A flash separation process for m-toluic acid

Abstract

The application discloses a rapid evaporation separation process of m-toluic acid, mainly including five steps of MX removal rapid evaporation, IPA removal rapid evaporation, MTA removal rapid evaporation, IPA refining and MTA refining. The process has the characteristics of short operation period, good separation effect and high MTA yield, and can recover IPA as a by-product, thereby avoiding generation of a large amount of residues.

Description

Technical Field

[0001] This invention belongs to the field of chemical processes, specifically relating to a novel flash evaporation process for m-methylbenzoic acid. Background Technology

[0002] m-Toluic acid (MTA) can be used to synthesize herbicides, mosquito repellents, polyesters, coatings, and pharmaceutical chemicals. It can also be used to synthesize fragrances and flavorings, and as an auxiliary packing material in chromatography to study the behavior of nucleotides. MTA is mainly synthesized by the catalytic oxidation of m-xylene (MX). After the reaction, the reaction solution needs to be separated to remove unreacted MX, byproducts, and other impurities to obtain MTA with high purity.

[0003] In industrial production, batch distillation is mainly used to separate MTA. However, due to the complex composition of the materials, MTA separation is difficult and the yield is low. Furthermore, the long distillation cycle and high temperature make the feed liquid prone to side reactions that generate high-boiling substances or even coking, resulting in a large amount of residue. Some researchers have also used multi-stage series continuous distillation units and short-path molecular distillation techniques for MTA separation, but these inevitably suffer from problems such as long distillation times, harsh separation conditions, high energy consumption, low MTA yield, and large amounts of residue.

[0004] During the catalytic oxidation of MX, in addition to generating MTA, byproducts such as isophthalic acid (IPA), m-tolualdehyde (MBA), and m-methyl2-cyanobenzoate (MTH) are also produced. MTA, IPA, MTH, and MBA are prone to esterification and condensation side reactions, which, under conventional distillation conditions, lead to the generation of substantial residues. IPA is a significant component of these residues, exhibiting strong heat and chemical resistance. It can participate in dehydration, hydrogenation, and halogenation reactions, and has wide applications in alkyd resin coatings, polyester resins, specialty fibers, and resin plasticization.

[0005] The MX oxidation liquid contains substances such as MX, MTA, MTH, MBA, and IPA, which have relatively different volatility and boiling points. This provides a basis for flash evaporation to separate key components such as MX, MTA, and IPA. Flash evaporation involves preheating the feed liquid, then rapidly reducing the pressure of the hot solution to cause the lighter components to boil and vaporize instantaneously, followed by condensation to separate the target product. During the preheating stage, flash evaporation effectively retains the original components of the material (e.g., equilibrium products of esterification reactions) and suppresses side reactions. During the flash separation stage, the short residence time effectively reduces the formation of by-products, thereby reducing the amount of waste generated in MTA production. Based on these considerations, this invention proposes a novel rapid evaporation process to achieve green and efficient separation of MTA. Summary of the Invention

[0006] The purpose of this section is to outline some aspects of embodiments of the present invention and to briefly describe some preferred embodiments. Simplifications or omissions may be made in this section, as well as in the abstract and title of this application, to avoid obscuring the purpose of these documents; however, such simplifications or omissions should not be construed as limiting the scope of the invention.

[0007] In view of the problems existing in the above and / or prior art, the present invention is proposed.

[0008] Therefore, the purpose of this invention is to overcome the shortcomings of the prior art and provide a novel rapid evaporation and separation process for m-methylbenzoic acid.

[0009] To solve the above-mentioned technical problems, the present invention provides the following technical solution: a novel rapid evaporation and separation process for m-methylbenzoic acid, comprising,

[0010] The MX oxidation liquid is preheated and then rapidly evaporated. The MX is recovered by condensation of the distillate, and the residue is used to obtain the MX-free evaporation mother liquor.

[0011] The mother liquor from the MX removal evaporation was preheated and then rapidly evaporated. The distillate was condensed and recovered to obtain the IPA removal liquid, and crude IPA was obtained.

[0012] The IPA removal liquid is preheated and then rapidly evaporated. The distillate is condensed to recover crude MTA and obtain MTA removal residue / slag.

[0013] The crude IPA was washed with MX washing solution and then filtered dry. The washed IPA filter cake was then dried to obtain the byproduct IPA.

[0014] Crude MTA was crystallized in MX solution, washed, filtered, and the washed MTA filter cake was dried to obtain the product MTA.

[0015] As a preferred embodiment of the preparation method described in this invention, the MX-removal rapid evaporation operation is a normal pressure flash evaporation or a reduced pressure flash evaporation with a pressure value not exceeding 20 kPa, the preheating temperature is higher than the boiling point value of the material corresponding to the flash evaporation pressure, and the temperature superheat value is 50℃-100℃.

[0016] As a preferred embodiment of the preparation method described in this invention, the MX removal rapid evaporation operation is a one-time continuous flash evaporation or a cyclic intermittent flash evaporation, and the final flash evaporation temperature is 30℃-80℃ higher than the MX boiling point value corresponding to the flash evaporation pressure.

[0017] In a preferred embodiment of the preparation method described in this invention, the condensate MX can be reused or recycled as a raw material.

[0018] As a preferred embodiment of the preparation method described in this invention, the MX washing solution is fresh industrial-grade MX or MX solution, and the amount used is 3-5 times the volume of the solid filter cake.

[0019] As a preferred embodiment of the preparation method described in this invention, the rapid evaporation operation for removing IPA is a reduced pressure flash evaporation with a pressure value not exceeding 30 kPa, the preheating temperature is higher than the boiling point value of the material corresponding to the flash evaporation pressure, and the temperature superheat value is 50℃-100℃.

[0020] As a preferred embodiment of the preparation method described in this invention, the rapid evaporation operation for removing IPA is either a one-time continuous flash evaporation or a cyclic intermittent flash evaporation, and the final flash evaporation temperature is 30℃-80℃ higher than the MTA boiling point value corresponding to the flash evaporation pressure.

[0021] As a preferred embodiment of the preparation method described in this invention, the MTA removal rapid evaporation operation is a one-time continuous flash evaporation or a cyclic intermittent flash evaporation, and the final flash evaporation temperature is 20℃-50℃ higher than the MTA boiling point value corresponding to the flash evaporation pressure.

[0022] As a preferred embodiment of the preparation method described in this invention, the rapid evaporation operation uses one or more of the following flash evaporation devices: flash tank, flash tower, thin film evaporator, and scraped evaporator. The IPA removal flash evaporation and MTA removal flash evaporation operations employ a scraped evaporator.

[0023] As a preferred embodiment of the preparation method described in this invention, the drying process includes vacuum drying, atmospheric pressure drying, and melt-forming, wherein IPA is dried under vacuum and MTA is melt-formed.

[0024] Another objective of this invention is to overcome the shortcomings of the prior art and provide a novel, highly efficient rapid evaporation and separation process for m-methylbenzoic acid.

[0025] Another objective of this invention is to overcome the shortcomings of the prior art and provide an application of a highly efficient and novel rapid evaporation and separation process for m-methylbenzoic acid in chemical processes.

[0026] Beneficial effects of this invention:

[0027] This invention employs a step-by-step flash evaporation method to separate MTA, which features a short cycle time, simple process, high operability, and easy industrial implementation. The MTA yield can reach up to 98.19%, and the byproduct IPA yield can reach up to 99.34%, avoiding the generation of large amounts of residue. The washing solution MA and the MTA removal residue containing a precious metal catalyst are reused for oxidation reactions, making it a green and efficient process. Attached Figure Description

[0028] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort. Wherein:

[0029] Figure 1 This is a schematic diagram of the process flow of the present invention. Detailed Implementation

[0030] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to the examples in the specification.

[0031] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein, and those skilled in the art can make similar extensions without departing from the spirit of the invention. Therefore, the invention is not limited to the specific embodiments disclosed below.

[0032] Secondly, the term "one embodiment" or "embodiment" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The phrase "in one embodiment" appearing in different places in this specification does not necessarily refer to the same embodiment, nor is it a single or selective embodiment that is mutually exclusive with other embodiments.

[0033] The names and corresponding abbreviations of the substances used in this invention are as follows: m-xylene (MX); isophthalic acid (IPA); m-methylbenzoic acid (MTA); m-methylbenzaldehyde (MBA); m-methylbenzyl alcohol (MTH);

[0034] Example 1

[0035] A flash evaporation separation process for m-methylbenzoic acid, such as Figure 1As shown, it includes the following steps:

[0036] (1) Rapid evaporation of MX-free material

[0037] 100g of MX oxidation solution (MX 45%, IPA 8%, MTA 33%) was heated to 170℃ and then rapidly evaporated under normal pressure. Cooling water was used for condensation to obtain 50.52g of MX solution and 49.48g of MX-free evaporation mother liquor. The concentration of MX solution was 83.86wt%, and the MX yield was 94.15%.

[0038] (2) Rapid evaporation to remove IPA

[0039] 49.48g of MX-removing evaporation mother liquor was heated to 240℃ for rapid IPA removal evaporation. Then, rapid evaporation was carried out under normal pressure and condensed with cooling water to obtain 7.95g of crude IPA and 41.53g of IPA-removing liquid.

[0040] (3) Rapid evaporation of MTA removal

[0041] 41.53g of IPA-removed feed solution was heated to 285℃ for rapid MTA removal evaporation. Then, rapid evaporation was carried out under normal pressure and condensed with cooling water to obtain 33.7g of crude MTA and 7.83g of MTA removal residue.

[0042] (4) IPA Refining

[0043] At room temperature, crude IPA was collected and washed with 8g of MX to obtain 8.84g of filter cake and 7.11g of filtrate. The wet IPA filter cake was vacuum dried at 60℃ for 4h to obtain 8.01g of IPA with a purity of 97.82% and an IPA yield of 97.91%.

[0044] (5) MTA Refining

[0045] At room temperature, crude MTA was collected and washed with 34g of MX to obtain 37.07g of filter cake and 30.63g of filtrate. The wet MTA filter cake was vacuum dried at 60℃ for 4h to obtain 33.45g of MTA with a purity of 98.86% and an MTA yield of 97.53%.

[0046] Example 2

[0047] A flash evaporation separation process for m-methylbenzoic acid includes the following steps:

[0048] (1) Rapid evaporation of MX-free material

[0049] 100g of MX oxidation solution (MX 45%, IPA 8%, MTA 33%) was heated to 160℃ and then rapidly evaporated under a pressure of 40kPa. Cooling water was used for condensation to obtain 52.32g of MX solution and 47.68g of MX-free evaporation mother liquor. The concentration of MX solution was 85.62wt%, and the MX yield was 99.55%.

[0050] (2) Rapid evaporation to remove IPA

[0051] 47.68g of MX-free evaporation mother liquor was heated to 190℃ for rapid IPA removal and then rapidly evaporated under a pressure of 10KPa. Cooling water was used for condensation to obtain 8.15g of crude IPA and 39.53g of IPA-free liquid.

[0052] (3) Rapid evaporation of MTA removal

[0053] 39.53g of IPA-removed feed solution was heated to 230℃ for rapid MTA removal evaporation, and then rapidly evaporated under a pressure of 10KPa. Cooling water was used for condensation to obtain 32.68g of crude MTA and 6.85g of MTA removal residue.

[0054] (4) IPA Refining

[0055] At room temperature, crude IPA was collected and washed with 8g of MX to obtain 9g of filter cake and 7.15g of filtrate. The wet IPA filter cake was vacuum dried at 60℃ for 4h to obtain 8.05g of IPA with a purity of 98.67% and an IPA yield of 99.34%.

[0056] (5) MTA Refining

[0057] At room temperature, crude MTA was collected and washed with 33g of MX to obtain 36.3g of filter cake and 29.38g of filtrate. The wet MTA filter cake was vacuum dried at 60℃ for 4h to obtain 32.48g of MTA with a purity of 99.76% and an MTA yield of 98.19%.

[0058] Example 3

[0059] A flash evaporation separation process for m-methylbenzoic acid includes the following steps:

[0060] (1) Rapid evaporation of MX-free material

[0061] 1000g of MX oxidation solution (MX 50%, IPA 5%, MTA 35%) was heated to 160℃ and then subjected to rapid evaporation at a pressure of 40KPa. Cooling water was used for condensation to obtain 589g of MX solution and 411g of MX-free evaporation mother liquor. The concentration of MX solution was 83.76wt%, and the MX yield was 98.67%.

[0062] (2) Rapid evaporation to remove IPA

[0063] 411g of MX-free evaporation mother liquor was heated to 190℃ for rapid IPA removal and then rapidly evaporated under a pressure of 10KPa. The liquid was condensed with cooling water to obtain 51g of crude IPA and 360g of IPA-free liquid.

[0064] (3) Rapid evaporation of MTA removal

[0065] 360g of IPA-removed feed liquid was heated to 230℃ for rapid evaporation to remove MTA. Then, rapid evaporation was carried out under a pressure of 10KPa and condensed with cooling water to obtain 338g of crude MTA and 22g of MTA-removed residue.

[0066] (4) IPA Refining

[0067] At room temperature, crude IPA was collected and washed with 51g of MX to obtain 55.3g of filter cake and 46.7g of filtrate. The wet IPA filter cake was vacuum dried at 60℃ for 4h to obtain 50g of IPA with a purity of 98.23% and an IPA yield of 98.03%.

[0068] (5) MTA Refining

[0069] At room temperature, crude MTA was collected and washed with 338g of MX to obtain 371g of filter cake and 305g of filtrate. The wet filter cake was melt-distilled and condensed to obtain 34g of MX condensate, while 337g of solid MTA was obtained with a purity of 99.56% and an MTA yield of 95.86%.

[0070] Example 4

[0071] A flash evaporation separation process for m-methylbenzoic acid includes the following steps:

[0072] (1) Rapid evaporation of MX-free material

[0073] 3000 kg of MX oxidation solution (MX 45%, IPA 6%, MTA 39%) was heated to 160 °C in a stirred tank and then rapidly evaporated at a pressure of 40 kPa. Cooling water was used for condensation to obtain 1592 kg of MX solution and 1408 kg of MX-free evaporation mother liquor. The MX solution concentration was 83.21 wt%, and the MX yield was 98.13%.

[0074] (2) Rapid evaporation to remove IPA

[0075] 1408 kg of MX-free evaporation mother liquor was heated to 190 °C for rapid IPA removal and then rapidly evaporated under a pressure of 10 kPa. Cooling water was used for condensation to obtain 179 kg of crude IPA and 1229 kg of IPA-free liquid.

[0076] (3) Rapid evaporation of MTA removal

[0077] 1229 kg of IPA-removed liquid was heated to 230 °C for rapid MTA removal evaporation. The liquid was then rapidly evaporated at a pressure of 10 kPa and cooled with water to obtain 1077 kg of crude MTA and 152 kg of MTA-removed residue.

[0078] (4) IPA Refining

[0079] At room temperature, crude IPA was collected and washed with 179 kg of MX to obtain 197 kg of filter cake and 161 kg of filtrate. The wet IPA filter cake was vacuum dried at 60 °C for 4 h to obtain 177 kg of IPA with a purity of 99.26% and an IPA yield of 97.6%.

[0080] (5) MTA Refining

[0081] At room temperature, crude MTA was collected and washed with 1077 kg of MX to obtain 1185 kg of filter cake and 969 kg of filtrate. The wet filter cake was melt-distilled and condensed to obtain 110 kg of MX condensate. Simultaneously, it was cooled and solidified to obtain 1073 kg of solid MTA with a purity of 99.45% and an MTA yield of 91.21%.

[0082] Comparative Example 1

[0083] Atmospheric distillation:

[0084] (1) 100g of MX oxidation liquid (MX 45%, IPA 8%, MTA 33%) was distilled under normal pressure, heated to 170℃, and condensed with cooling water to obtain 48.79g of MX solution and 51.21g of MX-free evaporation mother liquor. The concentration of MX solution was 80.95wt% and the MX yield was 87.77%.

[0085] (2) 51.21g of MX-free evaporation mother liquor was heated to perform IPA removal distillation at atmospheric pressure to 240℃ and condensed with cooling water to obtain 4.51g of crude IPA and 46.7g of IPA-free liquid. At room temperature, the crude IPA was collected and washed with 5g of MX to obtain 5g of filter cake and 4.51g of filtrate. The wet IPA filter cake was vacuum dried at 60℃ for 4h to obtain 4.5g of IPA with a purity of 95.23% and an IPA yield of 53.57%.

[0086] (3) 46.7g of IPA-removed feed solution was heated to 285℃ for MTA removal by atmospheric distillation. Then, it was condensed with cooling water to obtain 28.6g of crude MTA and 18.1g of MTA-removed residue. At room temperature, the crude MTA was collected and washed with 29g of MX to obtain 31.5g of filter cake and 26.1g of filtrate. The wet MTA filter cake was vacuum dried at 60℃ for 4h to obtain 28.3g of MTA with a purity of 60.1% and an MTA yield of 51.5%.

[0087] Comparative Example 2

[0088] Atmospheric distillation:

[0089] (1) 100g of MX oxidation liquid (MX 45%, IPA 8%, MTA 33%) was distilled under normal pressure, heated to 180℃, and condensed with cooling water to obtain 49.24g of MX solution and 50.76g of MX-free evaporation mother liquor. The concentration of MX solution was 81.45wt%, and the MX yield was 89.12%.

[0090] (2) 50.76g of MX-free evaporation mother liquor was heated to 250℃ and subjected to atmospheric distillation to remove IPA. The temperature was raised to 250℃ and condensed with cooling water to obtain 4.78g of crude IPA and 45.98g of IPA-free liquid. At room temperature, the crude IPA was collected and washed with 5g of MX to obtain 5.3g of filter cake and 4.48g of filtrate. The wet IPA filter cake was vacuum dried at 60℃ for 4h to obtain 4.75g of IPA with a purity of 94.41% and an IPA yield of 56.1%.

[0091] (3) 45.98g of IPA-removed feed solution was heated to 295℃ for MTA removal by atmospheric distillation. Then, it was condensed with cooling water to obtain 25.9g of crude MTA and 20.08g of MTA-removed residue. At room temperature, the crude MTA was collected and washed with 26g of MX to obtain 28.5g of filter cake and 23.4g of filtrate. The wet MTA filter cake was vacuum dried at 60℃ for 4h to obtain 23g of MTA with a purity of 69.7% and an MTA yield of 48.6%.

[0092] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the present invention.

Claims

1. A rapid evaporation separation process for m-methylbenzoic acid, characterized in that: include, The m-xylene oxide solution is preheated and then rapidly evaporated. The distillate is condensed to recover m-xylene, and the residue is used to obtain the m-xylene removal evaporation mother liquor. The mother liquor from the removal of xylene was preheated and then rapidly evaporated. The distillate was condensed and recovered to obtain crude isophthalic acid. The isophthalic acid removal solution is preheated and then rapidly evaporated. The distillate is condensed and the crude m-methylbenzoic acid product is recovered, yielding the isophthalic acid removal residue / slag. Crude isophthalic acid is washed with xylene washing solution and then filtered dry. The washed isophthalic acid filter cake is then dried to obtain the byproduct isophthalic acid. Crude m-methylbenzoic acid was crystallized in m-xylene solution, washed, filtered, and the washed m-methylbenzoic acid filter cake was dried to obtain the product m-methylbenzoic acid. The aforementioned rapid evaporation operation for removing xylene is an atmospheric or reduced pressure flash evaporation, with the preheating temperature higher than the boiling point value of the material corresponding to the flash evaporation pressure, and the temperature superheat value being 50℃-100℃. The rapid evaporation operation for removing m-xylene is either a one-time continuous flash evaporation or a cyclic intermittent flash evaporation, and the final flash temperature is 30℃-80℃ higher than the boiling point of m-xylene corresponding to the flash pressure. The aforementioned rapid evaporation operation for removing isophthalic acid is a reduced pressure flash evaporation with a pressure value not exceeding 30 kPa, a preheating temperature higher than the boiling point value of the material corresponding to the flash evaporation pressure, and a temperature superheat value of 50℃-100℃. The rapid evaporation operation for removing isophthalic acid is either a one-time continuous flash evaporation or a cyclic intermittent flash evaporation, and the final flash temperature is 30℃-80℃ higher than the boiling point of m-methylbenzoic acid corresponding to the flash pressure. The aforementioned rapid evaporation operation of dem-methylbenzoic acid is a reduced pressure flash evaporation with a pressure value not exceeding 20 kPa, a preheating temperature higher than the boiling point value of the material corresponding to the flash evaporation pressure, and a temperature superheat value of 30℃-80℃. The rapid evaporation operation of dem-methylbenzoic acid is either a one-time continuous flash evaporation or a cyclic intermittent flash evaporation. The final flash evaporation temperature is 20℃-50℃ higher than the boiling point of m-methylbenzoic acid corresponding to the flash evaporation pressure.

2. The evaporation separation process as described in claim 1, characterized in that: Xylene in condensate can be reused or recycled as a raw material.

3. The evaporation separation process as described in claim 1, characterized in that: The m-xylene washing solution is fresh industrial-grade m-xylene or m-xylene solution, and the amount used is 3-5 times the volume of the solid filter cake.

4. The evaporation separation process as described in claim 1, characterized in that: The rapid evaporation operation uses one or more of the following flash evaporation equipment: flash tank, flash tower, thin film evaporator, and scraped evaporator. The flash evaporation of isophthalic acid and the flash evaporation of m-methylbenzoic acid are carried out using a scraped evaporator. The drying process includes vacuum drying, atmospheric pressure drying, and melt-forming. The isophthalic acid is dried under vacuum, and the m-methylbenzoic acid is melt-formed.

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