Rafael Alcalde

The green solvent ethyl lactate: an experimental and theoretical characterization

Ethyl lactate is a green, and economically viable, alternative to traditional solvents whose extensive use and scale-up to industrial level requires a deep and accurate knowledge of its properties in wide pressure–temperature ranges. In this work, the pressure–volume–temperature and pressure–viscosity–temperature behaviors are reported together with several derived properties of remarkable importance for process design purposes. The structure of the liquid is analyzed at the microscopic level using the Density Functional Theory and from classical molecular dynamics simulations. It is shown the competing effect of intra and intermolecular hydrogen bonding mainly through preferred positions. The predictive ability of the forcefield used for molecular dynamics simulations is studied, showing good results for most of the considered properties. Monte Carlo/Gibbs ensemble simulations were carried out to predict the phase equilibria of the fluid, considering the absence of experimental data.

On the properties of 1-butyl-3-methylimidazolium octylsulfate ionic liquid

This work reports on a theoretical and experimental study on the ionic liquid 1-butyl-3-methylimidazolium octylsulfate ([BMIM]OS). The halogen-free ionic liquid [BMIM]OS is a stable solvent regarding hydrolysis, whose availability, toxicologically favourable features and well documented biodegradability turns it into a suitable candidate for different multiton-scale industrial applications. The pressure–volume–temperature behaviour of this fluid has been evaluated accurately over wide ranges of temperature and pressure, and correlated successfully with the empirical TRIDEN equation. From the measured data the relevant derived coefficients, isothermal compressibility, isobaric expansibility and internal pressure have been calculated. Other valuable properties such as isobaric heat capacity, speed of sound and refractive index were measured at several temperatures and atmospheric pressure. The molecular structure was looked into by quantum computations at the B3LYP/6-31 + g(d) level and classical molecular dynamics simulations in the NPT ensemble with the OPLS–AA forcefield. Both macroscopic and microscopic studies concur in a complex structure involving microheterogenous polar and non-polar domains, brought about by the aggregation of the non-polar anionic chains.

Formamide–(C1–C5) alkan-1-ols solvent systems

Excess volumes, excess viscosities, and exess Gibbs energies of activation for viscous flow of binary liquid mixtures of formamide with (C1–C5) alkan-1-ols have been calculated from the densities and viscosities measured at 298.15 K over the whole composition range. The viscosity–mole fraction data of the five systems were used to test various empirical laws proposed to describe the viscosity of mixtures: the one-parameter models by Nissan–Grunberg, Hind–McLaughlin–Ubbelohde and Teja–Rice, and the two-parameter models by McAllister, Heric, Lobe, and Cao–Fredenslund–Rasmussen were tested. All correlations were in good agreement except that of Teja–Rice. Deviations with respect to ideal behaviour were interpreted in terms of specific interactions between unlike molecules.

Shear viscosities of the N-methylformamide–andN,N-dimethylformamide–(C1–C10) alkan-1-ol solvent systems

Viscosities of some N-methylformamide– and N,N-dimethylformamide–(C 1 –C 10 ) alkan-1-ol binary mixtures have been measured at 298.15 K over the whole composition range. The excess viscosities and excess Gibbs energies of activation for viscous flow, compared with values for other amide–alcohol mixed solvents, suggest that the alcohol size does not play a significant role in the mixture behaviour. The alcohol mixtures with aliphatic amides gave heteroaggregates to a greater extent, the lower the self-association of the pure amides. An analysis in terms of solvent solubility parameters gave good agreement with experimental results.

On the viscosity of pyridinium based ionic liquids: an experimental and computational study.

A study on the viscosity of eight pyridinium based ionic liquids is reported for wide pressure and temperature ranges. Measurements were performed using an electromagnetic moving piston viscometer. Experimental data were fitted to a Tait-like equation demonstrating good correlations, which was used to calculate pressure/viscosity and temperature/viscosity coefficients. The effect of the involved anions and cation on the ionic liquid viscosity was analyzed from a molecular viewpoint using hole theory, quantum chemistry calculations using density functional theory, and classical molecular dynamics simulations. The analysis of the experimental and computational results shows the complex effects controlling viscosity of studied fluids, including strength of ionic pairs, molecular sizes, and mobility and effects rising from the availability and cavity sizes distributions in pyridinium-based ionic liquids.

High-Pressure Study of the Methylsulfate and Tosylate Imidazolium Ionic Liquids

The considerable interest aroused in recent years by the unique properties and industrial applications of ionic liquids has given rise to the need for a detailed statement of the linkage between their molecular features and the observed macroscopic behavior. A combined experimental/computational approach to the study of ionic liquids is submitted here and applied to the relevant, nonhalogenated ionic liquids 1,3-dimethylimidazolium methylsulfate and 1-ethyl-3-methylimidazolium tosylate. To establish a reliable equation of state pertinent to these fluids, density data over wide pressure (0.1-60 MPa) and temperature (318.15-428.15 K) ranges, along with high pressure (1-70 MPa) viscosities and other selected ambient pressure properties were measured to assemble sufficient experimental information for the seek of predictive models for process design. A computational method based on ab initio and classical molecular dynamics yielded a deal of structural information, borne out by the experimental readings. Likewise, the predictive ability of the force field applied in molecular dynamics simulations was faced with the measured properties. The pictorial description of the selected ionic liquids reached this way may become widespread to other relevant examples in order to infer valuable structure/property relationships.

Study on Hydroxylammonium-Based Ionic Liquids. I. Characterization

Two selected ammonium-based ionic liquids, 2-hydroxyethyltrimethylammonium L-(+)-lactate and tris(2-hydroxyethyl)methylammonium methylsulfate, were fully characterized. The most relevant thermophysical properties of pure fluids were measured and analyzed as a function of temperature. Structural features were inferred from solvatochromic and Fourier transform infrared (FTIR) studies. Moisture absorption ability was also studied by gravimetric, spectroscopic, and Karl Fischer methods. Likewise, the water effect on fluids properties was analyzed. Polarity was studied by approaches based on solvatochromic measurements and on the water effect on FTIR spectra. Moreover, as computational work, quantum chemistry and molecular dynamics simulation methods were used to analyze the main molecular-level structural features in these fluids. The work is divided into two parts; in this first paper, the main objective is fully characterizing these ionic liquids in the pure state, and in the second paper CO(2) absorption will be analyzed, therefore leading to a deep knowledge of factors controlling structuring, properties, and CO(2) absorption for this family of ionic liquids in comparison with available information for other relevant types of ionic liquids.

Insights into the ethyl lactate + water mixed solvent.

The mixed green solvent ethyl lactate + water is studied from macro- and microscopic viewpoints using a wide collection of experimental and computational tools. High-pressure thermophysical data, density, and dynamic viscosity provide valuable information on the macroscopic behavior of the mixed fluid, which is of remarkable importance for industrial purposes, and through the analysis of the derived excess and mixing properties lead to relationships with molecular level properties. Large deviations from ideality are obtained, which are related to the development of strong intermolecular hydrogen bonding between both molecules upon mixing. Computational studies, using the density functional theory, both in gas phase and water solution, allow to characterize, from energetic and structural viewpoints, the different ethyl lactate/water association complexes. The use of atoms in a molecule and natural bond orbital methods sheds light into the properties of ethyl lactate/water hydrogen bonding. Classical molecular dynamics simulations are carried out for the whole composition range, and as a function of pressure and temperature. Force field validation is done by comparison of predicted thermophysical properties with measured ones. Structural features are inferred from the analysis of radial distribution functions and their evolution with composition, pressure, and temperature, and dynamic aspects are inferred from the calculated self-diffusion constants and mean square displacements. The whole study points to a highly structured fluid, in which hydrogen bonding is developed both for water-rich and ethyl-lactate-rich solvents, showing a remarkable effect in the fluid structure upon the addition of the second component for both pure compounds, even more important for the effect of ethyl lactate on water hydrogen bonding network.

Study on hydroxylammonium-based ionic liquids. II. Computational analysis of CO2 absorption.

In the previous work of this series, we reported a wide experimental and computational analysis of the properties of hydroxylammonium-based ionic liquids. This family of ionic liquids shows very favorable economical, technological, and environmental properties in comparison with other ionic liquid types. We report in this work a computational study, using quantum chemistry and molecular dynamics methods, to analyze the absorption of carbon dioxide by hydroxylammonium ionic liquids. The selected compounds were 2-hydroxyethyl-trimethylammonium L-(+)-lactate and tris(2-hydroxyethyl)methylammonium methylsulfate. The main objective of this work is to study and analyze CO(2) absorption from the molecular point of view, therefore contributing to the knowledge and advancement on the absorption ability of ionic liquids. The computational study would lead to a deeper knowledge of factors controlling CO(2) absorption for this ionic liquid family in comparison with available information for other relevant types. The results were analyzed considering the effects of absorbed gas on the ionic liquid structuring from a molecular level viewpoint, interionic interactions, diffusion of the involved compounds, and interaction of CO(2) with anions and cations. The reported results show a strong effect of the presence of hydroxyl groups in the involved cations and anions through the interaction with CO(2) molecules, along with the effects rising from the size of cations on the fluid structure.

Volumetric properties, viscosities and refractive indices of binary mixed solvents containing methyl benzoate

Densities, dynamic viscosities, and refractive indices of the binary mixed solvents of methylbenzoate with a set of eleven organic solvents provided with six carbon atoms but different structure and functional groups were measured over the whole composition range. Thermodynamic, transport, solubility, and electrical properties were analyzed for all systems; from the experimental quantities, excess and mixing properties were deduced and interpreted in terms of intermolecular interactions and structural changes upon mixing. Mixing viscosities and excess Gibbs energies of activation for viscous flow support the role played by the size of the cosolvent on the mixture behaviour. Analysis in terms of solvent solubility parameters was in convincing good agreement with experimental results. The Soave and Peng–Robinson equations of state and the Wong–Sandler mixing rule are used to correlate volumetric properties. The predictive ability of several one-parameter and two-parameter viscosity models was also tested.