The roles of the low molecular weight compounds in the low-temperature pyrolysis of low-rank coal

Abstract

To investigate the roles of the low molecular weight compounds (LMWCs) in the low-temperature pyrolysis of low-rank coal, Hongliulin coal (HL) was firstly thermal dissolved in n-hexane (HEX) at 260–340 °C, and the pyrolysis characteristics and product distributions of HL and its residues of thermal dissolution (RTDs) were compared. Results show that the LMWCs have a significant effect on the low-temperature pyrolysis characteristics of HL. The pyrolysis liquid (PL260-340) and gaseous product yields of RTDs, which decrease with rising TD temperature (TDT), are dramatically lower than those of HL. The total amounts of HEX soluble portion (SP) and PL at the TDT of 260 and 280 °C are essentially equal to PLHL, implying that almost all LMWCs, which with relatively low boiling point, can be directly evaporated and transferred into tar during the pyrolysis of HL. The GC/MS analysis indicates that the LMWCs contain some hydrogen-donor components (such as tetralin and indane) which can act as hydrogen donor for the stabilization of radical fragments during HL pyrolysis process.