KR20020062311A - Process for preparation of benzene dicarboxylic acids - Google Patents

Abstract

The present invention relates to a method for producing benzene dicarboxylic acid by liquid phase oxidation of xylene isomers using oxygen or air by oxidation reaction in the presence of a solvent, a cobalt salt as a catalyst and an initiator. After the oxidation step, the reaction mixture is evaporated to remove volatiles, which is then cooled and filtered to afford the raw benzene dicarboxylic acid and filtrate as a solid product. The dicarboxylic acid solid product is recrystallized to obtain benzene with a purity of 99% or higher. The filtrate can be recycled.

Description

Process for preparing benzene dicarboxylic acid {PROCESS FOR PREPARATION OF BENZENE DICARBOXYLIC ACIDS}

Benzene dicarboxylic acid is produced industrially by oxidation of the corresponding xylene isomers. Phthalic acid can be produced by gas phase and liquid air oxidation of o-xylene, while terephthalic acid and isophthalic acid can only be produced by liquid phase processes. This is because the conversion of xylene and the selectivity to the corresponding phthalic acid are considerably lower in gas phase oxidation.

Known production of terephthalic acid often provides the system with free radicals to aid oxidation using cobalt acetate as catalyst and aldehyde or ketone as catalyst activator. Active agents are usually used in proportions similar to catalysts. Since this process uses a large amount of active agent and catalyst, acetic acid is produced as a by-product. In the conventional process, a relatively large amount of initiator was consumed. The phthalic acid purification process is energy consuming and cumbersome, and in the first step, terephthalic acid filtered in a high temperature absorption chamber is first filtered together with acetic acid for a time sufficient to dissolve impurities formed in the middle of the reaction with the catalyst in acetic acid. The mixture is then cooled and sent to the final purification step. Subsequently, the solid terephthalic acid is sublimed and catalyzed to remove organics and metal debris. In this process, a large amount of active agent and high energy are consumed, and time-consuming separation and purification steps are a big problem.

In other existing methods of preparing terephthalic acid, bromide-promoted cobalt and manganese catalysts are used as oxidants in an air atmosphere. However, this process does not produce the desired results because of the high concentration of carboxybenzaldehyde impurities.

U.S. Patent 5,132,480 (1992) describes a method for producing very high purity isophthalic acid in two steps in the presence of a liquid cobalt manganese bromide catalyst using acetic acid as a solvent at a temperature of 180-210 ° C. In the stage, the concentration of 3-carboxybenzaldehyde can be obtained up to 10,000 ppm, which is 100 ppm or lower in the second stage.

U.S. Patent 5,189,209 (1992) discloses the liquid phase hydrogenation of raw isophthalic acid in aqueous acetic acid in the presence of Group VIII noble metal catalysts at temperatures of 170-300 ° C. and pressures of 15-50 kg / cm 2. To insulate a very high purity isophthalic acid.

U.S. Patent 5,371,283 (1994) describes a method for preparing terephthalic acid. Acetic acid is present in the reaction system into which flammable dangerous substances related to acetic acid are introduced, and oxygen or oxygen-rich gas is used. This process basically uses a special type of reactor for terephthalic acid production.

U. S. Patent No. 5,770, 765 (1998) discloses a very high purity of iso-hydrogen by applying a mother liquor obtained from oxidation of m-xylene to a series of hydrogenation and oxidation steps using water as a solvent for dissolving isophthalic acid obtained by crystallization of an oxidizing solution. A method for preparing phthalic acid is described. The aqueous solution undergoes catalytic hydrogenation and oxidation to reduce intermediate impurities. Thus, the invention disclosed in this patent requires additional reaction steps to remove impurities of isophthalic acid.

U.S. Patent 3,74,214 (1976) describes a process for preparing isophthalic acid cobalt catalysts in which the formation of crude compounds such as meta toluic acid is reduced in the final product. The reaction is carried out in two reactors and the concentration of initiator and catalyst between the reactors is controlled. Careful control of the ratio of isophthalic acid and metatoluic acid between the reactors yields the desired result of less than 0.4% MTA in the final product. In the process between the first and second stages of the reactors, many glidants are added (at about the same rate as the MTA concentration of the first stage). It is argued that oxidizing MTA in the middle of the reaction without waiting for all isophthalic acid to form, reducing the amount of colorants occluded in isophthalic acid.

In short, bromide-promoted cobalt-manganese catalysts have been used so far in xylene oxidation. In the modification of these processes, a cobalt-manganese catalyst promoted by free radical generating compounds such as acetaldehyde and 2-butanone is used.

All of the above processes are problematic because they lead to corrosion of the equipment using bromide promoters. Since these processes are carried out in harsh conditions such as high temperatures and high pressures, the use of expensive corrosion-resistant materials for the corrosion of the equipment also results in safety concerns.

In addition, acetic acid is produced as a by-product while using an organic promoter in a predetermined molar ratio. These promoters are uneconomical because they are expensive raw materials for producing acetic acid. Dicarboxylic acids contain carboxybenzaldehyde as a by-product, which is very difficult to separate, making the product unsuitable for use as a monomer. Purification of the product also requires hydrogenation or oxidation of the impurities, which adds cost.

Thus, if the process does not use corrosive bromide compounds as catalysts, the complete conversion of intermediate products such as carboxybenzaldehyde, meta-toluic acid, etc. in the oxidation reactor will be guaranteed and the concentration of these compounds in the final product will be high and economical. .

The present invention relates to a method for preparing benzene dicarboxylic acid by liquid phase oxidation of xylene isomers using oxygen or air.

The process for the preparation of certain dicarboxylic acids such as phthalic acid, terephthalic acid or isophthalic acid is mainly achieved by the oxidation of the corresponding xylene isomers in the liquid phase with oxygen or air.

1 is a graph showing the effect of catalyst / xylene ratio on conversion and selectivity;

2 is a graph showing the selectivity for isophthalic acid and the conversion of m-xylene at a given pressure in the process of the present invention;

3 is a graph showing the effect of temperature on the selectivity for isophthalic acid and the degree of conversion of m-xylene;

4 is a graph showing the effect of initiator / catalyst ratio on the selectivity to isophthalic acid and the degree of conversion of m-xylene.

It is an object of the present invention to provide an improved process for improving the reactivity of carboxybenzaldehyde by-products using moderate concentrations of cobalt catalyst and process conditions without adversely affecting the selectivity to benzene dicarboxylic acid products and the conversion of xylenes. Thus, in this process almost no carboxybenzaldehyde impurities in the product are removed, so that no further purification steps downstream of the reactor are necessary. Very small amounts of catalyst activators are also used compared to conventional processes. The use of bromide catalysts can also be avoided.

The present invention relates to a process for producing benzene-dicarboxylic acid in which the catalyst contains no bromide promoter or organic promoter in mole fraction.

The process according to the invention utilizes 5.0-25 mole% cobalt salt of xylene feed as catalyst. The acid component of the cobalt salt is selected from acetate, propion ester, butyrate and phthalate, isophthalate and terephthalate. Significantly less than the amount used in the conventional process, the initiator is selected from ketones such as butanone and methyl ethyl ketone, acetaldehyde and tolualdehyde at a ratio of 0.05-1 mol% per mol of the metal salt mixture used as a catalyst. do. Certain xylene isomers are oxidized with air or oxygen for 1-6 hours in the presence of an acetic acid solvent at a pressure of 5-80 kg / cm 2 and a temperature range of 100-130 ° C. The weight ratio of solvent to xylene is 4-20. The reaction mixture is evaporated to room temperature and atmospheric pressure to remove volatiles such as water, unreacted xylene and other compounds, cooled to 20-40 ° C., and the crystallized raw product is filtered or centrifuged. The raw benzene dicarboxylic acid product is a material with a purity of at least 97% with only slight carboxybenzaldehyde. The product is recrystallized from appropriate solvents such as methanol, ethanol, water, acetic acid and the like and purified to 99% or more. The dewatered filtrate containing solvent, catalyst and intermediates is recycled after addition of catalyst, solvent and initiator.

The reaction is carried out in a 300 ml autoclave of stainless steel equipped with a mechanical stirrer, gas feed tube, reflux condenser, thermometer pocket, rupture disk. The pressure cooker is electrically heated and has a cooling coil therein. The system operates as a batch reactor. The exhaust gas captures all residual m-xylene while passing through an ice cooling trap and then through cold (-20 ° C) toluene.

Xylene is converted almost completely (98-100%) and the recycling selectivity for dicarboxylic acids is at least 98% based on the reacted xylenes. Carboxybenzaldehyde, an impurity in the product, is either completely lost or significantly reduced.

Through a series of experiments, the effects of various factors on the oxidation of xylene were obtained. The influence of the relevant factors is shown in the figure.

1 is a graph showing the effect of catalyst / xylene ratio on conversion and selectivity. As shown, selectivity and conversion also increase as the ratio of catalyst / xylene increases until the molar ratio is 0.1, but there is no change in conversion and selectivity when the molar ratio exceeds 0.1. Thus, the amount of catalyst suitable for use is 0.1 mole per mole of xylene dropped. At these catalyst concentrations, the reaction mechanism is an electron transfer system as opposed to the conventional one using the Co-Mn-Br catalyst system, which in the conventional case is a free radical mechanism, increasing the carboxybenzaldehyde concentration in the final product, thereby increasing the cost for purification of the dicarboxylic acid product. Requires a hydrogenation step. According to the method of the present invention, the hydrogenation step described above was completely eliminated by selecting the catalyst in the desired ratio to generate an oxidation reaction that completely converts the intermediate to the desired product.

2 is a graph showing the selectivity for isophthalic acid and the conversion of m-xylene at a given pressure in the process of the present invention.

3 is a graph showing the effect of temperature on the selectivity for isophthalic acid and the degree of conversion of m-xylene. Above 110 ° C., the conversion is 100%, but above 120 ° C., the selectivity for adipic acid drops sharply due to the inactivation of the cobalt catalyst.

4 is a graph showing the effect of initiator / catalyst ratio on the selectivity to isophthalic acid and the conversion of m-xylene. No matter how low the concentration of the initiator, the degree of conversion is basically perfect. However, the selectivity increases with the initiator concentration. A specific phthalic acid of 0.05 Kg was produced when the initiator / catalyst ratio was 1.0, which is much less than the initiator used in conventional processes.

Accordingly, the present invention relates to a process for preparing benzene-dicarboxylic acid by liquid phase oxidation of xylene isomers comprising the following steps.

In a pressure cooker with a pressure of 5-80 kg / cm 2 and a temperature range of 100-150 ° C., acetic acid solvent, a cobalt salt catalyst in a ratio of 5.0-25 mol% of xylene feed, and acetaldehyde in a ratio of 0.05-1 mol per mole of the catalyst, Oxidizing the xylene isomer for 1-6 hours in the presence of an initiator selected from tolualdehyde or ketone to form a reaction mixture;

Evaporating the reaction mixture to remove volatiles, cooling to 20-40 ° C., and filtering / centrifuging to obtain raw benzene dicarboxylic acid and filtrate as solid products; And

Recrystallizing the raw benzene dicarboxylic acid to obtain at least 99% pure benzene dicarboxylic acid in the presence of a solvent selected from methanol, ethanol, water or acetic acid.

The present invention also relates to a process for preparing benzene-dicarboxylic acid by liquid phase oxidation of xylene isomers comprising the following steps.

In a pressure cooker with a pressure of 5-80 kg / cm 2 and a temperature range of 100-150 ° C., acetic acid solvent, cobalt salt catalyst at a ratio of 5.0-25 mol% per xylene feed, and acetaldehyde at 0.05-1 mol per mole of the catalyst, Oxidizing the xylene isomer for 1-6 hours in the presence of an initiator selected from tolualdehyde or ketone to form a reaction mixture;

Evaporating the reaction mixture to remove volatiles, cooling to 20-40 ° C., and filtering / centrifuging to obtain raw benzene dicarboxylic acid and filtrate as solid products;

Recrystallizing the raw benzene dicarboxylic acid to obtain benzene dicarboxylic acid having a purity of 99% or higher in the presence of a solvent selected from methanol, ethanol, water or acetic acid; And

Recycling a filtrate having less than 1% water and containing the solvent, catalyst, intermediate, as well as unreacted xylene with organics.

Hereinafter, the present invention will be described in detail with reference to Examples, but the present invention is not limited to these Examples.

Example 1

21.2 g of m-xylene, 150 g of crystalline acetic acid, 5.0 g of cobalt acetate and 1.2 g of 2-butanone were charged into a 300 cc stirred stainless steel autoclave. Oxygen was injected at a rate of 100 cc / min through a steam injector and the mixture was oxidized at a pressure of 35 kg / cm 2 at 125 ° C. After injecting oxygen to the contents at 100 cc / min, the reaction mixture was evaporated to 35 ° C. at a pressure of 1 atm, cooled and centrifuged. The solid starting product obtained was 29.1 g and contained 98.5% of isophthalic acid, 1.4% of m-toluic acid, and 100 ppm of 3-carboxybenzaldehyde. The filtrate containing 3.6 g of organic product consisting of 80.3% m-toluic acid, 12.5% isophthalic acid and 7.2% unidentified compound is recycled. The crude product, crystallized from water, produced 28.5 g, 99.9% isophthalic acid and less than 15 ppm 3-carboxybenzaldehyde.

Example 2

21.2 g of m-xylene, 160 g of crystalline acetic acid, 4.0 g of cobalt acetate and 0.5 g of paraaldehyde were treated with 150 cc / min of oxygen in a pressure cooker of 130 ° C. and 30 kg / cm 2 for 3 hours. The reaction mixture was evaporated to 35 ° C. at 1 atm, cooled and centrifuged. The resulting solid crude product was 28.8 g and contained 98.3% isophthalic acid, 1.6% m-toluic acid and 120 ppm 3-carboxybenzaldehyde. Upon recrystallization, the pure product was 99.9% and 3-carboxybenzaldehyde was less than 15 ppm. The filtrate contained 4.5 g of organic product consisting of 84.5% m-toluic acid, 12.3% isophthalic acid and 3.2% unidentified compound.

Example 3

A mixture of 21.2 g of p-xylene, 200 g of crystalline acetic acid, 6.0 g of cobalt acetate, and 0.4 g of 2-butanone was heated at 120 ° C. in a 20 kg / cm 2 pressure cooker using a steam injector with 100 cc / min of oxygen for 4 hours. Took care of. The reaction mixture was evaporated to 25 ° C. at 1 atm, cooled and filtered. The yield of raw material (98.6%) terephthalic acid was 30.2 g. The filtrate containing 4.5 g of organic product consisting of 15.29% terephthalic acid, 75.8% toluic acid and 9.0% unidentified compound is recycled. The crude product by crystallization produced terephthalic acid with a purity of 99.9% and less than 15 ppm of 4-carboxybenzaldehyde.

Example 4

A mixture of 21.2 g of m-xylene, 200 g of crystalline acetic acid, 5.2 g of cobalt acetate, and 1.0 g of 2-butanone was mixed at 130 ° C. in a 40 kg / cm 2 pressure cooker using a steam injector with 500 cc / min of oxygen for 5 hours. Took care of. The reaction mixture was filtered to yield 30.1 g crude 98.1% isophthalic acid. The filtrate containing 21.2 g m-xylene, 0.25 g cobalt acetate and 0.4 g 2-butanone was oxidized at 130 ° C., 40 kg / cm 2 with 500 cc / min of oxygen for 5 hours. The reaction mixture in 350 cc of filtrate produced 32.5 g of raw material (98.5%) isophthalic acid. This was recrystallized from water to produce 31.5 g of isophthalic acid having a purity of 99.9%. 3-carboxybenzaldehyde contained in this product was less than 15 ppm.

Therefore, the process for producing benzene dicarboxylic acid according to the present invention liquid phase oxidizes xylene in the presence of a solvent using a cobalt catalyst with very low concentration of the active agent. Thus, there are no corrosive initiators / activators such as bromide based compounds. Under these reaction conditions, the catalyst concentration is chosen so that oxidation occurs through the electron transfer path. This converts intermediates such as toluic acid and carboxybenzaldehyde very rapidly to phthalic acid, resulting in a lower concentration of these compounds in the final product. Therefore, the purification of phthalic acid is easy and no hydrogenation process or other energy consuming process is necessary, but recrystallization from water or other suitable solvent is included.

It should be understood that the embodiments described above are merely examples, and do not limit the scope of the present invention.

Claims (5)

In the process for preparing benzene-dicarboxylic acid by liquid phase oxidation of xylene isomers: In a pressure cooker with a pressure of 5-80 kg / cm 2 and a temperature range of 100-150 ° C., acetic acid solvent, cobalt salt catalyst at a ratio of 5.0-25 mol% per xylene feed, and acetaldehyde at 0.05-1 mol per mole of the catalyst, Oxidizing the xylene isomer for 1-6 hours in the presence of an initiator selected from tolualdehyde or ketone to form a reaction mixture; Evaporating the reaction mixture to remove volatiles, cooling to 20-40 ° C., and filtering / centrifuging to obtain raw benzene dicarboxylic acid and filtrate as solid products; And Recrystallizing the raw material benzene dicarboxylic acid to obtain benzene dicarboxylic acid having a purity of 99% or higher in the presence of a solvent selected from methanol, ethanol, water or acetic acid; and a process for producing benzene-dicarboxylic acid. In the process for preparing benzene-dicarboxylic acid by liquid phase oxidation of xylene isomers: In a pressure cooker with a pressure of 5-80 kg / cm 2 and a temperature range of 100-150 ° C., acetic acid solvent, cobalt salt catalyst at a ratio of 5.0-25 mol% per xylene feed, and acetaldehyde at 0.05-1 mol per mole of the catalyst, Oxidizing the xylene isomer for 1-6 hours in the presence of an initiator selected from tolualdehyde or ketone to form a reaction mixture; Evaporating the reaction mixture to remove volatiles, cooling to 20-40 ° C., and filtering / centrifuging to obtain raw benzene dicarboxylic acid and filtrate as solid products; Recrystallizing the raw benzene dicarboxylic acid to obtain benzene dicarboxylic acid having a purity of 99% or higher in the presence of a solvent selected from methanol, ethanol, water or acetic acid; And Recycling a filtrate having less than 1% of water and containing the solvent, the catalyst, the intermediate, as well as the organics and unreacted xylene; and a process for producing benzene-dicarboxylic acid. The method according to claim 1 or 2, wherein the acid component of the cobalt salt is selected from acetate, propion ester, butyrate or phthalate, isophthalate, terephthalate and the like. A process according to claim 1 or 2, characterized in that the initiator is selected from butanone and methyl ethyl ketone at a rate of 0.05-1 mol% per mol of the metal salt mixture used as catalyst. Benzene dicarboxylic acid prepared by the process according to any one of the preceding claims.