Continuous production method and system of terephthalic acid diester

Abstract

The invention relates to a continuous production method and system of terephthalic acid diester. The method comprises the following steps: introducing terephthalic acid and alcohols into a first tubular reactor for primary esterification reaction, and condensing to obtain a reaction mixture; carrying out reverse osmosis treatment on the reaction mixture through a membrane module to respectively obtain a concentrated solution and a penetrating fluid containing water and alcohols; carrying out pervaporation separation treatment on the penetrating fluid to respectively obtain alcohols and water; and introducing the obtained alcohol and the concentrated solution into a second tubular reactor for secondary esterification reaction to obtain the terephthalic acid diester. According to the method, the tubular reactor is combined with the reverse osmosis membrane and the vaporizing osmosis membrane, so that the mass and heat transfer effects are enhanced, the use of a catalyst is avoided, the reaction time is shortened, and the generation of byproducts is reduced; meanwhile, by separating water and breaking reversible reaction balance, the reaction can be continuously and positively carried out, the yield of the target product terephthalic acid diester is increased, the technological process is simple, and the method is suitable for industrial production.

Description

Technical Field

[0001] This invention relates to the field of terephthalate, and more specifically, to a continuous production method and system for terephthalate. Background Technology

[0002] Diterephthalate is a class of compounds obtained by the esterification reaction of phthalic acid with alcohols. At room temperature and pressure, it is mostly a white crystal or powder, flammable, and soluble in strongly polar organic solvents. Some are used in the manufacture of cable materials and other PVC products; others are widely used as plasticizers in nitrile rubber, cellulose nitrate, and synthetic rubber; still others are used as coating additives and lubricants for precision instruments.

[0003] The traditional method for preparing diterephthalate involves an esterification reaction using terephthalic acid and alcohols as raw materials and concentrated sulfuric acid as a catalyst. However, concentrated sulfuric acid is highly hazardous, wastewater treatment is troublesome, and the catalyst readily generates ether byproducts. Furthermore, a large amount of water is generated during the reaction. When the water volume reaches a certain limit, a reaction equilibrium is reached, preventing the reaction from proceeding in the forward direction. Ultimately, this affects the purity and yield of the target product.

[0004] Traditional synthesis of terephthalate generally involves a heterogeneous batch reactor reaction of terephthalic acid and alcohols under the action of a catalyst. However, terephthalic acid suffers from low solubility in alcohol solvents, resulting in low mass transfer efficiency, slow reaction speed, long reaction time, difficulty in continuing the forward reaction after equilibrium, and numerous byproducts. Furthermore, the addition of substances such as toluene or cyclohexane during the esterification water separation process to facilitate the separation of alcohol and water increases the workload for subsequent separation and recovery.

[0005] CN101652343A discloses a traditional method for preparing terephthalic acid diester. This method involves esterifying terephthalic acid with n-butanol in a high-pressure reactor using an acidic catalyst. This type of reaction has problems such as long reaction time, many by-products, and high acid value of the product. Summary of the Invention

[0006] To address the problem of water generation inhibiting the forward reaction and resulting in low purity and yield of the target product during the diterephthalate (DTEB) reaction, this invention proposes a process for preparing DTEB that couples a reverse osmosis membrane and a vaporization osmosis membrane system to a tubular reaction system. This process continuously separates water from the reaction products, promoting a sustained forward reaction and significantly improving the purity and yield of the target product. Furthermore, membrane separation technology effectively solves the problems of high separation difficulty and energy consumption in traditional distillation separation of alcohols and water azeotropic systems, thus significantly reducing production costs.

[0007] One objective of this invention is to provide a continuous production method for diterephthalate, comprising the following steps:

[0008] (1) Terephthalic acid and alcohols are passed into the first tubular reactor for a first esterification reaction, and the reaction mixture is obtained after condensation.

[0009] (2) The reaction mixture is passed through a membrane module for reverse osmosis to obtain a concentrate and a permeate containing water and alcohol, respectively.

[0010] (3) The permeate was subjected to pervaporation separation to obtain alcohols and water, respectively;

[0011] (4) The alcohol obtained in step (3) and the concentrate obtained in step (2) are fed into the second tubular reactor for a secondary esterification reaction to obtain terephthalic acid diester.

[0012] In step (1):

[0013] The feedstock for a single esterification reaction includes terephthalic acid and alcohols;

[0014] The alcohol is selected from at least one of n-butanol, n-pentanol, and isopropanol, preferably n-butanol;

[0015] In the feed solution for a single esterification reaction, the mass concentration of terephthalic acid is 5% to 25% based on the total mass of terephthalic acid and alcohols, for example, it can be 5%, 10%, 15%, 20%, 25%, etc.

[0016] The temperature for a single esterification reaction is 340–380℃, for example, 340℃, 350℃, 360℃, 370℃, 380℃, etc.

[0017] The pressure for a single esterification reaction is 13.0–18.0 MPa, for example, 13 MPa, 14 MPa, 15 MPa, 16 MPa, 17 MPa, 18.0 MPa, etc.

[0018] The esterification reaction time is 10.0 to 16.0 min, for example, 10 min, 11 min, 12 min, 13 min, 14 min, 15 min, 16 min, etc.

[0019] Preferably, in step (1), terephthalic acid and alcohol are ground into an emulsion and then introduced into the first tubular reactor.

[0020] In step (2):

[0021] The reverse osmosis time is 40 to 60 minutes, for example, 40 minutes, 45 minutes, 50 minutes, 55 minutes, 60 minutes, etc.

[0022] The reverse osmosis pressure is 2.0 to 5.5 MPa, for example, it can be 2 MPa, 2.5 MPa, 3 MPa, 3.5 MPa, 4 MPa, 4.5 MPa, 5 MPa, 5.5 MPa, etc.;

[0023] After the reaction mixture is condensed, its temperature can be 10 to 35°C, for example, 10°C, 15°C, 20°C, 25°C, 30°C, 35°C, etc.

[0024] The membrane module includes at least three reverse osmosis membranes;

[0025] The reverse osmosis membrane is preferably an aromatic polyamide reverse osmosis membrane, such as a fully aromatic, highly cross-linked polyamide seawater-grade desalination membrane, and the membrane module stacking density can be 1178 / m³. 2 *m -3 The system has a recovery rate of 45-60%, a continuous operating pH range of 3.0-10.0, a maximum impact pressure of 8.3 MPa, and a maximum operating temperature of 45℃.

[0026] Reverse osmosis membranes can be any one or a combination of hollow fiber, spiral wound, tubular, or plate and frame types.

[0027] In step (3):

[0028] The vacuum degree of pervaporation is 50-80 kPa, for example, it can be 50 kPa, 60 kPa, 70 kPa, 80 kPa, etc.

[0029] Pervaporation separation uses a pervaporation membrane to separate water and alcohols;

[0030] Among them, the pervaporation membrane is preferably a polyacrylonitrile pervaporation membrane;

[0031] The pervaporation membrane can be any one of spiral wound, hollow fiber, plate and frame, or tubular types.

[0032] In step (4):

[0033] The secondary esterification reaction temperature is 340–380℃, for example, it can be 340℃, 350℃, 360℃, 370℃, 380℃, etc.

[0034] The secondary esterification reaction pressure is 13.0–18.0 MPa, for example, it can be 13 MPa, 14 MPa, 15 MPa, 16 MPa, 17 MPa, 18.0 MPa, etc.

[0035] The secondary esterification reaction time is 10.0 to 16.0 min, for example, 10 min, 11 min, 12 min, 13 min, 14 min, 15 min, 16 min, etc.

[0036] The continuous production method is preferably used in the production of dibutyl terephthalate.

[0037] The method of this invention first generates terephthalic acid diester, monoacrylic acid monoester, and water in a single-stage tubular reactor under certain temperature and pressure conditions without a catalyst. Second, the primary esterification mixture is pumped into a reverse osmosis membrane separation system to remove water by utilizing the difference in molecular diameter between organic macromolecules and inorganic small molecules. Finally, the concentrated retrieval solution is pumped into a secondary tubular reactor for secondary esterification, breaking the reversible reaction equilibrium and promoting the continuous forward reaction.

[0038] The method of this invention combines a tubular reactor with a reverse osmosis separation process. By enhancing mass and heat transfer, it avoids the use of catalysts, shortens reaction time, and reduces the generation of by-products. At the same time, by separating water, the reversible reaction equilibrium is broken, allowing the reaction to proceed continuously in the forward direction and improving the yield of the target product, terephthalic acid diester.

[0039] A second objective of this invention is to provide a continuous production system for diterephthalate, preferably used in the methods described above, comprising:

[0040] The first tubular reactor is configured to receive terephthalic acid and alcohols, and discharge the reaction mixture;

[0041] A reverse osmosis membrane module configured to receive a reaction mixture and discharge permeate and concentrate;

[0042] A pervaporation membrane configured to receive the permeate and discharge alcohols and water;

[0043] The second tubular reactor is configured to receive concentrate and alcohols discharged from the pervaporation membrane, as well as diterephthalate discharged from the pervaporation membrane.

[0044] A reverse osmosis membrane module includes at least three stages of reverse osmosis membranes.

[0045] According to a preferred embodiment of the present invention, the system further includes:

[0046] A first condenser and a crude terephthalate storage tank are connected sequentially between the first tubular reactor and the reverse osmosis membrane module.

[0047] The pervaporation membrane is connected to a second condenser, and the second condenser, gas-liquid separator, and water storage tank are connected in sequence.

[0048] The second tubular reactor is connected to a third condenser, which is connected to a refined terephthalic acid diester storage tank.

[0049] According to a preferred embodiment of the present invention, the system may further include:

[0050] The first tubular reactor is connected to a first feed pump and a second feed pump, which are connected to a grinding mill. The two feed pumps operate alternately, which can reduce the pulsation amplitude of fluid pressure and flow, and help to control the flow rate and pressure of the fluid entering the tubular reactor to be stable.

[0051] The second tubular reactor is connected to the third and fourth feed pumps respectively, and the two feed pumps run alternately.

[0052] The discharge lines of the reverse osmosis membrane module and the pervaporation membrane are combined and then connected to the third feed pump and the fourth feed pump, respectively.

[0053] A first pressure reducing valve and a second pressure reducing valve are respectively installed on the discharge pipelines of the reverse osmosis membrane module and the pervaporation membrane.

[0054] A first back pressure valve is installed between the first condenser and the crude terephthalate storage tank;

[0055] A first high-pressure pump is installed between the first tubular reactor and the crude terephthalate storage tank.

[0056] A second high-pressure pump is installed between the reverse osmosis membrane module and the pervaporation membrane;

[0057] A second back pressure valve is installed between the third condenser and the refined terephthalic acid diester storage tank.

[0058] The advantages of this invention are:

[0059] ① No catalyst is required during the reaction process, the reaction time is short, and there are few by-products, which can achieve efficient production of the target product.

[0060] ② The separation process does not introduce new substances or add extractants, avoiding problems such as difficulty in separating water and alcohol azeotropic systems by distillation and high energy consumption, thus significantly reducing production costs.

[0061] ③ It can achieve continuous feeding in the front and continuous uninterrupted output in the back, which is easy to promote industrially. Attached Figure Description

[0062] Figure 1 This is a schematic flow diagram of a continuous production method for dibutyl terephthalate provided by the present invention.

[0063] Figure 1 Marker explanation:

[0064] R1 - First tubular reactor; R2 - Second tubular reactor;

[0065] M1 - First feed pump; M2 - Second feed pump; M3 - Third feed pump; M4 - Fourth feed pump;

[0066] V1 - First back pressure valve; V2 - First pressure reducing valve; V3 - Second pressure reducing valve; V4 - Second back pressure valve;

[0067] P1 - First high-pressure pump; P2 - Second high-pressure pump;

[0068] T1 - Crude dibutyl terephthalate storage tank; T2 - Water storage tank; T3 - Refined dibutyl terephthalate storage tank;

[0069] M1 - Reverse osmosis membrane module; M2 - Pervaporation membrane;

[0070] 1-First condenser; 2-Permeate; 3-Concentrate; 4-Second condenser; 5-Gas-liquid separator; 6-Vacuum pump; 7-n-Butanol; 8-Third condenser.

[0071] Figure 1 In this process, n-butanol and terephthalic acid are mixed and ground into an emulsion using a grinder to obtain a primary esterification reaction feed solution. This solution is then alternately pumped into a first tubular reactor R1 by a first feed pump M1 and a second feed pump M2 for the primary esterification reaction. The reaction mixture is condensed by a first condenser 1 and collected in a crude dibutyl terephthalate storage tank T1. The reverse osmosis membrane module M1 includes three stages of reverse osmosis membranes. The reaction mixture from the crude dibutyl terephthalate storage tank T1 is pumped into the inlet of the first stage reverse osmosis membrane of the reverse osmosis membrane module M1 by a first high-pressure pump P1. Pressure is sequentially applied to the three stages of reverse osmosis membranes, and the concentrate obtained from the first stage reverse osmosis membrane is pumped into the inlet of the second stage reverse osmosis membrane. The concentrate obtained from the second stage reverse osmosis membrane is then pumped into the inlet of the third stage reverse osmosis membrane. The concentrate obtained from the sequential passage through the first to third stages of the reverse osmosis system is then subjected to deionization. After a period of dehydration, water is removed to obtain a concentrated solution 3 containing dibutyl terephthalate and monobutyl terephthalate, which is then depressurized through the first pressure reducing valve V2. The permeate 2 obtained from the first to third stage reverse osmosis system is pumped into the inlet of the pervaporation device through the second high-pressure pump P2. It is pervaporated through the pervaporation membrane M2 to separate n-butanol and esterified water. The esterified water is condensed by the second condenser 4 and collected in the water storage tank T2. The retained n-butanol 7 is combined with the concentrated solution 3 after passing through the second pressure reducing valve V3. It is then fed into the second tubular reactor R2 alternately by the third feed pump M3 and the fourth feed pump M4 for a secondary esterification reaction. The secondary esterified liquid is cooled by the third condenser 8 and then collected in the purified dibutyl terephthalate storage tank T3 through the second back pressure valve V4, finally yielding a high-purity DBT product.

[0072] Figure 2 This is a schematic diagram of a pervaporation device.

[0073] The permeate is pervaporated through the pervaporation membrane M2. The liquid phase chamber contains n-butanol and water. By drawing a vacuum under negative pressure, water molecules pass through the vaporization permeation membrane into the gas phase chamber, while n-butanol molecules are trapped, thus achieving separation of the two. Detailed Implementation

[0074] The present invention will now be described in detail with reference to the accompanying drawings and embodiments. It should be noted that the following embodiments are only used to further illustrate the present invention and should not be construed as limiting the scope of protection of the present invention. Some non-essential improvements and adjustments made by those skilled in the art based on the content of the present invention are still within the scope of protection of the present invention.

[0075] Unless otherwise specified, the raw materials used in the examples and comparative examples are all disclosed in the prior art, such as those that can be directly purchased or prepared according to the preparation methods disclosed in the prior art.

[0076] In this embodiment, the reverse osmosis membrane used is the CA Hydranautics SWC4-LD type aromatic polyamide reverse osmosis membrane from the United States. The pervaporation membrane used is a polyacrylonitrile pervaporation membrane from GFT GmbH, Germany.

[0077] According to a preferred embodiment of the present invention, taking dibutyl terephthalate as an example, the method for continuously preparing dibutyl terephthalate includes:

[0078] (1): Grind the prepared terephthalic acid and n-butanol until an emulsion is formed, which will be used as the raw material for the first esterification reaction.

[0079] (2): The esterification raw material liquid is pumped into the first tubular reactor at a certain temperature and pressure to carry out a first esterification reaction. The reaction mixture is condensed and collected in the crude terephthalic acid diester storage tank.

[0080] (3): The reaction mixture is pumped into the inlet of the reverse osmosis membrane module, which includes three reverse osmosis membranes, and the three reverse osmosis membranes are pressurized sequentially.

[0081] (4): The first stage concentrate is pumped into the inlet of the second stage reverse osmosis membrane, and the second stage concentrate is pumped into the inlet of the third stage reverse osmosis membrane. The concentrate that has passed through the first to third stage reverse osmosis system is dehydrated. After dehydration for a period of time, the pressure is reduced by a pressure reducing valve, and the concentrate that has been concentrated in the third stage is pumped into a two-stage tubular reactor for secondary esterification.

[0082] (5): The permeate from the three-stage reverse osmosis membrane module is pumped into the inlet of the pervaporation device for pervaporation to separate n-butanol and water. The pervaporation device uses a pervaporation membrane.

[0083] (6): The separated n-butanol is pumped into the concentrated liquid after three-stage concentration, and the raw material n-butanol is added. Together, they enter the second tubular reactor for secondary esterification reaction. The reaction product is condensed and collected in the product tank by the condenser, and finally high-yield dibutyl terephthalate is obtained.

[0084] In the above embodiments, dibutyl terephthalate, monobutyl terephthalate, n-butanol, and water are separated using a reverse osmosis membrane. Most of the water and a small amount of n-butanol pass through the reverse osmosis membrane, achieving the separation of large organic molecules and small inorganic molecules. Dibutyl terephthalate and monobutyl terephthalate are retained and concentrated. After three stages of retention and concentration, the dibutyl terephthalate and monobutyl terephthalate enter the second tubular reactor for further esterification. The water and a small amount of n-butanol that have passed through the reverse osmosis membrane are then separated by a permeate membrane to achieve a high concentration of n-butanol and membrane permeate. The n-butanol collected through the permeate membrane is pumped into the second tubular reactor for secondary esterification feedstock replenishment. The reaction products of the secondary esterification reaction are condensed and collected in a product tank, ultimately yielding a high yield of dibutyl terephthalate.

[0085] In this invention, the entire system requires two tubular reactors and one reverse osmosis separation system. Each reactor has a built-in turbulence-inducing component, and the entire reaction is carried out under catalyst-free, high-temperature, and high-pressure conditions.

[0086] In this invention, the membrane module uses a three-stage reverse osmosis membrane, with each membrane module referred to as a stage. The pervaporation membrane is considered a stage within the entire osmosis unit.

[0087] In this invention, the three-stage reverse osmosis membranes are used in series for permeation, see... Figure 1 The permeation units are arranged in series and parallel.

[0088] The reverse osmosis membrane module in this invention mainly adopts hollow fiber type, while other types such as tubular, spiral wound and plate and frame are not restricted and can be adjusted according to requirements.

[0089] The pervaporation membrane assembly in this invention is mainly spiral wound, but other types such as hollow fiber, plate and frame and tubular are not restricted and can be adjusted according to requirements.

[0090] The membrane separation described in this invention includes the following steps:

[0091] Step a: First, the primary esterification product from the first tubular reactor is pumped into the first-stage inlet of the reverse osmosis membrane, and then concentrated and dehydrated by passing through a third-stage reverse osmosis membrane. Step b: The concentrate from the first to third-stage reverse osmosis membranes is pumped into the second tubular reactor. Step c: All the permeate from the three stages is combined and pumped into a pervaporation device for vacuum separation of water and n-butanol. The permeate passes through a combined spiral wound pervaporation membrane; the permeate is then condensed in a condenser and enters a gas-liquid separator. The condensed liquid is the membrane permeate, and the residual permeate from the pervaporation device is the n-butanol solution, which is pumped into the second tubular reactor. Step d: The concentrate and n-butanol solution undergo a secondary esterification reaction in the second tubular reactor to obtain the high-purity target product.

[0092] The reaction temperature, reaction pressure, reaction residence time, alcohol-acid ratio, pressurization and vacuum conditions in this invention are not unique and can be adjusted according to the use of the membrane and the ratio of raw material components.

[0093] According to one embodiment of the present invention, a system for the continuous production of diterephthalate includes a first tubular reactor, a reverse osmosis membrane module, a pervaporation membrane, and a second tubular reactor. The first tubular reactor is connected to a first feed pump and a second feed pump to feed a primary esterification reaction feed solution comprising terephthalic acid and alcohols. A first condenser and a crude diterephthalate storage tank are sequentially connected between the first tubular reactor and the reverse osmosis membrane module. The reverse osmosis membrane module includes at least three stages of reverse osmosis membranes. The reverse osmosis membrane module is connected to the pervaporation membrane to pass the resulting permeate into the pervaporation membrane. The pervaporation membrane is connected to a third feed pump and a fourth feed pump to pass the resulting alcohols into the second tubular reactor. The reverse osmosis membrane module is connected to the third feed pump and the fourth feed pump to pass the resulting concentrate into the second tubular reactor. The second tubular reactor is connected to the third feed pump and the fourth feed pump. The second tubular reactor is connected to a third condenser, which is connected to a refined diterephthalate storage tank.

[0094] According to one embodiment of the present invention, the first feed pump and the second feed pump are respectively connected to the grinding mill, the pervaporation membrane is connected to the second condenser, the second condenser, the gas-liquid separator and the water storage tank are connected in sequence, the discharge pipelines of the reverse osmosis membrane module and the pervaporation membrane are respectively provided with a first pressure reducing valve and a second pressure reducing valve, and are then connected to the third feed pump and the fourth feed pump, the first condenser and the crude terephthalate storage tank are respectively provided with a first back pressure valve, the first tubular reactor and the crude terephthalate storage tank are provided with a first high pressure pump, the reverse osmosis membrane module and the pervaporation membrane are provided with a second high pressure pump, and the third condenser and the refined terephthalate storage tank are provided with a second back pressure valve.

[0095] Example 1

[0096] The process flow of this embodiment is as follows: Figure 1 As shown.

[0097] Using n-butanol as a solvent, 5000g of a 5% (w / w) terephthalic acid mixture was prepared and ground in a grinder for 1 hour for material preparation. The first and second tubular reactors were set to a reaction temperature of 340℃, a reaction pressure of 15MPa, and a reaction residence time of 12min, respectively. The grinding solution was alternately fed into the first tubular reactor via the first and second feed pumps. The primary esterification solution was cooled by the first condenser and then collected in a crude DBT storage tank via the first back pressure valve. The crude DBT solution was pressurized to 4.5 MPa by a first high-pressure pump and then subjected to three-stage permeation through a reverse osmosis membrane module for 50 minutes. The permeate was then pumped into a vaporization permeation membrane by a second high-pressure pump for the separation of esterified water and n-butanol. A vacuum pump controlled the vacuum level at 50 kPa. The esterified water passed through the vaporization permeation membrane and a gas-liquid separator, and was collected in an esterified water storage tank. The retained n-butanol solution was continuously added to the second tubular reactor system through a second pressure reducing valve. This, along with the dibutyl terephthalate and monobutyl terephthalate retained by the reverse osmosis membrane module, was alternately fed into the second tubular reactor through a third and fourth feed pump. The secondary esterified solution was cooled by a third condenser and then collected in a purified DBT storage tank through a second back pressure valve, ultimately yielding high-purity DBT product. The experimental results are shown in Table 1.

[0098] Example 2

[0099] The process flow of this embodiment is as follows: Figure 1 As shown.

[0100] Using n-butanol as a solvent, 5000g of a 10% (w / w) terephthalic acid mixture was prepared and ground in a grinder for 1 hour for material preparation. The first and second tubular reactors were set to a reaction temperature of 350℃, a reaction pressure of 13MPa, and a reaction residence time of 14min, respectively. The grinding solution was alternately fed into the first tubular reactor via the first and second feed pumps. The primary esterification solution was cooled by the first condenser and then collected in a crude DBT storage tank via the first back pressure valve. The crude DBT solution was pressurized to 3.5 MPa by a first high-pressure pump and then subjected to three-stage permeation through a reverse osmosis membrane module for 50 minutes. The permeate was then pumped into a vaporization permeation membrane by a second high-pressure pump for the separation of esterified water and n-butanol. A vacuum pump controlled the vacuum level at 50 kPa. The esterified water passed through the vaporization permeation membrane and a gas-liquid separator, and was collected in an esterified water storage tank. The retained n-butanol solution was continuously added to the second tubular reactor system through a second pressure reducing valve. This, along with the dibutyl terephthalate and monobutyl terephthalate retained by the reverse osmosis membrane module, was alternately fed into the second tubular reactor through a third and fourth feed pump. The secondary esterified solution was cooled by a third condenser and then collected in a purified DBT storage tank through a second back pressure valve, ultimately yielding high-purity DBT product. The experimental results are shown in Table 1.

[0101] Example 3

[0102] The process flow of this embodiment is as follows: Figure 1 As shown.

[0103] Using n-butanol as a solvent, 5000g of a 25% (w / w) terephthalic acid mixture was prepared and ground in a grinder for 1 hour for material preparation. The first and second tubular reactors were set to a reaction temperature of 370℃, a reaction pressure of 16MPa, and a reaction residence time of 15min, respectively. The grinding solution was alternately fed into the first tubular reactor via the first and second feed pumps. The primary esterification solution was cooled by the first condenser and then collected in a crude DBT storage tank via the first back pressure valve. The crude DBT solution was pressurized to 2.0 MPa by a first high-pressure pump and then subjected to three-stage permeation through a reverse osmosis membrane module for 50 minutes. The permeate was then pumped into a vaporization permeation membrane by a second high-pressure pump for the separation of esterified water and n-butanol. A vacuum pump controlled the vacuum level at 60 kPa. The esterified water passed through the vaporization permeation membrane and a gas-liquid separator, and was collected in an esterified water storage tank. The retained n-butanol solution was continuously added to the second tubular reactor system through a second pressure reducing valve. This, along with the dibutyl terephthalate and monobutyl terephthalate retained by the reverse osmosis membrane module, was alternately fed into the second tubular reactor through a third and fourth feed pump. The secondary esterified solution was cooled by a third condenser and then collected in a purified DBT storage tank through a second back pressure valve, ultimately yielding high-purity DBT product. The experimental results are shown in Table 1.

[0104] Example 4

[0105] The process flow of this embodiment is as follows: Figure 1 As shown.

[0106] Using n-butanol as a solvent, 5000g of a 20% (w / w) terephthalic acid mixture was prepared and ground in a grinder for 1 hour for material preparation. The first and second tubular reactors were set to a reaction temperature of 380℃, a reaction pressure of 18MPa, and a reaction residence time of 11min, respectively. The grinding solution was alternately fed into the first tubular reactor via the first and second feed pumps. The primary esterification solution was cooled by the first condenser and then collected in a crude DBT storage tank via the first back pressure valve. The crude DBT solution was pressurized to 4.5 MPa by a first high-pressure pump and then subjected to three-stage permeation through a reverse osmosis membrane module for 50 minutes. The permeate was then pumped into a vaporization permeation membrane by a second high-pressure pump for the separation of esterified water and n-butanol. A vacuum pump controlled the vacuum level at 70 kPa. The esterified water passed through the vaporization permeation membrane and a gas-liquid separator, and was collected in an esterified water storage tank. The retained n-butanol solution was continuously added to the second tubular reactor system through a second pressure reducing valve. This, along with the dibutyl terephthalate and monobutyl terephthalate retained by the reverse osmosis membrane module, was alternately fed into the second tubular reactor through a third and fourth feed pump. The secondary esterified solution was cooled by a third condenser and then collected in a purified DBT storage tank through a second back pressure valve, ultimately yielding high-purity DBT product. The experimental results are shown in Table 1.

[0107] Example 5

[0108] The process flow of this embodiment is as follows: Figure 1 As shown.

[0109] Using n-butanol as a solvent, 5000g of a 20% (w / w) terephthalic acid mixture was prepared and ground in a grinder for 1 hour for material preparation. The first and second tubular reactors were set to a reaction temperature of 350℃, a reaction pressure of 15MPa, and a reaction residence time of 10min, respectively. The grinding solution was alternately fed into the first tubular reactor via the first and second feed pumps. The primary esterification solution was cooled by the first condenser and then collected in a crude DBT storage tank via the first back pressure valve. The crude DBT solution was pressurized to 5.5 MPa by a first high-pressure pump and then subjected to three-stage permeation through a reverse osmosis membrane element for 50 minutes. The permeate was then pumped by a second high-pressure pump into a vaporization permeation membrane for the separation of esterified water and n-butanol. A vacuum pump controlled the vacuum level at 80 kPa. The esterified water passed through the vaporization permeation membrane and a gas-liquid separator, and was collected in an esterified water storage tank. The retained n-butanol solution was continuously added to the second tubular reactor system through a second pressure reducing valve. This, along with the dibutyl terephthalate and monobutyl terephthalate retained by the reverse osmosis membrane element, was alternately fed into the second tubular reactor through a third and fourth feed pump. The secondary esterified solution was cooled by a third condenser and then collected in a purified DBT storage tank through a second back pressure valve, ultimately yielding high-purity DBT product. The experimental results are shown in Table 1.

[0110] Example 6

[0111] The process flow of this embodiment is as follows: Figure 1 As shown.

[0112] Using n-butanol as a solvent, 5000g of a 15% (w / w) terephthalic acid mixture was prepared and ground for 1 hour. The first and second tubular reactors were set to a reaction temperature of 345℃, a reaction pressure of 14MPa, and a reaction residence time of 11min, respectively. The grinding solution was alternately fed into the first tubular reactor via the first and second feed pumps. The primary esterification solution was cooled by the first condenser and then collected in a crude DBT storage tank via the first back pressure valve. The crude DBT solution was pressurized to 4.5 MPa by a first high-pressure pump and then subjected to three-stage osmosis through a reverse osmosis membrane module for 50 minutes. The permeate was then pumped into a vaporization membrane by a second high-pressure pump for the separation of esterified water and n-butanol. A vacuum pump controlled the vacuum level at 55 kPa. The esterified water passed through the vaporization membrane and a gas-liquid separator and was collected in an esterified water storage tank. The retained n-butanol solution was continuously added to the second tubular reactor system through a second pressure reducing valve. This, along with the dibutyl terephthalate and monobutyl terephthalate retained by the reverse osmosis membrane module, was alternately fed into the second tubular reactor through a third and fourth feed pump. The secondary esterified solution was cooled by a third condenser and then collected in a purified DBT storage tank through a second back pressure valve, ultimately yielding high-purity DBT product. The experimental results are shown in Table 1.

[0113] Example 7

[0114] The process flow of this embodiment is as follows: Figure 1 As shown.

[0115] Using n-butanol as a solvent, 5000g of a 15% (w / w) terephthalic acid mixture was prepared and ground for 1 hour using a grinder. The first and second tubular reactors were set to a reaction temperature of 350℃, a reaction pressure of 15MPa, and a reaction residence time of 13min, respectively. The grinding solution was alternately fed into the first tubular reactor via the first and second feed pumps. The primary esterification solution was cooled by the first condenser and then collected in a crude DBT storage tank via the first back pressure valve. The crude DBT solution was pressurized to 4.5 MPa by a first high-pressure pump and then subjected to three-stage permeation through a reverse osmosis membrane module for 50 minutes. The permeate was then pumped into a vaporization permeation membrane by a second high-pressure pump for the separation of esterified water and n-butanol. A vacuum pump controlled the vacuum level at 50 kPa. The esterified water passed through the vaporization permeation membrane and a gas-liquid separator, and was collected in an esterified water storage tank. The retained n-butanol solution was continuously added to the second tubular reactor system through a second pressure reducing valve. This, along with the dibutyl terephthalate and monobutyl terephthalate retained by the reverse osmosis membrane module, was alternately fed into the second tubular reactor through a third and fourth feed pump. The secondary esterified solution was cooled by a third condenser and then collected in a purified DBT storage tank through a second back pressure valve, ultimately yielding high-purity DBT product. The experimental results are shown in Table 1.

[0116] Example 8

[0117] The process flow of this embodiment is as follows: Figure 1 As shown.

[0118] Using n-butanol as a solvent, 5000g of a 10% (w / w) terephthalic acid mixture was prepared and ground in a grinder for 1 hour for material preparation. The first and second tubular reactors were set to a reaction temperature of 350℃, a reaction pressure of 16MPa, and a reaction residence time of 13min, respectively. The grinding solution was alternately fed into the first tubular reactor via the first and second feed pumps. The primary esterification solution was cooled by the first condenser and then collected in a crude DBT storage tank via the first back pressure valve. The crude DBT solution was pressurized to 4.0 MPa by a first high-pressure pump and then subjected to three-stage permeation through a reverse osmosis membrane module for 50 minutes. The permeate was then pumped into a vaporization permeation membrane by a second high-pressure pump for the separation of esterified water and n-butanol. A vacuum pump controlled the vacuum level at 50 kPa. The esterified water passed through the vaporization permeation membrane and a gas-liquid separator, and was collected in an esterified water storage tank. The retained n-butanol solution was continuously added to the second tubular reactor system through a second pressure reducing valve. This, along with the dibutyl terephthalate and monobutyl terephthalate retained by the reverse osmosis membrane module, was alternately fed into the second tubular reactor through a third and fourth feed pump. The secondary esterified solution was cooled by a third condenser and then collected in a purified DBT storage tank through a second back pressure valve, ultimately yielding high-purity DBT product. The experimental results are shown in Table 1.

[0119] Table 1

[0120]

[0121] In the liquid phase composition analysis in Table 1, the results of the first-order reaction are as follows: Figure 1 The results of the liquid chromatography analysis of sample T1 were as follows: Secondary reaction results were... Figure 1 Results of liquid chromatography analysis of sample T3.

[0122] This invention employs a two-stage esterification reaction, achieving a terephthalic acid conversion rate greater than 99.8% and a dibutyl terephthalate yield greater than 98.5%. This invention enables continuous production of dibutyl terephthalate through continuous feeding at the front and continuous output at the back, with a simple process flow suitable for industrial production.

[0123] The purpose of this invention is to innovatively combine tubular reaction and reverse osmosis separation processes. The tubular reaction process shortens the reaction time and reduces byproduct formation by enhancing mass and heat transfer and avoiding the use of catalysts. The reverse osmosis separation process continuously separates the water generated throughout the reaction, disrupting the reaction equilibrium and promoting a sustained forward reaction, thereby improving the purity and yield of the target product. This two-stage tubular reaction process combined with reverse osmosis separation significantly simplifies the post-processing purification process and enables 24-hour continuous feeding and continuous production of high-purity target products, offering advantages for large-scale industrial application.

Claims

1. A continuous production method for diterephthalate, comprising the following steps: (1) Terephthalic acid and alcohols are passed into the first tubular reactor for a first esterification reaction, and the reaction mixture is obtained after condensation. (2) The reaction mixture is passed through a membrane module for reverse osmosis to obtain a concentrate and a permeate containing water and alcohol, respectively. (3) The permeate is subjected to pervaporation separation treatment to obtain alcohols and water respectively; (4) The alcohol obtained in step (3) and the concentrate obtained in step (2) are fed into the second tubular reactor for a secondary esterification reaction to obtain terephthalic acid diester.

2. The continuous production method of terephthalate according to claim 1, characterized in that... In step (1): The alcohol is selected from at least one of n-butanol, n-pentanol, and isopropanol; and / or, The mass concentration of terephthalic acid is 5% to 25% based on the total mass of terephthalic acid and alcohols; and / or, The primary esterification reaction temperature is 340–380 °C; and / or, The pressure for a single esterification reaction is 13.0–18.0 MPa; and / or, The esterification reaction time is 10.0–16.0 min.

3. The continuous production method of diterephthalate according to claim 1, characterized in that: In step (1), terephthalic acid and alcohols are ground into an emulsion and then introduced into the first tubular reactor.

4. The continuous production method of diterephthalate according to claim 1, characterized in that... In step (2): The reverse osmosis time is 40–60 min; and / or, The reverse osmosis pressure is 2.0–5.5 MPa; and / or, The membrane module includes at least three reverse osmosis membranes; Preferably, the reverse osmosis membrane is an aromatic polyamide reverse osmosis membrane; and / or, Preferably, the reverse osmosis membrane is a hollow fiber type, spiral wound type, tubular type, or plate and frame type.

5. The continuous production method of diterephthalate according to claim 1, characterized in that... In step (3): The vacuum degree of pervaporation is 50–80 kPa; and / or, Pervaporation separation uses a pervaporation membrane for separation; Preferably, the pervaporation membrane is a polyacrylonitrile pervaporation membrane; and / or, Preferably, the pervaporation membrane is spiral wound, hollow fiber, plate and frame, or tubular.

6. The continuous production method of diterephthalate according to claim 1, characterized in that... In step (4): The secondary esterification reaction temperature is 340–380℃; and / or, The secondary esterification reaction pressure is 13.0–18.0 MPa; and / or, The secondary esterification reaction time is 10.0–16.0 min.

7. A continuous production system for diterephthalate, preferably used in the method according to any one of claims 1 to 6, comprising: The first tubular reactor is configured to receive terephthalic acid and alcohols, and discharge the reaction mixture; A reverse osmosis membrane module configured to receive a reaction mixture and discharge permeate and concentrate; A pervaporation membrane configured to receive permeate and discharge alcohols and water; The second tubular reactor is configured to receive concentrate and alcohols discharged from the pervaporation membrane, as well as diterephthalate discharged from the pervaporation membrane.

8. The continuous production system for diterephthalate according to claim 7, characterized in that: A first condenser and a crude terephthalate storage tank are sequentially connected between the first tubular reactor and the reverse osmosis membrane module; and / or, The pervaporation membrane is connected to a second condenser, and the second condenser, gas-liquid separator, and water storage tank are connected in sequence; and / or, The second tubular reactor is connected to a third condenser, which is connected to a refined terephthalic acid diester storage tank.

9. The continuous production system for diterephthalate according to claim 8, characterized in that: The first tubular reactor is connected to a first feed pump and a second feed pump, which are connected to a grinding mill; and / or, The second tubular reactor is connected to a third feed pump and a fourth feed pump, respectively; and / or, The discharge lines of the reverse osmosis membrane module and the pervaporation membrane are combined and then connected to the third feed pump and the fourth feed pump, respectively.

10. The continuous production system for terephthalate according to claim 8, characterized in that: A first back pressure valve is installed between the first condenser and the crude terephthalate storage tank; and / or, A first high-pressure pump is installed between the first tubular reactor and the crude terephthalate storage tank; and / or, A second high-pressure pump is provided between the reverse osmosis membrane module and the pervaporation membrane; and / or, A first pressure-reducing valve and a second pressure-reducing valve are respectively installed on the discharge lines of the reverse osmosis membrane module and the pervaporation membrane; and / or, A second back pressure valve is installed between the third condenser and the refined terephthalic acid diester storage tank.

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