lithium orthosilicate, post combustion capture, CO2, solid absorbent
Capture of carbon dioxide from combustion processes presents a unique and challenging technical problem arising from low CO2 partial pressures, high flow rates, and the presence of water vapor and reactive contaminants such as SO2. A lithium orthosilicate (Li4SiO4) based absorbent from Toshiba Corporation was identified as a promising candidate for post combustion capture. The absorbent reacts chemically with CO2 at elevated temperatures and very large absorbent capacities can be achieved at typical flue gas CO2 pressures. Unlike many solid sorbents, the presence of water vapor greatly enhanced CO2 absorption rates without affecting capacity. Exposure to flue gas containing SO2 resulted in an irreversible reaction with the absorbent and a decrease in CO2 capacity. In this respect, the lithium orthosilicate absorbent is no different than other sorbents that react chemically with CO2. The absorbent used in a fixed bed process will likely require a thermal swing process with absorption at 550C and regeneration at 650C. Even for the high capacity of the Li4SiO4-based absorbent, an alternative to conventional fixed bed technology will be required for practical post combustion capture and some possible alternatives will be described. A brief overview of other CO2 capture efforts at Air Products will be presented.