CN116099456A - Production system and process of dimethyl terephthalate - Google Patents

Abstract

The invention relates to the technical field of organic synthesis, in particular to a production system and a production process of dimethyl terephthalate. The production system comprises a reaction unit and a purification unit, wherein the reaction unit is a place for carrying out esterification reaction on reaction raw materials, the reaction unit comprises a loop reactor, the loop reactor comprises a plurality of stages of differential side-stream reactors, the purification unit comprises a static crystallizer and a falling film crystallizer which are sequentially arranged along the production direction of a product, and the loop reactor is communicated with the static crystallizer along the production direction of the product. The production process comprises the following steps: taking terephthalic acid and methanol as raw materials, carrying out esterification reaction under the action of a catalyst to obtain crude dimethyl terephthalate esterified liquid, and then carrying out static crystallization and melt crystallization. The production system and the process improve the conversion rate of reactants and the yield of target products, reduce the production energy consumption while ensuring the purity of the products, and are easy to amplify the industrial productivity and realize continuous production.

Description

A kind of production system and technology of dimethyl terephthalate

technical field

The invention relates to the technical field of organic synthesis, in particular to a production system and process of dimethyl terephthalate.

Background technique

Dimethyl terephthalate, also known as 1,4-dimethyl phthalate; DMT; dimethyl terephthalate, molecular formula C ₁₀ H ₁₀ O ₄ , density 1.175g/cm ³ , melting point 140- 143°C, boiling point 288°C, it is a colorless orthorhombic crystal, soluble in hot ethanol, methanol, ether, chloroform, insoluble in water.

Dimethyl terephthalate (DMT) is a polyester monomer, mainly used for synthesizing polyester fibers, resins, films, polyester paints and engineering plastics, etc., and also for the manufacture of polyester films and fibers, and High-strength polyester insulating varnish. The most common use of dimethyl terephthalate is to make fibers for use in fabrics, fishing nets, carpets, tire cords, etc. Polyester film is mainly used as electrical insulation material and film production (such as film film, X-ray film, photo film Chemicalbook and audio tape, video tape, electronic computer tape, etc.). Polyester resins are also used to produce the plasticizer dioctyl terephthalate.

Dimethyl terephthalate is mainly obtained by esterification of terephthalic acid and methanol. For example, in the method disclosed in patent CN104072374A, terephthalic acid and methanol are used as raw materials, and concentrated sulfuric acid is used as a catalyst to carry out esterification reaction to obtain crude dimethyl terephthalate, and methanol is recovered by distillation. Add ethanol to the crude dimethyl terephthalate, add activated carbon or clay to absorb the impurities in the crude product, add styrene anions to remove iron cations in the crude product, and put the crude dimethyl terephthalate into the rectifying tower for separation The dimethyl terephthalate product is obtained. However, using this method and production system to prepare dimethyl terephthalate, the esterification time is very long (10-16h), the consumption of methanol is large, the energy consumption is high, the generation of hazardous waste is large, there are many steps, and the operation is complicated .

A kind of dimethyl terephthalate production method disclosed in the patent CN102219689A, adding tin, zinc, antimonide as catalyst and The methanol solution with a content of 90-99.5wt% is used for esterification reaction. The esterification liquid uses a flash evaporator to complete the separation of methanol and water vapor from the dimethyl terephthalate solution, and then filters it with activated carbon to obtain the dimethyl terephthalate product through rectification. However, this method uses alkali reduction waste water as a raw material to prepare terephthalic acid. Although it is waste utilization, it needs to be discharged by textile printing and dyeing enterprises, and it has limitations in large-scale use. Secondly, the esterified liquid must be filtered with activated carbon before rectification, and this process will generate a large amount of hazardous waste. Subsequent rectification and separation operations are complex and energy-intensive, and flash distillation also produces waste water. The production system used in the above method has the disadvantages of high production energy consumption, large amount of three wastes, and complicated operation steps.

Contents of the invention

In view of this, the object of the present invention is to provide a kind of production system and technique of dimethyl terephthalate, to improve the conversion rate of reactant and the yield of target product, and further improve the yield of dimethyl terephthalate Purity, reduce the production energy consumption of dimethyl terephthalate, reduce the production of three wastes at the same time, shorten the production time, simplify the preparation process, improve production efficiency, and then realize industrial scale-up and continuous production.

In order to achieve the above object and other related objects, in the first aspect, the present invention provides a production system of dimethyl terephthalate, including a reaction unit and a purification unit, and the reaction unit is a place where the reaction raw materials are subjected to an esterification reaction , the reaction unit includes a loop reactor, the loop reactor includes several stages of differential side flow reactors, the purification unit includes a static crystallizer and a falling film crystallizer arranged in sequence along the product production direction, the loop reactor It communicates with the static crystallizer along the product production direction.

Optionally, the connection mode of several stages of differential side flow reactors in the loop reactor is sequentially connected or connected in parallel, and all differential side flow reactors are provided with feed inlets and outlets, and the last stage of differential side flow reactors The discharge port of the flow reactor is connected to the feed port of the first-stage differential side-stream reactor or the discharge port of each stage of differential side-stream reactor is connected to the feed port of each stage of differential side-stream reactor.

Optionally, the reaction unit also includes a static mixer, which is used to mix the reaction raw materials evenly, and the static mixer is located at the feed inlet of the first-stage differential side flow reactor and the last-stage differential side flow reactor. On the connecting pipeline between the outlets of the flow reactors or between the outlets and the inlets of the differential side-flow reactors at all levels, the static mixer is provided with a raw material inlet, a raw material outlet and a circulation inlet, so The raw material outlet of the static mixer is connected to the feed ports of the first-stage differential side-stream reactors or differential side-stream reactors at all levels, and the circulation feed port of the static mixer is connected to the last-stage differential side-stream reactors or each stage of differential side-stream reactors. The discharge port of the differential side flow reactor.

Optionally, the reaction unit also includes a transfer pump, which is used to transfer the catalyst and/or the last stage of differential side flow reactor or the unreacted raw material in each stage of differential side flow reactor to the In the static mixer, the delivery pump is located on the communication pipeline between the circulation inlet of the static mixer and the outlet of the last differential side flow reactor or the differential side flow reactors of each stage.

Optionally, the static crystallizer is used to separate the initially purified reaction product, the static crystallizer is provided with a feeding port, a mother liquor outlet and a material outlet, and the feeding port of the static crystallizer is connected to the last stage differential side flow reaction The outlet of the reactor or the differential side flow reactor at all levels.

Optionally, the falling film crystallizer is used to purify the initially purified reaction product, the falling film crystallizer is provided with a material inlet and a feeding port, and the material inlet of the falling film crystallizer is connected to the static crystallizer The material outlet of the falling film crystallizer is communicated with the material inlet and the discharge port through pipelines.

Optionally, the static crystallizer and the falling film crystallizer are respectively connected with 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 enables the coupling of the static crystallizer and the falling film crystallizer, so that the waste heat of the static crystallizer and the falling film crystallizer can be used mutually, and then the static crystallizer and the falling film crystallizer can be used together. The falling film crystallizer supplies heat energy, thereby saving energy in production.

Optionally, the production system further includes a distillation recovery unit, the distillation recovery unit includes a connected distillation tower and a recovery tank for distilling the mother liquor discharged from the static crystallizer and recovering excess reaction raw materials, the The inlet of the distillation tower is connected to the mother liquor outlet of the static crystallizer, the outlet of the distillation tower 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.

Optionally, the production system also includes a product processing unit, the product processing unit includes a mother liquor tank, a raffinate tank and a product tank, the mother liquor tank is used to recover the mother liquor of molten crystallization, and the raffinate tank is used to recover Melting crystallized sweating liquid, the product tank is used to collect the purified reaction product, the inlets of the mother liquor tank, raffinate tank and product tank are all connected to the feeding port of the falling film crystallizer, and the mother liquor tank The outlet of the said static crystallizer is communicated with the feeding port of the static crystallizer through a pipeline, and the outlet of the raffinate tank is communicated with the material inlet of the falling film crystallizer through a pipeline.

In another aspect, the present invention provides a kind of production technology of dimethyl terephthalate, comprises the following steps:

S1. Using terephthalic acid and methanol as raw materials, the esterification reaction is carried out in a loop reactor under the action of a catalyst. The loop reactor is a series of differential side flow reactors connected in sequence or in parallel. Formic acid and methanol are subjected to esterification reaction in differential side flow reactors at various levels, and then the unreacted terephthalic acid and methanol are circulated in the loop reactor with the reaction solution until the esterification reaction is completed, and crude terephthalic acid is obtained. Dimethyl formate esterification solution;

S2. Place the crude dimethyl terephthalate esterified solution obtained in step S1 in a static crystallizer for static crystallization to obtain a preliminary purified dimethyl terephthalate solution;

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

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

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

Optionally, the temperature of the esterification reaction is 250-300° C., the pressure of the esterification reaction is 2-2.5 MPa, and the time of the esterification reaction is 3-6 hours.

Optionally, the static crystallization includes the steps of crystallization and sweating.

Optionally, the crystallization step includes: cooling down to 45-55°C at a rate of 5-10°C/min, and the crystallization time is 50-60min.

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.

Optionally, after the sweating step, further comprising: raising the temperature to 150-160° C. at a rate of 0.5-1° C./min to obtain a dimethyl terephthalate solution.

Optionally, said melt crystallization comprises the steps of crystallization, sweating and melting.

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

Optionally, the sweating step includes: first raising the temperature to 130-133°C at a rate of 3-5°C/min, and then raising the temperature to 139-141°C at a rate of 0.3-0.5°C/min. The temperature of the cold and heat medium is 145-150°C, and the sweating time is 40-50min.

Optionally, the temperature of the melting step is 150-155° C., and the melting time is 25-35 minutes.

As mentioned above, a kind of production system and technique of dimethyl terephthalate of the present invention have the following beneficial effects:

The production system of the present invention introduces loop reactors, and sets the loop reactors into several stages of differential side flow reactors connected in sequence or in parallel, and all differential side flow reactors are provided with feed ports and discharge ports. In several stages of differential side-flow reactors connected in sequence from end to end, the outlet of the last-stage differential side-stream reactor is connected to the feed port of the first-stage differential side-stream reactor, so that unreacted terephthalic acid and Methanol enters the differential side flow reactor of the next stage to continue the reaction; in several stages of differential side flow reactors connected in parallel, the outlets of the differential side flow reactors of each level are connected to the feed ports of the differential side flow reactors of each level , the mixed terephthalic acid and methanol are divided into different stages of differential side-stream reactors for esterification. Because several stages of differential side-stream reactors in the loop reactor have excellent mass transfer and heat transfer capabilities, the reaction can be avoided. Vigorously release a large amount of reaction heat in a short time, reduce the generation of by-products, and enable the continuous reaction, so that the reaction can be carried out more thoroughly.

The production process of the present invention adopts a production system including a loop reactor, and adopts high temperature and high pressure and uses a specific metal compound as a catalyst to carry out the esterification reaction, which improves the conversion rate of the reactant and the yield of the target product, and improves the safety of the reaction Responsibility shortens the reaction time; and through two purification steps, new solvent impurities are reduced, the process flow is shortened, and the purity of the product dimethyl terephthalate is guaranteed. At the same time, the method has the advantages of low energy consumption, simple operation, The product has the characteristics of high yield and high purity.

By adopting the production system and process of the present invention, the conversion rate of the reactant and the yield of the target product are improved, while ensuring the purity of the product, the production energy consumption is reduced, the process flow is simplified, the production efficiency is improved, and it is easy to enlarge the industrial production capacity and realize continuous production. chemical production.

Description of drawings

Fig. 1 is a structural schematic diagram of a dimethyl terephthalate production system in Example 1-3 of the present invention.

Fig. 2 is a schematic structural diagram of a dimethyl terephthalate production system in Example 4 of the present invention.

Fig. 3 is a structural schematic diagram of the differential side flow reactor used in the dimethyl terephthalate production system in Example 1-4 of the present invention.

Explanation of 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, circulation pump 23, distillation tower 31, recovery tank 32, centrifugal pump 41, mother liquor tank 42, raffinate tank 43, product tank 44, terephthalic acid import A1, methanol import A2, terephthalic acid Dimethyl formate is exported to B, and the catalyst is imported to C.

Detailed ways

Embodiments of the present invention are described below through specific examples, and 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 implementation modes, and various modifications or changes can be made to the details in this specification based on different viewpoints and applications without departing from the spirit of the present invention.

In an embodiment of the present application, a dimethyl terephthalate production system as shown in FIG. 1 is adopted, and the production system includes a reaction unit, a purification unit, a distillation recovery unit and a product treatment unit.

As shown in Figure 1, the reaction unit includes a static mixer 11, a loop reactor and a delivery pump, wherein the loop reactor includes several stages of differential side flow reactors connected successively from end to end as shown in Figure 3, preferably three stages of end to end The differential side flow reactors connected in sequence are respectively 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, and the delivery 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 sequentially connected through pipelines to form a loop.

Specifically, the static mixer 11 is a container for mixing reaction raw materials terephthalic acid and methanol and a catalyst, and the static mixer 11 is provided with a terephthalic acid inlet A1, a methanol inlet A2, a raw material outlet and a circulation feed port, through A terephthalic acid inlet A1 and a methanol inlet A2 enable feeding terephthalic acid and methanol into the static mixer 11 . The raw material outlet of the static mixer 11 is connected to the feed port of the first-stage differential side-flow reactor 1201 , so that the homogeneously mixed terephthalic acid, methanol and catalyst enter the first-stage differential side-flow reactor 1201 through the pipeline.

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 places where terephthalic acid and methanol undergo esterification reactions, and the differential side flow reactors at each stage The flow reactors are all provided with a feed port and a feed port, and the feed port of the third-stage differential side-stream reactor 1203 is connected to the feed port of the first-stage differential side-stream reactor 1201 .

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, raw materials terephthalic acid and methanol are in catalyst (such as tin chloride, zinc chloride ) under the catalysis of the esterification reaction, terephthalic acid and methanol first carried out the esterification reaction in the first-stage differential side flow reactor 1201, and then the unreacted terephthalic acid and methanol enter the next step with the reaction solution Continue the esterification reaction in the differential side flow reactor, and circulate in the loop of the reaction unit until the end of the esterification reaction to obtain the esterification liquid of crude dimethyl terephthalate.

Specifically, the dimethyl terephthalate production system of this embodiment introduces the first-stage differential side-stream reactor 1201, the second-stage differential side-stream reactor 1202, and the third-stage differential side-stream reactor connected in sequence from end to end. Device 1203, because the differential side flow reactor has excellent mass transfer and heat transfer capabilities, it can reduce the heat of reaction, reduce by-products, make the reaction continuous, and make the reaction more thorough. At the same time, the unreacted terephthalic acid and Methanol enters the next-stage differential side-flow reactor to continue the reaction, thereby increasing the conversion rate of the reactant and the yield of the target product.

Specifically, the multiphase flow pump 13 is located on the communication pipeline between the circulation feed port of the static mixer 11 and the feed port of the last stage differential side flow reactor 1203 .

The delivery pump is used to transport the catalyst and/or the unreacted raw material in the final differential side stream reactor to the static mixer, further, the multiphase flow pump 13 is used to transport the catalyst and the third differential side stream reactor The material discharged from the outlet of 1203 is pumped to the static mixer 11 and mixed again, and then sent to the first differential side flow reactor 1201, the second differential side flow reactor 1202 and the third differential side flow reactor 1203 continue the esterification reaction.

Specifically, by setting the multiphase flow pump 13, the catalyst can be sent into the static mixer 11 to mix with the raw materials dimethyl terephthalate and methanol, and the unreacted catalyst in the third stage differential side flow reactor 1203 can also be mixed. The complete dimethyl terephthalate and methanol are transported to the static mixer 11 and mixed evenly to continue the reaction, further improving the conversion rate of the reactant and the efficiency of the esterification reaction.

As shown in Figure 1, the purification unit includes a static crystallizer 21 and a falling film crystallizer 22 arranged in sequence along the product production direction.

Specifically, the upper part of the static crystallizer 21 is provided with a feeding port, and the feeding port is connected to the discharge port of the third-stage differential side flow reactor 1203, and the bottom is provided with a mother liquor outlet and a material outlet, and the mother liquor outlet is connected to the falling film crystallizer 22.

Specifically, by setting the static crystallizer 21 communicated with the third-stage differential side flow reactor 1203, components such as the esterification liquid of crude dimethyl terephthalate, unreacted methanol and water can be separated, and then obtained Preliminarily purified dimethyl terephthalate solution.

Specifically, the falling film crystallizer 22 is a place where the dimethyl terephthalate solution that has been initially separated and purified by the static crystallizer 21 is separated and purified again to remove the water contained in the dimethyl terephthalate solution. and methanol that was not completely removed. The falling film crystallizer 22 is provided with a material inlet and a discharge port, and the material inlet and the discharge port are connected through a pipeline, and a circulation pump 23 is provided on the communication pipeline between the material inlet and the discharge port.

Specifically, by connecting the material inlet and the feeding port of the falling film crystallizer 22, and setting the circulating pump 23 on the connecting pipeline between the material inlet and the feeding port of the falling film crystallizer 22, the p-phthalene can be made The dimethyl formate solution circulates in the falling film crystallizer 22, and then the dimethyl terephthalate is completely crystallized and further purified to improve the purity of the target product dimethyl terephthalate.

Wherein, the static crystallizer 21 and the falling film crystallizer 22 are respectively connected with a cooling and heating medium system, preferably a heat pump system (not shown in the figure).

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 enables the coupling of the static crystallizer 21 and the falling film crystallizer 22, and the static crystallizer 21 and the falling film crystallizer can be connected 22 for mutual utilization of waste heat, 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 in the static crystallization process cools down and transport it to the falling film crystallizer 22 for melt crystallization In the heat-up stage of the sweating step and the melting step in the process, on the contrary, the heat pump system can also collect the heat emitted by the static crystallizer 22 when the crystallization step cools down in the melting crystallization process and transport it to the static crystallizer 21 for static crystallization The sweating step in the process and the warming up phase after the sweating step, thereby saving energy in production.

As shown in FIG. 1 , the distillation recovery unit includes a distillation column 31 and a recovery tank 32 which are connected.

Please continue to refer to FIG. 1 , the inlet of the distillation tower 31 is connected to the mother liquor outlet of the static crystallizer 21 , the outlet of the distillation tower 31 is connected to the inlet of the recovery tank 32 , and the outlet of the recovery tank 32 is connected to the raw material inlet of the static mixer 11 .

Specifically, through the distillation recovery unit, the mother liquor discharged from the static crystallizer 21 can be distilled, and unreacted excess methanol can be recovered, and the methanol can be returned to the reaction unit as a reaction raw material for reuse, so as to improve the utilization rate of methanol. This reduces production losses.

As shown in FIG. 1 , the product processing unit includes a mother liquid tank 42 , a raffinate tank 43 and a product tank 44 .

Please continue to refer to Fig. 1, the mother liquor tank 42, the raffinate tank 43 and the product tank 44 are all connected to the feeding port of the falling film crystallizer 22, and the bottom of the mother liquor tank 42, the raffinate tank 43 and the product tank 44 and the falling film crystallizer 22 A centrifugal pump 41 is arranged on the connecting pipeline between the feed ports, the feeding port of the mother liquid tank 42 and the static crystallizer 21 is communicated through the pipeline (not shown in the figure), and the material inlet of the raffinate tank 43 and the falling film crystallizer 22 is connected through a pipe. connection (not shown in the figure).

Specifically, the mother liquor tank 42 is used to reclaim the mother liquor of molten crystallization, the raffinate tank 43 is used to reclaim the sweating liquid of molten crystallization, and the product tank 44 is used to collect the purified reaction product. Device 21 communicates with residual liquid tank 43 and communicates with falling film crystallizer 22, can reclaim the mother liquor of molten crystallization and carry out static crystallization again, and recover the sweating liquid of molten crystallization and carry out molten crystallization again, and be located in mother liquor tank 42, residue The centrifugal pump 41 on the connecting pipeline between the liquid tank 43 and the product tank 44 and the feeding port of the falling film crystallizer 22 can efficiently transport the reaction product after the falling film crystallizer 22 is separated and purified to the product tank 44 , to increase production efficiency.

On-off valves (not shown in the figure) are all arranged on the above-mentioned communicating pipelines.

In another embodiment of the present application, a dimethyl terephthalate production system as shown in FIG. 2 is adopted, and the production system includes a reaction unit, a purification unit, a distillation recovery unit and a product treatment unit.

As shown in Figure 2, the reaction unit includes a static mixer 11, a loop reactor and a delivery pump, wherein the loop reactor includes several stages of differential side flow reactors connected in parallel as shown in Figure 3, preferably three stages in parallel. The differential side flow reactors are respectively 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 , and the delivery pump is specifically the 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 with the static mixer 11 and the multiphase flow pump 13 through pipelines to form a loop .

Specifically, the static mixer 11 is a container for mixing reaction raw materials terephthalic acid and methanol and a catalyst, and the static mixer 11 is provided with a terephthalic acid inlet A1, a methanol inlet A2, a raw material outlet and a circulation feed port, through A terephthalic acid inlet A1 and a methanol inlet A2 enable feeding terephthalic acid and methanol into the static mixer 11 . The raw material outlet of the static mixer 11 is connected to the feed ports of the differential side-flow reactors at all levels, so that the homogeneously mixed terephthalic acid, methanol and catalysts are divided into the first-stage differential side-flow reactor 1201 and the second-stage differential side-flow reactor 1201 respectively through pipelines. The secondary differential side flow reactor 1202 and the third differential side flow reactor 1203.

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 places where terephthalic acid and methanol undergo esterification reactions, and the differential side flow reactors at each stage The flow reactors are all provided with feed ports and discharge ports, the feed ports of the differential side flow reactors at all levels are all connected, and the feed ports of the differential side flow reactors at all levels are all connected.

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, raw materials terephthalic acid and methanol are in catalyst (such as tin chloride, zinc chloride ) under the catalysis of the esterification reaction, terephthalic acid and methanol esterification reaction in the differential side flow reactor at various levels, and then unreacted terephthalic acid and methanol are circulated to the static mixer 11 with the reaction solution After mixing, enter the different levels of differential side flow reactors again to continue the esterification reaction until the end of the esterification reaction to obtain the esterification liquid of crude dimethyl terephthalate.

Specifically, the dimethyl terephthalate production system of this embodiment introduces the first-stage differential side-stream reactor 1201 connected in parallel, the second-stage differential side-stream reactor 1202 and the third-stage differential side-stream reactor 1203, because the differential side flow reactor has excellent mass transfer and heat transfer capabilities, it can reduce the heat of reaction, reduce by-products, make the reaction continuous, and make the reaction more thorough. At the same time, terephthalic acid and methanol enter the Differential side flow reactors at all levels carry out esterification reaction, which can improve production efficiency and reduce energy consumption.

Specifically, the multiphase flow pump 13 is located on the communication pipeline between the circulation feed port of the static mixer 11 and the feed ports of the differential side flow reactors at each stage.

The transfer pump is used to transfer the catalyst and/or the unreacted raw materials in the last stage differential side flow reactor to the static mixer, further, the multiphase flow pump 13 is used to transfer the catalyst and the first stage differential side flow reactor 1201, the materials discharged from the outlets of the second-stage differential side-stream reactor 1202 and the third-stage differential side-stream reactor 1203 are pumped to the static mixer 11 for re-mixing, and then sent to the first-stage differential side-stream reactor 1201 , the esterification reaction continues in the second-stage differential side-stream reactor 1202 and the third-stage differential side-stream reactor 1203 .

Specifically, by setting the multiphase flow pump 13, the catalyst can be sent into the static mixer 11 to mix with the raw materials dimethyl terephthalate and methanol, and the unreacted Dimethyl terephthalate and methanol are sent to the static mixer 11 to mix uniformly and continue to react, further improving the conversion rate of the reactant and the efficiency of the esterification reaction.

As shown in Figure 2, the purification unit includes a static crystallizer 21 and a falling film crystallizer 22 arranged in sequence along the product production direction.

Specifically, the upper part of the static crystallizer 21 is provided with a feeding port, and the feeding port is connected to the outlets of the differential side flow reactors at all levels, and the bottom is provided with a mother liquor outlet and a material outlet, and the mother liquor outlet is connected to the falling film crystallizer 22 .

Specifically, by installing a static crystallizer 21 connected to the differential side flow reactors at various levels, it is possible to separate components such as the esterification liquid of crude dimethyl terephthalate, unreacted methanol, and water, and then obtain preliminary purification. dimethyl terephthalate solution.

As shown in Figure 2, the settings and functions of the purification unit, distillation recovery unit and product treatment unit are the same as those of the above-mentioned embodiments.

An exemplary embodiment of the present invention provides a kind of production technology that adopts the above-mentioned production system to produce dimethyl terephthalate, comprising the following steps:

S1. Using terephthalic acid and methanol as raw materials, the esterification reaction is carried out in a loop reactor under the action of a catalyst. The loop reactor is a series of differential side flow reactors connected in sequence or in parallel. Formic acid and methanol are subjected to esterification reaction in differential side flow reactors at various levels, and then the unreacted terephthalic acid and methanol are circulated in the loop reactor with the reaction solution until the esterification reaction is completed, and crude terephthalic acid is obtained. Dimethyl formate esterification solution;

S2. Place the crude dimethyl terephthalate esterified solution obtained in step S1 in a static crystallizer for static crystallization to obtain a preliminary purified dimethyl terephthalate solution;

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

In yet another embodiment of the present application, the molar ratio of terephthalic acid to methanol is 1:3-6.

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

Optionally, the temperature of the esterification reaction is 250-300° C., the pressure of the esterification reaction is 2-2.5 MPa, and the time of the esterification reaction is 3-6 hours.

Optionally, the static crystallization includes the steps of crystallization and sweating.

Optionally, the crystallization step includes: cooling down to 45-55°C at a rate of 5-10°C/min, and the crystallization time is 50-60min.

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.

Optionally, after the sweating step, further comprising: raising the temperature to 150-160° C. at a rate of 0.5-1° C./min to obtain a dimethyl terephthalate solution.

Optionally, said melt crystallization comprises the steps of crystallization, sweating and melting.

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

Optionally, the sweating step includes: first raising the temperature to 130-133°C at a rate of 3-5°C/min, and then raising the temperature to 139-141°C at a rate of 0.3-0.5°C/min. The temperature of the cold and heat medium is 145-150°C, and the sweating time is 40-50min.

Optionally, the temperature of the melting step is 150-155° C., and the melting time is 25-35 minutes.

The present invention will be described in detail below through specific exemplary embodiments. It should also be understood that the following examples are only used to specifically illustrate the present invention, and should not be construed as limiting the protection scope of the present invention. Some non-essential improvements and adjustments made by those skilled in the art according to the above contents of the present invention all belong to this invention. protection scope of the invention. The specific process parameters and the like in the following examples are only examples of the appropriate range, that is, those skilled in the art can make a selection within the appropriate range through the description herein, and are not limited to the specific values exemplified below.

Example 1

Adopt production system as shown in Figure 1 to produce dimethyl terephthalate, concrete steps are as follows:

Add 16.6g terephthalic acid and 12.5ml concentration of 98wt% methanol solution (using water as solvent) in the static mixer 11 through the terephthalic acid inlet A1 and the methanol inlet A2 respectively, through the catalyst inlet C by multiphase flow Pump 13 sends 6.8 g of zinc chloride into static mixer 11 to mix with terephthalic acid and methanol solution.

Adjust the temperature of the first-stage differential side-stream reactor 1201, the second-stage differential side-stream reactor 1202 and the third-stage differential side-stream reactor 1203 to 250° C., the pressure to 2.5 MPa, and turn on the static mixer 11 and the second differential side-stream reactor. The on-off valve on the connecting pipeline between the primary differential side flow reactor 1201, the mixed solution of terephthalic acid, methanol and zinc chloride is sent into the first stage differential side flow reactor 1201, terephthalic acid and Methanol is subjected to an esterification reaction under the catalysis of zinc chloride for 2 hours to obtain a reaction solution containing dimethyl terephthalate, terephthalic acid, methanol and water.

Subsequently, the connecting pipeline between the first-stage differential side-stream reactor 1201 and the second-stage differential side-stream reactor 1202 and the connection between the second-stage differential side-stream reactor 1202 and the third-stage differential side-stream reactor 1203 are opened in sequence. The switching valve on the connecting pipeline between them, the reaction solution is sent into the second-stage differential side-stream reactor 1202 and the third-stage differential side-stream reactor 1203, and circulates in the loop of the reaction unit to make the unreacted The terephthalic acid and methanol continue to react for 4h under the catalysis of zinc chloride to obtain the thick dimethyl terephthalate esterification solution containing dimethyl terephthalate, methanol, water and other components. The component content includes: 82wt% of dimethyl terephthalate, about 9wt% of water, about 8wt% of methanol, and about 1wt% of others.

Then, open the switching valve between the third-stage differential side flow reactor 1203 and the feeding port of the static crystallizer 21, and the crude dimethyl terephthalate esterification liquid is sent into the static crystallizer 21 for static crystallization, Static crystallization includes crystallization and sweating steps, specifically:

Crystallization step: cool down to 45°C at a rate of 5°C/min, and control the crystallization time to 60min;

Sweating step: heat up to 130°C at a rate of 5°C/min, and control the sweating time to 30 minutes;

After the sweating step is completed, the temperature is raised to 155° C. at a rate of 0.5° C./min to obtain a dimethyl terephthalate solution. The content of each component includes: 97 wt % of dimethyl terephthalate, 2 wt % of water, and 1 wt % of methanol . After the static crystallization is completed, most of the methanol is separated from the esterification solution.

Open the switch valve on the connecting pipeline between the mother liquor outlet of the static crystallizer 21 and the distillation tower 31, and the crystallization mother liquor containing water and methanol is sent in the distillation tower 31 for distillation to obtain methanol, which is collected by the recovery tank 32 Send back to the static mixer 11 as raw material for esterification reaction, return the distillation raffinate to the static crystallizer 21, and discharge the distillation condensed water at the same time.

Then, open the on-off valve on the connecting pipeline between the static crystallizer 21 and the falling film crystallizer 22, the dimethyl terephthalate solution obtained is passed in the falling film crystallizer 22 to carry out melt crystallization, melt crystallization comprises crystallization , sweating and melting steps, specifically:

Equipment preheating: pass the dimethyl terephthalate solution with a purity of 97wt% into the falling film crystallizer 22, start the falling film crystallizer 22 and the heat pump system, adjust the temperature of the cold and heat medium to 120°C, and start the cycle Pump 23, the dimethyl terephthalate solution that passes into is circulated in falling film crystallizer 22;

Crystallization step: first lower the temperature of the solution to 145°C at a rate of 3°C/min, then cool down to 125°C at a rate of 0.3°C/min, control the crystallization time to 100min, turn off the circulation pump 23, and open the bottom of the falling film crystallizer 22 The switch valve on the connecting pipeline between the feed port and the mother liquor tank 42 discharges the mother liquor to the mother liquor tank 42 through the centrifugal pump 41;

Sweating step: first raise the temperature of the solution to 133°C at a rate of 3°C/min, then raise the temperature to 139°C at a rate of 0.3°C/min, adjust the temperature of the cooling and heating medium to 145°C, and control the sweating time to 50 minutes. After sweating is completed , open the switch valve on the connecting pipeline between the feeding port of the falling film crystallizer 22 and the raffinate tank 43, and the sweating liquid is discharged to the raffinate tank 43 through the centrifugal pump 41;

Melting step: adjust the temperature of the cooling and heating medium to 150°C to melt the crystallized product, and control the melting time to 35 minutes. After the melting is completed, open the on-off valve on the connecting pipeline between the feeding port of the falling film crystallizer 22 and the product tank 44, The crystallized product obtained is sent into the product tank 44 through the centrifugal pump 41, and 19.3 g of the product dimethyl terephthalate is obtained from the outlet B of the dimethyl terephthalate.

The purity of dimethyl terephthalate was determined to be 99.96% by sampling.

Example 2

Adopt production system as shown in Figure 1 to produce dimethyl terephthalate, concrete steps are as follows:

Add 16.6g terephthalic acid and 12.5ml concentration of 98wt% methanol solution (using water as solvent) in the static mixer 11 through the terephthalic acid inlet A1 and the methanol inlet A2 respectively, through the catalyst inlet C by multiphase flow Pump 13 sends 6.8 g of zinc chloride into static mixer 11 to mix with terephthalic acid and methanol solution.

Adjust the temperature of the first-stage differential side-stream reactor 1201, the second-stage differential side-stream reactor 1202 and the third-stage differential side-stream reactor 1203 to 280° C. and the pressure to 2.3 MPa, and turn on the static mixer 11 and the second differential side-stream reactor. The on-off valve on the connecting pipeline between the primary differential side flow reactor 1201, the mixed solution of terephthalic acid, methanol and zinc chloride is sent into the first stage differential side flow reactor 1201, terephthalic acid and Methanol was subjected to esterification under the catalysis of zinc chloride for 1.5 hours to obtain a reaction solution containing dimethyl terephthalate, terephthalic acid, methanol and water.

Subsequently, the connecting pipeline between the first-stage differential side-stream reactor 1201 and the second-stage differential side-stream reactor 1202 and the connection between the second-stage differential side-stream reactor 1202 and the third-stage differential side-stream reactor 1203 are opened in sequence. The switching valve on the connecting pipeline between them, the reaction solution is sent into the second-stage differential side-stream reactor 1202 and the third-stage differential side-stream reactor 1203, and circulates in the loop of the reaction unit to make the unreacted The terephthalic acid and methanol continue to react for 3h under the catalysis of zinc chloride to obtain the thick dimethyl terephthalate esterification solution containing dimethyl terephthalate, methanol, water and other components. The component content includes: 82wt% of dimethyl terephthalate, about 9wt% of water, about 8wt% of methanol, and about 1wt% of others.

Then, open the switching valve between the third-stage differential side flow reactor 1203 and the feeding port of the static crystallizer 21, and the crude dimethyl terephthalate esterification liquid is sent into the static crystallizer 21 for static crystallization, Static crystallization includes crystallization and sweating steps, specifically:

Crystallization step: cool down to 50°C at a rate of 8°C/min, and control the crystallization time to 55min;

Sweating step: heat up to 133°C at a rate of 8°C/min, and control sweating time to 25 minutes;

After the sweating step is completed, the temperature is raised to 155° C. at a rate of 0.8° C./min to obtain a dimethyl terephthalate solution. The content of each component includes: 97.5 wt % of dimethyl terephthalate, 1.8 wt % of water, methanol 0.7 wt%. After the static crystallization is completed, most of the methanol is separated from the esterification solution.

Open the switch valve on the connecting pipeline between the mother liquor outlet of the static crystallizer 21 and the distillation tower 31, and the crystallization mother liquor containing water and methanol is sent into the distillation tower 31 for distillation to obtain methanol, which is collected by the recovery tank 32 Send back to the static mixer 11 as raw material for esterification reaction, return the distillation raffinate to the static crystallizer 21, and discharge the distillation condensed water at the same time.

Then, open the on-off valve on the connecting pipeline between the static crystallizer 21 and the falling film crystallizer 22, the dimethyl terephthalate solution obtained is passed in the falling film crystallizer 22 to carry out melt crystallization, melt crystallization comprises crystallization , sweating and melting steps, specifically:

Equipment preheating: pass the dimethyl terephthalate solution to be treated with a purity of 97.5wt% into the falling film crystallizer 22, start the falling film crystallizer 22 and the heat pump system, adjust the temperature of the cold and heat medium to 123°C, and start Circulation pump 23, the dimethyl terephthalate solution that passes into circulates in falling film crystallizer 22;

Crystallization step: first cool down the solution to 140°C at a rate of 4°C/min, then cool down to 120°C at a rate of 0.4°C/min, control the crystallization time to 90min, turn off the circulating pump 23, and open the bottom of the falling film crystallizer 22 The switch valve on the connecting pipeline between the feed port and the mother liquor tank 42 discharges the mother liquor to the mother liquor tank 42 through the centrifugal pump 41;

Sweating step: first raise the temperature of the solution to 132°C at a rate of 4°C/min, then raise the temperature to 140°C at a rate of 0.4°C/min, adjust the temperature of the cooling and heating medium to 148°C, and control the sweating time to 45 minutes. , open the switch valve on the connecting pipeline between the feeding port of the falling film crystallizer 22 and the raffinate tank 43, and the sweating liquid is discharged to the raffinate tank 43 through the centrifugal pump 41;

Melting step: adjust the temperature of the cooling and heating medium to 153° C. to melt the crystallized product, and control the melting time to 30 minutes. After the melting is completed, open the switch valve on the connecting pipeline between the feeding port of the falling film crystallizer 22 and the product tank 44, The crystallization product that obtains is sent into product tank 44 by centrifugal pump 41, promptly obtains product dimethyl terephthalate 19.5g from outlet B of dimethyl terephthalate.

The purity of dimethyl terephthalate was determined to be 99.98% by sampling.

Example 3

Adopt production system as shown in Figure 1 to produce dimethyl terephthalate, concrete steps are as follows:

Add 16.6g terephthalic acid and 12.5ml concentration of 98wt% methanol solution (using water as solvent) in the static mixer 11 through the terephthalic acid inlet A1 and the methanol inlet A2 respectively, through the catalyst inlet C by multiphase flow Pump 13 sends 6.8 g of zinc chloride into static mixer 11 to mix with terephthalic acid and methanol solution.

Adjust the temperature of the first differential side stream reactor 1201, the second differential side stream reactor 1202 and the third differential side stream reactor 1203 to 300°C, adjust the pressure to 2.5MPa, open the static mixer 11 and the The on-off valve on the connecting pipeline between the primary differential side flow reactor 1201, the mixed solution of terephthalic acid, methanol and zinc chloride is sent into the first stage differential side flow reactor 1201, terephthalic acid and Methanol is subjected to an esterification reaction under the catalysis of zinc chloride for 1 hour to obtain a reaction solution containing dimethyl terephthalate, terephthalic acid, methanol and water.

Subsequently, the connecting pipeline between the first-stage differential side-stream reactor 1201 and the second-stage differential side-stream reactor 1202 and the connection between the second-stage differential side-stream reactor 1202 and the third-stage differential side-stream reactor 1203 are opened in sequence. The switching valve on the connecting pipeline between them, the reaction solution is sent into the second-stage differential side-stream reactor 1202 and the third-stage differential side-stream reactor 1203, and circulates in the loop of the reaction unit to make the unreacted The terephthalic acid and methanol continue to react for 2h under the catalysis of zinc chloride to obtain the crude dimethyl terephthalate esterification solution containing dimethyl terephthalate, methanol, water and other components. The component content includes: 82wt% of dimethyl terephthalate, about 9wt% of water, about 8wt% of methanol, and about 1wt% of others.

Then, open the switching valve between the third-stage differential side flow reactor 1203 and the feeding port of the static crystallizer 21, and the crude dimethyl terephthalate esterification liquid is sent into the static crystallizer 21 for static crystallization, Static crystallization includes crystallization and sweating steps, specifically:

Crystallization step: cool down to 45°C at a rate of 10°C/min, and control the crystallization time for 50 minutes;

Sweating step: heat up to 135°C at a rate of 10°C/min, and control sweating for 20 minutes;

After the sweating step is completed, the temperature is raised to 160° C. at a rate of 1° C./min to obtain a dimethyl terephthalate solution. The content of each component includes: 96.5 wt % of dimethyl terephthalate, 2.2 wt % of water, methanol 1.3 wt%. After the static crystallization is completed, most of the methanol is separated from the esterification solution.

Open the switch valve on the connecting pipeline between the mother liquor outlet of the static crystallizer 21 and the distillation tower 31, and the crystallization mother liquor containing water and methanol is sent in the distillation tower 31 for distillation to obtain methanol, which is collected by the recovery tank 32 Send back to the static mixer 11 as raw material for esterification reaction, return the distillation raffinate to the static crystallizer 21, and discharge the distillation condensed water at the same time.

Then, open the on-off valve on the connecting pipeline between the static crystallizer 21 and the falling film crystallizer 22, the dimethyl terephthalate solution obtained is passed in the falling film crystallizer 22 to carry out melt crystallization, melt crystallization comprises crystallization , sweating and melting steps, specifically:

Equipment preheating: pass the dimethyl terephthalate solution to be treated with a purity of 96.5wt% into the falling film crystallizer 22, start the falling film crystallizer 22 and the heat pump system, adjust the temperature of the cold and heat medium to 120°C, and start Circulation pump 23, the dimethyl terephthalate solution that passes into circulates in falling film crystallizer 22;

Crystallization process: first lower the temperature of the solution to 145°C at a rate of 5°C/min, then cool down to 125°C at a rate of 0.5°C/min, control the crystallization time to 90min, turn off the circulation pump 23, and open the bottom of the falling film crystallizer 22 The switch valve on the connecting pipeline between the feed port and the mother liquor tank 42 discharges the mother liquor to the mother liquor tank 42 through the centrifugal pump 41;

Sweating process: first raise the temperature of the solution to 133°C at a rate of 5°C/min, then raise the temperature to 141°C at a rate of 0.5°C/min, adjust the temperature of the cooling and heating medium to 150°C, and control the sweating time to 40 minutes. After sweating is completed , open the switch valve on the connecting pipeline between the feeding port of the falling film crystallizer 22 and the raffinate tank 43, and the sweating liquid is discharged to the raffinate tank 43 through the centrifugal pump 41;

Melting process: adjust the temperature of the cooling and heating medium to 155°C to melt the crystallized product, and control the melting time to 25 minutes. After the melting is completed, open the on-off valve on the connecting pipeline between the feeding port of the falling film crystallizer 22 and the product tank 44, The crystallization product that obtains is sent into product tank 44 by centrifugal pump 41, promptly obtains product dimethyl terephthalate 19.4g from outlet B of dimethyl terephthalate.

The purity of dimethyl terephthalate was determined to be 99.95% by sampling.

Example 4

Adopt production system as shown in Figure 1 to produce dimethyl terephthalate, concrete steps are as follows:

Add 16.6g terephthalic acid and 12.5ml concentration of 98wt% methanol solution (using water as solvent) in the static mixer 11 through the terephthalic acid inlet A1 and the methanol inlet A2 respectively, through the catalyst inlet C by multiphase flow Pump 13 sends 6.8 g of zinc chloride into static mixer 11 to mix with terephthalic acid and methanol solution.

Adjust the temperature of the first-stage differential side-stream reactor 1201, the second-stage differential side-stream reactor 1202 and the third-stage differential side-stream reactor 1203 to 250° C. and the pressure to 2.5 MPa, and open the static mixer 11 and each The on-off valve on the connecting pipeline between the first-stage differential side-stream reactors, the mixed solution of terephthalic acid, methanol and zinc chloride are respectively sent into the first-stage differential side-stream reactor 1201, the second-stage differential side-stream reaction In device 1202 and third-stage differential side flow reactor 1203, terephthalic acid and methanol carry out esterification reaction under the catalysis of zinc chloride, and react for 1h to obtain dimethyl terephthalate, terephthalic acid , methanol and water and other components of the reaction solution.

Subsequently, the on-off valve on the connecting pipeline between the outlets of the differential side flow reactors at each level and the multiphase flow pump 13 is opened, and the reaction solution circulates in the loop of the reaction unit to make the unreacted terephthalic diphenylene Formic acid and methanol continued to react for 2 hours under the catalysis of zinc chloride to obtain a crude dimethyl terephthalate esterification solution containing dimethyl terephthalate, methanol, water and other components, and the contents of each component included: Dimethyl terephthalate is 84 wt%, water is about 8 wt%, methanol is about 7 wt%, and others are about 1 wt%.

Then, open the on-off valve between the discharge ports of the differential side flow reactors at all levels and the feed port of the static crystallizer 21, the thick dimethyl terephthalate esterification liquid is sent into the static crystallizer 21 and the falling film crystallizer In the device 22, static crystallization and falling film crystallization are carried out, and the steps of the static crystallization process and the falling film crystallization process are all the same as in Embodiment 1.

After the static crystallization process and the falling film crystallization process were completed, 19.4 g of the product dimethyl terephthalate was obtained.

The purity of dimethyl terephthalate was determined to be 99.97% by sampling.

In the above examples, gas chromatography-mass spectrometry was used to detect the purity of dimethyl terephthalate.

In the static crystallization process and the falling film crystallization process in the above embodiments, the heat pump system collects the heat emitted by the static crystallizer 21 when the crystallization step in the static crystallization process cools down and transports it to the falling film crystallizer 22 for melting In the heat-up stage of the sweating step and the melting step in the crystallization process, correspondingly, the heat pump system also collects the heat emitted by the static crystallizer 22 when the crystallization step cools down in the melting crystallization process and transports it to the static crystallizer 21 for static crystallization The sweating step in the process and the warming phase after the sweating step. Produce and purify dimethyl terephthalate according to the method of the above-mentioned embodiment, and carry out industrial production capacity expansion, and the energy consumption of purification per ton of product is 20-25% less than that of purification per ton of product under the rectification process.

The above-mentioned embodiments only illustrate the principles and effects of the present invention, but are not intended to limit the present invention. Anyone skilled in the art can modify or change the above-mentioned embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or changes made by those skilled in the art without departing from the spirit and technical ideas disclosed in the present invention shall still be covered by the claims of the present invention.

Claims (10)

1. a production system of dimethyl terephthalate, it is characterized in that: comprise reaction unit and purification unit, described reaction unit is the place that reaction raw material carries out esterification reaction, described reaction unit comprises loop reactor, so The loop reactor includes several stages of differential side flow reactors, the purification unit includes a static crystallizer and a falling film crystallizer arranged in sequence along the product production direction, and the loop reactor communicates with the static crystallizer along the product production direction. 2. The production system according to claim 1, characterized in that: the connection mode of several stages of differential side flow reactors in the loop reactor is sequentially connected or connected in parallel, and all differential side flow reactors are provided with inlets. Feed port and discharge port, the discharge port of the last stage of differential side flow reactor is connected to the feed port of the first stage of differential side flow reactor or the discharge port of each stage of differential side flow reactor is connected to each stage of differential side flow feed port of the reactor. 3. The production system according to claim 2, characterized in that: the reaction unit also includes a static mixer, the static mixer is used to mix the reaction raw materials evenly, and the static mixer is located in the first stage differential side flow On the connecting pipeline between the feed port of the reactor and the discharge port of the last stage differential side flow reactor or between the feed port and the feed port of each level of differential side flow reactor, the static mixer is provided with Raw material inlet, raw material outlet and circulation feed port, the raw material outlet of the static mixer is connected to the feed port of the first-stage differential side flow reactor or the differential side flow reactor of each stage, and the circulation feed of the static mixer The port is connected to the outlet of the last stage differential side flow reactor or the differential side flow reactors at all levels; The reaction unit also includes a transfer pump, which is used to transfer the catalyst and/or the last-stage differential side-stream reactor or the unreacted raw materials in the differential side-stream reactors of each stage to the static mixer , the delivery pump is located on the communication pipeline between the circulation feed port of the static mixer and the last stage of differential side flow reactor or the outlets of each stage of differential side flow reactor. 4. The production system according to claim 1, characterized in that: the static crystallizer is used for separating and obtaining the reaction product of preliminary purification, and the static crystallizer is provided with a feed inlet, a mother liquor outlet and a material outlet, and the static crystallizer The feeding port of the reactor is connected to the last stage of differential side flow reactor or the output port of each stage of differential side flow reactor. 5. The production system according to claim 4, characterized in that: the falling film crystallizer is used to purify the preliminary purified reaction product, the falling film crystallizer is provided with a material inlet and a feeding port, and the falling film crystallizer The material inlet of the film crystallizer is connected to the material outlet of the static crystallizer, and the material inlet and the feeding port of the falling film crystallizer are connected through pipelines; And/or, the static crystallizer and the falling film crystallizer are respectively connected with a cooling and heating medium system, and the static crystallizer and the falling film crystallizer are coupled through the cooling and heating medium system. 6. production system according to claim 5, is characterized in that: described production system also comprises distillation recovery unit, and described distillation recovery unit comprises the distillation column that communicates and recovery tank, is used for the mother liquor that discharges from static crystallizer Carry out distillation, and reclaim excessive reaction raw material, the inlet of described distillation tower is connected with the mother liquor outlet of described static crystallizer, the outlet of described distillation tower is connected with the inlet of described recovery tank, and the outlet of described recovery tank is connected with all Raw material inlet for the static mixer described above. And/or, the production system also includes a product processing unit, the product processing unit includes a mother liquor tank, a raffinate tank and a product tank, the mother liquor tank is used to reclaim the mother liquor of molten crystallization, and the raffinate tank is used to reclaim Melting crystallized sweating liquid, the product tank is used to collect the purified reaction product, the inlets of the mother liquor tank, raffinate tank and product tank are all connected to the feeding port of the falling film crystallizer, and the mother liquor tank The outlet of the said static crystallizer is communicated with the feeding port of the static crystallizer through a pipeline, and the outlet of the raffinate tank is communicated with the material inlet of the falling film crystallizer through a pipeline. 7. a production system producing dimethyl terephthalate according to any one of claims 1-6, characterized in that: comprising the steps of: S1. Using terephthalic acid and methanol as raw materials, the esterification reaction is carried out in a loop reactor under the action of a catalyst. The loop reactor is a series of differential side flow reactors connected in sequence or in parallel. Formic acid and methanol are subjected to esterification reaction in differential side flow reactors at various levels, and then the unreacted terephthalic acid and methanol are circulated in the loop reactor with the reaction solution until the esterification reaction is completed, and crude terephthalic acid is obtained. Dimethyl formate esterification solution; S2. Place the crude dimethyl terephthalate esterified solution obtained in step S1 in a static crystallizer for static crystallization to obtain a preliminary purified dimethyl terephthalate solution; S3. Place the dimethyl terephthalate solution obtained in step S2 in a falling film crystallizer for melt crystallization to obtain the product dimethyl terephthalate. 8. The production process according to claim 7, characterized in that: the molar ratio of terephthalic acid to methanol is 1:3-6; And/or, the catalyst includes at least one of tin chloride, tin oxide, zinc chloride, zinc oxide, antimony chloride and zinc antimonide; And/or, the temperature of the esterification reaction is 250-300° C., the pressure of the esterification reaction is 2-2.5 MPa, and the time of the esterification reaction is 3-6 hours. 9. The production process according to claim 7, characterized in that: in step S2, the static crystallization includes crystallization and sweating steps, and the crystallization step includes: cooling down to 45-55°C at a rate of 5-10°C/min ℃, the crystallization time is 50-60min; The sweating step includes: heating up to 130-135°C at a rate of 5-10°C/min, and the sweating time is 20-30min; After the sweating step, it also includes: raising the temperature to 150-160° C. at a rate of 0.5-1° C./min to obtain a dimethyl terephthalate solution. 10. The production process according to claim 7, characterized in that: in step S3, the melting and crystallization includes crystallization, sweating and melting steps, and the crystallization step includes: first cooling down to 140-145°C, then cool down to 120-125°C at a rate of 0.3-0.5°C/min, and the crystallization time is 90-100min; The sweating step includes: first raising the temperature to 130-133°C at a rate of 3-5°C/min, and then raising the temperature to 139-141°C at a rate of 0.3-0.5°C/min. The temperature is 145-150°C, and the sweating time is 40-50min; The temperature of the melting step is 150-155° C., and the melting time is 25-35 minutes.

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