Method for treating waste liquid generated after glycolic acid ester is prepared from sodium glycolate in waste water

Abstract

The invention discloses a method for treating waste liquid generated after glycolic acid ester is prepared from sodium glycolate in waste water, which comprises the following steps of: hydrolyzing waste liquid which is left after glycolic acid ester is extracted and contains diglycolate under an alkaline condition to obtain alcohol; and recovering the alcohol obtained by hydrolysis, and applying the alcohol to the preparation of glycolic acid ester. According to the method, the waste liquid amount is reduced, the alcohol consumption is greatly reduced, the resourceful treatment income is further increased, and the product competitiveness is improved; and meanwhile, special equipment is not needed, the process is simple, the operation is convenient, the resourceful treatment benefit of the phenoxy carboxylic acid wastewater can be greatly improved, waste is turned into wealth, the environmental protection cost is effectively reduced, and the product competitiveness is improved.

Description

Technical Field

[0001] The invention relates to the technical field of phenoxycarboxylic acid wastewater treatment, in particular to a method for treating waste liquid obtained by preparing glycolic acid ester using sodium glycolate in wastewater. Background Art

[0002] The production wastewater of phenoxycarboxylic acids such as 2,4-dichlorophenoxyacetic acid and 2-methyl 4-chlorophenoxyacetic acid contains components such as sodium hydroxyacetate and diglycolic acid (the molar ratio of sodium hydroxyacetate to diglycolic acid is (1-2):1). The current method is to prepare sodium hydroxyacetate into a high-value-added product, hydroxyacetic acid ester, to increase the added value of wastewater treatment and reduce production costs. However, this method only effectively utilizes the sodium hydroxyacetate in the wastewater, and the diglycolic acid and its derivatives in the wastewater remain in the waste liquid after treatment, resulting in a huge waste of resources.

[0003] The existing technology for resource recovery of phenoxycarboxylic acid wastewater is to extract sodium hydroxyacetate from the wastewater or prepare it into hydroxy acid ethyl ester products and then extract it through distillation. However, impurities such as diglycolic acid, which account for a relatively high proportion in phenoxycarboxylic acid wastewater, will react with alcohol to form diglycolic acid esters and other products during the preparation of ester products such as hydroxy acid ethyl ester, resulting in high COD of wastewater and serious waste of alcohol products, which seriously affects the benefits of resource recovery of phenoxycarboxylic acid wastewater.

[0004] At present, there is no research in the industry on the resource disposal of waste liquid after the preparation of glycolic acid esters. Summary of the invention

[0005] In order to solve the shortcomings existing in the prior art, the present invention provides a method for disposing waste liquid after preparing hydroxyacetic acid esters from sodium hydroxyacetate in phenoxycarboxylic acid wastewater. The method further disposes of the waste liquid remaining after distillation and extraction after preparing hydroxyacetic acid esters from phenoxycarboxylic acid wastewater, extracts and recovers a large amount of alcohol, and recycles it back to the process of preparing hydroxyacetic acid esters with hydroxyacetic acid, thereby reducing the amount of hazardous waste and increasing the benefits of resource disposal.

[0006] The specific technical solutions of the present invention are as follows:

[0007] A method for disposing waste liquid after preparing glycolic acid ester using sodium glycolate in wastewater, the method comprising:

[0008] (1) hydrolyzing the waste liquid containing diglycolic acid ester remaining after extracting the glycolic acid ester under alkaline conditions to obtain alcohol;

[0009] (2) Recovering the alcohol obtained by hydrolysis and using it in the preparation of glycolic acid esters.

[0010] Furthermore, the waste liquid containing diglycolic acid ester remaining after the extraction of hydroxyacetic acid ester described in the present invention is produced by reacting phenoxycarboxylic acid wastewater containing sodium hydroxyacetate with alcohol to generate hydroxyacetic acid ester, and then extracting hydroxyacetic acid ester by distillation, and the waste liquid remaining after distillation is the waste liquid containing diglycolic acid ester. The phenoxycarboxylic acid wastewater containing sodium hydroxyacetate is the mother liquor obtained by MVR concentration of the production wastewater of phenoxycarboxylic acid compounds such as 2,4-dichlorophenoxyacetic acid and 2-methyl-4-chlorophenoxyacetic acid. The phenoxycarboxylic acid wastewater contains substances such as sodium hydroxyacetate and diglycolic acid, the content of sodium hydroxyacetate is 1-80wt%, the content of diglycolic acid is 25-60%, and while sodium hydroxyacetate reacts with alcohol to form hydroxyacetic acid ester, diglycolic acid also reacts with alcohol to form diglycolic acid ester.

[0011] Furthermore, when phenoxycarboxylic acid wastewater reacts with alcohol to form hydroxyacetic acid ester, the alcohol used is C1-C5 alkanol such as methanol, ethanol, propanol, isopropanol, n-butanol, isobutanol, and pentanol.

[0012] Furthermore, in step (1), the alkaline condition is provided by an alkaline substance, and the alkaline substance is at least one of sodium hydroxide, potassium hydroxide, calcium hydroxide, sodium carbonate, potassium carbonate or their aqueous solutions.

[0013] Furthermore, in step (1), the hydrolysis is carried out at a pH of ≥10, and an alkaline substance is added to adjust the pH of the waste liquid containing glycolate to ≥10, for example, the pH may be 10, 11, 12, 13, 14, etc. Preferably, the molar amount of the alkaline substance is 1-20 times the molar amount of diglycolate, for example, 1 time, 2 times, 3 times, 4 times, 5 times, 6 times, 7 times, 8 times, 9 times, 10 times, 11 times, 12 times, 13 times, 14 times, 15 times, 16 times, 17 times, 18 times, 19 times, 20 times.

[0014] Furthermore, in step (1), the hydrolysis reaction temperature is 30-150°C, for example, 30°C, 40°C, 50°C, 60°C, 70°C, 80°C, 90°C, 100°C, 110°C, 120°C, 130°C, 140°C, 150°C.

[0015] Furthermore, in step (1), the hydrolysis reaction time is 1-2 h.

[0016] Furthermore, in step (1), the reaction does not require a solvent.

[0017] Furthermore, in step (2), the alcohol-water mixture is extracted from the hydrolysis reaction solution by distillation, so that the alcohol is recovered and reused. The distillation can be carried out under normal pressure or under reduced pressure. The distillation temperature is 30-150° C., which varies depending on the alcohol.

[0018] Compared with the prior art, the present invention has the following beneficial effects:

[0019] The present invention further explores the potential of wastewater resource disposal based on the preparation of glycolic acid esters from phenoxycarboxylic acid production wastewater. The main components of the waste liquid after separating glycolic acid esters are impurity components such as diglycolic acid esters and glycolic acid polymer esters. By studying the components of the waste liquid, the waste liquid is further disposed of, and the diglycolic acid esters and other products in the waste liquid are alkaline hydrolyzed to recover alcohols, and the remaining components are disposed of as waste. The obtained alcohols can be recycled and used in glycolic acid to prepare glycolic acid esters, which reduces the amount of waste liquid, greatly reduces the consumption of alcohol, further improves the resource disposal benefits (resource disposal benefits increase by about 30%), and improves product competitiveness; at the same time, no special equipment is needed, the process is simple, and the operation is convenient, which can greatly improve the resource disposal benefits of phenoxycarboxylic acid wastewater, realize waste into treasure, effectively reduce environmental protection costs, and improve product competitiveness. DETAILED DESCRIPTION

[0020] The technical solutions in the embodiments of the present invention will be clearly and completely described below in combination with the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments.

[0021] The following concentrations are all mass percentages unless otherwise specified.

[0022] In the following embodiments, the distillation waste liquid used is the waste water produced by the condensation reaction of sodium 2-methyl-4-chlorophenol and sodium chloroacetate, and the mother liquor containing sodium hydroxyacetate is concentrated by MVR and subjected to esterification reaction with alcohol, followed by distillation to extract hydroxyacetic acid ester to obtain the waste liquid, and the distillation waste liquid contains 60-70% of diglycolic acid ester.

[0023] Example 1

[0024] 400 g of distillation waste liquid (with a content of 67% butyl glycolate) was added to a 1000 mL four-necked reaction bottle equipped with a thermometer, 340 g of a 30% sodium hydroxide solution was added to the distillation waste liquid, the pH was adjusted to ≥ 12, the temperature was raised for alkaline hydrolysis reaction, the reaction temperature was 80-90° C., and the alkaline hydrolysis reaction was stopped after 1 hour. The temperature was continued to be raised to carry out atmospheric distillation on the reaction liquid, the temperature was controlled to be ≤ 130° C., and the fractions of n-butanol and water were distilled off to obtain a total of 218.9 g of n-butanol aqueous solution, with a n-butanol content (HPLC) of 70% and a recovery rate of 95%. The recovered n-butanol aqueous solution can be used in the process for preparing butyl glycolate from hydroxyacetic acid.

[0025] Example 2

[0026] 380 g of distillation waste liquid (with a content of 64% ethyl glycolate) was added to a 1000 mL four-necked reaction bottle equipped with a thermometer, solid potassium hydroxide was added to the distillation waste liquid, the pH was adjusted to 11, the temperature was raised for alkaline hydrolysis, the reaction temperature was 110° C., and the alkaline hydrolysis reaction was stopped after 1 hour. The temperature was continued to be raised to carry out atmospheric distillation of the reaction liquid, the temperature was controlled at 90° C., ethanol and water were distilled out, and the ethanol recovery rate was 93%. The obtained ethanol was used in the process of preparing ethyl glycolate from hydroxyacetic acid.

[0027] The above are only preferred specific implementation modes of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical solutions and inventive concepts of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. A method for disposing waste liquid after preparing glycolic acid ester using sodium glycolate in wastewater, characterized in that The following steps are involved: (1) hydrolyzing the waste liquid containing diglycolic acid ester remaining after extracting the glycolic acid ester under alkaline conditions to obtain alcohol; (2) Recovering the alcohol obtained by hydrolysis and using it in the preparation of glycolic acid esters.

2. The waste liquid disposal method according to claim 1, characterized in that: The production process of the waste liquid containing diglycolic acid ester remaining after the extraction of hydroxyacetic acid ester is as follows: phenoxycarboxylic acid wastewater containing sodium hydroxyacetate is reacted with alcohol to generate hydroxyacetic acid ester, and then the hydroxyacetic acid ester is extracted by distillation, and the waste liquid remaining after the distillation is the waste liquid containing diglycolic acid ester.

3. The waste liquid disposal method according to claim 2, characterized in that: The phenoxycarboxylic acid wastewater is the production wastewater of phenoxycarboxylic acid compounds, and the phenoxycarboxylic acid compounds include 2,4-dichlorophenoxyacetic acid and 2-methyl-4-chlorophenoxyacetic acid.

4. The waste liquid disposal method according to claim 2, characterized in that: The alcohol reacted with sodium glycolate is a C1-C5 alkanol.

5. The waste liquid disposal method according to claim 2, characterized in that: The alcohols that react with sodium glycolate are methanol, ethanol, propanol, isopropanol, n-butanol, isobutanol, and amyl alcohol.

6. The waste liquid disposal method according to claim 1, characterized in that: In step (1), the hydrolysis is carried out at a pH ≥ 10.

7. The waste liquid disposal method according to claim 1 or 6, characterized in that: In step (1), the alkaline condition is provided by an alkaline substance, and the alkaline substance is at least one of sodium hydroxide, potassium hydroxide, calcium hydroxide, sodium carbonate, potassium carbonate or their aqueous solutions; preferably, the molar amount of the alkaline substance is 1-20 times the molar amount of diglycolate.

8. The waste liquid disposal method according to claim 1, characterized in that: In step (1), the hydrolysis reaction temperature is 30-150°C.

9. The waste liquid disposal method according to claim 1 or 8, characterized in that: In step (1), the hydrolysis reaction does not require a solvent.

10. The waste liquid disposal method according to claim 1, characterized in that: In step (2), the distillation is carried out under normal pressure at a distillation temperature of 30-150°C.