Comparison of hydrocarbon gases (C1–C5) production from Carboniferous Donets (Ukraine) and Cretaceous Sabinas (Mexico) coals

Abstract

The main purpose of this contribution is to compare the ability of Carboniferous coals from the Donets Basin of the Ukraine and Cretaceous coal from the Sabinas Basin of the Mexico to generate hydrocarbon gases (C1–C5). Two bituminous coals from the Donets Basin (2c10YD and 1l1Dim; 0.55 and 0.65%Rr respectively) and one bituminous coal from the Sabinas Basin (Olmos, 0.92%Rr) were studied using heating experiments in a confined-pyrolysis system. The highest rank reached during the heating experiments corresponds to the anthracite stage (2.78 and 2.57%Rr) for the 2c10YD and 1l1Dim coals and (2.65%Rr) for the Olmos coal. The composition of the generated (C1–C5) gases was evaluated using a thermodesorption-multidimensional gas chromatography. The results show that the Carboniferous Donets coals produced more wet gas and methane during pyrolysis than the Cretaceous Olmos coal. This is probably due to their higher liptinite (6–20%) and collodetrinite content and to the loss of a major part of the petroleum potential of the Olmos coal during natural coalification. C2–C5 compounds are mainly derived from the cracking of liquid hydrocarbons. Ethane is the most stable compound and formed from the cracking of higher hydrocarbon component. Large amounts of methane (up to 81 mg/g coal for the Donets coals and 50 mg/g coal for the Sabinas coal) were formed at high temperatures by cracking of previously formed heavier hydrocarbons and by dealkylation of the coal matrix. A linear relationship was observed between methane generation and the maturity level of both coal types.