Method for preparing high-flux acid-resistant nanofiltration membrane by using cosolvent

Abstract

The invention relates to the technical field of nanofiltration membranes, in particular to a method for preparing a high-flux acid-resistant nanofiltration membrane through a cosolvent. In order to solve the problems of weak acid resistance and poor oxidation resistance of the existing polyamide nanofiltration membrane, the preparation method comprises the following steps: step 1, dissolving an acid-resistant polymer in a solvent, adding an insoluble cosolvent, and mixing to obtain a coating solution; 2, coating a porous polymer base membrane with the coating liquid to obtain a pre-prepared acid-resistant nanofiltration membrane; and 3, carrying out heat treatment and drying on the prepared acid-resistant nanofiltration membrane to obtain the high-flux acid-resistant nanofiltration membrane. The acid-resistant polymer is separated out step by step in the vacuum heat treatment process by utilizing the volatility difference of the cosolvent, so that the polymer film is endowed with a unique microstructure. The acid-resistant antioxidant nanofiltration membrane can be widely applied to the fields of waste acid recovery, household water purification, oxidized wastewater recovery and the like.

Description

Technical Field

[0001] The present invention relates to the technical field of nanofiltration membranes, and more particularly to a method for preparing a high-flux acid-resistant nanofiltration membrane using a co-solvent. Background Art

[0002] Nanofiltration membrane is a selective semipermeable membrane that allows solvent molecules and monovalent ions to pass through. It has the characteristics of high interception accuracy and can effectively remove almost all substances in water, including bacteria, organic matter, and mineral ions, and produce pure water. It is currently the main water treatment method for industrial water supply and household water purification. However, the interfacial polymerized polyamide nanofiltration membrane, which dominates the field of nanofiltration membranes, cannot operate stably under highly acidic or strongly oxidizing conditions due to its chemical composition, which is not resistant to strong acids and has weak antioxidant properties. The production conditions of other polymer materials for nanofiltration membranes are harsh, and the resulting nanofiltration membranes have low performance and small flux. Therefore, it is still a huge challenge to prepare high-performance nanofiltration membranes by coating acid-resistant polymers through a simple and mild method. Summary of the Invention

[0003] The invention provides a method for preparing a high-flux acid-resistant nanofiltration membrane using a cosolvent, aiming to solve the problems of weak acid resistance and poor oxidation resistance of existing polyamide nanofiltration membranes.

[0004] The above objectives are achieved through the following technical solutions:

[0005] A method for preparing a high-flux acid-resistant nanofiltration membrane using a cosolvent comprises the following steps:

[0006] Step 1: dissolving the acid-resistant polymer in a solvent, adding an insoluble co-solvent, and mixing to obtain a coating solution;

[0007] Step 2: applying the coating liquid to a porous polymer ultrafiltration or microfiltration base membrane to obtain a pre-prepared acid-resistant nanofiltration membrane;

[0008] Step 3: The pre-prepared acid-resistant nanofiltration membrane is dried by heat treatment to obtain a high-flux acid-resistant nanofiltration membrane.

[0009] The porous polymer-based membrane is one of polyvinylidene fluoride membrane, polypropylene membrane, polytetrafluoroethylene membrane, polysulfone membrane or polyethersulfone membrane.

[0010] The acid-resistant polymer is at least one of sulfonated polyetheretherketone, sulfonated polysulfone, sulfonated polyethersulfone, sulfonated polyphenylsulfone, polyphthalimide, polyetherphthalimide and polyphthalamide.

[0011] The non-soluble co-solvent is at least one of methanol, ethanol, ethylene glycol, propylene glycol, glycerol, polyethylene glycol, acetone and polyvinyl pyrrolidone.

[0012] The concentration of the non-soluble co-solvent is 5 to 80 wt%.

[0013] The polymer concentration in the coating liquid is 0.05-10 wt%.

[0014] The heat treatment drying is carried out in a vacuum state, at a temperature of 25 to 150° C., and for a time of 0.5 to 24 hours.

[0015] Pretreatment before step 1: The porous polymer base membrane is soaked in water and solvent respectively.

[0016] After pretreatment, use inert gas to purge to remove residual solvent on the surface.

[0017] The solvent is at least one of N,N-dimethylformamide, N,N-dimethylacetamide, dimethylformamide, dimethylacetamide, dimethylpyrrolidone, dimethyl sulfoxide and ethylene glycol monomethyl ether.

[0018] The beneficial effects of the method for preparing a high-flux acid-resistant nanofiltration membrane using a cosolvent of the present invention are:

[0019] An acid-resistant polymer nanofiltration membrane is prepared by coating an acid-resistant polymer with a soluble solvent and a non-soluble solvent. The acid-resistant polymer is first dissolved in a soluble solvent to form a uniform and stable solution. A non-soluble solvent is then gradually introduced to blend with the solution to form a mixed solution. The acid-resistant polymer is gradually precipitated during vacuum heat treatment, utilizing the volatility differences of the co-solvents. This imparts a unique microstructure to the polymer membrane. The acid-resistant, antioxidant nanofiltration membrane prepared by the co-solvent method can be widely used in waste acid recovery, household water purification, oxidative wastewater recovery, and other fields. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 This is a water flux test diagram of the sulfonated polysulfone nanofiltration membrane co-coated with ethylene glycol in Example 1 and the sulfonated polysulfone nanofiltration membrane without ethylene glycol added in the control example;

[0021] Figure 2 This is a scanning electron microscope photograph of the sulfonated polysulfone nanofiltration membrane co-coated with ethylene glycol in Example 1;

[0022] Figure 3 This is a scanning electron microscope photograph of the sulfonated polysulfone nanofiltration membrane of the control example in Example 1 to which no ethylene glycol was added;

[0023] Figure 4 This is a test chart of the acid resistance stability performance of the sulfonated polysulfone nanofiltration membrane co-coated with ethylene glycol in Example 1;

[0024] Figure 5 This is a test chart of the antioxidant stability performance of the sulfonated polysulfone nanofiltration membrane co-coated with ethylene glycol in Example 1. DETAILED DESCRIPTION

[0025] A method for preparing a high-flux acid-resistant nanofiltration membrane using a cosolvent, embodiment 1, comprises the following steps:

[0026] Step 1: soaking the porous polyethersulfone polymer base membrane with water and ethylene glycol monomethyl ether respectively, and then purging with nitrogen to remove the residual solvent on the surface to obtain a wet base membrane;

[0027] Step 2: Dissolve sulfonated polysulfone (30% sulfonation degree) in ethylene glycol monomethyl ether to a concentration of 0.1 wt%, and add ethylene glycol, an insoluble co-solvent, dropwise to a concentration of 20 wt%, and stir for 20 minutes to obtain a uniform and stable coating solution;

[0028] Step 3: coating the coating liquid onto the surface of the wetted base membrane for 10 min to obtain a pre-prepared sulfonated polysulfone nanofiltration membrane;

[0029] Step 4: The pre-prepared sulfonated polysulfone nanofiltration membrane is placed in a vacuum drying oven at a vacuum drying temperature of 120° C. for 4 h to obtain a high-flux acid-resistant nanofiltration membrane.

[0030] According to the conventional membrane performance evaluation method, that is, under the conditions of a pressure of 0.4 MPa and a feed liquid temperature of 25°C, the performance of the high-flux acid-resistant nanofiltration membrane is as follows:

[0031] Pure water flux is 22.12Lm -2 h -1 bar -1 ;

[0032] The rejection rate of 2000ppm sodium sulfate is 92.7%;

[0033] The rejection rate for 2000ppm sodium chloride is 50.4%;

[0034] The rejection rate for 100 ppm of polyethylene glycol 1000 was 98.6%.

[0035] The flux comparison chart of the high flux acid-resistant nanofiltration membrane of this embodiment and its control example, i.e., the sulfonated polysulfone nanofiltration membrane without adding ethylene glycol, is shown in FIG. Figure 1 As shown. Figure 1 It can be seen that the flux of high-flux acid-resistant nanofiltration membrane is 22.12Lm -2 h -1 bar -1 The flux of the sulfonated polysulfone nanofiltration membrane coated with no ethylene glycol solvent was 2.65Lm -2 h -1 bar -1 , by comparison, it is known that co-solvent coating can improve the flux of nanofiltration membrane.

[0036] The scanning electron microscope photo of the high flux acid-resistant nanofiltration membrane of this embodiment is as follows: Figure 2 As shown in FIG. 1 , the scanning electron microscope photograph of the sulfonated polysulfone nanofiltration membrane without adding ethylene glycol is shown in FIG. Figure 3As shown. Figure 2 and Figure 3 By comparison, it is known that the ethylene glycol co-coating method gives the high-flux acid-resistant nanofiltration membrane a unique microstructure.

[0037] The long-term stability of the acid resistance (sulfuric acid concentration 5%) of the high-flux acid-resistant nanofiltration membrane of this embodiment is as follows Figure 4 As shown, the high-flux acid-resistant nanofiltration membrane prepared by co-solvent has excellent acid resistance and long-term stability.

[0038] The long-term stability of the oxidation resistance (sodium hypochlorite aqueous solution concentration 20ppm) of the high-flux acid-resistant nanofiltration membrane of this embodiment is as follows Figure 5 As shown, the high-flux acid-resistant nanofiltration membrane prepared by co-solvent has excellent long-term anti-oxidation stability.

[0039] Example 2:

[0040] Step 1: soaking a porous polyethersulfone polymer base membrane with water and ethylene glycol monomethyl ether respectively, and then purging with nitrogen to remove the residual solvent on the surface to obtain a wet base membrane;

[0041] Step 2: Dissolve sulfonated polysulfone (30% sulfonation degree) in ethylene glycol monomethyl ether to a concentration of 0.5 wt%, and add ethylene glycol, an insoluble co-solvent, dropwise to a concentration of 20 wt%, and stir for 30 minutes to obtain a uniform and stable coating solution;

[0042] Step 3: coating the coating liquid onto the surface of the wetted base membrane for 15 minutes to obtain a pre-prepared sulfonated polysulfone nanofiltration membrane;

[0043] Step 4: Place the pre-prepared sulfonated polysulfone nanofiltration membrane into a vacuum drying oven and vacuum dry it at 100° C. for 2 h to obtain a high-flux acid-resistant nanofiltration membrane.

[0044] According to conventional membrane performance evaluation methods, the performance of high-flux acid-resistant nanofiltration membranes is as follows:

[0045] Pure water flux is 46.43Lm -2 h -1 bar -1 ;

[0046] The rejection rate of 2000ppm sodium sulfate is 82.3%;

[0047] The rejection rate for 2000ppm sodium chloride is 35.1%;

[0048] The rejection rate for 100 ppm of polyethylene glycol 1000 was 90.1%.

[0049] Example 3:

[0050] Step 1: soaking a porous polyethersulfone polymer base membrane with water and ethylene glycol monomethyl ether respectively, and then purging with nitrogen to remove the residual solvent on the surface to obtain a wet base membrane;

[0051] Step 2: Dissolve sulfonated polysulfone (20% sulfonation degree) in ethylene glycol monomethyl ether to a concentration of 0.2 wt%, and add insoluble co-solvent ethylene glycol dropwise to a concentration of 10 wt%, and stir for 20 minutes to obtain a uniform and stable coating solution;

[0052] Step 3: coating the coating liquid onto the surface of the wetted base membrane for 15 minutes to obtain a pre-prepared sulfonated polysulfone nanofiltration membrane;

[0053] Step 4: The pre-prepared sulfonated polysulfone nanofiltration membrane is placed in a vacuum drying oven and vacuum dried at a temperature of 100° C. for 12 h to obtain a high-flux acid-resistant nanofiltration membrane.

[0054] According to conventional membrane performance evaluation methods, the performance of high-flux acid-resistant nanofiltration membranes is as follows:

[0055] Pure water flux is 42.12Lm -2 h -1 bar -1 ;

[0056] The rejection rate for 2000ppm sodium sulfate is 62.4%;

[0057] The rejection rate for 2000ppm sodium chloride is 30.1%;

[0058] The rejection rate for 100 ppm of polyethylene glycol 1000 was 87%.

[0059] Example 4:

[0060] Step 1: soaking a porous polyethersulfone polymer base membrane with water and ethylene glycol monomethyl ether respectively, and then purging with nitrogen to remove the residual solvent on the surface to obtain a wet base membrane;

[0061] Step 2: Dissolve sulfonated polysulfone (sulfonation degree 20%) in ethylene glycol monomethyl ether to a concentration of 1 wt%, and add ethanol as an insoluble co-solvent dropwise to a concentration of 10 wt%, and stir for 20 minutes to obtain a uniform and stable coating solution;

[0062] Step 3: coating the coating liquid onto the surface of the wetted base membrane for 2 minutes to obtain a pre-prepared sulfonated polysulfone nanofiltration membrane;

[0063] Step 4: The pre-prepared sulfonated polysulfone nanofiltration membrane is placed in a vacuum drying oven and vacuum dried at 60° C. for 4 h to obtain a high-flux acid-resistant nanofiltration membrane.

[0064] According to conventional membrane performance evaluation methods, the performance of high-flux acid-resistant nanofiltration membranes is as follows:

[0065] Pure water flux is 12.12Lm -2 h -1 bar -1 ;

[0066] The rejection rate of 2000ppm sodium sulfate is 91.1%;

[0067] The rejection rate for 2000ppm sodium chloride is 45.1%;

[0068] The rejection rate for 100 ppm of polyethylene glycol 1000 was 96.5%.

[0069] Example 5:

[0070] Step 1: soaking a porous polyethersulfone polymer base membrane with water and ethylene glycol monomethyl ether respectively, and then purging with nitrogen to remove the residual solvent on the surface to obtain a wet base membrane;

[0071] Step 2: Dissolve sulfonated polysulfone (30% sulfonation degree) in ethylene glycol monomethyl ether to a concentration of 1 wt%, and add ethylene glycol, an insoluble co-solvent, dropwise to a concentration of 5 wt%, and stir for 10 minutes to obtain a uniform and stable coating solution;

[0072] Step 3: coating the coating liquid onto the surface of the wetted base membrane for 2 minutes to obtain a pre-prepared sulfonated polysulfone nanofiltration membrane;

[0073] Step 4: The pre-prepared sulfonated polysulfone nanofiltration membrane is placed in a vacuum drying oven and vacuum dried at a temperature of 100° C. for 2 h to obtain a high-flux acid-resistant nanofiltration membrane.

[0074] According to conventional membrane performance evaluation methods, the performance of high-flux acid-resistant nanofiltration membranes is as follows:

[0075] Pure water flux is 52.52Lm -2 h -1 bar -1 ;

[0076] The rejection rate of 2000ppm sodium sulfate is 78.4%;

[0077] The rejection rate for 2000ppm sodium chloride is 37.1%;

[0078] The rejection rate for 100 ppm of polyethylene glycol 1000 was 87.2%.

[0079] Example 6:

[0080] Step 1: soaking a porous polyethersulfone polymer base membrane with water and ethylene glycol monomethyl ether respectively, and then purging with nitrogen to remove the residual solvent on the surface to obtain a wet base membrane;

[0081] Step 2: Dissolve sulfonated polysulfone (30% sulfonation degree) in ethylene glycol monomethyl ether to a concentration of 2 wt%, and add ethylene glycol, an insoluble co-solvent, dropwise to a concentration of 5 wt%, and stir for 30 minutes to obtain a uniform and stable coating solution;

[0082] Step 3: coating the coating liquid onto the surface of the wetted base membrane in step 1 for 2 minutes to obtain a pre-prepared sulfonated polysulfone nanofiltration membrane;

[0083] Step 4: The pre-prepared sulfonated polysulfone nanofiltration membrane is placed in a vacuum drying oven and vacuum dried at a temperature of 30° C. for 12 h to obtain an acid-resistant and oxidation-resistant high-flux acid-resistant nanofiltration membrane.

[0084] According to conventional membrane performance evaluation methods, the performance of high-flux acid-resistant nanofiltration membranes is as follows:

[0085] Pure water flux is 82.12Lm -2 h -1 bar -1 ;

[0086] The rejection rate for 2000ppm sodium sulfate is 43.5%;

[0087] The rejection rate for 2000ppm sodium chloride is 15.6%;

[0088] The rejection rate for 100 ppm of polyethylene glycol 1000 was 64.1%.

[0089] In summary, the present invention utilizes a co-solvent method to regulate the phase separation and solidification process of the acid-resistant polymer on the surface of the composite membrane, which not only effectively imparts acid and oxidation resistance to the nanofiltration membrane, but also imparts a unique microstructure to the modified membrane.

Claims

1. A method for preparing a high-throughput acid-resistant nanofiltration membrane using a cosolvent, characterized in that: The following steps are involved: Step 1: dissolving the acid-resistant polymer in a solvent, adding an insoluble co-solvent, and mixing to obtain a coating solution; Step 2: coating the coating liquid onto the porous polymer base membrane to obtain a pre-prepared acid-resistant nanofiltration membrane; Step 3: The pre-prepared acid-resistant nanofiltration membrane is dried by heat treatment to obtain a high-flux acid-resistant nanofiltration membrane.

2. The method for preparing a high-flux acid-resistant nanofiltration membrane using a cosolvent according to claim 1, wherein the porous polymer base membrane refers to a polymer ultrafiltration membrane or a microfiltration membrane; or, the porous polymer base membrane is one of a polyvinylidene fluoride membrane, a polypropylene membrane, a polytetrafluoroethylene membrane, a polyvinyl chloride, a polyethylene, a polysulfone membrane or a polyethersulfone membrane.

3. The method for preparing a high-flux acid-resistant nanofiltration membrane using a cosolvent according to claim 1, wherein the acid-resistant polymer is at least one of sulfonated polyetheretherketone, sulfonated polysulfone, sulfonated polyethersulfone, sulfonated polyphenylsulfone, polyphthalimide, polyetherphthalimide and polyphthalamide.

4. The method for preparing a high-flux acid-resistant nanofiltration membrane using a cosolvent according to claim 1, wherein the insoluble cosolvent is at least one of methanol, ethanol, ethylene glycol, propylene glycol, glycerol, polyethylene glycol, acetone and polyvinyl pyrrolidone.

5. The method for preparing a high-flux acid-resistant nanofiltration membrane using a co-solvent according to claim 1, wherein the concentration of the insoluble co-solvent is 5 to 80 wt%.

6. The method for preparing a high-flux acid-resistant nanofiltration membrane using a cosolvent according to claim 1, wherein the polymer concentration in the coating solution is 0.05 to 10 wt%.

7. The method for preparing a high-flux acid-resistant nanofiltration membrane using a cosolvent according to claim 6, wherein the heat treatment and drying is carried out in a vacuum state at a temperature of 25 to 150°C for a time of 0.5 to 24 hours.

8. The method for preparing a high-flux acid-resistant nanofiltration membrane using a cosolvent according to claim 1, wherein the pretreatment before step 1 is as follows: the porous polymer base membrane is soaked in water and the solvent respectively.

9. The method for preparing a high-flux acid-resistant nanofiltration membrane using a co-solvent according to claim 8, wherein the solvent remaining on the surface is purged with an inert gas after the pretreatment.

10. The method for preparing a high-flux acid-resistant nanofiltration membrane using a co-solvent according to any one of claims 1 to 9, wherein the solvent is at least one of N,N-dimethylformamide, N,N-dimethylacetamide, dimethylformamide, dimethylacetamide, dimethylpyrrolidone, dimethyl sulfoxide and ethylene glycol monomethyl ether.

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