Method for preparing glycolic acid from chloroacetic acid high-boiling residues

Abstract

The invention belongs to the technical field of acyclic compounds, and particularly relates to a method for preparing glycolic acid from chloroacetic acid high-boiling residues. Adding water and hydrogen chloride into the chloroacetic acid high-boiling residue, and carrying out primary hydrolysis reaction to obtain primary hydrolysate; adding a catalyst into the primary hydrolysate, and carrying out secondary hydrolysis reaction to obtain secondary hydrolysate; distilling and dehydrating the secondary hydrolysate, cooling, and adding a solvent for extraction and liquid separation to obtain a reaction liquid; cooling, crystallizing and centrifuging the reaction liquid to obtain a glycolic acid crude product; adding water into the glycolic acid crude product, pulping, cooling, crystallizing, filtering and drying to obtain a glycolic acid finished product. According to the method, alkali is not used as a reactant, and the utilization rate of byproducts in chloroacetic acid production can be increased in a manner of obtaining glycolic acid by hydrolyzing chloroacetic acid in a high-boiling residue at a high temperature; compared with the method for producing glycolic acid through alkali reaction, salt is not generated, and a large amount of waste water is not generated through application of evaporated water and post-treated water.

Description

Technical Field

[0001] This invention belongs to the field of acyclic compound technology, specifically relating to a method for preparing glycolic acid using high-boiling chloroacetic acid. Background Technology

[0002] The chloroacetic acid production process using acetic anhydride as a catalyst involves chlorination, hydration, hydrogenation, and then distillation of acetic acid as a raw material. Due to the interactions of different byproducts in each process and the tarring of substances at high temperatures, some high-boiling-point substances inevitably remain after distillation. Some of these high-boiling-point substances are chloroacetic acid, while others are complex compounds such as 2-(2-chloroacetoxy)acetic acid. Although these compounds are relatively complex, substances with structures related to chloroacetic acid are more abundant in the high-boiling-point substances produced by distillation.

[0003] There are generally two existing methods for treating high-boiling-point substances in chloroacetic acid: biochemical treatment and incineration. The main component of high-boiling-point substances in chloroacetic acid is chloroacetic acid, which typically accounts for more than 55% of the high-boiling-point components (this may vary depending on the specific process conditions). These substances are discharged intermittently during the continuous distillation process of chloroacetic acid production to control high-boiling impurities. Besides chloroacetic acid, the high-boiling-point components also include dichloroacetic acid, 2-(2-chloroacetoxy)acetic acid, and other substances, with esters primarily consisting of ester derivatives of chloroacetic acid.

[0004] Glycolic acid (GA) is the simplest hydroxy acid. It can be used as a leather tanning agent, water disinfectant, dairy farm disinfectant, and boiler descaling agent. Because it contains hydroxyl and carboxyl groups, it can undergo self-reaction. There are currently many reports on research into biodegradable materials using GA as a raw material. The current industrial production method for GA uses chloroacetic acid as a raw material, obtained through alkaline hydrolysis.

[0005] Due to cost considerations, using caustic soda or other types of alkali to treat high-boiling-point chloroacetic acid is not only relatively expensive, but also generates salt during the production process. Salt generated during the production process is usually treated as solid waste in industry. Therefore, using alkali to treat high-boiling-point chloroacetic acid is simply turning one type of waste into another.

[0006] Chinese patent CN104744239A discloses a method for preparing glycolic acid, comprising the following steps performed sequentially: hydrolyzing an aqueous solution of hydroxyacetonitrile with a 70%–90% sulfuric acid solution at 120°C–140°C to obtain a mixed solution of glycolic acid and ammonium sulfate acid salt; simultaneously adding methanol to the mixed solution for esterification while distilling off a mixture of methanol, water, and methyl glycolate, with the entire process controlled at 110°C–120°C; adjusting the mass percentage of methyl glycolate in the mixture to 10%–25% by adding water; and hydrolyzing the methyl glycolate to glycolic acid at ≤100°C, separating out methanol and water, with the separated methanol being recycled. This patented process is complex and does not involve the treatment and utilization of high-boiling-point chloroacetic acid. Summary of the Invention

[0007] The purpose of this invention is to provide a method for preparing glycolic acid using high-boiling-point chloroacetic acid, which can effectively utilize high-boiling-point chloroacetic acid, does not use alkali as a reactant, and facilitates the post-treatment of water generated during the preparation process because no salt is produced.

[0008] The method for preparing glycolic acid using high-boiling chloroacetic acid as described in this invention includes the following steps: (1) Water and hydrogen chloride are added to high-boiling chloroacetic acid to carry out a first-stage hydrolysis reaction to obtain a first-stage hydrolysate; (2) Add a catalyst to the primary hydrolysate obtained in step (1) to carry out a secondary hydrolysis reaction to obtain a secondary hydrolysate; (3) After distillation and dehydration, the secondary hydrolysate obtained in step (2) is cooled and then extracted with solvent to obtain the reaction solution; (4) The reaction solution was cooled to allow crystals to precipitate, and then centrifuged to obtain crude glycolic acid. (5) Add water to crude glycolic acid, slurry it, cool it to crystallize it, filter it, dry it to obtain the finished glycolic acid product.

[0009] In step (1), the high-boiling chloroacetic acid composition includes 55-60% chloroacetic acid, 8-12% dichloroacetic acid, and 10-15% 2-(2-chloroacetoxy)acetic acid, by mass percentage.

[0010] In step (1), the mass ratio of high-boiling chloroacetic acid to water is 1:0.8-1.3, and the mass ratio of high-boiling chloroacetic acid to hydrogen chloride is 1:0.5-0.8.

[0011] In step (1), the temperature of the first-order hydrolysis reaction is 60-80℃, and the time of the first-order hydrolysis reaction is 4-6h.

[0012] In step (2), the catalyst is aluminum trichloride and zinc chloride, with a mass ratio of 6-8:1. The amount of catalyst added is 0.5-1% of the mass of the high-boiling chloroacetic acid in step (1).

[0013] The temperature of the secondary hydrolysis reaction in step (2) is 140-160℃, and the time of the secondary hydrolysis reaction is 10-16h.

[0014] The amount of water dehydrated in step (3) is 55-70% of the water mass in step (1), and the temperature is reduced to 60-75℃.

[0015] In step (3), the solvent is toluene or xylene, and the amount of solvent added is 13-20% of the high-boiling mass of chloroacetic acid in step (1).

[0016] In step (4), the cooling temperature for crystallization is 10-20℃.

[0017] In step (5), the mass ratio of crude glycolic acid to water is 1:0.2-0.4, the pulping temperature is 40-50℃, the pulping time is 0.5-1h, and the cooling crystallization temperature is 10-20℃.

[0018] The water distilled in step (3) and the crude mother liquor obtained after centrifugation in step (4) can be collected and reused in the hydrolysis reaction.

[0019] This invention prepares glycolic acid from high-boiling chloroacetic acid as a starting reactant. The preparation process includes three steps: the first step is the hydrolysis of high-boiling chloroacetic acid, the second step is the metal-catalyzed high-temperature hydrolysis of chloroacetic acid, and the third step is post-treatment.

[0020] In this invention, hydrogen chloride is introduced into the high-boiling chloroacetic acid under conditions containing a certain amount of water to hydrolyze the 2-(2-chloroacetoxy)acetic acid in the high-boiling chloroacetic acid to chloroacetic acid. After the hydrolysis is complete, the resulting primary hydrolysate is further hydrolyzed and dechlorinated under the action of catalysts (aluminum trichloride and zinc chloride) and hydrogen chloride to convert chloroacetic acid into glycolic acid. The resulting secondary hydrolysate is evaporated to remove some water and then cooled. It is then extracted and separated by solvent extraction. The separated reaction solution is further cooled to precipitate crystals. After centrifugation, crude glycolic acid is obtained. The crude glycolic acid is then mixed with water to form a slurry, cooled to crystallize, filtered, and dried to obtain the finished glycolic acid product.

[0021] The synergistic mechanism of aluminum trichloride, zinc chloride, and hydrogen chloride in this invention is as follows: (1) Hydrogen chloride, as a strong protic acid, first protonates the carboxyl oxygen of chloroacetic acid, which enhances the positive charge of the carboxyl carbon; at the same time, the acidic environment provided by hydrogen chloride can also protonate water molecules in the system, activating them into better nucleophiles (H2O-H). +More importantly, under the combined action of aluminum trichloride and hydrogen chloride, chloroacetic acid is more easily converted into the highly reactive chloroacetyl chloride intermediate. The acyl carbon and α-carbon of this intermediate are extremely electron-deficient, paving the way for subsequent reactions.

[0022] (2) Al in aluminum trichloride 3+ Due to its extremely high charge density, aluminum trichloride coordinates simultaneously with the carbonyl oxygen and α-chlorine atom of the chloroacetyl chloride intermediate. This not only greatly enhances the electrophilicity of the carbonyl carbon but also further activates the C-Cl bond, making it a more easily leaving group. The coordination effect of aluminum trichloride essentially reduces the activation energy required for key steps (such as nucleophilic attack) by altering the electron cloud distribution of the substrate.

[0023] (3) Zinc chloride can stabilize leaving groups: Under the strong activation of aluminum trichloride, chloride ions are about to leave; at this time, Zn 2+ It can coordinate with this negatively charged leaving group to form a stable complex anion (such as [ZnCl3)). - This effectively prevents side reactions that could "follow up," ensuring the forward reaction proceeds. Zinc chloride, as a moderately strong Lewis acid, allows for precise control of the acidity around the reaction site, preventing side reactions such as polymerization of the product, glycolic acid, under strong acid conditions.

[0024] (4) Macroscopic manifestation of synergy: Reactivity: The combination of hydrogen chloride and aluminum trichloride creates a highly reactive electrophilic environment, enabling the hydrolysis reaction, which is normally difficult to occur, to proceed efficiently.

[0025] Product selectivity: The stabilizing effect of zinc chloride on leaving groups and the regulation of local acidity effectively suppress side reactions, thereby significantly improving the selectivity and yield of the target product, glycolic acid.

[0026] This invention first catalytically hydrolyzes high-boiling chloroacetic acid under acidic conditions to obtain chloroacetic acid. Then, using aluminum trichloride and zinc chloride as catalysts, the chloroacetic acid is hydrolyzed and dechlorinated at high temperature to obtain glycolic acid. At high temperature, due to the increased tendency of water to protonate carboxyl groups after ionization, the chlorine attached to chloroacetic acid is more easily removed than at low temperature to form glycolic acid.

[0027] In this invention, high-boiling-point chloroacetic acid is treated with hydrogen chloride, which is a byproduct of chloroacetic acid production. Treating high-boiling-point chloroacetic acid with hydrogen chloride makes full use of the hydrogen chloride byproduct generated during chloroacetic acid production.

[0028] The beneficial effects of this invention are as follows: This invention does not use alkali as a reactant. The method of obtaining glycolic acid by hydrolyzing chloroacetic acid in high-boiling substances at high temperature can improve the utilization rate of by-products in chloroacetic acid production. Compared with the production of glycolic acid by alkaline reaction, this invention does not produce salt, and the reuse of evaporation water and post-treatment water does not generate a large amount of wastewater. Detailed Implementation

[0029] The present invention will be further described below with reference to embodiments.

[0030] Example 1 (1) Add 2250 kg of high-boiling chloroacetic acid (main components include 57% chloroacetic acid, 10% dichloroacetic acid, and 12% 2-(2-chloroacetoxy)acetic acid by mass percentage) to the hydrolysis reactor, then add 2000 kg of water, raise the material temperature to 80°C, and introduce 1200 kg of hydrogen chloride. After the hydrogen chloride is introduced, keep the reaction at 80°C for 4 hours to obtain the first-stage hydrolysate. (2) Add 10.5 kg of aluminum trichloride and 1.5 kg of zinc chloride to the primary hydrolysate obtained in step (1) and continue heating to 150°C. Maintain the reaction temperature at 150°C for 12 hours to obtain the secondary hydrolysate. (3) After distilling 1200 kg of water from the secondary hydrolysate obtained in step (2), the temperature was lowered to 75°C. The resulting material was transferred to a transfer reactor. 300 kg of xylene was added to the transfer reactor. After stirring, the liquid was separated. The lower aqueous phase was the reaction liquid, and the upper solvent was left in the transfer reactor for the next batch. (4) The reaction solution was transferred to a refining kettle, cooled to 10°C, and centrifuged to obtain 1183 kg of crude glycolic acid. (5) 1183 kg of crude glycolic acid was put into a refining kettle, 280 kg of water was added, the temperature was raised to 40°C and pulped for 1 hour, then the temperature was lowered to 15°C and filtered to obtain 1158.7 kg of wet product. After drying, 1157.2 kg of dry glycolic acid with a purity of 99.77% was obtained.

[0031] Example 2 (1) Add 2250 kg of high-boiling chloroacetic acid (main components include 57% chloroacetic acid, 10% dichloroacetic acid, and 12% 2-(2-chloroacetoxy)acetic acid by mass percentage) to the hydrolysis reactor, then add 1800 kg of water, raise the material temperature to 70°C, and introduce 1300 kg of hydrogen chloride. After the hydrogen chloride is introduced, keep the reaction at 70°C for 5 hours to obtain the first-stage hydrolysate. (2) Add 12 kg of aluminum trichloride and 2 kg of zinc chloride to the primary hydrolysate obtained in step (1) and continue heating to 140°C. Maintain the reaction temperature at 140°C for 16 hours to obtain the secondary hydrolysate. (3) After distilling 990 kg of water from the secondary hydrolysate obtained in step (2), the temperature was lowered to 70°C. The resulting material was transferred to a transfer reactor. 400 kg of xylene was added to the transfer reactor. After stirring, the liquid was separated. The lower aqueous phase was the reaction liquid, and the upper solvent was left in the transfer reactor for the next batch of use. (4) The reaction solution was transferred to a refining vessel, cooled to 20°C, and centrifuged to obtain 1180.7 kg of crude glycolic acid. (5) 1180.7 kg of crude glycolic acid was put into a refining kettle, 370 kg of water was added, the temperature was raised to 45°C and pulped for 0.8 h, then the temperature was lowered to 10°C, and 1157.9 kg of wet product was obtained by filtration. After drying, 1155.4 kg of dry glycolic acid with a purity of 99.71% was obtained.

[0032] Example 3 (1) Add 2250 kg of high-boiling chloroacetic acid (main components include 57% chloroacetic acid, 10% dichloroacetic acid, and 12% 2-(2-chloroacetoxy)acetic acid by mass percentage) to the hydrolysis reactor, then add 2925 kg of water, raise the material temperature to 60°C, and introduce 1800 kg of hydrogen chloride. After the hydrogen chloride is introduced, keep the reaction at 60°C for 6 hours to obtain the first-stage hydrolysate. (2) Add 20 kg of aluminum trichloride and 2.5 kg of zinc chloride to the primary hydrolysate obtained in step (1) and continue heating to 160°C. Maintain the reaction temperature at 160°C for 10 h to obtain the secondary hydrolysate. (3) After distilling 2000 kg of water from the secondary hydrolysate obtained in step (2), the temperature was lowered to 60°C. The resulting material was transferred to a transfer reactor. 450 kg of toluene was added to the transfer reactor. After stirring, the liquid was separated. The lower aqueous phase was the reaction liquid, and the upper solvent was left in the transfer reactor for the next batch of use. (4) The reaction solution was transferred to a refining kettle, cooled to 12°C, and centrifuged to obtain 1195.1 kg of crude glycolic acid. (5) 1195.1 kg of crude glycolic acid was put into a refining kettle, 475 kg of water was added, the temperature was raised to 50°C and pulped for 0.5 h, then the temperature was lowered to 20°C, and 1158.5 kg of wet product was obtained by filtration. After drying, 1156.7 kg of dry glycolic acid with a purity of 99.75% was obtained.

[0033] Comparative Example 1 In step (2), aluminum trichloride was replaced with an equal mass of zinc chloride, and the other steps were the same as in Example 1, resulting in 939.4 kg of dry glycolic acid with a purity of 96.46%.

[0034] Comparative Example 2 In step (2), zinc chloride was replaced with an equal mass of aluminum trichloride, and the other steps were the same as in Example 1, resulting in 1001.3 kg of dry glycolic acid with a purity of 96.68%.

[0035] Comparative Example 3 The reaction temperature in step (2) was 90°C, and the other steps were the same as in Example 1. 1038.8 kg of dry glycolic acid was obtained with a purity of 96.73%.

Claims

1. A method for preparing glycolic acid using high-boiling-point chloroacetic acid, characterized in that... Includes the following steps: (1) Water and hydrogen chloride are added to high-boiling chloroacetic acid to carry out a first-stage hydrolysis reaction to obtain a first-stage hydrolysate; (2) Add a catalyst to the primary hydrolysate obtained in step (1) to carry out a secondary hydrolysis reaction to obtain a secondary hydrolysate; (3) After distillation and dehydration, the secondary hydrolysate obtained in step (2) is cooled and then extracted with solvent to obtain the reaction solution; (4) The reaction solution was cooled to allow crystals to precipitate, and then centrifuged to obtain crude glycolic acid. (5) Add water to crude glycolic acid, slurry it, cool it to crystallize it, filter it, dry it to obtain the finished glycolic acid product.

2. The method for preparing glycolic acid using high-boiling chloroacetic acid as described in claim 1, characterized in that... In step (1), the high-boiling chloroacetic acid composition includes 55-60% chloroacetic acid, 8-12% dichloroacetic acid, and 10-15% 2-(2-chloroacetoxy)acetic acid, by mass percentage.

3. The method for preparing glycolic acid using high-boiling chloroacetic acid as described in claim 1, characterized in that... In step (1), the mass ratio of high-boiling chloroacetic acid to water is 1:0.8-1.3, and the mass ratio of high-boiling chloroacetic acid to hydrogen chloride is 1:0.5-0.

8.

4. The method for preparing glycolic acid using high-boiling chloroacetic acid as described in claim 1, characterized in that... In step (1), the temperature of the first-order hydrolysis reaction is 60-80℃, and the time of the first-order hydrolysis reaction is 4-6h.

5. The method for preparing glycolic acid using high-boiling chloroacetic acid as described in claim 1, characterized in that... In step (2), the catalyst is aluminum trichloride and zinc chloride, with a mass ratio of 6-8:

1. The amount of catalyst added is 0.5-1% of the mass of the high-boiling chloroacetic acid in step (1).

6. The method for preparing glycolic acid using high-boiling chloroacetic acid as described in claim 1, characterized in that... The temperature of the secondary hydrolysis reaction in step (2) is 140-160℃, and the time of the secondary hydrolysis reaction is 10-16h.

7. The method for preparing glycolic acid using high-boiling chloroacetic acid as described in claim 1, characterized in that... The amount of water dehydrated in step (3) is 55-70% of the water mass in step (1), and the temperature is reduced to 60-75℃.

8. The method for preparing glycolic acid using high-boiling chloroacetic acid as described in claim 1, characterized in that... In step (3), the solvent is toluene or xylene, and the amount of solvent added is 13-20% of the high-boiling mass of chloroacetic acid in step (1).

9. The method for preparing glycolic acid using high-boiling chloroacetic acid as described in claim 1, characterized in that... In step (4), the cooling temperature for crystallization is 10-20℃.

10. The method for preparing glycolic acid using high-boiling chloroacetic acid as described in claim 1, characterized in that... In step (5), the mass ratio of crude glycolic acid to water is 1:0.2-0.4, the pulping temperature is 40-50℃, the pulping time is 0.5-1h, and the cooling crystallization temperature is 10-20℃.