The catalytic effect of calcium and potassium on CO(2) gasification of Shengli lignite: the role of carboxyl

The CO(2) gasification of Chinese Shengli lignite (SL) catalysed by K(+) and Ca(2+) was studied. The results showed that calcium could greatly decrease the gasification reaction temperature of SL, and the gasification reaction rates of acid-treated SL catalysed by calcium were significantly higher than that catalysed by potassium. Kinetic analysis showed that the activation energy of the reaction catalysed by calcium was much lower than that catalysed by potassium, which was the reason for the higher catalytic activity of calcium. Fourier transform infrared characterization showed that, compared with acid-treated SL, the addition of K(+)/Ca(2+) resulted in the significant weakening of C=O bond, and new peaks attributed to carboxylate species appeared. X-ray photoelectron spectroscopy results indicated that the numbers of C=O decreased after the metal ions were added, indicating the formation of metal–carboxylate complexes. Raman characterization showed that the I(D1)/I(G) values increased, suggesting more structural defects, which indicated that the reactivity of coal samples had a close relation with amorphous carbon structures. Ca(2+) could interact with the carboxyl structure in lignite by both ionic forces and polycarboxylic coordination, while K(+) interacted with carboxyl structure mainly via ionic forces.