Solid-supported CO2 Sorbents Based on Amine-free Phosphonium Carboxylate Ionic Liquids

Identifier:  TFM:722

Handle: https://hdl.handle.net/20.500.11797/TFM722

Authors:  Mohammad, Yousefe

Abstract:
Carbon capture is key to minimize the negative effects of CO2 emissions. There are large numbers of technologies for CO2 capture. Currently, amine-based CO2 sorbents are mostly used. Despite the reasonable performance of amine sorbents, they have serious disadvantages such as high energy cost for regeneration and thermal degradability. Thus, new sorbent materials and technologies for CO2 capture are still intensely sought. Ionic liquids with negligible vapor pressure can be designed to capture CO2. In this framework, carboxylate ionic liquids, when hydrated, enable a chemical CO2 sorption with moderate enthalpy, which leads to lower energy cost for regeneration. On the other hand, phosphonium-based ionic liquids exhibit superior thermal stability compared to ammonium counterparts. In this work, tetrabutylphosphonium acetate hydrate ([P4 4 4 4][AcO]·H2O) was synthesized by simple neutralization of the hydroxide with acetic acid in water characterized by NMR, and its thermal decomposition and glass transition temperatures were recorded. After impregnation on porous silica, a free-flowing solid-supported material ([P4 4 4 4][AcO]·H2O/SiO2) was produced and tested for CO2 sorption-desorption experiments from model flue gas (15% CO2) in a fixed-bed setup. Performance was compared to polyethyleneimine on silica (PEI/SiO2) as a competitor amine sorbent material used commercially. Both sorbents showed fast CO2 sorption, although the capacity of the amine system was higher. Desorption at low temperature (60 °C) was complete and rapid for CO2-saturated [P4 4 4 4][AcO]·H2O/SiO2, while for PEI-20/SiO2 desorption rate was much slower, and desorption of CO2 was not complete under same condition. Furthermore, thermogravimetric analysis indicated that [P4 4 4 4][AcO]·H2O/SiO2 has thermal stability up to 200°C.