Preparation of pyromellitic anhydride and terephthalic acid from anthracite

Abstract

Shanxi anthracite was subjected to oxygen-oxidation at 250°C in all aqueous solution of potassium hydroxide to produce solid benzene polycarboxylic acid (BPCA), and then the BPCA were selectively decarboxylated in the mixed medium of concentrated H₂SO₄ and KHSO₄ to produce crude pyromellitic acid (PA). Pure PA was obtained by solvent recrystallization method, and the best solvent was 2-pentanone. Pure pyromellitic anhydride (PMDA) was gotton by heating pure pyromellitic acid in vacuum chamber at 260°C for 3 h. The remaining BPCA which through 2-pentanone recrystallization was isomerizated with consistent temperature at 420°C for 2 h. Appropriation pH of BPCA, initial pressure of carbon dioxide and cadmium carbonate catalyst were provided to produce crude terephthalic acid (TPA). Pure TPA was obtained by washing and drying the crude TPA precipitation.