Structure-function, recyclability and calorimetry studies of CO2 adsorption on some amine modified Type I & Type II sorbents

CO2 adsorption was studied on different amines immobilized on silica, polymethyl methacrylate (PMMA) and mesoporous SBA-15 substrates. Hyperbranched polyethyleneimine (PEI) was impregnated onto silica and PMMA to generate Type I sorbents and their CO2 adsorption capacities were measured and compared to the respective unmodified supports. Amine-functionalized Type II sorbents were also synthesized by loading different amounts of a monoamine ((3-Aminopropyl) triethoxysilane), a diamine (N-[3-(Trimethoxysilyl) propyl] ethylenediamine) and a triamine (N1-(3-Trimethoxysilylpropyl) diethylenetriamine) onto mesoporous SBA-15 using grafting techniques. Nitrogen physisorption studies, surface density measurements and low angle XRD plots indicated a progressive filling of SBA-15 pores with increase in respective amine loadings. CO2 breakthrough studies conducted on PEI impregnated silica and PMMA at 40 °C and 60 °C showed that the temperature strongly influenced the CO2 adsorption capacities. The amount of total CO2 captured on amine-grafted SBA-15 sorbents increased with rise in amine density and amine type in the order Triamine > Diamine > Monoamine. All recyclability studies on the amine-modified sorbents yielded consistent CO2 capture capacities over a period of 3-5 adsorption-regeneration cycles. Simultaneous determination of adsorption capacities and corresponding associated heats at important stages of a complete CO2 breakthrough run (under both dry & moist conditions) provided critical real-time insights into the adsorption process and can be used as an effective tool for screening potential sorbents.