Catalysis and compensation effect of K2CO3 in low-rank coal — CO2 gasification

Abstract

AbstractThe CO2 gasification of a low rank coal catalysed by K2CO3 was studied, at 700–950°C and 1 atm. A two level full factorial design revealed that the gasification reaction was sensitive to the solid residence time, reaction temperature, CO2 partial pressure and catalyst load. K2CO3 was an efficient catalyst at all temperatures studied, particularly during the second stage when the Boudouard reaction dominates. The gasification rate was increased continuously with increasing catalyst load up to a load of ∼20% w/w K2CO3 concentration, following a sigmoid curve. Above this point, limited catalytic effect was observed, possibly due to the saturation of the lignite surface by K+. A correlation was found to exist between the catalytic gasification rate and the Alkali Index, which increased with the impregnation of the inorganic K2CO3 salt. When K2CO3 load increased, the Arrhenius parameters, E and k 0, increased simultaneously exhibiting a compensation effect. The isokinetic temperature was found about 600 to 650°C corresponding to the minimum temperature required for the formation of catalytic active intermediates. At temperatures studied, the catalytic active intermediates seemed to be always present and the catalysis progresses unhindered due to the redox cycle, resulting in high rates and conversion.