RU2137753C1 - High-purity isophthalic acid production process - Google Patents

Abstract

FIELD: industrial organic synthesis. SUBSTANCE: isophthalic acid is prepared by combination of two interrelated processes of liquid-phase catalytic oxidation of m-xylene with oxygen-containing gas in acetic acid medium followed by recrystallization of crude product. Oxidation process is carried out in two in-series disposed reactors within temperature range 180-198 C in presence of catalyst consisting of manganese and cobalt acetates and bromine compound mixture (HBr). Catalyst is further supplemented by chlorine in the form of lithium chloride or its mixture with manganese and cobalt chlorides as well as hydrogen chloride. Cl/Br atomic ratio is 1: (1-1.9). Duration of mixing reactants in oxidation zone is 12 s, and residual concentration of m-carboxybenzaldehyde in oxidation products is 0.15-0.25 wt %. Purification of isophthalic acid to remove intermediate and by-products is accomplished by recrystallization from acetic acid and/or water at 185-220 C followed by four-step cooling accompanied by recycling mother solutions after separation of crude and high-purity product. Reaction water is removed from oxidation reactors and crystallizes to achieve optimal composition of acetic acid-water solvent. EFFECT: increased productivity of process and improved quality of product. 4 cl, 1 tbl, 17 ex

Description

 The invention relates to organic and petrochemical synthesis, in particular to a method for producing high-purity isophthalic acid (IFC), one of the widely used monomers for the manufacture of polymeric materials: high-quality polyester fibers, films and coatings for food and technical purposes, isopolyester resins, fibrous plastics, synthetic leather , polymer concrete, etc.

 Most modern industrial syntheses of IFCs are based on two-stage processes. The first stage involves the process of liquid-phase catalytic oxidation of m-xylene with molecular oxygen in an acetic acid medium to produce technical isophthalic acid. At the second stage, technical IFC is purified by the method of catalytic hydrogenation of impurities in aqueous solutions or by the method of recrystallization in various solvents.

So, for example, according to the patent, technical IFCs are obtained by oxidation of m-xylene with air in a CH ₃ COOH medium at a temperature of 100 - 130 ^o C and a pressure of 0.07-3.5 MPa. As a catalyst, a cobalt salt with the addition of a promoting component of acetaldehyde is used. The oxidation is carried out in two stages with a total reaction time of 1.2-20 hours. The obtained technical IFC is purified by recrystallization in CH ₃ COOH. The disadvantage of this method is the low productivity of the process.

According to another method widely used on an industrial scale, the synthesis of high-purity IPA is also carried out in two stages. The first stage involves the oxidation of m-xylene with atmospheric oxygen in a medium of CH ₃ COOH in the presence of a cobalt-manganese-bromide catalyst at an elevated temperature (170-215 ^° C) and a pressure of 1.5-2.5 MPa to obtain IFC raw. The second stage involves the purification of "crude" isophthalic acid by the method of molecular hydrogenation of impurities of mainly m-carboxybenzaldehyde (m-CBA). The hydrogenation reaction is carried out in an aqueous medium in the presence of a catalyst - palladium on carbon (Pd / c) at a relatively high temperature (up to 280 ^o C). The process has increased efficiency and ensures the achievement of high quality IFC: the content of m-KBA ≤ 0.0025%, the color index ≤ 10 ^o N.

 The disadvantages of this method include the use of chemical reactions of a different nature (oxidation is used at the synthesis stage and hydrogenation is used at the purification stage), which entails the necessity of using different solvents, catalysts and other reagents. This, in turn, necessitates the attraction of significant costs for their regeneration. In the process of regeneration, a large amount of liquid and solid waste is inevitably generated, and under the conditions of operation of plants of large unit capacity, the conditions for the formation of environmental pressure are created.

R₁, R₂: (-CH₃) или (H) или (-CH₃O)
Массовое соотношение флегма: реакционная смесь составляет 0,3-0,6: 1. Содержание м-КБА в получаемой ИФК находится в пределах 0,006- 0,018%.There is also known a method of producing terephthalic (TFA) or isophthalic acids of high quality by liquid-phase oxidation of para- or meta-isomers of xylene with atmospheric oxygen in two stages in a CH ₃ COOH medium. In the first stage, the oxidation is carried out at 200-215 ^o C and a pressure of 2.0-2.6 MPa, in the second stage at a temperature of 180-200 ^o C and the reaction mass is treated simultaneously with an oxygen-containing vapor-gas mixture leaving the first stage and reflux taken from a zone of step crystallization and having in its composition 80-88% CH ₃ COOH, 10-16% H ₂ O, 1.5-4.0% aliphatic compounds with the general formula
R ₁ - O - R ₂ or

R ₁ , R ₂ : (-CH ₃ ) or (H) or (-CH ₃ O)
The mass ratio of phlegm: the reaction mixture is 0.3-0.6: 1. The content of m-KBA in the obtained IFC is in the range of 0.006-0.018%.

One of the advantages of this method is that IFC of monomeric purity is obtained without the use of complex purification methods, for example, by hydrogenation of impurities using Pd / c. However, like other previously described methods, this method is not without drawbacks. The most significant of them is that with an increase in the quality of IFCs, i.e. with a decrease in the content of the main impurity in it, m-CBA, the losses of CH ₃ COOH due to combustion significantly increase, which makes the process more expensive. In addition, the obtained quality of IFC ([m-CBA] = 0.006-0.018%) does not meet the requirements for high-purity IFC ([m-CBA] ≤ 0.0025%), which limits the possibility of using the obtained IFC.

The closest in technical essence and the achieved results is a method for producing very pure isophthalic acid by liquid-phase catalytic oxidation of m-xylene in acetic acid with an oxygen-containing gas in two stages, followed by purification of the obtained IFC by treatment with acetic acid at a temperature of 100-150 ^o C (prototype). In the first stage, oxidation is carried out at 180-210 ^o C with a continuous supply of O ₂ -gas and a reaction mixture containing acetic acid, m-xylene in a 1-15-fold amount from the solvent, a cobalt-manganese-bromide catalyst at a total concentration cobalt and manganese 500-1500 ppm, the atomic ratio of metals to bromine 0.5-1.5, until the m-KBA content in the oxidation products reaches 500-10000 ppm and the total concentration of isophthalic acid in the reaction mass is 10-35%.

In the second stage, the mixture is additionally oxidized with O ₂ gas to form isophthalic acid containing 0.01-0.08% m-KBA.

Next, the crude IFC obtained in the second stage is mixed with acetic acid and, under stirring and holding at a temperature of 100-150 ^o C, the following IFC quality is achieved: residual content of m-KBA 0.0027-0.0044%, color (according to the Hazen scale ) ≤ 20 ^o N. One of the disadvantages of this method is the insufficiently high quality of the purified IFC. Based on the current requirements of consumers manufacturing high-quality polymeric materials, the color index should not exceed 10 ^o N, and the content of m-KBA ≤ 0.0025%. In addition, the duration of the oxidation reaction in the first and second stages of ~ 80 min indicates a relatively low productivity of the process at the stage of synthesis of technical IFC.

 The aim of the present invention is to increase the efficiency of process performance and improving the quality of the target product of IFC.

This goal is achieved by combining two interconnected processes of the oxidation of m-xylene in acetic acid and recrystallization of technical IFC in an acetic-aqueous solvent and / or in water, while lithium chloride (LiCI) or its mixture with chlorine-containing XCI compounds are additionally added to the oxidation catalyst _n , where X is Mn, Co, H, n = 1.2 in the ratio Cl: Br = 1: 1-1.9 at a total concentration of halogen atoms of 350-900 ppm, and the atomic ratio of the metal-catalyst components is maintained within Mn : Co = 1: 0.1-2 at their total concentration in rea with a mass of 280-800 ppm and a liquid-phase oxidation process in the first stage are carried out at a reagent mixing time of ≤ 12 s, a temperature not exceeding 198 ^o C, for 30-45 min until a residual concentration of m-carboxybenzaldehyde in the oxidation products of 0.3-0 is reached , 7%, in the second stage, the oxidation is carried out at a temperature of 170-190 ^o C for 5-15 minutes to achieve a residual concentration of m-CBA in the oxidation products of 0.15-0.25%, after which the technical IFC extracted from the oxidate is subjected to recrystallization in an acetic aqueous solvent comprising 2-12% H ₂ O, and / or water, by heating (20-35% pure) slurry before IFC 185-220 ^o C, subsequent cooling it in four stages up to 30-70 ^o C at a speed of 2-5 ^o C / min and isolation of high purity IPA known methods.

The use of a Mn-Co-Br catalyst as an additional component (s) of a chlorine-containing compound, specifically LiCI or its mixtures with manganese, cobalt or HCI chlorides (LiCI + MnCl ₃ ) (LiCI + CoCl ₃ ), (LiCI + HCI) the found limits of concentrations and ratios of metal atoms — catalyst, bromine, and chlorine — made it possible to increase the rate of conversion of m-xylene to IPA, i.e., to increase the productivity of the oxidation process, as well as to reduce the content of intermediate products in IPA.

The combination of the found catalyst composition with effective mass transfer in the oxidation reaction zone, as a result of the use of experimentally established hydrodynamic parameters (specific power for mixing, reduced linear velocity of the gas in the cross section of the reactor, dispersed input of reagents, etc.), providing rapid mixing (homogenization) in the zone reaction, allowed to significantly improve the quality of IFC by the content of high-boiling reaction by-products, which are colored and evaluated m color. This opened up the possibility of purification of the obtained IPA by a simple physical method of recrystallization in an acetic-aqueous solvent and / or in water to obtain a high-purity target product (m-KBA content ≤ 0.002%, color ≤ 10 ^o N), eliminating the use of complex and expensive purification processes that currently used in industrial practice.

 The following is a description of the installations, experimental procedures and examples to reveal the essence of the present invention.

 Description of facilities and experimental techniques.

Obtaining high-purity IFC was carried out in a laboratory and industrial installations in a continuous mode. Reactors (V _lab. = 1.25 L, V _prom. = 1.25 m ³ ) are made of titanium and equipped with tube mixers, condensers, condensers, heating elements, instruments for controlling temperature, pressure, air flow and gas analyzers for measurements concentrations of O ₂ , CO ₂ , CO in the exhaust gases from the reactor. 95-98% CH ₃ COOH, manganese, cobalt acetates and activating bromine and chlorine compounds in the form of HBr and LiCI or a mixture of (LiCI + MnCl ₂ ), (LiCI + CoCl ₂ ) (LiCI + HCI) are loaded into the reactor. The contents of the reactor when the stirrer is heated in a stream of inert gas to a temperature of 170-198 ^o C and begin the dosage of the initial mixture. At the same time, air is supplied to the reactor in an amount ensuring a reduced velocity in the cross section of the reactor of 2.5-8 cm / s and an oxygen content of 3-5% by volume of gases leaving the reactor. At a fixed (predetermined) air flow rate, the required concentration of O ₂ in the exhaust gases is maintained by changing the feed of the initial reaction mixture (IRS) to the oxidation reactor or the concentration of m-xylene in the initial reaction mass. The oxidate after the first stage is subjected to additional oxidation in the second stage, after which it is cooled to 30-70 ^o C and filtered. In laboratory conditions, filtration is carried out on a Buchner funnel, in industrial conditions - on a horizontal filtering centrifuge type FGN.

The selected paste (precipitate) of technical IFC is diluted with 90-98% acetic acid in a repulpator equipped with a stirrer to obtain a 20-35% suspension. The resulting suspension is heated to complete or almost complete dissolution of the solvent in the apparatus, equipped with a turbine mixer and heating elements, and then cooled to 30-70 ^o C at a speed of 2-5 ^o C / min in the same apparatus (laboratory setting) or 4 sequentially installed molds (industrial installation).

 The cooled suspension of IFC is filtered in laboratory conditions on a Buchner funnel, in industrial conditions - in a centrifuge such as FGN. The precipitate paste of high-purity IFC is dried to constant weight in an oven (in a laboratory setting) or in a Venulet type dryer (in an industrial setting), after which its quality is analyzed. In a series of experiments, technical IFCs are recrystallized in water according to the method described above or sequentially in acetic acid and then in water.

 The experimental results are presented in table 1 (examples 1 to 17).

Example 1. The process of obtaining IFC is carried out in a laboratory setting (V _reactor 1.25 l).

An initial reaction mixture (IRS) is prepared in an amount of 2500 ml (2632.94 g), for which acetic acid (1886 ml), m-xylene (570 ml), manganese acetate tetrahydrate (3.08 g), cobalt acetate tetrahydrate ( 1.78 g), lithium chloride (0.85 g), 40% hydrobromic acid (2.5 g) and water (134 ml). These reagents are mixed and at 80 ^o C and stirring is brought to complete dissolution of the catalyst. After analysis, the following composition of IRS was obtained:
m-xylene - 18.73%
CH ₃ COOH - 74.52%
H ₂ O - 6.64:
Mn - 262 ppm
Co - 160 ppm
Li - 49 ppm
Cl - 269 ppm
Br - 380 ppm
Before oxidation begins, a catalyst solution (without m-xylene) is poured into the reactor, and IRS is poured into a stainless steel collector equipped with a heating jacket and a level gauge, from which it is continuously pumped to the reactor. After sealing, an inert gas (nitrogen) is fed into the reactor, a pressure of 1.6 MPa is established and heated to 196 ^° C. with the turbine mixer in operation and a continuous flow of nitrogen turned on.

 After reaching the indicated temperature in the reactor, the metering pump is switched on and IRS in the amount of 1100 ml is continuously supplied from the collector, which corresponds to a residence time of 35 minutes. At the same time, air is supplied from the compressor unit.

 The mixing (homogenization) time of 1.5 s is achieved by setting the stirrer speed (1800 rpm) at an air flow rate of ~ 12 nl / min, which corresponds to a linear gas velocity in the cross section of the reactor of 4.2 cm / s.

The concentration of water in the reaction zone is maintained at 8.5% by partial removal of the watered reflux after the second condenser cooler mounted above the reactor. After 3 hours of continuous oxidation, a sample is taken from the reactor, from which solid oxidation products are isolated after cooling to 60 ^° C. Analysis of the isolated solid products showed the following quality of crude IFC after stage I oxidation:
[m-KBA] = 0.68% (6800 ppm)
[m-TC] = 0.59% (5900 ppm)
[BC] = 0.03% (300 ppm)
Chromaticity = 21 ^o H
The oxidate after stage I is subjected to post-oxidation in a stage II reactor under the following conditions: temperature 185 ^° C, pressure 0.9 MPa, oxidation time 15 min. Analysis of the selected oxidation products after the reactor of stage II showed the following qualities of the crude IFC:
[m-KBA] = 0.16%
[m-TC] = 0.18%
[BC] = 0.06%
Color = 13 ^o N
Next, the obtained technical IFC is subjected to purification by recrystallization in 95% acetic acid. In a solvent apparatus, a 20% suspension is prepared and in a stream of inert gas (nitrogen) under a pressure of 1.6 MPa is heated to 198 ^o C until crystalline IFC is completely dissolved, after which the solution is cooled to 40 ^o C at a rate of 5 ^o C / min .

Pure IFC is isolated from the cooled suspension and a product of the following quality is obtained:
[m-KBA] = 0.0021%
[m-TC] ≤ 0.005%
[BC] ≤ 0.005%
Chromaticity = 6 ^o N
The yield of IFC was 95.8% of theory. Other process indicators of example 1, as well as the conditions and results of examples 2-17 are shown in table 1.

Example 2. The experiment is carried out under the conditions of example 1 with the only difference that the ratio of Mn: Co is measured from 1: 0.6 to 1: 1.6. The quality of IFC improved, [m-CBA] decreased from 19 ppm to 17 ppm, color decreased from 7 ^o N to 5 ^o N. However, the losses of CH ₃ COOH due to combustion at the oxidation stage increased from 37 kg / t IFC to 42 kg / t IFC.

Example 3. The experiment is carried out under the conditions of example 1 with the only difference that at the stage of oxidation the ratio of Mn: Co is increased from 1: 0.6 to 1: 0.1. and at the stage of purification, 2-fold recrystallization is used, first in CH ₃ COOH and then in H ₂ O. As follows from the results, a 10-fold increase in the manganese content with respect to cobalt in the composition of the catalyst decreased the “combustion” of CH ₃ COOH with 37 kg / t IFC up to 32 kg / t IFC, however, the quality of crude IFC slightly deteriorated, which required double recrystallization.

The result is a high quality product: the content of m-CBA ≤ 15 ppm, the total content of m-toluic and benzoic acids did not exceed 10 ppm, color 8 ^o N.

Example 4. The experiment is carried out under the conditions of example 2 with the only difference that the temperature in the oxidation stage is reduced to 190 ^o C, and the residence time is increased from 35 to 40 minutes by reducing the supply of IRS. At the purification stage, 2-fold recrystallization is used: first in CH ₃ COOH, then in H ₂ O. From the results of Example 4 it follows that lowering the temperature, ceteris paribus, reduces the depth of conversion of m-xylene to IFC, which requires the use of double recrystallization. At the same time, CH ₃ COOH losses due to combustion are reduced from 42 kg / t IFC to 29 kg / t IFC. Received a product that meets the requirements of high-purity IFC: [m-KBA) = 20 ppm, color index 9 ^o N.

Example 5. The experiment is carried out under the conditions of example 4 with the only difference that the oxidation temperature is increased to 198 ^o C, and at the stage of purification using a single recrystallization in water. A product is obtained that meets the requirements of highly pure IFC: [m-KBA] = 20 ppm, [m-TC] 80 ppm, color 10 ^o N.

Combustion of CH ₃ COOH increased from 29 kg / t IFC to 48 kg / t IFC.

Example 6. The experimental conditions correspond to example 1 with the difference that the concentration of the catalyst is increased by 1.9 times, and a single crystallization in CH ₃ COOH is used in the purification step. Result: high product quality is achieved ([m-KBA] = 16 ppm, color 6 ^o N). Losses of CH ₃ COOH due to combustion increased from 37 kg / t IFC to 46 kg / t IFC.

Example 7. The experimental conditions are similar to example 1 with the only difference being that the Cl: Br ratio is varied from 1: 1.4 to 1: 1.9. The results on the quality of IFC and solvent losses are close to the results of example 1. Combustion of CH ₃ COOH amounted to 36 kg / t IFC. IFC quality: [m-KBA] = 20 ppm, color 8 ^o N.

 Example 8 (comparative). The experiment is carried out under the conditions of example 1 with the only difference being that the Cl: Br ratio is increased from 1: 1.4 to 1: 0.5, i.e. increase ~ 3 times the chlorine content relative to bromine while maintaining the total concentration of halogen ions. The results showed a sharp deterioration in the quality of IFC, a decrease in the conversion of m-xylene to IFC.

Qualitative indicators of purified IFC ([m-CBA] = 360 ppm, [m-TC] = 271 ppm, color 56 ^o N) in terms of the content of intermediate products exceeds their permissible concentration by more than an order of magnitude, and in color more than 5 times .

Example 9 (comparative). The experimental conditions are similar to example 3 with the only difference that the ratio Mn: Co is increased from 1: 0.1 to 1: 0.05, i.e. increase the Mn content and catalyst composition without changing their total concentration. The results indicate a decrease in the activity of such a composition of the Mn-Co-Hal catalyst, which leads to a deterioration in the quality of the obtained IFC: [m-KBA] = 210 ppm, color 19.4 ^o N.

Example 10 (comparative). The experiment is carried out under the conditions of example 1 with the only difference that the depth of conversion of xylene to IFC at the first and second oxidation stages is increased to a residual content of m-CBA in IFC (less than 0.3% in the first stage and less than 0.15 % pa second stage) by increasing the reaction time more than 45 minutes From the results shown in table 1, it follows that under these conditions the required quality of high-purity IFC is achieved, but the loss of CH ₃ COOH due to thermocatalytic oxidative degradation increases to 80 kg / t IFC.

Example 11. The experiment is carried out in an industrial reactor (V = 1.25 m ³ ) equipped with two turbine mixers, two condensers, refrigerators, a heating jacket, pipes for the input and output of reagents, instrumentation and automation. The experimental conditions are similar to example 1 with the only difference that the time of mixing (homogenization) of the reactants in the reactor is 12 s with two inputs along the height of the initial reaction mixture and the reduced linear air velocity in the cross section of 7 cm / s.

From the results of the example it follows that in industrial-scale apparatuses the data of the laboratory setup are reproduced. A pure product is obtained that meets the requirements of IFC consumers: [m-KBA] = 18 ppm (m-TC) ≤ 5 ppm, color 6 ^o N.

 Example 12 (comparative). The experiment is carried out under the conditions of example 11 with the only difference being that the mixing (homogenization) time is increased to 40 s. By reducing the speed of the mixer, reducing the number of inputs of the IRS and reducing the reduced gas velocity in the cross section of the reactor to 1.1 cm / s

Under these conditions, the quality of IFC has significantly deteriorated according to the color:
[m-KBA] = 20%
[m-TC] = 16%
Chromaticity 18 ^o N
Example 13 (comparative). The experiment is carried out in a laboratory setup under the conditions of example 1 with the only difference being that lithium chloride is excluded from the composition of the catalyst.

 The oxidation results showed that the content of intermediate compounds in the technical IFC isolated after the first and second stages of oxidation increased ~ 1.2 times. This indicates a decrease in the conversion depth of m-xylene and IFC and a deterioration in the quality of technical

Claims (4)

1. The method of obtaining high-purity isophthalic acid (IFC) by stepwise liquid-phase oxidation of m-xylene with atmospheric oxygen in elevated temperature and pressure in the presence of cobalt salts, manganese and bromine compounds, followed by hot washing of the selected crystalline oxidation products with acetic acid, characterized in that high-purity IPA is obtained by combining two interconnected processes of oxidation of m-xylene in acetic acid and recrystallization of technical IPA in acetic-aqueous solvent and / or in water, while lithium chloride (LiCl) or its mixture with chlorine-containing compounds XCl _n , where X is Mn, Co, H, n = 1, 2, in the ratio Cl: Br = 1: 1 ^o C 1.9 at a total concentration of halogen atoms of 350 - 900 ppm, and the atomic ratio of the components of the metal catalyst is maintained within Mn: Co = 1: 0.1 ^o C 2 at their total concentration in the reaction mass of 280 - 800 ppm, and the liquid-phase oxidation process in the first stage is carried out at a reagent mixing time of ≤ 12 s, at a temperature not exceeding 198 ^o C (preferably approximately 189 - 197 ^o C) for 35 - 45 min until a residual concentration of m-carboxybenzaldehyde (m-KBA) in the oxidation products of 0.3 - 0.7 wt.% is reached, in the second stage, oxidation is carried out at a temperature of 170 - 190 ^o C for 5-15 minutes until the concentration of m-CBA in the oxidation products reaches 0.15 - 0.25%, after which the technical IFC extracted from the oxidate is subjected to recrystallization in an acetic-aqueous solvent containing 5 - 12% H ₂ O, and / or in water, by heating a 20 - 35% suspension of IFC to 185 - 220 ^o C, then cooling it in four steps to 30 - 70 ^o C at a speed of 2 - 5 ^o C / min and the allocation of high-purity IFC by known methods. 2. The method according to claim 1, characterized in that the mixing (homogenization) time of the reagents introduced into the oxidation zone is maintained within 1 - 12 s by setting the feed rate of O ₂ gas (air) into the reaction zone, which ensures the achievement of the reduced linear velocity in the cross section of the reactor is 2.5-8 cm / s.  3. The method according to claims 1 and 2, characterized in that the cleaning process of the technical IFC is carried out by its single recrystallization in acetic acid or water.  4. The method according to claims 1 to 3, characterized in that the purification process of the technical IFC is carried out by double recrystallization, while the first recrystallization is carried out in acetic acid, and the second in water.

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