Process and device for preparing m-toluic acid and m-phthalic acid through continuous flow selective oxidation of m-xylene

Abstract

The invention discloses a process and a device for preparing m-toluic acid and m-phthalic acid through continuous flow selective oxidation of m-xylene, and the process comprises the following steps: pumping m-xylene and a catalyst solution into a first vertical tubular reactor of a single oxidation reaction module, and introducing oxygen or air to carry out single oxidation reaction; after the reaction is finished, high-purity m-toluic acid is obtained through post-treatment, the yield reaches 93% or above, and the product purity reaches 99%; and switching the outlet of the tubular reactor of the mono-oxidation reaction module to the dual-oxidation reaction module, mixing the reaction liquid after the mono-oxidation reaction is finished with a second stream of catalyst solution, feeding the mixture into a second vertical tubular reactor of the dual-oxidation reaction module for dual-oxidation reaction, and after the reaction is finished, carrying out post-treatment to obtain the product isophthalic acid. The yield reaches 95% or above, and the purity reaches 99% or above; the method is high in reaction controllability, short in reaction retention time, stable in product quality, high in production safety, convenient to operate, high in continuous degree and suitable for industrial production.

Description

Technical Field

[0001] The present invention relates to the technical field of organic synthesis, and in particular to a process and device for preparing m-toluic acid and isophthalic acid by continuous flow selective oxidation of m-xylene. Background Art

[0002] Meta-toluic acid, white or yellow crystals, melting point 108 ° C, boiling point 263 ° C, can be used as an organic synthesis raw material and pesticide intermediates. It is the main raw material for the production of meta-toluonitrile, toluene diethylamine and meta-toluoyl chloride. In terms of pesticides, it is mainly used to synthesize herbicides and mosquito repellents. It can also be used as a material additive, such as in plastics, rubber and coatings.

[0003] Isophthalic acid (IPA), also known as 1,3-phthalic acid or isophthalic acid, is a white crystalline solid with a melting point of 345~347℃. It is flammable and low in toxicity. It has the characteristics of a general dibasic acid and can undergo reactions such as salt formation, dehydration, hydrogenation, and halogenation. Isophthalic acid is an important organic chemical intermediate with properties such as heat resistance, hydrolysis resistance, and chemical resistance. Therefore, it is increasingly used in coatings, polyester resins, unsaturated polyester resins, polyester fiber dyeing and modification, specialty fibers, hot melt adhesives, and resin plasticization.

[0004] Currently, literature reports mainly use the air oxidation method of meta-xylene to prepare meta-toluic acid.

[0005] The Chinese invention patent with publication number CN109999914A discloses a catalyst for preparing m-toluic acid, a preparation method and application thereof, wherein metal porphyrin sulfonate is used as a catalyst, and an oxidation reaction is carried out with m-xylene and air, and the product is directly distilled after the reaction is completed. The obtained m-toluic acid is in the form of white flakes or granules, with a total reaction yield of 82-94% and a content of more than 99%. However, the catalyst of this process is expensive, deactivated quickly, difficult to recycle, difficult to industrialize, and has a low single oxidation yield.

[0006] The Chinese invention patent with publication number CN117164447A discloses a method for producing m-toluic acid, which comprises subjecting a catalyst, m-xylene and air to oxidation reaction, filtering, crude steaming, rectification, slicing, crystallization, centrifugation and drying to obtain the m-toluic acid product. The catalyst is a mixture of sulfonated cobalt phthalocyanine or cobalt polyphthalocyanine and organic acid cobalt salt, the reaction time is 3.6 h, the conversion rate is 60%, and the total cycle yield is 94.6%. The invention has the disadvantages of low reaction conversion rate, long post-processing process, complex reaction system, poor stability of continuous operation, and low safety factor.

[0007] The Chinese invention patent with publication number CN107903165A discloses a method for continuously preparing m-toluic acid using a tubular reactor, which proposes using peracetic acid or hydrogen peroxide as an oxidant, acetic acid as a solvent, cobalt acetate and sodium bromide as catalysts, with a m-xylene conversion rate of 50%, a m-toluic acid selectivity of 77.5%, and a product yield of 60-90%. The temperature of the reaction zone of this process is always consistent, the initiation temperature is consistent with the reaction temperature, the product has many impurities, low yield, low product selectivity, high oxidation cost, and many by-products.

[0008] Currently, the literature reports that the synthesis of isophthalic acid generally adopts a kettle liquid phase oxidation method.

[0009] The Chinese invention patent with publication number CN107954850 A discloses a method for preparing isophthalic acid, which uses Co-Mn-Br as a catalyst and one or more of rare earth metal acetate, alkali metal acetate and transition metal acetate as a catalytic additive, and the reaction temperature is 190-200°C to oxidize meta-xylene to prepare isophthalic acid. Although this method reduces the use of bromine, the reduction is limited, and the amount of additives is too large, which has a potential impact on the quality of subsequent products.

[0010] The Chinese invention patents with publication numbers CN109369369 A and CN 109485557 A both disclose a method for the ozone oxidation of m-xylene. Under normal temperature and pressure, the reaction time is 10 to 40 hours under ultraviolet irradiation, and the product conversion rate is 98% and the yield is 96%. The reaction cycle of this preparation method is too long, and the product selectivity is poor, which is not suitable for industrial production. Song Hua et al. used 30% H 2 O 2 As an oxidant, cobalt acetate is a catalyst, and isophthalic acid is synthesized by liquid phase catalytic oxidation of m-xylene under normal pressure, with a reaction temperature of 90°C and a reaction time of 2h, and an isophthalic acid yield of 59.5%. This method has high reaction cost, long reaction cycle and low reaction yield.

[0011] The Chinese invention patent with publication number CN101704741A discloses a method for producing isophthalic acid from meta-xylene, which discloses that activated carbon loaded with 5% to 60% by weight of heteropoly acid is used as a solid catalyst to form a gas, liquid and solid three-phase reaction system to oxidize meta-xylene into isophthalic acid. Although the invention avoids the use of bromine, reduces equipment corrosion and reduces environmental pollution, the reaction time is long and the product selectivity is low.

[0012] In summary, the current industrial production process of m-toluic acid has many problems such as low reaction efficiency, high energy and material consumption, many by-products, low raw material conversion rate, high catalyst cost, poor product selectivity and low product yield. The existing process of oxidizing m-xylene to isophthalic acid mostly adopts intermittent kettle operation, which has a long reaction cycle and low conversion rate. At the same time, the reaction selectivity is poor, and there are too many reaction impurities, which makes it difficult to control the reaction parameters, resulting in poor product stability, low automation level, low output, poor quality, serious waste of resources and other problems. Therefore, the present invention proposes a process and device for preparing m-toluic acid and isophthalic acid by selectively oxidizing m-xylene in a continuous flow. Summary of the invention

[0013] In view of the above-mentioned technical problems existing in the prior art, the purpose of the present invention is to provide a process and apparatus for preparing m-toluic acid and isophthalic acid by selective oxidation of m-xylene in a continuous flow, which utilizes the fast heat exchange characteristics of a tubular reactor to avoid poor reaction selectivity, and at the same time utilizes the precise control of reaction parameters by the tubular reactor to effectively improve the conversion rate, selectivity and yield of the oxidation.

[0014] To achieve the above object, the technical solution of the present invention is as follows: The present invention provides a process for preparing m-toluic acid and isophthalic acid by continuous flow selective oxidation of m-xylene, comprising the following steps: 1) Meta-xylene and a catalyst are prepared into a first reaction liquid, which is transported to a first vertical tubular reactor through a metering pump according to a set flow rate, and air or oxygen is transported through a gas flow meter and a pressure reducing valve to control the delivery, and is fully contacted with the reaction liquid through a gas disperser in the first vertical tubular reactor to react, and is connected to a single oxidation reaction liquid storage tank through a three-way ball valve. After a single oxidation reaction is carried out at a set temperature and a certain residence time, the reaction liquid flows into the single oxidation reaction liquid storage tank, and the single oxidation reaction liquid is post-treated to obtain a single oxidation product, namely, meta-toluic acid; 2) According to the operation process of step 1), the outlet of the first vertical tubular reactor for single oxidation is switched to the second vertical tubular reactor for double oxidation by adjusting the three-way ball valve, the single oxidation reaction liquid and the second catalyst solution are transported into the mixing three-way according to the set flow rate for rapid mixing, and then enter the second vertical tubular reactor for double oxidation, the air or oxygen is transported through the gas flow meter 2 and the pressure reducing valve, and is fully contacted with the reaction liquid through the gas disperser in the second vertical tubular reactor to react, after the double oxidation reaction is carried out at the set temperature for a certain residence time, the reaction liquid flows into the double oxidation reaction liquid storage tank, and the double oxidation reaction liquid is post-treated to obtain the double oxidation product, i.e., isophthalic acid; The reaction formula involved in the present invention is as follows:

[0015] Furthermore, in step 1), the catalyst is cobalt acetylacetonate, and the amount of cobalt acetylacetonate added is 0.5% to 1.5%, preferably 0.5% to 1.0%, based on the molar number of meta-xylene.

[0016] Further, in step 2), the catalyst is mixed with a solvent to obtain a second catalyst reaction liquid, wherein the catalyst is cobalt manganese bromine, wherein the cobalt manganese bromine is a mixture of cobalt acetate, manganese acetate and sodium bromide, and the concentration ranges of Co ions, Mn ions and Br ions are 800-1000ppm, 800-1000ppm and 800-1000ppm respectively.

[0017] Furthermore, in step 2), the mass ratio of the solvent acetic acid to m-xylene is 6-15:1, preferably 10-15:1.

[0018] Furthermore, in step 1), the temperature of the single oxidation reaction is 100°C to 150°C, preferably 110°C to 130°C, and in step 2), the temperature of the double oxidation reaction is 150°C to 200°C, preferably 160°C to 180°C.

[0019] Furthermore, the residence time of the single oxidation reaction in step 1) is 30 min to 60 min, preferably 30 to 40 min; the residence time of the double oxidation reaction in step 2) is 60 min to 120 min, preferably 60 min to 80 min.

[0020] Furthermore, the single oxidation reaction pressure in step 1) is 0.5~2.0MPa, preferably 0.8~1.2MPa; the double oxidation reaction pressure in step 2) is 2.0~4.0MPa, preferably 2.0~3.0MPa.

[0021] Furthermore, in step 1), the post-treatment method of the single oxidation reaction liquid is to first cool it to room temperature for crystallization, filter it, and recover the mother liquor for reuse in the single oxidation stage, and the filter cake is the single oxidation product, m-toluic acid; in step 2), the post-treatment method of the double oxidation reaction liquid is to cool the above reaction liquid to room temperature for crystallization, filter it, wash it with water, and dry it to obtain high-purity double oxidation white crystals or powder, which is isophthalic acid.

[0022] The present invention also proposes a device for preparing m-toluic acid and isophthalic acid by continuous flow selective oxidation of m-xylene, comprising a single oxidation conveying module, a single oxidation reaction module, a single oxidation receiving module, a dual oxidation conveying module, a dual oxidation reaction module and a dual oxidation receiving module; The single oxidation transport module includes an air or oxygen steel cylinder and a first storage tank; the single oxidation reaction module includes a first vertical tubular reactor and a circulating heat exchange device; The air or oxygen steel cylinder 1 is connected to the gas disperser at the bottom of the first vertical tubular reactor through a pipeline 1, wherein a gas flowmeter 1 is provided on the pipeline 1; the first storage tank is connected to the bottom inlet of the first vertical tubular reactor through a pipeline 2, wherein a metering pump 1 is provided on the pipeline 2; a back pressure valve is provided on the top outlet pipeline of the first vertical tubular reactor, and the top outlet pipeline is divided into two routes, one of which is connected to the single oxidation receiving module, and the other is connected to the dual oxidation delivery module; The single oxidation receiving module comprises a reaction liquid sampling tube, a three-way ball valve and a single oxidation reaction liquid storage tank, the three-way ball valve has an inlet and two outlets, the inlet of the three-way ball valve is connected to the top outlet of the first upright tubular reactor through pipeline three, one of the outlets of the three-way ball valve is connected to the single oxidation reaction liquid storage tank through pipeline four, and the other outlet is connected to the dual oxidation reaction module; wherein a reaction liquid sampling tube is provided on pipeline three; The dual oxidation delivery module includes a second air or oxygen cylinder and a second storage tank; the dual oxidation reaction module includes a second upright tubular reactor and a second circulating heat exchange device; the dual oxidation receiving module includes a dual oxidation reaction liquid storage tank; The air or oxygen cylinder 2 is connected to the gas disperser at the bottom of the second vertical tubular reactor through a pipeline 5, and the second storage tank is connected to the bottom inlet of the second vertical tubular reactor through a pipeline 6; wherein a gas flow meter 2 is provided on the pipeline 5, and a metering pump 2 is provided on the pipeline 6; The mixing tee of the dual oxidation conveying module has three openings, which are respectively connected to one of the outlets of the three-way ball valve, the feed port of the second storage tank and the inlet of the second upright tubular reactor through pipelines; the top outlet of the second upright tubular reactor is connected to the dual oxidation reaction liquid storage tank through pipeline seven; wherein a back pressure valve two is provided on pipeline seven.

[0023] Furthermore, the inlet and outlet on both sides of the first upright tubular reactor are respectively connected to the circulating heat exchange equipment through pipelines; the inlet and outlet on both sides of the second upright tubular reactor are respectively connected to the circulating heat exchange equipment through pipelines.

[0024] Compared with the prior art, the beneficial effects of the present invention are as follows: 1) The present invention pumps meta-xylene and a catalyst solution into a first upright tubular reactor of a single oxidation reaction module, and simultaneously introduces oxygen or air to carry out a single oxidation reaction. After the reaction is completed, high-purity single oxidation product meta-toluic acid is obtained through post-treatment; the outlet of the tubular reactor of the single oxidation reaction module is switched to a double oxidation reaction module, and the reaction liquid after the single oxidation reaction is mixed with a second catalyst solution, and then enters a second upright tubular reactor of the double oxidation reaction module for a double oxidation reaction. After the reaction is completed, the product isophthalic acid is obtained through post-treatment, and the yield of the obtained meta-toluic acid is more than 93%, and the product purity is 99%. The yield of isophthalic acid is more than 95%, and its purity is 99%; 2) The process for preparing high-purity and high-yield m-toluic acid and isophthalic acid by a continuous flow tubular reactor disclosed in the present invention has strong reaction controllability, single oxidation uses a catalyst cobalt cyclohexaneate to prevent excessive oxidation, and double oxidation increases the catalytic strength and completely oxidizes. Compared with the traditional kettle reaction, the present invention improves the quality and greatly shortens the reaction time, the product is stable, the process is simplified, and the discharge of three wastes is greatly reduced; 3) When preparing single oxidation and double oxidation products in a continuous flow, the present invention only needs to adjust the process parameters to achieve seamless switching, without the need to replace the tubular reactor. The tubular reactor accurately controls the reaction parameters, improves the reaction selectivity and conversion rate, and then obtains high-purity and high-content m-toluic acid and isophthalic acid through post-treatment. Compared with the existing production process, the products prepared by this process are higher in purity and content; 4) Compared with the traditional kettle process, the tubular process and continuous operation mode adopted in the present invention are easier to realize process automation, improve the safety of the production process, are easy to operate, have a high degree of continuity, and are suitable for industrial production. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 The present invention is a schematic structural diagram of a device for preparing m-toluic acid and isophthalic acid by continuous flow selective oxidation of m-xylene.

[0026] In the figure: A, single oxidation delivery module; A1, one air or oxygen cylinder; A2, the first storage tank; A3, one gas flow meter; A4, one metering pump; B, single oxidation reaction module; B1, the first vertical tubular reactor; B2, one circulating heat exchange equipment; B3, one back pressure valve; C, single oxidation receiving module; C1, single oxidation reaction liquid storage tank; C2, reaction liquid sampling tube; C3, three-way ball valve; D, dual oxidation delivery module; D1, two air or oxygen cylinders; D2, the second storage tank; D3, two metering pumps; D4, two gas flow meters; E, dual oxidation reaction module; E1, the second vertical tubular reactor; E2, two circulating heat exchange equipment; E3, two white teeth; F, dual oxidation receiving module; F1, dual oxidation reaction liquid storage tank. DETAILED DESCRIPTION

[0027] The present invention will be further described below in conjunction with the accompanying drawings and embodiments, but the scope of protection of the present invention is not limited to the described scope.

[0028] Reference Figure 1 The present invention proposes a device for preparing m-toluic acid and isophthalic acid by continuous flow selective oxidation of m-xylene, comprising a single oxidation conveying module A, a single oxidation reaction module B, a single oxidation receiving module C, a dual oxidation conveying module D, a dual oxidation reaction module E and a dual oxidation receiving module F.

[0029] The single oxidation transport module A includes an air or oxygen steel cylinder A1 and a first storage tank A2; the single oxidation reaction module B includes a first vertical tubular reactor B1 and a circulating heat exchange device B2.

[0030] An air or oxygen steel cylinder A1 is connected to the gas disperser at the bottom of the first vertical tubular reactor B1 through a pipeline 1, wherein a gas flowmeter A3 is provided on the pipeline 1; a first storage tank A2 is connected to the bottom inlet of the first vertical tubular reactor B1 through a pipeline 2, wherein a metering pump A4 is provided on the pipeline 2; a back pressure valve B3 is provided on the top outlet pipeline of the first vertical tubular reactor B1, and its top outlet pipeline is divided into two routes, one of which is connected to the single oxidation receiving module C, and the other is connected to the double oxidation conveying module D.

[0031] The single oxidation receiving module C includes a reaction liquid sampling tube C2, a three-way ball valve C3 and a single oxidation reaction liquid storage tank C1. The three-way ball valve C3 has an inlet and two outlets. The inlet of the three-way ball valve C3 is connected to the top outlet of the first vertical tubular reactor B1 through pipeline three, one of the outlets of the three-way ball valve C3 is connected to the single oxidation reaction liquid storage tank C1 through pipeline four, and the other outlet is connected to the dual oxidation reaction module E; wherein a reaction liquid sampling tube C2 is provided on pipeline three.

[0032] The dual oxidation delivery module D includes an air or oxygen cylinder D1 and a second storage tank D2; the dual oxidation reaction module E includes a second vertical tubular reactor E1 and a circulating heat exchange device E2; the dual oxidation receiving module (F) includes a dual oxidation reaction liquid storage tank F1; The air or oxygen cylinder D1 is connected to the gas disperser at the bottom of the second vertical tubular reactor E1 through a pipeline 5, and the second storage tank D2 is connected to the bottom inlet of the second vertical tubular reactor E1 through a pipeline 6; wherein a gas flow meter D4 is provided on the pipeline 5, and a metering pump D3 is provided on the pipeline 6; The mixing tee of the dual oxidation conveying module has three openings, which are respectively connected to one of the outlets of the three-way ball valve C3, the feed port of the second storage tank D2 and the inlet of the second upright tubular reactor E1 through pipelines. The top outlet of the second upright tubular reactor E1 is connected to the dual oxidation reaction liquid storage tank F1 through pipeline seven; a back pressure valve E3 is provided on pipeline seven.

[0033] Furthermore, the inlet and outlet on both sides of the first upright tubular reactor B1 are respectively connected to the circulating heat exchange equipment B2 through pipelines; the inlet and outlet on both sides of the second upright tubular reactor E1 are respectively connected to the circulating heat exchange equipment E2 through pipelines.

[0034] In this embodiment, the pipe diameter of the first upright tubular reactor B1 of the single oxidation reaction module is 3.175 mm, and the pipe diameter of the second upright tubular reactor E1 of the dual oxidation reaction module is 3.175 mm.

[0035] Example 1 Preparation of mono-oxidation product m-toluic acid: First, 402.8 g of m-xylene was mixed with 4.878 g of catalyst cobalt acetylacetonate to form the first catalyst reaction liquid; then the air tightness of the device was checked, and 3.0 MPa of nitrogen was introduced into the reaction device for a 30-minute air tightness test. The pressure drop within 30 minutes was qualified if it was no more than 0.1 MPa. Then, oxygen was introduced, and the reaction oil bath was heated to 110°C. The delivery was controlled by a gas flowmeter and a pressure reducing valve. The flow and pressure of oxygen were maintained at 1.5 SLM and 0.8 MPa. After the gas flow was stable, a metering pump A4 was used to control the flow rate to 4.0 mL / min, residence time 30min, start to deliver the first stream of catalyst reaction liquid to the first vertical tubular reactor B1, so that oxygen fully contacts the reaction liquid in the reactor to react, the reaction liquid is sampled through the reaction liquid sampling tube C2 to timely detect and feedback the sample; after the reaction is completed, the reaction liquid enters the single oxidation reaction liquid storage tank C1 through the three-way ball valve C3, the single oxidation reaction liquid is first cooled to room temperature for crystallization, filtered, the filter cake is the single oxidation product m-toluic acid, the mother liquor and catalyst are recovered and reused in the single oxidation stage. The molar yield of the single oxidation product m-toluic acid is 93.2%, and the purity is 99.53%.

[0036] Example 2 Preparation of mono-oxidation product m-toluic acid: First, 402.8 g of m-xylene was mixed with 9.756 g of catalyst cobalt acetylacetonate to form the first catalyst reaction liquid. Then, the air tightness of the device was checked, and 3.0 MPa of nitrogen was introduced into the reaction device for a 30-minute air tightness test. The pressure drop within 30 minutes was qualified if it was no more than 0.1 MPa. Then, air was introduced, and the reaction oil bath was heated to 130°C. The flow rate and pressure of the transported air were maintained at 2.0 SLM and 1.2 MPa through the control of the gas flow meter and the pressure reducing valve. After the gas flow was stable, the flow rate was controlled to 3.0 with a metering pump A4. mL / min, residence time 40min, start to deliver the first stream of catalyst reaction liquid to the first vertical tubular reactor B1, so that the air in the reactor is fully in contact with the reaction liquid to react, the reaction liquid is sampled through the reaction liquid sampling tube C2, and the sample is tested and fed back in time; after the reaction is completed, the reaction liquid enters the single oxidation reaction liquid receiving tank C1 through the three-way ball valve C3, the single oxidation reaction liquid is first cooled to room temperature for crystallization, filtered, the filter cake is the single oxidation product m-toluic acid, the mother liquor and catalyst are recovered and reused in the single oxidation stage. The molar yield of the single oxidation product m-toluic acid is 97.8%, and the purity is 99.80%.

[0037] Example 3 Preparation of double oxidation product isophthalic acid: Switch the outlet direction of the three-way ball valve C3, and switch the outlet of the first vertical tubular reactor B1 of the single oxidation reaction module to connect to the dual oxidation reaction module; mix 402.8 g of m-xylene with 4.878 g of catalyst cobalt acetylacetonate to form the first catalyst reaction liquid; mix the catalyst cobalt acetate, manganese acetate, sodium bromide and solvent acetic acid, wherein the addition amount of Co is 800 ppm, Co:Mn:Br=1:1:1, and 4028 g of acetic acid is the second catalyst reaction liquid; use metering pump D3 to control the flow rate to 4.0 mL / min to start transporting the first catalyst and reaction liquid to the first vertical tubular reactor B1, and introduce oxygen. The flow rate and pressure of oxygen are maintained at 1.5 SLM and 0.8 MPa, so that oxygen is fully in contact with the reaction liquid in the reactor to react, and the reaction oil bath is heated to 110°C, and the residence time of the single oxidation reaction is 30 min; After the single oxidation reaction is completed, the single oxidation reaction liquid enters the double oxidation module through the three-way ball valve C3, and the second catalyst reaction liquid is injected into the double oxidation module at a flow rate of 8.0 mL / min by the metering pump D4, and the above two solutions are passed into the mixing tee for rapid mixing; after mixing, the reaction liquid is injected into the second vertical tubular reactor E1 for double oxidation reaction, and the flow rate and pressure of oxygen are maintained at 2.5SLM and 2.0MPa, and the reaction oil bath is heated to 160°C, and the residence time of the double oxidation reaction is 60min. The above reaction liquid is cooled to room temperature for crystallization, filtration, water washing, and drying to obtain high-purity double oxidation white crystals or powder, which is the target product isophthalic acid, and the molar yield is 95.0% after weighing and the purity of liquid phase detection is 99.50%.

[0038] Example 4 Preparation of double oxidation product isophthalic acid: Switch the outlet direction of the three-way ball valve C3, and switch the outlet of the first vertical tubular reactor B1 of the single oxidation reaction module to connect to the dual oxidation reaction module; mix 402.8 g of m-xylene with 9.756 g of catalyst cobalt acetylacetonate to form the first catalyst reaction liquid; mix the catalyst cobalt acetate, manganese acetate, sodium bromide and solvent acetic acid, wherein the addition amount of Co is 1000 ppm, Co:Mn:Br=1:1:1, and 6042 g of acetic acid is the second catalyst reaction liquid; use metering pump D3 to control the flow rate to 3.0 mL / min to start conveying the reaction liquid to the first vertical tubular reactor B1, and introduce air. The flow rate and pressure of the conveyed air are maintained at 2.0 SLM and 1.2 MPa, so that the air is fully in contact with the reaction liquid in the reactor to react, and the reaction oil bath is heated to 130°C, and the residence time of the single oxidation reaction is 40 min; After the single oxidation reaction is completed, the single oxidation reaction liquid enters the double oxidation module through the three-way ball valve C3, and the second catalyst reaction liquid is injected into the double oxidation module at a flow rate of 6.0 mL / min by the metering pump D3, and then the above two solutions are introduced into the mixing tee for rapid mixing; the mixed reaction liquid is injected into the second upright tubular reactor E1 for double oxidation reaction, oxygen is introduced, and the flow rate and pressure of oxygen are maintained at 3.8 SLM and 3.0 MPa, the reaction oil bath is heated to 180°C, and the residence time of the double oxidation reaction is 80 min; the above reaction liquid is cooled to room temperature for crystallization, filtration, water washing, and drying to obtain high-purity double oxidation white crystals or powder, which is the target product isophthalic acid, and the molar yield is 98.3% as measured by weighing, and the purity is 99.82% as measured by liquid phase.

Claims

1. A process for preparing m-toluic acid and isophthalic acid by selective oxidation of m-xylene in a continuous flow, characterized in that The steps include: 1) Meta-xylene and a catalyst are prepared into a first reaction liquid and transported to a first vertical tubular reactor (B1) through a metering pump (A4) at a set flow rate, and air or oxygen is transported through a gas flow meter (A3) and a pressure reducing valve to control the transport, and is fully contacted with the reaction liquid through a gas disperser in the first vertical tubular reactor (B1) to react, and is connected to a single oxidation reaction liquid storage tank (C1) through a three-way ball valve (C3). After a single oxidation reaction is carried out at a set temperature and for a certain residence time, the reaction liquid flows into the single oxidation reaction liquid storage tank (C1), and the single oxidation reaction liquid is post-treated to obtain a single oxidation product, namely, meta-toluic acid; 2) According to the operation process of step 1), the outlet of the first vertical tubular reactor (B1) for single oxidation is switched to the second vertical tubular reactor (E1) for double oxidation by adjusting the three-way ball valve (C3), and the single oxidation reaction liquid and the second catalyst solution are transported into the mixing tee at a set flow rate for rapid mixing, and then enter the second vertical tubular reactor (E1) for double oxidation. Air or oxygen is transported through a gas flow meter 2 (D4) and a pressure reducing valve, and is fully contacted with the reaction liquid through a gas disperser in the second vertical tubular reactor (E1) to react. After the double oxidation reaction is carried out at a set temperature and for a certain residence time, the reaction liquid flows into a double oxidation reaction liquid storage tank (F1), and the double oxidation reaction liquid is post-treated to obtain a double oxidation product, namely isophthalic acid.

2. A process for preparing m-toluic acid and isophthalic acid by selective oxidation of m-xylene in a continuous flow as claimed in claim 1, characterized in that In step 1), the catalyst is cobalt acetylacetonate, and the amount of cobalt acetylacetonate added is 0.5% to 1.5% of the molar number of meta-xylene, preferably 0.5% to 1.0%.

3. A process for preparing m-toluic acid and isophthalic acid by selective oxidation of m-xylene in a continuous flow as claimed in claim 1, characterized in that Step 2) Mixing the catalyst with the solvent to obtain a second catalyst solution, wherein the catalyst is cobalt manganese bromine, wherein the cobalt manganese bromine is a mixture of cobalt acetate, manganese acetate and sodium bromide, and the concentration ranges of Co ions, Mn ions and Br ions are 800-1000ppm, 800-1000ppm and 800-1000ppm respectively.

4. A process for preparing m-toluic acid and isophthalic acid by selective oxidation of m-xylene in a continuous flow as claimed in claim 3, characterized in that Step 2) The mass ratio of the solvent acetic acid to m-xylene is 6-15:1, preferably 10-15:

1.

5. A process for preparing m-toluic acid and isophthalic acid by selective oxidation of m-xylene in a continuous flow as claimed in claim 1, characterized in that The temperature of the single oxidation reaction in step 1) is 100°C to 150°C, preferably 110°C to 130°C, and the temperature of the double oxidation reaction in step 2) is 150°C to 200°C, preferably 160°C to 180°C.

6. A process for preparing m-toluic acid and isophthalic acid by selective oxidation of m-xylene in a continuous flow as claimed in claim 1, characterized in that The residence time of the single oxidation reaction in step 1) is 30 min to 60 min, preferably 30 to 40 min; the residence time of the double oxidation reaction in step 2) is 60 min to 120 min, preferably 60 min to 80 min.

7. A process for preparing m-toluic acid and isophthalic acid by continuous flow selective oxidation of m-xylene as claimed in claim 1, characterized in that The single oxidation reaction pressure in step 1) is 0.5-2.0 MPa, preferably 0.8-1.2 MPa; the double oxidation reaction pressure in step 2) is 2.0-4.0 MPa, preferably 2.0-3.0 MPa.

8. A process for preparing m-toluic acid and isophthalic acid by continuous flow selective oxidation of m-xylene as claimed in claim 1, characterized in that The post-treatment method of the mono-oxidation reaction liquid in step 1) is to first cool it to room temperature for crystallization, filter it, and recover the mother liquor for reuse in the mono-oxidation stage. The filter cake is the mono-oxidation product m-toluic acid. The post-treatment method of the double oxidation reaction liquid in step 2) is to cool the above reaction liquid to room temperature for crystallization, filter it, wash it with water, and dry it to obtain high-purity double oxidation white crystals or powder, which is isophthalic acid.

9. An apparatus for the process of preparing m-toluic acid and isophthalic acid by continuous flow selective oxidation of m-xylene as claimed in claim 1, characterized in that It includes a single oxidation transport module (A), a single oxidation reaction module (B), a single oxidation receiving module (C), a dual oxidation transport module (D), a dual oxidation reaction module (E) and a dual oxidation receiving module (F); The single oxidation transport module (A) comprises an air or oxygen steel cylinder (A1) and a first storage tank (A2); the single oxidation reaction module (B) comprises a first vertical tubular reactor (B1) and a circulating heat exchange device (B2); The air or oxygen steel cylinder (A1) is connected to the gas disperser at the bottom of the first vertical tubular reactor (B1) through a pipeline (1), wherein a gas flow meter (A3) is provided on the pipeline (1); the first storage tank (A2) is connected to the bottom inlet of the first vertical tubular reactor (B1) through a pipeline (2), wherein a metering pump (A4) is provided on the pipeline (2); a back pressure valve (B3) is provided on the top outlet pipeline of the first vertical tubular reactor (B1), and the top outlet pipeline is divided into two routes, one of which is connected to the single oxidation receiving module (C), and the other is connected to the dual oxidation delivery module (D); The single oxidation receiving module (C) comprises a reaction liquid sampling tube (C2), a three-way ball valve (C3) and a single oxidation reaction liquid storage tank (C1), wherein the three-way ball valve (C3) has an inlet and two outlets, the inlet of the three-way ball valve (C3) is connected to the top outlet of the first vertical tubular reactor (B1) through pipeline three, one of the outlets of the three-way ball valve (C3) is connected to the single oxidation reaction liquid storage tank (C1) through pipeline four, and the other outlet is connected to the dual oxidation reaction module (E); wherein a reaction liquid sampling tube (C2) is provided on pipeline three; The dual oxidation delivery module (D) includes a second air or oxygen cylinder (D1) and a second storage tank (D2); the dual oxidation reaction module (E) includes a second vertical tubular reactor (E1) and a second circulating heat exchange device (E2); the dual oxidation receiving module (F) includes a dual oxidation reaction liquid storage tank (F1); The second air or oxygen cylinder (D1) is connected to the gas disperser at the bottom of the second vertical tubular reactor (E1) through a pipeline (5), and the second storage tank (D2) is connected to the bottom inlet of the second vertical tubular reactor (E1) through a pipeline (6); wherein a gas flow meter (D4) is provided on the pipeline (5), and a metering pump (D3) is provided on the pipeline (6); The mixing tee of the dual oxidation conveying module has three openings, which are respectively connected to one of the outlets of the three-way ball valve (C3), the feed port of the second storage tank (D2) and the inlet of the second upright tubular reactor (E1) through pipelines; the top outlet of the second upright tubular reactor (E1) is connected to the dual oxidation reaction liquid storage tank (F1) through pipeline seven; wherein a back pressure valve 2 (E3) is provided on pipeline seven.

10. The device according to claim 9, characterized in that The inlet and outlet on both sides of the first upright tubular reactor (B1) are respectively connected to the circulating heat exchange equipment (B2) through pipelines; the inlet and outlet on both sides of the second upright tubular reactor (E1) are respectively connected to the circulating heat exchange equipment (E2) through pipelines.

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