A production system and process for dimethyl terephthalate

Abstract

The application relates to the technical field of organic synthesis, in particular to a production system and process of dimethyl terephthalate. The production system comprises a reaction unit and a purification unit, the reaction unit is a place for esterification reaction of reaction raw materials, the reaction unit comprises a loop reactor, the loop reactor comprises a plurality of stages of differential side flow reactors, the purification unit comprises a static crystallizer and a falling film crystallizer which are arranged in sequence along a product production direction, and the loop reactor is communicated with the static crystallizer along the product production direction. The production process comprises the following steps: taking terephthalic acid and methanol as raw materials, performing esterification reaction under the action of a catalyst to obtain a crude dimethyl terephthalate esterification liquid, and then performing static crystallization and melt crystallization. The production system and process improve the conversion rate of reaction substances and the yield of target products, reduce production energy consumption while ensuring product purity, and are easy for industrial capacity expansion and realization of continuous production.

Description

Technical Field

[0001] This invention relates to the field of organic synthesis technology, and specifically to a production system and process for dimethyl terephthalate. Background Technology

[0002] Dimethyl terephthalate, also known as dimethyl 1,4-phthalate; DMT; dimethyl p-phthalate, molecular formula C 10 H 10 O4, density is 1.175 g / cm³ 3 It has a melting point of 140-143℃ and a boiling point of 288℃. It is a colorless orthorhombic crystal, soluble in hot ethanol, methanol, ether, and chloroform, but insoluble in water.

[0003] Dimethyl terephthalate (DMT) is a monomer of polyester, primarily used in the synthesis of polyester fibers, resins, films, polyester varnishes, and engineering plastics. It is also used in the manufacture of polyester films and fibers, as well as high-strength polyester insulating varnishes. The most common use of DMT is in the manufacture of fibers for use in fabrics, fishing nets, carpets, tire cords, etc. Polyester films are mainly used as electrical insulation materials and in the production of films (such as as a substrate for motion picture film, X-ray film, photographic film, chemicalbooks, and audio / video tapes, computer tapes, etc.). Polyester resins can also be used to produce the plasticizer dioctyl terephthalate (DMT).

[0004] Dimethyl terephthalate (DMT) is mainly obtained by esterification of terephthalic acid and methanol. For example, the method disclosed in patent CN104072374A uses terephthalic acid and methanol as raw materials and concentrated sulfuric acid as a catalyst to carry out an esterification reaction to obtain crude DMT, which is then recovered by distillation. Ethanol is added to the crude DMT, and activated carbon or clay is added to adsorb impurities. Styrene anions are also added to remove iron cations from the crude DMT. The crude DMT is then fed into a distillation column to separate and obtain the final DMT product. However, the preparation of DMT using this method and production system involves a particularly long esterification time (10-16 hours), high methanol consumption, high energy consumption, large amounts of hazardous waste generated, and numerous complex steps.

[0005] For example, patent CN102219689A discloses a method for producing dimethyl terephthalate, which involves adding tin, zinc, and antimony compounds as catalysts and a methanol solution containing 90-99.5 wt% to terephthalic acid (prepared from alkali reduction wastewater) containing 40-60 wt% water for esterification. The esterification liquid is separated from the dimethyl terephthalate solution using a flash evaporator, then filtered with activated carbon, and finally distilled to obtain the dimethyl terephthalate product. However, this method uses alkali reduction wastewater as a raw material to prepare terephthalic acid, which, although a waste utilization process, requires discharge from textile printing and dyeing enterprises, limiting its large-scale application. Secondly, the activated carbon filtration before distillation of the esterification liquid generates a large amount of hazardous waste. Subsequent distillation separation is complex and energy-intensive, and flash evaporation also generates wastewater. The production system described above suffers from high energy consumption, large amounts of waste, and complex operating procedures. Summary of the Invention

[0006] In view of this, the purpose of the present invention is to provide a production system and process for dimethyl terephthalate, so as to improve the conversion rate of reactants and the yield of target products, further improve the purity of dimethyl terephthalate, reduce the energy consumption of dimethyl terephthalate production, reduce the amount of waste generated, shorten the production time, simplify the preparation process, improve the production efficiency, and thus realize industrial scale-up and continuous production.

[0007] To achieve the above and other related objectives, in a first aspect, the present invention provides a production system for dimethyl terephthalate, comprising a reaction unit and a purification unit. The reaction unit is the site for the esterification reaction of the reactants. The reaction unit includes a circulating reactor, which includes several stages of differential side-flow reactors. The purification unit includes a static crystallizer and a falling film crystallizer arranged sequentially along the product production direction. The circulating reactor is connected to the static crystallizer along the product production direction.

[0008] Optionally, the connection method of the several stages of differential side-flow reactors in the circulating reactor is to connect them sequentially or in parallel. All differential side-flow reactors are provided with inlet and outlet. The outlet of the last stage differential side-flow reactor is connected to the inlet of the first stage differential side-flow reactor, or the outlet of each stage differential side-flow reactor is connected to the inlet of each stage differential side-flow reactor.

[0009] Optionally, the reaction unit further includes a static mixer for uniformly mixing the reaction raw materials. The static mixer is located on the connecting pipeline between the inlet of the first-stage differential side-flow reactor and the outlet of the last-stage differential side-flow reactor, or between the outlet and inlet of each stage of the differential side-flow reactor. The static mixer is provided with a raw material inlet, a raw material outlet, and a circulation inlet. The raw material outlet of the static mixer is connected to the inlet of the first-stage differential side-flow reactor or each stage of the differential side-flow reactor, and the circulation inlet of the static mixer is connected to the outlet of the last-stage differential side-flow reactor or each stage of the differential side-flow reactor.

[0010] Optionally, the reaction unit further includes a transfer pump for conveying the catalyst and / or unreacted raw materials from the last stage differential side-flow reactor or each stage differential side-flow reactor to the static mixer. The transfer pump is located on the connecting pipeline between the circulation inlet of the static mixer and the outlet of the last stage differential side-flow reactor or each stage differential side-flow reactor.

[0011] Optionally, the static crystallizer is used to separate and obtain the reaction product that has been preliminarily purified. The static crystallizer is provided with a feed port, a mother liquor outlet and a material outlet. The feed port of the static crystallizer is connected to the outlet of the last stage differential side-flow reactor or the outlet of each stage differential side-flow reactor.

[0012] Optionally, the falling film crystallizer is used to purify the reaction product after preliminary purification. The falling film crystallizer is provided with a material inlet and a discharge port. The material inlet of the falling film crystallizer is connected to the material outlet of the static crystallizer. The material inlet and discharge port of the falling film crystallizer are connected by a pipeline.

[0013] Optionally, the static crystallizer and the falling film crystallizer are respectively connected to a cooling and heating medium system, and the static crystallizer and the falling film crystallizer are coupled through the cooling and heating medium system. The cooling and heating medium system couples the static crystallizer and the falling film crystallizer, enabling the mutual utilization of the waste heat of the static crystallizer and the falling film crystallizer, thereby supplying heat energy to the static crystallizer and the falling film crystallizer, and thus saving energy in production.

[0014] Optionally, the production system further includes a distillation recovery unit, which includes a distillation column and a recovery tank connected together, for distilling the mother liquor discharged from the static crystallizer and recovering excess reaction raw materials. The inlet of the distillation column is connected to the mother liquor outlet of the static crystallizer, the outlet of the distillation column is connected to the inlet of the recovery tank, and the outlet of the recovery tank is connected to the raw material inlet of the static mixer.

[0015] Optionally, the production system further includes a product processing unit, which includes a mother liquor tank, a residual liquor tank, and a product tank. The mother liquor tank is used to recover the mother liquor from molten crystallization, the residual liquor tank is used to recover the sweating liquid from molten crystallization, and the product tank is used to collect the purified reaction products. The inlets of the mother liquor tank, the residual liquor tank, and the product tank are all connected to the feed port of the falling film crystallizer. The outlet of the mother liquor tank is connected to the feed port of the static crystallizer via a pipeline, and the outlet of the residual liquor tank is connected to the material inlet of the falling film crystallizer via a pipeline.

[0016] In another aspect, the present invention provides a process for producing dimethyl terephthalate, comprising the following steps:

[0017] S1. Using terephthalic acid and methanol as raw materials, an esterification reaction is carried out in a circulating reactor under the action of a catalyst. The circulating reactor is a series of differential side-flow reactors connected end to end or in parallel. The esterification reaction of terephthalic acid and methanol is carried out in each stage of differential side-flow reactor. Then, the unreacted terephthalic acid and methanol are circulated in the circulating reactor with the reaction liquid until the esterification reaction is completed, to obtain crude dimethyl terephthalate esterified liquid.

[0018] S2. The crude dimethyl terephthalate esterification solution obtained in step S1 is placed in a static crystallizer for static crystallization to obtain a preliminarily purified dimethyl terephthalate solution.

[0019] S3. Place the dimethyl terephthalate solution obtained in step S2 into a falling film crystallizer for melt crystallization to obtain the product dimethyl terephthalate.

[0020] Optionally, the molar ratio of terephthalic acid to methanol is 1:3-6.

[0021] Optionally, the catalyst includes at least one of tin chloride, tin oxide, zinc chloride, zinc oxide, antimony chloride, and zinc antimony.

[0022] Optionally, the esterification reaction is carried out at a temperature of 250-300℃, a pressure of 2-2.5MPa, and a time of 3-6h.

[0023] Optionally, the static crystallization includes crystallization and sweating steps.

[0024] Optionally, the crystallization step includes: cooling to 45-55°C at a rate of 5-10°C / min for a crystallization time of 50-60min.

[0025] Optionally, the sweating step includes: raising the temperature to 130-135°C at a rate of 5-10°C / min, and the sweating time is 20-30 minutes.

[0026] Optionally, after the sweating step, the method further includes: heating to 150-160°C at a rate of 0.5-1°C / min to obtain a dimethyl terephthalate solution.

[0027] Optionally, the melt crystallization includes crystallization, sweating, and melting steps.

[0028] Optionally, the crystallization step includes: first cooling to 140-145°C at a rate of 3-5°C / min, then cooling to 120-125°C at a rate of 0.3-0.5°C / min, with a crystallization time of 90-100 min.

[0029] Optionally, the sweating step includes: first raising the temperature to 130-133°C at a rate of 3-5°C / min, then raising the temperature to 139-141°C at a rate of 0.3-0.5°C / min. During the sweating process, the temperature of the hot and cold medium used is 145-150°C, and the sweating time is 40-50 minutes.

[0030] Optionally, the temperature of the melting step is 150-155°C, and the melting time is 25-35 min.

[0031] As described above, the dimethyl terephthalate production system and process of the present invention have the following beneficial effects:

[0032] The production system of this invention introduces a circulating reactor, which is configured as several stages of differential side-flow reactors connected sequentially or in parallel. All differential side-flow reactors are equipped with inlets and outlets. In the sequentially connected stages, the outlet of the last stage is connected to the inlet of the first stage, allowing unreacted terephthalic acid and methanol to continue reacting in the next stage. In the parallel-connected stages, the outlets of each stage are connected to the inlets, allowing the mixed terephthalic acid and methanol to flow separately into each stage for esterification. Because the circulating reactors possess excellent mass and heat transfer capabilities, they prevent the reaction from releasing large amounts of heat in a short time, reducing the generation of byproducts and enabling continuous reaction, thus ensuring a more complete reaction.

[0033] The production process of this invention employs a production system including a circulating reactor, and utilizes high temperature and high pressure with a specific metal compound as a catalyst for esterification reaction. This improves the conversion rate of reactants and the yield of the target product, enhances reaction safety, and shortens reaction time. Furthermore, through two purification steps, new solvent impurities are reduced, the process flow is shortened, and the purity of the dimethyl terephthalate product is guaranteed. At the same time, this method features low energy consumption, simple operation, high product yield, and high purity.

[0034] The production system and process of this invention improve the conversion rate of reactants and the yield of target products, while ensuring product purity, reducing production energy consumption, simplifying the process flow, improving production efficiency, and facilitating industrial capacity scaling up and continuous production. Attached Figure Description

[0035] Figure 1 This is a schematic diagram of the dimethyl terephthalate production system in Examples 1-3 of the present invention.

[0036] Figure 2 This is a schematic diagram of the dimethyl terephthalate production system in Example 4 of the present invention.

[0037] Figure 3 This is a schematic diagram of the differential side-flow reactor used in the dimethyl terephthalate production system in Examples 1-4 of the present invention.

[0038] Figure reference numerals: Static mixer 11, first-stage differential side-flow reactor 1201, second-stage differential side-flow reactor 1202, third-stage differential side-flow reactor 1203, multiphase flow pump 13, static crystallizer 21, falling film crystallizer 22, circulating pump 23, distillation column 31, recovery tank 32, centrifugal pump 41, mother liquor tank 42, residual liquid tank 43, product tank 44, terephthalic acid inlet A1, methanol inlet A2, dimethyl terephthalate outlet B, catalyst inlet C. Detailed Implementation

[0039] The following specific examples illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention.

[0040] In one embodiment of this application, the following is employed: Figure 1 The dimethyl terephthalate production system shown includes a reaction unit, a purification unit, a distillation and recovery unit, and a product processing unit.

[0041] like Figure 1 As shown, the reaction unit includes a static mixer 11, a circulating reactor, and a transfer pump. The circulating reactor comprises several stages connected end-to-end, such as... Figure 3 The differential side-flow reactor shown is preferably a three-stage differential side-flow reactor connected end-to-end, namely a first-stage differential side-flow reactor 1201, a second-stage differential side-flow reactor 1202, and a third-stage differential side-flow reactor 1203. The transfer pump is specifically a multiphase flow pump 13. The static mixer 11, the first-stage differential side-flow reactor 1201, the second-stage differential side-flow reactor 1202, the third-stage differential side-flow reactor 1203, and the multiphase flow pump 13 are connected in sequence through pipelines to form a loop.

[0042] Specifically, the static mixer 11 is a container used to mix the reaction raw materials terephthalic acid and methanol, as well as the catalyst. The static mixer 11 is equipped with a terephthalic acid inlet A1, a methanol inlet A2, a raw material outlet, and a recirculation inlet. Terephthalic acid and methanol can be added to the static mixer 11 through the terephthalic acid inlet A1 and the methanol inlet A2. The raw material outlet of the static mixer 11 is connected to the inlet of the first-stage differential side-flow reactor 1201, so that the uniformly mixed terephthalic acid, methanol, and catalyst enter the first-stage differential side-flow reactor 1201 through the pipeline.

[0043] Specifically, the first-stage differential side-flow reactor 1201, the second-stage differential side-flow reactor 1202, and the third-stage differential side-flow reactor 1203 are sites for the esterification reaction of phthalic acid and methanol. Each stage of the differential side-flow reactor is equipped with an inlet and an outlet. The outlet of the third-stage differential side-flow reactor 1203 is connected to the inlet of the first-stage differential side-flow reactor 1201.

[0044] In the first-stage differential side-flow reactor 1201, the second-stage differential side-flow reactor 1202, and the third-stage differential side-flow reactor 1203, the raw materials terephthalic acid and methanol undergo an esterification reaction under the catalysis of a catalyst (such as tin chloride or zinc chloride). Terephthalic acid and methanol first undergo an esterification reaction in the first-stage differential side-flow reactor 1201. Then, the unreacted terephthalic acid and methanol enter the next-stage differential side-flow reactor along with the reaction liquid to continue the esterification reaction. The reaction is circulated in the loop of the reaction unit until the esterification reaction is completed, resulting in an esterified liquid of crude dimethyl terephthalate.

[0045] Specifically, the dimethyl terephthalate production system of this embodiment introduces a first-stage differential side-flow reactor 1201, a second-stage differential side-flow reactor 1202, and a third-stage differential side-flow reactor 1203 connected end to end. Because the differential side-flow reactor has excellent mass and heat transfer capabilities, it can reduce the heat of reaction, reduce by-products, make the reaction continuous, and thus make the reaction more thorough. At the same time, unreacted terephthalic acid and methanol enter the next stage differential side-flow reactor to continue the reaction, thereby improving the conversion rate of reactants and the yield of the target product.

[0046] Specifically, the multiphase flow pump 13 is located on the connecting pipeline between the circulating feed port of the static mixer 11 and the discharge port of the last stage differential side flow reactor.

[0047] The transfer pump is used to transfer the catalyst and / or unreacted raw materials in the last stage differential side-flow reactor to the static mixer. Furthermore, the multiphase flow pump 13 is used to pump the catalyst and the material discharged from the outlet of the third stage differential side-flow reactor 1203 to the static mixer 11 for re-mixing, and then send it into the first stage differential side-flow reactor 1201, the second stage differential side-flow reactor 1202 and the third stage differential side-flow reactor 1203 to continue the esterification reaction.

[0048] Specifically, by setting up a multiphase flow pump 13, the catalyst can be fed into the static mixer 11 to mix with the raw materials dimethyl terephthalate and methanol. It can also transport the unreacted dimethyl terephthalate and methanol in the third-stage differential side-flow reactor 1203 to the static mixer 11 for uniform mixing and continued reaction, thereby further improving the conversion rate of reactants and the efficiency of esterification reaction.

[0049] like Figure 1 As shown, the purification unit includes a static crystallizer 21 and a falling film crystallizer 22 arranged sequentially along the product production direction.

[0050] Specifically, the static crystallizer 21 has a feeding port at the top, which is connected to the discharge port of the third-stage differential side-flow reactor 1203, and a mother liquor outlet and a material outlet at the bottom, with the mother liquor outlet connected to the falling film crystallizer 22.

[0051] Specifically, by setting up a static crystallizer 21 connected to the third-stage differential side-flow reactor 1203, the esterification liquid of crude dimethyl terephthalate, unreacted methanol, and water can be separated to obtain a preliminarily purified dimethyl terephthalate solution.

[0052] Specifically, the falling film crystallizer 22 is a place for further separation and purification of the dimethyl terephthalate solution after preliminary separation and purification in the static crystallizer 21, in order to remove water and methanol contained in the dimethyl terephthalate solution that has not been completely removed. The falling film crystallizer 22 is provided with a material inlet and a discharge outlet, which are connected by a pipeline, and a circulation pump 23 is installed on the pipeline connecting the material inlet and the discharge outlet.

[0053] Specifically, by connecting the material inlet and the discharge port of the falling film crystallizer 22, and setting a circulation pump 23 on the connecting pipeline between the material inlet and the discharge port of the falling film crystallizer 22, the dimethyl terephthalate solution can be circulated in the falling film crystallizer 22, thereby allowing the dimethyl terephthalate to be completely crystallized and further purified to improve the purity of the target product, dimethyl terephthalate.

[0054] The static crystallizer 21 and the falling film crystallizer 22 are respectively connected to a cooling and heating medium system, preferably a heat pump system (not shown in the figure).

[0055] Specifically, the heat pump system is used to supply heat energy to the static crystallizer 21 and the falling film crystallizer 22. The heat pump system couples the static crystallizer 21 and the falling film crystallizer 22, enabling mutual utilization of the waste heat of the static crystallizer 21 and the falling film crystallizer 22. That is, in the continuous production process, the heat pump system can collect the heat emitted by the static crystallizer 21 when the crystallization step is cooled during the static crystallization process and transfer it to the falling film crystallizer 22 for the sweating step and the heating stage of the melting step during the melting crystallization process. Conversely, the heat pump system can also collect the heat emitted by the falling film crystallizer 22 when the crystallization step is cooled during the melting crystallization process and transfer it to the static crystallizer 21 for the sweating step and the heating stage after the sweating step during the static crystallization process, thereby saving energy in production.

[0056] like Figure 1 As shown, the distillation recovery unit includes a distillation column 31 and a recovery tank 32 connected together.

[0057] Please continue reading. Figure 1 The inlet of distillation column 31 is connected to the mother liquor outlet of static crystallizer 21, the outlet of distillation column 31 is connected to the inlet of recovery tank 32, and the outlet of recovery tank 32 is connected to the raw material inlet of static mixer 11.

[0058] Specifically, the distillation recovery unit can distill the mother liquor discharged from the static crystallizer 21 and recover the unreacted excess methanol, allowing the methanol to be returned to the reaction unit as a reaction raw material for reuse, thereby improving the utilization rate of methanol and reducing production losses.

[0059] like Figure 1As shown, the product processing unit includes a mother liquor tank 42, a residual liquor tank 43, and a product tank 44.

[0060] Please continue reading. Figure 1 The mother liquor tank 42, the residual liquor tank 43, and the product tank 44 are all connected to the discharge port of the falling film crystallizer 22. A centrifugal pump 41 is installed on the connecting pipeline between the mother liquor tank 42, the residual liquor tank 43, and the product tank 44 and the discharge port of the falling film crystallizer 22. The mother liquor tank 42 is connected to the feeding port of the static crystallizer 21 via a pipeline (not shown in the figure), and the residual liquor tank 43 is connected to the material inlet of the falling film crystallizer 22 via a pipeline (not shown in the figure).

[0061] Specifically, the mother liquor tank 42 is used to recover the mother liquor from molten crystallization, the residual liquid tank 43 is used to recover the sweating liquid from molten crystallization, and the product tank 44 is used to collect the purified reaction products. By setting the mother liquor tank 42 and connecting it to the static crystallizer 21, and the residual liquid tank 43 and connecting it to the falling film crystallizer 22, the mother liquor from molten crystallization can be recovered and statically crystallized again, and the sweating liquid from molten crystallization can be recovered and molten crystallized again. A centrifugal pump 41 is set on the connecting pipeline between the mother liquor tank 42, the residual liquid tank 43, and the product tank 44 and the discharge port of the falling film crystallizer 22, which enables the reaction products separated and purified by the falling film crystallizer 22 to be efficiently transported to the product tank 44, thereby improving production efficiency.

[0062] All of the above connecting pipelines are equipped with on / off valves (not shown in the figure).

[0063] In another embodiment of this application, the following is employed: Figure 2 The dimethyl terephthalate production system shown includes a reaction unit, a purification unit, a distillation and recovery unit, and a product processing unit.

[0064] like Figure 2 As shown, the reaction unit includes a static mixer 11, a circulating reactor, and a transfer pump, wherein the circulating reactor comprises several stages connected in parallel, such as... Figure 3 The differential side-flow reactor shown is preferably a three-stage differential side-flow reactor connected in parallel, namely a first-stage differential side-flow reactor 1201, a second-stage differential side-flow reactor 1202, and a third-stage differential side-flow reactor 1203. The transfer pump is specifically a multiphase flow pump 13. The first-stage differential side-flow reactor 1201, the second-stage differential side-flow reactor 1202, and the third-stage differential side-flow reactor 1203 are connected in parallel and then connected to the static mixer 11 and the multiphase flow pump 13 through pipelines to form a loop.

[0065] Specifically, the static mixer 11 is a container used to mix the reaction raw materials terephthalic acid and methanol, as well as the catalyst. The static mixer 11 is equipped with a terephthalic acid inlet A1, a methanol inlet A2, a raw material outlet, and a circulating feed inlet. Terephthalic acid and methanol can be added to the static mixer 11 through the terephthalic acid inlet A1 and the methanol inlet A2. The raw material outlet of the static mixer 11 is connected to the feed inlets of each stage of the differential side-flow reactor, so that the uniformly mixed terephthalic acid, methanol, and catalyst are diverted through pipelines into the first-stage differential side-flow reactor 1201, the second-stage differential side-flow reactor 1202, and the third-stage differential side-flow reactor 1203, respectively.

[0066] Specifically, the first-stage differential side-flow reactor 1201, the second-stage differential side-flow reactor 1202, and the third-stage differential side-flow reactor 1203 are sites for the esterification reaction of phthalic acid and methanol. Each stage of the differential side-flow reactor is equipped with an inlet and an outlet, and the inlets of each stage of the differential side-flow reactor are connected, as are the outlets of each stage of the differential side-flow reactor.

[0067] In the first-stage differential side-flow reactor 1201, the second-stage differential side-flow reactor 1202, and the third-stage differential side-flow reactor 1203, the raw materials terephthalic acid and methanol undergo an esterification reaction under the catalysis of a catalyst (such as tin chloride or zinc chloride). The esterification reaction of terephthalic acid and methanol takes place in each stage of the differential side-flow reactor. Then, the unreacted terephthalic acid and methanol are circulated with the reaction liquid to the static mixer 11 for mixing and then re-enter the stage of the differential side-flow reactor to continue the esterification reaction until the esterification reaction is completed, resulting in an esterified liquid of crude dimethyl terephthalate.

[0068] Specifically, the dimethyl terephthalate production system of this embodiment introduces a first-stage differential side-flow reactor 1201, a second-stage differential side-flow reactor 1202, and a third-stage differential side-flow reactor 1203 connected in parallel. Because the differential side-flow reactors have excellent mass and heat transfer capabilities, they can reduce the heat of reaction, reduce by-products, make the reaction continuous, and thus make the reaction more thorough. At the same time, terephthalic acid and methanol are diverted into the differential side-flow reactors of each stage for esterification reaction, which can improve production efficiency and reduce energy consumption.

[0069] Specifically, the multiphase flow pump 13 is located on the connecting pipeline between the circulating feed inlet of the static mixer 11 and the discharge outlet of each stage of differential side-flow reactor.

[0070] The transfer pump is used to transport the catalyst and / or unreacted raw materials in the last stage differential side-flow reactor to the static mixer. Further, the multiphase flow pump 13 is used to pump the catalyst and the material discharged from the outlet of the first stage differential side-flow reactor 1201, the second stage differential side-flow reactor 1202 and the third stage differential side-flow reactor 1203 to the static mixer 11 for re-mixing, and then send it into the first stage differential side-flow reactor 1201, the second stage differential side-flow reactor 1202 and the third stage differential side-flow reactor 1203 to continue the esterification reaction.

[0071] Specifically, by setting up a multiphase flow pump 13, the catalyst can be fed into the static mixer 11 to mix with the raw materials dimethyl terephthalate and methanol. It can also transport the unreacted dimethyl terephthalate and methanol in each stage of the differential side-flow reactor to the static mixer 11 for uniform mixing and continued reaction, thereby further improving the conversion rate of reactants and the efficiency of esterification reaction.

[0072] like Figure 2 As shown, the purification unit includes a static crystallizer 21 and a falling film crystallizer 22 arranged sequentially along the product production direction.

[0073] Specifically, the static crystallizer 21 has a feed port at the top, which is connected to the discharge port of each stage of differential side-flow reactor, and a mother liquor outlet and a material outlet at the bottom, with the mother liquor outlet connected to the falling film crystallizer 22.

[0074] Specifically, by setting up a static crystallizer 21 connected to the differential side-flow reactors at each stage, it is possible to separate the esterification liquid of crude dimethyl terephthalate, unreacted methanol, and water, thereby obtaining a preliminarily purified dimethyl terephthalate solution.

[0075] like Figure 2 As shown, the setup and function of the purification unit, distillation recovery unit, and product processing unit are the same as in the above embodiment.

[0076] An exemplary embodiment of the present invention provides a production process for producing dimethyl terephthalate using the production system described above, comprising the following steps:

[0077] S1. Using terephthalic acid and methanol as raw materials, an esterification reaction is carried out in a circulating reactor under the action of a catalyst. The circulating reactor is a series of differential side-flow reactors connected end to end or in parallel. The esterification reaction of terephthalic acid and methanol is carried out in each stage of differential side-flow reactor. Then, the unreacted terephthalic acid and methanol are circulated in the circulating reactor with the reaction liquid until the esterification reaction is completed, to obtain crude dimethyl terephthalate esterified liquid.

[0078] S2. The crude dimethyl terephthalate esterification solution obtained in step S1 is placed in a static crystallizer for static crystallization to obtain a preliminarily purified dimethyl terephthalate solution.

[0079] S3. Place the dimethyl terephthalate solution obtained in step S2 into a falling film crystallizer for melt crystallization to obtain the product dimethyl terephthalate.

[0080] In another embodiment of this application, the molar ratio of terephthalic acid to methanol is 1:3-6.

[0081] Optionally, the catalyst includes at least one of tin chloride, tin oxide, zinc chloride, zinc oxide, antimony chloride, and zinc antimony.

[0082] Optionally, the esterification reaction is carried out at a temperature of 250-300℃, a pressure of 2-2.5MPa, and a time of 3-6h.

[0083] Optionally, the static crystallization includes crystallization and sweating steps.

[0084] Optionally, the crystallization step includes: cooling to 45-55°C at a rate of 5-10°C / min for a crystallization time of 50-60min.

[0085] Optionally, the sweating step includes: raising the temperature to 130-135°C at a rate of 5-10°C / min, and the sweating time is 20-30 minutes.

[0086] Optionally, after the sweating step, the method further includes: heating to 150-160°C at a rate of 0.5-1°C / min to obtain a dimethyl terephthalate solution.

[0087] Optionally, the melt crystallization includes crystallization, sweating, and melting steps.

[0088] Optionally, the crystallization step includes: first cooling to 140-145°C at a rate of 3-5°C / min, then cooling to 120-125°C at a rate of 0.3-0.5°C / min, with a crystallization time of 90-100 min.

[0089] Optionally, the sweating step includes: first raising the temperature to 130-133°C at a rate of 3-5°C / min, then raising the temperature to 139-141°C at a rate of 0.3-0.5°C / min. During the sweating process, the temperature of the hot and cold medium used is 145-150°C, and the sweating time is 40-50 minutes.

[0090] Optionally, the temperature of the melting step is 150-155°C, and the melting time is 25-35 min.

[0091] The present invention will be described in detail below through specific examples and embodiments. It should also be understood that the following embodiments are only for specific illustration of the present invention and should not be construed as limiting the scope of protection of the present invention. Any non-essential improvements and adjustments made by those skilled in the art based on the above description of the present invention are within the scope of protection of the present invention. The specific process parameters, etc., in the following examples are merely examples within a suitable range; that is, those skilled in the art can make appropriate selections within the appropriate range based on the description herein, and are not intended to be limited to the specific values ​​in the examples below.

[0092] Example 1

[0093] Adopting such Figure 1 The production system shown produces dimethyl terephthalate, and the specific steps are as follows:

[0094] 16.6g of terephthalic acid and 12.5ml of 98wt% methanol solution (using water as solvent) are added to static mixer 11 through terephthalic acid inlet A1 and methanol inlet A2, respectively. 6.8g of zinc chloride is sent to static mixer 11 through catalyst inlet C by multiphase flow pump 13 to mix with terephthalic acid and methanol solution.

[0095] The temperature of the first-stage differential side-flow reactor 1201, the second-stage differential side-flow reactor 1202, and the third-stage differential side-flow reactor 1203 are adjusted to 250℃, and the pressure is adjusted to 2.5MPa. The switch valve on the connecting pipeline between the static mixer 11 and the first-stage differential side-flow reactor 1201 is opened, and a mixed solution of terephthalic acid, methanol, and zinc chloride is sent into the first-stage differential side-flow reactor 1201. Terephthalic acid and methanol undergo esterification reaction under the catalysis of zinc chloride. The reaction is carried out for 2 hours to obtain a reaction solution containing dimethyl terephthalate, terephthalic acid, methanol, and water.

[0096] Subsequently, the valves on the connecting pipes between the first-stage differential side-flow reactor 1201 and the second-stage differential side-flow reactor 1202, and between the second-stage differential side-flow reactor 1202 and the third-stage differential side-flow reactor 1203, are opened sequentially. The reaction liquid is fed into the second-stage differential side-flow reactor 1202 and the third-stage differential side-flow reactor 1203, and circulates in the loop of the reaction unit. This allows the unreacted terephthalic acid and methanol to continue reacting for 4 hours under the catalysis of zinc chloride, resulting in a crude dimethyl terephthalate esterification liquid containing dimethyl terephthalate, methanol, water, and other components. The content of each component includes: dimethyl terephthalate 82 wt%, water approximately 9 wt%, methanol approximately 8 wt%, and other components approximately 1 wt%.

[0097] Next, the switch valve between the feed port of the third-stage differential side-flow reactor 1203 and the static crystallizer 21 is opened, and the crude dimethyl terephthalate esterification liquid is fed into the static crystallizer 21 for static crystallization. Static crystallization includes crystallization and sweating steps, specifically:

[0098] Crystallization step: Cool down to 45℃ at a rate of 5℃ / min, and control the crystallization time to 60min;

[0099] Sweating procedure: Increase the temperature to 130℃ at a rate of 5℃ / min, and control the sweating time to 30min;

[0100] After the sweating step was completed, the temperature was increased to 155°C at a rate of 0.5°C / min to obtain a dimethyl terephthalate solution with the following components: dimethyl terephthalate 97 wt%, water 2 wt%, and methanol 1 wt%. After static crystallization, most of the methanol was separated from the esterification solution.

[0101] Open the valve on the connecting pipeline between the mother liquor outlet of the static crystallizer 21 and the distillation column 31. The crystallization mother liquor containing water and methanol is sent into the distillation column 31 for distillation to obtain methanol. The methanol is collected by the recovery tank 32 and sent back to the static mixer 11 as raw material for esterification reaction. The distillation residue is sent back to the static crystallizer 21, and the distillation condensate is discharged at the same time.

[0102] Then, the valve on the connecting pipe between the static crystallizer 21 and the falling film crystallizer 22 is opened, and the obtained dimethyl terephthalate solution is introduced into the falling film crystallizer 22 for melt crystallization. The melt crystallization includes crystallization, sweating, and melting steps, specifically:

[0103] Equipment preheating: A 97wt% dimethyl terephthalate solution to be treated is introduced into the falling film crystallizer 22. The falling film crystallizer 22 and the heat pump system are started, the temperature of the cold and hot medium is adjusted to 120℃, and the circulation pump 23 is started to make the introduced dimethyl terephthalate solution circulate in the falling film crystallizer 22.

[0104] Crystallization steps: First, cool the solution to 145°C at a rate of 3°C / min, then cool it to 125°C at a rate of 0.3°C / min. Control the crystallization time to 100 min. Turn off the circulation pump 23, open the switch valve on the connecting pipeline between the feed port of the falling film crystallizer 22 and the mother liquor tank 42, and discharge the mother liquor to the mother liquor tank 42 through the centrifugal pump 41.

[0105] Sweating steps: First, heat the solution to 133℃ at a rate of 3℃ / min, then heat it to 139℃ at a rate of 0.3℃ / min. Adjust the temperature of the hot and cold medium to 145℃ and control the sweating time to 50min. After sweating is completed, open the switch valve on the connecting pipeline between the feed port of the falling film crystallizer 22 and the residual liquid tank 43, and discharge the sweating liquid to the residual liquid tank 43 through the centrifugal pump 41.

[0106] Melting step: Adjust the temperature of the hot and cold medium to 150℃ to melt the crystallized product, control the melting time to 35min. After melting is completed, open the switch valve on the connecting pipeline between the feed port of the falling film crystallizer 22 and the product tank 44. The obtained crystallized product is sent into the product tank 44 through the centrifugal pump 41, and 19.3g of dimethyl terephthalate is obtained from the dimethyl terephthalate outlet B.

[0107] The purity of dimethyl terephthalate was measured to be 99.96% from the sample.

[0108] Example 2

[0109] Adopting such Figure 1 The production system shown produces dimethyl terephthalate, and the specific steps are as follows:

[0110] 16.6g of terephthalic acid and 12.5ml of 98wt% methanol solution (using water as solvent) are added to static mixer 11 through terephthalic acid inlet A1 and methanol inlet A2, respectively. 6.8g of zinc chloride is sent to static mixer 11 through catalyst inlet C by multiphase flow pump 13 to mix with terephthalic acid and methanol solution.

[0111] The temperature of the first-stage differential side-flow reactor 1201, the second-stage differential side-flow reactor 1202, and the third-stage differential side-flow reactor 1203 are adjusted to 280℃, and the pressure is adjusted to 2.3MPa. The switch valve on the connecting pipeline between the static mixer 11 and the first-stage differential side-flow reactor 1201 is opened, and a mixed solution of terephthalic acid, methanol, and zinc chloride is sent into the first-stage differential side-flow reactor 1201. Terephthalic acid and methanol undergo esterification reaction under the catalysis of zinc chloride. The reaction is carried out for 1.5 hours to obtain a reaction solution containing dimethyl terephthalate, terephthalic acid, methanol, and water.

[0112] Subsequently, the valves on the connecting pipes between the first-stage differential side-flow reactor 1201 and the second-stage differential side-flow reactor 1202, and between the second-stage differential side-flow reactor 1202 and the third-stage differential side-flow reactor 1203, are opened sequentially. The reaction liquid is fed into the second-stage differential side-flow reactor 1202 and the third-stage differential side-flow reactor 1203, and circulates in the loop of the reaction unit. This allows the unreacted terephthalic acid and methanol to continue reacting for 3 hours under the catalysis of zinc chloride, resulting in a crude dimethyl terephthalate esterification liquid containing dimethyl terephthalate, methanol, water, and other components. The content of each component includes: dimethyl terephthalate 82 wt%, water approximately 9 wt%, methanol approximately 8 wt%, and other components approximately 1 wt%.

[0113] Next, the switch valve between the feed port of the third-stage differential side-flow reactor 1203 and the static crystallizer 21 is opened, and the crude dimethyl terephthalate esterification liquid is fed into the static crystallizer 21 for static crystallization. Static crystallization includes crystallization and sweating steps, specifically:

[0114] Crystallization step: Cool down to 50℃ at a rate of 8℃ / min, and control the crystallization time to 55min;

[0115] Sweating procedure: Increase the temperature to 133℃ at a rate of 8℃ / min, and control the sweating time to 25min;

[0116] After the sweating step was completed, the temperature was increased to 155°C at a rate of 0.8°C / min to obtain a dimethyl terephthalate solution with the following components: dimethyl terephthalate 97.5 wt%, water 1.8 wt%, and methanol 0.7 wt%. After static crystallization, most of the methanol was separated from the esterification solution.

[0117] Open the valve on the connecting pipeline between the mother liquor outlet of the static crystallizer 21 and the distillation column 31. The crystallization mother liquor containing water and methanol is sent into the distillation column 31 for distillation to obtain methanol. The methanol is collected by the recovery tank 32 and sent back to the static mixer 11 as raw material for esterification reaction. The distillation residue is sent back to the static crystallizer 21, and the distillation condensate is discharged at the same time.

[0118] Then, the valve on the connecting pipe between the static crystallizer 21 and the falling film crystallizer 22 is opened, and the obtained dimethyl terephthalate solution is introduced into the falling film crystallizer 22 for melt crystallization. The melt crystallization includes crystallization, sweating, and melting steps, specifically:

[0119] Equipment preheating: A 97.5 wt% dimethyl terephthalate solution to be treated is introduced into the falling film crystallizer 22. The falling film crystallizer 22 and the heat pump system are started, the temperature of the cold and hot medium is adjusted to 123°C, and the circulation pump 23 is started to make the introduced dimethyl terephthalate solution circulate in the falling film crystallizer 22.

[0120] Crystallization steps: First, cool the solution to 140℃ at a rate of 4℃ / min, then cool it to 120℃ at a rate of 0.4℃ / min. Control the crystallization time to 90min. Turn off the circulation pump 23, open the switch valve on the connecting pipeline between the feed port of the falling film crystallizer 22 and the mother liquor tank 42, and discharge the mother liquor to the mother liquor tank 42 through the centrifugal pump 41.

[0121] Sweating steps: First, heat the solution to 132°C at a rate of 4°C / min, then heat it to 140°C at a rate of 0.4°C / min. Adjust the temperature of the hot and cold medium to 148°C and control the sweating time to 45 minutes. After sweating is completed, open the switch valve on the connecting pipeline between the feed port of the falling film crystallizer 22 and the residual liquid tank 43, and discharge the sweating liquid to the residual liquid tank 43 through the centrifugal pump 41.

[0122] Melting step: Adjust the temperature of the hot and cold medium to 153℃ to melt the crystallized product, control the melting time to 30min. After melting is completed, open the switch valve on the connecting pipeline between the feed port of the falling film crystallizer 22 and the product tank 44. The obtained crystallized product is sent into the product tank 44 through the centrifugal pump 41, and 19.5g of dimethyl terephthalate is obtained from the dimethyl terephthalate outlet B.

[0123] The purity of dimethyl terephthalate was measured to be 99.98% from the sample.

[0124] Example 3

[0125] Adopting such Figure 1 The production system shown produces dimethyl terephthalate, and the specific steps are as follows:

[0126] 16.6g of terephthalic acid and 12.5ml of 98wt% methanol solution (using water as solvent) are added to static mixer 11 through terephthalic acid inlet A1 and methanol inlet A2, respectively. 6.8g of zinc chloride is sent to static mixer 11 through catalyst inlet C by multiphase flow pump 13 to mix with terephthalic acid and methanol solution.

[0127] The temperature of the first-stage differential side-flow reactor 1201, the second-stage differential side-flow reactor 1202, and the third-stage differential side-flow reactor 1203 are adjusted to 300℃, and the pressure is adjusted to 2.5MPa. The switch valve on the connecting pipeline between the static mixer 11 and the first-stage differential side-flow reactor 1201 is opened, and a mixed solution of terephthalic acid, methanol, and zinc chloride is sent into the first-stage differential side-flow reactor 1201. Terephthalic acid and methanol undergo esterification reaction under the catalysis of zinc chloride. The reaction is carried out for 1 hour to obtain a reaction solution containing dimethyl terephthalate, terephthalic acid, methanol, and water.

[0128] Subsequently, the valves on the connecting pipes between the first-stage differential side-flow reactor 1201 and the second-stage differential side-flow reactor 1202, and between the second-stage differential side-flow reactor 1202 and the third-stage differential side-flow reactor 1203, are opened sequentially. The reaction liquid is fed into the second-stage differential side-flow reactor 1202 and the third-stage differential side-flow reactor 1203, and circulates in the loop of the reaction unit. This allows the unreacted terephthalic acid and methanol to continue reacting for 2 hours under the catalysis of zinc chloride, resulting in a crude dimethyl terephthalate esterification liquid containing dimethyl terephthalate, methanol, water, and other components. The content of each component includes: dimethyl terephthalate 82 wt%, water approximately 9 wt%, methanol approximately 8 wt%, and other components approximately 1 wt%.

[0129] Next, the switch valve between the feed port of the third-stage differential side-flow reactor 1203 and the static crystallizer 21 is opened, and the crude dimethyl terephthalate esterification liquid is fed into the static crystallizer 21 for static crystallization. Static crystallization includes crystallization and sweating steps, specifically:

[0130] Crystallization step: Cool down to 45℃ at a rate of 10℃ / min, and control the crystallization time to 50min;

[0131] Sweating procedure: Increase the temperature to 135℃ at a rate of 10℃ / min, and control the sweating time to 20min;

[0132] After the sweating step was completed, the temperature was increased to 160°C at a rate of 1°C / min to obtain a dimethyl terephthalate solution. The components included: dimethyl terephthalate 96.5 wt%, water 2.2 wt%, and methanol 1.3 wt%. After static crystallization, most of the methanol was separated from the esterification solution.

[0133] Open the valve on the connecting pipeline between the mother liquor outlet of the static crystallizer 21 and the distillation column 31. The crystallization mother liquor containing water and methanol is sent into the distillation column 31 for distillation to obtain methanol. The methanol is collected by the recovery tank 32 and sent back to the static mixer 11 as raw material for esterification reaction. The distillation residue is sent back to the static crystallizer 21, and the distillation condensate is discharged at the same time.

[0134] Then, the valve on the connecting pipe between the static crystallizer 21 and the falling film crystallizer 22 is opened, and the obtained dimethyl terephthalate solution is introduced into the falling film crystallizer 22 for melt crystallization. The melt crystallization includes crystallization, sweating, and melting steps, specifically:

[0135] Equipment preheating: A 96.5 wt% dimethyl terephthalate solution to be treated is introduced into the falling film crystallizer 22. The falling film crystallizer 22 and the heat pump system are started, the temperature of the cold and hot medium is adjusted to 120°C, and the circulation pump 23 is started to make the introduced dimethyl terephthalate solution circulate in the falling film crystallizer 22.

[0136] Crystallization process: First, cool the solution to 145°C at a rate of 5°C / min, then cool it to 125°C at a rate of 0.5°C / min. Control the crystallization time to 90 min. Turn off the circulation pump 23, open the switch valve on the connecting pipeline between the discharge port of the falling film crystallizer 22 and the mother liquor tank 42, and discharge the mother liquor to the mother liquor tank 42 through the centrifugal pump 41.

[0137] Sweating process: First, heat the solution to 133℃ at a rate of 5℃ / min, then heat it to 141℃ at a rate of 0.5℃ / min. Adjust the temperature of the hot and cold medium to 150℃ and control the sweating time to 40min. After sweating is completed, open the switch valve on the connecting pipeline between the feed port of the falling film crystallizer 22 and the residual liquid tank 43, and discharge the sweating liquid to the residual liquid tank 43 through the centrifugal pump 41.

[0138] Melting process: Adjust the temperature of the hot and cold medium to 155℃ to melt the crystallized product, control the melting time to 25min. After melting is completed, open the switch valve on the connecting pipeline between the feed port of the falling film crystallizer 22 and the product tank 44. The obtained crystallized product is sent into the product tank 44 through the centrifugal pump 41, and 19.4g of dimethyl terephthalate is obtained from the dimethyl terephthalate outlet B.

[0139] The purity of dimethyl terephthalate was measured to be 99.95% from the sample.

[0140] Example 4

[0141] Adopting such Figure 1 The production system shown produces dimethyl terephthalate, and the specific steps are as follows:

[0142] 16.6g of terephthalic acid and 12.5ml of 98wt% methanol solution (using water as solvent) are added to static mixer 11 through terephthalic acid inlet A1 and methanol inlet A2, respectively. 6.8g of zinc chloride is sent to static mixer 11 through catalyst inlet C by multiphase flow pump 13 to mix with terephthalic acid and methanol solution.

[0143] The temperature of the first-stage differential side-flow reactor 1201, the second-stage differential side-flow reactor 1202, and the third-stage differential side-flow reactor 1203 are adjusted to 250℃, and the pressure is adjusted to 2.5MPa. The switch valves on the connecting pipelines between the static mixer 11 and each stage of the differential side-flow reactor are opened, and a mixed solution of terephthalic acid, methanol, and zinc chloride is fed into the first-stage differential side-flow reactor 1201, the second-stage differential side-flow reactor 1202, and the third-stage differential side-flow reactor 1203, respectively. Terephthalic acid and methanol undergo esterification under the catalysis of zinc chloride. The reaction is carried out for 1 hour to obtain a reaction solution containing dimethyl terephthalate, terephthalic acid, methanol, and water.

[0144] Subsequently, the switch valves on the connecting pipeline between the outlet of each stage of the differential side-flow reactor and the multiphase flow pump 13 are opened, and the reaction liquid circulates in the loop of the reaction unit, allowing the unreacted terephthalic acid and methanol to continue reacting for 2 hours under the catalysis of zinc chloride, resulting in a crude dimethyl terephthalate esterification liquid containing dimethyl terephthalate, methanol, water, and other components. The content of each component includes: dimethyl terephthalate 84wt%, water approximately 8wt%, methanol approximately 7wt%, and others approximately 1wt%.

[0145] Next, the switch valve between the outlet of each stage of the differential side-flow reactor and the feed port of the static crystallizer 21 is opened, and the crude dimethyl terephthalate esterification liquid is sent into the static crystallizer 21 and the falling film crystallizer 22 for static crystallization and falling film crystallization. The steps of the static crystallization process and the falling film crystallization process are the same as those in Example 1.

[0146] After the static crystallization process and the falling film crystallization process are completed, 19.4g of dimethyl terephthalate is obtained.

[0147] The purity of dimethyl terephthalate was measured to be 99.97% from the sample.

[0148] In the above embodiments, the purity of dimethyl terephthalate was detected using gas chromatography-mass spectrometry.

[0149] In the static crystallization and falling film crystallization processes described in the above embodiments, the heat pump system collects the heat dissipated by the static crystallizer 21 during the cooling process of the crystallization step in the static crystallization process and transfers it to the falling film crystallizer 22 for the heating stage of the sweating and melting steps in the melt crystallization process. Correspondingly, the heat pump system also collects the heat dissipated by the static crystallizer 22 during the cooling process of the crystallization step in the melt crystallization process and transfers it to the static crystallizer 21 for the sweating step and the heating stage after the sweating step in the static crystallization process. Producing and purifying dimethyl terephthalate according to the above embodiments, and scaling up industrial production capacity, results in a 20-25% reduction in purification energy consumption per ton of product compared to the purification energy consumption per ton of product under the distillation process.

[0150] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the invention. Any person skilled in the art can modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by those skilled in the art without departing from the spirit and technical concept disclosed in the present invention should still be covered by the claims of the present invention.

Claims

1. A production system for dimethyl terephthalate, characterized in that: It includes a reaction unit and a purification unit. The reaction unit is the site where the reactants undergo esterification reaction. The reaction unit includes a circulating reactor, which includes several stages of differential side-flow reactors. The purification unit includes a static crystallizer and a falling film crystallizer arranged sequentially along the product production direction. The circulating reactor is connected to the static crystallizer along the product production direction. The circulating reactor is connected in the form of sequential or parallel connections between several stages of differential side-flow reactors. All differential side-flow reactors are equipped with inlets and outlets. The outlet of the last stage differential side-flow reactor is connected to the inlet of the first stage differential side-flow reactor, or the outlets of each stage differential side-flow reactor are connected to the inlets of each stage differential side-flow reactor.

2. The production system according to claim 1, characterized in that: The reaction unit also includes a static mixer, which is used to mix the reaction raw materials uniformly. The static mixer is located on the connecting pipeline between the feed inlet of the first-stage differential side-flow reactor and the discharge outlet of the last-stage differential side-flow reactor or between the discharge outlet and feed inlet of each stage of differential side-flow reactor. The static mixer is provided with a raw material inlet, a raw material outlet and a circulation inlet. The raw material outlet of the static mixer is connected to the feed inlet of the first-stage differential side-flow reactor or each stage of differential side-flow reactor, and the circulation inlet of the static mixer is connected to the discharge outlet of the last-stage differential side-flow reactor or each stage of differential side-flow reactor. And / or, the reaction unit further includes a transfer pump for conveying the catalyst and / or unreacted raw materials from the last stage differential side-flow reactor or each stage differential side-flow reactor to the static mixer, the transfer pump being located on the connecting pipeline between the circulation inlet of the static mixer and the outlet of the last stage differential side-flow reactor or each stage differential side-flow reactor.

3. The production system according to claim 2, characterized in that: The static crystallizer is used to separate and obtain the reaction product after preliminary purification. The static crystallizer is equipped with a feed port, a mother liquor outlet and a material outlet. The feed port of the static crystallizer is connected to the outlet of the last stage differential side-flow reactor or the outlet of each stage differential side-flow reactor.

4. The production system according to claim 3, characterized in that: The falling film crystallizer is used to purify the reaction product after preliminary purification. The falling film crystallizer is provided with a material inlet and a discharge port. The material inlet of the falling film crystallizer is connected to the material outlet of the static crystallizer. The material inlet and discharge port of the falling film crystallizer are connected by a pipeline. And / or, the static crystallizer and the falling film crystallizer are respectively connected to a cooling and heating medium system, and the static crystallizer and the falling film crystallizer are coupled through the cooling and heating medium system.

5. The production system according to claim 4, characterized in that: The production system also includes a distillation and recovery unit, which includes a distillation column and a recovery tank connected together, for distilling the mother liquor discharged from the static crystallizer and recovering excess reaction raw materials. The inlet of the distillation column is connected to the mother liquor outlet of the static crystallizer, the outlet of the distillation column is connected to the inlet of the recovery tank, and the outlet of the recovery tank is connected to the raw material inlet of the static mixer. And / or, the production system further includes a product processing unit, which includes a mother liquor tank, a residual liquor tank, and a product tank. The mother liquor tank is used to recover the mother liquor from molten crystallization, the residual liquor tank is used to recover the sweating liquid from molten crystallization, and the product tank is used to collect the purified reaction products. The inlets of the mother liquor tank, the residual liquor tank, and the product tank are all connected to the feed port of the falling film crystallizer. The outlet of the mother liquor tank is connected to the feed port of the static crystallizer via a pipeline, and the outlet of the residual liquor tank is connected to the material inlet of the falling film crystallizer via a pipeline.

6. A production process for producing dimethyl terephthalate using a production system according to any one of claims 1-5, characterized in that: Includes the following steps: S1. Using terephthalic acid and methanol as raw materials, an esterification reaction is carried out in a circulating reactor under the action of a catalyst. The circulating reactor is a series of differential side-flow reactors connected end to end or in parallel. The esterification reaction of terephthalic acid and methanol is carried out in each stage of differential side-flow reactor. Then, the unreacted terephthalic acid and methanol are circulated in the circulating reactor with the reaction liquid until the esterification reaction is completed, to obtain crude dimethyl terephthalate esterified liquid. S2. The crude dimethyl terephthalate esterification solution obtained in step S1 is placed in a static crystallizer for static crystallization to obtain a preliminarily purified dimethyl terephthalate solution. S3. Place the dimethyl terephthalate solution obtained in step S2 into a falling film crystallizer for melt crystallization to obtain the product dimethyl terephthalate.

7. The production process according to claim 6, characterized in that: The molar ratio of terephthalic acid to methanol is 1:3-6; And / or, the catalyst comprises at least one of tin chloride, tin oxide, zinc chloride, zinc oxide, antimony chloride, and zinc antimony. And / or, the esterification reaction is carried out at a temperature of 250-300°C, a pressure of 2-2.5 MPa, and a time of 3-6 h.

8. The production process according to claim 6, characterized in that: In step S2, the static crystallization includes crystallization and sweating steps. The crystallization step includes cooling to 45-55°C at a rate of 5-10°C / min for a crystallization time of 50-60min. The sweating step includes: raising the temperature to 130-135℃ at a rate of 5-10℃ / min, and the sweating time is 20-30min; Following the sweating step, the method further includes: heating to 150-160°C at a rate of 0.5-1°C / min to obtain a dimethyl terephthalate solution.

9. The production process according to claim 6, characterized in that: In step S3, the melting crystallization includes crystallization, sweating and melting steps. The crystallization step includes: first cooling to 140-145℃ at a rate of 3-5℃ / min, then cooling to 120-125℃ at a rate of 0.3-0.5℃ / min, with a crystallization time of 90-100min. The sweating process includes: first, raising the temperature to 130-133℃ at a rate of 3-5℃ / min, then raising the temperature to 139-141℃ at a rate of 0.3-0.5℃ / min. During the sweating process, the temperature of the hot and cold medium used is 145-150℃, and the sweating time is 40-50 minutes. The melting step is performed at a temperature of 150-155℃ for 25-35 minutes.

Images