A method for the separation and purification of lactobionic acid

Abstract

This invention discloses a method for separating and purifying lactobionic acid. The solid catalyst used is nitrogen-doped carbon nanotube-supported titanium dioxide. The preparation method includes the following steps: S1, preparing a chitosan-modified porous carbon nanotube precursor; S2, adding the porous precursor to a titanium dioxide sol and stirring to mix, resulting in a uniform mixture of carbon nanotube-supported chitosan and HNO3 sol with the titanium dioxide sol; S3, heating and stirring the sol obtained in S2 to obtain a gel; S4, calcining the gel obtained in S3 to obtain nitrogen-doped nanotube-supported titanium dioxide. This invention uses nitrogen-doped carbon nanotube-supported titanium dioxide, which effectively increases the probability of titanium dioxide selectively oxidizing lactose to lactobionic acid by adsorbing oxygen and cooperating with the transfer of photogenerated electrons and the activation of oxygen, thus significantly improving the stability and controllability of the production process.

Description

Technical Field

[0001] This invention relates to the field of lactobionic acid separation and purification technology, and in particular to a method for separating and purifying lactobionic acid. Background Technology

[0002] Lactobionic acid has eight hydroxyl groups in its molecular structure, which can bind a large number of water molecules. Its water-binding range extends from the skin's gel matrix to water molecules that vaporize at room temperature, and it can maintain a tightly bound state of hydration for a long time. Its moisturizing effect is far greater than that of glycolic acid, lactic acid, citric acid, and gluconic acid. Experiments have shown that each unit of lactobionic acid can absorb approximately 70g of water, achieving a water retention capacity of 55g. Commonly used moisturizers such as glycerin and sorbitol have lower water retention and absorption capacities than lactobionic acid.

[0003] Lactose is a disaccharide composed of one glucose molecule and one galactose molecule, with the molecular formula C6H2O. 12 H 22 O 11 The structural formula is as follows: When lactose is oxidized into lactobionic acid by biological enzymes...

[0004] Lactobionic acid is composed of one galactose molecule (D-galactose) and one gluconic acid molecule (D-gluconic acid), with the following structural formula:

[0005]

[0006] In existing technologies, lactobionic acid is mostly produced by biological enzyme conversion. During this process, the stability of pH value can interfere with the formation of the target product, lactobionic acid. The yield of lactobionic acid is unstable, which is not conducive to industrial production. Summary of the Invention

[0007] The purpose of this invention is to provide a method for the separation and purification of lactobionic acid. This invention uses nitrogen-doped carbon nanotubes loaded with titanium dioxide. Through oxygen adsorption, combined with the transfer of photogenerated electrons and the activation of oxygen, the probability of titanium dioxide selectively oxidizing lactose to lactobionic acid is effectively increased, significantly improving the stability and controllability of the production process.

[0008] To solve this technical problem, the technical solution of the present invention is: a method for separating and purifying lactobionic acid, comprising the following steps:

[0009] A1. Dissolve analytical grade lactose in deionized water, place it in a reaction vessel, and add a solid catalyst to the reaction system;

[0010] The ratio of lactose to deionized water is (50g to 60g): 1L;

[0011] The ratio of solid catalyst to deionized water is (1g to 3g): 1L;

[0012] The pH of the reaction system after adding sodium hydroxide is 8;

[0013] Turn on ultraviolet radiation;

[0014] Oxygen is introduced until the internal pressure of the reactor is 1.1 MPa to 1.3 MPa, and the reactor is then sealed.

[0015] A2. Heating and oxidation conversion;

[0016] As stirring occurs, the solid catalyst continuously adsorbs O2 dissolved in the aqueous solution onto its surface to convert lactose into lactobionic acid; oxygen from the environment continuously dissolves and enters the liquid phase.

[0017] A3. After the reaction time is reached, use an ice-water mixture to quickly cool the reactor to room temperature and vent the gas.

[0018] A4. Filter out the solid catalyst to obtain the liquid phase material;

[0019] A5. Concentrate under reduced pressure, add sodium carbonate until the material is neutral, add ethanol, centrifuge to crystallize, purify multiple times, filter, and obtain sodium lactobionate.

[0020] The preferred power for ultraviolet irradiation in A1 is 40W to 45W.

[0021] The preferred process conditions for the heating and oxidation conversion in A2 are as follows:

[0022] The reaction temperature is 50℃ to 55℃;

[0023] The reaction time is 30 to 40 minutes.

[0024] In A2, the heating process is preferably combined with intermittent stirring until the reaction time is reached;

[0025] The stirring process parameters are as follows:

[0026] Stir at 500 to 600 rpm for 20 to 30 seconds; let stand for 10 to 20 seconds; repeat this cycle for 30 to 40 minutes.

[0027] The liquid phase material is preferably concentrated under reduced pressure to 25% of the volume of the liquid material obtained in A4, sodium carbonate is added until the material is neutral, and the volume ratio of ethanol to deionized water added in A1 is 0.25:1.

[0028] Preferably, the solid catalyst is titanium dioxide supported on nitrogen-doped carbon nanotubes, and the preparation method of the solid catalyst includes the following steps:

[0029] S1. Preparation of chitosan-modified porous carbon nanotube precursors;

[0030] S2. The porous precursor is added to a titanium dioxide sol with a viscosity of 700 mPa·s to 1500 mPa·s and stirred and mixed. During the mixing process, the titanium dioxide sol is redispersed into the porous precursor along with the water in it to form carbon nanotube-loaded chitosan and HNO3 sol again. The resulting carbon nanotube-loaded chitosan and HNO3 sol is mixed evenly with the titanium dioxide sol.

[0031] S3. Heat and stir the sol obtained in S2 to obtain a gel;

[0032] The heating and stirring temperature is 60℃ to 70℃, and the heating and stirring time is 2h to 3h;

[0033] S4. The gel obtained by calcining S3 is calcined at a temperature of 500℃ to 600℃ for 2h to 3h to obtain nitrogen-doped nanotube-supported titanium dioxide.

[0034] Preferably, in S1, the amino groups of chitosan supported on carbon nanotubes and the carboxyl groups on the surface of carbon nanotubes in the HNO3 sol form amide bonds, and the chitosan electrostatically adsorbs HNO3, forming chitosan electrodes and nitrate groups that self-assemble on the carbon nanotubes. This invention utilizes chitosan as a bridge between nitrate groups and carbon nanotubes to effectively disperse nitrate groups, promoting the relatively uniform dispersion of the carbon nanotube-chitosan-nitrate gel and the titanium dioxide gel.

[0035] The preferred method for preparing the porous precursor in S1 includes the following steps:

[0036] S11. Disperse carbon nanotubes in concentrated nitric acid for etching, and soak for 6 to 12 hours; filter, wash, and dry to obtain etched carbon nanotubes; the concentration of concentrated nitric acid used to etch carbon nanotubes and increase surface defects of carbon nanotubes is 11 mol / L to 14 mol / L.

[0037] S12. Chitosan and carbon nanotubes prepared in S11 are dispersed in nitric acid solution and stirred to obtain a sol.

[0038] The amino groups of chitosan and the oxygen atoms of nitrate are surrounded by carbon nanotubes through electrostatic adsorption.

[0039] S13, freeze-drying to obtain a porous precursor;

[0040] The amounts of chitosan, HNO3, and carbon nanotubes used in S11 are as follows:

[0041] (2g to 3g): (2.5mmol to 7.5mmol): 1g;

[0042] The process parameters for freeze-drying the porous precursor in S13 are as follows:

[0043] The freeze-drying temperature is -50℃ to -60℃, and the freeze-drying time is 48 hours to 72 hours.

[0044] The preferred ratio of carbon nanotubes in the carbon nanotube-loaded chitosan and HNO3 sol to titanium dioxide in the titanium dioxide sol is 1 g: (0.1 g to 0.3 g).

[0045] The preferred method for preparing the titanium dioxide sol used in S2 is as follows:

[0046] Tetrabutyl titanate and anhydrous ethanol are mixed and stirred until homogeneous. Then, 6% to 9% by mass of dilute nitric acid is added dropwise until the pH of the mixture is 3 to 4, wherein the molar ratio of tetrabutyl titanate to anhydrous ethanol is 1:(25 to 30). The mixture is stirred to obtain a clear sol, which is then allowed to stand for 36 to 48 hours to obtain a titanium dioxide sol for mixing porous precursors.

[0047] By adopting the above technical solution, the beneficial effects of the present invention are:

[0048] This invention proposes a method of dissolving lactose in deionized water, placing it in a reaction vessel, and adding nitrogen-doped carbon nanotube-supported titanium dioxide. Under pressure and sealing with oxygen, the mixture is heated to oxidize lactose to lactobionic acid. The titanium dioxide / carbon nanotube solid catalyst adsorbs lactose and O2 molecules onto the catalyst, respectively. The defective carbon nanotubes are uniformly surrounded by chitosan. Then, when the titanium dioxide gel comes into contact with the carbon nanotube-supported chitosan and the freeze-dried porous precursor of HNO3 sol, the titanium dioxide sol, with a viscosity of 700 mPa·s to 1500 mPa·s, undergoes mixing. The titanium dioxide sol, along with its water, redisperses into the porous precursor, re-forming carbon nanotube-loaded chitosan and HNO3 sol. The resulting carbon nanotube-loaded chitosan and HNO3 sol mixes uniformly with the titanium dioxide sol, maintaining a carbon nanotube-chitosan-titanium dioxide distribution hierarchy during mixing. During the initial mixing process between the titanium dioxide sol and the porous precursor, the solid and titanium dioxide sols are mixed. In this process, the silica sol coats the surface of the porous precursor and, due to its fluidity, can penetrate the porous structure of the precursor, forming a certain solid-liquid mixture. After the titanium dioxide gel is dried, water diffuses into the precursor, which then forms a sol again. The dispersion of titanium dioxide and carbon nanotubes relies on the network structure of the silica sol and chitosan sol. During this process, the hydroxyl groups of chitosan molecules self-assembled on the surface of the carbon nanotubes participate in the network formation of the titanium dioxide sol. Chitosan effectively participates in the titanium dioxide sol network to a certain extent by utilizing the abundant surface area of ​​the carbon nanotubes. The steric hindrance and abundant specific surface area of ​​the carbon nanotubes effectively inhibit the condensation of the titanium dioxide sol, forming more uniform and finer gel particles, ensuring relatively uniform dispersion of both, and facilitating subsequent gelation. After drying and calcination, titanium dioxide particles are uniformly distributed on the surface of carbon nanotubes. Under ultraviolet light irradiation, electrons are generated, and the carbon nanotubes transfer photogenerated electrons from the anatase phase TiO2. Because the electrons generated by titanium dioxide are rapidly transferred through the nitrogen-doped carbon nanotubes to the adsorbed lactose molecules, hydroxide ions, and oxygen molecules on the surface of the carbon nanotubes, the entire catalytic reaction proceeds uniformly along the surface of the carbon nanotubes, effectively promoting the rapid oxidation of lactose with few byproducts. This invention uses a solid catalyst, which facilitates separation from the reaction system for lactose oxidation to lactobionic acid, and the resulting catalyst is easy to clean and recover, significantly improving its service life. Detailed Implementation

[0049] To further explain the technical solution of the present invention, the present invention will be described in detail below through specific embodiments.

[0050] This invention proposes a method of dissolving lactose in deionized water, placing it in a reaction vessel, and adding nitrogen-doped carbon nanotube-supported titanium dioxide. Under pressure and sealing with oxygen, the mixture is heated to oxidize lactose to lactobionic acid. The titanium dioxide / carbon nanotube solid catalyst adsorbs lactose and O2 molecules onto the catalyst, respectively. The defective carbon nanotubes are uniformly surrounded by chitosan. Then, when the titanium dioxide gel comes into contact with the carbon nanotube-supported chitosan and the freeze-dried porous precursor of HNO3 sol, the titanium dioxide sol, with a viscosity of 700 mPa·s to 1500 mPa·s, undergoes mixing. The titanium dioxide sol, along with its water, redisperses into the porous precursor, re-forming carbon nanotube-loaded chitosan and HNO3 sol. The resulting carbon nanotube-loaded chitosan and HNO3 sol mixes uniformly with the titanium dioxide sol, maintaining a carbon nanotube-chitosan-titanium dioxide distribution hierarchy during mixing. During the initial mixing process between the titanium dioxide sol and the porous precursor, the solid and titanium dioxide sols are mixed. In this process, the silica sol coats the surface of the porous precursor and, due to its fluidity, can penetrate the porous structure of the precursor, forming a certain solid-liquid mixture. After the titanium dioxide gel is dried, water diffuses into the precursor, which then forms a sol again. The dispersion of titanium dioxide and carbon nanotubes relies on the network structure of the silica sol and chitosan sol. During this process, the hydroxyl groups of chitosan molecules self-assembled on the surface of the carbon nanotubes participate in the network formation of the titanium dioxide sol. Chitosan effectively participates in the titanium dioxide sol network to a certain extent by utilizing the abundant surface area of ​​the carbon nanotubes. The steric hindrance and abundant specific surface area of ​​the carbon nanotubes effectively inhibit the condensation of the titanium dioxide sol, forming more uniform and finer gel particles, ensuring relatively uniform dispersion of both, and facilitating subsequent gelation. After drying and calcination, titanium dioxide particles are uniformly distributed on the surface of carbon nanotubes. Under ultraviolet light irradiation, electrons are generated, and the carbon nanotubes transfer photogenerated electrons from the anatase phase TiO2. Because the electrons generated by titanium dioxide are rapidly transferred through the nitrogen-doped carbon nanotubes to the adsorbed lactose molecules, hydroxide ions, and oxygen molecules on the surface of the carbon nanotubes, the entire catalytic reaction proceeds uniformly along the surface of the carbon nanotubes, effectively promoting the rapid oxidation of lactose with few byproducts. This invention uses a solid catalyst, which facilitates separation from the reaction system for lactose oxidation to lactobionic acid, and the resulting catalyst is easy to clean and recover, significantly improving its service life.

[0051] Example 1

[0052] This embodiment discloses a solid catalyst used in the separation and purification of lactobionic acid. The solid catalyst is titanium dioxide supported on nitrogen-doped carbon nanotubes. The preparation method of the solid catalyst includes the following steps:

[0053] S1. Preparation of chitosan-modified porous carbon nanotube precursors;

[0054] S2. The porous precursor is added to a titanium dioxide sol with a viscosity of 700 mPa·s and stirred and mixed. During the mixing process, the titanium dioxide sol is redispersed into the porous precursor along with the water in it to form carbon nanotube-loaded chitosan and HNO3 sol again. The resulting carbon nanotube-loaded chitosan and HNO3 sol is mixed evenly with the titanium dioxide sol.

[0055] S3. Heat and stir the sol obtained in S2 to obtain a gel;

[0056] The heating and stirring temperature was 60℃, and the heating and stirring time was 2 hours.

[0057] S4. The gel obtained by calcining S3 was calcined at 700℃ for 2 hours to obtain nitrogen-doped nanotube-supported titanium dioxide.

[0058] In this embodiment, the chitosan loaded on the carbon nanotube in S1 and the amino groups of chitosan in the HNO3 sol form amide bonds with the carboxyl groups on the surface of the carbon nanotube. The chitosan forms chitosan poles and nitrate groups by electrostatically adsorbing HNO3 and self-assembling them on the carbon nanotube.

[0059] In this embodiment, the preparation method of the porous precursor in S1 includes the following steps:

[0060] S11. Carbon nanotubes are dispersed and etched in concentrated nitric acid for 6 hours; filtered, washed, and dried to obtain etched carbon nanotubes; the concentration of concentrated nitric acid used to etch carbon nanotubes and increase surface defects of carbon nanotubes is 11 mol / L.

[0061] S12. Chitosan and carbon nanotubes prepared in S11 are dispersed in nitric acid solution and stirred to obtain a sol.

[0062] The amino groups of chitosan and the oxygen atoms of nitrate are surrounded by carbon nanotubes through electrostatic adsorption.

[0063] S13, freeze-drying to obtain a porous precursor;

[0064] The amounts of chitosan, HNO3, and carbon nanotubes used in S11 are as follows:

[0065] 2g: 2.5mmol: 1g;

[0066] The process parameters for freeze-drying the porous precursor in S13 are as follows:

[0067] The freeze-drying temperature was -50℃, and the freeze-drying time was 72 hours.

[0068] In this embodiment, the mass ratio of carbon nanotubes in the carbon nanotube-loaded chitosan and HNO3 sol to titanium dioxide in the titanium dioxide sol is 1g:0.1g.

[0069] The preparation method of the titanium dioxide sol used in S2 in this embodiment is as follows:

[0070] Tetrabutyl titanate and anhydrous ethanol were mixed and stirred until homogeneous. Then, 6% by mass of dilute nitric acid was added dropwise until the pH of the mixture was 3. The molar ratio of tetrabutyl titanate to anhydrous ethanol was 1:25. The mixture was stirred to obtain a clear sol, which was then allowed to stand for 36 hours to obtain a titanium dioxide sol for mixing porous precursors.

[0071] Example 2

[0072] This embodiment discloses a solid catalyst used in the separation and purification of lactobionic acid. The solid catalyst is titanium dioxide supported on nitrogen-doped carbon nanotubes. The preparation method of the solid catalyst includes the following steps:

[0073] S1. Preparation of chitosan-modified porous carbon nanotube precursors;

[0074] S2. The porous precursor is added to a titanium dioxide sol with a viscosity of 1000 mPa·s and stirred and mixed. During the mixing process, the titanium dioxide sol is redispersed into the porous precursor along with the water in it to form carbon nanotube-loaded chitosan and HNO3 sol again. The resulting carbon nanotube-loaded chitosan and HNO3 sol is mixed evenly with the titanium dioxide sol.

[0075] S3. Heat and stir the sol obtained in S2 to obtain a gel;

[0076] The heating and stirring temperature was 65℃, and the heating and stirring time was 3 hours.

[0077] S4, the gel obtained by calcining S3, the calcination temperature was 750℃ and the calcination time was 2.5h, to obtain nitrogen-doped nanotube-supported titanium dioxide.

[0078] In this embodiment, the chitosan loaded on the carbon nanotube in S1 and the amino groups of chitosan in the HNO3 sol form amide bonds with the carboxyl groups on the surface of the carbon nanotube. The chitosan forms chitosan poles and nitrate groups by electrostatically adsorbing HNO3 and self-assembling them on the carbon nanotube.

[0079] In this embodiment, the preparation method of the porous precursor in S1 includes the following steps:

[0080] S11. Carbon nanotubes are dispersed and etched in concentrated nitric acid for 9 hours; filtered, washed, and dried to obtain etched carbon nanotubes; the concentration of concentrated nitric acid used to etch carbon nanotubes and increase surface defects of carbon nanotubes is 12 mol / L.

[0081] S12. Chitosan and carbon nanotubes prepared in S11 are dispersed in nitric acid solution and stirred to obtain a sol.

[0082] The amino groups of chitosan and the oxygen atoms of nitrate are surrounded by carbon nanotubes through electrostatic adsorption.

[0083] S13, freeze-drying to obtain a porous precursor;

[0084] The amounts of chitosan, HNO3, and carbon nanotubes used in S11 are as follows:

[0085] 2.5g: 5.0mmol: 1g;

[0086] The process parameters for freeze-drying the porous precursor in S13 are as follows:

[0087] The freeze-drying temperature was -60℃, and the freeze-drying time was 60 hours.

[0088] In this embodiment, the mass ratio of carbon nanotubes in the carbon nanotube-loaded chitosan and HNO3 sol to titanium dioxide in the titanium dioxide sol is 1g:0.2g.

[0089] The preparation method of the titanium dioxide sol used in S2 in this embodiment is as follows:

[0090] Tetrabutyl titanate and anhydrous ethanol were mixed and stirred until homogeneous. Then, 6% by mass of dilute nitric acid was added dropwise until the pH of the mixture was 3. The molar ratio of tetrabutyl titanate to anhydrous ethanol was 1:30. The mixture was stirred to obtain a clear sol, which was then allowed to stand for 48 hours to obtain a titanium dioxide sol for mixing porous precursors.

[0091] Example 3

[0092] This embodiment discloses a solid catalyst used in the separation and purification of lactobionic acid. The solid catalyst is titanium dioxide supported on nitrogen-doped carbon nanotubes. The preparation method of the solid catalyst includes the following steps:

[0093] S1. Preparation of chitosan-modified porous carbon nanotube precursors;

[0094] S2. The porous precursor is added to a titanium dioxide sol with a viscosity of 1500 mPa·s and stirred and mixed. During the mixing process, the titanium dioxide sol is redispersed into the porous precursor along with the water in it to form carbon nanotube-loaded chitosan and HNO3 sol again. The resulting carbon nanotube-loaded chitosan and HNO3 sol is mixed evenly with the titanium dioxide sol.

[0095] S3. Heat and stir the sol obtained in S2 to obtain a gel;

[0096] The heating and stirring temperature is 70℃, and the heating and stirring time is 3 hours;

[0097] S4. The gel obtained by calcining S3 was calcined at 800℃ for 3 hours to obtain nitrogen-doped nanotube-supported titanium dioxide.

[0098] In this embodiment, the chitosan loaded on the carbon nanotube in S1 and the amino groups of chitosan in the HNO3 sol form amide bonds with the carboxyl groups on the surface of the carbon nanotube. The chitosan forms chitosan poles and nitrate groups by electrostatically adsorbing HNO3 and self-assembling them on the carbon nanotube.

[0099] In this embodiment, the preparation method of the porous precursor in S1 includes the following steps:

[0100] S11. Carbon nanotubes are dispersed and etched in concentrated nitric acid for 12 hours; filtered, washed and dried to obtain etched carbon nanotubes; the concentration of concentrated nitric acid used to etch carbon nanotubes and increase surface defects of carbon nanotubes is 14 mol / L.

[0101] S12. Chitosan and carbon nanotubes prepared in S11 are dispersed in nitric acid solution and stirred to obtain a sol.

[0102] The amino groups of chitosan and the oxygen atoms of nitrate are surrounded by carbon nanotubes through electrostatic adsorption.

[0103] S13, freeze-drying to obtain a porous precursor;

[0104] The amounts of chitosan, HNO3, and carbon nanotubes in S11 are as follows: 3g: 7.5mmol: 1g;

[0105] The process parameters for freeze-drying the porous precursor in S13 are as follows:

[0106] The freeze-drying temperature was -60℃, and the freeze-drying time was 48 hours.

[0107] In this embodiment, the mass ratio of carbon nanotubes in the carbon nanotube-loaded chitosan and HNO3 sol to titanium dioxide in the titanium dioxide sol is 1g:0.3g.

[0108] The preparation method of the titanium dioxide sol used in S2 in this embodiment is as follows:

[0109] Tetrabutyl titanate and anhydrous ethanol were mixed and stirred until homogeneous. Then, 9% dilute nitric acid was added dropwise until the pH of the mixture was 3. The molar ratio of tetrabutyl titanate to anhydrous ethanol was 1:25. The mixture was stirred to obtain a clear sol, which was then allowed to stand for 48 hours to obtain a titanium dioxide sol for mixing porous precursors.

[0110] Example 4

[0111] This embodiment discloses a method for separating and purifying lactobionic acid using a solid catalyst prepared in Example 1, including the following steps:

[0112] A1. Dissolve analytical grade lactose in deionized water, place it in a reaction vessel, and add the solid catalyst to obtain the reaction system;

[0113] The ratio of lactose to deionized water is 50g:1L;

[0114] The ratio of solid catalyst to deionized water is 1g:1L;

[0115] The pH of the reaction system after adding sodium hydroxide is 8;

[0116] Turn on ultraviolet irradiation, with an irradiation power of 40W;

[0117] Oxygen was introduced until the internal pressure of the reactor reached 1.2 MPa, and the reactor was then sealed.

[0118] A2. Heating and oxidation conversion;

[0119] As stirring occurs, the solid catalyst continuously adsorbs O2 dissolved in the aqueous solution onto its surface to convert lactose into lactobionic acid; oxygen from the environment continuously dissolves and enters the liquid phase.

[0120] The reaction temperature is 50℃;

[0121] The reaction time is 30 minutes;

[0122] A3. After the reaction time is reached, use an ice-water mixture to quickly cool the reactor to room temperature and vent the gas.

[0123] A4. Filter out the solid catalyst to obtain the liquid phase material;

[0124] A5. Concentrate under reduced pressure to 25% of the volume of the liquid material obtained in A4. Add sodium carbonate until the material is neutral. Add ethanol, with the volume ratio of ethanol to deionized water added in A1 being 0.25:1. Centrifuge to crystallize, purify multiple times, and filter to obtain sodium lactobionate.

[0125] In this embodiment, intermittent stirring is performed during the heating process until the reaction time is reached;

[0126] The stirring process parameters are as follows:

[0127] Stir at 500 rpm for 20 seconds; let stand for 10 seconds; repeat this cycle for 30 minutes.

[0128] Example 5

[0129] This embodiment discloses a method for separating and purifying lactobionic acid using a solid catalyst prepared in Example 2, including the following steps:

[0130] A1. Dissolve analytical grade lactose in deionized water, place it in a reaction vessel, and add the solid catalyst to obtain the reaction system;

[0131] The ratio of lactose to deionized water is 55g:1L;

[0132] The ratio of solid catalyst to deionized water is 2g:1L;

[0133] The pH of the reaction system after adding sodium hydroxide is 8;

[0134] Turn on ultraviolet irradiation, with an irradiation power of 45W;

[0135] Oxygen was introduced until the internal pressure of the reactor reached 1.2 MPa, and the reactor was then sealed.

[0136] A2. Heating and oxidation conversion;

[0137] As stirring occurs, the solid catalyst continuously adsorbs O2 dissolved in the aqueous solution onto its surface to convert lactose into lactobionic acid; oxygen from the environment continuously dissolves and enters the liquid phase.

[0138] The reaction temperature is 55℃;

[0139] The reaction time is 35 minutes;

[0140] A3. After the reaction time is reached, use an ice-water mixture to quickly cool the reactor to room temperature and vent the gas.

[0141] A4. Filter out the solid catalyst to obtain the liquid phase material;

[0142] A5. Concentrate under reduced pressure to 25% of the volume of the liquid material obtained in A4. Add sodium carbonate until the material is neutral. Add ethanol, with the volume ratio of ethanol to deionized water added in A1 being 0.25:1. Centrifuge to crystallize, purify multiple times, and filter to obtain sodium lactobionate.

[0143] In this embodiment, intermittent stirring is performed during the heating process until the reaction time is reached;

[0144] The stirring process parameters are as follows:

[0145] Stir at 600 rpm for 20 seconds; let stand for 20 seconds; repeat this cycle for 35 minutes.

[0146] Example 6

[0147] This embodiment discloses a method for separating and purifying lactobionic acid using a solid catalyst prepared in Example 3, including the following steps:

[0148] A1. Dissolve analytical grade lactose in deionized water, place it in a reaction vessel, and add the solid catalyst to obtain the reaction system;

[0149] The ratio of lactose to deionized water is 60g:1L;

[0150] The ratio of solid catalyst to deionized water is 3g:1L;

[0151] The pH of the reaction system after adding sodium hydroxide is 8;

[0152] Turn on ultraviolet irradiation, with an irradiation power of 45W;

[0153] Oxygen was introduced until the internal pressure of the reactor reached 1.2 MPa, and the reactor was then sealed.

[0154] A2. Heating and oxidation conversion;

[0155] As stirring occurs, the solid catalyst continuously adsorbs O2 dissolved in the aqueous solution onto its surface to convert lactose into lactobionic acid; oxygen from the environment continuously dissolves and enters the liquid phase.

[0156] The reaction temperature is 55℃;

[0157] The reaction time is 40 minutes;

[0158] A3. After the reaction time is reached, use an ice-water mixture to quickly cool the reactor to room temperature and vent the gas.

[0159] A4. Filter out the solid catalyst to obtain the liquid phase material;

[0160] A5. Concentrate under reduced pressure to 25% of the volume of the liquid material obtained in A4. Add sodium carbonate until the material is neutral. Add ethanol, with the volume ratio of ethanol to deionized water added in A1 being 0.25:1. Centrifuge to crystallize, purify multiple times, and filter to obtain sodium lactobionate.

[0161] In this embodiment, intermittent stirring is performed during the heating process until the reaction time is reached;

[0162] The stirring process parameters are as follows:

[0163] Stir at 600 rpm for 30 seconds; let stand for 20 seconds; repeat this cycle for 40 minutes.

[0164] Comparative Example

[0165] This comparative example discloses a method for separating and purifying lactobionic acid, comprising the following steps:

[0166] A1. Dissolve analytical grade lactose in deionized water, place it in a reaction vessel, and add the solid catalyst to obtain the reaction system;

[0167] The ratio of lactose to deionized water is 60g:1L;

[0168] The ratio of solid catalyst to deionized water is 3g:1L;

[0169] The pH of the reaction system after adding sodium hydroxide is 8;

[0170] Oxygen was introduced until the internal pressure of the reactor reached 1.2 MPa, and the reactor was then sealed.

[0171] A2. Heating oxidation conversion, reaction conditions are as follows:

[0172] The reaction temperature is 55℃;

[0173] The reaction time is 40 minutes;

[0174] A3. After the reaction time is reached, use an ice-water mixture to quickly cool the reactor to room temperature and vent the gas.

[0175] A4. Filter out the solid catalyst to obtain the liquid phase material;

[0176] A5. Concentrate under reduced pressure until the volume is 25% of the liquid phase material obtained in A4. Add sodium carbonate until the material is neutral. Add ethanol and centrifuge to crystallize. The volume ratio of ethanol to deionized water added in A1 is 0.25:1. Purify multiple times and filter to obtain sodium lactobionate.

[0177] In this embodiment, intermittent stirring is performed during the heating process until the reaction time is reached;

[0178] The stirring process parameters are as follows:

[0179] Stir at 600 rpm for 30 seconds; let stand for 20 seconds; repeat this cycle for 40 minutes.

[0180] The solid catalyst in this comparative example is carbon nanotube / titanium dioxide particles supported on carbon nanotubes prepared by the sol-gel method. The specific preparation method and material composition are as follows:

[0181] Measure 3.4 ml of tetrabutyl titanate, add 16 ml of anhydrous ethanol to it, and stir for about 30 minutes to mix it thoroughly.

[0182] Take 16.5 ml of 95% ethanol, add MWCNTs, add 5 ml of 0.1 M nitric acid and 3 ml of glacial acetic acid, and stir for 30 min.

[0183] MWCNTs and target nano-titanium dioxide were added at a mass ratio of 1g:0.3g;

[0184] Tetrabutyl titanate solution was slowly added dropwise to the MWCNTs dispersion system while stirring continuously. Ammonia was added dropwise to adjust the pH to about 7. Stirring was continued for 60 hours to form a uniform nano MWCNTs-TiO2 sol.

[0185] After standing for 24 hours, the solvent was evaporated by heating to 70°C to obtain a gel; after drying, it was calcined at 800°C for 3 hours to obtain a black powdery nano-MWCNTs-TiO2 solid catalyst.

[0186] The specific surface areas of the solid catalysts in Examples 1 to 3 and the comparative examples were tested respectively, as shown in Table 1.

[0187] Table 1. Specific surface area of ​​solid catalysts obtained in Examples 1 to 3 and comparative examples.

[0188] Example 1 603 Example 2 611 Example 3 624 Comparative Example 128

[0189] The conversion rate R of lactobionic acid in Examples 4 to 6 and the comparative example was tested respectively. The specific calculation method is that the mass of lactose input is M0 and the mass of lactobionic acid obtained is M1, R = M1 / M0*100%. The specific data are shown in Table 2.

[0190] Table 2 Yields of Examples 4 to 6 and Comparative Separation and Extraction Methods

[0191] Example 4 90.2％ Example 5 91.7％ Example 6 91.9％ Comparative Example 44.5％

[0192] Based on the data in Tables 1 and 2, it can be seen that the solid catalysts prepared in Examples 1 to 3 have significantly increased specific surface area, and at the same time, the corresponding conversion rate of lactobionic acid is also significantly improved.

[0193] This invention proposes a method of dissolving lactose in deionized water, placing it in a reaction vessel, adding nitrogen-doped carbon nanotube-supported titanium dioxide, pressurizing with oxygen, sealing, and heating to oxidize lactose into lactobionic acid. The improved conversion rate of lactobionic acid is mainly due to the combination of the following technical features:

[0194] Firstly, in the preparation of the porous precursor of the solid catalyst obtained in this invention, chitosan is used to modify the surface of carbon nanotubes. During the formation of the porous precursor, the amino and hydroxyl groups on the surface of chitosan and the carboxyl groups formed simultaneously by the defects created by concentrated nitric acid defect formation form ester or amide bonds. These chemical bonds promote the uniform distribution of chitosan on the surface of the chitosan, thus significantly improving the dispersibility and stability of carbon nanotubes in water. When the freeze-dried porous precursor is brought into contact with titanium dioxide sol again, the mixing process includes contact at the solid-liquid interface. The porous precursor gradually absorbs water from the titanium dioxide sol, and the chitosan dissolves. During the dissolution process, the hydroxyl groups of chitosan participate in the formation of the titanium dioxide sol network, i.e., Ti-OH, inhibiting the condensation of titanium dioxide sol and forming more uniform and finer gel particles. The solid catalyst prepared by this invention has uniform particles and a significantly improved specific surface area.

[0195] Because chitosan simultaneously connects carbon nanotubes and titanium dioxide sol, the amino groups doping carbon nanotubes and TiO2 during calcination effectively improve the electronic conductivity of carbon nanotubes and enhance the photogenerated electrons of TiO2 under ultraviolet light irradiation. These photogenerated electrons are rapidly transferred through nitrogen-doped carbon nanotubes to the adsorbed lactose molecules, hydroxide ions, and oxygen molecules on the surface of the carbon nanotubes, effectively promoting the rapid oxidation of lactose with fewer byproducts. The nitrogen atom doping of the carbon nanotubes provides not only electrons to the conjugated π-bond system but also a lone pair of electrons, which adsorb O2 molecules and their intermediates during oxygen reduction. As shown in Table 2, the solid catalyst effectively loads TiO2 particles on the surface of the carbon nanotubes, accompanied by the adsorption of oxygen and lactose molecules. Therefore, the lactobionic acid conversion rate of the lactobionic acid separation and purification method proposed in this invention is significantly improved.

[0196] The present invention uses a solid catalyst to facilitate the separation from the reaction system for lactose oxidation to lactobionic acid, and the resulting catalyst is easy to clean and recover, with a significantly improved service life.

Claims

1. A method for separating and purifying lactobionic acid, characterized in that: Includes the following steps: A1. Dissolve analytical grade lactose in deionized water, place it in a reaction vessel, and add a solid catalyst to the reaction system; The ratio of lactose to deionized water is 50g-60g:1L; The ratio of solid catalyst to deionized water is 1g-3g:1L; The pH of the reaction system after adding sodium hydroxide is 8. Turn on ultraviolet radiation; Oxygen is introduced until the internal pressure of the reactor is 1.1 MPa to 1.3 MPa, and the reactor is then sealed. A2. Heating and oxidation conversion; As stirring occurs, the solid catalyst continuously adsorbs O2 dissolved in the aqueous solution onto its surface to convert lactose into lactobionic acid; oxygen from the environment continuously dissolves and enters the liquid phase. A3. After the reaction time is reached, use an ice-water mixture to quickly cool the reactor to room temperature and vent the gas. A4. Filter out the solid catalyst to obtain the liquid phase material; A5. Concentrate under reduced pressure, add sodium carbonate until the material is neutral, add ethanol, centrifuge to crystallize, purify multiple times, filter, and obtain sodium lactobionate; The solid catalyst is titanium dioxide supported on nitrogen-doped carbon nanotubes, and the preparation method of the solid catalyst includes the following steps: S1. Preparation of chitosan-modified porous carbon nanotube precursors; S2. The porous precursor is added to a titanium dioxide sol with a viscosity of 700 mPa·s to 1500 mPa·s and stirred and mixed. During the mixing process, the titanium dioxide sol is redispersed into the porous precursor along with the water in it to form carbon nanotube-loaded chitosan and HNO3 sol again. The resulting carbon nanotube-loaded chitosan and HNO3 sol is mixed evenly with the titanium dioxide sol. S3. Heat and stir the sol obtained in S2 to obtain a gel; The heating and stirring temperature is 60℃ to 70℃, and the heating and stirring time is 2 hours to 3 hours; S4. The gel obtained by calcining S3 is calcined at a temperature of 500℃ to 600℃ for 2h to 3h to obtain nitrogen-doped nanotube-supported titanium dioxide.

2. The separation and purification method as described in claim 1, characterized in that: The power of ultraviolet irradiation in A1 is 40W to 45W.

3. The separation and purification method as described in claim 1, characterized in that: The process conditions for the heating oxidation conversion in A2 are as follows: The reaction temperature is 50℃ to 55℃; The reaction time is 30 to 40 minutes.

4. The method for separating and purifying lactobionic acid as described in claim 1, characterized in that: In A2, the heating process is combined with intermittent stirring until the reaction time is reached; The stirring process parameters are as follows: Stir at 500 rpm to 600 rpm for 20 to 30 seconds; let stand for 10 to 20 seconds; repeat this cycle for 30 to 40 minutes.

5. The method for separating and purifying lactobionic acid as described in claim 1, characterized in that: Concentrate under reduced pressure to 25% of the volume of the liquid material obtained in A4, add sodium carbonate until the material is neutral, and add ethanol in a volume ratio of 0.25:1 to the volume of deionized water added in A1.

6. The separation and purification method as described in claim 1, characterized in that: In S1, the chitosan loaded on carbon nanotubes and the chitosan in the HNO3 sol form amide bonds with the carboxyl groups on the surface of carbon nanotubes. Chitosan electrostatically adsorbs HNO3, forming chitosan poles and nitrate groups that self-assemble on the carbon nanotubes.

7. The separation and purification method as described in claim 1, characterized in that: The method for preparing the porous precursor in S1 includes the following steps: S11. Disperse carbon nanotubes in concentrated nitric acid for etching, and soak for 6 to 12 hours; filter, wash, and dry to obtain etched carbon nanotubes; the concentration of concentrated nitric acid used to etch carbon nanotubes and increase surface defects of carbon nanotubes is 11 mol / L to 14 mol / L. S12. Chitosan and carbon nanotubes prepared in S11 are dispersed in nitric acid solution and stirred to obtain a sol. The amino groups of chitosan and the oxygen atoms of nitrate are surrounded by carbon nanotubes through electrostatic adsorption. S13, freeze-drying to obtain a porous precursor; The amounts of chitosan, HNO3, and carbon nanotubes used in S11 are as follows: 2g-3g: 2.5mmol-7.5mmol: 1g; The process parameters for freeze-drying the porous precursor in S13 are as follows: The freeze-drying temperature is -50℃ to -60℃, and the freeze-drying time is 48 hours to 72 hours.

8. The separation and purification method as described in claim 1, characterized in that: In S2, the mass ratio of carbon nanotubes in the chitosan and HNO3 sol loaded with carbon nanotubes to titanium dioxide in the titanium dioxide sol is 1g:0.1g-0.3g.

9. The separation and purification method as described in claim 1, characterized in that: The preparation method of the titanium dioxide sol used in S2 is as follows: Tetrabutyl titanate and anhydrous ethanol are mixed and stirred until homogeneous. Then, 6% to 9% by mass of dilute nitric acid is added dropwise until the pH of the mixture is 3 to 4. The molar ratio of tetrabutyl titanate to anhydrous ethanol is 1:25-30. The mixture is stirred to obtain a clear sol, which is then allowed to stand for 36 to 48 hours to obtain a titanium dioxide sol for mixing porous precursors.

Images