Selective CO₂/CH₄ Separation by Fixed-Bed Technology Using Encapsulated Ionic Liquids

Abstract

The performance of encapsulated ionic liquid (ENIL) sorbents has been experimentally evaluated in CO 2 /CH 4 separation by means of gravimetric and fixed-bed measurements. Six ionic liquids (ILs) with CO 2 chemical absorption ([Emim][Acetate], [Bmim][Acetate], [P 66614 ][CNPyr], [Bmim][GLY], [Bmim][MET], and [Bmim]-[PRO]) were selected for the selective separation of CO 2 from CH 4 . ENIL materials were prepared by encapsulation of these ILs in synthesized carbon submicrocapsules, achieving a ∼70% in mass of IL. Fixed-bed experiments of CO 2 capture were carried out to evaluate the CO 2 /CH 4 separation performance of prepared ENIL materials at different CO 2 partial pressures and 303 K. Both thermodynamics and kinetics of CO 2 sorption were analyzed. The experimental CO 2 and CH 4 isotherms in ENIL materials obtained from fixed-bed experiments were successfully compared to those obtained by reliable gravimetric tests and fitted to the Langmuir− Freundlich equilibrium model. In addition, experimental CO 2 breakthrough curves were well-described by the linear driving force and Yoon and Nelson kinetic models, providing sorption rate constants. ENIL sorbents show high CO 2 uptake capacity, comparable to conventional adsorbents, but with drastically higher selectivity, in concordance with the negligible CH 4 solubility in ILs at the used operating conditions, with acetate-based ENIL materials being the best sorbents in thermodynamic terms. The obtained kinetic parameters revealed that the CO 2 chemical sorption with ENIL materials overcomes the IL mass transfer limitations. The sorption rates are faster than those obtained with ENIL using IL physical absorbents and seem to be controlled by the reaction kinetics. The [P 66614 ][CNPyrr]-based ENIL is found to be the most promising material, combining favorable kinetic and thermodynamic considerations for future development of CO 2 /CH 4 separation using fixed-bed technology.

First Measurements of the Sorption of Difluoromethane and Pentafluoroethane in Encapsulated Ionic Liquids

“…In recent years, ILs have also been investigated in combination with polymers in a variety of applications including supported ILs, mixed matrix membranes, and most recently encapsulated ILs (ENILs) for gas absorption and separation. ENILs are an emerging technology that takes advantage of the unique properties of the IL but allows it to be treated as a solid for the process design by encapsulating small droplets of IL within a polymer shell. − By creating these microsized capsules, the surface area of the IL is significantly increased so that it can improve the mass-transfer rate for using ILs in unique applications such as a packed bed. Further, as a solid, the ENIL can be used statically, which circumvents the challenges of bulk processing (i.e., high viscosity).…”

“…Four encapsulation methods are commonly employed: emulsion polymerization, Pickering emulsion, impregnation, and solvent evaporation . Thus far, ENILs have been investigated for ammonia capture, CO 2 capture, and other gas separations. − Through these studies, the ENILs have been found to have good stability, reusability, and an increase in gas capture rates and selectivity for specific gases. ,,, For these reasons, ENILs have great potential to be applied for refrigerant separation processes but have yet to be investigated for this critical application.…”

“…42−51 Through these studies, the ENILs have been found to have good stability, reusability, and an increase in gas capture rates and selectivity for specific gases. 44,48,50,51 For these reasons, ENILs have great potential to be applied for refrigerant separation processes but have yet to be investigated for this critical application. Herein, we report the production of ENILs and investigation of their use in gas uptake for with HFC-32 and HFC-125 for the first time.…”

Ionic Liquids for the Separation of Fluorocarbon Refrigerant Mixtures

“…An emerging technology that holds potential for aiding in the separation of gaseous refrigerant mixtures such as R-410A is encapsulated ionic liquids, or ENILs. − Although ILs are great solvents due to properties including low vapor pressure and thermal stability, ILs typically have high viscosities and surface tensions . This creates barriers for using ILs as a favorable separation media for filtration and extraction purposes.…”

“…The following studies also used ENILs for gas separation. 242,243,248,250 Since multiple studies done with ENILs on other gases showed increased gas capture rates and selectivity for certain gases, ENILs could be applied to the separation of refrigerant mixtures. 251 The results showed that the ENILs have very similar solubility trends compared to the neat ILs.…”