Catalysis of lignite char gasification by exchangeable calcium and magnesium

Abstract

A Montana lignite was pretreated in either HCI—HF or ammonium acetate. The former treatment replaced cations associated with carboxyl groups by hydrogen, as well as removing essentially all mineral matter. The latter treatment replaced cations by ammonium ions but left the mineral matter intact. The pretreated lignites were then loaded with varying amounts of Ca and Mg, separately or jointly, by ion exchange. Reactivities of chars produced from these exchanged lignites, as well as the raw and pretreated lignites, were determined in air, CO2 and steam. Gasification of exchanged lignites was strongly catalysed by Ca; its activity was not affected by the presence of Mg on the char. At a comparable Ca loading, gasification rates of the 1273 K raw lignite char in the various atmospheres was higher than that of the acid treated 1273 K char but lower than that of the ammonium acetate treated 1273 K char. The former finding is attributed to chlorine retention in the lignite and char; the latter, to enhanced sulphur release during lignite pyrolysis.