Optimization of Li4SiO4 synthesis conditions by solid state method for maximum CO2 capture at high temperature

Abstract

The aim of this research work is to optimize the synthesis of Li4SiO4 by solid state method to maximize CO2 capture. This includes evaluating the main characteristics of the synthesised material which enhance CO2 uptake performance. Starting from Li2CO3 and SiO2 pure reagents, the effect of the sintering process conditions (heating rate, synthesis temperature and holding time) of the previously mixed powders has been studied. The samples were characterized by N2 physisorption, particle size distribution and X-ray diffraction. The evaluation of the CO2 uptake performance of the samples has been carried out at 600ºC in a thermobalance under a flow of almost pure CO2. Unreacted Li2CO3 is present at low synthesis temperatures, and its content in the synthesised material decreases when higher temperatures are used, so complete conversion to Li4SiO4 is reached at 900°C. At this temperature, the maximum CO2 uptake was found 20%, although it was yet far from the stoichiometric CO2 uptake value of 36.7%. The holding time at a synthesis temperature of 900ºC was then varied and a maximum CO2 uptake of 30.5% was obtained for a holding time of 2 h. Lastly, under optimised synthesis temperature and holding time conditions, the heating rate was varied. A value of 5 oC/min was found as the optimum one as the use of either lower or higher heating rates have a negative effect on CO2 uptake performance. As crystalline phases, particle size and BET surface area were very similar among all prepared samples at 900º C, crystal size was identified as the main physical property that could explain the CO2 uptake performance of the samples, i.e., the lower crystal size, the higher CO2 uptake.