Production of isophthalic acid

Unlike o-xylene and p-xylene, the application of m-xylene is limited to the production of isophthalic acid, nitrated xylenes and m-xylylenediamine. Production of 3,5-dimethylphenol, which was carried out in earlier times by alkali fusion, has now been replaced by gas-phase aromatization of isophorone (see Chapter 53.4.3.2). 

The oxidation process for m-xylene is based on the liquid-phase oxidation for the production of terephthalic acid. Air oxidation in acetic acid is catalysed by cobalt and manganese salts and bromine and conducted at temperatures ranging from 170 to 230 °C and pressures of 20 to 25 bar. Following the reaction, isophthalic acid is separated by crystallization and the mother liquor is recycled. 

Isophthalic add is produced by only a small number of companies in the USA (Amoco% Japan Mitsubishi Gas Chemical) and Italy Sisas). Its main use is in the production of unsaturated polyester resins. It yields polyesters of greater strength and higher resistance to corrosion than those derived from phthalic add. 

Other uses are in the production of alkyd resins, although isophthalic acid has no noticeable advantage over PA. However, during the 1960 s, there was a shortage of PA in the USA for a time, and isophthalic add was used as a substitute, despite its higher cost. 

Isophthaloyl chloride is an industrially important derivative of isophthalic add. It is produced by chlorination (SOCI2/CI2) of m-xylene via the intermediate l,3-bis-(trichloromethyl)-benzene and its reaction with isophthalic add. Iso-phthaloylchloride, along with m-phenylenediamine, serves as a monomer component for the production of the high-strength and heat-resistant aramid fiber Nomex Du Pont), 

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The dominant current commercial process for the production of isophthalic acid (lA) and terephthalic acid (TA) is the catalytic oxidation of m-xylene and p-xylene (PX). Xylenes are oxidized to lA or TA, respectively, in the so called Amoco process at 110-205 °C and 15-30 bar and in the presence of 95% acetic acid [128]. Furthermore, Co and Mn need to be added as catalysts and NIttBr and tetrabromoethane as co-catalysts. It is important to realize that some routes towards bio-based lA and TA may involve the production of the xylenes as an intermediate, whereas others might not. Furthermore, production routes may rely on technologies generating a slate of products comprising mostly fuel components next to chemicals like PX, whereas other technologies rely on the dedicated production of PX. 

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