Generation of hydrocarbon gases and CO2 from a humic coal: Experimental study on the effect of water, minerals and transition metals

The yields and composition of hydrocarbon gases and CO2 generated from a humic coal were experimentally determined using the confined pyrolysis technique with different lithological conditions simulated by adding a variety of minerals (haematite, siderite, pyrrhotite, gypsum, KCl salt) and transition metals (including iron, nickel and vanadium). The experiments were conducted at 340 and 360 °C for time durations ranging from 24 to 240 h. The amount of water in the absence of minerals has negligible effect on the hydrocarbon gas yields; whereas some mineral-water environments impose a small, but measurable influence on both the yields and composition of the generated gases. The experiments with vanadium generated the highest hydrocarbon gas yield, while those with siderite yielded the least; with the difference as high as 15 mol%. The hydrocarbon gas yields increase slightly in the order from runs with Fe2O3, Ni, Fe, and V, and this trend becomes more pronounced at higher maturity. The dryness of HC gas decreases and then increases with increasing maturity, whereas the i-C4/n-C4 isomer ratios progressively decrease with increasing maturity. The effects of most studied mineral matrices on these two ratios are insignificant, except the effect of Fe and haematite on the butane isomers. The effects of mineral environments with siderite, Fe, Ni and KCl on the variations of CO2 yields are significant: CO2 yield is highest in siderite and lowest in metallic iron or nickel environments. The effect of mineral environments on the variations of CO2 yields is more pronounced than that of hydrocarbon gases.