A method for treating betaine hydrochloride mother liquor

Abstract

The present invention belongs to the field of betaine hydrochloride preparation, and specifically relates to a method for treating a betaine hydrochloride mother liquor. First, the mother liquor of betaine hydrochloride is concentrated and dehydrated, methanol is added for primary esterification, methanol is distilled off at normal pressure, and methyl hydroxyacetate is distilled under reduced pressure to obtain a methanol fraction, a methyl hydroxyacetate fraction, and a distilled solution; then, a secondary esterification is performed using the same method to obtain a methanol fraction, a methyl hydroxyacetate fraction, and a distilled solution, and activated carbon is added for decolorization and filtration to obtain a treated mother liquor, which can be applied to the production of betaine hydrochloride, thereby improving the comprehensive yield of betaine hydrochloride production, improving product quality, avoiding the solution being brown at high temperature, being simple and safe to operate, being environmentally friendly, saving the cost of hazardous waste treatment, and also being able to recycle hydroxyacetic acid, thereby generating better economic benefits.

Description

Technical Field

[0001] The invention belongs to the field of betaine hydrochloride preparation, and particularly relates to a method for treating a betaine hydrochloride mother liquor. Background Art

[0002] Betaine hydrochloride is a quaternary ammonium alkaloid. It can not only be used as a highly efficient methyl donor feed additive to replace choline and methionine in agriculture and animal husbandry, but also has many excellent pharmacological effects. As a surfactant, it has the characteristics of bactericidal, synergistic, antistatic, anti-hard water, anti-fog, low irritation, and viscosity increasing. It is widely used in daily chemical, printing and dyeing, petrochemical and other industries, with an annual demand of about hundreds of thousands of tons.

[0003] At present, the chemical synthesis process of betaine hydrochloride basically adopts the synthesis route of "quaternization reaction of chloroacetate", with chloroacetic acid and trimethylamine as the basic raw materials. According to the type of alkali, it can be subdivided into two different processes: calcium method and sodium method. The sodium method has four steps: neutralization, substitution, desalination, and acidification; the calcium method has three steps: neutralization, substitution, and acidification. Both types of processes require neutralization, substitution, and acidification. Since chloroacetate is unstable during the neutralization and substitution steps, it will react with water in the system to produce glycolic acid. In the subsequent concentration, desalination, acidification, and mother liquor application process, it will gradually enrich and undergo polymerization and carbonization reactions under high temperature conditions, making the viscosity of the betaine hydrochloride mother liquor increase and the color change to reddish brown, which ultimately affects the color, crystal particle size, content, transmittance and other product indicators of the betaine hydrochloride product. Therefore, it is necessary to regularly eliminate the betaine hydrochloride mother liquor with a high glycolic acid content. These eliminated mother liquors contain betaine hydrochloride, sodium chloride, and glycolic acid. There are generally two treatment options: 1. Directly treat it as hazardous waste, which has high treatment costs. In addition, the mother liquor contains betaine hydrochloride products, which will lead to low product yield and further increase production costs.

[0004] 2. Neutralize with calcium hydroxide, then filter and decolorize to remove calcium hydroxyacetate, and apply the filtrate to the concentration and desalination step. However, calcium hydroxyacetate has strong water absorption and is in a gel state in the neutralization solution, which makes filtration very difficult and not easy to operate.

[0005] Therefore, how to solve the problem that the chromaticity, crystal particle size, content and light transmittance of betaine hydrochloride in the prior art are not ideal, and the problem that the eliminated mother liquor of betaine hydrochloride is difficult to handle has become one of the problems that the inventors need to solve urgently. Summary of the invention

[0006] In view of the problems existing in the existing treatment process, the present invention provides a method for treating a betaine hydrochloride mother liquor, which can extract the hydroxyacetic acid in the betaine hydrochloride mother liquor from the mother liquor through esterification, distillation, filtration and decolorization, reduce the sodium chloride content and improve the color of the mother liquor; and make the extracted hydroxyacetic acid into a finished product through the steps of hydrolysis, concentration and crystallization, so that the eliminated betaine hydrochloride mother liquor can be recycled and reused, and the chromaticity, crystal particle size, content, transmittance and other indicators of the betaine hydrochloride product can be ensured, the yield is improved, and the production cost of the betaine hydrochloride is greatly reduced.

[0007] The method for treating the mother liquor of betaine hydrochloride provided by the present invention comprises the following steps: firstly concentrating and removing water from the mother liquor of betaine hydrochloride, then adding methanol to the remaining solution in the kettle for primary esterification, distilling methanol at normal pressure, and distilling methyl hydroxyacetate under reduced pressure to obtain a methanol fraction, a methyl hydroxyacetate fraction, and a distilled solution; then adding methanol to the distilled solution for secondary esterification, and then distilling methanol at normal pressure and distilling methyl hydroxyacetate under reduced pressure to obtain a methanol fraction, a methyl hydroxyacetate fraction, and a distilled solution. The distilled solution is filtered, and activated carbon is added for decolorization and filtration to obtain a treated mother liquor, which can be applied to the production of betaine hydrochloride.

[0008] The methanol fraction is applied to the esterification step through metering; water is added to the methyl glycolate fraction to carry out a hydrolysis reaction, and after the reaction is completed, it is concentrated under reduced pressure to obtain a concentrated solution, and the concentrated solution is slowly cooled and then added with glycolic acid crystals, and the glycolic acid crystals are obtained by filtering after low-temperature crystallization.

[0009] More specific technical solutions are as follows: A method for treating betaine hydrochloride mother liquor comprises the following steps: 1) Concentrate the mother liquor of betaine hydrochloride under reduced pressure at 80-100°C until no more water is produced, then cool to 60±5°C.

[0010] 2) adding methanol, heating to 90-110°C and reflux esterification to perform primary esterification; after the esterification is completed, distilling the methanol under normal pressure until no more methanol is distilled out, heating and distilling methyl glycolate under reduced pressure until no more methyl glycolate is distilled out, thereby obtaining a methanol fraction, a methyl glycolate fraction and a solution after primary distillation; The mother liquor of betaine hydrochloride is acidic in nature, which is beneficial to the esterification reaction.

[0011] 3) adding methanol to the distilled solution obtained in step 2) and filtering, the solid is a mixture of betaine hydrochloride and inorganic salt; repeating step 2) for secondary esterification and distillation of the filtrate to obtain a methanol fraction, a methyl glycolate fraction and a secondary distilled solution; The glycolic acid is removed through primary esterification and secondary esterification to ensure the removal rate of glycolic acid and ensure that the glycolic acid content of the mother liquor after treatment meets the requirements.

[0012] 4) Filter the solution obtained after secondary distillation in step 3), and obtain the treated betaine hydrochloride mother liquor after decolorization and filtration, which can be applied to the production of betaine hydrochloride.

[0013] Preferably, the mother liquor of betaine hydrochloride in step 1) comprises, by mass, 20-25% betaine hydrochloride, 10-15% glycolic acid, 10-15% inorganic salt, and the remainder water; the inorganic salt is a sodium salt or a calcium salt, more specifically, the sodium salt is sodium chloride, and the calcium salt is calcium sulfate.

[0014] The treated betaine hydrochloride mother liquor obtained in the corresponding final step 4) comprises, by mass, 20-25% betaine hydrochloride, 4-6% glycolic acid, 10-15% inorganic salt, and the remainder water.

[0015] Preferably, the mass ratio of methanol added in step 2) to hydroxyacetic acid in the betaine hydrochloride mother liquor is (3-5):1; the mass ratio of methanol added in step 3) to hydroxyacetic acid in the solution after the first distillation in step 2) is (3-5):1; the esterification time of the first esterification and the second esterification is 1-3h, and the esterification temperature is 90-110°C.

[0016] More preferably, the mass ratio of methanol added in step 2) to glycolic acid in the betaine hydrochloride mother liquor, and the mass ratio of methanol added in step 3) to glycolic acid in the solution after the first distillation in step 2) is 4:1, the time for the first esterification and the second esterification is 2h, and the esterification temperature is 95-100°C.

[0017] Due to the influence of water, betaine and inorganic salts in the betaine hydrochloride mother liquor, the esterification reaction needs to be carried out at the above-mentioned relatively high temperature of 90-110°C; too little or too much methanol will affect the removal effect of glycolic acid.

[0018] Preferably, in step 2) and step 3), the temperature for distilling methanol under normal pressure is 90-100°C, the temperature for distilling methyl glycolate under reduced pressure is 110-130°C, and the vacuum degree is ≤-0.095mpa; More preferably, the temperature for distilling methanol at normal pressure is 100°C, and the temperature for distilling methyl glycolate at reduced pressure is 120°C.

[0019] Preferably, in step 4), the specific method of decolorization and filtration is to add activated carbon to the solution after secondary distillation to make the mass concentration of activated carbon 0.2%, decolorize at 90°C for 2h, and then filter to remove the activated carbon to obtain the treated betaine hydrochloride mother liquor.

[0020] Preferably, the methanol fraction and the methyl glycolate fraction obtained in step 2) and step 3) are combined; the methanol fraction is applied to the esterification step as a raw material for primary and secondary esterification, and the methyl glycolate fraction is hydrolyzed to prepare glycolic acid.

[0021] The method for preparing glycolic acid by hydrolyzing the methyl glycolate fraction comprises the following steps: A) adding water to the methyl glycolate fraction, and then reflux hydrolyzing it at 110-120° C. under normal pressure, collecting the distilled methanol during the hydrolysis process, and reflux hydrolyzing it until the methyl glycolate is hydrolyzed by more than 90%, then cooling it to below 70° C., and concentrating it under reduced pressure until no water is distilled off, thereby obtaining a glycolate concentrate; Hydrolysis of methyl glycolate can produce methanol and glycolic acid, and the degree of hydrolysis can be monitored by ion chromatography. The mass of methyl glycolate can also be detected before the hydrolysis begins, and the acid value when the hydrolysis is 90% can be calculated based on the mass of methyl glycolate, and the degree of hydrolysis can be determined by monitoring the acid value.

[0022] B) slowly cooling the glycolic acid concentrated solution obtained in step A), adding glycolic acid crystals as seeds to the glycolic acid methyl ester concentrated solution to promote crystallization, and filtering and separating the glycolic acid crystals after low-temperature crystallization.

[0023] Preferably, the ratio of the mass of the methyl glycolate fraction to the mass of the added water in step A) is 1:1; if too little water is added, the hydrolysis rate of methyl glycolate will be reduced, and if too much water is added, the reactant concentration of methyl glycolate will be reduced, the hydrolysis rate will also be reduced, and the energy consumption of subsequent distillation will be increased.

[0024] Preferably, in the process of vacuum concentration until anhydrous distillation is performed in step A), the temperature of vacuum concentration is 50-70° C. and the vacuum degree is ≤-0.095 Mpa.

[0025] Preferably, in step A), the gas phase temperature at the top of the distillation tower is controlled to be 64° C., and the water content in the distilled methanol is controlled to be no higher than 1%.

[0026] Preferably, in step B), the hydroxyacetic acid crystals obtained by filtration and separation are dried to obtain hydroxyacetic acid crystals.

[0027] More specifically, in step B), the hydroxyacetic acid concentrate obtained in step A) is first slowly cooled to 10-15°C, hydroxyacetic acid crystals are added to the hydroxyacetic acid concentrate, and then the mixture is kept warm at 5-10°C for 2h, the hydroxyacetic acid crystals are filtered and separated, and the hydroxyacetic acid crystals are dried at 55-60°C to obtain hydroxyacetic acid crystals.

[0028] There is no particular requirement for the amount of glycolic acid crystals added in step B), and generally, the purpose of crystallization can be achieved when the amount added is several tens of grams.

[0029] The method for treating betaine hydrochloride mother liquor provided by the present invention has the following beneficial effects: 1. After the glycolic acid is extracted from the betaine hydrochloride mother liquor, it can be reused in the production of betaine hydrochloride, so that the comprehensive yield of the product in the betaine hydrochloride production process is increased by 1-2%; the reduction in the concentration of glycolic acid can better crystallize, and the solution will not turn brown at high temperature. In addition, the extracted and prepared glycolic acid can be sold as a product, which can generate good economic benefits and make the cost of betaine hydrochloride more competitive; 2. Betaine hydrochloride mother liquor does not need to be treated as hazardous waste, which is environmentally friendly, saves the cost of hazardous waste treatment, and reduces the environmental protection cost of betaine hydrochloride; 3. The preparation process of hydroxyacetic acid adopts basic chemical operation steps such as esterification, distillation, hydrolysis, concentration, and crystallization. There is no dangerous and complicated process. The process is easy to produce, simple to operate, and easy to implement. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 This is a schematic diagram of the betaine hydrochloride mother liquor before treatment in Example 1; Figure 2 This is a schematic diagram of the betaine hydrochloride mother liquor after treatment in Example 1; Figure 3 This is a schematic diagram of the product of applying the betaine hydrochloride mother liquor before treatment in Example 1 to the betaine hydrochloride production process; Figure 4 This is a schematic diagram of applying the betaine hydrochloride mother liquor treated in Example 1 to the product in the betaine hydrochloride production process. DETAILED DESCRIPTION

[0031] The technical solution of the present invention is further described below in conjunction with specific embodiments. These embodiments are only used to illustrate the technical solution of the present invention in more detail and should not be construed as limiting the protection scope of the present invention.

[0032] The betaine hydrochloride mother liquor used in the specific implementation manner is prepared by the chemical synthesis method of chloroacetic acid and trimethylamine in the prior art, and specifically can be the betaine hydrochloride mother liquor prepared by the sodium method or the calcium method. The method for preparing the betaine hydrochloride mother liquor by the sodium method can refer to the literature (Research on a New Process for Synthesizing Betaine. Chemistry and Bioengineering, 2005, 7: 48-49), and the method for preparing the betaine hydrochloride mother liquor by the calcium method can refer to the literature (Research on the Synthesis Process of Low-burning Residue Betaine Hydrochloride. Applied Chemical Industry, 2015, 44 (12): 2230-2233).

[0033] In this scheme, betaine hydrochloride, glycolic acid and inorganic salts in the betaine hydrochloride mother liquor are detected before treatment of the betaine hydrochloride mother liquor, after the first esterification and after the treatment. Betaine hydrochloride and glycolic acid are detected by ion chromatography (GB / T 7300.204-2019), and inorganic salts are detected by ash method (GB / T 6435).

[0034] In addition, the betaine hydrochloride mother liquor obtained by reacting calcium chloroacetate with trimethylamine in the prior art can also be applied to the treatment method of the present invention.

[0035] The materials and reagents used in the specific embodiments are generally commercially available products unless otherwise specified.

[0036] Example 1 A method for treating betaine hydrochloride mother liquor comprises the following steps: 1) Add 1500g of betaine hydrochloride mother liquor into a three-necked flask, concentrate under reduced pressure at 90°C until no more water is produced, then cool to 60°C; The betaine hydrochloride mother solution was tested and found to contain 12.1% hydroxyacetic acid, 22.3% betaine hydrochloride, 14.2% sodium chloride, and the remainder water by mass.

[0037] 2) Add 700 g of methanol to the concentrated system, raise the temperature to 100° C. and reflux for esterification for 2 h to carry out primary esterification.

[0038] 3) After the primary esterification is completed, the reflux is changed to distillation, and the methanol is distilled off at 100°C and normal pressure until almost no methanol is distilled off, and then the temperature is raised to 120°C and methyl glycolate is distilled under reduced pressure (vacuum degree ≤ -0.095 MPa) until methyl glycolate is no longer distilled off, thereby obtaining a methanol fraction and a methyl glycolate fraction, as well as 903 g of a solution after the primary distillation; After testing, the solution after the first distillation contained 22.8% betaine hydrochloride, 13.5% sodium chloride and 8.1% glycolic acid by mass, and also included a very small amount of methanol, and the rest was water. Methanol was further removed in the subsequent secondary esterification step; after calculation, the first removal rate of glycolic acid was 59.7%; Since the impurity content in the solution obtained after the single esterification and distillation is reduced, the solubility of betaine hydrochloride is increased, so the betaine hydrochloride content of the solution after the single distillation is slightly higher than that of the mother liquor before the treatment.

[0039] 4) The solution obtained in step 3) after the primary distillation was cooled to 60°C, 300g of methanol was added, and the filtrate was filtered and subjected to secondary esterification in the same manner as the primary esterification in steps 2) and 3). After the primary and secondary esterification, 955g of methanol fraction, 201g of methyl glycolate fraction and 643g of the solution after the secondary distillation were collected.

[0040] 5) Adding activated carbon to the solution after the secondary distillation in step 4) to make the mass concentration of activated carbon 0.2%, decolorizing at 90° C. for 2 hours, and filtering to remove the activated carbon to obtain the treated betaine hydrochloride mother liquor.

[0041] After testing, the treated mother liquor of betaine hydrochloride contained 23.5% betaine hydrochloride, 11.2% sodium chloride and 5.3% glycolic acid by mass. The total removal rate of glycolic acid was calculated to be 81.2%.

[0042] The methanol fraction obtained in the above step 3) and step 4) can be reused in the esterification reaction in step 2) and step 4), and the obtained methyl glycolate fraction can be used to prepare glycolic acid crystals.

[0043] In this embodiment, the methyl glycolate fraction of step 4) is used as an example to prepare glycolic acid crystals, and the specific steps are as follows: A) adding 201 g of the obtained methyl glycolate fraction into a three-necked flask, and adding 201 g of water, heating to 115° C. and reflux under normal pressure for hydrolysis; during the hydrolysis, controlling the gas phase temperature at 64° C. to extract methanol, monitoring the acid value of the solution during the process, and when the acid value of the solution reaches 282, it indicates that the hydrolysis rate of methyl glycolate reaches more than 90%; cooling to 55° C. and then concentrating under reduced pressure until water is no longer distilled out to obtain a concentrated solution, wherein the vacuum degree of the reduced pressure concentration for distilling water is less than or equal to -0.095 MPa; B) The concentrated solution was cooled to 10°C, 0.5 g of hydroxyacetic acid crystals were added as seed crystals to promote crystallization, and the temperature was further cooled to 5°C. Crystallization was carried out at 5°C for 2 h. The hydroxyacetic acid crystals and the concentrated solution were separated by filtration. The hydroxyacetic acid crystals were dried at 55-60°C to obtain 82 g of hydroxyacetic acid crystals. The purity of the hydroxyacetic acid was 99.3%, and the ash content was 0.

[0044] Figure 1 and Figure 2 betaine hydrochloride mother liquor before and after treatment by the method in this embodiment, respectively, Figure 3 and Figure 4 The products are obtained by using the betaine hydrochloride mother liquor before and after treatment in this embodiment in the betaine hydrochloride production process; Figure 1-4It can be observed that the use of this method to treat the betaine hydrochloride mother liquor not only significantly reduces the content of glycolic acid, but also significantly reduces the chromaticity of the betaine hydrochloride mother liquor. The mother liquor treated by this method is applied to the betaine hydrochloride production process, and the obtained product has uniform particle size, larger particle size and better light transmittance.

[0045] Example 2 A method for treating betaine hydrochloride mother liquor comprises the following steps: 1) Add 200 kg of betaine hydrochloride mother liquor into the reactor, concentrate under reduced pressure at 90°C, and cool to 60°C after no more water is produced; The betaine hydrochloride mother solution was tested and found to contain 13.3% glycolic acid, 23.1% betaine hydrochloride and 12.7% sodium chloride by mass.

[0046] 2) Add 110 kg of methanol to the concentrated system, heat to 100° C. and reflux for esterification for 2 hours to carry out primary esterification.

[0047] 3) After the primary esterification is completed, the reflux is changed to distillation, and the methanol is distilled out at 100°C and normal pressure until almost no methanol is distilled out. Then, the temperature is raised to 120°C and methyl glycolate is distilled under reduced pressure (vacuum degree ≤ -0.095 MPa) until no methyl glycolate is distilled out, thereby obtaining a methanol fraction, a methyl glycolate fraction, and 133.7 kg of a solution after the primary distillation; After testing, the solution after the first distillation contained 23.6% betaine hydrochloride, 12.0% sodium chloride and 7.9% hydroxyacetic acid by mass, and also included a very small amount of methanol, and the rest was water. Methanol was further removed in the subsequent secondary esterification step; the first removal rate of hydroxyacetic acid was calculated to be 60.3%.

[0048] 4) The solution obtained in step 3) after the primary distillation was cooled to 60°C, and then 42 kg of methanol was added and filtered, and the filtrate was subjected to secondary esterification in the same manner as the primary esterification in step 2) and step 3). After the primary and secondary esterification, 145 kg of methanol fraction, 28 kg of methyl glycolate fraction and 93.3 kg of the solution after the secondary distillation were collected; 5) Adding activated carbon to the solution after the secondary distillation in step 4) to make the mass concentration of activated carbon 0.2%, decolorizing at 90° C. for 2 hours, and filtering to remove the activated carbon to obtain the treated betaine hydrochloride mother liquor.

[0049] After testing, the treated mother liquor of betaine hydrochloride contained 24.2% betaine hydrochloride, 10.7% sodium chloride and 5.1% glycolic acid by mass. The total removal rate of glycolic acid was calculated to be 82.1%.

[0050] The methanol fraction obtained in the above step 3) and step 4) can be used again in the esterification reaction of step 2) and step 4), and the obtained methyl glycolate fraction can be used to prepare glycolic acid crystals. In this embodiment, the methyl glycolate fraction of step 4) is used as an example to prepare glycolic acid crystals. The methyl glycolate fraction in step 3) can also be used to prepare glycolic acid crystals by the following method, and the specific steps are as follows: A) adding 28 kg of the obtained methyl glycolate fraction into a reactor, and adding 28 kg of water, heating to 115° C. and reflux under normal pressure for hydrolysis; during the hydrolysis, controlling the gas phase temperature at 64° C. to extract methanol, monitoring the acid value of the solution during the process, and when the acid value of the solution reaches 303, it indicates that the hydrolysis rate of methyl glycolate reaches more than 90%; cooling to 55° C. and then concentrating the distilled water under reduced pressure until no water is distilled out to obtain a concentrated solution, wherein the vacuum degree of the distilled water under reduced pressure concentration is less than or equal to -0.095 MPa; B) The concentrated solution was cooled to 10°C, 0.5 g of hydroxyacetic acid crystals were added as seed crystals to promote crystallization, and the temperature was further cooled to 5°C. Crystallization was carried out at 5°C for 2 hours. The hydroxyacetic acid crystals and the concentrated solution were separated by filtration. The hydroxyacetic acid crystals were dried at 55-60°C to obtain 11.5 kg of hydroxyacetic acid crystals. The purity of the hydroxyacetic acid was 99.1%, and the ash content was 0.

[0051] Comparative Example 1 A method for treating betaine hydrochloride mother liquor comprises the following steps: 1) Add 1000g of betaine hydrochloride mother liquor (containing 13.3% hydroxyethyl acid, 23.1% betaine hydrochloride, and 12.7% sodium chloride by mass) into a three-necked flask, add calcium hydroxide powder to adjust the pH value to 9, and calcium hydroxyacetate precipitation will appear. Use a Buchner funnel for filtration. Since the calcium hydroxyacetate precipitation is fine, the filter paper needs to be replaced every ten minutes of filtration. It takes about 4 hours to complete the filtration, and 161g of calcium hydroxyacetate solid and filtrate (containing betaine, calcium hydroxyacetate, sodium chloride, and calcium chloride) are obtained.

[0052] 2) When the filtrate is acidified to pH 1.5 by adding 98% sulfuric acid, the calcium sulfate precipitate is filtered, and then activated carbon is added to make the filtrate contain 0.2% activated carbon by mass concentration and decolorized at 90°C for 2h. After filtering and removing the activated carbon, the hydroxyacetic acid content in the solution is detected to be 8.1%, and the calculated removal rate is 44%, which is applied to the production process of betaine hydrochloride.

[0053] 3) The calcium glycolate solid obtained in step 1) was added to 161 g of water, and 98% sulfuric acid was slowly added to acidify to pH = 1.5; concentrated at 65° C., vacuum degree ≤-0.095 MPa, and cooled to 10° C. when no water was evaporated; 0.5 g of glycolic acid crystals were added, and the temperature was further lowered to 5° C. for crystallization, and the glycolic acid crystals were filtered to obtain a drying content of 98.2% and an ash content of 0.5%.

[0054] This comparative example is compared with Examples 1 and 2: 1. In the comparative example, calcium ions were introduced into the betaine hydrochloride mother liquor containing sodium chloride, so that the subsequent by-product salt of betaine hydrochloride contained calcium chloride, which was difficult to handle.

[0055] 2. Limited by the solubility of calcium glycolate in water, the removal rate of glycolic acid in the comparative example is 44%, while the removal rate of the present invention is ≥80%.

[0056] 3. In the comparative example, metal ions are still introduced during the preparation of glycolic acid, resulting in the product containing some calcium sulfate. However, the present invention adopts esterification hydrolysis and distills the fraction to obtain glycolic acid of higher quality.

[0057] It can be seen that the treatment method provided by the present application can increase the comprehensive yield of the product of the betaine hydrochloride production process by 1-2%; the reduction in the concentration of hydroxyacetic acid can better crystallize, the solution will not turn brown at high temperature, and the extracted and prepared hydroxyacetic acid can be sold as a product, which can generate good economic benefits and make the cost of betaine hydrochloride more competitive; at the same time, the betaine hydrochloride mother liquor does not need to be treated as hazardous waste, which is environmentally friendly, and saves the cost of hazardous waste treatment, reducing the environmental protection cost of betaine hydrochloride; each operation process is a basic chemical operation step, there is no dangerous and complicated process, the process is easy to produce, simple to operate, and easy to implement.

[0058] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any equivalent substitutions, modifications, etc. made by technicians in this field without any creative work within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for treating betaine hydrochloride mother liquor, characterized in that: The specific steps include: 1) The mother liquor of betaine hydrochloride is concentrated under reduced pressure at 80-100°C until no more water is produced, and then cooled to 60±5°C; 2) adding methanol, heating to 90-110° C. and reflux esterification to perform primary esterification; after the esterification is completed, distilling the methanol under normal pressure until almost no methanol is distilled out, heating and distilling methyl glycolate under reduced pressure until methyl glycolate is no longer distilled out, thereby obtaining a methanol fraction, a methyl glycolate fraction and a solution after primary distillation; 3) adding methanol to the distilled solution obtained in step 2) and filtering, the solid is a mixture of betaine hydrochloride and inorganic salt; repeating step 2) for secondary esterification and distillation of the filtrate to obtain a methanol fraction, a methyl glycolate fraction and a secondary distilled solution; 4) Filter the solution obtained after secondary distillation in step 3), and obtain the treated betaine hydrochloride mother liquor after decolorization and filtration.

2. The processing method according to claim 1, characterized in that: The mass ratio of methanol added in step 2) to hydroxyacetic acid in the betaine hydrochloride mother liquor is (3-5):1; the mass ratio of methanol added in step 3) to hydroxyacetic acid in the solution after the first distillation in step 2) is (3-5):1; the esterification time of the first esterification and the second esterification is 1-3h, and the esterification temperature is 90-110°C.

3. The processing method according to claim 2, characterized in that: The mass ratio of methanol added in step 2) to hydroxyacetic acid in the betaine hydrochloride mother liquor and the mass ratio of methanol added in step 3) to hydroxyacetic acid in the solution after the first distillation in step 2) are 4:1, the time for the first esterification and the second esterification is 2 hours, and the esterification temperature is 95-100°C.

4. The processing method according to claim 1, characterized in that: In step 2) and step 3), the temperature for distilling methanol at normal pressure is 90-100°C, the temperature for distilling methyl glycolate at reduced pressure is 110-130°C, and the vacuum degree is ≤-0.095 MPa.

5. The processing method according to claim 4, characterized in that: The temperature for distilling methanol under normal pressure is 100°C, and the temperature for distilling methyl glycolate under reduced pressure is 120°C.

6. The processing method according to claim 1, characterized in that: In step 4), the specific method of decolorization and filtration is to add activated carbon to the solution after secondary distillation to make the mass concentration of activated carbon 0.2%, decolorize at 90° C. for 2 hours, and then filter to remove the activated carbon to obtain the treated betaine hydrochloride mother liquor.

7. The processing method according to claim 1, characterized in that: The methanol fraction and the methyl glycolate fraction obtained in step 2) and step 3) are combined respectively; the methanol fraction is applied to the esterification step as a raw material for primary esterification and secondary esterification, and the methyl glycolate fraction is hydrolyzed to prepare glycolic acid.

8. The processing method according to claim 7, characterized in that: The method for preparing glycolic acid by hydrolyzing the methyl glycolate fraction comprises the following steps: A) adding water to the methyl glycolate fraction, and then reflux hydrolyzing it at 110-120° C. under normal pressure, collecting the distilled methanol during the hydrolysis process, and reflux hydrolyzing it until the methyl glycolate is hydrolyzed by more than 90%, then cooling it to below 70° C., and concentrating it under reduced pressure until no water is distilled off, thereby obtaining a glycolate concentrate; B) slowly cooling the glycolic acid concentrated solution obtained in step A), adding glycolic acid crystals to the glycolic acid methyl ester concentrated solution as seeds to promote crystallization, and filtering and separating the glycolic acid crystals after low-temperature crystallization.

9. The processing method according to claim 8, characterized in that: In step A), the ratio of the mass of the methyl glycolate fraction to the mass of the added water is 1:1; in step A), during the process of vacuum concentration until anhydrous distillation is performed, the temperature of the vacuum concentrated distilled water is 50-70°C, and the vacuum degree is ≤-0.095Mpa; in step A), the gas phase temperature at the top of the tower is controlled to be 64°C.

10. The processing method according to claim 8, characterized in that: In step B), the hydroxyacetic acid concentrated solution obtained in step A) is first slowly cooled to 10-15° C., hydroxyacetic acid crystals are added to the hydroxyacetic acid concentrated solution, and then the mixture is kept warm at 5-10° C. for 2 hours, the hydroxyacetic acid crystals are filtered and separated, and the hydroxyacetic acid crystals are dried at 55-60° C. to obtain hydroxyacetic acid crystals.

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