PRETREATMENT OF HIGH-MOISTURE LIGNITES FOR SUBSEQUENT HYDROGENATION

Pretreatment of structurally different lignites with a high moisture content (approximately 50 wt%) at low temperatures (75-100-degrees-C) resulted in higher subsequent conversion to oil under low-severity hydrogenation conditions than did pretreatment at > 100-degrees-C. The increase in oil yield after the thermal pretreatment at low temperatures was strongly related to the original moisture content of the coal. Addition of n-hexane during pretreatment at 100-degrees-C led to only a small increase in oil yield in comparison with samples dried in air. Structural changes after pretreatment were characterized by solid-state C-13 n.m.r. spectrometry. No significant changes in lignite structure were detected in the samples pretreated at low temperatures. With increasing pretreatment temperature, drastic changes in structure were observed and the hydrogenation of these samples resulted in lower conversion and oil yield.