Martín Aznar

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.

Salt effect on liquid–liquid equilibrium of water+1-butanol+acetone system: experimental determination and thermodynamic modeling☆

Abstract Liquid–liquid equilibrium data for the quaternary systems (water+1-butanol+acetone+sodium chloride) and (water+1-butanol+acetone+sodium acetate) were measured at 20 and 40°C. The results were compared with experimental liquid–liquid equilibrium data for the ternary, salt-free systems, both from literature and determined in this work. In this way, the salt effect could be evaluated. Ternary liquid–liquid equilibrium data for the salt-free system water+acetone+1-butanol were also determined and found in good agreement with reported data from literature. The experimental data were correlated with the NRTL activity coefficient model. New thermodynamic interaction parameters were estimated with the Simplex method and the Maximum Likelihood principle, using binary water+1-butanol liquid–liquid equilibrium data from literature, ternary water+acetone+1-butanol, both from literature and determined in this work, and quaternary water+acetone+1-butanol+salt, determined in this work. The results are very satisfactory in accordance with root mean square deviations between experimental and calculated compositions of both equilibrium phases, that are always below 1.2%.

Correlation of (liquid + liquid) equilibrium of systems including ionic liquids

Ionic liquids are neoteric, environmentally friendly solvents (since they do not produce emissions) composed of large organic cations and relatively small inorganic anions. They have favorable physical properties, such as negligible volatility and wide range of liquid existence. Moreover, many different cations and anions can be used to synthesize ionic liquid, so the properties can be designed by the use of selected combinations of anions and cations. (Liquid + liquid) equilibrium (LLE) data for systems including ionic liquids, although essential for the design and operation of separation processes, are still scarce. However, some recent studies have presented ternary LLE data involving several ionic liquids and such organic compounds as alkanes, alkenes, alkanols, water, ethers and aromatics. In this work, LLE data for 24 ternary systems including ionic liquids from the literature are correlated by using the NRTL model for the activity coefficient. The results are very satisfactory, with rms deviations of about 1.4%.

Salt effect of KBr on the liquid-liquid equilibrium of the water/ethanol/1-pentanol system

Liquid-liquid equilibrium data for the water/ethanol/1-pentanol/potassium bromide systems were experimentally determined at 25° C and 40oC. The experimental data were correlated through the NRTL and UNIFAC-Dortmund models for the activity coefficient, with the estimation of new binary interaction parameters for both models, corresponding to the salt-solvent and solvent-solvent interactions for the NRTL model and the ion-ion and solvent-ion interactions for the UNIFAC-Dortmund model. The results obtained have shown that the NRTL model was more able to represent equilibrium data for the studied systems.

Thermodynamic modelling of phase equilibrium for water + poly(Ethylene glycol) + salt aqueous two-phase systems

The NRTL (nonrandom, two-liquid) model, expressed in mass fraction instead of mole fraction, was used to correlate liquid-liquid equilibria for aqueous two-phase polymer-salt solutions. New interaction energy parameters for this model were determined using reported data on the water + poly(ethylene glycol) + salt systems, with different molecular masses for PEG and the salts potassium phosphate, sodium sulfate, sodium carbonate and magnesium sulfate. The correlation of liquid-liquid equilibrium is quite satisfactory.

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.

Prediction of electrolyte vapor-liquid equilibrium by UNIFAC-Dortmund

The modified UNIFAC-Dortmund group contribution model is used for the correlation and prediction of salt effects in binary solvent-salt and ternary mixed solvent-salt systems. The long-range electrostatic interaction contribution, usually represented by a Debye-Huckel term, was empirically dropped. Previously published parameters for interactions between solvent groups (CH2, OH, CH3OH, H2O and CH3CO) were used, and group interactions between ions (Li+, Na+, K+, Ca+2, Cl-, Br-, NO3- and ACE-) and between ions and solvent groups have been estimated. The data base includes 29 binary and 56 ternary systems, used in part for the calculation of group interactions and in part for the testing of predictions.

Liquid-liquid equilibrium of water + PEG 8000 + magnesium sulfate or sodium sulfate aqueous two-phase systems at 35°C: experimental determination and thermodynamic modeling

Liquid-liquid extraction using aqueous two-phase systems is a highly efficient technique for separation and purification of biomolecules due to the mild properties of both liquid phases. Reliable data on the phase behavior of these systems are essential for the design and operation of new separation processes; several authors reported phase diagrams for polymer-polymer systems, but data on polymer-salt systems are still relatively scarce. In this work, experimental liquid-liquid equilibrium data on water + polyethylene glycol 8000 + magnesium sulfate and water + polyethylene glycol 8000 + sodium sulfate aqueous two-phase systems were obtained at 35°C. Both equilibrium phases were analyzed by lyophilization and ashing. Experimental results were correlated with a mass-fraction-based NRTL activity coefficient model. New interaction parameters were estimated with the Simplex method. The mean deviations between the experimental and calculated compositions in both equilibrium phases is about 2%.

Modeling vapor liquid equilibrium of ionic liquids + gas binary systems at high pressure with cubic equations of state

Ionic liquids (IL) have been described as novel environmentally benign solvents because of their remarkable characteristics. Numerous applications of these solvents continue to grow at an exponential rate. In this work, high pressure vapor liquid equilibria for 17 different IL + gas binary systems were modeled at different temperatures with Peng-Robinson (PR) and Soave-Redlich-Kwong (SRK) equations of state, combined with the van der Waals mixing rule with two binary interaction parameters (vdW-2). The experimental data were taken from the literature. The optimum binary interaction parameters were estimated by minimization of an objective function based on the average absolute relative deviation of liquid and vapor phases, using the modified Simplex algorithm. The solubilities of all gases studied in this work decrease as the temperature increases and increase with increasing pressure. The correlated results were highly satisfactory, with average absolute relative deviations of 2.10% and 2.25% for PR-vdW-2 and SRK-vdW-2, respectively.