Lithium Silicate Pellets for CO2 Capture at High Temperature

Abstract

In this study, lithium orthosilicate-based pellets were developed and characterized as potential regenarable high-temperature CO₂ sorbents. A mechanical method was used for pelletization of the powdered materials, namely K₂CO₃-doped lithium silicate (Li₄SiO₄) with cellulose fibres. Different amounts of cellulose fibres (20, 30 and 40 wt%) were added to powered doped-sorbent in order to identify the optimal amount to ensure an adequate porosity to the produced pellets. The CO₂ sorption properties of the produced pellets were investigated at high temperature (500 - 600 °C) by using a thermal gravimetric analyzer (TGA) at low CO₂ partial pressure with repeated calcination/carbonation cycles.
Compared to the pure K₂CO₃-doped lithium silicate pellets, the sorbents prepared using cellulose fibres showed greater CO₂ capture capabilities, which were ascribed to the higher porosity developed as a result of thermal degradation of cellulose. At 580 °C and a CO₂ partial pressure of 0.04 atm, the uptake of CO₂ in pellets prepared with 20 % of cellulose fibres reached about 20 wt% within 120 min corresponding to a Li₄SiO₄-conversion of 57 %. During multiple sorption/desorption cycles, a decay of the sorption capacity of the pellets was observed due to a partial sintering of the materials. This suggested that an appropriate binder should be added in order to improve the cyclic stability and the strength of the produced pellets.