CN114950150B - Extremely-low-pressure reverse osmosis membrane and preparation method thereof - Google Patents
Extremely-low-pressure reverse osmosis membrane and preparation method thereof Download PDFInfo
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D67/00—Processes specially adapted for manufacturing semi-permeable membranes for separation processes or apparatus
- B01D67/0002—Organic membrane manufacture
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D69/00—Semi-permeable membranes for separation processes or apparatus characterised by their form, structure or properties; Manufacturing processes specially adapted therefor
- B01D69/10—Supported membranes; Membrane supports
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D69/00—Semi-permeable membranes for separation processes or apparatus characterised by their form, structure or properties; Manufacturing processes specially adapted therefor
- B01D69/10—Supported membranes; Membrane supports
- B01D69/105—Support pretreatment
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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
- B01D69/12—Composite membranes; Ultra-thin membranes
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02A—TECHNOLOGIES FOR ADAPTATION TO CLIMATE CHANGE
- Y02A20/00—Water conservation; Efficient water supply; Efficient water use
- Y02A20/124—Water desalination
- Y02A20/131—Reverse-osmosis
Abstract
The invention provides an ultra-low pressure reverse osmosis membrane and a preparation method thereof. According to the preparation method provided by the invention, one surface of a substrate layer is coated with a polysulfone membrane casting solution, and then the substrate layer is placed in a gel bath solution for phase conversion to form a membrane, so that a polysulfone supporting layer is formed; then, the obtained membrane material is soaked in the aqueous phase solution 1, and then vacuum water absorption treatment is carried out; then, spraying the surface of the polysulfone supporting layer by using the aqueous phase solution 2, and finally heating and drying; then, coating an oil phase solution on the surface of the polysulfone supporting layer of the obtained membrane material, and then carrying out heat treatment to form a polyamide separation layer on the surface of the polysulfone supporting layer; then, rinsing the obtained membrane material; and finally, coating a PVA solution on the surface of the polyamide separation layer of the obtained membrane material, and then drying to obtain the ultra-low pressure reverse osmosis membrane. By the method, the air tightness of the membrane material can be effectively improved on the basis of ensuring the separation performance (flux and desalination rate) of the reverse osmosis membrane.
Description
Technical Field
The invention relates to the technical field of water treatment, in particular to an ultra-low pressure reverse osmosis membrane and a preparation method thereof.
Background
Reverse osmosis is a membrane separation technology which uses pressure as driving force by virtue of the function of a selective permeation (semi-permeation) membrane, when the pressure applied in a system is greater than the osmotic pressure of an inlet water solution, water molecules continuously permeate the membrane, impurities in water such as soluble solids, organic matters, colloidal substances, bacteria and the like are intercepted by the reverse osmosis membrane, and are concentrated and removed in intercepted liquid, so that the separation and purification purposes are achieved.
The technical core of reverse osmosis is reverse osmosis membrane, and the ultra-low pressure reverse osmosis membrane can effectively realize reverse osmosis under lower operating pressure, can stably and continuously output under the ultra-low pressure, keeps the effects of high flux, high desalination rate and the like, and is the main type of the current reverse osmosis membrane product.
Very low pressure hair permeable membranes are generally composed of a nonwoven fabric layer (i.e., a substrate layer), a porous support layer, and a separation layer (typically a polyamide layer). At present, a plurality of porous supporting layers are mainly formed on a non-woven fabric layer by polysulfone membrane casting liquid through a phase inversion method, and a separating layer is mainly formed on the porous supporting layers by m-phenylenediamine monomers and trimesoyl chloride monomers through an interfacial polymerization method. The separating layer determines the separating properties of the composite membrane, and the primary mechanical strength is provided by the primary backing membrane (i.e., the composite membrane of the porous support layer and the non-woven fabric). The performance of the composite film can be improved by changing the structural properties of the separating layer and the base film.
At present, in the production of an ultra-low pressure reverse osmosis membrane, the flux of the membrane is generally mainly improved, and the air tightness of the membrane is less concerned. The flux of the membrane is improved mainly by improving the aperture size of the bottom membrane and increasing the diffusion rate of a reactant MPD (namely 2-methyl-2,4-pentanediol) in the reaction process. However, if the pore diameter of the primary membrane is increased, the support strength is weak, and other substances are easily adsorbed during the rinsing process of the coating film, which causes subsequent moisture absorption and swelling, and damages the polyamide separation layer, thereby affecting the air tightness of the membrane. Moreover, the diffusion rate of a reactant MPD in the reaction process is increased, so that the thickness of the formed polyamide dense layer is easy to be thin, the integral strength of the polyamide dense layer is insufficient, the polyamide dense layer is easy to be damaged by external force and generate defects, and the air tightness of the membrane is influenced. Therefore, the means for improving the membrane separation effect often leads to the reduction of air tightness, but in the current production, the improvement of the membrane separation effect is generally mainly focused, and the problem of air tightness of the membrane sheet is neglected.
Generally, the reduction of the air tightness of the membrane does not have a significant influence on the separation performance of the reverse osmosis membrane, but the reverse osmosis membrane is finally used for forming a membrane element, the membrane element is mainly formed by assembling the membrane with a flow channel grid, a water production flow channel material, a water production central pipe and the like through an adhesive, the defects of glue leakage and the like exist in the manufacturing process of the membrane element, the air tightness of the element needs to be checked through air detection, and the air tightness of the membrane is poor, so that the misjudgment of the air detection is easily caused, and the production efficiency is influenced.
Disclosure of Invention
In view of the above, the present invention is directed to an ultra-low pressure reverse osmosis membrane and a method for preparing the same. The ultra-low pressure reverse osmosis membrane provided by the invention can effectively improve the air tightness of the membrane on the basis of ensuring the membrane separation performance.
The invention provides a preparation method of an ultra-low pressure reverse osmosis membrane, which comprises the following steps:
a) Coating a polysulfone membrane casting solution on one surface of the substrate layer, and then putting the substrate layer in a gel bath solution for phase inversion to form a membrane so as to form a polysulfone supporting layer;
the polysulfone membrane casting solution comprises the following components in percentage by mass:
12% -18% of polysulfone;
5% -15% of 2-dimethoxyethanol;
the balance of organic solvent;
the temperature of the gel bath solution is 12 to 15 ℃;
b) Dipping the membrane material obtained in the step a) in an aqueous phase solution 1, and then carrying out vacuum water absorption treatment; then, spraying the surface of the polysulfone supporting layer by using the aqueous phase solution 2, and finally heating and drying;
the aqueous phase solution 1 comprises the following components in percentage by mass:
1.0% -2.0% of aromatic amine monomer;
1% to 18% of additive;
the balance of water;
the additive 1 is an organic sulfur compound containing C2-C12 alkyl and/or an organic phosphorus compound containing C2-C12 alkyl;
the aqueous phase solution 2 comprises the following components in percentage by mass:
2% -12% of an additive;
the balance of water;
the additive 2 is an organic sulfur compound containing C2-C12 alkyl and/or an organic phosphorus compound containing C2-C12 alkyl;
c) Coating an oil phase solution on the surface of the polysulfone supporting layer of the membrane material obtained in the step b), and then carrying out heat treatment to form a polyamide separation layer on the surface of the polysulfone supporting layer;
the oil phase solution comprises the following components in percentage by mass:
0.1% -0.2% of aromatic acyl chloride monomer;
the balance of organic solvent;
d) Rinsing the membrane material obtained in the step c);
e) Coating PVA solution on the surface of the polyamide separation layer of the membrane material obtained in the step d), and then drying to obtain the ultra-low pressure reverse osmosis membrane.
Preferably, in the step b), the vacuum pressure of the vacuum water absorption treatment is-5 kPa to-15 kPa, and the treatment time is 9 to 18s.
Preferably, in the step b), the vacuum water absorption treatment is as follows: continuously carrying out three times of vacuum water absorption treatment by three groups of vacuum water absorption plates;
the vacuum pressure of each group of vacuum water absorption plates is independently selected from-5 kPa to-15 kPa, and the processing time is 3 to 6s.
Preferably, in the step d), the rinsing specifically includes sequentially performing the following rinsing steps:
d1 Rinsing with aqueous NaOH solution;
d2 Rinsing with an aqueous IPA solution;
d3 Rinsing with an aqueous IPA solution;
d4 Rinsing with an aqueous IPA solution;
d5 Rinsing with RO water;
d6 Rinsing with an aqueous glycerol solution;
wherein the content of the first and second substances,
the temperature of the aqueous IPA solution in step d 2) > the temperature of the aqueous IPA solution in step d 3), the temperature of the aqueous IPA solution in step d 3) < the temperature of the aqueous IPA solution in step d 4).
Preferably, in step d 1):
the temperature of the NaOH aqueous solution is as follows: the temperature is more than or equal to 20 ℃ and less than 30 ℃; the pH value of the NaOH aqueous solution is 11.5 to 12.5; rinsing time is 0.5 to 1min;
in the step d 2):
the temperature of the IPA aqueous solution is as follows: the temperature is more than or equal to 30 ℃ and less than or equal to 45 ℃; the mass percentage concentration of the IPA aqueous solution is 20-30%; rinsing time is 4 to 5min;
in said step d 3):
the temperature of the IPA aqueous solution is as follows: the temperature is more than or equal to 20 ℃ and less than 30 ℃; the mass percentage concentration of the IPA aqueous solution is 20-30%; rinsing time is 0.5 to 1min;
in the step d 4):
the temperature of the IPA aqueous solution is as follows: the temperature is more than or equal to 30 ℃ and less than or equal to 45 ℃; the mass percentage concentration of the IPA aqueous solution is 20-30%; rinsing time is 4 to 5min;
in said step d 5):
the temperature of the RO water is as follows: the temperature is more than or equal to 20 ℃ and less than 30 ℃; rinsing time is 0.5 to 1min;
in said step d 6):
the temperature of the glycerol aqueous solution is as follows: the temperature is more than or equal to 20 ℃ and less than or equal to 30 ℃; the mass percentage concentration of the glycerol aqueous solution is 4-5%; the rinsing time is 2 to 3min.
Preferably, in step b):
the additive 1 comprises one or more of sodium dodecyl sulfate, dimethyl sulfoxide, hexamethyl phosphoric triamide and camphorsulfonic acid;
the additive 2 comprises one or more of dimethyl sulfoxide and hexamethyl phosphoric triamide;
in the step c):
the organic solvent is at least one selected from n-hexane, isopar G and Isopar L.
Preferably, in the step e), the PVA solution comprises the following components in percentage by mass:
PVA 1%~5%；
5% -10% of glycerol;
0.1% -1% of a surfactant;
the balance of water.
Preferably, the surfactant is selected from one or more of sodium dodecyl sulfate, sodium dodecyl sulfate and hexadecyl trimethyl ammonium bromide.
Preferably, in step b):
the dipping time is 0.2 to 1min;
the spraying amount of the spraying is 15 to 25 g/m 2 ；
The temperature for heating and drying is 40 to 60 ℃;
in the step c):
the coating amount of the oil phase solution is 20 to 50 g/m 2 ；
The temperature of the heat treatment is 50 to 80 ℃.
The invention also provides the ultra-low pressure reverse osmosis membrane prepared by the preparation method in the technical scheme.
The preparation method provided by the invention is carried out according to the steps a) to e) in sequence, in the step a), firstly, a polysulfone membrane casting solution is coated on one surface of a substrate layer, then, the substrate layer is placed in a gel bath solution for phase conversion to form a membrane, wherein 2-methoxyethanol is added into the polysulfone membrane casting solution, the gel temperature is controlled to be within a specific range of 12 to 15 ℃, and the two aspects are matched, so that the compactness of a base membrane is favorably improved, the stable structure is ensured, and the air tightness of a membrane product is improved. In the step b), two aqueous phase solutions are coated in sequence, and vacuum water absorption treatment is added between the two aqueous phase solutions to promote the diffusion of aqueous phase components and ensure the effective concentration of a polar solvent, so that the performance requirement of extremely low pressure membrane is favorably ensured. In the step d), different rinsing treatments are performed according to a certain sequence, which is beneficial to improving the structural stability of the membrane material, improving the air tightness and ensuring the membrane separation performance. In the step e), a PVA solution is coated to form a protective layer, which is beneficial to improving the structural stability of the material. By the method, the air tightness of the membrane material can be effectively improved on the basis of ensuring the separation performance (flux and desalination rate) of the reverse osmosis membrane, and the problem that the air tightness is reduced by means of improving the membrane flux in the prior art is solved.
The experimental result shows that the gas detection value of the membrane obtained by the invention is below 1.44kPa, and the gas detection value is further remarkably reduced to be below 0.55kPa when the membrane is under the preferable vacuum pressure (-10 to-15 kPa) (by comparing the example 1 with the example 2,4). Meanwhile, the water flux of the membrane obtained by the invention is more than 27.8GFD, the desalination rate is more than 99.20, and good membrane flux and desalination rate are maintained.
Detailed Description
The invention provides a preparation method of an ultra-low pressure reverse osmosis membrane, which comprises the following steps:
a) Coating a polysulfone membrane casting solution on one surface of the substrate layer, and then putting the substrate layer in a gel bath solution for phase inversion to form a membrane so as to form a polysulfone supporting layer;
the polysulfone membrane casting solution comprises the following components in percentage by mass:
12% -18% of polysulfone;
5% -15% of 2-methoxy ethanol;
the balance of organic solvent;
the temperature of the gel bath solution is 12 to 15 ℃;
b) Dipping the membrane material obtained in the step a) in an aqueous phase solution 1, and then carrying out vacuum water absorption treatment; then, spraying the surface of the polysulfone supporting layer by using the aqueous phase solution 2, and finally heating and drying;
the aqueous phase solution 1 comprises the following components in percentage by mass:
1.0% -2.0% of aromatic amine monomer;
1% to 18% of additive;
the balance of water;
the additive 1 is an organic sulfur compound containing C2-C12 alkyl and/or an organic phosphorus compound containing C2-C12 alkyl;
the aqueous phase solution 2 comprises the following components in percentage by mass:
2% -12% of an additive;
the balance of water;
the additive 2 is an organic sulfur compound containing C2-C12 alkyl and/or an organic phosphorus compound containing C2-C12 alkyl;
c) Coating an oil phase solution on the surface of the polysulfone supporting layer of the membrane material obtained in the step b), and then carrying out heat treatment to form a polyamide separation layer on the surface of the polysulfone supporting layer;
the oil phase solution comprises the following components in percentage by mass:
0.1% -0.2% of aromatic acyl chloride monomer;
the balance of organic solvent;
d) Rinsing the membrane material obtained in the step c);
e) Coating PVA solution on the surface of the polyamide separation layer of the membrane material obtained in the step d), and then drying to obtain the ultra-low pressure reverse osmosis membrane.
The preparation method provided by the invention is sequentially carried out according to the steps a) to e), in the step a), a polysulfone membrane casting solution is coated on one surface of a base material layer, and then the base material layer is placed in a gel bath solution to carry out phase inversion membrane formation, wherein 2-methoxyethanol is added into the polysulfone membrane casting solution, the gel temperature is controlled to be within a specific range of 12 to 15 ℃, and the two aspects are matched, so that the compactness of a base membrane is favorably improved, the stable structure is ensured, and the air tightness of a membrane product is improved. In the step b), two aqueous phase solutions are coated in sequence, and vacuum water absorption treatment is added between the two aqueous phase solutions to promote the diffusion of aqueous phase components and ensure the effective concentration of a polar solvent, so that the performance requirement of extremely low pressure membrane is favorably ensured. In the step d), different rinsing treatments are performed according to a certain sequence, which is beneficial to improving the structural stability of the membrane material, improving the air tightness and ensuring the separation performance of the membrane. In the step e), a PVA solution is coated to form a protective layer, which is beneficial to improving the structural stability of the material. By the method, the air tightness of the membrane material can be effectively improved on the basis of ensuring the separation performance (flux and desalination rate) of the reverse osmosis membrane, and the problem that the air tightness is reduced by means of improving the membrane flux in the prior art is solved.
[ with respect to step a ]:
a) And coating the polysulfone membrane casting solution on one surface of the substrate layer, and then placing the substrate layer in a gel bath solution for phase conversion to form a membrane, thereby forming the polysulfone support layer.
In the present invention, the kind of the substrate layer is not particularly limited, and may be a substrate that is conventional in the art, and specifically may be a nonwoven fabric.
In the invention, the polysulfone membrane casting solution comprises the following components in percentage by mass:
12% -18% of polysulfone;
5% -15% of 2-methoxy ethanol;
the balance of organic solvent.
Wherein, the source of the polysulfone is not specially limited, and the polysulfone can be a commercial product. The consumption of the polysulfone is 12% -18%, and specifically can be 12%, 13%, 14%, 15%, 16%, 17% and 18%. The source of the 2-methoxyethanol is not particularly limited, and may be a commercially available product. The dosage of the 2-methoxy ethanol is 5-15%, and specifically can be 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14% and 15%. The organic solvent is preferably dimethylformamide. The organic solvent is used as the balance, namely, the balance is 100%.
In the invention, the polysulfone membrane casting solution can be prepared by the following preparation method: and mixing the polysulfone, the 2-methoxy ethanol and the organic solvent to obtain the polysulfone membrane casting solution. The mixing mode is not particularly limited, and the materials can be fully dissolved and uniformly mixed, such as stirring and mixing. The mixing temperature is not particularly limited, and may be at room temperature, specifically 15 to 30 ℃. And mixing to obtain the polysulfone membrane casting solution.
In the present invention, the method for coating the polysulfone membrane-casting solution on the substrate layer is not particularly limited, and may be performed according to a conventional coating operation in the art. In the present invention, the coating is performed on one surface of the base material layer (any one of the upper and lower surfaces of the base material layer).
In the invention, a polysulfone membrane casting solution is coated on one surface of a substrate layer, and then the substrate layer is placed in a gel bath solution for phase inversion membrane formation. In the present invention, the gel bath solution is preferably RO water. After the membrane material is placed in the gel bath solution, the organic solvent in the polysulfone membrane casting solution can be gradually enriched, so that gelation is realized to realize phase inversion membrane formation. In the invention, the temperature of the gel bath solution is 12 to 15 ℃, namely the gel temperature is 12 to 15 ℃, and specifically 12 ℃, 13 ℃, 14 ℃ and 15 ℃. And forming a polysulfone supporting layer on the surface of the base material layer after the treatment.
In the step a), firstly, coating a polysulfone membrane casting solution on one surface of a substrate layer, and then placing the substrate layer in a gel bath solution for phase inversion to form a membrane, wherein 2-methoxyethanol is added into the polysulfone membrane casting solution, the gel temperature is controlled within a specific range of 12-15 ℃, and the density of a base membrane is improved, the stable structure is ensured, and the air tightness of a membrane product is improved.
[ regarding step b ]:
b) Dipping the membrane material obtained in the step a) in an aqueous phase solution 1, and then carrying out vacuum water absorption treatment; then, spraying the surface of the polysulfone supporting layer by using the water phase solution 2, and finally heating and drying.
In the invention, the aqueous phase solution 1 comprises the following components in percentage by mass:
1.0% -2.0% of aromatic amine monomer;
1% to 18% of additive;
the balance of water.
Wherein:
the aromatic amine monomer is preferably at least one of p-phenylenediamine, m-phenylenediamine, trimesamine, 3,5-diaminobenzoic acid and 1,2,4-triaminobenzene, and more preferably m-phenylenediamine. The dosage of the aromatic amine monomer is 1.0-2.0%, and specifically can be 1.0%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2.0%.
The additive 1 is an organic sulfur compound containing C2-C12 alkyl and/or an organic phosphorus compound containing C2-C12 alkyl, preferably comprises one or more of sodium dodecyl sulfate, dimethyl sulfoxide, hexamethylphosphoric triamide and camphorsulfonic acid, and most preferably comprises dimethyl sulfoxide, hexamethylphosphoric triamide, sodium dodecyl sulfate and camphorsulfonic acid. When the additive 1 is dimethyl sulfoxide, hexamethyl phosphoric triamide, sodium dodecyl sulfate and camphorsulfonic acid, the dosage of the dimethyl sulfoxide is preferably 5-10%, and specifically 5%, 6%, 7%, 8%, 9% and 10%; the preferable dosage of hexamethylphosphoric triamide is 2-4%, and the specific dosage can be 2%, 2.5%, 3%, 3.5% and 4%; the dosage of the sodium dodecyl sulfate is preferably 0.01% -0.1%, and specifically can be 0.01%, 0.02%, 0.03%, 0.04%, 0.05%, 0.06%, 0.07%, 0.08%, 0.09% and 0.1%; the preferable dosage of the camphorsulfonic acid is 2% -3%, and specifically can be 2.0%, 2.1%, 2.2%, 2.3%, 2.4%, 2.5%, 2.6%, 2.7%, 2.8%, 2.9%, 3.0%. The dosage of the additive 1 is 10-18%, and specifically can be 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17% and 18%.
The water is used as the balance, namely, the water is used for complementing 100 percent.
In the present invention, the aqueous solution 1 can be prepared by the following preparation method: mixing aromatic amine monomer, additive 1 and water to obtain aqueous phase solution 1. The mixing mode is not particularly limited, and the materials can be fully dissolved and uniformly mixed, such as stirring and mixing. The mixing temperature is not particularly limited, and may be at room temperature, specifically 20 to 30 ℃. After mixing, an aqueous phase solution 1 was obtained.
In the invention, the temperature condition for soaking the membrane material obtained in the step a) in the aqueous phase solution 1 is not particularly limited, and the soaking can be carried out at room temperature, and specifically can be 20 to 25 ℃. The soaking time is preferably 0.2 to 1min. And after the soaking is finished, taking out the membrane material, and carrying out the next step of treatment.
In the present invention, after the immersion treatment, vacuum water absorption treatment is performed. In the invention, the vacuum water absorption treatment is carried out on the back surface (namely the polysulfone support layer) of the membrane material obtained in the step a), namely the direction of negative pressure suction is from the base material layer → the polysulfone support layer, so that the aqueous phase solution 1 is fully infiltrated into the polysulfone layer. In the present invention, the vacuum pressure of the vacuum water absorption treatment is preferably-5 kPa to-15 kPa, and more specifically-5 kPa, 6kPa, 7kPa, 8kPa, 9kPa, 10kPa, 11kPa, 12kPa, 13kPa, 14kPa, and 15kPa. The vacuum pressure = absolute pressure-atmospheric pressure. In the present invention, the total time length of the vacuum treatment is preferably 9 to 18s, and specifically may be 9s, 10s, 11s, 12s, 13s, 14s, 15s, 16s, 17s, and 18s. According to the invention, through vacuum water absorption treatment, under the action of vacuum negative pressure, effective components in a water phase fully permeate into membrane pores, and meanwhile, water in the membrane material migrates and diffuses to the surface of the membrane, so that the water phase solution 1 fully infiltrates the membrane material.
In the present invention, the vacuum water absorption treatment is preferably: three times of vacuum water absorption treatment are carried out continuously by three groups of vacuum water absorption plates. Wherein the vacuum pressure of each group of vacuum water absorption plates is independently selected from-5 kPa to-15 kPa, specifically can be-5 kPa, 6kPa, 7kPa, 8kPa, 9kPa, 10kPa, 11kPa, 12kPa, 13kPa, 14kPa and 15kPa, and more preferably is-10 kPa to-15 kPa. The processing time of each group of vacuum water absorption plates is independently selected from 3 to 6s, and specifically can be 3s, 4s, 5s and 6s.
In the invention, after vacuum water absorption treatment, the surface of the polysulfone supporting layer is sprayed by using the aqueous phase solution 2. In the invention, the aqueous phase solution 2 comprises the following components in percentage by mass:
2% -12% of an additive;
the balance of water.
The additive 2 is an organic sulfur compound containing C2-C12 alkyl and/or an organic phosphorus compound containing C2-C12 alkyl, preferably comprises one or more of dimethyl sulfoxide and hexamethylphosphoric triamide, and more preferably comprises dimethyl sulfoxide and hexamethylphosphoric triamide. When the additive 2 is dimethyl sulfoxide and hexamethylphosphoric triamide, the mass ratio of the dimethyl sulfoxide to the hexamethylphosphoric triamide is preferably (2~3) to 1, and specifically can be 2.0: 1, 2.1: 1, 2.2: 1, 2.3: 1, 2.4: 1, 2.5: 1, 2.6: 1, 2.7: 1, 2.8: 1, 2.9: 1 and 3.0: 1. The dosage of the additive 2 is 5% -10%, and specifically can be 5%, 6%, 7%, 8%, 9%, 9.5%, 10%, 10.5%, 11%, 11.5% and 12%. The water is used as the balance, namely, the water is used for complementing 100 percent.
In the present invention, the aqueous solution 2 can be prepared by the following preparation method: additive 2 was dissolved in water to give aqueous solution 2. The mode of mixing and dissolving the additive 2 and water is not particularly limited, and the materials can be fully dissolved and uniformly mixed, such as stirring, mixing and dissolving. The temperature of the dissolution is not particularly limited, and may be at room temperature, specifically 20 to 30 ℃. After dissolution, an aqueous phase solution 2 was obtained.
The inventionThe spraying amount of the aqueous solution 2 is preferably 15 to 25 g/m 2 Specifically, it may be 15g/m 2 、16g/m 2 、17g/m 2 、18g/m 2 、19g/m 2 、20g/m 2 、21g/m 2 、22g/m 2 、23g/m 2 、24g/m 2 、25g/m 2 。
In the present invention, the aqueous solution 2 is sprayed and then heated and dried. In the present invention, the heat drying is preferably performed by heating the back surface of the membrane material (i.e., polysulfone support layer) with a heated roller. In the present invention, the time for the heat drying is preferably 40 to 60 ℃, and specifically, 40 ℃, 45 ℃, 50 ℃, 55 ℃, 60 ℃.
In the step b), two aqueous phase solutions are coated in sequence, and vacuum water absorption treatment is added between the two aqueous phase solutions to promote the diffusion of aqueous phase components and ensure the effective concentration of a polar solvent, so that the performance requirement of extremely low pressure membrane is favorably ensured.
[ with respect to step c ]:
c) Coating the oil phase solution on the surface of the polysulfone supporting layer of the membrane material obtained in the step b), and then carrying out heat treatment to form a polyamide separation layer on the surface of the polysulfone supporting layer.
In the invention, the oil phase solution comprises the following components in percentage by mass:
0.1% -0.2% of aromatic acyl chloride monomer;
the balance of organic solvent.
Among them, the aromatic acid chloride monomer is preferably at least one of trimesoyl chloride and adipoyl chloride, and more preferably trimesoyl chloride. The dosage of the aromatic acyl chloride monomer is 0.1-0.2%, and specifically can be 0.1% or 0.2%. The organic solvent is preferably at least one of n-hexane, isopar G and Isopar L, more preferably Isopar L, and the use of Isopar L is more suitable for the diffusion reaction of the reaction monomers and has high safety. Wherein Isopar G and Isopar L are solvent types, and both belong to isoparaffin solvents. The organic solvent is used as the balance, namely, the balance is 100%.
In the invention, the oil phase solution can be prepared by the following preparation method: dissolving aromatic acyl chloride monomer in organic solvent to obtain oil phase solution. The mode of mixing and dissolving the aromatic acyl chloride monomer and the organic solvent is not particularly limited, and the aromatic acyl chloride monomer and the organic solvent can be fully dissolved and uniformly mixed, such as stirring, mixing and dissolving. The temperature of the dissolution is not particularly limited, and may be at room temperature, specifically 20 to 30 ℃. After dissolution, an oil phase solution is obtained.
In the present invention, the coating method of coating the oil phase solution on the surface of the membrane material polysulfone support layer is not particularly limited, and may be performed according to the conventional operation in the art. The coating amount of the coating is preferably 20 to 50 g/m 2 Specifically, it may be 20g/m 2 、25g/m 2 、30g/m 2 、35g/m 2 、40g/m 2 、45g/m 2 、50g/m 2 . In the present invention, after the oil phase solution is applied, the oil phase solution is brought into contact with the aqueous phase solution, and a polymerization reaction occurs at the coating interface to form polyimide.
In the present invention, heat treatment is performed after the coating. The oil phase is coated on the basement membrane after the interfacial polymerization reaction, and the further crosslinking reaction is carried out through heat treatment. In the present invention, the heat treatment temperature is preferably 50 to 80 ℃, and specifically 50 ℃, 55 ℃, 60 ℃, 65 ℃, 70 ℃, 75 ℃, 80 ℃. The time for the heat treatment is preferably 1 to 5min, and more preferably 2min. After heat treatment, a polyamide separation layer is formed on the surface of the polysulfone support layer.
[ with respect to step d ]:
d) Rinsing the membrane material obtained in step c).
In the present invention, the rinsing preferably comprises sequentially performing the following rinsing steps:
d1 Rinsing with aqueous NaOH solution;
d2 Rinsing with an aqueous IPA solution;
d3 Rinsing with an aqueous IPA solution;
d4 Rinsing with an aqueous IPA solution;
d5 Rinsing with RO water;
d6 Rinsing with an aqueous glycerol solution;
wherein the content of the first and second substances,
the temperature of the aqueous IPA solution in step d 2) > the temperature of the aqueous IPA solution in step d 3), the temperature of the aqueous IPA solution in step d 3) < the temperature of the aqueous IPA solution in step d 4). Specifically, the membrane material may be sequentially passed through 6 rinsing tanks, and the above 6 rinsing steps may be performed, respectively.
With respect to step d 1): rinsing with aqueous NaOH solution
The temperature of the aqueous NaOH solution is preferably: the temperature is not less than 20 deg.C and less than 30 deg.C, specifically 20 deg.C, 21 deg.C, 22 deg.C, 23 deg.C, 24 deg.C, 25 deg.C, 26 deg.C, 27 deg.C, 28 deg.C and 29 deg.C. The pH value of the NaOH aqueous solution is preferably 11.5 to 12.5, and specifically may be 11.5, 11.6, 11.7, 11.8, 11.9, 12.0, 12.1, 12.2, 12.3, 12.4, 12.5. The rinsing time is preferably 0.5-1min, and specifically may be 0.5min, 0.6min, 0.7min, 0.8min, 0.9min and 1min.
With respect to step d 2): rinsing with IPA aqueous solution
The temperature of the aqueous IPA (i.e., isopropyl alcohol) solution is preferably: the temperature is not less than 30 deg.C and not more than 45 deg.C, specifically 30 deg.C, 31 deg.C, 32 deg.C, 33 deg.C, 34 deg.C, 35 deg.C, 36 deg.C, 37 deg.C, 38 deg.C, 39 deg.C, 40 deg.C, 41 deg.C, 42 deg.C, 43 deg.C, 44 deg.C and 45 deg.C. The mass percentage concentration of the IPA aqueous solution is preferably 20-30%, and specifically can be 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, 30%. The rinsing time is preferably 4 to 5min, and specifically 4min, 4.5min and 5min.
With respect to step d 3): rinsing with IPA aqueous solution
The temperature of the aqueous IPA solution is preferably: the temperature is not less than 20 deg.C and less than 30 deg.C, specifically 20 deg.C, 21 deg.C, 22 deg.C, 23 deg.C, 24 deg.C, 25 deg.C, 26 deg.C, 27 deg.C, 28 deg.C and 29 deg.C. The mass percentage concentration of the IPA aqueous solution is preferably 20-30%, and specifically can be 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, 30%. The rinsing time is preferably 0.5 to 1min, and specifically can be 0.5min, 0.6min, 0.7min, 0.8min, 0.9min and 1min.
With respect to step d 4): rinsing with IPA aqueous solution
The temperature of the aqueous IPA solution is preferably: the temperature is not less than 30 deg.C and not more than 45 deg.C, specifically 30 deg.C, 31 deg.C, 32 deg.C, 33 deg.C, 34 deg.C, 35 deg.C, 36 deg.C, 37 deg.C, 38 deg.C, 39 deg.C, 40 deg.C, 41 deg.C, 42 deg.C, 43 deg.C, 44 deg.C and 45 deg.C. The mass percentage concentration of the IPA aqueous solution is preferably 20-30%, and specifically can be 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, 30%. The rinsing time is preferably 4 to 5min, and specifically 4min, 4.5min and 5min.
With respect to step d 5): rinsing with RO Water
The temperature of the RO water (also called RO pure water, i.e. water for reverse osmosis, also commonly called pure water) is preferably: the temperature is not less than 20 deg.C and less than 30 deg.C, specifically 20 deg.C, 21 deg.C, 22 deg.C, 23 deg.C, 24 deg.C, 25 deg.C, 26 deg.C, 27 deg.C, 28 deg.C and 29 deg.C. The rinsing time is preferably 0.5-1min, and specifically may be 0.5min, 0.6min, 0.7min, 0.8min, 0.9min and 1min.
With respect to step d 6): rinsing with aqueous glycerol solution
The temperature of the aqueous glycerol solution is preferably: the temperature is 20 deg.C or more and 30 deg.C or less, specifically 20 deg.C, 21 deg.C, 22 deg.C, 23 deg.C, 24 deg.C, 25 deg.C, 26 deg.C, 27 deg.C, 28 deg.C, 29 deg.C, and 30 deg.C. The mass percentage concentration of the glycerol aqueous solution is preferably 4-5%, and specifically can be 4%, 4.5% and 5%. The rinsing time is preferably 2 to 3min, and specifically can be 2min, 2.5min and 3min.
The steps d 1) to d 6) are carried out, the first step of rinsing is alkaline washing, and redundant H generated in the film forming process is removed + Meanwhile, slight hydrolysis is caused to the aromatic acyl chloride monomer, so that the permeability is further promoted to rise; the second step of rinsing is IPA solution rinsing, so that redundant substances such as aromatic amine monomers and the like are removed, the membrane surface is prevented from discoloring, and meanwhile, certain hole shrinkage effect is realized on membrane holes, so that the structure stability is facilitated; the third step of rinsing is IPA solution rinsing, which mainly has the function of preventing the substances from being enriched; the third step of rinsing is IPA solution rinsing, so that redundant substances such as aromatic amine monomers and the like are further removed, the membrane surface is prevented from discoloring, a certain hole shrinkage effect is realized on membrane holes, and the structural stability is further improved; the fourth rinsing step is RO water rinsing to further prevent the enrichment of residual substances. The sixth step is rinsing with glycerin water solution, and filling glycerin into the pores to prevent collapse of the poresThe traps cause the membrane flux to decay. According to the invention, six rinsing steps are sequentially carried out according to the sequence and are sequentially matched, so that the structural stability of the membrane material is improved, the air tightness is improved and the membrane separation performance is ensured.
[ with respect to step e ]:
e) Coating PVA solution on the surface of the polyamide separation layer of the membrane material obtained in the step d), and then drying to obtain the ultra-low pressure reverse osmosis membrane.
In the present invention, the PVA solution preferably comprises the following components in mass ratio:
PVA 1%~5%；
5% -10% of glycerol;
0.1% -1% of a surfactant;
the balance of water.
Wherein, the dosage of the PVA (namely polyvinyl alcohol) is 1-5 percent, and can be 1 percent, 2 percent, 3 percent, 4 percent and 5 percent. The glycerol is used in an amount of 5-10%, specifically 5%, 6%, 7%, 8%, 9% and 10%. The surfactant is preferably one or more of sodium dodecyl sulfate, sodium dodecyl sulfate and hexadecyl trimethyl ammonium bromide. The dosage of the surfactant is 0.1% -1%, and specifically can be 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%. The water is preferably RO water. The water is used as the balance, namely, the water is used for making up 100 percent.
In the present invention, the PVA solution may be prepared by the following preparation method: PVA, glycerol, a surfactant and water are mixed to obtain a PVA solution. The mixing is preferably stirring mixing. The temperature of the mixing is preferably 20 to 30 ℃. Stirring until the materials are completely dissolved to obtain a uniform and transparent PVA solution.
In the invention, PVA solution is coated on the surface of the polyamide separation layer of the membrane material obtained in the step d) and is evenly smeared by a smearing roller. In the present invention, drying is performed after the coating. In the present invention, the drying temperature is preferably 60 to 100 ℃. The drying time is preferably 1.5 to 4min. And forming a PVA protective layer on the surface of the polyamide separation layer after drying, thereby obtaining the ultra-low pressure reverse osmosis membrane.
The invention also provides the ultra-low pressure reverse osmosis membrane prepared by the preparation method in the technical scheme.
The preparation method provided by the invention is carried out according to the steps a) to e) in sequence, in the step a), firstly, a polysulfone membrane casting solution is coated on one surface of a substrate layer, then, the substrate layer is placed in a gel bath solution for phase conversion to form a membrane, wherein 2-methoxyethanol is added into the polysulfone membrane casting solution, the gel temperature is controlled to be within a specific range of 12 to 15 ℃, and the two aspects are matched, so that the compactness of a base membrane is favorably improved, the stable structure is ensured, and the air tightness of a membrane product is improved. In the step b), two aqueous phase solutions are coated in sequence, and vacuum water absorption treatment is added between the two aqueous phase solutions to promote the diffusion of aqueous phase components and ensure the effective concentration of a polar solvent, so that the performance requirement of extremely low pressure membrane is favorably ensured. In the step d), different rinsing treatments are performed according to a certain sequence, which is beneficial to improving the structural stability of the membrane material, improving the air tightness and ensuring the membrane separation performance. In the step e), a PVA solution is coated to form a protective layer, which is beneficial to improving the structural stability of the material. By the method, the air tightness of the membrane material can be effectively improved on the basis of ensuring the separation performance (flux and desalination rate) of the reverse osmosis membrane, and the problem that the air tightness is reduced by means of improving the membrane flux in the prior art is solved.
Experimental results show that the gas detection value of the membrane obtained by the invention is below 1.44kPa, and when the vacuum pressure is preferably (-10 to-15 kPa) (by comparing example 1 with example 2,4), the gas detection value is further remarkably reduced to be below 0.55 kPa. Meanwhile, the water flux of the membrane obtained by the invention is more than 27.8GFD, the desalination rate is more than 99.20, and good membrane flux and desalination rate are maintained.
For a further understanding of the invention, reference will now be made to the preferred embodiments of the invention by way of example, and it is to be understood that the description is intended to further illustrate features and advantages of the invention, and not to limit the scope of the claims.
Example 1
a) And (3) coating the polysulfone membrane casting solution on one surface of the non-woven fabric, and then placing the non-woven fabric in an RO hydrogel bath solution for phase conversion to form a membrane, wherein the gelation temperature is 12 ℃, so that a polysulfone support layer is formed on the surface of the non-woven fabric layer.
The polysulfone membrane casting solution comprises the following components in percentage by mass:
15% of polysulfone;
10% of 2-methoxyethanol;
the balance of dimethylformamide solvent.
b) Soaking the membrane material obtained in the step a) in an aqueous solution 1 at 22 ℃ for 1min, and then continuously carrying out vacuum water absorption treatment on the back surface of the basement membrane through three groups of vacuum water absorption plates, wherein the vacuum pressure of each vacuum water absorption plate is-5 kPa, and the treatment time is 5s. Then, the surface of the polysulfone support layer is sprayed with the aqueous solution 2 (the spraying amount is 20 g/m) 2 ) And finally, heating and drying the back surface of the film by using a heating roller at 50 ℃.
Wherein the content of the first and second substances,
the aqueous phase solution 1 comprises the following components in percentage by mass:
1.0 percent of m-phenylenediamine monomer;
7% of dimethyl sulfoxide;
2.5 percent of hexamethyl phosphoric triamide;
0.03 percent of sodium dodecyl sulfate;
2.70% of camphorsulfonic acid;
the balance of water.
The aqueous phase solution 2 comprises the following components in percentage by mass:
7% of dimethyl sulfoxide;
2.5 percent of hexamethyl phosphoric triamide;
the balance of water.
c) Coating the surface of the polysulfone support layer of the membrane material obtained in step b) with an oil phase solution (coating amount is 30 g/m) 2 ) And then, drying by HG for heat treatment (at the temperature of 70 ℃ for 2 min) to form a polyamide separation layer on the surface of the polysulfone support layer.
Wherein the oil phase solution comprises the following components in percentage by mass:
0.1 percent of trimesoyl chloride monomer;
the balance of organic solvent Isopar L.
d) Rinsing the membrane material obtained in the step c), wherein the rinsing is as follows:
d1 ) entering a first rinsing tank, and rinsing with NaOH aqueous solution with the temperature of 25 ℃ and the pH value of 12.0 for 1min;
d2 Into a second rinse tank, rinsing with 35 deg.C aqueous IPA (25% strength) for 4.5min;
d3 Into a third rinse tank, rinsing with 25 deg.C aqueous IPA (25% strength) for 1min;
d4 Into a fourth rinse tank, rinsing with 35 deg.C aqueous IPA (25% strength) for 4.5min;
d5 ) entering a fifth rinsing tank, and rinsing with RO water at 25 ℃ for 1min;
d6 Into a sixth rinse tank and rinsed with an aqueous solution of glycerol (5% strength) at 25 ℃ for 2.5min.
e) Coating a PVA solution on the surface of the polyamide separation layer of the membrane material obtained in the step d), uniformly smearing the PVA solution by a smoothing roller, and drying the PVA solution at 80 ℃ for 2min to obtain an ultra-low pressure reverse osmosis membrane;
wherein the PVA solution comprises the following components in percentage by mass:
PVA 3%；
7% of glycerol;
sodium dodecyl sulfate 0.5%;
the balance of water.
Example 2
Performed as in example 1, except that: in step b), the vacuum pressure of each vacuum suction plate is-10 kPa.
Example 3
Performed as in example 1, except that: in the step b), the vacuum pressure of each vacuum suction plate is-10 kPa; in the aqueous solution 2, the content of dimethyl sulfoxide was 8% and the content of hexamethylphosphoric triamide was 3.5%.
Example 4
Performed as in example 1, except that: in step b), the vacuum pressure of each vacuum suction plate is-15 kPa.
Example 5
Performed as in example 1, except that: in the step b), the vacuum pressure of each vacuum suction plate is-15 kPa; in addition, the aqueous solution 2 contained 8% of dimethyl sulfoxide and 3.5% of hexamethylphosphoric triamide.
Example 6
Performed as in example 1, except that: in step a), the gel temperature was 15 ℃.
Comparative example 1
Performed as in example 1, except that: in the step a), 2-methoxy ethanol is not added into the polysulfone membrane casting solution.
Comparative example 2
Performed as in example 3, except that: in step a), the gel temperature was 25 ℃.
Comparative example 3
Performed as in example 3, except that: in step a), the gel temperature was 10 ℃.
Comparative example 4
Performed as in example 1, except that: in the step b), the vacuum pressure of each vacuum water absorption plate is-20 kPa, and 2-methoxy ethanol is not added into the polysulfone membrane casting solution.
Comparative example 5
Performed as in example 1, except that: in step d), only the water wash of step d 5) is performed.
Example 7: product testing
The products obtained in examples 1 to 6 and comparative examples 1 to 4 were subjected to the airtightness test and the membrane separation performance test, and the results are shown in Table 1.
And (3) air tightness test: and (3) rolling the reverse osmosis membrane into a membrane element, fixing two ends of the membrane element on an air pressure pipe, introducing air with the air pressure of 50kpa at one end, keeping the pressure for 10s, and recording the pressure drop value after the membrane element passes through. The smaller the pressure drop value is, the better the air tightness of the membrane element is, and the more stable the performance of the membrane is. The standard gas detection value is generally 1.5kPa, values above which are regarded as unacceptable, while values below 1.0kPa and above 1.0kPa are already at distinctly different levels.
Membrane separability test: naCl solution (pH 7.2) with concentration of 1000mg/L is used as stock solution, separation treatment is carried out under pressure of 0.7MPa, test temperature is 25 +/-1 ℃, and desalination rate and water flux are respectively tested.
Table 1: preparation process conditions and film product performance
As can be seen from the test results in Table 1, the air test values of the membranes obtained in examples 1-6 of the present invention are below 1.44kPa, and the air test values are further significantly reduced to below 0.55kPa when the preferred vacuum pressure is (-10 to-15 kPa) (by comparing example 1 with example 2,4); meanwhile, the water flux of the membrane sheets obtained in the examples 1-5 is more than 27.8GFD, the salt rejection rate is more than 99.20, and good membrane flux and salt rejection rate are maintained.
Compared with the embodiment 1, the polysulfone membrane casting solution of the comparative example 1 is not added with 2-methoxy ethanol, and the air tightness of the obtained membrane product is obviously deteriorated. Compared with the example 3, the film product prepared by the method has obviously poor air tightness when the gel temperature of the comparative example 2 is too high and the gel temperature of the comparative example 3 is too low, and the fact that the air tightness of the film can be effectively improved by controlling the gel temperature to be within a range of 12-15 ℃ is proved. Compared with the example 1, the 2-methoxy ethanol is not added in the comparative example 4, but the vacuum negative pressure is increased, the air tightness is improved compared with the comparative example 1, but the air tightness is still obviously reduced compared with the example 1, the improvement of the air detection by vacuum water absorption is proved, but the effect of the 2-methoxy ethanol cannot be replaced, so that the 2-methoxy ethanol is added in the polysulfone membrane casting solution and the vacuum water absorption treatment is added, and the air tightness of the membrane can be effectively improved by matching. Compared with the embodiment 1, the comparative example 5 only carries out water washing in the rinsing step, and the result shows that the air tightness of the obtained membrane product is reduced, and the membrane flux is obviously reduced.
The foregoing examples are provided to facilitate an understanding of the principles of the invention and their core concepts, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. It should be noted that, for those skilled in the art, it is possible to make various improvements and modifications to the present invention without departing from the principle of the present invention, and those improvements and modifications also fall within the scope of the claims of the present invention. The scope of the invention is defined by the claims and may include other embodiments that occur to those skilled in the art. Such other embodiments are intended to be within the scope of the claims if they have structural elements that approximate the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims.
Claims (9)
1. The preparation method of the extremely low pressure reverse osmosis membrane is characterized by comprising the following steps:
a) Coating a polysulfone membrane casting solution on one surface of the substrate layer, and then placing the substrate layer in a gel bath solution for phase conversion to form a membrane so as to form a polysulfone supporting layer;
the polysulfone membrane casting solution comprises the following components in percentage by mass:
12% -18% of polysulfone;
5% -15% of 2-methoxy ethanol;
the balance of organic solvent;
the temperature of the gel bath solution is 12 to 15 ℃;
b) Dipping the membrane material obtained in the step a) in an aqueous phase solution 1, and then carrying out vacuum water absorption treatment; then, spraying the surface of the polysulfone supporting layer by using the aqueous phase solution 2, and finally heating and drying;
the aqueous phase solution 1 comprises the following components in percentage by mass:
1.0% -2.0% of aromatic amine monomer;
1% to 18% of additive;
the balance of water;
the additive 1 comprises one or more of sodium dodecyl sulfate, dimethyl sulfoxide, hexamethyl phosphoric triamide and camphorsulfonic acid;
the aqueous phase solution 2 comprises the following components in percentage by mass:
2% -12% of an additive;
the balance of water;
the additive 2 comprises one or more of dimethyl sulfoxide and hexamethyl phosphoric triamide;
c) Coating an oil phase solution on the surface of the polysulfone supporting layer of the membrane material obtained in the step b), and then carrying out heat treatment to form a polyamide separation layer on the surface of the polysulfone supporting layer;
the oil phase solution comprises the following components in percentage by mass:
0.1% -0.2% of aromatic acyl chloride monomer;
the balance of organic solvent;
d) Rinsing the membrane material obtained in the step c);
the rinsing specifically comprises the following rinsing steps in sequence:
d1 Rinsing with an aqueous NaOH solution;
d2 Rinsing with an aqueous IPA solution;
d3 Rinsing with an aqueous IPA solution;
d4 Rinsing with an aqueous IPA solution;
d5 Rinsing with RO water;
d6 Rinsing with an aqueous glycerol solution;
wherein the content of the first and second substances,
the temperature of the IPA aqueous solution in step d 2) is higher than the temperature of the IPA aqueous solution in step d 3), and the temperature of the IPA aqueous solution in step d 3) is lower than the temperature of the IPA aqueous solution in step d 4);
e) Coating PVA solution on the surface of the polyamide separation layer of the membrane material obtained in the step d), and then drying to obtain the ultra-low pressure reverse osmosis membrane.
2. The production method according to claim 1, wherein in the step b), the vacuum pressure of the vacuum water absorption treatment is-5 kPa to-15 kPa, and the treatment time is 9 to 18s.
3. The method for preparing according to claim 1 or 2, wherein in the step b), the vacuum water absorption treatment is: continuously carrying out three times of vacuum water absorption treatment by three groups of vacuum water absorption plates;
the vacuum pressure of each group of vacuum water absorption plates is independently selected from-5 kPa to-15 kPa, and the processing time is 3 to 6s.
4. The method of claim 1, wherein in step d 1):
the temperature of the NaOH aqueous solution is as follows: the temperature is more than or equal to 20 ℃ and less than 30 ℃; the pH value of the NaOH aqueous solution is 11.5 to 12.5; rinsing time is 0.5 to 1min;
in the step d 2):
the temperature of the IPA aqueous solution is as follows: the temperature is more than or equal to 30 ℃ and less than or equal to 45 ℃; the mass percentage concentration of the IPA aqueous solution is 20-30%; rinsing time is 4 to 5min;
in said step d 3):
the temperature of the IPA aqueous solution is as follows: the temperature is more than or equal to 20 ℃ and less than 30 ℃; the mass percentage concentration of the IPA aqueous solution is 20-30%; rinsing time is 0.5 to 1min;
in the step d 4):
the temperature of the IPA aqueous solution is as follows: the temperature is more than or equal to 30 ℃ and less than or equal to 45 ℃; the mass percentage concentration of the IPA aqueous solution is 20-30%; rinsing time is 4 to 5min;
in the step d 5):
the temperature of the RO water is as follows: the temperature is more than or equal to 20 ℃ and less than 30 ℃; rinsing time is 0.5 to 1min;
in said step d 6):
the temperature of the glycerol aqueous solution is as follows: the temperature is more than or equal to 20 ℃ and less than or equal to 30 ℃; the mass percentage concentration of the glycerol aqueous solution is 4-5%; the rinsing time is 2 to 3min.
5. The method of claim 1, wherein in step c):
the organic solvent is at least one selected from n-hexane, isopar G and Isopar L.
6. The preparation method according to claim 1, characterized in that in step e), the PVA solution comprises the following components in percentage by mass:
PVA 1%~5%；
5% -10% of glycerol;
0.1% -1% of a surfactant;
the balance of water.
7. The preparation method according to claim 6, wherein the surfactant is one or more selected from sodium dodecyl sulfate, sodium dodecyl sulfate and cetyl trimethyl ammonium bromide.
8. The method of claim 1, wherein in step b):
the dipping time is 0.2 to 1min;
the spraying amount of the spraying is 15 to 25 g/m 2 ；
The temperature for heating and drying is 40 to 60 ℃;
in the step c):
the coating amount of the oil phase solution is 20 to 50 g/m 2 ；
The temperature of the heat treatment is 50 to 80 ℃.
9. A very low pressure reverse osmosis membrane made by the method of making any one of claims 1~8.
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