High-boron-removal and high-desalination seawater desalination reverse osmosis composite membrane and preparation method thereof

Abstract

The invention relates to the technical field of reverse osmosis membranes, in particular to a high-boron-removal and high-desalination seawater desalination reverse osmosis composite membrane and a preparation method thereof.The preparation method comprises the following steps that an oil-phase monomer reactant and a water-phase monomer reactant are subjected to an interfacial polymerization reaction on the surface of a porous base membrane to form an interfacial polymer layer; the composite membrane before the interfacial polymer layer is not completely cured is defined as a nascent state composite membrane; and coating the surface of the nascent state composite membrane with a flexible macromolecular oil phase solution, and then removing an oil phase to form the seawater desalination reverse osmosis composite membrane with high boron removal and high desalination. The flexible polymer is introduced into the rigid polymer skeleton of the surface desalination layer of the nascent state composite membrane, so that the desalination rate and the boron removal rate of the composite membrane can be remarkably improved.

Description

Technical Field

[0001] The invention relates to the technical field of reverse osmosis membranes, and in particular to a high-boron removal and high-salinity removal seawater desalination reverse osmosis composite membrane and a preparation method thereof. Background Art

[0002] Reverse osmosis membranes have been widely used in the purification of salt water such as seawater desalination. Reverse osmosis membranes are usually prepared by interfacial polymerization of polyamines and polyacyl chlorides in water and oil phases. The process includes using a porous support membrane to contact the water phase containing polyamines by single-sided coating (spray coating, shower coating, slit coating, etc.) or double-sided coating (dip coating), removing the residual water phase droplets on the surface of the support membrane, and then contacting the oil phase for interfacial polymerization, and then removing the oil phase to form a solidified polyamide separation layer; the reverse osmosis membrane can adjust the permeability and desalination rate of the membrane by adjusting the monomer concentration and reaction conditions in the water and oil phases. However, the reverse osmosis membrane used for seawater desalination has a high influent salt concentration and requires a very high removal rate of salt ions. The above adjustment means are difficult to achieve a higher desalination rate; on the other hand, there will always be fluctuations in monomer concentration in the production batching link, so the stability of performance cannot be guaranteed by concentration adjustment alone.

[0003] CN103877875A discloses a sub-nanofiltration composite membrane. The composite membrane is prepared by coating PDMS as an intermediate layer on the surface of a porous base membrane and then performing an interfacial polymerization reaction to form a desalination layer. The introduction of the PDMS intermediate layer greatly improves the water flux of the membrane, but the membrane has poor removal effect on sodium chloride and boron. Summary of the invention

[0004] In order to solve the above technical problems, a high-boron removal and high-salinity removal seawater desalination reverse osmosis composite membrane and its preparation method are provided. In the early stage of the interfacial polymerization process, the present invention utilizes the plasticity of the surface desalination layer of the nascent composite membrane for modification, introduces flexible polymers into the rigid polymer skeleton of the surface desalination layer of the nascent composite membrane, and significantly improves the desalination rate and boron removal rate of the composite membrane.

[0005] In order to achieve the above objectives, the present invention is implemented through the following technical solutions:

[0006] A method for preparing a high-boron removal and high-salinity removal seawater desalination reverse osmosis composite membrane comprises the following steps:

[0007] The oil phase monomer reactant and the water phase monomer reactant are subjected to an interfacial polymerization reaction on the surface of the porous base film to form an interfacial polymer layer, and the composite film before the interfacial polymer layer is completely solidified is defined as a nascent composite film;

[0008] A flexible polymer oil phase solution is coated on the surface of the nascent composite membrane, and then the oil phase is removed to form a seawater desalination reverse osmosis composite membrane with high boron removal and high salt removal.

[0009] Furthermore, the preparation method of the high-boron removal and high-salinity removal seawater desalination reverse osmosis composite membrane specifically comprises the following steps:

[0010] S1, coating the oil phase monomer reactant on the surface of the porous base membrane carrying the water phase monomer reactant, and performing interfacial polymerization to form an interfacial polymer layer, wherein the composite membrane before the interfacial polymer layer is completely cured is defined as a nascent composite membrane;

[0011] S2. Coating a flexible polymer oil phase solution on the surface of the primary ecological composite membrane, reacting for more than 5 seconds, then removing the oil phase, and rinsing to form a seawater desalination reverse osmosis composite membrane with high boron removal and high salt removal.

[0012] Furthermore, the flexible polymer in the oil phase solution of the flexible polymer is selected from one or more of natural rubber, isoprene rubber, polybutadiene, nitrile rubber, styrene-butadiene rubber, EPDM rubber, polyisobutylene, fluororubber, silicone rubber (including polydimethylsiloxane, etc.), chloroprene rubber, polysulfide rubber, polyurethane rubber, epichlorohydrin rubber, acrylate rubber, ethylene-vinyl acetate copolymer, and ethylene-vinyl alcohol copolymer.

[0013] Furthermore, the mass percentage of the oil phase solution of the flexible polymer is 0.01%-10%.

[0014] Furthermore, the nascent composite membrane is a composite membrane which is not completely cured after the base membrane carrying the water-phase monomer reactant on the surface is coated with the oil-phase monomer reactant for 1 second to 5 minutes, and the residual solvent on the surface is in the range of 0.1wt%-100wt%.

[0015] Furthermore, the oil phase solvent in the oil phase solution of the flexible polymer is a good solvent capable of dissolving the flexible polymer, for example, it can be an oil phase solvent that dissolves the oil phase monomer reactant.

[0016] Furthermore, the interfacial polymerization reaction time is 1 second to 5 minutes; the reaction time after coating the oil phase solution of the flexible polymer is 10 seconds to 3 minutes. The coating method includes but is not limited to slit coating, immersion coating, single-sided back roller coating, etc.; the method of removing the oil phase includes but is not limited to oven heating to volatilize the solvent, liquid spraying, extrusion roller, air knife, air knife removal, etc.

[0017] Furthermore, the porous base membrane is selected from one of a polysulfone porous support membrane, a polyethersulfone porous support membrane, a polyetherimide porous support membrane, and a polytetrafluoroethylene porous support membrane.

[0018] Further, the oil phase monomer reactant is an oil phase solution containing an acyl halide functional group compound, the mass percentage of which is 2wt%-4wt%, wherein the acyl halide functional group compound includes but is not limited to phthaloyl chloride, isophthaloyl chloride, terephthaloyl chloride, trimesoyl chloride, biphenyltrichloride, etc.;

[0019] The aqueous phase monomer reactant is an aqueous phase solution containing amine monomers, with a mass percentage of 0.1wt%-0.3wt%, wherein the amine monomers include but are not limited to m-phenylenediamine, propylenediamine or triethylenetetramine.

[0020] Another aspect of the present invention provides a high-boron removal and high-salinity removal seawater desalination reverse osmosis composite membrane obtained by the above method.

[0021] Compared with the existing seawater desalination reverse osmosis composite membrane preparation technology, the advantages of the present invention are:

[0022] In the early stage of the interfacial polymerization process, the present invention utilizes the plasticity of the incompletely solidified interfacial polymer layer (i.e., the desalination layer) on the surface of the nascent composite membrane to modify it, introduces flexible polymers into the rigid polymer skeleton of the desalination layer, breaks through the performance upper limit of a single polymer, can flexibly regulate the performance of the composite membrane, and significantly improves the desalination rate and deboronization rate of the composite membrane;

[0023] The flexible polymer used is cheap and easily available, and the preparation process is simple. It only requires adding a flexible polymer solution coating step in the conventional interfacial polymerization reaction zone. There is no need to change the length and layout of the production line. The transformation is simple and the investment cost is low. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 The invention discloses a process for preparing a high-boron removal and high-salinity removal seawater desalination reverse osmosis composite membrane. DETAILED DESCRIPTION

[0025] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments. The following description of at least one exemplary embodiment is actually only illustrative and is by no means intended to limit the present invention and its application or use. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0026] Unless otherwise specifically stated, the numerical value set forth in these embodiments does not limit the scope of the present invention. The technology and method known to those of ordinary skill in the relevant art may not be discussed in detail, but in appropriate cases, the technology and method should be considered as a part of the specification. In all examples shown and discussed here, any specific value should be interpreted as being merely exemplary, rather than as a limitation. Therefore, other examples of exemplary embodiments may have different values.

[0027] The experimental methods in the following examples without specifying specific conditions are usually measured in accordance with national standards; if there is no corresponding national standard, the method is carried out in accordance with the general standard requirements or general methods.

[0028] The following cases use polysulfone porous support membrane as the porous base membrane, and its cut-off molecular weight is 35KDa. In other cases, porous base membranes of other materials can also be used, such as polyethersulfone porous support membrane, polyetherimide porous support membrane, polytetrafluoroethylene porous support membrane, etc. according to needs.

[0029] Example 1

[0030] A method for preparing a high-boron removal and high-salinity removal seawater desalination reverse osmosis composite membrane, the process preparation route is as follows Figure 1 As shown, the specific steps include:

[0031] S1, firstly fully contacting the polysulfone porous support membrane with an aqueous solution containing 4 wt% of m-phenylenediamine, and then contacting it with an Isopar E oil solution containing 0.2 wt% of trimesoyl chloride to perform interfacial polymerization for 1 minute to form an interfacial polymer layer, wherein the composite membrane before the interfacial polymer layer is completely cured is defined as a nascent composite membrane, and thus a nascent composite membrane is prepared;

[0032] S2. Evenly apply an IsoaprE solution containing 0.01 wt% polydimethylsiloxane (PDMS) on the surface of the primary eco-membrane. After reacting for 1 minute, use a roller to remove 80% of the solution on the membrane surface. Then, put the membrane into a 30°C oven to thoroughly dry the solution. Then, immerse it in 90°C hot water for rinsing for 3 minutes to obtain a high-boron removal and high-salinity removal seawater desalination reverse osmosis composite membrane.

[0033] Example 2

[0034] A method for preparing a high-boron removal and high-salinity removal seawater desalination reverse osmosis composite membrane, the process preparation route is as follows Figure 1 As shown, the specific steps include:

[0035] S1, firstly fully contacting the polysulfone porous support membrane with an aqueous solution containing 4 wt% of m-phenylenediamine, and then contacting it with an Isopar E oil solution containing 0.2 wt% of trimesoyl chloride to perform interfacial polymerization for 1 minute to form an interfacial polymer layer, wherein the composite membrane before the interfacial polymer layer is completely cured is defined as a nascent composite membrane, and thus a nascent composite membrane is prepared;

[0036] S2. Evenly apply an IsoaprE solution containing 0.1 wt% polydimethylsiloxane (PDMS) on the surface of the primary eco-membrane. After reacting for 1 minute, use a roller to remove 80% of the solution on the membrane surface. Then, put the membrane into a 30°C oven to thoroughly dry the solution. Then, immerse it in 90°C hot water for rinsing for 3 minutes to obtain a high-boron removal and high-salinity removal seawater desalination reverse osmosis composite membrane.

[0037] Example 3

[0038] A method for preparing a high-boron removal and high-salinity removal seawater desalination reverse osmosis composite membrane, the process preparation route is as follows Figure 1 As shown, the specific steps include:

[0039] S1, firstly fully contacting the polysulfone porous support membrane with an aqueous solution containing 4 wt% of m-phenylenediamine, and then contacting it with an Isopar E oil solution containing 0.2 wt% of trimesoyl chloride to perform interfacial polymerization for 1 minute to form an interfacial polymer layer, wherein the composite membrane before the interfacial polymer layer is completely cured is defined as a nascent composite membrane, and thus a nascent composite membrane is prepared;

[0040] S2. Evenly apply Isoapr E solution containing 1 wt% polydimethylsiloxane (PDMS) on the surface of the primary eco-membrane. After reacting for 1 minute, use a roller to remove 80% of the solution on the membrane surface. Then, put the membrane into a 30°C oven to thoroughly dry the solution. Then, immerse it in 90°C hot water for rinsing for 3 minutes to obtain a high-boron removal and high-salinity removal seawater desalination reverse osmosis composite membrane.

[0041] Example 4

[0042] A method for preparing a high-boron removal and high-salinity removal seawater desalination reverse osmosis composite membrane, the process preparation route is as follows Figure 1 As shown, the specific steps include:

[0043] S1, firstly fully contacting the polysulfone porous support membrane with an aqueous solution containing 4 wt% of m-phenylenediamine, and then contacting it with an Isopar E oil solution containing 0.2 wt% of trimesoyl chloride to perform interfacial polymerization for 1 minute to form an interfacial polymer layer, wherein the composite membrane before the interfacial polymer layer is completely cured is defined as a nascent composite membrane, and thus a nascent composite membrane is prepared;

[0044] S2. Evenly coat the surface of the primary eco-membrane with an Isoapr E solution containing 1 wt% polydimethylsiloxane (PDMS). After reacting for 10 seconds, use a roller to remove 80% of the solution on the membrane surface. Then, place the membrane in a 30°C oven to thoroughly dry the solution. Then, rinse it in 90°C hot water for 3 minutes to obtain a high-boron removal and high-salinity removal seawater desalination reverse osmosis composite membrane.

[0045] Example 5

[0046] A method for preparing a high-boron removal and high-salinity removal seawater desalination reverse osmosis composite membrane, the process preparation route is as follows Figure 1 As shown, the specific steps include:

[0047] S1, firstly fully contacting the polysulfone porous support membrane with an aqueous solution containing 4 wt% of m-phenylenediamine, and then contacting it with an Isopar E oil solution containing 0.2 wt% of trimesoyl chloride to perform interfacial polymerization for 10 seconds to form an interfacial polymer layer, wherein the composite membrane before the interfacial polymer layer is completely cured is defined as a nascent composite membrane, and thus a nascent composite membrane is prepared;

[0048] S2. Evenly apply Isoapr E solution containing 1 wt% polydimethylsiloxane (PDMS) on the surface of the primary eco-membrane. After reacting for 1 minute, use a roller to remove 80% of the solution on the membrane surface. Then, put the membrane into a 30°C oven to thoroughly dry the solution. Then, immerse it in 90°C hot water for rinsing for 3 minutes to obtain a high-boron removal and high-salinity removal seawater desalination reverse osmosis composite membrane.

[0049] Comparative Example 1

[0050] The preparation of the reverse osmosis composite membrane in this case is the same as that in Example 3, the difference is that in step S1, after obtaining the primary composite membrane, a pressure roller is used to remove 80% of the solution on the membrane surface, and then the solution is placed in a 30°C oven to be thoroughly dried; and then step S2 is the same as in Example 3.

[0051] Comparative Example 2

[0052] The preparation process of the reverse osmosis composite membrane in this case is as follows:

[0053] (1) firstly coating the surface of a polysulfone porous support membrane with an aqueous solution containing 4 wt% of m-phenylenediamine, and then coating the surface with an Isopar E oil solution containing 0.2 wt% of trimesoyl chloride and 1 wt% of polydimethylsiloxane (PDMS), and performing an interfacial polymerization reaction for 1 minute to form an interfacial polymer layer, wherein the composite membrane before the interfacial polymer layer is completely cured is defined as a nascent composite membrane, thereby preparing a nascent composite membrane;

[0054] (2) Use a roller to remove 80% of the solution on the surface of the resulting nascent composite membrane, then place the membrane in a 30°C oven to thoroughly dry the solution, and then rinse it in 90°C hot water for 3 minutes.

[0055] Performance evaluation of reverse osmosis composite membrane:

[0056] The composite membrane samples prepared in the above examples and comparative examples were tested under the following conditions: 32000 mg / L sodium chloride solution was used as the feed solution, and the feed solution also contained 5 ppm boric acid, the feed solution temperature was 25°C, the pH was 7.5, and the test pressure was 5.5 MPa. After the composite membrane was started and operated for 1 hour, the flux, salt rejection rate and boron rejection rate were tested, and the test results are shown in Table 1.

[0057] Table 1 Performance of composite membranes of examples and comparative examples

[0058] FluxLMH Desalination rate % Boron removal rate % Example 1 35.3 99.78 90.8 Example 2 34.2 99.81 92.1 Example 3 33.1 99.86 92.7 Comparative Example 1 17.9 99.75 91.1 Comparative Example 2 19.5 99.63 88.7 Example 4 34.6 99.80 91.3 Example 5 29.4 99.73 91.6

[0059] As can be seen from the test results of Examples 1-3, increasing the concentration of the PDMS oil phase solution can simultaneously improve the desalination rate and deboronization rate of the composite membrane, but the flux is reduced. As can be seen from Example 3 and Example 4, the residence time of the PDMS oil phase solution on the membrane surface affects the membrane performance, and extending the residence time can further improve the desalination rate and deboronization rate. As can be seen from Example 3 and Example 5, when the interfacial polymerization time is short, the polymer skeleton of the nascent desalination layer (i.e., the interfacial polymer layer that is not completely cured) is relatively fragile, and at this time, introducing PDMS in the skeleton can reduce membrane performance. As can be seen from Example 3 and Comparative Example 1, if the nascent desalination layer is completely cured and then coated with the PDMS oil phase solution on the surface, the membrane performance will be greatly reduced, because the polymer skeleton of the desalination layer has been completely cured, and the PMDS molecules cannot be introduced into the dense skeleton, and can only form a coating on the surface of the desalination layer, and forming a coating again on the surface of the desalination layer will significantly increase the permeation resistance, so that the flux is obviously reduced, the desalination rate and the deboronization rate are also reduced to a certain extent. It can be seen from Example 3 and Comparative Example 2 that when PDMS is directly incorporated into the oil phase monomer reactants, the PDMS molecules will affect the formation process of the polymer skeleton of the desalting layer, thereby affecting the density of the desalting layer, resulting in a decrease in membrane flux, while also adversely affecting the desalination rate and deboronization rate to a certain extent.

[0060] The present invention introduces flexible polymers into the basic structural skeleton of the nascent eco-membrane formed in the initial stage of interfacial polymerization for filling and modification. The micropore plasticity between the skeleton molecular chains of the nascent eco-membrane formed in the initial stage is relatively strong. At this time, the introduction of flexible polymers for filling and modification can reduce the pore structure, thereby significantly improving the removal rate of salt ions and boron.

[0061] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical scheme and inventive concept of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. A method for preparing a high-boron removal and high-salinity removal seawater desalination reverse osmosis composite membrane, characterized in that: The steps include: The oil phase monomer reactant and the water phase monomer reactant are subjected to an interfacial polymerization reaction on the surface of the porous base film to form an interfacial polymer layer, and the composite film before the interfacial polymer layer is completely solidified is defined as a nascent composite film; A flexible polymer oil phase solution is coated on the surface of the nascent composite membrane, and then the oil phase is removed to form a seawater desalination reverse osmosis composite membrane with high boron removal and high salt removal.

2. The method for preparing a high-boron removal and high-salinity removal seawater desalination reverse osmosis composite membrane according to claim 1, characterized in that: The specific steps include: S1, coating the oil phase monomer reactant on the surface of the porous base membrane carrying the water phase monomer reactant, and performing interfacial polymerization to form an interfacial polymer layer, wherein the composite membrane before the interfacial polymer layer is completely cured is defined as a nascent composite membrane; S2. Coating a flexible polymer oil phase solution on the surface of the primary ecological composite membrane, reacting for more than 5 seconds, then removing the oil phase, and rinsing to form a seawater desalination reverse osmosis composite membrane with high boron removal and high salt removal.

3. The method for preparing a high-boron removal and high-salinity removal seawater desalination reverse osmosis composite membrane according to claim 2, characterized in that: The flexible polymer in the oil phase solution of the flexible polymer is selected from one or more of natural rubber, isoprene rubber, polybutadiene, nitrile rubber, styrene-butadiene rubber, EPDM rubber, polyisobutylene, fluororubber, silicone rubber, chloroprene rubber, polysulfide rubber, polyurethane rubber, epichlorohydrin rubber, acrylate rubber, ethylene-vinyl acetate copolymer, and ethylene-vinyl alcohol copolymer.

4. The method for preparing a high-boron removal and high-salinity removal seawater desalination reverse osmosis composite membrane according to claim 3, characterized in that: The mass percentage of the oil phase solution of the flexible polymer is 0.01%-10%.

5. The method for preparing a high-boron removal and high-salinity removal seawater desalination reverse osmosis composite membrane according to any one of claims 1 to 4, characterized in that: The nascent composite film is a composite film which is not completely cured after the base film carrying the water-phase monomer reactant is coated with the oil-phase monomer reactant for 1 second to 5 minutes, and the residual solvent on the surface is in the range of 0.1wt%-100wt%.

6. The method for preparing a high-boron removal and high-salinity removal seawater desalination reverse osmosis composite membrane according to any one of claims 1 to 4, characterized in that: The oil phase solvent in the oil phase solution of the flexible polymer is a good solvent capable of dissolving the flexible polymer.

7. The method for preparing a high-boron removal and high-salinity removal seawater desalination reverse osmosis composite membrane according to any one of claims 1 to 4, characterized in that: The interfacial polymerization reaction time is 1 second to 5 minutes; the reaction time after coating the oil phase solution of the flexible polymer is 10 seconds to 3 minutes.

8. The method for preparing a high-boron removal and high-salinity removal seawater desalination reverse osmosis composite membrane according to any one of claims 1 to 4, characterized in that: The porous base membrane is selected from one of a polysulfone porous support membrane, a polyethersulfone porous support membrane, a polyetherimide porous support membrane, and a polytetrafluoroethylene porous support membrane.

9. A high-boron removal and high-salinity removal seawater desalination reverse osmosis composite membrane obtained by the preparation method according to any one of claims 1 to 8.

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