Less drastic conditions could be used for coal hydrogenation if a solvent could be
found that would hydrogenate the coal in a liquid–solid phase process. In the hydrogendonor
process, finely powered coal reacts for 1–2 hours with tetralin at about 200°C and
65 bar. The tetralin acts both as a solvent and a hydrogen donor, giving up four hydrogen
atoms to form naphthalene.