Examination of the Potential of Ionic Liquids for Gas Separations

TLDR

Ionic liquids are attractive for green separations due to their negligible vapor pressure. The study investigates ionic liquids for gas separations, specifically CO₂ removal from coal‑plant stack gas, by measuring N₂ and CO₂ permeance in supported ionic liquid membranes. The authors performed a preliminary economic analysis of supported ionic liquid membranes using existing CO₂ solubility data and measured transport characteristics. Results show a CO₂/N₂ selectivity of 127 and suggest that supported ionic liquid membranes could be economically competitive with amine scrubbing, though further technical and economic evaluation is needed.

Abstract

:Ionic liquids have received increasing interest in recent years for "green" synthesis and separations because they have essentially no vapor pressure. We have begun an investigation of the potential of ionic liquids for gas separations, including the removal of carbon dioxide from stack gas generated in coal-fired power plants. In this paper, we report results from measurements of the permeance of nitrogen and carbon dioxide in supported ionic liquid membranes. Preliminary results for a porous alumina membrane saturated with l-butyl-3-methyl imidazolium bis[trinuoromethylsulfonyl] amide yielded a CO2 : N2 selectivity of 127. Using previously reported measurements of CO2 solubility in ionic liquids (1) and the measured membrane transport characteristics, a preliminary economic analysis of a separation process based on supported ionic liquid membranes has been performed. A comparison of cost estimates for this membrane-based separation to cost estimates reported for carbon dioxide removal using a conventional amine scrubbing operation shows that, with continued technology development, an ionic liquid membrane process may potentially be economically competitive with amine scrubbing. A preliminary cost estimate for an ionic liquid scrubber indicates that an ionic liquid absorption process shows less favorable economics than a supported ionic liquid membrane or an amine scrubber. However, results indicate that a more comprehensive technical and economic assessment is warranted.