Hot CO2 Recovery Using Lithium Silicate Suspended in Molten Salt

The purpose of this study is to examine the possibility of establishing innovative chemical-wise CO2 recovery system with a lithium silicate slurry bubble column, which could collect hot CO2 from massive emission sources. This is realized by using the composite of lithium and silica, called lithium orthosilicate, Li4SiO4, which can reversibly absorb and strip CO2 gas at high temperatures, i.e. ca. 700 degrees C and 850 degrees C, respectively. Therefore, continuous recovery of CO2 is feasible simply by thermal swing. The fundamental chemical reaction is expressed as follows: Li4SiO4 + CO2 reversible arrow Li2SiO3 + Li2CO3. The reaction under high temperature conditions is possible by preparing molten salt as a reaction field. The lithium silicate is suspended in molten salt, and 20% CO2 containing gas is distributed to achieve absorption, both physically and chemically. To confirm the feasibility of the proposed system, two experiments were conducted to demonstrate CO2 capture ability: 1) physical absorption to Li-K-CO3 molten salt, and 2) chemical absorption to a Li4SiO4 suspended slurry. CO2 solubility and its level of mass transfer to Li-K-CO3 are investigated based on the results. Moreover, the performance of the CO2 recovery is investigated from the effects of gas feed rate, quantity of absorbent, and suspension concentration. Overall, the proposed system enables CO2 recovery under hot conditions, resulting in high efficiency recovery. This study establishes a lithium silicate suspended slurry system as an effective instrument for recovering CO2.