A system and method for the continuous synthesis of 2,4-dichlorophenoxyacetic acid isooctyl ester
By using a combination of a backpack-type reactive distillation column and a solid catalyst, the problems of high energy consumption and equipment corrosion in the synthesis of 2,4-dichlorophenoxyacetic acid isooctyl ester were solved, achieving continuous production with high conversion rate and reducing cost and energy consumption.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- SHANDONG WEIFANG RAINBOW CHEMICAL CO LTD
- Filing Date
- 2024-03-18
- Publication Date
- 2026-06-12
AI Technical Summary
The existing methods for synthesizing 2,4-dichlorophenoxyacetic acid isooctyl ester have problems such as high energy consumption, strong equipment corrosion, high equipment investment costs, and unsatisfactory conversion rates.
Continuous synthesis is achieved using a backpack-type reactive distillation column and solid catalysts such as macroporous styrene-based strong base anion exchange resins. Through the combination of multi-stage backpack-type reactors and distillation columns, continuous reaction of materials is realized, reaction residence time is increased, and conversion rate is improved.
It reduces energy consumption and equipment investment costs, improves conversion rate, simplifies process flow, reduces floor space and labor costs, and achieves efficient continuous transesterification production.
Smart Images
Figure CN118179061B_ABST
Abstract
Description
Technical Field
[0001] This invention relates to a system and method for the continuous synthesis of isooctyl 2,4-dichlorophenoxyacetic acid, belonging to the field of chemical synthesis technology. Background Technology
[0002] 2,4-Dichlorophenoxyacetic acid isooctyl ester is a phenoxycarboxylic acid ester herbicide that effectively controls the growth of various herbaceous plants, especially broadleaf weeds. It is widely used in agriculture, horticulture, and forestry. In addition, it can also be used as a plant growth regulator and a fruit tree spray.
[0003] The common methods and procedures for synthesizing isooctyl 2,4-dichlorophenoxyacetic acid are as follows:
[0004] Patent CN103772200A discloses a production process for isooctyl 2,4-dichlorophenoxyacetic acid, using 2,4-dichlorophenoxyacetic acid and isooctyl alcohol as raw materials under catalytic conditions. The process involves removing moisture from the system via an azeotropic reaction of toluene and water to promote the forward reaction. The specific reaction equation is as follows:
[0005]
[0006] In addition, patents CN108947837A, CN108947821A, CN108947815A, and CN108947814A disclose a production process for preparing 2,4-dichlorophenoxyacetic acid isooctyl ester using batch operation and multi-reactor series operation. The specific steps are as follows: using 2,4-dichlorophenoxyacetic acid methyl ester and isooctyl alcohol as raw materials, transesterification is carried out under strong acid catalyst conditions to produce methanol and 2,4-dichlorophenoxyacetic acid isooctyl ester. The reaction equation is:
[0007]
[0008] The aforementioned existing technologies have the following drawbacks: 1. The toluene azeotropic dehydration process using toluene as a solvent is energy-intensive and generates wastewater; 2. The use of strong acids as catalysts results in highly corrosive equipment and stringent material requirements. The high requirements for equipment lead to significant investment costs, coupled with high maintenance costs, resulting in high overall costs; 3. The use of conventional distillation columns results in insufficient residence time, making it impossible to obtain a reaction solution with a satisfactory conversion rate. Summary of the Invention
[0009] To address the shortcomings of existing technologies, this invention provides a system for the continuous synthesis of isooctyl 2,4-dichlorophenoxyacetic acid, and a method for its continuous synthesis using this system. This invention employs a backpack-type reactive distillation column, solving the problems of short residence time and inability to achieve continuous production with conventional distillation columns; it also solves the problem of increased energy consumption due to the need for additional distillation columns for post-processing in multiple reactors. The entire process is highly automated, energy-efficient, and has a high conversion rate of the reaction liquid, enabling continuous transesterification production and saving energy and equipment investment.
[0010] The specific technical solution of this invention is as follows:
[0011] A system for the continuous synthesis of isooctyl 2,4-dichlorophenoxyacetic acid, the system comprising:
[0012] The raw material tanks include a methyl 2,4-dichlorophenoxyacetate tank and an isooctyl alcohol tank;
[0013] A premixing kettle is used for premixing raw materials; the inlet is connected to the raw material tank.
[0014] A backpack-type distillation column includes a distillation column and at least one backpack-type reactor. The upper and middle parts of the distillation column are connected to a premixing vessel. The distillation column is composed of multiple distillation column sections. Each distillation column section has at most one backpack-type reactor. Each backpack-type reactor is provided with a first feed inlet, a second feed inlet, an overflow outlet, a first discharge outlet, and a vapor phase outlet. The first feed inlet of each backpack-type reactor is connected to the bottom of the corresponding distillation column section, the first discharge outlet is connected to the top of the corresponding distillation column section, and the vapor phase outlet is connected to the corresponding distillation column section. The second feed inlet of the first-stage backpack-type reactor is connected to the bottom of the previous distillation column section, and the second feed inlets of other backpack-type reactors are connected to the overflow outlet of the previous-stage backpack-type reactor.
[0015] The reboiler is connected to the bottom outlet of the distillation column; and
[0016] The methanol processing unit includes a top condenser connected to the gas outlet at the top of the distillation column, a liquid outlet connected to a reflux ratio controller, one outlet of the reflux ratio controller connected to the upper part of the distillation column, and the other outlet connected to a methanol receiving tank.
[0017] Furthermore, when the backpack reactors are multi-stage, they are arranged in descending order, with the first-stage backpack reactor being the highest. The premixing vessel is connected to the distillation column at a higher position than the first-stage backpack reactor.
[0018] Furthermore, the material is continuously fed into the distillation column via the premixing vessel, and then continuously fed into the backpack reactor. The material reacts continuously in the backpack reactor and the distillation column, which increases the reaction time and improves the conversion rate of the material.
[0019] Furthermore, backpack reactors can increase the reaction residence time, allowing for better material reaction, improving material conversion rates, and yielding a qualified reaction solution. Backpack reactors can be selected in different stages, such as two, three, four, five, etc., as needed. The number of distillation column sections can also be selected as required, such as 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, etc. The selection of distillation column sections and backpack reactors is based on actual needs to ensure that the final reaction solution achieves a qualified conversion rate.
[0020] Furthermore, the backpack reactor has two liquid feed lines, two liquid discharge lines, and one vapor phase line. The two liquid feed lines are respectively the liquid lines from the distillation column section to the backpack reactor and the liquid lines from the previous stage backpack reactor to this stage backpack reactor. The two liquid discharge lines are the liquid lines from this stage backpack reactor to the next stage backpack reactor and the liquid lines from the backpack reactor to the top of the corresponding column section. The vapor phase line connects the backpack reactor to the corresponding distillation column section to ensure vapor phase equilibrium between them.
[0021] Furthermore, when the backpack reactor is the first stage, since there is no previous backpack reactor, the second feed inlet is connected to the previous distillation column section, which is the distillation column section above the distillation column section corresponding to the backpack reactor.
[0022] Furthermore, when the backpack reactor is the last stage, since there is no next stage backpack reactor, its overflow port is closed, the material does not flow out from the overflow port, and the first feed port of the backpack reactor at this point is not connected to the distillation column section.
[0023] Furthermore, each distillation column section and each backpack reactor is equipped with a solid-phase catalyst. The solid-phase catalyst can be any catalyst reported in the prior art, preferably a mild catalyst with low corrosivity to the equipment, such as a macroporous styrene-based strong base anion exchange resin.
[0024] Furthermore, a transfer pump is installed between the premixing vessel and the distillation column. A transfer pump is installed on the pipeline connecting the first outlet of each backpack reactor to the corresponding distillation column section. The material coming out of the bottom of the backpack reactor re-enters the corresponding distillation column section for separation through the transfer pump.
[0025] Furthermore, the distillation column is connected to a vacuum pump to maintain negative pressure in both the backpack-type distillation column and the reboiler.
[0026] In a specific embodiment of the present invention, the distillation column consists of 5 sections, and the backpack reactor is in three stages, arranged in a top-to-bottom order: the first-stage backpack reactor is located at the third distillation column section, the second-stage backpack reactor is located at the fourth distillation column section, and the third-stage backpack reactor is located at the fifth distillation column section.
[0027] This invention also provides a method for the continuous synthesis of isooctyl 2,4-dichlorophenoxyacetic acid. This method uses methyl 2,4-dichlorophenoxyacetic acid and isooctyl alcohol as raw materials, and employs the aforementioned system for the continuous synthesis of isooctyl 2,4-dichlorophenoxyacetic acid. The catalyst used in the reaction process is a solid catalyst, which is fixed on the distillation column trays and the backpack reactor. The solid catalyst is preferably a macroporous styrene-based strong basic anion exchange resin.
[0028] Furthermore, the above method includes the following specific steps:
[0029] (1) Methyl 2,4-dichlorophenoxyacetic acid and isooctyl alcohol are introduced into the premixing vessel and reach reaction equilibrium in the premixing vessel;
[0030] (2) The material that has reached reaction equilibrium in the premixing kettle is continuously fed into the backpack distillation column. The material enters the first backpack reactor through the first feed port and the second feed port. The material in the backpack reactor re-enters the corresponding distillation column section through the first discharge port. The material in the previous backpack reactor overflows into the next backpack reactor to continue the reaction. The backpack reactor and the distillation column maintain gas phase equilibrium.
[0031] (3) The methanol formed in the distillation column and backpack reactor is discharged from the top of the column, and the reaction liquid at the bottom of the distillation column flows continuously into the bottom of the column, forming the final reaction liquid. The reaction liquid in the bottom of the column is distilled to recover isooctyl alcohol and obtain 2,4-dichlorophenoxyacetic acid isooctyl ester.
[0032] Furthermore, the materials are stirred and mixed in a premixing vessel at room temperature for 2-4 hours.
[0033] Furthermore, the methanol discharged from the top of the column is condensed by the top condenser. Part of the condensed methanol is refluxed back into the distillation column, and the remainder is recovered into the methanol receiving tank. The remaining gas after condensation is either discharged as tail gas or further treated. By refluxing methanol, the isooctyl alcohol content in the methanol is ensured to be below 0.1%, and the reflux ratio is generally controlled at 1:2.5-3.5.
[0034] Furthermore, the molar ratio of isooctanol to methyl 2,4-dichlorophenoxyacetate is 1.3-2.5:1, for example 1.3:1, 1.4:1, 1.5:1, 1.6:1, 1.7:1, 1.8:1, 1.9:1, 2.0:1, 2.1:1, 2.2:1, 2.3:1, 2.4:1, 2.5:1, preferably 1.5-1.75:1.
[0035] Furthermore, the vacuum absolute pressure in the distillation column is 3000pa-7000pa, for example 3000pa, 4000pa, 5000pa, 6000pa, 7000pa, preferably 4000pa-5000pa.
[0036] Furthermore, the reaction temperature in the distillation column and backpack reactor is 80-140℃, for example 80℃, 90℃, 100℃, 110℃, 120℃, 130℃, 140℃, preferably 100-120℃.
[0037] Furthermore, the temperature of the tower pot is maintained at 80-140℃, for example, 80℃, 90℃, 100℃, 110℃, 120℃, 130℃, 140℃.
[0038] Furthermore, a qualified reaction solution is finally obtained in the reactor, which is then distilled to remove the solvent, thus yielding the final product.
[0039] This invention uses methyl 2,4-dichlorophenoxyacetate as a raw material, isooctanol as a raw material and solvent, employs a solid catalyst, and utilizes a backpack-type distillation column for negative pressure reactive distillation. Methanol is obtained at the top of the column, and a reaction liquid with satisfactory conversion is obtained at the bottom. This reaction liquid is then distilled to remove solvent, and excess isooctanol is recovered and recycled to obtain the qualified product. Compared with existing technologies, this invention has the following advantages:
[0040] 1. This invention uses a backpack-style distillation column, which reduces the design difficulty of the distillation column, ensures sufficient residence time for the reaction liquid, achieves qualified conversion rate, simplifies the process, reduces equipment footprint, and reduces energy consumption. The backpack-style distillation column design solves the problems of short residence time and inability to achieve continuous operation of conventional distillation columns. It also solves the problem of increased energy consumption due to the need for additional distillation columns for post-processing of multiple reactors in series.
[0041] 2. The catalyst used in this invention is relatively mild, has low equipment requirements and no special requirements, is simple to manufacture and easy to implement.
[0042] 3. In this invention, methyl 2,4-dichlorophenoxyacetic acid isooctyl ester is directly transesterified to generate 2,4-dichlorophenoxyacetic acid, eliminating the complex process of hydrolysis to generate 2,4-dichlorophenoxyacetic acid and then esterification to generate 2,4-dichlorophenoxyacetic acid isooctyl ester.
[0043] 4. This invention enables continuous synthesis of 2,4-dichlorophenoxyacetic acid isooctyl ester. The reaction process is simple, energy consumption is reduced, and methanol is separated in time during the reaction, eliminating the need for an additional tower for further separation of methanol and isooctyl alcohol. The entire process is highly automated, with one-button start-up and shutdown capabilities. It occupies a small area, reducing labor costs, lowering the labor intensity of workers, reducing energy consumption and equipment investment costs, and saving space.
[0044] 5. This invention utilizes a continuous transesterification reaction under negative pressure conditions, with continuous feeding of raw materials and continuous discharge of products. Methanol is separated by negative pressure reactive distillation, which accelerates the reaction rate, improves the conversion rate, and saves energy.
[0045] 6. The heat of reaction for distillation to remove impurities and solvents can be coupled and utilized during the rectification process. Energy coupling can minimize energy consumption, reduce reactor volume and floor space for the same production capacity, lower overall investment costs, and reduce the production threshold. Attached Figure Description
[0046] Figure 1 This is a schematic diagram of the system for the continuous synthesis of isooctyl 2,4-dichlorophenoxyacetic acid ester according to the present invention.
[0047] Figure 2 This is a schematic diagram of the feeding and discharging process of a backpack-type reactor.
[0048] In the diagram, 1. Premixing vessel, 2. Distillation column, 3. Top condenser, 4. Methanol receiving tank, 5. First-stage backpack reactor, 6. Second-stage backpack reactor, 7. Third-stage backpack reactor, 8. Reboiler, 9. Transfer pump, 10. Reflux ratio controller, 11. 2,4-Dichlorophenoxyacetic acid methyl ester tank, 12. Isooctyl alcohol tank. Detailed Implementation
[0049] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the following description is merely exemplary and does not limit the scope of protection of the present invention.
[0050] Example 1
[0051] This invention provides a continuous synthesis system for 2,4-dichlorophenoxyacetic acid isooctyl ester, comprising a feed tank, a premixing vessel, a backpack-type distillation column, a reboiler, and a methanol processing unit. The feed tank contains two feed materials: a methyl 2,4-dichlorophenoxyacetic acid tank and an isooctyl alcohol tank. The feed tank is connected to the premixing vessel, which is equipped with a stirring device. The premixing vessel is then connected to the backpack-type distillation column, where the premixed feed is continuously fed.
[0052] Furthermore, the backpack-type distillation column includes a distillation column and at least one backpack-type reactor. The upper part of the distillation column has a feed inlet connected to a premixing vessel for material inflow; this feed inlet is positioned higher than all backpack-type reactors. The distillation column consists of multiple column sections, with a minimum of one section, which can be designed as needed, such as 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, etc. Backpack-type reactors are located at the distillation column sections, with a maximum of one reactor per section. This means that backpack-type reactors can be installed in only some sections or in all sections. They can be located in adjacent sections or in non-adjacent sections. The purpose of the backpack-type reactors is to increase the residence time of the material. From top to bottom, backpack-type reactors are defined as primary, secondary, etc. The distillation column is connected to a vacuum pump, which puts the entire backpack-style distillation column under negative pressure, so that the methanol formed by the reaction is collected at the top of the distillation column and discharged.
[0053] like Figure 2 As shown, each backpack reactor is equipped with a first feed inlet, a second feed inlet, an overflow outlet, a first discharge outlet, and a vapor phase outlet. The first feed inlet of each backpack reactor is connected to the bottom of the corresponding distillation column section, allowing the material from that section to flow into the backpack reactor. The first discharge outlet is connected to the top of the corresponding distillation column section, allowing the material in that backpack reactor to re-enter the distillation column section for separation. The vapor phase outlet is connected to the corresponding distillation column section, achieving vapor phase balance between the distillation column and the backpack reactor. The second feed inlet of the first-stage backpack reactor is connected to the bottom of the previous distillation column section, and the second feed inlets of other backpack reactors are connected to the overflow outlet of their preceding backpack reactor.
[0054] Preferably, the first discharge port is located at the bottom of the backpack reactor. The first inlet, the second inlet, the overflow port, and the gas phase outlet are located at the top or top of the backpack reactor.
[0055] Furthermore, if the backpack reactor is the last stage (in descending order), its overflow port is closed because there is no next stage backpack reactor, so the material does not flow out of the overflow port, and the first feed port of the backpack reactor at that point is not connected to the distillation column section.
[0056] Furthermore, each distillation column section and each backpack reactor is equipped with a solid-phase catalyst. The solid-phase catalyst can be any catalyst reported in the prior art, preferably a mild catalyst with low corrosivity to the equipment, such as a macroporous styrene-based strong base anion exchange resin.
[0057] Furthermore, the reboiler serves two purposes: providing a heat source and increasing the reaction residence time; it can also function as a reboiler. The reaction liquid at the bottom of the distillation column is continuously fed into the reboiler, where it forms the final qualified reaction liquid. The reaction liquid in the reboiler is then discharged into other processing equipment, such as a distillation vessel, for distillation and solvent removal to remove excess isooctyl alcohol, yielding isooctyl 2,4-dichlorophenoxyacetic acid.
[0058] Furthermore, the top of the distillation column is connected to a methanol processing unit, which includes a top condenser connected to the gas outlet at the top of the distillation column. The liquid outlet of the top condenser is connected to a reflux ratio controller. One outlet of the reflux ratio controller is connected to the upper part of the distillation column, and the other outlet is connected to a methanol receiving tank. The reflux ratio controller controls the methanol reflux ratio. Methanol reflux improves the purity of methanol, ensuring that the isooctanol content in the recovered methanol is below 0.1%. Typically, the methanol reflux ratio is controlled between 1:2.5 and 3.5.
[0059] Furthermore, a transfer pump is installed between the premixing vessel and the distillation column. A transfer pump is also installed on the connecting pipeline between the first outlet of each backpack reactor and the distillation column. The material coming out of the bottom of the backpack reactor is re-entered into the corresponding distillation column section for separation through the transfer pump.
[0060] Example 2
[0061] like Figure 1 The diagram illustrates a specific embodiment of the continuous synthesis system for 2,4-dichlorophenoxyacetic acid isooctyl ester according to the present invention. The system comprises five distillation column sections and three backpack reactors, arranged in a top-to-bottom order: the first-stage backpack reactor is located at the third distillation column section, the second-stage backpack reactor at the fourth distillation column section, and the third-stage backpack reactor at the fifth distillation column section. Each distillation column section and each backpack reactor contains a solid-phase catalyst, which is a macroporous styrene-based strong-base anion exchange resin.
[0062] The continuous synthesis process of 2,4-dichlorophenoxyacetic acid isooctyl ester using this system is as follows:
[0063] 1. The raw materials in the 2,4-dichlorophenoxyacetic acid methyl ester tank and the isooctanol tank are fed into the premixing kettle. When the materials reach reaction equilibrium, they are fed into the second section of the distillation column through the transfer pump.
[0064] 2. The material enters the distillation column. The gaseous methanol produced by the reaction enters the top of the column, while the liquid phase enters the first-stage backpack reactor to continue the reaction. There is a gas-phase equilibrium between the first-stage backpack reactor and the distillation column. The material in the first-stage backpack reactor is discharged from the first outlet and enters the third distillation column section through a transfer pump. The gaseous methanol produced by the reaction is separated and finally enters the top of the column. The liquid phase enters the first-stage backpack reactor at the bottom of the third distillation column section to continue the reaction. When there is enough liquid phase in the first-stage backpack reactor, it enters the second-stage backpack reactor through the overflow port to continue the reaction.
[0065] 3. After the material enters the secondary backpack reactor, it continues to react. Similarly, the material in the secondary backpack reactor is discharged from the first outlet and re-enters the fourth distillation column section. The material at the bottom of the fourth distillation column section enters the second backpack reactor. There is a gas phase equilibrium between the second backpack reactor and the distillation column. The material overflowing from the secondary backpack reactor enters the tertiary backpack reactor.
[0066] 4. After the material enters the three-stage backpack reactor, the reaction continues. There is a gas phase equilibrium between the three-stage backpack reactor and the distillation column. The material in the three-stage backpack reactor is discharged from the first outlet and enters the fifth distillation column section through the transfer pump. The reaction liquid from the fifth distillation column section continuously enters the column bottom. In the column bottom, a qualified reaction liquid is obtained. The reaction liquid is transferred from the column bottom to the distillation kettle for distillation to remove isooctyl alcohol, yielding 2,4-dichlorophenoxyacetic acid isooctyl ester.
[0067] 5. The methanol produced by the reaction enters the top condenser of the column, and the condensed methanol enters the methanol receiving tank for recovery. A reflux ratio controller is installed between the top condenser and the methanol receiving tank to control the reflux and the extraction.
[0068] Example 3
[0069] The continuous synthesis of 2,4-dichlorophenoxyacetic acid isooctyl ester using the structure described in Example 2 is as follows:
[0070] Isooctol (99% purity) and methyl 2,4-dichlorophenoxyacetate (99% purity) were continuously fed into a premixing reactor at a mass flow rate of 17.83 g / min and 18.57 g / min, respectively. The mixture was stirred at room temperature for 2-4 hours to reach reaction equilibrium. Then, it was continuously fed into a backpack-type distillation column at a flow rate of 36.4 g / min. The absolute pressure of the backpack-type distillation column was controlled at 3000-7000 Pa, and the temperature of the distillation column and each backpack-type reactor was controlled at 100-120℃. The reflux ratio controller was set to 1:3. After 8 hours of stable operation, methanol fraction was obtained from the top of the column, with a methanol content greater than 99.9% and an isooctanol content less than 0.1%. The reaction liquid from the bottom of the column continuously flowed into the reboiler. The reboiler temperature was controlled at 100-120℃ and the reboiler absolute pressure was 3000-7000 Pa. A qualified reaction liquid was obtained in the reboiler. The content of 2,4-dichlorophenoxyacetic acid isooctyl ester in the reaction liquid was ≥76.78%, and the conversion rate of 2,4-dichlorophenoxyacetic acid methyl ester was 99.80%.
[0071] Comparative Example 1
[0072] 2,4-Dichlorophenoxyacetic acid isooctyl ester was synthesized by a batch reaction using the same catalyst as in Example 3. The steps are as follows: A solid catalyst, isooctol (99% purity), and methyl 2,4-dichlorophenoxyacetic acid (99% purity) were separately added to flasks. The mass of isooctol (99% purity) was 178.3 g, and the mass of methyl 2,4-dichlorophenoxyacetic acid (99% purity) was 185.7 g. The reaction was carried out under vacuum pressure of 3000-7000 Pa, heated to 100-120℃, and carried out for 8-10 h. The resulting reaction solution contained 76.75% 2,4-dichlorophenoxyacetic acid isooctyl ester, with a conversion rate of 99.7%. During the reaction, the gaseous fraction was collected and condensed to obtain methanol, in which the isooctol content was approximately 1%.
[0073] Because the methanol produced during the batch operation contains unreacted isooctanol, further distillation is needed to separate methanol and isooctanol in order to reuse the isooctanol, which increases the reaction process, energy consumption, and cost.
Claims
1. A system for the continuous synthesis of isooctyl 2,4-dichlorophenoxyacetic acid, characterized in that: include: The raw material tanks include a methyl 2,4-dichlorophenoxyacetate tank and an isooctyl alcohol tank; A premixing kettle is used for premixing raw materials; the inlet is connected to the raw material tank. A backpack-type distillation column includes a distillation column and at least one backpack-type reactor. The upper and middle parts of the distillation column are connected to a premixing vessel. The distillation column is composed of multiple distillation column sections. Each distillation column section has at most one backpack-type reactor. Each backpack-type reactor is provided with a first feed inlet, a second feed inlet, an overflow outlet, a first discharge outlet, and a vapor phase outlet. The first feed inlet of each backpack-type reactor is connected to the bottom of the corresponding distillation column section, the first discharge outlet is connected to the top of the corresponding distillation column section, and the vapor phase outlet is connected to the corresponding distillation column section. The second feed inlet of the first-stage backpack-type reactor is connected to the bottom of the previous distillation column section, and the second feed inlets of other backpack-type reactors are connected to the overflow outlet of the previous-stage backpack-type reactor. The reboiler is connected to the bottom outlet of the distillation column; and The methanol processing unit includes a top condenser connected to the gas outlet at the top of the distillation column, a liquid outlet connected to a reflux ratio controller, one outlet of the reflux ratio controller connected to the upper part of the distillation column, and the other outlet connected to a methanol receiving tank.
2. The system according to claim 1, characterized in that: The premixing vessel is connected to the distillation column at a higher position than the backpack reactor.
3. The system according to claim 1, characterized in that: The distillation column is connected to a vacuum pump.
4. The system according to claim 1, characterized in that: When the backpack reactor is the last stage, the overflow port of the last stage backpack reactor is closed, and its first feed port is not connected to the distillation column section.
5. The system according to claim 1, characterized in that: Solid-phase catalysts are installed in each section of the distillation column and each backpack reactor.
6. The system according to claim 5, characterized in that: The solid-phase catalyst is a macroporous styrene-based strong basic anion exchange resin.
7. The system according to claim 1 or 2, characterized in that: The distillation column has two or more sections, and the backpack reactor has two or more sections.
8. The system according to claim 1, characterized in that: A transfer pump is installed between the premixing vessel and the distillation column. A transfer pump is also installed on the pipeline connecting the first outlet of each backpack reactor to the corresponding distillation column section.
9. A method for the continuous synthesis of isooctyl 2,4-dichlorophenoxyacetic acid using the system described in claim 1, characterized in that: Includes the following steps: (1) Methyl 2,4-dichlorophenoxyacetic acid and isooctyl alcohol are introduced into the premixing vessel and reach reaction equilibrium in the premixing vessel; (2) The material that has reached reaction equilibrium in the premixing kettle is continuously fed into the backpack distillation column. The material enters the first backpack reactor through the first feed port and the second feed port. The material in the backpack reactor re-enters the corresponding distillation column section through the first discharge port. The material in the previous backpack reactor overflows into the next backpack reactor to continue the reaction. The backpack reactor and the distillation column maintain gas phase equilibrium. (3) The methanol formed in the distillation column and backpack reactor is discharged from the top of the column, and the reaction liquid at the bottom of the distillation column flows continuously into the bottom of the column, forming the final reaction liquid. The reaction liquid in the bottom of the column is distilled to recover isooctyl alcohol and obtain 2,4-dichlorophenoxyacetic acid isooctyl ester.
10. The method according to claim 9, characterized in that: Methanol discharged from the top of the column is condensed by the top condenser. Part of the condensed methanol is returned to the distillation column, and the remainder is recovered to the methanol receiving tank.
11. The method according to claim 9, characterized in that: The molar ratio of isooctyl alcohol to methyl 2,4-dichlorophenoxyacetic acid is 1.3-2.5:
1.
12. The method according to claim 11, characterized in that: The molar ratio of isooctyl alcohol to methyl 2,4-dichlorophenoxyacetic acid is 1.5-1.75:
1.
13. The method according to claim 9, characterized in that: The vacuum pressure in the distillation column is 3000 Pa - 7000 Pa; the reaction temperature in the distillation column and backpack reactor is 80-140℃.
14. The method according to claim 13, characterized in that: The vacuum absolute pressure in the distillation column is 4000pa-5000pa.
15. The method according to claim 13, characterized in that: The reaction temperature in the distillation column and backpack reactor is 100-120℃.