CN111574363A - Production process of dimethyl phthalate - Google Patents
Production process of dimethyl phthalate Download PDFInfo
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- CN111574363A CN111574363A CN202010455474.0A CN202010455474A CN111574363A CN 111574363 A CN111574363 A CN 111574363A CN 202010455474 A CN202010455474 A CN 202010455474A CN 111574363 A CN111574363 A CN 111574363A
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Abstract
The invention relates to a production process of dimethyl phthalate for removing trace metal sodium ions in a product and reducing the content of methyl benzoate in the product, wherein in the production process, after material neutralization and water washing are finished, the material is treated, 1-5% phosphoric acid or sulfuric acid aqueous solution is mixed with the material for fully stirring, and a stripping technology is adopted to carry trace methyl benzoate out of the product through stripping, so that the content of methyl benzoate in the product is reduced. The production process of the invention is not limited by the quality of raw materials, and the raw materials with high content of impurity benzoic acid in the phthalic anhydride can also produce high-purity dimethyl phthalate, and can be applied to the industries of essence and spice. Through ion exchange, metal ions in the product are removed, and the obtained product can be used in industries such as electronics and the like. Through the measures, high-quality dimethyl phthalate can be produced, and the high requirements of high-end users are met.
Description
Technical Field
The invention belongs to the field of chemical industry, and particularly relates to a production process of dimethyl phthalate for removing trace metal sodium ions in a product and reducing the content of methyl benzoate in the product.
Background
Dimethyl phthalate (DMP) has strong dissolving capacity on various resins, has good film forming property, adhesiveness and water resistance, can be added into cellulose resin, acrylic resin and polyurethane resin, and has wide application in building materials, coatings, insecticides, cosmetics and other aspects. In addition, it is often used in combination with diethyl phthalate in the production of films, varnishes, transparencies and molding powders of cellulose acetate. The small amount of the product is used in the preparation of nitrocellulose, and can also be used as a plasticizer of nitrile rubber or used as a raw material for producing dicyclohexyl phthalate, higher alcohol phthalate and other organic synthesis by an ester exchange method.
At present, the mainstream production route of dimethyl phthalate in China is that phthalic anhydride and methanol react under the action of a catalyst to generate dimethyl phthalate crude ester, and the crude ester is neutralized, washed, dehydrated and filtered to obtain a product. The benzoic anhydride as the raw material contains benzoic acid as a byproduct, so that methyl benzoate is generated in the reaction process, and the methyl benzoate has a large smell and has influence on the use of high-end customers. Meanwhile, in the production process, sodium ion exists, and by-product sodium monomethyl phthalate can be formed. The presence of these impurities affects the purity of the product and also limits the field of use for the customer. In order to solve the problems, some domestic manufacturers adopt a rectification process for purification, but the energy consumption in the rectification process is high, so that the energy conservation and emission reduction are not facilitated.
Methyl benzoate and sodium monomethyl phthalate are introduced into raw materials or a production process, so that the purity of the product is influenced, the product has a large odor, and the application range is limited. At present, partial manufacturers adopt a rectification process for purification, and the energy consumption is high.
Disclosure of Invention
The invention provides a production process of dimethyl phthalate, which adopts gas and stripping technology to remove a small amount of methyl benzoate in a product aiming at the problem of high content of methyl benzoate in the product, and adopts phosphoric acid, sulfuric acid and the like to carry out ion exchange aiming at sodium ions introduced in the production process of the product so as to remove the sodium ions in the product.
In order to achieve the purpose, the invention adopts the following technical scheme:
a production process of dimethyl phthalate comprises the steps of raw material feeding, esterification, neutralization and water washing, filtration, ion exchange and azeotropic stripping;
the ion exchange step is after the neutralization and water washing step;
the azeotropic stripping step follows the ion exchange step.
The reaction principle is as follows:
main reaction:
in the production process, after the materials are neutralized and washed with water, the materials are treated, 1-5% phosphoric acid or sulfuric acid aqueous solution is adopted to be mixed with the materials for fully stirring, the acidity of sulfuric acid (phosphoric acid) is stronger than that of carboxylic acid, so that strong acid hydrogen ions in the aqueous solution are subjected to ion exchange with sodium ions of sodium carboxylate to generate weak carboxylic acid, a small amount of residual sodium monoester phthalate in the materials is subjected to ion exchange with hydrogen ions of the sulfuric acid, a small amount of sodium ions are dissolved in water to generate sodium bisulfate (sodium hydrogen phosphate), and then the sodium bisulfate is washed with water by deionized water, so that trace metal sodium ions in products are removed, and the temperature is lower and the sulfuric acid concentration is low in the treatment process.
The reaction principle is RCOONa + H+→RCOOH+Na+。
Under the concentration and temperature of the acid in the treatment process, the dimethyl phthalate product can not be hydrolyzed in a large amount, the quality of the product is not affected by trace hydrolysis, and the acid value meets the requirement of quality indexes.
After the dealcoholization is finished, a stripping technology is adopted under the vacuum condition to carry out stripping on trace amount of methyl benzoate out of the product, thereby reducing the content of the methyl benzoate in the product. The sodium ion content in the product is less than 1ppm and the methyl benzoate content is less than 100ppm by the method.
Preferably, the ion exchange is: and adding an acid solution into the washed material, heating and stirring, standing, separating a water phase, and washing with deionized water for multiple times.
Preferably, the adding amount of the acidic solution is 10% of the material amount after water washing, and the adding amount of the deionized water is 20% of the material amount.
Preferably, the acid solution is a sulfuric acid or phosphoric acid solution with the mass fraction of 1-5%.
Preferably, the heating temperature is 40-50 ℃, and the stirring time is 30-40 min; standing for 30-45min, and washing with deionized water at 40-50 deg.C.
Preferably, the azeotropic stripping is to transfer the material after the ion exchange step into a stripping kettle, vacuumize and heat up, and introduce steam or nitrogen for stripping; sampling and analyzing until the content of the methyl benzoate in the material is less than 100 ppm; then the steam stripping is closed, and the vacuum heat preservation is carried out, so that the water content is less than 0.1 percent.
Preferably, the vacuum degree is more than 0.09MPa, and steam is introduced after the temperature is raised to 120-130 ℃.
Preferably, the stripping time is 30-60min, and the vacuum heat preservation time is 30-60 min.
Preferably, the content of sodium ions in the product prepared by the production process is less than 1ppm, and the content of methyl benzoate is less than 100 ppm.
The invention has the beneficial effects that: in the production process, after the neutralization and water washing of the materials are finished, the materials are treated, 1-5% phosphoric acid or sulfuric acid aqueous solution is mixed with the materials for full stirring, the acidity of sulfuric acid (phosphoric acid) is stronger than that of carboxylic acid, so that strong acid hydrogen ions in the aqueous solution are subjected to ion exchange with sodium ions of sodium carboxylate to generate weak carboxylic acid, a small amount of residual sodium monoester phthalate in the materials is subjected to ion exchange with hydrogen ions of the sulfuric acid, a small amount of sodium ions are dissolved in water to generate sodium bisulfate (sodium hydrogen phosphate), and then the deionized water is used for water washing, so that trace metal sodium ions in the product are removed, and the temperature is lower and the sulfuric acid concentration is low in the treatment process.
Under the concentration and temperature of the acid in the treatment process, the dimethyl phthalate product can not be hydrolyzed in a large amount, the quality of the product is not affected by trace hydrolysis, and the acid value meets the requirement of quality indexes.
After the dealcoholization is finished, a stripping technology is adopted under the vacuum condition to carry out stripping on trace amount of methyl benzoate out of the product, thereby reducing the content of the methyl benzoate in the product. The sodium ion content in the product is less than 1ppm and the methyl benzoate content is less than 100ppm by the method.
The production process of the invention is not limited by the quality of raw materials, and the raw materials with high content of impurity benzoic acid in the phthalic anhydride can also produce high-purity dimethyl phthalate, and can be applied to the industries of essence and spice. Through ion exchange, metal ions in the product are removed, and the obtained product can be used in industries such as electronics and the like. Through the measures, high-quality dimethyl phthalate can be produced, and the high requirements of high-end users are met. The production process needs no distillation, and the steam consumption is reduced because the distillation needs more steam and the steam stripping needs less steam. Meanwhile, the phthalic anhydride with high benzoic acid content is 400-500 hundred/ton cheaper than the phthalic anhydride with low benzoic acid content, so that the production cost can be reduced.
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FIG. 1 is a process flow diagram of the present invention.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
Example 1
Referring to fig. 1, a process for the production of dimethyl phthalate, the process comprising:
step 1), esterification:
in the esterification kettle, the molar ratio of 1: 2, adding phthalic anhydride and methanol, adding catalyst sulfuric acid with the mass of 2 per thousand of that of the phthalic anhydride, heating to 80 ℃, carrying out reflux reaction for 2 hours, increasing the vacuum degree in the kettle to be more than 0.08MPa, slowly removing excessive methanol and water generated in the kettle until the temperature in the kettle is 120 ℃, then adding methanol into the kettle at the temperature of 120 ℃ under the vacuum degree of less than 0.01MPa, carrying out esterification reaction until the acid value of the material is less than 4mgKOH/g, carrying out esterification reaction for 15 hours, removing excessive methanol at the vacuum degree of more than 0.09MPa, and carrying out dealcoholization at the temperature of 130 ℃ to obtain crude ester, wherein the crude ester contains 98.5-99% of dimethyl phthalate, 0.1-0.2% of methyl benzoate, 0.5-1% of methanol and 0.2-0.4% of monomethyl phthalate.
Step 2) neutralizing and removing monomethyl phthalate and sulfuric acid from crude ester
The crude ester material obtained in the step 1) is put into a neutralization kettle, 4% of sodium carbonate solution with the mass of 10% of that of the crude ester is added to be stirred for 30 minutes at 70 ℃, neutralization is carried out, a small amount of unreacted monomethyl phthalate, catalyst sulfuric acid and sodium carbonate react to generate monomethyl phthalate sodium salt and sodium sulfate under the alkaline condition, the substances are easily dissolved in water, alkali liquor water is separated after standing for 20 minutes, and the materials are washed for 2 times with water with the mass of 20% and the temperature of 70 ℃, so that the impurities such as the monomethyl phthalate sodium, the sodium sulfate and the like in the materials are further removed.
Step 3) ion exchange:
and 2) adding 1% sulfuric acid aqueous solution accounting for 10% of the material amount into the washed material, stirring for 30 minutes at the temperature of 40 ℃ to fully mix the material and the water, wherein strong acid hydrogen ions in the aqueous solution and sodium ions of the sodium carboxylate are subjected to ion exchange to generate weak carboxylic acid because the acidity of the sulfuric acid is stronger than that of the carboxylic acid. After exchanging a small amount of residual sodium monoester phthalate in the material with hydrogen ions of sulfuric acid, the generated sodium bisulfate is dissolved in water, then the solution is stood for 30 minutes, the water phase is separated, and the solution is washed for 2 times by deionized water with the material amount of 20 percent at 40 ℃. The temperature is low and the concentration of sulfuric acid is low in the treatment process. Under the concentration and temperature of the acid in the treatment process, the dimethyl phthalate product can not be hydrolyzed in a large amount, the quality of the product is not affected by trace hydrolysis, and the acid value meets the requirement of quality indexes.
Step 4) azeotropic stripping:
and 3) pulling the treated material in the step 3) into a stripping kettle, heating to 120 ℃, introducing steam and nitrogen into the material under the condition that the vacuum degree is more than 0.09MPa, and removing the methyl benzoate in the product by utilizing the azeotropic principle. The stripping time was 0.5 hour, and a sample was taken for analysis until the content of methyl benzoate in the feed was less than 100 ppm. Then the steam stripping is turned off, and the temperature is kept for 0.5 hour under vacuum to ensure that the moisture content is less than 0.1 percent.
The steam stripping is carried out under the conditions that the vacuum degree is more than 0.098MPa and the temperature is 125 ℃, and part of experimental data are shown in a table 2.
Step 5), filtering:
and (4) carrying out filter pressing on the material stripped in the step 4) to obtain a product.
Example 2
Referring to fig. 1, a process for the production of dimethyl phthalate, the process comprising:
step 1), esterification:
in the esterification kettle, the molar ratio of 1: 2, adding phthalic anhydride and methanol, adding catalyst sulfuric acid with the mass of 2.5 per thousand of that of the phthalic anhydride, heating to 95 ℃, carrying out reflux reaction for 2.5 hours, increasing the vacuum degree in the kettle to be more than 0.08MPa, slowly removing excessive methanol and water generated in the kettle until the temperature in the kettle is 128 ℃, then adding methanol into the kettle at the temperature of 125 ℃ under the vacuum degree of less than 0.01MPa for dehydration, carrying out esterification reaction until the acid value of the material is less than 4mgKOH/g, carrying out esterification reaction for 13 hours, removing excessive methanol at the vacuum degree of more than 0.09MPa, and carrying out dealcoholization at the temperature of 136 ℃ to obtain crude ester, wherein the crude ester contains 98.5-99% of dimethyl phthalate, 0.1-0.2% of methyl benzoate, 0.5-1% of methanol and 0.2-0.4% of monomethyl phthalate.
Step 2) neutralizing and removing monomethyl phthalate and sulfuric acid from crude ester
The crude ester material obtained in the step 1) is thrown into a neutralization kettle, 5% sodium carbonate solution with 13% of the mass of the crude ester is added, the mixture is stirred for 33 minutes at 85 ℃, neutralization is carried out, a small amount of unreacted monomethyl phthalate, catalyst sulfuric acid and sodium carbonate react to generate monomethyl phthalate sodium salt and sodium sulfate under the alkaline condition, the substances are easily dissolved in water, alkali liquor water is separated after the mixture is stood for 25 minutes, and the mixture is washed for 2 times with water with the material amount of 20% at 78 ℃, so that impurities such as monomethyl phthalate sodium, sodium sulfate and the like in the material are further removed.
Step 3) ion exchange:
and 2) adding a 3% sulfuric acid aqueous solution accounting for 10% of the material amount into the washed material, stirring for 37 minutes at 47 ℃ to fully mix the material and water, wherein strong acid hydrogen ions in the aqueous solution and sodium ions of the sodium carboxylate are subjected to ion exchange to generate weak carboxylic acid because the acidity of the sulfuric acid is stronger than that of the carboxylic acid. After exchanging a small amount of residual sodium monoester phthalate in the material with hydrogen ions of sulfuric acid, the generated sodium bisulfate is dissolved in water, then the solution is stood for 40 minutes, the water phase is separated, and the solution is washed for 2 times by deionized water with the material amount of 20 percent at the temperature of 45 ℃. The temperature is low and the concentration of sulfuric acid is low in the treatment process. Under the concentration and temperature of the acid in the treatment process, the dimethyl phthalate product can not be hydrolyzed in a large amount, the quality of the product is not affected by trace hydrolysis, and the acid value meets the requirement of quality indexes.
Step 4) azeotropic stripping:
and 3) pulling the treated material in the step 3) into a stripping kettle, heating to 127 ℃, introducing steam and nitrogen into the material under the condition that the vacuum degree is more than 0.09MPa, and removing the methyl benzoate in the product by utilizing the azeotropic principle. The stripping time was 0.8 hour, and a sample was taken for analysis until the content of methyl benzoate in the feed was less than 100 ppm. Then the steam stripping is turned off, and the temperature is kept for 0.7 hour under vacuum to ensure that the moisture content is less than 0.1 percent.
The steam stripping is carried out under the conditions that the vacuum degree is more than 0.098MPa and the temperature is 125 ℃, and part of experimental data are shown in a table 2.
Step 5), filtering:
and (4) carrying out filter pressing on the material stripped in the step 4) to obtain a product.
Example 3
Referring to fig. 1, a process for the production of dimethyl phthalate, the process comprising:
step 1), esterification:
in the esterification kettle, the molar ratio of 1: 2, adding phthalic anhydride and methanol, adding catalyst sulfuric acid with the mass of 3 per thousand of that of the phthalic anhydride, heating to 100 ℃, carrying out reflux reaction for 3 hours, increasing the vacuum degree in the kettle to be more than 0.08MPa, slowly removing excessive methanol and water generated in the kettle until the temperature in the kettle is 130 ℃, then adding methanol into the kettle at the temperature of 130 ℃ under the vacuum degree of less than 0.01MPa, carrying out esterification reaction until the acid value of the material is less than 4mgKOH/g, carrying out esterification reaction for 12 hours, removing excessive methanol at the vacuum degree of more than 0.09MPa, and carrying out dealcoholization at the temperature of 140 ℃ to obtain crude ester, wherein the crude ester contains 98.5-99% of dimethyl phthalate, 0.1-0.2% of methyl benzoate, 0.5-1% of methanol and 0.2-0.4% of monomethyl phthalate.
Step 2) neutralizing and removing monomethyl phthalate and sulfuric acid from crude ester
The crude ester material obtained in the step 1) is thrown into a neutralization kettle, 6% sodium carbonate solution with 15% of the mass of the crude ester is added, the mixture is stirred for 40 minutes at 90 ℃, neutralization is carried out, a small amount of unreacted monomethyl phthalate, catalyst sulfuric acid and sodium carbonate react to generate monomethyl phthalate sodium salt and sodium sulfate under the alkaline condition, the substances are easily dissolved in water, alkali liquor water is separated after the mixture is stood for 30 minutes, and the mixture is washed for 2 times with water with the material amount of 20% and the temperature of 80 ℃, so that impurities such as monomethyl phthalate sodium, sodium sulfate and the like in the material are further removed.
Step 3) ion exchange:
and 2) adding a 5% phosphoric acid aqueous solution accounting for 10% of the material amount into the washed material, stirring for 30-40 minutes at the temperature of 40-50 ℃ to fully mix the material and the water, wherein strong acid hydrogen ions in the aqueous solution and sodium ions of the sodium carboxylate are subjected to ion exchange due to the fact that the acidity of the phosphoric acid is stronger than that of the carboxylic acid, and weak carboxylic acid is generated. After exchanging a small amount of residual sodium monoester phthalate in the material with hydrogen ions of phosphoric acid, the generated sodium hydrogen phosphate is dissolved in water, then the solution is stood for 45 minutes, the water phase is separated, and the solution is washed for 2 times by deionized water with the amount of 20 percent of the material at 50 ℃. The temperature is low and the concentration of phosphoric acid is low during the treatment process. Under the concentration and temperature of the acid in the treatment process, the dimethyl phthalate product can not be hydrolyzed in a large amount, the quality of the product is not affected by trace hydrolysis, and the acid value meets the requirement of quality indexes.
Step 4) azeotropic stripping:
and 3) pulling the treated material in the step 3) into a stripping kettle, heating to 130 ℃, introducing steam and nitrogen into the material under the condition that the vacuum degree is more than 0.09MPa, and removing the methyl benzoate in the product by utilizing the azeotropic principle. The stripping time was 1 hour, and a sample was taken for analysis until the content of methyl benzoate in the feed was less than 100 ppm. Then the steam stripping is turned off, and the temperature is kept for 1 hour under vacuum to ensure that the moisture content is less than 0.1 percent.
The steam stripping is carried out under the conditions that the vacuum degree is more than 0.098MPa and the temperature is 125 ℃, and part of experimental data are shown in a table 2.
Step 5), filtering:
and (4) carrying out filter pressing on the material stripped in the step 4) to obtain a product.
Example 4
Referring to fig. 1, a process for the production of dimethyl phthalate, the process comprising:
step 1), esterification:
in the esterification kettle, the molar ratio of 1: 2, adding phthalic anhydride and methanol, adding a catalyst of which the mass is 3 per thousand of that of the phthalic anhydride, hydrating ferric sulfate, heating to 100 ℃, carrying out reflux reaction for 3 hours, increasing the vacuum degree in the kettle to be more than 0.08MPa, slowly removing excessive methanol and water generated in the kettle until the temperature in the kettle is 130 ℃, then adding methanol into the kettle at the temperature of 130 ℃ under the vacuum degree of less than 0.01MPa, carrying out esterification reaction until the acid value of the material is less than 4mgKOH/g, carrying out esterification reaction for 12 hours, removing excessive methanol at the vacuum degree of more than 0.09MPa, and carrying out dealcoholization at the temperature of 140 ℃ to obtain crude ester, wherein the crude ester contains 98.5-99% of dimethyl phthalate, 0.1-0.2% of methyl benzoate, 0.5-1% of methanol and 0.2-0.4% of monomethyl phthalate.
Step 2) neutralizing and removing monomethyl phthalate and sulfuric acid from crude ester
The crude ester material obtained in the step 1) is thrown into a neutralization kettle, 6% sodium carbonate solution with 15% of the mass of the crude ester is added, the mixture is stirred for 40 minutes at 90 ℃, neutralization is carried out, a small amount of unreacted monomethyl phthalate, catalyst sulfuric acid and sodium carbonate react to generate monomethyl phthalate sodium salt and sodium sulfate under the alkaline condition, the substances are easily dissolved in water, alkali liquor water is separated after the mixture is stood for 30 minutes, and the mixture is washed for 2 times with water with the material amount of 20% and the temperature of 80 ℃, so that impurities such as monomethyl phthalate sodium, sodium sulfate and the like in the material are further removed.
Step 3) ion exchange:
and 2) adding a 5% phosphoric acid aqueous solution accounting for 10% of the material amount into the washed material, stirring for 30-40 minutes at the temperature of 40-50 ℃ to fully mix the material and the water, wherein strong acid hydrogen ions in the aqueous solution and sodium ions of the sodium carboxylate are subjected to ion exchange due to the fact that the acidity of the phosphoric acid is stronger than that of the carboxylic acid, and weak carboxylic acid is generated. After exchanging a small amount of residual sodium monoester phthalate in the material with hydrogen ions of phosphoric acid, the generated sodium hydrogen phosphate is dissolved in water, then the solution is stood for 45 minutes, the water phase is separated, and the solution is washed for 2 times by deionized water with the amount of 20 percent of the material at 50 ℃. The temperature is low and the concentration of phosphoric acid is low during the treatment process. Under the concentration and temperature of the acid in the treatment process, the dimethyl phthalate product can not be hydrolyzed in a large amount, the quality of the product is not affected by trace hydrolysis, and the acid value meets the requirement of quality indexes.
Step 4) azeotropic stripping:
and 3) pulling the treated material in the step 3) into a stripping kettle, heating to 130 ℃, introducing steam and nitrogen into the material under the condition that the vacuum degree is more than 0.09MPa, and removing the methyl benzoate in the product by utilizing the azeotropic principle. The stripping time was 1 hour, and a sample was taken for analysis until the content of methyl benzoate in the feed was less than 100 ppm. Then the steam stripping is turned off, and the temperature is kept for 1 hour under vacuum to ensure that the moisture content is less than 0.1 percent.
The stripping is carried out under the conditions that the vacuum degree is more than 0.098MPa and the temperature is 125 ℃, and partial experimental data are shown in a table 2.
Step 5), filtering:
and (4) carrying out filter pressing on the material stripped in the step 4) to obtain a product.
Comparative data for sodium ion content before and after ion exchange for the products of examples 1-3 are shown in Table 1.
TABLE 1 sodium ion content comparison data
TABLE 2 content of methyl benzoate after stripping
The production process of the invention is not limited by the quality of raw materials, and the raw materials with high content of impurity benzoic acid in the phthalic anhydride can also produce high-purity dimethyl phthalate, and can be applied to the industries of essence and spice. Through ion exchange, metal ions in the product are removed, and the obtained product can be used in industries such as electronics and the like. Through the measures, high-quality dimethyl phthalate can be produced, and the high requirements of high-end users are met. The production process needs no distillation, and the steam consumption is reduced because the distillation needs more steam and the steam stripping needs less steam. Meanwhile, the phthalic anhydride with high benzoic acid content is 400-500 hundred/ton cheaper than the phthalic anhydride with low benzoic acid content, so that the production cost can be reduced.
Finally, it should be noted that the above embodiments are only for illustrating the technical solutions of the present invention and not for limiting, and although the present invention has been described in detail with reference to examples, it should be understood by those skilled in the art that modifications or equivalent substitutions may be made on the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, which should be covered by the claims of the present invention.
Claims (9)
1. A production process of dimethyl phthalate comprises the steps of raw material feeding, esterification, neutralization and water washing and filtration, and is characterized by also comprising ion exchange and azeotropic stripping;
the ion exchange step is after the neutralization and water washing step;
the azeotropic stripping step follows the ion exchange step.
2. The process for the production of dimethyl phthalate according to claim 1, wherein said ion exchange is: and adding an acid solution into the washed material, heating and stirring, standing, separating a water phase, and washing with deionized water for multiple times.
3. The process for producing dimethyl phthalate according to claim 2, wherein the amount of the acidic solution added is 10% of the amount of the material after washing with water, and the amount of the deionized water added is 20% of the amount of the material.
4. The process for producing dimethyl phthalate according to claim 2 or 3, wherein the acidic solution is a 1-5% by mass solution of sulfuric acid or phosphoric acid.
5. The process for producing dimethyl phthalate according to claim 2 or 3, wherein the heating temperature is 40-50 ℃ and the stirring time is 30-40 min; standing for 30-45min, and washing with deionized water at 40-50 deg.C.
6. The process for producing dimethyl phthalate according to claim 1, wherein the azeotropic stripping is to transfer the material after the ion exchange step into a stripping kettle, vacuumize and heat up, and introduce steam or nitrogen for stripping; sampling and analyzing until the content of the methyl benzoate in the material is less than 100 ppm; then the steam stripping is closed, and the vacuum heat preservation is carried out, so that the water content is less than 0.1 percent.
7. The process for producing dimethyl phthalate as claimed in claim 6, wherein the vacuum degree is greater than 0.09MPa, and the temperature is raised to 120-130 ℃ before steam is introduced.
8. The process for producing dimethyl phthalate according to claim 6, wherein the stripping time is 30-60min, and the vacuum holding time is 30-60 min.
9. The process for producing dimethyl phthalate according to claim 1, wherein the product produced by the process contains less than 1ppm of sodium ions and less than 100ppm of methyl benzoate.
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| CN111574363B (en) | 2023-09-26 |
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