RU2415836C2 - Method of producing pure isophthalic acid and by-products from isomers of cymene and diisopropylbenzene - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention relates to organic and petrochemical synthesis, specifically to the technological process of producing pure isophthalic acid and by-products - terephthalic and formylic acid through oxidation of isomers of cymene or diisopropylbenzene with an oxygen-containing gas in an acetic acid medium in the presence of a catalyst which contains salts of heavy metals and halide compounds at high temperature and pressure to a defined degree of conversion of the said isomer mixtures to isophthalic acid and by-products, followed by separation and purification of pure isophthalic acid and by-products through re-crystallisation in water, where isomers of cymene or diisopropylbenzene are oxidised in two steps at temperature 120-140°C at the first step and 150-160°C at the second step, in conditions where concentration of the Co-Mn catalyst increases in steps in the range 1300-1800 ppm (0.130-0.180%) at the first step, 1800-2400 ppm (0.180-0.240%) at the second step, promoted by halide compounds, reducing pressure in the range 0.9-1.6 MPa with pressure fall gradient between the steps in the range 0.2-0.6 MPa; purification and separation of the reaction mass obtained after oxidation, separation of the solid crystalline product and washing with acetic acid, carrying out re-crystallisation in water with preliminary holding of the aqueous suspension of the isophthalic acid and terephthalic acid mixture at temperature 225-235°C for 10-15 minutes and successive step-by-step extraction of the desired products and by-products: at 150-190°C - extraction of solid terephthalic acid to obtain aqueous mother solution, and at 60-80°C - extraction of solid isophthalic acid form the said mother solution and washing the extracted isophthalic acid with 2-2.5-fold amount of water to obtain isophthalic acid with the following qualities: chromaticity, °H, ≤10 - m-carboxybenzaldehyde [M-CBA], %, ≤0.002 - m-toluic acid [M-TA], %, ≤0.005 - benzoic acid [BA] %, ≤0.005.

EFFECT: efficient method of producing pure isophthalic acid.

2 cl, 2 tbl, 17 ex

Description

The invention relates to organic and petrochemical synthesis, specifically to a process for the production of pure isophthalic acid (ChIFK) and related products - terephthalic (TPA) and formic (MK) acids by liquid-phase catalytic oxidation of a mixture of meta- and para-isomers of cymol or diisopropylbenzene O ₂ - gas in an acetic acid medium, followed by separation and purification of the reaction products.

Pure IFC is used to produce polyesters, which, in turn, are used for the production of coatings, paints, reinforced plastics, packaging and bottles (from polyethylene terephthalate - PET) for food and technical purposes. In addition, pure IFC as a comonomer or intermediate is used for the manufacture of durable and low-toxic electrical insulating varnishes, fibers with enhanced chemical and thermal stability, color-forming components for film and film films, synthetic leather, polymer concrete and other products. Purified terephthalic acid or its mixture with isophthalic acid in a ratio of 1: 0.02 ÷ 0.1 as a by-product resulting from the oxidation of residual amounts of p-cymol in a mixture of m-, p-cymols is widely used in the industrial production of PET in the manufacture of packaging products and bottles for food.

Formic acid, which is conjugated during the oxidation of the isopropyl substituent m-, p-cymol, is used in the textile industry for the manufacture of mordants and dyeing of wool and cotton yarn from an acid bath, and is also used in various fields of technology: as a coagulating agent in the production of natural rubber; in medicine for formylation of amines; as a feedstock for the production of various salts (formates), for example, copper formate, used for the purification of gas mixtures from carbon monoxide, cobalt and nickel salts as catalysts; in the food industry as a preservative; in the production of aromatic substances, ether solvents, etc.

Known methods for producing IFCs used in industry are based on 2-stage processes, usually including the so-called SD method for the oxidation of individual m-xylene in the liquid phase of the solvent (usually CH ₃ COOH) with air to obtain technical IFC, which is purified mainly by hydrogenation of impurities in an aqueous solution in the presence of a palladium catalyst supported on a carbon carrier (Pd / C) ([1] - US patent No. 5110984, 1992, [2] - RF application No. 95117934).

These methods relate to efficient industrial syntheses of pure (purified) IFC, however, they are based on using pure m-xylene with a basic substance content of ≥99.5% as a starting material. Obtaining feedstock of the specified quality is associated with a fairly significant cost for the separation of m-xylene from a mixture of xylene isomers, which affects the cost of IFC in the share of the cost of raw materials.

A known method for the synthesis of isophthalic and concomitant terephthalic acids from the fraction of isopropyltoluene (zymol) obtained by alkylation of toluene with propylene [British Patent No. 833357, 1960]. The isomers of zymols are oxidized with air in an acetic acid medium in the presence of manganese acetate and ammonium bromide at a temperature of 180 ° C. The oxidation time is 4 hours. The solid acids are separated by filtration, followed by washing the solid with acetic acid. The gas-vapor mixture from the reactor is discharged through cooled traps, and then the formed acetic acid condensate is mixed with the washing acetic acid. Water is distilled from the watered acetic acid and concentrated CH ₃ COOH is again sent to the oxidation reactor.

Phthalic acid, which is contained in a small amount in the mixture, is first separated from the resulting aromatic acid mixture by heating the acid mixture to form phthalic anhydride. The latter is separated from the mixture by evaporation. The remaining binary mixture of iso- and terephthalic acids is separated by extraction with acetic acid or esterified with methanol to give dimethyl isophthalate (DMI) and dimethyl terephthalate (DMT). The resulting esters are separated by distillation.

The main disadvantage of the proposed method is the complex scheme for the separation of isomers of benzenedicarboxylic acids (BDK). So, for the separation of phthalic acid, it is required to heat the entire obtained BDK mixture to a temperature of ≥200 ° C with the conversion of phthalic acid to a relatively volatile phthalic anhydride. This allows you to separate it by evaporation from the remaining mixture of IFC-TFA. However, this requires an increased temperature regime (up to 240 ° C), in which the impurities present in the BDK mixture, in particular, carboxybenzaldehydes, ketones, etc., can undergo oxygen catalytic decomposition in the presence of even a small amount of oxygen. The IPA-TFA mixture remaining after phthalic anhydride removal is recommended to be separated by extraction with acetic acid or rectification of their methyl esters. In the first case, the extraction process requires their dissolution. It is known that they are sparingly soluble both in acetic acid and in water. So, for example, to dissolve TFA in a 30% aqueous suspension, a temperature of 286 ° C is required, and in the case of IFC - not lower than 240 ° C. Although their solubility in acetic acid is slightly higher at a high temperature of 240-286 ° C in the presence of a residual content in the catalyst solution, acetic acid itself can undergo thermocatalytic decomposition (under normal conditions, it is stable up to 300 ° C).

In another proposed version of this patent, the separation of the mixture of IFC and TFA in the form of their methyl esters requires the process of esterification with methanol, followed by technological operations for distillation of the excess methanol, separation of DMI and DMT, followed by their separate crystallization, isolation and drying. This leads to the need to create an additional technological stage, which complicates the process.

To simplify the technology for the production of isophthalic acid, methods are proposed according to which a mixture of m-, p-cymols is preliminarily separated by rectification using a column with at least 150 plates with a reflux ratio of 40 to 150 [British Patent No. 1408058, 1975]. The proposed method for the isolation of m-cymol from an isomeric mixture of zymols is energy-intensive due to the extremely high reflux ratio and material-intensive due to the large number of plates (150). These negative factors, due to the close boiling point of the meta- and paraisomers of cymol (Δt _bp. ≤2 ° C), make this stage economically inefficient and technically difficult.

In the well-known [British Patent No. 1336726, 1974] method of selective sorption on a molecular sieve, a liquid binary mixture of m-, p-cymols isolated from an alkylate is passed through a layer of a molecular sieve of type X or Y, for example 13X, for exchange with salts Ba and K. The isomer of the sorbed cymol is displaced by a desorbent, for example benzene or toluene. A scheme of a model of a moving layer is proposed, which includes 4 sorbent zones connected in series, into which the initial mixture and desorbent are fed, extract and raffinate are removed. The inlet and outlet openings in 4 zones operate cyclically, the extract and raffinate are distilled off with the release of m-tsimol and p-tsimol. However, the sorption separation scheme of the mixtures under consideration is a relatively cumbersome semi-periodic (cyclic) process and requires sufficiently pure physico-chemical composition and stable separable mixtures. In addition, it is necessary to periodically carry out technological operations to restore (regenerate) the sorbent, desorbent to ensure the normative allowable emissions into the atmosphere, which complicates the separation scheme and leads to an increase in production costs to a level commensurate with the costs of separating the IFC-TFA mixture by recrystallization in solvents or by other methods, that is, without the use of preliminary separation of a mixture of meta- and steam of cimol isomers.

The oxidation of individual zymols to the corresponding BDK is known according to a simpler scheme according to the method [V.I. Ovchinnikov, V.N. Aleksandrov, S.S. Gittis, “Chemistry and Technology of Monomers”, Proceedings of VNIPIM, vol. 3, issue 3, Tula, 1972, p.25]. Terephthalic acid is obtained by liquid-phase catalytic oxidation of individual p-cymol with air in an acetic acid medium with the yield of the target product of ~ 70% of theory. The process is carried out in one stage at a temperature of 150-160 ° C at a pressure of 20 kg / cm ² in the presence of a Co-Mn-Br catalyst, the content of components of which is, g mol / mol p-cymol:

Co ^{+ 2} - 0.00625; Mn ^{+ 2} - 0.00625; Br ^- - 0.02335.

The main disadvantage of the one-stage method of oxidation of an individual isomer of cimol, for example p-cimol, to TFA is the low yield of the target product, not exceeding 70% of theory.

Also known are methods for producing isophthalic and terephthalic acids from isomers of diisopropylbenzene, synthesized usually by alkylation of benzene with propylene.

Thus, according to the Dutch patent [Holland Patent No. 108519, 1964], the IFC-TFA mixture is obtained by liquid-phase oxidation of a binary mixture of the meta and para isomers of diisopropylbenzene (DIPR) with air in a CH ₃ COOH medium in the presence of a Co-Mn catalyst. In continuous mode, the process is carried out at 120-150 ° C and a pressure of 2-8 kg / cm ² for 1.5-3 hours. The obtained crude mixture of IFC-TFA can be separated by known methods, for example, using the recrystallization process in a suitable solvent or by rectification of their dimethyl ethers after esterification of the isolated BDK with methanol. The purification processes of IFC and TFA in this method are not considered. A distinctive feature of this method of producing IFC-TFA is the reaction at relatively low temperature conditions of 120-150 ° C in the presence of Co-Mn catalyst, which, along with the main reaction leading to the formation of BDK, provides the concomitant oxidation of methyl groups in isopropyl substituents to formic acid, which, like phthalic acids, is a valuable product for various industrial syntheses.

However, the proposed method for the oxidation of isomers of diisopropylbenzene to IFC-TFA provides only technical (crude) mixture of BDK.

Of the many methods for the separation and purification of IFC-TFA, the closest in technical essence and the achieved results is an improved method for the separation of isomeric phthalic acids - IFC-TFA-FC, obtained by liquid-phase oxidation of an isomeric mixture of dialkylbenzenes, in particular xylene isomers, by fractional crystallization in an aqueous solution [US Patent No. 3082250, 1963].

The essence of this method is as follows. A mixture of phthalic acids is isolated from an oxidate, consisting mainly of the products of the oxidation of dialkylbenzene and a solvent (CH ₃ COOH), by crystallization and subsequent filtration. Next, the resulting precipitate is washed with pure CH ₃ COOH to remove residual solution containing the catalyst and partially dissolved impurities (mainly intermediate products). The dissolution of the BDK is carried out by dissolving in water with sequential removal of solutions of individual acids. By varying the temperature parameters and selecting appropriate concentrations of the phthalic acid mixture in the solvent (H ₂ O), a quite acceptable separation of the phthalic acids can be achieved.

The use of fractional dissolution of the 3-component BDK mixture and their subsequent isolation by crystallization from individual solutions is fundamentally possible, and this method is implemented on an industrial scale. However, taking into account the inevitable co-crystallization of both BDK itself and the impurities contained in them, in particular isomers of toluic acids, carboxybenzaldehydes, etc., it will be necessary to carry out the process in several steps, which leads to a significant complication of the phthalic acid separation scheme by the proposed method.

The aim of the proposed method is to increase the yield of IFC and related products (TFA and formic acid) during the oxidation of mixtures of cimol and diisopropylbenzene isomers, as well as to increase the efficiency of separation of phthalic acids and their purification to achieve high quality of the target products.

This goal is achieved by the fact that isomeric mixtures of m-, p-cimol and m-, p-diisopropylbenzene containing 70-96% m-cimol or m-diisopropylbenzene are oxidized in two stages under conditions of increasing concentration of Co-Mn catalyst in the limit of 1200-2600 ppm, promoted by the connection of the halogen, the temperature in the range of 120-165 ° C and a discrete (step) pressure reduction in the range of 1.6-0.9 MPa with a gradient of the differential drop between steps of 0.2-0.6 MPa such so that in the first stage, the process is carried out at a temperature of 120-140 ° C, a pressure of 1.4-1.6 M Pa, the concentration of m-, p-dialkylbenzene is 14-18%, the total concentration of Co and Mn is 0.130 ÷ 0.180% (1300 ÷ 1800 ppm) with the ratio Co: Mn = 1: 0.8 ÷ 1.2 with the addition of an equimolar amount of halogen in in the form of HBr or a mixture (HBr • Hcl) for 90-120 minutes until 90-98% conversion of the starting mixture of m-, p-cimol or m-, p-diisopropylbenzene to oxygen-containing compounds is achieved, and a steady-state concentration of the IFC-mixture is established in the oxidation products TFA 15-22%, after which the resulting reaction mixture (oxidate-1) is oxidized to the second foot under reduced pressure to 0.9-1.4 MPa and increased to 0, 180 ÷ 0.240% (1800-2400 ppm) of the concentration of Co-Mn catalyst and an increased atomic ratio of catalyst to halogen from 1: 1 to 1: 1.3, the reaction is continued for 40-60 minutes until the concentration of the IFC-TFA mixture in the oxidation products reaches 94 -99.5% and the total concentration of intermediate compounds (in terms of m-, p-diisopropylbenzaldehyde) 0.3-0.7%, after which the reaction mass of the second stage (oxidate-2) is removed from the reaction zone, cooled to 90- 116 ° C, a solid phase is isolated, which, after washing with acetic acid at an elevated temperature, is dried to constant weight and dry BDK admixture is suspended in water in a ratio of: BDK: H ₂ O = 1: 2 ÷ 2,5.

The resulting aqueous suspension is heated to 225-235 ° C, maintained at this temperature for 10-15 minutes, then cooled to 150-190 ° C and TFA is isolated from the resulting intermediate suspension, which, after washing with heated water, is taken to the drying and packaging step by known methods and the mother liquor after isolation of TFA (filtrate - 1) is cooled to 60-80 ° C and IFC is isolated from the resulting main suspension, which after washing with heated water in the ratio: IFC: N ₂ O = 1: 2 ÷ 2.5 is dried and packaging with known techniques to obtain IFC trace Quality:

- color, ° N, ≤10

- m-carboxybenzaldehyde [M-CBA],%, ≤0.002

- m-toluic acid [M-TC],%, ≤0.005

- benzoic acid [BK],%, ≤0.005

The invention is illustrated, but not limited to the following examples.

Example 1

For oxidation, a fraction of m-, p-cymols of the following composition was used,%:

m-cymol -81.01

p-cymol -19.97

other products -0.02.

In separate experimental experiments, the content of m-cymene in the alkylate was increased to 96% by the transalkylation method.

In the collection 1, the first batch of the initial reaction mixture (IRS) is prepared, for which 337 ml (289 g) of the obtained mixture of m-, p-cymol containing ~ 80% m-cymol and ~ 20% p-cymol, 20 ml are loaded into it (20 g of H ₂ O), 1287 ml (1475 g) of acetic acid, 7.5 g of Co acetate tetrahydrate, 7.5 g of Mn acetate tetrahydrate and 11 g of a 40% aqueous solution of HBr.

The resulting mixture is heated to 60-70 ° C and, after the dissolution of the catalyst has been achieved, 400 ml of IRS are pumped into the reactor by a metering pump, which is heated to 125 ° C in a stream of nitrogen at a pressure of 1.6 MPa. Upon reaching the indicated temperature, the nitrogen supply to the reactor is turned off and air is supplied in an amount providing the O ₂ content in the exhaust gas of not more than 5% by volume. The beginning of the reaction and its progress is determined by the absorption of oxygen and the readings of the concentrations of CO ₂ and CO in the exhaust gases at the gas analyzers.

After the establishment of a stable temperature and absorption of O ₂ serves IRS in the amount of 8.3 ml / min (0.5 l / h), providing a residence time in the reaction zone of 90 minutes. The reaction products (oxidate 1) flow into a stage II oxidizing reactor operating under the same pressure of 1.6 MPa. The oxidation process in the 2nd stage mode is carried out in a semi-continuous mode in the same reactor by introducing a solution of Co-Mn-Br catalyst in acetic acid of the same concentration and ratio of its components as in the initial reaction mixture. At the same time, the pressure is reduced from 1.6 MPa to 1.0 MPa and the reaction temperature is increased to 160 ° C. The oxidation reaction is continued for 40 minutes until the oxygen absorption in the autothermal mode decreases. The oxidation temperature of 160 ± 1 ° C and the associated CO and CO ₂ content in the exhaust gases are maintained by a pressure change in the range of ± 0.015 MPa.

The resulting reaction mass (oxidate 2) is cooled to 115 ° C, solid crystalline products are isolated from it, washed with acetic acid heated to 110 ° C in the ratio: crystalline products: CH ₃ COOH = 1: 2.5, and then dried to constant weight and subjected to analysis.

The product obtained at the 2nd stage has the following quality indicators:

Σ isomers [TC + cuminic acid],% 0.18 Σ isomers [CBA + AsBK],% 0.21 Σ [by-products and other products],% 0.36 Color, ° N 26

To carry out the processes of separation of IFC and TFA and their purification, water is used as a solvent.

A 20% aqueous suspension of the IFC-TFA mixture, isolated as a precipitate from the reaction mass of the 2nd oxidation stage after washing with acetic acid, is loaded into the reactor. In a stream of nitrogen, the suspension is heated to 232 ° C at a pressure of 3.0 MPa and kept at this temperature for 15 minutes, then the temperature is reduced to 190 ° C by evaporation of water by lowering the pressure of the reaction mass, kept at this temperature for 12 minutes, and the resulting suspension emit a solid precipitate of TFA, which after washing with water and drying has the following quality indicators:

Σ isomer [TC] + [BC],% 0.009 Σ isomer [CBA + acetylbenzoic acid (AsBK)],% 0.002 [IFK],% 3.8 Color, ° N 9.0

The aqueous mother liquor (filtrate 1) is cooled to 80 ° C, the formed solid (crystals) phase of IFC is isolated, it is washed by repulping with hot water in the ratio of IFC: H ₂ O = 1: 2.5, and after isolation and drying, the following indicators are obtained and purified IFC:

[m-TK + BK],% 0.005 [m-CBA],% 0.002 Color, ° N 6.0

The total yield of the target product of IFC in the stages of oxidation, separation and purification amounted to 91.1%, the associated product of TFA 94.8%.

The conditions and results of the first and subsequent examples are shown in tables 1 and 2.

Example 2. The experiment is carried out under the conditions of example 1 with the only difference that the oxidation process at the second stage is carried out continuously with air supplied to the reactor with a residence time of I and II stages for 65 minutes and maintaining the total residence time of example 130 minutes.

At the oxidation stage, the following results were obtained.

The total concentration of IFC-TFA in the oxidation products of the first stage is 22.5% with the degree of conversion of m-, p-cymols to oxygen-containing compounds, including in IFC-TFK, 96.3%.

The total content of IFC-TFA in the oxidation products isolated from oxidate 2 of the second stage reactor, 99.48% with a color index of 16 ° N, the total yield of IFC-TFA at the two-stage oxidation stage of 95.5% and the associated product is formic acid - 70.2%.

In the process of separation and purification of the mixture of IFC-TFA in the conditions of example 1 (table 2), the following quality indicators of pure IFC and the associated product of TFA were obtained.

Quality IFC Quality TFK [m-TK + BK],% 0.004 Σ isomer. [p-TC] + [BC],% 0,07 [m-CBA],% 0.0015 Σ isomer. [CBA + AsBK],% 0.0018 [IFK],% 3.6 Color, ° N 5,0 Color, ° N 9.0

The total yield of IFC according to the stage of oxidation and separation of the IFC-TFA mixture with their purification amounted to 91.6%, and the accompanying product - TFA - 94.6%.

Example 3. The experiment is carried out under the conditions of example 1, with the only difference being that the concentration of Co-Mn catalyst at the first and second oxidation stages is reduced by 1.3 times, and the reaction temperature is increased by 5 ° C. The mode of separation and purification of the obtained mixture of IFC-TFA is maintained at the same level of experiment 1.

Achieved results at the stage of oxidation.

The degree of conversion of the mixture of p-, m-cimol to oxygen-containing compounds at the first stage is 90.2%, at the second stage - quantitatively (100%); the concentration of IFC-TFA mixtures in the reaction products isolated from oxidate-1 reached 15.1%, from oxidate-2 it was 94.52% with color indices of 28 ° N; the yield of the IFC-TFA mixture is 92.0%, formic acid 60.4%.

The results of the stage of separation of the mixture of IFC-TFA and purification of the selected products.

The quality of the purified IFC Associated Product Quality - TFK [m-TK + BK],% 0.010 Σ isomer. [TK] + [BK],% 0.013 [m-CBA],% 0.002 Σ isomer. [CBA + AsBK],% 0.0025 [IFK],% 3.9 Color, ° N 8.0 Color, ° N 10.0

The total yield of purified IFC at the stages of oxidation, separation and purification of the mixture is 90.2%, and the total yield of the accompanying product, TFA, is 93.9%.

From the above data, it follows that with a decrease in the concentration of Co-Mn catalyst and an increase in temperature in the above ranges, the yield of IFC decreases slightly (from 95.1 to 92.0%), the content of impurities (intermediate and side compounds increases from 0.36% to 4 , 89%).

At the stage of separation and purification, the quality indicators of the purified IFC and the associated product - TPA - approach the limit values of the quality suitable for use in the production of polyethylene terephthalate (PET) or a mixture of polyethylene terephthalate (PET-IF) in terms of color (8 ° N and 10 ° N, respectively) and the content of m-CBA (0.002%) and CBA (0.0025%), respectively.

Example 4. The experiment is carried out under the conditions of example 2, with the only difference being that at the oxidation stage, the concentration of the mixture of m-, p-cymol in CH ₃ COOH medium is increased from 16% to 18%, washing of the IFC-TFA mixture extracted from the oxidate 2 by its repulpation in acetic acid at elevated temperature (165 ° C), and the isolation of washed IFC-TFA is carried out at 115 ° C.

The separation and purification of IFC-TFA in water is carried out according to the mode of example 2.

At the stage of separation and washing of the IFC-TFA mixture, the experiment is carried out under the conditions of Example 2 (Table 2) with the only difference that the heating temperature of the suspension is increased from 230 ° C to 235 ° C and, with a holding time of 10 minutes, the solution is cooled to the filtration temperature - 1 - 180 ° C.

Under the above conditions of example 4 (table 1, 2) the following results were obtained.

At the stage of oxidation: conversion of a mixture of m-, p-cymol in the first stage of oxidation of 90%;

additional oxidation of the oxidate in the second stage, followed by washing the extracted oxidation products with acetic acid at elevated temperature (165 ° C), leads to the production of the technical mixture IFC-TFA of the following quality:

Σ [IFC + TFA],% 99.37 Σ [isomers of TC and cuminic acid],% 0.18 Σ [isomers of CBA and acetylbenzoic acid],% 0.16 Σ [other intermediates and by-products],% 0.29 Color, ° N 27

Subsequent separation of the resulting mixture and purification of the isolated IFC and TFA by step crystallization in an aqueous solution leads to products with the following quality indicators (Table 2):

Quality IFC Associated Product Quality - TFK [m-TK and BK],% 0.012 Σ isomer. [TK] + [BK],% 014 [m-CBA],% 0.0021 Σ isomer. [CBA + AsBK],% 0.002 Color, ° N 7.0 [IFK],% 4.6 Color, ° N 9.0 The yield of IFC - 91.3%, of the associated product - TFA - 94.5%

Example 5. The experiment is carried out under the conditions of example 1, with the only difference being that a promoter is a mixture of HBr and Hcl in a 1: 1 ratio while maintaining the total concentration of the halogen ion at the same level as in example 1 (0.312%).

Result. When replacing half of the bromine with chlorine, used as a Co-Mn catalyst promoter, the quality indicators of the IFC-TFA mixture at the stage of oxidation of the mixture of m- and p-cymols, as well as their total yield, are practically at the same level as in Example 1, which allows partially use Hcl as promoter 1 as a cheaper and more affordable product.

At the stage of separation of the mixture of IFC-TFA and their purification, the following results were obtained:

Quality IFC Associated Product Quality - TFK Σ [m-TC and CD],% 0.008 Σ isomer. [TK] + [BK],% 0.009 [m-CBA],% 0.0021 Σ isomer. [CBA + AsBK],% 0.0022 Color, ° N 9.0 [IFK],% 4.02 Color, ° N 10 The yield of IFC - 91.1%, of the associated product - TFA - 94.1%

Example 6 (comparative). The experiment is carried out under the conditions of example 2, with the only difference being that the oxidation temperature of the mixture of m-, p-cymols in the reactors of stages I and II is set at one reduced level of 130 ° C.

The following results are obtained.

At the oxidation stage in the first-stage reactor with a residence time of 65 minutes, the degree of conversion of m-, p-cymols to intermediate oxygen-containing compounds, as well as to IFC-TFA, reaches 96.2%. The total concentration of IFC and TFA in the oxidation products isolated from oxidate 1 reaches 23.6%. These results are consistent with example 2.

Further oxidation of oxidate-1 in the second-stage reactor at a temperature of 135 ° C and the addition of an additional solution of Co and Mn catalyst and Br (in the form of 40% HBr) into it is inhibited; the absorption of oxygen is suspended and the main reaction products after 65 minutes of oxidation are intermediate and side compounds. Qualitative indicators of a mixture of oxidized products isolated from oxidate 2, reach values:

Σ [IFC + TFA],% 30.09 Σ [TC isomers and cuminic acids],% 46.1 Σ [isomers of CBA and acetyl benzoic acids],% 14.0 Σ [others including by-products],% 10.9 The color extracted from the oxidate is -2 solid (crystalline) mixture of products, ° N 196

The total yield of IFC-TFA to the initial mixture of m-, p-cymol reaches only 39.4%, formic acid 30.2%.

The reason for the low quality of the IFC-TFA mixture and their low yield are: 1) the accumulation in the oxidation products of hydroxy peroxides of cimol relatively stable at 130-135 ° C, the decomposition (transformation) of which leads to the formation of cresol isomers - inhibitors of the oxidation reaction; 2) a decrease in the reactivity of intermediate compounds (isomers of a mixture of toluic, cumin, acetylbenzoic acids and other carboxyl-containing compounds), which at a low temperature of 130 ° C are not subjected to further oxidative conversion.

Example 7 (comparative). The experiment is carried out under the conditions of example 2, with the only difference being that the process of oxidation of a mixture of m-, p-cymols is carried out in one step at an elevated temperature of 160 ° C.

results

1. The accumulation of CO ₂ and CO in the exhaust gas has more than tripled, which indicates an increase in side processes of oxidative decarbonylation and decarboxylation of intermediate oxygen-containing compounds, initial m-, p-cymols and solvent.

2. The color of the crude mixture of IFC-TFA increased from 16 ° N to 170 ° N, isolated from oxidate, as a result, the content of side colored compounds in the oxidation products increased by more than 10 times: achieved in Example 2 - 0.24%, in 7 comparative example - 2.46%.

3. The total yield of the crude mixture of IFC-TFA decreased from 95.5% to 86.9%.

4. At the stage of separation of the IFC-TFA mixture obtained in one oxidation step and purification of the separated products, the IFC quality in terms of color exceeds more than 5 times the permissible norm: 67 ° N is reached, the permissible norm is ≤10 ° N.

The main reason for the poor quality of IFC in terms of color and low yield of the target and associated (TFA) products is that, at elevated temperatures of 160 ° C, the primary oxidation products of the isopropyl group of m-, p-cymols (isomers of hydroperoxides, aldehydes and ketones) are not very stable and thermocatalytically decompose by oxidative destruction reactions with the formation and accumulation of active radicals, including radical radical compounds, the further conversion of which prevails by the oxidative condensation reaction with the formation of high-boiling, mainly colored, compounds - alkyl, hydroxy, keto and carboxy derivatives of biphenyl, benzophenone, fluorenone and other by-products, as well as oxidation products with less the number of substituents such as benzoic acid.

Example 8 (comparative). The experiment is carried out under the conditions of example 1, with the only difference being that a catalyst with a reduced ratio of cobalt to manganese Co: Mn = 1: 2 is used at the oxidation stage while maintaining their total concentration.

The results are obtained.

At the oxidation stage, the content of CO ₂ and CO in the exhaust gases decreased by a factor of 1, 2;

by [CO ₂ ] with 1.8% vol. up to 1.3% vol., according to [СО] from 0.3% vol. to 0.1% vol., which indicates a decrease in the occurrence of side processes of oxidative decarboxylation and decarbonylation.

However, along with the slowdown of adverse reactions, the degree of conversion of m-, p-cymols at I and II steps decreased from 96% to 93.5% and from 100% to 98.2%, respectively, as well as the content of the IFC-TFA mixture in the products oxidation from 99.25% to 96.8%. The yield of IFC-TFA decreased from 95.1% to 90.6%. At the stage of separation of IFC-TFA and their purification, the quality of IFC in terms of chromaticity exceeded the permissible norm by more than 2 times (26 ° N, acceptable norm indicator ≤10 ° N), and the content of intermediate compounds, such as m-KBA, in IFC exceeded after washing the permissible norm is 1.8 times (0.0045%, 0.0025% is acceptable). The total yield of IFC at the stages of oxidation, separation and purification decreased by 3.2%, from 91.1% to 87.9%.

Example 9. The experiment is carried out under the conditions of example 1, with the only difference being that they use a catalyst with a high ratio of cobalt to manganese Co: Mn = 2: 1 while maintaining their total concentration.

The results showed that the quality indicators of the crude mixture of IFC-TFA obtained at the oxidation stage, as well as of the purified IFC and the associated product of TFA at the separation and purification stage, are superior to the quality of IFC of experiment 1 and are within the limits of normative indices for purified IFC and TFA. At the same time, the yield of the target (IFC) and concomitant (TFA) product slightly decreased by only 0.4%, as a result of moderately increased decarboxylation and decarbonylation of intermediate compounds using a more active binary mixture with a higher Co content in Co-Mn-Br catalyst .

Example 10. The experiment is carried out under the conditions of example 9, with the only difference being that the total concentration of Co-Mn catalyst in the reaction mixtures at the first and second oxidation stages is reduced by 30% while maintaining the ratio Co: Mn = 2: 1 and the bromine concentration as in example 9, at stage I 0.240%, at stage II 0.312%.

The results are obtained.

At the oxidation stage, a yield of technical mixture of 95.6% was achieved with its quality suitable for separation and purification by the proposed method.

Σ _isom. [TK + cumic acid],% 0.21 Σ _isom. [CBA + AsBK],% 0.19 Σ [BC and other by-products.],% 0.57 Color, ° N twenty

At the stage of separation of the technical mixture of IFC-TFA and purification of the separated BDK, purified IFC and an accompanying product of TFA of the following quality were obtained:

Quality IFC Associated Product Quality - TFK Σ [m-TC + BK],% 0.006 Σ isomer. [TK] + [BK],% 0.012 [m-CBA],% 0.002 Σ isomer. [CBA + AsBK],% 0.0024 Color, ° N 6.0 [IFK],% 3,7 Color, ° N 9

The total (total over the stages of oxidation, separation and purification) yield of IFC 92.6%, of the associated product TFA 93.0% for the consumed raw materials is a mixture of cimol isomers.

Example 11 (comparative). The experiment is carried out under the conditions of example 1 with the only difference that the concentration of bromine at the first and second oxidation stages is reduced by half, i.e. increase the ratio [Co + Mn]: Br from 1: 1 ÷ 1.3 to 1: 0.5 ÷ 0.65.

The result is received.

The degree of conversion of m-, p-cymol decreased from 100% to 98.3%, the color index of the crude mixture of IFC-TFA increased from 26 ° N to 45 ° N (almost 2 times worsening), the yield of the crude mixture of IFC-TFA decreased from 95.1% to 92.2% i.e. by 2.9%.

At the stage of separation of the IFC-TFA mixture and purification, the quality indicators of the purified IFC and the accompanying TFA product exceed the maximum allowable values for color by 4 ° N, for CBA by 0.0015% (by 15 ppm).

Example 12 (comparative). The experiment is carried out under the conditions of example 4 with the only difference that at the oxidation stage, the concentration of m-, p-cymol in the initial reaction mixture is increased from 18% to 20%, and at the stage of separation of the IFA-TFA mixture, the concentration of the aqueous suspension is increased from 26.5 % to 27%.

The results are obtained.

At the stage of oxidation, the quality of the crude mixture of IFC-TFA reaches the limit boundary indices by which it is suitable for further separation and purification:

Σ _isom. [TK + cumin. acid],% 0.26 Σ _isom . [CBA + AsBK],% 0.23 Σ [bp],% 0.40 Color, ° N 29th

At the stage of separation of the mixture of crude IFC-TFA and purification of the separated products at an aqueous suspension concentration of 27%, the quality indicators of the target product — purified IFC — and the accompanying product — TFA — exceed the permissible values.

Quality IFC Associated Product Quality - TFK Σ [m-TC + BK],% 0.20 Σ isomer. [TK] + [BK],% 0.010 [m-CBA],% 0.005 Σ isomer. [Kba],% 0.006 Color, ° N 12 [IFK],% 4.0 Color, ° N 12

Example 13 (comparative). The experiment is carried out under the conditions of example 1, with the only difference being that the oxidation of the mixture of m-, p-cymols is carried out at a pressure of 0.3 MPa at the first stage, 0.9 MPa at the second stage, corresponding to the vapor pressure of the reaction mixtures at a temperature of 130 ° C (at the first stage) and 160 ° C (at the second stage), and the exposure time of the aqueous suspension of the mixture of IFC-TFA at a temperature of 232 ° C was reduced from 15 minutes to 9 minutes.

The results are obtained.

At the oxidation stage, the color of the technical mixture IFC-TFA increased from 26 ° N to 47 ° N.

After separation of the obtained technical mixture and purification, the color index of the target product of IFC and the associated product of TFA exceeded the permissible value (≤10 ° N) and amounted to 14 ° N and 16 ° N, respectively.

Qualitative indicators of IFC, as well as the associated product of TFA in the content of intermediate compounds (isomers of toluic and cuminic acids, isomers of CBA) are in the maximum permissible range.

Example 14 (comparative). The experiment is carried out under the conditions of example 2, with the only difference being that at the stage of separation of the IFA-TFA mixture, its aqueous solution heated to 230 ° C is cooled in the first case a) to 210 ° C, followed by isolation of the solid crystalline phase of TFA by filtration, and in the second case, b) up to 160 ° C.

The results are:

a) at an elevated temperature (210 ° C) of the release of TFA, a significant part of it in dissolved form leaves with the filtrate, which reduces the clarity of the separation of the mixture of IFC and TFA. In the crystalline IFC isolated from the filtrate after cooling the aqueous suspension to 90 ° C, more than 3% TFA is contained;

b) at a low temperature (160 ° C) of TFA release, a significant part of isophthalic acid co-crystallizes with TFA, which led to a decrease in the yield of the target product by 3.5% and an increased content of IFC in the isolated associated TFA product from 3.6% to 14%.

Example 15. The oxidation of a mixture of m-, p-diisopropylbenzene containing 80% m-diisopropylbenzene and 20% p-diisopropylbenzene was carried out under the conditions of example 1, with the only difference that the temperature in stages I and II was reduced by 10 ° C to 120 ° C and up to 150 ° C, respectively, and the time (duration) of the reaction was increased by 30 min for each step.

The result is received.

At the oxidation stage, the yield of the crude mixture of IFC-TFA was 94.1% with quality indicators suitable for separation and purification by the proposed method.

Σ _isom. [TK + cumic acid],% 0.21 Σ _isom. [CBA + AsBK],% 0.23 Σ [BC + other by-products],% 0.32 Color, ° N 28

At the stage of separation and purification, the following quality of the target (IFC) and associated (TFA) products was obtained:

Quality IFC Associated Product Quality - TFK Σ [m-TC + BK],% 0.009 Σ isomer. [TK + BK],% 0.011 Σ [m-CBA + m-AsBK],% 0.0018 Σ isomer. [CBA + AsBK],% 0.0024 Color, ° N 7 [IFK],% 3,7 Color, ° N 9

The total yield of IFC and TFA at the stages of oxidation, separation and purification was 91.3% and 93.6%, respectively.

Example 16. The experiment is carried out under the conditions of example 15 with the only difference that the oxidation temperature in the I and II steps was increased by 5 ° C, and the residence time (reaction time) in each step was reduced by 10 minutes, to 110 minutes and up to 60 minutes , respectively.

At the stage of separation of the technical mixture IFC-TFA and purification, the lower temperature limit of crystallization and the release of TFA was reduced by 5 ° C from 190 ° C to 185 ° C.

The results are obtained.

At the oxidation stage, the yield of the technical mixture IFK-TFK was reached - 95.2% with quality indicators suitable for separation and purification.

Σ _isom. [TK + cumic acid],% 0.18 Σ _isom. [CBA + AsBK],% 0.21 Σ [BC + other by-products],% 0.30 Color, ° N 24

At the stage of separation of the technical mixture IFC-TFK and purification of the separated products, the quality indicators of the obtained IFC and the accompanying TFK satisfy the requirements of the purified products:

Quality IFC Associated Product Quality - TFK Σ [m-TC + BK],% 0.005 Σ isomer. [TK + BK],% 0.012 Σ [m-CBA + m-AsBq],% 0.002 Σ isomer. [CBA + AsBK],% 0.0024 Color, ° N 6 [IFK],% 3.0 Color, ° N 10

The total yield of IFC at the stages of oxidation, separation and purification was 92.1%, and the yield of concomitant TFA was 93.9%.

Example 17. An experiment on the oxidation of m-, p-diisopropylbenzene is carried out under the conditions of Example 10 in the oxidation of m-, p-zimole, with the only difference being that instead of using a mixture of cimol isomers containing 80% meta-cimol and 20% para-cimol, a mixture of isomers of diisopropylbenzene containing 80% m-diisopropylbenzene and 20% p-diisopropylbenzene.

The results are obtained.

At the oxidation stage, the yield of the technical mixture IFC-TFA was 93.4% with quality indicators acceptable for the subsequent separation and purification of products according to the developed method:

Σ _isom. [cuminic acid],% 0.28 Σ _isom. [CBA + AsBK],% 0.24 [BC + other pos. prod.],% 0.31 Color, ° N 27

At the stage of separation and purification, the quality of IFC and associated TFA reached maximum permissible values for use as a comonomer in the production of film-grade PET (for containers and packaging materials).

Quality IFC Associated Product Quality - TFK Σ [m-TC + BK],% 0.01 Σp-, m-isomer. [TK + BK],% 0.014 Σ [m-CBA + m-AsBq],% 0.0023 Σp-, m-isomer. [CBA + AsBK],% 0.0025 Color, ° N 9 [IFK],% 3.2 Color, ° N 10

The obtained results of the oxidation of m-, p-diisopropylbenzene to IFC-TFA, as well as the separation and purification of the oxidation products showed their identity with the results achieved by the oxidation of m-, p-cymols under the found conditions of catalytic oxidation and purification of the reaction products.

As in the case of the oxidation of cimol isomers, when using isomers of diisopropylbenzene, the concentration of Co and Mn of the catalyst reduced by 30% with an increased ratio of Co: Mn = 1.3: 1 is the maximum permissible minimum concentration for both dialkylbenzenes.

A comparison of the conditions and results of examples 1,2 for the oxidation of isomers of cymol and examples 15, 16 for the oxidation of isomers of diisopropylbenzene to IFC-TFA (table 1), as well as the conditions and results of purification and isomers of benzenedicarboxylic acids - examples 1, 2 and 15, 16 ( table 2) showed that the developed method is versatile both in terms of the used technological methods and in the possibility of using more advanced sources of hydrocarbon raw materials for the synthesis of monomers and polymers based on them.

Claims (2)

1. A method of obtaining pure isophthalic acid by oxidizing isomers of cymol or diisopropylbenzene with an oxygen-containing gas in an acetic acid medium in the presence of a catalyst comprising salts of heavy metals and halogen compounds, at elevated temperature and pressure to a certain degree, the conversion of these isomeric mixtures to isophthalic acid and related products with subsequent separation and purification of IFC and related products by recrystallization in water, characterized in that the isomers of cimol or diisopropylbenz ol is oxidized in two stages at a temperature in the first stage of 120-140 ° C, in the second stage at 150-160 ° C under conditions of increasing concentration of Co-Mn catalyst in stages within the range of 1300-1800 million ^-1 (0,130-0,180%), the stage 2 mn ^-1 1800-2400 (0,180-0,240%) promoted with halogen compounds, the pressure reduction in the range of 0.9-1.6 MPa with a gradient of down-ramp between stages in the range of 0.2-0.6 MPa; purification and separation of the reaction mass obtained after oxidation, isolation of a solid crystalline product from it and washing it with acetic acid, is carried out by recrystallization in water with preliminary exposure of an aqueous suspension of a mixture of IFC-TFA at a temperature of 225-235 ° C for 10-15 minutes and sequential stepwise the allocation of target and related products: at 150-190 ° C - the allocation of solid TFA to obtain an aqueous mother liquor, and at 60-80 ° C - the allocation of solid IFC from the specified mother liquor, followed by washing venous IFC 2-2.5-fold amount of water. 2. The method according to claim 1, characterized in that the isomeric mixtures of m-, p-cymols or m-, p-diisopropylbenzenes containing 70-96% m-cymol or m-diisopropylbenzene are used as feedstock.