CN114369019A

CN114369019A - Preparation method of 2-methyl-3-methoxybenzoic acid

Info

Publication number: CN114369019A
Application number: CN202210088553.1A
Authority: CN
Inventors: 王兵; 杨宝玉; 王玉杰; 郭秋雨; 张萍; 李日翔
Original assignee: Shandong Youdao Chemical Co ltd
Current assignee: Shandong Youdao Chemical Co ltd
Priority date: 2022-01-25
Filing date: 2022-01-25
Publication date: 2022-04-19

Abstract

The disclosure relates to a preparation method of 2-methyl-3-methoxybenzoic acid, which comprises the following steps: (1) respectively enabling sodium phenolate solution formed by 2-methyl-3-hydroxybenzoic acid, sodium hydroxide and water and dimethyl sulfate to enter an alkylation reaction unit through different conveying units to carry out alkylation reaction at 50-90 ℃ to obtain alkylation reaction liquid; (2) and (3) allowing the alkylation reaction solution flowing out of the alkylation reaction unit to enter a hydrolysis reaction unit for hydrolysis reaction to obtain a hydrolysate containing the 2-methyl-3-methoxy sodium benzoate. The preparation method in the continuous production device simplifies the production flow, avoids refining steps such as recrystallization and the like, reduces the production cost, ensures a reliable and feasible scheme after industrial production and application, and can be applied to industrial continuous production.

Description

Preparation method of 2-methyl-3-methoxybenzoic acid

Technical Field

The disclosure relates to the technical field of compound preparation, in particular to a preparation method of 2-methyl-3-methoxybenzoic acid.

Background

The 2-methyl-3-methoxybenzoic acid is an important intermediate of medicines and pesticides, particularly a key intermediate of methoxyfenozide, the minimum content standard of the currently marketed product is 98.5%, and the content standard of most enterprises is 99%.

CN107778167A discloses a method for obtaining 2-methyl-3-methoxybenzoic acid by taking 2, 6-dichlorotoluene as a raw material through two-step reaction, wherein the purity of the obtained 2-methyl-3-methoxybenzoic acid can reach 99.6% to the maximum, but the reaction time of the first step in the disclosed two-step reaction is more than ten hours, copper salt treatment and rectification and recovery of a solvent are involved, the reaction condition of the second step is harsh, the reaction time is long, and if the method is used for industrial production, the problems of low production efficiency and high equipment investment cost exist. CN111018693A discloses a method for preparing 2-methyl-3-methoxybenzoic acid by reacting solid sodium methoxide, dimethyl sulfoxide and 2, 6-dichlorotoluene, dripping a methyl substituent to prepare an intermediate 2-methyl-3-chlorophenylmethyl ether, reacting with toluene, tetrahydrofuran and magnesium chips, and introducing carbon dioxide gas, wherein the yield is about 88%, the purity can reach 99.6% at most, but the synthesis process is complex, involves multiple distillations, and has long process consumption, low production efficiency and high energy consumption. CN106946685A discloses a method for preparing 2-methyl-3-methoxybenzoic acid by taking 3-chloro-o-xylene as an initial raw material and carrying out oxidation and alkylation reactions, wherein the purity of the product can reach 99% at most, but the first oxidation process involves recycling of a catalyst and rectification and recovery of a solvent, the risk coefficient of oxygen oxidation is high, the second alkylation process involves treatment of copper salt and rectification and recovery of the solvent, the process is complex, and the energy consumption is high.

Although the above patent applications can all obtain 2-methyl-3-methoxybenzoic acid with higher purity, but the defects of complex process flow, high energy consumption, low production efficiency and the like can not realize industrial production, the method adopted by the current common industrial production is to produce 2-methyl-3-methoxybenzoic acid by using 2-methyl-3-hydroxybenzoic acid as a raw material through hydroxylation and hydrolysis, the synthesis research of methoxyfenozide refers to a method for preparing 2-methyl-3-methoxybenzoic acid by using 2-methyl-3-methoxybenzoic acid through alkylation and hydrolysis, 7.9g (0.05mol) of 3-hydroxy-2-methylbenzoic acid and 13.4g (0.1mol) of 30% sodium hydroxide solution are added into a flask and stirred for 0.5h, then, 15.8g (0.125mol) of dimethyl sulfate is dropwise added, 6.7g (0.05mol) of 30% sodium hydroxide solution is dropwise added at the same time, the dropping speed is controlled, an alkaline system is kept, the reaction temperature is 40-45 ℃, after the dropwise addition is finished, the temperature is kept for 1h, then 6.7g (0.05mol) of 30% sodium hydroxide solution is added into the system, the temperature is raised to 60 ℃, the stirring is carried out for 0.5h, the cooling is carried out to the normal temperature, a proper amount of hydrochloric acid is dropwise added, the pH value is adjusted to be 1-2, the cooling is carried out to 5-10 ℃, the temperature is kept and the stirring is carried out for 0.5h, then the filtration is carried out, a filter cake is washed twice by cold water, and the solid product 3-methoxy-2-methylbenzoic acid is obtained by drying, the HPLC purity is 96.1%, and the yield is 96.1%.

The method for preparing the 2-methyl-3-methoxybenzoic acid by taking the 2-methyl-3-hydroxybenzoic acid as the raw material and dimethyl sulfate as the alkylating reagent through alkylation hydrolysis cannot directly obtain a product with high purity industrially, further needs to be purified through post-treatment processes such as recrystallization and the like, even a product with the purity meeting the requirement cannot be obtained by taking simple recrystallization as a post-treatment means, the process flow of the refining process is complex, and the energy consumption is increased by recovering the solvent.

Therefore, it is important to find a preparation method which can be applied to industrial production, realize continuous, safe and stable production and directly obtain a high-purity product on the basis of simplifying the process flow.

Disclosure of Invention

In order to solve the technical problem, the present disclosure provides a preparation method of 2-methyl-3-methoxybenzoic acid.

In a first aspect, the present disclosure provides a method for preparing 2-methyl-3-methoxybenzoic acid, comprising the steps of:

(1) respectively enabling sodium phenolate solution formed by 2-methyl-3-hydroxybenzoic acid, sodium hydroxide and water and dimethyl sulfate to enter an alkylation reaction unit through different conveying units to carry out alkylation reaction at 50-90 ℃ to obtain alkylation reaction liquid;

(2) and (3) allowing the alkylation reaction solution flowing out of the alkylation reaction unit to enter a hydrolysis reaction unit for hydrolysis reaction to obtain a hydrolysate containing the 2-methyl-3-methoxy sodium benzoate.

The method for continuously producing and preparing the 2-methyl-3-methoxybenzoic acid is simple in preparation process, high in raw material conversion rate and capable of being applied to industrial production.

At present, in the industrial production, in order to reduce the hydrolysis of dimethyl sulfate, alkylation reaction is generally carried out at a lower reaction temperature, however, the reaction rate of alkylation reaction carried out at a lower temperature is lower, so that the alkylation reaction time is longer, and more dimethyl sulfate is hydrolyzed to generate byproducts, the alkylation reaction is carried out at 50-90 ℃, the reaction rate of alkylation reaction can be improved, the reaction time is shortened, the hydrolysis of dimethyl sulfate is reduced, the generation of byproducts is reduced, the purity of direct products can be improved, the utilization rate of raw material 2-methyl-3-hydroxybenzoic acid is improved, and the production cost is equivalently reduced.

As a preferred embodiment of the present disclosure, the alkylation reaction in step (1) is carried out at 50-80 deg.C, preferably 55-75 deg.C, such as 56 deg.C, 58 deg.C, 60 deg.C, 62 deg.C, 64 deg.C, 65 deg.C, 68 deg.C, 70 deg.C, 72 deg.C, 74 deg.C, etc.

In the alkylation reaction stage, if the reaction temperature is too high, although the rate of the alkylation reaction between sodium phenolate and dimethyl sulfate can be increased, the hydrolysis of dimethyl sulfate can be accelerated by the too high reaction temperature, and the occurrence of side reactions is increased; too low a temperature will reduce the reaction rate of the alkylation reaction, prolong the reaction time, and also increase the hydrolysis of dimethyl sulfate.

In order to avoid incomplete hydrolysis of the by-product, which results in lower purity of the product obtained directly and lower difficulty of wastewater treatment, as a preferred technical scheme of the present disclosure, the temperature of the hydrolysis reaction in the step (2) is 90-120 ℃, more preferably 95-120 ℃, still more preferably 100-120 ℃, such as 105 ℃, 110 ℃, 115 ℃ and the like.

In the hydrolysis reaction process, if the hydrolysis temperature is too low, the hydrolysis rate is low, the hydrolysis time is prolonged, and the hydrolysis of the byproduct is incomplete, and in addition, under the condition that the hydrolysis temperature and the amount of sodium hydroxide are certain, the hydrolysis reaction time is short, the hydrolysis of the byproduct is incomplete, the incomplete hydrolysis of the byproduct can cause the byproduct such as methyl 2-methyl-3-methoxybenzoate mixed in the directly obtained product to reduce the purity, and the water phase is doped with the unhydrolyzed byproduct such as monomethyl sulfate, and the like, so that the difficulty and the burden of water phase treatment are increased.

As a preferred technical scheme of the present disclosure, the time of the hydrolysis reaction is 1.5-3h, such as 1.6h, 1.7h, 1.8h, 2.0h, 2.2h, 2.4h, 2.6h, 2.8h and the like.

As a preferred embodiment of the present disclosure, the equipment used in the alkylation reaction unit comprises a main reactor.

As a preferred technical scheme of the present disclosure, the residence time of the sodium phenolate solution and dimethyl sulfate in the main reactor in the step (1) is 3-300s, preferably 5-120s, such as 10s, 20s, 30s, 40s, 50s, 60s, 70s, 80s, 90s, 100s, 110s and the like.

When the dosage of dimethyl sulfate, the dosage of sodium hydroxide and the reaction temperature of alkylation reaction are in a certain range, if the reaction time is too short, the raw materials cannot be completely converted, the product purity is reduced, and the yield is reduced; if the reaction time is too long, the treatment capacity of a single set of equipment is reduced, and the production efficiency is reduced.

As a preferred embodiment of the present disclosure, the main reactor is selected from a microchannel reactor and/or a dynamic tube reactor, a combination of a microchannel reactor and/or a dynamic tube reactor and a tube reactor.

In the current industrial production, the reaction rate is slow due to the low alkylation reaction temperature, and simultaneously along with the alkylation reaction, the amount of dimethyl sulfate is gradually reduced in the later stage of the alkylation reaction, so that the reaction rate is further reduced, on one hand, the reaction of the raw material 2-methyl-3-hydroxybenzoic acid is incomplete, and if the subsequent hydrolysis reaction is continued, a small amount of raw material is directly doped in the product, so that the product purity is reduced; on the other hand, the alkylation reaction rate is slow, so that more byproducts are generated, the byproducts are possibly doped in the product finally, the purity of the product directly obtained finally cannot reach a higher level, multiple recrystallization is needed to meet the purity requirement, and meanwhile, the mixing of the byproducts which are not completely hydrolyzed (such as sodium monomethyl sulfate) in the water phase also increases the treatment difficulty of the water phase, and the product quality of the byproduct sodium sulfate is influenced.

According to the method, the condition of overlong reaction time can be avoided by adopting a continuous reaction mode in the alkylation reaction stage, the alkylation reaction temperature is increased, the reaction rate of the alkylation reaction can be increased, the reaction time is further shortened, the occurrence of side reactions is reduced, the conversion rate of the raw material 2-methyl-3-hydroxybenzoic acid can be increased, and the purity of a product directly obtained by subsequent hydrolysis can be increased.

As a preferred technical solution of the present disclosure, the step (1) further comprises performing an aging reaction on the reaction solution obtained after the alkylation reaction.

As a preferred embodiment of the present disclosure, the apparatus used in the alkylation reaction unit further comprises an aging reactor.

At alkylation reaction later stage, the volume of dimethyl sulfate reduces because of the consumption of reaction earlier stage and leads to reaction later stage reaction rate to reduce, may cause the raw materials can not change in the main reactor of alkylation reaction unit in short time completely, can shift the alkylation reaction liquid that flows out by main reactor this moment to carry out further ageing reaction in the ageing reactor, the raw materials that make not take place the reaction continue to participate in the reaction, avoid the raw materials surplus to cause the influence to product purity, can improve the utilization ratio of raw materials simultaneously.

As a preferred technical solution of the present disclosure, the time of the aging reaction is 3-15min, such as 4min, 5min, 6min, 7min, 8min, 9min, 10min, 11min, 12min, 13min, 14min, and the like.

As a preferred embodiment of the present disclosure, the temperature of the aging reaction is 40 to 70 ℃, preferably 45 to 65 ℃, and more preferably 55 to 65 ℃, for example, 56 ℃, 57 ℃, 58 ℃, 59 ℃, 60 ℃, 61 ℃, 62 ℃, 63 ℃, 64 ℃, etc.

In the alkylation reaction stage, besides the reaction between sodium phenolate formed by hydroxyl and dimethyl sulfate, sodium carboxylate formed by carboxyl also reacts with dimethyl sulfate to form carboxylic ester and consume the dimethyl sulfate, although the increase of the dosage of dimethyl sulfate is helpful for accelerating the reaction rate, the excessive dosage of dimethyl sulfate causes the increase of the treatment burden of a production device, the increase of the raw material cost and the increase of the generation amount of sodium sulfate; and too little dimethyl sulfate will also cause the reaction rate in the later stage of the reaction to be reduced, and part of dimethyl sulfate will be hydrolyzed to cause incomplete conversion of raw materials, thereby causing the purity of the direct product obtained subsequently to be reduced, therefore, as a preferred technical scheme of the present disclosure, in the step (1), the molar ratio of the 2-methyl-3-hydroxybenzoic acid, the sodium hydroxide and the dimethyl sulfate is 1 (2-5) to (2-3), such as 1:3:2.2, 1:4:2.5, 1:2.5:2.2, 1:3.5:2.8, 1:4.5:2.9, etc.

In the present disclosure, the molar ratio of 2-methyl-3-hydroxybenzoic acid to dimethyl sulfate is preferably 1 (2.2-2.8), such as 1:2.3, 1:2.4, 1:2.5, 1:2.6, 1:2.7, and the like.

As a preferable technical scheme of the present disclosure, in the step (1), the mass ratio of the sodium hydroxide to the water is (10-40):100, such as 15:100, 20:100, 25:100, 30:100, 35:100, etc.

As a preferred technical scheme of the present disclosure, in the step (1), the method further comprises supplementing sodium hydroxide solution in the alkylation reaction unit.

In the alkylation reaction stage, because a small amount of sulfuric acid generated by hydrolysis of dimethyl sulfate consumes alkali in a reaction system, the alkylation reaction is affected, and in order to ensure that the reaction system is in an alkaline environment in the alkylation reaction process and avoid the raw material residue, sodium hydroxide can be supplemented in an alkylation reaction unit under normal conditions, so that the alkylation reaction of 2-methyl-3-hydroxybenzoic acid is promoted.

As a preferred technical solution of the present disclosure, in the step (1), the sodium hydroxide solution is supplemented to the main reactor or the aging reactor.

As a preferred technical solution of the present disclosure, in the step (1), the concentration of the sodium hydroxide solution is 20 to 50%.

In a preferred embodiment of the present disclosure, in step (1), the amount of sodium hydroxide added is 1 to 3 times the molar amount of the 2-methyl-3-hydroxybenzoic acid.

As a preferred embodiment of the present disclosure, the step (2) further comprises adding sodium hydroxide to the hydrolysis reaction unit.

In the hydrolysis stage, the byproduct 2-methyl-3-methoxy sodium benzoate generated in the alkylation reaction, the monomethyl sulfate sodium and the excessive dimethyl sulfate are hydrolyzed, and in order to ensure the rapid progress of the hydrolysis reaction and the thorough hydrolysis of the byproduct, the alkaline environment of the hydrolysis reaction unit needs to be maintained, so the sodium hydroxide needs to be supplemented to the hydrolysis reaction unit, and 20-50% of sodium hydroxide solution can be supplemented or sodium hydroxide solid can be directly supplemented.

As a preferable embodiment of the present disclosure, in the step (2), the amount of the sodium hydroxide added is 1 to 5 times, for example, 1.5 times, 2 times, 2.5 times, 3 times, 3.5 times, 4 times, 4.5 times, etc., the molar amount of the 2-methyl-3-hydroxybenzoic acid.

As a preferred technical scheme of the present disclosure, the equipment used by the hydrolysis reaction unit comprises a reaction kettle, preferably a reaction kettle with a distillation or rectification device.

In the hydrolysis reaction stage, methanol is generated by hydrolysis of 2-methyl-3-methoxybenzoic acid methyl ester, in the disclosure, the methanol generated in the reaction can be distilled out of the reaction system by selecting higher hydrolysis temperature, the removal of the methanol is also beneficial to the reaction, and compared with the removal of the methanol in the water phase treatment process in the post-treatment stage, the effect of saving energy can be achieved.

In the method, a continuous reaction mode is adopted in an alkylation reaction stage, the temperature of the alkylation reaction is increased, the addition amount of each component is controlled to increase the reaction rate of the alkylation reaction, the hydrolysis of dimethyl sulfate is reduced, the utilization rate of the raw material 2-methyl-3-hydroxybenzoic acid is increased, the hydrolysis temperature of the hydrolysis stage is increased, the hydrolysis time is controlled, the by-product in the alkylation reaction stage can be subjected to a relatively thorough hydrolysis reaction, the purity of the directly obtained product is further increased, the direct product does not need to be subjected to refining processes such as recrystallization and the like, the production flow is simplified, and the energy consumption is reduced.

As a preferred technical solution of the present disclosure, the preparation method further comprises performing step (3) after step (2): and (3) allowing hydrolysis reaction liquid flowing out of the hydrolysis reaction unit to enter a product separation unit, and performing acid precipitation, filtration and drying to obtain the 2-methyl-3-methoxybenzoic acid.

And (2) allowing a product (2-methyl-3-methoxybenzoic acid) to exist in a hydrolysis reaction liquid flowing out of the hydrolysis reaction unit in a sodium salt form, transferring the hydrolysis reaction liquid into an acid precipitation kettle, adding sulfuric acid or hydrochloric acid, adjusting the pH to 1-3 to precipitate the product, pulping and washing the filtered solid with water, filtering and drying to obtain the product 2-methyl-3-methoxybenzoic acid.

The directly obtained product or the direct product in the present disclosure refers to a product that is subjected to acid precipitation, filtration and drying after the hydrolysis reaction, and is not subjected to a refining step such as recrystallization, and is referred to as a directly obtained product.

The preparation method of the 2-methyl-3-methoxybenzoic acid provided by the disclosure is continuous production, is carried out in a continuous production device, and can be used for industrial production.

The present disclosure provides a continuous production device for the above continuous production, the continuous production device comprises a conveying unit, an alkylation reaction unit, a hydrolysis reaction unit and a product separation unit.

The conveying unit is provided with a first feeding pump and a second feeding pump, the first feeding pump is used for conveying the sodium phenolate solution and is provided with a sodium phenolate solution inlet and a sodium phenolate solution outlet; the second feeding pump is used for conveying dimethyl sulfate and is provided with a dimethyl sulfate inlet and a dimethyl sulfate outlet, and the feeding pump of the conveying unit can be a conventional diaphragm pump, a gear pump, a screw pump or other feeding pumps capable of conveying slurry and liquid materials so as to realize the conveying of the materials.

The alkylation reaction unit is used for providing a place for alkylation reaction of raw material 2-methyl-3-hydroxybenzoic acid, and is provided with a sodium phenolate solution inlet, a dimethyl sulfate inlet and an alkylation reaction liquid outlet; the device comprises a main reactor part, wherein the main reactor comprises a microchannel reactor and/or a dynamic tubular reactor, or a combination of the microchannel reactor and/or the dynamic tubular reactor and a pipeline reactor, wherein the microchannel reactor is provided with a reaction channel and a heat exchange channel, the characteristic dimension of the reaction channel is 1-15mm, the effective liquid holding capacity of a single microchannel reactor is 0.1-5L, the number of reaction sheets of a single microchannel reactor is 1-20, the reaction sheets can be connected in series or in parallel, and a heat exchange medium can be introduced into the heat exchange channel for exchanging heat for reaction liquid in the reaction channel; the dynamic tubular reactor is provided with a reaction cavity with a stirring shaft and a heat exchange cavity which can be communicated with a heat exchange medium, the stirring shaft is provided with stirring paddles or fins which play a role in stirring and mixing, and the effective liquid holdup of a single dynamic tubular reactor is 1-200L; the rotation speed of the stirring shaft is adjusted within the range of 0-500r/min, the pipeline reactor comprises a static tubular mixed reactor with a mixing element in a channel or a static tubular reactor without the mixing element in the channel, the static tubular mixed reactor comprises an MIC tube bundle reactor, the static tubular reactor comprises a wound tubular reactor, a coil tubular reactor or a tube tubular reactor, the combination of the microchannel reactor and/or the dynamic tubular reactor and the pipeline reactor can be a microchannel reactor and a pipeline reactor which are connected in series or alternately in series, or a dynamic tubular reactor and a pipeline reactor which are connected in series or alternately in sequence, or a microchannel reactor, a dynamic tubular reactor and a pipeline reactor which are connected in series or alternately in sequence, or a coupling type reactor which is formed by alternately connecting a microchannel reactor and/or a dynamic tube reactor with a pipeline reactor is adopted.

Hydrolysis reaction unit is used for providing the place that alkylation reaction liquid takes place hydrolysis, has alkylation reaction liquid import, sodium hydroxide import, hydrolysis reaction liquid export, methanol liquid export, and hydrolysis reaction unit's main reactor is reation kettle, preferably has the reation kettle of distillation or rectifier unit, and the methanol outlet is located the top of distillation or rectifier unit.

The product separation unit is used for processing hydrolysis reaction liquid to obtain a product 2-methyl-3-methoxybenzoic acid, has a hydrolysis reaction liquid inlet, a product 2-methyl-3-methoxybenzoic acid outlet, and can realize single or combined equipment with the functions of acid regulation, solid-liquid separation, pulping, washing, drying and the like, and comprises an acid regulation reaction kettle, a solid-liquid separator, a beater, a dryer or equipment with multiple functions of solid-liquid separation, pulping and drying, wherein sodium 2-methyl-3-methoxybenzoate in the hydrolysis reaction liquid is converted into 2-methyl-3-methoxybenzoic acid after being regulated in the acid regulation reaction kettle to be separated out, the solid-liquid separator is used for separating solid and liquid phases to obtain a solid crude product, and the beater is used for pulping and washing the solid crude product with water, removing water-soluble impurities in the product, then carrying out solid-liquid separation by using the solid-liquid separator again, finishing pulping, washing and solid-liquid separation for multiple times in a single or complete equipment in order to ensure the appearance quality of the product, and finally transferring the obtained solid wet product to a dryer for drying to obtain the product 2-methyl-3-methoxybenzoic acid.

The acid adjusting reaction kettle receives hydrolysis reaction liquid from the hydrolysis reaction unit, is provided with an acid liquid inlet and a solid-liquid two-phase material outlet, and can adopt a conventional reaction kettle, wherein the 2-methyl-3-methoxybenzoic acid sodium in the hydrolysis reaction liquid is converted into 2-methyl-3-methoxybenzoic acid to be separated out after the acid adjustment in the acid adjusting reaction kettle, and is discharged from the solid-liquid two-phase material outlet; the solid-liquid separator is used for separating solid and liquid phases and can be one of a centrifugal machine, a filter press and a filter, and the beating machine and the dryer can be common equipment which can realize beating and drying in the market.

In the disclosure, a sodium phenolate solution outlet and a dimethyl sulfate outlet of a conveying unit are respectively connected with a sodium phenolate solution inlet and a dimethyl sulfate inlet of an alkylation reaction unit, an alkylation reaction liquid outlet of the alkylation reaction unit is connected with an alkylation reaction liquid inlet of a hydrolysis reaction unit, a hydrolysis reaction liquid outlet of the hydrolysis reaction unit is connected with a hydrolysis reaction liquid inlet of a product separation unit, and in the product separation unit, all functional devices can be connected for continuous operation or can be operated separately and intermittently, when all the functional devices are connected for continuous operation, a solid-liquid two-phase material outlet of an acid separation reaction kettle is connected with a solid-liquid two-phase material inlet of a first solid-liquid separator, a crude product outlet of the first solid-liquid separator is connected with a crude product inlet of a beater, and a slurry outlet of the beater is connected with a slurry inlet of a second solid-liquid separation device, the wet product outlet of the second solid-liquid separator is connected with the wet product inlet of the dryer.

As a preferred technical scheme of the present disclosure, the continuous production apparatus further includes a batching unit, configured to prepare a sodium phenolate solution, add 2-methyl-3-hydroxybenzoic acid to the batching kettle, start stirring with water, and then add the sodium hydroxide solution, or add 2-methyl-3-hydroxybenzoic acid and the sodium hydroxide solution to the batching kettle, start stirring with water, or add 2-methyl-3-hydroxybenzoic acid to the batching kettle, start stirring with water, and then add the sodium hydroxide solution and sodium hydroxide solid, so that the hydroxyl groups of the 2-methyl-3-hydroxybenzoic acid form sodium phenolate, and at the same time, some or all of the carboxyl groups may form sodium carboxylate; the batching kettle is provided with a feeding hole and a discharging hole, a conventional stirring kettle can be selected, and the discharging hole is connected with a sodium phenolate solution inlet of a first feeding pump in the conveying unit.

As a preferred technical solution of the present disclosure, the alkylation reaction unit further includes an aging reactor, an inlet of the aging reactor is connected to an outlet of a main reactor in the alkylation reaction unit, and the aging reactor is configured to receive an alkylation reaction solution flowing out from the main reactor to further perform an aging reaction under the condition that a conversion rate of sodium phenolate formed from 2-methyl-3-hydroxybenzoic acid in the main reactor cannot reach a high level, so as to improve the conversion rate of the raw material 2-methyl-3-hydroxybenzoic acid, thereby reducing the amount of the raw material doped in the product, and the aging reactor employs a conventional stirring kettle or an overflow reaction kettle.

As a preferred technical solution of the present disclosure, the alkylation reaction unit further has a sodium hydroxide solution inlet for supplementing the sodium hydroxide solution in the alkylation reaction stage, and the sodium hydroxide solution inlet may be located at a position on the main reactor of the alkylation reaction unit different from the sodium phenolate solution inlet and the dimethyl sulfate inlet, or may be located on the aging reactor in the alkylation reaction unit.

In the present disclosure, the manner of connection between elements or devices should be construed broadly unless otherwise explicitly stated or limited. For example, the connection may be direct pipe connection, or may be pipe connection connected to conventional conveying, metering, controlling, and temporary storage equipment such as pumping equipment, metering equipment, valve pipe fittings, and intermediate tanks, or may be fixed connection or detachable connection. The specific meaning of the above terms in the present invention can be understood by those skilled in the art according to specific situations.

As a specific embodiment of the disclosure, a sodium phenolate solution and dimethyl sulfate formed by raw materials of 2-methyl-3-hydroxybenzoic acid, sodium hydroxide and water are respectively conveyed into a main reactor of an alkylation reaction unit through a first feeding pump and a second feeding pump of a conveying unit, wherein the molar ratio of the raw materials of 2-methyl-3-hydroxybenzoic acid and sodium hydroxide is 1 (2-5), the molar ratio of the 2-methyl-3-hydroxybenzoic acid to dimethyl sulfate is 1 (2-3), the sodium phenolate solution and dimethyl sulfate are subjected to alkylation reaction in the main reactor of the alkylation reaction unit at 50-90 ℃ to form an alkylation reaction solution, the alkylation reaction solution stays in the main reactor for 3-300s and then is transferred to a hydrolysis reaction unit, and 1-5 times of molar ratio of the raw materials of 2-methyl-3-hydroxybenzoic acid is supplemented Hydrolyzing 20-50% sodium hydroxide solution at 90-120 deg.C for 1.5-3h to obtain hydrolysis reaction solution, evaporating methanol generated in the reaction process, transferring the hydrolysis solution to acid precipitation kettle of product separation unit, adjusting pH to 1-3 to separate out 2-methyl-3-methoxybenzoic acid product to obtain solid-liquid two phase, separating by solid-liquid separator to obtain crude product, pulping and washing the crude product by pulping machine, and drying the wet product obtained by solid-liquid separation to obtain 2-methyl-3-methoxybenzoic acid product by dryer.

As a specific embodiment of the present disclosure, raw materials of 2-methyl-3-hydroxybenzoic acid and sodium hydroxide solution are mixed in a blending kettle according to the molar ratio of 2-methyl-3-hydroxybenzoic acid to sodium hydroxide being 1 (2-5) to form sodium phenolate solution, then the sodium phenolate solution is conveyed to a main reactor of an alkylation reaction unit through a first feed pump of a conveying unit and is contacted with dimethyl sulfate conveyed by a second feed pump of the conveying unit in the main reactor of the alkylation reaction unit at the temperature of 50-90 ℃ to form alkylation reaction liquid, the alkylation reaction liquid stays in the main reactor for 3-300s and is transferred to an aging reactor, the aging reaction liquid is further aged for 3-15min at the temperature of 40-70 ℃, in addition, 20-50% of sodium hydroxide solution is conveyed to the main reactor or the aging reactor of the alkylation reaction unit through a third feed pump of the conveying unit, the molar weight of the sodium hydroxide added in the process is 1-3 times of that of the raw material, the aged alkylation reaction solution is transferred to a hydrolysis reaction unit, 20-50% of sodium hydroxide solution is added according to the molar weight of 1-5 times of the raw material 2-methyl-3-hydroxybenzoic acid, hydrolyzing at 90-120 deg.C for 1.5-3h to obtain hydrolysis reaction solution, and simultaneously evaporating methanol generated in the reaction process, transferring the hydrolysate to an acid precipitation kettle of a product separation unit, adjusting the pH value to 1-3, separating out the product 2-methyl-3-methoxybenzoic acid to form a solid-liquid two phase, separating by a solid-liquid separator to obtain a crude product, pulping and washing the crude product by a pulping machine, and drying the wet product obtained by solid-liquid separation again by a dryer to obtain the product 2-methyl-3-methoxybenzoic acid.

Compared with the prior art, the technical scheme provided by the embodiment of the disclosure has the following advantages:

(1) the method adopts a continuous reaction mode in the alkylation reaction stage, improves the temperature of the alkylation reaction, controls the addition of each component to improve the reaction rate of the alkylation reaction, reduces the hydrolysis of dimethyl sulfate, improves the utilization rate of the raw material 2-methyl-3-hydroxybenzoic acid, can lead the by-product in the alkylation reaction stage to generate more thorough hydrolysis reaction by improving the hydrolysis temperature in the hydrolysis stage and controlling the hydrolysis time, further improves the purity of the directly obtained product, leads the purity of the product to reach more than 99 percent and optimally reach 99.8 percent under the condition of not refining, avoids the process of repeated recrystallization, also reduces the content of the monomethyl sulfate in the water phase, reduces the processing difficulty of the water phase, improves the quality of the by-product sodium sulfate, and simplifies the production flow, energy consumption caused by recycling and reusing the solvent in the recrystallization process is avoided;

(2) the product directly obtained by the preparation method provided by the disclosure has higher purity, does not need further purification, and can be directly sold or used for the production of downstream products;

(3) the preparation method in the continuous production device simplifies the production flow, avoids refining steps such as recrystallization and the like, reduces the production cost, ensures a reliable and feasible scheme after industrial production and application, and can be applied to industrial continuous production.

Drawings

The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the present disclosure and together with the description, serve to explain the principles of the disclosure.

In order to more clearly illustrate the embodiments or technical solutions in the prior art of the present disclosure, the drawings used in the description of the embodiments or prior art will be briefly described below, and it is obvious for those skilled in the art that other drawings can be obtained according to the drawings without inventive exercise.

FIG. 1 is a schematic diagram of a continuous reaction apparatus used in an embodiment of the present disclosure;

wherein, 1-a dosing unit; 2-a conveying unit; 201-a first feed pump; 202-a second feed pump; a 3-alkylation reaction unit; 4-a hydrolysis reaction unit; 5-product separation unit.

Detailed Description

In order that the above objects, features and advantages of the present disclosure may be more clearly understood, aspects of the present disclosure will be further described below. It should be noted that the embodiments and features of the embodiments of the present disclosure may be combined with each other without conflict.

In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present disclosure, but the present disclosure may be practiced in other ways than those described herein; it is to be understood that the embodiments disclosed in the specification are only a few embodiments of the present disclosure, and not all embodiments.

Fig. 1 is a schematic structural diagram of a continuous reaction apparatus used in an embodiment of the present disclosure, when performing the preparation of 2-methyl-3-methoxybenzoic acid:

(1) in the preparation unit 1, 2-methyl-3-hydroxybenzoic acid and sodium hydroxide are mixed according to the molar ratio of 1 (2-5) and the mass ratio of sodium hydroxide to water (10-40) to 100 to obtain a sodium phenolate solution;

(2) the sodium phenolate solution and dimethyl sulfate are respectively conveyed to an alkylation reaction unit 3 through a first feeding pump 201 and a second feeding pump 202 of a conveying unit 2 according to the molar ratio of 2-methyl-3-hydroxybenzoic acid to dimethyl sulfate of 1 (2-3);

(3) the alkylation reaction solution is formed by contact reaction in a main reactor of an alkylation reaction unit 3 at the temperature of 50-90 ℃, the alkylation reaction solution stays in the main reactor for 3-300s and then is transferred to an aging reactor, the aging is further carried out for 3-15min at the temperature of 40-70 ℃, in addition, a third feed pump of a conveying unit conveys 20-50% of sodium hydroxide solution to the main reactor or the aging reactor of the alkylation reaction unit, and the molar weight of the sodium hydroxide added in the process is 1-3 times of that of the raw material;

(4) transferring the aged alkylation reaction solution to a hydrolysis reaction unit 4, supplementing 20-50% sodium hydroxide solution with 1-5 times of molar weight relative to the raw material 2-methyl-3-hydroxybenzoic acid, hydrolyzing at 90-120 ℃ for 1.5-3h to obtain hydrolysis reaction solution, and simultaneously distilling off methanol generated in the reaction process;

(5) transferring the hydrolysate to an acid precipitation kettle of a product separation unit 5, adjusting the pH value to 1-3, separating out the product 2-methyl-3-methoxybenzoic acid to form a solid-liquid two phase, separating by a solid-liquid separator to obtain a crude product, pulping and washing the crude product by a pulping machine, and drying the wet product obtained by solid-liquid separation again by a dryer to obtain the product 2-methyl-3-methoxybenzoic acid.

Example 1

This example provides a method for preparing 2-methyl-3-hydroxybenzoic acid.

(1) Preparing a sodium phenolate solution from a raw material of 2-methyl-3-hydroxybenzoic acid and a 20% sodium hydroxide solution in a batching kettle according to the molar ratio of 1:2.5 of the 2-methyl-3-hydroxybenzoic acid to the sodium hydroxide;

(2) conveying the sodium phenolate solution into a microchannel reactor with the liquid holdup of 1L through a first feeding pump at the flow rate of 18.17kg/min, carrying out contact reaction with dimethyl sulfate conveyed by a second feeding pump in the microchannel reactor at the temperature of 50 ℃ to form an alkylation reaction solution, wherein the molar ratio of the raw material to the dimethyl sulfate is 1:2.4, the alkylation reaction solution stays in the microchannel reactor for 3s and then is transferred into an aging reaction kettle, meanwhile, a 20% sodium hydroxide solution with the same molar amount as the raw material is conveyed into the aging reaction kettle through a third feeding pump at the flow rate of 4.57kg/min, and the alkylation reaction solution is further aged for 15min at the temperature of 50 ℃;

(3) transferring the aged alkylation reaction solution to a hydrolysis reaction kettle of a hydrolysis reaction unit through a pump, supplementing 20% sodium hydroxide solution with the same molar weight as the raw material 2-methyl-3-hydroxybenzoic acid, hydrolyzing for 3h at the temperature of 95 ℃ to obtain hydrolysis reaction solution, and simultaneously steaming out methanol generated in the reaction process;

(4) transferring the hydrolysate to an acid precipitation kettle of a product separation unit, adjusting the pH value to 2, separating out the product 2-methyl-3-methoxybenzoic acid to form a solid-liquid two phase, separating by a solid-liquid separator to obtain a crude product, pulping and washing the crude product by a pulping machine, and drying the wet product obtained by solid-liquid separation again by a dryer to obtain the product 2-methyl-3-methoxybenzoic acid.

Example 2

This example provides a method for preparing 2-methyl-3-hydroxybenzoic acid.

(1) Adding raw materials 2-methyl-3-hydroxybenzoic acid and water into a batching kettle, starting stirring, adding 30% sodium hydroxide solution to form sodium phenolate solution, wherein the molar ratio of the raw materials to the sodium hydroxide is 1:4, and the mass ratio of the sodium hydroxide to the water is 20: 100;

(2) conveying the sodium phenolate solution into a microchannel reactor with the liquid holdup of 5L through a first feeding pump at the flow rate of 26.53kg/min, and carrying out contact reaction with dimethyl sulfate conveyed by a second feeding pump in the microchannel reactor at the temperature of 55 ℃ to form an alkylation reaction solution, wherein the molar ratio of the raw material to the dimethyl sulfate is 1:2.5, the alkylation reaction solution stays in the microchannel reactor for 10s and then is transferred into an aging reaction kettle, and further aging is carried out for 10min at the temperature of 45 ℃;

(3) transferring the aged alkylation reaction solution to a hydrolysis reaction kettle of a hydrolysis reaction unit through a pump, supplementing 30% sodium hydroxide solution with 2 times of molar weight compared with the raw material 2-methyl-3-hydroxybenzoic acid, hydrolyzing for 2h at 120 ℃ to obtain hydrolysis reaction solution, and simultaneously steaming out methanol generated in the reaction process;

(4) transferring the hydrolysate to an acid precipitation kettle of a product separation unit, adjusting the pH value to 3, separating out the product 2-methyl-3-methoxybenzoic acid to form a solid-liquid two phase, separating by a solid-liquid separator to obtain a crude product, pulping and washing the crude product by a pulping machine, and drying the wet product obtained by solid-liquid separation again by a dryer to obtain the product 2-methyl-3-methoxybenzoic acid.

Example 3

This example provides a method for preparing 2-methyl-3-hydroxybenzoic acid.

(1) Raw materials of 2-methyl-3-hydroxybenzoic acid and 20% sodium hydroxide solution form sodium phenolate solution according to the molar ratio of 1:5 of 2-methyl-3-hydroxybenzoic acid and sodium hydroxide;

(2) conveying the sodium phenolate solution into a microchannel reactor with the liquid holdup of 40L through a first feeding pump at the flow rate of 32.1kg/min, and carrying out contact reaction with dimethyl sulfate conveyed by a second feeding pump in the microchannel reactor at the temperature of 60 ℃ to form an alkylation reaction solution, wherein the molar ratio of the raw materials to the dimethyl sulfate is 1:2.2, and the alkylation reaction solution stays in the microchannel reactor for 120 s;

(3) the alkyl reaction liquid flows into a hydrolysis reaction kettle of a hydrolysis reaction unit through a pipeline, 30 percent sodium hydroxide solution with 2.5 times of molar weight compared with the raw material 2-methyl-3-hydroxybenzoic acid is added, hydrolysis is carried out for 2.5h at the temperature of 90 ℃ to obtain hydrolysis reaction liquid, and methanol generated in the reaction process is evaporated;

(4) transferring the hydrolysate to an acid precipitation kettle of a product separation unit, adjusting the pH value to 1, separating out the product 2-methyl-3-methoxybenzoic acid to form a solid-liquid two phase, separating by a solid-liquid separator to obtain a crude product, pulping and washing the crude product by a pulping machine, and drying the wet product obtained by solid-liquid separation again by a dryer to obtain the product 2-methyl-3-methoxybenzoic acid.

Example 4

This example provides a method for preparing 2-methyl-3-hydroxybenzoic acid.

The difference from example 3 is that in this example, the alkylation reaction temperature in the microchannel reactor of step (2) was 80 ℃.

Example 5

This example provides a method for preparing 2-methyl-3-hydroxybenzoic acid.

The difference from example 3 is that in this example, the hydrolysis temperature in step (3) is 80 ℃.

Example 6

This example provides a method for preparing 2-methyl-3-hydroxybenzoic acid.

The difference from example 2 is that in step (2), the aging temperature is 55 ℃, and the residence time of the alkylation reaction solution in the aging kettle is 8 min.

Example 7

This example provides a method for preparing 2-methyl-3-hydroxybenzoic acid.

The difference from example 3 is that in this example, sodium phenolate solution is delivered to a microchannel reactor with a liquid holding capacity of 10L through a first feed pump at a flow rate of 32.1kg/min, and is contacted with dimethyl sulfate delivered by a second feed pump in the microchannel reactor at a temperature of 60 ℃ to react to form an alkylation reaction solution, the alkylation reaction solution stays in the microchannel reactor for 30s and then is transferred to an aging reaction kettle, the aging reaction solution is further aged for 7min at a temperature of 60 ℃, and the aged alkylation reaction solution is transferred to a hydrolysis reaction kettle of a hydrolysis reaction unit through a pump.

Comparative example 1

This comparative example provides a method of preparing 2-methyl-3-hydroxybenzoic acid.

The difference from example 3 is that in this comparative example, the alkylation reaction temperature in the microchannel reactor of step (2) was 100 ℃.

Comparative example 2

The difference from example 3 is that in this comparative example, the alkylation reaction temperature in the microchannel reactor of step (2) was 45 ℃.

Example 8

This example provides a method for preparing 2-methyl-3-hydroxybenzoic acid.

(1) Raw materials of 2-methyl-3-hydroxybenzoic acid and 40% sodium hydroxide solution are mixed in a batching kettle according to the molar ratio of 1:2 of 2-methyl-3-hydroxybenzoic acid to sodium hydroxide to form sodium phenolate solution;

(2) conveying the sodium phenolate solution to a dynamic tubular reactor with the liquid holdup of 15L through a first feeding pump at the flow rate of 9.81kg/min, carrying out contact reaction with dimethyl sulfate conveyed by a second feeding pump in the dynamic tubular reactor at the temperature of 65 ℃ to form an alkylation reaction solution, wherein the molar ratio of the raw material to the dimethyl sulfate is 1:3, the alkylation reaction solution stays in the dynamic tubular reactor for 60s and then is transferred to an aging reaction kettle, and meanwhile, conveying 40% of sodium hydroxide solution which is 2 times of the molar weight of the raw material to the aging reaction kettle through a third feeding pump at the flow rate of 3.9kg/min to promote further aging of the alkylation reaction solution for 5min at the temperature of 65 ℃;

(3) transferring the aged alkylation reaction solution into a hydrolysis reaction kettle of a hydrolysis unit through a pump, supplementing 30% sodium hydroxide solution with 2.5 times of molar weight compared with the raw material 2-methyl-3-hydroxybenzoic acid, hydrolyzing for 2.5h at the temperature of 100 ℃ to obtain hydrolysis reaction solution, and simultaneously steaming out methanol generated in the reaction process;

Example 9

This example provides a method for preparing 2-methyl-3-hydroxybenzoic acid.

(1) Raw materials of 2-methyl-3-hydroxybenzoic acid and 30% sodium hydroxide solution are mixed in a batching kettle according to the molar ratio of 1:2.5 of the 2-methyl-3-hydroxybenzoic acid to the sodium hydroxide to form sodium phenolate solution;

(2) conveying the sodium phenolate solution into a dynamic tubular reactor with the liquid holdup of 100L through a first feeding pump at the flow rate of 15.55kg/min, and carrying out contact reaction with dimethyl sulfate conveyed by a second feeding pump in the dynamic tubular reactor at the temperature of 70 ℃, wherein the molar ratio of the raw material to the dimethyl sulfate is 1:2.8, meanwhile, 30 percent of sodium hydroxide solution which is 1.5 times of the molar quantity of the raw material is conveyed into the dynamic tubular reactor from a middle feeding port of the dynamic tubular reactor through a third feeding pump at the flow rate of 4.8kg/min, and the alkylation reaction liquid stays in the dynamic tubular reactor for 300 s;

(3) then transferring the mixture into a hydrolysis reaction kettle of a hydrolysis unit through a pipeline, supplementing 20 percent sodium hydroxide solution with 3 times of molar weight compared with the raw material 2-methyl-3-hydroxybenzoic acid, hydrolyzing for 2.5h at the temperature of 95 ℃ to obtain hydrolysis reaction liquid, and simultaneously steaming out methanol generated in the reaction process;

Example 10

This example provides a method for preparing 2-methyl-3-hydroxybenzoic acid.

(1) Raw materials of 2-methyl-3-hydroxybenzoic acid and 30% sodium hydroxide solution are mixed in a batching kettle according to the molar ratio of 1:3.5 of the 2-methyl-3-hydroxybenzoic acid and the sodium hydroxide to form sodium phenolate solution;

(2) sodium phenolate solution is conveyed to a main reactor of a micro-channel reactor and a dynamic tubular reactor which are sequentially connected in series and have the total liquid holdup of 75L through a first feeding pump at the flow rate of 17.24kg/min, and dimethyl sulfate conveyed by a second feeding pump is contacted and reacted in the main reactor at the temperature of 75 ℃, wherein the molar ratio of raw materials to the dimethyl sulfate is 1:2, and alkylation reaction liquid stays in the main reactor for 240 s;

(3) then transferring the mixture into a hydrolysis reaction kettle of a hydrolysis unit through a pipeline, supplementing 20 percent sodium hydroxide solution with 4 times of molar weight compared with the raw material 2-methyl-3-hydroxybenzoic acid, hydrolyzing for 2h at the temperature of 110 ℃ to obtain hydrolysis reaction liquid, and simultaneously steaming out methanol generated in the reaction process;

Example 11

This example provides a method for preparing 2-methyl-3-hydroxybenzoic acid.

(1) Raw materials of 2-methyl-3-hydroxybenzoic acid and 10% sodium hydroxide solution are mixed in a batching kettle according to the molar ratio of 1:3 of 2-methyl-3-hydroxybenzoic acid and sodium hydroxide to form sodium phenolate solution;

(2) conveying the sodium phenolate solution to a main reactor of a sequentially-connected microchannel reactor and a static mixing reactor which have a total liquid holdup of 50L and are connected in series through a first feeding pump at a flow rate of 37.67kg/min, wherein the main reactor is in contact reaction with dimethyl sulfate conveyed by a second feeding pump at a temperature of 80 ℃ in the main reactor, the molar ratio of the raw material to the dimethyl sulfate is 1:2.3, the alkylation reaction solution stays in the main reactor for 180s and then is transferred to an aging reaction kettle, and meanwhile, 20% of sodium hydroxide solution which is 2 times of the molar amount of the raw material is conveyed to the aging reaction kettle through a third feeding pump at a flow rate of 4kg/min to promote further aging of the alkylation reaction solution for 3min at a temperature of 70 ℃;

(3) transferring the aged alkylation reaction solution into a hydrolysis reaction kettle of a hydrolysis unit through a pump, supplementing sodium hydroxide solid with 3 times of molar weight compared with the raw material 2-methyl-3-hydroxybenzoic acid, hydrolyzing for 1.5h at the temperature of 115 ℃ to obtain hydrolysis reaction solution, and simultaneously steaming out methanol generated in the reaction process;

(4) and transferring the hydrolysate to an acid precipitation kettle of a product separation unit by a pump to adjust the pH value to 2, separating out the product 2-methyl-3-methoxybenzoic acid to form a solid-liquid two phase, separating by a solid-liquid separator to obtain a crude product, pulping and washing the crude product by a pulping machine, and drying the wet product obtained by solid-liquid separation again by a dryer to obtain the product 2-methyl-3-methoxybenzoic acid.

Example 12

This example provides a method for preparing 2-methyl-3-hydroxybenzoic acid.

(1) Raw materials of 2-methyl-3-hydroxybenzoic acid and 30% sodium hydroxide solution are mixed in a batching kettle according to the molar ratio of 1:3 of 2-methyl-3-hydroxybenzoic acid and sodium hydroxide to form sodium phenolate solution;

(2) sodium phenolate solution is conveyed to a main reactor of a dynamic tubular reactor and a static mixing reactor which are sequentially connected in series and have a total liquid holdup of 200L through a first feeding pump at a flow rate of 34.61kg/min, and is in contact reaction with dimethyl sulfate conveyed by a second feeding pump in the main reactor at a temperature of 85 ℃, wherein the molar ratio of raw materials to the dimethyl sulfate is 1:2.6, 30 percent of sodium hydroxide solution which is 3 times of the molar quantity of the raw materials is conveyed to the dynamic tubular reactor through a middle feeding port of the dynamic tubular reactor through a third feeding pump at a flow rate of 18.85kg/min, and alkylation reaction solution stays in the main reactor for 290 s;

(3) then transferring the mixture into a hydrolysis reaction kettle of a hydrolysis unit through a pipeline, supplementing 50 percent sodium hydroxide solution with 4 times of molar weight compared with the raw material 2-methyl-3-hydroxybenzoic acid, hydrolyzing for 1.5h at the temperature of 95 ℃ to obtain hydrolysis reaction liquid, and simultaneously steaming out methanol generated in the reaction process;

Example 13

This example provides a method for preparing 2-methyl-3-hydroxybenzoic acid.

(1) Raw materials of 2-methyl-3-hydroxybenzoic acid and 30% sodium hydroxide solution are mixed in a batching kettle according to the molar ratio of 1:4 of 2-methyl-3-hydroxybenzoic acid and sodium hydroxide to form sodium phenolate solution;

(2) conveying the sodium phenolate solution to a main reactor of a sequentially-connected microchannel reactor and a static tubular reactor which have a total liquid holdup of 100L through a first feeding pump at a flow rate of 21kg/min, and carrying out contact reaction with dimethyl sulfate conveyed by a second feeding pump in the main reactor at a temperature of 90 ℃, wherein the molar ratio of the raw material to the dimethyl sulfate is 1:2.5, and an alkylation reaction solution stays in the main reactor for 300 s;

(3) then transferring the mixture into a hydrolysis reaction kettle of a hydrolysis unit through a pipeline, supplementing 30 percent sodium hydroxide solution with 5 times of molar weight compared with the raw material 2-methyl-3-hydroxybenzoic acid, hydrolyzing for 1.2h at 105 ℃ to obtain hydrolysis reaction liquid, and simultaneously steaming out methanol generated in the reaction process;

Comparative example 3

Adding 2-methyl-3-hydroxybenzoic acid into a reaction kettle, adding 30% NaOH to adjust the pH value to 10-11, heating to 30-40 ℃, keeping the temperature for 0.5h, then adding dimethyl sulfate and 30% NaOH, keeping the temperature in the kettle at 30-40 ℃ and the pH value at 10-11, continuing to keep the temperature and stir for 1h after the addition is finished, then adding 30% NaOH solution, heating to 85-90 ℃ to react for 1h, adding a proper amount of sulfuric acid, adjusting the pH value at 1-2, filtering to obtain a wet crude product, adding the wet crude product and toluene into a refining kettle, starting stirring, heating by steam to reflux for 30min, then carrying out hot filter pressing to obtain a crude wet product, washing and drying the crude wet product to obtain 2-methyl-3-methoxybenzoic acid, rectifying and recovering the toluene, and then using the 2-methyl-3-methoxybenzoic acid in the refining process.

And (3) performance testing: yield and product purity

(1) The product and the product purity detection method comprise the following steps:

weighing 50.0mg of 2-methyl-3-methoxybenzoic acid sample in a 50mL volumetric flask, adding methanol to completely dissolve the sample and diluting to a scale, shaking uniformly, filtering by using a filter to obtain a test solution, using a micro-syringe to take about 5 mu L of sample and injecting the sample into a liquid chromatogram, and repeatedly measuring each sample twice;

the specification of the chromatographic column is phi 4.6 x 150mm and 5 μm, the material of the column is C18, the temperature of the column is 35 ℃, the mobile phase is methanol and water (0.1 percent phosphoric acid) is 40:60, the flow rate is 1.0mL/min, and the detection wavelength is 254 nm.

(2) The product yield and the effective utilization rate of the raw materials are calculated by the following formula:

the product yield (mass of dried product/mass of theoretical product) × 100%;

the results of the tests on examples 1-13 and comparative examples 1-3 are shown in Table 1:

TABLE 1

Sample (I)	Purity of the product/%)	Product yield/%
			Example 1	99.3	98.6
Example 2	99.5	98.2
			Example 3	99.8	99.0
Example 4	99.5	98.4
			Example 5	98.8	98.1
Example 6	99.6	98.2
			Example 7	99.8	99.1
Comparative example 1	98.7	97.6
			Comparative example 2	98.1	97.3
Example 8	99.4	98.8
			Example 9	99.6	98.6
Example 10	99.8	98.8
			Example 11	99.6	98.0
Example 12	99.5	98.7
			Example 13	99.2	98.5
Comparative example 3	97.6	97

Note: yield: and collecting a sample obtained by hydrolyzing and post-treating an alkylation reaction solution obtained by continuously feeding for 10min in an alkylation reaction stage and drying the product, and calculating to obtain the product.

According to the embodiment and the performance test, the preparation method for continuous production can obtain the 2-methyl-3-methoxybenzoic acid with extremely high purity under the condition of a refining process without post-treatment such as recrystallization and the like, the purity of the 2-methyl-3-methoxybenzoic acid is over 99.3 percent, the 2-methyl-3-methoxybenzoic acid can be directly applied to downstream products or sold, and the yield is high and can reach over 98 percent.

As can be seen from a comparison of examples 2-3 and examples 4-6, the alkylation and hydrolysis reaction conditions (alkylation reaction temperature, hydrolysis reaction temperature, etc.) provided by the present disclosure are within the preferred ranges of the present disclosure, which results in higher product purity and yield. In addition, as can be seen from the comparison between example 7 and example 3, the aging reaction of the reaction solution obtained after the alkylation reaction is selected to complete the conversion of the raw materials, which can achieve the same effect as example 3, even better than example 3, and the equipment investment cost is lower than that of example 3; therefore, when alkylation reaction is carried out, the main reactor is utilized for alkylation reaction and then combined with the aging reactor for aging reaction, so that the obtained direct product can be used for subsequent application or sale, the production cost can be further reduced, and the method is more favorable for industrial production. As can be seen from the comparison of example 3 with comparative examples 1-2, the alkylation reaction carried out at a temperature of 50-90 ℃ can improve the purity and yield of the product and reduce the production cost. As can be seen from the comparison between the examples and comparative example 3, the preparation method performed in the continuous production apparatus provided by the present disclosure can obtain a product with high purity and yield, can avoid refining steps such as recrystallization, simplify the production flow, reduce the production cost, and can be applied to industrial continuous production.

It is noted that, in this document, relational terms such as "first" and "second," and the like, may be used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions. Also, the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. Without further limitation, an element defined by the phrase "comprising an … …" does not exclude the presence of other identical elements in a process, method, article, or apparatus that comprises the element.

The foregoing are merely exemplary embodiments of the present disclosure, which enable those skilled in the art to understand or practice the present disclosure. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the disclosure. Thus, the present disclosure is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. The preparation method of 2-methyl-3-methoxybenzoic acid is characterized by comprising the following steps:

2. The process according to claim 1, wherein the alkylation in step (1) is carried out at a temperature of 50 to 80 ℃, preferably 55 to 75 ℃.

3. The production method according to claim 1 or 2, wherein the temperature of the hydrolysis reaction in the step (2) is 90 to 120 ℃, more preferably 95 to 120 ℃, still more preferably 100-120 ℃;

and/or the time of the hydrolysis reaction is 1.5-3 h.

4. A production process according to any one of claims 1 to 3, characterized in that the equipment used in the alkylation reaction unit comprises a main reactor;

preferably, the residence time of the sodium phenolate solution and dimethyl sulfate in the main reactor in the step (1) is 3 to 300s, preferably 5 to 120 s;

preferably, the main reactor is selected from the group consisting of a microchannel reactor and/or a dynamic tube reactor, a combination of a microchannel reactor and/or a dynamic tube reactor and a tube reactor.

5. The preparation method according to any one of claims 1 to 4, further comprising, in the step (1), carrying out an aging reaction on the reaction solution obtained after the alkylation reaction;

preferably, the apparatus used in the alkylation reaction unit further comprises an aging reactor;

preferably, the time of the aging reaction is 3-15 min;

preferably, the temperature of the aging reaction is 40 to 70 ℃, preferably 45 to 65 ℃, further preferably 55 to 65 ℃.

6. The production method according to any one of claims 1 to 5, wherein in the step (1), the molar ratio of the 2-methyl-3-hydroxybenzoic acid, the sodium hydroxide and the dimethyl sulfate is 1 (2-5) to (2-3);

and/or in the step (1), the mass ratio of the sodium hydroxide to the water is (10-40): 100.

7. The method according to any one of claims 1 to 6, wherein in the step (1), the method further comprises supplementing a sodium hydroxide solution in the alkylation reaction unit;

preferably, in step (1), the sodium hydroxide solution is fed into the main reactor or the aging reactor;

preferably, in step (1), the concentration of the sodium hydroxide solution is 20-50%;

preferably, in the step (1), the amount of the sodium hydroxide added is 1 to 3 times the molar amount of the 2-methyl-3-hydroxybenzoic acid.

8. The production method according to any one of claims 1 to 7, wherein the step (2) further comprises adding sodium hydroxide to the hydrolysis reaction unit;

preferably, in the step (2), the sodium hydroxide is added in an amount of 1 to 5 times the molar amount of 2-methyl-3-hydroxybenzoic acid.

9. The production method according to any one of claims 1 to 8, wherein the equipment used in the hydrolysis reaction unit comprises a reaction tank, preferably a reaction tank with a distillation or rectification device.

10. The production method according to any one of claims 1 to 9, further comprising performing step (3) after step (2): and (3) allowing hydrolysis reaction liquid flowing out of the hydrolysis reaction unit to enter a product separation unit, and performing acid precipitation, filtration and drying to obtain the 2-methyl-3-methoxybenzoic acid.