Sustainable Degradation of Commercial Coal Pitch by Aqueous Sodium Hypochlorite under Mild Conditions

Abstract

To develop a sustainable approach for coal pitch utilization, oxidation of commercial coal pitch in aqueous NaOCl solution was investigated. Effects of feeding methods, reaction temperature and time on coal pitch oxidation conversion rate were investigated. The maximum oxidation conversion rate was 17.4% at the optimized conditions of 50°C and 6 h, with multi-stage feeding method using 75–25–25 mL NaOCl solution. A mathematical regression model is developed to predict the oxidation conversion rate of coal pitch, which can accurately capture the reaction behavior observed in the experimental data (R² = 0.976). The oxidized pitch residue was characterized by FTIR, and the extracted products were analyzed by GC-MS. The results suggest that NaOCl oxidation is an effective treatment under mild conditions, obtaining value-added organic chemicals. Hydroxyls and carbonyls were introduced into the structure of the oxidized coal-pitch; 33 organic-compound products were detected, including value-added chemicals, i.e. naphthalene, phenanthrene, and anthraquinone. Thus, the aqueous NaOCl treatment exhibits a good potential to improve the economy of commercial coal pitch application.