CN114828992B - Separation membrane and method for producing same - Google Patents
Separation membrane and method for producing same Download PDFInfo
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- CN114828992B CN114828992B CN202080089607.5A CN202080089607A CN114828992B CN 114828992 B CN114828992 B CN 114828992B CN 202080089607 A CN202080089607 A CN 202080089607A CN 114828992 B CN114828992 B CN 114828992B
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- 239000012528 membrane Substances 0.000 title claims abstract description 189
- 238000000926 separation method Methods 0.000 title claims abstract description 155
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- 239000003795 chemical substances by application Substances 0.000 claims description 45
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims description 40
- 239000011342 resin composition Substances 0.000 claims description 30
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- QTBSBXVTEAMEQO-UHFFFAOYSA-N Acetic acid Chemical compound CC(O)=O QTBSBXVTEAMEQO-UHFFFAOYSA-N 0.000 description 15
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- WYURNTSHIVDZCO-UHFFFAOYSA-N Tetrahydrofuran Chemical compound C1CCOC1 WYURNTSHIVDZCO-UHFFFAOYSA-N 0.000 description 8
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- YLQBMQCUIZJEEH-UHFFFAOYSA-N tetrahydrofuran Natural products C=1C=COC=1 YLQBMQCUIZJEEH-UHFFFAOYSA-N 0.000 description 3
- YEJRWHAVMIAJKC-UHFFFAOYSA-N 4-Butyrolactone Chemical compound O=C1CCCO1 YEJRWHAVMIAJKC-UHFFFAOYSA-N 0.000 description 2
- ZAMOUSCENKQFHK-UHFFFAOYSA-N Chlorine atom Chemical compound [Cl] ZAMOUSCENKQFHK-UHFFFAOYSA-N 0.000 description 2
- IAZDPXIOMUYVGZ-UHFFFAOYSA-N Dimethylsulphoxide Chemical compound CS(C)=O IAZDPXIOMUYVGZ-UHFFFAOYSA-N 0.000 description 2
- PEDCQBHIVMGVHV-UHFFFAOYSA-N Glycerol Natural products OCC(O)CO PEDCQBHIVMGVHV-UHFFFAOYSA-N 0.000 description 2
- CDBYLPFSWZWCQE-UHFFFAOYSA-L Sodium Carbonate Chemical compound [Na+].[Na+].[O-]C([O-])=O CDBYLPFSWZWCQE-UHFFFAOYSA-L 0.000 description 2
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- KRKNYBCHXYNGOX-UHFFFAOYSA-N citric acid Natural products OC(=O)CC(O)(C(O)=O)CC(O)=O KRKNYBCHXYNGOX-UHFFFAOYSA-N 0.000 description 2
- XBDQKXXYIPTUBI-UHFFFAOYSA-N dimethylselenoniopropionate Natural products CCC(O)=O XBDQKXXYIPTUBI-UHFFFAOYSA-N 0.000 description 2
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- SSADPHQCUURWSW-UHFFFAOYSA-N 3,9-bis(2,6-ditert-butyl-4-methylphenoxy)-2,4,8,10-tetraoxa-3,9-diphosphaspiro[5.5]undecane Chemical compound CC(C)(C)C1=CC(C)=CC(C(C)(C)C)=C1OP1OCC2(COP(OC=3C(=CC(C)=CC=3C(C)(C)C)C(C)(C)C)OC2)CO1 SSADPHQCUURWSW-UHFFFAOYSA-N 0.000 description 1
- 238000012935 Averaging Methods 0.000 description 1
- CURLTUGMZLYLDI-UHFFFAOYSA-N Carbon dioxide Chemical compound O=C=O CURLTUGMZLYLDI-UHFFFAOYSA-N 0.000 description 1
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- 239000004970 Chain extender Substances 0.000 description 1
- 229920000742 Cotton Polymers 0.000 description 1
- LFQSCWFLJHTTHZ-UHFFFAOYSA-N Ethanol Chemical compound CCO LFQSCWFLJHTTHZ-UHFFFAOYSA-N 0.000 description 1
- UFHFLCQGNIYNRP-UHFFFAOYSA-N Hydrogen Chemical compound [H][H] UFHFLCQGNIYNRP-UHFFFAOYSA-N 0.000 description 1
- FDBMBOYIVUGUSL-UHFFFAOYSA-N OP(O)OP(O)O.C(C)(C)(C)C1=C(C(=CC(=C1)C)C(C)(C)C)C(O)(C(CO)(CO)CO)C1=C(C=C(C=C1C(C)(C)C)C)C(C)(C)C Chemical compound OP(O)OP(O)O.C(C)(C)(C)C1=C(C(=CC(=C1)C)C(C)(C)C)C(O)(C(CO)(CO)CO)C1=C(C=C(C=C1C(C)(C)C)C)C(C)(C)C FDBMBOYIVUGUSL-UHFFFAOYSA-N 0.000 description 1
- OAICVXFJPJFONN-UHFFFAOYSA-N Phosphorus Chemical group [P] OAICVXFJPJFONN-UHFFFAOYSA-N 0.000 description 1
- 239000004695 Polyether sulfone Substances 0.000 description 1
- 239000004372 Polyvinyl alcohol Substances 0.000 description 1
- XBDQKXXYIPTUBI-UHFFFAOYSA-M Propionate Chemical compound CCC([O-])=O XBDQKXXYIPTUBI-UHFFFAOYSA-M 0.000 description 1
- XTXRWKRVRITETP-UHFFFAOYSA-N Vinyl acetate Chemical compound CC(=O)OC=C XTXRWKRVRITETP-UHFFFAOYSA-N 0.000 description 1
- NNLVGZFZQQXQNW-ADJNRHBOSA-N [(2r,3r,4s,5r,6s)-4,5-diacetyloxy-3-[(2s,3r,4s,5r,6r)-3,4,5-triacetyloxy-6-(acetyloxymethyl)oxan-2-yl]oxy-6-[(2r,3r,4s,5r,6s)-4,5,6-triacetyloxy-2-(acetyloxymethyl)oxan-3-yl]oxyoxan-2-yl]methyl acetate Chemical compound O([C@@H]1O[C@@H]([C@H]([C@H](OC(C)=O)[C@H]1OC(C)=O)O[C@H]1[C@@H]([C@@H](OC(C)=O)[C@H](OC(C)=O)[C@@H](COC(C)=O)O1)OC(C)=O)COC(=O)C)[C@@H]1[C@@H](COC(C)=O)O[C@@H](OC(C)=O)[C@H](OC(C)=O)[C@H]1OC(C)=O NNLVGZFZQQXQNW-ADJNRHBOSA-N 0.000 description 1
- 238000010521 absorption reaction Methods 0.000 description 1
- KXKVLQRXCPHEJC-UHFFFAOYSA-N acetic acid trimethyl ester Natural products COC(C)=O KXKVLQRXCPHEJC-UHFFFAOYSA-N 0.000 description 1
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- XNGIFLGASWRNHJ-UHFFFAOYSA-N phthalic acid Chemical class OC(=O)C1=CC=CC=C1C(O)=O XNGIFLGASWRNHJ-UHFFFAOYSA-N 0.000 description 1
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- WYVAMUWZEOHJOQ-UHFFFAOYSA-N propionic anhydride Chemical compound CCC(=O)OC(=O)CC WYVAMUWZEOHJOQ-UHFFFAOYSA-N 0.000 description 1
- IUVKMZGDUIUOCP-BTNSXGMBSA-N quinbolone Chemical compound O([C@H]1CC[C@H]2[C@H]3[C@@H]([C@]4(C=CC(=O)C=C4CC3)C)CC[C@@]21C)C1=CCCC1 IUVKMZGDUIUOCP-BTNSXGMBSA-N 0.000 description 1
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Classifications
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D71/00—Semi-permeable membranes for separation processes or apparatus characterised by the material; Manufacturing processes specially adapted therefor
- B01D71/06—Organic material
- B01D71/08—Polysaccharides
- B01D71/12—Cellulose derivatives
- B01D71/14—Esters of organic acids
-
- 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
- B01D67/002—Organic membrane manufacture from melts
-
- 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
- B01D67/0081—After-treatment of organic or inorganic membranes
- B01D67/0088—Physical treatment with compounds, e.g. swelling, coating or impregnation
-
- 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
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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
- B01D69/02—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
- 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
- B01D69/08—Hollow fibre membranes
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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
- B01D69/08—Hollow fibre membranes
- B01D69/087—Details relating to the spinning process
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D71/00—Semi-permeable membranes for separation processes or apparatus characterised by the material; Manufacturing processes specially adapted therefor
- B01D71/06—Organic material
- B01D71/08—Polysaccharides
- B01D71/12—Cellulose derivatives
- B01D71/14—Esters of organic acids
- B01D71/18—Mixed esters, e.g. cellulose acetate-butyrate
-
- D—TEXTILES; PAPER
- D01—NATURAL OR MAN-MADE THREADS OR FIBRES; SPINNING
- D01F—CHEMICAL FEATURES IN THE MANUFACTURE OF ARTIFICIAL FILAMENTS, THREADS, FIBRES, BRISTLES OR RIBBONS; APPARATUS SPECIALLY ADAPTED FOR THE MANUFACTURE OF CARBON FILAMENTS
- D01F2/00—Monocomponent artificial filaments or the like of cellulose or cellulose derivatives; Manufacture thereof
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- D—TEXTILES; PAPER
- D01—NATURAL OR MAN-MADE THREADS OR FIBRES; SPINNING
- D01F—CHEMICAL FEATURES IN THE MANUFACTURE OF ARTIFICIAL FILAMENTS, THREADS, FIBRES, BRISTLES OR RIBBONS; APPARATUS SPECIALLY ADAPTED FOR THE MANUFACTURE OF CARBON FILAMENTS
- D01F2/00—Monocomponent artificial filaments or the like of cellulose or cellulose derivatives; Manufacture thereof
- D01F2/24—Monocomponent artificial filaments or the like of cellulose or cellulose derivatives; Manufacture thereof from cellulose derivatives
- D01F2/28—Monocomponent artificial filaments or the like of cellulose or cellulose derivatives; Manufacture thereof from cellulose derivatives from organic cellulose esters or ethers, e.g. cellulose acetate
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D2323/00—Details relating to membrane preparation
- B01D2323/08—Specific temperatures applied
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D2323/00—Details relating to membrane preparation
- B01D2323/12—Specific ratios of components used
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D2323/00—Details relating to membrane preparation
- B01D2323/15—Use of additives
- B01D2323/18—Pore-control agents or pore formers
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D2325/00—Details relating to properties of membranes
- B01D2325/02—Details relating to pores or porosity of the membranes
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D2325/00—Details relating to properties of membranes
- B01D2325/02—Details relating to pores or porosity of the membranes
- B01D2325/0283—Pore size
- B01D2325/02833—Pore size more than 10 and up to 100 nm
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D2325/00—Details relating to properties of membranes
- B01D2325/02—Details relating to pores or porosity of the membranes
- B01D2325/0283—Pore size
- B01D2325/02834—Pore size more than 0.1 and up to 1 µm
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D2325/00—Details relating to properties of membranes
- B01D2325/04—Characteristic thickness
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D2325/00—Details relating to properties of membranes
- B01D2325/20—Specific permeability or cut-off range
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- Separation Using Semi-Permeable Membranes (AREA)
Abstract
The present invention provides a separation membrane comprising a cellulose ester, wherein the separation membrane has a plurality of pores in a cross section of the membrane parallel to the longitudinal direction and the film thickness direction, the average depth D of the plurality of pores is 0.7 to 20 [ mu ] m, the average length L of the plurality of pores is 3 [ mu ] m or more, and the average value (L/D) a of the ratio of the length L to the depth D of each pore is 2 to 40.
Description
Technical Field
The present invention relates to a separation membrane and a method for producing the same.
Background
In recent years, separation membranes have been used in various fields such as water treatment membranes for water purification, drainage, and the like, medical membranes for blood purification, membranes for food industry, separators for batteries, and electrolyte membranes for electric charge membranes or fuel cells.
Most separation membranes use polymers as raw materials. Among them, cellulose resins such as cellulose esters have permeability due to their hydrophilicity and chlorine resistance of chlorine-based bactericides, and are therefore widely used as raw materials for separation membranes such as water treatment membranes.
For example, patent document 1 discloses a technique of obtaining a hollow-fiber separation membrane by ejecting a film-forming raw liquid containing cellulose triacetate into a coagulation liquid containing a solvent, a non-solvent, and water, and performing phase separation.
Patent document 2 discloses a hollow-fiber separation membrane in which hydroxyalkyl cellulose is solidified in a particulate state on the surface.
Prior art literature
Patent literature
Patent document 1: japanese patent laid-open publication No. 2011-235204
Patent document 2: japanese patent application laid-open No. 2015-157278
Non-patent literature
Non-patent document 1: ind. Eng. Chem. Res.2011,50,3798-3817.
Disclosure of Invention
Problems to be solved by the invention
However, in the conventional separation membrane using cellulose ester as a raw material, since the size of the pores is reduced in order to improve the separation performance, the thickness of the membrane needs to be reduced in order to improve the permeation performance, and as a result, there is a problem that defects are likely to occur in the separation membrane.
Accordingly, an object of the present invention is to provide a separation membrane having both high separation performance and permeation performance, and a method for producing the same.
Means for solving the problems
As a result of intensive studies to solve the above problems, the present inventors have found that a separation membrane containing a cellulose ester has pores satisfying specific conditions, and can improve the permeation performance while maintaining high separation performance, thereby completing the present invention.
Namely, the present invention relates to the following [1] to [10].
[1] A separation membrane comprising a cellulose ester,
The separation membrane has a plurality of pores in a cross section of the membrane parallel to the longitudinal direction and the film thickness direction,
The average depth D of the plurality of pores is 0.7-20 μm,
The average length L of the pores is 3 μm or more and
The average value (l/d) a of the ratio of the length l to the depth d of each pore is 2 to 40.
[2] The separation membrane according to the above [1], wherein the occupancy rate of the plurality of pores in the cross section is 15 to 55%.
[3] The separation membrane according to the above [1] or [2], wherein the average thickness of the wall portion in the cross section is 0.7 to 5.0. Mu.m.
[4] The separation membrane according to any one of the above [1] to [3], wherein in at least one surface, the average pore diameter of the surface pores is 0.050 to 0.500. Mu.m.
[5] The separation membrane according to any one of the above [1] to [4], wherein in at least one surface, the average minor diameter X of the surface pores is 0.030 to 0.250 μm, the average major diameter Y of the surface pores is 0.060 to 0.450 μm, and the average value (Y/X) a of the ratio of the major diameter to the minor diameter is 1.00 to 1.50.
[6] The separation membrane according to any one of [1] to [5], wherein the longitudinal direction of the plurality of pores is along the longitudinal direction of the separation membrane.
[7] The separation membrane according to any one of the above [1] to [6], wherein the cellulose ester contains cellulose acetate propionate and/or cellulose acetate butyrate.
[8] The separation membrane according to any one of the above [1] to [7], which is in the shape of hollow filaments.
[9] A method for producing a separation membrane, comprising:
(1) A preparation step of melt-kneading a mixture containing 10 to 80 mass% of cellulose ester, 10 to 80 mass% of a structure-forming agent, and 2 to 20 mass% of a pore-forming agent to obtain a resin composition;
(2) A molding step of ejecting the resin composition from a nozzle using a filter having a pore diameter of 40 to 200 [ mu ] m, and obtaining a resin molded article at a draft ratio of 30 to 200; and
(3) And an impregnation step of immersing the resin molded product in a solvent having a solubility parameter distance D S from 10 to 25 relative to the cellulose ester.
[10] The method for producing a separation membrane according to the above [9], wherein the temperature of the resin molded product in the impregnation step is 50 to 80 ℃.
ADVANTAGEOUS EFFECTS OF INVENTION
According to the present invention, a separation membrane having both high separation performance and permeation performance and a method for producing the same can be provided.
Drawings
Fig. 1 (a) is a drawing schematically showing a cross section Z and an internal structure of the separation membrane, (b) is a side view of (a), and (c) is a top view of (a).
Fig. 2 is an example of an image of a cross section Z photographed by SEM.
Fig. 3 is an image of the noise-removed, binarized, and aperture-extracted image of fig. 2.
Fig. 4 is an image of the outline of the aperture further extracted from the image of fig. 3.
Detailed Description
The separation membrane of the present invention comprises a cellulose ester, and is characterized in that the membrane has a plurality of pores in a cross section parallel to the longitudinal direction and the film thickness direction, the average depth D of the plurality of pores is 0.7-20 [ mu ] m, the average length L of the plurality of pores is 3[ mu ] m or more, and the average value (L/D) a of the ratio of the length L to the depth D of each pore is 2-40. In the present specification, the mass-based ratio (percentage, part, etc.) is the same as the weight-based ratio (percentage, part, etc.).
(Resin composition constituting separation Membrane)
The resin composition constituting the separation membrane of the present invention contains cellulose esters shown in the following (1). Besides (1), the composition shown in the following (2) to (6) may be contained.
(1) Cellulose esters
The separation membrane of the present invention needs to contain cellulose ester. In order to further enhance the effect of the present invention, the separation membrane of the present invention preferably contains cellulose ester as a main component. The main component referred to herein means that the largest component is contained in the total components of the resin composition constituting the separation membrane on a mass basis.
Examples of the cellulose ester include cellulose esters such as cellulose acetate, cellulose propionate and cellulose butyrate, and cellulose mixed esters such as cellulose acetate propionate and cellulose acetate butyrate. Among them, from the viewpoints of processability of the resin molded product and film strength of the obtained separation film, cellulose mixed ester is preferable, cellulose acetate propionate and/or cellulose acetate butyrate are more preferable, and cellulose acetate propionate is further preferable. The cellulose acetate propionate herein refers to a cellulose ester having an average substitution degree of acetyl groups and propionyl groups of 0.1 or more, respectively.
The weight average molecular weight (Mw) of the cellulose ester is preferably 5 to 25 tens of thousands. The weight average molecular weight (Mw) is 5 ten thousand or more, whereby thermal decomposition of cellulose ester at the time of melting is suppressed at the time of producing the separation membrane, and the membrane strength of the separation membrane can be easily brought to a practical level. Since the weight average molecular weight (Mw) is 25 ten thousand or less, the melt viscosity is not excessively high, and thus stable melt film formation can be performed. The weight average molecular weight (Mw) is a value calculated by GPC (gel permeation chromatography). The calculation method is described in detail in examples.
Each of the exemplified cellulose mixed esters has an acetyl group and other acyl groups (propionyl group, butyryl group, etc.). In the cellulose mixed ester contained in the separation membrane, the average substitution degree of the acetyl group and other acyl groups preferably satisfies the following formula.
1.0.Ltoreq.3.0 (average degree of substitution of acetyl+average degree of substitution of other acyl groups)
The average degree of substitution of acetyl groups is more than or equal to 0.1 and less than or equal to 2.6
The average substitution degree of other acyl groups is less than or equal to 0.1 and less than or equal to 2.6.
By satisfying the above formula, the permeability of the separation membrane and the thermal fluidity when the resin composition constituting the separation membrane is melted are improved. The average substitution degree refers to the number of chemically bonded acyl groups (acetyl group+other acyl groups) among 3 hydroxyl groups present in each glucose unit of cellulose.
The separation membrane may contain only 1 cellulose ester or may contain 2 or more cellulose esters.
The content of the cellulose ester in the separation membrane is preferably 70 to 100% by mass, more preferably 80 to 100% by mass, and even more preferably 90 to 100% by mass, based on 100% by mass of the total components of the separation membrane. The content of the cellulose ester in the separation membrane is 70 mass% or more, whereby the membrane strength of the separation membrane becomes sufficient.
The content of the cellulose ester in the raw material for producing the separation membrane is preferably 10 to 80 mass% based on 100 mass% of the entire components constituting the raw material. When the content is 10 mass% or more, the membrane strength of the separation membrane becomes good. On the other hand, the content of 80 mass% or less improves the thermoplastic properties and the permeation performance of the separation membrane. The content is more preferably 15% by mass or more, and still more preferably 20% by mass or more. The content is more preferably 70% by mass or less, still more preferably 60% by mass or less, and particularly preferably 45% by mass or less.
(2) Plasticizer for cellulose esters
The resin composition constituting the separation membrane of the present invention may contain a plasticizer of cellulose ester.
The plasticizer for cellulose esters is not particularly limited as long as it is a compound that thermally plasticizes cellulose esters. In addition, only 1 plasticizer may be used, or 2 or more plasticizers may be used in combination.
Examples of the plasticizer for the cellulose ester include polyalkylene glycol compounds such as polyethylene glycol and polyethylene glycol fatty acid esters, glycerol compounds such as glycerol fatty acid esters and diglycerol fatty acid esters, citric acid ester compounds, phosphoric acid ester compounds, fatty acid ester compounds such as adipic acid esters, caprolactone compounds, derivatives thereof, and the like.
Examples of the polyalkylene glycol compound include polyethylene glycol, polypropylene glycol, polytetramethylene glycol, and the like having a weight average molecular weight (Mw) of 400 to 4,000.
The plasticizer of the cellulose ester may remain in the separation membrane after the separation membrane is formed, or may be eluted from the separation membrane. The content of the plasticizer of the cellulose ester is preferably 5 to 40 mass% based on 100 mass% of the entire components constituting the raw material.
When the content is 5 mass% or more, the thermoplastic properties of the cellulose ester are improved. On the other hand, when the content is 40 mass% or less, the membrane strength of the separation membrane becomes good. The content of the plasticizer of the cellulose ester is more preferably 5 to 35% by mass, still more preferably 5 to 30% by mass.
(3) Antioxidant agent
The resin composition constituting the separation membrane of the present invention preferably contains an antioxidant. When the resin composition contains an antioxidant, thermal decomposition of the polymer during melting is suppressed during production of the separation membrane, and as a result, the membrane strength of the obtained separation membrane is improved, and coloring of the separation membrane is suppressed.
The antioxidant is preferably a phosphorus-based antioxidant, and more preferably a pentaerythritol-based compound. Examples of the pentaerythritol compound include bis (2, 6-di-t-butyl-4-methylphenyl) pentaerythritol diphosphite and the like.
The content of the antioxidant is preferably 0.005 to 0.500 mass% based on 100 mass% of the entire components constituting the raw material. By having the content of the antioxidant in the above range, a uniform resin composition can be obtained in the compounding step.
(4) Structure forming agent
The resin composition constituting the separation membrane of the present invention may contain a structure-forming agent.
The structure-forming agent in the present invention is not particularly limited as long as it is partially compatible with the cellulose ester or the mixture of the cellulose ester and the plasticizer thereof, and can be dissolved or decomposed by a solvent in which the cellulose ester is not dissolved. The weight average molecular weight of the structure-forming agent is preferably 1000 or more from the viewpoint of appropriately controlling the value of L, D (l/d) a described later.
Partially compatible means that more than 2 species are fully compatible under one condition, but phase separate under another condition. The structure-forming agent is a substance which is separated from the cellulose ester by contact with a solvent satisfying specific conditions in an impregnation step described later. Specific conditions are described below.
The structure-forming agent in the present invention is preferably a hydrophilic compound from the viewpoint of easy elution. The hydrophilic compound is a compound that dissolves in water or has a contact angle with water smaller than that of cellulose ester contained in the separation membrane. Among the hydrophilic compounds, compounds dissolved in water are particularly preferable from the viewpoint of being easily eluted.
Examples of the structure-forming agent include a copolymer based on PVP such as polyvinylpyrrolidone (hereinafter referred to as "PVP"), PVP/vinyl acetate copolymer, PVP/methyl methacrylate copolymer, polyvinyl alcohol, and a polyester compound.
When PVP is used as the structure forming agent, it is difficult to dissolve out of the separation membrane if thermal crosslinking occurs, so that the weight average molecular weight (Mw) is preferably 2 ten thousand or less from the standpoint that intermolecular crosslinking is difficult to proceed and that dissolution is possible even if crosslinking. Furthermore, the use of a copolymer based on PVP as described above is also preferred in terms of suppressing thermal crosslinking.
In the steps subsequent to the impregnation step described later, at least a part of the structure-forming agent is eluted, whereby the trace of detachment (elution) of the structure-forming agent becomes pores in the film, and as a result, the permeability is improved.
The content of the structure-forming agent is preferably 10 to 80 mass% based on 100 mass% of the entire components constituting the raw material.
The content is 10 mass% or more, whereby the permeation performance of the separation membrane becomes good. On the other hand, the content is 80 mass% or less, whereby the film strength becomes good. The content of the structure-forming agent is more preferably 20 mass% or more, and still more preferably 25 mass% or more. The content of the structure-forming agent is more preferably 75 mass% or less, and still more preferably 70 mass% or less.
(5) Pore former
The resin composition constituting the separation membrane of the present invention may contain a pore former. The pore former herein refers to a compound that is incompatible with cellulose esters and plasticizes or melts by heat. By eluting the pore former incompatible with the cellulose ester, pores are formed at the sites where the pore former is present. Further, by plasticizing or melting the pore forming agent by heat, the average value (l/d) a of the ratio of the length l to the depth d of each pore formed can be increased.
Examples of the pore former include phthalate compounds, trimellitate compounds, polyalkylene glycol compounds such as polyethylene glycol, polypropylene glycol, and polytetramethylene glycol, and derivatives of these compounds. The weight average molecular weight (Mw) of these compounds is preferably 10 to 100 tens of thousands. Since the pore former exhibits moderate tackiness upon heating and the value L, D (l/d) a to be described later is easily controlled, the pore former preferably has a weight average molecular weight (Mw) of 10 to 100 tens of thousands, more preferably 10 to 50 tens of thousands, particularly preferably 10 to 30 tens of thousands.
The content of the pore former is preferably 2 to 20 mass% based on 100 mass% of the entire component constituting the raw material. The content is 2 mass% or more, whereby the permeation performance of the separation membrane becomes good. On the other hand, the content is 20 mass% or less, whereby the separation performance becomes good. The content of the pore former is more preferably 3% by mass or more, still more preferably 5% by mass or more, and particularly preferably 10% by mass or more. The content is more preferably 18% by mass or less, and still more preferably 15% by mass or less.
(6) Additive agent
The resin composition constituting the separation membrane of the present invention may contain additives other than those described in (2) to (5) within a range that does not impair the effects of the present invention.
Examples of the additives include resins such as cellulose ether, polyacrylonitrile, polyolefin, polyvinyl, polycarbonate, poly (meth) acrylate, polysulfone, and polyether sulfone, organic lubricants, crystallization nucleating agents, organic particles, inorganic particles, blocking agents, chain extenders, ultraviolet absorbers, infrared absorbers, coloring resists, matting agents, antibacterial agents, antistatic agents, deodorizing agents, flame retardants, weather-proofing agents, antistatic agents, antioxidants, ion exchangers, antifoaming agents, coloring pigments, fluorescent brighteners, and dyes.
(Shape of separation Membrane)
The shape of the separation membrane of the present invention is not particularly limited, and a separation membrane having a hollow fiber shape (hereinafter referred to as a "hollow fiber membrane") or a membrane having a planar shape (hereinafter referred to as a "flat membrane") is preferably used. Among these, hollow fiber membranes are more preferable because they can be efficiently filled in the module and the effective membrane area per unit volume of the module can be increased.
The thickness of the separation membrane is preferably 10 to 500 μm from the viewpoint of both the permeation performance and the membrane strength. The thickness is more preferably 30 μm or more, and still more preferably 50 μm or more. The thickness is more preferably 400 μm or less, and still more preferably 300 μm or less.
In the case of the hollow fiber membrane, the outer diameter of the hollow fiber membrane is preferably 50 to 2500 μm from the viewpoint of both the effective membrane area and the membrane strength at the time of filling in the module. The external shape of the hollow fiber membrane is more preferably 100 μm or more, still more preferably 200 μm or more, particularly preferably 300 μm or more. The external shape is more preferably 2000 μm or less, still more preferably 1500 μm or less, particularly preferably 1000 μm or less.
In the case of the hollow fiber membrane, the hollow fiber preferably has a hollow ratio of 15 to 70% in terms of the relationship between the pressure loss of the fluid flowing through the hollow portion and the buckling pressure. The hollow ratio is more preferably 20% or more, and still more preferably 25% or more. The hollow ratio is more preferably 65% or less, and still more preferably 60% or less.
The method for setting the outer diameter and the hollow percentage of the hollow fiber in the hollow fiber membrane to the above ranges is not particularly limited, and the method may be adjusted by appropriately changing the shape of the discharge hole of the spinning nozzle for producing the hollow fiber or the draft ratio calculated at the winding speed and the discharge speed.
(Cross-sectional Structure of separation Membrane)
The separation membrane of the present invention has a plurality of pores having an average depth D, an average length L, and a value of an average value (L/D) a of a ratio of depth D to length L of each pore reaching a specific range. The depth and length of the pore are measured in a section (hereinafter referred to as "section Z") of the separation membrane to be measured, the section being parallel to the longitudinal direction and the film thickness direction. The longitudinal direction of the membrane refers to a direction parallel to the central axis in the hollow fiber membrane, and the flat membrane refers to a mechanical direction at the time of production. Fig. 1 (a) is a drawing schematically showing a cross section Z and an internal structure of a separation membrane in the case where the separation membrane has a hollow fiber shape. Fig. 1 (b) is a side view of (a), and (c) is a top view of (a). In fig. 1, C denotes a central axis, and the central axis C is parallel to the longitudinal direction of the film. In fig. 1 (c), the double-headed arrow indicates the film thickness direction of the hollow fiber membrane, and the broken line indicates a direction parallel to the film thickness direction.
The "void" here means a recess having an area of 1 μm 2 or more when the cross section Z is observed at a magnification of 2,000 times by using a scanning electron microscope (hereinafter referred to as "SEM"). The detailed observation method is described in example (7) for measurement of a plurality of pores and wall portions. The term "concave portion" as used herein refers to a dark portion in an image observed by SEM, and the outline of the image can be extracted by binarizing the image captured by SEM using image analysis software (binarization of Huang).
Specifically, image j as image analysis software was first used to convert an image 8 taken by SEM into bit pieces, noise removal (DESPECKLE in image j) was performed by replacing all pixels with the center value of 3×3 pixels in the vicinity of the pixel 10 times, and then Huang was binarized. Next, in command Analyze Particles of ImageJ, the obtained image is processed as Masks display by setting Size to 0 to Infinity, circularity to 0 to 1, whereby an image of the extraction concave portion can be obtained. Based on the image obtained in this way, the contour of the concave portion can be extracted. Specifically, in command Analyze Particles of ImageJ, the Size is set to 0 to Infinity, circularity and is set to 0 to 1, and the outline of the recess can be extracted by processing the image as Bare Outlines display.
In addition, the extraction of the pores can be performed by setting the lower limit of Size so as to include the recess of 1 μm 2 or more in the extraction of the recess. For example, in an image of 1 μm 2 =100 pixels 2, by setting the lower limit to 100 pixels 2, the aperture can be extracted. In the image obtained in this way, the contour of the aperture can be extracted by the same process as the extraction of the contour of the concave portion described above. In the present application, the contour may be referred to as an outer edge.
Fig. 2 shows an example of an image photographed by SEM, fig. 3 shows an image obtained by removing noise, binarizing, and extracting pores from the image of fig. 2, and fig. 4 shows an image obtained by extracting the outline of the pores from the image of fig. 3.
When the cross section Z is observed at a magnification of 5,000 times using SEM, the ratio of the sum of the areas of all the recesses to the entire observation range is referred to as "recess area ratio", and the recess area ratio of the separation membrane of the present invention is preferably 50 to 85%, more preferably 60 to 80%, in order to further improve the permeation flux and separation performance. The concave portion herein is not limited to a concave portion having an area of 1 μm 2 or more, that is, a pore, and a concave portion having an area of less than 1 μm 2, that is, a pore, is also targeted. The concave portion in this case can be also extracted by performing noise removal and binarization (Huang binarization) on an image captured by SEM using image analysis software such as ImageJ, as described above.
The "depth d of the pore" refers to the maximum length in the depth direction of the pore to be measured in the case where the cross section Z is observed at a magnification of 2,000 times using SEM, and the film thickness direction of the separation film is referred to as the depth direction. The "length of the pore l" refers to the length of the longest straight line among straight lines that can directly connect two points on the outer edge of the pore to be measured when the cross section Z is observed at 2,000 times using the same SEM. Here, the straight line that can directly connect two points on the outer edge means a straight line that connects two points on the outer edge does not pass through straight lines on other outer edges. The average value (l/d) a of the ratio l/d of the length l to the depth d of each pore is obtained by calculating l/d for each pore among 30 pores selected at random, and taking the arithmetic average value.
The average depth D of the plurality of pores is a value calculated as an arithmetic average value of the depths of 30 pores selected at random when the cross section Z is observed at a magnification of 2,000 times using SEM. The average length L of the plurality of pores is a value calculated as an arithmetic average value of the lengths of 30 pores selected at random when the cross section Z is observed at a magnification of 2,000 times using the same SEM.
The average value (l/d) a of the ratio l/d of the length l to the depth d of each pore is required to be 2 to 40. The value of (l/d) a falls within this range, and it is presumed that pores are moderately dispersed thereby while reducing the substantial thickness of the separation membrane, and thus the separation membrane exhibits excellent permeation performance and separation performance. (l/d) a is preferably 3 to 20, more preferably 4 to 20, still more preferably 8 to 20. Among them, by setting the ratio to 4 to 20, particularly high permeability and high separation performance can be achieved, and by setting the ratio to 8 to 20, extremely high permeability and high separation performance can be achieved.
The average depth D of the plurality of pores is required to be 0.7 to 20 μm in order to properly disperse the pores and reduce the substantial thickness of the separation membrane. The average depth D of the plurality of pores is preferably 0.8 μm or more, more preferably 1.0 μm or more. The average depth D of the plurality of pores is preferably 5.0 μm or less, more preferably 2.0 μm or less.
The average length L of the plurality of pores is required to be 3 μm or more in order to properly disperse the pores. The average length L of the plurality of pores is preferably 4 μm or more, more preferably 5 μm or more, and still more preferably 10 μm or more. The average length L of the plurality of pores is preferably 50 μm or less, more preferably 30 μm or less.
The length direction of the plurality of pores is preferably along the length direction of the separation membrane. The longitudinal directions of the plurality of pores are approximately parallel, stress is easily dispersed even if the separation membrane is bent in the longitudinal direction of the plurality of pores, and the membrane strength of the separation membrane becomes high. When the cross section Z is observed at a magnification of 2,000 times by using SEM, and the angle between the direction of the length l of each of the 30 randomly selected pores and the longitudinal direction of the membrane is calculated, and the arithmetic average value (hereinafter, sometimes referred to as "angle of the longitudinal direction of the plurality of pores") is within 20 °, it can be determined that the longitudinal direction of the plurality of pores is along the longitudinal direction of the separation membrane. The angle in the longitudinal direction of the plurality of pores is preferably 15 ° or less, more preferably 10 ° or less.
In order to properly disperse the pores while further suppressing the substantial thickness of the separation membrane, the occupancy of the pores in the cross section of the separation membrane parallel to the longitudinal direction and the film thickness direction of the separation membrane of the present invention is preferably 15 to 55%, more preferably 18 to 50%, further preferably 20 to 50%, particularly preferably 30 to 50%, and most preferably 40 to 50%. Here, "occupancy of a plurality of pores" refers to the ratio of the sum S 1 of the areas of all pores to the area S 0 of the entire observation range when the cross section Z is observed at a magnification of 2,000 times using SEM.
The average thickness of the wall portion in the cross section Z of the separation membrane is preferably 0.7 to 5.0. Mu.m, more preferably 1.0 to 4.0. Mu.m, and even more preferably 1.0 to 3.0. Mu.m, in order to obtain good separation performance by properly dispersing pores while further suppressing the substantial thickness of the separation membrane. Among them, the use of 1.0 to 3.0 μm enables particularly excellent permeation performance and separation performance to be achieved. Here, "wall portion" of the hollow fiber membrane means a portion other than the pore in the case where the cross section Z is observed at a magnification of 2,000 times using SEM (fig. 1). The term "average wall thickness" refers to an average value of the lengths of the wall portions on the straight lines drawn in the direction perpendicular to the longitudinal direction of the separation membrane through the center of the observation image, and further when the straight lines are drawn on two adjacent sides thereof at a distance of 20 μm from each other.
(Shape of surface hole)
In order to further improve the separation performance and water permeability, the average pore diameter of the surface pores in at least one surface of the separation membrane of the present invention is preferably 0.050 to 0.500 μm. The average pore diameter of the surface pores is more preferably 0.080 μm or more, still more preferably 0.090 μm or more, particularly preferably 0.095 μm or more, and most preferably 0.100 μm or more. The average pore diameter of the surface pores is more preferably 0.450 μm or less, and still more preferably 0.400 μm or less. Here, the surface hole refers to a concave portion in an image of the surface of the separation membrane photographed at 10,000 times using SEM. The term "concave portion" as used herein refers to a dark portion in an image observed by SEM, and the outline thereof can be extracted by performing noise removal and binarization (binarization of Huang) on the image photographed by SEM using image analysis software such as ImageJ. The specific extraction method of the contour of the concave portion is as described above. The detailed observation method is described in the shape of the surface hole of example (3). The average pore diameter of the surface pores is sometimes referred to as surface pore diameter.
In the separation membrane of the present invention, the average minor diameter X, the average major diameter Y, and the average value (Y/X) a of the ratio of major diameter to minor diameter of the surface pores in at least one surface are preferably within a specific range. The average minor axis X is the arithmetic average of minor axes X when each surface hole is regarded as elliptical. The average major axis Y is the arithmetic average of major axes when each surface hole is regarded as elliptical. The average value (y/x) a is an arithmetic average of the values obtained by dividing the minor axis x by the major axis y of each surface hole. The average minor axis X, average major axis Y, and average value (Y/X) a of the ratio of major axis to minor axis of the surface pores were obtained by analyzing an image of the surface of the separation membrane taken at 10,000 times using SEM using image analysis software such as ImageJ. Specifically, in the Set Measurements of ImageJ, on the basis of selection FIT ELLIPSE, the Analyze Particles command of ImageJ is executed for the recess extracted in the same manner as described above. Thus, the short diameter X and the long diameter Y of each surface hole are calculated, and thus the average short diameter X and the average long diameter Y can be obtained by arithmetic averaging. Further, y/x is calculated for each surface hole, and arithmetic average is performed, whereby an average value (y/x) a of the ratio of the long diameter to the short diameter can be calculated.
The average minor diameter X of the surface pores is preferably 0.030 to 0.250 μm in order to further improve the separation performance and the water permeability. More preferably 0.040 to 0.160. Mu.m, still more preferably 0.045 to 0.160. Mu.m.
The average length Y of the surface pores is preferably 0.060 to 0.450. Mu.m, more preferably 0.070 to 0.240. Mu.m, still more preferably 0.075 to 0.240. Mu.m, particularly preferably 0.085 to 0.240. Mu.m, in order to further improve the separation performance and water permeability.
The average value (y/x) a of the ratio of the long diameter to the short diameter of the surface pores is preferably 1.00 to 1.50, more preferably 1.00 to 1.40, still more preferably 1.00 to 1.35, and particularly preferably 1.30 to 1.35, in order to further improve the separation performance and the water permeability.
(Membrane permeation flux)
The membrane permeation flux of the separation membrane of the present invention at 25℃is preferably 0.10 to 20m 3/m2/h, more preferably 0.25 to 15m 3/m2/h, still more preferably 0.30 to 10m 3/m2/h, particularly preferably 0.50 to 7.00m 3/m2/h. The calculation method is described in detail in examples.
(Separation Performance)
The separation performance of the polystyrene latex particles having an average particle diameter of 0.2 μm of the separation membrane of the present invention is preferably 50% or more, more preferably 90% or more, still more preferably 95% or more, and particularly preferably 99% or more. The calculation method is described in detail in examples.
(Method for producing separation Membrane)
The method for producing a separation membrane of the present invention comprises the following steps (1) to (3).
(1) And a preparation step of melt-kneading a mixture containing 10 to 80 mass% or less of a cellulose ester, 10 to 80 mass% of a structure-forming agent, and 2 to 20 mass% of a pore-forming agent to obtain a resin composition.
(2) And a molding step of ejecting the resin composition from a nozzle using a filter having a diameter of 40 to 200 μm and obtaining a resin molded article at a draft ratio of 30 to 200.
(3) And an impregnation step of impregnating the resin molded product in a solvent having a solubility parameter distance D S from the cellulose ester of 10 to 25.
Next, a method for producing a separation membrane according to the present invention will be specifically described by taking a case where the separation membrane is a hollow fiber membrane as an example.
In the preparation step of the resin composition for producing the separation membrane of the present invention, a mixture comprising 10 to 80 mass% of cellulose ester, 10 to 80 mass% of structure forming agent and 2 to 20 mass% of pore forming agent is melt kneaded. The mixture preferably contains 15 to 75 mass% of a cellulose ester, 20 to 75 mass% of a structure forming agent and 3 to 18 mass% of a pore forming agent, more preferably contains 20 to 60 mass% of a cellulose ester, 25 to 70 mass% of a structure forming agent and 5 to 15 mass% of a pore forming agent, and particularly preferably contains 20 to 60 mass% of a cellulose ester, 25 to 70 mass% of a structure forming agent and 10 to 15 mass% of a pore forming agent.
The apparatus used for melt kneading the mixture is not particularly limited, and a kneader, a roll mill, a Banbury mixer, a single-screw extruder, a twin-screw extruder, or the like may be used. Among them, a twin-screw extruder is preferably used in view of improving dispersibility of the structure-forming agent and the plasticizer, and a twin-screw extruder with vent holes is more preferably used in view of removing volatile matters such as moisture and low molecular weight. In addition, a twin-screw extruder having a screw with a spiral portion and a kneading disc portion may be used, and in order to reduce the kneading strength, a twin-screw extruder having a screw composed of only a spiral portion is preferably used.
The resin composition obtained in the preparation step may be pelletized temporarily, remelted for melt film formation, or directly introduced into a nozzle for melt film formation. In the case of temporary pelletization, it is preferable to use a resin composition in which the pellets are dried so that the moisture content is 200ppm (mass basis) or less. By setting the water content to 200ppm (mass basis) or less, deterioration of the resin can be suppressed.
The molding step is a step of forming a resin molded article by ejecting the resin composition obtained in the preparation step from a nozzle. The molding step may be, for example, a step of forming a resin molded article by ejecting the resin molded article into air from a nozzle having a double annular nozzle in which a gas flow path is arranged in a central portion, and cooling the resin molded article by a cooling device.
The resin composition previously passed through the filter is preferably ejected from the nozzle. In order to increase the values of L, L and (L/d) a and to suppress the bonding of pores to each other, the pore diameter of the filter is preferably 40 to 200 μm, more preferably 70 to 150 μm, still more preferably 70 to 120 μm. By passing the resin composition through the filter, it is presumed that the pore former contained in the resin composition is elongated, the values of L, L and (L/d) a are increased, and the effect of suppressing the bonding of the pores to each other is obtained.
The hollow fiber, which is the resin molded product cooled by the cooling device, may be wound by a winding device. In this case, the average thickness of the wall portion in the longitudinal direction of the separation membrane is preferably reduced by 30 to 200, more preferably 50 to 150, and particularly preferably 100 to 150, in order to increase the values of L, and (L/d) a by the value of the draft ratio calculated by (winding speed)/(ejection speed from nozzle) of the winding device. The resin composition ejected from the nozzle is elongated under the conditions of the above-described draft ratio, whereby it is presumed that the pore-forming agent contained in the resin composition is elongated, the values of L, L and (L/d) a are increased, and the effect of suppressing the bonding of the pores to each other is obtained. In the case of film formation from a solution obtained by mixing a polymer with 50 wt% or more of a low molecular compound having a molecular weight of less than 1000, it is difficult to spin at a high draft ratio as in the present invention, and the pore former is not sufficiently elongated, so that it is difficult to obtain such an effect.
The impregnation step is a step of impregnating the resin molded product with a solvent having a solubility parameter distance D S of 10 to 25 with respect to the cellulose ester as a raw material. In this case, the use of a solvent or a mixed solvent having a suitable affinity for cellulose esters can suppress the resin from extremely swelling and plasticizing. Therefore, the solvent is impregnated into the resin molded product while maintaining the shape of the resin. At this time, it is assumed that the plasticizer and the structure forming agent are eluted while causing phase separation in the resin molded product. The longer or higher the immersion time and temperature of the solvent, the larger the surface pore diameter, and the larger the existence ratio and size of the pores and the micropores in the cross section Z. In the present invention, a solvent having a certain affinity with cellulose ester is preferably selected. The affinity of cellulose ester with a solvent can be estimated by three-dimensional hansen solubility parameters (non-patent document 1). Specifically, the smaller the solubility parameter distance D S obtained from the following formula (1), the higher the affinity of the solvent for cellulose ester.
[ Number 1]
。
Here, δ Ad、δAp and δ Ah are dispersion terms, polarity terms, and hydrogen bond terms of solubility parameters of cellulose esters, and δ Bd、δBp and δ Bh are dispersion terms, polarity terms, and hydrogen bond terms of solubility parameters of solvents or mixed solvents. The solubility parameter (δ Mixture) of the mixed solvent can be obtained by the following formula (2).
[ Number 2]
。
Here, phi i、δi is the volume fraction and solubility parameter of component i, and the dispersion term, the polarity term, and the hydrogen bond term are each established. The "volume fraction of the component i" herein refers to the ratio of the volume of the component i before mixing to the sum of the volumes of all the components before mixing. The three-dimensional hansen solubility parameter of the solvent uses the value described in non-patent document 1. For the solvent parameters not described, the values recorded in the software "hansen Solubility PARAMETER IN PRACTICE" developed by Charles hansen et al were used. The three-dimensional Hansen solubility parameters of the solvent and polymer, which are not described in the above-described software, can be calculated by the Hansen ball method using the above-described software.
The inventors have found that, by impregnating the resin molded product with a solvent having the above-mentioned solubility parameter distance D S of 10 to 25, a film having a large D and D can be obtained as the depth D of each pore and the average depth D of a plurality of pores are larger. And it was found that the effect of reducing the substantial film thickness was thereby obtained more remarkably. The reason for obtaining such an effect is not determined, but is estimated as follows. That is, it is presumed that the pore former is incompatible with the cellulose ester, and therefore, the pore former is dispersed in the cellulose ester in a stage after the molding step and before the impregnation step, and the pore former is swelled by a solvent having a solubility parameter distance D s of 10 to 25 with respect to the cellulose ester in the impregnation step, whereby a film having a large D and D is obtained.
The temperature of the resin molded product in the impregnation step is preferably 50 to 80 ℃. If the temperature of the resin molded product in the impregnation step is set to 50 to 80 ℃, it is surprising that the pores (l/d) a of the cross section Z are found to be 2 to 40, but the average value (y/x) a of the ratio of the long diameter to the short diameter of the surface pores is as low as 1.0 to 1.5, i.e., nearly circular. For this reason, the following estimation is performed. That is, it is assumed that the resin molded article is in a state where molecules are relatively easily moved at a yarn temperature of 50 to 80 ℃, and that the surface is in a state where molecules are particularly easily moved than the inside, and therefore if the resin molded article is immersed in a solvent in the impregnation step to further promote plasticization, the structure forming agent elongated by the filter pores and the drawing is restored to a nearly circular shape on the surface.
In the present invention, as the solvent for impregnating the resin molded product, a solvent having a D S of 13 to 25 is preferable. The solvent is preferably a mixed solvent of water and a solvent for achieving D S of 4 to 12, and examples thereof include mixed solvents of water and at least 1 selected from γ -butyrolactone (hereinafter referred to as γ -BL), acetone, acetonitrile, 1, 4-dioxane, methyl acetate and tetrahydrofuran. By using a mixed solvent of water and a solvent having a D S of 4 to 12, the membrane strength of the obtained separation membrane is improved.
The resulting separation membrane may be used as it is, and it is preferable to hydrophilize the surface of the membrane before use, for example, by an aqueous solution containing alcohol or an aqueous alkali solution.
Even in the case where the pore forming agent remains after the above-described step, a step of removing the pore forming agent is preferably provided. Examples of the method for removing the pore former include immersing in a solution in which the cellulose ester is insoluble or decomposable and the pore former is soluble or decomposable.
Examples
The present invention will be further specifically described by way of examples, but the present invention is not limited to these examples.
[ Measurement and evaluation method ]
The characteristic values in the examples were obtained by the following methods.
(1) Average degree of substitution of cellulose mixed ester
The method for calculating the average substitution degree of the cellulose mixed ester in which acetyl group and other acyl groups are bonded to cellulose is as follows.
0.9G of cellulose mixed ester dried at 80℃for 8 hours was weighed, 35mL of acetone and 15mL of dimethyl sulfoxide were added thereto to dissolve the cellulose mixed ester, and then 50mL of acetone was further added thereto. 30mL of 0.5N-sodium hydroxide aqueous solution was added while stirring, and saponification was performed for 2 hours. 50mL of hot water was added, and the side of the flask was washed and then titrated with 0.5N-sulfuric acid using phenolphthalein as an indicator. In addition, the blank test was performed by the same method as the sample. The supernatant of the solution after the completion of the titration was diluted 100 times, and the composition of the organic acid was measured by ion chromatography. And calculating the substitution degree according to the measurement result and the acid composition analysis result by utilizing ion chromatography by the following formulas (3) - (5).
TA=(B-A)×F/(1000×W) ······(3)
DSace=(162.14×TA)/[{1-(Mwace-(16.00+1.01))×TA}+{1-(Mwacy-(16.00+1.01))×TA}×(Acy/Ace)] ······(4)
DSacy=DSace×(Acy/Ace) ······(5)
TA: total organic acid amount (mL)
A: sample titration amount (mL)
B: air test drop quantity (mL)
F: titer of sulfuric acid
W: sample mass (g)
DSace: average degree of substitution of acetyl group
DSacy: average degree of substitution of other acyl groups
Mwace: molecular weight of acetic acid
Mwacy: molecular weight of other organic acids
Ack/Ace: molar ratio of acetic acid (Ace) to other organic acids (Acy)
162.14: Molecular weight of repeating units of cellulose
16.00: Atomic weight of oxygen
1.01: Atomic weight of hydrogen.
(2) Weight average molecular weight (Mw) of cellulose esters
The cellulose ester was completely dissolved in tetrahydrofuran so that the concentration of the cellulose ester became 0.15 mass%, and a sample for GPC measurement was prepared. Using this sample, GPC measurement was performed using a GPC apparatus (Waters 2690) under the following conditions, and the weight average molecular weight (Mw) was determined by polystyrene conversion.
Column: connecting TSK GEL GMHHR-H of Tosoh system with 2 roots
A detector: waters2410 differential refractometer RI
Mobile phase solvent: tetrahydrofuran (THF)
Flow rate: 1.0 mL/min
Injection amount: 200. Mu.L.
(3) Shape of surface holes
The outer surface of the separation membrane sputtered with platinum was observed at a magnification of 10,000 times using SEM, and the pore diameters r of 50 surface pores selected at random were measured, and the arithmetic average thereof was recorded as the surface pore diameter r in tables 1 and 2.
The pore diameter r of each surface pore is calculated by the following formula (6) by measuring the area of the surface pore by image processing, assuming a true circular pore having the same area.
r=(4×A/π)0.5 ······(6)
A: area of the hole
The sputtering and observation conditions using SEM are as follows.
(Sputtering conditions)
The device comprises: hitachi hightech of Kagaku Co., ltd (E-1010)
Evaporation time: 40 seconds
Current value: 20mA.
(SEM conditions)
The device comprises: hitachi hightech, inc. (SU 1510)
Acceleration voltage: 5kV (kV)
Probe current: 30.
Further, the outer surface of the separation membrane was observed under the same observation conditions as described above, and the average minor axis X, the average major axis Y, and the average value (Y/X) a of the ratio of major axis to minor axis of the surface pores were obtained by the analysis method described above.
(4) Thickness of hollow fiber membrane
After freezing the hollow fiber membrane with liquid nitrogen, the hollow fiber membrane is subjected to stress (using a razor or microtome as necessary) and is cut so that a radial cross section is exposed. The obtained cross section was observed by an optical microscope, and the average value of the thicknesses of 10 sites selected at random was used as the thickness (film thickness) of the hollow fiber membrane.
(5) Outer diameter of hollow fiber membrane
The cross section of the above (4) was observed by an optical microscope, and the average value of the outer diameters at 10 positions selected at random was used as the outer diameter of the hollow fiber membrane.
(6) Membrane permeation flux of hollow fiber membrane
A small module having an effective length of 100mm and containing 1 hollow fiber membrane was produced. In this small module, distilled water was fed by total filtration under external pressure at a temperature of 25 ℃ for 30 minutes under a filtration differential pressure of 16kPa, and the obtained water permeation quantity (m 3) was measured and converted into a numerical value of a unit time (h) and a unit membrane area (m 2), and further converted into a pressure (50 kPa), and the pressure was recorded as the water permeation performance (unit=m 3/m2/h).
(7) Measurement for multiple pores and walls
After freezing the separation membrane with liquid nitrogen, the separation membrane is subjected to stress (using a razor or microtome as necessary) and is cut so that a cross section parallel to the longitudinal direction and the film thickness direction, that is, a cross section Z of the separation membrane is exposed. Next, after the pretreatment of the cross section Z by sputtering with platinum, the field of view was set so that the distances from both surfaces in the center of the field of view were equal, and the view was observed at a magnification of 2,000 times. Similarly, 5 fields of view were observed, 30 pores were randomly extracted in each field of view, and then the average depth D (μm) and the average length L (μm) of the pores and the average value L/D (L/D) a of the pores were calculated, and the occupancy (%) of the pores, the average thickness (μm) of the wall portion, and the angle (°) in the longitudinal direction of the pores were further calculated. The sputtering and observation conditions using SEM are as follows.
(Sputtering conditions)
The device comprises: hitachi hightech of Kagaku Co., ltd (E-1010)
Evaporation time: 40 seconds
Current value: 20mA.
(SEM conditions)
The device comprises: hitachi hightech, inc. (SU 1510)
Acceleration voltage: 5kV (kV)
Probe current: 30.
(8) Area ratio of concave portion
The separation film was cut in the same manner as in (7) above, and the exposed cross section Z was observed at a magnification of 5,000 times using SEM, and the area ratio of the concave portion (concave portion area ratio) was calculated.
(9) Separation performance
A small module was fabricated in the same manner as in (6) above. In this small module, an aqueous solution containing 20ppm of polystyrene latex particles (MAGSPHERE Co.) having an average particle diameter of 0.2 μm as a turbid component was fed by total filtration under external pressure for 30 minutes at a temperature of 25℃under a differential pressure of 16kPa, and the concentration of each turbid component of feed water and permeate water was calculated from the ultraviolet absorption coefficient of 234nm measured by a spectrophotometer (manufactured by Hitachi, co., ltd.; U-3200) by the following formula (7).
Separation performance (%) = [1-2× (turbid component concentration of permeate)/{ (turbid of feed water at the start of filtration). Component concentration) + (turbid component concentration of feed water at the end of filtration) } ] ×100.cndot.cndot.cndot.formula (7).
[ Cellulose ester (A) ]
The following were prepared as cellulose esters.
Cellulose ester (A1)
To 100 parts by mass of cellulose (cotton linter), 240 parts by mass of acetic acid and 67 parts by mass of propionic acid were added, and mixing was performed at 50 ℃ for 30 minutes. After the mixture was cooled to room temperature, 172 parts by mass of acetic anhydride and 168 parts by mass of propionic anhydride cooled in an ice bath were added as an esterifying agent and 4 parts by mass of sulfuric acid as an esterifying catalyst, and the mixture was stirred for 150 minutes to perform an esterification reaction. In the esterification reaction, cooling is carried out by using a water bath at the temperature of more than 40 ℃.
After the reaction, a mixed solution of 100 parts by mass of acetic acid and 33 parts by mass of water was added for 20 minutes as a reaction stopper, and the excess acid anhydride was hydrolyzed. Thereafter, 333 parts by mass of acetic acid and 100 parts by mass of water were added thereto, and the mixture was heated and stirred at 80℃for 1 hour. After the completion of the reaction, an aqueous solution containing 6 parts by mass of sodium carbonate was added, and the precipitated cellulose acetate propionate was filtered off, washed with water, and dried at 60℃for 4 hours. The average degree of substitution of acetyl groups and propionyl groups of the obtained cellulose acetate propionate was 1.9 and 0.7, respectively, and the weight average molecular weight (Mw) was 17.8 ten thousand.
Cellulose ester (A2): cellulose acetate propionate (average degree of substitution of acetyl group: 0.2, average degree of substitution of propionyl group: 2.5, weight average molecular weight (Mw): 18.5 ten thousand).
[ Other raw materials ]
As other raw materials, the following materials were prepared.
Plasticizer (B) of cellulose ester: polyethylene glycol (weight average molecular weight (Mw) 600)
Structure-forming agent (C): PVP/vinyl acetate copolymer (PVP/vinyl acetate=6/4 (molar ratio), weight average molecular weight 50,000)
Pore former (D): polyethylene glycol (weight average molecular weight (Mw) 30 ten thousand)
Antioxidants (E): bis (2, 6-di-tert-butyl-4-methylphenyl) pentaerythritol diphosphite.
Example 1
40 Mass% of cellulose ester (A1), 26.9 mass% of plasticizer (B), 30 mass% of structure-forming agent (C), 3 mass% of pore-forming agent (D) and 0.1 mass% of antioxidant (E) were melt-kneaded at 220℃by a twin-screw extruder, homogenized and pelletized to obtain a resin composition. The resin composition was dried under vacuum at 80℃for 8 hours.
The dried resin composition was fed to a twin-screw extruder having a screw composed only of a spiral portion, melt kneaded at 220℃and then introduced into a melt-spinning pack having a spinning temperature of 220℃and spun downward from an outer annular portion of a nozzle having 1 nozzle hole (double round tube type, discharge aperture 2.6mm, slit width 0.35 mm) at a discharge amount of 10 g/min. The hollow yarn thus spun was introduced into a cooling device, cooled by cooling air at 25℃and a wind speed of 1.5 m/sec, and wound up by a winding machine so that the draft ratio became 30. Here, as a filter in the melt-spinning dope, a metal filter having a pore diameter (filter diameter) of 200 μm was used. The wound hollow fiber (resin molded article) was heated to 30℃and immersed in an aqueous acetone solution having a volume fraction of 40% for 1 hour, followed by immersing in water for 1 hour or more, to dissolve out the plasticizer (B), the structure-forming agent (C) and the pore-forming agent (D), thereby obtaining a separation membrane. Physical properties of the obtained separation membrane are shown in table 1.
(Example 2 to 9 and comparative example 1 to 6)
A separation membrane was obtained in the same manner as in example 1, except that the composition of the resin composition and the production conditions were changed as shown in tables 1 and 2. Physical properties of the obtained separation membranes are shown in tables 1 and 2. In comparative example 1, no voids were observed, and in comparative example 2, spinning was not possible due to yarn breakage.
TABLE 1
TABLE 2
The separation membranes obtained in examples 1 to 9 had membrane permeation fluxes of 0.1m 3/m2/h or more and separation performance of 50% or more, and both high membrane permeation fluxes and separation performance were considered. On the other hand, comparative example 2 failed to spin due to yarn breakage, and failed to obtain a separation membrane. In the separation membranes of comparative examples 1 and 3 to 6, in which the shape of the plurality of pores does not satisfy the requirements of the present invention, at least one of the membrane permeation flux and the separation performance exhibits a low value, and it is not possible to achieve both high membrane permeation flux and separation performance.
While the present application has been described with reference to specific embodiments, it will be apparent to those skilled in the art that various changes and modifications can be made therein without departing from the spirit and scope thereof. The present application is based on japanese patent application filed on date 23 and 12 in 2019 (japanese patent application publication No. 2019-231579), the contents of which are incorporated herein by reference.
Industrial applicability
The separation membrane of the present invention is applicable to a membrane for water treatment such as industrial water or drinking water, a membrane for medical use such as artificial kidney or plasma separation, a membrane for food and beverage industry such as juice concentration, a gas separation membrane for separating exhaust gas, carbonic acid gas, or the like, a membrane for electronic industry such as a fuel cell separator, or the like, which is produced from seawater, saline-alkali water, sewage, or drainage, or the like.
Claims (8)
1. A hollow fiber-shaped separation membrane for water treatment comprising a cellulose ester,
The separation membrane has a plurality of pores in a cross section of the membrane parallel to the longitudinal direction and the film thickness direction,
The angle formed by the length direction of the plurality of pores and the length direction of the film is within 20 degrees,
The angle is an arithmetic average of angles formed by the direction of the length l of each of the randomly selected 30 pores and the length direction of the film calculated by observing the cross section Z at a magnification of 2,000 times using SEM,
The section Z is a section parallel to the longitudinal direction and the film thickness direction of the separation film to be measured,
The average depth D of the plurality of pores is 0.7-20 mu m,
The average length L of the pores is 3 μm or more and
The average value (l/d) a of the ratio of the length l to the depth d of each pore is 8 to 40,
The average thickness of the wall portion in the cross section is 0.7-5.0 μm,
In at least one surface, the average pore diameter of the surface pores is 0.050 to 0.500 μm,
The average value (y/x) a of the ratio of the long diameter to the short diameter of the surface hole is 1.00 to 1.50,
The membrane permeation flux at 50kPa and 25 ℃ is 0.10-20 m 3/m2/h,
The area ratio of the concave part is 60-80%,
The above-mentioned concave area ratio is a ratio in which the sum of areas of all concave portions is occupied in the entire observation range when the cross section Z is observed at a magnification of 5,000 times using SEM.
2. The hollow-fiber-shaped separation membrane for water treatment according to claim 1, wherein the occupancy rate of the plurality of pores in the cross section is 15 to 55%.
3. The hollow-fiber-shaped separation membrane for water treatment according to claim 1 or 2, wherein the average minor diameter X of the surface pores is 0.030 to 0.250 μm and the average major diameter Y of the surface pores is 0.060 to 0.450 μm in at least one surface.
4. The hollow-fiber-shaped separation membrane for water treatment according to claim 1 or 2, wherein the membrane permeation flux at 50kPa and 25 ℃ is 0.50 to 20m 3/m2/h.
5. The hollow-fiber-shaped separation membrane for water treatment according to claim 1 or 2, wherein cellulose acetate propionate and/or cellulose acetate butyrate are/is contained as the cellulose ester.
6. A method for producing a hollow-fiber-shaped separation membrane for water treatment, which comprises:
(1) A preparation step of melt-kneading a mixture containing 10 to 80 mass% of a cellulose ester, 10 to 80 mass% of a structure-forming agent selected from polyvinylpyrrolidone (PVP) having a weight average molecular weight (Mw) of 1000 or more, PVP/vinyl acetate copolymer and PVP/methyl methacrylate copolymer, and 10 to 20 mass% of a pore-forming agent which is at least one of a polyalkylene glycol compound having a weight average molecular weight (Mw) of 10 to 100 tens of thousands and a derivative of these compounds to obtain a resin composition;
(2) A molding step of ejecting the resin composition from a nozzle using a filter having a pore diameter of 40 to 200 μm to obtain a resin molded article at a draft ratio of 100 to 200; and
(3) An impregnation step of immersing the resin molded product in a solvent having a solubility parameter distance D S in a range of 10 to 25 relative to the cellulose ester,
The temperature of the resin molded product in the impregnation step is 50 to 80 ℃,
The separation membrane is a cellulose ester-containing separation membrane,
The separation membrane has a plurality of pores in a cross section of the membrane parallel to the longitudinal direction and the film thickness direction,
The angle formed by the length direction of the plurality of pores and the length direction of the film is within 20 degrees,
The angle is an arithmetic average of angles formed by the direction of the length l of each of the randomly selected 30 pores and the length direction of the film calculated by observing the cross section Z at a magnification of 2,000 times using SEM,
The section Z is a section parallel to the longitudinal direction and the film thickness direction of the separation film to be measured,
The average depth D of the plurality of pores is 0.7-20 mu m,
The average length L of the pores is 3 μm or more and
The average value (l/d) a of the ratio of the length l to the depth d of each pore is 8 to 40,
The average thickness of the wall portion in the cross section is 0.7-5.0 μm,
In at least one surface, the average pore diameter of the surface pores is 0.050 to 0.500 μm,
The average value (y/x) a of the ratio of the long diameter to the short diameter of the surface hole is 1.00 to 1.50,
The membrane permeation flux at 50kPa and 25 ℃ is 0.10-20 m 3/m2/h,
The area ratio of the concave part is 60-80%,
The above-mentioned concave area ratio is a ratio in which the sum of areas of all concave portions is occupied in the entire observation range when the cross section Z is observed at a magnification of 5,000 times using SEM.
7. The method for producing a hollow-fiber-shaped separation membrane for water treatment according to claim 6, wherein the structure-forming agent is a PVP/vinyl acetate copolymer having a weight-average molecular weight (Mw) of 1000 or more, and the pore-forming agent is polyethylene glycol having a weight-average molecular weight (Mw) of 10 to 100 tens of thousands.
8. The method for producing a hollow-fiber-shaped separation membrane for water treatment according to claim 6 or 7, wherein the solvent is a mixed solvent of water and a solvent having a solubility parameter distance D S of 4 to 12.
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- 2020-12-23 JP JP2021503174A patent/JP7107429B2/en active Active
- 2020-12-23 KR KR1020227020845A patent/KR20220112792A/en unknown
- 2020-12-23 WO PCT/JP2020/048296 patent/WO2021132397A1/en active Application Filing
Patent Citations (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN204485669U (en) * | 2015-02-09 | 2015-07-22 | 武汉恒通源环境工程技术有限公司 | A kind of filter membrane |
| CN107530644A (en) * | 2015-03-31 | 2018-01-02 | 东丽株式会社 | Seperation film |
| CN108136341A (en) * | 2015-09-30 | 2018-06-08 | 东丽株式会社 | The manufacturing method of seperation film, cellulose resin compositions and seperation film |
| CN110475606A (en) * | 2017-03-30 | 2019-11-19 | 东丽株式会社 | Seperation film and its manufacturing method |
| JP2019111476A (en) * | 2017-12-22 | 2019-07-11 | 東レ株式会社 | Separation membrane, and manufacturing method of separation membrane |
Also Published As
| Publication number | Publication date |
|---|---|
| WO2021132397A1 (en) | 2021-07-01 |
| JP7107429B2 (en) | 2022-07-27 |
| KR20220112792A (en) | 2022-08-11 |
| JPWO2021132397A1 (en) | 2021-07-01 |
| CN114828992A (en) | 2022-07-29 |
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