Evaluation of the microwave-assisted organic acid separation of organic sulfur from high-sulfur coal

Abstract

To explore the feasibility of organic sulfur removal using organic acids, oxalic acid, citric acid and ascorbic acid were selected as desulfurization reagents. Combined with microwave irradiation technology, desulfurization experiments of high-sulfur coal treated with nitric acid were conducted. The orthogonal experimental results showed that the microwave synergistic citric acid desulfurization had a better desulfurization effect. The removal efficiency of organic sulfur was 55.47% when the operating conditions of the reaction were 1 mol/L, 90 °C and 1000 W for 7 min. The desulfurization efficiency of oxalic acid and ascorbic acid was low, and their organic sulfur removal efficiencies were 32.35% and 21.37%, respectively. Fourier transform infrared spectroscopy showed that sulfones and sulfoxides were partially reduced and the removal effect of thiophene was poor. X-ray photoelectron spectroscopy showed that the mercapto group in the mercaptan combined with hydrogen ions and escaped in the form of H2S. The content of aromatic thioether and aromatic thiol in the coal treated with microwave irradiation was only 0.1%. Research indicates that organic sulfur in coal can be easily reduced to sulfur-containing compounds under microwave heat and acid environment of citric acid. The outcomes provide helpful references for further studies on organic desulfurization reagents.