Mining Publication: Low-Temperature Evolution of Hydrocarbon Gases From Coal

• Coal
• Coal byproducts
• Methane
• Temperature

Hydrocarbon gases, primarily methane but also the c2 through c5 paraffins, the c2 and c3 olefins, and possibly the c4 and c5 olefins, are byproducts of coal formation. Although it is generally believed that coal formation occurred at temperatures below 200 deg C, most experimental work on gas formation from coal has been performed at temperatures between 200 deg and 1,000 deg C. The objective of this Bureau of Mines experiment was to determine if observable changes in the gases from coal could be produced at temperatures below 200 deg C in relatively short periods of time. The experiment involved heating coal samples from six coalbeds at constant temperatures and analyzing evolved gases. The composition of the gases at three temperatures was compared. At 35 deg C, over 99 pct of the gas is methane; at 125 deg and 150 deg C, methane constitutes approximately half of the hydrocarbon gas. Isobutane and pentane are the predominant higher hydrocarbons at temperatures between 100 deg and 150 deg C.