Transformation of sulfur and nitrogen during Shenmu coal pyrolysis

Transformation of sulfur and nitrogen and properties of pyrolysates (semicoke, retorting gas, coal tar) during Shenmu coal pyrolysis were investigated using XPS, TG-FTIR-MS, GC-MS and GC-PFPD. The results showed that total sulfur content in the semicoke decreased gradually and turned to sulfate sulfur and thiophenic sulfur with increasing pyrolysis temperature. In Shenmu coal, predominant nitrogen species consisted of pyrrolic and pyridinic compounds. Total nitrogen content was decreased, resulting from mutual conversion of different nitrogen compounds. The composition of retorting gas from TG-FTIR indicated that H2S began to release at 400 degrees C and reached maximum at about 600 degrees C. This trend was consistent with the release of carbonyl sulfide (500-650 degrees C) and SO2. GC-PFPD analysis revealed that detected sulfur compounds in coal tar were benzothiophene, dibenzothiophene and thiophene with the contents of 0.141%, 0.110% and 0.0004%, respectively. In coal tar, 57 kinds of nitrogen-containing compounds were identified using GC-MS, in which basic nitrogen was 0.90% and non-basic nitrogen was 0.23%.