Investigation into the Cleavage of Chemical Bonds Induced by CO2 and Its Mechanism during the Pressurized Pyrolysis of Coal

Abstract

A Huo linhe coal sample and its N2-devolatilized char have been pyrolyzed in a pressurized fixed-bed reactor under N2 and 50% CO2/50% N2 atmospheres, respectively. With a view to avoiding any disturbance from the devolatilization process, N2-devolatilized char was used to study the effect of CO2 on the cleavage of chemical bonds. The results show that CO2 intensifies the consumption of H in the char before its release in the form of H2. More H in the char is transferred into gaseous aliphatic hydrocarbons and condensable volatiles, leading to a decrease in the yield of H2 under 50% CO2 atmosphere compared with that under N2 at elevated pressure in the range 550–900 °C. A CO2 atmosphere is the dominant factor in the release of H from char below 700 °C, such that more H in char induced by CO2 is transferred into volatiles at 550 °C than that at 800 °C, above which temperature controls the release of H from char. Thus, CO2 induces the decomposition of more H-containing organic groups to form CH4, C2H6, C2H4,...