Li4SiO4 pellets templated by rice husk for cyclic CO2 capture: Insight into the modification mechanism

Li4SiO4 stands out among various solid sorbents for CO2 capture. The commonly used mechanical granulation process for Li4SiO4 sorbents causes the destruction of the microstructures. Therefore, with the characteristics of huge production and low cost, an agricultural waste (rice husk) was employed as a pore former to improve the structures of Li4SiO4 pellets and, thus, enhance the cyclic CO2 sorption performance. The rice husk templating greatly enhanced the CO2 sorption capacity of Li4SiO4 pellets. Especially, 20 wt% rice husk-templated Li4SiO4 exhibited the capacity of 0.21 g/g, which was nearly twice that of the unmodified sorbent. The quick release of the combustion gases from burning rice husk could create porosity for the sorbents. In addition, the alkaline compositions in rice husk promoted the CO2 sorption due to the decreased CO2 diffusion resistance by the formation of molten phases. Moreover, the ashes of rice husk after high-temperature combustion were found to block the pores of the sorbents, leading to the capacity reduction. The comprehensive function of rice husk templating for Li4SiO4 pellets was the tradeoff between the positive effects of pore creation and alkaline doping and the negative effects of pore blockage by the ashes.