High-pressure reverse osmosis membrane based on pectin-assisted interfacial polymerization and preparation method of high-pressure reverse osmosis membrane

Abstract

The invention discloses a high-pressure reverse osmosis membrane based on pectin-assisted interfacial polymerization and a preparation method thereof, and the preparation method comprises the following steps: (1) fixing a polysulfone ultrafiltration membrane on an organic glass frame, and removing liquid drops on the surface of the membrane; (2) pouring an aqueous solution containing m-phenylenediamine, camphorsulfonic acid, triethylamine and pectin on the surface of the polysulfone ultrafiltration membrane, standing for a period of time, and removing a residual aqueous phase solution; (3) pouring an organic solution containing trimesoyl chloride on the surface of the membrane obtained in the step (2), standing for a period of time, and removing redundant organic phase solution; and (4) sequentially carrying out standing, heat treatment and pure water flushing on the membrane obtained in the step (3) to obtain the high-pressure reverse osmosis membrane. Natural polymer pectin is adopted as a regulator, so that the thickness and pore size distribution of a polyamide separation layer are reduced, the hydrophilicity and the charge property of the membrane are improved, and the effect of simultaneously improving the permeation flux and the rejection rate of the reverse osmosis membrane is achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of high-pressure reverse osmosis membrane preparation, and particularly to a high-pressure reverse osmosis membrane based on pectin-assisted interfacial polymerization and a preparation method thereof. Background Art

[0002] Aromatic polyamide (PA) thin-film composite (TFC) membranes are the most advanced commercial reverse osmosis membranes. Among them, the PA separation layer with desalination function is formed by rapid cross-linking on the surface of a polysulfone (PSF) support membrane through an interfacial polymerization (IP) reaction using m-phenylenediamine (MPD) and trimesoyl chloride (TMC) as reaction monomers. As a special type of reverse osmosis membrane, high-pressure reverse osmosis membranes are applicable to extremely high pressure (5.52 MPa) and salinity (32,000 mg / L NaCl) conditions, and have better water permeability and osmotic selectivity. However, due to the usually irregular and discontinuous sub-nanometer transport channels in the aromatic polyamide separation layer of high-pressure reverse osmosis membranes, there is a "seesaw" phenomenon of mutual compensation between water permeability and separation selectivity, that is, the "Trade-off" effect. Therefore, there is a huge challenge in preparing high-pressure reverse osmosis membranes to balance high permeability and high selectivity.

[0003] By precisely regulating the thickness, pore size distribution, hydrophilicity, and charge property of the aromatic polyamide separation layer, the desalination rate and water permeation flux of high-pressure reverse osmosis membranes can be adjusted. However, due to the fast diffusion rate of reaction monomers and the violent interfacial polymerization reaction, the aromatic polyamide separation layer has an extremely dense but non-uniform multi-scale structure, with a thickness usually higher than 250 nm and difficult to precisely control, which restricts the improvement of water permeability. On the other hand, due to the interaction between reaction monomers and the difficulty of uniform dispersion, the formed polyamide polymer chain structure has a strong disorder, resulting in a relatively large pore free volume (pore size) (usually ) and a wide pore size distribution in the polyamide separation layer, making it difficult to further improve the desalination rate. In summary, how to break through the "Trade-off" effect between water permeability and separation selectivity has become a bottleneck problem restricting the performance improvement of reverse osmosis membranes, especially high-pressure reverse osmosis membranes.

[0004] By regulating the distribution and diffusion of reaction monomers, controlling the interfacial polymerization reaction rate, and improving the orderliness of the interfacial polymerization reaction, while narrowing the pore size distribution and reducing the membrane thickness, it becomes an effective strategy and idea to break through the "Trade-off" effect. As a natural polymer, pectin is a typical anionic heteropolysaccharide widely present in the peels of citrus, lemon, and grapefruit. Due to the rich hydroxyl and carboxyl groups in its molecular structure, pectin has good hydrophilicity. In addition, as a commonly used food thickener, pectin can significantly increase the viscosity of liquids. Summary of the Invention

[0005] To solve the "Trade-off" effect problem of the mutual growth and decline between the permeation flux and rejection rate of high-pressure reverse osmosis membranes, the present invention provides a high-pressure reverse osmosis membrane based on pectin-assisted interfacial polymerization and a preparation method thereof. The present invention uses pectin as an additive in the aqueous solution of the interfacial polymerization reaction. By increasing the viscosity of the aqueous solution, slowing down the diffusion rate of MPD to the organic phase, and reducing the depth of the miscible zone of the interfacial polymerization reaction, the thickness of the PA separation layer is reduced. At the same time, by weakening the interaction between MPD reaction monomers in the aqueous solution, improving the dispersion uniformity of MPD, enhancing the orderliness of the interfacial polymerization reaction and the regularity of the entanglement of polyamide polymer chains, the packing density of polyamide is increased, the pore size distribution is narrowed, and the pore structure is optimized. In addition, the rich functional groups in the pectin molecular structure can endow the polyamide separation layer with higher hydrophilicity and chargeability, which helps to further improve the permeation selectivity of the high-pressure reverse osmosis membrane.

[0006] The present invention is implemented as follows. A preparation method of a high-pressure reverse osmosis membrane based on pectin-assisted interfacial polymerization includes the following steps:

[0007] (1) Fix the polysulfone ultrafiltration membrane on the plexiglass frame and drain the water droplets on the surface of the polysulfone ultrafiltration membrane;

[0008] (2) Pour an aqueous solution containing m-phenylenediamine, camphorsulfonic acid, triethylamine and an interfacial polymerization reaction regulator onto the surface of the polysulfone ultrafiltration membrane. After standing for a period of time, remove the residual aqueous solution on the surface; wherein, the interfacial polymerization reaction regulator is pectin, and the mass percentage is 0.05-0.3 wt%;

[0009] (3) Pour an organic solution containing trimesoyl chloride onto the surface of the membrane obtained in step (2). After standing and reacting for a period of time, remove the residual organic phase solution on the surface;

[0010] (4) Let the membrane obtained in step (3) stand. After the excess solution on the surface naturally evaporates, put it into a blast drying oven and heat-treat it at a certain temperature for a period of time. Rinse the membrane surface with deionized water to remove the residues on the membrane surface, and obtain a high-pressure reverse osmosis membrane.

[0011] Preferably, in the step (1), the pure water permeation flux of the polysulfone ultrafiltration membrane is 400-500 L·m -2 ·h -1 , and the bovine serum albumin rejection rate is 90.1-90.3%.

[0012] Preferably, in the aqueous solution of step (2), the mass percentage of m-phenylenediamine is 1.5-4 wt%, the mass percentage of camphorsulfonic acid is 2-3.5 wt%, the mass percentage of triethylamine is 0.8-2 wt%, the mass percentage of pectin is 0.05-0.3 wt%, and the solvent of the aqueous solution is deionized water.

[0013] More preferably, in the aqueous solution of step (2), the mass percentage of m-phenylenediamine is 2.8 wt%, the mass percentage of camphorsulfonic acid is 2.8 wt%, the mass percentage of triethylamine is 1.3 wt%, and the mass percentage of pectin is 0.05-0.3 wt%.

[0014] Preferably, in step (2), the standing time is 30-50 s.

[0015] Preferably, in the organic solution of step (3), the mass percentage of trimesoyl chloride is 0.1-0.25 wt%, and the solvent of the organic solution is one or more of n-hexane, Isopar G, Isopar H, Isopar L, and Isopar M.

[0016] More preferably, in the organic solution of step (3), the mass percentage of trimesoyl chloride is 0.17 wt%, and the solvent of the organic solution is n-hexane.

[0017] Preferably, in step (3), the standing time is 30-50 s.

[0018] Preferably, in step (4), the temperature of the forced air drying oven is 80-120 °C, and the heat treatment time is 100-300 s.

[0019] More preferably, the temperature of the forced air drying oven is 95 °C, and the heat treatment time is 190 s.

[0020] A high-pressure reverse osmosis membrane based on pectin-assisted interfacial polymerization is prepared by the above preparation method.

[0021] The interception rate of the high-pressure reverse osmosis membrane for 32000 mg / L NaCl can reach 99.57% at 5.52 MPa, and the permeation flux can reach 80.15 L·m -2 ·h -1 .

[0022] The advantages and positive effects of the present invention are:

[0023] In the present invention, in order to improve the permeation flux and permeation selectivity of the high-pressure reverse osmosis membrane, pectin is used as an auxiliary interfacial polymerization agent, and its advantages are:

[0024] 1. In the present invention, pectin is used as an additive in the aqueous solution for interfacial polymerization reaction. By increasing the viscosity of the aqueous solution, the diffusion rate of MPD into the organic phase is slowed down, and the depth of the miscible zone in the interfacial polymerization reaction is reduced, thereby decreasing the thickness of the PA separation layer.

[0025] 2. In the present invention, by weakening the interaction between MPD reaction monomers in the aqueous solution, the dispersion uniformity of MPD is improved, the orderliness of the interfacial polymerization reaction and the regularity of the entanglement of polyamide polymer chains are enhanced, thereby increasing the packing density of polyamide, narrowing the pore size distribution, and optimizing the pore structure.

[0026] 3. The abundant functional groups in the molecular structure of pectin can endow the polyamide separation layer with higher hydrophilicity and chargeability, which helps to further improve the permeation selectivity of the high-pressure reverse osmosis membrane.

[0027] 4. Pectin is a typical anionic heteropolysaccharide, which is widely present in the peels of citrus, lemon, and grapefruit. It is low-cost, green, natural, and pollution-free, meeting the current environmental protection requirements and the concept of sustainable development.

[0028] 5. The preparation method of the present invention is simple and easy to industrialize. As an interfacial auxiliary polymerization agent, pectin is added to the aqueous solution. Without participating in the polymerization reaction itself, it can improve the separation performance of the reverse osmosis membrane. Compared with other chemical modification methods, the operation is simple, and no additional production processes and equipment are required.

[0029] 6. Although the mass percentage of pectin added in the preparation method of the present invention is less than 0.3 wt%, the performance of the reverse osmosis membrane has been significantly improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 It is the infrared spectrogram of the high-pressure reverse osmosis membranes obtained in Example 2, Example 5, Comparative Example 1, and Comparative Example 2 of the present invention;

[0031] Figure 2 It is the positron annihilation lifetime spectrogram of the high-pressure reverse osmosis membranes obtained in Example 2, Example 5, Comparative Example 1, and Comparative Example 2 of the present invention;

[0032] Figure 3 It is the surface scanning electron micrograph of the high-pressure reverse osmosis membrane obtained in Example 2 of the present invention;

[0033] Figure 4 It is the surface scanning electron micrograph of the high-pressure reverse osmosis membrane obtained in Example 5 of the present invention;

[0034] Figure 5 It is the cross-section scanning electron micrograph of the high-pressure reverse osmosis membrane obtained in Example 2 of the present invention;

[0035] Figure 6 It is the cross-section scanning electron micrograph of the high-pressure reverse osmosis membrane obtained in Example 5 of the present invention;

[0036] Figure 7 Scanning electron micrograph of the surface of the high-pressure reverse osmosis membrane obtained in Comparative Example 1 of the present invention;

[0037] Figure 8 Scanning electron micrograph of the surface of the high-pressure reverse osmosis membrane obtained in Comparative Example 2 of the present invention;

[0038] Figure 9 Scanning electron micrograph of the cross-section of the high-pressure reverse osmosis membrane obtained in Comparative Example 1 of the present invention;

[0039] Figure 10 Scanning electron micrograph of the cross-section of the high-pressure reverse osmosis membrane obtained in Comparative Example 2 of the present invention. Detailed implementation manners

[0040] In order to enable those skilled in the art to more clearly understand the present invention, the present invention will be further described in detail below in conjunction with embodiments. However, it should be understood that the following embodiments are only the preferred embodiments of the present invention, and the scope of protection required by the present invention is not limited thereto.

[0041] The embodiment of the present invention provides a method for preparing a high-pressure reverse osmosis membrane based on pectin-assisted interfacial polymerization, which includes the following steps:

[0042] (1) Fix the polysulfone ultrafiltration membrane on the plexiglass frame and drain the water droplets on the surface of the polysulfone ultrafiltration membrane;

[0043] Among them, the pure water permeation flux of the polysulfone ultrafiltration membrane is 400-500 L·m -2 ·h -1 , and the bovine serum albumin rejection rate is 90.1-90.3%.

[0044] (2) Pour an aqueous solution containing m-phenylenediamine, camphorsulfonic acid, triethylamine and an interfacial polymerization reaction regulator onto the surface of the polysulfone ultrafiltration membrane. After standing for a period of time, remove the residual aqueous solution on the surface; among them, the interfacial polymerization reaction regulator is pectin, and the mass percentage is 0.05-0.3 wt%;

[0045] Among them, in the aqueous solution, the mass percentage of m-phenylenediamine is 1.5-4 wt%, the mass percentage of camphorsulfonic acid is 2-3.5 wt%, the mass percentage of triethylamine is 0.8-2 wt%, the mass percentage of pectin is 0.05-0.3 wt%, and the solvent of the aqueous solution is deionized water. In this embodiment, preferably, in the aqueous solution, the mass percentage of m-phenylenediamine is 2.8 wt%, the mass percentage of camphorsulfonic acid is 2.8 wt%, the mass percentage of triethylamine is 1.3 wt%, and the mass percentage of pectin is 0.05-0.3 wt%.

[0046] Among them, the standing time is 30-50 s. In this embodiment, the preferred standing time is 40 s.

[0047] (3) Pour the organic solution containing trimesoyl chloride onto the surface of the membrane obtained in step (2), let it stand for a period of time for reaction, and then remove the remaining organic phase solution on the surface.

[0048] Among them, in the organic solution, the mass percentage of trimesoyl chloride is 0.1 - 0.25 wt%, and the solvent of the organic solution is one or more of n - hexane, Isopar G, Isopar H, Isopar L, and Isopar M. In this example, preferably, in the organic solution, the mass percentage of trimesoyl chloride is 0.17 wt%, and the solvent of the organic solution is n - hexane.

[0049] Among them, the standing time is 30 - 50 s. In this example, the preferred standing time is 40 s.

[0050] (4) Let the membrane obtained in step (3) stand. After the excess solution on the surface naturally evaporates, put it into a blast drying oven and heat - treat it at a certain temperature for a period of time. Rinse the surface of the membrane with deionized water. After removing the residues on the surface of the membrane, a high - pressure reverse osmosis membrane is obtained.

[0051] Among them, the temperature of the blast drying oven is 80 - 120 °C, and the heat - treatment time is 100 - 300 s. In this example, the preferred temperature of the blast drying oven is 95 °C, and the heat - treatment time is 190 s.

[0052] In order to better understand the above - mentioned embodiments of the present invention, the following further illustrates them with specific examples.

[0053] In the following examples and comparative examples:

[0054] m - phenylenediamine, purchased from Shanghai Aladdin Biochemical Technology Co., Ltd., with a purity of 99 wt%;

[0055] Camphorsulfonic acid, purchased from Tokyo Chemical Industry Co., Ltd. (Shanghai), with a purity > 98 wt%;

[0056] Triethylamine, purchased from Tianjin Kemiou Chemical Reagent Co., Ltd., of analytical purity;

[0057] Pectin, purchased from Shanghai Aladdin Biochemical Technology Co., Ltd., with galacturonic acid (dry basis) ≥ 74.0%;

[0058] Polysulfone ultrafiltration membrane, with a pure water permeation flux of 400 - 500 L·m -2 ·h -1 , and a bovine serum albumin rejection rate of 90.1 - 90.3%;

[0059] Trimesoyl chloride, purchased from Alfa Aesar, purity > 98 wt.%;

[0060] n-Hexane, purchased from Shanghai Aladdin Biochemical Technology Co., Ltd., analytically pure.

[0061] Example 1:

[0062] A preparation method of a high-pressure reverse osmosis membrane based on pectin-assisted interfacial polymerization, comprising the following steps:

[0063] (1) Fix the polysulfone ultrafiltration membrane on an acrylic frame and drain the water droplets on the surface of the polysulfone ultrafiltration membrane;

[0064] (2) Pour an aqueous solution containing m-phenylenediamine, camphorsulfonic acid, triethylamine and pectin onto the surface of the polysulfone ultrafiltration membrane. After standing for 40 s, remove the remaining aqueous solution on the surface; among them, the mass percentage of m-phenylenediamine is 2.8 wt%, the mass percentage of camphorsulfonic acid is 2.8 wt%, the mass percentage of triethylamine is 1.3 wt%, and the mass percentage of pectin is 0.05 wt%;

[0065] (3) Pour a n-hexane solution containing trimesoyl chloride onto the surface of the membrane obtained in step (2). After standing and reacting for 40 s, remove the remaining organic phase solution on the surface; among them, the mass percentage of trimesoyl chloride is 0.17 wt%;

[0066] (4) Let the membrane obtained in step (3) stand. After the excess solution on the surface naturally evaporates, put it into a forced-air drying oven and heat-treat it at a temperature of 95 °C for 190 s. Rinse the membrane surface with deionized water to remove the residues on the membrane surface, and obtain a high-pressure reverse osmosis membrane.

[0067] Example 2:

[0068] A preparation method of a high-pressure reverse osmosis membrane based on pectin-assisted interfacial polymerization, which is different from Example 1 in that: in step (2), the mass percentage of pectin is 0.1 wt%, and the other conditions remain unchanged.

[0069] Example 3:

[0070] A preparation method of a high-pressure reverse osmosis membrane based on pectin-assisted interfacial polymerization, which is different from Example 1 in that: in step (2), the mass percentage of pectin is 0.15 wt%, and the other conditions remain unchanged.

[0071] Example 4:

[0072] A preparation method of a high-pressure reverse osmosis membrane based on pectin-assisted interfacial polymerization, which is different from Example 1 in that: in step (2), the mass percentage of pectin is 0.2 wt%, and the other conditions remain unchanged.

[0073] Example 5:

[0074] A preparation method of a high-pressure reverse osmosis membrane based on pectin-assisted interfacial polymerization, which is different from Example 1 in that: in step (2), the mass percentage of pectin is 0.3 wt%, and the remaining conditions remain unchanged.

[0075] Comparative Example 1:

[0076] A preparation method of a high-pressure reverse osmosis membrane based on pectin-assisted interfacial polymerization, which is different from Example 1 in that: pectin is not added in step (2), and the remaining conditions remain unchanged.

[0077] Comparative Example 2:

[0078] A preparation method of a high-pressure reverse osmosis membrane based on pectin-assisted interfacial polymerization, which is different from Example 1 in that: in step (2), the mass percentage of pectin is 0.5 wt%, and the remaining conditions remain unchanged.

[0079] Comparative Example 3:

[0080] A preparation method of a high-pressure reverse osmosis membrane based on pectin-assisted interfacial polymerization, which is different from Example 1 in that: in step (2), the mass percentage of pectin is 1 wt%, and the remaining conditions remain unchanged.

[0081] Performance Test

[0082] In the present invention, a cross-flow filtration evaluation system is used to perform performance tests on the high-pressure reverse osmosis membranes prepared in Examples 1-5 and Comparative Examples 1-3.

[0083] The obtained membrane samples are placed in 3 parallel filtration units, and the effective area of the membrane cell is 28.46 cm 2 . An aqueous NaCl solution with a concentration of 32000 mg / L is used as the feed liquid, and the pH of the feed liquid is adjusted to 7.0 ± 0.5. First, the high-pressure reverse osmosis membrane is pre-pressed for 30 min at 5.52 MPa and 25 ± 1 °C, and then the permeate is collected under a filtration pressure of 5.52 MPa and a cross-flow rate of 6 L·min -1 .

[0084] The water permeation flux is calculated by formula (1):

[0085]

[0086] In the formula, J w is the water permeation flux, with the unit of L·m -2 ·h -1 ; S is the effective membrane area, with the unit of m 2; Δt is the osmosis time, with the unit of h; Δv is the amount of osmotic water collected within a certain time Δt, with the unit of L.

[0087] The NaCl rejection rate R is calculated by formula (2):

[0088]

[0089] In the formula, C P is the NaCl concentration of the permeate, with the unit of mg / L; C f is the NaCl concentration of the feed liquid, with the unit of mg / L.

[0090] The water permeability coefficient A and the salt permeability coefficient B can be calculated by formulas (3) and (4) respectively:

[0091]

[0092] In the formula, A is the water permeability coefficient, with the unit of L·m -2 ·h -1 ·bar -1 ; B is the salt permeability coefficient, with the unit of L·m -2 ·h -1 ; ΔP and π are the transmembrane pressure difference and the osmotic pressure of the feed liquid respectively, both with the unit of bar.

[0093] The test results are shown in Table 1.

[0094] Table 1 Characterization results and separation performance of high-pressure reverse osmosis membranes

[0095]

[0096] It can be seen from the data in Table 1 that when the pectin content does not exceed 0.3 wt% (Examples 1 - 5), the electronegativity of the high-pressure reverse osmosis membrane gradually increases, and the NaCl rejection rate is greater than 99.4%; in addition, the water contact angle gradually decreases, the hydrophilicity increases, and the water permeation flux significantly increases, up to 80.15 L·m -2 ·h -1 . Especially when the pectin content is 0.3 wt%, the NaCl rejection rate is as high as 99.57%, and the water permeation flux is as high as 80.15 L·m -2 ·h -1 . Compared with the high-pressure reverse osmosis membrane without added pectin (Comparative Example 1), the permeation flux increases by 24.34%. Therefore, the effects of simultaneous improvement in water permeability, desalination rate, and permeation selectivity are achieved, breaking through the "Trade-off" effect of the inverse relationship between the permeation flux and the rejection rate.

[0097] The polyamide separation layers of the high-pressure reverse osmosis membranes obtained in Examples 2 and 5 and Comparative Examples 1 and 2 were characterized by infrared spectroscopy, asFigure 1 As shown. The characteristic absorption peaks of pectin are at 3300 cm -1 and 1047 cm -1 where 3300 cm -1 is caused by the stretching vibration of the O-H group, and 1047 cm -1 is caused by the stretching vibration between the carbon atom and the oxygen atom in the C-O-C of the α-1,4-glycosidic bond. As the concentration of pectin in the aqueous solution gradually increases, the above two characteristic peaks in Comparative Example 1, Example 2, Example 5, and Comparative Example 2 all gradually increase, indicating that pectin is doped in the polyamide layer. Due to the good hydrophilicity and rich carboxyl functional groups of pectin, the hydrophilicity and electronegativity of the high-pressure reverse osmosis membranes obtained in Examples 1-5 are gradually improved.

[0098] The surface and cross-sectional morphologies of the high-pressure reverse osmosis membranes obtained in Examples 2 and 5 and Comparative Examples 1 and 2 were analyzed, and the scanning electron micrographs are as Figures 3 to 10 shown. As Figure 3 , 4 , 7, and 8 show, a typical leaf-like structure of polyamide has formed on the surface of the high-pressure reverse osmosis membrane, and there is no obvious change in the surface morphology. As Figure 5 , 6 , 9, and 10 show, the cross-sectional morphologies of the high-pressure reverse osmosis membranes are similar. As Figure 9 shown, the thickness of the polyamide separation layer of the high-pressure reverse osmosis membrane obtained in Comparative Example 1 is about 260.49 nm; as Figure 5 , 6 , and 10 show, the thicknesses of the polyamide separation layers of the high-pressure reverse osmosis membranes obtained in Example 2, Example 5, and Comparative Example 2 gradually decrease, about 251.87 nm, 234.98 nm, and 207.37 nm respectively. Due to the introduction of pectin, the viscosity of the aqueous solution gradually increases, the diffusion rate slows down, and the thickness of the polyamide separation layer gradually thins, promoting the improvement of the water permeation flux. Introducing pectin into the aqueous phase does not significantly change the morphology of the membrane surface and makes the polyamide layer thinner, greatly improving the water permeation flux.

[0099] In addition, the interaction energy between MPD molecules and the interaction energy between pectin molecules and MPD molecules were calculated under different pectin addition amounts, and the calculation formula is:

[0100] E int = E A+B -(E A + E B ) (5)

[0101] where E int is the interaction energy between MPD molecules and pectin molecules, E A+B is the total energy of the MPD-pectin conjugate, and E Ais the energy of the MPD molecule in the complex, E B It is the energy of pectin molecules in the conjugate, and the unit is kcal / mol.

[0102] The test results are shown in Table 2.

[0103] Table 2 The interaction energy between MPD and MPD molecules and the interaction energy between pectin molecules and MPD molecules under different pectin addition conditions

[0104]

[0105] The results of molecular simulation calculations are shown in Table 2. The interaction energy between pectin and MPD is negative, indicating that there is a mutual attraction between the two. With the increase of pectin content, the viscosity of the aqueous solution gradually increases, which hinders the interaction between pectin and MPD, and the attraction between pectin and MPD weakens from 28.34 kcal / mol to 23.56 kcal / mol. At the same time, the π-π interaction force between MPD and MPD also gradually weakens due to the increase in the viscosity of the aqueous solution, and the attraction decreases from 8.63 kcal / mol to 3.99 kcal / mol, which means that the dispersion uniformity of MPD molecules in the aqueous solution has been improved.

[0106] The polyamide separation layer of the high pressure reverse osmosis membrane obtained in Examples 2 and 5 and Comparative Examples 1 and 2 was characterized by positron annihilation lifetime spectrum. The results are as follows: Figure 2 As shown. Since the intermolecular interaction force of MPD is weaker, the high-pressure reverse osmosis membrane obtained in Examples 2 and 5 has a narrower pore size distribution than the high-pressure reverse osmosis membrane without adding pectin (Comparative Example 1), and the free volume radius gradually decreases with the increase of pectin concentration. However, since the molecular structure of pectin contains a large number of carboxyl groups, when the amount added is large, the amino groups in the MPD molecules are protonated. Since the MPD molecules generate mutual repulsion (2.07 kcal / mol) after protonation, the free volume radius of the membrane in Comparative Example 2 is increased instead. Therefore, when the pectin content reaches or exceeds 0.5wt% (Comparative Examples 2 and 3), the permeation flux and NaCl retention rate are significantly reduced. In summary, when the amount of pectin added is low, with the introduction of pectin, the viscosity of the aqueous solution increases, the intermolecular interaction force of MPD weakens, the dispersibility of MPD is improved, the pore size distribution of the PA layer becomes narrower, the free volume radius becomes smaller, and the salt retention rate is improved. The invention uses natural polymer pectin as an additive. When its concentration is not higher than 0.3wt%, the permeation flux of the high-pressure reverse osmosis membrane can be greatly improved while ensuring the NaCl retention rate. The high-pressure reverse osmosis membrane prepared by the invention can be used in seawater desalination, high-salt industrial wastewater treatment and other processes.

[0107] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements on some or all of the technical features; and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the various embodiments of the present invention.

Claims

1. A method for preparing a high-pressure reverse osmosis membrane based on pectin-assisted interfacial polymerization, characterized in that: The steps include: (1) Fix the polysulfone ultrafiltration membrane on the organic glass frame and drain the water droplets on the surface of the polysulfone ultrafiltration membrane; (2) pouring an aqueous solution containing m-phenylenediamine, camphorsulfonic acid, triethylamine and an interfacial polymerization reaction regulator onto the surface of a polysulfone ultrafiltration membrane, leaving it to stand for a period of time, and removing the residual aqueous solution on the surface; wherein the interfacial polymerization reaction regulator is pectin, with a mass percentage of 0.05 to 0.3 wt %; (3) pouring an organic solution containing trimesoyl chloride onto the surface of the membrane obtained in step (2), allowing it to react for a period of time, and then removing the residual organic phase solution on the surface; (4) The membrane obtained in step (3) is allowed to stand for a period of time after the excess solution on the surface evaporates naturally, and then placed in a forced air drying oven for heat treatment at a certain temperature. The membrane surface is rinsed with deionized water to remove the residue on the membrane surface, thereby obtaining a high-pressure reverse osmosis membrane.

2. The method for preparing a high-pressure reverse osmosis membrane based on pectin-assisted interfacial polymerization according to claim 1, characterized in that: In the step (1), the pure water permeation flux of the polysulfone ultrafiltration membrane at 0.1 MPa is 400 to 500 L·m -2 ·h -1 The retention rate of bovine serum albumin is 90.1-90.3%.

3. The method for preparing a high-pressure reverse osmosis membrane based on pectin-assisted interfacial polymerization according to claim 1, characterized in that: In the aqueous solution of step (2), the mass percentage of m-phenylenediamine is 1.5-4wt%, the mass percentage of camphorsulfonic acid is 2-3.5wt%, the mass percentage of triethylamine is 0.8-2wt%, the mass percentage of pectin is 0.05-0.3wt%, and the solvent of the aqueous solution is deionized water.

4. The method for preparing a high-pressure reverse osmosis membrane based on pectin-assisted interfacial polymerization according to claim 1, characterized in that: In the step (2), the standing time is 30 to 50 seconds.

5. The method for preparing a high-pressure reverse osmosis membrane based on pectin-assisted interfacial polymerization according to claim 1, characterized in that: In the organic solution of step (3), the mass percentage of trimesoyl chloride is 0.1-0.25wt%, and the solvent of the organic solution is one or more of n-hexane, isoalkane G, isoalkane H, isoalkane L, and isoalkane M.

6. The method for preparing a high-pressure reverse osmosis membrane based on pectin-assisted interfacial polymerization according to claim 1, characterized in that: In the step (3), the standing time is 30 to 50 seconds.

7. The method for preparing a high-pressure reverse osmosis membrane based on pectin-assisted interfacial polymerization according to claim 1, characterized in that: In the step (4), the temperature of the blast drying oven is 80-120° C., and the heat treatment time is 100-300 seconds.

8. A high pressure reverse osmosis membrane based on pectin-assisted interfacial polymerization, characterized in that: The high-pressure reverse osmosis membrane is prepared by the method for preparing a high-pressure reverse osmosis membrane based on pectin-assisted interfacial polymerization according to any one of claims 1 to 7.

9. The high pressure reverse osmosis membrane based on pectin-assisted interfacial polymerization according to claim 8, characterized in that: The high-pressure reverse osmosis membrane can achieve a rejection rate of 99.57% for 32000mg / L NaCl at 5.52MPa, and a permeate flux of 80.15L·m -2 ·h -1 .

10. An application of the high-pressure reverse osmosis membrane based on pectin-assisted interfacial polymerization according to claim 8, characterized in that: The high-pressure reverse osmosis membrane can be used in processes such as seawater desalination and high-salinity industrial wastewater treatment.

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