Changes in the sulfur forms of subbituminous coals during oxidation with hydrogen peroxide and peracetic acid

We have investigated chemical desulfurization of subbituminous coals to prepare ultra-low sulfur coal for the converter process in the steel industry. Herein, we report the oxidative desulfurization of thiophene contained in two subbituminous coals using two peroxides, hydrogen peroxide and peracetic acid. Sulfur K-edge X-ray absorption near edge structure analysis was carried out to follow the change in sulfur form during oxidation. Sulfur form distribution was determined quantitatively by deconvolution of the pyrite, thiophene, sulfoxide, sulfone, and sulfate peaks in the Sulfur K-edge XANES spectra of the raw and oxidized samples using the least-squares method. In the presence of hydrogen peroxide, oxidation was promoted only at 60 °C. Furthermore, an oxidation treatment was carried out at 20 °C using peracetic acid generated by mixing hydrogen peroxide and acetic anhydride, which selectively reacted with the sulfur atoms. Treatment with peracetic acid promoted the oxidation of thiophene and improved the desulfurization extent with low carbon loss. Sulfone-type sulfur formed by the oxidation of thiophene could be completely volatilized by heat treatment at 400 °C under a N2 gas stream. By combining pre-oxidation with peracetic acid treatment and pyrolysis, 74 % of total sulfur and 72 % of thiophene could be removed while recovering approximately 90 % of total carbon as char.