Density of Methanolic Alkali Halide Salt Solutions by Experiment and Molecular Simulation

The density of methanolic alkali halide salt solutions is studied experimentally at 298.15 K, 308.15 K and 318.15 K at 1 bar for solutions containing all soluble combinations of alkali cations (Li+, Na+, K+, Rb+, Cs+) with halide anions (F-, Cl-, Br-, I-) at concentrations up to 0.05 mol/mol or 90% of the solubility limit. The density of the electrolyte solutions is also determined by molecular simulation in the same temperature and composition range. The used force fields of the ions were adjusted in previous works to properties of aqueous solutions and the solvent methanol to pure component properties. The force fields are of the Lennard-Jones (LJ) plus point charge type in case of the ions and of the LJ plus partial charges type in case of the solvent. For the present molecular simulations, no further adjustment of the force fields is carried out. The mixed interactions between the ions and methanol are predicted by the LorentzBerthelot combining rules. The predictions of the reduced density by molecular simulation are found to be in very good agreement with the experimental data. Furthermore, the radial distribution function of methanol around the ions, the solvation number and the residence time of methanol molecules in the first solvation shell, the self-diffusion coefficient of the ions, and the electric conductivity are systematically studied by molecular simulation and compared to experimental literature data where available.