Chemical Engineering Journal 147 (2009) 51–57 Contents lists available at ScienceDirect Chemical Engineering Journal journal homepage: www.elsevier.com/locate/cej Gas permeabilities, solubilities, diffusivities, and diffusivity correlations for ammonium-based room temperature ionic liquids with comparison to imidazolium and phosphonium RTIL data Ricardo Condemarin, Paul Scovazzo ∗ Department of Chemical Engineering, University of Mississippi, 138 Anderson Hall, University, MS 38677, United States article info Keywords: Room temperature ionic liquids Gas diffusion Gas solubility Gas permeability Ammonium ionic liquids abstract Like our previous work with imidazolium- and phosphonium-based ionic liquids, we report diffusiv- ities over a range of viscosities (71–532cP) and develop a predictive diffusivity correlation. Reported are the permeability, solubility, and diffusivity data for nine gases in nine ammonium RTILs liquids at 30 ◦ C, as determined with a lag-time technique. The gas solubilities and diffusivities of the ammonium RTILs are of the same magnitude as those for the phosphonium and imidazolium RTILs. The ammonium RTILs used, in this study, included cations with both N-alkyl groups and branched alkyl groups. We also report on ammonium-based RTILs derived from quaternary ammonium surfactants. These surfactants- derived ammonium-based RTILs offer a relatively inexpensive alternative to imidazolium-based RTILs. We compare and contrast the thermodynamic (solubility) and transport (diffusivities) phenomena in the ammonium-based RTILs with both the imidazolium and the phosphonium RTILs in the context of being working fluids in a chemical process. From this comparison came certain “universal” trends for diffusivity in RTILs. Specifically, diffusivity scales roughly with the inverse of the square-root of vis- cosity and inversely with solute molar volume to the power of 1–1.3. This means that diffusivity, in RTILs, is less dependent on viscosity, and more dependent on solute size than predicted by the conven- tional Stokes–Einstein model. The gases tested were carbon dioxide, nitrogen, oxygen, methane, ethylene, propylene, 1-butene, butane, and 1,3-butadiene. © 2008 Elsevier B.V. All rights reserved. 1. Introduction This paper is the continuation of transport phenomena studies in room temperature ionic liquids (RTILs). In our previous work we measured transport in imidazolium-based [1] and phosphonium- based RTILs [2]. We reported thermodynamic and transport properties such as Henry’s law constant and gas diffusivities. The gas permeabilities of imidazolium-based and phosphonium-based RTILs were similar with the exception that the imidazolium CO 2 - permeabilities are significantly higher than the phosphonium ones. The gas solubilities and diffusivities of the phosphonium-based and the imidazolium-based RTILs were of the same order of magnitude. Strong correlations were found for gas diffusion in imidazolium- based (r 2 = 0.97) and phosphonium-based (r 2 = 0.92) ionic liquids. Both, imidazolium-based and phosphonium-based RTILs had sim- ilar diffusivity correlations with respect to viscosity and gas molar volumes. ∗ Corresponding author. Tel.: +1 662 915 5354; fax: +1 662 915 7023. E-mail address: scovazzo@olemiss.edu (P. Scovazzo). The objective of our present work is to further our research into using RTILs as separating agents and support media for chemical reactions. We will report diffusivities, permeabilities, solubilities, and Henry’s law constant for ammonium-based ionic liquids over a range of viscosities (71–532cP). The molecular weight range for the tested ammonium-based ionic liquids was 396.4–648.8. We will develop a predictive diffusivity correlation for ammonium- based ionic liquids. There is a need for this correlation because the assumptions for classical models developed by Stokes–Einstein or Wilke–Chang do not fit the physical characteristics of RTILs [1]. There were two motivations for the present work. The first one is to make available transport properties for an economical alternative to imidazolium-based RTILs. Ammonium-based ionic liquids cost 20% of the cost of the imidazolium-based RTILs ($2/g versus $10/g for RTILs consisting of the Tf 2 N anion, based on 0.5–1 kg laboratory- scale purchases or synthesis by our laboratory; however, economy of scale should apply for commercial quantities). The second moti- vation is the possible electrochemical applications for these RTILs, because of their physical properties like conductivity and non- volatility [3]. We will compare and contrast the thermodynamic and transport phenomena properties of the ammonium-based ionic liq- uids with the two previously studied RTIL classes. 1385-8947/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.cej.2008.11.015