Víctor H. Álvarez

Specific Solvation Interactions of CO2 on Acetate and Trifluoroacetate Imidazolium Based Ionic Liquids at High Pressures

New classes of acidic or basic ionic liquids (ILs) are gaining special attention, since the efficiency of many processes can be enhanced by the judicious manipulation of these properties. The absorption of sour gases can be enhanced by the basic character of the IL. The fluorination of the cation or the anion can also contribute to enhance the gas solubility. In this work these two characteristics are evaluated through the study of the gas-liquid equilibrium of two ionic liquids based on similar anions, 1-butyl-3-methylimidazolium acetate ([C4mim][Ac]) and 1-butyl-3-methylimidazolium trifluoroacetate ([C4mim][TFA]), with carbon dioxide (CO2) at temperatures up to 363 K and pressures up to 76 MPa. The data reported are shown to be thermodynamically consistent. Henrys constants estimated from the experimental data show the solubility of CO2 on the [C4mim][Ac] to be spontaneous unlike in [C4mim][TFA] due to the differences in solvation enthalpies in these systems. Ab initio calculations were performed on simple intermolecular complexes of CO2 with acetate and trifluoroacetate using MP2/6-31G(d) and the G3 and G3MP2 theoretical procedures to understand the interactions between CO2 and the anions. The theoretical study indicates that although both anions exhibit a simultaneous interaction of the two oxygen of the carboxylate group with the CO2, the acetate acts as a stronger Lewis base than the trifluoroacetate. 13C high-resolution and magic angle spinning (HRMAS) NMR spectra provide further evidence for the acid/base solvation mechanism and the stability of the acetate ion on these systems. Further similarities and differences observed between the two anions in what concerns the solvation of CO2 are discussed.

Parameter estimation for VLE calculation by global minimization: the genetic algorithm

Vapor-liquid equilibrium calculations require global minimization of deviations in pressure and gas phase compositions. In this work, two versions of a stochastic global optimization technique, the genetic algorithm, the freeware MyGA program, and the modified mMyGA program, are evaluated and compared for vapor-liquid equilibrium problems. Reliable experimental data from the literature on vapor liquid equilibrium for water + formic acid, tert-butanol + 1-butanol and water + 1,2-ethanediol systems were correlated using the Wilson equation for activity coefficients, considering acid association in both liquid and vapor phases. The results show that the modified mMyGA is generally more accurate and reliable than the original MyGA. Next, the mMyGA program is applied to the CO2 + ethanol and CO2 + 1-n-butyl-3-methylimidazolium hexafluorophosphate systems, and the results show a good fit for the data.

Application of a Thermodynamic Consistency Test to Binary Mixtures Containing an Ionic Liquid

A thermodynamic consistency test developed for high pressure binary vapor-liquid mixtures is applied to mix- tures containing a supercritical solvent and an ionic liquid. Several authors have reported vapor-liquid equilibrium data on the binary systems supercritical CO2 + 1-butyl-3-methyl imidazolium hexafluorophosphate {(bmim)(PF6)}, supercritical CO2 + 1-butyl-3-methyl imidazolium nitrate {(bmim)(NO3)}, supercritical CO2 + 1-butyl-3-methyl imidazolium tetra- fluoroborate {(bmim)(BF4)} and supercritical CHF3 + 1-butyl-3-methyl imidazolium hexafluorophosphate {(bmim)(PF6)}, but some of these data differ dramatically. The Peng-Robinson equation of state, coupled with the Wong- Sandler mixing rules, has been used for modeling the vapor-liquid equilibrium of these binary mixtures. Then, the pro- posed thermodynamic consistency test has been applied. The results show that the consistency test can be applied with confidence, determining consistency or inconsistency of the experimental data.

Phase equilibria of binary mixtures containing methyl acetate, water, methanol or ethanol at 101.3 kPa

Isobaric vapor–liquid equilibria data at 101.3 kPa were reported for the binary mixtures (methyl acetate + (water or methanol or ethanol), methanol + (water or ethanol) and (ethanol + water)). The experimental data were tested for thermodynamic consistency by means of the Wisniak method and were demonstrated to be consistent. The experimental data were correlated using Wilson, NRTL and UNIQUAC models for the activity coefficients and predicted using the UNIFAC and PSRK equation of state for testing theirs capability. The results show that the obtained data for the studied binary systems are more reliable than other published data.

Production of Anhydrous Ethanol by Extractive Distillation of Diluted Alcoholic Solutions with Ionic Liquids

Abstract In this work, the use of the ionic liquid 1-methyl-3-methylimidazolium dimethylphosphate or ethylene glycol as an separation agent was evaluated in a two-column or three-column configuration extractive distillation for the production of anhydrous ethanol (99.8% weight, 99.5% mol) from diluted solutions (11% weight). The extractive distillation process was simulated and optimized with the HYSYS® software. The vapor liquid equilibrium for the system was calculated by the NRTL thermodynamic model, whose interactions parameters were previously published. Experimental design was used in combination with modeling and simulation to determine the operational conditions that minimize reboiler duty. Simulation results showed that both separating agents present similar reboiler duty to produce high-purity ethanol.

Bioethanol Production Optimization: A Thermodynamic Analysis

In this work, the phase equilibrium of binary mixtures for bioethanol production by continuous extractive process was studied. The process is composed of four interlinked units: fermentor, centrifuge, cell treatment unit, and flash vessel (ethanol-congener separation unit). A proposal for modeling the vapor–liquid equilibrium in binary mixtures found in the flash vessel has been considered. This approach uses the Predictive Soave–Redlich–Kwong equation of state, with original and modified molecular parameters. The congeners considered were acetic acid, acetaldehyde, furfural, methanol, and 1-pentanol. The results show that the introduction of new molecular parameters r and q in the UNIFAC model gives more accurate predictions for the concentration of the congener in the gas phase for binary and ternary systems.