Coal gasification in the presence of lithium orthosilicate. Part 1: Reaction kinetics

Abstract The aim of this work was to investigate the simultaneous steam gasification of a Brazilian subbituminous coal and CO 2 capture using lithium orthosilicate (Li 4 SiO 4 ), as a promising process for enhanced hydrogen production. Tests were carried out in a magnetic suspension thermobalance at several conditions (temperature range of 700–1000 °C, steam partial pressure range of 0.1–0.4 bar and Li 4 SiO 4 :C ratios between 1:1–10:1). Experimental and theoretical kinetic studies in the absence or presence of Li 4 SiO 4 were performed to describe the carbon consumption rate and gas production. The shrinking core model suitably described the kinetics of both reactions. Most notable, an important catalytic effect was found in the reactions containing Li 4 SiO 4 , with a substantial increase in the reaction rates. The catalytic effect appeared to be associated to the formation of lithium carbonate (Li 2 CO 3 ), from the reaction between Li 4 SiO 4 and the CO 2 -formed in the gasification process. The Li 2 CO 3 melts incipiently, improving the physical contact between the lithium metal and the coal char surface, thus increasing the reaction rate through catalysis. Finally, the use of steam as gasifying agent seemed to potentiate the catalytic effect. According to the results, the Li 4 SiO 4 showed to be a promising sorbent for high temperature applications, replacing the CaO in processes as coal gasification with in-situ CO 2 capture.