Sulfur K-edge XAS study of sulfur transformation behavior during pyrolysis and co-pyrolysis of biomass and coals under different atmospheres

Abstract

Three low rank coals and one biomass, YiMa (YM) and Chifeng (CF) with comparatively high FeS2, and Ximeng (XM) coals with high organic sulfur contents, and sawdust (SD), were selected to investigate sulfur transformation behavior during pyrolysis and co-pyrolysis under Ar and CO2 atmospheres. The sulfur transformation of those samples was investigated by X-ray absorption spectroscopy (XAS) combined with X-ray fluorescence (XRF). For SD, the coals and their mixtures, the subordinate peak of CaS is formed during pyrolysis under Ar atmosphere, but not under CO2 atmosphere. For XM and CF coals, sulfate peak of their chars and the chars of their mixture becomes more intense after pyrolysis under Ar atmosphere, while remain low under CO2 atmosphere. This indicates that CO2 atmosphere can impede the formation of CaS and sulfate. In addition, CO2 atmosphere and SD can promote the decomposition of FeS in CF coal before 900 °C, while SD has no significant effect on FeS in YM coal at the ratio of 3:1 (YM:SD). However, SD can also help the decomposition of FeS in YM coal at the ratio of 1:1. This suggests that SD is not enough for FeS to decompose at the ratio of 3:1. Thiophene peaks of all samples are more intense under CO2 atmosphere than under Ar atmosphere, meaning that more stable organic sulfur is formed and retained in the char after pyrolysis and co-pyrolysis under CO2 atmosphere.