CO2 capture over molecular basket sorbents: Effects of SiO2 supports and PEG additive

The objective of this work is to study the influences of silica supports and PEG additive on the sorption performance of molecular basket sorbent (MBS) for CO2 capture consisting of polyethylenimine and one of the following supports: SBA-15 (2-D structure), TUD-1 (3-D sponge-like structure) and fumed silica HS-5 (3-D disordered structure). Effects of the supports regarding pore structures and pore properties, the PEI loading amount as well as the sorption temperature were examined. Furthermore, polyethylene glycol (PEG) was introduced as an additive into the sorbents and its effect was investigated at different PEI loadings and sorption temperatures. The results suggest that the pore properties of MBS (after PEI loading) play a more important role in the CO2 sorption capacity, rather than those of the supports alone. MBS with 3D pore structure exhibits higher CO2 sorption capacity and amine efficiency than those with 2D-structured support. Among the sorbents studied, fumed silica (HS-5) based MBS showed the highest CO2 sorption capacity in the temperature range of 30–95 °C, probably due to its unique interstitial pores formed by the aggregation of polymer-loaded SiO2 particles. It was found that the temperature dependence is directly related to the PEI surface coverage layers. The more PEI surface coverage layers, the higher diffusion barrier for CO2 and the stronger temperature dependence of CO2 capacity. 3D MBS exceeds 2D MBS at the same PEI coverage layers due to lower diffusion barrier. Adding PEG can significantly enhance the CO2 sorption capacity and improve amine efficiency of all MBS, most likely by alleviating the diffusion barrier within PEI bulk layers through the inter-molecular interaction between PEI and PEG.