Experimental study on CO_2-coal interactions

Abstract：In order to probe CO2-coal interactions,differential scanning calorimetry（DSC） experiment was carried out in the atmosphere of He,N2 and CO2 with coals from Huozhou and Jincheng area in Shanxi Province.The results show that,in a He atmosphere,the curves are straightforward,the curves in the N2 atmosphere are smooth and upward compared with curves in the He atmosphere,however,in a CO2 atmosphere,all the three curves show exothermic peaks and endothermic peaks are irreversible.It is proposed that,as an inert gas,He can＇t be adsorbed on coal surface,hence no enthalpy released.For N2,physical adsorption occurs,charactered with lower enthalpy releasing.The larger enthalpy variation in a CO2 atmosphere indicates that,except for physical reactions,chemical reactions may also occur.Based on the analysis of coal interactions,CO2 interactions and molecular-scale interactions of CO2 with substances other than coal,the CO2-coal interactions were explained as follows：the C atom of CO2 accepted 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 complex,so to be easily broken during heating,hence endothermic peaks occured.The irreversibility of the curves indicates that coal structure is changed.