Method and device for preparing dibutyl terephthalate through micro-reaction

Abstract

The invention relates to a method and a device for preparing dibutyl terephthalate through micro-reaction, which are characterized in that a mixture of terephthalic acid and n-butyl alcohol continuously passes through a tubular reactor with a built-in turbulent flow component in the absence of a catalyst at certain temperature and pressure to generate the dibutyl terephthalate. The continuous tubular reaction is adopted, through esterification reaction, the conversion rate of terephthalic acid exceeds 99.5%, the selectivity of dibutyl terephthalate exceeds 90%, and the high-purity dibutyl terephthalate is obtained by distilling the mixed product. The continuous esterification reaction of terephthalic acid can be realized, the process flow is simple, the product quality is high, and the method is suitable for industrial production.

Description

Technical Field

[0001] The invention relates to a method and a device for preparing dibutyl terephthalate by micro-reaction, belonging to the technical field of organic chemistry. Background Art

[0002] Aromatic dibasic acid ester compounds are an important class of organic chemical intermediates, widely used in the fields of polymers, plasticizers, and are also used to prepare other fine chemical monomers. Aromatic dibasic acids mainly refer to terephthalic acid, phthalic acid and isophthalic acid, which are esterified with alcohols to generate corresponding dibasic acid esters, among which terephthalic acid esters are important raw materials for the preparation of 1,4-cyclohexanedimethanol, including aromatic dibasic acid esters formed by C1-C4 aliphatic alcohols, such as dimethyl terephthalate, diethyl terephthalate, di(iso)propyl terephthalate, di-n-(iso)butyl terephthalate, etc.

[0003] There are three main methods for the preparation of aromatic dibasic acid esters. One is to carry out the esterification reaction of alcohol acid in the presence of inorganic acid, such as sulfuric acid, but there is a disadvantage of equipment corrosion, which makes it difficult to carry out large-scale industrial production. The second is the catalytic esterification reaction of organic acid, such as using methanesulfonic acid or toluenesulfonic acid. Although the esterification reaction under acid catalysis can proceed smoothly and the reaction conditions are relatively mild, it is limited by the extremely low solubility of aromatic dibasic acid in alcohol. The reaction process is a heterogeneous solid-liquid two-phase state, so the reaction time is long, there are many by-products, and the residual catalyst needs to be removed. The product refining process is long. Under non-catalytic conditions, the self-catalytic effect of the raw aromatic acid can be used to cause the esterification reaction of acid and alcohol, but it needs to be carried out at a higher temperature and pressure. Among them, the preparation of terephthalic acid esters is particularly important. Since the solubility of terephthalic acid in alcohol solvent is very low, its esterification reaction usually needs to be carried out in a high-pressure reactor at high temperature and high pressure, and the reaction time is long. At the same time, long-term high-temperature reaction leads to excessive by-products. These disadvantages affect industrial application. Aromatic dibasic acid esters can also be prepared by ester exchange, but this is limited to the preparation of aromatic dibasic acid esters of high-carbon alcohols from aromatic dibasic acid esters of low-carbon alcohols, and usually requires the use of ester exchange catalysts, which has limitations. Therefore, the direct esterification reaction of alcoholic acids to prepare alcohols is the main industrial preparation method.

[0004] The Chinese invention patent application publication specification CN101652343A discloses a method for preparing di-n-butyl terephthalate, wherein terephthalic acid and n-butanol are subjected to an esterification reaction in a high-pressure reactor in the presence of an acidic catalyst, the reaction time is long (5 to 16 hours), and many by-products are produced; CN111132957A discloses a method for preparing terephthalic acid esters, wherein an acidic catalyst is used to carry out an esterification reaction of terephthalic acid and n-butanol in a high-pressure reactor for 3 to 5 hours, and the mixed product needs to be neutralized with an alkali, but dibutyl ether by-product is inevitably generated during the reaction, which increases the consumption of the raw alcohol, and the acid value of the product is relatively high. Summary of the invention

[0005] The purpose of the present invention is to solve the problems of the current discontinuous reaction process, long reaction time and many by-products in the preparation process of terephthalic acid esters. The present invention adopts a continuous tubular reaction. After the esterification reaction, the conversion rate of terephthalic acid exceeds 99.5%, and the selectivity of dibutyl terephthalate exceeds 90%. By distilling the mixed product, high-purity dibutyl terephthalate is obtained. Under non-catalytic conditions, by strengthening the reaction conditions, the reaction time at high temperature is greatly reduced, the generation of by-products is reduced, and the post-processing refining process is simplified, which has the advantage of large-scale industrial application. The present invention can realize the continuous esterification reaction of terephthalic acid, has a simple process flow, and has high product quality, and is suitable for industrial production.

[0006] On the one hand, the present invention provides a method for preparing dibutyl terephthalate, which adopts a continuous micro-reaction method, wherein raw materials containing terephthalic acid and C2-C6 low-carbon alcohols continuously enter a tubular micro-reactor to undergo an esterification reaction; the conditions of 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 raw material has a reaction residence time of 80 to 150 seconds in the tubular microreactor.

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

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

[0011] Optionally, the esterification reaction is carried out in the absence of a catalyst.

[0012] Optionally, the raw material is nano-grinded (grinded to a particle size of 20 to 100 microns), and the obtained emulsion is used as the esterification raw material liquid.

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

[0014] (1) the esterification raw material liquid is continuously passed through a tubular microreactor for esterification reaction to obtain a reaction mixture I, and water in the reaction mixture I is separated to obtain a primary esterification liquid;

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

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

[0017] Optionally, the separation is azeotropic distillation. Preferably, the separation is to cool the reaction mixture I to room temperature, then pump it into a distillation kettle equipped with a packing column, a condenser and a water separator for azeotropic distillation at normal pressure, the tower bottom is 130-145°C, the gas phase containing water and C2-C6 low-carbon alcohol (preferably n-butanol) is separated in a packing column equipped with a wire mesh packing, the tower top temperature is controlled at 112-117°C, the esterification reaction by-product water and a small amount of butanol are extracted from the tower top, and after cooling in a condenser, an upper oil phase (C2-C6 low-carbon alcohol) and a lower water phase are formed in the water separator, the oil phase is refluxed to the distillation kettle, the water phase is discharged, and the tower bottom obtains a primary esterification liquid (the main components are the product terephthalic acid ester, the intermediate product p-carboxybenzoic acid ester, and the unreacted raw material terephthalic acid);

[0018] Optionally, the primary esterification liquid is sequentially cooled and subjected to azeotropic distillation to remove water, and subjected to multiple tubular microchannel esterification reactions until the esterification reaction is complete.

[0019] On the other hand, the present invention provides a tubular continuous esterification micro-reaction device for preparing dibutyl terephthalate, characterized in that the device includes a solvent supply end, a raw material supply end, a tubular microreactor, a condensation tank, a condenser and a receiving tank; the tubular microreactor has a feed port and a discharge port; the solvent supply end and the raw material supply end are respectively connected to the feed port; the discharge port, the condensation tank, the condenser and the receiving tank are sequentially connected; a spoiler is provided in 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 volume void ratio in 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 an independent temperature control component.

[0022] Optionally, the spoiler runs through the preheating section reaction tube and the reaction section reaction tube.

[0023] Optionally, the spoiler is a spiral metal perforated plate; preferably, the spoiler has a thickness of 0.50.3-1.0 mm, an aperture of 0.8-1.5 mm, and an opening area ratio of 40%-55%.

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

[0025] Optionally, the spiral metal perforated plate is twisted 90 degrees at every 8 to 16 mm in the length direction to form a twist shape.

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

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

[0028] Optionally, the discharge port of the tubular microreactor is provided with a back pressure valve.

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

[0030] The solubility of terephthalic acid in alcohol solvents is very low, and the alcohol esterification reaction with terephthalic acid as raw material is generally a heterogeneous intermittent reaction, and the mass transfer efficiency of the reaction process is low. Even under catalytic conditions, the reaction rate is slow, the reaction time is long, and there are many by-products. In order to speed up the reaction process, it is necessary to strengthen the reaction conditions. The present invention adopts a microchannel reaction process, and by strengthening the mass transfer effect of the reaction process, it can well solve the shortcomings of the conventional esterification reaction process, greatly shorten the reaction time, reduce the generation of by-products, and improve product quality. For the esterification reaction of terephthalic acid and butanol, the tubular reaction technology can effectively reduce the reaction time, reduce the occurrence of side reactions, reduce the separation and purification process, reduce the manufacturing cost of dibutyl terephthalate, and realize large-scale industrial production by strengthening the reaction conditions under non-catalytic conditions. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 Tubular continuous esterification reaction device and process diagram;

[0032] Figure 2 A schematic diagram of the tubular reactor structure and a schematic diagram of the built-in flow-disturbing components;

[0033] Figure 3 A simplified diagram of the tubular reactor structure and a stereogram of the built-in spoiler components;

[0034] Figure 4 Stereoscopic image of spiral twist of built-in spoiler component;

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

[0036] In order to have a clearer understanding of the technical features, purposes and effects of the present invention, the technical solutions of the present invention are illustrated by the following examples and comparative examples, but they are not intended to limit the scope of implementation.

[0037] As one embodiment thereof, the present invention uses terephthalic acid and n-butanol to carry out an esterification reaction under non-catalytic conditions. The reaction uses a stainless steel tube with an inner diameter of 6 mm as a reactor. A spoiler component with a preset specific structure is installed in the tube. Terephthalic acid and n-butanol are ground and prepared into an emulsion with a mass concentration of 5 to 20%. The emulsion enters the tubular reactor under the action of a high-pressure metering pump, and the esterification reaction is rapidly carried out at a certain temperature and pressure to reach a reaction equilibrium. After cooling, the composition of the mixed product is analyzed.

[0038] The tubular reaction equipment used in the invention includes the following parts: a high-pressure metering pump, a tubular reactor with an electric heating component, an inner diameter of the reaction tube of 6 mm, a preheating section tube length of 1000 mm, a reaction section tube length of 8000 mm, a stainless steel orifice plate with a twisted spiral ribbon shape and a preset thickness of 0.5 mm and a width of 5.9 mm along the length direction is preset in the tube, the orifice diameter is 1 mm, the twisted spiral ribbon stainless steel orifice plate passes through the reaction tube, and the orifice opening rate is 46%. A back pressure valve is arranged at the discharge port of the tubular reactor to control the reaction pressure. The reaction liquid passes through the reaction tube quickly under the action of the high-pressure metering pump, and a turbulent effect is generated under the action of the filler in the tube, so as to achieve the effect of strengthening mass transfer and heat transfer, promote the esterification reaction, and quickly reach the reaction equilibrium. The reaction liquid is discharged from the reactor under the control of the back pressure valve, and enters the esterification product storage tank after being cooled by the condenser. The esterification product is filtered to filter out the unreacted raw material terephthalic acid, and is weighed after drying, and the single-pass conversion rate is calculated, and 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 in the form of powdered solid particles. It is mixed evenly with alcohol in a specified mass ratio, added to a high-speed grinder and ground 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, and the back pressure valve pressure 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 operation state with a stable flow rate is formed in the reactor. Subsequently, the reactor is heated up. When the temperature of the preheating section reaches 250-280°C and the temperature of the reaction section reaches 280-350°C, the raw material feed valve is switched in front of the high-pressure feed pump to pump in a prepared raw material liquid of a certain mass concentration. The raw material liquid undergoes alcohol acid esterification reaction through the preheating section and the reaction section. The reaction mixture enters a collecting tank through a condenser under the control of a back pressure valve, is filtered to filter out unreacted terephthalic acid, is dried and weighed, and the reaction conversion rate is calculated. The filtrate is pumped into a distillation kettle with a packing tower and a water separator, and is distilled under normal pressure to remove by-product water through azeotropy. When no more water is discharged from the water separator, a small amount of solvent n-butanol is continuously distilled to ensure that the esterification product is dehydrated to the maximum extent. The composition of the esterification product in the kettle is analyzed by liquid chromatography to determine the single-pass raw material conversion rate and yield. The esterification mixture from which by-product water and unreacted terephthalic acid have been removed in the distillation kettle is used as a raw material, and a secondary esterification reaction is carried out according to the esterification reaction process conditions. The esterification reaction discharge mixture is subjected to liquid chromatography analysis to determine the composition of the mixed product.

[0044] In the embodiment, the analysis instrument adopts Agilent 1260 liquid chromatograph, and the analysis conditions are as follows:

[0045] Chromatographic column model: C8

[0046] Wavelength: 220

[0047] Mobile phase: acetonitrile / water (V / V)

[0048] Flow rate: 0.8m / min

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

[0050]

[0051]

[0052]

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

[0054] Example 1 Tubular continuous esterification reaction device

[0055] The tubular continuous esterification reaction device comprises 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 distillation kettle 10, a packing column 11 and a second condenser 12.

[0056] The tubular reactor has a feed port and a discharge port; the solvent storage tank 1 and the raw material storage tank 2 are connected to the feed port respectively; the discharge port, 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] A spiral strip metal perforated plate 15 is provided in the reaction tube 15 of the tubular reactor, and the spiral metal perforated plate 15 penetrates 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 volume void ratio is 85%. The preheating section reaction tube 4 and the reaction section reaction tube 5 have independent temperature control components, respectively. The feed port of the tubular reactor is provided with a high-pressure metering pump 3, and the discharge port of the tubular reactor is provided with a back pressure valve 6.

[0058] Example 2 Preparation method of terephthalate

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

[0060] Esterification reaction: Add the prepared raw material liquid and solvent n-butanol (5000g) to the raw material storage tank 2 and the solvent storage tank 1 respectively, open the valve of the solvent storage tank 1, start the high-pressure metering pump 3, set the flow rate to 80ml / min, adjust the back pressure valve 6 at the outlet of the tubular reactor to 11MPa, and the solvent n-butanol enters the tubular reactor under the action of the high-pressure metering pump 3. After the solvent stays in the reactor for about 180 seconds, it enters the condenser 7 through the control of the back pressure valve 6, and enters the receiving tank 8 after condensation, forming a solvent cold operation for 5 to 10 minutes. Subsequently, gradually increase the temperature of the preheating section reaction tube 4 and the reaction section reaction tube 5. When the temperature of the preheating section reaction tube 4 and the reaction section reaction tube 5 reaches 260℃ and 300℃ respectively, switch the valve of the raw material storage tank 2, and the raw material liquid enters the tubular reactor through the high-pressure metering pump 3, and flows through the preheating section reaction tube 4 and the reaction section reaction tube 5 in turn. The esterification product enters the receiving tank 8 after condensation treatment by the condenser 7 under the control of the back pressure 6.

[0061] The esterification product was a slightly white emulsion. 200 g of the emulsion was taken as a sample and evaporated using a rotary evaporator. 3.34 g of white terephthalic acid powder remained in the rotary evaporator. It was calculated that the esterification mixture contained 83.6 g of terephthalic acid in total.

[0062] The terephthalic acid powder (3.34 g) remaining in the evaporator, the distillation collection liquid of the rotary evaporator and the esterification product in the receiving tank 8 were added to the atmospheric distillation kettle 10 for azeotropic distillation, and then entered the water separator 13 for stratification after passing through the packing column 11 and the condenser 12. The bottom water phase was discharged, and the upper n-butanol was refluxed to the distillation kettle. In order to achieve the purpose of complete water removal, after no more water was separated from the water separator, part of the n-butanol solvent containing trace water was continued to be distilled out. Finally, the weight of the liquid mixture obtained in the distillation kettle was 4351.4 g. Liquid chromatography analysis was performed. The analysis results are shown in Table 1.

[0063] Table 1 Single-pass (primary) reaction liquid phase composition

[0064]

[0065] The alcohol acid esterification reaction is a reversible equilibrium reaction. The byproduct water of the esterification reaction needs to be continuously removed to break the reaction equilibrium and keep the reaction going. Through the one-way (primary) reaction, combined with the analysis results in Table 1, it can be seen that due to the limitation of the reaction equilibrium, the one-way reaction conversion rate is incomplete, and a large amount of the intermediate product monobutyl terephthalate cannot be completely converted into the product dibutyl terephthalate. It is necessary to separate the byproduct water in the primary esterification reaction mixture and continue the secondary esterification reaction to further improve the conversion rate and target product selectivity.

[0066] The mixture containing the solvent n-butanol, dibutyl terephthalate and the intermediate product butyl benzoate obtained by azeotropic dehydration of the above-mentioned primary reaction mixed product was subjected to a tubular continuous secondary esterification reaction again according to the esterification reaction conditions in the embodiment. The esterification product was a light yellow transparent liquid. No sediment was observed at the bottom after standing. After azeotropic dehydration, a full liquid phase mixed product was obtained, weighing 3752.9 g. The composition was sampled and analyzed, as shown in Table 2.

[0067] Table 2 Secondary reaction liquid phase composition content

[0068]

[0069] After analysis, it can be seen from Table 2 that after the two-stage reaction, the conversion rate of terephthalic acid reaches 99.88%, and the yield of dibutyl terephthalate is 92.96%. 500g of n-butanol is added to the above-mentioned secondary reaction esterification product, and a tubular continuous secondary esterification reaction is carried out again according to the esterification reaction conditions in the embodiment. The esterification product is a light yellow transparent liquid. After azeotropic dehydration, a full liquid phase mixed product is obtained, weighing 3816.2g. The composition is analyzed by sampling, as shown in Table 3.

[0070] Table 3 Three-stage reaction liquid phase composition content

[0071]

[0072] It can be seen from Example 2 that after each single-pass reaction, the esterification water is removed by flash evaporation to break the water balance of the esterification reaction, and the tubular continuous esterification reaction is carried out again. The conversion rate of the raw material terephthalic acid and the intermediate product butyl benzoate is gradually improved, and the amount of the product dibutyl terephthalate is gradually increased. After the three-stage reaction, the terephthalic acid conversion rate reaches 99.93%, and the dibutyl terephthalate recovery rate is increased to 99.45%.

[0073] Example 3

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

[0075] Esterification reaction conditions: the flow rate was set to 80 ml / min, the back pressure valve at the reactor outlet was set to 12.5 MPa, the temperatures of the preheating section and the reaction section were set to 260° C. and 320° C., respectively. Referring to the operating method of Example 2, a tertiary esterification reaction was carried out. The reaction results are shown in Table 4.

[0076] Table 4 Esterification reaction results

[0077]

[0078] Note: The residual amount of each level of esterification liquid after azeotropic dehydration is different, resulting in irregular composition of dibutyl terephthalate in the table

[0079] Through the three-stage esterification reaction of Example 3, it can be seen that the conversion rate and yield of the two-stage esterification reaction exceed 99%. Although there is a third-stage esterification reaction, the improvement of the conversion rate and yield is not obvious.

[0080] Example 4

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

[0082] Esterification reaction conditions: the flow rate was set to 50 ml / min, the back pressure valve at the reactor outlet was set to 12.5 MPa, the temperatures of the preheating section and the reaction section were set to 260°C and 320°C, respectively. Referring to the operating method of Example 2, a two-stage esterification reaction was carried out. 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 into a high-speed grinder and grind at room temperature for 40 minutes to form a white emulsion of n-butanol containing terephthalic acid with a mass concentration of 10%, which is 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, the temperatures of the preheating section and the reaction section were set to 280° C. and 350° C., respectively. Referring to the operating method of Example 2, a two-stage esterification reaction was carried out. 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 into a high-speed grinder and grind at room temperature for 40 minutes to form a white emulsion of n-butanol containing terephthalic acid with a mass concentration of 10%, which is 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, the temperatures of the preheating section and the reaction section were set to 280° C. and 350° C., respectively. Referring to the operating method of Example 2, a two-stage esterification reaction was carried out. 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 into a high-speed grinder and grind at room temperature for 40 minutes to form a white emulsion of n-butanol containing terephthalic acid with a mass concentration of 10%, which is 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, the temperatures of the preheating section and the reaction section were set to 280° C. and 350° C., respectively. Referring to the operating method of Example 2, a two-stage esterification reaction was carried out. The reaction results are shown in Table 5.

[0092] Table 5

[0093]

[0094]

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

[0096] 50g of terephthalic acid and 450g of n-butanol were added into an autoclave with stirring, a packing column and a water separator, and the mixture was replaced with nitrogen for 3 times. The autoclave was sealed and gradually heated to 235-240°C under stirring, and the pressure was maintained at 2.5-2.8MPa. Under this condition, water and solvent butanol, a by-product of the esterification reaction, entered the water separator after passing through the packing column and a condenser to form an upper solvent butanol phase and a lower aqueous phase. The solvent butanol phase was refluxed into the autoclave, and the aqueous phase was continuously discharged. After reacting for 14 hours, the reaction mixture was discharged until no aqueous phase continued to be discharged, and the reaction mixture was gradually cooled to room temperature. The reaction mixture in the autoclave was discharged, and the mixture was light yellow-brown. White terephthalic acid powder was precipitated after standing. The mixture was distilled under reduced pressure in a rotary evaporator, and 9.1g of terephthalic acid remained in the evaporator. That is, the high-temperature esterification reaction rate of terephthalic acid and n-butanol under non-acid catalysis using an autoclave was low, and the conversion rate could only reach 81.8% after reacting for 14 hours.

[0097] Comparative Example 2 Acid-catalyzed esterification

[0098] 50g of terephthalic acid, 450g of n-butanol and 3g of methanesulfonic acid were added to a four-necked round-bottom glass flask with a stirrer, a filling column and a water separator. The temperature of the electric heating jacket was gradually increased under stirring. As the temperature gradually increased, after the reaction temperature reached 119°C, a water phase was gradually formed in the water separator. The final reaction temperature reached 160°C. The overall reaction time was 9 hours. The color of the reaction mixture gradually changed from white turbidity to light yellow clear liquid. About 11ml of water phase was generated at the bottom of the water separator. When it cooled to room temperature, there was no obvious precipitate. The mixture in the flask was transferred to a 2000 ml separating funnel, and 500 ml of deionized water was added for washing. The washing water phase was discharged from the bottom of the separating funnel. After washing twice, a 5% sodium carbonate aqueous solution was added for washing. The washing liquid was discharged from the bottom of the separating funnel. Finally, deionized water was used twice to obtain 462.4 g (theoretical 489.1 g, and there was solvent loss in the actual washing process) of the esterification reaction mixture after water washing and alkali washing. According to liquid chromatography analysis, the content of dibutyl terephthalate was 17.39%, and the content of monobutyl terephthalate was 0.58%. The yield of monobutyl terephthalate was 96%.

[0099] Example 8

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

[0101] 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, the temperatures of the preheating section and the reaction section were set to 280° C. and 350° C., respectively. The tertiary esterification reaction was carried out according to the operating 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 into a high-speed grinder and grind at room temperature for 40 minutes to form a white emulsion of n-butanol containing terephthalic acid with a mass concentration of 15%, which is 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, the temperatures of the preheating section and the reaction section were set to 280° C. and 350° C., respectively. Referring to the operating method of Example 2, a two-stage esterification reaction was carried out. The reaction results are shown in Table 7.

[0107] Table 7

[0108]

[0109] The above is a preferred embodiment of the present invention. The method is also applicable to the esterification reaction of C2-C6 low-carbon alcohols with terephthalic acid to prepare aromatic dibasic acid ester compounds. The reaction order is not a limiting condition of the invention, but falls within the scope of the technical disclosure of this patent.

Claims

1. A method for preparing dibutyl terephthalate, characterized in that: Using the continuous micro-reaction method, raw materials containing terephthalic acid and C2-C6 low-carbon alcohols continuously enter the tubular micro-reactor to undergo esterification reaction; The conditions of the esterification reaction include: reaction temperature of 250-350° C. and reaction pressure of 10.0-20.0 MPa.

2. The method for preparing dibutyl terephthalate according to claim 1, characterized in that: The esterification reaction temperature is 300-350° C., and the esterification reaction pressure is 10.0-18.0 MPa; And / or, the raw material has a reaction residence time of 80 to 150 seconds in the tubular microreactor; And / or, in the raw material, the mass concentration of terephthalic acid is 5% to 20%, preferably 5% to 15%; And / or, the C2-C6 low-carbon alcohol is n-butanol.

3. The preparation method according to claim 1 or 2, characterized in that: The esterification reaction is carried out in the absence of a catalyst.

4. The preparation method according to any one of claims 1 to 3, characterized in that: The raw material is nano-grinded to obtain an emulsion as an esterification raw material liquid.

5. The preparation method according to claim 4, characterized in that: The method comprises the following steps: (1) the esterification raw material liquid is continuously passed through a tubular microreactor for esterification reaction to obtain a reaction mixture I, and water in the reaction mixture I is separated to obtain a primary esterification liquid; (2) The primary esterification liquid is continuously passed through the tubular microreactor again to carry out a secondary esterification reaction, and the reaction mixture II is separated as described above to obtain a product containing dibutyl terephthalate.

6. A tubular continuous esterification microreactor for preparing dibutyl terephthalate, characterized in that: The device comprises a solvent supply end, a raw material supply end, a tubular microreactor, a condenser and a receiving tank; The tubular microreactor has a feed inlet and a discharge outlet; The solvent supply end and the raw material supply end are respectively connected to the feed port; The discharge port, condenser and receiving tank are connected in sequence; A flow spoiler is arranged in the reaction tube of the tubular microreactor.

7. The tubular continuous esterification micro-reactor according to claim 6, characterized in that: The inner diameter of the reaction tube in the tubular microreactor is 4 to 10 mm; Preferably, the volume void ratio in the reaction tube is 75-90%; And / or, the reaction tube is composed of a preheating section reaction tube and a reaction section reaction tube; Preferably, the preheating stage reaction tube and the reaction stage reaction tube each have an independent temperature control component.

8. The tubular continuous esterification micro-reactor according to claim 6 or 7, characterized in that: The spoiler penetrates the preheating section reaction tube and the reaction section reaction tube; And / or, the spoiler is a spiral strip metal perforated plate; preferably, the spoiler has a thickness of 0.3-1.0 mm, an aperture of 0.8-1.5 mm, and an opening area ratio of 40%-55%; Preferably, the spiral strip-shaped metal perforated plate is spirally twisted along the pipe diameter direction; Preferably, the width of the spiral strip metal perforated plate is a, and the spiral strip metal perforated plate is twisted 90 degrees along the same direction every 2a of the length direction.

9. The tubular continuous esterification micro-reactor according to any one of claims 6 to 8, characterized in that: The feed inlet of the tubular microreactor is provided with a high-pressure metering pump.

10. The tubular continuous esterification micro-reactor according to claim 9, characterized in that: The outlet of the tubular microreactor is provided with a back pressure valve.

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