A method for preparing lactulose by electrolysis

Abstract

The invention discloses a method for preparing lactulose by electrolysis, comprising the following steps: S1, electrolyzing water; applying a direct current power supply until the pH value of the solution is 14.0 to 14.8; stopping the electrolysis; S2, adding lactose and a montmorillonite / chitosan / Al(OH)3 complex to one side of a hydroxyl aggregation unit; S3, stirring, converting lactose into lactulose, reducing the pH value of the solution of the hydroxyl aggregation unit to 7.5 or below, and at the same time, adding a montmorillonite / chitosan / Al(OH)4 ‑ Converted into montmorillonite / chitosan / Al(OH)3 complex; S4, filter the material, separate the solution and the solid from each other, and obtain a mixture of lactose and lactulose; S5, separate the obtained mixture of lactose and lactulose through a membrane, crystallize, and dry to obtain lactulose; the present invention utilizes electrolysis in conjunction with an electric field to separate and enrich hydrogen ions and hydroxide ions, enriches and catalyzes the conversion of lactose into lactulose through adsorption, and the catalyst has a stable structure and is easy to separate.

Description

Technical Field

[0001] The invention relates to the technical field of lactulose, in particular to a method for preparing lactulose by electrolysis. Background Art

[0002] Lactulose, also known as lactulose, isomerized lactose, 4-O-β-D-pyranosyl-D-fructose, etc., is a disaccharide formed by connecting D-galactosyl and D-fructose with a β-1,4-glycosidic bond. Its molecular formula is C 12 H 22 O 11 , relative molecular mass 342.3, sweetness is 1.5 times that of lactose, solubility at room temperature is 2.06kg / L, water solubility is good, and it has many beneficial effects on the human body.

[0003] The current method for preparing lactulose still relies on the calcium hydroxide method with a low conversion rate. The reaction process is generally divided into three stages: the first stage is the stage of large-scale lactulose production; the second stage is the stage of sugar decomposition and by-product production, and at the same time, the pH value decreases and a small amount of lactulose is produced; the third stage is the pigment production stage, and the pH value is close to neutral. Analysis of the reaction products shows that D-galactose is a common reaction by-product in the chemical process, mainly from the decomposition of lactose and lactulose. Since sugars will undergo browning reactions in a strong alkaline environment, the chemical method is prone to produce pigments; decolorization is generally completed by activated carbon or decolorization resin, so the lactulose solution obtained by the chemical method is slightly yellow or yellow, and the obtained lactulose contains D-galactose and D-tagatose.

[0004] Regardless of whether it is the preparation method of lactulose disclosed in application number CN117567524A or CN103864858A, a large amount of sodium hydroxide is required to adjust the pH value of the lactose solution to 11 to 13, which requires a large amount of alkali and needs to be further treated with acid solution, which pollutes the environment and significantly increases the production cost. Summary of the invention

[0005] The object of the present invention is to provide a method for preparing lactulose by electrolysis. The present invention utilizes electrolysis in combination with an electric field to separate and enrich hydrogen ions and hydroxide ions, enriches and catalyzes the conversion of lactose into lactulose by adsorption, and has a stable catalyst structure, which is convenient for separation.

[0006] To solve this technical problem, the technical solution of the present invention is: a method for preparing lactulose by electrolysis,

[0007] The following steps are involved:

[0008] S1. Electrolyzed water

[0009] The DC power supply is powered on, and the hydrogen ions and hydroxides generated by the anode membrane connected to the positive electrode of the DC power supply and the cathode membrane connected to the negative electrode of the DC power supply are respectively enriched in the anode membrane and the cathode membrane area, and the solution is electrolyzed until the pH of the solution on one side of the hydroxide aggregation unit is 14.0 to 14.8; the electrolysis is stopped;

[0010] S2, lactose and montmorillonite / chitosan / Al(OH)3 complex are added to one side of the hydroxyl aggregation unit, wherein the montmorillonite / chitosan / Al(OH)3 complex is converted into montmorillonite / chitosan / Al(OH)4 in alkali solution. - ;

[0011] S3, stirring, lactose is converted into lactulose, the pH value of the solution of the hydroxyl aggregation unit is reduced to 7.5 and below, at the same time, montmorillonite / chitosan / Al (OH) 4 - converted into montmorillonite / chitosan / Al(OH)3 composite;

[0012] S4, filtering the material on one side of the hydroxide aggregation unit, separating the solution from the solid montmorillonite / chitosan / Al(OH)3 complex, and obtaining a mixed solution of lactose and lactulose;

[0013] S5. Separate the obtained lactose and lactulose mixture through a membrane, crystallize it, and dry it to obtain lactulose.

[0014] In the preferred step S3, montmorillonite and chitosan adsorb lactose molecules to the Al(OH)4 - The present invention utilizes electrolyzed water in combination with an anodic membrane to enrich hydroxide to a pH value suitable for preparing lactulose from lactose. In the above reaction process, the chitosan intercalated in the montmorillonite and the montmorillonite are both in a solid state, and the two structures are stable, which effectively promotes the relative dispersion uniformity between the lactose solution and the montmorillonite / chitosan / Al(OH)3 complex. The adsorption of chitosan and montmorillonite is conducive to promoting the enrichment of lactose molecules at the interface between the complex and the solution, and Al(OH)4 - The probability of contact with lactose molecules is significantly increased.

[0015] Preferably, the preparation method of montmorillonite / chitosan / Al(OH)3 composite comprises the following steps:

[0016] S111, dispersing montmorillonite using deionized water at room temperature to swell the montmorillonite;

[0017] S112, adding the montmorillonite swollen by S111 to the chitosan / chelated Al solution with a pH of 5.0 to 5.5 3+ Solution; Chitosan and montmorillonite in acidic solution adsorb each other through electrostatic interaction, chitosan / chelated Al 3+ The intercalation layer is distributed between the layers of montmorillonite;

[0018] S113. Adjust the pH value of the solution to 7.0 to 7.5, centrifuge, wash, and dry to obtain a montmorillonite / chitosan / Al(OH)3 complex.

[0019] The present invention utilizes the inherent characteristics of aluminum to maintain aluminum ions at a pH value suitable for the dissolution of chitosan, and can chelate with aluminum ions to achieve the enrichment of aluminum ions. While the chitosan is solidified, the aluminum ions further form precipitation, which is convenient for subsequent accurate feeding.

[0020] Chitosan / chelated Al 3+ The preparation method comprises the following steps:

[0021] A1, dissolving chitosan in acetic acid solution to obtain a chitosan solution;

[0022] AlCl3·6H2O was dissolved in anhydrous ethanol / deionized water mixture at room temperature, wherein the volume ratio of anhydrous ethanol to deionized water was 2:1, to obtain an AlCl3 solution;

[0023] A2. Add AlCl3 solution dropwise into chitosan acetic acid solution, and adjust the pH value of the mixture to 5.0 to 5.5; stir evenly, and let stand for 1 to 2 hours to obtain aluminum ions chelated in the chitosan solution.

[0024] When the present invention chelates aluminum ions, the aluminum ions form coordination bonds with the amino groups of chitosan, the aluminum ions are adsorbed on the chitosan, and the amino groups of the chitosan and the aluminum ions form a complex according to the following chemical reaction formula:

[0025] Al 3+ +3H2O+3(-NH2)→Al(OH)3+3(-NH3 + ).

[0026] Preferably, the ratio of montmorillonite to deionized water in S111 is (0.05 to 0.1): 1. The present invention needs to ensure that the obtained montmorillonite is fully swollen.

[0027] The preferred mass ratio of chitosan to montmorillonite in S112 is (3 to 6):1;

[0028] The stirring time of assembling chitosan and montmorillonite is 4 to 8 hours. The present invention uses montmorillonite as a carrier for chitosan loading to ensure that the structure of the montmorillonite / chitosan / Al (OH) 3 complex is stable in alkaline solution and is suitable for the recycling of the complex; when substances that are not conducive to lactose reaction are deposited on the surface of the obtained complex during use, the contaminated montmorillonite / chitosan / Al (OH) 3 complex can be dissolved in a solution with a pH value of 5.0 to 5.5. In this process, the amino (-NH2) group on the chitosan molecule can accept protons (H + ), forming ammonium salt (-NH3+ ), so that the chitosan molecules are positively charged. This protonation helps to destroy the hydrogen bonds between chitosan molecules, dissolving chitosan chelating aluminum ions and releasing pollutants. At the same time, the electrostatic interaction between chitosan and montmorillonite effectively positions chitosan and chelated aluminum ions, so that pollutants such as residual sugar molecules or pigments deposited during the isomerization process can be removed by cleaning. After sufficient cleaning, the montmorillonite / chitosan / chelated Al 3+ The composite is placed in a solution with a pH of 7.5, and solidified again, thereby achieving the regeneration of the composite. The process conditions for the regeneration of the montmorillonite / chitosan / Al(OH)3 composite used in the present invention are mild, and less acidic or alkaline substances are used.

[0029] The process parameters of direct current water electrolysis in step S1 are preferably:

[0030] The operating voltage is 10V to 15V.

[0031] Preferably, the mass ratio of montmorillonite / chitosan / Al(OH)3 complex to lactose added to the lactose solution is 1:(1 to 1.3).

[0032] Preferably, a cation exchange membrane and an anion exchange membrane are also provided in the reaction container, wherein the cation exchange membrane and the anion exchange membrane are located between the cathode membrane and the anode membrane, the space between the cation exchange membrane and the side wall of the reaction container surrounding the cathode membrane is a hydroxyl aggregation unit, and the space between the anion exchange membrane and the side wall of the reaction container surrounding the anode membrane is a hydrogen ion aggregation unit. The present invention utilizes a cation exchange membrane provided on one side of the cathode membrane to achieve the generation of OH - And gather OH -， Formation of Al(OH)4 - Resulting pH conditions.

[0033] Preferably, the montmorillonite / chitosan / Al(OH)3 complex obtained by filtration in step S4 is washed in a deionized water solution, dried, and then put back into step S2.

[0034] By adopting the above technical solution, the beneficial effects of the present invention are:

[0035] The present invention prepares lactulose by isomerizing lactose using a chitosan / Al(OH)3 complex dispersed by montmorillonite and enriching hydroxide generated by electrolysis of water, wherein the electrolysis reaction formula of the cathode membrane and the anode membrane is as follows:

[0036] Cathode: 2H2O+2e→H2↑+2OH - ;

[0037] Anode: 2H2O-4e→O2↑+4H + ;

[0038] Montmorillonite and chitosan dispersed uniformly in the montmorillonite work together to adsorb lactose molecules on the Al(OH)4 as the catalytic center converted by Al(OH)3. - Nearby, lactose molecules effectively contact with the catalytic center, improving the rearrangement efficiency of lactose and significantly improving production efficiency. When the pH value of one side of the lactose solution drops from the initial high value to about 7.5, the reaction ends and the conversion rate can reach 73% to 81%. As the pH value decreases, the catalytic center Al(OH)4 - Al(OH)3 is formed again and separated synchronously with montmorillonite and chitosan. The present invention enriches hydroxide to a concentration suitable for lactose by electrolyzing water in combination with an anodic membrane, thereby reducing the work of material transfer and quantitative analysis, and the catalytic center Al(OH)4 immobilized by montmorillonite and chitosan - The probability of contact with lactose molecules is high, which effectively improves the catalytic efficiency; and the montmorillonite / chitosan / Al (OH) 3 complex has a stable structure, is easy to use and recycle, has low self-loss, and can maintain a stable catalytic efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 This is a schematic diagram of a production device for preparing lactulose by electrolysis according to the present invention;

[0040] Figure 2 This is the infrared spectrum of the montmorillonite / chitosan / Al(OH)3 composite obtained in Example 1 of the present invention;

[0041] Reference numerals

[0042] Reaction container 100; cation exchange membrane 1; anion exchange membrane 2; cathode membrane 3; anode membrane 4; hydroxide aggregation unit 200; hydrogen ion aggregation unit 300. DETAILED DESCRIPTION

[0043] In order to further explain the technical solution of the present invention, the present invention is described in detail below through specific embodiments.

[0044] Example 1

[0045] This embodiment discloses a method for preparing lactulose by electrolysis, using a device such as Figure 1 As shown, the reaction vessel 100 is also provided with a cation exchange membrane 1 and an anion exchange membrane 2, wherein the cation exchange membrane 1 and the anion exchange membrane 2 are located between the cathode membrane 3 and the anode membrane 4, the space between the cation exchange membrane 1 and the side wall of the reaction vessel 100 surrounding the cathode membrane 4 is a hydroxyl aggregation unit 200, and the space between the anion exchange membrane 2 and the side wall of the reaction vessel 100 surrounding the anode membrane 4 is a hydrogen ion aggregation unit 300.

[0046] The method for preparing lactulose by electrolysis in this embodiment comprises the following steps:

[0047] S1. Electrolyzed water

[0048] The DC power supply is powered on, and the hydrogen ions and hydroxyl radicals generated by the anode membrane connected to the positive electrode of the DC power supply and the cathode membrane connected to the negative electrode of the DC power supply are respectively enriched in the anode membrane and cathode membrane areas, and the solution is electrolyzed until the pH of the solution on one side of the hydroxyl aggregation unit is 14.0; the electrolysis is stopped;

[0049] In the initial stage of electrolysis, the electrolyte on the cathode membrane and the cation exchange membrane side is 0.01 mmol / L KOH; the electrolyte on the anode membrane and the anion exchange membrane side is 0.01 mmol / L hydrochloric acid.

[0050] The process parameters of direct current water electrolysis in step S1 are:

[0051] The working voltage is 10V;

[0052] S2, lactose and montmorillonite / chitosan / Al(OH)3 complex are added to one side of the hydroxyl aggregation unit, wherein the montmorillonite / chitosan / Al(OH)3 complex is converted into montmorillonite / chitosan / Al(OH)4 in alkali solution. - ; The mass fraction of the lactose solution to be converted is 20%; the mass ratio of the montmorillonite / chitosan / Al(OH)3 complex to lactose added to the lactose solution is 1:1.

[0053] S3, stirring, lactose is converted into lactulose, the pH value of the solution of the hydroxyl aggregation unit is reduced to 7.5 and below, at the same time, montmorillonite / chitosan / Al (OH) 4 - converted into montmorillonite / chitosan / Al(OH)3 composite;

[0054] In step S3, montmorillonite and chitosan adsorb lactose molecules to the Al(OH)4 - nearby.

[0055] S4, filtering the material on one side of the hydroxide aggregation unit, separating the solution from the solid montmorillonite / chitosan / Al(OH)3 complex, and obtaining a mixed solution of lactose and lactulose;

[0056] The montmorillonite / chitosan / Al(OH)3 complex obtained by filtration in step S4 is washed in a deionized water solution, dried, and then put back into step S2.

[0057] S5. Separate the obtained lactose and lactulose mixed solution through a membrane, the conductivity of the lactulose solution after membrane separation is 50 μs / cm, and crystallize and dry to obtain lactulose.

[0058] The preparation method of the montmorillonite / chitosan / Al(OH)3 composite in this embodiment comprises the following steps:

[0059] S111, dispersing montmorillonite with deionized water at room temperature, stirring for 6 hours to swell the montmorillonite;

[0060] The dosage ratio of montmorillonite to deionized water in S111 is 0.05:1.

[0061] S112, adding the montmorillonite swollen by S111 to the chitosan / chelated Al solution with a pH of 5.0 3+ Solution; Chitosan and montmorillonite in acidic solution adsorb each other through electrostatic interaction, chitosan / chelated Al 3+ The intercalation layer is distributed between the layers of montmorillonite;

[0062] The mass ratio of chitosan to montmorillonite in S112 is 3:1;

[0063] The stirring time for the assembly of chitosan and montmorillonite was 4 hours.

[0064] S113. Adjust the pH value of the solution to 7.5, centrifuge, wash, and dry to obtain a montmorillonite / chitosan / Al(OH)3 composite.

[0065] The infrared spectrum of the composite obtained in this example is as follows Figure 2 As shown in the figure, the montmorillonite / chitosan / Al(OH)3 composite prepared in this example has a -1 Al-OH stretching vibration at 1039 cm -1 The Si-O-Si stretching vibration at 2930 cm -1 The asymmetric stretching vibration of -CH3 and -CH2 at 1600 cm -1 The stretching vibration absorption peak of -NH3 at the position moves to the low-wave direction, and the absorption intensity is significantly enhanced, indicating that the chitosan intercalation enters the interlayer of montmorillonite. + A strong electrostatic interaction was generated with the negative ions between the montmorillonite layers, thereby achieving the assembly of the complex and obtaining a complex catalyst for catalyzing the conversion of lactose into lactulose.

[0066] In this embodiment, chitosan / chelated Al 3+ The preparation method comprises the following steps:

[0067] A1, dissolving chitosan in acetic acid solution to obtain a chitosan solution;

[0068] AlCl3·6H2O was dissolved in anhydrous ethanol / deionized water mixture at room temperature, wherein the volume ratio of anhydrous ethanol to deionized water was 2:1, to obtain an AlCl3 solution;

[0069] A2. Add AlCl3 solution dropwise into chitosan acetic acid solution and adjust the pH value of the mixture to 5.0; wherein the mass ratio of chitosan to AlCl3·6H2O is 1:1; stir evenly and let stand for 1 hour to obtain aluminum ions chelated in the chitosan solution.

[0070] The deacetylation degree of chitosan used in this embodiment is 80%.

[0071] Example 2

[0072] The differences in process parameters between this embodiment and embodiment 1 regarding a method for preparing lactulose by electrolysis are shown in Table 1, and the differences in preparation of montmorillonite / chitosan / Al(OH)3 composites are shown in Table 2.

[0073] Example 3

[0074] The differences in process parameters between this embodiment and embodiment 1 regarding a method for preparing lactulose by electrolysis are shown in Table 1, and the differences in preparation of montmorillonite / chitosan / Al(OH)3 composites are shown in Table 2.

[0075] Example 4

[0076] The differences in process parameters between this embodiment and embodiment 1 regarding a method for preparing lactulose by electrolysis are shown in Table 1, and the differences in preparation of montmorillonite / chitosan / Al(OH)3 composites are shown in Table 2.

[0077] Example 5

[0078] The differences in process parameters between this embodiment and embodiment 1 regarding a method for preparing lactulose by electrolysis are shown in Table 1, and the differences in preparation of montmorillonite / chitosan / Al(OH)3 composites are shown in Table 2.

[0079] Table 1 Process parameters for preparing lactulose by electrolysis in Examples 1 to 5

[0080]

[0081] Table 2 Process parameters for preparing montmorillonite / chitosan / Al(OH)3 composites in Examples 1 to 5

[0082]

[0083] Comparative Example 1

[0084] This comparative example discloses a method for converting lactose into lactulose using sodium aluminate as a catalyst, comprising the following steps:

[0085] Step 1: Lactose isomerization:

[0086] Sodium aluminate was added to a 20% lactose solution, and the content of [Al(OH)4]- The mass ratio of the lactose substrate is the same as that in Example 1, and sodium hydroxide is added, and the pH value of the reaction system is adjusted to 14.0, and then stirred at 60° C. for 3 hours; after the reaction is completed, the reaction system is cooled to room temperature to obtain isomerized lactulose syrup;

[0087] Step 2: Acidity adjustment:

[0088] Under stirring conditions, adding an acidic substance to the isomerized lactulose syrup obtained in step 1, and adjusting the pH value of the system to 7.5, to obtain a mixed solution containing an aluminum hydroxide flocculation precipitation system;

[0089] Step 3: Dilution, dispersion and separation:

[0090] Adding 10 times the volume of water as that of the reaction solution to the mixed solution containing the aluminum hydroxide flocculation precipitation system obtained in step 2, stirring to disperse the aluminum hydroxide flocculation precipitation system into aluminum hydroxide particles, and separating the residue from the liquid to obtain a lactulose clear solution and an aluminum hydroxide precipitate;

[0091] Step 4: Purification of lactulose serum:

[0092] The lactulose clear solution obtained in step three is desalted and demonosaccharide-removed by using a nanofiltration membrane to obtain a high-purity lactulose solution; the molecular weight cutoff of the nanofiltration membrane is between 100 and 300 Da.

[0093] Comparative Example 2

[0094] This comparative example discloses a method for converting chitosan / Al(OH)3 complex into chitosan / Al(OH4 - The method for preparing lactulose, the preparation device used in this comparative example is the same as that in Example 1, and the specific preparation method comprises the following steps:

[0095] S1. Electrolyzed water

[0096] The DC power supply is powered on, and the hydrogen ions and hydroxyl radicals generated by the anode membrane connected to the positive electrode of the DC power supply and the cathode membrane connected to the negative electrode of the DC power supply are respectively enriched in the anode membrane and cathode membrane areas, and the solution is electrolyzed until the pH of the solution on one side of the hydroxyl aggregation unit is 14.0; the electrolysis is stopped;

[0097] In the initial stage of electrolysis, the electrolyte on the cathode membrane and the cation exchange membrane side is 0.01 mmol / L KOH; the electrolyte on the anode membrane and the anion exchange membrane side is 0.01 mmol / L hydrochloric acid.

[0098] The process parameters of direct current water electrolysis in step S1 are:

[0099] The working voltage is 10V;

[0100] S2, adding lactose and chitosan / chelated Al2O3 prepared in Example 1 to one side of the hydroxyl aggregation unit 3+ Chitosan / Al(OH)3 complex was obtained by vacuum drying at 60℃ for 2 hours. The chitosan / Al(OH)3 complex was converted into montmorillonite / chitosan / Al(OH)4 in alkali solution. - ;

[0101] The mass fraction of the lactose solution to be converted is 20%.

[0102] The mass ratio of chitosan / Al(OH)3 complex to lactose added is the same as that in Example 1.

[0103] S3, stirring, lactose is converted into lactulose, the pH value of the solution of the hydroxyl aggregation unit is reduced to 7.5 and below, at the same time, chitosan / Al (OH) 4 - converted into montmorillonite / chitosan / Al(OH)3 composite;

[0104] In step S3, chitosan adsorbs lactose molecules to the Al(OH)4 - nearby.

[0105] S4, filtering the material on one side of the hydroxide aggregation unit, separating the solution from the solid chitosan / Al(OH)3 complex, and obtaining a mixed solution of lactose and lactulose;

[0106] The chitosan / Al(OH)3 complex obtained by filtration in step S4 is washed in a deionized water solution, dried, and then put back into step S2.

[0107] S5. Separate the obtained lactose and lactulose mixed solution through a membrane, the conductivity of the lactulose solution after membrane separation is 50 μs / cm, and crystallize and dry to obtain lactulose.

[0108] The conversion rates of lactulose obtained in Examples 1 to 5 and Comparative Examples 1 and 2 and the purity of lactulose obtained by crystallization were tested respectively as shown in Table 3. The recovery rates of montmorillonite / chitosan / Al(OH)3 complex in Examples 1 to 5, the recovery rate of Al(OH)3 in Comparative Example 1 and the recovery rate of chitosan / Al(OH)3 complex in Comparative Example 2 are shown in Table 3.

[0109] Table 3 Conversion rate, purity and catalyst recovery rate of lactulose preparation

[0110]

[0111] Compared with Comparative Examples 1 and 2, the present invention prepares lactulose by isomerizing lactose using a chitosan / Al(OH)3 complex dispersed by montmorillonite and enriching hydroxide generated by electrolysis of water, wherein the electrolysis reaction formula of the cathode membrane and the anode membrane is as follows:

[0112] Cathode: 2H2O+2e→H2↑+2OH - ;

[0113] Anode: 2H2O-4e→O2↑+4H + ;

[0114] Montmorillonite and chitosan dispersed uniformly in the montmorillonite work together to adsorb lactose molecules on the Al(OH)4 as the catalytic center converted by Al(OH)3. - Nearby, lactose molecules effectively contact with the catalytic center, improving the rearrangement efficiency of lactose and significantly improving production efficiency. When the pH value of one side of the lactose solution drops from the initial high value to about 7.5, the reaction ends and the conversion rate can reach 73% to 81%. As the pH value decreases, the catalytic center Al(OH)4 - Al(OH)3 is formed again and separated synchronously with montmorillonite and chitosan. The present invention enriches hydroxide to a concentration suitable for lactose by electrolyzing water in combination with an anodic membrane, thereby reducing the work of material transfer and quantitative analysis, and the catalytic center Al(OH)4 immobilized by montmorillonite and chitosan - The probability of contact with lactose molecules is high, which effectively improves the catalytic efficiency; at the same time, the complex is easy to recycle, clean and reuse; and the montmorillonite / chitosan / Al (OH) 3 complex has a stable structure, is easy to use and recycle, has low self-loss, and can maintain a stable catalytic efficiency. The present invention uses montmorillonite to reduce the degree of cross-linking between chitosan molecules in the chitosan / Al (OH) 3 complex dispersed in montmorillonite, that is, the hydrophilicity of montmorillonite itself is used in combination with the cross-linking of chitosan under alkaline conditions to ensure that the structure of the complex is stable and can adapt to the effect of suction filtration, and at the same time, sufficient pores suitable for water molecules to pass through are constructed, which promotes the contact between lactose and the catalytic center during the conversion of lactose, promotes the improvement of the conversion rate, and in the separation process, cooperates with suction filtration to ensure the full separation of the liquid phase and the solid phase.

Claims

1. A method for preparing lactulose by electrolysis, characterized in that: The following steps are involved: S1. Electrolyzed water The DC power supply is powered on, and the hydrogen ions and hydroxides generated by the anode membrane connected to the positive electrode of the DC power supply and the cathode membrane connected to the negative electrode of the DC power supply are respectively enriched in the anode membrane and the cathode membrane area, and the solution is electrolyzed until the pH of the solution on one side of the hydroxide aggregation unit is 14.0 to 14.8; the electrolysis is stopped; S2, a montmorillonite / chitosan / Al(OH)3 complex is added to one side of the hydroxide aggregation unit, wherein lactose and the montmorillonite / chitosan / Al(OH)3 complex are converted into montmorillonite / chitosan / Al(OH)4 in an alkaline solution. - ; The preparation method of montmorillonite / chitosan / Al(OH)3 composite comprises the following steps: S111, dispersing montmorillonite using deionized water at room temperature to swell the montmorillonite; S112, adding the montmorillonite swollen by S111 to the chitosan / chelated Al solution with a pH of 5.0 to 5.5 3+ Solution; In acidic solution, chitosan and montmorillonite adsorb each other through electrostatic interaction, chitosan / chelated Al 3+ The intercalation layer is distributed between the layers of montmorillonite; S113, adjusting the pH value of the solution to 7.0 to 7.5, centrifuging, washing, and drying to obtain a montmorillonite / chitosan / Al(OH)3 composite; S3, stirring, lactose is converted into lactulose, the pH value of the solution of the hydroxyl aggregation unit is reduced to 7.5 and below, at the same time, montmorillonite / chitosan / Al (OH) 4 - converted into montmorillonite / chitosan / Al(OH)3 composite; S4, filtering the material on one side of the hydroxide aggregation unit, separating the solution from the solid montmorillonite / chitosan / Al(OH)3 complex, and obtaining a mixed solution of lactose and lactulose; S5, separating the obtained lactose and lactulose mixed solution through a membrane, crystallizing, and drying to obtain lactulose; Chitosan / chelated Al 3+ The preparation method comprises the following steps: A1, dissolving chitosan in acetic acid solution to obtain a chitosan solution; AlCl3·6H2O was dissolved in anhydrous ethanol / deionized water mixture at room temperature, wherein the volume ratio of anhydrous ethanol to deionized water was 2:1, to obtain an AlCl3 solution; A2. Add AlCl3 solution dropwise into chitosan acetic acid solution, and adjust the pH value of the mixture to 5.0 to 5.5; stir evenly, and let stand for 1 to 2 hours to obtain aluminum ions chelated in the chitosan solution.

2. The method for preparing lactulose by electrolysis according to claim 1, characterized in that: In step S3, montmorillonite and chitosan adsorb lactose molecules to the Al(OH)4 - nearby.

3. The method for preparing lactulose by electrolysis according to claim 1, characterized in that: The dosage ratio of montmorillonite and deionized water in S111 is (0.05 to 0.1):

1.

4. The method for preparing lactulose by electrolysis according to claim 1, characterized in that: The mass ratio of chitosan to montmorillonite in S112 is (3 to 6):1; The stirring time for assembling chitosan and montmorillonite is 4 to 8 hours.

5. The method for preparing lactulose by electrolysis according to claim 1, characterized in that: The process parameters of direct current water electrolysis in step S1 are: The operating voltage is 10V to 15V.

6. The method for preparing lactulose by electrolysis according to claim 1, characterized in that: The mass ratio of montmorillonite / chitosan / Al(OH)3 complex to lactose added to the lactose solution is 1:(1 to 1.3).

7. The method for preparing lactulose by electrolysis according to claim 1, characterized in that: A cation exchange membrane and an anion exchange membrane are also arranged in the reaction container, wherein the cation exchange membrane and the anion exchange membrane are located between the cathode membrane and the anode membrane, the space between the cation exchange membrane and the side wall of the reaction container surrounding the cathode membrane is a hydroxyl aggregation unit, and the space between the anion exchange membrane and the side wall of the reaction container surrounding the anode membrane is a hydrogen ion aggregation unit.

8. The method for preparing lactulose by electrolysis according to claim 1, characterized in that: The montmorillonite / chitosan / Al(OH)3 complex obtained by filtration in step S4 is washed in a deionized water solution, dried, and then put back into step S2.

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