Composite nanofiltration membrane with cyclodextrin middle layer and preparation method of composite nanofiltration membrane

Abstract

The invention discloses a composite nanofiltration membrane with a cyclodextrin middle layer and a preparation method of the composite nanofiltration membrane, and relates to the field of chemical manufacturing. Comprising the following steps: preparing aqueous-phase solutions including a piperazine aqueous-phase solution and a cyclodextrin aqueous-phase solution; the oil phase solution is prepared from trimesoyl chloride and normal hexane; pouring the piperazine water phase on the film, and then pouring out; after the membrane is air-dried, a cyclodextrin water phase is sprayed on the surface of the membrane; and after the membrane is air-dried, pouring an oil phase, then pouring out, washing the membrane with water, and finally heating to obtain the nanofiltration membrane. The CD middle layer is constructed by regulating and controlling the interfacial polymerization process to prepare the composite nanofiltration membrane. When alpha-CD is used, the retention rate of the membrane on 1, 2-PDO can reach 77.36%; after beta-CD or gamma-CD is used, the hydrophilic and hydrophobic properties, the water flux and the PDO rejection rate of the membrane are obviously different. The prepared membrane has the pure water permeability of 32.73 LMH / bar, the retention rate of Na2SO4 reaches 88.86%, and the membrane is the composite nanofiltration membrane with the optimal performance.

Description

Technical Field

[0001] The present invention relates to the field of chemical manufacturing, and particularly to a composite nanofiltration membrane with a cyclodextrin intermediate layer and a preparation method thereof. Background Art

[0002] So far, a simple and effective integrated separation and purification process has not been established for the recovery of 1,3-propanediol (1,3-PDO) from microbial fermentation broth. The interfacial polymerization method for preparing polyamide nanofiltration membranes has the advantages of a wide range of material sources and simple film-forming conditions. However, the diffusion behavior of monomers to the water / oil interface during the polymerization process makes it difficult to control the polymerization reaction, resulting in an uneven cross-linked structure and thus affecting the separation performance of the nanofiltration membrane. Summary of the Invention

[0003] The purpose of the present invention is to solve the above problems in the prior art, and to provide a composite nanofiltration membrane with a cyclodextrin (CD) intermediate layer and a preparation method thereof, so as to improve the selective separation ability of the nanofiltration membrane for two isomers of propanediol (1,2-PDO and 1,3-PDO).

[0004] To achieve the above purpose, the present invention adopts the following technical solutions:

[0005] A preparation method of a composite nanofiltration membrane with a cyclodextrin intermediate layer, comprising the following steps:

[0006] 1) Immerse the base membrane in water, then air-dry it and place it in a mold;

[0007] 2) Prepare an aqueous solution, and the aqueous solution includes a piperazine aqueous solution and a cyclodextrin aqueous solution;

[0008] 3) Prepare an oil-phase solution, and the oil-phase solution includes trimesoyl chloride and n-hexane;

[0009] 4) Pour the piperazine aqueous solution onto the base membrane in step 1), pour it out after the base membrane is infiltrated; after the membrane surface is air-dried, spray the cyclodextrin aqueous solution on the membrane surface; after the membrane surface is air-dried, pour in the oil-phase solution to react, then pour out the oil-phase solution, wash the membrane surface with water, and finally heat to obtain the nanofiltration membrane.

[0010] In step 1), the base membrane is a polysulfone (PSU) base membrane.

[0011] In step 2), the cyclodextrin includes at least one of α-cyclodextrin, β-cyclodextrin, and γ-cyclodextrin.

[0012] The cyclodextrin is α-cyclodextrin.

[0013] In step 2), the mass fraction of cyclodextrin in the cyclodextrin aqueous solution is 0.25 wt% - 2.0 wt%.

[0014] In step 2), the mass fraction of cyclodextrin in the aqueous cyclodextrin solution is 0.5 wt%.

[0015] In step 2), the mass fraction of piperazine in the aqueous piperazine solution is 0.18 wt% - 0.22 wt%.

[0016] In step 3), the mass - volume fraction of trimesoyl chloride in the oil - phase solution is 0.13 w / v% - 0.17 w / v%.

[0017] In step 4), the heating temperature is 50 - 65 °C.

[0018] A composite nanofiltration membrane with a cyclodextrin intermediate layer is prepared by the above - mentioned preparation method.

[0019] Compared with the prior art, the beneficial effects achieved by the technical solution of the present invention are as follows:

[0020] For the composite nanofiltration membrane with a cyclodextrin intermediate layer prepared by the present invention, by constructing a CD intermediate layer to affect the diffusion of PIP, it can regulate the interfacial polymerization process to form a thinner, more hydrophilic and smoother polyamide membrane layer. Moreover, the presence of the intermediate layer increases the number of CDs participating in the interfacial polymerization, making the distribution of CDs in the membrane layer concentrated and significantly reducing the cross - linking degree and thickness of the membrane layer, improving the selective separation ability and permeation performance of the nanofiltration membrane, which are not possessed by ordinary commercial nanofiltration membranes. In the piperazine aqueous solution of the present invention, the PIP is 0.2 wt%, the α - CD in the cyclodextrin aqueous solution is 0.5 wt%, and the TM in the oil - phase solution is 0.15 wt%. Under this condition, the prepared nanofiltration membrane has a pure water permeability of 32.73 LMH / bar for Na 2 SO 4 The rejection rate reaches 88.86%. The selective separation coefficient SE for 1,2 - PDO is 3.91, which is 334.4% higher than that of the nanofiltration membrane TFC - blank without adding CD, and it is the composite nanofiltration membrane with the best performance, effectively improving the separation selectivity of the PDO mixture. Description of the Drawings

[0021] Figure 1 It is the surface morphology and cross - section SEM characterization results of the nanofiltration membranes in Examples 1 - 3; among them, (a 1 ), and (a 2 ), are respectively the surface morphology and cross - section SEM images of the nanofiltration membrane TFC - α(i) - 0.5 in Example 1; (b 1 ), and (b 2 ), are respectively the surface morphology and cross - section SEM images of the nanofiltration membrane TFC - β(i) - 0.5 in Example 2; (c 1 ), and (c 2)(i) are the surface morphology and cross-section SEM images of the nanofiltration membrane TFC-γ(i)-0.5 in Example 3 respectively.

[0022] Figure 2 are the test results of the water contact angles of the nanofiltration membranes in Examples 1 to 4.

[0023] Figure 3 are the test results of the fluxes and inorganic salt retentions of the nanofiltration membranes under the conditions of adding different types of CDs in Examples 1 to 4.

[0024] Figure 4 is the working curve of PDO analyzed by the GC-FID method, where Figure 4 (a) is the working curve of the gradient concentration of 1,2-propanediol, Figure 4 (b) is the working curve of the gradient concentration of 1,3-propanediol.

[0025] Figure 5 are the test results of the separation of PDO by the nanofiltration membranes under the conditions of adding different types of CDs in Examples 1 to 4.

[0026] Figure 6 are the test results of the separation of PDO by the nanofiltration membranes under the conditions of adding different concentrations of α-CD in Examples 1, 4 to 7. Detailed implementation mode

[0027] In order to make the technical problems, technical solutions and beneficial effects to be solved by the present invention clearer and more understandable, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. All the reagents used in the present invention can be directly purchased from the market or can be prepared by the methods described in the invention.

[0028] The present invention uses piperazine (PIP) and cyclodextrin (CD) as the interfacial polymerization aqueous phase polymerization monomer and aqueous phase additive respectively, trimesoyl chloride (TMC) as the interfacial polymerization oil phase polymerization monomer, and constructs an intermediate layer with cyclodextrin (CD). On a polysulfone (PSU) ultrafiltration substrate membrane, a nanofiltration membrane is prepared by regulating the interfacial polymerization method and characterized and analyzed.

[0029] Example 1

[0030] The preparation method of the composite nanofiltration membrane with a cyclodextrin intermediate layer in this example is as follows:

[0031] 1) Add PIP to water to prepare an aqueous piperazine solution with a PIP mass fraction of 0.2 wt%; add α-CD to water to prepare an aqueous cyclodextrin solution with an α-CD mass fraction of 0.5 wt%. The above aqueous solutions are all ultrasonically treated for 10 min.

[0032] 2) Add TMC to n-hexane to prepare an oil-phase solution with a TMC volume fraction of 0.15 w / v%, and ultrasonically treat it for 10 min.

[0033] 3) Cut the PSU base membrane into a suitable size (70 mm × 90 mm), soak it fully in pure water for 2 h, and then fix it in a square polytetrafluoroethylene mold and air-dry it until there is no obvious water trace on the membrane surface (more than 15 min).

[0034] 3) Take 50 mL of the ultrasonically treated piperazine aqueous solution, pour it onto the PSU base membrane, soak it for 15 min and then pour it out; after the surface of the PSU base membrane is air-dried again, take 1.5 mL of the ultrasonically treated cyclodextrin aqueous solution in step 1 and evenly spray it onto the surface of the base membrane through a vacuum spray bottle; after the surface of the membrane is air-dried, quickly pour 50 mL of the oil-phase solution along the edge of the mold to trigger interfacial polymerization. When a dense polyamide layer is observed to form on the membrane surface after 2 min of reaction, quickly pour out the oil-phase solution, and rinse the surface of the membrane with pure water to terminate the reaction. Place the rinsed nanofiltration membrane in an oven at 60 °C for thermal crosslinking to accelerate film formation. The thermal crosslinking reaction time is 15 min to obtain the nanofiltration membrane TFC-α(i)-0.5.

[0035] Example 2

[0036] In Example 1, the CD added to the cyclodextrin aqueous solution is β-CD, and the rest is treated the same as in Example 1 to obtain the nanofiltration membrane TFC-β(i)-0.5.

[0037] Example 3

[0038] In Example 1, the CD added to the cyclodextrin aqueous solution is γ-CD, and the rest is treated the same as in Example 1 to obtain the nanofiltration membrane TFC-γ(i)-0.5.

[0039] Example 4

[0040] In Example 1, the cyclodextrin aqueous solution is not added, and the rest is treated the same as in Example 1 to obtain the nanofiltration membrane TFC-blank.

[0041] Example 5

[0042] In Example 1, the concentration of α-CD in the cyclodextrin aqueous solution is 0.25 wt%, and the rest is treated the same as in Example 1 to obtain the nanofiltration membrane TFC-α(i)-0.25.

[0043] Example 6

[0044] In Example 1, the concentration of α-CD in the cyclodextrin aqueous solution is 0.75 wt%, and the rest is treated the same as in Example 1 to obtain the nanofiltration membrane TFC-α(i)-0.75.

[0045] Example 7

[0046] In Example 1, the concentration of α-CD in the cyclodextrin aqueous solution was 1.0 wt%, and the rest was treated in the same manner as in Example 1 to obtain the nanofiltration membrane TFC-α(i)-1.0.

[0047] Example 8

[0048] In Example 1, the concentration of α-CD in the cyclodextrin aqueous solution was 2.0 wt%, and the rest was treated in the same manner as in Example 1 to obtain the nanofiltration membrane TFC-α(i)-2.0.

[0049] For the nanofiltration membranes prepared in each example of the present invention, the types and contents of CDs in the intermediate layer are shown in Table 1.

[0050] Table 1

[0051]

[0052] Morphological characterization of the prepared nanofiltration membranes: A scanning electron microscope uses an extremely narrow electron beam to scan the surface of a sample, magnifies the surface of the sample by point-by-point imaging, and thus qualitatively or quantitatively analyzes the microscopic structures such as the surface and cross-section morphology, pore structure, active layer thickness, and roughness of the membrane. In this experiment, a German ZEISS SIGMA scanning electron microscope (SEM) was used to characterize the morphology and structure of the membrane samples. The dried membrane samples were frozen, cut, fixed on the sample stage, and then treated by platinum spraying, and then observed at an acceleration voltage of 15 kV and magnification factors of 5.00 k, 10.00 k, or 20.00 k (the results of Examples 1 to 3 are as Figure 1 shown, and the thicknesses of each membrane sheet are marked in the figure).

[0053] Measurement of the hydrophilic and hydrophobic properties of the prepared nanofiltration membrane surface: The hydrophilic and hydrophobic properties of the membrane surface are usually measured by the size of the water contact angle. The contact angle, also known as the wetting angle, refers to the spreading angle of a liquid on a fixed surface when it reaches thermodynamic equilibrium. The better the hydrophilicity of the surface, the smaller the spreading angle of the liquid, and thus the smaller the contact angle. In this experiment, a HARKE SPCAX3 contact angle tester was used to measure the contact angle of the nanofiltration membrane surface, which can be used to characterize the hydrophilic and hydrophobic properties of the membrane. Each time, 3 μL of water was added, and the contact time between the liquid and the nanofiltration membrane surface was 30 s. To improve the accuracy of the measurement data, the contact angle of each membrane sample was measured 5 times and the average value was taken.

[0054] Gas chromatography analysis (GC-FID): Using a Shimadzu GC-2010 gas chromatograph (FID detector), the column temperature programming was optimized for testing. The initial temperature was 40 °C, maintained for 1 min, then increased to 160 °C at a rate of 15 °C / min and maintained for 2 min, and then further increased to 230 °C at a rate of 15 °C / min and held for 3 min. The injection port temperature was 240 °C and the detector temperature was 250 °C. The chromatographic column was Rtx®-5, the carrier gas was nitrogen (≥99.999%), and the flow rate was 2.0 mL / min; splitless injection was used with an injection volume of 0.4 μL. Before testing the experimental solution, a working curve was plotted using a standard solution to calibrate the systematic error, as Figure 4 shown.

[0055] The present invention conducts membrane separation performance tests on the prepared nanofiltration membranes, including water flux tests, rejection rate tests, and tests on the selective separation ability of the membrane for PDO.

[0056] The effective area of each membrane sheet is approximately 24 cm 2 , and the steps for measuring the water flux are as follows:

[0057] (1) Place the membrane sheet with the skin layer facing down and fix it in the membrane cell of a triple cross-flow device;

[0058] (2) Pour 3000 ml of pure water into the device and pre-pressurize it at 1 bar for about 10 min (if the filtration rate is too slow at 1 bar, the pressure can be appropriately increased);

[0059] (3) After the pre-pressurization, increase the pressure to 6 bar and start timing, record the pressure and the volume of pure water permeated within a certain time;

[0060] (4) The calculation formula for the flux is as follows:

[0061]

[0062] J is the flux of the membrane sheet (L·m -2 ·h -1 ·bar -1 ), V is the volume of the permeate (m 3 ), A is the effective membrane area of the membrane sheet (m 2 ), p is the filtration pressure (bar), and Δt is the filtration time (h).

[0063] The salt rejection rate of the nanofiltration membrane was measured using sodium sulfate, magnesium sulfate, magnesium chloride, and sodium chloride, and the measurement steps are as follows:

[0064] (1) Place the membrane sheet with the skin layer facing down and fix it in the membrane cell of a triple cross-flow device;

[0065] (2)Prepare 3000 mL of a 2 g / L sodium sulfate solution and pour it into the device. Pre-press for about 10 min at 1 bar (if the filtration rate is too slow at 1 bar, the pressure can be appropriately increased).

[0066] (3)After the pre-press is completed, increase the pressure to 6 bar. After the nanofiltration process stabilizes for 30 min, collect the permeate and the concentrate, and measure their conductivities respectively.

[0067] (4)According to the conductivity-concentration curves of various inorganic salts, obtain the concentration C p of the permeate and the concentration C f of the concentrate;

[0068] (5)The calculation formula for the rejection rate is as follows:

[0069]

[0070] In the formula, R1 is the rejection rate of the membrane sheet (%), and C p and C f are the concentrations of inorganic salts in the permeate and the concentrate (g / L), respectively.

[0071] Measure the selective separation ability of the nanofiltration membrane for PDO using an ultrafiltration cell. The measurement steps are as follows:

[0072] (1)Prepare 300 mL of a 0.5 mol / L PDO solution and pour it into the ultrafiltration cell;

[0073] (2)Introduce nitrogen and increase the pressure to 1 bar for pre-pressing for about 10 min (if the filtration rate is too slow at 1 bar, the pressure can be appropriately increased);

[0074] (3)After pre-pressing for a dozen milliliters, increase the pressure to 4 bar and collect the permeate and the concentrate. Collect the permeate and the feed solution for gas chromatography (GC) analysis;

[0075] (4)According to the PDO gas-phase working curve, obtain the concentration Cp of the permeate and the concentration Cf of the concentrate;

[0076] (5)The calculation formula for the rejection rate is as follows:

[0077]

[0078] In the formula, R2 is the rejection rate of the membrane sheet (%), and Sp and Sc respectively represent the peak areas of the target substances detected in the gas-phase experiments of the permeate and the feed solution samples.

[0079] (6)The calculation formula for the separation factor is as follows:

[0080]

[0081] Where C1,3-PDO and C1,2-PDO correspond to the PDO concentrations in the corresponding solutions, and P and f correspond to the permeate and feed solutions, respectively.

[0082] Example 1 According to the above characterization and measurement of the membrane:

[0083] (1) In the morphological characterization, from Figure 1 it can be seen that the surface microstructure of the nanofiltration membrane of the present invention is relatively regular, and the surface structure of the membrane is mainly granular protrusions, without large-area nodular structures; due to the use of different cyclodextrins, the thickness of the separation layer of the generated nanofiltration membrane is also different. The CD intermediate layer constructed in the present invention can utilize the diffusion behavior of PIP during the interfacial polymerization process to form a polyamide membrane layer with a thinner thickness and a smoother surface.

[0084] (2) In the hydrophilicity test, from Figure 2 it can be seen that the WCA values of each nanofiltration membrane are significantly reduced, indicating that the hydrophilicity of the membrane surface is also enhanced. By constructing a CD intermediate layer, the presence of the intermediate layer can induce the formation of a structure with a lower degree of crosslinking. Under the action of this factor, the hydrophilicity of the nanofiltration membrane surface is significantly improved.

[0085] (3) In the water flux test and salt rejection rate test, as Figure 3 shown, the rejection rate of TFC-α(i)-0.5 for Na 2 SO 4 reaches 88.86%, and it has the highest water flux of 32.73 L·m -2 ·h -1 ·bar -1 (LMH / bar), which means it has the strongest hydrophilicity and helps to adsorb more water molecules on the membrane surface and promote their further diffusion into the membrane.

[0086] (4) In the rejection rate test for 1,2-PDO and 1,3-PDO, different CDs have a greater impact on the rejection effect of 1,2-PDO. As Figure 5 shown, the rejection rate of the nanofiltration membrane TFC-α(i)-0.5 for 1,2-PDO is 77.36%, and the corresponding calculated result of the selective separation coefficient SE is 3.91, which is 334.4% higher than that of TFC-blank; the rejection rate of the nanofiltration membrane TFC-α(i)-0.5 for 1,3-PDO is 11.10%. While the rejection rates of TFC-β(i)-0.5 and TFC-γ(i)-0.5 for 1,2-PDO are 32.50% and 24.85% respectively; the rejection rates for 1,3-PDO are 9.27% and 8.50% respectively, showing a very obvious decrease compared to TFC-blank. And from Figure 6It can be found that there are obvious differences in the variation rules of the rejection rates of the nanofiltration membrane for 1,2-PDO and 1,3-PDO. With the increase in the concentration of α-CD, the rejection rate of the former by the nanofiltration membrane first increases and then decreases, while the rejection rate of the latter first decreases and then increases.

[0087] The above embodiments are only preferred embodiments of the present invention and cannot be considered as limiting the scope of implementation of the present invention. All equivalent changes and improvements made within the scope of the application of the present invention shall still fall within the scope covered by the present invention.

Claims

1. A method for preparing a composite nanofiltration membrane having a cyclodextrin intermediate layer, characterized in that: The following steps are involved: 1) Soak the base film in water, then air-dry it and place it in the mold; 2) preparing an aqueous phase solution, wherein the aqueous phase solution includes a piperazine aqueous phase solution and a cyclodextrin aqueous phase solution; 3) preparing an oil phase solution, wherein the oil phase solution comprises trimesoyl chloride and n-hexane; 4) pouring the piperazine aqueous solution onto the basement membrane in step 1) and pouring it out after the basement membrane is soaked; after the membrane surface is air-dried, spraying the cyclodextrin aqueous solution onto the membrane surface; After the membrane surface is air-dried, the oil phase solution is poured in for reaction, and then the oil phase solution is poured out, and the membrane surface is rinsed with water, and finally heated to obtain a nanofiltration membrane.

2. The method for preparing a composite nanofiltration membrane having a cyclodextrin intermediate layer according to claim 1, characterized in that: In step 1), the base membrane is a polysulfone base membrane.

3. The method for preparing a composite nanofiltration membrane having a cyclodextrin intermediate layer according to claim 1, characterized in that: In step 2), the cyclodextrin includes at least one of α-cyclodextrin, β-cyclodextrin and γ-cyclodextrin.

4. The method for preparing a composite nanofiltration membrane having a cyclodextrin intermediate layer according to claim 1, characterized in that: The cyclodextrin is α-cyclodextrin.

5. The method for preparing a composite nanofiltration membrane having a cyclodextrin intermediate layer according to claim 1, characterized in that: In step 2), the mass fraction of cyclodextrin in the cyclodextrin aqueous solution is 0.25wt%~2.0wt%.

6. The method for preparing a composite nanofiltration membrane having a cyclodextrin intermediate layer according to claim 1, characterized in that: In step 2), the mass fraction of cyclodextrin in the cyclodextrin aqueous solution is 0.5wt%.

7. The method for preparing a composite nanofiltration membrane having a cyclodextrin intermediate layer according to claim 1, characterized in that: In step 2), the mass fraction of piperazine in the piperazine aqueous solution is 0.18 wt% to 0.22 wt%.

8. The method for preparing a composite nanofiltration membrane having a cyclodextrin intermediate layer according to claim 1, characterized in that: In step 3), the mass volume fraction of trimesoyl chloride in the oil phase solution is 0.13 w / v% to 0.17 w / v%.

9. The method for preparing a composite nanofiltration membrane having a cyclodextrin intermediate layer according to claim 1, characterized in that: In step 4), the heating temperature is 50-65°C.

10. A composite nanofiltration membrane having a cyclodextrin intermediate layer, characterized in that: Prepared by the preparation method according to any one of claims 1 to 9.

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