Method for separating and purifying glutaric acid from mixed binary acid

Abstract

The invention belongs to the technical field of fine chemical engineering, and provides a method for separating and purifying glutaric acid from mixed dibasic acid, which mainly comprises the following steps: decoloring and filtering mixed dibasic acid flakes and alcohol under certain conditions, adding a catalyst into the mixed dibasic acid solution, fully reacting, filtering to obtain a mixed ester solution, carrying out alkali washing to obtain mixed dibasic acid diester, and separating and purifying glutaric acid from the mixed dibasic acid diester. The method comprises the following steps: rectifying mixed dibasic acid diester under a certain condition to obtain glutaric acid diester, hydrolyzing the glutaric acid diester and deionized water under a certain condition, recrystallizing, filtering, washing and drying to obtain more than 99.5% glutaric acid, evaporating a solvent from an alkali washing solution, and pressurizing and esterifying with alcohol under a CO2 atmosphere to obtain a mixed ester solution for reuse. The process is simple, easy to control, energy-saving and environment-friendly, the waste liquid can be recycled, obvious advantages are shown in the aspects of manufacturing cost, product performance and the like, and the prepared glutaric acid is widely applied to the industries of medicine, building, agriculture, electronics and the like.

Description

Technical Field

[0001] The invention belongs to the technical field of fine chemical industry, and particularly relates to a method for separating and purifying glutaric acid from mixed dibasic acids. Background Art

[0002] Mixed dibasic acid (DBA) is a byproduct of the production process of adipic acid (ADA) by oxidation of cyclohexane. It mainly contains succinic acid, glutaric acid, adipic acid, and a small amount of nitric acid and metal ions such as copper and vanadium. Every ton of adipic acid produced will produce 50 to 60 kilograms of mixed dibasic acid. With the rapid development of the nylon industry, the demand for adipic acid continues to increase, and a large amount of mixed dibasic acid needs to be processed. Since mixed dibasic acid contains metal ions, it is not suitable for biological treatment and is mainly treated by combustion. This method not only wastes resources but also pollutes the environment. In recent years, distillation, esterification distillation, crystallization, amination reaction, urea complexation, adsorption, extraction crystallization, etc. have been developed for the treatment of mixed dibasic acid. Since the three dibasic acids have high boiling points and will decompose when close to the boiling point, the distillation method can only obtain the corresponding acid anhydrides; the esterification distillation method needs to be carried out under high temperature and high pressure, and the obtained ester is a mixed ester of various monoesters and dibasic esters, which is difficult to post-process; the crystallization method requires multiple crystallizations under vacuum flash evaporation, and the process route is long, the yield is low, and the energy consumption is high.

[0003] The mass content of glutaric acid in mixed dibasic acid is more than 60%, which is an important organic chemical raw material and intermediate, and is widely used in synthetic resin, medicine, construction, agriculture and electronics industries. The current market research results show that the market price of mixed dibasic acid is 3,000 to 5,000 yuan / ton, while the market price of glutaric acid is 60,000 to 80,000 yuan / ton. The development of a method for separating glutaric acid from mixed dibasic acid has good economic value and social significance. Chinese patent CN106957223A discloses a method for purifying C4-C6 dibasic acid monomers from adipic acid byproduct mixed dibasic acid, wherein the mixed dibasic acid and methanol are subjected to esterification reaction under nitric acid or sulfuric acid catalysis, and then the mixed dibasic acid dimethyl ester is obtained by distillation, and then distilled by two distillation towers to obtain dimethyl succinate, dimethyl glutarate and dimethyl adipate; the obtained dibasic acid dimethyl ester is subjected to two hydrolysis reactions of preliminary hydrolysis and complete hydrolysis in the presence of a hydrolysis catalyst to achieve ester group conversion to obtain dibasic acid. Chinese patent CN107522614A discloses a method for separating and purifying glutaric acid from mixed dibasic acids using low-carbon halogenated alkanes. The mixed dibasic acid is crushed and sieved, then added to a low-carbon polyhalogenated alkane solvent, heated and stirred, filtered while hot after being fully dissolved, and the obtained hot filtrate is added to a crystallizer and stirred. After the temperature stabilizes, the temperature is lowered and crystallized to the final crystallization temperature, and after maintaining the temperature for a period of time, the crude glutaric acid crystals are filtered to obtain a crude glutaric acid crystal product; the crude glutaric acid crystal product is then dissolved in a fresh polyhalogenated alkane solvent and recrystallized to obtain glutaric acid. Chinese patent CN105130790A discloses a method for separating and purifying succinic acid, glutaric acid and adipic acid from the residual liquid of preparing adipic acid by oxidizing cyclohexanone with nitric acid, wherein the residual liquid is evaporated and concentrated to obtain a solution in which the total amount of dibasic acid accounts for 50-55% of the total amount of waste liquid; the solution is then cooled and crystallized to 15-20°C to precipitate succinic acid and adipic acid crystals, which are dissolved in a certain solvent after centrifugal separation, filtered to obtain adipic acid crystals, and the solution is subjected to reduced pressure distillation to obtain succinic acid crystals; then, magnesium oxide is added to the filtrate after cooling and crystallization to generate a magnesium glutaric acid precipitate, which is filtered and dissolved in a sulfuric acid solution, and after standing and stratification, the oil phase is evaporated and dried to obtain glutaric acid.

[0004] At present, these methods still have problems such as low product purity, complex preparation process, high toxicity of reagents, difficult to control crystallization process, low product yield, high energy consumption, etc. Developing an efficient and green process for separating and purifying glutaric acid from mixed dibasic acids is an urgent technical demand. Summary of the invention

[0005] The purpose of the present invention is to provide a method for separating and purifying glutaric acid from mixed dibasic acids, so as to achieve high added value utilization of the mixed dibasic acids, and the purity of the prepared glutaric acid is higher than 99.5%.

[0006] The technical solution of the present invention:

[0007] A method for separating and purifying glutaric acid from a mixed dibasic acid, comprising the following steps:

[0008] Step 1: Mix the mixed dibasic acid flakes and alcohol in a certain mass ratio, add an adsorbent, stir, and filter to obtain a decolorized mixed dibasic acid solution;

[0009] Step 2: After heating the mixed dibasic acid solution obtained in step 1, an esterification catalyst is added, stirred, and filtered after the reaction is complete to obtain a mixed ester solution, and the esterification catalyst is reused;

[0010] Step 3: adding an alkaline solution to the mixed ester solution obtained in step 2, stirring and washing, standing and stratifying, and separating to obtain an alkaline washing solution and a mixed dibasic acid diester;

[0011] Step 4: The mixed dibasic acid diester obtained in step 3 is subjected to rectification to obtain glutaric acid diester, succinic acid diester and adipic acid diester respectively; the glutaric acid diester is then mixed with deionized water, a hydrolysis catalyst is added, and after sufficient reaction, a glutaric acid aqueous solution is obtained by fractionation, and then recrystallization, filtration, washing and drying are performed to obtain pure glutaric acid; the hydrolysis catalyst is separated and reused;

[0012] Step 5: evaporate the alkaline washing solution obtained in step 3 to remove the solvent, crystallize, and vacuum dry to obtain a mixed dibasic acid salt; then mix the mixed dibasic acid salt with alcohol, add a catalyst, introduce carbon dioxide gas, stir at a certain temperature until the reaction is complete, cool and filter to obtain a mixed ester solution, and return it to step 3 for reuse.

[0013] In step 1, the mixed dibasic acid flakes are a byproduct of the process for preparing adipic acid;

[0014] In step 1, the adsorbent is one of activated carbon, macroporous adsorption resin D001, and 5A molecular sieve;

[0015] In step 1, the alcohol is one of anhydrous methanol, anhydrous ethanol, and anhydrous n-butanol;

[0016] In step 1, the mass ratio of the mixed dibasic acid flakes to the alcohol is 1:1 to 1:10; the mass ratio of the mixed dibasic acid flakes to the adsorbent is 1:0.05 to 1:0.35; stirring is performed at a temperature of 25 to 50° C. for 4 to 24 hours;

[0017] In step 2, the esterification catalyst is one of sodium bisulfate monohydrate, 001×4 type strong acid cation exchange resin, D001 type strong acid cation exchange resin, and 742 type strong acid cation exchange resin;

[0018] In step 2, the mass ratio of the mixed dibasic acid to the esterification catalyst is 1:0.02 to 1:0.10; the reaction time is 1.0 to 6.0 hours, and the reaction temperature is 60 to 110° C.;

[0019] In step 3, the alkaline solution is one of an aqueous solution of sodium carbonate, sodium bicarbonate, potassium bicarbonate, sodium hydroxide, and ammonium carbonate, and the mass percentage of the alkali is 2%-10%;

[0020] In step 3, the volume ratio of the mixed ester solution to the alkaline solution is 1:0.2 to 1:2; the stirring washing temperature is 60 to 80° C., and the time is 0.2 to 1.0 h;

[0021] In step 4, the initial tower top temperature during the distillation process is 180-260°C;

[0022] In step 4, the hydrolysis catalyst is one of 001×4 type strong acid cation exchange resin, D001 type strong acid cation exchange resin, and 742 type strong acid cation exchange resin;

[0023] In step 4, the mass ratio of glutaric acid diester to hydrolysis catalyst is 1:0.02 to 1:0.1; the reaction temperature is 100 to 130° C., and the reaction time is 2.0 to 5.0 h;

[0024] In step 5, the vacuum drying temperature of the mixed dibasic acid salt is 60 to 80° C.;

[0025] In step 5, the catalyst is one of HY molecular sieve, ferrous sulfate, copper sulfate, and titanium dioxide; the mass ratio of the mixed dibasic acid salt to the catalyst is 1:0.02 to 1:0.1;

[0026] In step 5, CO is introduced into the reactor. 2 The initial pressure after is 0.5~2.5Mpa;

[0027] In step 5, the mass ratio of the mixed dibasic acid salt to the alcohol is 1:5 to 1:20; the reaction temperature is 130 to 200° C., and the reaction time is 4 to 12 hours.

[0028] The invention has the following beneficial effects: glutaric acid is prepared by using nylon acid, a byproduct of adipic acid production, and its purity is higher than 99.5%; the alkali washing process used can effectively solve the problem of separation of unreacted acid from monoester and diester after esterification, and compared with the method of preparing mixed dibasic acid diester by atmospheric distillation and reduced pressure distillation, the process flow is shortened, the process cost is low, and the production efficiency is high; after the alkali washing solution evaporates the solvent, it can be pressurized with alcohol under a carbon dioxide atmosphere to obtain a mixed ester solution, which is recycled and no three wastes are generated. The whole process is simple and easy to control, energy-saving and environmentally friendly, and shows obvious advantages in terms of manufacturing cost, product performance, etc., and has good practical value. DETAILED DESCRIPTION

[0029] The specific implementation of the present invention is described in detail below in conjunction with the technical solution.

[0030] Example 1

[0031] Take 100g of mixed dibasic acid and 200g of anhydrous methanol and place them in a 500mL three-necked flask, add 25g of activated carbon, and then heat in a water bath to reflux for decolorization. The water bath temperature is 40°C and the decolorization time is 12h. After the decolorization is completed, transfer to a Buchner funnel for filtration, transfer the filtrate to the original 500mL three-necked flask, and recover the decolorizer. Add 10g of sodium bisulfate monohydrate to the three-necked flask, set the water bath temperature to 60°C, and the reaction time is 2h. After the reaction is completed, remove the three-necked flask, transfer the reaction solution to a Buchner funnel for filtration to obtain 300mL of mixed ester solution. Transfer the mixed ester solution to a 1L beaker, add 200mL of 5% sodium carbonate solution to it under a 75°C water bath, the alkali washing time is 0.5h, and collect 60.5mL of mixed dibasic acid dimethyl ester after standing and stratification. The mixed dibasic acid dimethyl ester was placed in a 100 mL three-necked flask, heated by an electric heating jacket, and the distillation column was insulated with an electric heating belt. The initial temperature of the top of the tower was 190°C, and 36.5 mL of dimethyl glutarate was obtained by distillation. The dimethyl glutarate was placed in a 200 mL distillation flask, and 60 mL of deionized water and 2.5 g of 001×4 type strong acid cation exchange resin were added thereto. The oil bath temperature was 125°C, the reaction time was 3.0 h, and the purity of the hydrolyzed product was 99.78% by recrystallization.

[0032] The alkaline washing solution was evaporated to remove solvent, and after recrystallization, it was transferred to a 70°C vacuum drying oven for drying to obtain 17.8g of mixed dibasic acid salt. The mixed dibasic acid salt and 150mL of methanol were transferred to a 500mL stainless steel high-temperature and high-pressure magnetic stirring reactor, and 0.5g of HY molecular sieve, CO 2 After the air in the kettle was replaced by gas for 3 times, CO 2 The initial pressure in the reactor was 1.0 MPa. The reaction was stirred and heated for 8 hours. After the reaction was completed, the mixture was cooled and filtered. The obtained mixed ester solution was subjected to repeated alkali washing steps. After three cycles, the total yield was increased to more than 90%.

[0033] Example 2

[0034] Take 100g of mixed dibasic acid and 200g of anhydrous ethanol and place them in a 500mL three-necked flask, add 25g of macroporous adsorption resin D001, and then heat in a water bath to reflux for decolorization. The water bath temperature is 40°C and the decolorization time is 12h. After the decolorization is completed, transfer it to a Buchner funnel for filtration, transfer the filtrate to the original 500mL three-necked flask, and recover the decolorizer. Add 5g742 type strong acid cation exchange resin to the three-necked flask, set the water bath temperature to 80°C, and the reaction time is 2h. After the reaction is completed, remove the three-necked flask, transfer the reaction solution to a Buchner funnel for filtration to obtain 290mL of mixed ester solution. Transfer the mixed ester solution to a 1L beaker, add 200mL of 5% ammonium carbonate solution to it under a 75°C water bath, the alkali washing time is 0.75h, and collect 58.5mL of mixed dibasic acid diethyl ester after standing and stratification. The mixed dibasic acid diethyl ester was placed in a 100 mL three-necked flask, heated by an electric heating jacket, the distillation column was insulated by an electric heating belt, the initial temperature of the tower top was set to 215°C, and 35 mL of diethyl glutarate was obtained by distillation. The diethyl glutarate was placed in a 200 mL distillation flask, 55 mL of deionized water and 3.5 g of 742 type strong acid cation exchange resin were added thereto, the oil bath temperature was 130°C, and the reaction time was 3.0 h. The purity of the hydrolyzed product obtained by recrystallization was 99.59% of glutaric acid.

[0035] The alkaline washing solution was evaporated to remove solvent, and after recrystallization, it was transferred to a vacuum drying oven at 80°C to dry to obtain 17.5g of mixed dibasic acid salt. The mixed dibasic acid salt and 145mL of anhydrous ethanol were transferred to a 500mL stainless steel high-temperature and high-pressure magnetic stirring reactor, and 1.0g of titanium dioxide, CO 2 After the air in the kettle was replaced by gas for 3 times, CO 2 The initial pressure in the reactor was 1.5 MPa. The reaction was stirred and heated for 10 hours. After the reaction was completed, the mixture was cooled and filtered. The obtained mixed ester solution was repeated with alkali washing. After three cycles, the total yield was increased to more than 90%.

[0036] Example 3

[0037] Take 100g of mixed dibasic acid and 200g of n-butanol and place them in a 500mL three-necked flask, add 25g of 5A molecular sieve, and then heat and reflux in an oil bath for decolorization. The oil bath temperature is 50°C and the decolorization time is 24h. After the decolorization is completed, transfer it to a Buchner funnel for filtration, transfer the filtrate to the original 500mL three-necked flask, and recover the decolorizer. Add 7.0g of 742 type strong acid cation exchange resin to the three-necked flask, set the oil bath temperature to 110°C, and the reaction time is 3h. After the reaction is completed, remove the three-necked flask, transfer the reaction solution to a Buchner funnel for filtration to obtain 285mL of mixed ester solution. Transfer the mixed solution to a 1L beaker, add 200mL of 5% ammonium carbonate solution at 75°C, and the alkali washing time is 1.0h. After standing and stratification, collect 56.8mL of mixed dibasic acid dibutyl ester. The mixed dibasic acid dibutyl ester was placed in a 100 mL three-necked flask, heated by an electric heating jacket, the distillation column was insulated by an electric heating belt, the initial temperature of the tower top was set to 270°C, and 34.5 mL of dibutyl glutarate was obtained by distillation. The dibutyl glutarate was placed in a 200 mL distillation flask, 60 mL of deionized water and 3 g of D001 type strong acid cation exchange resin were added thereto, the oil bath temperature was 115°C, and the reaction time was 4.0 h. The purity of the hydrolyzed product obtained by recrystallization was 99.6% of glutaric acid.

[0038] The alkaline washing solution was evaporated to remove the solvent, and then transferred to a vacuum drying oven at 80°C to dry to obtain 19.5 g of mixed dibasic acid salt. The mixed dibasic acid salt and 160 mL of n-butanol were transferred to a 500 mL stainless steel high temperature and high pressure magnetic stirring reactor, and 1.0 g of HY molecular sieve, CO 2 After the air in the kettle was replaced by gas for 3 times, CO 2 The initial pressure in the reactor was 2.5 MPa. The reaction was stirred and heated for 6 hours. After the reaction was completed, the mixture was cooled and filtered. The alkaline washing step was repeated for the obtained mixed ester solution. After three cycles, the total yield was increased to more than 90%.

[0039] Example 4

[0040] Take 300g of mixed dibasic acid and 800g of anhydrous methanol and place them in a 2L double-layer glass reactor, add 90g of activated carbon, pass circulating water into the interlayer for heating, reflux decolorization, the temperature is 25°C, and the decolorization time is 16h. After the decolorization is completed, transfer it to a Buchner funnel for filtration, transfer the filtrate to the original 2L double-layer glass reactor, and recover the decolorizer. Add 15g of 001×4 type strong acid cation exchange resin to the glass reactor, set the circulating water temperature to 65°C, and the reaction time is 3.5h. After the reaction is completed, transfer the reaction solution to a Buchner funnel for filtration to obtain 1.17L of mixed ester solution. Transfer the mixed ester solution to a 5L double-layer glass reactor, set the circulating water heating temperature to 75°C, add 500mL of 10% sodium bicarbonate solution, the alkali washing time is 1.0h, and collect 172.5mL of mixed dibasic acid dimethyl ester after standing and stratification. The mixed dibasic acid dimethyl ester was placed in a 500mL three-necked flask, heated by an electric heating jacket, and the distillation column was insulated with an electric heating belt. The initial temperature of the top of the tower was 185°C, and 98.4mL of dimethyl glutarate was obtained by distillation. The dimethyl glutarate was placed in a 500mL distillation flask, and 165mL of deionized water and 8g of 001×4 type strong acid cation exchange resin were added thereto. The oil bath temperature was 120°C, and the reaction time was 4.5h. The purity of the hydrolyzed product obtained by recrystallization was 99.63%.

[0041] The alkaline washing solution was evaporated to remove solvent, and after recrystallization, it was transferred to a 60°C vacuum drying oven for drying to obtain 50.75g of mixed dibasic acid salt. The mixed dibasic acid salt and 400mL of methanol were transferred to a 1L stainless steel high temperature and high pressure magnetic stirring reactor, and 4.0g of ferrous sulfate, CO 2 After the air in the kettle was replaced by gas for 3 times, CO 2 The initial pressure in the reactor was 1.5 MPa. The reaction was stirred and heated for 10 hours. After the reaction was completed, the mixture was cooled and filtered. The obtained mixed ester solution was repeated with alkali washing. After three cycles, the total yield was increased to more than 90%.

[0042] Example 5

[0043] Take 500g of mixed dibasic acid and 2000g of anhydrous methanol and place them in a 5L double-layer glass reactor, add 150g of activated carbon, pass circulating water into the interlayer for heating, reflux decolorization, the temperature is 30°C, and the decolorization time is 12h. After the decolorization is completed, transfer it to a positive pressure microporous filtration device for filtration, transfer the filtrate to the original 5L double-layer glass reactor, and recover the decolorizer. Add 20g of D001 type strong acid cation exchange resin to the glass reactor, set the circulating water heating temperature to 75°C, and the reaction time is 3.5h. After the reaction is completed, transfer the reaction solution to a positive pressure microporous filtration device for filtration to obtain 2.75L of mixed ester solution. Transfer the mixed ester solution to the original 5L double-layer glass reactor, set the circulating water heating temperature to 80°C, add 500mL of 7.5% sodium hydroxide solution, the alkali washing time is 0.5h, and collect 285mL of mixed dibasic acid dimethyl ester after standing and stratification. The mixed dibasic acid dimethyl ester was placed in a 500mL three-necked flask, heated by an electric heating jacket, the distillation column was insulated by an electric heating belt, the initial temperature of the tower top was set to 190°C, and 167.5mL of dimethyl glutarate was obtained by distillation. The dimethyl glutarate was placed in a 500mL distillation flask, 275mL of deionized water and 15.0g of D001 type strong acid cation exchange resin were added thereto, the oil bath temperature was 115°C, and the reaction time was 5h. The purity of the hydrolyzed product obtained by recrystallization was 99.55% of glutaric acid.

[0044] The alkaline washing solution was evaporated to remove solvent, and after recrystallization, it was transferred to a 60°C vacuum drying oven for drying to obtain 81.4 g of mixed dibasic acid salt. The mixed dibasic acid salt and 900 mL of methanol were transferred to a 2.5 L stainless steel high temperature and high pressure magnetic stirring reactor, and 6.5 g of copper sulfate, CO 2 After the air in the kettle was replaced by gas for 3 times, CO 2 The initial pressure in the reactor was 2.0 MPa. The reaction was stirred and heated for 6 hours. After the reaction was completed, the mixture was cooled and filtered. The obtained mixed ester solution was washed with alkali repeatedly. After three cycles, the total yield was increased to more than 90%.

Claims

1. A method for separating and purifying glutaric acid from a mixed dibasic acid, characterized in that: Here are the steps: Step 1: Mix the mixed dibasic acid flakes and alcohol in a certain mass ratio, add an adsorbent, stir, and filter to obtain a decolorized mixed dibasic acid solution; Step 2: After heating the mixed dibasic acid solution obtained in step 1, an esterification catalyst is added, stirred, and filtered after the reaction is complete to obtain a mixed ester solution, and the esterification catalyst is reused; Step 3: adding an alkaline solution to the mixed ester solution obtained in step 2, stirring and washing, standing and stratifying, and separating to obtain an alkaline washing solution and a mixed dibasic acid diester; Step 4: The mixed dibasic acid diester obtained in step 3 is subjected to rectification to obtain glutaric acid diester, succinic acid diester and adipic acid diester respectively; the glutaric acid diester is then mixed with deionized water, a hydrolysis catalyst is added, and after sufficient reaction, a glutaric acid aqueous solution is obtained by fractionation, and then recrystallization, filtration, washing and drying are performed to obtain pure glutaric acid; the hydrolysis catalyst is separated and reused; Step 5: evaporate the alkaline washing solution obtained in step 3 to remove the solvent, crystallize, and vacuum dry to obtain a mixed dibasic acid salt; then mix the mixed dibasic acid salt with alcohol, add a catalyst, introduce carbon dioxide gas, stir at a certain temperature until the reaction is complete, cool and filter to obtain a mixed ester solution, and return it to step 3 for reuse.

2. The method for separating and purifying glutaric acid from a mixed dibasic acid according to claim 1, characterized in that: In step 1, Mixed dibasic acid flakes are a byproduct of the process for preparing adipic acid; The adsorbent is one of activated carbon, macroporous adsorption resin D001, and 5A molecular sieve; The alcohol is one of anhydrous methanol, anhydrous ethanol and anhydrous n-butanol; The mass ratio of the mixed dibasic acid flakes to the alcohol is 1:1-1:10; the mass ratio of the mixed dibasic acid flakes to the adsorbent is 1:0.05-1:0.35; and the stirring is carried out at a temperature of 25-50° C. for 4-24 hours.

3. The method for separating and purifying glutaric acid from a mixed dibasic acid according to claim 1, characterized in that: In step 2, The esterification catalyst is one of sodium hydrogen sulfate monohydrate, 001×4 type strong acid cation exchange resin, D001 type strong acid cation exchange resin, and 742 type strong acid cation exchange resin; The mass ratio of the mixed dibasic acid to the esterification catalyst is 1:0.02 to 1:0.10; the reaction time is 1.0 to 6.0 hours, and the reaction temperature is 60 to 110°C.

4. The method for separating and purifying glutaric acid from a mixed dibasic acid according to claim 1, characterized in that: In step 3, The alkaline solution is one of aqueous solutions of sodium carbonate, sodium bicarbonate, potassium bicarbonate, sodium hydroxide and ammonium carbonate, and the mass percentage of the alkali is 2%-10%; The volume ratio of the mixed ester solution to the alkaline solution is 1:0.2 to 1:2; the temperature of the stirring washing is 60 to 80°C, and the time is 0.2 to 1.0h.

5. The method for separating and purifying glutaric acid from a mixed dibasic acid according to claim 1, characterized in that: In step 4, The initial tower top temperature during the distillation process is 180-260°C; The hydrolysis catalyst is one of 001×4 type strong acid cation exchange resin, D001 type strong acid cation exchange resin, and 742 type strong acid cation exchange resin; The mass ratio of glutaric acid diester to the hydrolysis catalyst is 1:0.02 to 1:0.1; the reaction temperature is 100 to 130° C., and the reaction time is 2.0 to 5.0 h.

6. The method for separating and purifying glutaric acid from a mixed dibasic acid according to claim 1, characterized in that: In step 5, The vacuum drying temperature of the mixed dibasic acid salt is 60-80°C; The catalyst is one of HY molecular sieve, ferrous sulfate, copper sulfate and titanium dioxide; the mass ratio of the mixed dibasic acid salt to the catalyst is 1:0.02 to 1:0.1; The initial pressure after CO2 is introduced into the reactor is 0.5-2.5Mpa; The mass ratio of the mixed dibasic acid salt to the alcohol is 1:5-1:20; the reaction temperature is 130-200° C., and the reaction time is 4-12 hours.