Influence of the Concentration of CO2 and SO2 on the Absorption of CO2 by a Lithium Orthosilicate-Based Absorbent

A novel, high temperature solid absorbent based on lithium orthosilicate (Li4SiO4) has shown promise for postcombustion CO2 capture. Previous studies utilizing a clean, synthetic flue gas have shown that the absorbent has a high CO2 capacity, >25 wt %, along with high absorption rates, lower heat of absorption and lower regeneration temperature than other solids such as calcium oxide. The current effort was aimed at evaluating the Li4SiO4 based absorbent in the presence of contaminants found in typical flue gas, specifically SO2, by cyclic exposure to gas mixtures containing CO2, H2O (up to 25 vol. %), and SO2 (up to 0.95 vol. 96). In the absence of SO2, a stable CO2 capacity of similar to 25 wt % over 25 cycles at 550 degrees C was achieved. The presence of SO2, even at concentrations as low as 0.002 vol. %, resulted in an irreversible reaction with the absorbent and a decrease in CO2 capacity. Analysis of SO2-exposed samples revealed that the absorbent reacted chemically and irreversibly with SO2 at 550 degrees C forming Li2SO4. Thus, industrial application would require desulfurization of flue gas prior to contacting the absorbent. Reactivity with SO2 is not unique to the lithium orthosilicate material, so similar steps would be required for other absorbents that chemically react with SO2.