Study on organic sulfur functionalities of pyridine extracts from coals of different rank using reductive pyrolysis

Abstract

The organic sulfur functionalities in the pyridine extracts obtained from lignite (lignite A), subbituminous coal (subA), and bituminous coal (mvb) were studied by atmospheric pressure-temperature-programmed reduction (AP-TPR) method. The extraction yield was in the range of 6.7-29.3 wt % with a maximum for medium volatile bituminous coal. The H2S AP-TPR recovery for the pyridine extracts was relatively low, not higher than 45%. The coupling of the AP-TPR reactor with a different detection system from potentiometric one, i.e., with a mass spectrometer, enables the detection not only of H2S but also of other sulfur-containing compounds, which were released in the volatile products during reductive pyrolysis. Alkanethiols, thiophene, and its C-1-C-2 alkylated derivatives were detected in the volatiles. Both the char and the tar produced during an AP-TPR experiment were also studied by atmospheric pressure-temperature-programmed oxidation (AP-TPO) to monitor the sulfur compounds left and captured in the AP-TPR solid and liquid residues, respectively. The obtained extracts were characterized by high sulfur content, 1.18-3.74 wt %. The organic sulfur functionalities distribution of the pyridine extract reflects the rank of coal subjected to extraction. The AP-TPR analysis showed that for the extract from lignite thiols, alkyl and alkyl aryl sulfides dominate, whereas for the extract from subbituminous coal a comparable proportion of alkyl and alkyl aryl sulfides and thiophenes is found. Thiophenes are the major organic functionalities in the pyridine extract from bituminous coal.