Derek Farnham Williams, Terence Geoffrey Martin: Extraction of oil shales and tar sands. Coal, Stevens Davis Miller & Mosher, August 22, 1978: US04108760 (72 worldwide citation)

This invention relates to the extraction of oil shales and tar sands by using a solvent under supercritical conditions at a temperature within 200.degree. C. or its critical temperature in order to effect extraction of kerogen from the sand or shale.

Terence Geoffrey Martin: Hydrogenation of coal. Coal, Stevens Davis Miller & Mosher, July 19, 1977: US04036731 (25 worldwide citation)

The present invention relates to a process for the hydrogenative extraction of coal which comprises extracting finely divided coal at an elevated temperature between 340.degree. and 480.degree. C. with a gaseous solvent and a hydrogen donor, which solvent at the extraction temperature is above its c ...