Formation of benzene polycarboxylic acids using alkali‑oxygen oxidation of coal-tar pitch pre-treated by extraction and air-blowing

Benzene polycarboxylic acids (BPCAs) could be produced from oxidation of a coal-tar pitch (CTP) by oxygen in NaOH solution. In this work, CTP was extracted by methanol and subsequently air-blown prior to oxidation by oxygen at 260 °C for 1 h, during which the amount and condensed degree of aromatic portion obviously increased, while the oxygen-containing groups were successfully introduced into CTP. The pre-treatment of CTP not only increased the yield of BPCAs in the resulting oxidation products, but also improved the distribution of BPCAs, especially selectively increasing the content of mellitic acid and benzenepentacarboxylic acid in the BPCAs. This investigation provides a promising approach for obtaining BPCAs especially high value-added mellitic acid and benzenepentacarboxylic acid using inexpensive and underutilized CTP. [Display omitted] •CTP was extracted and air-blown to enhance the amount and condensed degree of aromatic portion.•The yield and distribution of BPCAs were greatly improved by oxidation of pre-treated CTP.•The content of mellitic acid and benzenepentacarboxylic acid in BPCAs was selectively increased.