Superior catalytic effect of calcium oxide on the hydrogasification of char for CH4

Coal/char catalytic hydrogasification (CCHG) is regarded as a direct and efficient method to produce CH4 (synthetic natural gas, SNG) and has been studied extensively in recent decades. Although many catalysts and processes have been investigated, few were reported to be successful in commercial scale operation. Ca-compounds are studied in this paper as catalysts for hydrogasification of an ash-free char in a pressurized fixed-bed reactor. It is found that CaO has a superior catalytic effect for CH4 production but the temperature has to be 750 °C or higher and the Ca loading has to be 0.42 mmol/g or higher. The activity of CaO is much higher than that of the extensively studied catalysts such as K2CO3 and Ni(NO3)2. A long induction time is found to be necessary for CaO to be active, although it can be shortened by increases in temperature and in H2 partial pressure. CaO is found diffusing into the interior of char during hydrogasification, and the catalytic production of CH4 is attributed to the breakage of amorphous aromatic C-C bonds in char by CaO.