Optimization of sol–gel combustion synthesis of calcium looping CO2 sorbents, Part Ⅱ: Effects of thermal activation conditions

Abstract

This work is the extension of part Ⅰ. The last procedure in the technical route of sol–gel combustion synthesis for CaO sorbents preparation, i.e. the thermal activation process was studied. The effects of the relevant preparation parameters including temperature, duration, and heating rate on the cyclic CO2 sorption performance, micromorphology, pore size distribution, and physical parameters of the prepared pure CaO sorbents were investigated. Results were obtained that high temperature (>950 ℃), long duration (>1 h), and low heating rate (<2 ℃/min) in the thermal activation process accelerated the formation of a stable structure in CaO sorbents. Accordingly, the sorbent showed low initial conversion, an opposite increasing trend in the first several cycles, and high cyclic stability. The optimal thermal activation condition was 850 ℃ for 5 min without heating rate. Furthermore, by integrating the optimization results of the whole technical route, the optimal CaO sorbent was prepared, which showed excellent performance. With the cyclic condition of 10 minutes of carbonation at 650 ℃ under 15% volume CO2 and 10 minutes of calcination at 850 ℃ under 100% volume N2, its carbonation conversion varied from 98.2% to 52.1% through 50 cycles. An average enhancement of 21.8% in 50 cycles was obtained compared to the sorbent before optimization and the average enhancement was 168.3% compared to CaCO3. Moreover, the pH value of the precursor solution was the most influential factor among the preparation variables.