Study on the product distribution and thermal behavior of coal, extract and extracted residue over FeCl3

Abstract

Catalytic depolymerization of lignite for improving tar yield has been proved feasible in our previous work. While the correlation between coal structure and catalyst was not clear owing to the heterogeneous nature and complicated compositions of coal, along with the multiple reactions during coal pyrolysis. In this study, two coals were extracted by tetrahydrofuran to afford residues and extracts. The thermal behavior and product distribution of coals, residues and extracts with/without FeCl3 were studied by Gray-King assay reactor and thermogravimetry coupled with mass spectrometry. The results showed that the catalyst not only affects the cleavage of chain aliphatic hydrocarbons at lower temperature, but also facilitates the cracking of oxygen-containing functional groups, leading to the variation of liquid products generation and gaseous products evolution. With the FeCl3 catalyst addition, tar yields of all samples (coals and residues) increased, meanwhile, the conversion of residues enlarged in comparison with that of corresponding raw coals. The composition of tars obtained from coals and residues with catalyst addition varied greatly, especially for phenols and two-ring aromatics. With the catalyst addition, the conversion of extracts increased, and the temperature at which the residual yield kept nearly unchanged was decreased. The extracts act as hydrogen donors to stabilize the radical fragments in the catalytic depolymerization of lignite.