RU2412178C1 - Method of producing intramolecular anhydrides of benzene polycarboxylic acids - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention relates to production of ortho-substituted benzene polycarboxylic acids and their intramolecular anhydrides, particularly trimellitic acid and its anhydride, pyromellitic acid and its dianhydride. The object of invention is achieved due that the initial hydrocarbons used are tri- and tetra-alkylbenzenes which contain methyl and isopropyl, methyl and ethyl or only methyl substitutes of general formula:

a)

b)

where: a) R₁, R₃-CH₃, R₂-C₃H₇ or -C₂H₅; R₁, R₂, R₃-CH₃ b) R₁, R₂, R₃-CH₃, R₄-C₃H₇ or C₂H₅; R₁, R₃-CH₃, R₂, R₄-C₃H₇ or C₂H₅; R₁, R₂, R₃, R₄-CH₃, for example isopropyl-p-xylene, ethyl-p-xylene, pseudocumene, 5-isopropylpseudocumene, 2,5-diisopropyl-p-xylene, 5-ethylpseudocumene, durene and others. Said compounds are oxidised in three steps with concentration of the dissolved oxygen in the liquid phase of oxidation products at each step in the range of 0.11-0.15 mol/l while maintaining pressure which is 16-18, 3.6-4.16 and 1.25-1.4 times higher, respectively, in reaction zones P_izb relative vapour pressure of the liquid reaction mass P_up, while raising temperature step-by-step in the range, °C: 120-135, 140-185, 190-215, discrete increase in concentration of metal ions of a Co²⁺ and Mn²⁺ catalyst and a Br- promoter. Obtained acids undergo thermal dehydration at temperature 230-240°C. The obtained anhydride solution undergoes purification through crystallisation in two steps in naturally different individual and binary solvents. The precipitated complex salt of the intramolecular anhydride is dried at temperature ≥125°C, which ensures decomposition of the complex to form a highly pure end product.

EFFECT: high efficiency of the process and high output of the end product.

3 cl, 2 dwg, 2 tbl, 11 ex

Description

The invention relates to the production of ortho-substituted benzenepolycarboxylic acids and their intramolecular anhydrides, in particular trimellitic acid (TMK) and its anhydride (TMA), pyromellitic acid (PMA) and its dianhydride (PMDA).

Trimellitic anhydride. They are widely used in the manufacture of polymeric materials: high-quality plasticizers, high-temperature polyamide imide coatings, electrical insulating varnishes.

Pyromellitic dianhydride. PMDA is the starting monomer feedstock for producing high molecular weight polyimide materials with high mechanical strength, heat resistance in a wide temperature range (from -200 ° С to + 400 ÷ 500 ° С), as well as resistance to radiation and organic solvents.

The industrial method for producing TMA is currently based on two-stage processes, which are based on the first stage using liquid-phase oxidation of pseudocumene O ₂ -gas in an acetic acid medium in the presence of a Co-Mn-Br catalyst, and thermal dehydration of oxidation products to technical TMA is carried out in the second stage and its purification by physical methods (distillation, recrystallization, etc.). The industrial processes for the production of PMDA are based in the vast majority on vapor-phase catalytic (V ₂ O ₅ ) processes for the oxidation of durene in one stage in the temperature range 400-450 ° C, followed by purification of the PMDA raw in various solvents.

Known two-stage method for the synthesis of pyromellitic acid by oxidation of durene [US Pat. US No. 3532746, 1970]. At the first stage, the oxidation of durene is carried out with air at a temperature of 137 ° C in acetic acid in the presence of catalysts - cobalt, cerium acetates, and promoters in the form of sodium bromide and tetrabromoethane after absorption of 75-95% of the theoretically necessary amount of oxygen for complete oxidation of all metal groups. Next, the oxidate is subjected to further oxidation in the second stage with a gradual increase in temperature to 204-276 ° C, while diluted nitric acid and tetrabromoethane dissolved in it are added to the oxidate. Oxidation is continued at 204-276 ° C with the supply of oxygen enriched air (up to 30%) until the reaction is complete.

The disadvantages of the described process include severe corrosion of equipment and, first of all, of the reactor with an aggressive reaction system containing bromine, nitric acid and PMA at elevated temperatures up to 276 ° C, as well as the accumulation of nitro compounds in the reaction products.

A known method of producing trimellitic and pyromellitic acids by liquid-phase oxidation of tri- and tetraalkylbenzenes by air in CH ₃ COOH medium in the presence of Co, Mn, Zr and bromine catalysts [US patent No. 4755622, 1988]. The essence of the method lies in the fact that the oxidation reaction of pseudocumene or durene is carried out in two stages in the temperature range of 100-250 ° C, while from the first stage 10 to 35% of the total amount of bromine used in the process is introduced, and in the second stage, the rest is quantity. The temperature in the first stage is maintained in the range of 125-165 ° C, and in the second stage the temperature is increased from ~ 175 ° C to ~ 250 ° C.

The main disadvantage of this process is the relatively high reaction temperature in the second stage (250 ° C), which, as is known, leads to destructive processes of both pseudocumene or durene and the solvent — CH ₃ COOH with their inevitable loss due to “combustion” and formation by-products of high boiling oxidative condensation and destruction.

A known method of producing intramolecular anhydride of trimellitic acid [US Pat. RF RU 2152937, 1998] by liquid-phase oxidation of pseudocumene with atmospheric oxygen to trimellitic acid in one stage in the presence of a catalyst containing heavy metal salts and bromine compounds in an acetic acid medium at a temperature of 160-225 ° C and pressure, followed by purification, characterized in that the oxidation is carried out under conditions of a countercurrent of oxygen-containing compounds and reaction products, in the presence of a manganese catalyst, modified by the addition of salts of heavy metals from the series Ni, Co, Zr, taken together and / or in binary form Ms Mt (Ni-Co), (Ni-Zr), (Zr-Co). As the promoter, bromine compounds, such as hydrobromic acid and / or its mixture with hydrochloric acid are used with the ratios of the components of the catalyst and the promoter Mn: Mt = 1: 0.1-0.3; Br: Cl = 1: 0.01-0.5; [Mn + Mt]: Br (or [Br + Cl]) = 1: 0.5-4.0. The total concentration in the reaction mixture of catalyst metals is 0.05-0.12%, and the concentration of bromine and / or a mixture of bromine and chlorine is 0.12-0.44. The supply of hydrohalic acid is distributed over the height of the reaction zone. The proposed method allows to simplify the process and achieve satisfactory quality of TMA. At the same time, the use of a 4-component catalyst (Mn, Co, Ni, Zr), as well as a 2-component Br-Cl promoter complicates the process of regeneration of their mother liquors.

A known method of obtaining and purification of dianhydride pyromellitic acid [US Pat. RF No. 2314301, 2004] by the stepwise oxidation of durene to pyromellitic acid with oxygen in an acetic acid medium at elevated pressure and temperature, followed by thermal anhydridation of the oxidation products. The essence of the method lies in the fact that the oxidation reaction is carried out in the presence of hydrohalic acids (Gc) of the series HBr, HCl, HF in the form of binary or ternary mixtures (HBr + HCl), (HBr + HF), (HBr + HCl + HF) in the ratio Br: Cl: F = 1: 0.15 ÷ 1.0: 0.01 ÷ 0.5 and / or HBr, and as catalyst metals (Mk) - salts of Mn, Co, Zn in the form of acetates, bromides, chlorides or fluorides in the ratio of metal ions (1: 0.5 ÷ 3.0.0: 0.1 ÷ 0.2, respectively, with a general ratio of Mk: Gk ÷ 1: 1.2 ÷ 3, while the oxidation is carried out in 4 steps in the temperature range of 140-220 ° C and a pressure of 2.0-3.0 MPa so that the temperature at each the second stage is increased by 10-15 ° C, and the pressure is reduced by 0.2-0.3 MPa to an excess pressure at the 4th stage, which exceeds the vapor pressure of the reaction mass by at least 0.25 MPa, and with a reaction time of each step within 20-60 minutes achieve the conversion of durene to pyromellitic acid in the range of 22-35%, 50-78%, 88-93%, 95-98%, respectively, and PMDA is purified by recrystallization in a mixed solvent consisting of benzene and ethyl acetate in a ratio of 1: 1. The described method is the most effective among the previously considered processes in terms of process speed, as well as in the quality of the target PMDA product. At the same time, the use as a promoter of a mixture of protic halogen derivatives of acids HBr, HCl, HF under conditions of their high concentration and elevated temperature have a fairly high activity against structural metals of reactors (cause increased corrosion). In addition, the multicomponent nature of the used catalysts and promoters complicates the process of their regeneration.

Close in technical essence is a method for producing intramolecular anhydrides of benzenepolycarboxylic acids (pyromellitic dianhydride and trimellitic anhydride) [Pat. RF (SU) No. 1584342, 1987], according to which the oxidation of durene or pseudocumene is carried out in the liquid phase in the temperature range 100-220 ° C with atmospheric oxygen in the presence of acetic acid in the presence of a Co-Mn-Zr-Ni-Br catalyst at a ratio bromine to the sum of metals (2.5-8.0): 1 and the Ni content of the total mass of metals 0.5-8%. As bromine compounds, HBr, CoBr ₂ and / or MnBr _{2 are used} ; or NH ₄ Br, which is introduced at the beginning of the reaction in the amount of 36-65% in terms of Br, and when the reaction products reach 70-98% of benzene polycarboxylic acids, the remaining amount of bromine (at 220 ° C) is introduced in the form of hydrobromic acid in mixtures with an aliphatic compound selected from the group (methyl ethyl ketone, acetic acid, pentanehexane fraction, etc.) in an amount of 4.8-82.3% by weight of oxidizable hydrocarbon. The resulting trimellitic or pyromellitic acid, after removing all liquid products from the oxidate, is subjected to thermal anhydridation in pseudocumene at a temperature of 230-235 ° C to obtain PMDA. Significant disadvantages of this method include a large number of oxidizable reagents and catalyst introduced into the synthesis process, which complicates the scheme of both the main process and auxiliary stages, in particular, catalyst regeneration.

The aim of the present invention is to increase the efficiency of the process, providing an increase in the yield of intramolecular anhydrides of trimellitic and pyromellitic acids and expanding the raw material base - alternative sources of petrochemical raw materials of tri- and tetraalkylbenzenes containing in the ortho-position methyl and isopropyl, methyl and ethyl or only methyl groups.

This goal is achieved by the fact that as the initial hydrocarbons use tri- and tetraalkylbenzenes containing methyl and isopropyl, methyl and ethyl or only methyl substituents of the General formula:

where a) R ₁ , R ₃ —CH ₃ , R ₂ —C ₃ H ₇ or C ₂ H ₅ ; R ₁ , R ₂ , R ₃ - CH ₃

b) R ₁ , R ₂ , R ₃ —CH ₃ , R ₄ —C ₃ H ₇ or C ₂ H ₅ ;

R ₁ , R ₃ —CH ₃ , R ₂ , R ₄ —C ₃ H ₇ or C ₂ H ₅ ; R ₁ , R ₂ , R ₃ , R ₄ - CH ₃ ,

for example, isopropyl-n-xylene, ethyl-n-xylene, pseudocumene, 5-isopropyl pseudocumene, 2,5-diisopropyl-n-xylene, 5-ethylpsevdocumene, durol and others.

These compounds are oxidized in three stages at a concentration of dissolved oxygen in the liquid phase of the oxidants of each stage in the range of 0.11-0.15 mol / l (3.5-5.0 g / l) while maintaining an increased in 16-18, 3, 6-4.16 and 1.25-1.4 times, respectively, the pressure in the reaction zones P _h. (MPa) in relation to the vapor pressure of the liquid reaction mass P _UP. (MPa), the temperature is raised stepwise within, ° C: 120-135, 140-185, 190-215, discrete steps of increasing concentration of the catalytic metal ions such as Co ²⁺ and Mn ²⁺ and promoter Br ^- in the range [ With ²⁺ + Mn ²⁺ ] / [Br ^- ] in the intervals (ppm):

650 ÷ 750/800, 1550/1950; 2700/3000 ÷ 3500.

At a reaction time of 15-50 minutes in each step, a stepwise conversion of the starting hydrocarbon and intermediates to benzenetri and tetracarboxylic acids is achieved in the range,%: 9-14; 55-70; 96-99, after which the reaction products are isolated from the 3rd stage oxidate and subjected to thermal dehydration in a solvent liquid at a temperature of 230-240 ° C until the reaction H ₂ O ceases to be isolated. The resulting anhydride solution is purified and subsequent products are isolated by crystallization in two steps in different in nature individual and binary solvents.

In the first stage, the anhydride is purified by stepwise cooling of a 20-30% solution of anhydride in trialkylbenzene: isopropyl-n-xylene, ethyl-n-xylene or pseudocumene, first from 230-240 ° C to 180-186 ° C with separation of precipitated organic impurities and a catalyst, and then from 180-186 ° C to 15-25 ° C, followed by isolation of the target product of medium purity - technical TMA, technical PMDA.

At the 2nd stage, the technical TMA and PMDA are purified by recrystallization in a binary solvent (BR), consisting of benzene and alkyl acetate, by heating a 20-30% suspension of the technical product to 120-130 ° C, holding it at the indicated temperature for 20-30 minutes after which the reaction mixture is cooled to 20-25 ° C, the complex salt of intramolecular anhydride precipitated is precipitated from it, which is dried at a temperature of ≥125 ° C, which ensures decomposition of the complex with the formation of the target product of high purity (RF TMA or RF PMDA) .

In the process of liquid-phase oxidation of polyalkylbenzenes with an O ₂ -gas in the presence of a Co-Mn-Br catalyst, oxidative transformations undergo oxidative transformations without affecting the benzene ring. Substituents of the series —CH ₃ , —C ₂ H ₅ , —C ₃ H ₃ (methyl, ethyl, isopropyl) in alkylbenzenes have different oxidation reactivity and the amount of intermediate compounds when they are subsequently converted to a carboxyl group. Therefore, in the presence of substituents of different nature in alkylbenzenes, the oxidation process is complicated and it is impossible to carry out a selective reaction in one stage in any one parameter range (T, P, [Ct], [O ₂ ], [substrate], etc.) to benzene polycarboxylic acid . This, along with the difference in energy factors (activation energies), the number of intermediate compounds with different compositions and possible routes for their transformations, there arises the problem of catalyst deactivation by orthosubstituted polycarboxylic acids formed during the reaction at intermediate or final stages. Catalyst deactivation occurs as a result of the formation of chelate complexes of Co and Mn with orthosubstituted benzene polycarboxylic acids (TMK, PMA), which exhibit reduced activity and precipitate.

In the inventive method for producing intramolecular anhydrides of TMA and PMDA, 2-isopropyl-p-xylene, 2-ethyl-p-xylene, respectively, are used as their initial hydrocarbon feed when they are oxidized to trimellitic acid, as well as 1,2,3-trimethyl, 5- isopropylbenzene or 1,4-dimethyl, 2,5-diisopropylbenzene when they are oxidized to pyromellitic acid.

The above-mentioned polyalkylbenzenes, when oxidized, have the above features and a complex reaction in comparison with tri- and tetrapolymethylbenzenes, which have single substituents in nature. To confirm the literary information of mainly theoretical and rare experimental studies, preliminary oxidation of ortho-substituted and tri- and tetraalkylbenzenes was carried out in the range of low and high temperatures, pressures and concentrations of reagents in order to select the range of parameters for the process.

In the declared temperature range, as shown by the results of experiments, the oxidation reaction of orthosubstituted polyalkylbenzenes to tri- and tetrabenzenecarboxylic can be carried out in three steps with a discrete (step) temperature increase in the experimentally found range (120 ° C-215 ° C). In the process of oxidation of tri- and tetrasubstituted alkylbenzenes containing methyl and isopropyl groups or methyl and ethyl groups, at temperatures below 120 ° C (90-110 ° C) and other things being equal, the reaction proceeds mainly to the primary oxidation products - peroxide compounds , alcohols, aldehydes or ketones. Monocarboxylic acids are formed in small quantities during a long reaction time. Polycarboxylic acids (TMK or PMK) are not formed.

Carrying out oxidation at temperatures above 216 ° C and other conditions being equal leads to acceleration of side reactions of oxidative degradation and condensation of not only the original hydrocarbon, but also of the solvent (CH ₃ COOH): the content of products of oxidative degradation of CO ₂ , CO increases more than 3 times; the color index characterizing the concentration of secondary, usually colored condensed compounds increases by 2-3 times. The yield of target products (TMK or PMK) is reduced and amounts to 87-90%.

It is known that an increase in gas pressure above a solution of a liquid phase, ceteris paribus, leads to an increase in its solubility. In the oxidation of orthosubstituted tri- and tetraalkylbenzenes to TMC and PMA, the limiting stage is the oxidative conversion of methylphthalic and methyltrimellitic acids due to the strong influence of two or three acceptor carboxyl groups on the remaining alkyl substituent in methylpolycarboxylic acid.

As a result of negative σ-π conjugation, activation energy arises in these intermediate compounds, which requires an increase in temperature or an increase in oxygen concentration in the reaction mass. Since increasing the temperature above the limit value negatively affects the process, as described above, the most suitable method to speed up the reaction at the final stage is to increase the concentration of dissolved oxygen in the reaction mass. Since the solubility of O ₂ , ceteris paribus, is associated with excess pressure, these two factors are considered together. It was experimentally established that with an increase in the total pressure in the reaction zone over the vapor pressure of the reaction mixture in steps I, II, and III by 16–18, 3.6–4.16, and 1.25–1.4 times, respectively, leads to an increase in oxygen concentration in solution, which, in turn, accelerates the delayed (limiting) stage of oxidation of methylpolycarboxylic acids to polycarboxylic acids (TMK, PMK). This is probably due to an increase in the content of peroxide compounds in the reaction zone, the active form of metal halide catalyst complexes with metal ions in a higher valence form:

where R is an intermediate compound that provides oxidation in the intermediate compounds of highly deactivated alkyl groups to carboxylic acid radical chain pathways. It was experimentally established that if the oxidation reaction is carried out under a pressure equal to the vapor pressure of the oxidizing reaction mixture, ceteris paribus, the oxidation products contain a large number of intermediate compounds - alkylbenzenecarboxylic acids ([ABA] = 14.7%), which indicates low conversion of the source hydrocarbon to the target product. In the liquid phase oxidation of polymethylbenzenes (xylene isomers, pseudocumene, durene, etc.) in one step to benzene polycarboxylic acids (phthalic acids, TMK, PMA), mainly Co-Mn-Br catalyst with a specific constant concentration of Co and Mn ions in their chosen ratio is used. In the case of oxidation of pseudocumene or durene, the bromine concentration is increased in the course of the reaction while maintaining a constant total concentration of Co ²⁺ and Mn ²⁺ .

In the inventive method for producing TMA and PMDA using other naturally occurring aromatic hydrocarbons containing different alkyl substituents in the benzene ring (—CH ₃ and —C ₃ H ₇ or CH ₃ and C ₂ H ₅ ), the above approach (constancy [Co ^{2 +} and Mn ²⁺ ]) was not acceptable. This is due to the following factors:

a) during the oxidation of orthosubstituted polyalkylbenzenes with different in nature alkyl substituents, the quantity and composition of the intermediate compounds changes more sharply than occurs in the case of the oxidation of polymethylbenzenes;

b) isopropyl and ethyl substituents at the initial stages of oxidation have a sufficiently high degree of reactivity to oxidation compared to metal ones, and the reaction is initiated by small (even trace) catalyst concentrations. However, as the depth of the reaction increases and the intermediate compounds in the form of methylbenzenecarboxylic acids, keto acids and other intermediates are accumulated at low concentrations of Co-Mn-Br catalyst, the oxidation process stops due to inhibition of the catalyst by ortho-substituted methyl polycarboxylic or polycarboxylic acids with the formation of low-activity chelate complexes catalyst, and also as a result of reducing the influence of the above factors on the oxidation process, experimentally found the ratio of comp Co-Mn-Br compounds in the catalyst and their concentration at each stage, which, ceteris paribus, ensure the progressive oxidative conversion of tri- and tetra-alkylbenzenes to TMC and PMA, respectively. The result on the quality of the target products and their composition during the oxidation process with a discrete increase in the found limits over the steps of the concentration of metal ions of the catalyst Co ²⁺ and Mn ²⁺ (in an atomic ratio of 1: 1) and Br ^- in experimentally established intervals was completely unexpected. Co ²⁺ + Mn ²⁺ ] / [Br ^- ], ppm:

I Art. 500 ÷ 700/800 ÷ 900,

II Art. 1900 ÷ 2100/2400 ÷ 2600,

III art. 2700 ÷ 2900/3000 ÷ 3500.

A decrease in the concentrations of metal catalysts (Co ²⁺ and Mn ²⁺ ), as well as the promoter (Br ^- ) below the lower limit, reduces the conversion of hydrocarbons in TMC and PMC to 89% and lower, and hence the yield of the target products. An increase in the concentration of Co-Mn-Br components of the catalyst above the experimentally established limit leads, ceteris paribus, to an increase in the rates of both the main and side reactions, which generally reduces the yield of the target products. It was experimentally established that the oxidation of tetraalkylbenzene, for example, 6-isopropyl-p-xylene, in one step in the presence of an upper limit of Co ²⁺ , Mn ^2+, and Br ^- concentrations (1320 ppm, 1400 ppm, 2500 ppm, respectively), PMC yield reduced to 89%.

The degree of conversion of the initial hydrocarbon and intermediates to benzene, tri- and tetracarboxylic acids in steps has been established experimentally,%: 9-14; 55-70 and 96-99 and provides the optimal process with a discrete increase in temperature and concentrations of components of Co-Mn-Br catalyst within the found limits. Deviation of the degree of conversion of hydrocarbon and intermediate compounds to a greater or lesser extent leads to a deviation of the process from the optimal mode, reduces the quality of the target product and its yield.

The temperature regime of the anhydride stage in the limit of 230-240 ° C was established experimentally. Lowering the temperature below the lower limit (<230 ° C) leads to a slowdown of the reaction with the formation of the anhydride cycle, an increase in the duration of the process, and a decrease in the completeness of the conversion of orthosubstituted benzene polycarboxylic acid to anhydride.

An increase in temperature above the upper limit from 240 ° C to 250 ° C accelerates the anhydridization process, however, for the removal of the reaction water vapor, increased pressure is required, which makes the anhydride stage apparatus more expensive. A further increase in temperature (more than 250 ° C) leads to an increase in the rate of the process of thermocatalytic destruction, condensation of intermediate compounds (aldehydes, ketones) contained in technical TMK and PMK, and a deterioration in the quality of technical anhydride in terms of impurity content. The temperature regime of the first stage of anhydride purification was established experimentally. At a reaction mass temperature of 180-186 ° C, TMA and PMDA are in a soluble form, and impurities - intermediate and by-products, as well as catalyst residues due to their low solubility - in the solid phase. When filtering the suspension, impurities are separated from the solution of anhydride in trialkylbenzene and thus the technical product is purified. Lowering the temperature, the release of impurities below the lower limit (<180 ° C) leads to the onset of crystallization of the main product (TMA or PMDA). This entails its loss in the process of separation of impurities. An increase in the temperature of the first purification step above the upper limit increases the solubility of impurities, which leads to a deterioration in the quality of the target products due to their co-crystallization with impurities when the reaction mixture is cooled to the temperature of TMA or PMDA (15-25 ° С). The temperature regime for the isolation of the target products by crystallization in trialkylbenzene (15-25 ° C) was established experimentally. Lowering the temperature below the lower limit (<15 ° C) leads to a deterioration in the quality of the target product in the content of readily soluble impurities. An increase in temperature above the upper limit (> 25 ° C) leads to an increase in the solubility of the target products and an increase in their losses with the mother liquor.

The temperature regime of additional purification of TMA and PMDA by recrystallization in a binary solvent from benzene and alkyl acetate of 120-130 ° C was established experimentally. Lowering the temperature below the lower limit slows down the complexation reaction, and increasing the temperature above the upper limit (> 130 ° C) requires higher pressures, leading to more expensive equipment at the additional purification stage and partial destruction of the complex compounds of TMA and PMDA in a binary solvent. This reduces the cleaning efficiency.

The experimentally found temperature regime for drying TMA and PMDA at the stage of additional purification (≥125 ° С) provides not only the removal of the binary solvent, but also the decomposition of complex compounds leading to the formation of high-purity target products. Lowering the drying temperature (<125 ° C) leads to a slowdown in the process of solvent removal and the destruction of complex compounds.

Figure 1: Scheme of an integrated pilot plant for the stepwise oxidation of tri- and tetraalkylbenzenes to trimellitic and pyromellitic acids.

Figure 2: Scheme of an integrated pilot plant for the anhydridation of TMK, PMK and purification of technical TMA and PMDA.

Table 1: Conditions and results of liquid-phase catalytic oxidation of tri- and tetraalkylbenzenes by air in three steps to trimellitic and pyromellitic acids.

Table 2: Conditions and results of anhydrides of trimellitic and pyromellitic acids and purification of intramolecular anhydrides TMA and PMDA.

The following are examples and diagrams of the stages of the process, characterizing, but not limiting the essence of the invention.

Example 1

The experiments were conducted on a pilot installation of continuous operation made of metal (titanium VT1-0 and stainless steel), consisted of the stages of oxidation and isolation of reaction products (Figure 1), anhydride of TMK or PMA and purification of the anhydride by recrystallization in solvents (Figure 2 )

The oxidation reaction unit consists of three sequentially operating reactors of the first 1, second 2, third 3 stages with a total volume of 3.6 l. The anhydride process was carried out in an apparatus with a stirrer 11, equipped with a condenser 12 and a Florentine vessel 13 for the separation of organic and aqueous phases. Cleaning was carried out in a crystallizer apparatus 16 with a stirrer and a jacket. The isolated anhydrides on a vacuum filter 17 were dried.

Mono-isopropyl-p-xylene (99.2% of the main product) is used as the initial hydrocarbon in the preparation of trimellitic anhydride.

To conduct the experiment on the oxidation stage, a reaction mixture (IRS) was prepared in the amount of 2.96 l of the following composition:

ml g % of the mass. monoisopropyl p-xylene 483 420 14.0 acetic acid 2435 2533 84.43 Co (CH ₃ COOH) ₂ × 4H ₂ O - 4.43 0.147 ([Co] = 348 ppm) Mn (CH ₃ COOH) ₂ × 4H ₂ O - 4.68 0.156 ([Mn] = 350 ppm) HBr (40%) 4.3 (like Br) 2,4 0.080 ([Br] = 800 ppm) H ₂ O 35.5 35.49 1,187 2957.8 3000 one hundred

In parallel, in a vessel 5, a catalyst solution is prepared in acetic acid (without hydrocarbon), the concentration of components of which is similar to IRS in the bromine content, and 2 times lower in the concentration of Co and Mn than in the initial reaction mixture containing hydrocarbon. The prepared solution of fresh catalyst is poured into the reactor 1, 2, 3. After sealing the reaction unit of each reactor 1, 2, 3, increase the pressure with an inert gas (argon) to 2.5 ± 0.5 MPa and at the same time increase the temperature in the reactors 1, 2 , 3 to 120-130 ° C using a vertically movable external electric heater.

When this temperature is reached, the inert gas consumption is reduced and the air supply is connected based on the achievement of the oxygen concentration in the mixture of nitrogen and air 8.5-9% (the average oxygen concentration introduced into the air oxidation process is 21% and the oxygen concentration in the exhaust air leaving the reactor - 3-4% vol.). According to the developed method, using a high-resolution NMR spectrometer (recording NMR spectra at a frequency of 60 MHz, resolution 0.2 Hz), the concentration of dissolved oxygen in an acetic acid catalyst solution was determined. Analogous measurements were carried out in solution DCI (with a hydrocarbon) at a discrete temperature increase corresponding mode of operation of reactors 2 ^nd, 3 ^s intervals in steps 140-185 ° C, 190-215 ° C. The following concentrations of dissolved oxygen were obtained in the catalyst solution and in the oxidants of the 1st, 2nd and 3rd stages (g / l):

Concentration 1 tbsp. 2 tbsp. 3 tbsp. [O ₂ ] in the catalyst solution 4.9 4.3 3,7 [O ₂ ] in the oxidate 4.8 4.0 3.2

After obtaining the above data, the process was carried out in a continuous mode by supplying IRS from the collection 4 by pump 6 to the oxidation reactor of the first stage 1 and simultaneously supplying air to all three stages in an amount providing the content of O ₂ in the exhaust air not more than 4.5% vol., which is regulated with the help of a gas analyzer 7 (for safety reasons - excluding the formation of explosive concentrations with solvent vapor CH ₃ COOH). The consumption of IRS was determined from the calculation of the residence time at each stage for 35 minutes (a total of 105 minutes).

The vapor-gas mixture leaving the reactors 1, 2, 3 is cooled in condensers-refrigerators 10 _1,2,3 . Phlegm is partially returned to reactors 1, 2, 3, and the rest is allocated for regeneration. The oxidate from the rector of the 3rd stage 3 enters the crystallizer 8 and after cooling, the formed crystalline phase of the product is separated on the vacuum filter 9.

Experiments on the anhydride and purification of intramolecular anhydrides were carried out on an integrated pilot plant (Figure 2).

Anhydridizer 11 - apparatus with a stirrer, equipped with a condenser 12, a Florentine vessel 13 for the separation of organic and aqueous phases. Preliminary purification of impurities is carried out in a crystallizer 14. The impurities precipitated at a temperature of 185 ° C are separated on a drum filter 15, the clarified anhydride solution is cooled in a crystallizer 16, and the resulting suspension is filtered on a vacuum filter 17.

If it is necessary to obtain improved anhydrides, additional purification is carried out. For this, technical anhydride is loaded into crystallizer 16, where a binary solvent is supplied: alkyl acetate and benzene. The resulting suspension is heated to 120 ° C, maintained at this temperature for 20-30 minutes, then cooled to a temperature of 20-25 ° C, pure anhydride is isolated on a vacuum filter 17 and dried.

The conditions and results of example 1 and subsequent experiments on the oxidation of tri- and tetraalkylbenzenes to TMC and PMC, as well as their anhydridation and purification of the products are presented in tables 1 and 2, respectively.

From the obtained data of example 1 it follows that under the given conditions of three-stage oxidation of isopropyl-p-xylene, the yield of TMC reaches 94.6% with a content of the main substance in the isolated product of 98.0% (Table 1).

When thermal anhydridation of TMC in isopropyl-p-xylene (IP-p-KS) medium and a temperature of 240 ° C, the yield of technical TMA for TMC taken from the oxidation stage was 98% with an impurity content of 0.3% (table 2). According to the results of the analysis, the technical TMA had the following quality indicators:

appearance - light gray crystals;

melting point, ° С - 165;

acid number, mg KOH / g of product - 867;

mass fraction of the residue after calcination,% - 0.05;

mass fraction of anhydride groups,% - 36.3.

The obtained technical TMA is suitable for use in the production of plasticizers, enamel varnishes and other polymeric materials of wide consumption.

To obtain high-quality TMA (CTMA) for polymer products with enhanced mechanical or physico-chemical characteristics, it was further purified by recrystallization of technical TMA in an experimentally found binary solvent consisting of benzene and methyl acetate. Under the above conditions (table 2), a high-purity product is achieved (to the initial technical TMA) - 98.6% with a basic substance content of 99.95% purified at the 2nd stage of ChTMA (table 2).

According to the results of the analysis, CTMA had the following quality indicators:

appearance - a crystalline product of white color;

melting point, ° C - 166;

acid number, mg KOH / g of product - 868;

mass fraction of the residue after calcination,% - 0.01;

mass fraction of impurities (by-products),% - 0.04;

mass fraction of anhydride groups,% - 37.3.

Example 2. The experiment is carried out under the conditions of example 1, with the only difference that at the oxidation stage, the concentration of isopropyl-p-xylene is increased to 16%, and the reaction time at each stage increased by 15 minutes with a total oxidation time of 150 minutes. At the stage of anhydride and the first stage of purification, the crystallization temperature of the impurities and their isolation is maintained under the conditions of example 1 (table 2) at 180 ° C. For comparison, in example 2'-a, the temperature is lowered to 165 ° C, and in example 2'-b, on the contrary, it is raised to 200 ° C. The second stage of purification in a binary solvent is carried out in the mode of example 1.

The following results were obtained for the stages of the process. At the stage of oxidation: the amount of carbon dioxide and carbon monoxide in the exhaust air flows leaving the reactors of 3 stages increased by 1.2-1.3 times; the total content of impurities (by-products of oxidative degradation and condensation) in the oxidation products extracted from the oxidate of the 3rd stage reactor increased from 0.8% to 1.0%; TMK yield decreased from 94.6% to 93.3%, i.e. by 1.3%.

At the anhydride stage of TMC and the first stage of purification of trimellitic anhydride, the content of impurities (benzene-polycarboxylic acids containing no ortho substituents, oxygen-containing products of the biphenyl series, etc.) increased from 0.3% to 0.5%; the yield of technical TMA decreased by 1% (from 98.0% to 97.0%).

At the second stage of purification of technical TMA in a binary solvent benzene methyl acetate, the quality of high-purity TMA in terms of the content of the basic substance (99.92%) is close to the quality of Example 1 '(99.95%), however, the yield of CTMA on the used technical TMA decreased from 98.6% up to 97.5%, i.e. by 1.1%.

The results showed that with an increase in the concentration of isopropyl-p-xylene in the initial reaction mixture, the yields of TMK and TMA markedly decrease. The required quality indicators of the target product are achieved using only two stages of purification.

Example 2a The experiment is carried out under the conditions of example 2, with the only difference being that the crystallization temperature of impurities and their release (T _cr-1 ) is reduced from 180 ° C to 165 ° C. The result was obtained: the quality of technical TMA improved and became close to the quality of high-purity TMA in terms of the content of the main substance (99.8%), but its yield decreased from 97.0% to 91.0%, i.e. by 6%. Lowering the temperature Т _кр-1 to 165 ° С led to the co-crystallization of TMA with by-products and ≈5% of the target product is lost when impurities are isolated by filtration.

Example 2b The experiment is carried out under the conditions of example 2, with the only difference being that at the anhydride stage and the first stage of TMA purification, the crystallization temperature and their isolation are increased from 180 ° C to 200 ° C, and the conditions of the second stage of purification are left unchanged with example 2 '. The following results are obtained.

The quality of TMA at the anhydride stage and the first stage of purification has deteriorated sharply due to an increase in impurities from 0.5% to 1.16% and a decrease in the content of the main substance (TMA) from 99.6% to 97.94%.

The data presented show that at elevated temperatures up to 200 ° С, a significant part of the impurities is in dissolved form and, upon subsequent cooling to 20 ° С (TMA isolation mode), they precipitate together with the main product, forming a difficult to clean mixture of crystalline products.

Subsequent purification of the obtained technical TMA using a binary solvent in the second stage of crystallization did not lead to the production of pure TMA of the required quality: the content of the main substance TMA after the second stage of purification is 99.3%, which exceeds the permissible norm (99.6%).

Example 3. The experiment is carried out under the conditions of example 1 (table 1), with the only difference that the temperature at the 3 stages of oxidation is increased by 15 ° C, the pressure by 0.2 MPa, and the consumption of IRS is increased based on the reduction in residence time by each step for 10 minutes from 35 minutes to 25 minutes (the total oxidation time at 3 steps is 75 minutes).

The process conditions at the stages of the anhydrides of TMC and the 1st stage of purification of TMA are maintained at the level of Example 1 '(table 2), and at the 2nd stage of purification along with methyl acetate (example 3') individually used with benzene ethyl acetate (example 3'a) , propyl acetate (example 3'b) and butyl acetate (example 3'c).

The following results are obtained. At the oxidation stage, the yield of TMC was 93.4%, i.e. slightly decreased (by 0.8%). The content of by-product impurities in the TMK isolated from the 3rd stage oxidate is 0.75%. The content of TMK is 98.15%. Thus, the yield of TMC in the conditions of example 3 remained practically at the level of example 1 with a slight improvement in quality.

At the anhydride stage of TMC and the first stage of TMA purification, the TMA yields and quality of the purified product are close to the results of Example 1 '(table 2).

At the 2nd stage of technical TMA purification using binary mixtures of benzene with individual methyl, ethyl, propyl and butyl ether of acetic acid (R-Ac), the results on the quality of PTMA, estimated by the content of the basic substance, as well as by the yield of anhydride, are close to each other and are comparable with example 1 '(table 2). A slight advantage in the purification and release of TMA is achieved by using binary mixtures of benzene with ethyl and methyl acetate. When using them, the content of the main substance in CTMA is 99.96%, yield 98.8-98.9%.

Example 4. The experiment is carried out under the conditions of example 1, with the only difference being that at the oxidation stage the concentration of bromine and catalyst is reduced by 1.5 times with an increase in the Co: Mn ratio from 1: 1 to 1: 0.5 and an increase in the residence time in each step for 10 minutes. At the stage of anhydride and purification, the conditions are similar to Example 1. The results are obtained: at the oxidation stage, the yield of TMC decreased from 94.6% to 92.8% (by 1.8%).

The content of the main substance in the TMK extracted from the 3rd stage oxidate decreased from 98% to 96.0% (2.0%). The concentration of impurities (by-products) increased from 0.8% to 0.95%. At the stage of anhydrides of TMC and the first stage of purification, the yield of TMA decreased by 1.5% (from 98.0% to 96.5%). At the stage of cleaning the second stage, the yield decreased from 98.6% to 97.8% (0.8%), and the purity of the anhydride in the content of the main substance decreased from 99.95% to 99.90%.

The results show that the above concentrations of the components of the Co-Mn catalyst and bromine are the minimum allowable, which allow to obtain TMA with a reduced by 1.5% yield and maximum acceptable quality of the target product.

Example 5 (comparative). The experiment is carried out under the conditions of example 1, with the only difference being that the oxidation process is carried out at a pressure corresponding to the vapor pressure of the mixture of the reaction mixture - oxidate (mainly acetic acid and reaction water), at a concentration of dissolved O ₂ in the reaction mixture on the 1st, 2nd, 3rd steps (g / l): 2.1; 0.2; ≤0.1, respectively.

The results on the oxidation stage were obtained: the yield of TMC decreased from 94.6% to 82.0%. The content of TMC in the oxidation products isolated from oxidate decreased from 98% to 83.8%. This indicates the incompleteness of the oxidation process of intermediate products (mainly alkylbenzenecarboxylic acids), the residual total concentration of which in the oxidation products isolated from stage 3 oxidate was 14.7%. The release of TMA to the initial TMC at the anhydride stage and the first stage of purification was 92.1%, at the second stage of purification 94.2%, the total yield at the process stages ≤80%. Qualitative indicators of technical and purified TMA do not meet the requirements for them. In technical TMA (table 2), the concentration of impurities is 5.3%, and after recrystallization in a binary solvent, the content of the main substance in the target product is 96.5%.

Example 6. The experiment on the oxidation stage is carried out under the conditions of example 1, with the only difference being that ethyl p-xylene is used instead of monoisopropyl-p-xylene and the temperature in the first and second steps is increased by 15 ° C (table 1). The anhydridation of TMC and the purification of TMA in the first and second steps are carried out under the conditions of Example 1 '(table 2), with the only difference being that ethyl p-xylene is used instead of IP-p-KS.

The results were achieved: at the oxidation stage, the yield of TMC reached 93.8% when its content in the selected oxidation products after the 3rd stage was 98.15%; at the stage of anhydrides of TMC and purification of TMA at the 1st and 2nd stages, the yield and quality of the target product are close to the results of example 1.

The yield of technical and purified TMA is 98.3% and 98.4%, respectively. The content of the main substance in purified TMA is 99.79%.

Example 7. The experiment is carried out under the conditions of example 1, with the only difference being that instead of isopropyl-p-xylene, pseudocumene is used and the temperature in the first and second steps is increased by 15 ° C. The conditions for the anhydridation of TMC and the purification of TMA correspond to Example 1, with the only difference being that pseudocumene is used in the anhydridization step of the first purification step.

The results were achieved: according to the oxidation stage, the yield of TMC is 95.2% when its content in the oxidation products isolated from oxidate is 98.7%; yields of 98.5% and 98.8%, respectively, were obtained at the stages of anhydrides of TMC and purification of TMA in the first and second steps; the impurity content in technical TMA is 0.6%, the concentration of the main substance in CTMA is 99.92%.

Example 8. The experiment is carried out under the conditions of example 1, with the only difference being that 2,5-diisopropyl-p-xylene is used instead of isopropyl-p-xylene as the initial hydrocarbon, i.e. tetraalkylbenzene, and the residence time at the 1st, 2nd, and 3rd oxidation stages are increased by 15 minutes by 40% reduction in the consumption of IRS in the first oxidation stage. The starting 2,5-diisopropyl-p-xylene containing 98.9% of the basic substance was obtained by alkylation of monoisopropyl-p-xylene with propylene at 85 ° C in the presence of AlCl ₃ . The conditions for the anhydridation of PMA and the purification of PMDA are similar to Example 1, with the only difference being that a binary mixture of benzene with ethyl acetate instead of methyl acetate is used as a solvent in the second stage of purification.

The results were obtained: the PMC yield at the oxidation stage of 92.4% with an impurity content (oxidation products isolated from oxidation products) of 1.1%; at the stages of anhydridation of PMC and purification of PMDA, the yields were 97.1% 97.0%, respectively; impurity concentration in technical PMDA 0.4%; the content of the main substance in the purified at the second stage PMDA 99.96%.

Example 9. The experiment is carried out under the conditions of example 8, with the only difference being that a different hydrocarbon by nature is used instead of 2,5-diisopropyl-p-xylene, 98% 6-isopropyl-pseudocumene, which is synthesized by alkylation of pseudocumene, is used as the starting tetraalkylbenzene propylene at 85 ° C in the presence of AlCl ₃ .

The results were obtained: at the oxidation stage, the PMC yield of 93.8% was achieved with a concentration of impurities (by-products) in the extracted crude PMC of 0.6% and a basic substance content of 98.3% in the oxidation products; yields of 98.3% and 98.7%, respectively, were achieved at the anhydride stage of PMC and purification of the formed technical PMDA at the first and second crystallization stages.

Example 10. The experiment is carried out under the conditions of example 9, with the only difference being that instead of 6-isopropyl pseudocoumol, durene is used with quality indicators corresponding to the technical conditions, and the pressure at 3 oxidation stages is increased by 0.3 MPa.

The results were obtained: at the oxidation stage, the PMC yield of 95.0% was achieved with impurities (side compounds) and the main substance in the oxidation products of 0.5% and 98.6%, respectively; yields of 98.2% and 98.9%, respectively, were achieved at the stage of anhydridization of PMC and purification of technical PMDA.

Example 11 (comparative). The experiment is carried out under the conditions of example 9, with the difference that the oxidation of 6-isopropyl-pseudocumene was carried out in one step at a temperature of the 3rd step and the total residence time in one step equal to the sum of the residence times in 3 steps.

The results were obtained: the content of the products of oxidative destruction of CO ₂ and CO in the exhaust air leaving the oxidation reactor increased by more than 2 times, which indicates increased irreversible losses of both the solvent (CH ₃ COOH) and the oxidized starting hydrocarbon (6-isopropyl pseudocumene); the concentration of impurities isolated from the oxidation products of the 3rd stage increased from 0.6% to 3.6%, which in turn led to a decrease in the yield of PMC from 93.8% to 89.0%. At the stage of anhydride and purification by recrystallization in two stages, a product was obtained that did not meet the technical specifications for the content of impurities of side compounds (0.62% instead of ≤0.4%) and for the content of the main substance (PMDA) in the target product obtained after cleaning (98, 8% instead of ≥99.5%).

Claims (3)

1. The method of producing intramolecular anhydrides of trimellitic and pyromellitic acids by liquid-phase oxidation of an oxygen-containing gas of tri- and tetraalkylbenzenes containing alkyl groups in the ortho position to benzoltri and tetracarboxylic acids at elevated temperature and pressure in an acetic acid medium in the presence of a metal halide catalyst in the form of a mixture compounds and salts of heavy metal of group VI, VII, VIII of the Periodic system of elements, followed by thermal dehydration of products isolated from oxidate oxidation and purification of the obtained anhydrides in a solvent medium, characterized in that the starting hydrocarbons are tri- and tetraalkylbenzenes containing methyl and isopropyl, methyl and ethyl or only methyl substituents of the general formula:

where a) R ₁ , R ₃ —CH ₃ , R ₂ —C ₃ H ₇ or —C ₂ H ₅ ; R ₁ , R ₂ , R ₃ —CH ₃ ;
b) R ₁ , R ₂ , R ₃ —CH ₃ , R ₄ —C ₃ H ₇ or C ₂ H ₅ ;
R ₁ , R ₃ —CH ₃ , R ₂ , R ₄ —C ₃ H ₇ or C ₂ H ₅ ; R ₁ , R ₂ , R ₃ , R ₄ —CH ₃ ,
which are oxidized in three stages at a concentration of dissolved oxygen in the liquid phase of the oxidants of each stage in the range of 0.11-0.15 mol / l while maintaining an excess of 1.3-13 times the excess pressure in the reaction zone P _hut relative to the vapor pressure of the liquid the reaction mass R _UP , a stepwise temperature increase in the range, ° C: 120-135, 140-185, 190-215, a discrete increase in the concentration of metal ions of the catalyst and promoter [Co ²⁺ + Mn ²⁺ ] / [Br ^- ] in intervals (ppm): 500 ÷ 700/800 ÷ 900; 1900 ÷ 2100/2400 ÷ 2600; 2700 ÷ 2900/3000 ÷ 3500 and with a reaction time of 15-50 minutes at each stage until a stepwise conversion of the starting hydrocarbon and intermediate compounds to benzene tri- and tetracarboxylic acids is achieved in the range,%: 9-14; 55-70; 96-99, after which the reaction products are isolated from the oxidate of the 3rd stage and subjected to thermal dehydration in a solvent liquid at a temperature of 230-240 ° C until the evolution of reaction water stops; the resulting solution of the corresponding anhydride is purified by crystallization in two stages in different in nature individual and binary solvents in such a way that individual trialkylbenzenes - isopropyl-p-xylene, ethyl-p-xylene or pseudocumene are used in the first stage, and binary is used in the second stage a mixture containing, in equimolar ratios, benzene and ethyl acetate, methyl acetate, ethyl acetate, propyl acetate or butyl acetate to obtain highly pure products. 2. The method according to claim 1, characterized in that the first stage of purification and isolation of the anhydride formed during thermal anhydrides in an environment of trialkylbenzene is carried out by stepwise cooling of a 20-30% solution of anhydride in trialkylbenzene, first from 230-240 ° C to 180-186 ° C with the separation of precipitated organic impurities and catalyst, and then from 180-186 ° C to 15-25 ° C with the subsequent separation of the target product of medium purity - technical trimellitic acid anhydride or technical pyromellitic dianhydride. 3. The method according to claim 2, characterized in that the trimellitic anhydride or pyromellitic dianhydride previously purified in the first step is subjected to additional purification by recrystallization in a binary solvent consisting of benzene and alkyl acetate by heating a 20-30% suspension of the technical product to 120-130 ° C, its exposure at the indicated temperature for 20-30 min, cooling to 20-25 ° C and the precipitation of the precipitated complex salt of intramolecular anhydride, followed by drying at a temperature of ≥125 ° C, providing decomposition of the complex with rofessional desired product of high purity.

Images