Study On Synergistic Effect And Mechanism Of A Bimetallic Catalyst For Steam Gasification Of Coal Char

To investigate the synergistic effect of the Ca-K bimetallic catalyst on the steam gasification and its mechanism, several ash-free carbon samples including a graphite sample, three acid-washed coals of different ranks and a pine wood sample were used for gasification. The contents of study include three following parts.First, three coals of different ranks (JY anthracite coal, DLT bituminous coal, YN lignite coal) were subjected to the demineralization by staged leaching under mild conditions. The ash content of JY anthracite coal, DLT bituminous coal, YN lignite coal was removed from19.68%,15.65%and16.67%for the original samples, respectively, to0.20%,0.19%and0.48%.Second, the gasification experiment was carried out for graphite, three mineral-free coal chars and pine wood char using the mixtures of K2CO3with three calcium species (Ca(OH)2, Ca(Ac)2, CaCO3) as catalysts. It was found that three bimetallic catalysts behaved with a higher catalytic activity than K.2CO3alone, indicating that there was a synergistic effect between each calcium species and K2CO3on the char gasification, which was not associated with mineral matter present in coal. Ca(OH)2and Ca(Ac)2demonstrated a stronger effect than CaCO3. The average rate of gasification increased with different materials in an order: graphite<<JY char<DLT char<YN char<Pine wood char. However, the magnitude of increase became narrower from pine wood to graphite when Ca(OH)2/K2CO3was used.Third, to gain insights into the mechanism underlying the synergistic effect between calcium species and K2CO3, TG-DSC XRD, SEM and XANES were applied for examining the interactions between calcium additive, K2CO3and chars. It was found that a well-crystalline bimetallic carbonate K2Ca(CO3)2was derived even when the char was mixed with Ca(OH)2and K2CO3. The bimetallic catalyst had a melting temperature (525℃) much lower than that of K2CO3(890℃) and thus allowed it to more intensely interact with char forming more active intermediates. XANES analysis revealed that Ca(OH)2was apt to the formation of some organically bound calcium on the char surface, which led to more active carbon sites and thus effectively accelerating the char gasification.