CN215026118U - Processing system of xylol oxidation reaction liquid - Google Patents

Abstract

The utility model relates to a fine chemistry industry technical field, in particular to processing system of xylol oxidation reaction liquid, include: the system comprises: a light component removal system (A) which is provided with a first light component removal unit (011), an oxidation reaction liquid (a1) inlet, a light component (a2) outlet and a light component removal mother liquid (a3) outlet; a de-weighting system (B) having a first rectification device (021), an inlet for high boiling point solvent (c1), an inlet for light weight removal mother liquor (a3), an outlet for benzoic acid (B1), an outlet for methylbenzoic acid (B2), and an outlet for heavy components (B3), wherein the inlet for high boiling point solvent (c1) introduces high boiling point solvent (c1) into the de-weighting system (B). The utility model discloses the method not only can reduce the product loss to oxidation reaction liquid treatment in-process, but also can reduce the content of single impurity benzoic acid, improves methyl benzoic acid's purity.

Description

Processing system of xylol oxidation reaction liquid

Technical Field

The utility model relates to a fine chemistry industry technical field, in particular to processing system (equipment or device) of xylol oxidation reaction liquid. The system not only can reduce the product loss to the oxidation reaction liquid processing in-process, but also can show the content that reduces single impurity benzoic acid, improves methyl benzoic acid's purity.

Background

According to the oxidation principle of the dimethylbenzene, products with sequentially deepened oxidation degrees such as methylbenzyl alcohol, methylbenzaldehyde, methylbenzoic acid, hydroxymethylbenzoic acid, carboxybenzaldehyde, phthalic acid and the like can be generated in the oxidation process of the dimethylbenzene, and the conversion rate of the dimethylbenzene is generally 20-40% in order to control the selectivity of the methylbenzoic acid product in actual production. Therefore, the above-mentioned products having different oxidation degrees are simultaneously present in the oxidation reaction liquid of xylene.

In order to obtain the main product methyl benzoic acid in the oxidation reaction liquid of the dimethylbenzene, according to the boiling point conditions of various substances, namely phthalic acid > carboxybenzaldehyde > methyl benzoic acid > methylbenzyl alcohol > methylbenzaldehyde > dimethylbenzaldehyde > dimethylbenzene, the oxidation reaction liquid is generally rectified industrially, components with boiling points lower than that of the methylbenzene acid are sequentially distilled out and recycled to an oxidation stage, and then the product methyl benzoic acid is distilled out.

In CN106831393A, the oxidation reaction liquid of m-xylene is directly distilled in a distillation still for 3-4 hours, the m-xylene which is not completely distilled out is recycled and recycled to an oxidation system for use, then the residue in the distillation still is intermittently rectified in a rectifying tower, the obtained front fraction with the boiling point lower than that of m-toluic acid is recycled to a reactor for continuous reaction, the m-toluic acid product is obtained by continuous rectification, in order to recover the m-toluic acid as much as possible, the temperature of the tower kettle is gradually increased to 285 ℃ in the later stage of rectification, and the rectification residue is obtained after the rectification is finished. The rectification residue is rectified at high temperature for a long time, and the content of aldehyde and alcohol in the reaction liquid is higher, so that a large amount of high-boiling-point ester formed by esterification of alcohol acid, high-boiling-point colored impurities formed by condensation of aldol and simple dimerization of aldehyde, high-boiling-point biphenyl compounds formed by decarboxylation coupling of carboxyl and the like and other high-boiling-point impurities exist in the rectification residue. According to the general knowledge of the technical personnel in the field, in the rectification process, the tower bottom is always kept to be completely dissolved, components with boiling points lower than that of methyl benzoic acid are sequentially evaporated out in the rectification process, the only solvent capable of dissolving high-boiling-point peroxidation impurities and high-boiling-point impurities generated by deep side reactions in the tower bottom liquid is the methyl benzoic acid product, when the methyl benzoic acid and the high-boiling-point impurities are separated by rectification, a part of the methyl benzoic acid as the solvent is left in the rectification residual liquid at the tower bottom and cannot be recovered, so that the loss of a part of the methyl benzoic acid product is caused, the product yield is low, the effective utilization rate of xylene is low, the content of the benzoic acid is increased due to the fact that the impurity benzoic acid directly generated in the oxidation process of the xylene is low, the decarboxylation and other side reactions in the rectification separation process are ignored, the influence of the benzoic acid on the quality of downstream products is considered to be small, and, The methyl benzyl alcohol and the benzoic acid have larger boiling point difference and are not suitable for separating a small amount of benzoic acid to increase energy consumption and the like, so that the content of the impurity benzoic acid in the product is too high due to the fact that no impurity benzoic acid is exported in the rectification process, and the purity of the product methyl benzoic acid cannot directly meet the requirement of products such as high-quality deet on the purity of raw materials.

CN105061187A replaces intermittent operation with continuous operation on the basis of CN106831393A, the heating time of the mixture to be separated is greatly shortened, various deep byproducts generated by chemical reaction of materials due to heating in the rectification process are obviously inhibited, the one-way yield can be improved to about 90%, according to the common sense of technicians in the field, the selectivity of the oxidation reaction of dimethylbenzene is strictly controlled when the product yield of 90% is achieved, and the consumption of methylbenzoic acid used as a solvent is reduced to the maximum extent in the rectification separation stage so as to reduce the loss of the methylbenzoic acid, so that the operation is complex and the potential safety hazard exists, the problem of the loss of the methylbenzoic acid product caused by using the methylbenzoic acid as the solvent when high-boiling-point impurities are separated is not effectively solved, and the problem of high content of the methylbenzoic acid impurity in the product is not solved.

CN107903165A utilizes a continuous production mode to carry out the oxidation of the dimethylbenzene, and a multi-stage series rectifying tower is adopted for separation and purification, the yield can reach 60-90%, the purity can reach 99% at most, but the reaction is stopped at one step of m-toluic acid through exploration conditions, although the loss of m-toluic acid is reduced to some extent, according to the general knowledge of those skilled in the art, in order to make the oxidation of m-xylene stay in the process of m-toluic acid, the conversion per pass of m-xylene is very low, generally not higher than 10%, thus, the treatment capacity of the oxidation process and the post-treatment process is increased, the overall investment cost is over high, and the formation of peroxide impurities cannot be completely avoided despite the low control of the conversion of xylene, in the post-treatment process, the oxidation reaction still needs to be rectified, and after gradual accumulation, the loss of the methyl benzoic acid caused by dissolving high-boiling-point peroxide impurities is still high. In addition, impurity benzoic acid can not be avoided in the process of multistage rectification, along with the continuous improvement of the downstream product quality requirement of the methyl benzoic acid, the purity of the raw material methyl benzoic acid is required, the content of single impurity benzoic acid is also limited, and the 99% raw material purity can not meet the requirement of high-quality mosquito-repellent amine products on the raw material.

In conclusion, the common technology of the existing treatment method of the xylene oxidation reaction liquid is direct rectification, and the common defects are that the loss of methyl benzoic acid is more, the yield of the product is low, the content of key impurities, namely benzoic acid, in the product is high, and the purity of the product is low in the treatment process of the oxidation reaction liquid.

Therefore, there is a need for a simple and suitable method and system for treating xylene oxidation reaction solution, which is both environmentally friendly and economical, so as to increase the product yield and improve the purity of methylbenzoic acid.

SUMMERY OF THE UTILITY MODEL

An object of the present exemplary embodiments is to solve the above and other disadvantages in the prior art.

The utility model discloses an aspect provides a system for handle xylol oxidation reaction liquid, the system includes:

a light ends removal system (a) having a first light ends removal unit (011), an oxidation reaction liquid (a1) inlet, a light components (a2) outlet containing xylene, methylbenzaldehyde and methylbenzyl alcohol, and a light ends removal mother liquid (a3) outlet;

a de-weighting system (B) having a first rectification device (021), an inlet for high boiling point solvent (c1), an inlet for light weight removal mother liquor (a3), an outlet for benzoic acid (B1), an outlet for methylbenzoic acid (B2), and an outlet for heavy components (B3), wherein the inlet for high boiling point solvent (c1) introduces high boiling point solvent (c1) into the de-weighting system (B).

In an embodiment of the present invention, the light-weight removal system (B) further comprises a second rectification device (022), wherein the first rectification device (021) separates the byproduct impurity benzoic acid in the light-weight removal mother liquor before introducing the high boiling point solvent (c1) into the second rectification device (022).

In an embodiment of the present invention, the lightness-removing system (a) further comprises a second lightness-removing unit (012), wherein the first lightness-removing unit (011) separates a light component containing xylene, and the second lightness-removing unit (012) separates a light component containing methylbenzaldehyde and methylbenzyl alcohol.

In an embodiment of the present invention, the lightness-removing system (a) further comprises a second lightness-removing unit (012) and a third lightness-removing unit (013), wherein the first lightness-removing unit (011) separates a light component containing xylene, the second lightness-removing unit (012) separates a light component containing methylbenzaldehyde, and the third lightness-removing unit (013) separates a light component containing methylbenzyl alcohol.

The utility model discloses another aspect provides a system for handle xylol oxidation reaction liquid, the system includes:

a light component removal system (A) having a first light component removal unit (011), an oxidation reaction liquid (a1) inlet, a light component (a4) outlet containing xylene, and a light component removal mother liquid (a10) outlet;

a heavies removal system (B) having a first rectification apparatus (021), a second rectification apparatus (022), a third rectification apparatus (023), an inlet for a high boiling point solvent (c1), an inlet for a light-ends removal mother liquor (a10), an outlet for benzoic acid (B1), an outlet for methylbenzoic acid (B2), an outlet for heavy components (B3), an outlet for an intermediate component (B6) comprising methylbenzaldehyde and methylbenzyl alcohol, and an outlet for a refined raffinate (B8),

wherein the high boiling point solvent (c1) inlet introduces the high boiling point solvent (c1) into the first rectification means (021);

a first rectification means (021) separates the heavy fraction (b 3);

a second rectification means (022) separating an intermediate component (b6) comprising methylbenzaldehyde and methylbenzyl alcohol;

the third rectifying unit (023) separates benzoic acid (b1) and refined raffinate (b8) to obtain methyl benzoic acid (b 2).

In the embodiment of the utility model, the weight-removing system (B) also comprises a fourth rectifying device (024),

wherein, the third rectifying device (023) separates benzoic acid (b1), the fourth rectifying device (024) separates refined raffinate (b8), and the product of methyl benzoic acid (b2) is obtained; or

The second rectification apparatus (022) separates an intermediate component (b10) comprising methylbenzaldehyde, the third rectification apparatus (023) separates an intermediate component (b11) comprising methylbenzyl alcohol, and the fourth rectification apparatus (024) separates benzoic acid (b1) and a refined raffinate (b8) to obtain a product methylbenzoic acid (b 2).

In an embodiment of the present invention, the de-weighting system (B) further comprises a fifth rectification apparatus (025), wherein the second rectification apparatus (022) separates the intermediate component (B10) comprising methylbenzaldehyde, the third rectification apparatus (023) separates the intermediate component (B11) comprising methylbenzyl alcohol, the fourth rectification apparatus (024) separates benzoic acid (B1), and the fifth rectification apparatus (025) separates the refined raffinate (B8) to obtain methyl benzoic acid (B2) as a product.

In an embodiment of the present invention, the lightness-removing system (a) comprises one or more distillation apparatuses and/or rectification apparatuses; and said de-weighting system (B) comprises one or more distillation units and/or rectification units.

In the embodiment of the utility model, the outlet of the light component is positioned at the top of each lightness removing unit, and the outlet of the lightness removing mother liquor is positioned at the bottom of the lightness removing unit;

the outlet of the middle component is positioned at the top of each rectifying device, and the outlet of the heavy component and the outlet of the refined residual liquid are positioned at the bottom of each distilling device and/or rectifying device; and

the outlet of the benzoic acid is positioned at the top of the corresponding rectifying device, and the outlet of the methyl benzoic acid is positioned at the top or the middle upper part of the corresponding rectifying device; and

the inlet of the high boiling point solvent is positioned at the middle lower part of the corresponding rectifying device.

In an embodiment of the present invention, the boiling point of the high boiling point solvent is 270-.

The utility model discloses in, adopt to take off light operation and take off heavy operation to introduce high boiling point solvent and regard as the solvent with replacing methylbenzoic acid in taking off heavy system, thereby dissolve the high boiling point impurity that the boiling point is higher than methylbenzoic acid, guarantee to wait to separate the material and be liquid state, thereby reduce the loss as the methylbenzoic acid of product, improve the product yield, avoid simply reducing the potential safety hazard that the loss volume of methylbenzoic acid caused through improving separation temperature. Moreover, the utility model discloses set up impurity benzoic acid export in the processing system of xylol oxidation reaction liquid, got rid of impurity benzoic acid in taking off heavy operation, improved the purity of product methyl benzoic acid. Compared with the prior art, the utility model discloses the content of most core single impurity benzoic acid can reduce to below 0.5 wt% in the methyl benzoic acid product, and methyl benzoic acid product purity is not less than 99 wt%.

Drawings

The present invention may be better understood by describing exemplary embodiments thereof in conjunction with the accompanying drawings. In the drawings, there is shown in the drawings,

FIG. 1 is a schematic diagram showing a system for treating a reaction solution for oxidizing xylene according to an embodiment of the present invention.

Fig. 2 is a schematic view showing a system for treating a reaction liquid for oxidizing xylene according to another embodiment of the present invention.

Fig. 3 is a schematic view showing a system for treating the reaction liquid for oxidizing xylene according to another embodiment of the present invention.

Fig. 4 is a schematic view showing a system for treating the reaction liquid for oxidizing xylene according to another embodiment of the present invention.

Fig. 5 is a schematic view showing a system for treating the reaction liquid for oxidizing xylene according to another embodiment of the present invention.

Fig. 6 is a schematic view showing a system for treating the reaction liquid for oxidizing xylene according to another embodiment of the present invention.

Fig. 7 is a schematic view showing a system for treating the reaction liquid for oxidizing xylene according to another embodiment of the present invention.

Fig. 8 is a schematic view showing a system for treating the reaction liquid for oxidizing xylene according to another embodiment of the present invention.

Fig. 9 is a schematic view showing a system for treating the reaction liquid for oxidizing xylene according to another embodiment of the present invention.

Fig. 10 is a schematic view showing a system for treating the reaction liquid for oxidizing xylene according to another embodiment of the present invention.

Wherein the reference numerals are explained below.

A, a light component removal system; b: a de-weighting system; 011: a first lightness-removing unit; 012: a second lightness-removing unit; 013: a third light component removal unit; 021: a first rectification device; 022: a second rectification device; 023: a third rectifying device; 024: a fourth rectifying unit; 025: a fifth rectifying device; a 1: oxidizing the reaction solution; a 2: a light component comprising xylene, methylbenzaldehyde and methylbenzyl alcohol; a 3: removing light mother liquor; a 4: a light fraction comprising xylene; a 5: a light component comprising methylbenzaldehyde and methylbenzyl alcohol; a 6: a component comprising methylbenzaldehyde and methylbenzyl alcohol; a 7: a light component comprising methylbenzaldehyde; a 8: a light component comprising methylbenzyl alcohol; a 9: a component comprising methylbenzyl alcohol; b 1: benzoic acid as an impurity; b 2: methyl benzoic acid; b 3: heavy components; b 4: removing components of benzoic acid in advance; b 5: removing heavy mother liquor; b 6: an intermediate component comprising methylbenzaldehyde and methylbenzyl alcohol; b 7: rectifying the mother liquor; b 8: refining residual liquid; b 9: removing components of benzoic acid and heavy components in advance; b 10: an intermediate component comprising methylbenzaldehyde; b 11: an intermediate component comprising methylbenzyl alcohol; b 12: a component having a boiling point higher than that of tolualdehyde; and c 1: a high boiling point solvent.

Detailed Description

The present invention will be described more fully hereinafter with reference to exemplary embodiments thereof. These exemplary embodiments are described so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. Indeed, the invention may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; moreover, these embodiments are provided so that this disclosure will satisfy applicable legal requirements.

In addition, in case of conflict, the technical features presented in the detailed description of the present application can be combined with each other to form a complete technical solution and fall within the scope of the present disclosure.

In the present invention, the manner of connection between the various systems/devices should be understood in a broad sense unless otherwise expressly stated or limited. For example, the connection may be a direct pipe connection, or a pipe connection connected with a pumping device, a metering device, a valve pipe fitting, or other conventional conveying, metering, and control devices, or may be a fixed connection or a 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.

In the present invention, the term "product yield" is defined as follows:

the product yield is (amount of the isolated methyl benzoic acid substance + amount of the isolated methyl benzaldehyde substance + amount of the isolated methyl benzyl alcohol)/(amount of the methyl benzoic acid substance in the oxidation reaction liquid + amount of the methyl benzaldehyde substance in the oxidation reaction liquid + amount of the methyl benzyl alcohol substance in the oxidation reaction liquid + amount of the m-carboxybenzaldehyde substance in the oxidation reaction liquid + amount of the benzoic acid substance in the oxidation reaction liquid + amount of the phthalic acid substance in the oxidation reaction liquid).

In the present invention, the term "limit yield" is a theoretical yield calculated according to the content of the product in the oxidation reaction liquid detected in the liquid phase, that is, a yield calculated under the condition that the product has no quality loss in the process of treating the oxidation reaction liquid.

The ultimate yield is (amount of methyl benzoic acid substance + amount of methyl benzaldehyde substance + amount of methyl benzyl alcohol)/(amount of methyl benzoic acid substance + amount of methyl benzaldehyde substance + amount of methyl benzyl alcohol substance + amount of m-carboxybenzaldehyde substance + amount of benzoic acid substance + amount of phthalic acid substance).

At present, it is known that an oxidation reaction solution of xylene contains an intermediate product such as methylbenzyl alcohol, methylbenzaldehyde, etc., an over-oxidized product such as hydroxymethylbenzoic acid, carboxybenzaldehyde, and phthalic acid, and benzoic acid produced by decarboxylation of a compound containing a carboxyl group on a benzene ring by heating. Generally, the target methyl benzoic acid can be obtained by separating and treating the oxidation reaction liquid of the dimethylbenzene by a rectification mode according to the boiling point condition of each substance.

Taking the oxidation of m-xylene as an example, the main byproducts generated in the oxidation process and the boiling points (from high to low) of the raw materials of m-xylene and m-toluic acid are as follows: isophthalic acid, m-carboxybenzaldehyde, m-methylbenzoic acid, benzoic acid, m-methylbenzyl alcohol, m-methylbenzaldehyde and m-xylene. According to the boiling point condition of each substance, a person skilled in the art can separate and treat the oxidation reaction liquid of the m-xylene by a rectification mode to obtain the target product m-toluic acid.

Xylene oxidation reaction liquid

In the present invention, the xylene oxidation reaction liquid is derived from an oxidation reaction using xylene. In order to control the selectivity of the desired product methylbenzoic acid, the oxidation reaction must be left in the intermediate reaction step, which results in xylene conversions generally not exceeding 40%. Thus, 60 to 70% of the xylene is left in the oxidation reaction liquid without participating in the oxidation reaction. Further, a large amount of intermediate products, such as benzoic acid, methylbenzyl alcohol, methylbenzaldehyde, and phthalic acid and carboxybenzaldehyde, which are impurities by-produced from oxidation, are inevitably produced during the oxidation of xylene. Therefore, the oxidation reaction liquid of the present invention contains xylene, methylbenzaldehyde, methylbenzyl alcohol, methylbenzoic acid, carboxybenzaldehyde, benzoic acid, and phthalic acid, or substantially consists of xylene, methylbenzaldehyde, methylbenzyl alcohol, methylbenzoic acid, carboxybenzaldehyde, benzoic acid, and phthalic acid.

The xylene suitable for use in the process of the present invention may be ortho-xylene or meta-xylene depending on whether the final desired product is ortho-or meta-toluic acid. Therefore, when the xylene is o-xylene, the oxidation reaction liquid includes o-xylene, o-methylbenzaldehyde, o-methylbenzyl alcohol, o-methylbenzoic acid, o-carboxybenzaldehyde, benzoic acid, and phthalic acid; when the xylene is m-xylene, the oxidation reaction liquid includes m-xylene, m-methylbenzaldehyde, m-methylbenzyl alcohol, m-methylbenzoic acid, m-carboxybenzaldehyde, benzoic acid, and isophthalic acid.

Lightness removing operation

In the utility model, it is right to carry out the lightness removing operation on the oxidation reaction liquid to obtain light components and lightness removing mother liquid. In one embodiment of the present invention, the light component removal operation is to separate xylene, methylbenzaldehyde, methylbenzyl alcohol, and the like (light components) that do not participate in the oxidation reaction solution, to obtain a light component removal mother liquor, and the light component removal mother liquor contains by-product impurities such as methyl benzoic acid, phthalic acid, and carboxybenzaldehyde, which are target products.

In another embodiment of the present invention, the light component removal operation is to separate the xylene (light component) that does not participate in the oxidation reaction from the oxidation reaction solution to obtain a light component removal mother solution, and the light component removal mother solution contains methyl benzoic acid, and by-product impurities such as methyl benzaldehyde, methyl benzyl alcohol, benzoic acid, phthalic acid, and carboxybenzaldehyde.

The equipment (including the number of tower plates, etc.), the operation temperature and/or the operation pressure, etc. suitable for the light component removing operation of the utility model have no special requirements per se. The equipment for the light ends removal operation may be conventional distillation (including flash) or rectification equipment as is known in the art. Generally, the operation temperature and/or the operation pressure are determined depending on the components xylene, methylbenzaldehyde, methylbenzyl alcohol and the like to be separated and the distillation and/or rectification apparatus selected. In some embodiments, the equipment, operating temperature, and/or operating pressure used for the present invention lightness-removal operations can be determined by simulation with various industrial software (e.g., Aspen Plus available from AspenTech corporation).

Meanwhile, the equipment for the lightness-removing operation, the operation temperature and/or the operation pressure, etc. may be selected so as to have as little influence as possible on the mother liquor for lightness-removing while separating the raw materials xylene, methylbenzaldehyde and methylbenzyl alcohol from the oxidation reaction liquid.

In one embodiment of the present invention, the light component removal system used in the light component removal operation comprises a conventional distillation apparatus, a flash distillation apparatus and/or a rectification apparatus. The main equipment of the distillation device is any combination of equipment with simple distillation operation function and a distiller; the main equipment of the flash evaporation device is a flash evaporation tower; the main equipment of the rectifying device is a rectifying tower. And the distillation device and/or the rectification device respectively comprise conventional auxiliary equipment matched with the distillation device and/or the rectification device, and the conventional auxiliary equipment comprises a preheater, a condenser, a collecting tank and the like.

In the light component removing system of the present invention, the material having a boiling point not higher than xylene, methylbenzaldehyde or methylbenzyl alcohol in the oxidation reaction liquid is vaporized and concentrated on the top of the main body of the distillation apparatus and/or the rectification apparatus to form a light component. And the substances with the boiling point higher than that of the methylbenzyl alcohol are enriched at the bottom of the main body equipment to form light-weight-removing mother liquor containing the target product methyl benzoic acid, and the impurities of benzoic acid, phthalic acid, carboxybenzaldehyde and high-boiling-point peroxidation byproducts. The light components are discharged from the light component removal system, and preferably, the light components can be recycled to the oxidation system. The light weight removal mother liquor is transferred to a subsequent heavy weight removal system through a transfer system such as a pipeline.

In a particular embodiment of the present invention, the lightness-removing operation is carried out in an apparatus selected from a tank distillation apparatus and/or a column rectification apparatus.

In a specific embodiment of the present invention, the light fraction mainly comprising xylene methylbenzaldehyde and/or methylbenzyl alcohol obtained by the light removal operation can be recovered, and it is necessary to use the light fraction for the oxidation reaction of xylene, thereby improving the utilization rate of xylene.

Removal of heavy material I

The utility model discloses in, it is right take off light mother liquor and take off heavy operation, obtain heavy component, byproduct impurity benzoic acid and the target product methyl benzoic acid that contains phthalic acid and carboxybenzaldehyde. In one embodiment of the present invention, the light component removing mother liquor mainly comprises methyl benzoic acid, phthalic acid, and carboxybenzaldehyde. The main purpose of the heavy component removal operation of the utility model is to separate the components (such as benzene dicarboxylic acid, carboxybenzaldehyde and other high boiling point peroxidation byproduct impurities) with boiling points higher than methyl benzoic acid in the light component removal mother liquor from the light component removal mother liquor, and obtain the heavy component mainly comprising benzene dicarboxylic acid, carboxybenzaldehyde and the like, impurity benzoic acid and product methyl benzoic acid respectively.

The utility model discloses in, adopt and take off heavy system to the mother liquor that takes off light that obtains through taking off light system processing and carry out the separation processing, obtain heavy ends, benzoic acid and methyl benzoic acid. The high boiling point solvent is introduced into the de-weighting system to replace the methyl benzoic acid as the solvent, so that the high boiling point impurities with the boiling point higher than that of the methyl benzoic acid are dissolved, the substance to be separated is ensured to be in a liquid state, the loss of the methyl benzoic acid as a product is reduced, the product yield is improved, and the potential safety hazard caused by reducing the loss of the methyl benzoic acid by simply increasing the separation temperature is avoided.

The equipment (including the number of tower plates, etc.), the operation temperature and/or the operation pressure, etc. suitable for the heavy-duty operation of the utility model have no special requirements per se. The equipment used for the de-weighting operation may be conventional distillation or rectification equipment known in the art. Generally, the operating temperature and/or operating pressure are determined in accordance with the components to be separated (e.g., high boiling peroxide by-product impurities such as phthalic acid, carboxybenzaldehyde, and benzoic acid) and the distillation and/or rectification apparatus selected. In some embodiments, the equipment, operating temperature, and/or operating pressure used in the de-duplication operations of the present invention may be determined by simulation with various industrial software (e.g., Aspen Plus available from AspenTech, inc.).

In one embodiment of the present invention, the de-weighting system comprises a distillation apparatus and/or a rectification apparatus. The main apparatus of the distillation apparatus may be any combination of apparatuses having a function of simple distillation operation (i.e., a distiller). The main body equipment of the rectification apparatus may include a rectification column. The distillation device and/or the rectification device comprises matched conventional auxiliary equipment, including a heater, a condenser, a collecting tank and the like.

The utility model discloses an in taking off heavy system, take off the material of light mother liquor boiling point not higher than methyl benzoic acid and take place the vaporization, enrich the top to distillation plant and/or the main part equipment of rectifier unit, form impurity benzoic acid. And the substances with the boiling point higher than that of the methyl benzoic acid in the light component removal mother liquor are enriched at the bottom of the main body equipment to form heavy components. The methyl benzoic acid product is enriched to the middle upper part of the main body equipment, and is led out of the main body equipment.

As mentioned above, the introduction of the high-boiling solvent ensures that the heavy components remain in the liquid state at the bottom of the main apparatus of the distillation apparatus and/or rectification apparatus during the de-weighting operation. Therefore, the heavy components obtained by the rectification operation in the above-mentioned de-heavy step contain a high-boiling solvent in addition to substances having a boiling point higher than that of methylbenzoic acid.

In the present invention, the high boiling point solvent is a solvent having a boiling point higher than that of methylbenzoic acid but lower than that of carboxybenzaldehyde under normal pressure. In a specific embodiment, the boiling point range of the high boiling point solvent is 270-. In particular embodiments, the high boiling solvent includes, but is not limited to, dimethyl isophthalate, diethyl phthalate, dimethyl terephthalate, diethyl isophthalate, dibutyl tartrate, dibutyl maleate, or combinations thereof.

Removal of weight II

In another embodiment of the present invention, the light removal mother liquor mainly comprises methyl benzoic acid, methyl benzaldehyde, methyl benzyl alcohol, benzoic acid, phthalic acid, and carboxybenzaldehyde. The main purpose of the heavy component removal operation of the present invention is to separate the components (e.g., high boiling point peroxidation byproduct impurities such as phthalic acid and carboxybenzaldehyde) with boiling points higher than that of methylbenzoic acid in the light component removal mother liquor from the light component removal mother liquor, and to obtain heavy components mainly including phthalic acid and carboxybenzaldehyde and heavy component removal mainly including methylbenzaldehyde, methylbenzyl alcohol, benzoic acid and methylbenzoic acid.

Rectification of

In the utility model, the heavy and light components are removed and rectified to obtain intermediate components and rectification mother liquor. The rectification is used for separating the heavy and light components, the intermediate components comprise methylbenzyl alcohol and methylbenzaldehyde with boiling points lower than that of benzoic acid and methylbenzoic acid, and the rectification mother liquor comprises benzoic acid and a target product of methylbenzoic acid.

The utility model discloses in, the purpose of rectification is before obtaining high-purity methylbenzoic acid, separates out methylbenzaldehyde and methyl benzyl alcohol earlier, avoids by-product impurity such as alcohol, aldehyde to be heated for a long time in production system and generates the high boiling point by-product impurity that is difficult to the separation and recovery, improves the utilization ratio of xylol, reduces the content of alcohol, aldehyde in the methylbenzoic acid simultaneously, improves the purity of methylbenzoic acid.

The utility model discloses in, the main part equipment that is used for the rectifier unit of rectification is rectifying column and supporting conventional auxiliary assembly, including reboiler, condenser, holding vessel etc..

In the rectifying device, substances with boiling points lower than that of benzoic acid in the heavy and light components are evaporated and concentrated to the top of a rectifying tower to form an intermediate component containing methyl benzyl alcohol and methyl benzaldehyde. And the substances with the boiling point not lower than that of the benzoic acid are enriched to the bottom of the rectifying tower to form a rectifying mother liquor containing the benzoic acid and the target product methyl benzoic acid.

The equipment (including the number of the tower plates, etc.), the operation temperature and/or the operation pressure, etc. which are suitable for the rectification step of the utility model have no special requirements per se. The equipment used for the rectification step may be conventional rectification equipment known in the art. Generally, the operating temperature and/or operating pressure are determined according to the components to be separated (methylbenzyl alcohol and methylbenzaldehyde) and the rectification apparatus selected. In some embodiments, the equipment, operating temperature and/or operating pressure used in the rectification step of the present invention may be simulated by various industrial software, such as determined by the Aspen Plus software available from AspenTech corporation.

In one embodiment of the present invention, the intermediate component can be recycled to the oxidation reaction system of xylene, thereby improving the utilization of xylene participating in the oxidation reaction.

In another embodiment of the present invention, the intermediate component comprises mainly methylbenzyl alcohol and methylbenzaldehyde, and is available for further oxidation to form methylbenzoic acid. In an embodiment of the present invention, the intermediate component can be circulated back to the oxidation reaction of xylene, and continuously participate in the oxidation reaction, thereby improving the utilization rate of xylene participating in the oxidation reaction and the yield of methyl benzoic acid, and reducing the amount of waste treatment.

II.b. refining

The utility model discloses in, it is used for separating the rectification mother liquor into product methyl benzoic acid, by-product impurity and refined raffinate respectively to refine, and wherein, the by-product impurity mainly contains benzoic acid, and refined raffinate then contains high boiling solvent.

In the present invention, the refining system includes a rectifying device. The main equipment of the rectifying device comprises a rectifying tower and matched conventional auxiliary equipment, including a reboiler, a condenser, a collecting tank and the like.

In a rectifying device/a rectifying tower of the refining system, substances with boiling points lower than that of the methyl benzoic acid, substances with boiling points higher than that of the methyl benzoic acid and the methyl benzoic acid in the rectifying mother liquor are separated. At the top of the rectifying apparatus/rectifying column, by-product impurities whose main component is benzoic acid are formed, at the bottom of the rectifying apparatus/rectifying column, a refined raffinate containing high-boiling impurities is formed, and at the middle upper position (not the top) of the rectifying apparatus/rectifying column, the objective product methylbenzoic acid is formed.

In one embodiment of the present invention, the rectification apparatus of the refining system comprises a refining column, wherein the byproduct impurity outlet is located at the top of the refining column, the target methyl benzoic acid outlet is located at the middle upper part of the refining column, and the refined raffinate outlet is located at the bottom of the refining column.

In another embodiment of the present invention, the rectification apparatus of the refining system comprises a plurality of stages of refining towers, wherein the outlet of the byproduct impurities is located at the top of the first refining tower, the outlet of the target product methylbenzoic acid is located at the top or the middle upper part of the last refining tower, and the outlet of the refined residual liquid is located at the bottom of the last refining tower. In a preferred embodiment of the present invention, the rectifying apparatus of the refining system comprises a first refining tower and a second refining tower, wherein the byproduct impurity outlet is located at the top of the first refining tower, the target methyl benzoic acid outlet is located at the top or middle upper portion of the second refining tower, and the refined raffinate outlet is located at the bottom of the second refining tower.

The equipment (including the number of plates, etc.), the operating temperature and/or the operating pressure, etc. suitable for the refining step of the present invention have no particular requirements per se. The equipment used for the refining step may be conventional rectification equipment known in the art. Generally, the operating temperature and/or operating pressure are determined depending on the component to be separated (benzoic acid) and the rectification apparatus selected. In some embodiments, the equipment, operating temperature and/or operating pressure used in the refining step of the present invention can be determined by various industrial software simulations, such as by AspenPlus.

Method for treating xylene oxidation reaction liquid

As shown in fig. 1, the method for treating a reaction solution for oxidizing xylene according to the present invention comprises:

in the first lightness-removing unit 011, for example, the oxidation reaction liquid a1 is subjected to lightness-removing operation to separate a light component a2 containing xylene, methylbenzaldehyde and methylbenzyl alcohol to form lightness-removing mother liquid a 3; wherein a light component a2 containing xylene, methylbenzaldehyde and methylbenzyl alcohol is led out from the top of the first lightness-removing unit 011, and a mother liquor a3 for lightness removal is led out from the bottom of the first lightness-removing unit 011; and

carrying out a heavy component removal operation on the light component removal mother liquor a3 by introducing a high-boiling point solvent c1, and separating a heavy component b3 containing phthalic acid and carboxybenzaldehyde and a byproduct impurity benzoic acid b1 to obtain a target product methylbenzoic acid b 2; wherein the byproduct impurity benzoic acid b1 is led out from the top of the first rectification device 021, the target product methylbenzoic acid b2 is led out from the middle upper part of the first rectification device 021, and the heavy component b3 is led out from the bottom of the first rectification device 021.

In a specific embodiment of the present invention, as shown in fig. 2, before the high boiling point solvent c1 is introduced into the second rectification apparatus 022, the byproduct impurity benzoic acid b1 in the light component removal mother liquor a3 is separated in the first rectification apparatus 021 to form a component b4 from which benzoic acid is removed in advance. Wherein the byproduct impurity benzoic acid b1 is led out from the top of the first rectification device 021, the target product methylbenzoic acid b2 is led out from the top of the second rectification device 022, and the heavy component b3 is led out from the bottom of the second rectification device 022.

In one embodiment of the present invention, as shown in fig. 3 and 4, in the first lightness-removing unit 011, the oxidation reaction liquid a1 is subjected to a lightness-removing operation to separate a light component a4 containing xylene to form a component a6 containing methylbenzaldehyde and methylbenzyl alcohol, and then in the second lightness-removing unit 012, the component a6 is subjected to a lightness-removing operation to separate a light component a5 containing methylbenzaldehyde and methylbenzyl alcohol to form a lightness-removing mother liquid a 3; wherein a light fraction a4 containing xylene is drawn from the top of the first lightness-removing unit 011, a light fraction a5 containing methylbenzaldehyde and methylbenzyl alcohol is drawn from the top of the second lightness-removing unit 012, and the mother liquid a3 for lightness removal is drawn from the bottom of the second lightness-removing unit 012.

In one embodiment of the present invention, as shown in fig. 5 and 6, in the first lightness-removing unit 011, the oxidation reaction liquid a1 is subjected to a lightness-removing operation to separate a light component a4 containing xylene to form a component a6 containing methylbenzaldehyde and methylbenzyl alcohol, and then in the second lightness-removing unit 012, the component a6 is subjected to a lightness-removing operation to separate a light component a7 containing methylbenzaldehyde to form a component a9 containing methylbenzyl alcohol, and then in the third lightness-removing unit 013, the component a9 containing methylbenzyl alcohol is subjected to a lightness-removing operation to separate a light component a8 containing methylbenzyl alcohol to form a lightness-removing mother liquid a 3; wherein a light component a4 containing xylene is led out from the top of the first lightness-removing unit 011, a light component a7 containing methylbenzaldehyde is led out from the top of the second lightness-removing unit 012, a light component a8 containing methylbenzyl alcohol is led out from the top of the third lightness-removing unit 013, and a mother liquor a3 for lightness removal is led out from the bottom of the third lightness-removing unit 013.

As shown in fig. 7, the method for treating the reaction solution for oxidizing xylene according to the present invention comprises:

in the first lightness-removing unit 011, for example, the oxidation reaction liquid a1 is subjected to lightness-removing operation to separate a light component a4 containing xylene to form a lightness-removing mother liquid a 10; wherein a light component a4 containing xylene is led out from the top of the first lightness-removing unit 011, and the lightness-removing mother liquor a10 is led out from the bottom of the first lightness-removing unit 011; and

in a first rectification means 021, the light weight removal mother liquor a10 is subjected to a heavy weight removal operation by introducing a high boiling point solvent c1, and a heavy component b3 containing phthalic acid and carboxybenzaldehyde is separated to form heavy weight removal mother liquor b 5; wherein the heavy component removal mother liquor b5 is led out from the top of the first rectification device 021, and the heavy component b3 is led out from the bottom of the first rectification device 021;

rectifying the heavy component-removed mother liquor b5 in a second rectifying device 022 to separate an intermediate component b6 containing methylbenzaldehyde and methylbenzyl alcohol to form a rectified mother liquor b 7; wherein an intermediate component b6 comprising methylbenzaldehyde and methylbenzyl alcohol is led out from the top of the second rectification device 022, and the heavy component b3 is led out from the bottom of the second rectification device 022;

refining the rectification mother liquor b7 in a third rectification device 023, separating benzoic acid b1 and refined raffinate b8 to obtain a target product, namely methyl benzoic acid b 2; wherein the by-product impurity benzoic acid b1 is drawn from the top of the third rectification apparatus 023, the target product methylbenzoic acid b2 is drawn from the middle upper part of the third rectification apparatus 023, and the refined raffinate b8 is drawn from the bottom of the third rectification apparatus 023.

In a specific embodiment of the present invention, as shown in fig. 8, in the third distillation apparatus 023, the distillation mother liquor is first refined to separate benzoic acid b1 to form a component b9 which is removed benzoic acid and heavy components in advance, then the component b9 is refined to a second time to separate refined raffinate b8 to obtain methyl benzoic acid b2 as a target product.

In one embodiment of the present invention, as shown in fig. 9 and 10, the de-heavy mother liquor b5 is first rectified once in the second rectifying device 022 to separate the intermediate component b10 containing methylbenzaldehyde, and then rectified twice in the third rectifying device 023 to separate the intermediate component b11 containing methylbenzyl alcohol, and finally to form the rectified mother liquor b 7. Then, in a fourth rectifying device 024, refining the rectifying mother liquor b7, separating benzoic acid b1 and refined raffinate b8 to obtain a target product methyl benzoic acid b 2; wherein the by-product impurity benzoic acid b1 is extracted from the top of the fourth rectifying device 024, the target product methylbenzoic acid b2 is extracted from the middle upper part of the fourth rectifying device 024, and the refined raffinate b8 is extracted from the bottom of the fourth rectifying device 024. Or, in a fourth rectifying device 024, refining the rectifying mother liquor b7, separating benzoic acid b1, and forming a component b9 with benzoic acid and heavy components removed in advance; then refining the component b9 in a fifth rectifying device 025, and separating refined raffinate b8 to obtain a target product methyl benzoic acid b 2; wherein the by-product impurity benzoic acid b1 is led out from the top of a fourth rectification device 024, the target product methylbenzoic acid b2 is led out from the top of a fifth rectification device 025, and the refined raffinate b8 is led out from the bottom of the fifth rectification device 025.

In one embodiment of the present invention, the light fraction a2 containing xylene, methylbenzaldehyde and methylbenzyl alcohol, the light fraction a4 containing xylene, the light fraction a5 containing methylbenzaldehyde and methylbenzyl alcohol, the light fraction a7 containing methylbenzaldehyde, and the light fraction a8 containing methylbenzyl alcohol, which are obtained in the light removal operation, can be returned to the oxidation reaction of xylene, thereby reducing the amount of waste and improving the yield of methyl benzoic acid as a product.

In one embodiment of the present invention, the intermediate component b6 containing methylbenzaldehyde and methylbenzyl alcohol, the intermediate component b10 containing methylbenzaldehyde, and the intermediate component b11 containing methylbenzyl alcohol obtained in the weight removal operation can be returned to the oxidation reaction of xylene, thereby reducing the amount of waste and improving the yield of methylbenzoic acid as a product.

Apparatus and system

In one embodiment of the present invention, the light removal system and the heavy removal system may both be a distillation apparatus/distiller. In another embodiment of the present invention, the light ends removal system is a distillation apparatus and the heavy ends removal system is a rectification apparatus. In another embodiment of the present invention, the light component removal system is a distillation apparatus, and the heavy component removal system is a combination of a distillation apparatus and a rectification apparatus. In another embodiment of the present invention, the light component removal system is a distillation apparatus and the heavy component removal system is a rectification apparatus. In another embodiment of the present invention, the light removal system and the heavy removal system may both be a rectification apparatus/rectifier. In another embodiment of the present invention, the light component removal system is a distillation apparatus, and the heavy component removal system is a combination of a distillation apparatus and a distillation apparatus. In another embodiment of the present invention, the light component removal system is a combination of a distillation apparatus and a rectification apparatus, and the heavy component removal system is a distillation apparatus. In another embodiment of the present invention, the light component removal system is a combination of a distillation apparatus and a rectification apparatus, and the heavy component removal system is a rectification apparatus. In another embodiment of the present invention, the light component removal system is a combination of a distillation apparatus and a rectification apparatus, and the heavy component removal system is a combination of a distillation apparatus and a rectification apparatus.

In one embodiment of the present invention, the light component removal system comprises a first light component removal unit, wherein the main component of the light component is xylene.

In another embodiment of the present invention, the lightness-removing system comprises a first lightness-removing unit in which the main components of the light component are xylene, methylbenzaldehyde and methylbenzyl alcohol; wherein, the methyl benzaldehyde is m-methyl benzaldehyde or o-methyl benzaldehyde, and the methyl benzyl alcohol is m-methyl benzyl alcohol or o-methyl benzyl alcohol.

In an embodiment of the present invention, the lightness-removing system further includes a second lightness-removing unit, wherein the first lightness-removing unit has a first lightness-removing outlet and a first lightness-removing outlet, the second lightness-removing unit has a first lightness-removing inlet and a second lightness-removing outlet, the first lightness-removing outlet of the first lightness-removing unit is connected to the first lightness-removing inlet of the second lightness-removing unit, a main component of the first lightness-removing unit is xylene, and a main component of the second lightness-removing unit is tolualdehyde and methylbenzyl alcohol;

the utility model discloses an in an embodiment, take off light system and still include that the second takes off light unit and third and take off light unit, wherein first taking off light unit has first light component export and the export of first light mother liquor of taking off, the second takes off light unit has the import of first light mother liquor of taking off, the export of second light mother liquor, the third takes off light unit has the export of third light component, the export of third light mother liquor of taking off, the import of second light mother liquor, the export of first light mother liquor of taking off light unit with the import of first light mother liquor of taking off of second light unit links to each other, the export of second light mother liquor of taking off light unit of second takes off light mother liquor and the import of second light mother liquor of third light unit to link to each other, the principal component of first light component is xylol, the principal component of second light component is methylbenzaldehyde, the principal component of third light component is methylbenzyl alcohol.

In the present invention, it should be noted that, unless explicitly specified or limited, the connection mode between the systems should be understood in a broad sense, for example, the connection mode may be a direct pipe connection, a pipe connection through a conventional transportation, measurement and control device such as a pumping device, a metering device, a valve pipe, etc., a fixed connection, or a 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.

The utility model discloses an in one embodiment, take off heavy system and include one or more rectifying column, the export of impurity benzoic acid is located the rectifying column top, the export of methyl benzoic acid is located the well upper portion of rectifying column, high boiling point solvent import is located the well lower part of rectifying column, heavy component export is located the bottom of rectifying column.

The utility model discloses an in the embodiment, take off heavy system and include first rectifying column and second rectifying column, the export of impurity benzoic acid is located the top of first rectifying column, the export of methyl benzoic acid is located the top of second rectifying column, high boiling point solvent import is located the well lower part of first rectifying column or second rectifying column, the heavy ends export is located the bottom of second rectifying column.

The utility model discloses an in an embodiment, heavy system of taking off includes first rectifying column, second rectifying column, third rectifying column, the export of impurity benzoic acid is located the top of third rectifying column, the export of methylbenzoic acid is located the well upper portion of third rectifying column, high boiling point solvent import is located the well lower part of first rectifying column, the heavy ends export is located the bottom of first rectifying column, the second rectifying column has the export of retrieving the component, it includes methylbenzaldehyde and methyl benzyl alcohol to retrieve the component.

The utility model discloses an in an embodiment, heavy system of taking off includes first rectifying column, second rectifying column, third rectifying column, fourth rectifying column, the export of impurity benzoic acid is located the top of third rectifying column, the export of methylbenzoic acid is located the top of fourth rectifying column, high boiling point solvent import is located the well lower part of first rectifying column, the heavy ends export is located the bottom of first rectifying column, the second rectifying column has the export of retrieving the component, it includes methylbenzaldehyde and methyl benzyl alcohol to retrieve the component.

The utility model discloses an in an embodiment, heavy system of taking off includes first rectifying column, second rectifying column, third rectifying column, fourth rectifying column, the export of impurity benzoic acid is located the top of fourth rectifying column, the export of methylbenzoic acid is located the well upper portion of fourth rectifying column, high boiling point solvent import is located the well lower part of first rectifying column, the heavy ends export is located the bottom of first rectifying column, the second rectifying column has the export of first recovery component, first recovery component includes the methylbenzaldehyde, the third rectifying column has the export of second recovery component, the second recovery component includes methyl benzyl alcohol.

The utility model discloses an in an embodiment, heavy system of taking off includes first rectifying column, second rectifying column, third rectifying column, fourth rectifying column, fifth rectifying column, the export of impurity benzoic acid is located the top of fourth rectifying column, the export of toluic acid is located the top of fifth rectifying column, high boiling point solvent import is located the well lower part of first rectifying column, the heavy ends export is located the bottom of first rectifying column, the second rectifying column has the export of first recovery component, first recovery component includes the tolualdehyde, the third rectifying column has the export of second recovery component, the second recovery component includes methyl benzyl alcohol.

In one embodiment of the present invention, the heavy component outlet of the de-weighting system is connected to a high boiling point solvent recovery device (not shown) to recover the high boiling point solvent and reduce the amount of waste.

In one embodiment of the present invention, the light component removal system has a first light component removal unit, the first light component removal unit employs a distiller and/or a rectifying tower, a light component outlet of the distiller and/or the rectifying tower is connected to an oxidation section of the preceding xylene, and a light component removal mother liquor outlet of the distiller and/or the rectifying tower is connected to a light component removal mother liquor inlet of the rectifying tower in the heavy component removal system. The oxidation reaction liquid of the dimethylbenzene from the preorder oxidation reaction section enters a first light component removal unit of a light component removal system for distillation and/or rectification, components with boiling points lower than that of benzoic acid are enriched to the top of a distiller and separated out, and light components containing the dimethylbenzene, methylbenzaldehyde and methylbenzyl alcohol are obtained and return to the preorder oxidation reaction section of the dimethylbenzene. The method comprises the steps of enriching components with boiling points not lower than that of benzoic acid to the bottom of a distiller and/or a rectifying tower, entering a rectifying tower of a heavy component removal system from a light component removal mother liquor outlet for rectification, introducing a high-boiling-point solvent between methylbenzoic acid and carboxybenzaldehyde under normal pressure from a high-boiling-point solvent inlet of the rectifying tower, distilling off impurity benzoic acid from the top of the rectifying tower, separating at the middle upper part of the rectifying tower to obtain a product methylbenzoic acid, and separating heavy components containing the high-boiling-point solvent, phthalic acid, carboxybenzaldehyde and other high-boiling-point impurities from the bottom of the rectifying tower.

In an embodiment of the present invention, the light component removing system has a first light component removing unit, the first light component removing unit employs a distiller and/or a rectifying tower, the light component outlet of the distiller and/or the rectifying tower is connected to the oxidation section of the preorder xylene, the light component removing mother liquor outlet of the distiller and/or the rectifying tower is connected to the light component removing mother liquor inlet of the first rectifying tower in the heavy component removing system, and the first rectifying tower in the heavy component removing system is connected to the second rectifying tower. The oxidation reaction liquid of the dimethylbenzene from the preorder oxidation reaction section enters a first light component removal unit of a light component removal system for distillation and/or rectification, components with boiling points lower than that of benzoic acid are enriched to the top of a distiller and separated out, and light components containing the dimethylbenzene, methylbenzaldehyde and methylbenzyl alcohol are obtained and return to the preorder oxidation reaction section of the dimethylbenzene. The method comprises the steps of enriching components with boiling points not lower than that of benzoic acid to the bottom of a distiller and/or a rectifying tower, entering a first rectifying tower of a heavy component removal system from a light component removal mother liquor outlet for rectification, distilling off impurity benzoic acid from the top of the first rectifying tower, introducing a high-boiling-point solvent between methylbenzoic acid and carboxybenzaldehyde under normal pressure from a high-boiling-point solvent inlet of the first rectifying tower or a high-boiling-point solvent inlet of a second rectifying tower, separating the top of the second rectifying tower to obtain a product methylbenzoic acid, and separating heavy components containing the high-boiling-point solvent, phthalic acid, carboxybenzaldehyde and other high-boiling-point impurities from the bottom of the second rectifying tower.

In an embodiment of the present invention, the light component removing system has a first light component removing unit and a second light component removing unit, the first light component removing unit adopts a distiller and/or a rectifying tower, a first light component outlet of the distiller and/or the rectifying tower is connected with an oxidation section of the preorder xylene, the second light component removing unit adopts a rectifying device, a first light component removing mother liquor outlet of the distiller and/or the rectifying tower in the first light component removing unit is connected with a first light component removing mother liquor inlet of the rectifying tower in the second light component removing unit, and a second light component removing mother liquor outlet of the rectifying tower in the second light component removing unit is connected with a light component removing mother liquor inlet of the rectifying tower in the heavy component removing system. The oxidation reaction liquid of the dimethylbenzene from the preorder oxidation reaction section enters a first light component removal unit of a light component removal system for distillation and/or rectification operation to obtain a first light component with dimethylbenzene as a main component, the first light component removal mother liquor returns to the preorder dimethylbenzene oxidation reaction section, the first light component removal mother liquor enters a rectification tower of a second light component removal unit for continuous rectification operation to obtain a second light component with methylbenzaldehyde and methylbenzyl alcohol as main components, the component with the boiling point not lower than that of the benzoic acid is enriched to the bottom of the rectification tower of the second light component removal unit, the second light component removal mother liquor enters a rectification tower of a heavy component removal system for rectification operation, a high boiling point solvent between the methylbenzoic acid and the carboxybenzaldehyde under normal pressure is introduced from a high boiling point solvent inlet of the rectification tower, the benzoic acid as an impurity is distilled out from the top of the rectification tower, and the methylbenzoic acid product is obtained by separation at the middle upper part of the rectification tower, heavy components containing high-boiling solvent, phthalic acid, carboxybenzaldehyde and other high-boiling impurities are separated at the bottom of the rectifying tower.

In an embodiment of the present invention, the light component removing system has a first light component removing unit and a second light component removing unit, the first light component removing unit adopts a distiller and/or a rectifying tower, a first light component outlet of the distiller and/or the rectifying tower is connected with an oxidation section of the preorder xylene, the second light component removing unit adopts a rectifying device, a first light component removing mother liquor outlet of the distiller and/or the rectifying tower in the first light component removing unit is connected with a first light component removing mother liquor inlet of the rectifying tower in the second light component removing unit, a second light component removing mother liquor outlet of the rectifying tower in the second light component removing unit is connected with a light component removing mother liquor inlet of the first rectifying tower in the heavy component removing system, and the first rectifying tower of the heavy component removing system is connected with the second rectifying tower. The oxidation reaction liquid of the dimethylbenzene from the preorder oxidation reaction section enters a first light component removal unit of a light component removal system for distillation and/or rectification operation to obtain a first light component with dimethylbenzene as a main component, the first light component removal mother liquor enters a rectification tower of a second light component removal unit for continuous rectification operation to obtain a second light component with methylbenzaldehyde and methylbenzyl alcohol as main components, the component with the boiling point not lower than that of the benzoic acid is enriched to the bottom of the rectification tower of the second light component removal unit, the second light component removal mother liquor enters a first rectification tower of a heavy component removal system from a second light component removal mother liquor outlet for rectification operation, the benzoic acid as an impurity is distilled from the top of the first rectification tower, and a high-boiling point solvent between the methylbenzoic acid and the carboxybenzaldehyde under normal pressure is introduced from a high-boiling point solvent inlet of the first rectification tower or the second rectification tower, separating at the top of the second rectifying tower to obtain methyl benzoic acid product, and separating heavy components containing high boiling point solvent, phthalic acid, carboxybenzaldehyde and other high boiling point impurities at the bottom of the second rectifying tower.

The utility model discloses an in one embodiment, the lightness-removing system has first lightness-removing unit, the second lightness-removing unit, the third lightness-removing unit, first lightness-removing unit adopts distiller and/or rectifying column, the first light component export of this distiller and/or rectifying column links to each other with the oxidation workshop section of preorder xylene, second lightness-removing unit adopts rectifier unit with the third lightness-removing unit, the first lightness-removing mother liquor export of distiller and/or rectifying column links to each other with the first lightness-removing mother liquor import of rectifying column in the second lightness-removing unit in the first lightness-removing unit, the second lightness-removing mother liquor export of rectifying column links to each other with the second lightness-removing mother liquor import of third lightness-removing unit in the second lightness-removing unit, the third lightness-removing mother liquor export of third lightness-removing unit links to each other with the lightness-removing mother liquor import of rectifying column in the weight-removing system. The oxidation reaction liquid of the dimethylbenzene from the preorder oxidation reaction section enters a first light component removing unit of a light component removing system for distillation and/or rectification operation, the first light component with the main component of the dimethylbenzene is obtained and returns to the preorder oxidation reaction section of the dimethylbenzene, the first light component removing mother liquid of the dimethylbenzene enters a rectification tower of a second light component removing unit for continuous rectification operation, the second light component with the main component of methylbenzaldehyde is obtained at the tower top, the second light component removing mother liquid of the dimethylbenzene and the methylbenzaldehyde is enriched at the bottom of the rectification tower in the second light component removing unit, the second light component removing mother liquid is discharged from a second light component removing mother liquid outlet and enters a rectification tower of a third light component removing unit for continuous rectification operation, the third light component with the main component of methylbenzyl alcohol is obtained at the tower top, and the third light component removing mother liquid of the dimethylbenzene, the methylbenzyl aldehyde and the methylbenzyl alcohol is enriched at the bottom of the rectification tower in the third light component removing unit, discharging the third light component-removing mother liquor from a third light component-removing mother liquor outlet, feeding the third light component-removing mother liquor into a rectifying tower of a heavy component-removing system for rectification, introducing a high-boiling-point solvent between methyl benzoic acid and carboxybenzaldehyde under normal pressure from a high-boiling-point solvent inlet of the rectifying tower, distilling off impurity benzoic acid from the top of the rectifying tower, separating the impurity benzoic acid from the middle upper part of the rectifying tower to obtain methyl benzoic acid product, and separating heavy components containing the high-boiling-point solvent, phthalic acid, carboxybenzaldehyde and other high-boiling-point impurities from the bottom of the rectifying tower.

In one embodiment of the utility model, the light component removing system is provided with a first light component removing unit, a second light component removing unit and a third light component removing unit, the first light component removing unit adopts a distiller and/or a rectifying tower, a first light component outlet of the distiller and/or the rectifying tower is connected with an oxidation working section of a preorder xylene, a second lightness-removing unit and a third lightness-removing unit adopt a rectifying device, a first lightness-removing mother liquor outlet of the distiller and/or the rectifying tower in the first lightness-removing unit is connected with a first lightness-removing mother liquor inlet of the rectifying tower in the second lightness-removing unit, a second lightness-removing mother liquor outlet of the rectifying tower in the second lightness-removing unit is connected with a second lightness-removing mother liquor inlet of the third lightness-removing unit, a third lightness-removing mother liquor outlet of the third lightness-removing unit is connected with a lightness-removing mother liquor inlet of the first rectifying tower in the weight-removing system, and a first rectifying tower of the weight-removing system is connected with the second rectifying tower. The oxidation reaction liquid of the dimethylbenzene from the preorder oxidation reaction section enters a first light component removing unit of a light component removing system for distillation and/or rectification operation, the first light component with the main component of the dimethylbenzene is obtained and returns to the preorder oxidation reaction section of the dimethylbenzene, the first light component removing mother liquid of the dimethylbenzene enters a rectification tower of a second light component removing unit for continuous rectification operation, the second light component with the main component of methylbenzaldehyde is obtained at the tower top, the second light component removing mother liquid of the dimethylbenzene and the methylbenzaldehyde is enriched at the bottom of the rectification tower in the second light component removing unit, the second light component removing mother liquid is discharged from a second light component removing mother liquid outlet and enters a rectification tower of a third light component removing unit for continuous rectification operation, the third light component with the main component of methylbenzyl alcohol is obtained at the tower top, and the third light component removing mother liquid of the dimethylbenzene, the methylbenzyl aldehyde and the methylbenzyl alcohol is enriched at the bottom of the rectification tower in the third light component removing unit, discharging the third light-component-removed mother liquor from a third light-component-removed mother liquor outlet, allowing the third light-component-removed mother liquor to enter a first rectifying tower of a heavy component removal system for rectification, distilling off benzoic acid serving as an impurity from the top of the first rectifying tower, introducing a high-boiling-point solvent between methylbenzoic acid and carboxybenzaldehyde at normal pressure from a high-boiling-point solvent inlet of the first rectifying tower or a high-boiling-point solvent inlet of a second rectifying tower, separating the second high-boiling-point solvent from the top of the second rectifying tower to obtain methyl benzoic acid serving as a product, and separating heavy components containing the high-boiling-point solvent, phthalic acid, carboxybenzaldehyde and other high-boiling-point impurities from the bottom of the second rectifying tower.

In an embodiment of the present invention, the light component removing system has a first light component removing unit, the first light component removing unit employs a distiller and/or a rectifying tower, the light component outlet of the distiller and/or the rectifying tower is connected to the oxidation section of the preorder xylene, the light component removing mother liquor outlet of the distiller and/or the rectifying tower is connected to the light component removing mother liquor inlet of the first rectifying tower in the heavy component removing system, and the first rectifying tower, the second rectifying tower and the third rectifying tower in the heavy component removing system are sequentially connected in series. The oxidation reaction liquid of the dimethylbenzene from the preorder oxidation reaction section enters a first light component removal unit of a light component removal system for distillation and/or rectification operation, components with boiling points lower than that of the benzoic acid are enriched to the top of a distiller and separated out, light components containing the dimethylbenzene are obtained and return to the oxidation reaction section of the preorder dimethylbenzene, the bottom of a first light component removal mother liquor distiller and/or a rectifying tower for removing the dimethylbenzene enters a first rectifying tower of a heavy component removal system from a light component removal mother liquor outlet for rectification operation, a high boiling point solvent between the methylbenzoic acid and the carboxybenzaldehyde under normal pressure is introduced from a high boiling point solvent inlet of the first rectifying tower, heavy components containing the high boiling point solvent, the phthalic acid, the carboxybenzaldehyde and other high boiling point impurities are separated from the bottom of the first rectifying tower, tower top liquid with the heavy components removed enters a second rectifying tower for continuous rectification operation, and (3) obtaining a recovered component containing methylbenzaldehyde and methylbenzyl alcohol at the tower top of the second rectifying tower, enabling the tower bottom liquid of the second rectifying tower to enter a third rectifying tower for continuous rectifying operation, distilling off impurity benzoic acid at the tower top of the third rectifying tower, separating at the middle upper part of the third rectifying tower to obtain a product methylbenzoic acid, and discharging a small amount of rectifying residues at the tower bottom of the third rectifying tower.

In an embodiment of the present invention, the light component removing system has a first light component removing unit, the first light component removing unit employs a distiller and/or a rectifying tower, the light component outlet of the distiller and/or the rectifying tower is connected to the oxidation section of the preorder xylene, the light component removing mother liquor outlet of the distiller and/or the rectifying tower is connected to the light component removing mother liquor inlet of the first rectifying tower in the heavy component removing system, and the first rectifying tower, the second rectifying tower, the third rectifying tower and the fourth rectifying tower in the heavy component removing system are sequentially connected in series. The oxidation reaction liquid of the dimethylbenzene from the preorder oxidation reaction section enters a first light component removal unit of a light component removal system for distillation and/or rectification operation, components with boiling points lower than that of the benzoic acid are enriched to the top of a distiller and separated out, light components containing the dimethylbenzene are obtained and return to the oxidation reaction section of the preorder dimethylbenzene, the bottom of a first light component removal mother liquor distiller and/or a rectifying tower for removing the dimethylbenzene enters a first rectifying tower of a heavy component removal system from a light component removal mother liquor outlet for rectification operation, a high boiling point solvent between the methylbenzoic acid and the carboxybenzaldehyde under normal pressure is introduced from a high boiling point solvent inlet of the first rectifying tower, heavy components containing the high boiling point solvent, the phthalic acid, the carboxybenzaldehyde and other high boiling point impurities are separated from the bottom of the first rectifying tower, tower top liquid with the heavy components removed enters a second rectifying tower for continuous rectification operation, and (2) obtaining a recovered component containing methylbenzaldehyde and methylbenzyl alcohol at the top of the second rectifying tower, allowing the tower bottom liquid of the second rectifying tower to enter a third rectifying tower for continuous rectifying operation, distilling off impurity benzoic acid at the top of the third rectifying tower, allowing the tower bottom liquid of the third rectifying tower to enter a fourth rectifying tower for continuous rectifying operation, separating at the top of the fourth rectifying tower to obtain a product methylbenzoic acid, and discharging a small amount of rectifying residues at the bottom of the fourth rectifying tower.

In an embodiment of the present invention, the light component removing system has a first light component removing unit, the first light component removing unit employs a distiller and/or a rectifying tower, the light component outlet of the distiller and/or the rectifying tower is connected to the oxidation section of the preorder xylene, the light component removing mother liquor outlet of the distiller and/or the rectifying tower is connected to the light component removing mother liquor inlet of the first rectifying tower in the heavy component removing system, and the first rectifying tower, the second rectifying tower, the third rectifying tower and the fourth rectifying tower in the heavy component removing system are sequentially connected in series. The oxidation reaction liquid of the dimethylbenzene from the preorder oxidation reaction section enters a first light component removal unit of a light component removal system for distillation and/or rectification operation, components with boiling points lower than that of the benzoic acid are enriched to the top of a distiller and separated out, light components containing the dimethylbenzene are obtained and return to the oxidation reaction section of the preorder dimethylbenzene, the bottom of a first light component removal mother liquor distiller and/or a rectifying tower for removing the dimethylbenzene enters a first rectifying tower of a heavy component removal system from a light component removal mother liquor outlet for rectification operation, a high boiling point solvent between the methylbenzoic acid and the carboxybenzaldehyde under normal pressure is introduced from a high boiling point solvent inlet of the first rectifying tower, heavy components containing the high boiling point solvent, the phthalic acid, the carboxybenzaldehyde and other high boiling point impurities are separated from the bottom of the first rectifying tower, tower top liquid with the heavy components removed enters a second rectifying tower for continuous rectification operation, and (2) obtaining a methylbenzaldehyde-containing recovery component on the top of the second rectifying tower, allowing the tower bottom liquid of the second rectifying tower to enter a third rectifying tower for continuous rectifying operation, obtaining a methylbenzyl alcohol-containing recovery component on the top of the third rectifying tower, allowing the tower bottom liquid of the third rectifying tower to enter a fourth rectifying tower for continuous rectifying operation, distilling off impurity benzoic acid on the top of the fourth rectifying tower, separating the upper middle part of the fourth rectifying tower to obtain a product methylbenzoic acid, and discharging a small amount of rectifying residues at the bottom of the fourth rectifying tower.

In an embodiment of the present invention, the light component removing system has a first light component removing unit, the first light component removing unit employs a distiller and/or a rectifying tower, the light component outlet of the distiller and/or the rectifying tower is connected to the oxidation section of the preorder xylene, the light component removing mother liquor outlet of the distiller and/or the rectifying tower is connected to the light component removing mother liquor inlet of the first rectifying tower in the heavy component removing system, and the first rectifying tower, the second rectifying tower, the third rectifying tower, the fourth rectifying tower and the fifth rectifying tower in the heavy component removing system are sequentially connected in series. The oxidation reaction liquid of the dimethylbenzene from the preorder oxidation reaction section enters a first light component removal unit of a light component removal system for distillation and/or rectification operation, components with boiling points lower than that of the benzoic acid are enriched to the top of a distiller and separated out, light components containing the dimethylbenzene are obtained and return to the oxidation reaction section of the preorder dimethylbenzene, the bottom of a first light component removal mother liquor distiller and/or a rectifying tower for removing the dimethylbenzene enters a first rectifying tower of a heavy component removal system from a light component removal mother liquor outlet for rectification operation, a high boiling point solvent between the methylbenzoic acid and the carboxybenzaldehyde under normal pressure is introduced from a high boiling point solvent inlet of the first rectifying tower, heavy components containing the high boiling point solvent, the phthalic acid, the carboxybenzaldehyde and other high boiling point impurities are separated from the bottom of the first rectifying tower, tower top liquid with the heavy components removed enters a second rectifying tower for continuous rectification operation, and (2) obtaining a methylbenzaldehyde-containing recovery component on the top of the second rectifying tower, allowing the tower bottom liquid of the second rectifying tower to enter a third rectifying tower for continuous rectifying operation, obtaining a methylbenzyl alcohol-containing recovery component on the top of the third rectifying tower, allowing the tower bottom liquid of the third rectifying tower to enter a fourth rectifying tower for continuous rectifying operation, distilling off impurity benzoic acid on the top of the fourth rectifying tower, allowing the tower bottom liquid of the fourth rectifying tower to enter a fifth rectifying tower for continuous rectifying operation, separating at the top of the fifth rectifying tower to obtain a product methylbenzoic acid, and discharging a small amount of rectifying residues at the bottom of the fifth rectifying tower.

In the present invention in the 1 st aspect, a method for treating a reaction liquid for oxidizing xylene, the method comprising:

carrying out light component removal operation on the oxidation reaction liquid, and separating light components containing dimethylbenzene, methylbenzaldehyde and methylbenzyl alcohol to form light component removal mother liquid;

and (3) carrying out weight removal operation on the light-weight removal mother liquor by introducing a high-boiling point solvent, and separating heavy components containing phthalic acid and carboxybenzaldehyde and byproduct impurity benzoic acid to obtain a target product methyl benzoic acid.

In the present invention according to claim 2, the removing operation includes: separating the byproduct impurity benzoic acid in the light component removal mother liquor before introducing the high boiling point solvent.

In the present invention in the 3 rd aspect, the lightening operation includes: separating light components containing xylene, separating light components containing methylbenzaldehyde and methylbenzyl alcohol, and finally forming light component removing mother liquor.

In the present invention in the 4 th aspect, the lightening operation includes: the light fraction containing xylene is separated first, then the light fraction containing methylbenzaldehyde is separated, then the light fraction containing methylbenzyl alcohol is separated, and finally a light component removal mother liquor is formed.

In the present invention in the 5 th aspect, a method for treating a reaction liquid for oxidizing xylene, the method comprising:

carrying out light component removal operation on the oxidation reaction liquid, and separating a light component containing dimethylbenzene to form light component removal mother liquid;

carrying out weight removal operation on the light-weight-removed mother liquor by introducing a high-boiling-point solvent, and separating heavy components containing phthalic acid and carboxybenzaldehyde to form heavy-weight-removed mother liquor;

wherein the heavy component removal mother liquor is rectified, and intermediate components containing methylbenzaldehyde and methyl benzyl alcohol are separated to form rectification mother liquor; and is

And refining the rectification mother liquor, and separating benzoic acid and refined residual liquid to obtain a target product methyl benzoic acid.

In the utility model discloses in the 6 th aspect, the rectification mother liquor at first carries out a refining, separates benzoic acid, then carries out the secondary refining, separates the refined raffinate, obtains the target product methyl benzoic acid.

In the utility model discloses in the 7 th aspect, the heavy mother liquor that takes off at first carries out a rectification, and the separation contains the light component of methylbenzaldehyde, carries out the secondary rectification after that, and the separation contains the light component of methyl benzyl alcohol, forms the rectification mother liquor at last.

In the 8 th aspect of the present invention, the boiling point of the high boiling point solvent is 270-.

In the present invention according to the 9 th aspect, the light fraction containing xylene, methylbenzaldehyde and methylbenzyl alcohol, the light fraction containing xylene, the light fraction containing methylbenzaldehyde and the light fraction containing methylbenzyl alcohol may be recycled to the xylene oxidation reaction.

In the present invention, in the 10 th aspect, there is provided a system for the method of the present invention

In the utility model, each part such as bubble column, distillation plant and rectifier unit etc. in the processing system of xylol oxidation reaction liquid all can be purchased from market and obtained, nevertheless the production system can't directly purchase and obtain, also not known to the technical staff in the field. The ordinary bubble column, distillation plant and the rectifier unit of technical staff's optional conventionality in this field are connected according to the utility model, obtain this production system to technological parameters such as temperature, pressure, liquid level, extraction rate in the reaction temperature and the pressure of adjusting the oxidation reaction process and distilling and the rectification process are nimble according to the general knowledge that technical staff in this field mastered and are carried out intermittent type, semi-intermittent type or continuous operation, in order to reach the utility model discloses in the requirement of producing high-purity methyl benzoic acid. The utility model discloses the method not only can improve the product yield, but also can show the purity that improves methyl benzoic acid.

The utility model discloses in, can reduce the loss to oxidation reaction liquid treatment in-process product methyl benzoic acid, can also obtain target product methyl benzaldehyde and methyl benzyl alcohol to can also show the content that reduces single impurity benzoic acid, improve methyl benzoic acid's purity. The utility model orderly carries out the operations of lightness removal, weight removal, rectification, refining and the like on the p-xylene oxidation reaction liquid. On the one hand, a series of deep side reactions caused by long-time heating of alcohol, aldehyde and acid generated in the oxidation reaction process, especially peroxide byproduct impurities, are avoided to a certain extent, the generation of high-boiling point waste is reduced, the waste amount is reduced, the condition that benzoic acid cannot be removed all the time due to continuous decarboxylation of carboxyl-containing heavy components caused by long-time heating in a production system is also avoided, and the generation amount of impurity benzoic acid is reduced to a certain extent. On the other hand, the utility model discloses a product refining system, main separation impurity benzoic acid is showing the content that has reduced impurity such as benzoic acid in the main product methyl benzoic acid, has guaranteed the purity of product methyl benzoic acid. Compared with the prior art, the utility model discloses the content of most core single impurity benzoic acid reduces to below 0.5 weight percent in the steerable product, and methyl benzoic acid product purity is not less than 99 weight percent.

Examples

According to the utility model, the main product obtained after the oxidation and treatment of the dimethylbenzene is methyl benzoic acid. The amount of each component in the oxidation reaction solution obtained by oxidizing xylene was analyzed and quantified by a liquid chromatography internal standard (cumene was used as an internal standard). The utility model discloses methyl benzoic acid's purity is by liquid chromatography detection and analysis. The utility model discloses in, the liquid chromatography detects and uses the Agilent LC1260 liquid chromatograph of purchasing from Agilent company.

The oxidation reaction solution 1 of m-xylene from the preceding oxidation section was examined to have the following composition

The ultimate yield of m-toluic acid is 95.1% calculated according to the mass fraction of each component in the oxidation reaction liquid of m-xylene.

The oxidation reaction liquid 2 of o-xylene from the preoxidation section is detected to have the following composition

The ultimate yield of the o-toluic acid is 94.9% by calculation according to the mass fraction of each component in the oxidation reaction liquid of the m-xylene.

Comparative example 1:

and (2) conveying the m-xylene oxidation reaction liquid 1 into a m-xylene removal rectifying tower through a conveying pump, carrying out reduced pressure rectification under the conditions that the pressure is 30kPa and the temperature of a tower kettle is 152 ℃, and collecting a light component with the main component of m-xylene from the top of the rectifying tower, wherein the light component can be recovered for further oxidation reaction. The components with boiling point higher than m-xylene enriched at the bottom of the tower are conveyed to a m-tolualdehyde recovery tower by a conveying pump, the reduced pressure rectification is carried out under the conditions that the pressure is 3.5kPa and the temperature of a tower kettle is 176 ℃, m-tolualdehyde is extracted at the top of the tower, the m-tolualdehyde is collected into a m-tolualdehyde collection tank for temporary storage, the m-tolualdehyde is conveyed to a bubble tower by the conveying pump to participate in oxidation reaction, the components with boiling point higher than m-tolualdehyde, such as m-phthalic acid, m-carboxybenzaldehyde, m-toluic acid, m-methylbenzyl alcohol, benzoic acid, and the like, are extracted at the bottom of the tower, the components are conveyed to a m-toluic acid refining tower by the conveying pump, the reduced pressure rectification is carried out under the conditions that the pressure is 3.5kPa and the temperature of the tower kettle is 198 ℃, light components with boiling point lower than m-toluic acid, such as m-methylbenzyl alcohol, benzoic acid, and the like, are extracted at the top of the tower, the light components with boiling point lower than m-toluic acid, are returned to the bubble tower, the refined residual liquid containing part of m-toluic acid and the boiling point higher than m-toluic acid is discharged at the bottom of the bubble tower, transferring to a waste production system, and collecting the m-toluic acid product at the middle upper part of the refining tower.

In comparative example 1, the purity of m-toluic acid was 97.4% and the content of impurity benzoic acid was as high as 0.77% as measured by liquid chromatography, the product yield was 76.5%, and the product loss was 19.6% in the treatment of the oxidation reaction liquid.

Comparative example 2:

and (3) conveying the o-xylene oxidation reaction liquid 2 into an o-xylene removal rectifying tower through a conveying pump, carrying out reduced pressure rectification under the conditions of the pressure of 30kPa and the temperature of a tower kettle of 152 ℃, and collecting a light component with the main component of o-xylene from the top of the rectifying tower, wherein the light component can be recovered for further oxidation reaction. The components with the boiling point higher than that of o-xylene at the bottom of the tower are conveyed to an o-methyl benzaldehyde recovery tower through a conveying pump, the components are rectified under the conditions that the pressure is 3.5kPa and the temperature of a tower kettle is 177 ℃, o-methyl benzaldehyde is extracted from the top of the tower and collected into an o-methyl benzaldehyde collecting tank for temporary storage, and the o-methyl benzaldehyde is conveyed to a bubble tower through the conveying pump to participate in oxidation reaction. Extracting components with boiling points higher than that of o-methylbenzaldehyde such as phthalic acid, o-carboxybenzaldehyde, o-methylbenzoic acid, o-methylbenzyl alcohol and benzoic acid from the bottom of the tower, conveying the components into an o-methylbenzoic acid refining tower through a conveying pump, carrying out reduced pressure rectification under the conditions of the pressure of 3.5kPa and the temperature of a tower kettle of 203 ℃, and extracting light components with boiling points lower than that of o-methylbenzoic acid such as o-methylbenzyl alcohol and benzoic acid from the top of the tower and returning the light components to the bubbling tower. Discharging refined raffinate containing partial o-methylbenzoic acid and having a boiling point higher than that of o-methylbenzoic acid from the bottom of the tower, transferring the refined raffinate to a waste production system, and collecting the product o-methylbenzoic acid from the middle upper part of the refining tower.

In comparative example 2, the purity of o-methylbenzoic acid was 98% and the content of impurity benzoic acid was as high as 0.67% as detected by liquid chromatography, the product yield was 78.1%, and the product loss was 17.7% in the treatment of the oxidation reaction liquid.

Example 1:

in this embodiment, the oxidation reaction liquid 1 of the m-xylene is treated, the oxidation reaction liquid 1 of the m-xylene is conveyed to a light component removal system through a conveying pump, preheated by a preheater and then enters a rectifying tower for reduced pressure rectification, the m-xylene in the oxidation reaction liquid, m-tolualdehyde, m-methylbenzyl alcohol and other components are vaporized and enriched to the top of the tower under the conditions of the pressure of 3.5kPa and the temperature of a tower kettle of 176 ℃, then the vaporized and enriched m-xylene, the light component, the condensed m-toluic acid, m-phthalic acid, m-carboxybenzaldehyde and other components are collected to a light component collecting tank for temporary storage after being condensed by a condenser, the light component, the m-toluic acid, m-carboxybenzaldehyde and other components are conveyed to an oxidation section of the m-xylene through the conveying pump, the light component removed mother liquor enriched to the bottom of the tower, which contains the m-toluic acid, m-phthalic acid, m-carboxybenzaldehyde and other components, is continuously conveyed to the rectifying tower through the conveying pump, the dimethyl isophthalate is introduced to the middle lower part of the rectifying tower of the heavy component removal system, the reduced pressure of 3.5kPa and the temperature of the tower kettle of 190 ℃, impurity benzoic acid is extracted from the top of the tower, the product m-toluic acid is extracted from the middle upper part of the rectifying tower, and heavy components containing dimethyl isophthalate, m-phthalic acid and m-carboxybenzaldehyde are separated from the bottom of the tower.

The extracted m-toluic acid is detected, the purity of the product is 99.6% by liquid phase detection, and the content of impurity benzoic acid is 0.12%. The yield of the product obtained by the treatment system of the reaction liquid for oxidizing xylene was 93.8%, and the product loss during the treatment of the reaction liquid for oxidizing was 1.4%, which was 92.9% lower in the treatment of the reaction liquid for oxidizing in this example than in comparative example 1.

Example 2:

this example was conducted to treat the oxidation reaction liquid 1 of the above-mentioned m-xylene, the light removal treatment of the oxidation reaction liquid was the same as in example 1, and the difference from example 1 was that the heavy removal system in this example included two rectifying columns, and after the light removal treatment, a light removal mother liquid containing benzoic acid, m-toluic acid, isophthalic acid, and m-carboxybenzaldehyde, etc. was taken out from the bottom of the rectifying column and continuously fed into the first rectifying column of the heavy removal system by a feed pump, and diethyl isophthalate was fed into the middle-lower portion of the first rectifying column, and the distillation was conducted under reduced pressure at a pressure of 3.5kPa and a column bottom temperature of 182.7 ℃, whereby impure benzoic acid was taken out from the top of the column, and a bottom liquid was fed into the second rectifying column, and the distillation was conducted under reduced pressure at a pressure of 3.5kPa and a column bottom temperature of 189.8 ℃, and the product of m-toluic acid was taken out from the top of the column, and the bottom of the column containing diethyl isophthalate was separated, Isophthalic acid, and m-carboxybenzaldehyde.

The extracted m-toluic acid is detected, the purity of the product is 99.6% by liquid phase detection, and the content of impurity benzoic acid is 0.09%. The yield of the product obtained by the treatment system of the reaction liquid for oxidizing xylene was 93.4%, and the product loss during the treatment of the reaction liquid for oxidizing was 1.8%, which was 90.8% lower in the treatment of the reaction liquid for oxidizing in this example than in comparative example 1.

Example 3:

in this embodiment, the oxidation reaction liquid 2 of o-xylene is treated, the oxidation reaction liquid is conveyed to a first lightness removing unit of a lightness removing system through a conveying pump, preheated by a preheater and then enters a distillation still for reduced pressure distillation, o-xylene in the oxidation reaction liquid is vaporized and enriched to the top of the still under the conditions of 30kPa and 130.2 ℃, then condensed by a condenser and collected into a light component collection tank for temporary storage, and then conveyed to an oxidation section of o-xylene through the conveying pump, the first lightness removing mother liquid enriched to the bottom of the still enters a rectification tower of a second lightness removing unit for reduced pressure rectification under the conditions of 3.5kPa of pressure and 176.7 ℃ of the bottom of the tower, a second light component containing o-methylbenzaldehyde and o-methylbenzyl alcohol is extracted from the top of the tower and conveyed to the oxidation section of o-xylene through the conveying pump, and the second lightness removing mother liquid containing benzoic acid, o-methylbenzoic acid, phthalic acid, o-carboxybenzaldehyde and the like is enriched to the rectification tower bottom of the heavy removing system through the conveying pump and continuously conveyed to a rectification tower And introducing diethyl phthalate into the middle lower part of a rectifying tower of a de-heavy system, carrying out reduced pressure rectification under the conditions that the pressure is 3.5kPa and the temperature of a tower kettle is 189.7 ℃, collecting impurity benzoic acid at the top of the tower, collecting a product o-methylbenzoic acid at the middle upper part of the rectifying tower, and separating heavy components containing diethyl phthalate, phthalic acid and o-carboxybenzaldehyde at the bottom of the tower.

The purity of the extracted o-methylbenzoic acid is detected to be 99.6% by liquid phase detection, and the content of impurity benzoic acid is 0.18%. The yield of the product obtained by the treatment system of the reaction liquid for oxidizing xylene was 93.2%, and the product loss during the treatment of the reaction liquid for oxidizing was 1.8%, which was 89.8% lower in the treatment of the reaction liquid for oxidizing in this example than in comparative example 2.

Example 4:

the present example is to treat the oxidation reaction liquid 2 of o-xylene, the light weight removal treatment of the oxidation reaction liquid is the same as that in example 3, and the difference from example 3 is that the heavy weight removal system in this example includes two rectification towers, after the light weight removal treatment, a second light weight removal mother liquid containing components such as benzoic acid, o-toluic acid, phthalic acid, o-carboxybenzaldehyde is extracted from the bottom of the rectification tower in a second light weight removal unit and is continuously conveyed to the first rectification tower of the heavy weight removal system by a conveying pump, diethyl phthalate is introduced into the middle lower part of the first rectification tower, the reduced pressure rectification is performed under the conditions of the pressure of 3.5kPa and the temperature of the bottom of the tower of 181.8 ℃, the impurity benzoic acid is extracted from the top of the tower, the bottom liquid is introduced into the second rectification tower, the reduced pressure rectification is continuously performed under the conditions of the pressure of 3.5kPa and the temperature of the bottom of the tower of the second rectification tower of 188.5 ℃, the product o-toluic acid is extracted from the top of the tower, the product o-toluic acid is separated from the bottom of the tower, the product containing diethyl phthalate, Heavy components of phthalic acid and o-carboxybenzaldehyde.

The purity of the extracted o-methylbenzoic acid is detected to be 99.7% by liquid phase detection, and the content of impurity benzoic acid is 0.17%. The yield of the product obtained by the treatment system of the reaction liquid for oxidizing xylene was 93.5%, and the product loss during the treatment of the reaction liquid for oxidizing xylene was 1.5%, which was 91.5% lower in the treatment of the reaction liquid for oxidizing xylene in this example than in comparative example 2.

Example 5:

in this embodiment, the oxidation reaction liquid 1 of the m-xylene is treated, the oxidation reaction liquid is conveyed to a first light component removal unit of a light component removal system through a conveying pump, preheated by a preheater and then enters a rectifying tower for reduced pressure rectification, the m-xylene in the oxidation reaction liquid is vaporized and enriched to the top of the tower under the conditions of the pressure of 30kPa and the temperature of a tower kettle of 148.8 ℃, then condensed by a condenser and collected to a light component collection tank for temporary storage, and then conveyed to an oxidation section of the m-xylene through the conveying pump, the first light component removal mother liquid enriched to the bottom of the tower enters a rectifying tower of a second light component removal unit for continuous reduced pressure distillation under the conditions of the pressure of 3.5kPa and the temperature of the tower kettle of 176.2 ℃, a product of m-tolualdehyde is extracted from the top of the tower, the second light component removal mother liquid enriched to the bottom of the tower enters a rectifying tower of a third light component removal unit for continuous reduced pressure rectification under the conditions of the pressure of 3.5kPa and the temperature of the tower kettle of 176.5 ℃, and (3) extracting a product of m-methylbenzyl alcohol from the tower top, continuously conveying the third light component removal mother liquor enriched to the tower bottom to a rectifying tower of a heavy component removal system through a conveying pump, introducing dimethyl tartrate into the middle lower part of the rectifying tower of the heavy component removal system, carrying out reduced pressure rectification under the conditions that the pressure is 3.5kPa and the temperature of a tower kettle is 193.5 ℃, extracting impurity benzoic acid from the tower top, extracting a product of m-methylbenzoic acid from the middle upper part of the rectifying tower, and separating heavy components containing dimethyl tartrate, m-phthalic acid and m-carboxybenzaldehyde from the tower bottom.

The extracted m-toluic acid is detected, the purity of the product is 99.5% by liquid phase detection, and the content of impurity benzoic acid is 0.21%. The yield of the product obtained by the treatment system of the reaction liquid for oxidizing xylene was 92.6%, and the product loss during the treatment of the reaction liquid for oxidizing xylene was 2.6%, which was 86.7% lower in the treatment of the reaction liquid for oxidizing xylene in this example than in comparative example 1.

Example 6:

this example is to treat the oxidation reaction liquid 1 of the above-mentioned meta-xylene, the light removal treatment of the oxidation reaction liquid is the same as that in example 5, and the difference from example 5 is that the heavy removal system of this example includes two rectification towers, after the light removal treatment, the third light removal mother liquid containing components such as benzoic acid, m-toluic acid, isophthalic acid, and m-carboxybenzaldehyde is extracted from the bottom of the rectification tower of the third light removal unit, and is continuously transported to the first rectification tower of the heavy removal system by a transport pump, and tripentylbenzene is introduced into the middle lower portion of the first rectification tower, and is rectified under reduced pressure at a pressure of 3.5kPa and a column bottom temperature of 182.5 ℃, impurity benzoic acid is extracted from the top of the tower, and the bottom liquid is introduced into the second rectification tower, and is rectified under reduced pressure at a pressure of 3.5kPa and a column bottom temperature of 189.7 ℃, and product m-toluic acid is extracted from the top of the tower, and is separated out product m-toluic acid containing tripentylbenzene, m-toluic acid, m-benzaldehyde, and m-benzaldehyde, Isophthalic acid, and m-carboxybenzaldehyde.

The extracted m-toluic acid is detected, the purity of the product is 99.6% by liquid phase detection, and the content of impurity benzoic acid is 0.19%. The yield of the product obtained by the treatment system of the reaction liquid for oxidizing xylene was 92.9%, and the product loss during the treatment of the reaction liquid for oxidizing xylene was 2.3%, which was 88.3% lower in the treatment of the reaction liquid for oxidizing xylene in this example than in comparative example 1.

Example 7:

in this embodiment, the oxidation reaction liquid 2 of o-xylene is treated, the oxidation reaction liquid is conveyed to a light component removal system through a conveying pump, preheated by a preheater and then enters a rectifying tower for reduced pressure rectification, o-xylene in the oxidation reaction liquid is vaporized and enriched to the top of the tower under the conditions of 30kPa and 151.6 ℃ of the tower kettle temperature, then condensed by a condenser and collected in a light component collecting tank for temporary storage, and then conveyed to an oxidation section of the o-xylene through the conveying pump, the light component removal mother liquid enriched to the bottom of the tower is conveyed to a first rectifying tower of a heavy component removal system through the conveying pump, dibutyl maleate is introduced into the middle lower part of the rectifying tower of the heavy component removal system, reduced pressure rectification is carried out under the conditions of 3.5kPa and 191.5 ℃ of the tower kettle temperature, heavy components containing dibutyl maleate, phthalic acid and o-carboxybenzaldehyde are separated at the bottom of the tower, components with boiling points lower than dibutyl maleate are collected at the top of the tower, the product is conveyed to a second rectifying tower of a de-weighting system by a conveying pump and is continuously rectified under reduced pressure under the conditions of 3.5kPa and 178.2 ℃ of a tower kettle, o-methylbenzaldehyde and o-methylbenzyl alcohol separated from the tower top are conveyed to an oxidation working section of preorder o-xylene by the conveying pump, tower bottom liquid enters a third rectifying tower of the de-weighting system and is continuously rectified under reduced pressure under the conditions of 3.5kPa and 191.1 ℃ of the tower kettle, impurity benzoic acid is removed from the tower top, a product o-methylbenzoic acid is extracted from the middle upper part of the rectifying tower, and a small amount of rectified residual liquid discharged from the tower bottom returns to a first rectifying tower of the de-weighting system.

The purity of the extracted o-methylbenzoic acid is detected to be 99.9% by liquid phase detection, and the content of impurity benzoic acid is 0.07%. The yield of the product obtained by the treatment system of the reaction liquid for oxidizing xylene was 94.2%, and the product loss during the treatment of the reaction liquid for oxidizing was 0.7%, which was 96% lower in the treatment of the reaction liquid for oxidizing in this example than in comparative example 2.

Example 8:

the present example treats the oxidation reaction liquid 2 of o-xylene, the light weight removal treatment of the oxidation reaction liquid is the same as that of example 7, and the difference from example 7 is that the heavy weight removal system in the present example comprises four rectifying towers, the light weight removal mother liquor from which o-xylene is removed is extracted from the bottom of the rectifying tower of the light weight removal system after the light weight removal treatment is continuously conveyed to the first rectifying tower of the heavy weight removal system through a conveying pump, dibutyl maleate is introduced into the middle lower part of the rectifying tower of the heavy weight removal system, the heavy components containing dibutyl maleate, phthalic acid and o-carboxybenzaldehyde are separated from the bottom of the tower under the conditions of the pressure of 3.5kPa and the temperature of the bottom of the tower of 191.5 ℃, the components with the boiling point lower than dibutyl maleate are extracted from the top of the tower, the components are conveyed to the second rectifying tower of the heavy weight removal system through the conveying pump, the reduced pressure rectification is continuously carried out under the conditions of the pressure of 3.5kPa and the temperature of the bottom of the tower of 178.2 ℃, the o-methyl benzaldehyde and o-methyl benzyl alcohol separated from the tower top are conveyed to an oxidation working section of the preorder o-xylene through a conveying pump, the tower bottom liquid enters a third rectifying tower of a de-weighting system to be continuously rectified under the conditions of the pressure of 3.5kPa and the temperature of a tower kettle of 181.6 ℃, the impurity benzoic acid is removed from the tower top, the tower bottom liquid enters a fourth rectifying tower to be continuously rectified under the conditions of the pressure of 3.5kPa and the temperature of the tower kettle of 191.1 ℃, the product o-methyl benzoic acid is extracted from the tower top, and a small amount of rectified residual liquid discharged from the tower bottom returns to a first rectifying tower of the de-weighting system.

The purity of the extracted o-methylbenzoic acid is detected to be 99.9% by liquid phase detection, and the content of impurity benzoic acid is 0.06%. The yield of the product obtained by the treatment system of the reaction liquid for oxidizing xylene was 93.8%, and the product loss during the treatment of the reaction liquid for oxidizing was 1.2%, which was 93.2% lower in the treatment of the reaction liquid for oxidizing in this example than in comparative example 2.

Example 9:

in this embodiment, the oxidation reaction liquid 1 of the above-mentioned meta-xylene is treated, the oxidation reaction liquid is conveyed to a light component removal system through a conveying pump, preheated by a preheater and then enters a rectification column for rectification under reduced pressure, the meta-xylene in the oxidation reaction liquid is vaporized and enriched to the top of the column under the conditions of 30kPa and 148.7 ℃ of the column bottom temperature, then condensed by a condenser and collected to a light component collection tank for temporary storage, and then conveyed to the oxidation section of the meta-xylene through the conveying pump, the light component removal mother liquid enriched to the bottom of the column is conveyed to a first rectification column of a heavy component removal system through the conveying pump, dimethyl terephthalate is introduced into the middle lower part of the rectification column of the heavy component removal system, the rectification under the conditions of 1.5kPa and 176.6 ℃ of the column bottom temperature is decompressed, heavy components containing dimethyl terephthalate, isophthalic acid and m-carboxybenzaldehyde are separated at the bottom of the column, components with boiling point lower than dimethyl terephthalate are collected at the top of the column, the mixed solution is conveyed to a second rectifying tower of a de-weighting system by a conveying pump and is continuously rectified under reduced pressure under the conditions of the pressure of 3.5kPa and the temperature of a tower kettle of 176.2 ℃, a product of m-tolualdehyde is separated out at the tower top, a tower bottom solution enters a third rectifying tower of the de-weighting system and is continuously rectified under reduced pressure under the conditions of the pressure of 3.5kPa and the temperature of the tower kettle of 177.1 ℃, a product of m-toluyl alcohol is separated out at the tower top, a tower bottom solution enters a fourth rectifying tower of the de-weighting system and is continuously rectified under reduced pressure under the conditions of the pressure of 3.5kPa and the temperature of the tower kettle of 189.4 ℃, impurity benzoic acid is removed at the tower top, a product of m-toluic acid is extracted at the middle upper part of the rectifying tower, and a small amount of rectified residual liquid discharged from the tower bottom returns to a first rectifying tower of the de-weighting system.

The extracted m-toluic acid is detected, the purity of the product is 99.9% by liquid phase detection, and the content of impurity benzoic acid is 0.07%. The yield of the product obtained by the treatment system of the reaction liquid for oxidizing xylene was 93.6%, and the product loss during the treatment of the reaction liquid for oxidizing xylene was 1.6%, which was 91.8% lower in the treatment of the reaction liquid for oxidizing xylene in this example than in comparative example 1.

Example 10:

the present example treats the above-mentioned oxidation reaction liquid 1 of meta-xylene, the light weight removal treatment of the oxidation reaction liquid is the same as that in example 9, and the difference from example 9 is that the heavy weight removal system in this example comprises five rectifying towers, the light weight removal mother liquor obtained after the light weight removal treatment is conveyed to the first rectifying tower of the heavy weight removal system by a conveying pump, dimethyl terephthalate is introduced into the middle lower part of the rectifying tower of the heavy weight removal system, the heavy weight components including dimethyl terephthalate, isophthalic acid and m-carboxybenzaldehyde are separated at the bottom of the tower by vacuum rectification under the conditions of 1.5kPa of pressure and 176.6 ℃ of the bottom of the tower, the components with the boiling point lower than dimethyl terephthalate are collected at the top of the tower, the components are conveyed to the second rectifying tower of the heavy weight removal system by the conveying pump, the vacuum rectification is continued under the conditions of 3.5kPa of pressure and 176.2 ℃ of the bottom of the tower, the product of m-methylbenzaldehyde is separated at the top of the tower, and the tower bottom liquid enters a third rectifying tower of the de-weighting system to be continuously rectified under the conditions of the pressure of 3.5kPa and the temperature of a tower kettle of 177.1 ℃, the product m-methylbenzyl alcohol is separated from the tower top, the tower bottom liquid enters a fourth rectifying tower of the de-weighting system to be continuously rectified under the conditions of the pressure of 3.5kPa and the temperature of the tower kettle of 182.9 ℃, the impurity benzoic acid is removed from the tower top, the tower bottom liquid enters a fifth rectifying tower to be continuously rectified under the conditions of the pressure of 3.5kPa and the temperature of the tower kettle of 190.3 ℃, the product m-methylbenzoic acid is collected from the tower top, and a small amount of rectified residual liquid discharged from the tower bottom returns to the first rectifying tower of the de-weighting system.

The extracted m-toluic acid is detected, the purity of the product is 99.9% by liquid phase detection, and the content of impurity benzoic acid is 0.05%. The yield of the product obtained by the treatment system of the reaction liquid for oxidizing xylene was 93%, and the product loss during the treatment of the reaction liquid for oxidizing was 2.2%, which was 88.8% lower in this example than in comparative example 1.

Claims (10)

1. A system for treating a reaction liquid for oxidizing xylene, comprising:

a light ends removal system (a) having a first light ends removal unit (011), an oxidation reaction liquid (a1) inlet, a light components (a2) outlet containing xylene, methylbenzaldehyde and methylbenzyl alcohol, and a light ends removal mother liquid (a3) outlet;

a de-weighting system (B) having a first rectification device (021), an inlet for high boiling point solvent (c1), an inlet for light weight removal mother liquor (a3), an outlet for benzoic acid (B1), an outlet for methylbenzoic acid (B2), and an outlet for heavy components (B3), wherein the inlet for high boiling point solvent (c1) introduces high boiling point solvent (c1) into the de-weighting system (B).

2. The system according to claim 1, wherein the de-weighting system (B) further comprises a second rectification device (022), wherein the first rectification device (021) separates the by-product impurity benzoic acid in the de-weighting mother liquor before the high boiling point solvent (c1) is introduced into the second rectification device (022).

3. The system according to claim 1 or 2, characterized in that the lightness-removing system (a) further comprises a second lightness-removing unit (012), wherein the first lightness-removing unit (011) separates the light components comprising xylene and the second lightness-removing unit (012) separates the light components comprising methylbenzaldehyde and methylbenzyl alcohol.

4. The system according to claim 1 or 2, characterized in that the lightness-removing system (a) further comprises a second lightness-removing unit (012) and a third lightness-removing unit (013), wherein the first lightness-removing unit (011) separates a light component comprising xylene, the second lightness-removing unit (012) separates a light component comprising methylbenzaldehyde, and the third lightness-removing unit (013) separates a light component comprising methylbenzyl alcohol.

5. A system for treating a reaction liquid for oxidizing xylene, comprising:

a light component removal system (A) having a first light component removal unit (011), an oxidation reaction liquid (a1) inlet, a light component (a4) outlet containing xylene, and a light component removal mother liquid (a10) outlet;

a heavies removal system (B) having a first rectification apparatus (021), a second rectification apparatus (022), a third rectification apparatus (023), an inlet for a high boiling point solvent (c1), an inlet for a light-ends removal mother liquor (a10), an outlet for benzoic acid (B1), an outlet for methylbenzoic acid (B2), an outlet for heavy components (B3), an outlet for an intermediate component (B6) comprising methylbenzaldehyde and methylbenzyl alcohol, and an outlet for a refined raffinate (B8),

wherein the high boiling point solvent (c1) inlet introduces the high boiling point solvent (c1) into the first rectification means (021);

a first rectification means (021) separates the heavy fraction (b 3);

a second rectification means (022) separating an intermediate component (b6) comprising methylbenzaldehyde and methylbenzyl alcohol;

the third rectifying unit (023) separates benzoic acid (b1) and refined raffinate (b8) to obtain methyl benzoic acid (b 2).

6. The system according to claim 5, characterized in that the de-weighting system (B) further comprises a fourth rectification device (024),

wherein, the third rectifying device (023) separates benzoic acid (b1), the fourth rectifying device (024) separates refined raffinate (b8), and the product of methyl benzoic acid (b2) is obtained; or

The second rectification apparatus (022) separates an intermediate component (b10) comprising methylbenzaldehyde, the third rectification apparatus (023) separates an intermediate component (b11) comprising methylbenzyl alcohol, and the fourth rectification apparatus (024) separates benzoic acid (b1) and a refined raffinate (b8) to obtain a product methylbenzoic acid (b 2).

7. The system according to claim 6, wherein the de-weighting system (B) further comprises a fifth rectification unit (025), wherein the second rectification unit (022) separates the intermediate component (B10) comprising methylbenzaldehyde, the third rectification unit (023) separates the intermediate component (B11) comprising methylbenzyl alcohol, the fourth rectification unit (024) separates benzoic acid (B1), and the fifth rectification unit (025) separates the refined raffinate (B8) to obtain product methylbenzoic acid (B2).

8. The system for treating a reaction liquid for xylene oxidation according to claim 1 or 5,

the light component removal system (A) comprises one or more distillation devices and/or rectification devices; and

the de-weighting system (B) comprises one or more distillation units and/or rectification units.

9. The system for treating reaction liquid for oxidation of xylene according to claim 1 or 5, characterized in that an outlet for light components is located at the top of each lightness-removing unit, and an outlet for mother liquid for lightness-removing is located at the bottom of the lightness-removing unit;

the outlet of the middle component is positioned at the top of each rectifying device, and the outlet of the heavy component and the outlet of the refined residual liquid are positioned at the bottom of each distilling device and/or rectifying device; and

the outlet of the benzoic acid is positioned at the top of the corresponding rectifying device, and the outlet of the methyl benzoic acid is positioned at the top or the middle upper part of the corresponding rectifying device; and

the inlet of the high boiling point solvent is positioned at the middle lower part of the corresponding rectifying device.

10. The system for treating a reaction liquid for xylene oxidation as set forth in claim 1 or 5, wherein the boiling point of the high-boiling solvent is 270-320 ℃.

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