Quantitative Description of Catalysis of Inherent Metallic Species in Lignite Char during CO2 Gasification

Chars from 20 lignite samples were prepared from two types of original lignites by multistage removal of inherent metallic species and subsequent pyrolysis and then were gasified with CO2. A kinetic model, which assumed the progress of noncatalytic and catalytic gasification in parallel, quantitatively described the time-dependent changes in char conversion up to 0.999 for all the chars by employing multicatalytic species having different initial activities and deactivation kinetics. A single piecewise linear function, which followed a nucleation–growth mechanism of the catalysts, showed the relationship between the total concentration of Na, K, Ca, and Fe and the initial total catalytic activity (ICA-2) for the chars. The overall rate of catalyst deactivation (ICD-2) was given by a single linear function of ICA-2 and a factor for the composition of metallic species. This function was also applicable to previously reported ICA-2/ICD-2 relationships for chars from lignite and biomass, showing fast deactivation of Fe catalyst and an important role of Mg in the promotion of catalyst deactivation.