Study on the mechanism of calcium catalyzed CO2 gasification of lignite

Abstract

The gasification of solid fuels with CO2 as gasifying agent is one way to utilize the greenhouse gas. As a catalyst, calcium (Ca) can improve the CO2 gasification rate of coal char, while its catalytic mechanism remains unclear. In this study, the chars derived from the pyrolysis of lignite samples loaded with different calcium-based catalysts were subject to CO2 gasification, enabling the comparative evaluation of catalytic performance. X-ray diffraction (XRD), Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS) analyses were employed to systematically reveal the transformation of Ca species during the CO2 gasification process. The results indicate that the catalytic effect of organically-bonded Ca2+ is more pronounced than that of CaO, which was long considered to be the unique catalytic Ca species. The electron distribution of the aromatic macromolecules in char matrix could be altered by the OCa structure bonded with it, thus promoting the cleavage of aromatic CC bond under the attack of gasifying agent (CO2). Consequently, the gasification reaction would take place at a lower temperature with enhanced reaction rates. In addition, the pyrolysis process activates the organic calcium to gain the capability of electrons transfer.