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.