Effectiveness of both ZnCl 2- and SnCl 2-containing molten salt catalysts for hydrogenation of Big Ben coal in the absence of a solvent

Abstract

Hydrogenation of Big Ben coal (Australian bituminous coal) with 9.8 MPa H 2 for 3h at 400 °C has been carried out using a batch autoclave system in the presence of a molten salt catalyst such as ZnCl 2, SnCl 2, ZnCl 2-KCl-NaCl (3:1:1 mol ratio) and SnCl 2-KCl (3:2). The hexane-soluble (HS) yield decreases in the order: SnCl 2-KCl, SnCl 2, ZnCl 2-KCl-NaCl, ZnCl 2. The use of SnCl 2-containing melt is characterized by higher yields of both HS and benzene-soluble (BS) fractions and the suppression of gas yield compared with the use of ZnCl 2. The average aromatic unit and the molecular weight of HS increase in the order: ZnCl 2, ZnCl 2-KCl-NaCl, SnCl 2, SnCl 2-KCl. Chromatographic separation of HS fractions indicates that the saturate content is lowest and polar-material content is highest with the SnCl 2-KCl melt: this fact coupled with the structural parameters suggests that HS material with SnCl 2-KCl melt has, on average, a reasonably-high-molecular-weight skeleton which has more alkyl chains and heteroatoms. Micrographs of resulting benzene-insoluble (Bl) materials clearly indicated that the Bl particles were larger when ZnCl 2 was used than when the other melts were used, the Bl particles in these cases being of similar size. Lewis acidity and the viscosity of the molten salt appear to be related, in part, to the size of the Bl particles.