Abstract
CaCO3, Ca(CH3COO)2 and Ca(C6H5COO)2 were selected as representatives of calcium species formed by calcium ions with organic structures and added to an acid-leached Shengli lignite (SL+) to study the catalytic mechanism of calcium on the steam gasification. The main gasification temperature range of the calcium-added samples was surprisingly consistent with the specific thermal decomposition temperature of the added calcium compounds. XPS and FTIR revealed that the added calcium interacted strongly with the oxygen-containing functional groups in lignite to form calcium-carboxylate, which were further converted to CaCO3 analogous structure during the thermal process (confirmed by XRD). The significant catalytic effect of calcium on the steam gasification all occurred simultaneously with the decomposition of CaCO3 analogous. The formed calcium species from the decomposition of in-situ formed CaCO3 could interact with the adjacent carbonaceous organic structures in lignite under the presence of gaseous water molecules to form calcium-centered complexes. The calcium-catalyzed effects on the steam gasification were depended on the decomposition processes of in-situ formed CaCO3 species. Finally, the possible mechanism for the catalytic effect of calcium on the steam gasification of Shengli lignite was proposed.
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