Keywords: calcium oxide, carbon capture, carbon sequestration, lithium zirconate, solid regenerable sorbents
Dry regenerable sorbents for the separation and capture of CO2 from large point sources
The combustion of fossil fuels generates large quantities of carbon dioxide (CO2), a greenhouse gas most likely to influence global warming and climate change. Large stationary sources that include coal-based electric generating stations are plausible targets for the removal of CO2. Chemical absorption of CO2 is viewed as one option that could be applicable for its separation from both fuel gas and flue gas streams. Processes based on solid regenerable sorbents that efficiently absorb CO2 and release it in concentrated form have the potential to be cost-effective relative to solvent-based practices. This communication summarises a preliminary investigation exploring the reaction of CO2 with a number of calcium-based sorbents using a thermogravimetric (TG) analyser. Upon reaction at high temperature with pure CO2, these materials are converted into metal carbonates. Thermal regeneration of the sorbents was accomplished upon heating spent materials to higher temperature in a nitrogen stream. TG studies show the absorption reaction for Ca-based materials was initially rapid and then entered into a slower kinetic regime. Multi-cycle testing conducted within the TG analyser indicated sorbents could be regenerated and reused. Theoretical conversions ranging from 50–75% were observed for the calcium/zirconia sorbents in comparison to 15–20% for the calcium/lanthanum-doped alumina sorbent. Improved conversion was attributed to the pore size differential between mesoporous zirconia and microporous lanthanum-alumina. TG studies performed at 500°C with lithium zirconate show that the rate of CO2 absorption was continuous with time on stream. Under nitrogen, rapid regeneration of the lithium carbonate product occurred at temperatures greater than 700°C.