Fabrice Mutelet

Understanding the impact of the central atom on the ionic liquid behavior: Phosphonium vs ammonium cations

The influence of the cations central atom in the behavior of pairs of ammonium- and phosphonium-based ionic liquids was investigated through the measurement of densities, viscosities, melting temperatures, activity coefficients at infinite dilution, refractive indices, and toxicity against Vibrio fischeri. All the properties investigated are affected by the cations central atom nature, with ammonium-based ionic liquids presenting higher densities, viscosities, melting temperatures, and enthalpies. Activity coefficients at infinite dilution show the ammonium-based ionic liquids to present slightly higher infinite dilution activity coefficients for non-polar solvents, becoming slightly lower for polar solvents, suggesting that the ammonium-based ionic liquids present somewhat higher polarities. In good agreement these compounds present lower toxicities than the phosphonium congeners. To explain this behavior quantum chemical gas phase DFT calculations were performed on isolated ion pairs at the BP-TZVP level of theory. Electronic density results were used to derive electrostatic potentials of the identified minimum conformers. Electrostatic potential-derived CHelpG and Natural Population Analysis charges show the P atom of the tetraalkylphosphonium-based ionic liquids cation to be more positively charged than the N atom in the tetraalkylammonium-based analogous IL cation, and a noticeable charge delocalization occurring in the tetraalkylammonium cation, when compared with the respective phosphonium congener. It is argued that this charge delocalization is responsible for the enhanced polarity observed on the ammonium based ionic liquids explaining the changes in the thermophysical properties observed.

Probing the Interactions between Ionic Liquids and Water: Experimental and Quantum Chemical Approach

For an adequate choice or design of ionic liquids, the knowledge of their interaction with other solutes and solvents is an essential feature for predicting the reactivity and selectivity of systems involving these compounds. In this work, the activity coefficient of water in several imidazolium-based ionic liquids with the common cation 1-butyl-3-methylimidazolium was measured at 298.2 K. To contribute to a deeper insight into the interaction between ionic liquids and water, COSMO-RS was used to predict the activity coefficient of water in the studied ionic liquids along with the excess enthalpies. The results showed good agreement between experimental and predicted activity coefficient of water in ionic liquids and that the interaction of water and ionic liquids was strongly influenced by the hydrogen bonding of the anion with water. Accordingly, the intensity of interaction of the anions with water can be ranked as the following: [CF3SO3](-) < [SCN](-) < [TFA](-) < Br(-) < [TOS](-) < Cl(-) < [CH3SO3](-) [DMP](-) < [Ac](-). In addition, fluorination and aromatization of anions are shown to reduce their interaction with water. The effect of temperature on the activity coefficient of water at infinite dilution was measured by inverse gas chromatography and predicted by COSMO-RS. Further analysis based on COSMO-RS provided information on the nature of hydrogen bonding between water and anion as well as the possibility of anion-water complex formation.

Pretreatment of miscanthus using 1,3-dimethyl-imidazolium methyl phosphonate (DMIMMPh) ionic liquid for glucose recovery and ethanol production

An environmentally friendly method for the extraction of cellulose from miscanthus using 1,3-dimethyl-imidazolium methyl phosphonate (DMIMMPh) ionic liquid is described. The parameters affecting the extraction process are temperature and time. Extraction results were evaluated using a Box–Behnken Design. The pretreatment of miscanthus with ionic liquids resulted in the regeneration of amorphous, porous cellulose almost free of lignin, which is suitable for enzymatic hydrolysis and fermentation processes. The regenerated cellulose can be hydrolyzed efficiently into glucose using cellulase enzyme with glucose hydrolysis efficiency exceeding 93%. The hydrolysate is converted into ethanol with fermentation using Saccharomyces cerevisaie yeast with an ethanol conversion rate reaching up to 85%. A successful ethanol production was obtained with an overall ethanol yield reaching up to 148 g ethanol kg−1 miscanthus. This indicates the high performance of DMIMMPh ionic liquid in converting biomass feedstocks into ethanol.

Physico-Chemical Properties and Phase Behavior of the Ionic Liquid-β-Cyclodextrin Complexes

The solubility of β-cyclodextrin (β-CD) in ionic liquids (ILs) and the activity coefficients at infinite dilution ( γ13∞) of more than 20 solutes (alkanes, aromatic hydrocarbons, alcohols) were measured in four chosen ionic liquids, their mixtures with β-CD, and in the β-CD at high temperatures from 338 to 398 K using the inverse gas chromatography. The intermolecular interactions, inclusion complexes and the possible increasing of the solubility of β-CD in water using the IL are presented. The solubility of β-CD in ten chosen hydrophobic ILs at the temperature T = 423 K was detected. The solid-liquid phase diagrams (SLE) of {IL (1) + β-CD (2)} binary systems at the high mole fraction of the IL were measured for three systems (1-ethyl-3-methylimidazolium chloride, [EMIM][Cl], 1-ethyl-3-methylimidazolium bromide, [EMIM][Br]; and for 1-butyl-3-methylimidazolium chloride, [BMIM][Cl]). The eutectic points were determined at the high IL concentration for all binary systems. The intermolecular interaction and the possibility of inclusion complexes of the IL and/or solvents with β-CD were discussed. The infrared spectroscopy, IR was used for the description of the intermolecular interactions in the (β-CD + IL) systems. It was shown via the activity coefficients at infinite dilution results that the inclusion complexes are dependent on the temperature. The addition of β-CD to the IL does not improve the selectivity of the separation of the aliphatics from aromatics.

Computational study on the molecular conformations of phenolic compounds

The study of the conformation of eight phenolic compounds (i.e. phenol, guaiacol, syringol, pyrocatechol, o-, m-, p-cresol and vanillin) was carried out using B3LYP (Becke, 3-parameter, Lee-Yan-Parr) method and cc-pVTZ (correlation consistent polarized polarisation Valence triple zêta) basis set. Potential energy surfaces were plotted in order to identify the minimum energy structures and the transition states. For the first time, structures of vanillin and syringol were completely determined. Moreover, our work also confirms that the most stable conformations of m-cresol and p-cresol are obtained when the methyl group presents a hydrogen atom at the perpendicular of the benzene ring. The possibility of intramolecular hydrogen bonding was also investigated. Guaiacol, pyrocatechol, syringol and vanillin present a structure stabilized by the presence of a moderate hydrogen bond. Finally, potential energy barriers and rotational potential functions were calculated. The comparison of the rotational potential parameters for each molecule highlights the presence of similarities specific to each substituent and their neighbours.

Experimental and thermodynamic comparison of the separation of CO 2 /toluene and CO 2 /tetralin mixtures in the process of organogel supercritical drying for aerogels production

An organogel is firstly prepared by synthesizing an aminoacid-type organogelator which is able to immobilize aromatic solvents, such as tetralin or toluene. Aerogels are obtained from organogels by extracting the solvent with a stream of supercritical CO2 in an autoclave. The CO2/solvent mixture leaving the autoclave is separated in a cascade of three cyclone separators. The experimental results showed a good solvent recovery rate in the case of tetralin, exceeding 90%, but an unsatisfactory separation for toluene with a yield below 65%. A thermodynamic study was carried out to model the separation for both solvents. The Peng–Robinson equation of state with van der Waals mixing rules and temperature-dependent binary interaction coefficients was selected to predict the CO2/solvent thermodynamic behavior. Measurements of isothermal bubble points of the CO2/tetralin system were conducted using a high-pressure variable-volume visual cell confirming the relevancy of this model. Then, the first separator was simulated as a simple theoretical equilibrium stage. Simulations using PRO/II software were in good agreement with experimental solvent recovery rate for both toluene and tetralin. The best operating pressure and temperature for the separation were computed by a numerical parametric study.Graphical abstractThermodynamic study to explain theoretical recovery in organogel supercritical drying: comparison between two solvents (T=20u2009°C, P=50 bar).