Plasticizer dimethyl phthalate and synthesis method thereof

Abstract

The invention provides a plasticizer dimethyl phthalate and a synthesis method thereof, and relates to the field of dimethyl phthalate. The synthesis method of the plasticizer dimethyl phthalate comprises the following steps: esterification, neutralization and impurity removal, and light component removal. The esterification comprises the following steps: adding phthalic anhydride, methanol and a solid acid catalyst into an esterification kettle, heating and esterifying under the protection of inert gas until the acid value of the material in the esterification kettle is less than 2mgKOH / g, and filtering and recovering the solid acid catalyst to obtain an esterified material. According to the plasticizer dimethyl phthalate and the synthetic method thereof disclosed by the invention, while the defects of the existing synthetic method of dimethyl phthalate are specifically overcome, the downstream application defects of the plasticizer dimethyl phthalate are overcome through the specific pH range of the plasticizer dimethyl phthalate, so that the specific downstream application requirements are met.

Description

Technical Field

[0001] The present invention relates to the field of dimethyl phthalate, and in particular to a plasticizer dimethyl phthalate and a synthesis method thereof. Background Art

[0002] In the existing synthesis methods of the plasticizer dimethyl phthalate, an inert solvent is generally used as a water-carrying agent and sulfuric acid is used as a catalyst; however, this method has high production energy consumption and the problem of equipment corrosion, and the production economy is poor; at the same time, in the post-treatment process of the crude product, a large amount of sodium hydroxide is required for neutralization, resulting in a large amount of wastewater and high production costs; the existing synthesis methods of the plasticizer dimethyl phthalate cannot meet the synthesis requirements of the plasticizer dimethyl phthalate within a specific pH range.

[0003] At the same time, the pH characteristics of the plasticizer dimethyl phthalate synthesized by the existing method limit its specific application range and cannot fully meet the application requirements of the downstream, especially cannot meet the downstream users with specific pH requirements. The pH characteristics of dimethyl phthalate are specifically manifested as the pH value of the water layer obtained by detecting after stirring and washing dimethyl phthalate with a certain amount of water for 5 minutes. In the conventional plasticization process of dimethyl phthalate, affected by process environment fluctuations and the acid-base properties of raw materials, its stability is poor, the plasticization effect on materials is limited, and the environmental friendliness is not good.

[0004] In the existing technologies at home and abroad, there is no disclosure of a synthesis method for the plasticizer dimethyl phthalate within a specific pH range; based on this, providing a plasticizer dimethyl phthalate within a specific pH range and a synthesis method thereof to meet the downstream application requirements has important technical significance and research value. Summary of the Invention

[0005] In order to solve the technical problems existing in the prior art, the present invention provides a plasticizer dimethyl phthalate and a synthesis method thereof. While specifically overcoming the defects of the existing dimethyl phthalate synthesis method, through the specific pH range of the plasticizer dimethyl phthalate, its downstream application defects are overcome to meet the specific application requirements of the downstream.

[0006] In order to solve the above technical problems, the technical solutions adopted by the present invention are as follows: A synthesis method of a plasticizer dimethyl phthalate, comprising the following steps: esterification, neutralization and impurity removal, and light component removal; For the esterification, phthalic anhydride, methanol and a solid acid catalyst are added to an esterification kettle, and under the protection of an inert gas, the temperature is raised for esterification until the acid value of the material in the esterification kettle is less than 2 mgKOH / g. After filtering and recovering the solid acid catalyst, an esterification material is obtained; The solid acid catalyst is one of the following: sulfonic acid type solid acid catalyst, supported solid acid catalyst, composite solid acid resin catalyst; For neutralization and impurity removal, a neutralizing agent is used to neutralize the esterification material to a pH of 6-7 to obtain a neutralized material; For light component removal, under the protection of an inert gas, the neutralized material is heated for light component removal treatment, cooled after no light components are removed, and then decolorized and filtered to obtain dimethyl phthalate plasticizer; the pH of the water layer of the washing liquid of the dimethyl phthalate plasticizer is ≥5.

[0007] Preferably, in the esterification, the esterification temperature is 80-120°C; The molar ratio of phthalic anhydride to methanol is 1:7-10; The added weight of the solid acid catalyst is 0.3-0.5% of the total weight of phthalic anhydride and methanol.

[0008] Further, the preparation method of the composite solid acid resin catalyst is as follows: D001 macroporous sulfonic acid type cation exchange resin is put into hydrochloric acid, stirred at room temperature, filtered out and washed with deionized water to a pH of 6, and dried to obtain an activated resin carrier; the activated resin carrier is put into a composite impregnating solution, impregnated after heating, filtered out, washed and dried to obtain the composite solid acid resin catalyst; The composite impregnating solution is an aqueous deionized solution dissolving ferric chloride, zinc chloride and yttrium chloride.

[0009] Preferably, the concentration of the hydrochloric acid is 2-2.3 mol / L; The weight ratio of D001 macroporous sulfonic acid type cation exchange resin to hydrochloric acid is 1:3-3.5; The stirring time at room temperature is 2-3 h.

[0010] Preferably, the weight ratio of the activated resin carrier to the composite impregnating solution is 1:2.5-3; The impregnation temperature of the activated resin carrier in the composite impregnating solution is 40-45°C, and the impregnation time is 8-10 h.

[0011] Preferably, in the composite impregnating 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.

[0012] Preferably, in the neutralization and impurity removal, the neutralizing agent is one of the following: sodium hydroxide, potassium hydroxide, magnesium oxide, carbonate, bicarbonate.

[0013] Preferably, in the light component removal, the light component removal temperature is 50-150°C, and the absolute pressure for light component removal is 0.1-1 KPa.

[0014] A dimethyl phthalate plasticizer prepared by the aforementioned method, wherein the content of dimethyl phthalate in the dimethyl phthalate plasticizer is ≥99.5 wt%, the alcohol content is ≤0.01 wt%; the color number of the dimethyl phthalate plasticizer is ≤10#, the acid value is ≤0.1 mgKOH / g, and the pH of the water layer of the washing liquid is ≥5.

[0015] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) In the synthesis method of the dimethyl phthalate plasticizer of the present invention, in the esterification step, according to the raw material characteristics of phthalic anhydride and methanol, and the process conditions of the esterification step, a solid acid catalyst (especially a composite solid acid resin catalyst) is configured to catalyze the esterification reaction to a predetermined acid value (less than 2 mgKOH / g) to obtain an esterification material; after the esterification material is neutralized, there is no need to perform a water washing and impurity removal operation, and directly perform a light component removal treatment; in the light component removal treatment with specific process parameters, by reducing the content of alcohol and water in the material, the alkaline compound (neutralizing agent, etc.) used in the neutralization step or the phthalic acid monomethyl ester salt compound generated in the material is precipitated; finally, through decolorization and filtration, a dimethyl phthalate plasticizer with high purity, high yield, and a specific pH range is prepared; the aforementioned technical means cooperate with each other and act synergistically, effectively avoiding the defects of a large amount of sodium hydroxide being required for neutralization in the traditional preparation of dimethyl phthalate, generating a large amount of wastewater, and having a high production cost; and effectively improving the application performance of the prepared dimethyl phthalate in a specific environment, meeting the application requirements with specific pH requirements.

[0016] (2) In the synthesis method of the dimethyl phthalate plasticizer of the present invention, the content of dimethyl phthalate in the prepared dimethyl phthalate plasticizer is ≥99.5%, and the alcohol content is ≤0.01%; the color number of the dimethyl phthalate plasticizer is ≤10#, the acid value is ≤0.1 mgKOH / g, and the pH of the water layer of the washing liquid is ≥5.

[0017] (3) In the synthesis method of the dimethyl phthalate plasticizer of the present invention, the composite solid acid resin catalyst used is specifically optimized according to the raw material characteristics of phthalic anhydride and methanol, and the process conditions of the esterification step. The catalyst has a good cycle service life, can be reused more than 35 times on the premise of maintaining the dimethyl phthalate yield exceeding 99.6%, and the product qualification rate of dimethyl phthalate prepared in each batch is 100%, and stable and efficient industrial-scale production can be achieved.

[0018] (4) The synthesis method of the dimethyl phthalate plasticizer of the present invention has a simple process flow, and the synthesis process is easy to control, and is suitable for industrial-scale production. Specific Embodiments

[0019] For a clearer understanding of the technical features, objectives, and effects of the present invention, the specific embodiments of the present invention will now be described. It should be noted that the following detailed descriptions are all exemplary and are intended to provide further explanations of the present invention. Unless otherwise specified, all technical and scientific terms used in the present invention have the same meaning as commonly understood by those of ordinary skill in the technical field to which the present invention belongs.

[0020] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present invention. As used herein, "first", "second", etc. are used to distinguish similar objects and are not used to describe a specific order or sequence. In addition, it should also 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.

[0021] An embodiment of the present invention provides a method for synthesizing dimethyl phthalate plasticizer, which includes the following steps: esterification, neutralization and impurity removal, and light component removal.

[0022] The method of the esterification is as follows: phthalic anhydride, methanol, and a solid acid catalyst are added to an esterification kettle. Under the protection of an inert gas, stirring and heating are carried out, and at the same time, an inert gas is continuously introduced into the esterification kettle; when stirring and heating to 80 - 120 °C (preferably 100 - 110 °C), heat preservation is carried out for the esterification reaction; when the acid value of the material in the esterification kettle is less than 2 mgKOH / g during the esterification reaction, the esterification reaction is completed. After the esterification reaction material is filtered through a filtering device, an esterification material is obtained; the esterification material is transported to a neutralization kettle in the neutralization process through a buffer tank; the catalyst recovered by filtration is returned to the esterification kettle for reuse.

[0023] During the esterification reaction, the vapor generated by the heating of the material in the esterification kettle enters an alcohol-water separation tank. After being dehydrated by a dehydrating agent (such as 3A molecular sieve and other dehydrating agents) added to the alcohol-water separation tank, it overflows through a U-shaped tube. The dehydrated alcohol collected (alcohol content is about 97 - 99 wt%, water content is about 1 - 2 wt%) can be used in other processes with low requirements for alcohol content and water content; at the same time, after the dehydrated alcohol is distilled to remove water under normal pressure, it can be used as reflux alcohol (alcohol content is higher than 99.5 wt%, water content is lower than 0.5 wt%) and refluxed to the esterification kettle to continue to participate in the esterification reaction.

[0024] After the dehydrating agent used in the alcohol-water separation tank is saturated with water absorption, it is heated to remove water and then reused. The water collected during the process of heating to remove water is transported to a water washing tank and reused as water for water washing.

[0025] In the esterification, the molar ratio of phthalic anhydride to methanol is 1:7 - 10; The solid acid catalyst can be selected from sulfonic acid type solid acid catalysts, supported solid acid catalysts, and composite solid acid resin catalysts; preferably, it is a composite solid acid resin catalyst. The added weight of the solid acid catalyst is 0.3 - 0.5% (preferably 0.4 - 0.5%) of the total weight of phthalic anhydride and methanol.

[0026] The preparation method of the composite solid acid resin catalyst is as follows: Put D001 macroporous sulfonic acid type cation exchange resin into hydrochloric acid (with a concentration of 2 - 2.3 mol / L) with a weight 3 - 3.5 times that of the resin. Stir at room temperature for 2 - 3 h, then filter out and wash with deionized water until the pH is 6, and dry to obtain an activated resin carrier; then put the activated resin carrier into a composite impregnating solution with a weight 2.5 - 3 times that of the carrier, stir and heat up to 40 - 45 °C, keep stirring for 8 - 10 h, then filter out and wash with 3 - 4 times the volume of deionized water, and dry to prepare the composite solid acid resin catalyst.

[0027] In the preparation of the composite solid acid resin catalyst, the composite impregnating solution is an aqueous deionized solution dissolved with ferric chloride, zinc chloride, and yttrium chloride; in the composite impregnating 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.

[0028] The method of neutralization and impurity removal is as follows: The esterification material enters the neutralization kettle, and under normal temperature conditions, it is neutralized with a neutralizing agent to remove a small amount of incompletely reacted monomethyl phthalate and free acid, thereby preventing the acid value from being unstable during the subsequent light component removal process and making it impossible to obtain qualified dimethyl phthalate within the predetermined pH range; after neutralization for 30 min until the pH of the material is 6 - 7, a neutralized material is obtained; the neutralized material is directly introduced into the light component removal kettle in the light component removal process without washing and alcohol removal treatment.

[0029] In the neutralization and impurity removal, the neutralizing agent is one of the following: sodium hydroxide, potassium hydroxide, magnesium oxide, carbonate, bicarbonate. The addition amount of the neutralizing agent is calculated based on the acid value of the esterification material (in terms of KOH, mgKOH / g), and the specific addition amount is 2 - 2.2 times the acid value of the esterification material.

[0030] The light component removal method is as follows: the neutralized material enters the light component removal kettle. After introducing an inert gas to displace the air in the light component removal kettle, it is heated through the coil in the light component removal kettle. The light component removal temperature is controlled at 50 - 150 °C (preferably 110 - 125 °C), and the light component removal pressure is 0.1 - 1 KPa (absolute pressure). Keep the temperature and pressure constant for light component removal treatment, and by reducing the contents of alcohol and water in the material, the alkaline compound (neutralizing agent, etc.) used in the neutralization step or the phthalic acid monomethyl ester salt compound generated in the material precipitates out; after the light component removal treatment until no light components are removed (i.e., the light component removal is complete), cool down. The cooled material is decolorized with activated carbon and filtered to obtain a plasticizer dimethyl phthalate with the pH of the water layer of the washing solution ≥ 5.

[0031] The stirring used in the above esterification, neutralization and impurity removal, and light component removal steps is axial flow stirring to ensure better mixing of the materials in each reaction kettle.

[0032] The embodiment of the present invention also provides a plasticizer dimethyl phthalate prepared by the aforementioned method. The content of dimethyl phthalate in the plasticizer dimethyl phthalate ≥ 99.5 wt%, and the alcohol content ≤ 0.01 wt%; the color number of the plasticizer dimethyl phthalate ≤ 10#, the acid value ≤ 0.1 mgKOH / g, and the pH of the water layer of the washing solution ≥ 5.

[0033] The following further illustrates the present invention in conjunction with some specific embodiments.

[0034] Example 1 This example provides a method for synthesizing a plasticizer dimethyl phthalate, specifically as follows: (1) Esterification Add 909 kg of phthalic anhydride, 1967 kg of methanol, and 14 kg of solid acid catalyst to the esterification kettle. Under the protection of an inert gas, stir and heat, and continuously introduce an inert gas into the esterification kettle; when the stirring and heating reach 100 °C, keep the temperature constant for the esterification reaction; when the acid value of the material in the esterification kettle is less than 2 mgKOH / g after the esterification reaction (the esterification reaction time is 12 h, and the esterification acid value is 1.58 mgKOH / g), the esterification reaction is completed. After the esterification reaction material is filtered through a filtration device, the esterified material is obtained; the esterified material is transported to the neutralization kettle in the neutralization process through a buffer tank; the catalyst recovered by filtration is returned to the esterification kettle for reuse.

[0035] During the esterification reaction, the vapor generated by the heating of the material in the esterification kettle enters the alcohol-water separation tank. After dehydration by the 3A molecular sieve added in the alcohol-water separation tank, it overflows through the U-shaped tube, and the dehydrated alcohol collected can be used in other sections with low requirements for alcohol content and water content; at the same time, after the dehydrated alcohol is dehydrated by atmospheric distillation, it can be used as reflux alcohol (alcohol content higher than 99.5 wt%, water content lower than 0.5 wt%) and refluxed to the esterification kettle to continue participating in the esterification reaction.

[0036] After the dehydrating agent used in the alcohol-water separation tank is saturated with water absorption, it is reheated to remove water and then reused. The water collected during the process of reheating to remove water is transported to the water washing tank and reused as water for water washing.

[0037] Among them, the molar ratio of phthalic anhydride to methanol is 1:10.

[0038] 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.

[0039] The preparation method of the composite solid acid resin catalyst is as follows: Put D001 macroporous sulfonic acid cation exchange resin into hydrochloric acid (concentration 2.2mol / L) with a weight 3.2 times that of the resin, stir at room temperature for 2.5h, then filter out and wash with deionized water until the pH is 6, and dry to obtain an activated resin carrier; then put the activated resin carrier into a composite impregnating solution with a weight 2.8 times that of the resin, stir and heat up to 42°C, keep stirring for 9h, then filter out and wash with deionized water with a volume 3.5 times that of the resin, and dry to prepare the composite solid acid resin catalyst.

[0040] Among them, the composite impregnating solution is an aqueous deionized solution dissolved with ferric chloride, zinc chloride, and yttrium chloride; in the composite impregnating solution, the concentration of ferric chloride is 0.85mol / L, the concentration of zinc chloride is 1.03mol / L, and the concentration of yttrium chloride is 0.27mol / L.

[0041] (2) Neutralization and impurity removal The esterification material enters the neutralization kettle, and under normal temperature conditions, it is neutralized with a neutralizing agent to remove a small amount of incompletely reacted monomethyl phthalate and free acid, thereby preventing the acid value from being unstable during the subsequent light component removal process and making it impossible to obtain qualified dimethyl phthalate within the predetermined pH range; when the neutralization treatment is carried out for 30 minutes until the pH of the material is within the range of 6 - 7, a neutralized material is obtained; the neutralized material is directly introduced into the light component removal kettle in the light component removal process without washing and alcohol removal treatment.

[0042] Among them, the neutralizing agent is sodium hydroxide; its addition amount is calculated based on the acid value of the esterification material (calculated as KOH, mgKOH / g), and the specific addition amount is 2 times the acid value of the esterification material.

[0043] (3) Light component removal The neutralized material enters the light - removal kettle. After introducing an inert gas to displace the air in the light - removal kettle, it is heated through the coil in the light - removal kettle. The light - removal temperature is controlled at 110 °C, and the light - removal pressure is 1 KPa (absolute pressure). Keep the temperature and pressure constant for light - removal treatment, and by reducing the content of alcohol and water in the material, the residual alkaline compounds (neutralizing agents, etc.) or the generated monomethyl phthalate salt compounds in the neutralization step of the material precipitate out. After the light - removal treatment until no light components are removed (i.e., complete light - removal), the temperature is lowered. The cooled material is decolorized with activated carbon and filtered to obtain the plasticizer dimethyl phthalate, with a yield of 99.82% (calculated based on phthalic anhydride).

[0044] This example also provides dimethyl phthalate plasticizer prepared by the aforementioned method. The content of dimethyl phthalate is 99.87 wt%, and the alcohol content is 0.0046 wt%. The color number of the dimethyl phthalate plasticizer is 8.78#, the acid value is 0.046 mgKOH / g, and the pH of the water layer of the washing solution is 5.25.

[0045] Example 2 This example provides a method for synthesizing dimethyl phthalate plasticizer, specifically as follows: (1) Esterification Add 909 kg of phthalic anhydride, 1967 kg of methanol, and 13.5 kg of solid acid catalyst into the esterification kettle. Under the protection of an inert gas, stir and heat, and continuously introduce an inert gas into the esterification kettle. When the stirring and heating reach 105 °C, keep the temperature for the esterification reaction. When the acid value of the material in the esterification kettle is less than 2 mgKOH / g (the esterification reaction time is 12.1 h, and the esterification acid value is 1.62 mgKOH / g), the esterification reaction is completed. The esterification reaction material is filtered through a filtration device to obtain the esterified material. The esterified material is transported to the neutralization kettle in the neutralization process through a buffer tank. The catalyst recovered by filtration is returned to the esterification kettle for reuse.

[0046] During the esterification reaction, the vapor generated by the heating of the material in the esterification kettle enters the alcohol - water separation tank. After dehydration by the 3A molecular sieve added in the alcohol - water separation tank, it overflows through the U - shaped tube. The dehydrated alcohol collected can be used in other processes with low requirements for alcohol and water content. At the same time, after the dehydrated alcohol is distilled to remove water at atmospheric pressure, it can be used as reflux alcohol (alcohol content higher than 99.5 wt%, water content lower than 0.5 wt%) and refluxed to the esterification kettle to continue participating in the esterification reaction.

[0047] After the dehydrating agent in the alcohol - water separation tank is saturated with water absorption, it is heated to remove water and then reused. The water collected during the process of heating to remove water is transported to the washing tank and reused as washing water.

[0048] Among them, the molar ratio of phthalic anhydride to methanol is 1:10.

[0049] 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.

[0050] The preparation method of the composite solid acid resin catalyst is as follows: Put D001 macroporous sulfonic acid type cation exchange resin into hydrochloric acid (concentration: 2 mol / L) with a weight 3 times that of the resin, stir at room temperature for 2 h, then filter out and wash with deionized water until the pH is 6, and dry to obtain the activated resin support; then put the activated resin support into a composite impregnating solution with a weight 2.5 times that of the resin, stir and heat up to 40 °C, keep stirring for 8 h, then filter out and wash with deionized water with a volume 3 times that of the resin, and dry to obtain the composite solid acid resin catalyst.

[0051] Among them, the composite impregnating solution is an aqueous deionized solution dissolving ferric chloride, zinc chloride and yttrium chloride; in the composite impregnating solution, the concentration of ferric chloride 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.

[0052] (2) Neutralization and impurity removal The esterification material enters the neutralization kettle, and under normal temperature conditions, it is neutralized with a neutralizing agent to remove a small amount of incompletely reacted monomethyl phthalate and free acid, thereby preventing the acid value from being unstable during the subsequent light component removal process and making it impossible to obtain qualified dimethyl phthalate within the predetermined pH range; when the neutralization treatment is carried out for 30 min until the pH of the material is within the range of 6 - 7, the neutralized material is obtained; the neutralized material is directly introduced into the light component removal kettle of the light component removal process without washing and alcohol removal treatment.

[0053] Among them, the neutralizing agent is sodium hydroxide; its addition amount is calculated based on the acid value of the esterification material (calculated as KOH, mgKOH / g), and the specific addition amount is 2 times the acid value of the esterification material.

[0054] (3) Light component removal The neutralized material enters the light component removal kettle. After introducing an inert gas to displace the air in the light component removal kettle, it is heated through the coil in the light component removal kettle. The light component removal temperature is controlled at 105 °C, and the light component removal pressure is 1 KPa (absolute pressure). Keep the temperature and pressure for light component removal treatment, and by reducing the content of alcohol and water in the material, the basic compound (such as the neutralizing agent) used in the neutralization step or the monomethyl phthalate salt compound generated in the material precipitates; after the light component removal treatment until no light components are removed (i.e., the light component removal is complete), cool down. The cooled material is decolorized with activated carbon and filtered to obtain the plasticizer dimethyl phthalate with a yield of 99.80% (calculated based on phthalic anhydride).

[0055] This example also provides dimethyl phthalate plasticizer prepared by the aforementioned method. The content of dimethyl phthalate is 99.85 wt%, and the alcohol content is 0.0047 wt%. The color number of the dimethyl phthalate plasticizer is 8.80#, the acid value is 0.049 mgKOH / g, and the pH of the water layer of the washing solution is 5.28.

[0056] Example 3 This example provides a synthesis method of dimethyl phthalate plasticizer, specifically as follows: (1) Esterification Add 909 kg of phthalic anhydride, 1967 kg of methanol, and 11.5 kg of solid acid catalyst into the esterification kettle. Under the protection of inert gas, stir and heat, and continuously introduce inert gas into the esterification kettle. When the stirring and heating reach 110 °C, keep warm for the esterification reaction. When the acid value of the materials in the esterification kettle is less than 2 mgKOH / g during the esterification reaction (the esterification reaction time is 12 h, and the esterification acid value is 1.50 mgKOH / g), the esterification reaction is completed. After the esterification reaction materials are filtered through the filtration device, the esterification materials are obtained. The esterification materials are transported to the neutralization kettle in the neutralization process through the buffer tank. The catalyst recovered by filtration is returned to the esterification kettle for reuse.

[0057] During the esterification reaction, the vapor generated by the heating of the materials in the esterification kettle enters the alcohol-water separation tank. After being dehydrated by the 3A molecular sieve added in the alcohol-water separation tank, it overflows through the U-shaped tube. The dehydrated alcohol collected can be used in other processes with low requirements for alcohol content and water content. At the same time, after the dehydrated alcohol is dehydrated by atmospheric distillation, it can be used as reflux alcohol (alcohol content higher than 99.5 wt%, water content lower than 0.5 wt%) and refluxed into the esterification kettle to continue participating in the esterification reaction.

[0058] After the dehydrating agent used in the alcohol-water separation tank is saturated with water absorption, it is heated to remove water and then reused. The water collected during the process of heating to remove water is transported to the washing tank and reused as washing water.

[0059] Among them, the molar ratio of phthalic anhydride to methanol is 1:10.

[0060] 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.

[0061] The preparation method of the composite solid acid resin catalyst is as follows: Put D001 macroporous sulfonic acid cation exchange resin into hydrochloric acid (concentration: 2.3 mol / L) with a weight 3.5 times that of the resin. Stir at room temperature for 3 h, then filter and wash with deionized water until the pH is 6, and dry to obtain the activated resin support. Then put the activated resin support into the composite impregnating solution with a weight 3 times that of the support, stir and heat up to 45 °C, keep stirring for 10 h, then filter and wash with deionized water with a volume 4 times that of the support, and dry to obtain the composite solid acid resin catalyst.

[0062] Among them, the composite impregnating solution is an aqueous deionized solution dissolving ferric chloride, zinc chloride and yttrium chloride. In the composite impregnating solution, the concentration of ferric chloride 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.

[0063] (2) Neutralization and impurity removal The esterification material enters the neutralization kettle. Under normal temperature conditions, it is neutralized with a neutralizing agent to remove a small amount of incompletely reacted monomethyl phthalate and free acid, thereby preventing the acid value from being unstable during the subsequent light component removal process and making it impossible to obtain qualified dimethyl phthalate within the predetermined pH range. When the neutralization treatment lasts for 30 min until the pH of the material is within the range of 6 - 7, the neutralized material is obtained. The neutralized material is directly introduced into the light component removal kettle in the light component removal process without washing and alcohol removal treatment.

[0064] Among them, the neutralizing agent is sodium hydroxide, and its addition amount is calculated based on the acid value of the esterification material (in terms of KOH, mgKOH / g), and the specific addition amount is 2 times the acid value of the esterification material.

[0065] (3) Light component removal The neutralized material enters the light component removal kettle. After introducing an inert gas to displace the air in the light component removal kettle, it is heated through the coil in the light component removal kettle. Control the light component removal temperature at 125 °C and the light component removal pressure at 1 KPa (absolute pressure), keep the temperature and pressure constant for light component removal treatment, and by reducing the contents of alcohol and water in the material, make the alkaline compounds (such as neutralizing agents) used in the neutralization step or the monomethyl phthalate salt compounds generated in the material precipitate. After the light component removal treatment until no light components are removed (i.e., the light component removal is complete), cool down. The cooled material is decolorized with activated carbon and filtered to obtain the plasticizer dimethyl phthalate, and the yield is 99.81% (calculated based on phthalic anhydride).

[0066] This example also provides the plasticizer dimethyl phthalate prepared by the aforementioned method. The content of dimethyl phthalate is 99.88 wt%, and the alcohol content is 0.0047 wt%. The color number of the plasticizer dimethyl phthalate is 8.79#, the acid value is 0.050 mgKOH / g, and the pH of the water layer of the washing solution is 5.26.

[0067] Furthermore, a cyclic test was carried out using the composite solid acid resin catalyst of Example 1. Specifically, according to the synthesis method of the plasticizer dimethyl phthalate in Example 1, the composite solid acid resin catalyst of Example 1 was reused 35 times. The esterification reaction time, esterification acid value when the acid value of the material in the esterification kettle was less than 2 mg KOH / g during the esterification reaction, and the yield of dimethyl phthalate obtained in each batch were recorded respectively. At the same time, it was detected whether the pH of the water layer of the water washing solution of dimethyl phthalate prepared in each batch was ≥5 and whether it met the qualified product index, and the product qualification rate was calculated. The specific results are as follows:

[0068] Comparative Example 1 For intuitive comparison, Comparative Example 1 adopted the technical solution of Example 1, and the changes were as follows: directly using D001 macroporous sulfonic acid type cation exchange resin as the catalyst for the esterification step, and controlling the added weight of D001 macroporous sulfonic acid type cation exchange resin to be equal to the added weight of the composite solid acid resin catalyst used in the original example.

[0069] The content of dimethyl phthalate in the plasticizer dimethyl phthalate prepared in Comparative Example 1 was 99.71 wt%, and the alcohol content was 0.023 wt%. The color number of the plasticizer dimethyl phthalate was 9.87#, the acid value was 0.056 mg KOH / g, and the pH of the water layer of the water washing solution was 5.38. The yield of the plasticizer dimethyl phthalate prepared in Comparative Example 1 was 99.32%. At the same time, after 12 times of repeated use of the catalyst used in Comparative Example 1, the product qualification rate and yield could no longer meet the preparation requirements and could not be recycled continuously.

[0070] It can be seen that the synthesis method of the plasticizer dimethyl phthalate of the present invention is to set a solid acid catalyst (especially a composite solid acid resin catalyst) in the esterification step according to the raw material characteristics of phthalic anhydride and methanol and the process conditions of the esterification step to catalyze the esterification reaction to a predetermined acid value (less than 2 mgKOH / g) to obtain an esterified material; after the esterified material is neutralized, it does not need to be washed and impurity-removed, and is directly subjected to a light removal treatment; in the light removal treatment with specific process parameters, by reducing the content of alcohol and water in the material, the content of The residual neutralization step uses an alkaline compound (neutralizing agent, etc.) or the generated monomethyl phthalate salt compound to precipitate; finally, after decolorization and filtration, a high-purity, high-yield, plasticizer dimethyl phthalate within a specific pH range is obtained. The aforementioned technical means cooperate and work synergistically with each other, effectively avoiding the defects of traditional dimethyl phthalate preparation that require the use of a large amount of sodium hydroxide for neutralization, resulting in a large amount of wastewater and high production costs; and effectively improve the application performance of dimethyl phthalate in specific environments, meeting the needs of applications with specific pH requirements. Furthermore, in the synthesis method of the plasticizer dimethyl phthalate, the composite solid acid resin catalyst used is specifically optimized for the raw material properties of phthalic anhydride and methanol, as well as the process conditions of the esterification step. The catalyst has a long cycle life and can be reused more than 35 times while maintaining a dimethyl phthalate yield of more than 99.6%. The qualified rate of dimethyl phthalate prepared in each batch is 100%, which can achieve stable and efficient industrial-scale production.

[0071] Unless otherwise specified, all percentages used in the present invention are by mass.

[0072] 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 aforementioned embodiments, those skilled in the art will be able to modify the technical solutions described in the aforementioned embodiments or substitute equivalents for some of the technical features. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention shall be included within the scope of protection of the present invention.

Claims

1. A method for synthesizing dimethyl phthalate, a plasticizer, characterized in that, It includes the following steps: esterification, neutralization and impurity removal, and light component removal; For the said esterification, phthalic anhydride, methanol and a solid acid catalyst are added into an esterification kettle. Under the protection of an inert gas, the temperature is raised for esterification until the acid value of the material in the esterification kettle is less than 2mgKOH / g. After filtering and recovering the solid acid catalyst, an esterification material is obtained; The said solid acid catalyst is one of the following: sulfonic acid type solid acid catalyst, supported solid acid catalyst, composite solid acid resin catalyst; For the said neutralization and impurity removal, a neutralizing agent is used to neutralize the esterification material to a pH of 6 - 7 to obtain a neutralized material; For the said light component removal, under the protection of an inert gas, the neutralized material is heated for light component removal treatment. After no light components are removed, the temperature is lowered, and then through decolorization and filtration, dimethyl phthalate plasticizer is prepared; the pH of the water layer of the washing liquid of the dimethyl phthalate plasticizer is ≥5.

2. The synthesis method of dimethyl phthalate plasticizer according to claim 1, wherein In the said esterification, the esterification temperature is 80 - 120°C; The molar ratio of phthalic anhydride to methanol is 1:7 - 10; The added weight of the solid acid catalyst is 0.3 - 0.5% of the total weight of phthalic anhydride and methanol; 3. The synthesis method of dimethyl phthalate plasticizer according to claim 1, characterized in that, The preparation method of the said composite solid acid resin catalyst is as follows: D001 macroporous sulfonic acid type cation exchange resin is put into hydrochloric acid. After stirring at room temperature, it is filtered out and washed with deionized water until the pH is 6, and then dried to obtain an activated resin carrier; the activated resin carrier is put into a composite impregnating solution. After heating for impregnation, it is filtered out, washed and dried to prepare a composite solid acid resin catalyst; The said composite impregnating solution is an aqueous solution of deionized water in which ferric chloride, zinc chloride and yttrium chloride are dissolved; 4. The synthesis method of dimethyl phthalate as a plasticizer according to claim 3, characterized in that, The concentration of the said hydrochloric acid is 2 - 2.3mol / L; The weight ratio of D001 macroporous sulfonic acid type cation exchange resin to hydrochloric acid is 1:3 - 3.5; The stirring time at room temperature is 2 - 3h; 5. The synthesis method of dimethyl phthalate as a plasticizer according to claim 3, wherein The weight ratio of the activated resin carrier to the composite impregnating solution is 1:2.5 - 3; The impregnation temperature of the activated resin carrier in the composite impregnating solution is 40 - 45°C, and the impregnation time is 8 - 10h; 6. The synthesis method of dimethyl phthalate plasticizer according to claim 3, characterized in that, In the composite impregnating solution, the concentration of ferric chloride is 0.8 - 0.9mol / L, the concentration of zinc chloride is 1 - 1.1mol / L, and the concentration of yttrium chloride is 0.2 - 0.3mol / L; 7. The synthesis method of dimethyl phthalate as a plasticizer according to claim 1, characterized in that, In the said neutralization and impurity removal, the neutralizing agent is one of the following: sodium hydroxide, potassium hydroxide, magnesium oxide, carbonate, bicarbonate; 8. The synthetic method of dimethyl phthalate plasticizer according to claim 1, characterized in that, In the said light component removal, the light component removal temperature is 50 - 150°C, and the absolute pressure for light component removal is 0.1 - 1KPa; 9. A dimethyl phthalate plasticizer prepared by the synthesis method according to any one of claims 1-8, characterized in that, The content of dimethyl phthalate in the said dimethyl phthalate plasticizer is ≥99.5wt%, and the alcohol content is ≤0.01wt%; the color number of the dimethyl phthalate plasticizer is ≤10#, the acid value is ≤0.1mgKOH / g, and the pH of the water layer of the washing liquid is ≥5.

Images