Analysis of chemical reaction between Li4SiO4 and CO2 by thermogravimetry under various CO2 partial pressures—Clarification of CO2 partial pressure and temperature region of CO2 absorption or desorption

Abstract

Chemical reaction between CO2 and Li4SiO4 was investigated using thermogravimetry under various P(CO2). Under P(CO2) of 1.0bar, weight increase originating from CO2 absorption reaction was observed from ∼500°C and abrupt weight reduction due to CO2 desorption was detected at ∼700°C. With decreasing P(CO2), the latter temperature decreased. Since fair agreement was observed between the latter temperatures and thermodynamically calculated equilibrium temperatures of Li4SiO4+CO2↔Li2CO3+Li2SiO3, the latter temperatures could be regarded as approximate equilibrium. Dependence of the calculated equilibrium temperatures and approximate equilibrium temperatures on P(CO2) was represented with Ellingham diagram, showing P(CO2) and temperature region of CO2 absorption or desorption. Approximate equilibrium temperature under P(CO2) of 1.0bar agreed with the calculation, whereas deviation was observed under low P(CO2), resulted in larger apparent ΔS° and ΔH° than the calculated ones. Using specimen with smaller particle size, the deviation reduced due to enhancement of CO2 desorption kinetics.