Preparation process of low-chroma high-purity isosorbide

Abstract

This invention discloses a preparation process for high-purity isosorbide with low color intensity, belonging to the field of bio-based fine chemical preparation technology. Using sorbitol as a raw material, a dehydration and cyclization reaction is carried out under the protection of a composite solid acid catalyst and an inert atmosphere. This is combined with online dehydration, mild decolorization, electrodialysis desalination, and low-temperature solvent-induced crystallization techniques to achieve the preparation of high-purity isosorbide. By introducing hydrogen or nitrogen to suppress carbonization side reactions and using a gradient decolorization-purification process, the product color intensity is significantly reduced, and the purity and yield are improved.

Description

Technical Field

[0001] This invention relates to the field of bio-based fine chemical preparation technology, and in particular to a preparation process for low-color, high-purity isosorbide. Background Technology

[0002] Isosorbide is an important bio-based platform compound with the chemical name 1,4:3,6-diadehydr-D-sorbitol and the molecular formula C6H2O. 10 O4, with its rigid bicyclic structure, is widely used in pharmaceuticals (such as nitrate cardiovascular drugs), food additives, and bio-based polymer materials. With the trend of bio-based materials replacing petroleum-based materials, the demand for isosorbide, as a green monomer, continues to grow.

[0003] Currently, isosorbide is mainly prepared industrially using the catalytic dehydration method of sorbitol. This reaction is a typical intramolecular two-step dehydration pathway: sorbitol is first dehydrated to sorbitol (sorbitan), and then further dehydrated to isosorbide. This process usually needs to be carried out under acidic catalytic conditions and at relatively high temperatures, and the reaction conditions have a significant impact on the selectivity and quality of the product.

[0004] (1) Traditional liquid acid catalysis processes have significant drawbacks: In existing technologies, strong liquid acids such as concentrated sulfuric acid are widely used as catalysts. For example, in the patent with publication number US6407266B2 and related technologies, a 70% sorbitol solution is usually used for dehydration reactions. However, this type of method has the following problems: strong acid corrodes equipment, increasing production costs; waste acid emissions are serious, causing significant environmental pollution; side reactions (carbonization, condensation reactions) are serious, resulting in a darker product color; and the isosorbide content in the product is low, requiring complex post-processing. Therefore, traditional liquid acid methods are gradually becoming unable to meet the demands of green manufacturing and high-quality products.

[0005] (2) Although there have been improvements in solid acid catalysis systems, there are still shortcomings: In order to overcome the defects of liquid acids, researchers have developed solid acid catalysis systems. For example, in the patent with authorization announcement number CN109734722B, a sulfonic acid-functionalized carbon-based solid acid catalyst was used to achieve a conversion rate of nearly 100% for sorbitol and a yield of up to 83%; the patent application with publication number CN101691376A used a supported heteropolyacid catalyst and reacted at about 250°C with a yield of about 71.4%; the patent application with publication number CN104822684A also proposed to prepare dehydrated sugar alcohols by improving the catalytic system.

[0006] Although the above methods offer improvements in terms of environmental friendliness and catalyst recyclability, the following problems still exist: high reaction temperatures (typically above 200°C), resulting in high energy consumption; insufficient catalyst stability or high cost; significant side reactions affecting product color; and long reaction times limiting industrial efficiency. (3) The preparation of high-purity products still relies on complex separation processes: In recent years, some patents have attempted to improve product purity through post-processing. For example, patent application with publication number CN114437099A proposes to improve purity through purification and separation steps; patent application with patent number CN107141301A introduces crystallization process to improve product purity.

[0007] However, such methods typically have the following drawbacks: they rely on multi-stage distillation or high-temperature concentration, which can easily lead to thermal degradation; the color problem is not fundamentally solved; and the separation process is complex, increasing energy consumption and costs.

[0008] Therefore, it is necessary to develop a method for preparing isosorbide with low color intensity, high purity, stable process, and environmental friendliness. By synergistically optimizing the reaction process control, side reaction suppression, and post-processing purification, the product quality can be fundamentally improved and energy consumption reduced to meet the needs of high-end application fields. Summary of the Invention

[0009] Based on the problems raised in the background technology mentioned above, this invention proposes a preparation process for low-color, high-purity isosorbide.

[0010] The technical solution is as follows: A process for preparing low-color, high-purity isosorbide includes the following steps, in parts by mass: (1) Dehydration reaction steps Add 100 parts of sorbitol to the reactor, add 3-6 parts of composite solid acid catalyst, and carry out a melt dehydration reaction at 140-165℃ for 3-5 hours. At the same time, carry out a continuous dehydration reaction under a hydrogen or nitrogen protective atmosphere of 0.10-0.30 MPa, and remove the generated water simultaneously. (2) Neutralization and adjustment steps After the reaction is complete, the reaction solution is cooled to 80-100℃, and 1.5-3.0 parts of alkaline neutralizing agent are added to adjust the pH of the system to 6.5-7.5. (3) Primary decolorization steps Add 2-4 parts of activated carbon to the neutralized material, stir at 70-90℃ for 20-40 minutes, and then filter to remove the activated carbon. (4) Deep decolorization step Add 3-6 parts of anion exchange resin containing pyridine heterocyclic sorbate to the filtrate and treat at 50-70℃ for 30-60 min to remove colored impurities and trace metal ions; (5) Desalination and refining steps The decolorized solution was subjected to electrodialysis, with the voltage controlled at 5–15V and the treatment time at 30–90 minutes, in order to remove inorganic salts and ionic impurities. (6) Reduced pressure concentration step Vacuum concentration was carried out at 60–85℃ and -0.08–-0.095 MPa to achieve a solid content of 85–92% in the system. (7) Solvent-induced crystallization step Add 80-120 parts of crystallization induction solvent to the concentrate, stir and crystallize at 0-10℃ for 6-10 hours to precipitate crystals; (8) Separation and drying steps The crystals were filtered and separated, and then dried under vacuum at -10 to 0°C for 6 to 12 hours to obtain a low-color, high-purity isosorbide product.

[0011] Furthermore, the sorbitol is in the form of an aqueous solution with a mass fraction of 70-75%.

[0012] Furthermore, the composite solid acid catalyst is composed of the following components, in parts by mass: Sulfonic acid type cation exchange resin: 2-4 parts; Molecular sieve or sulfated zirconium oxide: 1-2 parts.

[0013] Furthermore, the alkaline neutralizing agent is one or a combination of two of calcium carbonate, sodium carbonate, or sodium hydroxide.

[0014] Furthermore, the activated carbon is wood-based activated carbon or coconut shell activated carbon, with a specific surface area of ​​800–1200 m². 2 / g.

[0015] Furthermore, the preparation method of the anion exchange resin containing pyridine heterocyclic sorbate is as follows, according to parts by mass: T1: 100-130 parts of acrylate-based macroporous white spheres are pre-swollen with 1000-1300 parts of N,N-dimethylformamide at 40-60℃ for 2-4 hours to fully expand the pore structure; 7.5-15.0 parts by weight of 1-(pyridin-4-yl)but-3-en-1-amine, 3-5 parts by weight of dimethylethanolamine, 0.6-2 parts by weight of vinyl sorbate, and 1-4 parts by weight of triethylamine are added and stirred until evenly dispersed; T2: The reaction is carried out in stages. The first stage is a constant temperature reaction at 50°C for 3 hours to complete the nucleophilic addition of amino-olefin and the primary grafting of pyridine heterocycle. The second stage is heated to 60°C and the reaction continues for 4-7 hours to achieve sorbate stabilization and deep amination. After the reaction is completed, the mixture is filtered and washed in sequence with hot DMF, ethanol and sterile deionized water to remove unreacted monomers and residual reagents. T3: The washed resin is dried at 50-70℃ and under a vacuum of -0.09 to -0.07 MPa for 4-7 hours to obtain anion exchange resin containing pyridine heterocyclic sorbate.

[0016] Furthermore, the electrodialysis employs a combination of anion and cation exchange membranes.

[0017] Furthermore, the system comprises alternating arrangements of cation exchange membranes and anion exchange membranes, wherein: the cation exchange membrane is selected from sulfonated polystyrene membranes, sulfonated polyether ether ketone membranes, or perfluorosulfonic acid membranes; and the anion exchange membrane is selected from quaternized polystyrene membranes, quaternized polysulfone membranes, or polyolefin-based anion exchange membranes.

[0018] Furthermore, the crystallization-inducing solvent is ethyl acetate or isopropanol.

[0019] The reaction mechanism of the ion exchange resin is as follows: After the acrylate macroporous white spheres are fully swollen, the pore structure is fully expanded, and the active sites are efficiently exposed; 1-(pyridin-4-yl)but-3-en-1-amine undergoes an amino-olefin nucleophilic addition reaction with dimethylethanolamine, and the pyridine heterocycle is covalently grafted onto the resin skeleton to construct stable basic adsorption sites; vinyl sorbate participates in in-situ copolymerization, forming an affinity interface on the resin surface that matches the structure of sorbitol, improving the compatibility between the resin and the sorbitol system, while optimizing the micropore distribution and increasing the effective contact area between the resin micropores and the reaction solution; triethylamine provides a mild basic catalytic environment, promoting the efficient conduct of addition and grafting reactions and avoiding side reactions; finally, a stable adsorption structure with a synergistic distribution of pyridine heterocycle sites, amino sites, and affinity ester sites is formed on the resin surface, which can specifically remove colored impurities and trace metal ions.

[0020] The technical advantages of ion exchange resins are as follows: the synergistic effect of pyridine heterocycles and amino sites can efficiently adsorb colored impurities and polar byproducts in the system, significantly improving the decolorization effect and ensuring the appearance quality of the product; vinyl sorbate optimizes the resin surface affinity and pore structure, improves the compatibility between the resin and sorbitol, increases the contact area between the resin micropores and the reaction solution, and improves the adsorption mass transfer efficiency; the simultaneous action of multiple types of adsorption sites can deeply remove trace metal ions and organic impurities, reduce the subsequent purification load, and improve the purity and yield of isosorbitol products.

[0021] Compared with the prior art, the present invention has the following advantages: 1. This invention effectively inhibits the carbonization and condensation side reactions of sorbitol under acidic high temperature conditions by introducing inert gas or hydrogen into the dehydration reaction process to protect the environment and controlling the timely removal of water, thereby reducing the generation of colored byproducts from the source.

[0022] 2. This invention employs a composite solid acid catalytic system to regulate the acid strength and acid quantity distribution of the catalyst, enabling it to both promote the complete dehydration of sorbitol and avoid side reactions caused by excessive acidity, thereby improving the selectivity of isosorbitol formation.

[0023] 3. By controlling the reaction temperature and combining it with continuous dehydration, this invention effectively reduces the probability of further side reactions such as cracking, condensation, and polymerization of the sorbitan intermediate. Simultaneously, the synergistic effect of the catalyst stabilizes the reaction intermediate, improving its conversion efficiency to the target product.

[0024] 4. By introducing electrodialysis or membrane separation desalination steps, catalyst residues and inorganic ions introduced during the neutralization process can be effectively removed, significantly reducing ionic impurities in the system. Detailed Implementation

[0025] The features of the present invention are further illustrated below through embodiments, but the scope of protection of this patent is not limited to the embodiments.

[0026] Example 1: A process for preparing low-color, high-purity isosorbide, comprising the following steps: (1) Dehydration reaction steps Weigh out 100g of sorbitol and add it to the reactor. Add 3g of composite solid acid catalyst and carry out a melt dehydration reaction at 140℃ for 3 hours. At the same time, carry out a continuous dehydration reaction under a 0.10MPa hydrogen protective atmosphere and remove the generated water simultaneously. The sorbitol is in the form of a 70% by mass aqueous solution; the composite solid acid catalyst is composed of the following components: 2g of sulfonic acid cation exchange resin and 1g of molecular sieve.

[0027] (2) Neutralization and adjustment steps After the reaction is complete, the reaction solution is cooled to 80°C, 1.5g of alkaline neutralizing agent is added, and the pH of the system is adjusted to 6.5. The alkaline neutralizing agent is calcium carbonate.

[0028] (3) Primary decolorization steps Add 2g of activated carbon to the neutralized material, stir at 70℃ for 20min, and then filter to remove the activated carbon. The activated carbon is wood-based activated carbon with a specific surface area of ​​800 m². 2 / g.

[0029] (4) Deep decolorization step Add 3g of anion exchange resin containing pyridine heterocyclic sorbate to the filtrate and treat at 50℃ for 30min to remove colored impurities and trace metal ions; The preparation method of the anion exchange resin containing pyridine heterocyclic sorbate is as follows: T1: 100g of acrylate-based macroporous white spheres were pre-swelled with 1000g of N,N-dimethylformamide at 40℃ for 2 hours to fully expand the pore structure; by weight, 7.5g of 1-(pyridin-4-yl)but-3-en-1-amine, 3g of dimethylethanolamine, 0.6g of vinyl sorbate, and 1g of triethylamine were added and stirred to disperse evenly; T2: The reaction was carried out in stages with temperature control. The first stage was a constant temperature reaction at 50°C for 3 hours to complete the nucleophilic addition of amino-olefins and the primary grafting of pyridine heterocycles. The second stage was a further reaction at 60°C for 4 hours to achieve sorbate stabilization and deep amination. After the reaction was completed, the mixture was filtered and washed sequentially with hot DMF, ethanol and sterile deionized water to remove unreacted monomers and residual reagents. T3: The washed resin was dried at 50°C and -0.09MPa vacuum for 4 hours to obtain anion exchange resin containing pyridine heterocyclic sorbate.

[0030] (5) Desalination and refining steps The decolorized solution was subjected to electrodialysis, with the voltage controlled at 5V and the treatment time at 30min, in order to remove inorganic salts and ionic impurities. The electrodialysis employs a combination of cation and anion exchange membranes; the system comprises alternating arrangements of cation exchange membranes and anion exchange membranes, wherein: the cation exchange membrane is selected from sulfonated polystyrene membranes; and the anion exchange membrane is selected from quaternized polystyrene membranes.

[0031] (6) Reduced pressure concentration step Vacuum concentration was carried out at 60℃ and -0.08MPa to achieve a solid content of 85% in the system.

[0032] (7) Solvent-induced crystallization step Add 80g of crystallization-inducing solvent to the concentrate, stir and crystallize at 0℃ for 6h to precipitate crystals; The crystallization-inducing solvent is ethyl acetate.

[0033] (8) Separation and drying steps The crystals were filtered and separated, and then dried at -10℃ under vacuum for 6 hours to obtain a low-color, high-purity isosorbide product.

[0034] Example 2: A process for preparing low-color, high-purity isosorbide, comprising the following steps: (1) Dehydration reaction steps Weigh out 100g of sorbitol and add it to the reactor. Add 4g of composite solid acid catalyst and carry out a melt dehydration reaction at 150℃ for 3.5h. At the same time, carry out a continuous dehydration reaction under a nitrogen protective atmosphere of 0.17MPa and remove the generated water simultaneously. The sorbitol is in the form of a 72% (w / w) aqueous solution; the composite solid acid catalyst is composed of the following components: 2.5g of sulfonic acid cation exchange resin and 1.5g of molecular sieve.

[0035] (2) Neutralization and adjustment steps After the reaction is complete, the reaction solution is cooled to 85°C, and 2.0g of alkaline neutralizing agent is added to adjust the pH of the system to 6.8. The alkaline neutralizing agent is sodium carbonate.

[0036] (3) Primary decolorization steps Add 2.5g of activated carbon to the neutralized material, stir at 75℃ for 27min, and then filter to remove the activated carbon. The activated carbon is coconut shell activated carbon with a specific surface area of ​​900 m². 2 / g.

[0037] (4) Deep decolorization step Add 4g of anion exchange resin containing pyridine heterocyclic sorbate to the filtrate and treat at 55℃ for 40min to remove colored impurities and trace metal ions. The preparation method of the anion exchange resin containing pyridine heterocyclic sorbate is as follows: T1: 110g of acrylate-based macroporous white spheres were pre-swelled with 1100g of N,N-dimethylformamide at 50℃ for 3 hours to fully expand the pore structure; 10g of 1-(pyridin-4-yl)but-3-en-1-amine, 4g of dimethylethanolamine, 1.0g of vinyl sorbate, and 2g of triethylamine were added by weight and stirred to disperse evenly; T2: The reaction was carried out in stages with temperature control. The first stage was a constant temperature reaction at 50°C for 3 hours to complete the nucleophilic addition of amino-olefins and the primary grafting of pyridine heterocycles. The second stage was a further reaction at 60°C for 5 hours to achieve sorbate stabilization and deep amination. After the reaction was completed, the mixture was filtered and washed in sequence with hot DMF, ethanol and sterile deionized water to remove unreacted monomers and residual reagents. T3: The washed resin was dried at 55°C and under a vacuum of -0.085 MPa for 5 hours to obtain anion exchange resin containing pyridine heterocyclic sorbate.

[0038] (5) Desalination and refining steps The decolorized solution was subjected to electrodialysis, with the voltage controlled at 8V and the treatment time at 50min, in order to remove inorganic salts and ionic impurities. The electrodialysis employs a combination of cation and anion exchange membranes; the system comprises alternating arrangements of cation exchange membranes and anion exchange membranes, wherein: the cation exchange membrane is selected from sulfonated polyether ether ketone membranes; and the anion exchange membrane is selected from quaternized polysulfone membranes.

[0039] (6) Reduced pressure concentration step Vacuum concentration was carried out at 70℃ and -0.085MPa to achieve a solid content of 87% in the system.

[0040] (7) Solvent-induced crystallization step Add 95g of crystallization-inducing solvent to the concentrate, stir at 3℃ for 7h to crystallize, and crystals will precipitate. The crystallization-inducing solvent is isopropanol.

[0041] (8) Separation and drying steps The crystals were filtered and separated, and then dried at -7℃ under vacuum for 8 hours to obtain a low-color, high-purity isosorbide product.

[0042] Example 3: A process for preparing low-color, high-purity isosorbide, comprising the following steps: (1) Dehydration reaction steps Weigh out 100g of sorbitol and add it to the reactor. Add 5g of composite solid acid catalyst and carry out a melt dehydration reaction at 160℃ for 4.5h. At the same time, carry out a continuous dehydration reaction under a 0.25MPa hydrogen protective atmosphere and remove the generated water simultaneously. The sorbitol is in the form of a 74% by mass aqueous solution; the composite solid acid catalyst is composed of the following components: 3.5g of sulfonic acid cation exchange resin and 1.8g of zirconium oxide sulfate.

[0043] (2) Neutralization and adjustment steps After the reaction was completed, the reaction solution was cooled to 95°C, and 2.6g of alkaline neutralizing agent was added to adjust the pH of the system to 7.2. The alkaline neutralizing agent is a combination of sodium hydroxide and calcium carbonate (mass ratio 1:1).

[0044] (3) Primary decolorization steps Add 3.5g of activated carbon to the neutralized material, stir at 85℃ for 35min, and then filter to remove the activated carbon. The activated carbon is wood-based activated carbon with a specific surface area of ​​1100 m². 2 / g.

[0045] (4) Deep decolorization step Add 5g of anion exchange resin containing pyridine heterocyclic sorbate to the filtrate and treat at 65℃ for 55min to remove colored impurities and trace metal ions. The preparation method of the anion exchange resin containing pyridine heterocyclic sorbate is as follows: T1: 125g of acrylate-based macroporous white spheres were pre-swelled with 1250g of N,N-dimethylformamide at 55℃ for 3.5 hours to fully expand the pore structure; 13g of 1-(pyridin-4-yl)but-3-en-1-amine, 4.5g of dimethylethanolamine, 1.7g of vinyl sorbate, and 3.5g of triethylamine were added by weight and stirred to disperse evenly; T2: The reaction was carried out in stages with temperature control. The first stage was a constant temperature reaction at 50°C for 3 hours to complete the nucleophilic addition of amino-olefins and the primary grafting of pyridine heterocycles. The second stage was heated to 60°C and the reaction continued for 6.5 hours to achieve sorbate stabilization and deep amination. After the reaction was completed, the mixture was filtered and washed sequentially with hot DMF, ethanol, and sterile deionized water to remove unreacted monomers and residual reagents. T3: The washed resin was dried at 65°C and under a vacuum of -0.075 MPa for 6.5 hours to obtain anion exchange resin containing pyridine heterocyclic sorbate.

[0046] (5) Desalination and refining steps The decolorized solution was subjected to electrodialysis at a controlled voltage of 13V for 80 minutes to remove inorganic salts and ionic impurities. The electrodialysis employs a combination of cation and anion exchange membranes; the system comprises alternating arrangements of cation exchange membranes and anion exchange membranes, wherein: the cation exchange membrane is selected from perfluorosulfonic acid membranes; and the anion exchange membrane is selected from polyolefin-based anion exchange membranes.

[0047] (6) Reduced pressure concentration step Vacuum concentration was carried out at 80℃ and -0.092MPa to achieve a solid content of 90%.

[0048] (7) Solvent-induced crystallization step Add 110g of crystallization-inducing solvent to the concentrate, stir at 8℃ for 9h to crystallize, and crystals will precipitate. The crystallization-inducing solvent is ethyl acetate.

[0049] (8) Separation and drying steps The crystals were filtered and separated, and then dried at -2℃ under vacuum for 10 hours to obtain a low-color, high-purity isosorbide product.

[0050] Example 4: A process for preparing low-color, high-purity isosorbide, comprising the following steps: (1) Dehydration reaction steps Weigh out 100g of sorbitol and add it to the reactor. Add 6g of composite solid acid catalyst and carry out a melt dehydration reaction at 165℃ for 5 hours. At the same time, carry out a continuous dehydration reaction under a nitrogen protective atmosphere of 0.30MPa and remove the generated water simultaneously. The sorbitol is in the form of a 75% (w / w) aqueous solution; the composite solid acid catalyst is composed of the following components: 4g of sulfonic acid cation exchange resin and 2g of zirconium oxide sulfate.

[0051] (2) Neutralization and adjustment steps After the reaction is complete, the reaction solution is cooled to 100℃, 3.0g of alkaline neutralizing agent is added, and the pH of the system is adjusted to 7.5. The alkaline neutralizing agent is sodium hydroxide.

[0052] (3) Primary decolorization steps Add 4g of activated carbon to the neutralized material, stir at 90℃ for 40min, and then filter to remove the activated carbon. The activated carbon is coconut shell activated carbon with a specific surface area of ​​1200 m². 2 / g.

[0053] (4) Deep decolorization step Add 6g of anion exchange resin containing pyridine heterocyclic sorbate to the filtrate and treat at 70℃ for 60min to remove colored impurities and trace metal ions; The preparation method of the anion exchange resin containing pyridine heterocyclic sorbate is as follows: T1: 130g of acrylate-based macroporous white spheres were pre-swelled with 1300g of N,N-dimethylformamide at 60℃ for 4 hours to fully expand the pore structure; 15.0g of 1-(pyridin-4-yl)but-3-en-1-amine, 5g of dimethylethanolamine, 2g of vinyl sorbate, and 4g of triethylamine were added by weight and stirred to disperse evenly; T2: The reaction was carried out in stages with temperature control. The first stage was a constant temperature reaction at 50°C for 3 hours to complete the nucleophilic addition of amino-olefins and the primary grafting of pyridine heterocycles. The second stage was a further reaction at 60°C for 7 hours to achieve sorbate stabilization and deep amination. After the reaction was completed, the mixture was filtered and washed in sequence with hot DMF, ethanol and sterile deionized water to remove unreacted monomers and residual reagents. T3: The washed resin was dried at 70°C and -0.07MPa vacuum for 7 hours to obtain anion exchange resin containing pyridine heterocyclic sorbate.

[0054] (5) Desalination and refining steps The decolorized solution was subjected to electrodialysis at a controlled voltage of 15V for 90 minutes to remove inorganic salts and ionic impurities. The electrodialysis employs a combination of cation and anion exchange membranes; the system comprises alternating arrangements of cation exchange membranes and anion exchange membranes, wherein: the cation exchange membrane is selected from perfluorosulfonic acid membranes; and the anion exchange membrane is selected from polyolefin-based anion exchange membranes.

[0055] (6) Reduced pressure concentration step Vacuum concentration was carried out at 85℃ and -0.095MPa to achieve a solid content of 92% in the system.

[0056] (7) Solvent-induced crystallization step Add 120g of crystallization induction solvent to the concentrate, stir at 10℃ for 10h to crystallize, and crystals will precipitate. The crystallization-inducing solvent is isopropanol.

[0057] (8) Separation and drying steps The crystals were filtered and separated, and then dried at 0°C under vacuum for 12 hours to obtain a low-color, high-purity isosorbide product.

[0058] Comparative Example 1: A process for preparing low-color, high-purity isosorbide, comprising the following steps: (1) Dehydration reaction steps Weigh out 100g of sorbitol and add it to the reactor. Add 3g of composite solid acid catalyst and carry out a melt dehydration reaction at 140℃ for 3 hours. At the same time, carry out a continuous dehydration reaction under a 0.10MPa hydrogen protective atmosphere and remove the generated water simultaneously. The sorbitol is in the form of a 70% by mass aqueous solution; the composite solid acid catalyst is composed of the following components: 2g of sulfonic acid cation exchange resin and 1g of molecular sieve.

[0059] (2) Neutralization and adjustment steps After the reaction is complete, the reaction solution is cooled to 80°C, 1.5g of alkaline neutralizing agent is added, and the pH of the system is adjusted to 6.5. The alkaline neutralizing agent is calcium carbonate.

[0060] (3) Primary decolorization steps Add 2g of activated carbon to the neutralized material, stir at 70℃ for 20min, and then filter to remove the activated carbon. The activated carbon is wood-based activated carbon with a specific surface area of ​​800 m². 2 / g.

[0061] (4) Deep decolorization step Add 3g of acrylate-based macroporous white spheres to the filtrate and treat at 50℃ for 30min to remove colored impurities and trace metal ions; (5) Desalination and refining steps The decolorized solution was subjected to electrodialysis, with the voltage controlled at 5V and the treatment time at 30min, in order to remove inorganic salts and ionic impurities. The electrodialysis employs a combination of cation and anion exchange membranes; the system comprises alternating arrangements of cation exchange membranes and anion exchange membranes, wherein: the cation exchange membrane is selected from sulfonated polystyrene membranes; and the anion exchange membrane is selected from quaternized polystyrene membranes.

[0062] (6) Reduced pressure concentration step Vacuum concentration was carried out at 60℃ and -0.08MPa to achieve a solid content of 85% in the system.

[0063] (7) Solvent-induced crystallization step Add 80g of crystallization-inducing solvent to the concentrate, stir and crystallize at 0℃ for 6h to precipitate crystals; The crystallization-inducing solvent is ethyl acetate.

[0064] (8) Separation and drying steps The crystals were filtered and separated, and then dried at -10℃ under vacuum for 6 hours to obtain a low-color, high-purity isosorbide product.

[0065] Comparative Example 2: A process for preparing low-color, high-purity isosorbide, comprising the following steps: (1) Dehydration reaction steps Weigh out 100g of sorbitol and add it to the reactor. Add 3g of composite solid acid catalyst and carry out a melt dehydration reaction at 140℃ for 3 hours. At the same time, carry out a continuous dehydration reaction under a 0.10MPa hydrogen protective atmosphere and remove the generated water simultaneously. The sorbitol is in the form of a 70% by mass aqueous solution; the composite solid acid catalyst is composed of the following components: 2g of sulfonic acid cation exchange resin and 1g of molecular sieve.

[0066] (2) Neutralization and adjustment steps After the reaction is complete, the reaction solution is cooled to 80°C, 1.5g of alkaline neutralizing agent is added, and the pH of the system is adjusted to 6.5. The alkaline neutralizing agent is calcium carbonate.

[0067] (3) Primary decolorization steps Add 2g of activated carbon to the neutralized material, stir at 70℃ for 20min, and then filter to remove the activated carbon. The activated carbon is wood-based activated carbon with a specific surface area of ​​800 m². 2 / g.

[0068] (4) Deep decolorization step Add 3g of anion exchange resin containing pyridine heterocyclic sorbate to the filtrate and treat at 50℃ for 30min to remove colored impurities and trace metal ions; The preparation method of the anion exchange resin containing pyridine heterocyclic sorbate is as follows: T1: 100g of acrylate-based macroporous white spheres are pre-swelled with 1000g of N,N-dimethylformamide at 40℃ for 2 hours to fully expand the pore structure; by weight, add 3g of dimethylethanolamine, 0.6g of vinyl sorbate, and 1g of triethylamine, and stir to disperse evenly; T2: The reaction was carried out in stages with temperature control. The first stage was a constant temperature reaction at 50°C for 3 hours to complete the nucleophilic addition of amino-olefins and the primary grafting of pyridine heterocycles. The second stage was a further reaction at 60°C for 4 hours to achieve sorbate stabilization and deep amination. After the reaction was completed, the mixture was filtered and washed sequentially with hot DMF, ethanol and sterile deionized water to remove unreacted monomers and residual reagents. T3: The washed resin was dried at 50°C and -0.09MPa vacuum for 4 hours to obtain anion exchange resin containing pyridine heterocyclic sorbate.

[0069] (5) Desalination and refining steps The decolorized solution was subjected to electrodialysis, with the voltage controlled at 5V and the treatment time at 30min, in order to remove inorganic salts and ionic impurities. The electrodialysis employs a combination of cation and anion exchange membranes; the system comprises alternating arrangements of cation exchange membranes and anion exchange membranes, wherein: the cation exchange membrane is selected from sulfonated polystyrene membranes; and the anion exchange membrane is selected from quaternized polystyrene membranes.

[0070] (6) Reduced pressure concentration step Vacuum concentration was carried out at 60℃ and -0.08MPa to achieve a solid content of 85% in the system.

[0071] (7) Solvent-induced crystallization step Add 80g of crystallization-inducing solvent to the concentrate, stir and crystallize at 0℃ for 6h to precipitate crystals; The crystallization-inducing solvent is ethyl acetate.

[0072] (8) Separation and drying steps The crystals were filtered and separated, and then dried at -10℃ under vacuum for 6 hours to obtain a low-color, high-purity isosorbide product.

[0073] Comparative Example 3: A process for preparing low-color, high-purity isosorbide, comprising the following steps: (1) Dehydration reaction steps Weigh out 100g of sorbitol and add it to the reactor. Add 3g of composite solid acid catalyst and carry out a melt dehydration reaction at 140℃ for 3 hours. At the same time, carry out a continuous dehydration reaction under a 0.10MPa hydrogen protective atmosphere and remove the generated water simultaneously. The sorbitol is in the form of a 70% by mass aqueous solution; the composite solid acid catalyst is composed of the following components: 2g of sulfonic acid cation exchange resin and 1g of molecular sieve.

[0074] (2) Neutralization and adjustment steps After the reaction is complete, the reaction solution is cooled to 80°C, 1.5g of alkaline neutralizing agent is added, and the pH of the system is adjusted to 6.5. The alkaline neutralizing agent is calcium carbonate.

[0075] (3) Primary decolorization steps Add 2g of activated carbon to the neutralized material, stir at 70℃ for 20min, and then filter to remove the activated carbon. The activated carbon is wood-based activated carbon with a specific surface area of ​​800 m². 2 / g.

[0076] (4) Deep decolorization step Add 3g of anion exchange resin containing pyridine heterocyclic sorbate to the filtrate and treat at 50℃ for 30min to remove colored impurities and trace metal ions; The preparation method of the anion exchange resin containing pyridine heterocyclic sorbate is as follows: T1: 100g of acrylate-based macroporous white spheres were pre-swelled with 1000g of N,N-dimethylformamide at 40℃ for 2 hours to fully expand the pore structure; 7.5g of 1-(pyridin-4-yl)but-3-ene-1-amine, 0.6g of vinyl sorbate, and 1g of triethylamine were added by weight and stirred to disperse evenly; T2: The reaction was carried out in stages with temperature control. The first stage was a constant temperature reaction at 50°C for 3 hours to complete the nucleophilic addition of amino-olefins and the primary grafting of pyridine heterocycles. The second stage was a further reaction at 60°C for 4 hours to achieve sorbate stabilization and deep amination. After the reaction was completed, the mixture was filtered and washed sequentially with hot DMF, ethanol and sterile deionized water to remove unreacted monomers and residual reagents. T3: The washed resin was dried at 50°C and -0.09MPa vacuum for 4 hours to obtain anion exchange resin containing pyridine heterocyclic sorbate.

[0077] (5) Desalination and refining steps The decolorized solution was subjected to electrodialysis, with the voltage controlled at 5V and the treatment time at 30min, in order to remove inorganic salts and ionic impurities. The electrodialysis employs a combination of cation and anion exchange membranes; the system comprises alternating arrangements of cation exchange membranes and anion exchange membranes, wherein: the cation exchange membrane is selected from sulfonated polystyrene membranes; and the anion exchange membrane is selected from quaternized polystyrene membranes.

[0078] (6) Reduced pressure concentration step Vacuum concentration was carried out at 60℃ and -0.08MPa to achieve a solid content of 85% in the system.

[0079] (7) Solvent-induced crystallization step Add 80g of crystallization-inducing solvent to the concentrate, stir and crystallize at 0℃ for 6h to precipitate crystals; The crystallization-inducing solvent is ethyl acetate.

[0080] (8) Separation and drying steps The crystals were filtered and separated, and then dried at -10℃ under vacuum for 6 hours to obtain a low-color, high-purity isosorbide product.

[0081] Test method: (1) Purity and content determination (HPLC method) The purity of isosorbide was determined by high performance liquid chromatography (HPLC).

[0082] Test conditions: Column: Sugar-Ca 2+ Type glycoside analysis column (300mm × 7.8mm) Mobile phase: deionized water Flow rate: 0.5 mL / min Column temperature: 80℃ Detector: Differential refractive index detector (RID) Injection volume: 5 μL (2) Colorimetric determination (APHA method) The platinum-cobalt standard colorimetric method (APHA colorimetric method) was used: Test method: Dissolve the sample in a 10 wt% aqueous solution. The absorbance was measured at 455 nm using a spectrophotometer. Calculate the colorimetric value by comparing it with a standard platinum-cobalt solution. (3) Moisture determination (Karl Fischer method) Moisture content was determined by Karl Fischer volumetric titration. Test principle: Water reacts quantitatively with iodine and sulfur dioxide, and the amount consumed is directly proportional to the amount of water.

[0083] Test conditions: Solvent: Anhydrous methanol Injection volume: 10–50 mg Titration method: Automatic potentiometric endpoint (4) Yield determination Based on the amount of sorbitol used, calculate according to the following formula: Yield (%) = (Actual product mass / Theoretical yield) × 100% The test results are shown in Table 1 below: Table 1: Test results of each embodiment and comparative example

[0084] The pyridine heterocyclic + sorbate anion exchange resin adsorbent prepared by this method, when applied to the deep decolorization step of isosorbide, significantly improves the purity, color, moisture content, and yield of the product. Specifically, 1-(pyridin-4-yl)but-3-en-1-amine provides pyridine heterocyclic adsorption sites, efficiently removing conjugated colored impurities and metal ions; dimethylethanolamine constructs tertiary amine sites, enhancing the adsorption and decolorization capabilities of anionic impurities; vinyl sorbate improves the compatibility between the resin and the sorbitol system, optimizes the microporous structure, and increases the contact area between the resin and the reaction solution, resulting in more complete adsorption and faster mass transfer, while also improving the binding strength of functional groups, ensuring a stable and long-lasting adsorption process. The synergistic effect of each component results in lower color and higher purity of the product, while also controlling yield and moisture content. Overall performance is significantly superior to conventional resin systems, meeting the requirements for preparing low-color, high-purity isosorbide.

[0085] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A preparation process for low-color, high-purity isosorbide, characterized in that, Includes the following steps, by weight: (1) Dehydration reaction steps Add 100 parts of sorbitol to the reactor, add 3-6 parts of composite solid acid catalyst, and carry out a melt dehydration reaction at 140-165℃ for 3-5 hours. At the same time, carry out a continuous dehydration reaction under a hydrogen or nitrogen protective atmosphere of 0.10-0.30 MPa, and remove the generated water simultaneously. (2) Neutralization and adjustment steps After the reaction is complete, the reaction solution is cooled to 80-100℃, and 1.5-3.0 parts of alkaline neutralizing agent are added to adjust the pH of the system to 6.5-7.

5. (3) Primary decolorization steps Add 2-4 parts of activated carbon to the neutralized material, stir at 70-90℃ for 20-40 minutes, and then filter to remove the activated carbon. (4) Deep decolorization step Add 3-6 parts of anion exchange resin containing pyridine heterocyclic sorbate to the filtrate and treat at 50-70℃ for 30-60 min to remove colored impurities and trace metal ions; (5) Desalination and refining steps The decolorized solution was subjected to electrodialysis, with the voltage controlled at 5–15V and the treatment time at 30–90 minutes, in order to remove inorganic salts and ionic impurities. (6) Reduced pressure concentration step Vacuum concentration was carried out at 60–85℃ and -0.08–-0.095 MPa to achieve a solid content of 85–92% in the system. (7) Solvent-induced crystallization step Add 80-120 parts of crystallization induction solvent to the concentrate, stir and crystallize at 0-10℃ for 6-10 hours to precipitate crystals; (8) Separation and drying steps The crystals were filtered and separated, and then dried under vacuum at -10 to 0°C for 6 to 12 hours to obtain a low-color, high-purity isosorbide product. The anion exchange resin containing pyridine heterocyclic sorbate was prepared by reacting acrylate macroporous white spheres with 1-(pyridin-4-yl)but-3-en-1-amine, dimethyl ethanol, vinyl sorbate, and triethylamine after pre-swelling with N,N-dimethylformamide.

2. The preparation process of low-color, high-purity isosorbide according to claim 1, characterized in that: The sorbitol is in the form of an aqueous solution with a mass fraction of 70-75%.

3. The preparation process of low-color, high-purity isosorbide according to claim 1, characterized in that: The composite solid acid catalyst is composed of the following components, in parts by mass: Sulfonic acid type cation exchange resin: 2-4 parts; Molecular sieve or sulfated zirconium oxide: 1-2 parts.

4. The preparation process of low-color, high-purity isosorbide according to claim 1, characterized in that: The alkaline neutralizing agent is one or a combination of two of calcium carbonate, sodium carbonate, or sodium hydroxide.

5. The preparation process of low-color, high-purity isosorbide according to claim 1, characterized in that: The activated carbon is wood-based activated carbon or coconut shell activated carbon, with a specific surface area of ​​800–1200 m². 2 / g.

6. The preparation process of low-color, high-purity isosorbide according to claim 1, characterized in that: The preparation method of the anion exchange resin containing pyridine heterocyclic sorbate is as follows, according to parts by mass: T1: 100-130 parts of acrylate-based macroporous white spheres are pre-swollen with 1000-1300 parts of N,N-dimethylformamide at 40-60℃ for 2-4 hours to fully expand the pore structure; 7.5-15.0 parts by weight of 1-(pyridin-4-yl)but-3-en-1-amine, 3-5 parts by weight of dimethylethanolamine, 0.6-2 parts by weight of vinyl sorbate, and 1-4 parts by weight of triethylamine are added and stirred until evenly dispersed; T2: The reaction is carried out in stages. The first stage is a constant temperature reaction at 50°C for 3 hours to complete the nucleophilic addition of amino-olefin and the primary grafting of pyridine heterocycle. The second stage is heated to 60°C and the reaction continues for 4-7 hours to achieve sorbate stabilization and deep amination. After the reaction is completed, the mixture is filtered and washed in sequence with hot DMF, ethanol and sterile deionized water to remove unreacted monomers and residual reagents. T3: The washed resin is dried at 50-70℃ and under a vacuum of -0.09 to -0.07 MPa for 4-7 hours to obtain anion exchange resin containing pyridine heterocyclic sorbate.

7. The preparation process of low-color, high-purity isosorbide according to claim 1, characterized in that: The electrodialysis employs a combination of anion and cation exchange membranes.

8. The preparation process of low-color, high-purity isosorbide according to claim 7, characterized in that: The cation and anion exchange membrane combination system comprises alternating arrangements of cation exchange membranes and anion exchange membranes, wherein: the cation exchange membrane is selected from sulfonated polystyrene membrane, sulfonated polyether ether ketone membrane or perfluorosulfonic acid membrane; and the anion exchange membrane is selected from quaternized polystyrene membrane, quaternized polysulfone membrane or polyolefin-based anion exchange membrane.

9. The preparation process of low-color, high-purity isosorbide according to claim 1, characterized in that: The crystallization-inducing solvent is ethyl acetate or isopropanol.

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