(418b) Sustainable Product Separation from a Silylamine-Type Switchable Electrolyte in Electrochemical Reactions

Electrolyte separation from the products in an electrochemical reaction adds challenges to the overall manufacturing process [1], requiring additional separation units to be installed or causing downstream contamination of the products. While traditional salts serve as high conductivity electrolytes in aqueous systems, their poor solubility in organic solvents restrict electrochemical reaction performance in non-aqueous systems.

The ideal properties of an alternative electrolyte for electrochemical reactions are high conductivity, high solubility for various reactants and efficient separation.  Ionic liquids (ILs) can be used as alternative electrolytes. ILs are defined as ionic salts with low melting points. The properties of ILs can be tuned by changing the cation or anion. They can have both good solubility in organic solvents and high conductivity, which leads to more promising organic-based electrochemical systems. In order to resolve both the product separation and electrolyte recovery concerns, switchable IL-like solvents can be used [2].     

These switchable systems, known as reversible ionic liquids (RevILs), can be in an ionic state during the electrochemical processing and be changed to a molecular state for product separation and/or its recovery through use of an external stimulus. Silylamines can be used as a type of RevIL. They form a RevIL-state with addition of CO₂ and turn back to a molecular liquid-state with mild heating [3, 4].

We previously found that the conductivity of neat silylamine-type RevILs were insufficient to be used as an electrolyte when the model silylamine (3-aminopropyl) triethoxysilane (TEtoxySA) was examined electrochemically [5]. However, the RevIL conductivity drastically increased up to electrochemically-appropriate values in the presence of protic organic solvents [5], though it did not increase with aprotic organic solvents near as much.

Now that the concept of a switchable electrolyte has been proposed where solutions of TEtoxySA-RevIL and protic solvents have high conductivity, high solubility in organic solvents and a simple separation procedure with mild heat, they will be investigated in electrochemical applications. In this presentation, we report the electrochemical reaction and separation procedure using these new switchable electrolytes. Also, the effect of the switchable electrolytes on the reaction will be presented, comparing the system with traditional aqueous electrolytes.

References

[1] A.J. Fry, Electrochemical processing, organic,  Kirk-Othmer Encyclopedia of Chemical Technology, John Wiley & Sons, Inc.2000, pp. 652-685.

[2] P.G. Jessop, S.M. Mercer, D.J. Heldebrant, CO₂-triggered switchable solvents, surfactants, and other materials, Energy & Environmental Science, 5 (2012) 7240-7253.

[3] A.L. Rohan, J.R. Switzer, K.M. Flack, R.J. Hart, S. Sivaswamy, E.J. Biddinger, M. Talreja, M. Verma, S. Faltermeier, P.T. Nielsen, P. Pollet, G.F. Schuette, C.A. Eckert, C.L. Liotta, The synthesis and the chemical and physical properties of non-aqueous silylamine solvents for carbon dioxide capture, ChemSusChem, 5 (2012) 2181-2187.

[4] J.R. Switzer, A.L. Ethier, E.C. Hart, K.M. Flack, A.C. Rumple, J.C. Donaldson, A.T. Bembry, O.M. Scott, E.J. Biddinger, M. Talreja, M.-G. Song, P. Pollet, C.A. Eckert, C.L. Liotta, Design, synthesis, and evaluation of nonaqueous silylamines for efficient CO₂ capture, ChemSusChem, 7 (2014) 299-307.

[5] J.D. Jimenez, S. Jung, E.J. Biddinger, Ionicity analysis of silylamine-type reversible ionic liquids as a model switchable electrolyte, Journal of The Electrochemical Society, 162 (2015) H460-H465.