CO2 capture and CO2/CH4 separation by silicas with controlled porosity and functionality

Microporous, mesoporous and hydrophobic silica materials with high specific surface area are obtained by an easy and cheap sol-gel synthesis. The effect of pore size and of water content on gas adsorption and separation are investigated. We also identified the relative amounts of different types of water in the porous silica, around 25% and 75% for bound and free water. The kinetics of rehydration is extremely slow, 60% recovery after 4 days implying that the material can be used as is over several hours. Adsorption isotherms of pure gaseous CO2 and CH4, and of their mixtures at different pressures, show that among the materials synthesised, the microporous hydrophilic silica exhibits the best performance in terms of CO2 adsorption capacity (2.8 mmol.g(-1)) and a separation factor over 10 at low CO2 content and low pressure. Both properties are highly sensitive to the presence of residual water and to terminal chemical groups. This work highlights the possibility to develop competitive and cheap silica materials that could be scaled up to industrial uses.