A plasticizer, dimethyl phthalate, and its synthesis method

Abstract

This invention provides a plasticizer, dimethyl phthalate, and its synthesis method, relating to the field of dimethyl phthalate. The synthesis method of the plasticizer dimethyl phthalate includes the following steps: esterification, neutralization and impurity removal, and removal of light components. In the esterification step, phthalic anhydride, methanol, and a solid acid catalyst are added to an esterification reactor. Under inert gas protection, the temperature is raised until the acid value of the material in the esterification reactor is less than 2 mg KOH / g. After filtration to recover the solid acid catalyst, the esterified material is obtained. This invention, by specifically overcoming the defects of existing dimethyl phthalate synthesis methods, and by utilizing the specific pH range of dimethyl phthalate, overcomes the defects in its downstream applications, thereby meeting specific downstream application requirements.

Description

Technical Field

[0001] This invention relates to the field of dimethyl phthalate, and in particular to a plasticizer dimethyl phthalate and its synthesis method. Background Technology

[0002] Existing methods for synthesizing dimethyl phthalate (DMT), a plasticizer, generally employ inert solvents as dehydrating agents and sulfuric acid as a catalyst. However, these methods are energy-intensive, corrode equipment, and are economically unfeasible. Furthermore, the post-processing of the crude product requires the use of large amounts of sodium hydroxide for neutralization, resulting in significant wastewater generation and high production costs. Furthermore, existing methods for synthesizing DMT cannot meet the specific pH range requirements for DMT synthesis.

[0003] Meanwhile, the pH characteristics of dimethyl phthalate (DMT), a plasticizer synthesized using existing methods, limit its specific application range and cannot fully meet the requirements of downstream applications, especially those with specific pH requirements. Specifically, the pH characteristics of DMT are determined by measuring the pH value of the water layer obtained after stirring and washing DMT with a certain amount of water for 5 minutes. In the plasticizing process using conventional DMT, its stability is poor due to fluctuations in the process environment and the acidity or alkalinity of raw materials, limiting its plasticizing effect on materials and resulting in poor environmental friendliness.

[0004] No existing technologies, both domestically and internationally, disclose a method for synthesizing dimethyl phthalate (DMT), a plasticizer with a specific pH range. Therefore, this paper provides a method for synthesizing DMT with a specific pH range to meet downstream application requirements, which has significant technical importance and research value. Summary of the Invention

[0005] To address the technical problems existing in the prior art, the present invention provides a plasticizer, dimethyl phthalate, and its synthesis method. While specifically overcoming the defects of existing dimethyl phthalate synthesis methods, the present invention also overcomes the defects of downstream applications by utilizing the specific pH range of dimethyl phthalate, thereby meeting the specific application requirements of downstream applications.

[0006] To solve the above technical problems, the technical solution adopted by the present invention is as follows:

[0007] A method for synthesizing dimethyl phthalate, a plasticizer, includes the following steps: esterification, neutralization and impurity removal, and light component removal;

[0008] The esterification process involves adding phthalic anhydride, methanol, and a solid acid catalyst into an esterification reactor. Under inert gas protection, the temperature is raised to esterify the material until the acid value of the material in the esterification reactor is less than 2 mg KOH / g. After filtration and recovery of the solid acid catalyst, the esterified material is obtained.

[0009] The solid acid catalyst is one of the following: sulfonic acid type solid acid catalyst, supported solid acid catalyst, or composite solid acid resin catalyst;

[0010] The neutralization and impurity removal process involves using a neutralizing agent to neutralize the esterified material to a pH of 6-7, thereby obtaining a neutralized material.

[0011] The process of removing light components involves heating the neutralized material under inert gas protection until no light components are released, then cooling it down, followed by decolorization and filtration to obtain the plasticizer dimethyl phthalate; the aqueous layer of the washing solution containing the plasticizer dimethyl phthalate has a pH ≥ 5.

[0012] Preferably, the esterification temperature is 80-120℃.

[0013] The molar ratio of phthalic anhydride to methanol is 1:7-10;

[0014] The weight of the solid acid catalyst added is 0.3-0.5% of the total weight of phthalic anhydride and methanol.

[0015] Furthermore, the preparation method of the composite solid acid resin catalyst is as follows: D001 macroporous sulfonic acid type cation exchange resin is added to hydrochloric acid, stirred at room temperature, filtered out and washed with deionized water until pH 6, dried to obtain an activated resin support; the activated resin support is added to a composite impregnation solution, heated for impregnation, filtered out, washed and dried to obtain the composite solid acid resin catalyst.

[0016] The composite impregnation solution is a deionized aqueous solution containing ferric chloride, zinc chloride, and yttrium chloride.

[0017] Preferably, the concentration of the hydrochloric acid is 2-2.3 mol / L;

[0018] The weight ratio of D001 macroporous sulfonic acid cation exchange resin to hydrochloric acid is 1:3-3.5;

[0019] Stirring at room temperature for 2-3 hours.

[0020] Preferably, the weight ratio of the activated resin carrier to the composite impregnation solution is 1:2.5-3;

[0021] The immersion temperature of the activated resin carrier in the composite impregnation solution is 40-45℃, and the immersion time is 8-10h.

[0022] Preferably, in the composite impregnation solution, the concentration of ferric chloride is 0.8-0.9 mol / L, the concentration of zinc chloride is 1-1.1 mol / L, and the concentration of yttrium chloride is 0.2-0.3 mol / L.

[0023] Preferably, in the neutralization and impurity removal process, the neutralizing agent is one of the following: sodium hydroxide, potassium hydroxide, magnesium oxide, carbonate, or bicarbonate.

[0024] Preferably, in the process of removing light pollutants, the temperature for removing light pollutants is 50-150℃, and the absolute pressure for removing light pollutants is 0.1-1KPa.

[0025] A plasticizer, dimethyl phthalate, prepared by the aforementioned method, wherein the dimethyl phthalate content is ≥99.5wt% and the alcohol content is ≤0.01wt%; the color number of the plasticizer is ≤10#, the acid value is ≤0.1mgKOH / g, and the pH of the aqueous layer of the washing solution is ≥5.

[0026] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0027] (1) The method for synthesizing dimethyl phthalate, a plasticizer of the present invention, in the esterification step, takes into account the characteristics of the raw materials phthalic anhydride and methanol, as well as the process conditions of the esterification step, and sets up a solid acid catalyst (especially a composite solid acid resin catalyst) to catalyze the esterification reaction to a predetermined acid value (less than 2 mg KOH / g) to obtain the esterified material; after neutralization treatment, the esterified material does not need to be washed with water to remove impurities, and is directly subjected to light-light removal treatment; in the light-light removal treatment with specific process parameters, by reducing the content of alcohol and water in the material, the residual alcohol in the material is reduced. The neutralization step involves the precipitation of alkaline compounds (neutralizing agents, etc.) or the generated monomethyl phthalate salts; finally, after decolorization and filtration, high-purity, high-yield plasticizer dimethyl phthalate with a specific pH range is obtained. The aforementioned technical methods work together synergistically to effectively avoid the defects of traditional dimethyl phthalate preparation, which requires a large amount of sodium hydroxide for neutralization, resulting in a lot of wastewater and high production costs; and effectively improve the application performance of the obtained dimethyl phthalate in specific environments, meeting the application requirements with specific pH requirements.

[0028] (2) The method for synthesizing the plasticizer dimethyl phthalate of the present invention provides that the plasticizer dimethyl phthalate has a dimethyl phthalate content ≥99.5% and an alcohol content ≤0.01%; the color number of the plasticizer dimethyl phthalate is ≤10#, the acid value is ≤0.1mgKOH / g, and the pH of the aqueous layer of the washing solution is ≥5.

[0029] (3) The method for synthesizing dimethyl phthalate, a plasticizer of the present invention, uses a composite solid acid resin catalyst that is specifically optimized for the characteristics of raw materials such as phthalic anhydride and methanol, as well as the process conditions of the esterification step. The catalyst has a good cycle life and can be reused more than 35 times while maintaining a dimethyl phthalate yield of more than 99.6%. Moreover, the product qualification rate of dimethyl phthalate prepared in each batch is 100%, which can achieve stable and efficient industrial-scale production.

[0030] (4) The method for synthesizing dimethyl phthalate, a plasticizer of the present invention, has a simple process flow, is easy to control, and is suitable for industrial-scale production. Detailed Implementation

[0031] To provide a clearer understanding of the technical features, objectives, and effects of this invention, specific embodiments are now described. It should be noted that the following detailed descriptions are exemplary and intended to provide further explanation of the invention. Unless otherwise specified, all technical and scientific terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0032] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the exemplary embodiments of the present invention. As used herein, "first," "second," etc., are used to distinguish similar objects and are not used to describe a particular order or sequence. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0033] This invention provides a method for synthesizing the plasticizer dimethyl phthalate, comprising the following steps: esterification, neutralization and impurity removal, and light-weight removal.

[0034] The esterification method involves adding phthalic anhydride, methanol, and a solid acid catalyst to an esterification reactor. Under inert gas protection, the reactor is stirred and heated while continuously purging inert gas. The mixture is then heated to 80-120°C (preferably 100-110°C) and held at this temperature for esterification. The esterification reaction is completed when the acid value of the material in the reactor is less than 2 mg KOH / g. The esterified material is then filtered to obtain the esterified material. The esterified material is then transported via a buffer tank to the neutralization reactor in the neutralization process. The filtered and recovered catalyst is returned to the esterification reactor for reuse.

[0035] During the esterification reaction, the steam generated by the heating of the material in the esterification kettle enters the alcohol-water separation tank. After being dehydrated by the dehydrating agent (such as 3A molecular sieve) added to the alcohol-water separation tank, the overflow passes through a U-shaped pipe, and the obtained dehydrated alcohol (alcohol content of about 97-99 wt% and water content of about 1-2 wt%) can be used in other processes where the requirements for alcohol and water content are not high. At the same time, after the dehydrated alcohol is dehydrated by atmospheric distillation, it can be returned to the esterification kettle as reflux alcohol (alcohol content higher than 99.5 wt% and water content lower than 0.5 wt%) to continue to participate in the esterification reaction.

[0036] After the dehydrating agent used in the alcohol-water separation tank becomes saturated with water, it is heated to remove water and then reused. The water collected during the heating and water removal process is transported to the washing tank for reuse as washing water.

[0037] In the esterification process, the molar ratio of phthalic anhydride to methanol is 1:7-10;

[0038] The solid acid catalyst can be selected from sulfonic acid type solid acid catalysts, supported solid acid catalysts, or composite solid acid resin catalysts; preferably, it is a composite solid acid resin catalyst. The weight of the solid acid catalyst added is 0.3-0.5% (preferably 0.4-0.5%) of the total weight of phthalic anhydride and methanol.

[0039] The preparation method of the composite solid acid resin catalyst is as follows: D001 macroporous sulfonic acid cation exchange resin is added to 3-3.5 times its weight of hydrochloric acid (concentration of 2-2.3 mol / L), stirred at room temperature for 2-3 hours, filtered out and washed with deionized water until pH 6, dried to obtain an activated resin support; then the activated resin support is added to 2.5-3 times its weight of composite impregnation solution, stirred and heated to 40-45℃, kept at the temperature and stirred for 8-10 hours, filtered out and washed with 3-4 times its volume of deionized water, dried to obtain the composite solid acid resin catalyst.

[0040] In the preparation of the composite solid acid resin catalyst, the composite impregnation solution is a deionized aqueous solution containing ferric chloride, zinc chloride, and yttrium chloride; in the composite impregnation solution, the concentration of ferric chloride is 0.8-0.9 mol / L, the concentration of zinc chloride is 1-1.1 mol / L, and the concentration of yttrium chloride is 0.2-0.3 mol / L.

[0041] The neutralization and impurity removal method is as follows: the esterified material is introduced into the neutralization vessel and neutralized at room temperature using a neutralizing agent to remove a small amount of unreacted monomethyl phthalate and free acid, thereby preventing the acid value from being unstable during the subsequent light removal process and making it impossible to obtain qualified dimethyl phthalate within the predetermined pH range; the neutralization process is carried out for 30 minutes until the pH of the material is 6-7, and the neutralized material is obtained; the neutralized material does not require washing or alcohol removal treatment and is directly introduced into the light removal vessel of the light removal process.

[0042] In the neutralization and impurity removal process, the neutralizing agent is one of the following: sodium hydroxide, potassium hydroxide, magnesium oxide, carbonate, or bicarbonate. The amount of neutralizing agent added is calculated based on the acid value of the esterified material (calculated as KOH, mgKOH / g), and the specific amount added is 2-2.2 times the acid value of the esterified material.

[0043] The method for removing light components is as follows: the neutralized material enters the light component removal kettle, and after the air in the kettle is replaced by inert gas, the material is heated by a coil inside the kettle to control the light component removal temperature at 50-150℃ (preferably 110-125℃) and the light component removal pressure at 0.1-1KPa (absolute pressure). The material is kept at the same temperature and pressure for the light component removal process. By reducing the alcohol and water content in the material, the residual neutralization step in the material is precipitated out by alkaline compounds (neutralizing agents, etc.) or the generated monomethyl phthalate salt compounds. After the light component removal process is completed until no light components are removed (i.e., the light component removal is complete), the material is cooled down. The cooled material is then decolorized by activated carbon and filtered to obtain dimethyl phthalate, a plasticizer with a water layer pH ≥ 5 in the washing liquid.

[0044] The stirring used in the above-mentioned esterification, neutralization and impurity removal, and light-weight removal steps is axial flow stirring to ensure better mixing of materials in each reactor.

[0045] The present invention also provides a plasticizer dimethyl phthalate prepared by the aforementioned method, wherein the plasticizer dimethyl phthalate has a dimethyl phthalate content ≥99.5wt% and an alcohol content ≤0.01wt%; the plasticizer dimethyl phthalate has a color number ≤10#, an acid value ≤0.1mgKOH / g, and an aqueous layer pH ≥5 in the washing solution.

[0046] The present invention will be further described below with reference to some specific embodiments.

[0047] Example 1

[0048] This embodiment provides a method for synthesizing the plasticizer dimethyl phthalate, specifically as follows:

[0049] (1) Esterification

[0050] 909 kg of phthalic anhydride, 1967 kg of methanol, and 14 kg of solid acid catalyst were added to an esterification reactor. Under inert gas protection, the reactor was stirred and heated while continuously purging inert gas. The reactor was heated to 100°C and held at that temperature for esterification. The esterification reaction was completed when the acid value of the material in the reactor was less than 2 mg KOH / g (esterification reaction time 12 h, esterification acid value 1.58 mg KOH / g). The esterified material was then filtered to obtain the esterified material. The esterified material was then transported to the neutralization reactor in the neutralization process via a buffer tank. The catalyst recovered from filtration was returned to the esterification reactor for reuse.

[0051] During the esterification reaction, the steam generated by the heating of the material in the esterification kettle enters the alcohol-water separator. After being dehydrated by the 3A molecular sieve added to the alcohol-water separator, the overflow passes through a U-shaped pipe, and the collected dehydrated alcohol can be used in other processes where the requirements for alcohol and water content are not high. At the same time, after being dehydrated by atmospheric distillation, the dehydrated alcohol can be returned to the esterification kettle as reflux alcohol (alcohol content higher than 99.5 wt% and water content lower than 0.5 wt%) to continue participating in the esterification reaction.

[0052] After the dehydrating agent used in the alcohol-water separation tank becomes saturated with water, it is heated to remove water and then reused. The water collected during the heating and water removal process is transported to the washing tank for reuse as washing water.

[0053] The molar ratio of phthalic anhydride to methanol is 1:10.

[0054] The solid acid catalyst is a composite solid acid resin catalyst; its added weight is 0.49% of the total weight of phthalic anhydride and methanol.

[0055] The composite solid acid resin catalyst is prepared by adding D001 macroporous sulfonic acid cation exchange resin to 3.2 times its weight of hydrochloric acid (concentration of 2.2 mol / L), stirring at room temperature for 2.5 h, filtering out and washing with deionized water until pH 6, drying to obtain an activated resin support; then adding the activated resin support to 2.8 times its weight of a composite impregnation solution, stirring and heating to 42℃, stirring and holding at this temperature for 9 h, filtering out and washing with 3.5 times its volume of deionized water, drying to obtain the composite solid acid resin catalyst.

[0056] The composite impregnation solution is a deionized aqueous solution containing ferric chloride, zinc chloride, and yttrium chloride. The concentration of ferric chloride in the composite impregnation solution is 0.85 mol / L, the concentration of zinc chloride is 1.03 mol / L, and the concentration of yttrium chloride is 0.27 mol / L.

[0057] (2) Neutralization and impurity removal

[0058] The esterified material enters the neutralization reactor and is neutralized at room temperature using a neutralizing agent to remove a small amount of unreacted monomethyl phthalate and free acid, thereby preventing unstable acid values ​​during the subsequent light removal process and ensuring that qualified dimethyl phthalate within the predetermined pH range can be obtained. The neutralization process lasts for 30 minutes until the pH of the material is in the range of 6-7, at which point the neutralized material is obtained. The neutralized material does not require washing or alcohol removal and is directly introduced into the light removal reactor of the light removal process.

[0059] The neutralizing agent is sodium hydroxide; its addition amount is calculated based on the acid value of the esterified material (calculated as KOH, mgKOH / g), and the specific addition amount is twice the acid value of the esterified material.

[0060] (3) Remove light

[0061] The neutralized material enters the light component removal reactor. After the air in the reactor is replaced by inert gas, the material is heated by a coil inside the reactor to control the light component removal temperature at 110℃ and the light component removal pressure at 1 kPa (absolute pressure). The light component removal process is carried out under the same temperature and pressure. By reducing the alcohol and water content in the material, the residual neutralization step in the material is precipitated out by alkaline compounds (neutralizing agents, etc.) or the generated monomethyl phthalate salt compounds. After the light component removal process continues until no light component is removed (i.e., the light component removal is complete), the material is cooled down. The cooled material is then decolorized by activated carbon and filtered to obtain the plasticizer dimethyl phthalate with a yield of 99.82% (based on phthalic anhydride).

[0062] This embodiment also provides a plasticizer, dimethyl phthalate, prepared by the aforementioned method, with a dimethyl phthalate content of 99.87 wt% and an alcohol content of 0.0046 wt%. The color number of the plasticizer, dimethyl phthalate, is 8.78#, the acid value is 0.046 mg KOH / g, and the pH of the aqueous layer of the washing solution is 5.25.

[0063] Example 2

[0064] This embodiment provides a method for synthesizing the plasticizer dimethyl phthalate, specifically as follows:

[0065] (1) Esterification

[0066] 909 kg of phthalic anhydride, 1967 kg of methanol, and 13.5 kg of solid acid catalyst were added to the esterification reactor. Under inert gas protection, the reactor was stirred and heated while continuously purging inert gas. The reactor was heated to 105°C and held at this temperature for esterification. The esterification reaction was completed when the acid value of the material in the reactor was less than 2 mg KOH / g (esterification reaction time 12.1 h, esterification acid value 1.62 mg KOH / g). The esterified reaction material was filtered to obtain esterified material. The esterified material was then transported to the neutralization reactor in the neutralization process via a buffer tank. The catalyst recovered from filtration was returned to the esterification reactor for reuse.

[0067] During the esterification reaction, the steam generated by the heating of the material in the esterification kettle enters the alcohol-water separator. After being dehydrated by the 3A molecular sieve added to the alcohol-water separator, the overflow passes through a U-shaped pipe, and the collected dehydrated alcohol can be used in other processes where the requirements for alcohol and water content are not high. At the same time, after being dehydrated by atmospheric distillation, the dehydrated alcohol can be returned to the esterification kettle as reflux alcohol (alcohol content higher than 99.5 wt% and water content lower than 0.5 wt%) to continue participating in the esterification reaction.

[0068] After the dehydrating agent used in the alcohol-water separation tank becomes saturated with water, it is heated to remove water and then reused. The water collected during the heating and water removal process is transported to the washing tank for reuse as washing water.

[0069] The molar ratio of phthalic anhydride to methanol is 1:10.

[0070] The solid acid catalyst is a composite solid acid resin catalyst; its added weight is 0.47% of the total weight of phthalic anhydride and methanol.

[0071] The method for preparing the composite solid acid resin catalyst is as follows: D001 macroporous sulfonic acid cation exchange resin is added to 3 times its weight of hydrochloric acid (concentration of 2 mol / L), stirred at room temperature for 2 hours, filtered out and washed with deionized water until pH 6, dried to obtain an activated resin support; then the activated resin support is added to 2.5 times its weight of composite impregnation solution, stirred and heated to 40°C, kept at this temperature and stirred for 8 hours, filtered out and washed with 3 times its volume of deionized water, dried to obtain the composite solid acid resin catalyst.

[0072] The composite impregnation solution is a deionized aqueous solution containing ferric chloride, zinc chloride, and yttrium chloride. The concentration of ferric chloride in the composite impregnation solution is 0.8 mol / L, the concentration of zinc chloride is 1 mol / L, and the concentration of yttrium chloride is 0.2 mol / L.

[0073] (2) Neutralization and impurity removal

[0074] The esterified material enters the neutralization reactor and is neutralized at room temperature using a neutralizing agent to remove a small amount of unreacted monomethyl phthalate and free acid, thereby preventing unstable acid values ​​during the subsequent light removal process and ensuring that qualified dimethyl phthalate within the predetermined pH range can be obtained. The neutralization process lasts for 30 minutes until the pH of the material is in the range of 6-7, at which point the neutralized material is obtained. The neutralized material does not require washing or alcohol removal and is directly introduced into the light removal reactor of the light removal process.

[0075] The neutralizing agent is sodium hydroxide; its addition amount is calculated based on the acid value of the esterified material (calculated as KOH, mgKOH / g), and the specific addition amount is twice the acid value of the esterified material.

[0076] (3) Remove light

[0077] The neutralized material enters the light component removal reactor. After the air in the reactor is replaced by inert gas, the material is heated by a coil inside the reactor to control the light component removal temperature at 105℃ and the light component removal pressure at 1KPa (absolute pressure). The light component removal process is carried out under the same temperature and pressure. By reducing the alcohol and water content in the material, the residual neutralization step in the material is precipitated out by alkaline compounds (neutralizing agents, etc.) or the generated monomethyl phthalate salt compounds. After the light component removal process continues until no light component is removed (i.e., the light component removal is complete), the material is cooled down. The cooled material is then decolorized by activated carbon and filtered to obtain the plasticizer dimethyl phthalate with a yield of 99.80% (based on phthalic anhydride).

[0078] This embodiment also provides a plasticizer, dimethyl phthalate, prepared by the aforementioned method, with a dimethyl phthalate content of 99.85 wt% and an alcohol content of 0.0047 wt%. The color number of the plasticizer, dimethyl phthalate, is 8.80#, the acid value is 0.049 mg KOH / g, and the pH of the aqueous layer of the washing solution is 5.28.

[0079] Example 3

[0080] This embodiment provides a method for synthesizing the plasticizer dimethyl phthalate, specifically as follows:

[0081] (1) Esterification

[0082] 909 kg of phthalic anhydride, 1967 kg of methanol, and 11.5 kg of solid acid catalyst were added to the esterification reactor. Under inert gas protection, the reactor was stirred and heated while continuously purging inert gas. The reactor was heated to 110°C and held at this temperature for esterification. The esterification reaction was completed when the acid value of the material in the reactor was less than 2 mg KOH / g (esterification reaction time 12 h, esterification acid value 1.50 mg KOH / g). The esterified reaction material was filtered to obtain the esterified material. The esterified material was then transported to the neutralization reactor in the neutralization process via a buffer tank. The catalyst recovered from filtration was returned to the esterification reactor for reuse.

[0083] During the esterification reaction, the steam generated by the heating of the material in the esterification kettle enters the alcohol-water separator. After being dehydrated by the 3A molecular sieve added to the alcohol-water separator, the overflow passes through a U-shaped pipe, and the collected dehydrated alcohol can be used in other processes where the requirements for alcohol and water content are not high. At the same time, after being dehydrated by atmospheric distillation, the dehydrated alcohol can be returned to the esterification kettle as reflux alcohol (alcohol content higher than 99.5 wt% and water content lower than 0.5 wt%) to continue participating in the esterification reaction.

[0084] After the dehydrating agent used in the alcohol-water separation tank becomes saturated with water, it is heated to remove water and then reused. The water collected during the heating and water removal process is transported to the washing tank for reuse as washing water.

[0085] The molar ratio of phthalic anhydride to methanol is 1:10.

[0086] The solid acid catalyst is a composite solid acid resin catalyst; its added weight is 0.4% of the total weight of phthalic anhydride and methanol.

[0087] The composite solid acid resin catalyst is prepared by adding D001 macroporous sulfonic acid cation exchange resin to 3.5 times its weight of hydrochloric acid (concentration of 2.3 mol / L), stirring at room temperature for 3 hours, filtering out and washing with deionized water until pH 6, drying to obtain an activated resin support; then adding the activated resin support to 3 times its weight of a composite impregnation solution, stirring and heating to 45°C, keeping warm and stirring for 10 hours, filtering out and washing with 4 times its volume of deionized water, drying to obtain the composite solid acid resin catalyst.

[0088] The composite impregnation solution is a deionized aqueous solution containing ferric chloride, zinc chloride, and yttrium chloride. The concentration of ferric chloride in the composite impregnation solution is 0.9 mol / L, the concentration of zinc chloride is 1.1 mol / L, and the concentration of yttrium chloride is 0.3 mol / L.

[0089] (2) Neutralization and impurity removal

[0090] The esterified material enters the neutralization reactor and is neutralized at room temperature using a neutralizing agent to remove a small amount of unreacted monomethyl phthalate and free acid, thereby preventing unstable acid values ​​during the subsequent light removal process and ensuring that qualified dimethyl phthalate within the predetermined pH range can be obtained. The neutralization process lasts for 30 minutes until the pH of the material is in the range of 6-7, at which point the neutralized material is obtained. The neutralized material does not require washing or alcohol removal and is directly introduced into the light removal reactor of the light removal process.

[0091] The neutralizing agent is sodium hydroxide; its addition amount is calculated based on the acid value of the esterified material (calculated as KOH, mgKOH / g), and the specific addition amount is twice the acid value of the esterified material.

[0092] (3) Remove light

[0093] The neutralized material enters the light component removal reactor. After the air inside the reactor is replaced by inert gas, it is heated by a coil inside the reactor to control the light component removal temperature at 125℃ and the light component removal pressure at 1KPa (absolute pressure). The light component removal process is carried out under the same temperature and pressure. By reducing the alcohol and water content in the material, the residual neutralization step in the material is precipitated out by alkaline compounds (neutralizing agents, etc.) or the generated monomethyl phthalate salt compounds. After the light component removal process is completed until no light component is removed (i.e., the light component removal is complete), the material is cooled down. The cooled material is then decolorized by activated carbon and filtered to obtain the plasticizer dimethyl phthalate with a yield of 99.81% (based on phthalic anhydride).

[0094] This embodiment also provides a plasticizer, dimethyl phthalate, prepared by the aforementioned method, with a dimethyl phthalate content of 99.88 wt% and an alcohol content of 0.0047 wt%. The color number of the plasticizer, dimethyl phthalate, is 8.79#, the acid value is 0.050 mg KOH / g, and the pH of the aqueous layer of the washing solution is 5.26.

[0095] Furthermore, a cyclic test was conducted using the composite solid acid resin catalyst from Example 1. Specifically, following the synthesis method of the plasticizer dimethyl phthalate from Example 1, the composite solid acid resin catalyst from Example 1 was reused 35 times. During each batch's preparation, the esterification reaction time, esterification acid value (until the acid value of the material in the esterification vessel was less than 2 mg KOH / g), and the yield of dimethyl phthalate obtained in each batch were recorded. Simultaneously, the pH of the aqueous layer of the washing solution of the dimethyl phthalate prepared in each batch was tested to ensure it was ≥5 and met the qualified product indicators. The product qualification rate was calculated. The specific results are shown below:

[0096]

[0097] Comparative Example 1

[0098] For a direct comparison, Comparative Example 1 adopts the technical solution of Example 1, with the following changes: D001 macroporous sulfonic acid cation exchange resin is directly used as a catalyst for the esterification step, and the added weight of D001 macroporous sulfonic acid cation exchange resin is controlled to be equal to the added weight of the composite solid acid resin catalyst used in the original example.

[0099] The dimethyl phthalate plasticizer prepared in Comparative Example 1 contained 99.71 wt% dimethyl phthalate and 0.023 wt% alcohol; the color number of the plasticizer was 9.87#, the acid value was 0.056 mg KOH / g, and the pH of the aqueous layer of the washing solution was 5.38; the yield of the plasticizer dimethyl phthalate prepared in Comparative Example 1 was 99.32%. However, the catalyst used in Comparative Example 1, after 12 reuses, could no longer meet the preparation requirements in terms of product qualification rate and yield, and could not be recycled further.

[0100] As can be seen, the synthesis method of the plasticizer dimethyl phthalate of the present invention, in the esterification step, takes into account the characteristics of the raw materials phthalic anhydride and methanol, as well as the process conditions of the esterification step, and sets up a solid acid catalyst (especially a composite solid acid resin catalyst) to catalyze the esterification reaction to a predetermined acid value (less than 2 mg KOH / g) to obtain the esterified material; after neutralization treatment, the esterified material does not need to be washed with water to remove impurities, and can be directly subjected to light alcohol removal treatment; in the light alcohol removal treatment with specific process parameters, by reducing the content of alcohol and water in the material, the content of alcohol and water in the material is reduced. The residual neutralization step involves the precipitation of alkaline compounds (neutralizing agents, etc.) or the generated monomethyl phthalate salts. Finally, after decolorization and filtration, high-purity, high-yield plasticizer dimethyl phthalate with a specific pH range is obtained. The aforementioned technical methods work together synergistically to effectively avoid the defects of traditional dimethyl phthalate preparation, which requires a large amount of sodium hydroxide for neutralization, resulting in a lot of wastewater and high production costs. It also effectively improves the application performance of dimethyl phthalate in specific environments and meets the application requirements with specific pH requirements. Furthermore, in the synthesis method of the plasticizer dimethyl phthalate, the composite solid acid resin catalyst is specifically optimized for the raw material characteristics of phthalic anhydride and methanol, as well as the process conditions of the esterification step. The catalyst has a good cycle life and can be reused more than 35 times while maintaining a dimethyl phthalate yield of more than 99.6%. Moreover, the product qualification rate of dimethyl phthalate prepared in each batch is 100%, which can achieve stable and efficient industrial-scale production.

[0101] Unless otherwise stated, all percentages used in this invention are mass percentages.

[0102] Finally, it should be noted that the above descriptions are merely preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for synthesizing dimethyl phthalate, a plasticizer, characterized in that, The process includes the following steps: esterification, neutralization and impurity removal, and removal of light components; The esterification process involves adding phthalic anhydride, methanol, and a solid acid catalyst into an esterification reactor. Under inert gas protection, the temperature is raised to esterify the material until the acid value of the material in the esterification reactor is less than 2 mg KOH / g. After filtration and recovery of the solid acid catalyst, the esterified material is obtained. The solid acid catalyst is a composite solid acid resin catalyst; The method for preparing the composite solid acid resin catalyst is as follows: D001 macroporous sulfonic acid cation exchange resin is added to hydrochloric acid, stirred at room temperature, filtered out and washed with deionized water until the pH is 6, dried to obtain an activated resin support; the activated resin support is added to a composite impregnation solution, heated for impregnation, filtered out, washed and dried to obtain the composite solid acid resin catalyst. The composite impregnation solution is a deionized aqueous solution containing ferric chloride, zinc chloride, and yttrium chloride; in the composite impregnation solution, the concentration of ferric chloride is 0.8-0.9 mol / L, the concentration of zinc chloride is 1-1.1 mol / L, and the concentration of yttrium chloride is 0.2-0.3 mol / L. In the preparation of the composite solid acid resin catalyst, the concentration of hydrochloric acid is 2-2.3 mol / L; the weight ratio of D001 macroporous sulfonic acid cation exchange resin to hydrochloric acid is 1:3-3.5; and the stirring time at room temperature is 2-3 h. In the preparation of the composite solid acid resin catalyst, the weight ratio of the activated resin support to the composite impregnation liquid is 1:2.5-3; the impregnation temperature of the activated resin support in the composite impregnation liquid is 40-45℃, and the impregnation time is 8-10h. The neutralization and impurity removal process involves using a neutralizing agent to neutralize the esterified material to a pH of 6-7, thereby obtaining a neutralized material. The process of removing light components involves heating the neutralized material under inert gas protection until no light components are released, then cooling it down, followed by decolorization and filtration to obtain the plasticizer dimethyl phthalate; the aqueous layer of the washing solution containing the plasticizer dimethyl phthalate has a pH ≥ 5.

2. The method for synthesizing dimethyl phthalate, a plasticizer according to claim 1, is characterized in that, In the esterification process, the esterification temperature is 80-120℃; The molar ratio of phthalic anhydride to methanol is 1:7-10; The weight of the solid acid catalyst added is 0.3-0.5% of the total weight of phthalic anhydride and methanol.

3. The method for synthesizing dimethyl phthalate, a plasticizer according to claim 1, is characterized in that, In the neutralization and impurity removal process, the neutralizing agent is one of the following: sodium hydroxide, potassium hydroxide, magnesium oxide, carbonate, or bicarbonate.

4. The method for synthesizing dimethyl phthalate, a plasticizer according to claim 1, is characterized in that, During the removal of light-duty materials, the removal temperature is 50-150℃, and the absolute pressure is 0.1-1KPa.

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