Process and device for the microreactor preparation of dibutyl terephthalate

Abstract

The present application relates to a method and device for preparing dibutyl terephthalate by micro-reaction, which continuously passes a mixture of terephthalic acid and n-butanol through a tubular reactor with built-in turbulence components at a certain temperature and pressure in the absence of a catalyst to produce dibutyl terephthalate. The present application uses continuous tubular reaction, and the conversion rate of terephthalic acid is over 99.5% and the selectivity of dibutyl terephthalate is over 90% through esterification. High-purity dibutyl terephthalate is obtained through distillation treatment of the mixed product. The present application can realize continuous esterification of terephthalic acid, has a simple process flow, high product quality, and is suitable for industrial production.

Description

Technical Field

[0001] This invention relates to a method and apparatus for the microreaction preparation of dibutyl terephthalate, belonging to the field of organic chemistry technology. Background Technology

[0002] Aromatic diesters are an important class of organic chemical intermediates, widely used in polymers, plasticizers, and other fields, as well as in the preparation of other fine chemical monomers. Aromatic diacids mainly refer to terephthalic acid, phthalic acid, and isophthalic acid. Through esterification reactions with alcohols, the corresponding diesters are generated. Terephthalic acid esters are an important raw material for the preparation of 1,4-cyclohexanediethanol, including aromatic diesters formed from C1-C4 aliphatic alcohols, such as dimethyl terephthalate, diethyl terephthalate, di(iso)propyl terephthalate, and di-n-(iso)butyl terephthalate.

[0003] There are three main methods for preparing aromatic dicarboxylic esters. The first is the esterification reaction of alcohols and acids in the presence of inorganic acids, such as sulfuric acid. However, this method suffers from equipment corrosion, making large-scale industrial production difficult. The second method is the catalytic esterification reaction of organic acids, such as methanesulfonic acid or methylbenzenesulfonic acid. Although the esterification reaction under acid catalysis proceeds smoothly and the reaction conditions are relatively mild, it is limited by the extremely low solubility of aromatic dicarboxylic acids in alcohols. The reaction process is a heterogeneous solid-liquid two-phase state, resulting in long reaction times, numerous byproducts, and the need to remove residual catalysts, leading to a lengthy product purification process. Under non-catalytic conditions, the autocatalytic effect of the aromatic acid in the raw material can be used to carry out the esterification reaction of acids and alcohols. However, this requires high temperatures and pressures. In particular, the preparation of terephthalic esters is challenging because the very low solubility of terephthalic acid in alcohol solvents necessitates the use of high-pressure reactors at high temperatures and pressures, resulting in long reaction times and excessive byproducts. These drawbacks all affect industrial applications. Aromatic diesters can also be prepared via transesterification, but this method is limited to preparing aromatic diesters of higher alcohols from aromatic diesters of lower alcohols, and usually requires a transesterification catalyst, which has limitations. Therefore, direct esterification of alcohols with acids is the main industrial preparation method.

[0004] Chinese invention patent application publication CN101652343A discloses a method for preparing di-n-butyl terephthalate, which involves esterification of terephthalic acid and n-butanol in a high-pressure reactor in the presence of an acidic catalyst. The reaction time is long (5-16 hours) and produces many byproducts. CN111132957A discloses a method for preparing terephthalic acid esters, which uses an acidic catalyst to carry out the esterification reaction of terephthalic acid and n-butanol in a high-pressure reactor for 3-5 hours. The mixed product needs to be neutralized with alkali, but the reaction inevitably produces dibutyl ether byproducts, which increases the consumption of raw alcohol and results in a product with a high acid value. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of current discontinuous reaction processes in the preparation of terephthalic acid esters, such as long reaction times and numerous byproducts. This invention employs a continuous tubular reaction, achieving a terephthalic acid conversion rate exceeding 99.5% and a dibutyl terephthalate selectivity exceeding 90% through esterification. High-purity dibutyl terephthalate is obtained through distillation of the mixed products. Under non-catalytic conditions, by enhancing reaction conditions, the reaction time at high temperatures is significantly reduced, byproduct formation is minimized, and post-processing purification is simplified, offering advantages for large-scale industrial application. This invention enables continuous esterification of terephthalic acid, with a simple process flow, high product quality, and suitability for industrial production.

[0006] The present invention provides a method for preparing dibutyl terephthalate using a continuous microreaction method. Raw materials containing terephthalic acid and C2-C6 low-carbon alcohols are continuously fed into a tubular microreactor to undergo esterification. The conditions for the esterification reaction include: a reaction temperature of 250-350°C and a reaction pressure of 10.0-20.0 MPa.

[0007] Optionally, the esterification reaction temperature is 300–350°C and the esterification reaction pressure is 10.0–18.0 MPa.

[0008] Optionally, the reaction residence time of the raw material in the tubular microreactor is 80 to 150 seconds.

[0009] Optionally, the mass concentration of terephthalic acid in the raw material is 5% to 20%, preferably 5% to 15%;

[0010] Optionally, the C2-C6 lower alcohol is n-butanol.

[0011] Optionally, the esterification reaction is carried out under catalyst-free conditions.

[0012] Optionally, the raw material is nano-ground (grinding particle size to 20-100 micrometers) to obtain an emulsion, which is used as the esterification raw material solution.

[0013] Optionally, the method includes the following steps:

[0014] (1) The esterification feed liquid is continuously passed through a tubular microreactor for esterification reaction, and the resulting reaction mixture I is separated from the water in the reaction mixture I to obtain a primary esterification liquid.

[0015] (2) The primary esterification liquid is continuously passed through a tubular microreactor for a secondary esterification reaction. The reaction mixture II is separated as described above (i.e., azeotropic distillation separation in (1)) and (the bottom of the distillation vessel) to obtain a product containing dibutyl terephthalate.

[0016] Optionally, the primary esterification liquid is cooled before separation, preferably to 20°C to 30°C.

[0017] Optionally, the separation is azeotropic distillation. Preferably, the separation involves cooling the reaction mixture I to room temperature and then pumping it into a distillation vessel equipped with a packed column, condenser, and water separator for azeotropic distillation at atmospheric pressure. The temperature in the bottom of the column is 130–145°C. The gas phase containing water and C2–C6 low-carbon alcohols (preferably n-butanol) is separated in a packed column filled with wire mesh. The temperature at the top of the column is controlled at 112–117°C. The esterification reaction byproducts water and a small amount of butanol are collected from the top of the column. After being cooled by the condenser, an upper oil phase (C2–C6 low-carbon alcohols) and a lower water phase are formed in the water separator. The oil phase is refluxed to the distillation vessel, and the water phase is discharged. The bottom of the column yields a primary esterification liquid (the main components of which are the product terephthalate, the intermediate product p-carboxybenzoate, and the unreacted raw material terephthalic acid).

[0018] Optionally, the primary esterification solution is subjected to cooling and azeotropic distillation to remove water, and then undergoes multiple tubular microchannel esterification reactions until the esterification reaction is complete.

[0019] On the other hand, the present invention provides a tubular continuous esterification microreactor for preparing dibutyl terephthalate, characterized in that the apparatus includes a solvent supply end, a raw material supply end, a tubular microreactor, a condenser, a condenser, and a receiving tank; the tubular microreactor has an inlet and an outlet; the solvent supply end and the raw material supply end are respectively connected to the inlet; the outlet, the condenser, the condenser, and the receiving tank are sequentially connected; and a flow-turbing element is provided inside the reaction tube of the tubular microreactor.

[0020] Optionally, the inner diameter of the reaction tube in the tubular microreactor is 4 to 10 mm; preferably, the volumetric porosity of the reaction tube is 75% to 90%.

[0021] Optionally, the reaction tube consists of a preheating section reaction tube and a reaction section reaction tube; preferably, the preheating section reaction tube and the reaction section reaction tube each have independent temperature control components.

[0022] Optionally, the turbulence-inducing element extends through the preheating section reaction tube and the reaction section reaction tube.

[0023] Optionally, the agitator is a spiral metal perforated plate; preferably, the agitator has a thickness of 0.5-0.3-1.0 mm, a hole diameter of 0.8-1.5 mm, and an opening area ratio of 40%-55%.

[0024] Optionally, the spiral metal orifice plate is spirally twisted along the pipe diameter direction.

[0025] Optionally, the spiral metal perforated plate is twisted 90 degrees at every 8-16 mm along its length, forming a twisted shape.

[0026] Optionally, the spiral metal perforated plate has a width of a and is twisted 90 degrees at a position 2a along its length.

[0027] Optionally, the feed inlet of the tubular microreactor is equipped with a high-pressure metering pump.

[0028] Optionally, the outlet of the tubular microreactor is equipped with a back pressure valve.

[0029] Optionally, the mixture collected in the condenser and the solvent collected in the receiving tank are mixed and then recycled into the tubular reactor for esterification.

[0030] Terephthalic acid has very low solubility in alcohol solvents, and the esterification reaction of terephthalic acid as a raw material is generally a heterogeneous batch reaction with low mass transfer efficiency. Even under catalytic conditions, the reaction rate is slow, the reaction time is long, and there are many by-products. To accelerate the reaction process, it is necessary to enhance the reaction conditions. This invention uses a microchannel reaction process to enhance the mass transfer in the reaction process, which can effectively solve the shortcomings of conventional esterification reaction processes, greatly shorten the reaction time, reduce the formation of by-products, and improve product quality. For the esterification reaction of terephthalic acid and butanol, the tubular reaction technology, under non-catalytic conditions, can effectively reduce the reaction time, reduce the occurrence of side reactions, simplify the separation and purification process, reduce the manufacturing cost of dibutyl terephthalate, and realize large-scale industrial production. Attached Figure Description

[0031] Figure 1 Schematic diagram of tubular continuous esterification reactor and process flow;

[0032] Figure 2 Simplified structural diagram of a tubular reactor and schematic diagram of its built-in turbulence-inducing components;

[0033] Figure 3 Simplified structural diagram of a tubular reactor and 3D view of its built-in turbulence-inducing components;

[0034] Figure 4 3D view of the spiral torsion of the built-in aerodynamic component;

[0035] In the diagram, 1 is the solvent storage tank, 2 is the raw material storage tank, 3 is the high-pressure metering pump, 4 is the preheating section reaction tube, 5 is the reaction section reaction tube, 6 is the back pressure valve, 7 is the first condenser, 8 is the receiving tank, 9 is the discharge pump, 10 is the atmospheric distillation kettle, 11 is the packing column, 12 is the second condenser, 13 is the water separator, 14 is the reaction tube, and 15 is the metal orifice plate. Detailed Implementation

[0036] To provide a clearer understanding of the technical features, objectives, and effects of this invention, the technical solutions of this invention are illustrated through the following embodiments and comparative embodiments, but these are not intended to limit the scope of implementation.

[0037] In one embodiment, the present invention uses terephthalic acid and n-butanol for esterification under non-catalytic conditions. The reaction uses a stainless steel tube with an inner diameter of 6 mm as a reactor. The tube is equipped with a pre-set flow-turbulence component with a specific structure. The terephthalic acid and n-butanol are ground and prepared into an emulsion with a mass concentration of 5-20%. The emulsion is then introduced into the tubular reactor under the action of a high-pressure metering pump. The esterification reaction is carried out rapidly under certain temperature and pressure to reach reaction equilibrium. After cooling, the composition of the mixed product is analyzed.

[0038] The tubular reaction apparatus used in this invention includes the following components: a high-pressure metering pump, a tubular reactor with an electric heating element, a reaction tube with an inner diameter of 6 mm, a preheating section tube with a length of 1000 mm, a reaction section tube with a length of 8000 mm, and a pre-installed 0.5 mm thick and 5.9 mm wide twisted ribbon-shaped stainless steel perforated plate with a diameter of 1 mm along its length. The twisted ribbon-shaped stainless steel perforated plate penetrates the reaction tube, with an orifice opening rate of 46%. A back pressure valve is installed at the outlet of the tubular reactor to control the reaction pressure. Under the action of the high-pressure metering pump, the reaction liquid rapidly passes through the reaction tube, generating turbulence under the action of the packing material inside the tube, thereby enhancing mass transfer and heat transfer, promoting the esterification reaction, and rapidly reaching reaction equilibrium. Under the control of the back pressure valve, the product is discharged from the reactor, cooled by a condenser, and enters an esterification product storage tank. The esterification product is filtered to remove unreacted raw material terephthalic acid, dried, weighed, and the single-pass conversion rate is calculated. The composition of the filtrate is analyzed.

[0039] The reaction process includes the following steps:

[0040] 1. Preparation of raw material solution

[0041] Terephthalic acid is a powdered solid particle. It is mixed with alcohol in a specified mass ratio, and then ground in a high-speed grinder at room temperature to obtain a homogeneous emulsion, which is used as a reaction raw material.

[0042] 2. Esterification reaction

[0043] At room temperature, n-butanol is pumped into the tubular reactor at a set flow rate by a high-pressure feed pump. The back pressure valve is adjusted to 10.0-20.0 MPa. Under the control of the back pressure valve, n-butanol enters the collection tank through the condenser, and a solvent operating state with stable flow rate is formed in the reactor. The reactor is then heated. When the preheating section reaches 250–280°C and the reaction section reaches 280–350°C, the feed valve is switched before the high-pressure feed pump to pump in a prepared feed liquid of a certain mass concentration. The feed liquid undergoes an alcohol-esterification reaction in the preheating and reaction sections. The reaction mixture enters the collection tank through the condenser under the control of the back pressure valve. After filtration, unreacted terephthalic acid is filtered out. After drying, it is weighed, and the reaction conversion rate is calculated. The filtrate is pumped into a distillation vessel equipped with a packed tower and a water separator. Distillation is carried out at atmospheric pressure. Byproduct water is removed by azeotropic distillation. When no more water is discharged from the water separator, a small amount of solvent n-butanol is distilled out to ensure that the esterification product is dehydrated to the maximum extent. The composition of the esterification product in the vessel is analyzed by liquid chromatography to determine the single-pass feed conversion rate and yield. The esterified mixture, from which byproduct water and unreacted terephthalic acid have been removed in the distillation vessel, was then used as raw material for a two-stage esterification reaction according to the esterification reaction process conditions. The esterification reaction effluent mixture was analyzed by liquid chromatography to determine the composition of the mixed product.

[0044] In this embodiment, an Agilent 1260 liquid chromatograph was used as the analytical instrument, and the analytical conditions were as follows:

[0045] Column type: C8

[0046] Wavelength: 220

[0047] Mobile phase: Acetonitrile / water (v / v)

[0048] Flow rate: 0.8 m / min

[0049] The formula for calculating the raw material conversion rate is:

[0050]

[0051]

[0052]

[0053] Note: Terephthalic acid is abbreviated as PTA, and dibutyl terephthalate is abbreviated as DBT.

[0054] Example 1: Tubular Continuous Esterification Reactor

[0055] The tubular continuous esterification reactor includes a solvent storage tank 1, a raw material storage tank 2, a tubular reactor (composed of a preheating section reaction tube 4 and a reaction section reaction tube 5), a first condenser 7, a receiving tank 8, an atmospheric pressure distillation kettle 10, a packing column 11, and a second condenser 12.

[0056] The tubular reactor has an inlet and an outlet; the solvent storage tank 1 and the raw material storage tank 2 are respectively connected to the inlet; the outlet, the first condenser 7, the receiving tank 8, the atmospheric distillation kettle 10, the packing column 11 and the second condenser 12 are connected in sequence.

[0057] The tubular reactor has a spiral metal perforated plate 15 inside the reaction tube 14, which penetrates both the preheating section reaction tube and the reaction section reaction tube. The inner diameter of the reaction tube in the tubular reactor is 6 mm, and the volumetric porosity is 85%. The preheating section reaction tube 4 and the reaction section reaction tube 5 each have independent temperature control components. The feed inlet of the tubular reactor is equipped with a high-pressure metering pump 3, and the discharge outlet of the tubular reactor is equipped with a back pressure valve 6.

[0058] Example 2: Preparation method of terephthalate

[0059] Preparation of raw material solution: Add 500g of terephthalic acid and 4500g of n-butanol to a high-speed grinder, start the motor and grind at room temperature for 40 minutes to form a n-butanol emulsion with a mass concentration of 10% terephthalic acid, which can be used as raw material solution for later use.

[0060] Esterification reaction: The prepared raw material solution and solvent n-butanol (5000g) are added to raw material storage tank 2 and solvent storage tank 1 respectively. The valve of solvent storage tank 1 is opened, and high-pressure metering pump 3 is started, with a flow rate set to 80ml / min. The back pressure valve 6 at the outlet of the tubular reactor is adjusted to 11MPa. The solvent n-butanol enters the tubular reactor under the action of high-pressure metering pump 3. After the solvent stays in the reactor for about 180 seconds, it enters condenser 7 under the control of back pressure valve 6. After condensation, it enters receiving tank 8, forming a solvent cold run for 5-10 minutes. Subsequently, the temperature of preheating section reaction tube 4 and reaction section reaction tube 5 is gradually increased. When the temperature of preheating section reaction tube 4 and reaction section reaction tube 5 reaches 260℃ and 300℃ respectively, the valve of raw material storage tank 2 is switched. The raw material solution enters the tubular reactor through high-pressure metering pump 3, flowing sequentially through preheating section reaction tube 4 and reaction section reaction tube 5. The esterification product is condensed by condenser 7 under the control of back pressure 6 and then enters receiving tank 8.

[0061] The esterification product was a slightly white emulsion. 200g of it was taken as a sample and evaporated using a rotary evaporator. 3.34g of white terephthalic acid powder remained in the rotary evaporator. According to calculations, the total content of the esterification mixture was 83.6g of terephthalic acid.

[0062] The terephthalic acid powder (3.34 g) remaining in the evaporator, the distillation collection liquid from the rotary evaporator, and the esterification product in the receiving tank 8 were added to the atmospheric distillation kettle 10 for azeotropic distillation. After passing through the packed column 11 and the condenser 12, the mixture entered the water separator 13 for stratification. The bottom aqueous phase was discharged, and the upper n-butanol was refluxed back to the distillation kettle. To achieve complete dehydration, after no more water was discharged from the water separator, a portion of the n-butanol solvent containing trace amounts of water was distilled off. Finally, the weight of the liquid mixture obtained in the distillation kettle was 4351.4 g. Liquid chromatography analysis was performed, and the results are shown in Table 1.

[0063] Table 1. Liquid phase composition of a single-pass (first stage) reaction

[0064]

[0065] Alkylation is a reversible equilibrium reaction. The byproduct water from esterification needs to be continuously removed to disrupt the equilibrium and allow the reaction to continue. Analysis of the single-pass (first-order) reaction, combined with the results in Table 1, shows that the conversion rate is incomplete due to equilibrium limitations. Furthermore, a large amount of the intermediate product, monobutyl terephthalate, is not completely converted to the product, dibutyl terephthalate. Therefore, it is necessary to separate the byproduct water from the first-order esterification reaction mixture and continue the first-order esterification reaction to further improve the conversion rate and the selectivity of the target product.

[0066] The mixture of the above-mentioned primary reaction mixture was subjected to azeotropic dehydration to obtain a mixture containing the solvent n-butanol, dibutyl terephthalate and the intermediate product butyl benzoate p-carboxylic acid. The mixture was subjected to a tubular continuous secondary esterification reaction under the esterification reaction conditions in the example. The esterification product was a slightly yellow transparent liquid. No sediment was observed at the bottom after standing. After azeotropic dehydration, a total liquid phase mixture weighing 3752.9 g was obtained. The composition of the sample was analyzed and is shown in Table 2.

[0067] Table 2 Composition and content of the liquid phase in the secondary reaction

[0068]

[0069] Analysis, as shown in Table 2, revealed that the conversion rate of terephthalic acid reached 99.88% after the two-stage reaction, and the yield of dibutyl terephthalate was 92.96%. 500g of n-butanol was added to the esterified product from the second-stage reaction, and a continuous tubular two-stage esterification reaction was carried out again under the esterification reaction conditions described in the examples. The esterification product was a slightly yellow transparent liquid. After azeotropic dehydration, a total liquid-phase mixed product weighing 3816.2g was obtained. The composition of the sample is shown in Table 3.

[0070] Table 3. Composition and content of the liquid phase in the third-stage reaction.

[0071]

[0072] As can be seen from Example 2, after each single-pass reaction, the esterification water is removed by flash evaporation, breaking the water balance of the esterification reaction, and a tubular continuous esterification reaction is carried out again. The conversion rates of the raw material terephthalic acid and the intermediate product butyl terephthalate gradually increase, and the amount of product dibutyl terephthalate gradually increases. After three-stage reaction, the conversion rate of terephthalic acid reaches 99.93%, and the yield of dibutyl terephthalate increases to 99.45%.

[0073] Example 3

[0074] Preparation of raw materials for esterification reaction: Add 500g of terephthalic acid and 4500g of n-butanol to a high-speed grinder and grind for 40 minutes at room temperature to form a white emulsion of n-butanol containing terephthalic acid with a mass concentration of 10%, and set aside.

[0075] Esterification reaction conditions: The flow rate was set to 80 ml / min, the reactor outlet back pressure valve was set to 12.5 MPa, and the temperatures of the preheating section and the reaction section were set to 260℃ and 320℃, respectively. The three-stage esterification reaction was carried out according to the operation method of Example 2. The reaction results are shown in Table 4.

[0076] Table 4 Results of esterification reaction

[0077]

[0078] Note: The remaining amounts of esterification solutions after azeotropic dehydration vary at each stage, resulting in irregularities in the dibutyl terephthalate composition shown in the table.

[0079] The three-stage esterification reaction in Example 3 shows that the conversion and yield of the two-stage esterification reaction exceed 99%. Although there is a third-stage esterification reaction, its improvement on the conversion and yield is not significant.

[0080] Example 4

[0081] Preparation of raw materials for esterification reaction: Add 500g of terephthalic acid and 4500g of n-butanol to a high-speed grinder and grind for 40 minutes at room temperature to form a white emulsion of n-butanol containing terephthalic acid with a mass concentration of 10%, and set aside.

[0082] Esterification reaction conditions: The flow rate was set to 50 ml / min, the reactor outlet back pressure valve was set to 12.5 MPa, and the temperatures of the preheating section and the reaction section were set to 260℃ and 320℃, respectively. The two-stage esterification reaction was carried out in accordance with the operation method of Example 2. The reaction results are shown in Table 5.

[0083] Example 5

[0084] Preparation of raw materials for esterification reaction: Add 500g of terephthalic acid and 4500g of n-butanol to a high-speed grinder and grind for 40 minutes at room temperature to form a white emulsion of n-butanol containing terephthalic acid with a mass concentration of 10%, and set aside.

[0085] Esterification reaction conditions: The flow rate was set to 110 ml / min, the back pressure valve at the reactor outlet was set to 16.5 MPa, and the temperatures of the preheating section and the reaction section were set to 280℃ and 350℃, respectively. The two-stage esterification reaction was carried out in accordance with the operation method of Example 2. The reaction results are shown in Table 5.

[0086] Example 6

[0087] Preparation of raw materials for esterification reaction: Add 500g of terephthalic acid and 4500g of n-butanol to a high-speed grinder and grind for 40 minutes at room temperature to form a white emulsion of n-butanol containing terephthalic acid with a mass concentration of 10%, and set aside.

[0088] Esterification reaction conditions: The flow rate was set to 80 ml / min, the back pressure valve at the reactor outlet was set to 16.5 MPa, and the temperatures of the preheating section and the reaction section were set to 280℃ and 350℃, respectively. The two-stage esterification reaction was carried out in accordance with the operation method of Example 2. The reaction results are shown in Table 5.

[0089] Example 7

[0090] Preparation of raw materials for esterification reaction: Add 500g of terephthalic acid and 4500g of n-butanol to a high-speed grinder and grind for 40 minutes at room temperature to form a white emulsion of n-butanol containing terephthalic acid with a mass concentration of 10%, and set aside.

[0091] Esterification reaction conditions: The flow rate was set to 50 ml / min, the back pressure valve at the reactor outlet was set to 16.5 MPa, and the temperatures of the preheating section and the reaction section were set to 280℃ and 350℃, respectively. The two-stage esterification reaction was carried out in accordance with the operation method of Example 2. The reaction results are shown in Table 5.

[0092] Table 5

[0093]

[0094]

[0095] Comparative Example 1: Esterification reaction under non-catalytic conditions

[0096] 50g of terephthalic acid and 450g of n-butanol were added to a high-pressure reactor equipped with a stirrer, a packed column, and a water separator. The reactor was purged with nitrogen three times, then sealed. Under stirring, the temperature was gradually increased to 235–240°C, and the pressure was maintained at 2.5–2.8 MPa. Under these conditions, the esterification reaction byproducts water and solvent butanol passed through a packed column and a condenser before entering the water separator, forming an upper solvent butanol phase and a lower aqueous phase. The solvent butanol phase was refluxed into the reactor, while the aqueous phase was continuously discharged. After reacting for 14 hours, until no more aqueous phase was discharged, the mixture was gradually cooled to room temperature. The reaction mixture was discharged from the reactor and was light yellowish-brown. After standing, a white terephthalic acid powder precipitate was formed. The mixture was then distilled under reduced pressure in a rotary evaporator. 9.1g of terephthalic acid remained in the evaporator. This indicates that the high-temperature esterification reaction of terephthalic acid and n-butanol under non-acid catalysis using a high-pressure reactor has a low rate, with a conversion rate of only 81.8% after 14 hours of reaction.

[0097] Comparative Example 2: Acid-catalyzed esterification reaction

[0098] 50g of terephthalic acid, 450g of n-butanol, and 3g of methanesulfonic acid were added to a four-necked round-bottom glass flask equipped with a stirrer, a packed column, and a water separator. The temperature of the electric heating mantle was gradually increased with stirring. As the temperature gradually rose, the reaction temperature reached 119℃, and an aqueous phase gradually formed in the water separator. The final reaction temperature reached 160℃, and the total reaction time was 9 hours. The color of the reaction mixture gradually changed from white and turbid to light yellow and clear. About 11ml of aqueous phase was generated at the bottom of the water separator. After cooling to room temperature, there was no obvious precipitate. The mixture in the flask was transferred to a 2000 ml separatory funnel. First, 500 ml of deionized water was added for washing, and the washing aqueous phase was discharged from the bottom of the separatory funnel. After washing twice, a 5% sodium carbonate aqueous solution was added for further washing, and the washing liquid was discharged from the bottom of the separatory funnel. Finally, the mixture was washed twice more with deionized water, yielding 462.4 g of the esterification reaction mixture after water and alkali washing (theoretical 489.1 g, but solvent loss occurred during the actual washing process). Liquid chromatography analysis showed that the dibutyl terephthalate content was 17.39% and the monobutyl terephthalate content was 0.58%, indicating a monobutyl terephthalate yield of 96%.

[0099] Example 8

[0100] Preparation of raw materials for esterification reaction: Add 750g of terephthalic acid and 4250g of n-butanol to a high-speed grinder and grind for 40 minutes at room temperature to form a white emulsion of n-butanol containing terephthalic acid with a mass concentration of 15%, and set aside.

[0101] Esterification reaction conditions: The flow rate was set to 80 ml / min, the reactor outlet back pressure valve was set to 16.5 MPa, and the temperatures of the preheating section and the reaction section were set to 280℃ and 350℃, respectively. The three-stage esterification reaction was carried out according to the operation method of Example 2. The reaction results are shown in Table 6.

[0102] Table 6

[0103]

[0104] Example 9

[0105] Preparation of raw materials for esterification reaction: Add 750g of terephthalic acid and 4250g of n-butanol to a high-speed grinder and grind for 40 minutes at room temperature to form a white emulsion of n-butanol containing terephthalic acid with a mass concentration of 15%, and set aside.

[0106] Esterification reaction conditions: The flow rate was set to 50 ml / min, the back pressure valve at the reactor outlet was set to 16.5 MPa, and the temperatures of the preheating section and the reaction section were set to 280℃ and 350℃, respectively. The two-stage esterification reaction was carried out in accordance with the operation method of Example 2. The reaction results are shown in Table 7.

[0107] Table 7

[0108]

[0109] The above are preferred embodiments of the present invention. This method is also applicable to the preparation of aromatic diester compounds by esterification reaction of C2-C6 low alcohols with terephthalic acid. The reaction order is not a limiting condition of the invention, but falls within the scope of the technology taught in this patent.

Claims

1. A method for preparing dibutyl terephthalate, wherein the preparation is carried out using a tubular continuous esterification microreactor, characterized in that, The device includes a solvent supply end, a raw material supply end, a tubular microreactor, a condenser, and a receiving tank. The tubular microreactor has an inlet and an outlet; The solvent supply end and the raw material supply end are respectively connected to the feed inlet; The discharge port, condenser, and receiving tank are connected in sequence. The inner diameter of the reaction tube in the tubular microreactor is 4–10 mm; The tubular microreactor is equipped with a flow-turbing element inside the reaction tube. The baffle is a spiral-shaped perforated metal plate; The thickness of the baffle is 0.3–1.0 mm, the aperture is 0.8–1.5 mm, and the opening area ratio is 40%–55%. The spiral strip-shaped metal perforated plate is twisted spirally along the pipe diameter direction; The width of the spiral metal perforated plate is a, and it is twisted 90 degrees in the same direction every 2a along its length. The continuous microreaction method is used, in which raw materials containing terephthalic acid and butanol are continuously fed into a tubular microreactor to undergo esterification reaction; The esterification reaction was carried out under catalyst-free conditions; The conditions for the esterification reaction include: a reaction temperature of 320–350°C and a reaction pressure of 12.5–18.0 MPa; The raw material is nano-ground to obtain an emulsion, which is used as the esterification raw material solution. The mass concentration of terephthalic acid in the raw material is 5% to 10%.

2. The method according to claim 1, characterized in that, The volumetric porosity inside the reaction tube is 75-90%.

3. The method according to claim 1, characterized in that, The reaction tube consists of a preheating section reaction tube and a reaction section reaction tube.

4. The method according to claim 3, characterized in that, The preheating section reaction tube and the reaction section reaction tube each have independent temperature control components.

5. The method according to claim 3, characterized in that, The turbulence-disrupting element penetrates the preheating section reaction tube and the reaction section reaction tube.

6. The method according to any one of claims 1-5, characterized in that, The tubular microreactor is equipped with a high-pressure metering pump at its feed inlet.

7. The method according to claim 6, characterized in that, The tubular microreactor is equipped with a back pressure valve at its outlet.

8. The method according to claim 1, characterized in that, The reaction residence time of the raw materials in the tubular microreactor is 80 to 150 seconds; And / or, the butanol is n-butanol.

9. The method according to claim 1, characterized in that: The method includes the following steps: (1) The esterification raw material liquid is continuously passed through a tubular microreactor for esterification reaction. The resulting reaction mixture I is then separated from the water in the reaction mixture I to obtain a primary esterification liquid. (2) The primary esterification liquid is continuously passed through a tubular microreactor for a secondary esterification reaction. The reaction mixture II is separated to obtain a product containing dibutyl terephthalate.

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