RU2163592C2 - Method of preparing isophthalic acid - Google Patents

Abstract

FIELD: chemistry of polymers, more particularly preparation of chemical fibers, polyester film, varnishes, coloring agents, and plastic materials. SUBSTANCE: invention makes it possible to increase efficiency of withdrawal of reaction water and to improve quality of isophthalic acid by using catalyst which comprises zinc and nickel salts or mixture of said metal salts at (Co+Mn): HT ratio of 1:0.01-0.2, and content of water in oxidation zone is regulated by three-step cooling of vapor-gas mixture going out of reactor in direct flow of gas condensed CH₃COOH-H₂O vapors in first and third stages and counterflow in second stage in combination with rectification process and subsequently recycling dehydrated stream of liquid acetic acid from first and second cooling stages into oxidation zone, withdrawing dehydrated acetic and out of process from third cooling stage in ratio that allows for water concentration of 4-10% in reaction zone. After additional oxidation of impurities, isophthalic acid is treated with acetic acid or with acetic acid and water at 170-230 C. EFFECT: more efficient preparation method. 2 cl, 1 dwg, 1 tbl

Description

 The invention relates to an improved method for the production of isophthalic acid (IPA), which is the most important monomer and intermediate in polymer chemistry for the production of chemical fibers, polyester films, varnishes, dyes, plastics.

 A known method for the continuous production of aromatic carboxylic acid by liquid-phase oxidation of the corresponding xylene with atmospheric oxygen in an acetic acid medium containing a small amount of water in the presence of a cobalt-manganese-bromide catalyst at elevated temperature and pressure (US N 4792621).

The improvement of the process consists in a method for controlling the concentration of water in the oxidation reaction zone in the desired range, which includes:
- separation of the vapor in parallel to a condensate having a relatively small weight ratio of water: solvent, and a vapor phase having a relatively high weight ratio of water: solvent;
- return of a part of the condensate directly to the oxidation reactor in the form of a direct reflux stream;
- removal of the vapor phase from the reflux circuit in the form of a vapor-gas mixture stream;
- cooling the resulting vapor-gas stream enriched in water vapor at a pressure lower than in the oxidation reactor to obtain, as a result of the condensation of the vapor, a stream of water-saturated acetic acid in a ratio of H ₂ O: CH ₃ COOH exceeding the ratio in the direct reflux stream;
- the combination of the pre-calculated (calculated) part of the reflux stream with an indirect recycle phlegm stream so that the weight ratio of water recycled to the oxidation reactor in the indirect recycle stream and in the direct phlegm stream is kept within the range of 0.01-0.15, preferably 0 , 02-0.06.

The disadvantages of this method are:
- the need to install a relatively large number of heat exchangers - condensers in the condensation unit to provide fractional (stepwise) condensation of the CH ₃ COOH - H ₂ O mixture from the vapor-gas mixture leaving the reactor, which increases the cost of the H ₂ O regulation unit in the reaction zone;
- even with 4-stage cooling of the vapor-gas mixture, the efficiency of water removal from the reaction zone is relatively low and its residual content in the liquid phase in the oxidation reactor remains elevated (12-14%), which necessitates the use of elevated pressures (1.5-1.6 MPa) and temperature (198-200 ^o C).

There is also a method of producing isophthalic acid by oxidation of m-xylene in acetic acid for 30-40 minutes at a temperature of 190-205 ^o C and a pressure of 1.9-2.7 MPa in the presence of Co, Mn acetates and bromine compounds in the ratio Co : Mn = 2-5: 1, and the molar ratio m-xylene: water: the total concentration of Co and Mn acetates in the supplied reaction mixture was maintained in the range 1.0-1.75: 1.0-2.5: 1.0 -1.2 · 10 ² . The water content in the reaction zone is regulated by changing its content in the initial reaction mixture (IRS) or the concentration of m-xylene in the recommended range of ratios. Get isophthalic acid of the following quality:
m-KBA = 0.005-0.22%
Color - 19-20 ^o H
The disadvantage of this method is the relatively low concentration of m-xylene and IRS (1.5-1.75 mol / l), which necessitates increased costs for recycling and regeneration of the solvent (CH ₃ COOH). In addition, the insufficient quality of IFC to obtain high-quality polyester fibers and other polymeric materials (necessary [m-KBA] ≅ 0.0025%, color ≅ 10 ^o H) requires the use of complex and expensive purification methods, for example, by hydrogenating impurities in aqueous medium at a temperature of 280-290 ^o C in the presence of a Pd / s catalyst. The selected oxidation parameters of m-xylene (T = 190-200 ^° C and a pressure of 1.9-2.7 MPa) do not allow water to be removed directly from the reaction zone, for example, by fractional condensation CH ₃ COOH - H ₂ O by step cooling gas-vapor mixture exiting the reactor.

The closest in technical essence and the achieved result is a method for producing high-purity isophthalic acid (US N 5132450) by 2-stage liquid-phase oxidation of m-xylene with an oxygen-containing gas in aqueous acetic acid, used as a solvent, in the presence of a catalyst containing compounds of cobalt, manganese and bromine with subsequent purification obtained after the 2nd stage of IFC by treating it with acetic acid at a temperature of ≅ 150 ^o C with recycling of the mother liquor.

In the first stage, the oxidation is carried out with an O ₂ -gas at 180-210 ^o C with the content of m-xylene in the initial reaction mixture introduced into the process in a 1-15-fold amount from the solvent until the m-KBA content in the oxidation products reaches 500-10000 ppm and the total concentration of isophthalic acid in the reaction mass is 10-35%.

In the second stage, the reaction mass is additionally treated with O ₂ gas until a residual concentration of m-CBA of 0.01-0.08% is reached.

The IFC obtained in the second stage is mixed with acetic acid, kept at a temperature of ≅ 150 ^o C and purified to achieve a residual content of m-KBA in IFC of 0.0027-0.0044% and a color index of ≥ 20 ^o H.

 Significant disadvantages of this method.

1). Not an effective way to control the water content in the reaction zone by changing its concentration in the initial reaction mixture in the preferred range of 5-12%. Given the inevitable formation of reaction water, its concentration in the reaction zone reaches a high limit, 10-19%. If the concentration of water is too high, then the activity of the oxidation reaction decreases, the quality of IFC deteriorates. In fact, this is confirmed by examples in which the IFC quality indicators for the content of m-CBA (0.0027-0.0044%) and color index (≥ 20 ^o H) do not reach the values shown for pure IFC ([m-CBA] ≅ 0 , 0025%, color ≅ 10 ^o H).

2). Using as a method of cleaning the process of processing IFC acetic acid at a temperature of ≅ 150 ^o C is not effective and does not achieve the goal: the content of m-CBA decreases from 0.01-0.08 to 0.0027-0.0044% (necessary ≅ 0 , 0025%).

 3). The duration of the oxidation reaction in the first and second steps (≈ 80 min) indicates a relatively low productivity of the process.

 The aim of the invention is to increase the efficiency of removal of reaction water from the reaction zone and to improve the quality of isophthalic acid.

This goal is achieved by liquid-phase oxidation of m-xylene with an oxygen-containing gas in an acetic acid medium at elevated temperature and pressure in the presence of catalysts consisting of cobalt, manganese and bromide compounds, controlling the water content in the oxidation zone, followed by further oxidation of the impurities and treating with acetic acid using recycling stock solutions after isolation of IFC from acetic acid solutions to the I or II stage. Moreover, the catalyst additionally contains zinc, nickel salts or a mixture of the indicated metal salts [MT] with the ratio [Co + Mn]: [MT] = 1: 0.01-0.2, and the water content in the oxidation zone is controlled by three-stage cooling of the vapor-gas mixture leaving the reactor, under the conditions of gas direct flow and condensed vapors CH ₃ COOH - H ₂ O at the first and third stages and counterflow at the second stage in combination with a rectification process with subsequent return of the dehydrated stream of liquid acetic acid in total from the first and second cooling stages to zones in oxidation, the withdrawal from the process of irrigated acetic acid from the third cooling stage in a ratio providing a water concentration in the reaction zone of 4-10%. The processing of isophthalic acid after the oxidation of impurities is carried out with acetic acid or acetic acid and water at a temperature of preferably 170-230 ^o C.

New in the method of producing isophthalic acid is that the catalyst additionally contains zinc, nickel salts or a mixture of these metal salts at a ratio of [Co + Mn]: [MT] = 1: 0.01-0.2, and the water content in the oxidation zone controlled by a three-stage cooling of gas-vapor mixture leaving the reactor, under conditions and cocurrent gas condensed vapor CH ₃ COOH - H ₂ O in the first and third stages and countercurrent to the second stage in conjunction with the process of distillation followed by returning the flow of dehydrated liquid acetic acid cumulatively with the first and second cooling stages in the oxidation zone of the process output watered acetic acid with a third stage of cooling in a ratio that provides a water concentration in the reaction zone is 4-10%. The processing of isophthalic acid after the oxidation of impurities is carried out with acetic acid or acetic acid and water at a temperature of preferably 170-230 ^o C.

 Description of the installation scheme for the oxidation of m-xylene.

 The process diagram is shown in the drawing.

Initial reagents: m-xylene, metal - bromide catalyst, modified with additives of salts of Zn and Ni, and acetic acid are continuously fed into the oxidation reactor 1, equipped with a two-level turbine stirrer. Air is supplied to the bottom of the reactor. The process is carried out at a temperature of 185-195 ^o C and at elevated pressure. The heat of reaction is reduced by evaporation of the solvent (CH ₃ COOH) and reaction water.

A mixture of vapors and exhaust gases (ASG) is sent to the first stage of cooling in the pipe space of a once-through cooler - condenser 2, in which the temperature of the ASG is reduced by 20-50 ^o C due to the evaporation of water in the annulus.

 Condensed vapors of acetic acid and water from the lower separation part of the refrigerator-condenser 2 are sent to the upper separation part of the reactor, and the vapor-gas mixture is fed to the lower part of the column - prefixes under the lower plate.

As a result of countercurrent movement of the ASG and reflux draining from the countercurrent counterflow condenser 4 in the lower part of the distillation column prefix, CH ₃ COOH is concentrated to a residual H ₂ O content of not more than 10%, preferably 6-8%, which returns by gravity into the reactor in the form of streams dispersed along the height of the reactor.

In the reverse counter-current refrigerator-condenser, along with the cooling of the ASG to 125-135 ^o C, an additional separation of water from acetic acid occurs as a result of mass transfer between the liquid phase flowing down in the form of a film through vertical tubes and the first (vapor-gas) phase rising up . The PGS enriched in water vapor after the second stage is sent to the third cooling stage in a once-through condenser cooler 5, where the temperature is reduced to 40-50 ^o C.

 In the lower separation part of the refrigerator-condenser, the liquid phase, consisting of watered acetic acid, is separated from the gas phase. An acetic acid solution containing 35-50% water is sent to the dehydration unit, and the gases are supplied under pressure to clean by absorption. The oxidate from the first reactor enters the oxidation reactor of the second stage 6.

 The invention is illustrated by the following examples.

Example 1
The initial reaction mixture (IRS) is prepared in a 3-liter collector, where it is loaded:
m-xylene - (589 ml) 509.5 g;
CH ₃ COOH - (1906 ml) 2011.0 g;
Co (OAc) ₂ · 4H ₂ O — 2.84 g;
Mn (OAc) ₂ · 4H ₂ O — 1.43 g;
Zn (OAc) ₂ ; Ni (OAc) ₂ · 4H ₂ O — 0.14 g;
HBr (40%) - 0.21 g;
H ₂ O - (170.2 ml) 170.2 g;
Total: 2,698.93 g.

The contents of the collection are heated to 80 ^o C and stirred until complete dissolution of the catalyst components.

After analysis, the following composition of the initial reaction mixture was determined:
m-xylene - 18.9%;
Co ²⁺ - 0.0249%; 249 ppm;
Mn ²⁺ - 0.0117%; 117 ppm;
Zn ²⁺ - 0.018%; 18 ppm;
Ni ²⁺ - 0.018%; 18 ppm;
H ₂ O - 6.3%;
CH ₃ COOH - the rest.

Перед началом процесса окисления в реактор (V = 1 л) заливают 650 мл раствора катализатора (без м-ксилола), продувают его инертным газом (азотом), затем герметизируют, набирают давление 1,5 МПа и нагревают раствор в реакторе до 180^oC в условиях непрерывного протока азота через реактор в систему конденсации, состоящую из 3-х ступеней охлаждения.

Before starting the oxidation process, 650 ml of the catalyst solution (without m-xylene) is poured into the reactor (V = 1 L), flushed with an inert gas (nitrogen), then sealed, the pressure is increased to 1.5 MPa and the solution is heated to 180 ^o C under conditions of a continuous flow of nitrogen through the reactor into a condensation system consisting of 3 stages of cooling.

After reaching the indicated temperature, the metering pump is turned on and the IRS is continuously fed into the reactor in an amount of 1000 ml / h. Almost simultaneously with this, the nitrogen supply is stopped and instead of it, air is supplied into the reactor in an amount ensuring the maintenance of the excess oxygen in the exhaust gases of not more than 5% by volume. The residence time (oxidation) at a flow rate of IRS of 1000 ml / hour corresponds to 38 minutes. At a pressure of 1.5 MPa, the temperature in the reactor is maintained at 195 ^° C. by a temperature controller.

The spent vapor-gas mixture leaving the reactor is cooled in the first condenser to 165 ^° C and then the liquid gas mixture is sent in separate streams to the second cooling stage, where the temperature is lowered to 130 ^° C. The entire liquid reflux stream from stage I and II is returned via the supply line the reactor and watered steam-gas mixture is fed to the cooling stage III, where its temperature is lowered to 40 ^o C. The water concentration of 6.5% in the oxidation zone is set by varying the amount and composition of withdrawn from the assembly after cooling ASG reflux 3rd mortar and cooling 5. To install this ASG temperature leaving the condenser cooling stage II 130 ^o C by evaporating water pressure changes in the annulus countercurrent condenser 4 in the range 1.2-1.5 MPa (i.e., change the temperature gradient between refrigerant - evaporating water and a cooling flow of ASG and thereby regulate the heat transfer value ΔQ) and when the concentration of water in reflux on the upper blind plate of the prefix column 3 is at least 20%, the bypass line is opened: cavity of the blind plate ---> cubo chamber of the refrigerator-condenser 5. The total concentration of H ₂ O in the reflux from the terminal refrigerator-condenser 5 is supported by ≥ 35% by changing the amount of reflux going through the bypass line (flow regulator with correction according to [H ₂ O]) and changing the temperature of the ASG after countercurrent condenser (temperature regulator installed on the secondary steam line of the separator 4).

At the achieved concentration of H ₂ O in the liquid part of the reactor oxidate of 6.5%, the reaction is continued in continuous mode until a stable stationary concentration of m-CBA of 1504 ppm is established in the oxidation products. When the m-CBA in the oxidation products reaches not more than 0.2% IFC, the oxidate is removed from the first-stage reactor to the second-stage reactor, where it is additionally treated with O ₂ -gas, after which the oxidate is subjected to stepwise cooling in three stages to 60 ^o C, while in the first stage, cooling is carried out in an atmosphere of O ₂ gas containing not more than 5% O ₂ , and in the last stages in an atmosphere of inert gas (nitrogen). Separated from the IFC oxidate cooled to 60 ^° C, it contained 495 ppm [m-KBA] and had a color index of 12 ^o H. After processing the obtained IFC with acetic acid at 200 ^° C in the ratio of IFC: CH ₃ COOH = 1: 4 and subsequent cooling of the acetic acid IFC solution up to 60 ^o C, the isolated product satisfied the quality of high-purity IFC:
[m-kba] = 18 ppm
[m-TC] ≅ 50 ppm
Chromaticity - 5 ^o H
Losses of CH ₃ COOH due to combustion amounted to 37.9 kg / t IFC.

 Other parameters of the example are given in the table.

Example 2. The experiment was carried out under the conditions of example 1, with the only difference being that the temperature of the oxidation reaction was reduced from 195 ^° C to 192 ^° C, and the reaction time was increased from 38 minutes to 45 minutes. The results of the example are shown in the table.

IFC Quality: [m-KBA] = 21 ppm
[m-TC] ≅ 50 ppm
Chromaticity - 8 ^o H
Satisfies the requirements of a highly pure product.

Losses of CH ₃ COOH due to combustion amounted to 37.7 kg / t IFC.

 Example 3. The experiment was carried out under the conditions of example 1, with the same difference that the concentration of m-xylene in the IRS was increased from 18.9% to 20%, the catalyst - 1.87 times, bromine - 1.125 times. The concentration of water in the reaction zone was increased from 6.5 to 10%.

Results:
IFC obtained, satisfying the quality of a high-purity product: [m-CBA] = 24 ppm, m-TC ≅ 50 ppm, color 9 ^o H. Losses of CH ₃ COOH due to combustion amounted to 43.0 kg / t IFC.

Example 4. The experiment is carried out under the conditions of example 3, with the only difference that the concentration of water in the oxidation zone is reduced from 10 to 5.1%, and the ratio of IFC: CH ₃ COOH at the processing stage is from 1: 4 to 1: 4, 5.

Result:
Product quality meets the requirements of high-purity IFC. Losses of CH ₃ COOH due to combustion increased from 43 kg / t IFC to 48.9 kg / t IFC.

Example 5. The experiment was carried out under the conditions of example 4, with the only difference being that the temperature of the oxidation reaction was reduced from 198 ^o C to 185 ^o C, the reaction time was increased to 45 minutes, and the water concentration was reduced to 4%. The results of the example are shown in the table.

IFC Quality:
[m-KBA] = 22 ppm
[m-TC] ≅ 50 ppm
Chromaticity - 6 ^o H
Example 6. The experiment was carried out under the conditions of example 1, with the only difference being that the temperature of the oxidation reaction was reduced from 195 ^o C to 190 ^o C, and the concentration of water was reduced to 4%. The results of the example are shown in the table.

IFC Quality:
[m-kba] = 19 ppm
[m-TC] ≅ 50 ppm
Chromaticity - 6 ^o H
Example 7 (comparative). The experiment is carried out under the conditions of example 3, with the only difference being that the second stage of cooling is excluded from the cooling unit of the vapor-gas mixture leaving the reactor (3, 4).

Result:
The concentration of H ₂ O in the oxidation zone increased from 10% to 15.8% due to the impossibility of its removal using only 2 steps and, as a result, the quality of the obtained IFC significantly deteriorated and did not meet the requirements of a high-purity product:
[m-KBA] = 120 ppm
[m-TC] ≅ 80 ppm
Chromaticity - 14 ^o H
Example 8 (comparative). The experiment is carried out under the conditions of example 3, with the only difference being that the III stage of cooling is excluded from the ASG cooling unit leaving the reactor.

Result:
The water content in the reaction zone increased from 10% to 15.2%. IFC quality does not meet the requirements of a high-purity product.

[m-KBA] = 92 ppm
[m-TC] ≅ 68 ppm
Chromaticity - 12 ^o H
Example 9 (comparative). The experiment is carried out under the conditions of example 3, with the only difference being that the second and third stages of cooling are excluded from the condensation unit and only the first stage of cooling is retained.

Result:
The water content in the oxidation zone of the reactor increased from 10 to 16.9%, which in turn led to a significant deterioration in the quality of IFC:
[m-KBA] = 238 ppm
[m-TC] ≅ 60 ppm
Chromaticity - 15 ^o H
Example 10. The experiment was carried out under the conditions of example 1, with the only difference being that the water concentration in the oxidation reaction zone was lowered to 2.5% and "ice" dehydrated CH ₃ COOH was used to prepare IRS.

Result:
Losses of CH ₃ COOH due to combustion increased from 37.9 kg / t IFC to 58.0 kg / t IFC.

IFC Quality:
[m-KBA] = 16 ppm
[m-TC] ≅ 50 ppm
Chromaticity - 12 ^o H
According to the color index does not reach the value (≅ 10 ^o H) presented for high-purity IFC.

Example 11. The experiment is carried out under the conditions of example 1, with the only difference being that the processing of the obtained IPA with acetic acid was carried out at 160 ^o C in the ratio of IFC: CH ₃ COOH = 1: 4. The quality of the obtained product significantly worsened in all respects and did not meet the requirements high purity product:
[m-KBA] = 27 ppm
[m-TC] ≅ 50 ppm
Chromaticity - 12 ^o H
Example 12. The experiment is carried out under the conditions of example 2, with the only difference that the processing of the obtained IFC was carried out with acetic acid at 170 ^o C. The results of the example are shown in the table.

IFC quality: [m-KBA] = 18 ppm
[m-TC] ≅ 50 ppm
Chromaticity - 8 ^o H
Satisfies the requirements of a highly pure product.

Example 13. The experiment is carried out under the conditions of example 3, with the only difference that the processing of the obtained IFC is carried out with acetic acid at 230 ^o C in the ratio of IFC: CH ₃ COOH = 1: 4 and subsequent cooling of the acetic acid solution of IFC to 60 ^o C. The isolated product Satisfied the quality of high-purity IFC: [m-KBA] = 9 ppm
[m-TC] ≅ 50 ppm
Chromaticity - 4 ^o H
Example 14. The experiment is carried out under the conditions of example 4, with the only difference being that the IFC is re-treated with water at a temperature of 230 ^o C. The results of the example are shown in the table.

IFC quality: [m-KBA] = 19 ppm
[m-TC] ≅ 50 ppm
Chromaticity - 6 ^o H
Satisfies the requirements of a highly pure product.

Example 15. The experiment is carried out under the conditions of example 4, with the only difference being that IFC is re-treated with water at a temperature of 170 ^o C. The results of the example are shown in the table.

IFC quality: [m-KBA] = 20 ppm
[m-TC] ≅ 50 ppm
Chromaticity - 7 ^o H
Example 16. The experiment is carried out under the conditions of example 1, with the only difference being that the zinc salt is replaced by the same amount of nickel salt.

Результаты примера приведены в таблице.

The results of the example are shown in the table.

IFC quality: [m-KBA] = 18 ppm
[m-TC] ≅ 50 ppm
Chromaticity - 5 ^o H
Example 17. The experiment is carried out under the conditions of example 1, with the only difference being that the nickel salt is replaced by the zinc salt in the same amount.

Результаты примера приведены в таблице.

The results of the example are shown in the table.

IFC quality: [m-KBA] = 20 ppm
[m-TC] ≅ 50 ppm
Chromaticity - 7 ^o H
Example 18. The experiment is carried out under the conditions of example 1, with the only difference that the addition of zinc and nickel salts is not performed. The quality of the product obtained has deteriorated significantly in all respects and did not meet the requirements of a high-purity product:
[m-KBA] = 30 ppm
[m-TC] ≅ 50 ppm
Chromaticity - 13 ^o H
Example 19. The experiment is carried out under the conditions of example 1, with the only difference being that the addition of nickel and zinc salts is very insignificant.

Результаты примера приведены в таблице.

The results of the example are shown in the table.

[m-KBA] = 25 ppm
[m-TC] ≅ 50 ppm
Chromaticity - 9 ^o H
Example 20. The experiment is carried out under the conditions of example 1, with the only difference being that the addition of zinc and nickel salts is substantially increased.

Результаты примера приведены в таблице.

The results of the example are shown in the table.

Результаты примера приведены в таблице.[m-KBA] = 25 ppm
[m-TC] ≅ 50 ppm
Chromaticity - 8 ^o H
Example 21. The experiment is carried out under the conditions of example 1, with the only difference being that zinc salt in the ratio

The results of the example are shown in the table.

Результаты приведены в таблице.[m-KBA] = 24 ppm
[m-TC] ≅ 50 ppm
Chromaticity - 10 ^o H
Example 22. The experiment is carried out under the conditions of example 1, with the only difference being that zinc salt in the ratio

The results are shown in the table.

Результаты приведены в таблице.[m-KBA] = 25 ppm
[m-TC] ≅ 50 ppm
Chromaticity - 10 ^o H
Example 23. The experiment was carried out under the conditions of example 1, with the only difference being that nickel salts in the ratios were used as additives

The results are shown in the table.

Результаты приведены в таблице.[m-KBA] = 24 ppm
[m-TC] ≅ 50 ppm
Chromaticity - 10 ^o H
Example 24. The experiment is carried out under the conditions of example 1, with the only difference being that nickel salts in the ratios were used as additives

The results are shown in the table.

Продукт не соответствует качеству высокочистого продукта.[m-KBA] = 25 ppm
[m-TC] ≅ 50 ppm
Chromaticity - 10 ^o H
Example 25. The experiment is carried out under the conditions of example 1, with the only difference being that zinc and nickel salts in the ratios were used as additives

The product does not match the quality of the high-purity product.

 The results are shown in the table.

Продукт не соответствует качеству высокочистого продукта. Результаты приведены в таблице.[m-KBA] = 30 ppm
[m-TC] ≅ 50 ppm
Chromaticity - 25 ^o H
Example 26. The experiment is carried out under the conditions of example 1, with the only difference being that zinc and nickel salts in the ratios were used as additives

The product does not match the quality of the high-purity product. The results are shown in the table.

[m-KBA] = 30 ppm
[m-TC] ≅ 50 ppm
Chromaticity - 25 ^o H
The proposed method for producing isophthalic acid has the following advantages compared with the prototype.

 1. Provides an effective way to control the composition of the reaction mass in the reaction zone according to the water content, and thereby contributes to an increase in the conversion of m-xylene to IFC, to a decrease in the rate of side reactions leading to deterioration of color, and also increases the efficiency of mass transfer of oxygen from the gas to the liquid phase due to its increased solubility in aqueous acetic, medium containing 4-10% water.

2. Improves the quality of IFC (content of m-CBA 0.0025%, color ≅ 10 ^o H) compared with the prototype: m-CBA 0.0027-0.0044%, color ≥ 20 ^o H.

Claims (2)

1. A method of producing isophthalic acid (IFC) by liquid-phase oxidation of m-xylene with an oxygen-containing gas in an acetic acid medium at elevated temperature and pressure in the presence of catalysts consisting of cobalt, manganese and bromide salts, regulating the water content in the oxidation zone, followed by post-oxidation impurities and treatment with acetic acid using recycle of the mother liquor after the separation of IFC from acetic acid solutions at stage I or II, characterized in that the catalyst additionally contains it contains zinc, nickel salts or a mixture of the indicated metal salts [MT] with the ratio [Co + Mn]: [MT] = 1: 0.01 - 0.2, and the water content in the oxidation zone is controlled by three-stage cooling of the vapor-gas mixture leaving reactor in the direct flow of gas and condensed vapor CH ₃ COOH-H ₂ O - at the first and third stages and counterflow at the second stage in combination with the rectification process, followed by the return of the dehydrated stream of liquid acetic acid in total from the first and second cooling stages to the oxidation zone , conclusion from the process acetic acid from the third cooling stage in a ratio providing a water concentration in the reaction zone of 4-10%. 2. The method according to claim 1, characterized in that the processing of isophthalic acid after the oxidation of impurities is carried out with acetic acid or acetic acid and water at a temperature of 170 - 230 ^o C.

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