Microporous Ceramic Tubule Based and Dendrimer-Facilitated Immobilized Ionic Liquid Membrane for CO2 Separation

Abstract

A solvent evaporation method has been used to prepare a supported ionic liquid (IL) membrane in a microporous ceramic tubule-based module; its separation performance for CO2–N2 and CO2–He mixtures has been reported here over a pressure range of 50−250 psig (344.7−1724 kPag) and temperatures up to 100 °C. Solutions of IL-ethanol having different IL contents were used to prepare 1-butyl-3-methylimidazolium dicyanamide ([bmim][DCA]) membranes having different thicknesses. Membranes prepared from 25 wt % IL in ethanol solution showed the best gas permeation and separation performance. Ionic liquid membranes prepared from 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide ([emim][Tf2N]) under the same conditions displayed a slightly higher gas permeance, but its separation capability was somewhat lower. Tests at higher temperatures using the [bmim][DCA] membrane generated obviously higher gas permeances, but the ideal separation factors of CO2 over N2 and He dropped sharply. These tests were carried out with a dry feed gas. Adding polyamidoamine (PAMAM) dendrimer generation 0 to IL did not show any improvement when the feed gas was dry. After the feed gas was humidified, both the permeance and the separation factor of CO2 over N2 and He were improved greatly. This is due to lower viscosity caused by dissolved water in the IL membrane and additional reactions between CO2 and tertiary amine units of dendrimer in the presence of water. A set of gas mixture-based test results confirmed the facilitating effects of dendrimer to enhance CO2 permeation with humidified feed gas.