Experimental and modeling investigation on CO2 sorption kinetics over K2CO3-modified silica aerogels

Abstract

K2CO3-modified silica aerogels (K2CO3/SG) were synthesized by the two-step sol-gel and wet impregnation method using K2CO3 and tetraethoxysilane (TEOS) as starting materials and ethanol as solvent. CO2 sorption behaviors of the sorbent were tested under ultra-dilute flue gas conditions of 20–60°C, 1%CO2, 2%H2O and balanced N2 with gas hourly space velocity (GHSV) of 4000h−1 using a modified fixed-bed reactor. Experimental CO2 uptakes of the sorbent under different temperatures were correlated to several kinetics models to study the kinetics performances. The effects of temperature, K2CO3 loading, GHSV, H2O:CO2 molar ratio and H2O pretreatment time on CO2 sorption capacity and kinetics performances of the sorbent were further demonstrated. It is found that the two-step sol-gel and wet impregnation method could benefit the sorbent improved physical properties, superior surface characteristics and enhanced CO2 sorption performances. Amongst various kinetics equations, the modified Avrami fractional kinetics model could well describe the CO2 sorption process over K2CO3/SG. CO2 sorption capacity decreases with the increase of temperature. With the increasing K2CO3 loading, GHSV, H2O:CO2 molar ratio and H2O pretreatment time, CO2 sorption capacity increases first and then decreases. CO2 sorption kinetics increases with the increasing temperature and H2O pretreatment time, while it decreases with the increasing K2CO3 loading. CO2 sorption kinetics keeps rather stable and then increases significantly with the increasing GHSV and H2O:CO2 molar ratio.