Method and device for circularly preparing 3-methyl-2-nitrobenzoate compound

Abstract

The invention belongs to the technical field of chemical engineering, and particularly relates to a method and a device for circularly preparing a 3-methyl-2-nitrobenzoate compound. The preparation method of the 3-methyl-2-nitrobenzoate compound comprises the following steps: (1) adding 3-methyl-2-nitrobenzoic acid and saturated fatty alcohol into a preparation kettle for dissolving, and adding an obtained homogeneous mixed solution and a catalyst into a mixing storage tank; and (2) opening a circulating pump to enable the material to circularly flow and dehydrate in a device consisting of the mixing storage tank, the filter and the membrane equipment until the flow speed is stable. And (3) opening the preheater to heat the reaction liquid in the mixing storage tank under the condition that the reaction liquid circularly flows, performing esterification reaction, performing in-situ water separation on the permeation side of the membrane equipment in the reaction process, and finally circulating the esterification product into the mixing storage tank. According to the method provided by the invention, the alcohol-acid ratio in the esterification process is reduced, the reaction period is greatly shortened, the consumption of electric power, steam and circulating cooling water is saved, and the operation cost is reduced.

Description

Technical Field

[0001] The invention belongs to the technical field of chemical industry, and specifically relates to a method and a device for cyclically preparing 3-methyl-2-nitrobenzoic acid ester compounds. Background Art

[0002] 3-Methyl-2-nitrobenzoate, especially methyl 3-methyl-2-nitrobenzoate, is a raw material for synthesizing 2-amino-5-chloro-N,3-dimethylbenzamide, which is a key intermediate of chlorfenapyr. Methyl 3-methyl-2-nitrobenzoate is widely used in the pesticide and pharmaceutical markets. In the synthesis process of 3-methyl-2-nitrobenzoate compounds, the generation of water will cause the chemical reaction to be limited by thermodynamic equilibrium and the activity of the catalyst will be weakened. In industry, the product yield is improved by making one component in the reactants excessive (such as a catalyst) or removing one of the products.

[0003] Combining the esterification reaction with membrane separation technology provides an efficient production method because the separation is not limited by relative volatility. In addition, the energy consumption is usually low because only a small part of the feed permeates to undergo a phase change from liquid to gas, and it can also be operated at a lower temperature to better match the optimal conditions of the reaction, which is particularly important in bioconversion. In the 1960s, the foreign patent US2956070 first proposed this concept and applied it to the esterification reaction. The patent CN113522029A designs a method and device for producing ester products by coupling the esterification reaction with a pervaporation membrane. Through two cycles: the esterification reaction cycle and the membrane pervaporation dehydration cycle, the water produced by the reaction is continuously removed, and ester products can be produced intermittently. Due to the limitation of the membrane area, the fluid leaving the membrane unit is recycled to the reactor unit to improve the dehydration efficiency. The split design of the membrane material and the reactor easily causes difficulties such as complex device process and high design cost. CN 116747797A also mentions the problem of low generation rate and conversion rate in the prior art, and the new continuous and efficient esterification reaction method solves the current situation and improves the conversion rate and rate. However, the patent proposes to fill the inside of the membrane with a solid acid catalyst, which makes it inconvenient to replace the catalyst during use, and the solid acid catalyst is in direct contact with the membrane, which is also a challenge to the life of the membrane.

[0004] In addition, continuous in-situ dehydration shows better enhancement effect in esterification reaction due to its high dehydration efficiency, but it poses a challenge to the selection of membrane under the typical acidic conditions of esterification reaction. At present, the separation membranes used in most industrial applications are organic polymer membranes. The main advantage of polymer membranes is their low manufacturing cost and high economy. However, the main disadvantage of polymer membranes is the limited solvents that can be separated and their low thermal stability. The occurrence of swelling of polymer membranes will also change the properties of the membrane, usually resulting in lower selectivity of the separation membrane and an increase in the number of organic macromolecules passing through the separation membrane, which is not suitable for esterification reactions with strongly acidic materials. Summary of the invention

[0005] In view of the above technical problems, the present invention provides a cyclic esterification technology using 3-methyl-2-nitrobenzoic acid and alkyl alcohol as raw materials. The cyclic esterification and in-situ dehydration reaction can be carried out under the condition of using a catalyst. The esterification pressure is low, the process is short, the quality is stable, and it is suitable for large-scale industrialization. The molar ratio of alcohol and acid is greatly reduced compared with the reported technology, which reduces energy consumption and material consumption, reduces costs, and solves the problem of low generation rate and conversion rate of 3-methyl-2-nitrobenzoic acid ester compounds.

[0006] To achieve the above purpose, the technical method adopted by the present invention is as follows:

[0007] A method for cyclically preparing 3-methyl-2-nitrobenzoate compounds, comprising the following specific steps:

[0008] (1) 3-Methyl-2-nitrobenzoic acid powder and saturated fatty alcohol are added to a preparation kettle to dissolve, and the resulting homogeneous mixed solution and catalyst are added to a mixing tank, and the mixing tank is filled with nitrogen for ventilation until the oxygen content in the tail gas is less than 1%;

[0009] (2) Turn on the circulation pump to allow the reaction solution to circulate in the device consisting of the mixing tank, filter, and membrane equipment until the flow rate stabilizes.

[0010] (3) When the reaction liquid is circulating, the preheater is turned on to heat the reaction liquid in the mixing tank. The reaction liquid circulates in the device to carry out esterification reaction. During the reaction, water is separated in situ on the permeate side of the membrane device. The esterification product is circulated back to the mixing tank from the membrane outlet, and dehydrated during the reaction.

[0011] The membrane device is provided with a membrane for in-situ separation of water, and the membrane is one or more of a ceramic membrane, a metal membrane, a PM membrane, a molecular sieve membrane, and an organosilicon hybrid membrane.

[0012] The saturated fatty alcohol is one of methanol, ethanol, n-propanol, isopropanol, n-butanol, isobutanol, and tert-butanol. The molar ratio of 3-methyl-2-nitrobenzoic acid to the saturated fatty alcohol is 1:5.6-282, preferably 1:17-170, further preferably 1:17-113, and further preferably 1:25-80.

[0013] Furthermore, the saturated fatty alcohol is one of methanol, ethanol, isopropanol and tert-butanol.

[0014] Furthermore, the saturated fatty alcohol is one of methanol and ethanol.

[0015] The esterification reaction temperature is 90-230° C., the pressure of the mixing storage tank is 0.3-3.5 MPa, and the reaction liquid flow rate is 100 L / h-500 L / h.

[0016] Furthermore, the esterification reaction temperature is 100-200° C., the pressure of the mixing tank is 0.5-3.0 MPa, and the reaction liquid flow rate is 150 L / h-400 L / h.

[0017] Furthermore, the esterification reaction temperature is 125-175° C., the pressure of the mixing tank is 0.6-2.5 MPa, and the reaction liquid flow rate is 200 L / h-350 L / h.

[0018] The esterification reaction time is 20 to 50 hours, and the preferred reaction time is 50 hours.

[0019] The catalyst is one or more of sulfuric acid, nitric acid, hydrochloric acid, methanesulfonic acid, benzenesulfonic acid, and p-toluenesulfonic acid, and the molar ratio of the catalyst to 3-methyl-2-nitrobenzoic acid is 0.005-0.25:1, preferably 0.01-0.2:1.

[0020] Furthermore, the catalyst is one or more of sulfuric acid, benzenesulfonic acid, and p-toluenesulfonic acid.

[0021] The in-situ separation of water on the permeate side of the membrane device is that the permeate side of the membrane device is under negative pressure conditions, water leaves the esterification device from the permeate side of the membrane device and is cooled into a vacuum water collection tank. The negative pressure condition is that the absolute pressure on the permeate side is 0.5kPa to 5kPa, preferably 0.7kPa to 4kPa, and further preferably 1.0kPa to 3.0kPa.

[0022] The cooling medium of the vacuum water collecting tank is methanol, ethanol, ethylene glycol solvent, and the cooling temperature is -5 to -30°C, preferably -10 to -15°C.

[0023] The product discharged from the mixing tank is distilled to recover methanol, and the remaining oil layer is washed with alkali and water to obtain methyl 3-methyl-2-nitrobenzoate.

[0024] The reaction liquid can be circulated back to the mixing storage tank from the pump outlet, and can also continue to pass through the membrane device and circulate back to the mixing storage tank from the membrane device outlet, so that the size of the material entering the membrane flow rate can be adjusted.

[0025] A branch is set after the circulation pump to allow the reaction liquid to flow directly back to the mixing storage tank. The reaction liquid leaving the pump and entering the membrane equipment accounts for 1 / 3 to 1 / 2 of the total reaction liquid volume leaving the pump.

[0026] The catalyst can be added into the preparation kettle at the material inlet of the preparation kettle, or added all at once at any position of the connecting pipeline between the preparation kettle and the material inlet of the mixing tank.

[0027] A device for cyclically preparing 3-methyl-2-nitrobenzoate used in the method, the device comprising a mixing storage tank, a filter, and a membrane device, wherein the reaction liquid circulates in the device composed of the above components in sequence to perform an esterification reaction;

[0028] A circulation pump is provided between the mixing tank and the filter;

[0029] The mixing tank heats the material through a preheater; the mixing tank is also provided with a discharge valve for discharging the product;

[0030] The membrane device is connected to the water collecting pipe, and the water separated from the membrane device is condensed by the condenser and enters the water collecting tank.

[0031] The mixing storage tank is also connected to the preparation kettle; a sampling point is set between the membrane equipment and the mixing storage tank.

[0032] The mixing storage tank, membrane equipment or dehydration device is composed of a single device or two or more corresponding devices connected in parallel or in series or in a series-parallel mixed manner through pipelines.

[0033] Beneficial effects of the present invention:

[0034] The present invention discloses a method for preparing 3-methyl-2-nitrobenzoate by cyclic esterification of 3-methyl-2-nitrobenzoic acid, which utilizes membrane equipment for dehydration and reaction. The traditional process is mainly a one-pot process, which has high energy consumption and very slow conversion in the later stage of the reaction. The specific advantages are as follows: (1) The present invention adopts an integrated continuous flow fixed bed membrane reactor, which can not only enhance the esterification reaction rate, but also continuously and timely remove the water generated in the esterification reaction process of 3-methyl-2-nitrobenzoate by selecting a suitable membrane for in-situ water separation, thereby breaking through the thermodynamic equilibrium limit and improving the primary product yield and raw material conversion rate. (2) The saturated fatty alcohol of the present invention reacts under high temperature and positive pressure conditions, which reduces the amount of catalyst used (the catalyst consumption is greater under normal pressure conditions, and the acidic system of the catalyst is not conducive to protecting the equipment, and the equipment requirements are relatively high), and improves the reaction rate, and the conversion rate is better than that under normal pressure reaction conditions; (3) The present invention avoids the large amount of wastewater generated while recovering the raw materials during the production process. (3) The present invention reduces energy consumption and reduces production costs. (4) The catalyst of the present invention is added into the system together with the raw materials, and the acid catalyst is diluted in the solvent in a phase-changed manner, thereby reducing the impact on the service life of the membrane.

[0035] The method provided by the present invention reduces the alcohol-acid ratio in the esterification process, greatly shortens the reaction cycle, saves the consumption of electricity, steam and circulating cooling water, and reduces the operating cost; it greatly reduces the pressure of the esterification reaction, thereby reducing the pressure level of the equipment and saving costs. The method of the present invention has good reaction condition selectivity, high yield, and is suitable for industrial production. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 Flow chart for the cyclic esterification of 3-methyl-2-nitrobenzoic acid to prepare 3-methyl-2-nitrobenzoate.

[0037] The main equipment is: preparation kettle, preheater, mixing tank, circulation pump, filter, membrane equipment, condenser, water collection tank;

[0038] The main instruments are: T1 (preheater thermometer), T2 (mixing tank thermometer), T3 (membrane inlet temperature), T4 (membrane outlet temperature), P (mixing tank pressure), P1 (pump inlet pressure), P2 (pump outlet pressure), F (membrane inlet flow), P3 (permeate side absolute pressure) DETAILED DESCRIPTION

[0039] The following examples are used to further explain the specific implementation of the present invention. The following examples are used to understand the present invention and do not constitute a limitation of the method of the present invention.

[0040] The devices and connection relationships used in the following embodiments of the present invention are as follows: Figure 1As shown. According to the flow order of materials, it includes: preparation kettle, mixing tank, circulation pump, filter, membrane equipment, dehydration and return to the mixing tank, and the water goes to the water collection tank through the condenser. The circulation pump can be a centrifugal pump, a high-speed centrifugal pump, a magnetic pump or an alkali pump.

[0041] Example 1

[0042] 500 g of 3-methyl-2-nitrobenzoic acid solid powder (3-methyl-2-nitrobenzoic acid purity is greater than or equal to 98%) and 5000 g of methanol are added to the preparation kettle respectively, and after preparing a homogeneous mixed liquid, 5 g of p-toluenesulfonic acid catalyst is added, stirred, discharged into the mixing storage tank, and the bottom valve of the kettle is closed; nitrogen is filled to 0.3 MPa, and then the emptying and pressure relief are opened, and after repeating 3 times, the tail gas oxygen content is detected to be less than 1%. If it is unqualified, this operation is performed again until the tail oxygen is detected to be less than 1%; if the oxygen content is less than 1%, the emptying valve is closed, the circulation pump is opened, and the raw material mixed liquid flowing out from the bottom of the mixing storage tank is filtered to remove trace After the impurities, it enters the membrane equipment, adjusts the circulating membrane flow rate to 200L / hr, and the mixed liquid returns to the mixing storage tank through the membrane equipment equipped with molecular sieve membrane. After the flow rate stabilizes, turn on the preheater and set it to 140℃ to heat the mixed liquid. The mixed liquid temperature rises to 125℃, the pressure of the mixing storage tank is 0.95Mpa, the pressure before the pump is 0.8Mpa, the pressure after the pump is 0.8Mpa, the membrane inlet temperature is 128℃, and the membrane outlet temperature is 127℃. At this time, the absolute pressure on the permeate side is 2.0Kpa, and the cooling temperature of the water collection tank is -11℃. After reacting for 20 hours, samples are taken at the sampling point to analyze the product composition (gas chromatography area normalization method, the same below) ), the product contained 85% 3-methyl-2-nitrobenzoic acid methyl ester, 14% 3-methyl-2-nitrobenzoic acid, and 1% isomeric impurities. The operation was continued under this condition for 10 hours. The product composition was analyzed by sampling at the sampling point. The product contained 90% 3-methyl-2-nitrobenzoic acid methyl ester, 8.7% 3-methyl-2-nitrobenzoic acid, and 1.3% isomeric impurities. The esterified methanol liquid contained 1.9% water. The subsequent reaction was slower and slower. 120g of methanol water was collected on the permeate side. When the reaction reached 50 hours, the product composition was analyzed by sampling at the sampling point. 5.5% of 3-methyl-2-nitrobenzoic acid remained (3-methyl-2-nitrobenzoic acid was detected at the sampling point). The reaction was stopped when the content of methyl-2-nitrobenzoic acid was less than 6%), containing 92.8% of methyl-2-nitrobenzoic acid methyl ester, 1.7% of isomeric impurities, 2.1% of water in esterified methanol solution, and 94.5% of the conversion rate of raw material 3-methyl-2-nitrobenzoic acid. The reaction was terminated, and after the system was cooled to 50°C, 3-methyl-2-nitrobenzoic acid methyl ester methanol solution was discharged through the discharge port of the mixing storage tank, and methanol was recovered through rectification. The remaining oil layer liquid was washed with alkali (the alkali used was 5% sodium hydroxide aqueous solution, the same below), and washed with water to obtain 496g of methyl-2-nitrobenzoic acid methyl ester, with a yield of 92%. The specific conversion rate and average reaction rate data are shown in Table 1.

[0043] Under the conditions listed in Example 1, the device was operated continuously for 50 hours, and no obstruction was found in the membrane equipment, and the flow rate was always stable. To ensure that the esterification of 3-methyl-2-nitrobenzoic acid is complete, the molar ratio of methanol to 3-methyl-2-nitrobenzoic acid needs to exceed the stoichiometric ratio. In all embodiments, the alkyl alcohol of the esterification product and the methanol water on the permeate side need to be recovered, and the methanol is separated and recycled. The separation of methanol and water is usually carried out by distillation.

[0044] Example 2

[0045] Add 500g of 3-methyl-2-nitrobenzoic acid solid powder and 5000g of methanol to the preparation kettle respectively, prepare a homogeneous mixed liquid, add 7.5g of catalyst sulfuric acid (98% concentrated sulfuric acid), stir, discharge into the mixing storage tank, close the bottom valve of the kettle; fill with nitrogen to 0.3MPa, then open the emptying pressure relief, repeat 3 times, after which, detect the tail gas oxygen content <1%, if unqualified, perform this operation again until the tail oxygen is detected <1%; if the oxygen content is <1%, close the emptying valve, open the circulation pump, and the raw material mixed liquid flowing out of the bottom of the mixing storage tank is filtered out. After removing trace impurities, the mixture enters the membrane device and the circulating membrane flow rate is adjusted to 300L / hr. The mixed liquid passes through the membrane device equipped with a molecular sieve membrane and returns to the mixed storage tank. After the flow rate stabilizes, the preheater is turned on and set to 145°C to heat the mixed liquid. The mixed liquid temperature rises to 133°C, the pressure of the mixed storage tank is 1.05Mpa, the pressure before the pump is 0.9Mpa, the pressure after the pump is 0.9Mpa, the membrane inlet temperature is 134°C, and the membrane outlet temperature is 132°C. At this time, the absolute pressure on the permeate side is 1.8Kpa, and the cooling temperature of the water collection tank is -11°C. After reacting for 20 hours, take The sample point was sampled and analyzed for product composition. The product contained 87% of methyl 3-methyl-2-nitrobenzoate, 12% of 3-methyl-2-nitrobenzoic acid, and 1% of isomeric impurities. The operation was continued for 10 hours under this condition. The sample point was sampled and analyzed for product composition. The product contained 91% of methyl 3-methyl-2-nitrobenzoate, 7.5% of 3-methyl-2-nitrobenzoic acid, and 1.5% of isomeric impurities. The esterified methanol liquid contained 1.7% of water. The subsequent reaction was slower and slower. 115g of methanol water was collected on the permeate side. When the reaction reached 50 hours, the sample point was sampled and analyzed for product The invention discloses a method for preparing the present invention, wherein the residual 3-methyl-2-nitrobenzoic acid is 5.7%, the methyl 3-methyl-2-nitrobenzoate is 92.5%, the isomeric impurities are 1.8%, the esterified methanol liquid contains 1.9% water, the conversion rate of the raw material 3-methyl-2-nitrobenzoic acid is 94.3%, the reaction is terminated, the system is cooled to 50°C, the methyl 3-methyl-2-nitrobenzoate methanol liquid is discharged through the discharge port of the mixing tank, the methanol is recovered through distillation, the remaining oil layer liquid is washed with alkali and water, and 499g of methyl 3-methyl-2-nitrobenzoate is obtained, with a yield of 92.6%.

[0046] Under the conditions listed in Example 2, the device was operated continuously for 50 hours, and no obstruction was found in the membrane equipment, and the flow rate remained stable.

[0047] Example 3

[0048] Add 500g of 3-methyl-2-nitrobenzoic acid solid powder and 5000g of methanol to the preparation kettle respectively, prepare a homogeneous mixed liquid, add 15g of catalyst sulfuric acid (98% concentrated sulfuric acid), stir, discharge into the mixing storage tank, close the bottom valve of the kettle; fill with nitrogen to 0.3MPa, then open the evacuation pressure relief, repeat 3 times, detect the tail gas oxygen content <1%, if unqualified, perform this operation again until the tail oxygen is detected <1%; if the oxygen content is <1%, close the evacuation valve, open the circulation pump, and the raw material mixed liquid flowing out of the bottom of the mixing storage tank is filtered to remove trace impurities and enter the membrane device , adjust the circulating membrane flow rate to 300L / hr, the mixed liquid returns to the mixed storage tank through the membrane device equipped with organic silicon hybrid membrane, after the flow rate stabilizes, turn on the preheater, set 150℃, heat the mixed liquid, the mixed liquid temperature rises to 140℃, the mixed storage tank pressure is 1.15Mpa, the pressure before the pump is 1.05Mpa, the pressure after the pump is 1.05Mpa, the membrane inlet temperature is 141℃, the membrane outlet temperature is 138℃, at this time, the absolute pressure of the permeate measurement is 1.4Kpa, the cooling temperature of the water collection tank is -11℃, after the reaction for 20 hours, take samples at the sampling point for analysis The product composition was 92% methyl-2-nitrobenzoate, 6.5% 3-methyl-2-nitrobenzoic acid, and 1.5% isomeric impurities. The reaction was continued under this condition for 10 hours. The product composition was analyzed at the sampling point. The product contained 96% methyl-2-nitrobenzoate, 2.4% 3-methyl-2-nitrobenzoic acid, and 1.6% isomeric impurities. The esterified methanol liquid contained 0.9% water. The subsequent reaction was slower and slower. 135g of methanol water was collected on the permeate side. When the reaction reached 50 hours, the product composition was analyzed at the sampling point. , 1.3% of 3-methyl-2-nitrobenzoic acid remains, 96.9% of methyl 3-methyl-2-nitrobenzoate, 1.8% of isomeric impurities, 1.0% of water in the esterified methanol solution, and the conversion rate of the raw material 3-methyl-2-nitrobenzoic acid is 98.7%. The reaction is terminated, and the system is cooled to 50°C. 3-methyl-2-nitrobenzoic acid methyl ester methanol solution is released through the discharge port of the mixing storage tank, and methanol is recovered by distillation. The remaining oil layer liquid is washed with alkali and water to obtain 522g of methyl 3-methyl-2-nitrobenzoate with a yield of 96.9%.

[0049] Under the conditions listed in Example 3, the device was operated continuously for 50 hours, and no obstruction was found in the membrane equipment, and the flow rate remained stable.

[0050] Example 4

[0051] Add 500g of 3-methyl-2-nitrobenzoic acid solid powder and 5000g of methanol to the preparation kettle respectively, prepare a homogeneous mixed liquid, add 15g of p-toluenesulfonic acid, stir, discharge into the mixing storage tank, close the bottom valve of the kettle; fill with nitrogen to 0.3MPa, then open the emptying and pressure relief, repeat 3 times, detect the tail gas oxygen content <1%, if unqualified, perform this operation again until the tail oxygen is detected <1%; if the oxygen content is <1%, close the emptying valve, open the circulation pump, and the raw material mixed liquid flowing out of the bottom of the mixing storage tank is filtered to remove trace impurities and enter Membrane equipment, adjust the circulating membrane flow rate to 300L / hr, the mixed liquid returns to the mixed storage tank through the membrane equipment equipped with organic silicon hybrid membrane, after the flow rate stabilizes, turn on the preheater, set 150℃, heat the mixed liquid, the mixed liquid temperature rises to 140℃, the mixed storage tank pressure is 1.15Mpa, the pressure before the pump is 1.05Mpa, the pressure after the pump is 1.05Mpa, the membrane inlet temperature is 141℃, the membrane outlet temperature is 138℃, at this time, the osmotic pressure is 1.4Kpa, the cooling temperature of the water collection tank is -11℃, after the reaction for 20 hours, the sampling point is sampled and analyzed The product composition was 93.5% methyl 3-methyl-2-nitrobenzoate, 4.8% 3-methyl-2-nitrobenzoic acid, and 1.7% isomeric impurities. The reaction was continued under this condition for 10 hours. The product composition was analyzed at the sampling point. The product contained 94.7% methyl 3-methyl-2-nitrobenzoate, 3.5% 3-methyl-2-nitrobenzoic acid, and 1.8% isomeric impurities. The esterified methanol liquid contained 0.8% water. The subsequent reaction was slower and slower. 138g of methanol water was collected on the permeate side. When the reaction reached 50 hours, the product was analyzed at the sampling point. The invention discloses a method for preparing the method of the present invention, wherein the residual 3-methyl-2-nitrobenzoic acid is 2.8%, the methyl 3-methyl-2-nitrobenzoate is 95.2%, the isomeric impurities are 2.0%, the esterified methanol liquid contains 0.9% water, the conversion rate of the raw material 3-methyl-2-nitrobenzoic acid is 97.2%, the reaction is terminated, the system is cooled to 50°C, the methyl 3-methyl-2-nitrobenzoate methanol liquid is discharged through the discharge port of the mixing storage tank, the methanol is recovered through rectification, the remaining oil layer liquid is washed with alkali and water, and 514g of methyl 3-methyl-2-nitrobenzoate is obtained, and the yield is 95.4%.

[0052] Under the conditions listed in Example 4, the device was operated continuously for 50 hours, and no obstruction was found in the membrane equipment, and the flow rate remained stable.

[0053] Example 5

[0054] Add 500g of 3-methyl-2-nitrobenzoic acid solid powder and 5000g of methanol to the preparation kettle respectively, prepare a homogeneous mixed liquid, add 10g of p-toluenesulfonic acid, stir, discharge into the mixing storage tank, close the bottom valve of the kettle; fill with nitrogen to 0.3MPa, then open the emptying and pressure relief, repeat 3 times, detect the tail gas oxygen content <1%, if unqualified, perform this operation again until the tail oxygen is detected <1%; if the oxygen content is <1%, close the emptying valve, open the circulation pump, and the raw material mixed liquid flowing out of the bottom of the mixing storage tank is filtered to remove trace impurities and enter Membrane equipment, adjust the circulating membrane flow rate to 350L / hr, the mixed liquid returns to the mixing tank through the membrane equipment equipped with organic silicon hybrid membrane, after the flow rate stabilizes, turn on the preheater, set 160℃, heat the mixed liquid, the mixed liquid temperature rises to 147℃, the mixing tank pressure is 1.35Mpa, the pressure before the pump is 1.2Mpa, the pressure after the pump is 1.2Mpa, the membrane inlet temperature is 147℃, the membrane outlet temperature is 145℃, the osmotic pressure is 1.6Kpa, the water collection tank cooling temperature is -15℃, after 20 hours of reaction, take samples at the sampling point for product analysis The product contained 94% methyl 3-methyl-2-nitrobenzoate, 4.5% 3-methyl-2-nitrobenzoic acid, and 1.5% isomeric impurities. The reaction was continued under the same conditions for 10 hours. The product composition was analyzed at the sampling point. The product contained 97.8% methyl 3-methyl-2-nitrobenzoate, 0.6% 3-methyl-2-nitrobenzoic acid, and 1.6% isomeric impurities. The esterified methanol solution contained 0.5% water. The subsequent reaction was slower and slower. 138g of methanol water was collected on the permeate side. When the reaction reached 50 hours, the product composition was analyzed at the sampling point. The residue of 3-methyl-2-nitrobenzoic acid was 0.15%, 3-methyl-2-nitrobenzoic acid methyl ester was 98.0%, isomeric impurities were 1.85%, the esterified methanol liquid contained 0.5% water, and the conversion rate of raw material 3-methyl-2-nitrobenzoic acid was 99.85%. The reaction was terminated, and after the system was cooled to 50°C, 3-methyl-2-nitrobenzoic acid methyl ester methanol liquid was discharged through the discharge port of the mixing storage tank, and methanol was recovered by distillation. The remaining oil layer liquid was washed with alkali and water to obtain 529g of 3-methyl-2-nitrobenzoic acid methyl ester with a yield of 98.2%.

[0055] Under the conditions listed in Example 5, the device was operated continuously for 50 hours, and no obstruction was found in the membrane equipment, and the flow rate remained stable.

[0056] Example 6

[0057] Add 500g of 3-methyl-2-nitrobenzoic acid solid powder and 5000g of methanol to the preparation kettle respectively, prepare a homogeneous mixed liquid, add 15g of p-toluenesulfonic acid, stir, discharge into the mixing storage tank, close the bottom valve of the kettle; fill with nitrogen to 0.3MPa, then open the evacuation pressure relief, repeat 3 times, detect the oxygen content of the tail gas <1%, if unqualified, perform this operation again until the tail oxygen is detected <1%; if the oxygen content is <1%, close the evacuation valve, open the circulation pump, and the raw material mixed liquid flowing out of the bottom of the mixing storage tank is filtered to remove trace impurities, and then enters the membrane equipment, and adjusts the circulating membrane flow The flow rate is 300L / hr. The mixed liquid passes through two-stage membrane equipment equipped with organic silicon hybrid membranes in series and returns to the mixed storage tank. After the flow rate stabilizes, the preheater is turned on and set to 140°C to heat the mixed liquid. The mixed liquid temperature rises to 125°C, the pressure of the mixed storage tank is 0.95Mpa, the pressure before the pump is 0.8Mpa, the pressure after the pump is 0.8Mpa, the membrane inlet temperature is 128°C, and the membrane outlet temperature is 125°C. At this time, the absolute pressure of the permeate measurement is 1.4Kpa, and the cooling temperature of the water collection tank is -11°C. After reacting for 20 hours, samples are taken from the sampling point to analyze the product composition. The product contained 97% methyl 3-methyl-2-nitrobenzoate, 1.5% 3-methyl-2-nitrobenzoic acid, and 1.5% isomeric impurities. The reaction was continued under this condition for 10 hours. The product composition was analyzed by sampling at the sampling point. The product contained 98% methyl 3-methyl-2-nitrobenzoate, 0.5% 3-methyl-2-nitrobenzoic acid, and 1.5% isomeric impurities. The esterified methanol solution contained 0.1% water. The subsequent reaction was slower and slower. 138g of methanol water was collected on the permeate side. When the reaction reached 50 hours, the product composition was analyzed by sampling at the sampling point. 3-methyl-2-nitrobenzoate was 98% methyl 3-methyl-2-nitrobenzoate, 0.5% 3-methyl-2-nitrobenzoic acid, and 1.5% isomeric impurities. The esterified methanol solution contained 0.1% water. The subsequent reaction was slower and slower. 138g of methanol water was collected on the permeate side. The reaction mixture was stirred for 2 hours and then dried over medium temperature for 30 minutes. The residue of methyl-2-nitrobenzoic acid was 0.15%, 3-methyl-2-nitrobenzoic acid methyl ester was 98.0%, isomer impurities were 1.85%, the esterified methanol liquid contained 0.5% water, the conversion rate of raw material 3-methyl-2-nitrobenzoic acid was 99.85%, the reaction was terminated, the system was cooled to 50°C, 3-methyl-2-nitrobenzoic acid methyl ester methanol liquid was discharged through the discharge port of the mixing tank, methanol was recovered by distillation, the remaining oil layer liquid was washed with alkali and water, and 529g of 3-methyl-2-nitrobenzoic acid methyl ester was obtained with a yield of 98.2%.

[0058] Under the conditions listed in Example 6, the device was operated continuously for 50 hours, and no obstruction was found in the membrane equipment, and the flow rate remained stable; the secondary organosilicon hybrid membrane series reaction can greatly reduce the reaction temperature and extend the service life of the membrane.

[0059] Comparative Example 1

[0060] The conventional experiment adopts an intermittent kettle method to synthesize methyl 3-methyl-2-nitrobenzoate. 500 g of 3-methyl-2-nitrobenzoic acid solid powder and 5000 g of methanol and 100 g of concentrated sulfuric acid are added to the preparation kettle respectively, and the temperature is raised to 65-70° C. for room temperature esterification reaction. After the reaction for 20 hours, the product composition is analyzed by sampling at the sampling point. The product contains 81% of methyl 3-methyl-2-nitrobenzoate, 17% of 3-methyl-2-nitrobenzoic acid, and 2% of isomer impurities. The operation is continued under this condition for 10 hours, and the product composition is analyzed by sampling at the sampling point. The product contains 85% of methyl 3-methyl-2-nitrobenzoate, 12.5% ​​of 3-methyl-2-nitrobenzoic acid, and 2% of isomer impurities. The esterification methanol liquid contained 2.6% water, and the subsequent reaction was slower and slower. When the reaction reached 50 hours, the product composition was analyzed by sampling at the sampling point. The residual 3-methyl-2-nitrobenzoic acid was 10%, 3-methyl-2-nitrobenzoic acid methyl ester was 87.3%, and the isomer impurities were 2.7%. The esterification methanol liquid contained 2.8% water, and the conversion rate of the raw material 3-methyl-2-nitrobenzoic acid was 90%. The reaction was terminated, and methanol was recovered by distillation. The remaining oil layer liquid was washed with alkali and water to obtain 473g of 3-methyl-2-nitrobenzoic acid methyl ester with a yield of 87.8%.

[0061] The comparison of the conversion rate and reaction rate of the embodiments of the present invention and the comparative examples is shown in Table 1:

[0062] Table 1 Comparison of conversion rate and average reaction rate of implementation scheme

[0063]

[0064] Note: The first stage is for reaction of 0 to 20 hours, the second stage is for reaction of 20 to 30 hours, and the third stage is for reaction of 30 to 50 hours.

[0065] According to the comparison of conversion rate, compared with the traditional method of comparative example 1, the continuous membrane equipment of Examples 1-6 has a faster conversion in the first 20 hours, and the conversion of 3-methyl-2-nitrobenzoic acid can reach up to 98.5%. The conversion slows down in 20-30 hours, and the conversion rate further decreases in 30-50 hours. According to the comparison of average reaction rate, it is found that there are three stages of 0-20 hours, 20-30 hours, and 30-50 hours. Compared with the traditional method of comparative example 1, the continuous membrane equipment of Examples 1-6 has a faster reaction rate in the first stage, and the effect is better. The average hourly reaction raw material can reach up to 4.93%, and the difference between the second stage and the third stage is not too obvious.

[0066] The above description is only a preferred embodiment of the present invention. All equivalent changes and modifications made according to the scope of the patent application of the present invention should fall within the scope of the present invention.

Claims

1. A method for cyclically preparing 3-methyl-2-nitrobenzoic acid ester compounds, characterized in that: (1) 3-methyl-2-nitrobenzoic acid and saturated fatty alcohol are added to a preparation kettle to dissolve, and the resulting homogeneous mixed solution and a catalyst are added to a mixing tank; (2) Turn on the circulation pump to allow the reaction solution to circulate in the device consisting of the mixing tank, the filter, and the membrane device until the flow rate stabilizes; (3) When the reaction liquid is circulating, the preheater is turned on to heat the reaction liquid in the mixing tank to carry out the esterification reaction. During the reaction, water is separated in situ on the permeate side of the membrane device, and the esterification product is finally circulated into the mixing tank.

2. The method according to claim 1, characterized in that The membrane device is provided with a membrane for in-situ separation of water, and the membrane is one or more of a ceramic membrane, a metal membrane, a PM membrane, a molecular sieve membrane, and an organosilicon hybrid membrane.

3. The method according to claim 1, characterized in that The saturated fatty alcohol is one of methanol, ethanol, n-propanol, isopropanol, n-butanol, isobutanol and tert-butanol, and the molar ratio of 3-methyl-2-nitrobenzoic acid to the saturated fatty alcohol is 1:5.6-282.

4. The method according to claim 1, characterized in that: The esterification reaction temperature is 90-230° C., the esterification reaction time is 20-50 h, the pressure of the mixing storage tank is 0.3-3.5 MPa, and the reaction liquid flow rate is 100 L / h-500 L / h.

5. The method according to claim 1, characterized in that The catalyst is one or more of sulfuric acid, nitric acid, hydrochloric acid, methanesulfonic acid, benzenesulfonic acid and p-toluenesulfonic acid, and the molar ratio of the catalyst to 3-methyl-2-nitrobenzoic acid is 0.005-0.25:

1.

6. The method according to claim 1, characterized in that The in-situ water separation on the permeate side of the membrane device is that the permeate side of the membrane device is under negative pressure conditions, water leaves the esterification device from the permeate side of the membrane device and is cooled into a vacuum water collection tank. The negative pressure condition is that the absolute pressure on the permeate side is 0.5kPa to 5kPa.

7. The method according to claim 1, characterized in that A branch is set after the circulation pump to allow the reaction liquid to flow directly back to the mixing storage tank. The reaction liquid leaving the pump and entering the membrane equipment accounts for 1 / 3 to 1 / 2 of the total reaction liquid volume leaving the pump.

8. A device for cyclically preparing 3-methyl-2-nitrobenzoate used in the method of claim 1, characterized in that: The device includes a mixing tank, a filter, and a membrane device, and the raw materials circulate in the device composed of the above components in sequence to perform an esterification reaction; A circulation pump is provided between the mixing tank and the filter; The mixing tank heats the material through a preheater; the mixing tank is also provided with a discharge valve for discharging the product; The membrane device is connected to the water collecting pipe, and the water separated from the membrane device is condensed by the condenser and enters the water collecting tank.

9. The device according to claim 8, characterized in that The mixing tank is also connected to the preparation kettle; A sampling point is set between the membrane equipment and the mixing tank.

10. The device according to claim 9, characterized in that The mixing storage tank, membrane equipment or dehydration device is composed of two or more corresponding devices connected in parallel, in series or in series-parallel hybrid through pipelines.

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