Hybrid solvent ([emim][Ac]+water) to improve the CO2 capture efficiency in a PVDF hollow fiber contactor

Abstract

Postcombustion processes based on membrane contactors and ionic liquids have emerged in recent years as an alternative to traditional systems used to capture CO2. In this work, nondispersive absorption in a polyvinylidene fluoride (PVDF) hollow fiber membrane contactor was used as a CO2 capture system. The ionic liquid (IL) 1-ethyl-3-methylimidazolium acetate ([emim][Ac]) was chosen for the study due to its chemical reaction with CO2. Different amounts of distilled water were added to [emim][Ac] to address the issues associated with the viscosity of the ionic liquid. The presence of water may also facilitate the binding of CO2. The purpose of this combined sorbent containing water and an ionic liquid comprising a carboxylate moiety such as acetate, which provides reversible chemical interaction with CO2, was to achieve competitive efficiencies with traditional processes based on power stations and alkanolamines. The best combination of water?IL was found to be, 70% [emim][Ac]?30 vol % water. This mixture achieved a Koverall coefficient 5 times higher than that obtained with only the IL. By using 30 vol % water, a CO2 capture efficiency of 72.5% and an overall mass transfer coefficient (Koverall) of 9.34 × 10?5 m s?1 were accomplished. The values of Koverall achieved in the present work lead to the conclusion that the hybrid solvent is clearly competitive with traditional alkanolamine solvents. The simulation results of sensitivity analysis showed that only two hollow fiber membrane contactors (total length 0.6 m) or a Koverall of 1.70 × 10?4 m s?1 were required to reach an efficiency of 90%. The addition of water to the ionic liquid allows the hybrid solvent to be used in an intensified process.