Selective CO<sub>2</sub>/CH<sub>4</sub> Separation by Fixed-Bed Technology Using Encapsulated Ionic Liquids
Jesús Lemus, C. Paramio, Daniel Hospital-Benito, Cristian Moya, Rubén Santiago, José Palomar
Abstract
The performance of encapsulated ionic liquid (ENIL) sorbents has been \nexperimentally evaluated in CO2/CH4 separation by means of gravimetric and fixed-bed \nmeasurements. Six ionic liquids (ILs) with CO2 chemical absorption ([Emim][Acetate], \n[Bmim][Acetate], [P66614][CNPyr], [Bmim][GLY], [Bmim][MET], and [Bmim]- \n[PRO]) were selected for the selective separation of CO2 from CH4. ENIL materials \nwere prepared by encapsulation of these ILs in synthesized carbon submicrocapsules, \nachieving a ∼70% in mass of IL. Fixed-bed experiments of CO2 capture were carried out \nto evaluate the CO2/CH4 separation performance of prepared ENIL materials at different CO2 partial pressures and 303 K. Both \nthermodynamics and kinetics of CO2 sorption were analyzed. The experimental CO2 and CH4 isotherms in ENIL materials obtained \nfrom fixed-bed experiments were successfully compared to those obtained by reliable gravimetric tests and fitted to the Langmuir− \nFreundlich equilibrium model. In addition, experimental CO2 breakthrough curves were well-described by the linear driving force \nand Yoon and Nelson kinetic models, providing sorption rate constants. ENIL sorbents show high CO2 uptake capacity, comparable \nto conventional adsorbents, but with drastically higher selectivity, in concordance with the negligible CH4 solubility in ILs at the \nused operating conditions, with acetate-based ENIL materials being the best sorbents in thermodynamic terms. The obtained kinetic \nparameters revealed that the CO2 chemical sorption with ENIL materials overcomes the IL mass transfer limitations. The sorption \nrates are faster than those obtained with ENIL using IL physical absorbents and seem to be controlled by the reaction kinetics. The \n[P66614][CNPyrr]-based ENIL is found to be the most promising material, combining favorable kinetic and thermodynamic \nconsiderations for future development of CO2/CH4 separation using fixed-bed technology