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 CO2 capture using lithium orthosilicate (Li4SiO4), 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 0.1–0.4bar and Li4SiO4:C ratios between 1:1–10:1). Experimental and theoretical kinetic studies in the absence or presence of Li4SiO4 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 Li4SiO4, with a substantial increase in the reaction rates. The catalytic effect appeared to be associated to the formation of lithium carbonate (Li2CO3), from the reaction between Li4SiO4 and the CO2-formed in the gasification process. The Li2CO3 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 Li4SiO4 showed to be a promising sorbent for high temperature applications, replacing the CaO in processes as coal gasification with in-situ CO2 capture.