Yields of longer chain n-alkanes, consistently higher than those resulting from hydrous pyrolysis, are obtained when coals are hydrogenated using a sulphided nickel-molybdenum catalyst rather than a copper chromite catalyst. The lower yields of n-alkanes are attributed to: the incomplete conversion of carboxylic acids together with thermal chain splitting reactions under hydrous pyrolysis conditions; and deterioration in the activity of the copper chromite catalyst used in hydrogenation. A sequential hydrous pyrolysis/hydrogenation procedure failed to demonstrate that the physical release of n-alkanes from coal is significantly favoured by hydrous pyrolysis. Therefore, hydrogenation in the presence of a sulphided catalyst is superior to hydrous pyrolysis in the determination of n-alkyl content of coals.
- n-alkyl yield