Preparation method of PPTA / polyelectrolyte composite nanofiltration membrane resistant to temperature, acid and alkali, and solvent

Abstract

The invention discloses a preparation method of a PPTA / polyelectrolyte composite nanofiltration membrane with temperature resistance, acid and alkali resistance, and solvent resistance. First, a polycation solution and a polyanion solution are prepared; then the PPTA ultrafiltration base membrane is immersed in one of the polycation solution or the polyanion solution, and then immersed in the other to form an in-situ polymerization cycle process; then the in-situ polymerization cycle process is repeated n / 2 times, and the PPTA ultrafiltration base membrane is alternately immersed in the polycation solution and the polyanion solution to obtain a primary PPTA / polyelectrolyte composite nanofiltration membrane, and then it is immersed in a salt solution for salt treatment and heat treatment, taken out and immersed in deionized water and left standing to obtain the PPTA / polyelectrolyte composite nanofiltration membrane. The invention first uses LBL to achieve precise regulation of the membrane structure and performance, and constructs multilayer polyelectrolyte layers on the surface of the PPTA ultrafiltration base membrane to prepare a PPTA / polyelectrolyte composite nanofiltration membrane with high flux, high rejection, long cycle, temperature resistance, acid and alkali resistance, and solvent resistance.

Description

Technical Field

[0001] The present invention belongs to the field of membrane separation, and specifically relates to a method for preparing a PPTA / polyelectrolyte composite nanofiltration membrane with temperature resistance, acid and alkali resistance, and solvent resistance. Background Art

[0002] High-temperature acid-base and organic solvent nanofiltration (OSN) is a green, efficient, and energy-saving new membrane separation technology for treating severely polluted wastewater containing acids, alkalis, or organic solvents. In addition to requiring the membrane itself to have excellent physical and chemical stability, controlling the density and pore size of the surface separation layer structure is also a key factor for the efficient operation of composite nanofiltration membranes. Currently, the main method for preparing commercial composite nanofiltration membranes is interfacial polymerization (IP). This method optimizes the permeation / separation performance of composite nanofiltration membranes by changing the materials of the surface separation layer and the porous substrate membrane. However, its polymerization reaction activity is strong, the reaction rate is too fast, there are many control factors in the "reaction-diffusion" process, the resulting composite nanofiltration membrane has a high operating pressure, and its acid and alkali resistance and solvent resistance are poor, thus affecting the application range of composite nanofiltration membranes.

[0003] Layer-by-Layer (LBL) assembly is a new method for preparing composite nanofiltration membranes that has emerged in recent years. The properties of the substrate membrane have a great influence on the internal structure and surface morphology of the composite nanofiltration membrane prepared by the LBL method. The porous substrate membranes of traditional LBL composite nanofiltration membranes are mostly made of materials such as polyacrylonitrile and polyethersulfone, which have poor hydrophilicity and chemical resistance. At the same time, structural defects are likely to appear on the surface separation layer of the obtained separation layer, and it cannot be applied to special separation systems such as high temperature, acids and alkalis, and organic solvents. Poly(p-phenyleneterephthalamide) (PPTA) is a high-performance aromatic polyamide. The solvent-resistant PPTA composite nanofiltration membrane prepared with PPTA as the porous substrate membrane exhibits excellent characteristics such as high temperature resistance, organic solvent resistance, and chemical corrosion resistance. However, it has defects such as high operating pressure, low permeation flux, and insufficient long-term stability of the rejection rate. Therefore, there is currently no relevant report on the research of composite nanofiltration membranes for the application of treating severely polluted wastewater such as high temperature, acids and alkalis, and organic solvents. Summary of the Invention

[0004] Aiming at the deficiencies of the prior art, the technical problem to be solved by the present invention is to provide a method for preparing a PPTA / polyelectrolyte composite nanofiltration membrane with temperature resistance, acid and alkali resistance, and solvent resistance.

[0005] The technical solution for the present invention to solve the above technical problem is to provide a method for preparing a PPTA / polyelectrolyte composite nanofiltration membrane with temperature resistance, acid and alkali resistance, and solvent resistance, which is characterized in that the method comprises the following steps:

[0006] Step 1. Prepare a polycation solution and a polyanion solution: The polyelectrolyte monomers include polycation monomers and polyanion monomers; dissolve the polycation monomers and polyanion monomers in their respective buffers to prepare a polycation solution and a polyanion solution respectively;

[0007] Step 2. In-situ polymerization cycle process:

[0008] S2.1. Immerse the PPTA ultrafiltration base membrane in one of the polycation solution or the polyanion solution, so that the polyelectrolyte in-situ polymerizes on the surface of the PPTA ultrafiltration base membrane; after taking it out, rinse to remove the unpolymerized polyelectrolyte on the surface, and then perform surface drying;

[0009] S2.2. Immerse the membrane obtained in step S2.1 in the other of the polycation solution or the polyanion solution, take it out and rinse, and then perform surface drying;

[0010] Step 3. Prepare the primary PPTA / polyelectrolyte composite nanofiltration membrane: Repeat the in-situ polymerization cycle process in step 2 for n / 2 times, where n is a positive integer, and alternately immerse the PPTA ultrafiltration base membrane in the polycation solution and the polyanion solution until the separation and purification effect of the PPTA / polyelectrolyte composite nanofiltration membrane meets the requirements of the separation system to obtain the primary PPTA / polyelectrolyte composite nanofiltration membrane;

[0011] Step 4. Prepare the PPTA / polyelectrolyte composite nanofiltration membrane: Immerse the primary PPTA / polyelectrolyte composite nanofiltration membrane in a salt solution for salt treatment and heat treatment to improve the high-temperature stability and anti-pollution ability of the composite nanofiltration membrane; then take it out and immerse it in deionized water and let it stand for at least 24 h, so that the internal structure of the polyelectrolyte layer is induced by the mutual electrostatic force to promote the tight combination of polyanions and polycations, forming a denser and more regular composite nanofiltration membrane to obtain the PPTA / polyelectrolyte composite nanofiltration membrane.

[0012] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0013] (1) The present invention first uses the layer-by-layer self-assembly method (LBL) to prepare a PPTA / polyelectrolyte composite nanofiltration membrane that is resistant to temperature, acids and alkalis, and solvents. Compared with the mainstream interfacial polymerization (IP) preparation method of commercial composite nanofiltration membranes, the method of the present invention overcomes the problems of many side reactions and difficult control in the "reaction-diffusion" process between traditional monomers and the base membrane. At the same time, the anionic and cationic polyelectrolyte reaction monomers used in the LBL method are less affected by the pH value and organic solvents than the monomers in the IP method.

[0014] (2) By regulating parameters such as the type of polyelectrolyte, polymerization time, ionic strength, and number of layers, the present invention realizes precise regulation of the membrane structure and performance to obtain a special separation layer structure, constructs multilayer polyelectrolyte layers on the surface of the PPTA ultrafiltration substrate membrane in an oriented manner, and finally obtains a PPTA / polyelectrolyte composite nanofiltration membrane with high flux, high rejection, long cycle, and resistance to temperature, acids and alkalis, and solvents.

[0015] (3) The composite nanofiltration membrane prepared by the present invention not only exhibits excellent long-term service stability and structural stability in the filtration and separation of high temperature, organic solvents, and strong acid solutions (pH = 1), but also takes into account the performance of high flux and high rejection.

[0016] (4) Compared with the problems of poor tolerance to high temperature, acids and alkalis, and organic solvents existing in the substrate membrane materials such as polyacrylonitrile and polysulfone used in traditional composite nanofiltration membranes, the PPTA ultrafiltration membrane with high temperature resistance, acid and alkali resistance, and solvent resistance used in the present invention, as a porous substrate membrane, its unique physicochemical properties such as superhydrophilicity, narrow pore size distribution, and strong surface negative charge can effectively increase the stability of the interfacial bonding state between the polyelectrolyte layer on the membrane surface and the substrate membrane prepared by the LBL method, and enable the obtained PPTA / polyelectrolyte composite nanofiltration membrane to have both high permeability, high rejection, and high tolerance performance in environments such as high temperature, acids and alkalis, and organic solvents.

[0017] (5) The method of the present invention has few control factors, simple process, mild process, short process flow, and can construct a separation layer with different electric properties and thicknesses on the membrane surface according to the physical properties of small molecules in the separation system.

[0018] (6) The temperature-resistant, acid and alkali-resistant, and solvent-resistant PPTA / polyelectrolyte composite nanofiltration membrane obtained by the present invention can be used for the concentration and separation of severely polluted sewage containing oligomers or small molecule impurities or the efficient removal of inorganic salts in special industrial fields such as petrochemical, textile, and medicine, and has good application value and prospects. Description of the Drawings

[0019] Figure 1 It is the surface SEM morphology diagram of the PPTA / polyelectrolyte composite nanofiltration membrane of Example 1 of the present invention;

[0020] Figure 2 It is the surface roughness morphology diagram of the PPTA / polyelectrolyte composite nanofiltration membrane of Example 1 of the present invention. Detailed Embodiments

[0021] The following are specific embodiments of the present invention. The specific embodiments are only used to further illustrate the present invention in detail and do not limit the protection scope of the claims of the present invention.

[0022] The present invention provides a method for preparing a temperature-resistant, acid and alkali-resistant, and solvent-resistant PPTA / polyelectrolyte composite nanofiltration membrane (hereinafter referred to as the method), which is characterized in that the method comprises the following steps:

[0023] Step 1: Prepare a polycation solution and a polyanion solution: The polyelectrolyte monomers include polycation monomers and polyanion monomers; the polycation monomers and polyanion monomers are respectively dissolved in their respective buffer solutions to prepare a polycation solution and a polyanion solution;

[0024] Preferably, in Step 1, during the dissolution process, ultrasonic oscillation is simultaneously performed to accelerate the action process of the buffer solution, and more preferably, ultrasonic oscillation is performed for 1 to 20 minutes.

[0025] Preferably, in Step 1, the polycation monomer is a macromolecule containing an amino group, specifically poly(diallyldimethylammonium chloride) (PDADMAC), polyacrylamide (PAH), polyethyleneimine (PEI), or chitosan (CS); the weight-average molecular weight of the polycation monomer is 600 Da to 30 kDa; the concentration of the polycation solution is 0.01 to 1 mol / L.

[0026] Preferably, in Step 1, the polyanion monomer is a macromolecule containing a carboxyl group or a sulfonic acid group, specifically polystyrene sulfonic acid (PSS), polyacrylic acid (PAA), polyvinyl sulfonic acid (PVS), or hyaluronic acid (HA); the weight-average molecular weight of the polyanion is 200 Da to 90 kDa; the concentration of the polyanion solution is 0.01 to 1 mol / L.

[0027] Preferably, in Step 1, the buffer solution can promote the ionization of polyelectrolyte molecules and increase the activity of the polyelectrolyte, and is composed of a buffer salt solution and a pH regulator; the pH regulator uses an acid or a base to adjust the pH of the polycation solution and the polyanion solution to the optimal value for polymerization on the surface of the PPTA ultrafiltration base membrane; the acid is hydrochloric acid, glacial acetic acid, or citric acid, and the pH of the solution is adjusted to 1 to 6; the base is sodium hydroxide, sodium acetate, or ammonia water, and the pH of the solution is adjusted to 8 to 14; the solute of the buffer salt solution of the polycation monomer is sodium chloride, potassium chloride, sodium sulfate, potassium sulfate, sodium phosphate, potassium phosphate, or sodium acetate, the solvent is deionized water, and the concentration is 0.05 to 1 mol / L; the solute of the buffer salt solution of the polyanion monomer is sodium chloride, potassium chloride, copper chloride, manganese chloride, sodium sulfate, potassium sulfate, or copper sulfate, the solvent is deionized water, and the concentration is 0.05 to 1 mol / L.

[0028] Preferably, in Step 1, the solution preparation temperature is room temperature.

[0029] Step 2: In-situ polymerization cycle process:

[0030] S2.1. Immerse the prefabricated PPTA ultrafiltration base membrane in one of the polycationic solution or polyanionic solution, so that the polyelectrolyte in-situ polymerizes on the surface of the PPTA ultrafiltration base membrane; after taking it out, rinse to remove the unpolymerized polyelectrolyte on the surface, and then perform surface drying;

[0031] S2.2. Immerse the membrane obtained in step S2.1 in the other (i.e., the opposite electric charge) of the polycationic solution or polyanionic solution, take it out and rinse, and then perform surface drying;

[0032] Preferably, in step S2.1, the porosity of the PPTA ultrafiltration base membrane is 10 - 100 nm, the thickness is 50 - 300 μm, and the cut-off molecular weight is 3000 - 60000 Da.

[0033] Preferably, in steps S2.1 and S2.2, the immersion temperature is 25 - 50 °C, and the immersion time is 1 - 30 min.

[0034] Preferably, in steps S2.1 and S2.2, the rinsing process is to rinse with a rinsing solution, and the rinsing time is 1 - 20 min; the rinsing solution is a 0.05 - 0.5 mol / L sodium salt (preferably sodium chloride) solution.

[0035] Preferably, in steps S2.1 and S2.2, the drying process is to blow the surface residual rinsing solution away with high-speed gas loop until the surface is dry.

[0036] Step 3. Prepare the primary PPTA / polyelectrolyte composite nanofiltration membrane: Repeat the in-situ polymerization cycle process of step 2 for n / 2 times, where n is a positive integer. Immerse the PPTA ultrafiltration base membrane alternately and intermittently in the polycationic solution and the polyanionic solution until the separation and purification effect of the PPTA / polyelectrolyte composite nanofiltration membrane meets the requirements of the separation system, and obtain the primary PPTA / polyelectrolyte composite nanofiltration membrane;

[0037] Preferably, in step 3, when there is a half time in the repetition times of the in-situ polymerization cycle process of step 2, only perform step S2.1.

[0038] Preferably, in step 3, n is a positive integer greater than or equal to 2, preferably 2 - 20.

[0039] Preferably, in step 3, for negatively charged target retention substances, the surface layer of the PPTA / polyelectrolyte composite nanofiltration membrane is preferably a polyanionic layer (i.e., the membrane is finally immersed in the polyanionic solution); for positively charged target retention substances, the surface layer of the PPTA / polyelectrolyte composite nanofiltration membrane is preferably a polycationic layer (i.e., the membrane is finally immersed in the polycationic solution).

[0040] Step 4: Prepare the PPTA / polyelectrolyte composite nanofiltration membrane: Immerse the as-prepared PPTA / polyelectrolyte composite nanofiltration membrane in a salt solution for salt treatment and heat treatment to improve the high-temperature stability and anti-pollution ability of the composite nanofiltration membrane; then take it out and immerse it in deionized water and let it stand for at least 24 h (preferably 24 - 72 h), so that the internal structure of the polyelectrolyte layer is induced by the mutual electrostatic force to promote the tight binding of polycation and polyanion, forming a denser and more regular composite nanofiltration membrane with better anti-pollution and structural stability, and obtain the PPTA / polyelectrolyte composite nanofiltration membrane.

[0041] Preferably, in Step 4, the salt solution is a potassium salt solution and a sodium salt solution, preferably sodium chloride solution, potassium chloride solution, sodium sulfate solution and potassium sulfate solution, with a concentration of 0.1 - 3 mol / L; the salt treatment can reduce the surface roughness of the composite nanofiltration membrane and improve its anti-pollution ability.

[0042] Preferably, in Step 4, the heat treatment temperature is 50 - 80 °C; the heat treatment can improve the stability of the membrane in high-temperature filtration.

[0043] Preferably, in Step 4, the immersion time is 1 - 5 h.

[0044] Example 1

[0045] (1) Prepare the polycation solution and the polyanion solution: Ultrasonically oscillate at room temperature for 5 min;

[0046] The polycation solution is 0.05 mol / L PDADMAC (Mw≈200k), the buffer solution is 0.3 mol / L sodium chloride, and the pH is adjusted to 5 with hydrochloric acid;

[0047] The polyanion solution is 0.05 mol / L PSS (Mw≈70k), the buffer solution is 0.3 mol / L sodium chloride, and the pH is adjusted to 2 with hydrochloric acid;

[0048] (2) In-situ polymerization cycle process: The immersion temperature is 38 - 40 °C;

[0049] S2.1: Immerse the PPTA ultrafiltration substrate membrane in the PDADMAC solution for 5 min, then rinse it with 0.05 mol / L sodium chloride solution for 2 min, and then use a high-speed gas ring to blow off the residual rinsing liquid on the surface until the surface is dry;

[0050] S2.2: Immerse the membrane obtained in Step S2.1 in the PSS solution for 5 min, then rinse it with 0.05 mol / L sodium chloride solution for 2 min, and then use a high-speed gas ring to blow off the residual rinsing liquid on the surface until the surface is dry;

[0051] (3) Preparation of as - prepared PPTA / polyelectrolyte composite nanofiltration membrane: Repeat the in - situ polymerization cycle process in step 2 six times. For each additional in - situ polymerization cycle process, extend the flushing time of the flushing solution by 1 min to obtain the as - prepared PPTA / polyelectrolyte composite nanofiltration membrane;

[0052] (4) Preparation of PPTA / polyelectrolyte composite nanofiltration membrane: Immerse the as - prepared PPTA / polyelectrolyte composite nanofiltration membrane in a 0.5 mol / L sodium chloride solution at 60 °C for 100 min; After taking it out, immerse it in deionized water and let it stand for 24 h to obtain the PPTA / polyelectrolyte composite nanofiltration membrane.

[0053] After testing, for the PPTA / polyelectrolyte composite nanofiltration membrane, at 0.2 MPa and 70 °C, the DMAc solvent flux is 40.28 L·m -2 ·h -1 ·MPa -1 , the flux of 0.1 mol / L HCl solution is 57.14 L·m -2 ·h -1 ·MPa -1 , the molecular rejection rate of 100 mg / L eosin Y dye is 88.2%, and the salt rejection rate of 500 mg / L Na2SO4 is 90.5%.

[0054] After 100 h of testing, for the PPTA / polyelectrolyte composite nanofiltration membrane, at 0.2 MPa and 70 °C, the DMAc solvent flux is 40.13 L·m -2 ·h -1 ·MPa -1 , the flux of 0.1 mol / L HCl solution is 57.08 L·m -2 ·h -1 ·MPa -1 , the molecular rejection rate of 100 mg / L eosin Y dye is 87.5%, and the salt rejection rate of 500 mg / L Na2SO4 is 90.4%.

[0055] From Figure 1 and Figure 2 it can be seen that the surface of the composite nanofiltration membrane obtained in Example 1 has high smoothness and low roughness. Such a surface morphology is not only beneficial to maintaining its structural stability in extreme environments, but also conducive to the long - term stable service of the PPTA / polyelectrolyte composite nanofiltration membrane and reducing embedded pollution.

[0056] Example 2

[0057] This example is exactly the same as Example 1, except that in step 3, repeat the in - situ polymerization cycle process in step 2 three times.

[0058] After testing, the PPTA / polyelectrolyte composite nanofiltration membrane has a DMAc solvent flux of 45.57 L·m -2 ·h -1 ·MPa -1 at 0.2 MPa and 70 °C, and a flux of 69.34 L·m -2 ·h -1 ·MPa -1 for a 0.1 mol / L HCl solution. The molecular rejection rate for 100 mg / L eosin Y dye is 76.5%, and the salt rejection rate for 500 mg / L Na2SO4 is 81.2%.

[0059] After 100 h of testing, the PPTA / polyelectrolyte composite nanofiltration membrane has a DMAc solvent flux of 45.37 L·m -2 ·h -1 ·MPa -1 at 0.2 MPa and 70 °C, and a flux of 69.04 L·m -2 ·h -1 ·MPa -1 for a 0.1 mol / L HCl solution. The molecular rejection rate for 100 mg / L eosin Y dye is 75.4%, and the salt rejection rate for 500 mg / L Na2SO4 is 81.0%.

[0060] Example 3

[0061] This example is exactly the same as Example 1, except that in step 4, the concentration of the sodium chloride solution is 0.1 mol / L. After testing, the PPTA / polyelectrolyte composite nanofiltration membrane has a DMAc solvent flux of 35.62 L·m -2 ·h -1 ·MPa -1 at 0.2 MPa and 70 °C, and a flux of 56.28 L·m -2 ·h -1 ·MPa -1 for a 0.1 mol / L HCl solution. The molecular rejection rate for 100 mg / L eosin Y dye is 80.6%, and the salt rejection rate for 500 mg / L Na2SO4 is 81.3%.

[0062] After 100 h of testing, the PPTA / polyelectrolyte composite nanofiltration membrane has a DMAc solvent flux of 35.47 L·m -2 ·h -1 ·MPa -1 at 0.2 MPa and 70 °C, and a flux of 56.06 L·m -2 ·h -1 ·MPa -1, the molecular rejection rate of eosin Y dye at 100 mg / L was 80.0%, and the salt rejection rate of Na2SO4 at 500 mg / L was 81.1%.

[0063] Example 4

[0064] This example is exactly the same as Example 1, except that in Step 1, the Mw of PSS ≈ 45k.

[0065] After testing, for the PPTA / polyelectrolyte composite nanofiltration membrane at 0.2 MPa and 70 °C, the DMAc solvent flux was 31.28 L·m -2 ·h -1 ·MPa -1 , the flux of 0.1 mol / L HCl solution was 52.86 L·m -2 ·h -1 ·MPa -1 , the molecular rejection rate of eosin Y dye at 100 mg / L was 92.3%, and the salt rejection rate of Na2SO4 at 500 mg / L was 95%.

[0066] After 100 h of testing, for the PPTA / polyelectrolyte composite nanofiltration membrane at 0.2 MPa and 70 °C, the DMAc solvent flux was 31.14 L·m -2 ·h -1 ·MPa -1 , the flux of 0.1 mol / L HCl solution was 52.65 L·m -2 ·h -1 ·MPa -1 , the molecular rejection rate of eosin Y dye at 100 mg / L was 91.8%, and the salt rejection rate of Na2SO4 at 500 mg / L was 94.6%.

[0067] Example 5

[0068] This example is exactly the same as Example 1, except that in Step 1, the Mw of PDADMAC ≈ 300k and the Mw of PSS ≈ 45k.

[0069] After testing, for the PPTA / polyelectrolyte composite nanofiltration membrane at 0.2 MPa and 70 °C, the DMAc solvent flux was 28.97 L·m -2 ·h -1 ·MPa -1 , the flux of 0.1 mol / L HCl solution was 42.86 L·m -2 ·h -1 ·MPa -1 , the molecular rejection rate of eosin Y dye at 100 mg / L was 99.6%, and the salt rejection rate of Na2SO4 at 500 mg / L was 98.6%.

[0070] After 100 h of testing, under the conditions of 0.2 MPa and 70 °C, the DMAc solvent flux of the PPTA / polyelectrolyte composite nanofiltration membrane was 28.86 L·m -2 ·h -1 ·MPa -1 , the flux of 0.1 mol / L HCl solution was 42.65 L·m -2 ·h -1 ·MPa -1 , the molecular rejection rate of eosin Y dye at 100 mg / L was 99.2%, and the salt rejection rate of Na2SO4 at 500 mg / L was 98.5%.

[0071] Example 6

[0072] This example is exactly the same as Example 5, except that in step 1, the concentrations of both the polycation solution and the polyanion solution were 0.1 mol / L.

[0073] After testing, under the conditions of 0.2 MPa and 70 °C, the DMAc solvent flux of the PPTA / polyelectrolyte composite nanofiltration membrane was 20.43 L·m -2 ·h -1 ·MPa -1 , the flux of 0.1 mol / L HCl solution was 32.14 L·m -2 ·h -1 ·MPa -1 , the molecular rejection rate of eosin Y dye at 100 mg / L was 99.4%, and the salt rejection rate of Na2SO4 at 500 mg / L was 98.5%.

[0074] After 100 h of testing, under the conditions of 0.2 MPa and 70 °C, the DMAc solvent flux of the PPTA / polyelectrolyte composite nanofiltration membrane was 20.13 L·m -2 ·h -1 ·MPa -1 , the flux of 0.1 mol / L HCl solution was 32.02 L·m -2 ·h -1 ·MPa -1 , the molecular rejection rate of eosin Y dye at 100 mg / L was 98.9%, and the salt rejection rate of Na2SO4 at 500 mg / L was 98.5%.

[0075] Example 7

[0076] This example is exactly the same as Example 5, except that in step 1, the polycation was PAH (Mw≈65k). After testing, under the conditions of 0.2 MPa and 70 °C, the DMAc solvent flux of the PPTA / polyelectrolyte composite nanofiltration membrane was 36.26 L·m -2 ·h-1 ·MPa -1 The flux of 0.1 mol / L HCl solution is 60.71 L·m -2 ·h -1 ·MPa -1 , the molecular rejection rate of eosin Y dye at 100 mg / L is 95.3%, and the salt rejection rate of Na2SO4 at 500 mg / L is 93.9%.

[0077] After 100 h of testing, the flux of DMAc solvent of the PPTA / polyelectrolyte composite nanofiltration membrane is 36.19 L·m -2 ·h -1 ·MPa -1 , the flux of 0.1 mol / L HCl solution is 60.63 L·m -2 ·h -1 ·MPa -1 , the molecular rejection rate of eosin Y dye at 100 mg / L is 95%, and the salt rejection rate of Na2SO4 at 500 mg / L is 93.5%.

[0078] Example 8

[0079] This example is exactly the same as Example 5, except that in step 1, the pH of the polycation solution is adjusted to 3 with hydrochloric acid.

[0080] After testing, the flux of DMAc solvent of the PPTA / polyelectrolyte composite nanofiltration membrane is 32.59 L·m -2 ·h -1 ·MPa -1 , the flux of 0.1 mol / L HCl solution is 52.04 L·m -2 ·h -1 ·MPa -1 , the molecular rejection rate of eosin Y dye at 100 mg / L is 99.6%, and the salt rejection rate of Na2SO4 at 500 mg / L is 98.8%.

[0081] After 100 h of testing, the flux of DMAc solvent of the PPTA / polyelectrolyte composite nanofiltration membrane is 32.42 L·m -2 ·h -1 ·MPa -1 , the flux of 0.1 mol / L HCl solution is 51.96 L·m -2 ·h -1 ·MPa -1 , the molecular rejection rate of eosin Y dye at 100 mg / L is 99.3%, and the salt rejection rate of Na2SO4 at 500 mg / L is 98.3%.

[0082] Example 9

[0083] This example is exactly the same as Example 5, except that in Step 3, the in-situ polymerization cycle process of Step 2 is repeated 5.5 times.

[0084] After testing, for the PPTA / polyelectrolyte composite nanofiltration membrane, at 0.2 MPa and 70 °C, the DMAc solvent flux is 48.68 L·m -2 ·h -1 ·MPa -1 , the flux of 0.1 mol / L HCl solution is 71.81 L·m -2 ·h -1 ·MPa -1 , the molecular rejection rate of 100 mg / L eosin Y dye is 65.6%, and the salt rejection rate of 500 mg / L Na2SO4 is 54.3%.

[0085] After 100 h of testing, for the PPTA / polyelectrolyte composite nanofiltration membrane, at 0.2 MPa and 70 °C, the DMAc solvent flux is 48.66 L·m -2 ·h -1 ·MPa -1 , the flux of 0.1 mol / L HCl solution is 71.79 L·m -2 ·h -1 ·MPa -1 , the molecular rejection rate of 100 mg / L eosin Y dye is 65.0%, and the salt rejection rate of 500 mg / L Na2SO4 is 53.3%.

[0086] The test conditions for Examples 1 - 9 are DMAc at 70 °C and 0.1 mol / L HCl solution (pH = 1) at 70 °C. Ordinary organic membrane materials will have their structures disappear and their performance deteriorate severely when exposed to a high temperature of 70 °C, DMAc, and such a strong acid environment. The stable permeation flux and rejection rate data obtained in Examples 1 - 9 indicate that the composite nanofiltration membrane of the present invention has excellent temperature resistance, acid and alkali resistance, and solvent resistance.

[0087] Comparative Example 1

[0088] Preparation of PPTA / PA composite nanofiltration membrane: Immerse the PPTA ultrafiltration base membrane in a 1.5 w / v% piperazine monomer (PIP) solution for 1 min, then take it out and remove the excess liquid droplets on its surface; then immerse it in a 0.15 w / v% trimesoyl chloride (TMC) n-hexane solution for 60 s for interfacial polymerization reaction to form a polyamide PA surface separation layer; after taking it out, dry it to remove the excess liquid droplets on its surface; then heat-treat it in a 60 °C environment for 8 min to obtain the PPTA / PA composite nanofiltration membrane.

[0089] After testing, the DMAc solvent flux of the PPTA / PA composite nanofiltration membrane under the conditions of 0.6 MPa and 70 °C is 35.23 L·m -2 ·h -1 ·MPa -1 , and the flux of 0.1 mol / L HCl solution is 51.61 L·m -2 ·h -1 ·MPa -1 . The molecular rejection rate of eosin Y dye with a concentration of 100 mg / L is 98.9%, and the salt rejection rate of Na2SO4 with a concentration of 500 mg / L is 97.5%.

[0090] After 100 h of testing, the structure of the composite nanofiltration membrane is damaged. Under the conditions of 0.2 MPa and 70 °C, the DMAc solvent flux of the PPTA / polyelectrolyte composite nanofiltration membrane is 80.23 L·m -2 ·h -1 ·MPa -1 , and the flux of 0.1 mol / L HCl solution is 106.82 L·m -2 ·h -1 ·MPa -1 . It basically returns to the level of the PPTA ultrafiltration base membrane. The molecular rejection rate of eosin Y dye with a concentration of 100 mg / L is 6.5%, and the salt rejection rate of Na2SO4 with a concentration of 500 mg / L is 3.0%.

[0091] Table 1 Comparison of performance parameters of the composite nanofiltration membranes obtained in the examples and comparative examples

[0092]

[0093]

[0094] Table 2 Comparison of performance parameters of the composite nanofiltration membranes obtained in the examples and comparative examples after 100 h of testing

[0095]

[0096] It can be seen from Table 1 and Table 2 that: (1) The reduction of the number of cycles of the PPTA / polyelectrolyte composite nanofiltration membrane, the decrease of the concentrations of polycation and polyanion monomers, and the strong acidic monomer dissolution system are all beneficial to the rapid electrostatic attraction balance between the two-phase monomers, thereby achieving the improvement of the permeation flux and showing a high organic solvent flux under low operating pressure. (2) The increase of the number of cycles of the PPTA / polyelectrolyte composite nanofiltration membrane, the decrease of the molecular weight difference between polycation and polyanion monomers, and the decrease of the post-treatment temperature of the as-cast membrane are likely to lead to the decrease of the retention rate of small dye molecules, showing a separation efficiency of <90%. (3) Different properties of polyelectrolyte monomers will result in different diffusion forms and rates between polycation and polyanion monomers, thereby affecting the formation structure of the surface separation layer of the polyelectrolyte and showing different compatibility differences in permeation-retention performance. (4) Compared with the permeation-retention performance of the PPTA / PA composite nanofiltration membrane shown in Comparative Example 1, the PPTA / polyelectrolyte composite nanofiltration membrane of the present invention shows higher high-temperature organic solvent and acid-base tolerance stability. After 100 h of testing, the attenuation rate of the permeation flux of the composite nanofiltration membrane does not exceed 0.5%, and the decrease of the retention rate is less than 1%. The parts not described in the present invention are applicable to the prior art.

Claims

1. A preparation method of a PPTA / polyelectrolyte composite nanofiltration membrane resistant to temperature, acids and alkalis, and solvents, characterized in that, The method comprises the following steps: Step 1, preparing a polycation solution and a polyanion solution: The polyelectrolyte monomers include polycation monomers and polyanion monomers; the polycation monomers and the polyanion monomers are respectively dissolved in their respective buffer solutions to prepare a polycation solution and a polyanion solution; The polycation monomer is a macromolecule containing amino groups, with a weight-average molecular weight of 600 Da to 30 kDa; the concentration of the polycation solution is 0.01 to 1 mol / L; the polyanion monomer is a macromolecule containing carboxyl or sulfonic acid groups, with a weight-average molecular weight of 200 Da to 90 kDa; the concentration of the polyanion solution is 0.01 to 1 mol / L; Step 2, in-situ polymerization cycle process: S2.1, immersing the PPTA ultrafiltration base membrane in one of the polycation solution or the polyanion solution, so that the polyelectrolyte in-situ polymerizes on the surface of the PPTA ultrafiltration base membrane; after taking out, rinsing to remove the unpolymerized polyelectrolyte on the surface, and then performing surface drying; S2.2, immersing the membrane obtained in step S2.1 in the other of the polycation solution or the polyanion solution, taking out, rinsing, and then performing surface drying; Step 3, preparing a primary PPTA / polyelectrolyte composite nanofiltration membrane: repeating the in-situ polymerization cycle process in step 2 for n / 2 times, where n is a positive integer from 2 to 20, and alternately immersing the PPTA ultrafiltration base membrane in the polycation solution and the polyanion solution until the separation and purification effect of the PPTA / polyelectrolyte composite nanofiltration membrane meets the requirements of the separation system, to obtain a primary PPTA / polyelectrolyte composite nanofiltration membrane; Step 4, preparing a PPTA / polyelectrolyte composite nanofiltration membrane: immersing the primary PPTA / polyelectrolyte composite nanofiltration membrane in a salt solution for salt treatment and heat treatment to improve the high-temperature stability and anti-pollution ability of the composite nanofiltration membrane; then taking it out and immersing it in deionized water and standing for at least 24 h, so that the internal structure of the polyelectrolyte layer is induced by the mutual electrostatic force to promote the tight combination of polycation and polyanion, forming a denser and more regular composite nanofiltration membrane, to obtain a PPTA / polyelectrolyte composite nanofiltration membrane.

2. The preparation method of the temperature-resistant, acid-alkali-resistant, and solvent-resistant PPTA / polyelectrolyte composite nanofiltration membrane according to claim 1, characterized in that, The polycation monomer is poly(diallyldimethylammonium chloride), polyacrylamide, polyethyleneimine or chitosan; The polyanion monomer is polystyrene sulfonic acid, polyacrylic acid, polyethylene sulfonic acid or hyaluronic acid.

3. The preparation method of the temperature-resistant, acid- and alkali-resistant, and solvent-resistant PPTA / polyelectrolyte composite nanofiltration membrane according to claim 1, characterized in that, In step 1, the buffer solution is composed of a buffer salt solution and a pH regulator; The pH regulator uses an acid or a base to adjust the pH of the polycation solution and the polyanion solution to the optimal value for polymerization on the surface of the PPTA ultrafiltration base membrane; The acid is hydrochloric acid, glacial acetic acid or citric acid, and adjusts the pH of the solution to 1 to 6; the base is sodium hydroxide, sodium acetate or ammonia water, and adjusts the pH of the solution to 8 to 14; The solute of the buffer salt solution of the polycation monomer is sodium chloride, potassium chloride, sodium sulfate, potassium sulfate, sodium phosphate, potassium phosphate or sodium acetate, the solvent is deionized water, and the concentration is 0.05 to 1 mol / L; The solute of the buffer salt solution of the polyanion monomer is sodium chloride, potassium chloride, copper chloride, manganese chloride, sodium sulfate, potassium sulfate or copper sulfate, the solvent is deionized water, and the concentration is 0.05 to 1 mol / L.

4. The preparation method of the temperature-resistant, acid- and alkali-resistant, and solvent-resistant PPTA / polyelectrolyte composite nanofiltration membrane according to claim 1, characterized in that, In step S2.1, the porosity of the PPTA ultrafiltration base membrane is 10-100 nm, the thickness is 50-300 μm, and the cut-off molecular weight is 3000-60000 Da.

5. The preparation method of the temperature-resistant, acid-alkali-resistant, and solvent-resistant PPTA / polyelectrolyte composite nanofiltration membrane according to claim 1, characterized in that, In steps S2.1 and S2.2, the impregnation temperature is 25-50 °C, and the impregnation time is 1-30 min; The rinsing process is to rinse with a rinsing solution, and the rinsing time is 1-20 min; the rinsing solution is a sodium salt solution with a concentration of 0.05-0.5 mol / L; The drying process is to blow off the residual rinsing solution on the surface with high-speed gas until the surface is dry.

6. The preparation method of the temperature-resistant, acid and alkali-resistant, solvent-resistant PPTA / polyelectrolyte composite nanofiltration membrane according to claim 1, characterized in that, In step 3, when there is a half-time in the number of repetitions of the in-situ polymerization cycle in step 2, only step S2.1 is executed.

7. The preparation method of the temperature-resistant, acid- and alkali-resistant, and solvent-resistant PPTA / polyelectrolyte composite nanofiltration membrane according to claim 1, characterized in that, In step 3, n is a positive integer greater than or equal to 2.

8. The preparation method of the temperature-resistant, acid- and alkali-resistant, solvent-resistant PPTA / polyelectrolyte composite nanofiltration membrane according to claim 1, characterized in that, In step 4, the salt solution is a potassium salt solution and a sodium salt solution, with a concentration of 0.1-3 mol / L; the temperature of the heat treatment is 50-80 °C; the impregnation time is 1-5 h.

9. The preparation method of the temperature-resistant, acid and alkali-resistant, solvent-resistant PPTA / polyelectrolyte composite nanofiltration membrane according to claim 1 or 8, characterized in that, In step 4, the salt solution is sodium chloride solution, potassium chloride solution, sodium sulfate solution and potassium sulfate solution.

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