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

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 of a high-permeability composite reverse osmosis membrane with reduced intrinsic thickness of polyamide layer preparation method

technical field

The invention relates to a method for preparing a high-permeability composite reverse osmosis membrane with reduced intrinsic thickness of a polyamide layer.

Background technique

Water resources on the earth are extremely rich, about 75% of the world is covered with water, but most of this water is seawater, and it accounts for 96.5% of all water resources. According to research and investigation, it is found that seawater contains about 92 kinds of chemical elements, of which 11 kinds (chlorine, sodium, magnesium, sulfur, calcium, potassium, bromine, strontium, boron, carbon, fluorine) account for 99.8% of the total dissolved substances in seawater, and others The content is very small; some metal elements such as potassium and sodium are necessities in the human body, but once these high-concentration metal and non-metal elements in seawater enter the human body, they will increase the metabolism of organs such as the kidneys, and aggravate the damage of the body organs. burden. If we try to desalinate the high-concentration seawater into low-concentration freshwater resources, then these vast freshwater resources can be used by human beings.

Under such circumstances, reverse osmosis technology came into being. As early as 1953, Professor CE Reid of Florida, USA proposed this idea, using phase inversion membrane technology to prepare a symmetrical cellulose acetate membrane, which realized the seawater desalination process for the first time, although it is harmful to sodium chloride salt. The rejection rate is more than 99%, but its water permeability coefficient is only 0.00012m ³ /(m ² ·d·atm), which greatly hinders the commercial application of this membrane. Subsequently, Indian scientist Srinivasa Sourirajan and American scientist Sidney Loeb developed an asymmetric cellulose acetate membrane, and by optimizing a series of phase inversion process parameters, the salt rejection rate of the prepared membrane was It can also reach 99%. In addition, its permeability is greatly improved, reaching an astonishing 0.0048 m ³ /(m ² ·d·atm). This is the famous immersion gel phase inversion method (LS method). The birth of LS membrane has brought dawn to the industrial application of reverse osmosis technology. However, in order to realize its commercial application, it is obvious that a crucial engineering problem needs to be solved, that is, the design of the membrane module. The membranes they prepared at that time were of plate type and tube type. They all had defects such as complex assembly and small membrane area per unit volume, so they failed to develop into the mainstream form of commercial reverse osmosis membrane modules. This has prompted another dawn of reverse osmosis membrane development, the application of membrane technology in the field of desalinated water treatment - thin film composite membrane (Thin film composite).

In 1977, John E. Cadotte and three others founded FilmTec. By 1979, he applied for the world's first patent (US4277344) for the preparation of reverse osmosis membranes by interfacial polymerization. The interfacial polymerization method enables the support layer and separation layer of the reverse osmosis membrane to be optimized separately during the preparation process, thereby further improving the performance of the membrane, which is the so-called thin-layer composite membrane (TFC). In 1985, after giving up the hollow fiber reverse osmosis membrane, Dow Chemical wholly acquired FilmTec. This is the origin of the famous Dow film. Today, Dow reverse osmosis membrane products still use the FilmTec trademark. In 2017, Dow Chemical and DuPont, which had been sympathetic to each other on hollow fiber reverse osmosis membranes, merged. From the beginning of the birth of the interface polymerization method, most of the experimental explorations revolved around the optimization of the physical and chemical structures of the separation layer and the support layer. (Dow Chemical) and Korea LG Chemical and other well-known enterprises. Interfacial polymerization has also become a standard preparation process for modern commercial reverse osmosis membranes. Since the overall thickness of the polyamide separation layer of the reverse osmosis membrane is between 10-300 nm, which is much smaller than the symmetrical and asymmetrical cellulose acetate membranes, and the aggregation pores between the polyamide molecules are smaller than the molecular diameters of water and sodium chloride, The membrane layer has better compactness, which can meet the screening of small molecular substances while improving the membrane permeability.

It is true that there are a large number of reports in the literature that reduce the thickness of the separation layer to improve the permeability of the membrane, but the membrane thickness they emphasize refers to the height from the surface of the polyamide layer to the back, ignoring the tens of nanometer-sized particles wrapped during the period. Hollow pores that do not participate in brine separation. Therefore, generally speaking, reducing the thickness of the membrane to improve its permeability is not rigorous, because the resistance of water and salt transmembrane transport comes from its homogeneous intrinsic part (6 ~ 30 nm); on the other hand, some studies have also reported that, Increasing the membrane surface roughness significantly increases its permeability, but this gain does not appear to be apparent with an increase in the intrinsic thickness of the membrane. Therefore, the following problems exist in the prior art literature: the understanding of the thickness of the separation layer is not clear, and the definition of "thickness" in "reducing the thickness of the separation layer to improve the permeability of the membrane" is not accurate, and there is controversy.

In addition, in most of the current experimental studies on interfacial polymerization, the ratio of the concentration of the amine monomer in the aqueous phase solution to the concentration of the acid chloride monomer in the oil phase solution is basically 20:1, that is, the concentration of the amine monomer in the aqueous phase solution is usually about The concentration of the acid chloride monomer in the oil phase solution is usually about 0.1wt%. Under the condition that the traditional membrane-making process formula is amine monomer:acyl chloride monomer concentration ratio of 20:1, the prepared reverse osmosis membrane has an insurmountable empirical upper limit theory, which improves the permeation flux of the membrane. Inevitably it will lose its retention rate. That is to say, the permeate flux and salt selectivity of the composite membranes prepared under this condition show obvious trade-off effect, that is, the increase of membrane flux will inevitably lose the salt rejection rate.

The patent of this invention aims to reduce the intrinsic thickness of the membrane and increase the roughness of the membrane surface by adjusting the concentration of the amine monomer in the aqueous phase solution and the concentration of the acid chloride monomer in the oil phase solution, so as to improve the permeability of the membrane . The patent of the present invention comprehensively analyzes and discusses the influence of the intrinsic thickness and surface roughness of the membrane on the performance of the membrane, which can provide a reference monomer concentration ratio for the preparation of a high-flux reverse osmosis membrane.

Contents of the invention

In view of the above-mentioned technical problems existing in the prior art, the object of the application of the present invention is to provide a method for preparing a high-permeability composite reverse osmosis membrane with reduced intrinsic thickness of the polyamide layer. The present invention considers controlling the loss of membrane rejection rate while improving the membrane permeability to the greatest extent by regulating the concentration of the amine monomer in the aqueous phase solution and the concentration of the acid chloride monomer in the oil phase solution (for example, in the existing conventional 20 : Under the condition of ratio of amine monomer concentration and acid chloride monomer concentration ratio of 1, reduce the concentration of acid chloride monomer slightly or greatly increase the concentration of amine monomer to reduce the intrinsic thickness of the separation layer or increase the roughness of the membrane surface ), to optimize the performance of the composite reverse osmosis membrane. In addition, the patent of this invention defines the micro-nano structure information of the separation layer in detail for the first time: the intrinsic thickness and apparent thickness of the membrane. This provides some new ideas for the basic process formulation of idealized membranes (high flux or high rejection).

A kind of preparation method of the described high-permeability composite reverse osmosis membrane with reducing intrinsic thickness of polyamide layer, is characterized in that, comprises the following steps:

1) Preparation of aqueous phase solution: add amine monomer and organic weak acid with hydrophilic groups into ultrapure water, and add organic base to adjust its pH to 9-11, and mix it uniformly by ultrasonic to obtain aqueous phase solution; In the prepared aqueous solution, the added concentration of the amine monomer is 0.25 to 5wt%, and the added concentration of the organic weak acid is 3 to 5wt%;

2) Preparation of the oil phase solution: dissolve the acid chloride monomer in Isopar-G solvent, and mix it uniformly by ultrasonic to obtain the oil phase solution; the mass concentration of the acid chloride monomer in the oil phase solution is the same as that in the aqueous phase solution obtained in step 1). 1/40 ~ 1/30 of the mass concentration of amine monomer;

3) Interfacial polymerization reaction: Use two hollow plates to hold the polysulfone membrane pre-soaked in ultrapure water, pour the aqueous phase solution obtained in step 1) on the surface of the polysulfone membrane to soak for 0.5-10 min, Then pour off the aqueous phase solution on the surface of the polysulfone membrane, and dry the surface of the polysulfone membrane; when there are no obvious droplets on the surface of the polysulfone membrane, pour the oil phase solution obtained in step 2) and carry out interfacial polymerization for 20-120 s Then pour off the remaining oil phase solution;

4) Membrane post-treatment: After the polysulfone membrane treated in step 3) was vertically drained for 15-30 s, it was placed in a blast oven for drying treatment to obtain a composite reverse osmosis membrane product.

The method for preparing a high-permeability composite reverse osmosis membrane to reduce the intrinsic thickness of the polyamide layer is characterized in that the amine monomer in step 1) is m-phenylenediamine, and the amine monomer is in the aqueous phase solution The concentration in the solution is 1.0-3.0wt%; the weak organic acid is camphorsulfonic acid, the added organic base is triethylamine, and the added concentration of triethylamine in the aqueous phase solution is 2.5-3.0wt%.

The method for preparing a high-permeability composite reverse osmosis membrane with reduced intrinsic thickness of the polyamide layer is characterized in that the acyl chloride monomer in step 2) is trimesoyl chloride.

The method for preparing a high-permeability composite reverse osmosis membrane by reducing the intrinsic thickness of the polyamide layer is characterized in that the method of drying the surface of the polysulfone membrane in step 3) is natural drying in the air, Fume hood blast drying, roller spread drying or air knife blow drying.

The method for preparing a high-permeability composite reverse osmosis membrane by reducing the intrinsic thickness of the polyamide layer is characterized in that, in step 3), the method of drying the surface of the polysulfone membrane is air knife purge drying After the surface of the membrane is just free of liquid visible to the naked eye, the polysulfone membrane is placed in a fume hood to dry naturally for 10 s, that is, the drying process is completed.

The method for preparing a high-permeability composite reverse osmosis membrane by reducing the intrinsic thickness of the polyamide layer is characterized in that the drying temperature in an oven in step 4) is 90-95°C, and the drying time is 8 minutes.

The method for preparing a high-permeability composite reverse osmosis membrane to reduce the intrinsic thickness of the polyamide layer is characterized in that, in step 3), the water phase solution is poured on the surface of the polysulfone membrane for 1-3 minutes to infiltrate , preferably 2 min; the time for interfacial polymerization is 30 s.

The present invention has obtained following beneficial effect:

1) For the first time, it was established through experiments that the osmotic resistance of water-salt transport comes from its homogeneous intrinsic part, that is, the intrinsic thickness of the membrane (in this experiment, it is only between 6 and 30 nm); reducing the separation layer of polyamide Intrinsic thickness can greatly improve the permeability of the membrane;

2) By adjusting the concentration of amine monomers in the aqueous phase solution and the concentration of acid chloride monomers in the oil phase solution, the intrinsic thickness of the separation layer can be reduced, and the roughness of the membrane surface can be increased to improve the permeability of the membrane, which can break the "existing The trade-off effect brought by the prepared reverse osmosis membrane under the conventional 20:1 ratio of amine monomer concentration to acid chloride monomer concentration”;

3) Starting from the adjustment of the reaction monomer concentration of the basic formula, it provides a new guiding idea for the preparation of an ideal thin film composite reverse osmosis membrane.

Description of drawings

Figure 1 is a schematic diagram of polyamide cross-sectional micro-nano structure information.

Fig. 2 is a graph showing the relationship between the brine flux and the salt rejection of the membranes of Comparative Examples 1-6.

Figure 3 is a TEM image of the cross-section of the films of Comparative Examples 7-11.

Fig. 4 is the AFM picture of the film surface of Comparative Examples 7-11.

Figure 5 is the analysis of the membrane permeability selectivity of comparative examples 7 to 11: sub-graph a is the relationship diagram of the change of membrane brine flux and salt rejection rate; sub-figure b is the relationship diagram of the change of membrane water permeability constant and intrinsic thickness of the membrane.

Figure 6 is a TEM image of the cross-section of the films of Comparative Examples 12-15.

Figure 7 is an AFM image of the film surface of Comparative Examples 12-15.

Figure 8 is the analysis of the membrane permeability selectivity of Comparative Examples 12 to 15: sub-graph a is the relationship diagram of the change of membrane brine flux and salt rejection rate; sub-figure b is the relationship diagram of the change of membrane water permeability constant and membrane intrinsic thickness.

Figure 9 is a comparison of three-dimensional membrane structures of membrane products C-2, M-1, and M-4 (SEM images of membrane surfaces, AFM images of membrane surfaces, and TEM images of membrane cross-sections).

Fig. 10 is an analysis diagram of the magnitude of the intrinsic thickness in the TEM image.

Detailed ways

The present invention will be further described below in conjunction with specific examples, but the protection scope of the present invention is not limited thereto.

In the following examples and comparative examples, the support bottom membrane is selected from the polysulfone ultrafiltration membrane from Zhejiang Huzhou Research Institute, and its cut molecular weight is 35KDa. Before use, rinse the back and surface with ultrapure water for future use .

In order to find out the corresponding relationship between the permeation flux and the salt cut-off rate of the upper limit of the trade-off experience, and to compare and analyze with the subsequent monomer concentration control experiment group, the patent of the present invention has done some comparative experiments: The ratio of the concentration of amine monomer to the concentration of acid chloride monomer in the oil phase solution is 20:1, that is, the concentration of amine monomer in the aqueous phase solution is about 2wt%, and the concentration of acid chloride monomer in the oil phase solution is about 0.1wt%. Next, a series of thin-film composite membranes were prepared by changing the dry state of the polysulfone membrane surface after soaking in the aqueous phase solution. In order to explore the role of the water-phase amine monomer and the oil-phase acid chloride monomer in the interfacial polymerization process, the present invention regulates the concentration of the amine monomer in the water-phase solution and the concentration of the acid-chloride monomer in the oil-phase solution respectively to prepare a reverse osmosis membrane. Correspondence between the change of intrinsic thickness and surface roughness of polyamide membrane and the flux and rejection rate of the membrane.

After comparative experiments, in the implementation case of the experimental plan group, the "amine monomer concentration in the aqueous phase solution, the acid chloride monomer concentration in the oil phase solution, and the ratio of the amine monomer concentration to the acid chloride monomer concentration" were optimized, for example: simultaneously reduce The concentration of small amine monomers and acid chloride monomers can reduce the intrinsic thickness of the separation layer and improve the permeability of the membrane. Increasing the monomer concentration of the aqueous phase while controlling the intrinsic thickness of the membrane increases the roughness of the membrane surface and also improves the permeability of the membrane.

Some of the comparative examples and examples are now described.

A pair of proportions

1. Establish the Trade-off area under the conventional film-making process formula

Comparative example 1

A method for preparing a reverse osmosis membrane, comprising the steps of:

1) Preparation of aqueous phase solution: Add m-phenylenediamine and camphorsulfonic acid to ultrapure water, add triethylamine, and mix them uniformly by ultrasonic to obtain an aqueous phase solution; in the prepared aqueous phase solution, the content of m-phenylenediamine Concentration is 2.2wt%, and 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 ultrasonically mixing to obtain an oil phase solution; wherein the concentration of trimesoyl chloride in the oil phase solution is 0.10wt%;

3) Interfacial polymerization reaction: Use two hollow frames to clamp the polysulfone membrane soaked in ultrapure water in advance, pour the aqueous phase solution obtained in step 1) on the surface of the polysulfone membrane to infiltrate for 2 minutes, then pour Remove the excess water phase solution on the surface of the polysulfone membrane, blow the surface of the membrane with a nitrogen air knife to remove water droplets and droplets, and when there is no visible liquid on the membrane surface, pour the prepared oil phase solution on the Wet the surface of the membrane with the aqueous phase solution, and after performing interfacial polymerization for 30 s, pour off the excess oil phase on the surface of the polysulfone ultrafiltration membrane;

4) Post-treatment of the membrane: After the membrane treated in step 3) was vertically drained for 20 s, it was placed in an oven set at 95 °C for 8 min to dry. Subsequently, the prepared membrane was taken out and stored in ultrapure water for 12 h to prepare for the subsequent characterization of the permeation selectivity of the membrane. The film number is designated as C-1.

Comparative example 2 ~ 6

The preparation steps of the membrane were repeated in Comparative Example 1, the only difference being that in "step 3), the surface of the membrane was purged with a nitrogen air knife to remove water droplets and liquid droplets, and after the surface of the membrane was just free of liquid visible to the naked eye, the The sulfone membrane is placed in a fume hood to dry naturally for a period of time", and the rest of the steps are the same as in Example 1 to finally obtain the membrane product.

The time for the films in Comparative Examples 2 to 6 to be placed in a fume hood to dry naturally was 10 s, 30 s, 1 min, 2 min and 4 min, respectively, and the final film products were named C-2, C-3, C-4, C5 and C-6.

2. Regulate the concentration of amine monomer c(MPD) in the aqueous phase

Comparative example 7

The preparation steps of the membrane were repeated in Comparative Example 2, the only difference being that "in the preparation process of the aqueous phase solution, the concentration of m-phenylenediamine was 0.25wt%", and the rest of the steps were the same as in Comparative Example 1, and finally a polyamide reverse osmosis was prepared membrane. The film number was designated A-1.

Comparative example 8

The preparation steps of the membrane were repeated in Comparative Example 2, the only difference being that "in the preparation process of the aqueous phase solution, the concentration of m-phenylenediamine was 0.50wt%", and the rest of the steps were the same as in Comparative Example 1, and finally a polyamide reverse osmosis was prepared membrane. The film number was designated A-2.

Comparative example 9

The preparation steps of the membrane were repeated in Comparative Example 2, the only difference being that "in the preparation process of the aqueous phase solution, the concentration of m-phenylenediamine was 1.1wt%", and the rest of the steps were the same as in Comparative Example 1, and finally a polyamide reverse osmosis was prepared. membrane. The film number was designated A-3.

Comparative example 10

The preparation steps of the membrane were repeated in Comparative Example 2, the only difference being that "in the preparation process of the aqueous phase solution, the concentration of m-phenylenediamine was 4.4wt%", and the rest of the steps were the same as in Comparative Example 1, and finally a polyamide reverse osmosis was prepared membrane. The film number was designated A-4.

Comparative example 11

The preparation steps of the membrane were repeated in Comparative Example 2, the only difference being that "in the preparation process of the aqueous phase solution, the concentration of m-phenylenediamine was 8.8wt%", and the rest of the steps were the same as in Comparative Example 1, and finally a polyamide reverse osmosis was prepared membrane. The membrane number was designated A-5.

3. Regulate the oil phase acid chloride monomer concentration c(TMC)

Comparative example 12

The preparation steps of the membrane were repeated in Comparative Example 2, the only difference being that "in the preparation process of the oil phase solution, the concentration of trimesoyl chloride was 0.02wt%", and the rest of the steps were the same as in Comparative Example 1, and finally a polyamide reverse osmosis was prepared. membrane. The film number is designated as O-1.

Comparative example 13

The preparation steps of the membrane were repeated in Comparative Example 2, the only difference being that "in the preparation process of the oil phase solution, the concentration of trimesoyl chloride was 0.05wt%", and the rest of the steps were the same as in Comparative Example 1, and finally a polyamide reverse osmosis product was prepared. membrane. The film number is designated as O-2.

Comparative example 14

The preparation steps of the membrane were repeated in Comparative Example 2, the only difference being that "in the preparation process of the oil phase solution, the concentration of trimesoyl chloride was 0.22wt%", and the rest of the steps were the same as in Comparative Example 1, and finally a polyamide reverse osmosis product was prepared. membrane. The film number is designated as O-3.

Comparative example 15

The preparation steps of the membrane were repeated in Comparative Example 2, the only difference being that "during the preparation of the oil phase solution, the concentration of trimesoyl chloride was 0.44wt%", and the rest of the steps were the same as in Comparative Example 1, and finally a polyamide reverse osmosis product was prepared. membrane. The film number is designated as O-4.

Two, the embodiment

Summarizing the experimental formula in the comparative example, the concentration ratio of the membrane can be optimized to reduce the intrinsic thickness of the separation layer or improve the roughness of the membrane surface. Some specific implementation cases are listed in the examples, but the scope of protection of this patent Not limited to the following implementation cases.

Example 1

The preparation steps of the film were repeated in Comparative Example 2, the only difference being that "in the preparation process of the aqueous phase solution, the concentration of m-phenylenediamine was 1.0wt%; in the preparation process of the oil phase solution, the concentration of trimesoyl chloride is 0.025wt%", and the rest of the steps are the same as in Comparative Example 1, and finally a polyamide reverse osmosis membrane is prepared. The film number is designated as M-1.

Example 2

The preparation steps of the film were repeated in Comparative Example 2, the only difference being that "in the preparation process of the aqueous phase solution, the concentration of m-phenylenediamine was 1.0wt%; in the preparation process of the oil phase solution, the concentration of trimesoyl chloride is 0.03wt%", and the rest of the steps are the same as in Comparative Example 1, and finally a polyamide reverse osmosis membrane is prepared. The film number is designated as M-2.

Example 3

The preparation steps of the film were repeated in Comparative Example 2, the only difference being that "in the preparation process of the aqueous phase solution, the concentration of m-phenylenediamine was 2.0wt%; in the preparation process of the oil phase solution, the concentration of trimesoyl chloride 0.035wt%", and the rest of the steps were the same as in Comparative Example 1 to finally prepare a polyamide reverse osmosis membrane. The film number is designated as M-3.

Example 4

The preparation steps of the film were repeated in Comparative Example 2, the only difference being that "in the preparation process of the aqueous phase solution, the concentration of m-phenylenediamine was 2.0wt%; in the preparation process of the oil phase solution, the concentration of trimesoyl chloride is 0.05wt%", and the rest of the steps are the same as in Comparative Example 1, and finally a polyamide reverse osmosis membrane is prepared. The film number was designated M-4.

Example 5

The preparation steps of the membrane were repeated in Comparative Example 2, the only difference being that "in the preparation process of the aqueous phase solution, the concentration of m-phenylenediamine was 3.0wt%; in the preparation process of the oil phase solution, the concentration of trimesoyl chloride is 0.05wt%", and the rest of the steps are the same as in Comparative Example 1, and finally a polyamide reverse osmosis membrane is prepared. The film number is designated as M-5.

Example 6

The preparation steps of the membrane were repeated in Comparative Example 2, the only difference being that "in the preparation process of the aqueous phase solution, the concentration of m-phenylenediamine was 3.0wt%; in the preparation process of the oil phase solution, the concentration of trimesoyl chloride is 0.08wt%", and the rest of the steps are the same as in Comparative Example 1, and finally a polyamide reverse osmosis membrane is prepared. The film number was designated M-6.

Application Example 1

The cross-flow filtration system is used to evaluate the permeability selectivity of the reverse osmosis membrane. The high-concentration NaCl aqueous solution (the concentration of NaCl is 32g/L) is used as the feed liquid to simulate seawater. penetrant. The test conditions are set as follows: the temperature of the feed liquid is 25 °C, the pH of the feed liquid is 7.5 ± 0.5, and the test pressure is 5.5 MPa. After the membrane was preloaded for 1 hour, the formal test of the membrane's permeation selectivity was started.

The polyamide reverse osmosis membranes prepared in the comparative examples and examples of the present invention were tested by the above method, and the membrane performance test results are shown in Table 1 below.

According to the test results in Table 1, the membrane products C-1, C-2, C-3, C-4, C-5 and C-6 finally prepared in Comparative Examples 1 to 6, they are used in the evaluation of reverse osmosis membranes. In the permeation selectivity experiment of the membrane, the relationship between the brine flux and the salt interception change of the membrane is shown in Figure 2.

In the 6 groups of control experiments in Comparative Examples 1 to 6, the formula in the interfacial polymerization reaction was kept consistent, and the dry state of the polysulfone bottom film after being infiltrated by the water phase was changed. The permselectivity performance data of the membrane are shown in Table 1. When the flux of the membrane increased from 42.38 Lm ^-2 h ^-1 to 56.50 L m ^-2 h ^-1 , the corresponding NaCl rejection decreased from 99.70% to 99.33%. This is in good agreement with the empirical upper bound theory in reverse osmosis membranes, as shown in Figure 2 for comparison. The greater the dryness of the membrane surface after contact with the water phase, the lower the membrane flux. This is because most of the m-phenylenediamine molecules penetrate into the pores in the polysulfone membrane, which is not conducive to the diffusion of m-phenylenediamine molecules to participate in the interface. The reaction at the place forms a rough film surface.

Application Example 2

In this application, the field emission scanning electron microscope FE-SEM is used to characterize the physical structure information of the film surface; the atomic force microscope AFM is used to characterize the roughness of the film surface, and the scanning method adopts the tapping mode, and the scanning area of each film is 2.5 μm G 2.5 μm; The structural information of the membrane cross section (membrane intrinsic thickness, apparent thickness, etc.) was characterized by transmission electron microscope TEM; the intrinsic thickness change of the membrane was analyzed by Image J software, and 15 different positions of the polyamide layer were selected in each TEM image The measurement is carried out at the place, and finally the average value is taken to obtain the intrinsic thickness of the film. Take the film product A-5 as an example to illustrate the specific measurement position of the intrinsic thickness of the film, as shown in Figure 10, and finally calculate the intrinsic thickness of each film, and the intrinsic thickness of the film is the thickness of the black line in Figure 10 part.

The intrinsic thickness of the polyamide membrane mentioned in the specific embodiment of this patent is only in the range of 6-30 nm. In the present invention, the intrinsic thickness of the membrane is controlled within 20 nm in Examples 1-6, which reduces the resistance of the transport of water and salt molecules across the membrane.

Figure 1 is a schematic diagram of the micro-nano structure information in the cross-section of the polyamide membrane. It includes an intrinsic thickness part with a thickness of only 6 to 30 nm (the intrinsic thickness of the membrane is the thickness of the peripheral wall of the hollow nanovesicle in Figure 1), a porous back structure, and hollow nanovesicles with a size of 10 to 200 nm part and the apparent thickness part of about 100 ~ 300 nm. It is also due to the existence of 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 larger than its intrinsic thickness.

Using a transmission electron microscope to compare the final film products A-1, A-2, A-3, A-4, A-5 and the film product C-2 finally made in Comparative Example 2 in Comparative Examples 7 to 11 The membrane cross-sections were characterized separately and the results are summarized in Fig. 3. Parts a, b, c, d, e, and f in Figure 3 correspond to the membrane cross-section TEM characterization of membrane products A-1, A-2, A-3, C-2, A-4, and A-5, respectively As a result, it can be seen from Figure 3 that the intrinsic thickness of the polyamide of the film products A-1, A-2, A-3, C-2, A-4, and A-5 became black and thick in sequence. Combined with the micro-nano structure of the polyamide layer described in Figure 1, the intrinsic thickness of the polyamide is obviously blackened and thickened, because during the preparation of the membrane, the concentration of phenylenediamine monomer in the aqueous phase solution increases The improvement of the reaction and the continuous improvement of the adequacy of the reaction will lead to better compactness of the membrane. The thicker may mean the increase of the intrinsic thickness of the membrane. We use Image J software to analyze the intrinsic thickness of the membrane. The amide layer was measured at 15 different positions, and finally the average value was taken. Using Image J software to analyze the TEM image of the film, the measurement results show that: from film products A-1 to A-5, the intrinsic thickness of the film increases from 5.95 ± 0.80 nm to 29.75 ± 0.97 nm.

Using an atomic force microscope to compare the membranes of the membrane products A-1, A-2, A-3, A-4, A-5 and the membrane product C-2 finally prepared in Comparative Example 2 in Comparative Examples 7 to 11 The surface roughness is characterized and analyzed separately, and its AFM diagram is shown in Figure 4. The sub-images a, b, c, d, e, and f in Figure 4 correspond to the membrane products A-1, A-2, A-3, Film surface roughness results of C-2, A-4, and A-5. When the atomic force microscope is used for characterization and analysis, the sample scanning mode is tapping mode, and the scanning area of each sample is: 2.5 μm G 2.5 μm. Use the Roughness tool in the NanoScope Analysis analysis software to select 5 different positions (0.5 μm G 0.5 μm size area) for analysis on each AFM image, and directly obtain the surface roughness data of the film in the result window, and finally take the average value to calculate The average roughness of the membrane surface was obtained. In addition, the height scale on the right side of the AFM image can also reflect the size of the roughness. According to the above method analysis and statistics, the order of film surface roughness is: 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 shows that m-phenylenediamine can promote the increase of membrane surface roughness.

The cross-flow filtration system was used to evaluate the permeability selectivity of the reverse osmosis membrane. The high-concentration NaCl aqueous solution (the concentration of NaCl was 32 g/L) was used as the feed liquid to simulate seawater. Collect permeate. The test conditions are set as follows: the temperature of the feed liquid is 25 °C, the pH of the feed liquid is 7.5 ± 0.5, and the test pressure is 5.5 MPa. After the membrane was preloaded for 1 hour, the formal test of the membrane's permeation selectivity was started.

In addition, the water permeability constant (A) (L m ^-2 h ^-1 bar ^-1 ) is used to evaluate the membrane permeability, and its value is calculated by the formula A=F/(ΔP-Δπ). Where F is the brine flux (L m ^-2 h ^-1 ), ΔP is the test applied pressure (bar), Δπ is the osmotic pressure of water (bar), Δπ=c*R*T. c is the concentration of the salt solution (mg/L), R is the thermodynamic constant (8.3144 J mol ^-1 K ^-1 ), and T is the thermodynamic temperature (K). Especially when the salt concentration is 0, Δπ=0.

The film products A-1, A-2, A-3, A-4, A-5 and the film product C-2 finally made in comparative example 2 in comparative examples 7 to 11 were carried out by the above method respectively. Test the permeability selectivity of the membrane. In the experiment of evaluating the permeability selectivity of the reverse osmosis membrane, the comparison diagram of the relationship between the salt water flux and the salt rejection rate of the membrane is shown in sub-graph a in Figure 5. It can be seen from sub-graph a in Figure 5 that during the membrane preparation process, with the increase of the concentration of phenylenediamine monomer in the aqueous phase solution, the membrane flux and rejection rate of the final membrane product are first Decrease after increasing.

According to the results of sub-graph a in Figure 5, and according to the formula A=F/(ΔP-Δπ), the water permeability constant (A) of each membrane product is calculated. The membrane products A-1, A-2, A-3, A-4, A-5 and the membrane product C-2 finally prepared in Comparative Example 7 to 11 were respectively characterized by TEM images , and use Image J software to analyze the TEM images of each film product, and obtain the intrinsic thickness results of each film product. The comparison diagram of the relationship between the water permeability constant (A) and the intrinsic thickness change of the membrane is shown in sub-graph b in Figure 5.

It can be seen from subgraph b in Figure 5 that the intrinsic thickness of the film continues to increase, 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 decreases significantly, which just means that the increase of the intrinsic thickness of the membrane increases the water transport resistance. However, from A-1 to A3, the intrinsic thickness of the membrane and its permeation flux increase simultaneously, because the roughness of the membrane also plays a role in the water transport process, and a larger roughness will provide more Water transport area.

Application Example 3

Referring to the film products A-1, A-2, A-3, A-4, A-5 and the final film product C- 2, the same method was used to compare the membrane products O-1, O-2, O-3, O-4 finally prepared in Comparative Examples 12 to 15 and the final membrane product C- 2 for analytical characterization.

The membrane cross-sectional TEM images of membrane products O-1, O-2, O-3, O-4 and membrane product C-2 are shown in Fig. 6 . Parts a, b, c, d, and e in Figure 6 correspond to the TEM characterization results of membrane cross-sections of membrane products O-1, O-2, C-2, O-3, and O-4, respectively. It can be analyzed from Figure 6 that during the preparation of the film, as the concentration of trimesoyl chloride in the oil phase solution increases, the intrinsic thickness of the film increases from 17.20 ± 2.50 nm (O-1) to 27.00 ± 4.50 nm (O-4). This also shows that the oil phase monomer concentration has a positive impact on the actual separation layer thickness of the membrane.

Figure 7 is the AFM image of the film surface of the film products O-1, O-2, C-2, O-3, O-4, and the analysis results: 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 (membrane surface roughness R _a =23.60 ± 1.25 nm), it was found that when the concentration of trimesoyl chloride was lower, the membrane surface roughness was larger, this is because once the nascent polyamide film layer is formed Inhibits the diffusion-reaction process of amine monomers. The reaction area shrinks, so the surface of the membrane tends to be flat.

Fig. 8 is a graph showing the permeation selectivity performance of membrane products O-1, O-2, C-2, O-3, and O-4. It can be seen from sub-graph a in Figure 8 that as the concentration of trimesoyl chloride in the oil phase increases, the water permeability constants of membrane products O-1, O-2, C-2, O-3 and O-4 ( A) Continuing decline while salt rejection continues to increase. The reduction of membrane permeability may be due to the continuous increase of the intrinsic thickness of the membrane. Part b of Figure 8 shows that the permeability constant of water and the intrinsic thickness of the membrane show an obviously opposite trend. This can again illustrate that the permeation resistance of the membrane comes from its homogeneous intrinsic thickness fraction. In addition, when the concentration of trimesoyl chloride is 0.02 ~ 0.05%, the brine flux of the membrane is 55 ~ 80 L m ^-2 h ^-1 , and the intrinsic thickness of the membrane is as high as 17 nm. Attributable to the greater roughness of the membrane surface.

Referring to the film products A-1, A-2, A-3, A-4, A-5 and the final film product C- 2, use the same method to analyze and characterize polyamide membranes (M-1, M-4) and membrane product C-2. Fig. 9 is a comparison of the intrinsic thickness and surface roughness of the prepared polyamide membranes (M-1, M-4) and the blank membrane (C-2) in specific implementation cases. Combined with Table 1, the brine fluxes of M-1, M-4, and C-2 are 81.30 L m ^-2 h ^-1 , 53.21 L m ^-2 h ^-1 , and 43.32 L m ^-2 h ^-1 , respectively. The increase of M-1 membrane flux can be attributed to the reduction of the intrinsic thickness of the membrane: M-1 (the intrinsic thickness of the membrane δ _int = 7.54 ± 0.74 nm) < C-2 (the intrinsic thickness of the membrane δ _int = 21.00 ± 2.54 nm). The increase of M-4 membrane flux can be attributed to the decrease of membrane intrinsic thickness and the increase of membrane surface roughness: M-4 (membrane intrinsic thickness δ _int = 18.54 ± 2.72 nm) < C-2 (membrane Intrinsic thickness δ _int = 21.00 ± 2.54nm), M-4 (film surface roughness R _a = 60.02 ± 3.60 nm) > C-2 (film surface roughness R _a = 23.60 ± 1.25 nm).

According to the above data analysis, the increase of the intrinsic thickness of the polyamide membrane will significantly reduce the permeability of the membrane, which also shows that the resistance of water molecule expansion and transport comes from its homogeneous and dense separation layer of 6 ~ 30 nm. The present invention controls the intrinsic thickness of the membrane within 20 nm by optimizing the monomer concentration of the water-oil phase in Examples 1-6, thereby reducing the actual resistance of water and salt molecules transporting across the membrane and improving the permeability of the membrane .

The content described in this specification is only an enumeration of the implementation forms of the inventive concepts, and the protection scope of the present invention should not be regarded as limited to the specific forms stated in the embodiments.

Claims (8)

1. a kind of preparation method to reduce the high-permeability composite reverse osmosis membrane of polyamide layer intrinsic thickness, it is characterized in that, may further comprise the steps: 1) Preparation of aqueous phase solution: add amine monomer and organic weak acid with hydrophilic groups into ultrapure water, and add organic base to adjust its pH to 9-11, and mix it uniformly by ultrasonic to obtain aqueous phase solution; In the prepared aqueous solution, the amine monomer is m-phenylenediamine, the concentration of the amine monomer in the aqueous solution is 1.0%, and the added concentration of the organic weak acid is 3 to 5wt%; 2) Preparation of the oil phase solution: dissolve the acid chloride monomer in Isopar-G solvent, and mix it uniformly by ultrasonic to obtain the oil phase solution. The mass concentration of the acid chloride monomer in the oil phase solution is the amine in the aqueous phase solution obtained in step 1). 1/40 ~1/30 of the monomer mass concentration; 3) Interfacial polymerization reaction: Use two hollow plates to hold the polysulfone membrane pre-soaked in ultrapure water, pour the aqueous phase solution obtained in step 1) on the surface of the polysulfone membrane to soak for 0.5-10 min, Then pour off the aqueous phase solution on the surface of the polysulfone membrane, and dry the surface of the polysulfone membrane; when there are no obvious droplets on the surface of the polysulfone membrane, pour the oil phase solution obtained in step 2) and carry out interfacial polymerization for 20-120 s Then pour off the remaining oil phase solution; 4) Membrane post-treatment: After the polysulfone membrane treated in step 3) was vertically drained for 15-30 s, it was placed in a blast oven for drying treatment to obtain a composite reverse osmosis membrane product. 2. A kind of preparation method to reduce the high-permeability composite reverse osmosis membrane of polyamide layer intrinsic thickness as claimed in claim 1, it is characterized in that, the organic weak acid described in step 1) is camphorsulfonic acid, add The organic base is triethylamine, and the addition concentration of triethylamine in the aqueous phase solution is 2.5 ~ 3.0wt%. 3. A method for preparing a high-permeability composite reverse osmosis membrane with reduced intrinsic thickness of the polyamide layer as claimed in claim 1, wherein the acid chloride monomer in step 2) is trimesoyl chloride. 4. A method for preparing a high-permeability composite reverse osmosis membrane to reduce the intrinsic thickness of the polyamide layer as claimed in claim 1, characterized in that, in step 3), the surface of the polysulfone membrane is dried Natural air drying, fume hood blast drying, roller spread drying or air knife blow drying. 5. A method for preparing a high-permeability composite reverse osmosis membrane to reduce the intrinsic thickness of the polyamide layer as claimed in claim 1, wherein the drying temperature in the oven in step 4) is 90 to 95 °C , drying time 8 min. 6. A method for preparing a high-permeability composite reverse osmosis membrane to reduce the intrinsic thickness of the polyamide layer as claimed in claim 1, wherein the aqueous phase solution in step 3) is poured on the surface of the polysulfone membrane to infiltrate The time is 1-3 min; the time for interfacial polymerization is 30 s. 7. A method for preparing a high-permeability composite reverse osmosis membrane to reduce the intrinsic thickness of the polyamide layer as claimed in claim 6, wherein the aqueous phase solution in step 3) is poured on the surface of the polysulfone membrane to infiltrate The time is 2 min. 8. A method for preparing a high-permeability composite reverse osmosis membrane with reduced intrinsic thickness of the polyamide layer as claimed in claim 1, characterized in that, in step 3), the surface of the polysulfone membrane is dried For air knife purging and drying, the polysulfone membrane was placed in a fume hood to dry naturally for 10 s after the surface of the membrane was just free of liquid visible to the naked eye, that is, the drying process was completed.

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