Alkali promoted lithium orthosilicate for CO2 capture at high temperature and low concentration

In this study, lithium orthosilicate (Li4SiO4) based sorbents containing different amounts of alkali carbonates (K2CO3, Na2CO3), binary (K2CO3/Li2CO3, Na2CO3/Li2CO3) and ternary (K2CO3/Na2CO3/Li2CO3) eutectic mixtures were prepared and characterized by X-ray diffraction and scanning electron microscopy. The CO2 adsorption properties of the sorbents were investigated by thermogravimetric analysis (TGA) at low CO2 partial pressure (0.04atm) and temperatures between 500 and 600°C. The durability of the selected sorbents was investigated by multiple CO2 adsorption/desorption cycles. The results showed that all the promoters used noticeably improved the CO2 uptake rate and sorption capacity in comparison to no-promoted Li4SiO4. At the optimum sorption temperature of 580°C, Li4SiO4 with addition of 30wt% of K2CO3 or Na2CO3 showed the best CO2 adsorption proprieties with sorption capacity of 230mg CO2/g sorbent corresponding to a Li4SiO4 conversion of about 80%. But, the addition of Na2CO3 caused sintering during multiple sorption/desorption cycles reducing significantly the sorption capacity within the defined sorption time. Whereas, the sample with addition 30wt% K2CO3 maintained its original capacity during 25 CO2 sorption/desorption cycles, showing an excellent cyclic stability.