Kinetic analysis for cyclic CO2 capture using lithium orthosilicate sorbents derived from different silicon precursors

Abstract

A series of Li₄SiO₄ was synthesized using LiNO₃ and six different silicon precursors. The precipitated-silica-derived Li₄SiO₄ presented the highest CO₂ capacity in a 10 h sorption test, and ZSM-5-derived Li₄SiO₄ demonstrated the most rapid CO₂ sorption. The CO₂ sorption kinetics predominantly followed the nucleation mode and could be accurately described by the Avrami-Erofeev model. The Avrami-Erofeev model provided an in-depth analysis of correlation between sorption performance and material properties. Both the nucleation speed and nucleation dimensionality affected the overall sorption kinetics. The kinetics and pore-size distribution suggest that the sorption kinetics was dependent on the quantity of ∼4 nm-pores which favors nucleation dimensionality. For the cyclic tests, the precipitated-silica-derived sample presented the poorest performance with the capacity decreasing from 31.33 wt% at the 1^st cycle to only 11.52 wt% at the 30^th cycle. However, the sample made from fumed silica displayed an opposite trend with the capacity increasing from 19.90 wt% at the 1^st cycle to 34.23 wt% at the 30^th cycle. The radically distinct behaviour of samples during cycles was on account of the alternation of sorption kinetics. The decrease in ∼4 nm-pores after cycles was responsible for the decrease of nucleation dimensionality for the precipitated-silica-derived sample. The rearrangement during cycles could enrich the pores of ∼4 nm for the fumed silica-derived sample, which improved the nucleation growth, thus enhancing the kinetics with cycles.