A method for separating and purifying d-tagatose

Abstract

This invention discloses a method for separating and purifying D-tagatose, comprising the following steps: Step 1, the reactant D-galactose aggregates on the MgO surface of the carbon skeleton under the adsorption of magnesium oxide and the carbon skeleton. MgO acts as a catalytic center, and under alkaline conditions, OH- attacks D-galactose to isomerize it into D-tagatose; the solid base catalyst has a hollow network spherical structure; Step 2, the solid phase material in Step 1 is filtered, and deionized water is used to slowly soak and wash away cations; Step 3, the supernatant obtained by centrifugation is a D-tagatose solution; Step 4, the D-tagatose solution obtained in Step 3 is concentrated by vacuum heating until the D-tagatose content is 80 to 90°Bx; Step 5, crystallization and vacuum drying are performed to obtain D-tagatose crystals; This invention utilizes the hydrothermal composite of magnesium oxide and chitosan to effectively load MgO particles, resulting in a solid base catalyst with multiple active sites, which is beneficial for the separation and purification of D-tagatose.

Description

Technical Field

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

[0002] D-Tagose is an epimer of fructose, a type of ketose that is relatively rare in nature. It is an isomer of galactose through chemical or biological processes. D-Tagose has a similar sweetness to sucrose, but its metabolic energy is only 30% that of sucrose.

[0003] Although research on the synthesis of D-tagatose from D-galactose is quite comprehensive, D-galactose remains expensive. The invention patent with authorization announcement number CN107974474B describes a simple method for removing glucose, a byproduct, from the D-tagatose conversion solution using lactose as a substrate through enzyme conversion with high enzyme specificity. The principle involves using immobilized β-galactosidase to convert lactose into galactose and glucose, using immobilized L-arabinose isomerase to convert galactose into D-tagatose, using immobilized glucose oxidase to convert glucose, a byproduct of lactose hydrolysis, into negatively charged gluconic acid, and using ion exchange resin to adsorb and remove gluconic acid from the conversion solution. However, this reaction route is lengthy, involving the conversion of lactose into galactose and glucose, followed by the isomerization of galactose into D-tagatose. Furthermore, the biological conversion method requires stricter control over temperature and pH, making the preparation process relatively unstable. The chemical catalytic isomerization of galactose to tagatose requires the use of a large amount of alkali metal or alkaline earth metal as a catalytic center and the introduction of a large amount of salt. The subsequent separation and purification process of tagatose is complex, which not only prolongs the production cycle but also increases the difficulty of separation and purification. Summary of the Invention

[0004] The purpose of this invention is to provide a method for the separation and purification of D-tagatose. This invention utilizes a hydrothermal composite of magnesium oxide and chitosan to effectively load MgO particles, resulting in a solid base catalyst with multiple active sites, which is beneficial for the separation and purification of D-tagatose.

[0005] To solve this technical problem, the technical solution of the present invention is: a method for separating and purifying D-tagatose, comprising the following steps:

[0006] Step 1: Place the MgO-carbon solid base catalyst in an aqueous solution of D-galactose, adjust the pH of the reaction system to 10 to 12, and stir at room temperature to 35°C for 30 to 60 minutes. The reactant D-galactose aggregates on the MgO on the surface of the carbon skeleton under the adsorption of magnesium oxide and carbon skeleton. MgO acts as a catalytic center. Under alkaline conditions, OH- attacks D-galactose and isomerizes it into D-tagatose.

[0007] The MgO-carbon solid base catalyst has a hollow network spherical structure.

[0008] The mass ratio of MgO-carbon solid base catalyst to D-galactose is (0.3 to 0.4):1;

[0009] Step 2: Filter the solid phase material from Step 1 to separate the solid base catalyst adsorbed with D-tagatose. Use deionized water to slowly soak and wash to remove cations. During the process of removing cations, deionized water enters the solid base catalyst through the carbon skeleton network structure to remove cations simultaneously.

[0010] Step 3: Place the solid base catalyst adsorbed with D-tagatose in deionized water and centrifuge to separate the D-tagatose adsorbed on the surface of the solid base catalyst from the solid base catalyst by centrifugation. The supernatant obtained by centrifugation is the D-tagatose solution.

[0011] Step 4: Vacuum heating to concentrate the D-tagatose solution obtained in Step 3 until the D-tagatose content is 80 to 90°Bx;

[0012] Step 5: Crystallize and vacuum dry to obtain D-tagatose crystals.

[0013] The preferred step of crystallization in step five includes the following steps:

[0014] S51. Take a volume of V of the concentrated solution obtained in step four, add anhydrous ethanol solution, and turbidity will appear. The volume of ethanol added is 2.0 to 2.5 times the volume of the concentrated solution.

[0015] S52. Heat until the D-tagatose dispersion to be purified is clarified; then cool.

[0016] S53. Add D-tagatose seed crystals, place at 2℃ to 4℃ for 4 to 6 hours, stir, then add anhydrous ethanol at 2℃ to 4℃ with a volume of V, and let stand for 24 to 36 hours until a large amount of crystals precipitate.

[0017] S54. Centrifuge the ethanol solution containing crystals;

[0018] S55. The obtained crystals are stirred with anhydrous ethanol, filtered, and vacuum dried to obtain D-tagatose crystals. Compared with using liquid alkali as a catalyst, the hollow network spherical structure magnesium oxide-carbon solid alkali catalyst used in this invention effectively enriches D-galactose and facilitates rapid conversion through the adsorption of magnesium oxide and carbon skeleton. Furthermore, during hydrothermal treatment, magnesium ions are chelated and positioned on the surface of the growth template by the abundant amino groups of chitosan. During hydrothermal treatment, the hollow spherical network serving as the magnesium hydroxide growth template maintains its hollow porous network structure due to its spherical structure, forming a carbon skeleton and preventing chitosan from directly condensing into solid particles.

[0019] The preferred method for preparing MgO-carbon solid base catalyst with a hollow network spherical structure includes the following steps:

[0020] S11. Place the hollow spherical network framework, which serves as a template for the growth of magnesium oxide particles, in a magnesium nitrate solution.

[0021] S12. Adjust the pH of the mixture obtained in S11 to 7, and the -NH2 chelate of magnesium ions in the solution by chitosan in the spherical network framework; the specific chelation method is as follows:

[0022]

[0023] S13, hydrothermal reaction, chitosan and polyacrylic acid carbonize to form a carbon skeleton, while magnesium hydroxide grows on the surface of the carbon skeleton.

[0024] S14, MgO-carbon solid base catalyst obtained by calcining the solid obtained from S13.

[0025] Preferably, the mass ratio of magnesium nitrate to the spherical network skeleton in S11 is 1:(1.0 to 1.3). The present invention aims to fully distribute magnesium oxide particles on the inner and outer surfaces of the carbon skeleton, fully exposing the magnesium oxide particles. The basicity of magnesium oxide itself and its abundant basic sites effectively improve the conversion rate of D-tagatose.

[0026] The hollow spherical network framework in S12 is preferably placed in a magnesium nitrate solution for 2 to 3 hours, maintaining the pH of the system at 7 during this process. During this process, the amino groups of chitosan chelate magnesium ions, controlling the uniform distribution of magnesium oxide particles on the surface of the porous hollow spherical carbon framework. This invention requires ensuring sufficient and complete chelation of magnesium ions to achieve effective loading and exposure of magnesium oxide particles on the carbon framework in the solid base catalyst.

[0027] The preferred process parameters for the S13 hydrothermal reaction are as follows:

[0028] The temperature is 200℃ to 220℃;

[0029] The time is from 12:00 to 18:00.

[0030] The preferred calcination conditions in S14 are calcination at 600°C to 700°C for 2 to 3 hours under nitrogen protection. This invention promotes the formation of oxygen vacancies in magnesium oxide particles through high-temperature calcination, thereby promoting the adsorption and conversion of D-galactose by the solid base catalyst.

[0031] Preferably, the diameter of the hollow spherical network framework used as a template for the growth of magnesium hydroxide particles is between 10 μm and 60 μm. This invention utilizes a carbon framework to fully and uniformly disperse magnesium hydroxide or magnesium oxide particles, reducing the limitations imposed by liquid-phase mass transfer and adsorption competition on the catalytic conversion of solid base catalysts in the adsorption of D-galactose.

[0032] Preferably, the spherical network framework is a porous chitosan hollow microsphere or a porous chitosan-polyacrylic acid hollow microsphere.

[0033] In step two, the solid material filtered from step one is allowed to stand for 10 to 20 minutes before being slowly rinsed with deionized water to remove cations.

[0034] The MgO-carbon solid alkali catalyst obtained in step three is preferably regenerated and recycled after being washed multiple times with ethanol and deionized water and calcined at 200°C to 300°C. In this invention, the solid alkali catalyst can be repeatedly used after calcination under nitrogen protection, and the magnesium oxide particles are dispersed by the carbon skeleton, resulting in stable catalytic performance.

[0035] By adopting the above technical solution, the beneficial effects of the present invention are as follows: The present invention utilizes the adsorption of reactant D-galactose on MgO on the surface of carbon skeleton under the adsorption of magnesium oxide and carbon skeleton. MgO serves as a catalytic center. Under alkaline conditions, OH- attacks D-galactose to isomerize it into D-tagatose. The MgO-carbon solid base catalyst has a hollow network spherical structure. Therefore, during the adsorption and isomerization process, D-galactose or D-tagatose has abundant adsorption and catalytic sites. The D-tagatose obtained after isomerization is adsorbed on the inner and outer surfaces of the spherical network of the solid base catalyst. In order to ensure the complete isomerization, the solid base catalyst with D-tagatose adsorbed in step two is allowed to stand for 10 to 20 minutes before washing to remove cations, so as to ensure that the D-galactose adsorbed on the solid base catalyst is fully converted into D-tagatose.

[0036] Step 3 involves directly filtering the solid phase material to separate the solid base catalyst adsorbed with D-tagatose. Deionized water is then used to slowly soak and wash away the cations. During the cation removal process, the deionized water enters the solid base catalyst through the carbon skeleton network structure to remove the cations simultaneously. Step 3 emphasizes the slow use of deionized water to remove soluble cations, reducing the residue of cations in subsequent separations and obtaining high-purity D-tagatose.

[0037] Further utilizing phase differences, the solid base catalyst adsorbed with D-tagatose was centrifuged in deionized water. Centrifugal force separated the D-tagatose adsorbed on the surface of the solid base catalyst from the catalyst itself, and the supernatant obtained was a D-tagatose solution. The D-tagatose solution obtained in step three was then concentrated under vacuum heating, crystallized, and vacuum dried to obtain D-tagatose crystals. Through the above separation and purification, this invention utilizes the adsorption properties of the solid base catalyst and its effective dispersion in the liquid phase to achieve sufficient adsorption-isomerization of D-galactose and maintain the adsorption of D-tagatose, effectively enriching D-tagatose without the need for ion exchange resins by utilizing phase differences and centrifugal force to desorb the adsorption. Attached Figure Description

[0038] Figure 1 These are the XRD patterns of the solid base catalysts obtained in Examples 1 and 2;

[0039] Figure 2 This is a SEM image of the solid base catalyst obtained in Example 4. Detailed Implementation

[0040] To further explain the technical solution of the present invention, the present invention will be described in detail below through specific embodiments.

[0041] This invention utilizes the adsorption of D-galactose by magnesium oxide and the carbon skeleton, which aggregates at MgO on the surface of the carbon skeleton. MgO acts as a catalytic center, and under alkaline conditions, OH- attacks D-galactose to isomerize it into D-tagatose. The MgO-carbon solid base catalyst has a hollow network spherical structure, thus providing abundant adsorption and catalytic sites for either D-galactose or D-tagatose during adsorption and isomerization. The D-tagatose obtained after isomerization is adsorbed on the inner and outer surfaces of the spherical network of the solid base catalyst. To ensure complete isomerization, the solid base catalyst with D-tagatose adsorbed in step two is allowed to stand for 10 to 20 minutes before step three to ensure that the D-galactose adsorbed on the solid base catalyst is fully converted into D-tagatose.

[0042] Step 3 involves directly filtering the solid phase material to separate the solid base catalyst adsorbed with D-tagatose. Deionized water is then used to slowly soak and wash away the cations. During the cation removal process, the deionized water enters the solid base catalyst through the carbon skeleton network structure to remove the cations simultaneously. Step 3 emphasizes the slow use of deionized water to remove soluble cations, reducing the residue of cations in subsequent separations and obtaining high-purity D-tagatose.

[0043] Further utilizing phase differences, the solid base catalyst adsorbed with D-tagatose was centrifuged in deionized water. Centrifugal force separated the D-tagatose adsorbed on the surface of the solid base catalyst from the catalyst itself, and the supernatant obtained was a D-tagatose solution. The D-tagatose solution obtained in step three was then concentrated under vacuum heating, crystallized, and vacuum dried to obtain D-tagatose crystals. Through the above separation and purification, this invention utilizes the adsorption properties of the solid base catalyst and its effective dispersion in the liquid phase to achieve sufficient adsorption-isomerization of D-galactose and maintain the adsorption of D-tagatose, effectively enriching D-tagatose without the need for ion exchange resins by utilizing phase differences and centrifugal force to desorb the adsorption.

[0044] Example 1

[0045] This embodiment discloses a method for preparing a MgO-carbon solid base catalyst with a hollow network spherical structure, comprising the following steps:

[0046] S11. Place the hollow spherical network framework, which serves as a template for the growth of magnesium oxide particles, in a magnesium nitrate solution.

[0047] The mass ratio of magnesium nitrate to the spherical network skeleton is 1.0:1.0.

[0048] In this embodiment, the spherical network framework is a porous chitosan-polyacrylic acid hollow microsphere. The mass ratio of chitosan to acrylic acid is 1:2.

[0049] S12, adjust the pH of the mixture obtained from S11 to 7, and the -NH2 chelation of magnesium ions in the solution by chitosan in the spherical network framework;

[0050] The hollow spherical network framework of S12 was placed in magnesium nitrate solution for 2 hours, and the pH of the system was maintained at 7 during the process. During this process, the amino chelate magnesium ions of chitosan controlled the uniform distribution of magnesium oxide particles on the surface of the porous hollow spherical carbon framework.

[0051] S13, hydrothermal reaction, chitosan and polyacrylic acid carbonize to form a carbon skeleton, while magnesium hydroxide grows on the surface of the carbon skeleton.

[0052] The process parameters for the S13 hydrothermal reaction are as follows:

[0053] The temperature was 200℃; the time was 12 hours.

[0054] S14, the solid obtained from S13 was calcined at 600℃ for 2 hours under nitrogen protection to obtain MgO-carbon solid base catalyst.

[0055] Example 2

[0056] This embodiment discloses a method for preparing a MgO-carbon solid base catalyst with a hollow network spherical structure, comprising the following steps:

[0057] S11. Place the hollow spherical network framework, which serves as a template for the growth of magnesium oxide particles, in a magnesium nitrate solution.

[0058] The mass ratio of magnesium nitrate to the spherical network skeleton is 1:1.1.

[0059] The hollow spherical network framework, which serves as a template for the growth of magnesium hydroxide particles, has a diameter of approximately 30 μm.

[0060] In this embodiment, the spherical network framework is a porous chitosan hollow microsphere.

[0061] S12, adjust the pH of the mixture obtained from S11 to 7, and the -NH2 chelation of magnesium ions in the solution by chitosan in the spherical network framework;

[0062] The hollow spherical network framework of S12 was placed in magnesium nitrate solution for 3 hours, and the pH of the system was maintained at 7 during the process. During this process, the amino chelate magnesium ions of chitosan controlled the uniform distribution of magnesium oxide particles on the surface of the porous hollow spherical carbon framework.

[0063] S13, hydrothermal reaction, chitosan and polyacrylic acid carbonize to form a carbon skeleton, while magnesium hydroxide grows on the surface of the carbon skeleton.

[0064] The process parameters for the S13 hydrothermal reaction are as follows:

[0065] The temperature was 220℃; the time was 12 hours.

[0066] S14, the solid obtained from S13 was calcined at 700℃ for 2 hours under nitrogen protection to obtain MgO-carbon solid base catalyst.

[0067] Example 3

[0068] This embodiment discloses a method for preparing a MgO-carbon solid base catalyst with a hollow network spherical structure, comprising the following steps:

[0069] S11. Place the hollow spherical network framework, which serves as a template for the growth of magnesium oxide particles, in a magnesium nitrate solution.

[0070] The mass ratio of magnesium nitrate to the spherical network skeleton is 1:1.2.

[0071] The hollow spherical network framework, which serves as a template for the growth of magnesium hydroxide particles, has a diameter of approximately 40 μm.

[0072] In this embodiment, the spherical network framework is a porous chitosan hollow microsphere.

[0073] S12, adjust the pH of the mixture obtained from S11 to 7, and the -NH2 chelation of magnesium ions in the solution by chitosan in the spherical network framework;

[0074] The hollow spherical network framework of S12 was placed in magnesium nitrate solution for 2 hours, and the pH of the system was maintained at 7 during the process. During this process, the amino chelate magnesium ions of chitosan controlled the uniform distribution of magnesium oxide particles on the surface of the porous hollow spherical carbon framework.

[0075] S13, hydrothermal reaction, chitosan and polyacrylic acid carbonize to form a carbon skeleton, while magnesium hydroxide grows on the surface of the carbon skeleton.

[0076] The process parameters for the S13 hydrothermal reaction are as follows:

[0077] The temperature was 200℃; the time was 18 hours.

[0078] S14, the solid obtained from S13 was calcined at 600℃ for 3 hours under nitrogen protection to obtain MgO-carbon solid base catalyst.

[0079] Example 4

[0080] This embodiment discloses a method for preparing a MgO-carbon solid base catalyst with a hollow network spherical structure, comprising the following steps:

[0081] S11. Place the hollow spherical network framework, which serves as a template for the growth of magnesium oxide particles, in a magnesium nitrate solution.

[0082] The mass ratio of magnesium nitrate to the spherical network skeleton is 1:1.3.

[0083] The hollow spherical network framework, which serves as a template for the growth of magnesium hydroxide particles, has a diameter of approximately 60 μm.

[0084] In this embodiment, the spherical network framework is a porous chitosan hollow microsphere.

[0085] S12, adjust the pH of the mixture obtained from S11 to 7, and the -NH2 chelation of magnesium ions in the solution by chitosan in the spherical network framework;

[0086] The hollow spherical network framework of S12 was placed in magnesium nitrate solution for 3 hours, and the pH of the system was maintained at 7 during the process. During this process, the amino chelate magnesium ions of chitosan controlled the uniform distribution of magnesium oxide particles on the surface of the porous hollow spherical carbon framework.

[0087] S13, hydrothermal reaction, chitosan and polyacrylic acid carbonize to form a carbon skeleton, while magnesium hydroxide grows on the surface of the carbon skeleton.

[0088] The process parameters for the S13 hydrothermal reaction are as follows:

[0089] The temperature was 220℃; the time was 12 hours.

[0090] S14, the solid obtained from S13 was calcined at 700℃ for 3 hours under nitrogen protection to obtain MgO-carbon solid base catalyst.

[0091] Example 5

[0092] This embodiment discloses a method for the separation and purification of D-tagatose, the process of which is as follows: Figure 1 As shown, it includes the following steps:

[0093] Step 1: The MgO-carbon solid base catalyst prepared in Example 1 was placed in a 20% (w / w) D-galactose aqueous solution. The pH of the reaction system was adjusted to 10 using sodium hydroxide solution. The mixture was stirred at 25°C for 60 min. The reactant D-galactose was adsorbed onto the MgO on the surface of the carbon skeleton by magnesium oxide and carbon skeleton. MgO served as the catalytic center. Under alkaline conditions, OH- attacked D-galactose and isomerized it into D-tagatose.

[0094] The MgO-carbon solid base catalyst has a hollow network spherical structure.

[0095] The mass ratio of MgO-carbon solid base catalyst to D-galactose is 0.3:1;

[0096] Step 2: Filter the solid phase material from Step 1 to separate the solid base catalyst adsorbed with D-tagatose, and slowly soak and wash it with deionized water to remove cations.

[0097] The solid base catalyst with D-tagatose adsorbed obtained in step two was allowed to stand for 20 minutes before washing to remove cations;

[0098] The solid material obtained in step one is brought to a volume equal to that of the reactants in step one using deionized water. During the removal of cations, deionized water enters the solid base catalyst through the carbon skeleton network structure to remove cations simultaneously. The process is repeated until the cation concentration is 7% of the initial cation concentration.

[0099] Step 3: Place the solid base catalyst adsorbed with D-tagatose in deionized water and centrifuge to separate the D-tagatose adsorbed on the surface of the solid base catalyst from the solid base catalyst by centrifugation. The supernatant obtained by centrifugation is the D-tagatose solution. The centrifugation process parameters are 5000 rpm and 15 min.

[0100] Step 4: Vacuum heating to concentrate the D-tagatose solution obtained in Step 3 until the D-tagatose content is 82°Bx;

[0101] Step 5: Crystallize and vacuum dry to obtain D-tagatose crystals.

[0102] Crystallization in step five includes the following steps:

[0103] S51. Take a volume of V of the concentrated solution obtained in step four, add anhydrous ethanol solution, and turbidity will appear. Add ethanol in a volume that is 2.0 times the volume of the concentrated solution.

[0104] S52. Heat to 60℃ until the purified D-tagatose dispersion system is clarified; then cool.

[0105] S53. Add D-tagatose seed crystals, place at 2℃ to 4℃ for 4 hours, stir, then add anhydrous ethanol at 2℃ to 4℃ with a volume of V, and let stand for 24 hours. A large amount of crystals will precipitate.

[0106] S54. Centrifuge the ethanol solution containing crystals;

[0107] S55. The crystals were stirred with anhydrous ethanol, filtered, and dried under vacuum to obtain D-tagatose crystals.

[0108] Example 6

[0109] This embodiment discloses a method for the separation and purification of D-tagatose, the process of which is as follows: Figure 1 As shown, it includes the following steps:

[0110] Step 1: The MgO-carbon solid base catalyst prepared in Example 2 was placed in a 20% D-galactose aqueous solution. The pH of the reaction system was adjusted to 12 using sodium hydroxide solution. The mixture was stirred at 30°C for 50 min. The reactant D-galactose was adsorbed onto the MgO on the surface of the carbon skeleton by magnesium oxide and carbon skeleton. MgO served as the catalytic center. Under alkaline conditions, OH- attacked D-galactose and isomerized it into D-tagatose.

[0111] The MgO-carbon solid base catalyst has a hollow network spherical structure.

[0112] The mass ratio of MgO-carbon solid base catalyst to D-galactose is 0.4:1;

[0113] Step 2: Filter the solid phase material from Step 1 to separate the solid base catalyst adsorbed with D-tagatose. Use deionized water to slowly soak and wash to remove cations. Use deionized water to adjust the volume of the solid phase material obtained in Step 1 to the same volume as the reaction material in Step 1.

[0114] The solid base catalyst with D-tagatose adsorbed obtained in step two was allowed to stand for 20 minutes before washing to remove cations;

[0115] During the cation removal process, deionized water enters the solid base catalyst through the carbon skeleton network structure to remove cations simultaneously; the process is repeated until the cation concentration is 6% of the initial cation concentration.

[0116] Step 3: Place the solid base catalyst adsorbed with D-tagatose in deionized water and centrifuge to separate the D-tagatose adsorbed on the surface of the solid base catalyst from the solid base catalyst by centrifugation. The supernatant obtained by centrifugation is the D-tagatose solution. The centrifugation process parameters are 5000 rpm and 15 min.

[0117] Step 4: Vacuum heating to concentrate the D-tagatose solution obtained in Step 3 until the D-tagatose content is 80°Bx;

[0118] Step 5: Crystallize and vacuum dry to obtain D-tagatose crystals.

[0119] Crystallization in step five includes the following steps:

[0120] S51. Take a volume of V of the concentrated solution obtained in step four, add anhydrous ethanol solution, and turbidity will appear. The volume of ethanol added is 2.5 times the volume of the concentrated solution.

[0121] S52. Heat to 60℃ until the purified D-tagatose dispersion system is clarified; then cool.

[0122] S53. Add D-tagatose seed crystals, place at 2℃ to 4℃ for 4 hours, stir, then add anhydrous ethanol at 2℃ to 4℃ with a volume of V, and let stand for 36 hours. A large amount of crystals will precipitate.

[0123] S54. Centrifuge the ethanol solution containing crystals;

[0124] S55. The crystals were stirred with anhydrous ethanol, filtered, and dried under vacuum to obtain D-tagatose crystals.

[0125] Example 7

[0126] This embodiment discloses a method for the separation and purification of D-tagatose, the process of which is as follows: Figure 1 As shown, it includes the following steps:

[0127] Step 1: The MgO-carbon solid base catalyst prepared in Example 3 was placed in a 20% D-galactose aqueous solution. The pH of the reaction system was adjusted to 11 using sodium hydroxide solution. The mixture was stirred at 32°C for 30 min. The reactant D-galactose was adsorbed onto the MgO on the surface of the carbon skeleton by magnesium oxide and carbon skeleton. MgO served as the catalytic center. Under alkaline conditions, OH- attacked D-galactose and isomerized it into D-tagatose.

[0128] The MgO-carbon solid base catalyst has a hollow network spherical structure.

[0129] The mass ratio of MgO-carbon solid base catalyst to D-galactose is 0.3:1;

[0130] Step 2: Filter the solid phase material from Step 1 to separate the solid base catalyst adsorbed with D-tagatose. Use deionized water to slowly soak and wash to remove cations. Use deionized water to adjust the volume of the solid phase material obtained in Step 1 to the same volume as the reaction material in Step 1.

[0131] The solid base catalyst with D-tagatose adsorbed obtained in step two was allowed to stand for 20 minutes before washing to remove cations;

[0132] During the cation removal process, deionized water enters the solid base catalyst through the carbon skeleton network structure to remove cations simultaneously; the process is repeated until the cation concentration is 7% of the initial cation concentration.

[0133] Step 3: Place the solid base catalyst adsorbed with D-tagatose in deionized water and centrifuge to separate the D-tagatose adsorbed on the surface of the solid base catalyst from the solid base catalyst by centrifugation. The supernatant obtained by centrifugation is the D-tagatose solution. The centrifugation process parameters are 5000 rpm and 15 min.

[0134] Step 4: Vacuum heating to concentrate the D-tagatose solution obtained in Step 3 until the D-tagatose content is 86°Bx;

[0135] Step 5: Crystallize and vacuum dry to obtain D-tagatose crystals.

[0136] Crystallization in step five includes the following steps:

[0137] S51. Take a volume of V of the concentrated solution obtained in step four, add anhydrous ethanol solution, and turbidity will appear. Add ethanol in a volume that is 2.0 times the volume of the concentrated solution.

[0138] S52. Heat to 60℃ until the purified D-tagatose dispersion system is clarified; then cool.

[0139] S53. Add D-tagatose seed crystals, place at 2℃ to 4℃ for 6 hours, stir, then add anhydrous ethanol at 2℃ to 4℃ with a volume of V, and let stand for 36 hours. A large amount of crystals will precipitate.

[0140] S54. Centrifuge the ethanol solution containing crystals;

[0141] S55. The crystals were stirred with anhydrous ethanol, filtered, and dried under vacuum to obtain D-tagatose crystals.

[0142] Example 8

[0143] This embodiment discloses a method for the separation and purification of D-tagatose, the process of which is as follows: Figure 1 As shown, it includes the following steps:

[0144] Step 1: The MgO-carbon solid base catalyst prepared in Example 4 was placed in a 20% D-galactose aqueous solution. The pH of the reaction system was adjusted to 10 using sodium hydroxide solution. The mixture was stirred at 30°C for 40 min. The reactant D-galactose was adsorbed onto the MgO on the surface of the carbon skeleton by magnesium oxide and carbon skeleton. MgO served as the catalytic center. Under alkaline conditions, OH- attacked D-galactose and isomerized it into D-tagatose.

[0145] The MgO-carbon solid base catalyst has a hollow network spherical structure.

[0146] The mass ratio of MgO-carbon solid base catalyst to D-galactose is 0.2:1;

[0147] Step 2: Filter the solid phase material from Step 1 to separate the solid base catalyst adsorbed with D-tagatose. Use deionized water to slowly soak and wash to remove cations. Use deionized water to adjust the volume of the solid phase material obtained in Step 1 to the same volume as the reaction material in Step 1.

[0148] The solid base catalyst with D-tagatose adsorbed obtained in step two was allowed to stand for 20 minutes before washing to remove cations;

[0149] During the cation removal process, deionized water enters the solid base catalyst through the carbon skeleton network structure to remove cations simultaneously; the process is repeated until the cation concentration is 7% of the initial cation concentration.

[0150] Step 3: Place the solid base catalyst adsorbed with D-tagatose in deionized water and centrifuge to separate the D-tagatose adsorbed on the surface of the solid base catalyst from the solid base catalyst by centrifugation. The supernatant obtained by centrifugation is the D-tagatose solution. The centrifugation process parameters are 5000 rpm and 15 min.

[0151] Step 4: Vacuum heating to concentrate the D-tagatose solution obtained in Step 3 until the D-tagatose content is 80°Bx;

[0152] Step 5: Crystallize and vacuum dry to obtain D-tagatose crystals.

[0153] Crystallization in step five includes the following steps:

[0154] S51. Take a volume of V of the concentrated solution obtained in step four, add anhydrous ethanol solution, and turbidity will appear. The volume of ethanol added is 2.5 times the volume of the concentrated solution.

[0155] S52. Heat until the D-tagatose dispersion to be purified is clarified; then cool.

[0156] S53. Add D-tagatose seed crystals, place at 2℃ to 4℃ for 6 hours, stir, then add anhydrous ethanol at 2℃ to 4℃ with a volume of V, and let stand for 36 hours. A large amount of crystals will precipitate.

[0157] S54. Centrifuge the ethanol solution containing crystals;

[0158] S55. The crystals were stirred with anhydrous ethanol, filtered, and dried under vacuum to obtain D-tagatose crystals.

[0159] Comparative Example

[0160] This comparative example discloses a method for the separation and purification of D-tagatose, which includes the following steps:

[0161] Isomerization: 500 mL of 6 mol / L calcium hydroxide slurry was slowly poured into 500 mL of 20% D-galactose solution and stirred continuously to react and generate metal hydroxide-D-tagatose complex. The isomerization reaction was carried out under alkaline and low temperature conditions, with a pH of 11 and an isomerization time of 60 min, within the range of room temperature to 35°C.

[0162] Acid neutralization: The metal hydroxide-D-tagatose complex is neutralized with acid dropwise, and the pH value is adjusted to below 5.4. In this way, the metal hydroxide in the complex is neutralized by acid and D-tagatose is released. In order to avoid adverse side reactions, the temperature of the reaction system is controlled below 25°C during the acid addition process.

[0163] The collected liquid phase is passed into a cation exchange resin column (D61), and the collected effluent is passed into an anion exchange resin column (D201). The effluent from the anion exchange resin column (D201) is collected.

[0164] Chromatographic separation: The effluent from the anion exchange resin column (D201) was separated by simulated moving bed chromatography (the packing material in the moving bed was potassium-type cation exchange resin). The eluent was deionized water. The operating temperature during separation was 40℃, the feed flow rate was 85 ml / min, the eluent flow rate was 110 ml / min, and the circulation flow rate was 110 ml / min. The purified tagatose solution was collected.

[0165] The D-tagatose solution obtained from step three of vacuum heating concentration was reduced to a D-tagatose content of 80°Bx.

[0166] Crystallization and vacuum drying yield D-tagatose crystals.

[0167] Crystallization includes the following steps:

[0168] S1. Take a volume of V of the concentrated solution obtained in step four, add anhydrous ethanol solution, and turbidity will appear. The volume of ethanol added is 2.5 times the volume of the concentrated solution.

[0169] S2. Heating, the D-tagatose dispersion to be purified becomes clear; cooling.

[0170] S3. Add D-tagatose seed crystals, place at 2℃ to 4℃ for 6 hours, stir, then add anhydrous ethanol at 2℃ to 4℃ with a volume of V, and let stand for 36 hours. A large amount of crystals will precipitate.

[0171] S4. Centrifuge the ethanol solution containing crystals;

[0172] S5. The crystals were stirred with anhydrous ethanol, filtered, and dried under vacuum to obtain D-tagatose crystals.

[0173] The specific surface areas of the solid base catalysts obtained in Examples 1 to 4 and the comparative examples are shown in Table 1.

[0174] Table 1. Specific surface area of ​​the solid base catalysts obtained in Examples 1 to 4

[0175] project <![CDATA[Specific surface area m 2 / g]]> Example 1 533 Example 2 588 Example 3 632 Example 4 687

[0176] Examples 5 to 8 and comparative examples evaluate the adsorption capacity of solid base catalysts for D-galactose during the isomerization process by measuring the ratio of unisomerized D-galactose concentration to the initial D-galactose concentration in the isomerized solution.

[0177] Table 2 shows the D-galactose content in the reaction solutions of Examples 5 to 8 and the comparative examples after isomerization.

[0178] project The percentage of D-galactose in the solution after isomerization Example 5 4.31％ Example 6 1.28％ Example 7 1.56％ Example 8 2.02％ Comparative Example 25.6％

[0179] The yields and purities of D-tagatose obtained in Examples 5 to 8 and the comparative examples are shown in Table 3.

[0180]

[0181]

[0182] Combination Figure 1 , Figure 2As shown in Tables 1 to 3, the MgO-carbon solid alkali catalyst prepared by the present invention enhances adsorption, enriches reactants, improves catalytic efficiency, facilitates subsequent separation and purification, and significantly reduces the equipment requirements for separation and purification. Furthermore, the MgO-carbon solid alkali catalyst obtained in step three of the present invention is regenerated and recycled after being washed multiple times with ethanol and deionized water and calcined at 200°C to 300°C, which effectively reduces the use and consumption of acids and alkalis in the production process. Further analysis of the yield and purity of D-tagatose obtained in Examples 5 to 8 and the comparative examples reveals that the magnesium oxide-carbon solid base catalysts obtained in Examples 2 to 4 exhibit superior adsorption performance for D-galactose compared to the solid base catalyst shown in Example 1. This enhanced adsorption performance promotes the enrichment of D-galactose, resulting in a low proportion of unadsorbed D-galactose. The adsorbed D-galactose aggregates around the surface of the magnesium oxide particles, which are uniformly loaded onto the surface of the carbon framework. Consequently, D-galactose is uniformly dispersed and enriched at the solid-liquid interface, effectively improving the conversion rate. Furthermore, this invention utilizes a solid base catalyst in conjunction with slow washing, centrifugation, and crystallization, effectively promoting the efficiency of separation and purification.

Claims

1. A method for separating and purifying D-tagatose, characterized in that: Includes the following steps: Step 1: Place the MgO-carbon solid base catalyst in an aqueous solution of D-galactose, adjust the pH of the reaction system to 10 to 12, and stir at room temperature to 35°C for 30 to 60 minutes. The reactant D-galactose aggregates on the MgO on the surface of the carbon skeleton under the adsorption of magnesium oxide and carbon skeleton. MgO acts as a catalytic center. Under alkaline conditions, OH- attacks D-galactose and isomerizes it into D-tagatose. The MgO-carbon solid base catalyst has a hollow network spherical structure; The mass ratio of MgO-carbon solid base catalyst to D-galactose is (0.3 to 0.4):1; Step 2: Filter the solid phase material from Step 1 to separate the solid base catalyst adsorbed with D-tagatose. Use deionized water to slowly soak and wash to remove cations. During the process of removing cations, deionized water enters the solid base catalyst through the carbon skeleton network structure to remove cations simultaneously. Step 3: Place the solid base catalyst adsorbed with D-tagatose in deionized water and centrifuge to separate the D-tagatose adsorbed on the surface of the solid base catalyst from the solid base catalyst by centrifugation. The supernatant obtained by centrifugation is the D-tagatose solution. Step 4: Vacuum heating to concentrate the D-tagatose solution obtained in Step 3 until the D-tagatose content is 80 to 90°Bx; Step 5: Crystallize and vacuum dry to obtain D-tagatose crystals; The preparation method of MgO-carbon solid base catalyst with hollow network spherical structure includes the following steps: S11. The hollow spherical network framework, which serves as a template for the growth of magnesium oxide particles, is placed in a magnesium nitrate solution. S12, adjust the pH of the mixture obtained from S11 to 7, and the -NH2 chelation of magnesium ions in the solution by chitosan in the spherical network framework; S13, hydrothermal reaction, chitosan and polyacrylic acid carbonize to form a carbon skeleton, while magnesium hydroxide grows on the surface of the carbon skeleton. S14, MgO-carbon solid base catalyst obtained by calcining the solid obtained from S13; The diameter of the hollow spherical network framework used as a template for the growth of magnesium hydroxide particles ranges from 10 μm to 60 μm. The spherical network framework is composed of porous chitosan-polyacrylic acid hollow microspheres.

2. The method for separating and purifying D-tagatose as described in claim 1, characterized in that: Step five, crystallization, includes the following steps: S51. Take a volume of V of the concentrated solution obtained in step four, add anhydrous ethanol solution, and turbidity will appear. Add ethanol in a volume of 2.0 to 2.5 times the volume of the concentrated solution. S52. Heat until the D-tagatose dispersion to be purified is clarified; then cool. S53. Add D-tagatose seed crystals, place at 2℃ to 4℃ for 4 to 6 hours, stir, then add anhydrous ethanol at 2℃ to 4℃ with a volume of V, and let stand for 24 to 36 hours until a large amount of crystals precipitate. S54. Centrifuge the ethanol solution containing crystals; S55. The crystals were stirred with anhydrous ethanol, filtered, and dried under vacuum to obtain D-tagatose crystals.

3. The method for separating and purifying D-tagatose as described in claim 1, characterized in that: The mass ratio of magnesium nitrate to the spherical network skeleton in S11 is 1: (1.0 to 1.3).

4. The method for separating and purifying D-tagatose as described in claim 1, characterized in that: The hollow spherical network framework of S12 is placed in magnesium nitrate solution for 2 to 3 hours, and the pH of the system is maintained at 7 during the process. During this process, the amino chelate magnesium ions of chitosan control the uniform distribution of magnesium oxide particles on the surface of the porous hollow spherical carbon framework.

5. The method for separating and purifying D-tagatose as described in claim 1, characterized in that: The process parameters for the S13 hydrothermal reaction are as follows: The temperature is 200℃ to 220℃; The time is from 12:00 to 18:

00.

6. The method for separating and purifying D-tagatose as described in claim 1, characterized in that: The calcination process conditions for S14 are: calcination at 600℃ to 700℃ for 2 to 3 hours under nitrogen protection.

7. The method for separating and purifying D-tagatose as described in claim 1, characterized in that: In step two, after filtering the solid material from step one and letting it stand for 10 to 20 minutes, slowly rinse with deionized water to remove cations.

8. The method for separating and purifying D-tagatose as described in claim 1, characterized in that: The MgO-carbon solid base catalyst obtained in step three is regenerated and recycled after being washed multiple times with ethanol and deionized water and calcined at 200°C to 300°C.

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