A device and process for switchable production of fine methyl acetate or acetic acid and methanol products

Abstract

The application discloses a device capable of switching production of refined methyl acetate or acetate and methyl alcohol products, which comprises a fourth rectifying tower capable of switching for separating an aqueous solution of acetate or for rectifying and extracting crude methyl acetate, an eighth rectifying tower capable of switching for removing low-boiling impurities or for evaporating and purifying an extractant and a first rectifying tower capable of switching for extractive rectification of methyl acetate or for removing light components; the fourth rectifying tower is connected with the first rectifying tower, a fifth rectifying tower for refining acetate and a decomposition tower for hydrolyzing methyl acetate respectively; the first rectifying tower is connected with a second rectifying tower for purifying methyl alcohol and a third rectifying tower for removing light components again respectively, and the third rectifying tower is connected with a seventh rectifying tower for removing light components for the third time. The device has two functions, i.e. production of acetate, methyl alcohol and refined methyl acetate can be adjusted in time according to market conditions.

Description

Technical Field

[0001] This invention relates to methyl acetate, and more specifically to an apparatus and process for switching between producing refined methyl acetate or acetic acid and methanol products. Background Technology

[0002] Methyl acetate, a colorless, transparent, low-boiling-point, fast-drying solvent, evaporates at a rate very close to that of acetone, slightly faster than ethyl acetate and butyl acetate. Simultaneously, methyl acetate exhibits a higher flash point and better anti-whitening properties (less whitening of the adhesive surface after fast drying). In formulations requiring low-boiling-point volatile organic solvents, methyl acetate can partially replace ethyl acetate, butyl acetate, cyclopentane, acetone, and methyl ethyl ketone (MEK). Methyl acetate is not classified as a restricted organic pollutant and meets the new environmental standards for paint, ink, resin, and adhesive manufacturers. It possesses broad solubility, capable of dissolving acrylic, vinyl, nitrocellulose, epoxy, polyurethane, polyester, and phenolic resins. Therefore, methyl acetate can be widely used in the production of paint cleaners, fuel system cleaners and additives, polymer solvents, foaming agents, fine chemical and pharmaceutical intermediates, and other fields.

[0003] Currently, methyl acetate is produced through two processes. One is to use methanol and acetic acid as raw materials, and then separate the unreacted residual monomers through esterification reaction and distillation. The other is to use by-products from the production of polyvinyl alcohol as raw materials, and then separate methanol, acetaldehyde, acetone, water, etc. through distillation to obtain refined methyl acetate. The latter is the dominant process.

[0004] Chinese patent document CN205035300U discloses a production system for high-purity refined methyl acetate, comprising: a first distillation column (1), a second distillation column (2), and a third distillation column (3), wherein the first distillation column (1) is connected to the second distillation column (2) and the third distillation column (3) respectively; a crude methyl acetate solution with a mass concentration of 78-81% is introduced into the first distillation column (1) through the feed inlet (4) and heated by 0.6 MPa steam or a bottom heater (16). As a heat source, after extraction and distillation, the material with a purity of about 99.8-99.85% is discharged from the top outlet (5) of the column. Part of it is returned to the first distillation column, and most of it is distilled into the third distillation column. The third distillation column is heated by 0.6 MPa steam or bottom heater (16). The light components such as acetaldehyde and acetone and a certain amount of methyl acetate are distilled from the top outlet (8) and sent to the waste liquid tank (15). The refined methyl acetate with a concentration of more than 99.90% is discharged from the bottom outlet (9). The first distillation column (1) sends the distilled methanol-containing ethylene glycol solvent to the second distillation column (2) to recover ethylene glycol. The second distillation column uses 3.6 MPa steam or a bottom heater (16) as a heat source. The methanol and other impurities obtained from the top outlet (11) are sent back to the alcoholysis raw liquid tank (14) for recycling, and the ethylene glycol with a purity of over 99.80% obtained from the bottom outlet (12) is sent to the ethylene glycol tank (13) for recycling. This utility model uses crude methyl acetate recovered from alcoholysis waste liquid as raw material and ethylene glycol as extractant. It adopts a three-column distillation method to obtain refined methyl acetate with a purity of over 99.90%, which solves the problem that light component impurities such as acetaldehyde and acetone of about 0.1% cannot be removed in the traditional process.

[0005] The existing technology has the following shortcomings: it can only produce pure methyl acetate and cannot flexibly adjust the output of pure methyl acetate, acetic acid and methanol products in a timely manner according to market demand. Summary of the Invention

[0006] The purpose of this invention is to provide an apparatus and process for switching between producing methyl acetate or acetic acid and methanol products, which can flexibly control the yield of refined methyl acetate, acetic acid and methanol.

[0007] On one hand, the present invention provides an apparatus for switching between producing refined methyl acetate or acetic acid and methanol products, comprising a fourth distillation column switchable for separating aqueous acetic acid solution or for distilling crude methyl acetate, an eighth distillation column switchable for removing impurities of low boiling point or for evaporating and purifying the extractant, and a first distillation column switchable for extracting and distilling methyl acetate or for removing light components; the fourth distillation column is connected to the first distillation column, a fifth distillation column for refining acetic acid, and a decomposition column for hydrolyzing methyl acetate; the first distillation column is connected to a second distillation column for purifying methanol and a third distillation column for further removing light components, and the third distillation column is connected to a seventh distillation column for a third removal of light components.

[0008] Furthermore, in the production of acetic acid and methanol, the fourth distillation column is connected to the fifth distillation column for refining acetic acid, the decomposition column for hydrolyzing methyl acetate, and the first distillation column, respectively; the first distillation column is connected to the second distillation column, the decomposition column, and the third distillation column for purifying methanol, respectively; the third distillation column is connected to the seventh distillation column; the eighth distillation column is also connected to the first separator for separating azeotropic agents and the second separator for separating azeotropic agents; the first separator is connected to the sixth distillation column and the fifth distillation column for distilling aqueous solutions of azeotropic agents, respectively; this allows for more flexible and timely adjustment of the production of refined methyl acetate, acetic acid, and methanol products according to market demand.

[0009] Furthermore, in the production of methyl acetate, the fourth distillation column is also connected to a ninth distillation column and a first distillation column for separating the extractant; the first distillation column is connected to a third distillation column; the third distillation column is connected to a seventh distillation column; the eighth distillation column is also connected to the ninth distillation column and an intermediate tank for storing the extractant; the intermediate tank for storing the extractant is connected to the fourth distillation column; this allows for more flexible and timely adjustment of the production of refined methyl acetate, acetic acid, and methanol products according to market demand.

[0010] Secondly, the present invention provides a process for producing refined methyl acetate or acetic acid and methanol using a switchable apparatus for producing refined methyl acetate or acetic acid and methanol products. This process involves controlling the fourth distillation column to switch between separating an aqueous acetic acid solution or distilling and extracting crude methyl acetate, the eighth distillation column to switch between removing impurities of low boiling points or evaporating and purifying the extractant, and the first distillation column to switch between extracting and distilling methyl acetate or removing light components, thereby producing refined methyl acetate or acetic acid and methanol.

[0011] Furthermore, when the fourth distillation column is switched to distillate and extract crude methyl acetate, the eighth distillation column is switched to evaporate and purify the extractant, and the first distillation column is switched to remove light components, it is used to produce refined methyl acetate. This allows for more flexible and timely adjustment of the output of refined methyl acetate, acetic acid, and methanol products according to market demand.

[0012] Furthermore, when switching the fourth distillation column for separating acetic acid aqueous solution, the eighth distillation column for removing low-boiling-point impurities, and the first distillation column for extracting and distilling methyl acetate, acetic acid and methanol are produced; the process for producing acetic acid and methanol includes:

[0013] S1: Using methyl acetate byproduct from the polyvinyl alcohol production process as raw material, an extractant is added for extractive distillation to obtain an aqueous solution of methyl acetate and an aqueous solution of methanol; the obtained aqueous solution of methyl acetate is added to a decomposition tower, and demineralized water and a catalyst are added to undergo a hydrolysis reaction; the obtained aqueous solution of methanol is added to a second distillation tower for methanol distillation to produce methanol;

[0014] S2: Extract and separate the mixture of acetic acid, methanol, unreacted methyl acetate, and water obtained from hydrolysis in step S1; obtain an aqueous solution of acetic acid and a mixed solution of methyl acetate and methanol azeotrope; add the obtained aqueous solution of acetic acid to the fifth distillation column for acetic acid purification, and reflux the obtained mixed solution of methyl acetate and methanol azeotrope into the first distillation column.

[0015] S3: An azeotropic agent is added to the acetic acid aqueous solution for azeotropic distillation to obtain an aqueous solution of acetic acid and the azeotropic agent; the acetic acid is collected.

[0016] Furthermore, the process for producing acetic acid and methanol also includes recovering the azeotropic agent and removing light components, wherein the step of recovering the azeotropic agent is as follows:

[0017] S1: The azeotropic aqueous solution flowing into the first separator is separated to obtain the azeotropic agent and a mixed solution containing the azeotropic agent; the azeotropic agent is recycled back into the fifth distillation column for reuse.

[0018] S2: The mixed solution containing the azeotropic agent obtained in S1 is added to the sixth distillation column for separation. The aqueous azeotropic agent obtained is added to the second separator for further separation. The bottom liquid of the distillation column is fed into the wastewater tank for neutralization and treatment.

[0019] S3: Separate the aqueous azeotropic agent to obtain a mixed solution of the azeotropic agent and the decomposition product of the azeotropic agent; add the obtained mixed solution containing the decomposition product of the azeotropic agent to the eighth distillation column to separate the impurities of low boiling point substances, the separated low boiling point substances are discharged, and the bottom liquid of the distillation column is returned to the first separator;

[0020] The step of removing the light components is as follows:

[0021] The aqueous solution of methyl acetate flowing into the third distillation column is used to separate light components. The resulting mixture containing methyl acetate is added to the seventh distillation column for further separation of light components. The bottom liquid of the distillation column is refluxed into the first distillation column.

[0022] The resulting mixed solution containing methyl acetate is further separated into light components. The light components are collected and processed in a recovery waste liquid tank, while the bottom liquid of the distillation column is refluxed into the third distillation column.

[0023] Furthermore, the extractants used in the production of refined methyl acetate or acetic acid and methanol are water and ethylene glycol; the extractant being ethylene glycol is used in the production of refined methyl acetate, and the extractant being water is used in the production of acetic acid and methanol.

[0024] The present invention has the following beneficial effects:

[0025] 1) This invention is a system with two functions, which can adjust the production of acetic acid, methanol and methyl acetate in a timely manner according to market conditions.

[0026] 2) The device of the present invention can be used with azeotropic agents, so that the azeotropic agents can be recycled, saving resources and protecting the environment.

[0027] 3) The device of the present invention can reduce the acetaldehyde content in the entire production process.

[0028] 4) This invention provides a method for significantly reducing the content of light component impurities such as acetaldehyde and acetone in methyl acetate to obtain high-purity methyl acetate.

[0029] 5) This invention minimizes investment costs for modifying existing distillation towers, pipelines, and storage tanks.

[0030] 6) The technology of this invention is mature and reliable, and allows for flexible production without affecting output during operation.

[0031] 7) The process of this invention is mature and has been industrialized. Attached Figure Description

[0032] Figure 1 This is a schematic diagram of the process apparatus for producing acetic acid and methanol in the apparatus for producing refined methyl acetate, acetic acid and methanol according to the present invention.

[0033] Figure 2 This is a schematic diagram of the process apparatus for producing refined methyl acetate in the apparatus for producing refined methyl acetate, acetic acid and methanol according to the present invention.

[0034] In the attached diagram, the arrows indicate the flow direction of each processing component, and the broken lines in the diagram indicate that the component does not pass through that route. Detailed Implementation

[0035] The examples provided are for illustrative purposes only and are not intended to limit the scope of the invention. Therefore, non-essential modifications and adjustments made to the embodiments by those skilled in the art based on the above description are still within the protection scope of this invention.

[0036] 1. Definition

[0037] Azeotropic agent: In azeotropic distillation, the third additive component used to form an azeotrope with one or two of the feed components is called an "azeotropic agent".

[0038] Extractant: A chemical reagent that can form an extract that is soluble in the organic phase with the extracted substance.

[0039] 2. The present invention also includes the following preferred embodiments.

[0040] Preferably, the azeotropic agent is n-butyl acetate.

[0041] Example 1

[0042] An apparatus for switching between producing refined methyl acetate or acetic acid and methanol products includes a fourth distillation column 4 switchable for separating aqueous acetic acid solution or for distilling crude methyl acetate; an eighth distillation column 8 switchable for removing impurities of low boiling point or for evaporating and purifying the extractant; and a first distillation column 1 switchable for extracting and distilling methyl acetate or for removing light components. The fourth distillation column 4 is connected to the first distillation column 1, a fifth distillation column 5 for refining acetic acid, and a decomposition column 10 for hydrolyzing methyl acetate. The first distillation column 1 is connected to a second distillation column 2 for purifying methanol and a third distillation column 3 for further removing light components. The third distillation column 3 is connected to a seventh distillation column 7 for a third removal of light components.

[0043] When switching between the fourth distillation column 4 for separating acetic acid aqueous solution, the eighth distillation column 8 for removing low-boiling-point impurities, and the first distillation column 1 for extracting and distilling methyl acetate:

[0044] The methyl acetate aqueous solution outlet at the top of the first distillation column 1 is connected to the feed inlet of the decomposition column 10 and the feed inlet of the third distillation column 3, respectively. The methanol aqueous solution tank outlet at the bottom of the column is connected to the second distillation column 2. The discharge outlet of the decomposition column 10 is connected to the feed inlet of the fourth distillation column 4, and the acetic acid aqueous solution tank outlet at the bottom of the fourth distillation column 4 is connected to the feed inlet of the fifth distillation column 5. The azeotropic distillate outlet at the top of the fifth distillation column 5 is connected to the first separator 11, and the bottom O section of the column has an acetic acid outlet. The azeotropic agent outlet at the top of the first separator 11 is connected to the reflux of the fifth distillation column 5. The outlet of the lower layer of the mixed solution containing the azeotropic agent is connected to the feed port of the sixth distillation column 6; the outlet of the aqueous azeotropic agent at the top of the sixth distillation column 6 is connected to the second separator 12, and the bottom of the column is provided with a bottom liquid tank outlet; the outlet of the upper layer of the azeotropic agent at the second separator 12 is connected to the reflux port of the fifth distillation column 5, and the outlet of the lower layer of the mixed solution containing the azeotropic agent decomposition products is connected to the feed port of the eighth distillation column 8; the top of the eighth distillation column 8 is provided with a low-boiling-point distillate outlet; the bottom liquid tank outlet of the column is connected to the upper reflux port of the first separator 11.

[0045] The outlet of the mixture of methyl acetate and methanol at the top of the fourth distillation column 4 is connected to the feed inlet of the first distillation column 1; the first distillation column 1 is also provided with a raw material feed inlet; the outlet of the acetaldehyde solution containing methyl acetate at the top of the third distillation column 3 is connected to the feed inlet of the seventh distillation column 7; the top of the seventh distillation column 7 is provided with a light component distillation outlet connected to a waste liquid tank; the bottom liquid distillation outlet of the column is connected to the distillation tank of the third distillation column 3; the bottom liquid distillation outlet of the third distillation column 3 is connected to the reflux port of the first distillation column 1.

[0046] When switching between the fourth distillation column 4 for distillation extraction of crude methyl acetate, the eighth distillation column 8 for evaporation purification of the extractant, and the first distillation column 1 for removal of light components:

[0047] The outlet of the mixture of methanol, methyl acetate, acetaldehyde, and acetone at the top of the fourth distillation column 4 is connected to the feed inlet of the first distillation column 1. The bottom of the first distillation column 1 has a refined methyl acetate tank outlet, and the outlet of the mixture of methyl acetate (greater than 98.3%), methanol, acetaldehyde, and acetone at the top of the column is connected to the feed inlet of the fourth distillation column 4 and the feed inlet of the third distillation column 3, respectively. The outlet of the mixture of methyl acetate, acetaldehyde, and acetone at the top of the third distillation column 3 is connected to the feed inlet of the seventh distillation column 7, and the outlet of the refined methyl acetate tank at the bottom of the column is connected to the distillation tank of the first distillation column 1. The mixture of methanol, acetaldehyde (90%), and acetone at the top of the seventh distillation column 7 is connected to the distillation tank of the seventh distillation column 7, and the outlet of the refined methyl acetate tank at the bottom of the column is connected to the distillation tank of the third distillation column 3.

[0048] The outlet of the methanol, methyl acetate, and ethylene glycol mixture at the bottom of the fourth distillation column 4 is connected to the feed inlet of the ninth distillation column 9. The distillation outlet of the methyl acetate and methanol mixture at the top of the ninth distillation column 9 is connected to the raw liquid tank. The outlet of the extractant tank containing methanol and carbonized heavy component impurities at the bottom of the column is connected to the feed inlet of the intermediate extractant tank 13 used for storage and the feed inlet of the eighth distillation column 8, respectively. The extractant distillation outlet at the top of the eighth distillation column 8 is connected to the feed inlet of the intermediate extractant tank 13, and a solid mixture tank outlet is provided at the bottom of the column. The outlet of the intermediate extractant tank 13 is connected to the reflux port of the fourth distillation column 4.

[0049] Example 2

[0050] 1) Reference Figure 1 When switching between the fourth distillation column 4 for separating acetic acid aqueous solution, the eighth distillation column 8 for removing low-boiling-point impurities, and the first distillation column 1 for extracting and distilling methyl acetate:

[0051] The preparation process for producing acetic acid and methanol is as follows:

[0052] Methyl acetate byproduct from the polyvinyl alcohol production process is added through the feed inlet of the first distillation column 1, and then extraction water is added at the top of the column. Methyl acetate and methanol are separated by extractive distillation, that is, methyl acetate and a small amount of water are distilled from the top of the column and mainly enter the decomposition column 10; the methanol-water solution at the bottom of the column enters the second distillation column 2 for methanol distillation to produce methanol.

[0053] Methyl acetate, a small amount of water, and secondary deionized water (DW2) are added to the decomposition tower 10 at a molar ratio of 1.25. Under the catalysis of the cation exchange resin, methyl acetate is hydrolyzed to produce acetic acid and methanol.

[0054] The decomposition liquid coming out of the decomposition tower 10 is a mixture of unreacted methyl acetate, water, and the acetic acid and methanol produced by the reaction. It is added to the fourth distillation tower 4. The methyl acetate and methanol azeotrope in vapor state from the top of the fourth distillation tower 4 is fed into the first distillation tower 1. The acetic acid aqueous solution at the bottom of the fourth distillation tower 4 enters the fifth distillation tower 5.

[0055] In the fifth distillation column 5, azeotropic agent n-butyl acetate is added from the top of the column for azeotropic distillation. Water and n-butyl acetate are distilled out together from the top of the column. The liquid phase in section O at the bottom of the column is collected to recover acetic acid. After cooling, it is sent to other processes, and the liquid phase in the tank is sent to the outside of the boundary for recycling and treatment.

[0056] The azeotropic liquid distilled from the top of the fifth distillation column 5 is separated by the first separator 11. The upper layer of n-butyl acetate is entirely returned to the column for reflux, while the lower layer of water is added to the seventh distillation column. N-butyl acetate and some water are distilled from the top of the sixth distillation column 6. After separation in the second separator 12, the upper layer of n-butyl acetate is returned to the sixth distillation column for reflux; the lower layer of water, containing n-butanol produced from the decomposition of n-butyl acetate, other water-soluble impurities, and a small amount of n-butyl acetate, is added to the eighth distillation column 8. Low-boiling-point substances are distilled from the top of the eighth distillation column 8 and sent outside the boundary area, while the bottom liquid is returned to the lower layer of the first separator 11. The bottom liquid of the sixth distillation column 6 is sent to a wastewater tank for neutralization treatment.

[0057] The top distillate of the first distillation column 1 contains methyl acetate and a small amount of water. A portion of this water is fed into the third distillation column 3 in the form of steam to separate the light components containing acetaldehyde. The top distillate of the third distillation column 3 (a mixture containing methyl acetate) is added to the seventh distillation column 7 to separate the light components containing acetaldehyde. The bottom liquid of the seventh distillation column 7 is returned to the first distillation column 1 as its reflux liquid. The highly concentrated light components containing acetaldehyde distilled from the top of the seventh distillation column 7 flow into the recovery waste liquid tank for collection and further treatment. The bottom liquid of the seventh distillation column 7 is returned to the distillation tank of the third distillation column 3.

[0058] The methyl acetate and methanol distilled from the top of the fourth distillation column 4 are recycled into the first distillation column 1 in vapor form.

[0059] 2) Reference Figure 2When switching the fourth distillation column 4 for distillation extraction of crude methyl acetate, the eighth distillation column 8 for evaporation purification of the extractant, and the first distillation column 1 for removal of light components:

[0060] The preparation process for producing refined methyl acetate is as follows:

[0061] The fourth distillation column 4 is used for the extractive distillation of crude methyl acetate: Crude methyl acetate, a byproduct of polyvinyl alcohol production, is used as raw material and fed into the fourth distillation column 4, where ethylene glycol is added for extractive distillation. A mixture of methanol, methyl acetate, and ethylene glycol is discharged from the bottom of the column and sent to the ninth distillation column 9 for recovery. A mixture of methanol, methyl acetate, acetaldehyde, and acetone is distilled from the top of the column and sent to the first distillation column 1 to remove light components and refine methyl acetate.

[0062] The ninth distillation column 9 separates the extractant: the mixture of methanol, methyl acetate and ethylene glycol from the bottom of the fourth distillation column 4 is fed into the ninth distillation column 9 for distillation. The methyl acetate and methanol distilled from the top of the column are sent to the raw liquid tank. A portion of the ethylene glycol from the bottom of the column is sent to the intermediate extractant tank 13 for use as a circulating extractant, and a portion is sent to the eighth distillation column 8 for evaporation.

[0063] First distillation column 1 removes light components: The mixture distilled from fourth distillation column 4 is sent to first distillation column 1 for purification, and qualified refined methyl acetate product with a purity of 99.98% or higher is produced. The methyl acetate with a purity greater than 98.3% distilled from the top of the column, which contains methanol, acetaldehyde and acetone, is partially sent to fourth distillation column 4 for recycling, and the other part is sent to third distillation column 3 to remove light components and purify methyl acetate.

[0064] The seventh distillation column 7 removes light components for the third time: Methyl acetate, methanol, acetaldehyde and acetone distilled from the third distillation column 3 are sent to the seventh distillation column 7 for distillation to remove light components methanol, acetaldehyde (90%) and acetone. The acetaldehyde product is sent to other processes at a rate of 20L / h; the product is sent to the distillation tank of the third distillation column 3.

[0065] The eighth distillation column 8 evaporates and purifies the extractant: Ethylene glycol and methanol from the ninth distillation column 9 are sent to the eighth distillation column 8 for evaporation. The ethylene glycol distilled from the top of the column is sent to the intermediate extractant tank 13, and then sent from the intermediate extractant tank 13 to the fourth distillation column 4 for recycling as extractant. The solid-liquid mixture at the bottom of the column is discharged periodically.

[0066] The third distillation column 3 removes light components again: methyl acetate, acetaldehyde, acetone and methanol distilled from the first distillation column 1 are sent to the third distillation column 3 for distillation. Methyl acetate, methanol, acetaldehyde (20%) and acetone distilled from the top of the column are sent to the seventh distillation column 7 for further distillation. Refined methyl acetate from the bottom of the column is sent to the distillation tank of the first distillation column 1.

[0067] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. An apparatus capable of switching between producing refined methyl acetate or acetic acid and methanol, characterized in that: It includes a fourth distillation column (4) that can be switched for separating acetic acid aqueous solution or for distilling crude methyl acetate, an eighth distillation column (8) that can be switched for removing impurities of low boiling point substances or for evaporating and purifying the extractant, and a first distillation column (1) that can be switched for extracting and distilling methyl acetate or for removing light components; the fourth distillation column (4) is connected to the first distillation column (1), the fifth distillation column (5) for refining acetic acid, and the decomposition column (10) for hydrolyzing methyl acetate; the first distillation column (1) is connected to the second distillation column (2) for purifying methanol and the third distillation column (3) for removing light components again, and the third distillation column (3) is connected to the seventh distillation column (7) for removing light components for the third time.

2. The apparatus for switching between producing refined methyl acetate or acetic acid and methanol products according to claim 1, characterized in that: When used for the production of acetic acid and methanol, the fourth distillation column (4) is connected to the fifth distillation column (5) for refining acetic acid, the decomposition column (10) for hydrolyzing methyl acetate and the first distillation column (1), respectively; the first distillation column (1) is connected to the second distillation column (2), the decomposition column (10) and the third distillation column (3) for purifying methanol, respectively; the third distillation column (3) is connected to the seventh distillation column (7); the eighth distillation column (8) is also connected to the first separator (11) for separating azeotropic agents and the second separator (12) for separating azeotropic agents; the first separator (11) is connected to the sixth distillation column (6) and the fifth distillation column (5) for distilling aqueous solutions of azeotropic agents, respectively.

3. The apparatus for switching between producing refined methyl acetate or acetic acid and methanol products according to claim 1, characterized in that: When used in the production of methyl acetate, the fourth distillation column (4) is also connected to the ninth distillation column (9) and the first distillation column (1) for separating the extractant; the first distillation column (1) is connected to the third distillation column (3); the third distillation column (3) is connected to the seventh distillation column (7); the eighth distillation column (8) is also connected to the ninth distillation column (9) and the intermediate tank (13) for storing the extractant in the transition; the intermediate tank (13) is connected to the fourth distillation column (4).

4. A process for switching between producing refined methyl acetate or acetic acid and methanol using the apparatus described in any one of claims 1-3, characterized in that: By controlling the fourth distillation column (4) to be switched for separating acetic acid aqueous solution or for distillation extraction of crude methyl acetate, the eighth distillation column (8) to be switched for removing impurities of low boiling point substances or for evaporation purification of extractant, and the first distillation column (1) to be switched for extraction distillation of methyl acetate or for removing light components, refined methyl acetate or acetic acid and methanol can be produced.

5. The process for switching between producing refined methyl acetate or acetic acid and methanol products as described in claim 4, characterized in that: When the fourth distillation column (4) is used for distillation extraction of crude methyl acetate, the eighth distillation column (8) is used for evaporation purification of the extractant, and the first distillation column (1) is used to remove light components, it is used to produce refined methyl acetate.

6. The process for switching between producing refined methyl acetate or acetic acid and methanol products according to claim 4, characterized in that: When switching between the fourth distillation column (4) for separating acetic acid aqueous solution, the eighth distillation column (8) for removing impurities of low boiling point substances, and the first distillation column (1) for extracting and distilling methyl acetate, acetic acid and methanol are produced; the process for producing acetic acid and methanol includes: S1: Using methyl acetate byproduct from the polyvinyl alcohol production process as raw material, extractant is added for extractive distillation to obtain methyl acetate aqueous solution and methanol aqueous solution; the obtained methyl acetate aqueous solution is added to decomposition tower (10), and demineralized water and catalyst are added to undergo hydrolysis reaction; the obtained methanol aqueous solution is added to second distillation tower (2) for methanol distillation to produce methanol; S2: Extract and separate the mixture of acetic acid, methanol, unreacted methyl acetate, and water obtained from hydrolysis in step S1; obtain an aqueous solution of acetic acid and a mixed solution of methyl acetate and methanol azeotrope; add the obtained aqueous solution of acetic acid to the fifth distillation column (5) for acetic acid purification, and reflux the obtained mixed solution of methyl acetate and methanol azeotrope into the first distillation column (1). S3: An azeotropic agent is added to the acetic acid aqueous solution for azeotropic distillation to obtain an aqueous solution of acetic acid and the azeotropic agent; the acetic acid is collected.

7. The process for switching between producing refined methyl acetate or acetic acid and methanol products according to claim 4 or 6, characterized in that: The process for producing acetic acid and methanol further includes recovering the azeotropic agent and removing light components. The step of recovering the azeotropic agent is as follows: S1: The azeotropic aqueous solution flowing into the first separator (11) is separated to obtain the azeotropic agent and a mixed solution containing the azeotropic agent; the azeotropic agent is recycled back into the fifth distillation column (5) for reuse; S2: The mixed solution containing the azeotropic agent obtained in S1 is added to the sixth distillation column (6) for separation, and the water-containing azeotropic agent is added to the second separator (12) for further separation; the bottom liquid of the distillation column is fed into the wastewater pool for neutralization treatment; S3: Separate the aqueous azeotropic agent to obtain a mixed solution of the azeotropic agent and the decomposition product of the azeotropic agent; add the obtained mixed solution of the decomposition product of the azeotropic agent to the eighth distillation column (8) to separate the impurities of low boiling point substances, discharge the separated low boiling point substances, and return the bottom liquid of the distillation column to the first separator (11). The step of removing the light components is as follows: The aqueous solution of methyl acetate flowing into the third distillation column (3) is used to separate light components. The resulting mixture containing methyl acetate is added to the seventh distillation column (7) for further separation of light components. The bottom liquid of the distillation column is refluxed into the first distillation column (1). The obtained mixed solution containing methyl acetate is further separated into light components. The light components are collected and processed in the recovery waste liquid tank, and the bottom liquid of the distillation column is refluxed into the third distillation column (3).

8. The process for switching between producing refined methyl acetate or acetic acid and methanol products according to any one of claims 4-6, characterized in that: The extractants used in the production of refined methyl acetate or acetic acid and methanol are water and ethylene glycol; the extractant of ethylene glycol is used in the production of refined methyl acetate, and the extractant of water is used in the production of acetic acid and methanol.

9. The process for switching between producing refined methyl acetate or acetic acid and methanol products according to claim 7, characterized in that: The extractants used in the production of refined methyl acetate or acetic acid and methanol are water and ethylene glycol; the extractant of ethylene glycol is used in the production of refined methyl acetate, and the extractant of water is used in the production of acetic acid and methanol.

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