Hot CO₂ Recovery Using Lithium Silicate Suspended in Molten Salt

Abstract

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°C and 850°C, respectively. Therefore, continuous recovery of CO₂ is feasible simply by thermal swing. The fundamental chemical reaction is expressed as follows: Li₄SiO₄+CO₂ ⇄ 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.