Evidence of free but trapped hydrocarbons in coals

Pyrolysis experiments in a confined system (in sealed gold tubes under pressure) were performed on a lignite. The temperature range was 250–550 °C, under isothermal conditions (24 h). Solid and chloroform-extractable products of heat treatments were examined by various analytical techniques (e.g. thermovaporization, infrared spectrometry, pyrochromatography, liquid chromatography). A reference coal series was submitted to parallel analytical investigations. All samples came from the Mahakam Delta, Indonesia. Comparison between natural and artificial series leads to the conclusion that natural coals are able to retain appreciable quantities of free but trapped hydrocarbons, whereas artificially derived solid residues are not.