equation 1] (P2/P1) × (R2/R1) ≥ 1.2wherein P1 is an acetone permeability of a separation membrane before step (d), P2 is an acetone permeability of the separation membrane after step (d), R1 is a rejection rate of the separation membrane for polypropylene glycol having a number average molecular weight of 100 to 1200 g/mol before step (d), and R2 is a rejection rate of the separation membrane after step (d) under the same condition.
- A solvent-resistant nanofiltration separation membrane produced by the production method of any one of claims 1 to 9.
- A solvent-resistant nanofiltration separation membrane comprising: a porous support layer and a crosslinked benzimidazole selective layer formed on the porous support layer, wherein the solvent-resistant nanofiltration separation membrane satisfies the following Equation 1:[Equation 1] (P2/P1) × (R2/R1) ≥ 1.2wherein P1 is a permeability of a separation membrane before post-treatment solvent permeation, P2 is a permeability of the separation membrane after post-treatment solvent permeation, R1 is a rejection rate of the separation membrane for polypropylene glycol having a number average molecular weight of 100 to 1200 g/mol before post-treatment solvent permeation, and R2 is a rejection rate of the separation membrane after post-treatment solvent permeation under the same condition.
- The solvent-resistant nanofiltration separation membrane of claim 11,wherein the post-treatment solvent is a good solvent in which polybenzimidazole is soluble, and the good solvent is any one or a mixture of two or more selected from the group consisting of toluene, isopropyl alcohol, dimethylformamide, dimethylacetamide, and tetrahydrofuran.
- The solvent-resistant nanofiltration separation membrane of claim 11, wherein the solvent-resistant nanofiltration separation membrane has an average thickness of 20 to 500 ㎛.
- The solvent-resistant nanofiltration separation membrane of claim 11, wherein the solvent-resistant nanofiltration separation membrane satisfies both the following Equations 2 and 3:[Equation 2] P2/P1 ≥ 1.1[Equation 3] R2/R1 ≥ 1.01wherein P1, P2, R1, and R2 are as defined in Equation 1.
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| US20160375410A1 (en) * | 2015-06-23 | 2016-12-29 | Los Alamos National Security, Llc | Polybenzimidazole hollow fiber membranes and method for making an asymmetric hollow fiber membrane |
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| KR20140031627A (en) * | 2012-09-05 | 2014-03-13 | 주식회사 그린앤텍 | A manufacturing method of polysulfone membrane improved internal pressure stability |
| US20160375410A1 (en) * | 2015-06-23 | 2016-12-29 | Los Alamos National Security, Llc | Polybenzimidazole hollow fiber membranes and method for making an asymmetric hollow fiber membrane |
| US20190176092A1 (en) * | 2016-06-06 | 2019-06-13 | Imperial Innovations Limited | Process for the production of solvent stable polymeric membranes |
| WO2019171276A1 (en) * | 2018-03-05 | 2019-09-12 | King Abdullah University Of Science And Technology | Green membranes for organic solvent nanofiltration and pervaporation |
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