Solution structure of propane and propene dissolved in the ionic liquid 1-butyl-3-methylimidazolium bis{(trifluoromethyl)sulfonyl}imide from neutron diffraction with H/D substitution and empirical potential structure refinement modelling

Abstract

Neutron scattering combined with H/D-isotopic substitution, fitting the experimental data using the Empirical Potential Structure Refinement (EPSR) method has been used to investigate the liquid structure of 1-butyl-3-methylimidazolium bis{(trifluoromethyl)sulfonyl}imide ($\left[C4mim\right]\left[NTf2\right]$) and solutions of propane (0.15 mol fraction) and propene (0.23 mol fraction) dissolved in the ionic liquid dissolved after pressurising at 6 bar. Both strong cation-anion and cation-cation correlations are observed in the first coordination shell with anions and cations occupying mutually exclusive positions around the imidazolium cation, consistent with previous models derived from molecular dynamics simulation. No significant changes in the neutron scattering data were observed after dissolution of either propane and propene suggesting that the primary coulombic structure of the ionic liquid is preserved. Modelling the data with EPSR reveals subtle differences in the cation-hydrocarbon correlations, with propene associated with all three imidazolium ring C-H positions whereas propane exhibits less association with the C(2)-H ring position and has a greater level of correlation with the terminal $-{\mathrm{C}\mathrm{H}}_3$ group of the cation butyl-chain.

GRAPHICAL ABSTRACT

Keywords:

• Neutron scattering
• ISIS
• ionic liquids

Data availability statement

Raw data were collected on the SANDALS instrument at The ISIS Neutron and Muon Source, Rutherford Appleton Laboratory and will be publicly available at https://doi.org/10.5286/ISIS.E.84424468 from 29 February 2020 in accordance with ISIS data management policy. Derived data supporting the findings of this study are available from the corresponding author (JDH) on request.

Disclosure statement

No potential conflict of interest was reported by the authors.

ORCID

Leila Moura  http://orcid.org/0000-0002-7938-5892

Mark Gilmore  http://orcid.org/0000-0003-3314-592X

Tristan G. A. Youngs  http://orcid.org/0000-0003-3538-5572

John D. Holbrey  http://orcid.org/0000-0002-3084-8438

Additional information

Funding

This project has received funding from the European Union's Horizon 2020 Research and Innovation Programme through a Marie Skłodowska-Curie Action Individual Fellowship under grant agreement No. 655334, the Science and Technology Facilities Research Council (STFC) through beam-time on SANDALS (ISIS experiment RB1620078) and was also supported by the Royal Academy of Engineering in the form of a Research Fellowship awarded to Dr Leila Moura and her project “Liquid engineering for gas separation”.