Lithium silicate pellets for CO2 capture at high temperature

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.