Polymeric ionic liquid modified silica for CO2 adsorption and diffusivity

Two types of polymeric ionic liquids (PILs) modified porous silica for CO2 sorption were synthesized by the polymerization of dialkylphosphate di-butyl phosphate [VYIM][Bu2PO4] and 1-allyl-3-methylimidazolium tetrafluoroborate [AMIM][BF4] with alkoxyl-modified silica. The PILs-modified silica (SiO2-P[VYIM][Bu2PO4] and SiO2-P[AMIM][BF4]) were evaluated by CO2 adsorption isotherms at 273 K for investigating the porous structures. The adsorption and desorption behaviors of CO2 (at 298, 313, and 333 K) and N-2 (at 313 K) up to 0.2 MPa were also investigated using a gravimetric method. In comparison with bare silica, the grafting of PILs on the support surface leads to a loss of microporosity, resulting in a slight decrease in CO2 sorption capacity. The difference of CO2 sorption capacity between SiO2-P[VYIM][Bu2PO4] and SiO2-P[AMIM][BF4] is little, especially under 0.1 MPa. CO2/N-2 selectivity is however notably improved, and especially [AMIM][BF4] modified silica shows the best performance. The homogeneous surface diffusion model (HSDM) was used to estimate the diffusivities and good agreement between experimental values and fitting curves was obtained. The diffusion coefficients of CO2 in the PILs-modified silica are level with that of bare silica at level of 10(-7)-10(-8) m(2)/s, about two to three orders of magnitude faster than that of reported [BMIM][BF4]. POLYM. COMPOS., 38:759-766, 2017. (c) 2015 Society of Plastics Engineers