Process and apparatus for the continuous flow synthesis of mercaptoacetic acid methyl ester and uses thereof

Abstract

This invention relates to the synthesis of methyl thioglycolate, and discloses a method and apparatus for the continuous flow synthesis of methyl thioglycolate, as well as its applications. The method includes: introducing a catalyst, methyl thioglycolate, and methanol into a micromixer for contact; introducing the resulting feedstock into a microreactor for reaction; subjecting the resulting reaction solution to a first vacuum distillation to obtain an overhead effluent and a bottom effluent; heating the overhead effluent and then subjecting it to atmospheric distillation to obtain a methanol effluent and a wastewater effluent; refluxing the methanol effluent for the contact process; heating the bottom effluent and then subjecting it to a second vacuum distillation to obtain a methyl thioglycolate product and a feedstock effluent; cooling the feedstock effluent and then refluxing for the contact process; the feedstock effluent contains unreacted methyl thioglycolate and catalyst. This method and apparatus enable the continuous preparation of methyl thioglycolate, allowing for the reuse of feedstock and catalyst, resulting in a short reaction time, minimal environmental pollution, and high purity, yield, and selectivity of the methyl thioglycolate product.

Description

Technical Field

[0001] This invention relates to the field of methyl mercaptoacetate synthesis technology, and more specifically to a method and apparatus for continuous flow synthesis of methyl mercaptoacetate, as well as its applications. Background Technology

[0002] Methyl mercaptoacetate, also known as methyl thioglycolate, is an important intermediate in the synthesis of pharmaceuticals, pesticides, food flavorings, and tobacco flavorings. It can be used as a heat stabilizer for organotin compounds in PVC and a molecular weight regulator for high-molecular-weight polymers. Polymethyl mercaptoacetate can also be used as a low-temperature curing agent for epoxy resins, in optical lenses, and in the manufacture of adhesives. Anhui Fengle Agricultural Chemical Co., Ltd. has successfully synthesized methyl mercaptoacetate and used it to further synthesize the herbicide pesticide 3-(4-methoxy-6-methyl-1,3,5-triazin-2-ylcarbamoylaminosulfonyl)thiophene-2-carboxylic acid, namely thiophenesulfuron. Guizhou Provincial Chemical Research Institute Yisheng Fine Chemical Co., Ltd. has also successfully synthesized methyl mercaptoacetate and used it to further synthesize flavoring raw materials: methyl 3-carbonyl-2-methylhydrothiophene carboxylate and methyl 4-carbonyl-2-tetrahydrothiophene carboxylate.

[0003] There are six main processes for synthesizing methyl mercaptoacetate: (1) sodium hydrosulfide method; (2) thiourea method; (3) sodium polysulfide method; (4) sodium thiosulfate method; (5) N-alkyl-2(1H)-pyridinethione method; and (6) methyl mercaptoacetate esterification method. Among them, methyl mercaptoacetate esterification method is currently the most important production method in industry. Lin Changzhi. "Research on the Synthesis of Methyl Mercaptoacetate [J]. Anhui Chemical Industry, 2004, 30(3):2." disclosed that methanol and methyl mercaptoacetate were used as raw materials, with a molar ratio of methanol to methyl mercaptoacetate of 1.2:1, and the amount of catalyst was 10% of the molar amount of methyl mercaptoacetate. The reaction was carried out in a batch stirred tank at a reaction temperature of 38-40℃ for 8 hours, and the yield of methyl mercaptoacetate was ≥85%. Then, the esterification liquid was distilled in a batch distillation tank to obtain methyl mercaptoacetate product with high purity. However, there are many drawbacks when using the above methods and devices: (1) long reaction time and low selectivity; (2) many intermediate material transfers and pouring, which consume manpower and heat, and at the same time, odors will be emitted, causing local environmental pollution; (3) methanol and water cannot be separated well, and the methanol in the obtained pre-distillate contains a lot of water and cannot be reused; (4) due to the material staying in the reactor at high temperature for a long time, a lot of by-products are generated; (5) the product purity is not high.

[0004] Microstructured reactors are continuous-flow tubular reactors with pipe dimensions far smaller than conventional tubular reactors, typically defined in the micrometer to millimeter range. They possess an extremely large specific surface area, resulting in significantly higher heat exchange and mass transfer efficiencies. This allows for precise control of reaction temperature and ensures instantaneous mixing of reactants in precise proportions. These are all key factors in improving yield, selectivity, safety, reaction rate, and product quality.

[0005] Jia Shaoming et al., “Application of Microstructured Reactors in the Synthesis of Methyl Mercaptoacetate [J]. Chemical Industry and Engineering Progress, 2011, 30(S1): 56-58.” disclosed the synthesis of methyl mercaptoacetate under atmospheric pressure using a microstructured reactor. The effects of the diameter, material, reaction temperature, and residence time of the microstructured reactor on the yield of methyl mercaptoacetate were investigated. Although the yield of methyl mercaptoacetate could reach as high as 97.78%, which is higher than the 85% yield obtained by the conventional 8h reaction time, the method did not consider or realize the continuous synthesis and separation of methyl mercaptoacetate. After the reaction, the reaction solution was neutralized with dilute sodium bicarbonate solution, then washed with water, dried, and excess alcohol was first distilled off under atmospheric pressure. Then, the fraction with a certain boiling point was collected by vacuum distillation. The subsequent separation process of the method failed to solve the problem of recovery and reuse of methanol, expensive methyl mercaptoacetic acid raw materials, and catalyst. In addition, although increasing the temperature is beneficial to improving the yield of methyl mercaptoacetate, methanol has a relatively low boiling point under normal pressure. If the temperature is too high, the methanol will vaporize, causing the reaction to change from a liquid-liquid reaction to a gas-liquid reaction, thus affecting the reaction effect. Therefore, the temperature of this method is only 90℃.

[0006] CN110256311A discloses a purification process for methyl mercaptoacetate. This process involves refining an esterified liquid synthesized from methanol and mercaptoacetic acid using a first distillation column and a second distillation column. The first component obtained from the first distillation column is used as a reactant and fed into the esterification reactor. The second component obtained from the first distillation column is settled in a settling tank, and the upper layer is then fed back into the first distillation column for further distillation. While this purification process can significantly improve product purity and allows for the recovery and reuse of methanol, the separation of methanol and water is ineffective. This results in methanol circulating to the reaction system containing water, affecting the reaction results. Furthermore, the water separated in the settling tank contains methyl mercaptoacetate and unreacted mercaptoacetic acid, leading to complicated wastewater treatment. Additionally, it fails to achieve the recovery and reuse of the expensive mercaptoacetic acid feedstock and catalyst. Summary of the Invention

[0007] The purpose of this invention is to overcome the problems existing in the synthesis of methyl mercaptoacetate (MGA), such as the inability to achieve a closed-loop reaction of reactants, leakage of methyl mercaptoacetate and methyl mercaptoacetic acid odors, poor separation of methanol and methyl mercaptoacetic acid, and the impact on raw material recovery and reuse. This invention provides a method and apparatus for the continuous synthesis of MGA, which enables the continuous preparation of MGA, allows for the reuse of unreacted methanol and methyl mercaptoacetic acid raw materials and catalysts, and features low cost, short reaction time, minimal environmental pollution, and high purity, yield, and selectivity of the MGA product.

[0008] To achieve the above objectives, a first aspect of the present invention provides a method for the continuous synthesis of methyl mercaptoacetate, the method comprising:

[0009] (1) The catalyst, mercaptoacetic acid and methanol are introduced into a micro mixer for contact, and then the resulting raw materials are introduced into a microreactor for reaction to obtain a reaction solution;

[0010] (2) The reaction solution is subjected to a first vacuum distillation to obtain the overhead effluent and the bottom effluent;

[0011] (3) The effluent from the top of the column is heated and then subjected to atmospheric distillation to obtain methanol effluent and wastewater effluent. The methanol effluent is then returned to step (1) for the contact described above.

[0012] (4) The bottom effluent is heated and then subjected to a second vacuum distillation to obtain methyl mercaptoacetate product and raw material effluent. The raw material effluent is cooled and then refluxed to step (1) for the contact described above.

[0013] The raw material effluent contains unreacted mercaptoacetic acid and a catalyst.

[0014] A second aspect of the present invention provides an apparatus for the continuous flow synthesis of methyl mercaptoacetate, the apparatus comprising:

[0015] The system comprises a micromixer, a microreactor, a first vacuum distillation column, an atmospheric distillation column, and a second vacuum distillation column, wherein the micromixer, the microreactor, and the first vacuum distillation column are connected in sequence; wherein...

[0016] The first vacuum distillation column has a first outlet at the top, which is connected to the atmospheric distillation column via a first reboiler to heat the effluent from the top of the column and then deliver it to the atmospheric distillation column; the first vacuum distillation column has a second outlet at the bottom, which is connected to the second vacuum distillation column via a second reboiler to heat the effluent from the bottom of the column and then deliver it to the second vacuum distillation column.

[0017] The atmospheric distillation column is provided with a methanol outlet at the top, which is connected to the micro mixer to return the methanol effluent to the micro mixer; the atmospheric distillation column is provided with a wastewater outlet at the bottom to discharge the wastewater effluent.

[0018] The second vacuum distillation column has a product outlet at the top to discharge methyl mercaptoacetate product; the second vacuum distillation column has a raw material outlet at the bottom, which is connected to the micro mixer to return the raw material effluent to the micro mixer.

[0019] The third aspect of the present invention provides the use of the method as described in the first aspect and the apparatus as described in the second aspect in the synthesis of methyl mercaptoacetate.

[0020] In existing batch production methods for methyl mercaptoacetate, after the batch reactor reaction, the mixture is allowed to settle and separate water (or reboil) to obtain crude ester. The crude ester is then distilled under reduced pressure. Because thiol compounds are extremely odorous (methyl mercaptoacetate and thiol acetate contain thiol functional groups, have a strong pungent odor, and are highly toxic chemicals), the subsequent separation process is environmentally unfriendly. Existing batch reactor or atmospheric pressure microreactor synthesis methods fail to achieve continuous synthesis and separation of methyl mercaptoacetate, particularly failing to recycle the expensive thiol acetate feedstock and catalyst. Furthermore, in existing atmospheric pressure microreactor synthesis methods, methanol feedstock is prone to vaporization at high temperatures, affecting reaction efficiency and the stability of pressure within the reaction system.

[0021] During their research, the inventors of this invention discovered that by connecting a micro-mixer and a microreactor in series, the reaction liquid obtained under high temperature and pressure remains liquid and can be directly separated by distillation without the need for reboiler preheating. Directly subjecting the reaction liquid to a first vacuum distillation can effectively separate the low-boiling-point components (methanol and water) from the reaction liquid. Combining this with atmospheric distillation can completely separate the unreacted methanol, which can then participate in the reaction again for reuse. Directly subjecting the reaction liquid to a first vacuum distillation followed by a second vacuum distillation can yield a high-purity methyl mercaptoacetate product and enable the recycling of expensive methyl mercaptoacetic acid raw materials and catalysts.

[0022] Through the above technical solution, the present invention has the following advantages:

[0023] (1) The device provided by the present invention connects a micro-mixer and a micro-reactor (microscale mixer and microscale reactor) in series, enabling the reaction raw materials methanol and mercaptoacetic acid, as well as the catalyst, to be fully and rapidly mixed. Within the microscale reactor, the heat and mass transfer effects of the reaction are enhanced, significantly shortening the reaction time. Simultaneously, the occurrence of side reactions is suppressed, and the selectivity of methyl mercaptoacetate is improved. Preferably, the reaction system employs higher reaction pressure and temperature, which not only shortens the reaction time but also improves the utilization rate of the expensive mercaptoacetic acid raw material.

[0024] (2) The device provided by the present invention connects a micro mixer and a micro reactor (microscale mixer and microscale reactor) in series, preferably using two micro mixers in series, which not only avoids the vaporization of methanol at high temperature and improves the mixing effect of raw materials, but also ensures the pressure stability of the reaction system.

[0025] (3) This invention connects a micro-mixer and a micro-reactor (microscale mixer and microscale reactor) in series. The reaction liquid obtained under high temperature and high pressure remains in a liquid-liquid state, eliminating the need for reboiler preheating and allowing for direct distillation separation. Furthermore, since the reaction liquid remains liquid, direct first-stage vacuum distillation effectively separates the low-boiling-point components (methanol and water). After heating and then distilling at atmospheric pressure, the unreacted methanol can be completely separated and can participate in the reaction again. In addition, the effective separation of methanol and water avoids the impact of the large amount of water contained in the refluxed methanol on the reaction efficiency.

[0026] (4) After the reaction liquid is directly subjected to the first vacuum distillation, the bottom effluent obtained is heated and then subjected to the second vacuum distillation to obtain high-purity methyl mercaptoacetate product. This also enables the recycling of expensive methyl mercaptoacetic acid raw materials and catalysts, avoiding the waste of methyl mercaptoacetic acid raw materials and catalysts. This not only saves costs but also avoids environmental pollution.

[0027] In summary, the method and apparatus provided by this invention achieve continuous operation throughout the entire process from reaction to separation, which greatly improves production efficiency. Furthermore, because the reactants form a closed loop, the leakage of product odors is reduced, thus avoiding harm to human health and environmental pollution. Attached Figure Description

[0028] Figure 1 This is a schematic diagram of the reaction process and apparatus according to a preferred embodiment of the present invention.

[0029] Explanation of reference numerals in the attached figures

[0030] 1. Methanol tank; 2. Thioglycolic acid tank; 3. Methanol metering pump

[0031] 4. Thioglycolic acid metering pump; 5. First micro mixer; 6. Second micro mixer

[0032] 7. Microreactor; 8. First vacuum distillation column; 9. First metering pump

[0033] 10. Second metering pump; 11. First reboiler; 12. Second reboiler

[0034] 13. Atmospheric distillation column; 14. Second vacuum distillation column; 15. Wastewater effluent.

[0035] 16. Methyl mercaptoacetate products 17. Heat exchangers Detailed Implementation

[0036] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0037] In the description of this invention, it should be understood that the terms "top", "bottom", "top", "bottom", "tower top", "tower bottom", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limiting this invention.

[0038] The first aspect of this invention provides a method for continuous flow synthesis of methyl mercaptoacetate, the method comprising:

[0039] (1) The catalyst, mercaptoacetic acid and methanol are introduced into a micro mixer for contact, and then the resulting raw materials are introduced into a microreactor for reaction to obtain a reaction solution;

[0040] (2) The reaction solution is subjected to a first vacuum distillation to obtain the overhead effluent and the bottom effluent;

[0041] (3) The effluent from the top of the column is heated and then subjected to atmospheric distillation to obtain methanol effluent and wastewater effluent. The methanol effluent is then returned to step (1) for the contact described above.

[0042] (4) The bottom effluent is heated and then subjected to a second vacuum distillation to obtain methyl mercaptoacetate product and raw material effluent. The raw material effluent is cooled and then refluxed to step (1) for the contact described above.

[0043] The raw material effluent contains unreacted mercaptoacetic acid and a catalyst.

[0044] According to some embodiments of the present invention, in step (1), the catalyst, mercaptoacetic acid, and methanol are introduced into a micromixer for contact, and then the obtained raw materials are introduced into a microreactor for reaction to obtain a reaction solution. The reaction solution is liquid and does not require preheating in a reboiler, and can be directly separated by distillation.

[0045] According to some embodiments of the present invention, preferably, the micromixer includes a first micromixer and a second micromixer, wherein the first micromixer, the second micromixer, and the microreactor are sequentially connected. Preferably, the first micromixer is a stacked micromixer or a chaotic micromixer; preferably, the second micromixer is a static micromixer. The present invention employs two micromixers connected in series, particularly a second micromixer, and the second micromixer is a static micromixer. This not only further prevents the methanol feedstock from vaporizing at high temperatures and improves the mixing effect of the feedstock, but also ensures the pressure stability of the reaction system.

[0046] According to some embodiments of the present invention, preferably, the microchannel equivalent diameter of the first micromixer is 50-500 μm, and more preferably 60-150 μm.

[0047] According to some embodiments of the present invention, preferably, the microchannel equivalent diameter of the second micromixer is 90-220 μm, more preferably 100-200 μm.

[0048] According to some embodiments of the present invention, preferably, the microreactor is selected from microchannel reactors and / or microtube reactors.

[0049] According to some embodiments of the present invention, preferably, the microchannel equivalent diameter of the microreactor is 100-2000 μm, more preferably 200-1000 μm.

[0050] According to some embodiments of the present invention, preferably, the contact in step (1) includes:

[0051] (a) The catalyst is mixed with mercaptoacetic acid to form a first mixture, and then the first mixture is mixed with methanol in a first micro mixer to obtain a second mixture;

[0052] (b) The second mixture is passed into a second micro mixer for a second mixing to obtain a feed stream.

[0053] According to some embodiments of the present invention, there are no particular limitations on the formation method of the first mixture. Preferably, the catalyst is dissolved in mercaptoacetic acid to form the first mixture.

[0054] According to some embodiments of the present invention, preferably, the first mixing is carried out at room temperature and pressure; wherein, room temperature refers to 20-30°C, and normal pressure refers to 1 standard atmosphere, i.e., 0.1 MPa. In this invention, all pressures mentioned are gauge pressures.

[0055] According to some embodiments of the present invention, preferably, the residence time of the second mixture in the second micromixer is 10 ms to 1 s. Using the above preferred embodiments, the short residence time avoids the decomposition of crude esters.

[0056] According to some embodiments of the present invention, preferably, the amount of catalyst used in step (1) is 1-10 wt% of mercaptoacetic acid, more preferably 5-10 wt% of mercaptoacetic acid. Using the above preferred embodiments is beneficial for cost savings.

[0057] According to some embodiments of the present invention, preferably, the catalyst is selected from sulfuric acid, p-toluenesulfonic acid, methanesulfonic acid, titanium trichloride, and SO4. 2- One or more of the following superacids: / TiO2, preferably sulfuric acid and / or p-toluenesulfonic acid.

[0058] According to some embodiments of the present invention, preferably, the molar ratio of methanol to mercaptoacetic acid is (1-5):1, more preferably (1-4):1. Using the above preferred embodiments is beneficial for improving the utilization rate of mercaptoacetic acid.

[0059] According to some embodiments of the present invention, metering pumps can be used to deliver and meter streams such as raw materials, overhead effluents and bottom effluents, as well as to adjust the proportions of methanol, mercaptoacetic acid and catalysts.

[0060] According to some embodiments of the present invention, preferably, the reaction conditions include: a reaction temperature of 50-120°C, preferably 70-110°C; and / or a reaction pressure of atmospheric pressure -0.4 MPa, preferably 0.2-0.4 MPa; and / or a reaction residence time of 8-60 min, preferably 10-50 min. Using a higher reaction pressure and / or a reaction temperature within the preferred range not only shortens the reaction time but also improves the utilization rate of expensive thioglycolic acid raw materials, further enhancing the purity, yield, and selectivity of the methyl thioglycolic acid product. Furthermore, a higher reaction pressure also helps reduce methanol vaporization at higher reaction temperatures, ensuring a liquid-liquid reaction between the raw materials and improving the reaction efficiency.

[0061] According to some embodiments of the present invention, in step (2), the reaction solution is subjected to a first vacuum distillation to obtain an overhead effluent and a bottom effluent. The overhead effluent mainly consists of low-boiling-point components (methanol and water) from the reaction solution; the bottom effluent mainly consists of methyl mercaptoacetate, mercaptoacetic acid, and a catalyst.

[0062] According to some embodiments of the present invention, preferably, the pressure of the first vacuum distillation in step (2) is 0.01-0.08 MPa, more preferably 0.01-0.05 MPa; and / or, the top distillation yield of the first vacuum distillation is 50-84%, more preferably 60-80%. By controlling the pressure and top distillation yield of the first vacuum distillation within the above-mentioned preferred ranges, the effective separation of low-boiling-point components (methanol and water) in the reaction liquid can be further promoted.

[0063] According to some embodiments of the present invention, in step (3), the overhead effluent is heated and then subjected to atmospheric distillation to obtain methanol effluent and wastewater effluent, wherein the methanol effluent is unreacted methanol, and the wastewater effluent is mainly water generated in the reaction. Recirculating the methanol effluent back to step (1) for the contact process allows the unreacted methanol to participate in the reaction again, achieving methanol recovery. Heating the overhead effluent and then subjecting it to atmospheric distillation enables effective separation of methanol and water, avoiding the adverse effects of a large amount of water in the recirculated methanol on the reaction efficiency.

[0064] According to some embodiments of the present invention, preferably, in step (3), the effluent from the top of the column is heated to 50-100°C, more preferably to 60-90°C. The present invention does not impose any particular limitations on the heating method and equipment; conventional methods and equipment in the art can be used. Preferably, a reboiler is used for the heating.

[0065] According to some embodiments of the present invention, preferably, the top temperature of the atmospheric distillation column is 55-70°C, more preferably 60-70°C. Using the above-mentioned preferred embodiments is beneficial for further promoting the effective separation of methanol and water.

[0066] According to some embodiments of the present invention, in step (4), the bottom effluent is heated and then subjected to a second vacuum distillation to obtain methyl mercaptoacetate product and raw material effluent. The above steps can effectively separate methyl mercaptoacetate from unreacted mercaptoacetic acid and catalyst, and the methyl mercaptoacetate product has high purity.

[0067] According to some embodiments of the present invention, preferably, in step (4), the bottom effluent of the column is heated to 60-120°C, more preferably to 65-110°C. The present invention does not impose any particular limitations on the heating method and equipment; conventional methods and equipment in the art can be used. Preferably, a reboiler is used for the heating.

[0068] According to some embodiments of the present invention, preferably, the pressure of the second vacuum distillation is 0.001-0.02 MPa, more preferably 0.002-0.02 MPa.

[0069] According to some embodiments of the present invention, preferably, the top temperature of the second vacuum distillation column is 40-60°C, more preferably 40-55°C. By controlling the pressure and top temperature of the second vacuum distillation column within the above-mentioned preferred ranges, the effective separation of methyl mercaptoacetate from unreacted mercaptoacetic acid and catalyst can be further promoted, and the methyl mercaptoacetate product has high purity.

[0070] According to some embodiments of the present invention, preferably, the pressure of the second vacuum distillation is lower than the pressure of the first vacuum distillation. Using the above preferred embodiments facilitates better separation of methanol, water, and methyl mercaptoacetate, further improving the conversion rate of mercaptoacetic acid, and further improving the purity, yield, and selectivity of the methyl mercaptoacetate product.

[0071] According to some embodiments of the present invention, in step (4), the raw material effluent is cooled and then returned to step (1) for the contact, wherein the raw material effluent contains unreacted thioglycolic acid and catalyst. Returning the raw material effluent to the reaction system allows the unreacted thioglycolic acid and catalyst to participate in the reaction again, avoiding the waste of thioglycolic acid raw material and catalyst. Reuse not only saves costs but also avoids environmental pollution.

[0072] According to some embodiments of the present invention, preferably, the raw material effluent is cooled to 20-30°C. The present invention does not impose particular limitations on the cooling method and equipment; conventional methods and equipment in the art can be used. Preferably, a heat exchanger is used for the cooling.

[0073] A second aspect of the present invention provides an apparatus for the continuous flow synthesis of methyl mercaptoacetate, the apparatus comprising:

[0074] The system comprises a micromixer, a microreactor, a first vacuum distillation column, an atmospheric distillation column, and a second vacuum distillation column, wherein the micromixer, the microreactor, and the first vacuum distillation column are connected in sequence; wherein...

[0075] The first vacuum distillation column has a first outlet at the top, which is connected to the atmospheric distillation column via a first reboiler to heat the effluent from the top of the column and then deliver it to the atmospheric distillation column; the first vacuum distillation column has a second outlet at the bottom, which is connected to the second vacuum distillation column via a second reboiler to heat the effluent from the bottom of the column and then deliver it to the second vacuum distillation column.

[0076] The atmospheric distillation column is provided with a methanol outlet at the top, which is connected to the micro mixer to return the methanol effluent to the micro mixer; the atmospheric distillation column is provided with a wastewater outlet at the bottom to discharge the wastewater effluent.

[0077] The second vacuum distillation column has a product outlet at the top to discharge methyl mercaptoacetate product; the second vacuum distillation column has a raw material outlet at the bottom, which is connected to the micro mixer to return the raw material effluent to the micro mixer.

[0078] According to some embodiments of the present invention, the micromixer is used to contact the catalyst, mercaptoacetic acid and methanol to obtain a feed stream, and to deliver the feed stream to the microreactor.

[0079] According to some embodiments of the present invention, preferably, the micromixer includes a first micromixer and a second micromixer, wherein the first micromixer, the second micromixer, and the microreactor are sequentially connected. Preferably, the first micromixer is a stacked micromixer or a chaotic micromixer; preferably, the second micromixer is a static micromixer.

[0080] According to some embodiments of the present invention, preferably, the microchannel equivalent diameter of the first micromixer is 50-500 μm, and more preferably 60-150 μm.

[0081] According to some embodiments of the present invention, preferably, the microchannel equivalent diameter of the second micromixer is 90-220 μm, more preferably 100-200 μm.

[0082] According to some embodiments of the present invention, the microreactor is used to carry out the synthesis reaction of methyl mercaptoacetate on the feed stream to obtain a reaction solution, and the reaction solution is then transported to the first vacuum distillation column.

[0083] According to some embodiments of the present invention, preferably, the microreactor is selected from microchannel reactors and / or microtube reactors.

[0084] According to some embodiments of the present invention, preferably, the microchannel equivalent diameter of the microreactor is 100-2000 μm, more preferably 200-1000 μm.

[0085] According to some embodiments of the present invention, the first vacuum distillation column is used to perform a first vacuum distillation on the reaction liquid to obtain an overhead effluent and a bottom effluent. The first vacuum distillation column has a first outlet at its top, which is connected to the atmospheric distillation column via a first reboiler to heat the overhead effluent before it is delivered to the atmospheric distillation column. The first vacuum distillation column has a second outlet at its bottom, which is connected to the second vacuum distillation column via a second reboiler to heat the bottom effluent before it is delivered to the second vacuum distillation column. The first reboiler is used to heat the overhead effluent, and the second reboiler is used to heat the bottom effluent.

[0086] According to some embodiments of the present invention, the atmospheric distillation column is used to perform atmospheric distillation on the heated overhead effluent to obtain methanol effluent and wastewater effluent. The top of the atmospheric distillation column is provided with a methanol outlet, which is connected to the micromixer to return the methanol effluent to the micromixer, allowing unreacted methanol to participate in the reaction again; the bottom of the atmospheric distillation column is provided with a wastewater outlet to discharge the wastewater effluent.

[0087] According to some embodiments of the present invention, the second vacuum distillation column is used to perform a second vacuum distillation on the heated bottom effluent to obtain methyl mercaptoacetate product and feed effluent. The top of the second vacuum distillation column is provided with a product outlet to discharge the methyl mercaptoacetate product; the bottom of the second vacuum distillation column is provided with a feed outlet, which is connected to the micromixer to recirculate the feed effluent (containing unreacted methyl mercaptoacetate and catalyst) back to the micromixer, allowing the unreacted methyl mercaptoacetate and catalyst to participate in the reaction again.

[0088] According to some embodiments of the present invention, preferably, the apparatus further includes a methanol tank and a thioglycolic acid tank respectively connected to the micromixer; preferably, the methanol outlet is connected to the methanol tank via a pipeline to deliver the methanol effluent to the methanol tank; and / or, the raw material outlet is connected to the thioglycolic acid tank via a pipeline to deliver the raw material effluent to the thioglycolic acid tank. The methanol tank is used to store methanol raw material and / or methanol effluent; the thioglycolic acid tank is used to store at least one of thioglycolic acid raw material, a first mixture containing a catalyst and thioglycolic acid, and raw material effluent.

[0089] According to some embodiments of the present invention, preferably, the wastewater outlet is connected to a wastewater treatment system to transport the wastewater effluent to the wastewater treatment system;

[0090] Preferably, the product outlet is connected to the product storage tank to transport the methyl mercaptoacetate product to the product storage tank.

[0091] According to some embodiments of the present invention, preferably, the device further includes a metering pump and / or a heat exchanger, wherein the metering pump is used to meter, regulate and transport materials such as raw materials, overhead effluent and bottom effluent; and the heat exchanger is used to cool the raw material effluent.

[0092] The third aspect of the present invention provides the application of the method as described in the first aspect and the apparatus as described in the second aspect in the synthesis of methyl mercaptoacetate.

[0093] According to a particularly preferred embodiment of the present invention, the continuous flow synthesis method for methyl thioacetate comprises:

[0094] (S1) The catalyst is mixed with mercaptoacetic acid to form a first mixture, and then the first mixture is mixed with methanol in a first micro mixer to obtain a second mixture;

[0095] (S2) The second mixture is fed into a second micro mixer for a second mixing to obtain a raw material stream, and then the raw material stream is fed into a microreactor for reaction to obtain a reaction solution;

[0096] (S3) The reaction liquid is subjected to a first vacuum distillation to obtain the overhead effluent and the bottom effluent;

[0097] (S4) The effluent from the top of the column is heated and then subjected to atmospheric distillation to obtain methanol effluent and wastewater effluent. The methanol effluent is then returned to step (S1) for the first mixing.

[0098] (S5) The bottom effluent is heated and then subjected to a second vacuum distillation to obtain methyl mercaptoacetate product and raw material effluent. The raw material effluent is cooled and then refluxed to step (S1) for the first mixing.

[0099] The raw material effluent contains unreacted mercaptoacetic acid and a catalyst.

[0100] Figure 1 This is a schematic diagram of a reaction process and apparatus according to a preferred embodiment of the present invention, wherein the apparatus includes:

[0101] Methanol tank 1, mercaptoacetic acid tank 2, first micromixer 5, second micromixer 6, microreactor 7, first vacuum distillation column 8, first reboiler 11, atmospheric distillation column 13, second reboiler 12, and second vacuum distillation column 14;

[0102] Methanol tank 1 is connected to the first micro-mixer 5 via methanol metering pump 3; mercaptoacetic acid tank 2 is connected to the first micro-mixer 5 via mercaptoacetic acid metering pump 4.

[0103] The first micro mixer 5, the second micro mixer 6, the microreactor 7, and the first vacuum distillation column 8 are connected in sequence;

[0104] The first vacuum distillation column 8 has a first outlet at the top, which is connected to the atmospheric distillation column 13 via a first metering pump 9 and a first reboiler 11 in sequence; the first vacuum distillation column 8 has a second outlet at the bottom, which is connected to the second vacuum distillation column 14 via a second metering pump 10 and a second reboiler 12 in sequence.

[0105] The top of the atmospheric distillation column 13 is provided with a methanol outlet, which is connected to the methanol tank 1 through a pipeline; the bottom of the atmospheric distillation column 13 is provided with a wastewater outlet.

[0106] The second vacuum distillation column 14 has a product outlet at the top and a raw material outlet at the bottom. The raw material outlet is connected to the mercaptoacetic acid tank 2 via a pipe. A heat exchanger 17 is installed between the raw material outlet and the mercaptoacetic acid tank 2.

[0107] The reaction process includes:

[0108] (1-1) The first mixture (containing catalyst and mercaptoacetic acid) from methanol tank 1 and mercaptoacetic acid tank 2 are metered by methanol metering pump 3 and mercaptoacetic acid metering pump 4 respectively, and then introduced into the first micro mixer 5 for first mixing to obtain the second mixture;

[0109] (2-1) The second mixture is fed into the second micro mixer 6 for a second mixing to obtain a raw material stream. Then the raw material stream is fed into the micro reactor 7 for reaction to obtain a reaction liquid.

[0110] (3-1) The reaction liquid is fed into the first vacuum distillation column 8 for the first vacuum distillation to obtain the top effluent and the bottom effluent.

[0111] (4-1) After the effluent from the top of the first vacuum distillation column 8 is discharged from the first outlet, it is metered by the first metering pump 9 and heated by the first reboiler 11 before being fed into the atmospheric distillation column 13 for atmospheric distillation to obtain methanol effluent and wastewater effluent. The methanol effluent is discharged from the methanol outlet at the top of the atmospheric distillation column 13 and then returned to the methanol tank 1 through a pipeline. The wastewater effluent is discharged from the wastewater outlet at the bottom of the atmospheric distillation column 13 and then transported to the wastewater treatment system.

[0112] (5-1) After the bottom effluent is discharged from the second outlet at the bottom of the first vacuum distillation column 8, it is metered by the second metering pump 10 and heated by the second reboiler 12 before being fed into the second vacuum distillation column 14 for second vacuum distillation to obtain methyl mercaptoacetate product and raw material effluent. The methyl mercaptoacetate product is discharged from the product outlet at the top of the second vacuum distillation column 14 and then transported to the product storage tank. The raw material effluent is discharged from the raw material outlet at the bottom of the second vacuum distillation column 14 and cooled by the heat exchanger 17 before being returned to the mercaptoacetic acid tank 2 through a pipeline.

[0113] The present invention will be described in detail below through embodiments.

[0114] Unless otherwise specified, all raw materials used in the following embodiments are commercially available products.

[0115] In the following examples, the content of methyl mercaptoacetate in the methyl mercaptoacetate product was determined by high performance liquid chromatography with external standard (HPLC).

[0116] Selectivity of methyl thioglycolate = methyl thioglycolate yield ÷ methyl thioglycolate conversion rate × 100%

[0117] The following embodiments are all in accordance with Figure 1 The reaction process and apparatus shown are used for the synthesis of methyl mercaptoacetate, wherein the first micromixer 5 is a chaotic micromixer with an equivalent diameter of 100 μm; the second micromixer 6 is a static micromixer with an equivalent diameter of 100 μm; and the microreactor 7 is a microtube reactor with an equivalent diameter of 500 μm.

[0118] Example 1

[0119] Using p-toluenesulfonic acid as a catalyst, the catalyst is dissolved in mercaptoacetic acid feedstock to obtain a first mixture, which is stored in mercaptoacetic acid tank 2. The amount of catalyst used is 5 wt% of the mercaptoacetic acid feedstock. Methanol feedstock is stored in methanol tank 1. At a methanol to mercaptoacetic acid molar ratio of 3:1, under normal temperature and pressure, the methanol feedstock from methanol tank 1 and the first mixture from mercaptoacetic acid tank 2 are metered by methanol metering pump 3 and mercaptoacetic acid metering pump 4, respectively, and then fed into a first micro-mixer 5 for thorough liquid-liquid mixing. The mixture is then rapidly fed into a second micro-mixer 6 for further mixing. After a 50 ms dwell time, it enters a microreactor 7 for reaction. Under reaction pressure of 0.2 MPa and reaction temperature of 100 °C, the reaction is held for 30 min. The resulting reaction solution enters a first vacuum distillation column 8 for first vacuum distillation. The pressure of the first vacuum distillation column 8 is controlled at 0.04 MPa, and the top product yield is 75%. The obtained top effluent is drawn from the top of the first vacuum distillation column 8. After being discharged from the first outlet of the first distillation column, the methanol effluent is heated to 80°C by the first metering pump 9 and then enters the first reboiler 11 for atmospheric distillation. The top temperature of the atmospheric distillation column 13 is controlled at 65°C. The methanol effluent discharged from the top outlet of the atmospheric distillation column 13 is returned to the methanol tank 1. The wastewater effluent discharged from the bottom outlet of the atmospheric distillation column 13 is transported to the wastewater treatment system. The bottom effluent discharged from the second outlet of the first vacuum distillation column 8 is transported to the first... After being metered by the second metering pump 10, the product enters the second reboiler 12 and is heated to 100°C. Then, it enters the second vacuum distillation column 14, where the pressure is controlled at 0.002 MPa and the top temperature at 45°C. The product discharged from the top of the second vacuum distillation column 14 is a high-purity methyl thioglycolate product. The feed effluent from the bottom of the second vacuum distillation column 14 is cooled to 25°C by the heat exchanger 17 and then returned to the methyl thioglycolate tank 2. Analysis shows that the methyl thioglycolate product has a purity of up to 99.8%, a yield of 98.5%, a conversion rate of 99.2%, and a selectivity of up to 99.3%.

[0120] Example 2

[0121] The method of Example 1 was followed, except that the reaction in microreactor 7 was carried out at atmospheric pressure; otherwise, it was the same as in Example 1. The obtained methyl thioacetate product had a purity of 99.2%, a yield of methyl thioacetate of 80%, a conversion rate of 85% for methyl thioacetic acid, and a selectivity of up to 94%.

[0122] Example 3

[0123] The method was followed in Example 1, except that the pressure of the first vacuum distillation column 8 was 0.02 MPa, and the pressure of the second vacuum distillation column 14 was 0.02 MPa; all other aspects were the same as in Example 1. The obtained methyl thioacetate product had a purity of up to 90%, a yield of methyl thioacetate of 90%, a conversion rate of 94% for methyl thioacetic acid, and a selectivity of up to 95.7%.

[0124] Example 4

[0125] The method of Example 1 was followed, except that sulfuric acid was used as the catalyst; otherwise, it was the same as in Example 1. The obtained methyl thioacetate product had a purity of 99.5%, a yield of methyl thioacetate of 92%, a conversion rate of 96% for methyl thioacetic acid, and a selectivity of up to 95.8%.

[0126] Example 5

[0127] The method of Example 4 was followed, except that the amount of catalyst used was 10 wt% of the mercaptoacetic acid feedstock, while the rest were the same as in Example 4. The obtained methyl mercaptoacetate product had a purity of 99.4%, a yield of methyl mercaptoacetate of 93%, a conversion rate of 97% for mercaptoacetic acid, and a selectivity of up to 95.9%.

[0128] Example 6

[0129] The method of Example 5 was followed, except that the reaction in microreactor 7 was carried out at atmospheric pressure; otherwise, it was the same as in Example 5. The obtained methyl thioglycolate product had a purity of up to 99.0%, a yield of methyl thioglycolate of 70%, a conversion rate of 80% for methyl thioglycolate, and a selectivity of up to 87.5%.

[0130] Example 7

[0131] The method of Example 6 was followed, except that the reaction in microreactor 7 was carried out at a reaction temperature of 70°C; otherwise, it was the same as in Example 6. The obtained methyl thioacetate product had a purity of 99.2%, a yield of methyl thioacetate of 91%, a conversion rate of 95% for methyl thioacetic acid, and a selectivity of up to 95.7%.

[0132] Example 8

[0133] The method of Example 7 was followed, except that the molar ratio of methanol to thioglycolic acid was 1.2:1, while all other aspects remained the same as in Example 7. The obtained methyl thioglycolic acid product achieved a purity of 99.2%, a yield of 90%, a conversion rate of 94%, and a selectivity of 95.7%.

[0134] Example 9

[0135] The method of Example 1 was followed, except that the reaction in microreactor 7 was carried out at a reaction pressure of 0.2 MPa and a reaction temperature of 110 °C; all other conditions were the same as in Example 1. The obtained methyl thioglycolate product had a purity of 99.8%, a yield of 98.6%, a conversion rate of 99.5% for methyl thioglycolate, and a selectivity of up to 99.1%.

[0136] Comparative Example 1

[0137] In a batch stirred tank, the same feed amount as in Example 8 was added, and the reaction conditions were also the same as in Example 8. After reacting for 8 hours, the mixture was allowed to stand and the water was separated to obtain crude ester. The crude ester was then subjected to vacuum distillation. The turbid liquid of the fore-fraction at 12-38℃ / 1.33kPa was first distilled off, and then the main fraction of methyl mercaptoacetate at 42-43℃ / 1.33kPa was accepted. The obtained methyl mercaptoacetate product had a purity of 95% and a yield of 88.7%, a conversion rate of 94% for methyl mercaptoacetate, and a selectivity of 94.4%.

[0138] The results above show that the method and apparatus of the present invention can achieve continuous preparation of methyl mercaptoacetate. Unreacted methanol and methyl mercaptoacetic acid raw materials and catalysts can be reused, saving costs, greatly shortening the reaction time, reducing environmental pollution, and producing methyl mercaptoacetate products with high purity, yield and selectivity.

[0139] Comparing the results of Examples 1 and 2, and Examples 5 and 6, it can be seen that the higher reaction pressure used in Examples 1 and 5 is beneficial to further improve the conversion rate of mercaptoacetic acid, as well as the purity, yield and selectivity of the methyl mercaptoacetate product.

[0140] Comparing the results of Example 1 and Example 3, it can be seen that the pressure of the second vacuum distillation is lower than that of the first vacuum distillation, which is beneficial to further improve the conversion rate of mercaptoacetic acid, as well as the purity, yield and selectivity of the methyl mercaptoacetate product.

[0141] Comparing the results of Examples 6 and 7, and Examples 1 and 9, it can be seen that using the reaction temperature within the preferred range of the present invention is beneficial to further improve the conversion rate of mercaptoacetic acid, as well as to further improve the purity, yield and selectivity of the methyl mercaptoacetate product.

[0142] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A method for continuous flow synthesis of methyl mercaptoacetate, characterized in that, The method includes: (1) The catalyst, mercaptoacetic acid and methanol are introduced into a micro mixer for contact, and then the resulting raw materials are introduced into a microreactor for reaction to obtain a reaction solution; (2) The reaction solution is subjected to a first vacuum distillation to obtain the overhead effluent and the bottom effluent; (3) The effluent from the top of the column is heated and then subjected to atmospheric distillation to obtain methanol effluent and wastewater effluent. The methanol effluent is then returned to step (1) for the contact described above. (4) The bottom effluent is heated and then subjected to a second vacuum distillation to obtain methyl mercaptoacetate product and raw material effluent. The raw material effluent is cooled and then refluxed to step (1) for the contact described above. The raw material effluent contains unreacted mercaptoacetic acid and a catalyst; The micro mixer includes a first micro mixer and a second micro mixer, and the first micro mixer, the second micro mixer and the microreactor are connected in sequence. Wherein, the first micro-mixer is a stacked micro-mixer or a chaotic micro-mixer; the second micro-mixer is a static micro-mixer; The first micromixer has a microchannel equivalent diameter of 50-500 μm, and the second micromixer has a microchannel equivalent diameter of 90-220 μm.

2. The method according to claim 1, wherein, The microreactor is selected from microchannel reactors and / or microtube reactors.

3. The method according to claim 1, wherein, The equivalent diameter of the microchannels in the first micromixer is 60-150 μm.

4. The method according to claim 1, wherein, The equivalent diameter of the microchannels in the second micromixer is 100-200 μm.

5. The method according to claim 1, wherein, The microchannel equivalent diameter of the microreactor is 100-2000 μm.

6. The method according to claim 5, wherein, The microchannel equivalent diameter of the microreactor is 200-1000 μm.

7. The method according to claim 1, wherein, The contact mentioned in step (1) includes: (a) The catalyst is mixed with mercaptoacetic acid to form a first mixture, and then the first mixture is mixed with methanol in a first micro mixer to obtain a second mixture; (b) The second mixture is passed into a second micro mixer for a second mixing to obtain a feed stream.

8. The method according to claim 7, wherein, The first mixing was carried out at room temperature and pressure.

9. The method according to claim 7, wherein, The residence time of the second mixture in the second micro mixer is 10 ms-1 s.

10. The method according to any one of claims 1-9, wherein, The amount of catalyst used in step (1) is 1-10 wt% of mercaptoacetic acid.

11. The method according to claim 10, wherein, The amount of catalyst used in step (1) is 5-10 wt% of mercaptoacetic acid.

12. The method according to any one of claims 1-9, wherein, The catalyst is selected from sulfuric acid, p-toluenesulfonic acid, methanesulfonic acid, titanium trichloride, and SO4. 2- One or more of the following: / TiO2 superacids.

13. The method according to claim 12, wherein, The catalyst is sulfuric acid and / or p-toluenesulfonic acid.

14. The method according to any one of claims 1-9, wherein, The molar ratio of methanol to mercaptoacetic acid is (1-5):

1.

15. The method according to claim 14, wherein, The molar ratio of methanol to mercaptoacetic acid is (1-4):

1.

16. The method according to any one of claims 1-9, wherein, The reaction conditions include: a reaction temperature of 50-120℃; and / or a reaction pressure of atmospheric pressure to 0.4MPa; and / or a reaction residence time of 8-60 min.

17. The method according to claim 16, wherein, The reaction conditions include: a reaction temperature of 70-110℃; and / or a reaction pressure of 0.2-0.4MPa; and / or a reaction residence time of 10-50 min.

18. The method according to any one of claims 1-9, wherein, The pressure of the second vacuum distillation is lower than the pressure of the first vacuum distillation.

19. The method according to any one of claims 1-9, wherein, In step (2), the pressure of the first vacuum distillation is 0.01-0.08 MPa.

20. The method according to claim 19, wherein, In step (2), the pressure of the first vacuum distillation is 0.01-0.05 MPa.

21. The method according to any one of claims 1-9, wherein, In step (2), the top recovery rate of the first vacuum distillation column is 50-84%.

22. The method according to claim 21, wherein, In step (2), the top recovery rate of the first vacuum distillation column is 60-80%.

23. The method according to any one of claims 1-9, wherein, In step (3), the effluent from the top of the tower is heated to 50-100°C.

24. The method according to claim 23, wherein, In step (3), the effluent from the top of the tower is heated to 60-90°C.

25. The method according to any one of claims 1-9, wherein, In step (3), the top temperature of the atmospheric distillation column is 55-70℃.

26. The method of claim 25, wherein, In step (3), the top temperature of the atmospheric distillation column is 60-70℃.

27. The method according to any one of claims 1-9, wherein, In step (4), the effluent from the bottom of the tower is heated to 60-120°C.

28. The method according to claim 27, wherein, In step (4), the effluent from the bottom of the tower is heated to 65-110°C.

29. The method according to any one of claims 1-9, wherein, In step (4), the pressure of the second vacuum distillation is 0.001-0.02 MPa.

30. The method according to claim 29, wherein, In step (4), the pressure of the second vacuum distillation is 0.002-0.02 MPa.

31. The method according to any one of claims 1-9, wherein, In step (4), the top temperature of the second vacuum distillation column is 40-60℃.

32. The method according to claim 31, wherein, In step (4), the top temperature of the second vacuum distillation column is 40-55℃.

33. The method according to any one of claims 1-9, wherein, In step (4), the raw material effluent is cooled to 20-30°C.

34. An apparatus for the continuous flow synthesis of methyl mercaptoacetate, characterized in that, The device includes: The system comprises a micromixer, a microreactor, a first vacuum distillation column, an atmospheric distillation column, and a second vacuum distillation column, wherein the micromixer, the microreactor, and the first vacuum distillation column are connected in sequence; wherein... The first vacuum distillation column has a first outlet at the top, which is connected to the atmospheric distillation column via a first reboiler to heat the effluent from the top of the column and then deliver it to the atmospheric distillation column; the first vacuum distillation column has a second outlet at the bottom, which is connected to the second vacuum distillation column via a second reboiler to heat the effluent from the bottom of the column and then deliver it to the second vacuum distillation column. The atmospheric distillation column is provided with a methanol outlet at the top, which is connected to the micro mixer to return the methanol effluent to the micro mixer; the atmospheric distillation column is provided with a wastewater outlet at the bottom to discharge the wastewater effluent. The second vacuum distillation column is provided with a product outlet at the top to discharge methyl mercaptoacetate product; the second vacuum distillation column is provided with a raw material outlet at the bottom, which is connected to the micro mixer to return the raw material effluent to the micro mixer; The micro mixer includes a first micro mixer and a second micro mixer, and the first micro mixer, the second micro mixer and the microreactor are connected in sequence. Wherein, the first micro-mixer is a stacked micro-mixer or a chaotic micro-mixer; the second micro-mixer is a static micro-mixer; The first micromixer has a microchannel equivalent diameter of 50-500 μm, and the second micromixer has a microchannel equivalent diameter of 90-220 μm.

35. The apparatus according to claim 34, wherein, The microreactor is selected from microchannel reactors and / or microtube reactors.

36. The apparatus according to claim 34, wherein, The equivalent diameter of the microchannels in the first micromixer is 60-150 μm.

37. The apparatus according to claim 34, wherein, The equivalent diameter of the microchannels in the second micromixer is 100-200 μm.

38. The apparatus according to claim 34, wherein, The microchannel equivalent diameter of the microreactor is 100-2000 μm.

39. The apparatus according to claim 38, wherein, The microchannel equivalent diameter of the microreactor is 200-1000 μm.

40. The apparatus according to any one of claims 34-39, wherein, The device also includes a methanol tank and a thioglycolic acid tank, which are respectively connected to the micromixer.

41. The apparatus according to claim 40, wherein, The methanol outlet is connected to the methanol tank via a pipeline.

42. The apparatus according to claim 40, wherein, The raw material outlet is connected to the mercaptoacetic acid tank via a pipeline.

43. The apparatus according to any one of claims 34-39, wherein, The wastewater outlet is connected to the wastewater treatment system.

44. The apparatus according to any one of claims 34-39, wherein, The product outlet is connected to the product storage tank.

45. The use of the method according to any one of claims 1-33 and the apparatus according to any one of claims 34-44 in the synthesis of methyl mercaptoacetate.

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