Composite membrane for purifying sucralose-6-acetate alcoholysis product as well as preparation and application of composite membrane

Abstract

The invention discloses a membrane separation material for purifying a sucralose-6-acetate alcoholysis product. The technology comprises three main parts, namely MOF (Metal Organic Framework) synthesis, membrane preparation and membrane dialysis separation. The method comprises the following steps: firstly, taking gamma-cyclodextrin and sodium hydroxide as raw materials, carrying out morphology adjustment by using hexadecyl trimethyl ammonium bromide, and synthesizing Na-gamma-CD-MOF by using a solvent method; then mixing the MOF material with N, N-dimethylacetamide and polyvinylidene fluoride in proportion to prepare a membrane casting solution, and preparing the membrane casting solution into a composite membrane material by using a phase inversion method; finally, the membrane is placed in a liquid phase dialysis device, dialysis separation is conducted on all components in the sucralose-6-acetate alcoholysis product, and efficient separation of impurities and efficient purification of the main product sucralose are achieved. The advantages of the membrane separation technology are fully utilized, conditions are mild, the device is simple, operation is convenient, and the method has good application prospects.

Description

Technical Field

[0001] The present invention belongs to the technical field of chemical separation, and particularly relates to a composite membrane for purifying the alcoholysis product of sucralose-6-acetate, and its preparation and application. Background Art

[0002] Sucralose (TGS) is a sugar substitute product synthesized from sucrose. Its chemical name is 4,1',6'-trichloro-4,1',6'-trideoxygalactosucrose, and its molecular formula is C 12 H 19 O8Cl3, with a molecular weight of 397.64. It was first jointly developed by Professor Leslie Hough of University College London and Tate&Lyle in 1976. Sucralose has a very high sweetness, reaching 600-800 times that of sucrose. Its sweetness is pure without obvious peculiar smell, and its taste is similar to that of sucrose. It has no rodent risk, and at the same time resists enzymatic hydrolysis. It has high biosafety of not participating in human metabolism and not being absorbed by the human body, and has now become a high-end sugar substitute widely used in the fields of food, medicine, etc.

[0003] The existing industrial synthesis route of sucralose mainly adopts the single-group protection method, and its synthesis process is a three-step synthesis using sucrose as the raw material: first, the hydroxyl group at the 6-position of sucrose is esterified to sucrose-6-acetate; then, the hydroxyl groups at the 4, 1', and 6'-positions of sucrose-6-acetate are chlorinated to 4,1',6'-trichlorosucrose-6-acetate; finally, the 6-position acyl group of 4,1',6'-trichlorosucrose-6-acetate is removed by alcoholysis to obtain sucralose. Although the reaction route is simple, during the reaction process, affected by reaction conditions such as temperature, catalyst, and solvent, as well as the accumulation of side reactions in each step, a large number of complex by-products will ultimately be generated. According to production and experimental data verification, the by-products in the process of alcoholysis of 4,1',6'-trichlorosucrose-6-acetate to obtain sucralose mainly include some unreacted upstream raw material 4,1',6'-trichlorosucrose-6-acetate, as well as 4 kinds of dichlorosucrose, 2 kinds of trichlorosucrose, and 1 kind of tetrachlorosucrose: 4,1'-dichlorosucrose (4,1'-DGS), 4,6'-dichlorosucrose (4,6'-DGS), 3,6'-anhydro-4,1'-dichlorosucrose (3,6'-A-4,1'-DGS), 1',6'-dichlorosucrose (1',6'-DGS), 4,1',6'-trichlorosucrose (4,1',6'-TGS), 6,1',6'-trichlorosucrose (6,1',6'-TGS), 4,6,1',6'-tetrachlorosucrose (4,6,1',6'-QGS). The most important by-product among them is 3,6'-anhydro-4,1'-dichlorosucrose (3,6'-A-4,1'-DGS, abbreviated as DGS). In particular, when a slightly excessive amount of NaOH is added during the reaction process, the content of DGS will increase sharply, reaching 10-20 wt%. 3',6'-glycoside-4,1'-dichlorosucrose has an obvious bitter taste, which affects the product flavor. Improving the purity of the main product TGS is the key to affecting the quality of TGS products, and the key to improving the purity of the main product TGS lies in separating out DGS.

[0004] Membrane separation technology is a process of separating media by using the selective permeability of membranes. The core of membrane separation is the selective transport characteristics of membrane materials, which have the characteristics of high separation efficiency, low energy consumption, and can realize continuous and synchronous separation of products. In practical applications, synthetic organic polymer membrane materials dominate. This type of material has a wide variety of varieties, wide sources, relatively low prices, and good comprehensive film-forming properties. Most industrial polymer membranes are prepared by the phase inversion method. The phase inversion membrane preparation method is to prepare a homogeneous solution of a polymer with a certain composition, and by changing the thermodynamic state of the solution, the homogeneous polymer solution undergoes phase separation, and finally forms a three-dimensional macromolecular network gel structure, where the polymer concentrated phase is the continuous phase as the main framework of the membrane, and the polymer dilute phase is the dispersed phase as the pores of the membrane. So far, there has been no relevant report on the use of membrane separation technology in the synthesis process of sucralose. Summary of the Invention

[0005] The present invention is to separate the main and by-products (TGS, DGS, and TSA-6) in the alcoholysis solution in the industrial synthesis process of sucralose, and to achieve the high-efficiency purification of sucralose. A membrane separation technology is provided, which is reasonably designed, efficient, and convenient.

[0006] To achieve the above-mentioned invention purpose, the process steps of the present invention are as follows: A preparation method of a composite membrane for purifying the alcoholysis product of sucralose-6-acetate, comprising the following steps: The first step: Using γ-cyclodextrin (γ-CD) and sodium hydroxide (NaOH) as raw materials, and cetyltrimethylammonium bromide (CTAB) for morphology regulation, synthesize Na-γ-CD-MOF by the solvent method; The second step: Mix the Na-γ-CD-MOF prepared in the first step with N,N-dimethylacetamide (DMAc) and polyvinylidene fluoride (PVDF) in proportion to prepare a casting solution, and use the phase inversion method to prepare the casting solution into a Na-γ-CD-MOF / PVDF composite membrane.

[0007] Further, in the above first step, the molar ratio of γ-cyclodextrin: sodium hydroxide: cetyltrimethylammonium bromide is 1:8:1.

[0008] Further, in the above second step, the mass ratio of Na-γ-CD-MOF: N,N-dimethylacetamide (DMAc): polyvinylidene fluoride (PVDF) is 0.3:5:0.5.

[0009] Further, the above first step includes the following specific steps: Add 1.63 g of γ-cyclodextrin (γ-CD) (1.25 mol) to a glass container containing 50 mL of 0.2 mol / L sodium hydroxide, stir well to obtain a uniform solution; After filtering the solution, transfer it to 50 mL of methanol containing 0.4 g of cetyltrimethylammonium bromide (CTAB) (CTAB is a surfactant that plays a role in regulating crystal size); Then stir the reaction mixture, let it stand overnight at room temperature to complete crystal growth, and centrifuge at 10,000 rpm for 10 minutes to obtain a white precipitate; The precipitate is washed three times with isopropanol and dried in an oven at 50 °C to obtain Na-γ-CD-MOF; Further, the second step described above includes the following specific steps: First, add the Na-γ-CD-MOF prepared in the first step to N,N-dimethylacetamide (DMAc), and ultrasonically dissolve it completely; then add polyvinylidene fluoride (PVDF) to the N,N-dimethylacetamide (DMAc) solution containing Na-γ-CD-MOF, and stir in a 70 °C water bath until it is completely dissolved to form a uniform casting solution; the mass ratio of Na-γ-CD-MOF:DMAc:PVDF is 0.3 g:5 g:0.5 g; after defoaming the casting solution in an oven at 70 °C for 24 hours, pour it onto a clean glass plate, and scrape it into a uniform thin film with a 100 µm scraper. After exposing it to the air for 30 s, immediately immerse the glass plate in a coagulation bath at room temperature to form a Na-γ-CD-MOF / PVDF composite membrane (the final film thickness is about 40 µm). After coagulation, transfer it to deionized water for more than 24 hours, and change the deionized water every 12 hours to thoroughly wash away the organic solvents.

[0010] A composite membrane prepared by the above method.

[0011] Application of the above Na-γ-CD-MOF / PVDF composite membrane in a food-grade separation and purification system.

[0012] Further, application of the above Na-γ-CD-MOF / PVDF composite membrane in the separation and purification of sucralose.

[0013] Compared with the prior art, the advantages of the present invention are as follows: (1) The present invention uses cyclodextrin to prepare a membrane material for separating a food-grade sucralose system, which has the advantages of being green and safe.

[0014] (2) Membrane separation technology has the characteristics of high separation efficiency, low energy consumption, and can achieve continuous and synchronous separation of products. Membrane separation technology is convenient to operate, and the process is stable without introducing other impurities. The Na-γ-CD-MOF / PVDF composite membrane (Na-γ-CD-MOF:DMAc:PVDF = 0.3 g:5 g:0.5 g, the MOF particle size is about 7 µm, and the film thickness is about 40 µm) has a good separation effect on the TGS / TGS system. The composite membrane can directionally separate DGS in the system. After 5 consecutive dialysis experiments on the crude product of alcoholysis, the purity of TGS in the raw material can reach 95.78%. Description of the Drawings

[0015] Figure 1 It is a schematic diagram of the dialysis device in Example 5.

[0016] Figure 2It is the scanning electron microscope image of the Na-γ-CD-MOF crystal in Example 3. (a) Crystal with an average particle size of 6.97 μm; (b) Crystal with an average particle size of 12.21 μm; (c) Crystal with an average particle size of 14.99 μm.

[0017] Figure 3 It is the scanning electron microscope image of the Na-γ-CD-MOF / PVDF composite membrane in Example 1.

[0018] Figure 4 It is the reaction diagram of the alcoholysis of TSA-6 to prepare TGS in Example 5.

[0019] Figure 5 It is the HPLC diagram of the components before and after dialysis in Example 5. Detailed implementation mode To make the content of the present invention easier to understand, the present invention will be further described below in conjunction with specific implementation cases: Example 1 A preparation method of a separation membrane for purifying the alcoholysis product of sucralose-6-acetate, comprising the following steps: The first step is to synthesize Na-γ-CD-MOF by the solvent method: Add 1.63 g of γ-cyclodextrin (γ-CD) (1.25 mol) to a glass container containing 50 mL of 0.2 mol / L sodium hydroxide, stir well to obtain a uniform solution; After filtering the solution, transfer it to 50 mL of methanol containing 0.4 g of cetyltrimethylammonium bromide (CTAB) (CTAB is a surfactant that plays a role in adjusting the crystal size); Then stir the reaction mixture, let it stand overnight at room temperature to complete crystal growth, and centrifuge at 10000 rpm for 10 minutes to obtain a white precipitate; The precipitate is washed three times with isopropanol and dried in an oven at 50 °C to obtain Na-γ-CD-MOF; Step 2: Synthesize the Na-γ-CD-MOF / PVDF composite membrane by the phase inversion method: First, add the Na-γ-CD-MOF prepared in Step 1 into N,N-dimethylacetamide (DMAc) and sonicate it until it is completely dissolved; then add polyvinylidene fluoride (PVDF) into the N,N-dimethylacetamide (DMAc) solution containing Na-γ-CD-MOF and stir it in a 70 °C water bath until it is completely dissolved to form a homogeneous casting solution; the mass ratio of Na-γ-CD-MOF:DMAc:PVDF is 0.3:5:0.5; after degassing the casting solution in an oven at 70 °C for 24 hours, pour it onto a clean glass plate and scrape it into a uniform thin film with a 100 µm blade. After exposing it to the air for 30 s, immediately immerse the glass plate in the coagulation bath at room temperature to form the Na-γ-CD-MOF / PVDF composite membrane (the final film thickness is about 40 µm). After solidification, transfer it to deionized water for more than 24 hours and change the deionized water every 12 hours to thoroughly wash away the organic solvents; Example 2 Optimization of the content of Na-γ-CD-MOF in the Na-γ-CD-MOF / PVDF composite membrane.

[0021] First, when synthesizing Na-γ-CD-MOF in Step 1, add 0.4 g of CTAB to the methanol solution to adjust the size of Na-γ-CD-MOF to about 7 µm. Then, in Step 2, prepare the casting solution with the ratio of Na-γ-CD-MOF:DMAc:PVDF = 0.20 g / 0.25 g / 0.30 g / 0.35 g:5 g:0.5 g. Finally, in the dialysis reaction of Step 3, use a 50 mL mixture of 3 µmol / mL TGS:DGS = 1:1 (n:n) as the feed phase to obtain the optimal content of Na-γ-CD-MOF as 0.30 g. The remaining steps are the same as in Example 1.

[0022] Table 1 Separation performance of composite membranes with different MOF contents Example 3 Optimization of the particle size of Na-γ-CD-MOF in the Na-γ-CD-MOF / PVDF composite membrane.

[0023] First, in the first step of synthesizing Na-γ-CD-MOF, 0.4, 0.2, and 0 g of CTAB were added to the methanol solution to adjust the size of Na-γ-CD-MOF to 6.97, 12.21, and 14.99 μm, respectively. Then, in the second step, a casting solution was prepared with a ratio of Na-γ-CD-MOF:DMAc:PVDF = 0.30 g:5 g:0.5 g. Finally, in the third step of the dialysis reaction, a 50 mL mixture of 3 μmol / mL TGS:DGS = 1:1 (n:n) was used as the feed phase, and the optimal particle size of Na-γ-CD-MOF was 6.97 μm. The remaining steps were the same as in Example 1.

[0024] Table 2 Separation performance of composite membranes of MOFs with different particle sizes Example 4 Optimization of the membrane thickness in the Na-γ-CD-MOF / PVDF composite membrane.

[0025] First, in the first step of synthesizing Na-γ-CD-MOF, 0.4 g of CTAB was added to the methanol solution to adjust the size of Na-γ-CD-MOF to about 7 μm. Then, in the second step, when preparing the membrane, a 50, 100, or 150 μm doctor blade was used to scrape and form the composite membrane. Finally, in the third step of the dialysis reaction, a 50 mL mixture of 3 μmol / mL TGS:DGS = 1:1 (n:n) was used as the feed phase, and the optimal membrane thickness was 100 μm. The remaining steps were the same as in Example 1.

[0026] Table 3 Separation performance of composite membranes with different doctor blade thicknesses Example 5 Preparation of the alcoholysis product: 47.5 g (0.1 mol) of TSA-6 crystals were dissolved in an equal mass of methanol, and a mixed solution containing 5.2 g (0.13 mol) of NaOH as a catalyst and 95 g of methanol was added dropwise at 283.2 K. Then, the reaction was maintained at 313.2 K for 2 h. Then, cation exchange resin NKC-9 was added at 293.2 K to terminate the reaction, and the mixture was stirred for 0.5 h until the pH reached 7.0. NKC-9 was recovered by filtration and acidification. Finally, the methanol solvent was removed from the alcoholysis solution by vacuum distillation at 323.2 K, and the crystal product was precipitated. The crystal product was collected and vacuum-dried in an oven at 50 °C to obtain the crude product: the purity of TGS was about 90%, and the main by-product was DGS.

[0027] Separation of alcoholysis products: First, when synthesizing MOF, 0.4 g of CTAB was added to the methanol solution to adjust the size of Na-γ-CD-MOF to about 7 µm. Then, a casting solution was prepared with a ratio of Na-γ-CD-MOF: DMAc: PVDF = 0.3 g: 5 g: 0.5 g, and the remaining steps were the same as in Example 1 to obtain a Na-γ-CD-MOF / PVDF composite membrane. The Na-γ-CD-MOF / PVDF composite membrane was placed at the membrane phase connection of the dialysis device (as Figure 1 shown). In the device, the feed chamber and the permeation chamber were separated by the composite membrane, and the connection was sealed with a fluororubber gasket to ensure that permeation occurred only through the membrane. A certain volume of the feed solution was filled into the feed chamber, and an equal volume of deionized water was loaded into the permeation chamber to form a transmembrane concentration gradient for permeation separation. The feed chamber and the permeation chamber were continuously stirred with a magnetic stirring device to ensure that the concentrations of the solutions on both sides were uniform enough. Samples of the solution in the permeation chamber were taken at preset time intervals, and the components of the permeate were determined by HPLC. Preparation of the feed solution: 0.1 g of the crude alcoholysis product was ultrasonically dissolved in 50 mL of deionized water. The feed solution and an equal volume of deionized water were respectively filled into the feed chamber and the dialysis chamber. After stirring and reacting for 1 h, the deionized water in the membrane phase and the dialysis phase was replaced, and the dialysis experiment was repeated 5 times. Each time, an appropriate amount of the feed solution was taken to determine the components by HPLC. Finally, the components of the feed solution were: the relative content of TGS was 95.78%, and the relative content of DGS was 4.22%.

[0028] Table 4 Mass percentages of all components in the alcoholysis products (determined by HPLC-ELSD)

Claims

1. A preparation method of a composite membrane for purifying the alcoholysis product of sucralose-6-acetate, characterized in that, It includes the following steps: In the first step, using γ-cyclodextrin and sodium hydroxide as raw materials, cetyltrimethylammonium bromide is used for morphology regulation, and Na-γ-CD-MOF is synthesized by the solvent method; In the second step, the Na-γ-CD-MOF prepared in the first step is mixed with N,N-dimethylacetamide and polyvinylidene fluoride in a certain proportion to prepare a casting solution, and the casting solution is prepared into a Na-γ-CD-MOF / PVDF composite membrane by the phase inversion method.

2. The preparation method according to claim 1, characterized in that: In the first step, the molar ratio of γ-cyclodextrin:sodium hydroxide:cetyltrimethylammonium bromide is 1:8:

1.

3. The preparation method according to claim 1, characterized in that: In the second step, the mass ratio of Na-γ-CD-MOF:N,N-dimethylacetamide:polyvinylidene fluoride is 0.3:5:0.

5.

4. The preparation method according to claim 1, characterized in that: The first step includes the following specific steps: Add 1.63 g of γ-cyclodextrin to a glass container containing 50 mL of 0.2 mol / L sodium hydroxide, stir well to obtain a homogeneous solution; After filtering the solution, transfer it to 50 mL of methanol containing 0.4 g of cetyltrimethylammonium bromide; Then stir the reaction mixture, let it stand overnight at room temperature to complete crystal growth, and centrifuge at 10000 rpm for 10 minutes to obtain a white precipitate; Wash the precipitate three times with isopropanol and dry it in an oven at 50 °C to obtain Na-γ-CD-MOF.

5. The preparation method according to claim 1, characterized in that: The second step includes the following specific steps: First, add the Na-γ-CD-MOF prepared in the first step to N,N-dimethylacetamide and ultrasonically dissolve it completely; Then add polyvinylidene fluoride to the N,N-dimethylacetamide solution containing Na-γ-CD-MOF and stir in a 70 °C water bath until it is completely dissolved to form a homogeneous casting solution; The mass ratio of Na-γ-CD-MOF:DMAc:PVDF is 0.3 g:5 g:0.5 g; After degassing the casting solution in an oven at 70 °C for 24 hours, pour it onto a clean glass plate and scrape it into a uniform film with a 100 µm scraper. After exposing it to the air for 30 s, immediately immerse the glass plate in a coagulation bath at room temperature to form a Na-γ-CD-MOF / PVDF composite membrane. After coagulation, transfer it to deionized water for more than 24 hours and change the deionized water every 12 hours to thoroughly wash away the organic solvents.

6. A composite membrane prepared by the method according to any one of claims 1-5.

7. Application of the composite membrane according to claim 7 in a food-grade separation and purification system.

8. The application according to claim 7, wherein: Application of the composite membrane in the separation and purification of sucralose.

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