Molecular Simulation and Experimental Characterization of Ionic-Liquid-Based Cosolvent Extraction Solvents

Understanding liquid–liquid equilibria in binary mixtures of hydrocarbons with a thermally robust perarylphosphonium-based ionic liquid

Binary mixtures of hydrocarbons and a thermally robust ionic liquid (IL) incorporating a perarylphosphonium-based cation are investigated experimentally and computationally. Experimentally, it is seen that excess toluene added to the IL forms two distinct liquid phases, an “ion-rich” phase of fixed composition and a phase that is nearly pure toluene. Conversely, n-heptane is observed to be essentially immiscible in the neat IL. Molecular dynamics simulations capture both of these behaviours. Furthermore, the simulated composition of the toluene-rich IL phase is within 10% of the experimentally determined composition. Additional simulations are performed on the binary mixtures of the IL and ten other small hydrocarbons having mixed aromatic/aliphatic character. It is found that hydrocarbons with a predominant aliphatic character are largely immiscible with the IL, while those with a predominant aromatic character readily mix with the IL. A detailed analysis of the structure and energetic changes that occur on mixing reveals the nature of the ion-rich phase. The simulations show a bicontinuous phase with hydrocarbon uptake akin to absorption and swelling by a porous absorbent. Aromatic hydrocarbons are driven into the neat IL via dispersion forces with the IL cations and, to a lesser extent, the IL anions. The ion–ion network expands to accommodate the hydrocarbons, yet maintains a core connective structure. At a certain loading, this network becomes stretched to its limit. The energetic penalty associated with breaking the core connective network outweighs the gain from new hydrocarbon–IL interactions, leaving additional hydrocarbons in the neat phase. The spatially alternating charge of the expanded IL network is shown to interact favourably with the stacked aromatic subphase, something not possible for aliphatic hydrocarbons.

Binary mixtures of hydrocarbons and a thermally robust ionic liquid (IL) incorporating a perarylphosphonium-based cation are investigated experimentally and computationally.

A combination of FTIR and DFT to study the microscopic structure and hydrogen-bonding interaction properties of the [BMIM][BF4] and water

The structure and hydrogen-bond interaction property of water and a model ionic liquid (IL): 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIM][BF₄]) were studied using the combination of Fourier transform infrared spectroscopy (FTIR) and density functional theory (DFT) calculations. The O‒D stretching vibration region of the deuterated water was an area of special focus. Excess infrared spectroscopy with enhanced resolution was applied to analyse the original infrared spectra of v(O‒D). It is found that: (1) [BMIM][BF₄] forms stable hydrogen-bonds with water in the mixture. (2) The hydrogen-bonds are weak strength, closed shell and electrostatic dominant interactions. The preferred interaction site of [BMIM]⁺ cation is the hydrogen atom at the C2. (3) Cage hexamer water, cyclic tetramer water, cyclic trimer water, ion cluster-water complex, ion pair-water, and anion-water complexes are identified in the mixture. When the mole fraction of D₂O (x(D₂O)) is larger than 0.9, ion cluster and ion pair were broken apart into individual cations and anions. The cage hexamer water, cyclic tetramer water, and cyclic trimer water disappear at x(D₂O) < 0.8, 0.5, and 0.3, respectively. HDO formed by H/D isotope exchange was detected when x(D₂O) is less than 0.3.