A system and control method for producing 4-chlorobutanoic acid methyl ester by thionyl chloride method

Abstract

The application discloses a system for producing 4-chlorobutanoic acid methyl ester by means of chlorosulfoxide, which comprises a precooling system, a synthetic reaction kettle, a rectification system and a tail gas treatment system. The precooling system comprises a first precooler and a second precooler. Gamma-butyrolactone and excessive chlorosulfoxide are preliminarily pre-cooled by the first precooler and the second precooler respectively, and then the pre-cooled gamma-butyrolactone and chlorosulfoxide are preliminarily mixed in a mixing tank and then enter the reaction kettle for esterification. Methanol is added into a dropping tank and then added into the reaction kettle through a distribution disc to prepare 4-chlorobutanoic acid methyl ester. The crude 4-chlorobutanoic acid methyl ester produced in the reaction kettle is taken out from the bottom of the reaction kettle and then enters a batch rectification tower for rectification and purification. The mixed gas in the upper part of the reaction kettle enters a condenser for preliminary condensation. The liquid condensed by the condenser is returned to the reaction kettle. The mixed gas condensed by the condenser enters the tail gas treatment system.

Description

Technical Field

[0001] This invention relates to the field of fine chemical intermediate organic synthesis technology, and more specifically, to a system and control method for producing methyl 4-chlorobutyrate by the thionyl chloride method. Background Technology

[0002] Methyl 4-chlorobutyrate is a stable organic synthetic intermediate and a raw material for cyclopropane (a pharmaceutical intermediate) and some other products. Currently, the common synthetic methods for methyl 4-chlorobutyrate are as follows: 1. A process for synthesizing methyl 4-chlorobutyrate from γ-butyrolactone using phosphorus trichloride as a raw material under the action of a catalyst. Although this process does not generate a large amount of waste gas, the chlorinating agent phosphorus trichloride used is a controlled highly toxic substance, and therefore it is not suitable for large-scale industrial production.

[0003] 2. A method for synthesizing 4-chlorobutyryl chloride from γ-butyrolactone using phosgene or solid phosgene as raw material, followed by esterification to obtain methyl 4-chlorobutyrate, such as Hou Zhongke et al. Research on green synthesis of methyl 4-chlorobutyrate. Fine Chemical Intermediates, 2009, 39(4): 14-16. This process is simple, has a high yield and less waste, but phosgene is a highly toxic gas, which greatly limits its industrial application. Although solid phosgene has reduced toxicity, it is more expensive and not suitable for large-scale industrial production.

[0004] 3. A process for synthesizing methyl 4-chlorobutyrate using γ-butyrolactone, methanol, and silicon tetrachloride, is costly and the toxic substance silicon tetrachloride is difficult to handle, which is detrimental to the environment.

[0005] Patent CN107721850B discloses a method for preparing methyl γ-chlorobutyrate. The method involves thoroughly mixing γ-butyrolactone and zinc chloride or aluminum chloride in a reaction vessel, sealing the vessel, and purging nitrogen gas to create a closed space. Hydrogen chloride and chloromethane are then added to the reaction vessel, and the temperature is maintained at 70℃–150℃, the pressure at 1.7–7.5 MPa, and the reaction is carried out for 2–20 hours to produce methyl γ-chlorobutyrate. However, the reaction temperature is relatively high, close to the boiling point of methyl γ-chlorobutyrate, which easily leads to leakage, and the product yield is low, making it unsuitable for industrial production.

[0006] Therefore, in large-scale industrial production, zinc chloride is often used as a catalyst, thionyl chloride is used to chloride γ-butyrolactone, and methanol is added to obtain methyl 4-chlorobutyrate. The reaction principle is as follows: γ-butyrolactone and thionyl chloride are used as raw materials to produce 4-chlorobutyryl chloride through ring-opening and chlorination under normal pressure, which is then esterified with methanol to obtain methyl 4-chlorobutyrate. This process is simple to operate, the raw materials are readily available, and the cost is low, but it generates a large amount of mixed waste gas of sulfur dioxide and hydrochloric acid, which is difficult to treat and poses a significant environmental hazard.

[0007]

[0008] Furthermore, the production of methyl chlorobutyrate via thionyl chloride may involve the two side reactions mentioned above. When thionyl chloride is first mixed with butyrolactone, chlorobutyryl chloride and sulfur dioxide gas are produced, with the sulfur dioxide gas causing an increase in pressure within the reactor. When methanol is added, it reacts with chlorobutyryl chloride to produce hydrogen chloride gas. However, hydrogen chloride gas reacts with either butyrolactone or chlorobutyryl chloride, thus the addition of methanol can promote the ring-opening and esterification reactions of butyrolactone in the forward direction. However, the hydrogen chloride gas produced by the reaction of methanol and chlorobutyryl chloride may also cause the pressure within the reactor to continue to rise, and excess methanol can react with the product methyl chlorobutyrate to form methyl 4-methoxybutyrate. Therefore, the addition of methanol has a significant impact on the composition of the materials within the reactor. How to avoid drastic changes in temperature and pressure within the reactor that affect the yield of methyl chlorobutyrate is a problem that urgently needs to be solved in this field. Summary of the Invention

[0009] Based on the above description, to address the problems in the existing technology of producing large amounts of mixed sulfur dioxide and hydrochloric acid waste gas during the preparation of methyl 4-chlorobutyrate from thionyl chloride and γ-butyrolactone, which are difficult to treat, and the problem that improper addition of methanol can easily affect the yield of methyl 4-chlorobutyrate, this invention provides a system for producing methyl 4-chlorobutyrate using the thionyl chloride method. This invention provides a system for producing methyl 4-chlorobutyrate using the thionyl chloride process. Basic reaction equation: C4H6O2 + CH3OH + SOCl2 Cl(CH2)3COOCH3+SO2+HCl The system includes a precooling system, a reaction vessel, a distillation system, and a tail gas treatment system. The precooling system comprises a first precooler and a second precooler. γ-Butyrolactone and excess thionyl chloride are precooled by the first and second precoolers, respectively. The precooled γ-butyrolactone and thionyl chloride are then premixed in a first mixing tank before entering the reaction vessel for esterification. Methanol is added to the reaction vessel via a distribution plate from a dropping tank to prepare methyl 4-chlorobutyrate. The crude methyl 4-chlorobutyrate produced in the reaction vessel enters a batch distillation column from the bottom of the reaction vessel for further distillation and purification. The mixed gas in the upper part enters the condenser for preliminary condensation. The liquid after condensation in the condenser returns to the reactor. The mixed gas after condensation in the condenser enters the tail gas treatment system, which includes a tail gas buffer tank, a compressor, a second mixing tank, and a pressurized distillation column. After passing through the tail gas buffer tank, the mixed gas enters the compressor for compression and mixing, and then enters the pressurized distillation column for distillation and separation. The separated and cooled sulfur dioxide is returned to the thionyl chloride production process for recycling. The unrecoverable hydrogen chloride is absorbed into hydrochloric acid by a water falling film absorption tower, and the unseparated sulfur dioxide is absorbed by caustic soda.

[0010] Furthermore, both thionyl chloride and γ-butyrolactone are liquids. The butyrolactone transfer pump for transporting γ-butyrolactone is a centrifugal corrosion-resistant transfer pump, and the thionyl chloride transfer pump for transporting thionyl chloride is a closed material transfer pump.

[0011] Furthermore, a distribution plate is installed near the upper part of the inside of the reactor, and liquid methanol in the dropping tank enters the reactor through the distribution plate via a high-level tank pipeline, a pneumatic regulating valve, and a metering pump.

[0012] Furthermore, the thionyl chloride and γ-butyrolactone are fed uniformly into the reactor, the reaction temperature inside the reactor is controlled at -10 to -20°C, and the reaction pressure is controlled at -0.05 to -0.10 MPa.

[0013] Furthermore, the reaction time is 6-7 hours.

[0014] Furthermore, the crude methyl 4-chlorobutyrate obtained in the reaction vessel is fed into a distillation vessel via a transfer pump, and a batch distillation column is installed at the top of the distillation vessel for distillation purification.

[0015] Furthermore, the distillation process employs steam heating, controlling the top temperature of the column at 80±2℃, the bottom temperature at 125±2℃, and the vacuum pressure at -0.05MPa.

[0016] Furthermore, a buffer feeding device is installed in front of the reactor, and a Venturi tube is installed on the pipeline between the first mixing tank and the reactor. The inlet of the Venturi tube is connected to the first mixing tank, and the outlet of the Venturi tube is connected to the reactor.

[0017] This invention also provides a control method for the production of methyl 4-chlorobutyrate via the thionyl chloride process, comprising the following control steps: The flow rates of thionyl chloride, butyrolactone, and methanol in drop tank 6 are set according to the preset ratio; and the initial reaction temperature of the reactor is controlled at -15℃. Start the DCS control system; During operation, the pressure changes and temperature changes at the center of the reactor are acquired, and the flow rate of methanol added is adjusted according to these changes.

[0018] Furthermore, the preset ratio is as follows: the flow ratio of thionyl chloride to γ-butyrolactone is 2.3~2.8:1, and the initial flow ratio of methanol to γ-butyrolactone is 1:1.4.

[0019] This invention solves the problem of sulfur dioxide disposal, a toxic substance, while producing methyl 4-chlorobutyrate. Sulfur dioxide is recovered and used in the synthesis of thionyl chloride, enabling the entire reaction to be controlled in a circular manner. This is beneficial to environmental protection, achieving a green circular economy and yielding significant social benefits. Furthermore, the system and control method described in this invention, by adjusting the amount of methanol added based on the reaction vessel temperature and pressure and a curve, can effectively utilize the hydrogen chloride gas produced by the reaction of thionyl chloride and butyrolactone, effectively promoting the synthesis of methyl chlorobutyrate, increasing product yield, and reducing the generation of hydrogen chloride and sulfur dioxide gas. This significantly reduces production costs and improves economic efficiency. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the overall system for producing methyl 4-chlorobutyrate according to an embodiment of the present invention; Figure 2 This is a schematic diagram of the crude methyl 4-chlorobutyrate synthesis system described in an embodiment of the present invention; Figure 3 The curve showing the relationship between methanol addition and product yield in the thionyl chloride process for the production of methyl 4-chlorobutyrate. Figure 4 This is a flowchart of the control method for producing methyl 4-chlorobutyrate according to an embodiment of the present invention.

[0021] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used together with the embodiments of the invention to explain the invention and do not constitute a limitation thereof.

[0022] 1-Butyrolactone transfer pump, 2-Thionyl chloride transfer pump, 3-First precooler, 4-Second precooler, 5-First mixing tank, 6-Droplet tank, 61-Regulating valve, 62-Metering pump, 7-Reaction vessel, 71-Distribution plate, 72-Buffer feeding device, 73-Venturi tube, 74-Methanol feeding tank, 75-Hydrogen chloride feeding tank, 76-First control valve, 77-Second control valve, 78-Buffer tank, 8-Condenser, 9-Transfer pump, 10-Batch distillation column, 11-First vapor phase condenser, 12-First reflux tank, 13-First intermediate tank, 14-Tail gas buffer tank, 15-Compressor, 16-Second mixing tank, 17-Pressurized distillation column, 18-Second vapor phase condenser, 19-Second reflux tank Detailed Implementation

[0023] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0024] like Figure 1 As shown, this invention provides a process for producing methyl 4-chlorobutyrate using the thionyl chloride method. The process includes pre-cooling γ-butyrolactone and excess thionyl chloride in a first precooler 3 and a second precooler 4, respectively. The pre-cooled γ-butyrolactone and thionyl chloride are then pre-mixed in a first mixing tank 5 and subsequently esterified in a reaction vessel 7. Methanol is added to a dropping tank 6 and then distributed into the reaction vessel 7 to prepare methyl 4-chlorobutyrate. The crude methyl 4-chlorobutyrate produced in the reaction vessel 7 is purified by distillation from the bottom of the reaction vessel 7 into a batch distillation column 10. The mixed gas in the upper part of the reaction vessel 7 is pre-condensed in a condenser 8. The liquid condensed in the condenser 8 is returned to the reaction vessel 7, and the mixed gas condensed in the condenser 8 enters the tail gas treatment system. The exhaust gas treatment system includes an exhaust gas buffer tank 14, a compressor 15, a second mixing tank 16, and a pressurized distillation column 17. After passing through the exhaust gas buffer tank 14, the mixed gas enters the compressor 15 for compression and mixing, and then enters the pressurized distillation column 17 for distillation separation. The separated and cooled sulfur dioxide is returned to the thionyl chloride production process for recycling. The unrecoverable hydrogen chloride is absorbed by a water falling film absorption tower to form hydrochloric acid, and the unseparated sulfur dioxide is absorbed by caustic soda. This effectively treats the generated exhaust gas, preventing it from being released into the atmosphere and impacting the environment.

[0025] The mixed gases of sulfur dioxide and hydrogen chloride are compressed and collected by compressor 15 into the second mixing tank 16, and then enter the distillation kettle. They are effectively recovered by using the principle that the boiling points of each component are different under different temperature and pressure conditions through pressurized distillation column 17.

[0026] The crude methyl 4-chlorobutyrate obtained in reactor 7 is purified by a batch distillation device using the principle that the boiling points of each component are different under different conditions, and impurities are removed to obtain the finished methyl 4-chlorobutyrate product.

[0027] Furthermore, both thionyl chloride and γ-butyrolactone are liquids. The butyrolactone transfer pump 1, which transports γ-butyrolactone, is a centrifugal, corrosion-resistant pump, while the thionyl chloride transfer pump 2, which transports thionyl chloride, is a closed-loop material transfer pump, ensuring the entire system remains closed. A distribution plate 71 is installed near the top inside the reactor 7. Liquid methanol from the dropping tank 6 enters the reactor 7 via a high-level pipeline, a pneumatic regulating valve 61, and a metering pump 62 through the distribution plate 71. Each process is a closed operation to avoid pressure changes within the reactor and ensure the normal progress of the reaction.

[0028] Furthermore, the feed of thionyl chloride and γ-butyrolactone into reactor 7 is uniform. The reaction temperature in reactor 7 is controlled at -10 to -20°C, and the reaction pressure is controlled at -0.05 to -0.10 MPa. Preferably, the reaction temperature is controlled at around -15°C, the reaction pressure is controlled at around -0.08 MPa, and the reaction time is 6-7 hours. After the reaction is completed, crude methyl 4-chlorobutyrate is obtained.

[0029] Since the thionyl chloride in the reactor is in excess, the mixed gases of sulfur dioxide and hydrogen chloride are compressed into a liquid by a compressor after passing through the tail gas buffer tank during the reaction. The liquid then enters a pressurized distillation column. Utilizing the principle that the boiling points of each component in the liquid are different under a certain pressure, sulfur dioxide and hydrogen chloride are separated and recovered. After separation and cooling, the sulfur dioxide is returned to the thionyl chloride production process for recycling. The unrecoverable hydrogen chloride is absorbed into hydrochloric acid by a water falling film absorption tower. The sulfur dioxide is absorbed by 32% caustic soda to obtain sodium sulfite.

[0030] Furthermore, the crude methyl 4-chlorobutyrate obtained in reactor 7 is fed into a distillation vessel via transfer pump 9. A batch distillation column 10 is installed at the top of the distillation vessel for further distillation and purification. Distillation is performed using steam heating, with the top temperature controlled at 80±2℃ and the bottom temperature at 125±2℃, while the vacuum pressure is controlled at -0.05MPa. The vapor phase passes through the first vapor condenser 11 at the top of the column. Part of the condensate is refluxed back into the column, and part enters a reflux tank and is then collected into an intermediate tank. The reflux tank level is controlled at 55%, and the vapor phase enters the tail gas treatment system. Utilizing the principle that the components of crude methyl 4-chlorobutyrate have different boiling points under a certain vacuum, impurities in the crude methyl 4-chlorobutyrate are removed, and the crude methyl 4-chlorobutyrate is purified. After purification, the product is kept at a certain temperature for 2 hours to obtain the final methyl 4-chlorobutyrate product.

[0031] Furthermore, a buffer feeding device 72 is installed before the reactor 7, and a Venturi tube 73 is installed on the pipeline between the first mixing tank 5 and the reactor 7. The inlet of the Venturi tube 73 is connected to the first mixing tank 5, and the outlet of the Venturi tube 73 is connected to the reactor 7. The buffer feeding device 72 includes a methanol feeding tank 74, a hydrogen chloride feeding tank 75, and a buffer tank 78. A first control valve 76 is installed between the methanol feeding tank 74 and the buffer tank 78 to control the flow rate of methanol, and a second control valve 77 is installed between the hydrogen chloride feeding tank 75 and the buffer tank 78 to control the flow rate of hydrogen chloride. Methanol and hydrogen chloride are mixed evenly in the buffer tank 78 before entering the reactor. The outlet of the buffer tank 78 is connected to the throat of the Venturi tube 73, and an on / off valve is installed on the connecting pipeline between the buffer tank 78 and the Venturi tube 73 to control whether the buffer tank 78 is connected to the reactor 7. Methanol and hydrogen chloride are first mixed in a buffer tank, and then added to the reactor along with a mixture of thionyl chloride and butyrolactone. This ensures that methanol and hydrogen chloride are fully mixed with the raw materials in the reactor, thereby improving the reaction efficiency.

[0032] Furthermore, to ensure efficient adjustment of the entire control process, before the system starts running, the effect curve of methanol addition on the yield of methyl chlorobutyrate was first obtained. Specifically, the flow ratio of thionyl chloride to γ-butyrolactone was controlled at 2.5:1, and the effect curves of different methanol flow rates on the product were investigated, as shown below. Figure 3 The curve shown represents the volumetric flow rate ratio of methanol to thionyl chloride. The curve indicates that when the amount of methanol added is 0.17 to 0.22 times that of thionyl chloride, increasing the methanol flow rate does not improve the product yield. This range of methanol addition is referred to as the plateau period. Part of the added methanol participates in the reaction, producing hydrogen chloride gas. However, the hydrogen chloride gas does not react with butyrolactone, causing the pressure inside the reactor to rise, leading to the termination of the synthesis reaction. The latter half of the curve shows that when the amount of methanol added is 0.37 to 0.42 times that of thionyl chloride, the product yield is relatively high. This range of methanol addition is called the safe plateau period. The added methanol reacts effectively with chlorobutyryl chloride to produce methyl chlorobutyrate. At the same time, the excess methanol can react with the hydrogen chloride gas generated from the ring-opening reaction and butyrolactone to synthesize methyl chlorobutyrate in one step, accelerating the ring-opening esterification of butyrolactone and reducing the generation of sulfur dioxide. However, when the amount of methanol added is less than the lower limit of this range, the product yield drops sharply, possibly affecting the one-step synthesis reaction. When the amount of methanol added is greater than the upper limit of this range, the product yield also drops sharply because the excess methanol reacts with the product methyl chlorobutyrate to generate methyl methoxybutyrate. Therefore, ideally, the amount of methanol added should be controlled within the safe plateau period.

[0033] As part of the embodiments of the present invention, a control method for the production of methyl 4-chlorobutyrate by the thionyl chloride process is also provided, specifically including the following control process: S1. Set the flow rates of thionyl chloride, γ-butyrolactone, and methanol in dropping tank 6 according to the preset ratio; and control the initial reaction temperature of the reactor to -15℃. Based on the reaction characteristics of thionyl chloride and γ-butyrolactone, an excess of thionyl chloride is beneficial for the forward reaction. Therefore, control the flow rate ratio of thionyl chloride to γ-butyrolactone to be 2.3~2.8:1, and the initial flow rate ratio of methanol to γ-butyrolactone to be 1:1.4. S2. Start the DCS control system; S3. During operation, obtain the pressure changes and center temperature changes inside the reactor, and adjust the flow rate of methanol added according to the pressure changes and center temperature changes inside the reactor.

[0034] The ring-opening esterification reaction of thionyl chloride with γ-butyrolactone and methanol is exothermic. Therefore, the temperature inside the reactor may change as the reaction proceeds. If the heat generated inside the reactor is not released in time, it can easily affect the synthesis reaction and thus the product yield. Furthermore, the ring-opening reaction of thionyl chloride with γ-butyrolactone releases sulfur dioxide. Some of this sulfur dioxide dissolves in the liquid phase inside the reactor. When the temperature inside the reactor rises, some of the sulfur dioxide may accumulate in gaseous form, leading to an increase in reactor pressure. This increased pressure may, in turn, affect the opening of the pneumatic regulating valve, thus affecting the flow rate of methanol into the reactor. Therefore, it is necessary to adjust the amount of methanol added in real time based on changes in reactor pressure and core temperature.

[0035] S4. Determine whether the pressure change ΔP inside the reactor is greater than the threshold of 0.05 MPa and whether the temperature increase ΔT is greater than 5℃.

[0036] S5. When the pressure change ΔP inside the reactor is detected to be greater than the threshold of 0.05 MPa and the temperature increase ΔT is greater than 5°C, the control system controls the reactor to cool down to -15°C and continuously monitors the pressure. When the pressure change ΔP inside the reactor is detected to be greater than the threshold of 0.05 MPa and the temperature increase ΔT is greater than 5°C, it is determined that the heat generated by the reaction cannot be dissipated in time, leading to an increase in material temperature and a large amount of sulfur dioxide vaporization, resulting in a pressure increase. Here, the pressure change ΔP is the difference between the current pressure P1 and the initial pressure P0, and the temperature increase ΔT is the difference between the current temperature T1 and the initial set temperature T0.

[0037] S6. Check whether the pressure change is significant after the reactor is cooled to -15℃.

[0038] If the pressure changes significantly after the reactor is cooled to -15℃, it indicates that lowering the reactor temperature has effectively reduced the vaporization of sulfur dioxide, and the system can continue to operate normally under its current condition.

[0039] If the pressure change is not significant after the reactor is cooled to -15℃, it indicates that the methanol addition is at a plateau and the methanol flow rate needs to be increased. Specifically, the criterion for judging whether the pressure change is significant is: whether the difference between the pressure P1 before cooling and the current pressure P2 is less than 0.02 MPa. If the difference is less than 0.02 MPa, it indicates that the pressure reduction is not significant, meaning the pressure increase in the reactor is not entirely caused by sulfur dioxide. It may be due to a small amount of methanol participating in the reaction, producing some hydrogen chloride gas. The excess hydrogen chloride gas and sulfur dioxide together cause the pressure increase in the reactor. Therefore, the methanol addition should be significantly increased to allow the unreacted γ-butyrolactone in the reactor to react with the excess hydrogen chloride gas and the newly added methanol in one step to produce methyl 4-chlorobutyrate, increasing the yield of methyl 4-chlorobutyrate and effectively consuming the hydrogen chloride gas in the reactor. Specifically, after increasing the methanol addition, the following judgment process should be performed: S7. Determine whether the methanol addition has increased to the high content threshold, while continuously monitoring the pressure inside the reactor. The high content threshold is the upper limit of the safe plateau period; preferably, the high content threshold is when the methanol flow rate is 0.42 times the thionyl chloride flow rate. When the methanol-to-thionyl chloride ratio exceeds this range, further increasing methanol may lead to a sharp decrease in reaction yield, possibly due to excessive methanol consumption of the reaction product methyl chlorobutyrate.

[0040] S8. If the methanol addition amount does not increase to the high content threshold and the current pressure meets the standard, maintain the current methanol addition amount, control the entire system to operate normally according to the current parameters, and return to step S3 to continuously monitor the pressure and temperature changes inside the reactor. The standard for the current pressure is: the difference between the pressure P1 before cooling and the current pressure P3 is less than 0.04 MPa, and the difference between the current pressure and the initial pressure P0 is less than 0.05 MPa. Meeting the current pressure standard indicates that increasing the methanol addition amount can effectively reduce the pressure inside the reactor, ensuring the normal progress of the synthesis reaction.

[0041] S9. If the amount of methanol added increases to the high content threshold, determine whether the current pressure meets the standard. If the current pressure meets the standard, slowly reduce the methanol dropping rate to the lower limit of the safe plateau period. Preferably, reduce the methanol dropping rate to 0.37 times the thionyl chloride flow rate.

[0042] S10. If the amount of methanol added increases to the high content threshold and the current pressure still does not meet the standard, increase the speed of the exhaust pump between the reactor 7 and the first gas phase condenser 11 to accelerate the discharge of gas from the reactor. At the same time, close the regulating valve 61 of the dripping tank 6, open the buffer device feeding system, and feed the reactor through the buffer device. At the same time, return to step S3 and continuously monitor the pressure change and the temperature change at the center of the reactor.

[0043] Specifically, when the exhaust pump is turned on to discharge the gas in the reactor, some hydrogen chloride gas will be carried out. This will cause the excess methanol to react with methyl chlorobutyrate after adding excess methanol, reducing the yield and product purity. Therefore, this embodiment is equipped with a buffer feeding device. When the amount of methanol added increases to the high content threshold, the buffer feeding device is switched to add methanol and hydrogen chloride at the same time to promote the conversion of the intermediate product chlorobutyryl chloride in the reactor into methyl chlorobutyrate. At the same time, the excess methanol and hydrogen chloride react together with the excess thionyl chloride to produce methyl chlorobutyrate.

[0044] Furthermore, in step S10, when feeding through the buffer feeding device, the buffer feeding device controls the ratio of the methanol addition rate to the thionyl chloride addition rate to be 0.37, while the buffer feeding device controls the ratio of the hydrogen chloride addition rate to the methanol addition rate to be between 0.3 and 0.4.

[0045] It should be noted that the flow rates mentioned in this embodiment are all volumetric flow rates.

[0046] Experimental Example When the methanol is fed in a pre-set ratio and the feed is uniform, the entire system will stop after less than 72 hours due to an alarm. Product yield testing revealed a yield of only 78%. However, when the control method described in this invention is used, the system can run continuously for 192 hours. Furthermore, compared to the same raw material feed rate, the product yield obtained by the control method of this invention reaches 94.7%.

[0047] Finally, it should be noted that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A system for producing methyl 4-chlorobutyrate via the thionyl chloride process, characterized in that, The system includes a precooling system, a reaction vessel (7), a distillation system, and a tail gas treatment system. The precooling system includes a first precooler (3) and a second precooler (4). γ-Butyrolactone and excess thionyl chloride are precooled by the first precooler (3) and the second precooler (4), respectively. The precooled γ-butyrolactone and thionyl chloride are premixed in a first mixing tank (5) and then enter the reaction vessel (7) for esterification. Methanol is added to a dropping tank (6) and then to the reaction vessel (7) via a distribution plate to prepare methyl 4-chlorobutyrate. The crude methyl 4-chlorobutyrate produced in the reaction vessel (7) enters a batch distillation column (10) from the bottom of the reaction vessel (7) for distillation purification. The upper part of the reaction vessel (7) The mixed gas enters the condenser (8) for preliminary condensation. The liquid after condensation in the condenser (8) is returned to the reactor (7). The mixed gas after condensation in the condenser (8) enters the tail gas treatment system. The tail gas treatment system includes a tail gas buffer tank (14), a compressor (15), a second mixing tank (16), and a pressurized distillation column (17). After passing through the tail gas buffer tank (14), the mixed gas enters the compressor (15) for compression and mixing, and then enters the pressurized distillation column (17) for distillation and separation. The separated and cooled sulfur dioxide is returned to the thionyl chloride production process for recycling. The unrecoverable hydrogen chloride is absorbed into hydrochloric acid by a water falling film absorption tower. The unseparated sulfur dioxide is absorbed by caustic soda. A buffer feeding device (72) is provided in front of the reactor (7). A Venturi tube (73) is provided on the pipeline between the first mixing tank (5) and the reactor (7). The inlet of the Venturi tube (73) is connected to the first mixing tank (5), and the outlet of the Venturi tube (73) is connected to the reactor (7). The buffer feeding device (72) includes a methanol feeding tank (74), a hydrogen chloride feeding tank (75), and a buffer tank (78). Methanol and hydrogen chloride are mixed evenly in the buffer tank (78) and then enter the reactor. The outlet of the buffer tank (78) is connected to the throat of the Venturi tube (73). An on / off valve is provided on the connecting pipeline between the buffer tank (78) and the Venturi tube (73) to control whether the buffer tank (78) is connected to the reactor (7).

2. The system for producing methyl 4-chlorobutyrate by the thionyl chloride method according to claim 1, characterized in that, Both thionyl chloride and γ-butyrolactone are liquids. The butyrolactone transfer pump (1) for transporting γ-butyrolactone is a centrifugal corrosion-resistant transfer pump, and the thionyl chloride transfer pump (2) for transporting thionyl chloride is a closed material transfer pump.

3. The system for producing methyl 4-chlorobutyrate by the thionyl chloride process according to claim 1, characterized in that, A distribution plate (71) is installed near the top inside the reactor (7). Liquid methanol in the dripping tank (6) enters the reactor (7) through the distribution plate (71) via the high-level tank pipeline, pneumatic regulating valve (61), and metering pump (62).

4. The system for producing methyl 4-chlorobutyrate by the thionyl chloride process according to claim 1, characterized in that, The thionyl chloride and γ-butyrolactone in the reactor (7) are fed uniformly. The reaction temperature in the reactor (7) is controlled at -10~-20℃ and the reaction pressure is controlled at -0.05~-0.10MPa.

5. The system for producing methyl 4-chlorobutyrate by the thionyl chloride process according to claim 4, characterized in that, The reaction time is 6-7 hours.

6. The system for producing methyl 4-chlorobutyrate by the thionyl chloride process according to claim 1, characterized in that, The crude methyl 4-chlorobutyrate obtained in the reaction vessel (7) is fed into the distillation vessel via a transfer pump (9), and a batch distillation column (10) is installed at the top of the distillation vessel for distillation purification.

7. The system for producing methyl 4-chlorobutyrate by the thionyl chloride process according to claim 6, characterized in that, The distillation process uses steam heating, with the top temperature controlled at 80±2℃ and the bottom temperature at 125±2℃, and the vacuum pressure controlled at -0.05MPa.

8. A method for controlling the production of methyl 4-chlorobutyrate via the thionyl chloride process, characterized in that, Using the system according to any one of claims 1 to 7, the control method includes the following control process: The flow rates of thionyl chloride, butyrolactone, and methanol in the dropping tank are set according to the preset ratio; and the initial reaction temperature of the reactor is controlled at -15℃. Start the DCS control system; During operation, the pressure changes and temperature changes at the center of the reactor are acquired, and the flow rate of methanol added is adjusted according to these changes.

9. The control method according to claim 8, characterized in that, The preset ratio is as follows: the flow ratio of thionyl chloride to γ-butyrolactone is 2.3~2.8:1, and the initial flow ratio of methanol to γ-butyrolactone is 1:1.4.

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