Peering into the mechanisms of granulation and CO2 capture on alginate-assisted Li2CaSiO4-decorated Li4SiO4 sorbents

In recent years, high-temperature CO2 capture technology based on Li4SiO4-based sorbents has received widespread attention. However, powder elutriation and low sorption performance of Li4SiO4 hinder its practical application. In this work, these two obstacles have been solved in one step via a novel alginate-assisted route, via which the granulation and performance enhancement of Li4SiO4 sorbents were simultaneously achieved. The obtained Li4SiO4 pellets exhibited good mechanical strength (i.e., anti-attrition ability), demonstrating the suitability for the realistic application in circulating fluidized bed systems. In addition, Li2CaSiO4 phase was formed in the synthesis process and well dispersed in the sorbent. Meanwhile, the produced Li4SiO4 pellets (especially the pellets derived from lithium acetate) were featured with wrinkled surfaces. As a result, Li2CaSiO4-decorated Li4SiO4 sorbents displayed satisfactory CO2 sorption capacity reaching 0.24 g CO2/g sorbent. To clarify the mechanism of Li2CaSiO4 decorating, Li2CaSiO4-Li4SiO4-CO2 sorption model based on the double-shell reaction mechanism was proposed. Following this model, Li2CaSiO4 functioned as a ‘catalyst’ layer that greatly promoting the diffusion of Li+ and O2–, thus improving the cyclic CO2 sorption performance of Li4SiO4 sorbent. In conclusion, two main problems (elutriation and poor sorption performance) of Li4SiO4-based CO2 sorbent have been well mitigated in one step via alginate-assisted technique, which surely helps pave the way for the practical application of Li4SiO4 sorbents for CO2 capture.