CN116003485B - Preparation method of lactulose - Google Patents

Abstract

The invention discloses a preparation method of lactulose, which includes the following steps: S1, prepare a lactose solution; S2, add boric acid to the lactose solution of S1, and the reaction solution performs lactose isomerization; S3, add acid to dissolve tetrahydroxyboron ions Complexation with lactulose; S4, add mannitol to the solution of S2, and the mannitol forms a complex with boron; S5, add graphene oxide evenly dispersed in deionized water; with stirring, the flakes are oxidized The hydroxyl groups on the graphene surface form hydrogen bonds with the mannitol-boron complex and tetrahydroxyboron ions to form agglomeration; filter and separate the graphene oxide agglomerates with boron captured; S6, remove the graphene oxide-boron material The target lactulose is obtained by sequentially desalting and removing unisomerized lactose; the present invention uses boric acid to selectively complex to obtain isomerized lactose, while effectively recovering boric acid and reducing boron separation costs.

Description

A kind of preparation method of lactulose

Technical field

The present invention relates to the technical field of lactulose preparation, and in particular to a preparation method of lactulose.

Background technique

Chemical isomerization is a common way to produce lactulose. After reducing lactose is heat treated under alkaline conditions, the glucose on the lactose unit undergoes LA rearrangement and is directly isomerized into fructose, thereby producing lactulose. There are many types of alkaline catalysts used in chemical isomerization methods, including NaOH, Ca(OH) ₂ , strong organic base tertiary amines as composite catalysts such as Al ₂ O ₃ and Na ₂ CO ₃ , tertiary amine composite boric acid and H ₃ BO ₃ /NaOH, NaAlO ₂ system and other complex catalysts.

The problem with the existing technology is that the large amount of soluble catalysts is used, which on the one hand easily leads to the occurrence of side reactions. At the same time, the reaction system contains a large amount of salt, which makes the separation and purification of lactulose more difficult.

Contents of the invention

The object of the present invention is to provide a method for preparing lactulose. The present invention utilizes selective complexation of boric acid to prepare isomerized lactose, while effectively recovering boric acid and reducing the cost of boron separation.

In order to solve this technical problem, the technical solution of the present invention is: a preparation method of lactulose, including the following steps:

S1. Prepare lactose solution, the lactose concentration is (30g to 50g)/100ml;

S2. Add boric acid to the lactose solution in S1. The dosage of boric acid is (4g to 5g)/100ml;

The reaction solution undergoes lactose isomerization. The process conditions for isomerization are as follows:

The pH value of lactose solution is 9 to 11;

The reaction temperature is 70°C to 90°C;

The reaction time is 100min to 140min;

S3. Add acid to the isomerized reaction solution of S2 to adjust the pH value of the solution to 2.2 to 2.8 to release the complexation of tetrahydroxyboron ions and lactulose;

S4. Add mannitol to the solution of S2, and the mannitol forms a complex with boron;

S5. Add graphene oxide evenly dispersed in deionized water to the material passing through S4 step by step;

With stirring, the hydroxyl groups on the surface of the flake graphene oxide form hydrogen bonds with the mannitol-boron complex and tetrahydroxyboron ions, and the flake graphene oxide bonds to capture the mannitol-boron complex and tetrahydroxyboron ions. Boron ions, and further agglomerates in contact with the surrounding sheet graphene oxide connected with mannitol-boron complex and tetrahydroxyboron ions;

Filter and separate the graphene oxide agglomerates with boron captured;

S6. Desalt and remove unisomerized lactose from the graphene oxide-boron material in order to obtain the target lactulose;

The materials that pass through S5 are passed through an ion exchange resin to remove salts and through a primary boron selective adsorption resin to remove boron.

The preferred mass ratio of graphene oxide and boric acid is (2.1 to 2.2):1. The invention ensures that graphene oxide can effectively capture boric acid.

Preferably, recovering the graphene oxide-mannitol-boron complex and graphene oxide-tetrahydroxyboron ions separated and collected by S5 includes the following steps:

S51. Clean the graphene oxide-mannitol-boron complex and graphene oxide-tetrahydroxyboron ions and then dry them;

S52. Heat-treat the graphene oxide-mannitol-boron complex and graphene oxide-tetrahydroxyboron ions obtained in S51 under an inert gas. The boron in the mannitol-boron complex and tetrahydroxyboron ion Loss of water molecules converts into B2O3;

S53 and B ₂ O ₃ melt during the heating process; at the same time, the oxygen-containing functional groups of graphene oxide decompose to generate water molecules and carbon dioxide, and the molten boron is bonded to the graphene.

In the present invention, tetrahydroxyboron ions complexed with graphene oxide are embedded into the graphene oxide during the heating process.

Part of the graphene oxide/graphene obtained through the above recovery is doped with B or bonded with graphene oxide/graphene with B ₂ O ₃ to effectively ensure the constant B. In order to further ensure the complete and effective utilization of the obtained B element, the graphite oxide is The mixture of graphene, graphene and B ₂ O ₃ is ground, and the heat treatment temperature of S52 is increased to 800 to 1000°C. Part of the oxygen-containing groups of graphene oxide is decomposed and reduced to graphene, and the mixture of graphene and boric acid crystals is quenched at high temperature. To the molten state, along with heat preservation, boron atoms diffuse and connect to graphene and form a sheet structure with graphene to form a graphene-B ₂ O ₃ catalyst that can be used repeatedly. The catalyst connected to graphene-B ₂ O ₃ is used Alcohol washing separation enables direct reuse of graphene-B ₂ O ₃ catalyst.

In order to improve the catalytic performance of the graphene-B ₂ O ₃ catalyst, B ₂ O ₃ can be added according to actual needs to improve the catalytic performance of the catalyst.

The preferred process conditions for S52 heat treatment are:

Ar gas atmosphere;

Temperature is 680℃ to 750℃;

The time is 3 hours to 6 hours.

Preferably, the graphene-B ₂ O ₃ prepared in S53 is put into the lactose solution of S1, and the graphene-B ₂ O ₃ is converted into graphene-B(OH) ₄ ^- and recycled as a catalyst for lactose isomerization. The invention utilizes graphene oxide and boric acid to bond and capture to effectively realize the recovery of boric acid without affecting the reuse of boric acid.

It is preferred that the target lactose solution obtained in S6 be concentrated under reduced pressure at 55°C to 75°C to a concentration of 70% to 80%, cooled to 45°C, add seed crystals, naturally cool down and stir for crystallization, the stirring rate is 30 rpm, crystallize for 24 hours, and centrifuge. Experience lactulose solids.

The present invention now separates tetrahydroxyboron ions from the isomerization reaction system to facilitate subsequent purification of lactulose.

Preferably, S6 desalination is to pass the materials that have passed S5 through an ion exchange resin to remove salts and through a primary boron selective adsorption resin to remove boron, which includes sulfuric acid used to release the boric acid-lactulose complex.

It is preferred that the sulfuric acid recovered through S6 is passed into S3 for recycling. The invention realizes the reuse of sulfuric acid and reduces the use of acidic substances.

Preferably, the method for removing unisomerized lactose in S6 is as follows:

S61. Pass the materials that have passed through S5 to the first group of moving beds to separate lactose;

S62. Pass the material passing through S61 into the second set of moving beds to separate miscellaneous sugars;

Get target lactulose.

The preferred method of filtering the graphene oxide agglomerate capturing the mannitol-boron complex and tetrahydroxyboron ions is suction filtration. During the suction filtration process, the present invention utilizes the aggregation of flake graphene oxide to delay the relative flow rate between graphene oxide and boron, thereby promoting more tetrahydroxyboron ions or mannitol-boron complexes to flow through the graphene oxide. On the surface, the relative distance between the two substances that undergo hydrogen bonding interaction is shortened, the formation of hydrogen bonds is easier, and graphene oxide effectively captures boron.

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

The present invention uses boric acid as a catalyst for lactose isomerization, and utilizes boric acid and lactulose to form a complex to effectively inhibit the occurrence of side reactions. The lactulose molecule contains a furan six-membered ring and a pyran six-membered ring, and the furan ring has The cis-di-ortho-hydroxyl complexes with tetrahydroxyboron ions in an alkaline environment. The principle of complexation is as follows:

Tetrahydroxyboron ions effectively capture the isomerized lactulose and improve the degree of forward reaction of lactulose; however, a problem in the existing technology is that boric acid is difficult to separate from the reaction materials, and resin needs to be used for separation. Separation is similar to filtration. Since the resin has a certain limit to the acidic tolerance of the solution, in order to protect the resin during the process of using the resin to absorb boron, the pH value of the material must be greater than 3.0. There is still a part of the boron complexed with lactulose, which affects the lactulose. Separation of fructose and prone to boron contamination.

In the present invention, under alkali catalysis, when lactose isomerization is completed, tetrahydroxyboron ions are complexed with lactulose, and acid is added to the reacted material system to adjust the pH value of the liquid environment to 2.2 to 2.8. The complex of boron ions and lactulose is fully separated; at this time, graphene oxide evenly dispersed in deionized water is added to the system. With stirring, the surface of GO has sufficient hydroxyl groups, and the GO has a lamellar structure to form a network-like structure. Capture tetrahydroxyboron ions in a liquid environment. However, the tetrahydroxyboron ions at this time will be reversely hydrolyzed and converted into boric acid because the pH value of the system is 2.2 to 2.8. That is, the tetrahydroxyboron ions cannot be used alone to directly interact with oxidation. Graphene forms hydrogen bonds, so mannitol is added to the system while adding acid to decomplex, and the following complexation reaction occurs between boric acid and mannitol using the dynamic process of decomplexing mannitol with tetrahydroxyboron ions;

In response to the existence of the above-mentioned mannitol-boron complex, graphene oxide and tetrahydroxyboron ions directly form hydrogen bonds or graphene oxide and the mannitol-boron complex are connected through mannitol's hydrogen bonds; boron is flake-shaped. GO captures, boron-captured GO continues to further capture the surrounding graphene oxide that has captured boron through mannitol-boron complex or tetrahydroxyboron ions. The originally dispersed graphene oxide is equivalent to capturing boron. The number of hydroxyl groups on the surface further increases, and obvious agglomeration occurs with stirring;

The graphene oxide of the present invention captures, enriches and separates boron from the system. The distribution of the graphene oxide is captured in micro-areas in the entire liquid environment, the separation is complete, and it is easy to filter and separate from the system;

Among them, mannitol used to complex with boron is decomposed and removed during high-temperature treatment, and the recovered B can be recycled into the lactose isomerization reaction for reuse;

On the premise of using boric acid to improve the conversion rate of lactulose and suppressing side reactions, the present invention uses graphene oxide to bond with boric acid under acidic conditions to facilitate the recovery of boric acid.

Detailed ways

In order to further explain the technical solution of the present invention, the present invention will be described in detail below through specific examples.

Example 1

This embodiment discloses a preparation method of lactulose, which includes the following steps:

S1. Prepare 30g/100ml lactose solution;

S2. Add boric acid to the lactose solution in S1. The amount added is 4g/100ml; the solution undergoes lactose isomerization reaction. The process conditions of isomerization are as follows:

The pH value of lactose solution is 9;

The reaction temperature is 70°C;

The reaction time is 100min;

S3. Add acid to the isomerized reaction solution of S2 to adjust the pH value of the solution to 2.2 to release the complexation of tetrahydroxyboron ions and lactulose;

S4. While adding acid, add mannitol to the solution of S2. The mannitol forms a complex with boron; the dosage of mannitol is 3g/100ml;

S5. Add graphene oxide evenly dispersed in deionized water to the material passing through S4 step by step;

Graphene oxide 8.4g/100ml.

With stirring, the hydroxyl groups on the surface of the flake graphene oxide form hydrogen bonds with the mannitol-boron complex and tetrahydroxyboron ions, and the flake graphene oxide bonds to capture the mannitol-boron complex and tetrahydroxyboron ions. Boron ions, and further agglomerates in contact with the surrounding sheet graphene oxide connected with mannitol-boron complex and tetrahydroxyboron ions;

Recycling the graphene oxide-mannitol-boron complex and graphene oxide-tetrahydroxyboron ions separated and collected by S5 includes the following steps:

S51. Clean the graphene oxide-mannitol-boron complex and graphene oxide-tetrahydroxyboron ions and then dry them;

S52. Heat-treat the graphene oxide-mannitol-boron complex and graphene oxide-tetrahydroxyboron ions obtained in S51 under an inert gas. The boron in the mannitol-boron complex and tetrahydroxyboron ion Loss of water molecules converts into B ₂ O ₃ ;

The process conditions of S52 heat treatment are:

Ar gas atmosphere;

The temperature is 720℃;

The time is 4 hours.

S53 and B ₂ O ₃ melt during the heating process; at the same time, the oxygen-containing functional groups of graphene oxide decompose to generate water molecules and carbon dioxide, and the molten boron is bonded to the graphene.

Separate the graphene oxide agglomerates captured with mannitol-boron complex and tetrahydroxyboron ions by suction filtration;

The graphene-B ₂ O ₃ prepared in S53 is put into the lactose solution of S1, and the graphene-B ₂ O ₃ is converted into graphene-B(OH) ₄ ^- and recycled as a catalyst for lactose isomerization.

S6. Remove the salt and unisomerized lactose from the material from which the mannitol-boron complex is removed, respectively, to obtain the target lactulose.

S6. Pass the material from which GO captures and removes boron into an anion exchange resin column and a cation exchange resin column to remove sodium sulfate, and then remove boron through a boron selective adsorption resin;

Then the unisomerized lactose is removed to obtain the target lactulose.

The sulfuric acid recovered through S6 is passed into S3 for recycling.

The method for removing unisomerized lactose in S6 is as follows:

S61. Pass the materials that have passed through S5 to the first group of moving beds to separate lactose;

S62. Pass the material passing through S61 into the second set of moving beds to separate miscellaneous sugars;

Get target lactulose.

The target lactose solution obtained in S5 is concentrated under reduced pressure at 55°C to a concentration of 70%, cooled to 45°C, seed crystals are added, the temperature is naturally cooled and the mixture is stirred for crystallization at a stirring rate of 30 rpm, crystallized for 24 hours, and centrifuged to obtain lactulose solid.

Example 2

This embodiment discloses a preparation method of lactulose, which includes the following steps:

S1. Prepare 40g/100ml lactose solution;

S2. Add boric acid to the lactose solution in S1, the amount added is 5g/100ml; the solution undergoes lactose isomerization reaction. The process conditions of isomerization are as follows:

The pH value of lactose solution is 10;

The reaction temperature is 70°C;

The reaction time is 120min;

S3. Add acid to the isomerized reaction solution of S2 to adjust the pH value of the solution to 2.4 to release the complexation of tetrahydroxyboron ions and lactulose;

S4. While adding acid, add mannitol to the solution of S2. The mannitol forms a complex with boron; the dosage of mannitol is 3.3g/100ml;

S5. Add graphene oxide evenly dispersed in deionized water to the material passing through S4 step by step; 11g/100ml of graphene oxide.

With stirring, the hydroxyl groups on the surface of the flake graphene oxide form hydrogen bonds with the mannitol-boron complex and tetrahydroxyboron ions, and the flake graphene oxide bonds to capture the mannitol-boron complex and tetrahydroxyboron ions. Boron ions, and further agglomerates in contact with the surrounding sheet graphene oxide connected with mannitol-boron complex and tetrahydroxyboron ions;

Recycling the graphene oxide-mannitol-boron complex and graphene oxide-tetrahydroxyboron ions separated and collected by S5 includes the following steps:

S51. Clean the graphene oxide-mannitol-boron complex and graphene oxide-tetrahydroxyboron ions and then dry them;

S52. Heat-treat the graphene oxide-mannitol-boron complex and graphene oxide-tetrahydroxyboron ions obtained in S51 under an inert gas. The boron in the mannitol-boron complex and tetrahydroxyboron ion Loss of water molecules converts into B ₂ O ₃ ;

The process conditions of S52 heat treatment are:

Ar gas atmosphere;

The temperature is 680℃;

The time is 3 hours.

S53 and B ₂ O ₃ melt during the heating process; at the same time, the oxygen-containing functional groups of graphene oxide decompose to generate water molecules and carbon dioxide, and the molten boron is bonded to the graphene.

Separate the graphene oxide agglomerates captured with mannitol-boron complex and tetrahydroxyboron ions by suction filtration;

The graphene-B ₂ O ₃ prepared in S53 is put into the lactose solution of S1, and the graphene-B ₂ O ₃ is converted into graphene-B(OH) ₄ ^- and recycled as a catalyst for lactose isomerization.

S6. Remove the salt and unisomerized lactose from the material from which the mannitol-boron complex is removed, respectively, to obtain the target lactulose.

S6. Pass the material from which GO captures and removes boron into an anion exchange resin column and a cation exchange resin column to remove sodium sulfate, and then remove boron through a boron selective adsorption resin;

Then the unisomerized lactose is removed to obtain the target lactulose.

The sulfuric acid recovered through S6 is passed into S3 for recycling.

The method for removing unisomerized lactose in S6 is as follows:

S61. Pass the materials that have passed through S5 to the first group of moving beds to separate lactose;

S62. Pass the material passing through S61 into the second set of moving beds to separate miscellaneous sugars;

Get target lactulose.

The target lactose solution obtained in S5 was concentrated under reduced pressure at 65°C to a concentration of 80%, cooled to 45°C, seed crystals were added, and the temperature was naturally cooled and stirred for crystallization at a stirring rate of 30 rpm, crystallized for 24 hours, and centrifuged to obtain lactulose solid.

Example 3

This embodiment discloses a preparation method of lactulose, which includes the following steps:

S1. Prepare 50g/100ml lactose solution;

S2. Add boric acid to the lactose solution in S1. The amount added is 4g/100ml; the solution undergoes lactose isomerization reaction. The process conditions of isomerization are as follows:

The pH value of lactose solution is 11;

The reaction temperature is 70°C;

The reaction time is 140min;

S3. Add acid to the isomerized reaction solution of S2 to adjust the pH value of the solution to 2.6 to release the complexation of tetrahydroxyboron ions and lactulose;

S4. While adding acid, add mannitol to the solution of S2. The mannitol forms a complex with boron; the dosage of mannitol is 3.1g/100ml;

S5. Add graphene oxide evenly dispersed in deionized water to the material passing through S4 step by step;

Graphene oxide 8.8g/100ml.

With stirring, the hydroxyl groups on the surface of the flake graphene oxide form hydrogen bonds with the mannitol-boron complex and tetrahydroxyboron ions, and the flake graphene oxide bonds to capture the mannitol-boron complex and tetrahydroxyboron ions. Boron ions, and further agglomerates in contact with the surrounding sheet graphene oxide connected with mannitol-boron complex and tetrahydroxyboron ions;

Recycling the graphene oxide-mannitol-boron complex and graphene oxide-tetrahydroxyboron ions separated and collected by S5 includes the following steps:

S51. Clean the graphene oxide-mannitol-boron complex and graphene oxide-tetrahydroxyboron ions and then dry them;

S52. Heat-treat the graphene oxide-mannitol-boron complex and graphene oxide-tetrahydroxyboron ions obtained in S51 under an inert gas. The boron in the mannitol-boron complex and tetrahydroxyboron ion Loss of water molecules converts into B ₂ O ₃ ;

The process conditions of S52 heat treatment are:

Ar gas atmosphere;

The temperature is 750℃;

The time is 6 hours.

S53 and B ₂ O ₃ melt during the heating process; at the same time, the oxygen-containing functional groups of graphene oxide decompose to generate water molecules and carbon dioxide, and the molten boron is bonded to the graphene.

Separate the graphene oxide agglomerates captured with mannitol-boron complex and tetrahydroxyboron ions by suction filtration;

The graphene-B ₂ O ₃ prepared in S53 is put into the lactose solution of S1, and the graphene-B ₂ O ₃ is converted into graphene-B(OH) ₄ ^- and recycled as a catalyst for lactose isomerization.

S6. Pass the material from which GO captures and removes boron into an anion exchange resin column and a cation exchange resin column to remove sodium sulfate, and then remove boron through a boron selective adsorption resin;

Then the unisomerized lactose is removed to obtain the target lactulose.

The sulfuric acid recovered through S6 is passed into S3 for recycling.

The method for removing unisomerized lactose in S6 is as follows:

S61. Pass the materials that have passed through S5 to the first group of moving beds to separate lactose;

S62. Pass the material passing through S61 into the second set of moving beds to separate miscellaneous sugars;

Get target lactulose.

The target lactose solution obtained in S6 is concentrated under reduced pressure at 75°C to a concentration of 70%, cooled to 45°C, seed crystals are added, the temperature is naturally cooled and the mixture is stirred for crystallization at a stirring rate of 30 rpm, crystallized for 24 hours, and centrifuged to obtain lactulose solid.

Example 4

This embodiment discloses a preparation method of lactulose, which includes the following steps:

S1. Prepare 40g/100ml lactose solution;

S2. Add boric acid to the lactose solution in S1, the amount added is 5g/100ml; the solution undergoes lactose isomerization reaction. The process conditions of isomerization are as follows:

The pH value of lactose solution is 10

The reaction temperature is 80°C;

The reaction time is 100min;

S3. Add acid to the isomerized reaction solution of S2 to adjust the pH value of the solution to 2.8 to release the complexation of tetrahydroxyboron ions and lactulose;

S4. While adding acid, add mannitol to the solution of S2. The mannitol forms a complex with boron; the dosage of mannitol is 3.6g/100ml;

S5. Add graphene oxide evenly dispersed in deionized water to the material passing through S4 step by step;

Graphene oxide 10.5g/100ml.

With stirring, the hydroxyl groups on the surface of the flake graphene oxide form hydrogen bonds with the mannitol-boron complex and tetrahydroxyboron ions, and the flake graphene oxide bonds to capture the mannitol-boron complex and tetrahydroxyboron ions. Boron ions, and further agglomerates in contact with the surrounding sheet graphene oxide connected with mannitol-boron complex and tetrahydroxyboron ions;

Recycling the graphene oxide-mannitol-boron complex and graphene oxide-tetrahydroxyboron ions separated and collected by S5 includes the following steps:

S51. Clean the graphene oxide-mannitol-boron complex and graphene oxide-tetrahydroxyboron ions and then dry them;

S52. Heat-treat the graphene oxide-mannitol-boron complex and graphene oxide-tetrahydroxyboron ions obtained in S51 under an inert gas. The boron in the mannitol-boron complex and tetrahydroxyboron ion Loss of water molecules converts into B ₂ O ₃ ;

The process conditions of S52 heat treatment are:

Ar gas atmosphere;

The temperature is 750℃;

The time is 4 hours.

S53 and B ₂ O ₃ melt during the heating process; at the same time, the oxygen-containing functional groups of graphene oxide decompose to generate water molecules and carbon dioxide, and the molten boron is bonded to the graphene.

Separate the graphene oxide agglomerates captured with mannitol-boron complex and tetrahydroxyboron ions by suction filtration;

The graphene-B ₂ O ₃ prepared in S53 is put into the lactose solution of S1, and the graphene-B ₂ O ₃ is converted into graphene-B(OH) ₄ ^- and recycled as a catalyst for lactose isomerization.

S6. Remove the salt and unisomerized lactose from the material from which the mannitol-boron complex is removed, respectively, to obtain the target lactulose.

S6. Pass the material from which GO captures and removes boron into an anion exchange resin column and a cation exchange resin column to remove sodium sulfate, and then remove boron through a boron selective adsorption resin;

Then the unisomerized lactose is removed to obtain the target lactulose.

The sulfuric acid recovered through S6 is passed into S3 for recycling.

The method for removing unisomerized lactose in S6 is as follows:

S61. Pass the materials that have passed through S5 to the first group of moving beds to separate lactose;

S62. Pass the material passing through S61 into the second set of moving beds to separate miscellaneous sugars;

Get target lactulose.

The target lactose solution obtained in S6 was concentrated under reduced pressure at 55°C to a concentration of 80%, cooled to 45°C, seed crystals were added, and the temperature was naturally cooled and stirred for crystallization at a stirring rate of 30 rpm, crystallized for 24 hours, and centrifuged to obtain lactulose solid.

Example 5

This embodiment discloses a preparation method of lactulose, which includes the following steps:

S1. Prepare 30g/100ml lactose solution;

S2. Add boric acid to the lactose solution in S1, the amount added is 4g/100ml; the solution undergoes lactose isomerization reaction.

The process conditions for isomerization are as follows:

The pH value of lactose solution is 9;

The reaction temperature is 90°C;

The reaction time is 120min;

S3. Add acid to the isomerized reaction solution of S2 to adjust the pH value of the solution to 2.8 to release the complexation of tetrahydroxyboron ions and lactulose;

S4. While adding acid, add mannitol to the solution of S2. The mannitol forms a complex with boron; the dosage of mannitol is 3.0g/100ml;

S5. Add graphene oxide evenly dispersed in deionized water to the material passing through S4 step by step;

Graphene oxide 8.4g/100ml.

With stirring, the hydroxyl groups on the surface of the flake graphene oxide form hydrogen bonds with the mannitol-boron complex and tetrahydroxyboron ions, and the flake graphene oxide bonds to capture the mannitol-boron complex and tetrahydroxyboron ions. Boron ions, and further agglomerates in contact with the surrounding sheet graphene oxide connected with mannitol-boron complex and tetrahydroxyboron ions;

Recycling the graphene oxide-mannitol-boron complex and graphene oxide-tetrahydroxyboron ions separated and collected by S5 includes the following steps:

S51. Clean the graphene oxide-mannitol-boron complex and graphene oxide-tetrahydroxyboron ions and then dry them;

S52. Heat-treat the graphene oxide-mannitol-boron complex and graphene oxide-tetrahydroxyboron ions obtained in S51 under an inert gas. The boron in the mannitol-boron complex and tetrahydroxyboron ion Loss of water molecules converts into B ₂ O ₃ ;

The process conditions of S52 heat treatment are:

Ar gas atmosphere;

The temperature is 720℃;

The time is 6 hours.

S53 and B ₂ O ₃ melt during the heating process; at the same time, the oxygen-containing functional groups of graphene oxide decompose to generate water molecules and carbon dioxide, and the molten boron is bonded to the graphene.

Separate the graphene oxide agglomerates captured with mannitol-boron complex and tetrahydroxyboron ions by suction filtration;

The graphene-B ₂ O ₃ prepared in S53 is put into the lactose solution of S1, and the graphene-B ₂ O ₃ is converted into graphene-B(OH) ₄ ^- and recycled as a catalyst for lactose isomerization.

S6. Remove the salt and unisomerized lactose from the material from which the mannitol-boron complex is removed, respectively, to obtain the target lactulose.

S6. Pass the material from which GO captures and removes boron into an anion exchange resin column and a cation exchange resin column to remove sodium sulfate, and then remove boron through a boron selective adsorption resin;

Then the unisomerized lactose is removed to obtain the target lactulose.

The sulfuric acid recovered through S6 is passed into S3 for recycling.

The method for removing unisomerized lactose in S6 is as follows:

S61. Pass the materials that have passed through S5 to the first group of moving beds to separate lactose;

S62. Pass the material passing through S61 into the second set of moving beds to separate miscellaneous sugars;

Get target lactulose.

The target lactose solution obtained in S6 was concentrated under reduced pressure at 65°C to a concentration of 70%, cooled to 45°C, seed crystals were added, and the temperature was naturally cooled and stirred for crystallization at a stirring rate of 30 rpm, crystallized for 24 hours, and centrifuged to obtain lactulose solid.

Comparative ratio

This comparative example uses a preparation method of lactulose disclosed in CN113150042B, and its specific production method is as follows:

The solution for lactose isomerization and the isomerization process conditions are the same as Example 1, specifically as follows:

S1. Prepare 30g/100ml lactose solution;

S2. Add boric acid to the lactose solution in S1, the amount added is 4g/100ml; the solution undergoes lactose isomerization reaction.

The process conditions for isomerization are as follows:

The pH value of lactose solution is 9;

The reaction temperature is 70°C;

The reaction time is 100min;

The obtained material is concentrated and purified through ion exchange. The specific method is as follows:

Pour the lactulose reaction solution (30L) from the storage tank through the pump into the first cation exchange resin - the second boron selective adsorption resin - the third boron selective adsorption resin - the fourth boron selective adsorption resin - the fifth cation exchange resin - For the resin column of the sixth boron selective adsorption resin, after the reaction solution is completed, use purified water to sequentially elute the resin column. Control the elution flow rate of the sixth boron selective adsorption resin column to 2BV/hour; collect the outflow from the sixth boron selective adsorption resin column. For liquids, qualified components are collected according to the conditions of conductivity less than 10μs/cm (20℃) and density 1.001-1.200g/ ^cm3 .

Flame atomic absorption spectrometry was used to indirectly determine the boron concentration in the S5 lactulose solution in Examples 1 to 5, which was C ₀ . The boron content in the lactulose solution before concentration after desalting in Examples 1 to 5 was measured indirectly. The concentration of boron in the lactulose solution obtained in the standard comparative example after passing through the sixth boron selective adsorption resin is C _f . The specific test data are shown in Table 1.

Table 1 Boron content of Examples 1 to 5 and Comparative Examples

project _{CGO f} Example 1 68ppm 1.4ppm Example 2 72ppm 1.5 ppm Example 3 67ppm 1.3ppm Example 4 74ppm 1.6ppm Example 5 66ppm 1.3ppm Comparative ratio / 1.2ppm

Combining the data in Table 1, it can be seen that the present invention uses graphene oxide to capture and enrich boron and separate it from the system. The graphene oxide is distributed in the entire liquid environment for micro-area capture, the separation is complete, and it is easy to filter and separate from the system; and it is used with The boron-complexed mannitol is decomposed and removed during the high-temperature treatment, so that the obtained graphene-B can be put into the lactose isomerization for recycling; on the premise of using boric acid to increase the conversion rate of lactulose and suppress side reactions, the present invention can The use of graphene oxide to bond with boric acid under acidic conditions facilitates the recovery of boric acid, and has a boron removal effect similar to the process of repeatedly using boron selective adsorption resin to remove boron.

Claims (10)

1. A preparation method of lactulose is characterized in that: the method comprises the following steps:

s1, preparing lactose solution with lactose concentration of (30 g to 50 g)/100 ml;

s2, adding boric acid into the lactose solution of S1, wherein the dosage of the boric acid is (4 g to 5 g)/100 ml;

lactose isomerization is carried out on the reaction solution, and the process conditions of the isomerization are as follows:

lactose solution pH 9 to 11;

the reaction temperature is 70 ℃ to 90 ℃;

the reaction time is 100min to 140min;

s3, adding acid into the isomerised reaction solution of S2 to adjust the pH value of the solution to 2.2-2.8, and removing complexation of tetrahydroxy boron ions and lactulose;

s4, mannitol is added into the solution of the S2, and the mannitol and boron form a complex;

s5, adding graphene oxide uniformly dispersed in deionized water into the material passing through the step S4 step by step for multiple times;

with stirring, hydroxyl groups on the surface of the flaky graphene oxide form hydrogen bond connection with mannitol-boron complex and tetrahydroxy boron ions, and the flaky graphene oxide is bonded to capture mannitol-boron complex and tetrahydroxy boron ions and further contacts with surrounding flaky graphene oxide connected with mannitol-boron complex and tetrahydroxy boron ions to generate agglomeration;

filtering and separating the graphene oxide agglomerates captured with boron;

s6, sequentially desalting the graphene oxide-boron removed material and removing non-isomerized lactose to obtain target lactulose;

the desalting in S6 is to subject the material passing through S5 to the desalting through ion exchange resin and the boron removing through primary boron selective adsorption resin.

2. The method of manufacturing according to claim 1, characterized in that:

the mass ratio of graphene oxide to boric acid is (2.1 to 2.2): 1.

3. the method of manufacturing according to claim 1, characterized in that: recovering S5 the graphene oxide-mannitol-boron complex and the graphene oxide-tetrahydroxy boron ion which are separated and collected comprises the following steps:

s51, cleaning the graphene oxide-mannitol-boron complex and graphene oxide-tetrahydroxy boron ions, and drying;

s52, placing the graphene oxide-mannitol-boron complex obtained in S51 and graphene oxide-tetrahydroxy boron ions under inert gas for heat treatment, and converting the boron in the mannitol-boron complex and the tetrahydroxy boron ions into B after losing water molecules ₂ O ₃ ；

S53、B ₂ O ₃ Melting in the heating process; at the same time, the oxygen-containing functional groups of graphene oxide decompose to produce water molecules and carbon dioxide, and the molten boron bonds to the graphene.

4. A method of preparation according to claim 3, characterized in that: the process conditions of the S52 heat treatment are as follows:

an Ar gas atmosphere;

the temperature is 680 ℃ to 750 ℃;

the time is 3 hours to 6 hours.

5. A method of preparation according to claim 3, characterized in that:

graphene-B prepared by S53 ₂ O ₃ Putting into lactose solution of S1, and graphene-B ₂ O ₃ Conversion to graphene-B (OH) ₄ ^- Can be used as a catalyst for lactose isomerization for recycling.

6. The method of manufacturing according to claim 1, characterized in that: concentrating the target lactulose solution obtained in the step S6 at 55-75 ℃ under reduced pressure until the concentration is 70-80%, cooling to 45 ℃, adding seed crystals, naturally cooling, stirring for crystallization, stirring for 30 r/min, crystallizing for 24 h, and centrifuging to obtain lactulose solid.

7. The method of manufacturing according to claim 1, characterized in that: s6, removing salt through ion exchange to remove salt and recovering sulfuric acid for removing boric acid-lactulose complexation.

8. The method of manufacturing according to claim 7, wherein: and (3) introducing the sulfuric acid recovered in the step (S6) into the step (S3) for recycling.

9. The method of manufacturing according to claim 1, characterized in that: the method for removing non-isomerized lactose in S6 is as follows:

s61, respectively introducing the materials subjected to S5 into a first group of moving beds to separate lactose;

s62, introducing the material subjected to S61 into a second group of moving beds to separate the mixed sugar;

obtaining the target lactulose.

10. The method of manufacturing according to claim 1, characterized in that: the mode of filtration of the graphene oxide agglomerates captured with mannitol-boron complexes and tetrahydroxy boron ions is suction filtration.