CN112957925B - Preparation method of high-permeability composite reverse osmosis membrane for reducing intrinsic thickness of polyamide layer - Google Patents

Preparation method of high-permeability composite reverse osmosis membrane for reducing intrinsic thickness of polyamide layer Download PDF

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CN112957925B
CN112957925B CN202110264643.7A CN202110264643A CN112957925B CN 112957925 B CN112957925 B CN 112957925B CN 202110264643 A CN202110264643 A CN 202110264643A CN 112957925 B CN112957925 B CN 112957925B
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reverse osmosis
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osmosis membrane
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CN112957925A (en
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宋潇潇
胡向阳
巫碧勤
张娜
周勇
高从堦
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Zhejiang University of Technology ZJUT
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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
    • B01D67/0081—After-treatment of organic or inorganic membranes
    • B01D67/0095—Drying
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D61/00—Processes of separation using semi-permeable membranes, e.g. dialysis, osmosis or ultrafiltration; Apparatus, accessories or auxiliary operations specially adapted therefor
    • B01D61/02—Reverse osmosis; Hyperfiltration ; Nanofiltration
    • B01D61/025—Reverse osmosis; Hyperfiltration
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D69/00—Semi-permeable membranes for separation processes or apparatus characterised by their form, structure or properties; Manufacturing processes specially adapted therefor
    • B01D69/02—Semi-permeable membranes for separation processes or apparatus characterised by their form, structure or properties; Manufacturing processes specially adapted therefor characterised by their properties
    • 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
    • B01D69/125—In situ manufacturing by polymerisation, polycondensation, cross-linking or chemical reaction
    • 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
    • B01D71/56—Polyamides, e.g. polyester-amides
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2325/00—Details relating to properties of membranes
    • B01D2325/04—Characteristic thickness
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    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
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    • Y02A20/00—Water conservation; Efficient water supply; Efficient water use
    • Y02A20/124—Water desalination
    • Y02A20/131—Reverse-osmosis

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Abstract

The invention discloses a preparation method of a high-permeability composite reverse osmosis membrane for reducing the intrinsic thickness of a polyamide layer. Wherein in the aqueous phase solution, the adding concentration of the amine monomer is 0.25 to 5wt%, the adding concentration of the organic weak acid is 3 to 5wt%, and the pH value is adjusted to 9 to 11 by adding the organic base; the mass concentration of the acyl chloride monomer in the oil phase solution is 1/40 to 1/30 of the mass concentration of the amine monomer in the water phase solution. According to the invention, the permeability of the membrane is improved by optimizing the micro-nano structure of the polyamide layer through regulating and controlling the concentration of the amine monomer in the aqueous phase solution and the concentration of the acyl chloride monomer in the oil phase solution, reducing the intrinsic thickness of the separation layer, improving the roughness of the surface of the membrane and the like.

Description

Preparation method of high-permeability composite reverse osmosis membrane for reducing intrinsic thickness of polyamide layer
Technical Field
The invention relates to a preparation method of a high-permeability composite reverse osmosis membrane for reducing the intrinsic thickness of a polyamide layer.
Background
Water resources on earth are extremely abundant, with about 75% of the world's area covering water, but most of this water is seawater, and it accounts for 96.5% of all water resources. According to research and investigation, the seawater contains about 92 chemical elements, wherein 11 chemical elements (chlorine, sodium, magnesium, sulfur, calcium, potassium, bromine, strontium, boron, carbon and fluorine) account for 99.8 percent of the total dissolved substances in the seawater, and the other chemical elements are very little; some metal elements are as follows: although potassium and sodium are necessary in the human body, these high concentrations of metal and non-metal elements in seawater once enter the human body, increase the metabolism of organs such as the kidney and increase the burden on the body organs. By trying to dilute the high-concentration seawater into low-concentration fresh water resources, the vast fresh water resources can be utilized by human beings.
In such a situation, reverse osmosis techniques have been developed. As early as 1953, professor C.E. Reid of Florida in USA proposed that a symmetric cellulose acetate membrane was prepared by phase inversion film-forming technology, and the seawater desalination process was realized for the first time, although the rejection rate of sodium chloride salt was above 99%, the water permeability coefficient was only 0.00012 m 3 /（m 2 D atm), which greatly hinders the commercial application of the film. Subsequently, indian scientists soreirajin (Srinivasa Sourirajan) and american scientist lobb (Sidney Loeb) developed asymmetric cellulose acetate membranes and by optimizing a series of phase inversion process parameters, the membrane salt retention rate could reach 99% and the permeability was greatly improved to reach the surprising 0.0048 m 3 /（m 2 D atm), which is the well-known immersion gel phase inversion method (L-S method). The emergence of the L-S membrane has brought about eosin for the industrial application of reverse osmosis technology. However, for the commercial application, it is obvious that a crucial engineering problem needs to be solved, namely the design of the membrane module. The membranes prepared by the membrane preparation method at that time have plate type and tube type, and the membrane preparation method has the defects of complex assembly, small membrane area filled in unit volume and the like, so that the membrane preparation method can not be developed into the mainstream form of a commercial reverse osmosis membrane module finally. This has prompted the development of another technique for applying eosin-light membrane technology to the field of desalination treatment, thin film composite membranes (Thin film composite).
In 1977, cardott (John e. Cadotte) established FilmTec corporation with 3 others. By 1979, he applied for the first interfacial polymerization process to produce reverse osmosis membranes worldwide (US 4277344). The interfacial polymerization method allows the support layer and the separation layer of the reverse osmosis membrane to be optimized separately during the preparation process, thereby further improving the membrane performance, which is a so-called thin layer composite membrane (TFC). In 1985, filmTec was fully procured by Dow chemical after giving up hollow fiber reverse osmosis membranes. This is the origin of the Dow film of the famous tripod. To date, the FilmTec brand continues to be used in dow reverse osmosis membrane products. In 2017, the combination of DuPont and Dow chemical, which was the least sensible on hollow fiber reverse osmosis membranes, was achieved. Most of the experimental research around optimizing the physicochemical structure of the separation layer and the support layer from the beginning of the birth of the interfacial polymerization method has emerged from well-known companies such as Toray (Toray), hydranautics (Hydranautics) and Dow Chemical (Dow Chemical) in Japan, and LG Chemical in Korea. Interfacial polymerization has also become a standard manufacturing process for modern commercial reverse osmosis membranes. The whole thickness of polyamide of the reverse osmosis membrane separation layer is 10-300 nm and is far smaller than that of a symmetrical or asymmetrical cellulose acetate membrane, and in addition, the aggregation pores among polyamide molecules are smaller than the molecular diameters of water and sodium chloride, so that the membrane layer has better compactness, and the filtration of the membrane on small molecular substances can be met while the permeability of the membrane is improved.
There are indeed a large number of documents in which it has been reported that the permeability of the membrane is increased by reducing the thickness of the separating layer, but their emphasis is on the thickness of the polyamide layer from the surface to the rear surface, ignoring the hollow pores of several tens of nanometers which are wrapped during this period and which do not participate in the separation of brine. It is not critical to reduce the thickness of the membrane in general to improve its permeability, since the resistance to transport of water and salt across the membrane derives from its homogeneous intrinsic part (6-30 nm); on the other hand, it has been reported that an increase in the roughness of the membrane surface significantly increases its permeability, but this gain effect is not seen with an increase in the intrinsic thickness of the membrane. Therefore, the following problems exist in the prior art documents: it is controversial that the definition of "thickness" in "reducing the thickness of the separation layer increases the permeability of the membrane" is not clear.
In addition, in most of the experimental researches on interfacial polymerization at present, the ratio of the concentration of the amine monomer in the aqueous phase solution to the concentration of the acyl chloride monomer in the oil phase solution is basically 20:1, i.e., the concentration of amine monomer in the aqueous phase solution is typically about 2 weight percent and the concentration of acid chloride monomer in the oil phase solution is typically about 0.1 weight percent. The formula of the traditional film preparation process is as follows: under the condition that the concentration ratio of the acyl chloride monomer to the acyl chloride monomer is 20. That is, the permeate flux and salt selectivity of the composite membrane prepared under such conditions exhibit a significant trade-off effect, i.e., an increase in membrane flux inevitably results in a loss of salt rejection.
The invention aims to reduce the intrinsic thickness of the membrane and increase the roughness of the membrane surface by regulating and controlling the concentration of amine monomers in an aqueous phase solution and the concentration of acyl chloride monomers in an oil phase solution, thereby improving the permeability of the membrane. The invention comprehensively analyzes and discusses the influence of the intrinsic thickness and the surface roughness of the membrane on the membrane performance, and can provide a referable monomer concentration ratio for preparing the high-flux reverse osmosis membrane.
Disclosure of Invention
In view of the above technical problems in the prior art, the present invention provides a method for preparing a high permeability composite reverse osmosis membrane with reduced intrinsic thickness of a polyamide layer. The invention considers that the loss of the membrane retention rate is controlled while the membrane permeability is greatly improved by regulating and controlling the concentration of the amine monomer in the aqueous phase solution and the concentration of the acyl chloride monomer in the oil phase solution in a large range (for example, under the condition of the existing conventional ratio of the concentration of the amine monomer to the concentration of the acyl chloride monomer of 20: intrinsic thickness, apparent thickness of the film. This provides new ideas for the basic process recipe for the preparation of idealized membranes (high flux or high rejection).
The preparation method of the high-permeability composite reverse osmosis membrane for reducing the intrinsic thickness of the polyamide layer is characterized by comprising the following steps of:
1) Preparation of aqueous phase solution: adding an amine monomer and an organic weak acid with a hydrophilic group into ultrapure water, adding an organic base to adjust the pH value to 9-11, and uniformly mixing by ultrasonic to obtain an aqueous phase solution; in the prepared aqueous phase solution, the addition concentration of an amine monomer is 0.25-5 wt%, and the addition concentration of the organic weak acid is 3-5 wt%;
2) Preparation of oil phase solution: dissolving acyl chloride monomers in Isopar-G solvent, and uniformly mixing by ultrasonic waves to obtain oil phase solution; wherein the mass concentration of the acyl chloride monomer in the oil phase solution is 1/40-1/30 of the mass concentration of the amine monomer in the water phase solution obtained in the step 1);
3) Interfacial polymerization reaction: clamping a polysulfone membrane soaked in ultrapure water in advance by using two hollow plate frames, pouring the water-phase solution obtained in the step 1) on the surface of the polysulfone membrane for soaking for 0.5-10 min, pouring the water-phase solution on the surface of the polysulfone membrane, and drying the surface of the polysulfone membrane; pouring the oil phase solution obtained in the step 2) when no obvious liquid drops exist on the surface of the polysulfone membrane, carrying out interfacial polymerization for 20-120 s, and then pouring out the residual oil phase solution;
4) Post-treatment of the film: and (3) vertically standing the polysulfone membrane treated in the step 3), draining for 15-30 s, and then putting the polysulfone membrane into a blast oven for drying treatment to obtain the composite reverse osmosis membrane product.
The preparation method of the high-permeability composite reverse osmosis membrane for reducing the intrinsic thickness of the polyamide layer is characterized in that in the step 1), the amine monomer is m-phenylenediamine, and the concentration of the amine monomer in the aqueous solution is 1.0-3.0 wt%; the organic weak acid is camphorsulfonic acid, the added organic base is triethylamine, and the adding concentration of the triethylamine in the aqueous phase solution is 2.5-3.0 wt%.
The preparation method of the high-permeability composite reverse osmosis membrane for reducing the intrinsic thickness of the polyamide layer is characterized in that in the step 2), the acyl chloride monomer is trimesoyl chloride.
The preparation method of the high-permeability composite reverse osmosis membrane for reducing the intrinsic thickness of the polyamide layer is characterized in that the polysulfone membrane surface is dried in the step 3) in the modes of natural drying in air, fume hood forced air drying, roller spreading drying or air knife blowing drying.
The preparation method of the high-permeability composite reverse osmosis membrane for reducing the intrinsic thickness of the polyamide layer is characterized in that the polysulfone membrane surface is dried by air knife blowing in the drying treatment mode in the step 3), and after the membrane surface has no macroscopic liquid, the polysulfone membrane is placed in a fume hood to be naturally dried for 10 s, namely the drying treatment is completed.
The preparation method of the high-permeability composite reverse osmosis membrane for reducing the intrinsic thickness of the polyamide layer is characterized in that the drying temperature in the drying oven in the step 4) is 90-95 ℃, and the drying time is 8 min.
The preparation method of the high-permeability composite reverse osmosis membrane for reducing the intrinsic thickness of the polyamide layer is characterized in that in the step 3), the water phase solution is poured on the surface of the polysulfone membrane for soaking for 1-3 min, preferably 2 min; the interfacial polymerization reaction was carried out for 30 seconds.
The invention achieves the following beneficial effects:
1) The experiment establishes that the osmotic resistance of water and salt transmission comes from the homogeneous intrinsic part, namely the intrinsic thickness of the membrane (only between 6 and 30 nm in the experiment) for the first time; reducing the intrinsic thickness of the polyamide separating layer can greatly improve the permeability of the membrane;
2) By regulating and controlling the concentration of the amine monomer in the aqueous phase solution and the concentration of the acyl chloride monomer in the oil phase solution, the intrinsic thickness of the separation layer can be reduced, and the roughness of the membrane surface can be improved, so that the permeability of the membrane can be improved, and the conventional 20:1 under the condition that the concentration of the amine monomer is matched with that of the acyl chloride monomer, the prepared reverse osmosis membrane brings a trade-off effect;
3) Starting from regulating and controlling the concentration of the reaction monomer of the basic formula, a new guiding idea is provided for preparing the ideal film composite reverse osmosis membrane.
Drawings
FIG. 1 is a schematic diagram of polyamide cross-section micro-nano structure information.
FIG. 2 is a graph showing the relationship between the flux of brine and the rejection of salt for the membranes of comparative examples 1 to 6.
FIG. 3 is a TEM image of a cross section of a film of comparative examples 7 to 11.
FIG. 4 is an AFM image of the film surface of comparative examples 7 to 11.
FIG. 5 is a permeation selectivity analysis of comparative examples 7 to 11: a is a graph of the change relationship between the membrane saline flux and the salt rejection rate; the b-plot is the water permeability constant of the membrane as a function of the intrinsic thickness of the membrane.
FIG. 6 is a TEM image of a cross section of a film of comparative examples 12 to 15.
FIG. 7 is an AFM image of the surface of films of comparative examples 12 to 15.
FIG. 8 is a permeation selectivity analysis of comparative examples 12-15: a is a graph of the change of membrane saline flux and salt retention rate; the b-plot is the water permeability constant of the membrane as a function of the intrinsic thickness of the membrane.
FIG. 9 is a comparison of the three-dimensional structures of films of film products C-2, M-1 and M-4 (SEM image of film surface, AFM image of film surface, TEM image of film cross section).
Fig. 10 is an analysis view of the intrinsic thickness size in the TEM image.
Detailed Description
The present invention is further illustrated by the following examples, which should not be construed as limiting the scope of the invention.
In the following examples and comparative examples, the supporting base film was a polysulfone ultrafiltration membrane from Huzhou research institute of Zhejiang province, with a cut molecular weight of 35kDa, and the back and surface thereof were cleaned with ultrapure water before use.
In order to find out the corresponding relation between the permeation flux and the salt rejection rate of the membrane at the upper empirical limit of trade-off and compare and analyze the corresponding relation with a subsequent monomer concentration regulation experiment group, the invention patent makes some control experiments: the ratio of the concentration of the amine monomer in the aqueous phase solution to the concentration of the acyl chloride monomer in the oil phase solution is 20:1, namely the concentration of the amine monomer in the aqueous phase solution is about 2wt%, and the concentration of the acyl chloride monomer in the oil phase solution is about 0.1wt%, and a series of thin film composite membranes are prepared by changing the drying state of the polysulfone membrane surface after being soaked in the aqueous phase solution. In order to explore the effect of the water-phase amine monomer and the oil-phase acyl chloride monomer in the interfacial polymerization process, the invention respectively controls the concentration of the amine monomer in the water-phase solution and the concentration of the acyl chloride monomer in the oil-phase solution to prepare the reverse osmosis membrane, and discusses the corresponding relation between the change of the intrinsic thickness and the surface roughness of the polyamide membrane and the flux and the desalination rejection rate of the membrane.
Through comparative experiments, the experimental scheme group embodiment optimizes the amine monomer concentration in the aqueous phase solution, the acyl chloride monomer concentration in the oil phase solution, and the ratio of the amine monomer concentration to the acyl chloride monomer concentration, for example: meanwhile, the concentration of the amine monomer and the concentration of the acyl chloride monomer are reduced, and the effect of reducing the intrinsic thickness of the separation layer is achieved, so that the permeability of the membrane is improved. The water phase monomer concentration is increased, the intrinsic thickness of the membrane is controlled, the roughness of the membrane surface is increased, and the permeability of the membrane is also improved.
Some of these comparative examples and examples will now be described.
A pair of proportions
1. Establishing the Trade-off area under the formula of the conventional film-making process
Comparative example 1
A preparation method of a reverse osmosis membrane comprises the following steps:
1) Preparation of aqueous phase solution: adding m-phenylenediamine and camphorsulfonic acid into ultrapure water, adding triethylamine, and performing ultrasonic mixing uniformly to obtain an aqueous phase solution; wherein in the prepared aqueous phase solution, the concentration of m-phenylenediamine is 2.2wt%, the concentration of camphorsulfonic acid is 4wt%, and the concentration of triethylamine is 2.8wt%;
2) Preparation of oil phase solution: dissolving trimesoyl chloride in Isopar-G solvent, and uniformly mixing by ultrasonic waves to obtain oil phase solution; wherein the concentration of trimesoyl chloride in the oil phase solution is 0.10wt%;
3) Interfacial polymerization reaction: clamping a polysulfone membrane which is soaked in ultrapure water in advance by using two hollow plate frames, pouring the water phase solution obtained in the step 1) on the surface of the polysulfone membrane for soaking for 2 min, pouring excessive water phase solution on the surface of the polysulfone membrane, blowing the surface of the membrane by using a nitrogen air knife to remove water drops and liquid drops, pouring the prepared oil phase solution on the surface of the membrane which is just soaked in the water phase solution when the surface of the membrane just has no macroscopic liquid, and pouring excessive oil phase on the surface of the polysulfone ultrafiltration membrane after carrying out interfacial polymerization reaction for 30 s;
4) Post-treatment of the membrane: standing the membrane treated in the step 3) vertically, draining for 20 s, and then drying in an oven set at 95 ℃ for 8 min. Subsequently, the prepared membrane was taken out and stored in ultrapure water for 12 h in preparation for subsequent characterization of the membrane's permselectivity. The membrane was numbered as C-1.
Comparative examples 2 to 6
Membrane preparation procedure comparative example 1 was repeated except that "in step 3), the membrane surface was purged with a nitrogen air knife to remove water droplets and liquid droplets, and after the membrane surface had just no liquid visible to the naked eye, the polysulfone membrane was left in a fume hood to air-dry for a certain period of time", and the rest of the procedure was the same as in example 1 to finally obtain a membrane product.
The membranes in comparative examples 2 to 6 were placed in a fume hood and air-dried for 10 s, 30 s, 1 min, 2 min and 4 min, respectively, and the finally prepared membrane products were named C-2, C-3, C-4, C5 and C-6, respectively.
2. Regulation of aqueous amine monomer concentration c (MPD)
Comparative example 7
Preparation of membrane step comparative example 2 was repeated except that "the concentration of m-phenylenediamine was 0.25wt% in the preparation of aqueous solution", and the remaining steps were the same as in comparative example 1, to finally prepare a polyamide reverse osmosis membrane. The membrane was numbered A-1.
Comparative example 8
Preparation of Membrane Steps comparative example 2 was repeated except that "m-phenylenediamine concentration was 0.50wt% in the preparation of aqueous solution", and the remaining steps were the same as in comparative example 1 to finally prepare a polyamide reverse osmosis membrane. The membrane was numbered A-2.
Comparative example 9
Preparation of membrane comparative example 2 was repeated except that "concentration of m-phenylenediamine was 1.1% by weight in preparation of aqueous solution" and the remaining steps were the same as in comparative example 1 to finally prepare a polyamide reverse osmosis membrane. The membrane was numbered as A-3.
Comparative example 10
Preparation of membrane comparative example 2 was repeated except that "concentration of m-phenylenediamine was 4.4wt% in preparation of aqueous solution", and the remaining steps were the same as in comparative example 1 to finally prepare a polyamide reverse osmosis membrane. The membrane was numbered as A-4.
Comparative example 11
Preparation of membrane step comparative example 2 was repeated except that "the concentration of m-phenylenediamine was 8.8wt% in the preparation of aqueous solution", and the remaining steps were the same as in comparative example 1, to finally prepare a polyamide reverse osmosis membrane. The membrane was numbered A-5.
3. Control of the oil phase acid chloride monomer concentration c (TMC)
Comparative example 12
Preparation of membrane comparative example 2 was repeated except that "the concentration of trimesoyl chloride was 0.02wt% during the preparation of the oil phase solution", and the remaining steps were the same as in comparative example 1, to finally prepare a polyamide reverse osmosis membrane. The membrane was numbered O-1.
Comparative example 13
Preparation of membrane comparative example 2 was repeated except that "the concentration of trimesoyl chloride was 0.05wt% during the preparation of the oil phase solution", and the remaining steps were the same as in comparative example 1, to finally prepare a polyamide reverse osmosis membrane. The membrane was numbered O-2.
Comparative example 14
Preparation of membrane comparative example 2 was repeated except that "the concentration of trimesoyl chloride was 0.22wt% during the preparation of the oil phase solution", and the remaining steps were the same as in comparative example 1, to finally prepare a polyamide reverse osmosis membrane. The membrane was numbered O-3.
Comparative example 15
Preparation of membrane comparative example 2 was repeated except that "the concentration of trimesoyl chloride was 0.44wt% during the preparation of the oil phase solution", and the remaining steps were the same as in comparative example 1, to finally prepare a polyamide reverse osmosis membrane. The membrane was numbered O-4.
2. Examples of the embodiments
Summarizing the experimental formulation in the comparative example, the membrane concentration ratio can be optimized to reduce the intrinsic thickness of the separation layer or to increase the roughness of the membrane surface, and specific examples are shown in the examples, but the scope of protection of the present invention is not limited to the following examples.
Example 1
Preparation procedure of the film comparative example 2 was repeated except for the point that "the concentration of m-phenylenediamine was 1.0% by weight in the preparation of the aqueous solution; in the preparation process of the oil phase solution, the concentration of trimesoyl chloride is 0.025wt%, and the rest steps are the same as the comparative example 1, so that the polyamide reverse osmosis membrane is finally prepared. The membrane was numbered M-1.
Example 2
Preparation of the membrane comparative example 2 was repeated except that "the concentration of m-phenylenediamine was 1.0wt% in the preparation of the aqueous solution"; in the preparation process of the oil phase solution, the concentration of trimesoyl chloride is 0.03wt%, and the other steps are the same as the comparative example 1, so that the polyamide reverse osmosis membrane is finally prepared. The membrane was numbered M-2.
Example 3
Preparation of the membrane comparative example 2 was repeated except that "the concentration of m-phenylenediamine was 2.0wt% in the preparation of the aqueous solution"; in the preparation process of the oil phase solution, the concentration of trimesoyl chloride is 0.035wt%, and the other steps are the same as the comparative example 1, so that the polyamide reverse osmosis membrane is finally prepared. The membrane was numbered M-3.
Example 4
Preparation of the membrane comparative example 2 was repeated except that "the concentration of m-phenylenediamine was 2.0wt% in the preparation of the aqueous solution"; in the preparation process of the oil phase solution, the concentration of trimesoyl chloride is 0.05wt%, and the other steps are the same as the comparative example 1, so that the polyamide reverse osmosis membrane is finally prepared. The membrane was numbered M-4.
Example 5
Preparation of the membrane comparative example 2 was repeated except that "the concentration of m-phenylenediamine was 3.0wt% in the preparation of the aqueous solution"; in the preparation process of the oil phase solution, the concentration of trimesoyl chloride is 0.05wt%, and the rest steps are the same as the comparative example 1, so that the polyamide reverse osmosis membrane is finally prepared. The membrane was numbered M-5.
Example 6
Preparation procedure of the film comparative example 2 was repeated except for the point that "the concentration of m-phenylenediamine was 3.0% by weight in the preparation of the aqueous solution; in the preparation process of the oil phase solution, the concentration of trimesoyl chloride is 0.08wt%, and the rest steps are the same as the comparative example 1, so that the polyamide reverse osmosis membrane is finally prepared. The membrane was numbered M-6.
Application example 1
The osmotic selectivity of the reverse osmosis membrane is evaluated by a cross-flow filtration system, high-concentration NaCl aqueous solution (the concentration of NaCl is 32 g/L) is used as feed liquid to simulate seawater, and penetrating fluid is collected from the other side of the membrane under the driving of external test pressure. The test conditions were set as: the temperature of the feed liquid was 25 ℃, the pH of the feed liquid was 7.5. + -. 0.5, and the test pressure was 5.5 MPa. After the membrane is pre-pressed for 1 hour, the permeation selectivity of the membrane is formally tested.
The polyamide reverse osmosis membranes prepared in the comparative examples and examples of the present invention were tested by the above-described method, and the results of the membrane performance tests are shown in table 1 below.
Figure DEST_PATH_IMAGE002
According to the test results in Table 1, the relationship between the salt water flux and the salt rejection of the finally prepared membrane products C-1, C-2, C-3, C-4, C-5 and C-6 in the test for evaluating the permselectivity of the reverse osmosis membrane is shown in a comparison graph of 2.
In the 6 groups of comparative examples 1-6, the formula in the interfacial polymerization reaction was kept consistent, and the drying state of the polysulfone base film after being soaked in the water phase was changed. The permselective performance data of the membranes are shown in table 1. When the flux of the membrane is from 42.38L m -2 h -1 Increased to 56.50L m -2 h -1 Corresponding to this, the sodium chloride rejection rate decreased from 99.70% to 99.33%. This is well in line with the empirical upper limit theory in reverse osmosis membranes, as shown in comparison to FIG. 2. The greater the degree of drying of the membrane surface after contact with water, the lower the membrane flux, since m-phenylenediamine molecules mostly permeate into polysulfoneIn the holes in the film, m-phenylenediamine molecules are not favorable to diffuse upward to participate in the reaction at the interface, so that the film surface with larger roughness is formed.
Application example 2
The method comprises the steps of representing physical structure information of a membrane surface by using a field emission scanning electron microscope (FE-SEM); an Atomic Force Microscope (AFM) is adopted to represent the roughness condition of the surface of the membrane, a tapping mode is adopted in a scanning mode, and the scanning area of each membrane is 2.5 mu m G2.5 mu m; adopting a Transmission Electron Microscope (TEM) to represent the structural information of the cross section of the film (intrinsic thickness, apparent thickness and the like of the film); and analyzing the intrinsic thickness change of the film by adopting Image J software, selecting 15 different positions of the polyamide layer in each TEM picture for measurement, and finally averaging to obtain the intrinsic thickness of the film. The specific measurement position of the intrinsic thickness of the film is illustrated by taking the film product a-5 as an example, as shown in fig. 10, the intrinsic thickness of each film is finally obtained by statistics, and the intrinsic thickness of each film is the thickness part of the black line in fig. 10.
The intrinsic thickness of the polyamide film mentioned in the specific embodiment of the patent is only in the range of 6-30 nm. The invention controls the intrinsic thickness of the membrane within 20 nm in examples 1-6, and reduces the resistance of water salt molecule transportation across the membrane.
FIG. 1 is a schematic diagram of information of a micro-nano structure of a cross section of a polyamide membrane. The membrane comprises an intrinsic thickness part (the intrinsic thickness of the membrane is the thickness of a peripheral wall of the hollow nano vesicle in the figure 1) with the thickness of 6-30 nm, a porous back structure, a hollow nano vesicle part with the size of 10-200 nm and an apparent thickness part with the thickness of about 100-300 nm. It is also due to the presence of the hollow nanovesicles in the membrane that the apparent thickness of the polyamide membrane layer (the vertical height from the back of the polyamide to the surface of the polyamide layer) is about an order of magnitude greater than its intrinsic thickness.
The film cross sections of the film products A-1, A-2, A-3, A-4, A-5 finally prepared in comparative examples 7-11 and the film product C-2 finally prepared in comparative example 2 were respectively characterized by a transmission electron microscope, and the results are summarized in FIG. 3. The partial images a, b, C, d, e, f in FIG. 3 correspond to the TEM characterization results of the film cross sections of the film products A-1, A-2, A-3, C-2, A-4, A-5, respectively, and it can be seen from FIG. 3 that the intrinsic thickness portions of the polyamides of the film products A-1, A-2, A-3, C-2, A-4, A-5 are successively clearly darkened and thickened. In combination with the micro-nano structure of the polyamide layer described in fig. 1, the intrinsic thickness of polyamide is obviously blackened and thickened, because in the preparation process of the membrane, along with the increase of the concentration of m-phenylenediamine monomer in the aqueous solution, the sufficiency of the reaction is continuously improved, so that the compactness of the membrane is improved, thickening possibly means the increase of the intrinsic thickness of the membrane, image J software is used for analyzing the intrinsic thickness of the membrane, 15 different positions of the polyamide layer are selected in each TEM picture for measurement, and finally the average value is obtained. TEM Image analysis of the film using Image J software resulted in measurements found: from film products A-1 to A-5, the intrinsic thickness of the film increased from 5.95. + -. 0.80 nm to 29.75. + -. 0.97 nm.
And (3) respectively performing characterization analysis on the film surface roughness of the film products A-1, A-2, A-3, A-4 and A-5 finally prepared in the comparison examples 7-11 and the film surface roughness of the film product C-2 finally prepared in the comparison example 2 by using an atomic force microscope, wherein an AFM (atomic force microscope) graph is shown in figure 4, and sub-graphs a, b, C, d, e and f in the figure 4 respectively correspond to the film surface roughness results of the film products A-1, A-2, A-3, C-2, A-4 and A-5. When an atomic force microscope is adopted for characterization analysis, a tapping mode is selected as a sample scanning mode, and each sample scanning area is as follows: 2.5 μ m G2.5 μm. 5 different positions (0.5 μm G0.5 μm area) are selected for each AFM image by using a Roughress tool in NanoScope Analysis software for Analysis, the surface Roughness data of the film is directly obtained in a result window, and finally the average value is taken to obtain the average Roughness of the surface of the film. In addition, the height scale on the right side of the AFM image can reflect the roughness. The order of the roughness of the film surface is analyzed and counted according to the method as follows: a-5 (film surface roughness)R a =32.52 ± 8.19 nm) >A-4 (film surface roughness)R a =24.70 ± 0.72 nm) >C-2 (film surface roughness)R a =23.60 ± 1.25 nm) >A-3 (film surface roughness)R a =20.30 ± 0.68 nm) >A-2 (film surface roughness)R a =19.7 ± 0.73 nm) >A-1 (film surface roughness)R a =19.78 ± 0.95 nm). This indicates that m-phenylenediamine contributes to an increase in the surface roughness of the film.
The osmotic selectivity of the reverse osmosis membrane is evaluated by a cross-flow filtration system, high-concentration NaCl aqueous solution (the concentration of NaCl is 32 g/L) is used as feed liquid to simulate seawater, and penetrating fluid is collected from the other side of the membrane under the driving of external test pressure. The test conditions were set as: the temperature of the feed liquid was 25 ℃, the pH of the feed liquid was 7.5. + -. 0.5, and the test pressure was 5.5 MPa. And after the membrane is pre-pressed for 1 hour, formally testing the permeability selectivity of the membrane.
Further, the water permeability constant (A) (Lm) -2 h -1 bar -1 ) The degree of membrane permeability was evaluated and the value was calculated by the formula a = F/(Δ P- Δ π). Wherein F is the saline flux (Lm) -2 h -1 ) Δ P is the applied pressure tested (bar), Δ pi is the osmotic pressure of water (bar), Δ pi = c R T. c is the concentration of the salt solution (mg/L) and R is the thermodynamic constant (8.3144J mol) -1 K -1 ) And T is the thermodynamic temperature (K). Particularly when the salt concentration is 0, Δ pi = 0.
The membrane products A-1, A-2, A-3, A-4 and A-5 finally prepared in the comparative examples 7-11 and the membrane product C-2 finally prepared in the comparative example 2 are respectively tested for the permselectivity of the membrane by adopting the method, and a comparison graph of the change relationship between the salt water flux and the salt rejection rate of the membrane in the osmotic selectivity test of the reverse osmosis membrane is shown as a partial graph a in figure 5. As can be seen from the panel a in FIG. 5, in the preparation process of the membrane, as the concentration of the m-phenylenediamine monomer in the aqueous phase solution is increased, the membrane flux and the rejection rate of the finally prepared membrane product are increased and then decreased.
The water permeability constant (a) of each membrane product was calculated from the panel a results in fig. 5 and according to the formula a = F/(Δ P- Δ pi). And respectively performing TEM Image characterization on the film products A-1, A-2, A-3, A-4 and A-5 finally prepared in the comparative examples 7-11 and the film product C-2 finally prepared in the comparative example 2, and analyzing the TEM Image of each film product by adopting Image J software to obtain the intrinsic thickness result of each film product. The water permeability constant (a) and the intrinsic thickness variation of the membrane are plotted in comparison with the panel b in fig. 5.
As can be seen from panel b of FIG. 5, the intrinsic thickness of the film is increasing continuously, from 6 nm (A-1) to 30 nm (A-5). From C-2 to A-4 and then to A-5, the permeability of the membrane decreased significantly, indicating an increase in the intrinsic thickness of the membrane and thus an increase in the water transport resistance. From a-1 to A3, the intrinsic thickness of the membrane and its permeation flux increase at the same time, since the membrane roughness also contributes to the water transport process, with a larger roughness providing more water transport area.
Application example 3
Referring to the analytical characterization methods of the film products A-1, A-2, A-3, A-4, A-5 finally obtained in comparative examples 7-11 and the film product C-2 finally obtained in comparative example 2 in application example 2, the film products O-1, O-2, O-3, O-4 finally obtained in comparative examples 12-15 and the film product C-2 finally obtained in comparative example 2 were analyzed and characterized in the same manner.
TEM images of film cross sections of film products O-1, O-2, O-3, O-4 and film product C-2 are shown in FIG. 6. The partial images a, b, C, d and e in FIG. 6 correspond to the TEM characterization results of the film cross sections of the film products O-1, O-2, C-2, O-3 and O-4, respectively. From fig. 6 it can be analyzed that: during the preparation of the membrane, the intrinsic thickness of the membrane increased from 17.20 + -2.50 nm (O-1) to 27.00 + -4.50 nm (O-4) as the concentration of trimesoyl chloride in the oil phase solution increased. This also indicates that the oil phase monomer concentration has a positive effect on the actual separation layer thickness of the membrane.
FIG. 7 is an AFM image of the film surface of the film products O-1, O-2, C-2, O-3, O-4, analyzed to yield: o-2 (film surface roughness)R a =61.62 ± 2.07 nm) >O-1 (film surface roughness)R a =60.02 ± 3.60 nm) >O-3 (film surface roughness)R a =30.24 ± 2.21 nm) >O-4 (film surface roughness)R a =27.04 ± 1.31 nm) >C-2 (film surface roughness)R a =23.60 ± 1.25 nm), it was found that the film surface roughness was greater when the trimesoyl chloride concentration was lower because the polyamide film layer was formed once nascentDiffusion-reaction processes of the amine monomer are inhibited. So that the reaction region shrinks and the film surface tends to be flat.
FIG. 8 is a graph of the permselectivity performance of the membrane products O-1, O-2, C-2, O-3, O-4. It can be seen from Panel a of FIG. 8 that as the concentration of trimesoyl chloride in the oil phase increases, the water permeability constants (A) of the membrane products O-1, O-2, C-2, O-3 and O-4 continue to decrease, while the salt rejection continues to increase. The decrease in membrane permeability may result from a continuous increase in the intrinsic thickness of the membrane, shown in panel b of fig. 8: the permeability constant of water and the intrinsic thickness of the membrane exhibit distinctly opposite trends. This again indicates that the permeation resistance of the membrane is due to its homogeneous intrinsic thickness portion. In addition, when the concentration of trimesoyl chloride is 0.02-0.05%, the saline flux of the membrane is 55-80L m -2 h -1 While the intrinsic thickness of the membrane is also as high as 17 nm, the higher membrane permeability is attributable to the greater roughness of the membrane surface.
The polyamide membranes (M-1, M-4) and the membrane product C-2 were analyzed and characterized in the same manner as in application example 2 with reference to the method for analyzing and characterizing the membrane products A-1, A-2, A-3, A-4, A-5 finally obtained in comparative examples 7 to 11 and the membrane product C-2 finally obtained in comparative example 2. FIG. 9 is a comparison of intrinsic thickness and film surface roughness of the prepared polyamide films (M-1, M-4) and the blank film (C-2) in the embodiment. In Table 1, the brine fluxes of M-1, M-4 and C-2 are respectively: 81.30 L m -2 h -1 ，53.21 L m -2 h -1 ，43.32 L m -2 h -1 . The increase in membrane flux for M-1 can be attributed to a decrease in intrinsic membrane thickness: m-1 (intrinsic thickness of film)δ int = 7.54 ± 0.74 nm) <C-2 (intrinsic thickness of film)δ int = 21.00 ± 2.54 nm). The improvement in membrane flux for M-4 can be attributed to a reduction in intrinsic membrane thickness and an improvement in membrane surface roughness: m-4 (intrinsic thickness of film)δ int = 18.54 ± 2.72 nm) <C-2 (intrinsic thickness of film)δ int 21.00 ± 2.54 nm), M-4 (film surface roughness)R a = 60.02 ± 3.60 nm) >C-2 (film surface roughness)R a = 23.60 ± 1.25 nm)。
The above data analysis that an increase in intrinsic thickness of the polyamide membrane would significantly reduce the permeability of the membrane, also suggests that the resistance to water molecule diffusion membrane transport derives from its 6-30 nm homogeneous dense separation layer. The invention in examples 1-6 improves membrane permeability by optimizing the water-oil phase monomer concentration to control the intrinsic thickness of the membrane to within 20 nm, thereby reducing the actual resistance to transport of water salt molecules across the membrane.
The description is given for the sole purpose of illustrating the invention concept in its implementation form and the scope of the invention should not be considered as being limited to the particular form set forth in the examples.

Claims (8)

1. A method for preparing a high permeability composite reverse osmosis membrane for reducing the intrinsic thickness of a polyamide layer, comprising the steps of:
1) Preparation of aqueous phase solution: adding an amine monomer and an organic weak acid with a hydrophilic group into ultrapure water, adding an organic base to adjust the pH value to 9-11, and uniformly mixing by ultrasonic to obtain an aqueous phase solution; in the prepared aqueous phase solution, an amine monomer is m-phenylenediamine, the concentration of the amine monomer in the aqueous phase solution is 1.0%, and the addition concentration of the weak organic acid is 3-5 wt%;
2) Preparation of oil phase solution: dissolving acyl chloride monomers in an Isopar-G solvent, and uniformly mixing by ultrasonic to obtain an oil phase solution, wherein the mass concentration of the acyl chloride monomers in the oil phase solution is 1/40-1/30 of the mass concentration of the amine monomers in the water phase solution obtained in the step 1);
3) Interfacial polymerization: clamping a polysulfone membrane soaked in ultrapure water in advance by using two hollow plate frames, pouring the water-phase solution obtained in the step 1) on the surface of the polysulfone membrane for soaking for 0.5-10 min, pouring the water-phase solution on the surface of the polysulfone membrane, and drying the surface of the polysulfone membrane; pouring the oil phase solution obtained in the step 2) when no obvious liquid drops exist on the surface of the polysulfone membrane, carrying out interfacial polymerization reaction for 20-120 s, and pouring the residual oil phase solution;
4) Post-treatment of the membrane: and (3) vertically standing the polysulfone membrane treated in the step 3), draining for 15-30 s, and then putting the polysulfone membrane into a blast oven for drying treatment to obtain the composite reverse osmosis membrane product.
2. The method for preparing a high-permeability composite reverse osmosis membrane capable of reducing the intrinsic thickness of a polyamide layer according to claim 1, wherein the weak organic acid in step 1) is camphorsulfonic acid, the added organic base is triethylamine, and the added concentration of triethylamine in the aqueous solution is 2.5 to 3.0wt%.
3. The method for preparing a high permeability composite reverse osmosis membrane having reduced intrinsic thickness of polyamide layer according to claim 1 wherein the acid chloride monomer in step 2) is trimesoyl chloride.
4. The method for preparing a high permeability composite reverse osmosis membrane for reducing intrinsic thickness of polyamide layer according to claim 1, wherein the polysulfone membrane surface is dried in step 3) by air drying, fume hood drying, roller spreading drying or air knife blowing drying.
5. The method for preparing a high-permeability composite reverse osmosis membrane capable of reducing the intrinsic thickness of a polyamide layer according to claim 1, wherein the drying temperature in the oven in the step 4) is 90-95 ℃ and the drying time is 8 min.
6. The method for preparing a high permeability composite reverse osmosis membrane capable of reducing the intrinsic thickness of polyamide layer according to claim 1, wherein the soaking time of pouring the aqueous solution on the surface of polysulfone membrane in step 3) is 1-3 min; the interfacial polymerization reaction was carried out for 30 s.
7. The method for preparing a high permeability composite reverse osmosis membrane having reduced intrinsic thickness of polyamide layer according to claim 6, wherein the soaking time of pouring the aqueous solution on the surface of polysulfone membrane in step 3) is 2 min.
8. The method for preparing a high permeability composite reverse osmosis membrane for reducing the intrinsic thickness of a polyamide layer according to claim 1, wherein the polysulfone membrane surface is dried in step 3) by air knife blowing, and after the membrane surface has just no macroscopic liquid, the polysulfone membrane is naturally dried in a fume hood for 10 s, i.e. the drying is completed.
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