Single component, reversible ionic liquids for energy applications Vittoria Blasucci, Ryan Hart, Veronica Llopis Mestre, Dominique Julia Hahne, Melissa Burlager, Hillary Huttenhower, Beng Joo Reginald Thio, Pamela Pollet, Charles L. Liotta, Charles A. Eckert * Georgia Institute of Technology, Chemical & Biomolecular Eng., 311 Ferst Drive NW, 30332-0100 Atlanta, GA, United States article info Article history: Received 1 June 2009 Received in revised form 6 October 2009 Accepted 13 November 2009 Available online 1 December 2009 Keywords: Reversible ionic liquids Carbon capture Tar sands/oil shale Scale-up abstract Single component, reversible ionic liquids have excellent potential as novel solvents for a variety of energy applications. Our energy industry is faced with many new challenges including increased energy consumption, depleting oil reserves, and increased environmental awareness. We report the use of reversible ionic liquids to solve two energy challenges: extraction of hydrocarbons from contaminated crude oil and carbon capture from power plant flue gas streams. Our reversible solvents are derived from silylated amine molecular liquids which react with carbon dioxide reversibly to form ionic liquids. Here we compare the properties of various silylated amine precursors and their corresponding ionic liquids. We show how the property changes are advantageous in the two aforementioned energy applications. In the case of hydrocarbon purification, we take advantage of the polarity switch between precursor and ionic liquid to enable separations. In carbon capture, our solvents act as dual physical and chemical capture agents for carbon dioxide. Finally, we show the potential economics of scale-up for both processes. Ó 2009 Elsevier Ltd. All rights reserved. 1. Introduction When activated, reversible solvents undergo vast solvent prop- erty transformations which can be exploited in a wide range of industrial applications. The ability of these solvents to combine multiple processing steps (e.g. coupling reactions and separations) and be recycled for reuse yields reductions in process waste, oper- ating costs, and environmental impact. There have been several re- cent publications on the development and application of reversible solvents [1–5]. Towards this goal of developing sustainable tech- nologies, our group has created reversible, single component, ionic liquids derived from silylated amines (see Scheme 1). Not only can these molecules switch between neutral and ionic forms, but they can also be tuned by varying their molecular architecture. This arti- cle focuses on two applications of these reversible ionic liquids in the energy industry: (1) extraction of hydrocarbons from crude oil and (2) carbon capture from post-combustion power plant flue gas streams. Depletion of conventional oil reserves, increasing focus on en- ergy independence, and rising oil prices may lead to the increased use of tar sands and oil shale as alternate fossil fuel resources. The United States has the world’s largest oil shale deposits located in the Green River Formation which contains an estimated 800 billion barrels of recoverable oil [6]. Currently, the isolation of hydrocar- bons from tar sands and oil shale is difficult mainly due to the physical properties of these materials, such as high viscosity and density [7,8]. Steam has been used to extract oil from these uncon- ventional sources, but the process is energy-intensive and pro- duces large quantities of contaminated waste water. Although oil-miscible organic solvents can cut the viscosity of these oils, the process is cumbersome and wasteful. The common method for organic solvent recovery, distillation, is energy-intensive and low-end carbon fractions from the oil will be distilled along with the solvent. Our reversible solvents solve this problem by utilizing a built-in, energy-efficient and environmentally benign solvent separation technique. First, mixing the molecular liquid with oil al- lows for simple filtration of the oil’s contaminants. Second, a phase split is enacted between the oil and solvent phase upon the forma- tion of the ionic liquid. And finally, the ionic liquid is reversed to its precursor and recycled. Although conventional ionic liquids can separate CO 2 from mixed gas streams [9–13], our reversible solvents are superior by enabling a dual-capture mechanism. Specifically, they function not only as physical absorbents but also as chemical adsorbents for CO 2 capture. Two moles of solvent react with one mole of CO 2 to form the ionic liquid, which then acts as a solvent to absorb physically additional CO 2 . The benefits of using reversible ionic liq- uids include the high selectivity of CO 2 over N 2 in dilute post-com- bustion flue gas streams, high capacity loadings of CO 2 , and a drastic reduction in solvent quantity compared to conventional amine scrubbing processes. We have found that these solvents pro- duce a clean CO 2 stream upon reversal. Also, we show that process variables, such as viscosity and capacity, can be tuned by structural 0016-2361/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.fuel.2009.11.015 * Corresponding author. Tel.: +1 404 894 7070; fax: +1 404 894 9085. E-mail address: cae@gatech.edu (C.A. Eckert). Fuel 89 (2010) 1315–1319 Contents lists available at ScienceDirect Fuel journal homepage: www.elsevier.com/locate/fuel