Natural content of gases: Carbon monoxide, carbon dioxide, hydrogen and unsaturated hydrocarbons of ethylene, propylene and acetylene in selected bituminous coal seams

Abstract

Chromatographic analysis of gas desorbed from coal reveals the presence of carbon monoxide, carbon dioxide, hydrogen, ethylene, propylene and acetylene, i.e. gaseous components liberated into the mine atmosphere with the increasing temperature of self-heating coal. Elevated levels of carbon monoxide, dioxide and ethylene were registered as well. Investigations showed that these gases are contained in the coal structure and their liberation to the mine air can be triggered by other factors apart from coal self-heating, for example coal fragmentation or disturbing of the virgin coalbeds by mining operations. The amounts of thus desorbed gases can alter their actual concentrations in the mine air, which serve as indicators of the self-heating propensity of coal. No straightforward relationship was established between the concentrations of individual gaseous components in the mixed-gas desorbed from coals sample and the rank and other physico-chemical properties of coals.Sorption and desorption tests by the volumetric method demonstrated that the volume of sorbed carbon monoxide and dioxide, hydrogen, ethylene, propylene and acetylene is closely related to the coal rank and its porous structure. Low-rank coals with well-developed pore systems tend to absorb/adsorb greater amounts of gases than low-rank coals with a less developed pore structure.Tests established the intensity of gas desorption from coals, showing that nearly 80–90% of carbon monoxide, dioxide and hydrogen accumulated in coals would be released. In the case of adsorbed ethylene, propylene and acetylene that proportion is the lowest (50%–70%).Recalling the Ideal Adsorbed Solution (IAS) theory, simulations were performed to predict the mixed-gas adsorption isotherms for binary gas mixtures containing non-saturated hydrocarbons-gas components that are indicators of the self-heating propensity of coal. It appears that acetylene adsorption in the systems C2H2C2H4 and C2H2C3H6 is a favoured process whilst preferential adsorption in the system C3H6C2H4 is that of propylene.