Probe into CO2-Coal Interactions with Differential Scanning Calorimetry

Abstract

In order to probe CO2-coal interactions, differential scanning calorimetry (DSC) experiment was carried out in the atmosphere of He and CO2with coals from Huozhou, Changzhi and Jincheng areas in Shanxi Province (classified as high-volatile bituminous coal, low-volatile bituminous coal and anthracite, respectively). It was found that, in a He atmosphere, all the three curves show no enthalpy and are almost reversible, indicating no adsorption occurs. However, in a CO2atmosphere, all the three curves show exothermic peaks and endothermic peaks and are irreversible, indicating, except for physical reactions, chemical reactions may also occur. It was proposed that the C atom of CO2accepted electrons from coal molecular, and formed an electron donor-acceptor complex (i.e., an EDA complex), in other words, chemical reactions occured, hence exothermic peaks occured. The interconnections of the active sites to other groups in coal molecular are weakened due to the formation of EDA complexes, so easily to be broken during heating, hence endothermic peaks occured. The irreversibility of the curves indicate structure change of coal, which may be influenced by two factors: a) during slow cooling, the ordering of side chains, which were expanded in high temperature, leads to a less associated structure; b) in heating process, the breakage of side chains enhances the associations of coal macromolecular, and leads to a more highly associated structure.