(231h) A Study on the CO2 Uptake Behaviour of Supported [Hmim][NTf2] IL Sorbents

Ionic liquids (ILs) are regarded as promising alternatives to the relatively mature amine scrubbing in CO₂ capture. However, how to dramatically improve the gas−liquid mass transfer rate is still a pending problem duo to their high or superhigh viscosities. In this regard, some researchers immobilized various ILs into porous supports. After ILs’ loading, the sorbents exhibited rapid mass transfer rates. The long equilibrium time of ILs was shortened significantly. This was attributed to the decrease of film thickness, the shortened diffusion path, and the enlarged gas-liquid contact area after immobilization of ILs. It is well-known that when IL is immobilized into these solids, the property of the support, the IL itself and their interface have great impact on the mass transfer rate of CO₂. Nevertheless, effect of such factors has not been closely studied before.

In this study, the [Hmim][NTf₂] IL was loaded into titanium dioxide supports by means of simple impregnation under ambient condition. Factors (such as the pore size and surface chemistry of the support, the film thickness of IL) that affect the CO₂ capacity and mass transfer rate of IL in the as-prepared sorbents were investigated.

Results showed that both the geometric size and the surface chemistry of the support can affect the CO₂ uptake behaviour of these sorbents. The CO₂ capacity and mass transfer rate of IL were 3 times and 7 times lower when the hydrophilic surface of titanium dioxide support was modified to hydrophobic (contact angle 124.0°). It is also worth noting that the amount of CO₂ absorbed by IL immobilized in some sorbents was larger than that of the bulk IL. As the film thickness of IL loaded into titanium dioxide supports was thinner than ~50 nm, the amount of CO₂ absorbed by IL was larger than that of the bulk IL. When the thickness was thinner than ~10 nm, the CO₂ capacity was 2.5 times larger than that of the bulk IL and the mass transfer rate increased remarkably.