Pore reconstruction mechanism of wheat straw-templated Li4SiO4 pellets for CO2 capture

Abstract

The traditional Li4SiO4-based CO2 sorbent pellets prepared from mechanical granulation methods usually presented densified microstructures. Hence, wheat straw, an agricultural waste featured with huge production and low cost, was used as porosity creator to improve the microstructures and CO2 capture performance of Li4SiO4 pellets. The results indicated that wheat straw effectively enhanced the cyclic CO2 sorption capacity of the pellets. In particular, 30 wt% wheat straw-templated Li4SiO4 pellets (LA-WS30) exhibited the capacity of ~0.15 g/g that is almost twice as high as that of unmodified pellets. The enriched porosity and improved porous structures resulted from the quick release of burning gases was considered as the main reason for the performance enhancement. In addition, the alkaline (K and Na) salts in wheat straw played a positive role in CO2 sorption of Li4SiO4 pellets due to the reduced diffusion resistance. However, the pore plugging of residual wheat straw ashes after high-temperature treatment decreased the contact areas and, thus, led to the capacity reduction. To conclude, the comprehensive performance of wheat straw-templated Li4SiO4 pellets is the result of the combined effects of porosity creation, alkali doping and pore plugging by ashes.