DD299375A7 - PROCESS FOR PREPARING TEREPHTHALIC ACID - Google Patents

Abstract

The invention relates to a process for the preparation of terephthalic acid by liquid phase oxidation of p-xylene, with particular regard to the treatment of the residue. The aim is to develop a process for the preparation of terephthalic acid in the use of the residue. According to the invention, the residue after the distillative separation of the benzoic acid and the phthalic anhydride is burned at 480-500 ° C., the oxide ash is thermally treated at 750-850 ° C. for 0.1-2 h and the insoluble cobalt and manganese oxides are used directly in the process. {Residue; aromatic acids; Catalyst ions; Combustion; oxide ash; Prozeszrueckfuehrung}

Description

Characteristic of the known state of the art The production of terephthalic acid by liquid phase oxidation of p-xylene In acetic acid using atmospheric oxygen under Addition of heavy metal catalysts such as cobalt and manganese as well as a bromide source is disclosed in US Pat. No. 2,833,816

basically described.

In the liquid-phase oxidation of p-xylene in acetic acid, the more easily soluble oxidation intermediates and Oxidation by-products and the catalysts in the solvent. In the continuous process it comes to the enrichment

These products in the solvent acetic acid and to maintain the high purity of terephthalic acid must be part of the

Solvent acetic acid is removed from the process with the impurities and the acetic acid distilled off

become. The solvent acetic acid is recycled to the process. The distillation residue contains the

Oxidation intermediates p-toluic acid and 4-carboxybenzaldehyde, the oxidation by-products i-phthalic, phthalic and Benzoic acid in addition to other oxygen-containing difficult to identify aromatic compounds and the catalysts Cobalt, manganese and bromide as well as metal contaminants due to corrosion. Since this residue contains the valuable catalysts and also versatile aromatic acids, methods

have been developed for the recovery of these recyclables.

In US Pat. No. 3,950,409, the residue is extracted with water and the resulting solution is subjected to the oxidation process

recycled.

The remaining acid mixture is burned. The extraction with water has the consequence that the very easily soluble Sodium ions preferably go into solution and are returned to the process. The sodium ions cause in the p-xylene Oxidation the increase of oxidation intermediate and oxidation by-product formation in addition to a higher Totaioxidation of Solvent acetic acid, as shown in DD-WP 242940. By dissolving the residue in caustic soda or sodium carbonate as set forth in U.S. Patent 3,080,920

precipitated the hydroxides or carbonates of the catalyst elements and after washing the precipitated hydroxides or

Carbonates are dissolved in acetic acid with the addition of hydrobromic acid and recycled to the process. This residue processing requires a high expenditure on equipment, a considerable consumption of auxiliary substances and leads to Environmental problems by the dissipation of dissolved sodium salts of organic acids in the wastewater. Another method is described in US Pat. No. 4,546,202, according to which the metal oxides are dissolved in acetic acid and

this solution is attributed to the process.

Again, it comes to the accumulation of interfering sodium ions. The production of benzoic acid and phthalic anhydride represents an economic use of much of the

aromatic acids.

A solution for the most economical use of highly corrosive aromatic acids and the Catalyst elements without high consumption of additives and high expenditure on equipment and without affecting the Effectiveness of the oxidation process of terephthalic acid production, could be due to the high technological Difficulties have yet to be developed. Object of the invention

The object of the invention is to increase the effectiveness and reduce the environmental impact of the terephthalic acid process by the reuse of the catalyst elements contained in the residue.

Explanation of the essence of the invention

The invention has for its object to improve the process for the production of terephthalic acid by the use of the catalyst elements contained in the residue, without affecting the effectiveness of the liquid-phase oxidation process of p-xylene and the quality of terephthalic acid.

According to the invention, the residue is after the greatest possible separation by distillation of the benzoic acid and the Phthaljäureanhydrids spontaneously burned at 480-500 ° C, the oxidase thermally treated at 800 ⁰ C for 1.5 h, with Structural changes of the oxide ash of the water-soluble sodium ion content is increased up to 95% of the total content and

after separation of the cobalt and manganese oxides, these are recycled directly to the process.

The thermal treatment of the oxide ash to 900 ⁰ C is a maximum of acetic acid-soluble cobalt · and Manganese oxides reached. The separation of the manganese and cobalt oxides by sedimentation or centrifugation is due to the high density

these metal oxides easily.

AusfOhrungsbelsplel In a platinum crucible 5.5 g residue from the terephthalic acid production are heated with the Bunsen burner and at the Spontaneously burned at 480-500 ° C, then thermally treated in the muffle furnace bsi 800 ⁰ C for 1.5 h and the oxide ash,

containing sodium, cobalt and manganese ions, wherein the content of cobalt and manganese oxide is 0.106 g and sodium ions of 0.027 g is stirred with 10 ml of water at 90-100 ° C for 20 min and the black suspension at 4 000 min " Centrifuged for ¹ min and the sodium ion content in the filtrate by atomic absorption spectrophotometry determined.

The filtrate contains 0.0256 g of sodium, which corresponds to a removal of 95% based on the total amount. The cobalt and manganese oxides are substituted for the equivalent amount of cobalt and manganese acetate in the p-xylene oxidation Process used. The p-xylene oxidation is carried out in a 1 liter titanium apparatus. For this purpose, the reactor is heated to 212 ⁰ C and the Reaction batch of 100 g of p-xylan, 300 g of acetic acid, 0.1688 g of cobalt acetate 4H ₂ 0.0.5352 g of manganese acetate · 4H ₂ 0.0205 g Sodium bromide and 0.1062g cobalt and manganese oxide ash filled under pressure and passed through air while stirring. The Reacto / pressure is maintained at 2.4 MPa and the temperature at 213-215 ⁰ C. With the increase of the oxygen content to 6%, the oxidation is interrupted by the release of nitrogen. The sodium ion content in the feed mixture is 0.025%. The crude terephthalic acid is filtered off, with acetic acid

washed, dried and the 4-CBA content determined. The content of 4CBA is 0.3Ma%.

The acetic acid consumption is 65g per 1000g of terephthalic acid. Vörglelchsbelsplel 1 The p-xylenoride ion is carried out in a 1 liter titanium apparatus without using the cobalt and manganese oxide ashes. For this

The reactor is heated to 212 ° C and the Reaktionsansalz of 100g p-Xy lan, 300 g of acetic acid, 0.185 g of cobalt acetate · 4Η ₂ Ο, ü,: 88g manganese acetate · 4H ₂ O <Jnd and 0.205g sodium bromide filled under pressure and stirring Air passed through.

The reactor pressure is kept at 2.4 MPa and the temperature at 213-215 ⁰ C. With the increase in the oxygen content

6%, the oxidation is interrupted by abandonment of nitrogen.

The sodium ion content in the feed mixture is 0.024%. The crude terephthalic acid is filtered off, with acetic acid

washed, dried and the 4-CBA content determined.

The content of 4CBA is 0.3 mass%. The acetic acid consumption is 65g per 1000g of terephthalic acid.

Claims (1)

Process for the preparation of terephthalic acid by liquid phase oxidation of p-xylene in acetic acid using the catalyst combination cobalt, manganese and bromide ions by means of atmospheric oxygen, characterized in that the residue in the terephthalic acid preparation consisting of aromatic acids and the catalyst ions spontaneously at 480-500 ⁰ C. burned, subjected to a thermal post-treatment at 800 ⁰ C within 1.5 h, treated the Oxidasche mif water in the ratio 1:10 to 1: 100 at 90-100 ⁰ C, the insoluble cobalt and manganese oxides separated and in the p-xylene Liquid phase oxidation process can be used directly again. Field of application of the invention The invention relates to a process for the liquid phase oxidation of p-xylene to terephthalic acid, with special consideration of the treatment of the residue.