CN115297954A - Hollow fiber membrane and method for producing hollow fiber membrane - Google Patents
Hollow fiber membrane and method for producing hollow fiber membrane Download PDFInfo
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- CN115297954A CN115297954A CN202180020949.6A CN202180020949A CN115297954A CN 115297954 A CN115297954 A CN 115297954A CN 202180020949 A CN202180020949 A CN 202180020949A CN 115297954 A CN115297954 A CN 115297954A
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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
- 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
- B01D71/10—Cellulose; Modified cellulose
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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
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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
Abstract
A hollow fiber membrane comprising a cellulose ester and a cellulose-based nanofiber.
Description
Technical Field
The present invention relates to a hollow fiber membrane and a method for producing a hollow fiber membrane.
Background
Patent document 1 (japanese patent laid-open No. 2012-81533), patent document 2 (international publication No. 2016/136294), and patent document 3 (japanese patent laid-open No. 2018-506161) disclose hollow fiber membranes containing cellulose-based resins other than cellulose acetate and cellulose-based nanofibers.
Documents of the prior art
Patent document
Patent document 1: japanese laid-open patent publication No. 2012-81533
Patent document 2: international publication No. 2016/136294
Patent document 3: JP 2018-506161A
Disclosure of Invention
Problems to be solved by the invention
When a hollow fiber membrane is used for membrane separation treatment such as Reverse Osmosis (RO) method, there is a problem that the amount of permeated water of the hollow fiber membrane decreases with time. When the amount of permeated water in the hollow fiber membrane decreases with time, there arises a problem that the operation energy required for the membrane separation treatment increases with time.
By adding cellulose nanofibers to the polymer material constituting the hollow fiber membrane, it is generally expected that the strength of the hollow fiber membrane is improved, physical changes with time are suppressed, and the effect of suppressing the decrease in the amount of permeated water with time is obtained.
The purpose of the present invention is to provide a hollow fiber membrane having excellent water permeability and its retention rate of water permeability.
Means for solving the problems
(1) A hollow fiber membrane comprising a cellulose ester and a cellulose nanofiber.
(2) The hollow fiber membrane according to (1), wherein,
the ratio of the amount of the cellulose-based nanofibers to the total amount of the cellulose ester and the cellulose-based nanofibers is 0.01 to 10% by mass.
(3) The hollow fiber membrane according to (1) or (2), wherein,
the cellulose-based nanofibers have a fiber width (fiber diameter) of 1 to 200nm.
(4) A method for producing a hollow fiber membrane comprising a cellulose ester and a cellulose nanofiber, the method comprising:
a spinning step of ejecting a spinning dope from a nozzle through an air travel section into a coagulating liquid, and drawing out a coagulated product of the spinning dope from the coagulating liquid to obtain a hollow fiber membrane as a hollow fiber type semipermeable membrane,
the spinning dope contains cellulose ester, cellulose nanofibers, a solvent and a non-solvent, and is kneaded before the spinning step.
(5) The production method according to (4), wherein,
mixing the cellulose ester, the cellulose nanofiber powder, the solvent and the non-solvent to obtain the spinning dope, or
Mixing a slurry obtained by dispersing a powder of the cellulose-based nanofibers in the solvent with the cellulose ester and the non-solvent, and kneading the obtained spinning dope, or
Mixing a slurry obtained by dispersing a powder of the cellulose-based nanofibers in the non-solvent, the cellulose ester and the solvent, and kneading the obtained spinning dope.
(6) The production method according to (4) or (5), wherein,
in the spinning dope, the ratio of the amount of the cellulose-based nanofibers to the total amount of the cellulose ester and the cellulose-based nanofibers is 0.01 to 10% by mass.
(7) The production method according to any one of (4) to (6), wherein,
the concentration of the cellulose ester in the dope is 20 to 60 mass%.
(8) The production method according to any one of (4) to (7), wherein,
the temperature for kneading the spinning dope is 150 to 200 ℃.
(9) The production method according to any one of (4) to (8), wherein,
the shear rate of the spinning dope is 500 to 3500sec -1 。
(10) The production method according to any one of (4) to (9), wherein,
in the spinning dope, the cellulose-based nanofibers have a fiber width (fiber diameter) of 1 to 200nm.
(11) A hollow-fiber membrane produced by the production method according to any one of (4) to (10), comprising a cellulose ester and a cellulose-based nanofiber.
Effects of the invention
According to the present invention, a hollow fiber membrane having excellent water permeability and maintenance of water permeability can be provided.
Drawings
Fig. 1 is a schematic diagram for explaining an example of a method for producing a hollow fiber membrane.
Fig. 2 is a microphotograph of the hollow fiber membrane of example 3 after the dyeing test.
Fig. 3 is a microphotograph of the hollow fiber membrane of comparative example 2 after the dyeing test.
Fig. 4 is a microphotograph of the hollow fiber membrane of example 3 after the breakage in the measurement of the strength and elongation.
Fig. 5 is a microphotograph of the hollow fiber membrane of comparative example 2 after the breakage in the measurement of the strength and elongation.
Fig. 6 is a schematic diagram for explaining an example of the membrane performance test apparatus.
FIG. 7 shows the fracture strength and FR for the examples and comparative examples 4 A graph of the relationship of (a).
Detailed Description
Embodiments of the present invention will be described with reference to the accompanying drawings. The dimensional relationships such as the length, width, thickness, and depth are appropriately changed for the sake of clarity and simplification of the drawings, and do not indicate actual dimensional relationships.
< hollow fiber Membrane >
The hollow fiber membrane of the present embodiment is a hollow fiber type semipermeable membrane.
The hollow fiber membrane comprises cellulose ester and cellulose nanofibers.
(cellulose ester)
Examples of the cellulose ester include: cellulose acetate (cellulose triacetate, cellulose monoacetate, cellulose diacetate, cellulose acetate butyrate, cellulose acetate propionate, etc.), cellulose phthalate, cellulose succinate, etc.
The cellulose ester is preferably cellulose acetate. Cellulose acetate is resistant to chlorine as a bactericide and has a characteristic of inhibiting the growth of microorganisms. From the viewpoint of durability, cellulose acetate is preferably cellulose triacetate.
(cellulose-based nanofiber)
Cellulose Nanofibers (CNF) are obtained by, for example, micronizing (converting) cellulose derived from natural sources such as wood and plants into a nanometer-sized cellulose.
As a method for opening the fiber, for example, at least either of a mechanical pulverization method and a chemical pulverization method can be used. Examples of the chemical refinement method include: TEPMO (2, 6-tetramethylpiperidine-1-oxyl) oxidation, phosphorylation, carboxymethylation, sulfonation, xanthation, enzyme treatment, and the like.
As a commercially available CNF, products such as CNF powder, CNF gel dispersed in water or an organic solvent, and the like can be purchased.
Cellulose nanofibers (hereinafter sometimes simply referred to as "CNF") contain a cellulose resin (cellulose or a cellulose derivative).
Examples of the cellulose derivative include: cellulose esters, cellulose ethers, mixtures thereof, and the like.
Examples of the cellulose ester include: cellulose acetates (cellulose triacetate, cellulose monoacetate, and cellulose diacetate), cellulose phthalate, cellulose succinate, and the like.
Examples of the cellulose ether include: methyl cellulose, ethyl cellulose, hydroxypropyl methyl cellulose, and the like.
The ratio of the amount of CNF to the total amount of cellulose ester and CNF (CNF ratio) is preferably 0.01 to 10% by mass, more preferably 0.01 to 5% by mass, even more preferably 0.01 to 3% by mass, and most preferably 0.01 to 1% by mass. The CNF content is calculated by the following formula.
CNF ratio (% by mass) = [ amount of CNF ]/([ amount of cellulose ester ] + [ amount of CNF ]) × 100
When the CNF ratio is too low, the strength of the hollow fiber membrane becomes low. On the other hand, when the CNF ratio is too high, the hollow fiber membrane has a low fractionation property (Japanese: fractionation property) (salt removal rate).
The fiber width (fiber diameter) of the CNF is preferably 1 to 200nm, more preferably 1 to 50nm. The fiber width of the CNF can be measured by SEM (scanning electron microscope), TEM (transmission electron microscope), SPM (scanning probe electron microscope), E-SEM (environmental control scanning electron microscope), cryosem, or the like.
The fiber length of CNF is preferably 100 μm or less, and more preferably 20nm to 10 μm. The fiber length of CNF can be measured by SEM (scanning electron microscope), TEM (transmission electron microscope), SPM (scanning probe electron microscope), E-SEM (environmental control scanning electron microscope), cryosem, or the like.
(shape of hollow fiber Membrane, etc.)
The inner diameter of the hollow fiber membrane is preferably 30 μm or more and 300 μm or less, and more preferably 35 μm or more and 260 μm or less.
The thickness of the hollow fiber membrane (the whole membrane) is preferably 20 to 200. Mu.m, more preferably 30 to 150. Mu.m. The film thickness can be calculated by (outer diameter-inner diameter)/2.
The hollow fiber membrane preferably has a hollow ratio of 10 to 65%, more preferably 12 to 55%. The hollow ratio is a ratio of the area of the hollow portion in the cross section of the hollow fiber membrane, and is represented by "hollow portion sectional area/(membrane portion sectional area + hollow portion sectional area) × 100 (%)".
The average pore diameter of the hollow fiber membrane (average pore diameter of micropores in the entire membrane) is preferably 2nm or less. Examples of the method for measuring the average pore diameter include: differential Scanning Calorimetry (DSC).
The hollow fiber membrane of the present embodiment can exhibit an effect of suppressing a decrease in the amount of permeated water with time when used in a Reverse Osmosis (RO) method, a Brine Concentration (BC) method, and the like, particularly in a membrane separation process in which the hollow fiber membrane is exposed to high pressure. This suppresses an increase in the operating energy required for the membrane separation process using the hollow fiber membrane with time.
The BC method is, for example, a membrane separation method as described in japanese patent application laid-open No. 2018-65114: a part of the target solution flows into one 1 st chamber of the hollow fiber membrane module, the other part of the target solution flows into the other 2 nd chamber, the target solution in the 1 st chamber is pressurized, so that the solvent (water, etc.) contained in the target solution in the 1 st chamber moves into the 2 nd chamber through the hollow fiber membrane, the target solution in the 1 st chamber is concentrated, and the target solution in the 2 nd chamber is diluted.
In addition, since the treatment using the RO method or the BC method is often used as a part of a system in combination with other treatments, if the amount of permeated water of the hollow fiber membrane is reduced with time, it may be difficult to control the entire system. Therefore, the hollow fiber membrane of the present embodiment having a high retention rate of the permeated water amount is used in a system in which the RO method, the BC method and other treatments are combined, whereby the entire system can be particularly easily controlled.
In addition, the hollow fiber membrane of the present embodiment can suppress a decrease in the amount of permeated water of the hollow fiber membrane with time, particularly in the case of pressurization from the outside of the hollow fiber membrane (that is, in the case where the liquid pressure outside the hollow fiber membrane is higher than the inside of the hollow fiber membrane).
< method for producing hollow fiber membrane >
The present invention also relates to a method for producing a hollow fiber membrane, which is used for obtaining a hollow fiber membrane comprising the cellulose ester and cellulose nanofibers.
The method for producing a hollow fiber membrane of the present embodiment includes at least a spinning step described later.
The spinning method used in the method for producing a hollow fiber membrane of the present embodiment is a method called "solution spinning" and is a spinning method different from the method (melt spinning) disclosed in patent document 2 (international publication No. 2016/136294).
[ spinning Process ]
Referring to fig. 1, in the spinning step, a spinning dope (spinning dope) 10 is discharged from a nozzle 11 into a coagulating liquid 21 through an air traveling section, and a coagulated product of the spinning dope is pulled out from the coagulating liquid, thereby obtaining a hollow fiber membrane as a hollow fiber type semipermeable membrane. The hollow fiber membrane is drawn out, for example, by rollers 12, 13, 14, and 15. The drawing speed is the surface speed of the roller 13.
(dope for spinning)
The spinning dope (spinning dope) contains a raw material of the hollow fiber membrane (a material containing the cellulose ester and the cellulose-based nanofibers constituting the hollow fiber membrane), a solvent, and a non-solvent. The solvent is a liquid that can dissolve the cellulose ester, and the non-solvent is a liquid that does not dissolve the cellulose ester (excluding water). The dope may contain water in addition to the solvent and the non-solvent.
The concentration of the cellulose ester in the dope is preferably 20 to 60% by mass, more preferably 30 to 50% by mass.
If the concentration of the cellulose ester is too low, the fractionation property and the strength of the film become low. On the other hand, when the concentration of cellulose ester is too high, the water permeability becomes low. In addition, when the concentration of the cellulose ester is too high, the viscosity of the dope may become too high, and it may be difficult to carry out spinning.
The ratio of the amount of CNF to the total amount of cellulose ester and CNF (CNF ratio) is preferably 0.01 to 10% by mass, more preferably 0.01 to 5% by mass, even more preferably 0.01 to 3% by mass, and most preferably 0.01 to 1% by mass. The CNF content is calculated by the following formula.
CNF ratio (% by mass) = [ amount of CNF charged ]/([ amount of cellulose ester charged ] + [ amount of CNF charged ]) × 100
When the CNF ratio is too low, the strength of the hollow fiber membrane becomes low. On the other hand, if the CNF ratio is too high, the fractionation performance of the hollow fiber membrane becomes low. If the CNF ratio is too high, the viscosity of the spinning dope may become too high, and it may be difficult to perform spinning.
The mass ratio of the solvent (S)/the non-solvent (NS) (S/NS ratio) in the spinning dope is preferably 40/60 to 70/30. If the mass ratio of the solvent/non-solvent in the dope is too small (the NS ratio is excessively increased), the homogeneity of the structure of the film cross section may be high, but the spinning stability may be lowered, and therefore, the S/NS ratio is more preferably 50/50 to 70/30.
(kneading)
In the present embodiment, the spinning dope is kneaded before the spinning step. "kneading" means: after mixing the materials of the spinning dope, a shearing force in a specific range as described later is further applied, and the CNF is forcedly dispersed in the spinning dope by a high temperature and/or pressure system. By carrying out such kneading, it is expected that: the dispersion (dispersion uniformity) of CNF in the spinning dope is improved, the occurrence of defects in the hollow fiber membrane due to aggregation of CNF and the like is suppressed, the strength of the hollow fiber membrane is improved, and the maintenance rate of water permeability is improved.
The kneading step is carried out using, for example, a planetary mixer, an extruder, a kneader (a pressure kneader, a twin arm kneader, or the like), or the like.
In view of solubility of cellulose ester and modification by heat, the temperature at the time of kneading the dope is preferably 150 to 200 ℃, more preferably 160 to 190 ℃.
In view of improvement in the degree of kneading and thermal deterioration due to shearing, the shear rate at the time of kneading is preferably 500 to 3500sec -1 More preferably 500 to 2000sec -1 。
The order of adding the polymer containing cellulose ester, which is a constituent material of the hollow fiber membrane, the cellulose-based nanofibers (CNF), the polymer when the solvent and the non-solvent are mixed, the CNF, and the like, and the mixing method are not particularly limited.
For example, CNF may be added to a kneaded product of a polymer, a solvent, and a non-solvent, or a slurry obtained by dispersing CNF in a solvent or a non-solvent may be added to a kneaded product containing a polymer.
After the final kneading of the dope, CNFs or large clusters having a large fiber length are preferably removed from the dope by filtration. This can expect that: the dispersibility (dispersion uniformity) of CNF in the dope is further improved, the occurrence of defects in the hollow fiber membrane due to aggregation of CNF and the like is suppressed, the strength of the hollow fiber membrane is further improved, and the maintenance ratio of water permeability is further improved.
(solidification liquid)
The solidification solution preferably contains a solvent and a non-solvent (excluding water). In this case, the coagulation liquid may further contain water in addition to the solvent and the non-solvent. The ratio of the total amount of the solvent and the non-solvent in the coagulation liquid (hereinafter, sometimes referred to as "concentration of the coagulation liquid") is preferably 30 to 70% by mass, and more preferably 33 to 50% by mass.
The temperature of the solidification solution is preferably 10 to 30 ℃. In this case, the structural homogeneity of the hollow fiber membrane in the thickness direction can be improved.
Examples
The present invention will be described in more detail below with reference to examples, but the present invention is not limited thereto.
[ example 1]
The hollow fiber membrane of example 1 was produced under the following conditions by the method for producing a hollow fiber membrane described in the embodiment.
(composition of spinning dope)
Cellulose ester: cellulose Triacetate (CTA) (LT 35, manufactured by Daiiol corporation)
Cellulose ester concentration: 41.2% by mass (in the dope)
CNF: powder of CNF (first Industrial pharmaceutical Co., ltd., I-2 SX)
CNF ratio (ratio of amount of CNF to total amount of CTA to CNF): 1.0% by mass
Solvent: n-methylpyrrolidone (NMP)
Non-solvent: ethylene Glycol (EG)
[ solvent/non-solvent (S/NS) ratio =55/45]
Benzoic acid [ 0.3% by mass ]
(preparation of dope)
The CNF powder is mixed with other materials, and the mixed materials (spinning dope) are kneaded to prepare a spinning dope used in a spinning step.
The mixing temperature is as follows: 185 ℃ and shear rate: 1500 to 1700[ 2 ] (1/sec), the kneading retention time of the dope was adjusted to 30 minutes.
(conditions of spinning step)
Dissolution temperature of spinning dope: 185 deg.C
Spinning dope ejection temperature: 158 deg.C
Nozzle for ejection: three-divided nozzle (sectional area of nozzle: 0.05 mm) 2 )
[ the sectional area of the nozzle means: the cross-sectional area of the dope discharge hole in the tip portion of the nozzle. ]
Air travel unit (AG) residence time: 0.06 second
Temperature of the solidification liquid: 18 deg.C
The pulling-out speed: 40 m/min
(composition of solidification liquid)
Solvent (S): NMP
Non-solvent (NS): EG
Water (W)
Concentration of solidification solution [ (mass of S + mass of NS)/mass of solidification solution ]:45 percent of
The S/NS ratio was the same as the dope.
[ conditions of post-treatment Process ]
Conditions of Hot Water treatment
The temperature is 98 DEG C
The time is 20 minutes
Conditions of salting (salt annealing) treatment
Concentration of salt solution 4.5% by mass
The temperature of the salt water is 82 DEG C
The time is 20 minutes
[ examples 2 to 11]
The CNF addition concentration, the cellulose ester type, the S/NS ratio of the raw material solution, the kneading temperature, the shear rate during kneading, and the coagulation bath temperature were changed as shown in Table 1. In example 7, the ratio LT35/LT75 was 88/12. Except for this, the hollow fiber membranes of examples 2 to 11 were produced in the same manner as in example 1. (Note that, in Table 1, the left arrow indicates the same as the left column.)
Comparative example 1
CNF was not added to the dope. The hollow fiber membrane of comparative example 1 was obtained in the same manner as in example 1 except for the above.
Comparative examples 2 to 4
The CNF addition concentration, the S/NS ratio of the raw material solution, and the kneading temperature were changed as shown in Table 1. Except for this, the hollow fiber membranes of comparative examples 2 to 4 were produced in the same manner as in comparative example 1.
< measurement of outer diameter and inner diameter >
The inner and outer diameters of the hollow fiber membranes of examples 1 to 11 and comparative examples 1 to 4 were measured by the following methods.
The outer diameter and the inner diameter of the hollow fiber membrane were obtained as follows: the hollow fiber membranes were cut along the upper and lower surfaces of the slide glass with a razor through a hole having a diameter of 3mm provided in the center of the slide glass to such an extent that the hollow fiber membranes did not fall off, to obtain a sample of a cross section of the hollow fiber membranes, and then the short and long diameters of the cross section of the hollow fiber membranes were measured by a projector (Nikon PROFILE PROJECTORV-12).
Regarding the outer diameter, the dimensions in the X-X direction and the Y-Y direction of the outer surface of the hollow fiber membrane were measured for each 1 section of the hollow fiber membrane, and the arithmetic average of the values thereof was taken as the outer diameter of the 1 section of the hollow fiber membrane. Further, the inner diameter was measured in the X-X direction and Y-Y direction of the hollow portion for each 1 cross section of the hollow fiber membrane, and the arithmetic average was taken as the inner diameter of 1 cross section of the hollow fiber membrane. The measurement was performed in the same manner for 10 cross sections including the maximum and minimum, and the average values were defined as the inner diameter and the outer diameter.
The measurement results of the outer diameter and the inner diameter of the hollow fiber membrane are shown in table 1.
< measurement of Strength elongation >
The strength and elongation (yield strength, breaking strength, yield elongation, and breaking elongation) of the hollow fiber membranes of examples 1 to 11 and comparative examples 1 to 4 were measured by the following methods.
The strength and elongation were measured by using a fiber tensile tester (Model No. RTC1210A, manufactured by A & D).
Using a member having a full scale of 5000g (conditions were set to 200 g), a monofilament having a total length of about 15cm was fixed to a chuck (inter-chuck distance: 5 cm), and the lower chuck was lowered at a speed of 50 mm/min.
The load (breaking strength) and elongation (breaking elongation) of each monofilament at the breaking point of the hollow fiber membrane and the load (yield strength) and elongation (yield elongation) of each monofilament at the yield point were read from the S-S curve imprinted on the recording sheet. Specifically, the load and the elongation were obtained by the method shown in [0061] of Japanese patent application laid-open No. 2011-212638.
The strength and elongation were measured using a hollow fiber membrane in a wet state at a temperature of 20 ℃ and a humidity of 65%.
The measurement results are shown in table 1. In each of examples and comparative examples, 5 measurements were performed, and the average values are shown in table 1.
[ Table 1]
As shown in table 1, the examples have a lower yield elongation and an increased yield strength compared to the comparative examples, and the ratio of yield strength (gf/root)/yield elongation (%) is higher (i.e., the stress required per unit elongation), indicating a reversible increase in strength in the yield region.
The elongation at break was suppressed, the breaking strength was improved, and the breaking strength (gf/root)/elongation at break (%) (i.e., the stress/elongation ratio at the breaking point) was increased, and this indicated that the hollow fiber membrane had a small change in shape and was less likely to break.
In fig. 7, the fracture strength and FR are shown in the form of a graph for the examples and comparative examples 4 (amount of permeated water after 4 years under accelerated pressure resistance conditions).
The upper range from the line separating the example and the comparative example shown in fig. 7 is a range satisfying the following relational expression (see the lowermost 2 rows of table 1). That is, the examples satisfy the following relational expressions.
Breaking Strength [ gf/root]/3+FR 4 [L/m 2 /D]≥4.58×10 -3 X (OD after AN) 2 [μm]
As described above, the hollow fiber membrane of the present invention can maintain a permeability equal to or higher than a predetermined value even when the breaking strength is high.
< measurement of permeated Water amount >
The hollow fiber membranes of examples 1 to 11 and comparative examples 1 to 4 were subjected to a confirmation test of RO performance using a high concentration brine.
Specifically, first, the hollow fiber membranes are bundled into a U shape, and after a plastic sleeve is inserted, a thermosetting resin is injected into the sleeve, cured, and sealed. Cutting the end of the hollow fiber membrane cured with the thermosetting resin to obtain the open face of the hollow fiber membrane, and making the membrane area of the outer diameter standard 0.16m 2 The module for evaluation 30 (fig. 6).
The RO performance of the module for evaluation 30 was evaluated using a membrane performance test apparatus equipped with an evaluation liquid tank 40, a feed pump 42, a casing 31, a flow rate adjustment valve 43, a pressure adjustment valve 44, and the like as shown in fig. 6.
[ evaluation of Standard conditions ]
Specifically, water was permeated from the outside to the inside of the hollow fiber membranes under conditions (standard conditions) in which an aqueous solution of sodium chloride (NaCl) having a concentration of 35000ppm was allowed to flow at 25 ℃ and a pressure of 5.4MPa on the outside of the hollow fiber membranes. This RO treatment was carried out for 1 hour. Then, the membrane permeation water was collected from the open surface of the hollow fiber membrane, and the amount of permeation water was measured.
Based on the amount of permeated water, the amount of permeated water per 1 day per unit membrane area under the above standard conditions (standard condition permeated stream: FRs) was calculated by the following formula.
FRs[L/m 2 Day/day]= amount of permeated Water [ L ]]Area of membrane [ m ] 2 ]Time of acquisition [ min ]]X (60 [ min.)]X 24[ hour])
[ evaluation of accelerated pressure resistance conditions ]
Next, the pressure resistance acceleration test conditions were changed according to the standard conditions, and water was allowed to permeate from the outside to the inside of the hollow fiber membranes under the conditions that an aqueous solution of sodium chloride (NaCl) having a concentration of 47300ppm was allowed to flow at 35 ℃ and a pressure of 6.76MPa on the outside of the hollow fiber membranes. This RO treatment was carried out for 2 hours, membrane permeate was collected from the open surface of the hollow fiber membrane, the amount of permeate was measured, and the amount of permeate per unit membrane area per 1 day was calculated by the following formula (pressure resistance accelerated test condition permeate: FR 0).
FR 0 [L/m 2 Day/day]= amount of permeated Water [ L ]]Area of membrane [ m ] 2 ]Collection time [ minutes ]]X (60 [ min.)]X 24[ hour])
[ calculation of the coefficient of variation (-m value) of permeation Water amount ]
The value of m is determined as follows.
The amount of permeated water was continuously measured for 100 hours, and changes in the amount of permeated water were confirmed. The coefficient of change (-m value) of the permeated water amount indicates the gradient of the change in the permeated water amount according to the elapsed time.
The value of "m" is calculated from the slope of a regression line of the logarithmic value of time and permeated water amount, x = log (elapsed time), and y = log (permeated water amount) (the following formula).
[ mathematical formula 1]
Next, the retention rate (MF) of the permeated water amount after 4 years under the pressure resistance acceleration condition and the permeated water amount after 4 years under the pressure resistance acceleration condition were calculated by the above equations.
Retention rate of permeation Water volume after 4 years under accelerated pressure resistance (MF)
= (4 years X365 days X24 hours/2 hours) (-m) ＝17520 (-m)
Permeation Water volume after 4 years under accelerated pressure resistance conditions (FR) 4 )
＝FR 0 ×MF
The results of the above measurements and the like are shown in table 1.
As shown in table 1, in examples 1 to 11, compared with comparative examples 1 to 4, hollow fiber membranes excellent in both water permeability and retention rate of water permeability after the lapse of time were obtained.
< staining test >
The dyeing test was performed for example 3 and comparative example 2. Specifically, in the membrane performance test apparatus shown in fig. 6, a fluorescent dye (molecular weight 570) manufactured by NACALAI tesquue was added to the evaluation liquid 41 in the evaluation liquid tank 40, and RO evaluation operation was performed for 1 hour under the above standard conditions. In addition, the dyeing test stains a portion of the film where a partial defect occurs.
Fig. 2 and 3 show micrographs of the hollow fiber membranes of example 3 and comparative example 2 after the dyeing test, respectively. Fig. 2 shows a hollow fiber membrane obtained in example 3, and fig. 3 shows a hollow fiber membrane obtained in comparative example 2.
In addition, as for example 3 and comparative example 2, the microphotographs of the hollow fiber membranes of example 3 and comparative example 2 after the breakage when the measurement of the strength and elongation is performed after the dyeing test are respectively shown in fig. 4 and 5. Fig. 4 (a) and (b) are photographs corresponding to fig. 2 (a) and (b), and fig. 5 (a) to (c) are photographs corresponding to fig. 3 (a) to (c).
As is clear from the photograph shown in fig. 5, the hollow fiber membrane was broken at the portion dyed by the dyeing test.
< determination of salt removal Rate >
The salt removal rate was measured for example 3 and comparative example 2. Specifically, the NaCl concentration (salt concentration) was measured using a conductivity meter (CM-25R, DKK-TOA) for the feed aqueous solution having a NaCl concentration of 35000ppm used for the measurement of the amount of permeated water and the membrane permeated water collected for the measurement of the amount of permeated water. Based on the measurement results, the salt removal rate was calculated by the following formula.
Salt removal rate [% ] = (1-membrane permeated water salt concentration [ mg/L ]/supplied aqueous solution salt concentration [ mg/L ]) × 100
As a result, the salt removal rate of example 3 was 99.9% (0.1% in terms of salt permeability), and the salt removal rate of comparative example 2 was 95.0% (5% in terms of salt permeability). From the results, it is understood that comparative example 2 has a large salt permeability, and thus the dispersibility of CNF is also poor, suggesting the possibility of occurrence of partial defects.
The embodiments and examples disclosed herein are illustrative in all respects, rather than restrictive. The scope of the present invention is defined not by the above description but by the claims, and is intended to include all modifications within the meaning and scope equivalent to the claims.
Description of the reference numerals
10 spinning dope, 11 nozzles, 12, 13, 14, 15 rolls, 16 hollow fiber membranes, 21 coagulation liquid, 30 evaluation modules, 31 casing, 40 evaluation liquid tank, 41 evaluation liquid, 42 supply pump, 43 flow rate regulating valve, 44 pressure regulating valve.
Claims (11)
1. A hollow fiber membrane comprising a cellulose ester and a cellulose-based nanofiber.
2. The hollow fiber membrane of claim 1,
the ratio of the amount of the cellulose-based nanofibers to the total amount of the cellulose ester and the cellulose-based nanofibers is 0.01 to 10% by mass.
3. The hollow-fiber membrane according to claim 1 or 2,
the cellulose-based nanofibers have a fiber width, i.e., a fiber diameter, of 1nm to 200nm.
4. A method for producing a hollow fiber membrane comprising a cellulose ester and a cellulose nanofiber, the method comprising:
a spinning step of discharging a spinning dope from a nozzle through an air-traveling part into a coagulating liquid, and drawing out a coagulated product of the spinning dope from the coagulating liquid to obtain a hollow fiber membrane as a hollow fiber type semipermeable membrane,
the spinning solution comprises cellulose ester, cellulose nano-fiber, solvent and non-solvent,
the spinning dope is kneaded before the spinning step.
5. The manufacturing method according to claim 4,
mixing the cellulose ester, the cellulose nanofiber powder, the solvent and the non-solvent to obtain the spinning dope, or
Mixing a slurry obtained by dispersing a powder of the cellulose-based nanofibers in the solvent with the cellulose ester and the non-solvent, and kneading the obtained spinning dope, or
Mixing a slurry obtained by dispersing a powder of the cellulose-based nanofibers in the non-solvent, the cellulose ester and the solvent, and kneading the obtained spinning dope.
6. The manufacturing method according to claim 4 or 5,
in the spinning dope, the ratio of the amount of the cellulose-based nanofibers to the total amount of the cellulose ester and the cellulose-based nanofibers is 0.01 to 10 mass%.
7. The production method according to any one of claims 4 to 6,
the concentration of the cellulose ester in the spinning dope is 20 to 60 mass%.
8. The production method according to any one of claims 4 to 7,
the temperature for mixing the spinning solution is 150-200 ℃.
9. The production method according to any one of claims 4 to 8,
the shear rate at the time of kneading the spinning dope was 500sec -1 ～3500sec -1 。
10. The production method according to any one of claims 4 to 9,
in the spinning dope, the cellulose-based nanofibers have a fiber width, i.e., a fiber diameter, of 1nm to 200nm.
11. A hollow fiber membrane produced by the production method according to any one of claims 4 to 10, comprising a cellulose ester and a cellulose nanofiber.
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| JPWO2021200427A1 (en) | 2021-10-07 |
| WO2021200427A1 (en) | 2021-10-07 |
| JP7396464B2 (en) | 2023-12-12 |
| JP2024015003A (en) | 2024-02-01 |
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