Nanofiltration membrane, reverse mass transfer preparation method and application of nanofiltration membrane in dye / salt separation

Abstract

The invention belongs to the field of separation membranes, and particularly relates to a nanofiltration membrane, a reverse mass transfer preparation method and application of dye / salt separation. The preparation method comprises the following steps: firstly, coating the surface of one side of a base membrane with an aqueous phase solution, then enabling a cross-linking agent solution to be in contact with the other side of the base membrane, and diffusing cross-linking agent molecules in the cross-linking agent solution to pass through membrane pore channels in a reverse mass transfer manner to be in contact reaction with the aqueous phase solution, so as to prepare the nanofiltration membrane. The nanofiltration membrane prepared on the basis of the self-inhibition effect of the reverse mass transfer reaction is thin in separation layer thickness, and correspondingly, compared with the prior art, the hollow fiber composite nanofiltration membrane prepared through the method is higher in water flux. Meanwhile, the reverse mass transfer reaction can repair defective pores in the reaction process, so that compared with the prior art, the hollow fiber composite nanofiltration membrane prepared by the invention is more uniform in pore size distribution, simple in preparation method and lower in cost, and has obvious economic benefits.

Description

Technical Field

[0001] The invention belongs to the field of separation membranes, and in particular relates to a nanofiltration membrane and a reverse mass transfer preparation method and application thereof in dye / salt separation. Background Art

[0002] Membrane separation technology has been widely used in the field of dye / salt separation due to its advantages such as low energy consumption and high separation efficiency. Interfacial polymerization is a common method for preparing composite nanofiltration membranes for organic desalination. However, in the process of solution circulation coating and cross-linking reaction on hollow fiber membranes, there is often a problem of uneven distribution of water phase monomers and oil phase monomers in the radial direction of hollow fiber membranes, which leads to uneven overall pore size distribution of the prepared nanofiltration membrane, easy formation of defective macropores, and low dye / salt separation performance of the prepared nanofiltration membrane. Moreover, under conventional process steps, the thickness of the prepared separation layer is also difficult to be accurately controlled. In addition, the original process usually requires a high-temperature post-treatment process, and an air compressor is required to purge and remove the residual water droplets on the inner surface of the membrane fiber during the reaction process. It is also necessary to use a circulating pump to pass the reaction solution into the inner surface of the hollow fiber membrane for circulation, resulting in a high preparation cost of the hollow fiber composite nanofiltration membrane under conventional methods. Summary of the invention

[0003] The purpose of the present invention is to overcome the shortcomings of the prior art and provide a nanofiltration membrane and a reverse mass transfer preparation method and an application of dye / salt separation.

[0004] To achieve the above object, the technical solution adopted by the present invention is:

[0005] A method for preparing a nanofiltration membrane by reverse mass transfer comprises the following steps: firstly, coating an aqueous solution onto the surface of one side of a base membrane, then contacting a crosslinker solution with the other side of the base membrane, diffusing crosslinker molecules in the crosslinker solution through membrane pore channels by reverse mass transfer, and contacting and reacting with the aqueous solution, thereby preparing a nanofiltration membrane.

[0006] The hollow fiber-based membrane is a hydrophobic membrane, preferably one of polyvinylidene fluoride PVDF, polyvinyl chloride PVC, and polytetrafluoroethylene PTFE.

[0007] The aqueous phase solution is a polyvinyl alcohol aqueous solution; the mass concentration of the aqueous phase solution is 0.1-0.5%, preferably 0.2%.

[0008] The aqueous phase solution is a polyvinyl alcohol ionic liquid solution; the mass concentration of the polyvinyl alcohol ionic solution is 0.1-0.5%, preferably 0.2%; the ionic liquid is one or a mixture of 1-butyl-3-methylimidazolium tetrafluoroborate, 1-aminopropyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide, and 1-butyl-3-methylimidazolium hexafluorophosphate.

[0009] The cross-linking agent solution is an oil phase solution.

[0010] The oil phase solution is a solution of multifunctional acyl chloride; the multifunctional acyl chloride is one of trimesoyl chloride, adipoyl chloride and sebacyl chloride; the solvent of the oil phase solution is one of n-hexane, cyclohexane and heptane; the mass concentration of the oil phase solution is 0.15-0.3%; preferably 0.2-0.3%.

[0011] The base film is soaked with an oil phase solvent before being coated with the water phase solution; the oil phase solvent is one of n-hexane, cyclohexane and heptane.

[0012] The method specifically comprises the following steps: first, immersing the base membrane in an oil phase solvent for wetting, so that the pores of the hydrophobic base membrane are filled with the oil phase solvent; then, passing an aqueous phase solution into the tube side of the membrane assembly; then, passing the oil phase solution into the shell side of the membrane assembly and filling it, and standing the shell side at room temperature for reaction to obtain a nanofiltration membrane.

[0013] The present invention also includes a nanofiltration membrane of the method.

[0014] The present invention also includes an application of the nanofiltration membrane, which is applied to the separation of dyes and salts; the dyes are anionic dyes; preferably, the anionic dyes are Congo red, reaction red 120, or orange G; and the salts are NaCl or Na2SO4.

[0015] Compared with the prior art, the present invention has the following beneficial effects:

[0016] The nanofiltration membrane prepared based on the self-inhibition effect of the reverse mass transfer reaction of the present application has a thin separation layer thickness, and accordingly, compared with the prior art, the hollow fiber composite nanofiltration membrane prepared by the present invention has a higher water flux. At the same time, the reverse mass transfer reaction can repair defective pores during the reaction process, so that compared with the prior art, the pore size distribution of the hollow fiber composite nanofiltration membrane prepared by the present invention is more uniform, and the preparation method is simple, and the cost is lower, which has obvious economic benefits. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 It is a schematic diagram of the preparation process of reverse mass transfer of the nanofiltration membrane of the present invention. DETAILED DESCRIPTION

[0018] In order to enable those skilled in the art to better understand the technical solution of the present invention, the present invention is further described in detail below in conjunction with the accompanying drawings and the best embodiments.

[0019] Example 1

[0020] A method for preparing nanofiltration membrane by reverse mass transfer ( Figure 1The schematic diagram thereof is shown, which includes a base membrane 1, an aqueous solution 22, a solute 21 of the aqueous solution; an oily solution 32, a solute 31 of the oily solution), and includes the following steps: first, soak the hollow fiber hydrophobic PVC base membrane module in n-hexane overnight, so that the pores of the hydrophobic base membrane are filled with n-hexane. Next, a 0.2wt% polyvinyl alcohol aqueous solution is passed into the tube side of the hollow fiber PVC membrane module by utilizing the liquid level height difference; then, a 0.15wt% n-hexane solution of trimesoyl chloride is passed into the shell side of the membrane module and filled with the solution, and the reaction is allowed to stand at room temperature for 2 minutes; finally, a hollow fiber composite nanofiltration membrane for dye / salt separation is obtained. Before the membrane performance test, the membrane is first moistened and cleaned with ethanol, and then the ethanol in the membrane pores is replaced with deionized water.

[0021] Example 2

[0022] A method for preparing a nanofiltration membrane by reverse mass transfer comprises the following steps: first, soaking a hollow fiber hydrophobic PVC membrane assembly in n-hexane overnight, so that the pores of the hydrophobic base membrane are filled with n-hexane. Next, using the liquid level difference, a polyvinyl alcohol aqueous solution with a concentration of 0.2wt% is passed into the tube side of the hollow fiber PVC membrane assembly; then, a 0.20wt% n-hexane solution of trimesoyl chloride is passed into the shell side of the membrane assembly and filled with it, and the reaction is allowed to stand at room temperature for 2 minutes; finally, a hollow fiber composite nanofiltration membrane for dye / salt separation is obtained. Before the membrane performance test, the membrane is first wetted and cleaned with ethanol, and then the ethanol in the membrane pores is replaced with deionized water.

[0023] Example 3

[0024] A method for preparing a nanofiltration membrane by reverse mass transfer comprises the following steps: first, soaking a hollow fiber hydrophobic PVC membrane assembly in n-hexane overnight, so that the pores of the hydrophobic base membrane are filled with n-hexane. Next, using the liquid level difference, a polyvinyl alcohol aqueous solution with a concentration of 0.2wt% is passed into the tube side of the hollow fiber PVC membrane assembly; then, a 0.25wt% n-hexane solution of trimesoyl chloride is passed into the shell side of the membrane assembly and filled with it, and the reaction is allowed to stand at room temperature for 2 minutes; finally, a hollow fiber composite nanofiltration membrane for dye / salt separation is obtained. Before the membrane performance test, the membrane is first wetted and cleaned with ethanol, and then the ethanol in the membrane pores is replaced with deionized water.

[0025] Example 4

[0026] A method for preparing a nanofiltration membrane by reverse mass transfer comprises the following steps: first, soaking a hollow fiber hydrophobic PVC membrane assembly in n-hexane overnight, so that the pores of the hydrophobic base membrane are filled with n-hexane. Next, using the liquid level difference, a polyvinyl alcohol aqueous solution with a concentration of 0.2wt% is passed into the tube side of the hollow fiber PVC membrane assembly; then, a 0.30wt% n-hexane solution of trimesoyl chloride is passed into the shell side of the membrane assembly and filled with it, and the reaction is allowed to stand at room temperature for 2 minutes; finally, a hollow fiber composite nanofiltration membrane for dye / salt separation is obtained. Before the membrane performance test, the membrane is first wetted and cleaned with ethanol, and then the ethanol in the membrane pores is replaced with deionized water.

[0027] Example 5

[0028] A method for preparing a nanofiltration membrane by reverse mass transfer comprises the following steps: first, soaking a hollow fiber hydrophobic PVC membrane assembly in n-hexane overnight, so that the pores of the hydrophobic base membrane are filled with n-hexane. Next, using the liquid level difference, a polyvinyl alcohol / 1-butyl-3-methylimidazole hexafluorophosphate solution with a concentration of 0.2wt% is passed into the tube side of the hollow fiber PVC membrane assembly; then, a 0.30wt% n-hexane solution of trimesoyl chloride is passed into the shell side of the membrane assembly and filled with it, and the reaction is allowed to stand at room temperature for 2 minutes; finally, a hollow fiber composite nanofiltration membrane for dye / salt separation is obtained. Before the membrane performance test, the membrane is first wetted and cleaned with ethanol, and then the ethanol in the membrane pores is replaced with deionized water.

[0029] Comparative Example 1

[0030] Conventional interfacial polymerization was used to prepare a dye / salt separation nanofiltration membrane, including the following steps: first, a polyvinyl alcohol aqueous solution with a concentration of 0.2wt% was passed from bottom to top into the tube side of the PVC hollow fiber membrane module using a peristaltic pump, and after soaking for 5 minutes, an air compressor was used to purge the membrane module tube side from top to bottom at a linear speed of 13.0m / s to remove excess aqueous solution, and the purge time was 5 minutes; then, a 0.20wt% trimesoyl chloride n-hexane solution was passed from bottom to top using a peristaltic pump, and the reaction lasted for 2 minutes to prepare a hollow fiber polyester nanofiltration membrane. After the experiment, the prepared nanofiltration membrane was stored in deionized water for testing.

[0031] Table 1 shows the performance test results of nanofiltration membranes prepared by reverse mass transfer reaction and conventional interfacial polymerization process;

[0032]

[0033] Result analysis:

[0034] The hollow fiber nanofiltration membrane assembly prepared in Examples 1-5 and Comparative Example 1 was fixed on a cross-flow filtration test device, and pure water passed through the membrane assembly under internal pressure mode. The pressure of the cross-flow filtration test device was set to pre-press at 0.30 MPa for 1 hour. After the membrane was completely compacted, it was tested at 0.2 MPa, and the water obtained within 10 minutes was collected, and the pure water flux was tested by weighing method; then the pure water was replaced with a mixed solution containing 0.2 g / L Congo red and 1 g / L NaCl as the feed liquid to continue the test, and the feed liquid passed through the membrane assembly under internal pressure mode. The operating pressure of the cross-flow filtration test device was 0.20 MPa, and the dye concentration in the produced water was measured using an ultraviolet spectrophotometer every 10 minutes until the dye concentration on the produced water side was stable, and the dye and salt retention results of the nanofiltration membrane were calculated.

[0035] Comparison of Example 2 and Comparative Example 1: The hollow fiber composite nanofiltration membrane prepared by the reverse mass transfer reaction has a higher pure water flux and better dye / salt separation performance. This is due to the self-inhibition effect of the reverse mass transfer reaction, that is, trimesoyl chloride preferentially contacts with polyvinyl alcohol at the opening of the membrane surface. As the reaction proceeds, after a perfect separation layer is formed, the diffusion of trimesoyl chloride is inhibited, and it is difficult to contact with polyvinyl alcohol at the interface, resulting in the termination of the reaction. Finally, the formed separation layer presents a discontinuous pore cap structure, which is different from the complete continuous coverage separation layer structure prepared by the conventional interfacial polymerization process. Therefore, compared with the conventional process, the thickness of the separation layer prepared by the reverse mass transfer reaction is greatly reduced. In addition, the reverse mass transfer reaction can repair the unnecessary macropores generated in the nanofiltration membrane preparation process in situ during the preparation process, thereby effectively improving the dye / salt separation performance of the nanofiltration membrane, overcoming the problem that the overall pore size radial distribution of the hollow fiber composite nanofiltration membrane prepared by the conventional method is uneven, and defective macropores are easily formed.

[0036] The result analysis of embodiment 1-4: with the reverse mass transfer reaction process, the concentration of trimesoyl chloride increases, and because the concentration difference increases, the mass transfer rate of trimesoyl chloride across the membrane pore channel is accelerated, and there will be more trimesoyl chloride in contact with polyvinyl alcohol, resulting in the formation of a more compact nanofiltration membrane, and thus, the pure water flux of the nanofiltration membrane is gradually reduced, and the NaCl retention rate is gradually increased. In addition, since Orange G belongs to anionic dyes, with the increase of the concentration of trimesoyl chloride, the negative charge on the membrane surface is gradually enhanced, and according to the Donnan exclusion effect, the interception of Orange G by the nanofiltration membrane is gradually increased.

[0037] Comparative analysis of Example 2 and Example 5: After the solvent is replaced from deionized water to ionic liquid, the hydrolysis of the acyl chloride is avoided during the reaction process, so that the prepared hollow fiber composite nanofiltration membrane becomes denser and the pore size distribution becomes more uniform, further improving the dye / salt separation performance of the prepared nanofiltration membrane. Correspondingly, the pure water flux of the nanofiltration membrane decreases slightly.

[0038] In summary, the nanofiltration membrane prepared based on the self-inhibition effect of the reverse mass transfer reaction of the present application has a thin separation layer thickness, and accordingly, compared with the prior art, the hollow fiber composite nanofiltration membrane prepared by the present invention has a higher water flux. At the same time, the reverse mass transfer reaction can repair defective pores during the reaction process, so that compared with the prior art, the pore size distribution of the hollow fiber composite nanofiltration membrane prepared by the present invention is more uniform, and the preparation method is simple, and the cost is lower, which has obvious economic benefits.

[0039] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for preparing a nanofiltration membrane by reverse mass transfer, characterized in that: The method comprises the following steps: firstly coating an aqueous solution onto the surface of one side of a base membrane, then contacting a crosslinker solution with the other side of the base membrane, diffusing the crosslinker molecules in the crosslinker solution through the membrane pore channel by reverse mass transfer, and contacting and reacting with the aqueous solution, thereby preparing a nanofiltration membrane.

2. The method for preparing nanofiltration membrane by reverse mass transfer according to claim 1, characterized in that: The aqueous phase solution is a polyvinyl alcohol aqueous solution; the mass concentration of the aqueous phase solution is 0.1-0.5%, preferably 0.2%.

3. The method for preparing nanofiltration membrane by reverse mass transfer according to claim 1, characterized in that: The aqueous phase solution is an ionic liquid solution of polyvinyl alcohol; the mass concentration of the polyvinyl alcohol solution is 0.1-0.5%, preferably 0.2%; The ionic liquid is one of 1-butyl-3-methylimidazolium tetrafluoroborate, 1-aminopropyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide, and 1-butyl-3-methylimidazolium hexafluorophosphate, or a mixture thereof.

4. The method for preparing nanofiltration membrane by reverse mass transfer according to claim 1, characterized in that: The cross-linking agent solution is an oil phase solution.

5. The method for preparing nanofiltration membrane by reverse mass transfer according to claim 4, characterized in that: The oil phase solution is a solution of multifunctional acyl chloride; the multifunctional acyl chloride is one of trimesoyl chloride, adipoyl chloride and sebacoyl chloride; the solvent of the oil phase solution is one of n-hexane, cyclohexane and heptane; the mass concentration of the oil phase solution is 0.15-0.30%.

6. The method for preparing nanofiltration membrane by reverse mass transfer according to claim 1, characterized in that: The base film is soaked with an oil phase solvent before being coated with the water phase solution; the oil phase solvent is one of n-hexane, cyclohexane and heptane.

7. The method for preparing nanofiltration membrane by reverse mass transfer according to claim 1, characterized in that: The method specifically comprises the following steps: first, immersing the base membrane in an oil phase solvent for wetting, so that the pores of the hydrophobic base membrane are filled with the oil phase solvent; then, passing an aqueous phase solution into the tube side of the membrane assembly; then, passing the oil phase solution into the shell side of the membrane assembly and filling it, and standing the shell side at room temperature for reaction to obtain a nanofiltration membrane.

8. A nanofiltration membrane according to the method according to any one of claims 1 to 7.

9. An application of the nanofiltration membrane according to claim 8, characterized in that: Applicable to the separation of dyes or salts; the dye is an anionic dye; preferably, the anionic dye is Congo red, reaction red 120, or orange G; the salt is NaCl or Na2SO4.

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