ESCA INVESTIGATIONS ON SCHLEENHAIN LIGNITE LITHOTYPES AND THE HYDROGENATION RESIDUES

Electron spectroscopy for chemical analysis (ESCA) was carried out on Schleenhain lignite lithotypes (yellow, brown and black) and the hydroliquefaction residues. The hydrogenation was carried out over the temperature range of 330-450-degrees-C. ESCA is a surface analysis method, but owing to special sample pretreatment the element concentrations and the binding forms of oxygen and sulphur were estimated in the same way as for a bulk method. The concentration changes of oxygen, sulphur and nitrogen in the organic matter are characteristic of hydrogenation conditions and sample properties. The investigation of oxygen and, especially, sulphur binding forms allows further insight into lithotype reactivity. For characterization of organic sulphur groups oxidation with H2O2 in an acidic medium was carried out. In this manner, bridging and non-bridging and reactive and non-reactive sulphur forms were distinguished. Some sulphur atoms are resistant to oxidation and hydrogenation; these sulphur atoms were enriched in the residues by the hydrogenation process. The enrichments are due to the original coal's properties. A phosphorus-containing catalyst retarded the formation of active iron sulphides in the hydrogenation reaction.