Hydroliquefaction of coal catalysed by tin compounds

Although tin compounds have been shown to be active in hydroliquefaction of coal, the active tin species during the liquefaction has not yet been elucidated. Some recent work suggests that metallic tin promotes the liquefaction reaction. In this study, the hydroliquefaction of French Freyming coal was investigated in a batch reactor between 350 ° and 430 °C, using non-porous SnO2 aerosol with a low particle size (15 nm) as a catalyst precursor, or presulphided tin oxide or commercial metallic tin. Chemical analysis of the liquid phase was achieved by solvent extraction in n-hexane, toluene or THF. The hydrogen consumptions (from the gas phase or from the donor solvent), were also estimated. The main experimental techniques used for catalyst characterizations were applied to the residue of hydroliquefaction: 119Sn and 57Fe Mössbauer spectrometry, X-ray diffraction and electron microscopy associated with X-ray spectrometry. Tin sulphide was generally observed as the main product with small amounts of oxidized tin species. The size of SnS particles implies sintering, possibly due to mobile tin species such as metal, although this latter could not be detected. No evidence of coking of the surface of SnS was found. In some cases the intermetallic compound FeSn2 was shown, as formed by reaction of tin with pyritic iron of the mineral matter. By comparing the results of coal conversion with those of tin characterization, the active species was thought to be SnS, on which a competitive adsorption of H2S should proceed. This results in a shift of the mode of hydrogen transfer to the coal (from H-donor solvent as opposed to hydrogen itself), as the partial pressure of H2S in H2 increased.