An interface polymerization preparation method of a cyclodextrin modified membrane

Abstract

The application discloses an interface polymerization preparation method of a cyclodextrin modified membrane, and relates to the field of chemical manufacturing.The nanofiltration membrane is prepared by using piperazine, 1,3,5-benzene tricarbonyl chloride and different cyclodextrin (CD) additives as membrane preparation materials through an interface polymerization method.The influence of different CD types and concentrations on the performance of the nanofiltration membrane is explored.The optimal concentration condition of the CD incorporation is 0.5 wt%, when the CD additive is alpha-CD, the rejection rate of the membrane to 1,2-PDO can reach 71.9%;after the additive is beta-CD or gamma-CD, the hydrophilicity and hydrophobicity of the membrane, the water flux and the PDO rejection rate are obviously different.The membrane prepared under the preferred condition has a pure water permeability of 11.5 LMH*bar^(-1), the rejection rate of Na2SO4 reaches 96.62%, and is the composite nanofiltration membrane with the optimal performance.

Description

TECHNICAL FIELD

[0001] The application relates to the chemical manufacturing field, in particular to an interface polymerization preparation method of a cyclodextrin modified membrane. BACKGROUND

[0002] Recovery of 1,3-propanediol (1,3-PDO) from bio-based fermentation broth has been a challenge in the separation industry. Polyamide thin-film composite (TFC) membranes have been widely used in the separation of bio-based products, but it is very difficult to construct the porous structure of the membrane at the molecular level to achieve the ideal separation performance due to the uncontrollability of the interface polymerization (IP) process.

[0003] Cyclodextrins (CDs) are a class of polysaccharide macrocyclic molecules, and due to their unique molecular cavity structure, they can form inclusion compounds with a variety of substances, so they are often used in the field of membrane separation to improve the selective separation performance of the membrane. CDs have abundant hydroxyl groups, which can react with acyl chloride to form a polyester layer, so they can participate in the interface reaction as water-phase monomers. CDs have a special structure of an electron-rich cavity, which is not only conducive to improving the membrane flux by improving the solvent molecules, but also can improve the separation performance of the membrane by using the volume and charge difference. At the same time, as a classic macrocyclic molecule, CDs have extraordinary application potential in the field of membrane separation. Liu et al. [1] prepared a composite nanofiltration membrane using beta-cyclodextrin as a water-phase monomer, which had excellent flux under polar / non-polar solution conditions; Lu et al. [2] assembled cyclodextrin on a nanocellulose (CNF) layer on an anodic aluminum oxide (AAO) substrate, and then crosslinked the CD layer using trimesoyl chloride (TMC) as a crosslinking agent to prepare a high-flux nanofiltration membrane with chiral separation ability; Tang et al. [3] added beta-cyclodextrin to the water-phase solution to introduce it into the polyamide functional layer, and prepared a nanofiltration membrane with 3D microstructure, which greatly improved the flux of the nanofiltration membrane and showed good separation performance for Na2SO4 / NaCl mixed salt solution.

[0004] Although CDs have been more fully applied in nanofiltration membrane technology, further research is still needed on how to fully develop the advantages of the special structure of CDs to develop molecular / ion selective separation nanofiltration membranes. SUMMARY

[0005] The purpose of the present application is to solve the problems in the prior art, and provide an interface polymerization preparation method of a cyclodextrin modified membrane, which improves the selective separation ability of the nanofiltration membrane for two kinds of propylene glycol (1,2-PDO and 1,3-PDO) isomers.

[0006] To achieve the above-mentioned purpose, the technical scheme adopted by the present application is as follows:

[0007] The application discloses an interface polymerization preparation method of a cyclodextrin modified membrane, and the cyclodextrin modified membrane (a nanofiltration membrane) is prepared by using an interface polymerization method with piperazine, 1,3,5-benzene trichloride and different cyclodextrin additives as membrane preparation materials. The cyclodextrin is one or several of alpha-cyclodextrin, beta-cyclodextrin and gamma-cyclodextrin.

[0008] The application comprises the following steps:

[0009] 1) taking out a polysulfone base membrane from a protective solution, cutting to a proper size, soaking in pure water for more than 2 hours, and then naturally air-drying and fixing the base membrane in a square polytetrafluoroethylene mold;

[0010] 2) preparing a mixed aqueous solution of piperazine by adding a certain amount of cyclodextrin;

[0011] 3) pouring the prepared aqueous phase on the polysulfone base membrane after ultrasonic treatment, pouring out the aqueous phase from the mold after the aqueous phase is soaked in the base membrane for a period of time, and air-drying until no obvious water trace is observed on the membrane surface;

[0012] 4) preparing a benzene trichloride / n-hexane oil phase solution with a certain volume fraction;

[0013] 5) quickly pouring the oil phase along the edge of the mold, carrying out interface polymerization, pouring out the oil phase after reaction, and stopping the reaction;

[0014] 6) further heat-crosslinking the membrane after interface polymerization in an oven.

[0015] In step 2), the mass fraction of piperazine in the mixed aqueous solution is 0.1 wt%, the mass fraction of cyclodextrin is 0.25-3.0 wt%, and 0.28 wt% of NaOH is added as a solubilizing agent. Preferably, the mass fraction of cyclodextrin is 0.5 wt%.

[0016] In step 3), the ultrasonic treatment time is 20 min, and the soaking time of the base membrane is 15 min.

[0017] In step 4), the volume fraction of the benzene trichloride / n-hexane oil phase solution is 0.15 w / v%.

[0018] In step 5), the reaction time is 2 min, the oil phase is quickly poured out when a dense polyamide layer is observed on the membrane surface, and the membrane surface is washed with pure water to stop the reaction.

[0019] In step 6), the heat-crosslinking temperature is 50-65 DEG C, and the heat-crosslinking time is 5-20 min. Preferably, the heat-crosslinking treatment is carried out at 50 DEG C for 15 min.

[0020] Compared with the prior art, the technical scheme of the application has the following beneficial effects:

[0021] The cyclodextrin modified membrane prepared by the application is a cyclodextrin-polyamide composite nanofiltration membrane, the interface diffusion process of piperazine (PIP) monomers is affected by cyclodextrin CDs, a thinner and rougher polyamide (PA) layer can be induced to be formed, so that the total mass transfer resistance is reduced and the effective filtration area of the membrane is increased. Moreover, CDs are introduced into the separation layer as a separation module, the selective separation of 1,2-PDO and 1,3-PDO is realized by utilizing the difference in molecular shape between 1,2-PDO and 1,3-PDO, which is not possessed by ordinary commercial nanofiltration membranes.

[0022] The optimal conditions screened by the application are that the piperazine (PIP) concentration is 0.1wt%, the trimesoyl chloride (TMC) concentration is 0.15wt%, and the cyclodextrin (CD) addition condition is 0.5wt% of α-CD. The nanofiltration membrane prepared under the conditions has a pure water permeability of 11.5LMH·bar^(-1) and a Na2SO4 rejection rate of 96.62%. The rejection rate of 1,2-PDO is 71.87%, which is increased by 179.3% compared with the blank control. It is the composite nanofiltration membrane with the optimal performance, which effectively improves the separation selectivity of PDO mixture. BRIEF DESCRIPTION OF DRAWINGS

[0023] Figure 1 The scanning images of the surfaces (a1-d1) and cross sections (a2-d2) of the membranes of Examples 1-4 are shown. Among them, (a) TFC-blank (Example 4); (b) TFC-α-0.5 (Example 1); (c) TFC-β-0.5 (Example 2); (d) TFC-γ-0.5 (Example 3).

[0024] Figure 2 The water contact angle test results of the nanofiltration membranes of Examples 1-4 are shown. In Figure 2 , the abscissa is the name of each example, and the ordinate is the water contact angle (°).

[0025] Figure 3 The influence of CDs on the permeability of the membranes and the rejection rates of various inorganic salts in Examples 1-4 is shown. In Figure 3 , the abscissa is the name of each example.

[0026] Figure 4 The PDO working curve analyzed by the gas chromatography (GC-FID) method is shown. In Figure 4 , the abscissa is the concentration, and the ordinate is the peak area. (a) 1,2-PDO, (b) 1,3-PDO.

[0027] Figure 5 The influence of different types of CDs under the addition conditions on the performance of the selective separation of PDO in Examples 1-4 is shown. In Figure 5 , the abscissa is the name of each example, and the ordinate is the rejection rate of the corresponding PDO.

[0028] Figure 6 The results of the gas phase test of the mixed PDO sample isolated in Example 1 are shown in Table 1. Figure 6 In Table 1, the abscissa is time; the ordinate is peak signal intensity. DETAILED DESCRIPTION

[0029] In order to make the objectives, technical solutions and advantages of the present application clearer, the following examples will further illustrate the present application with reference to the accompanying drawings. It should be understood that the specific examples described herein are merely intended to explain the present application and are not intended to limit the present application. The reagents used in the present application can be directly purchased from the market or can be prepared by the methods described in the present application.

[0030] The present application utilizes piperazine (PIP) and cyclodextrin (CDs) as the interfacial polymerization aqueous phase monomer and aqueous phase additive, respectively, and utilizes trimesoyl chloride (TMC) as the interfacial polymerization oil phase monomer, to prepare a nanofiltration membrane on a polysulfone (PSU) ultrafiltration base membrane by an interfacial polymerization method, and to perform characterization analysis on the nanofiltration membrane.

[0031] 1) The polysulfone (PSU) base membrane is taken out from the protective solution, cut to a suitable size, and then immersed in pure water for more than 2 h, after which the base membrane is taken out and fixed in a square polytetrafluoroethylene mold and naturally air-dried;

[0032] 2) A mixed aqueous phase solution is prepared by introducing a certain amount of CDs and piperazine (PIP), wherein the mass fraction of PIP is 0.1 wt%, the mass fraction of CDs is 0.25-3.0 wt%, and the mass fraction of CDs is preferably 0.5 wt%, and 0.28 wt% of NaOH is added as a cosolvent;

[0033] 3) After the pre-prepared aqueous phase is ultrasonically treated for 20 min, 50 mL of the aqueous phase is poured onto the PSU base membrane, the base membrane is soaked for 15 min, and then the aqueous phase is poured out, and the membrane surface is air-dried for 15 min until no obvious water marks are observed on the membrane surface;

[0034] 4) A certain amount of TMC is added to a certain volume of n-hexane to prepare an interfacial polymerization oil phase solution, wherein the volume fraction of the TMC / n-hexane oil phase solution is 0.15 w / v%;

[0035] 5) The oil phase solution is quickly poured along the edge of the mold to trigger the interfacial polymerization reaction at room temperature, and when a dense polyamide layer is observed on the membrane surface after 2 min of reaction, the oil phase is quickly poured out, and the membrane surface is washed with pure water to terminate the reaction;

[0036] 6) The polytetrafluoroethylene mold after washing is placed in an oven at 50-65°C for heat crosslinking to accelerate film formation, and the heat crosslinking reaction time is 5-20 min, and the preferred condition is 50°C for 15 min.

[0037] The following are the specific implementation steps in the membrane preparation process.

[0038] 1. Preparation of nanofiltration membrane by interfacial polymerization process

[0039] Example 1: The aqueous phase solution is configured with a PIP mass fraction of 0.1 wt% and an α-CD mass fraction of 0.5 wt%, and 0.28 wt% NaOH is added as a cosolvent; the TMC / n-hexane oil phase solution is configured with a volume fraction of 0.15 w / v%, and the above solutions are all ultrasonically treated for 20 min. The PSU base film is taken out from the protective solution, cut to an appropriate size (60 mm x 80 mm), immersed in pure water for 2 h, and then fixed in a square polytetrafluoroethylene mold and air-dried until there is no obvious water mark on the film surface (more than 15 min). 50 mL of the ultrasonically treated aqueous phase solution is poured onto the PSU base film and soaked for 15 min, then poured out. After the film surface is air-dried again, 50 mL of oil phase is quickly poured along the mold edge to trigger interfacial polymerization, and the oil phase is quickly poured out after 2 min of reaction when a dense polyamide layer is observed on the film surface, and the film surface is washed with pure water to terminate the reaction. The washed nanofiltration membrane is placed in a 50°C oven for heat crosslinking to accelerate film formation, and the heat crosslinking reaction time is 15 min.

[0040] Example 2: In the first step of Example 1, the type of CDs added to the aqueous phase solution is changed to β-CD, and the rest is the same as Example 1.

[0041] Example 3: In the first step of Example 1, the type of CDs added to the aqueous phase solution is changed to γ-CD, and the rest is the same as Example 1.

[0042] Example 4: In the first step of Example 1, no CDs are added to the aqueous phase solution configured, and the rest is the same as Example 1, i.e. blank control.

[0043] Example 5: In the first step of Example 1, the concentration of α-CD in the aqueous phase solution configured is changed to 0.25 wt%, and the rest is the same as Example 1.

[0044] Example 6: In the first step of Example 1, the concentration of α-CD in the aqueous phase solution configured is changed to 0.75 wt%, and the rest is the same as Example 1.

[0045] Example 7: In the first step of Example 1, the concentration of α-CD in the aqueous phase solution configured is changed to 1.5 wt%, and the rest is the same as Example 1.

[0046] Example 8: In the first step of Example 1, the concentration of α-CD in the aqueous phase solution configured is changed to 3.0 wt%, and the rest is the same as Example 1.

[0047] Table 1. Naming rules for each example

[0048]

[0049] 2. Membrane morphology characterization:

[0050] Scanning electron microscope (SEM) is a kind of microscope that uses a very narrow electron beam to scan the surface of the sample, and then magnifies the sample surface by point-by-point imaging, so as to qualitatively or quantitatively analyze the microstructure of the membrane surface and cross-section morphology, pore structure, active layer thickness, roughness, etc. In this experiment, the morphology and structure of the membrane sample surface were characterized by using a ZEISS SIGMA type scanning electron microscope (SEM) made in Germany. After the dried membrane sample was frozen, cut and fixed on the sample stage, it was treated with platinum, and then observed under the conditions of 15 kV accelerating voltage, 5.00 k, 10.00 k or 20.00 k magnification (the results of Examples 1-4 are shown in FIG. 1, and the thickness of each membrane sheet is marked in the figure). Figure 1

[0051] 3. Measurement of hydrophilic and hydrophobic properties of membrane surface:

[0052] 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 the liquid on the surface when it reaches thermodynamic equilibrium. The better the hydrophilicity of the surface, the smaller the spreading angle of the liquid, and therefore the smaller the contact angle. In this experiment, the contact angle of the nanofiltration membrane surface was measured by using a HARKE SPCAX3 type contact angle tester, which can be used to characterize the hydrophilic and hydrophobic properties of the membrane. The amount of water added each time was 3 μL, and the contact time between the liquid and the nanofiltration membrane surface was 30 s. In order 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. Figure 2 The results of the water contact angle test of the nanofiltration membranes of Examples 1-4 are shown in Table 1.

[0053] 4. Gas chromatography analysis (GC-FID) method:

[0054] The test was performed using a Shimadzu GC-2010 type gas chromatograph (FID detector) with an optimized column temperature program: the initial temperature was 40°C, maintained for 1 min, then increased to 160°C at a rate of 15°C / min, maintained for 2 min, then increased to 230°C at a rate of 15°C / min, maintained for 3 min. The injection port temperature was 240°C, and the detector temperature was 250°C. The chromatographic column used was a DB-5MS column (30 m x 0.25 mm x 0.25 μm). The carrier gas was nitrogen (≥99.999%), with a flow rate of 2.0 mL / min; no split injection, with a sample size of 0.4 μL. Before testing the experimental solution, a standard solution was used to draw a working curve to calibrate the system error.

[0055] 5. Membrane separation performance test:

[0056] 5.1 Water flux test: ​

[0057] The effective area of each membrane is about 24 cm 2 The flux measurement procedure is as follows:

[0058] (1) The membrane skin layer is fixed in the triple cross-flow device membrane cell with the skin layer facing down;

[0059] (2) 3000 ml of pure water is poured into the device and pre-pressurized at 1 bar for about 10 minutes (if the filtration speed is too slow at 1 bar, the pressure can be appropriately increased);

[0060] (3) After pre-pressurization, the pressure is increased to 6 bar and timing is started. The pressure and the volume of the permeate liquid within a certain time are recorded;

[0061] (4) The flux calculation formula is as follows:

[0062]

[0063] J is the flux of the membrane (L·m -2 ·h -1 ·bar -1 ), V is the volume of the permeate liquid (m 3 ), A is the effective membrane area of the membrane (m 2 ), p is the filtration pressure (bar), and Δt is the filtration time (h).

[0064] 5.2 Retention rate test:

[0065] Sodium sulfate, magnesium sulfate, magnesium chloride, and sodium chloride are used to measure the salt retention rate of the nanofiltration membrane. The measurement procedure is as follows:

[0066] (1) The membrane skin layer is fixed in the triple cross-flow device membrane cell with the skin layer facing down;

[0067] (2) 3000 ml of 2 g / L sodium sulfate solution is prepared and poured into the device, and pre-pressurized at 1 bar for about 10 minutes (if the filtration speed is too slow at 1 bar, the pressure can be appropriately increased);

[0068] (3) After pre-pressurization, the pressure is increased to 6 bar. After 30 minutes of stable nanofiltration process, the permeate liquid and the concentrated liquid are collected, and the conductivities are measured, respectively;

[0069] (4) According to the conductivity-concentration curves of each inorganic salt, the permeate liquid concentration C p and the concentrated liquid concentration C f are obtained;

[0070] (5) The retention rate calculation formula is as follows:

[0071]

[0072] In the formula, R1 is the retention rate of the membrane (%), Cp and C f The inorganic salt concentration (g / L) in the permeate and concentrate, respectively.

[0073] The influence of CDs on the membrane permeability and the retention rate of each inorganic salt in Examples 1-4 is shown in Table 1. Figure 3 .

[0074] 5.3 Test of the selective separation ability of the membrane for PDO:

[0075] The selective separation ability of the nanofiltration membrane for PDO was measured by using an ultrafiltration cup. The measurement procedure was as follows:

[0076] (1) 300 mL of 0.5 mol / L PDO solution was prepared and poured into the ultrafiltration cup;

[0077] (2) Nitrogen was introduced to pressurize to 1 bar for about 10 min (if the filtration speed is too slow at 1 bar, the pressure can be increased appropriately);

[0078] (3) After about 10 mL of pre-pressurization, the pressure was increased to 4 bar to collect the permeate and concentrate, and the permeate was collected and analyzed by gas chromatography (GC) with the feed liquid;

[0079] (4) The permeate concentration Cp and the concentrate concentration Cf were obtained according to the PDO gas phase working curve;

[0080] (5) The calculation formula of the retention rate was as follows:

[0081]

[0082] In the formula, R2 is the retention rate of the membrane (%), and Sp and Sc represent the peak areas of the target substance detected in the gas phase experiment of the permeate and the feed liquid sample, respectively.

[0083] Figure 4 The gas chromatography (GC-FID) method for analyzing the PDO working curve is shown in the following figures. Figure (a) is 1,2-PDO, and figure (b) is 1,3-PDO. Figure 5 The influence of different types of CDs on the selective separation performance of the membrane for PDO under the conditions of Examples 1-4 is shown in Table 2. Figure 6 The gas phase test results of the separation of mixed PDO samples in Example 1 are shown in Table 3.

[0084] Experiments show that the optimal conditions screened by the application are that the PIP concentration is 0.1 wt%, the TMC concentration is 0.15 wt%, and the CDs addition condition is 0.5 wt% of alpha-CD. The nanofiltration membrane prepared under the condition has a pure water permeability of 11.5 LMH*bar^(-1), and the rejection rate of Na2SO4 reaches 96.62%. The rejection rate of 1,2-PDO is 71.87%, which is increased by 179.3% compared with the blank control. The composite nanofiltration membrane is the performance optimal one, and effectively improves the separation selectivity of the PDO mixture.

[0085] The above examples are only the preferred embodiments of the application and cannot be considered as limiting the scope of the application. Any equivalent changes and improvements made within the scope of the application should still belong to the patent coverage of the application.

Claims

1. A method for preparing a cyclodextrin modified membrane by interfacial polymerization, characterized in that: The cyclodextrin modified membrane is prepared by interfacial polymerization using piperazine, 1,3,5-benzenetricarboxylic acid chloride and cyclodextrin additives as membrane materials; Follow the preparation steps below: 1) Remove the polysulfone base membrane from the protective solution, cut it into suitable size, soak it in pure water for more than 2 hours, and fix it in a square polytetrafluoroethylene mold after natural air drying; 2) A mixed aqueous solution of piperazine was prepared by introducing a certain amount of α-cyclodextrin; the mixed aqueous solution had a piperazine mass fraction of 0.1 wt%, an α-cyclodextrin mass fraction of 0.5 wt%, and 0.28 wt% NaOH was added as a cosolvent; 3) The prefabricated aqueous phase is poured onto the polysulfone-based membrane after ultrasonic treatment. After soaking the membrane for a period of time, it is poured out of the mold and air-dried until no obvious water marks are left on the membrane surface. 4) Prepare a certain volume fraction of benzyl chloride / n-hexane oil phase solution; the volume fraction of benzyl chloride / n-hexane oil phase solution is 0.15 w / v; 5) Pour the oil phase quickly along the edge of the mold to carry out interfacial polymerization. After the reaction, pour out the oil phase to terminate the reaction. 6) The interfacially polymerized film is further thermally cross-linked in an oven.

2. The method for preparing a cyclodextrin modified membrane by interfacial polymerization according to claim 1, wherein: In step 3), the ultrasonic treatment time is 20 min; the basement membrane soaking time is 15 min.

3. The method for preparing a cyclodextrin modified membrane by interfacial polymerization according to claim 1, wherein: In step 5), the reaction time is 2 min. When a dense polyamide layer is observed to be formed on the membrane surface, the oil phase is quickly poured out and the membrane surface is rinsed with pure water to terminate the reaction.

4. The method for preparing a cyclodextrin modified membrane by interfacial polymerization according to claim 1, wherein: In step 6), the thermal crosslinking temperature is 50-65° C., and the thermal crosslinking time is 5-20 min.

5. The method for preparing a cyclodextrin modified membrane by interfacial polymerization according to claim 4, wherein: The thermal crosslinking temperature was 50°C, and the thermal crosslinking time was 15 min.

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