CO2 capture at high temperature using fly ash-derived sodium silicates

Despite the fact that Na- silicates have been indicated as good sorbent at ambient temperature, their potential as HT CO2 sorbent has not yet been examined. In this work, CO2 sorption of fly ash derived sodium silicates was evaluated at 500, 600 and 700°C. The effect of 2-12vol% moisture, 12.5-100 vol% CO2 and CO2 sorption promoters on CO2 sorption was also evaluated. The results indicate that the carbonate:silica ratio used in the sorbents synthesis significantly affects the CO2 sorption capacity and regeneration temperature. Calcination at 800°C is preferred due to formation of metastable sodium silicate phases, which resulted in higher CO2 uptake. Among the developed sorbents, Na-FA 0.5:1 was preferred because able to maintain CO2 sorption/desorption capacity after 5 cycles (compared to 1:1 and 1.5:1). NA-FA 0.5:1 had good capacity at post-combustion conditions (12.5%CO2, 12%H2O, 700°C). The presence of 20% Li2CO3 additive enhanced the CO2 sorption of 20%. Overall, the Na-FA 0.5:1 sorbent showed a CO2 capture capacity and recyclability comparable to those of other high-temperature sorbents.