[show abstract][hide abstract] ABSTRACT: The industrial application of ionic liquids (ILs) requires the knowledge of their physical properties and phase behavior. This work addresses the experimental determination of the vapor-liquid equilibria (VLE) of binary systems composed of water + imidazolium-based ILs. The ILs under consideration are 1-butyl-3-methylimidazolium trifluoromethanesulfonate, 1-butyl-3-methylimidazolium thiocyanate, 1-butyl-3-methylimidazolium tosylate, 1-butyl-3-methylimidazolium trifluoroacetate, 1-butyl-3-methylimidazolium bromide, 1-butyl-3-methylimidazolium chloride, 1-butyl-3-methylimidazolium methanesulfonate and 1-butyl-3-methylimidazolium acetate, which allows the evaluation of the influence of the IL anion through the phase behavior. Isobaric VLE data were measured at 0.05 MPa, 0.07 MPa and 0.1 MPa for IL mole fractions ranging between 0 and 0.7. The observed increase in the boiling temperatures of the mixtures is related with the strength of the interaction between the IL anion and water. The Perturbed-Chain Statistical Associating Fluid Theory (PC-SAFT) was further used to describe the obtained experimental data. The ILs were treated as molecular associating species with two association sites per IL. The model parameters for the pure fluids and the binary interaction parameter k_ij between water and ILs were determined by a simultaneous fitting to pure-IL densities, water activity coefficients at 298.15 K and VLE data at 0.1 MPa. Pure-IL densities, water activity coefficients and VLE data were well described by PC-SAFT in broad temperature, pressure and composition ranges. The PC-SAFT parameters were applied to predict the water activity coefficients at infinite dilution in ILs and a satisfactory prediction of experimental data were observed.
[show abstract][hide abstract] ABSTRACT: We use highly accurate ab initio calculations of binding enthalpies and entropies of gas phase clusters of alcohols to demonstrate how they can be used to obtain association parameters for PC-SAFT. The thermochemical results demonstrate that cooperativity effects and state dependent cluster distributions cause a strongly varying average enthalpy and entropy per bond as function of temperature and density for alcohols. In contrast to this, the two association parameters of PC-SAFT lead to density independent bond enthalpy and entropy and are thus effective parameters. Therefore, we choose to compute the cluster distribution at a universal state point and show that the thus obtained association parameters can be used to reduce the number of adjustable parameters from 5 to 3 with only a marginal loss of accuracy for most of the studied systems, and even an estimation of thermodynamic properties without adjusted parameters is possible. The ab initio calculations suggest that the 2B association scheme is more appropriate for 1-alkanols than the 3B one.
[show abstract][hide abstract] ABSTRACT: In this work thermodynamic properties of electrolyte/amino acid/water solutions were measured and modeled. Osmotic coefficients at 298.15 K were measured by means of vapor-pressure osmometry. Amino-acid solubility at 298.15 K was determined gravimetrically. Considered aqueous systems contained one of the four amino acids: glycine, L-/DL-alanine, L-/DL-valine, and L-proline up to the respective amino-acid solubility limit and one of 13 salts composed of the ions Li+, Na+, K+, NH4+, Cl−, Br−, I−, NO3−, and SO42− at salt molalities of 0.5, 1.0, and 3.0 mol · kg−1, respectively. The data show that the salt influence is more pronounced on osmotic coefficients than on amino-acid solubility.
The electrolyte Perturbed-Chain Statistical Association Theory (ePC-SAFT) was applied to model thermodynamic properties in aqueous electrolyte/amino-acid solutions. In previous works, this model had been applied to binary salt/water and binary amino acid/water systems. Without fitting any additional parameters, osmotic coefficients and amino-acid solubility in the ternary electrolyte/amino acid/water systems could be predicted with overall deviations of 3.7% and 9.3%, respectively, compared to the experimental data.
The Journal of Chemical Thermodynamics 01/2014; 68:1–12. · 2.30 Impact Factor
[show abstract][hide abstract] ABSTRACT: ePC-SAFT was used to model the gas solubility in ionic liquids (ILs). The gases under consideration were CO, H2, H2S and O2, and the imidazolium-based ILs studied were [Cnmim][Tf2N], [Cnmim][PF6] and [Cnmim][BF4] (n = 2, 4, 6 and 8). For the ePC-SAFT modeling, each IL was considered to be completely dissociated into a cation and an anion. Each ion was modeled as a non-spherical species exerting repulsive, dispersive and Coulomb forces. CO, H2 and O2 were modeled as non-spherical molecules exerting repulsive and dispersive forces, and H2S was modeled as a non-spherical, associating molecule. ePC-SAFT reasonably predicts the gas solubility in the considered gas/IL mixtures. In order to describe the experimental gas solubilities quantitatively in a broad temperature and pressure range, one ion-specific binary interaction parameter between the IL-anion and the gas was applied, which was allowed to depend linearly on temperature.
[show abstract][hide abstract] ABSTRACT: In this work the ePC-SAFT equation of state is applied to model aqueous two-phase systems (ATPS) containing polyethylene glycol (PEG) and one of 16 different inorganic salts at temperatures between 277.15 K and 333.15 K. To ensure an accurate modeling of thermodynamic properties in PEG containing solutions, a novel modeling approach for PEG is applied considering different molecular interactions of PEG chain segments and PEG end-group segments. Applying this approach, the influence of PEG molecular weight, kind of salt, pH, as well as of temperature on the phase split as well as on the densities of the two phases can be modeled accurately. The overall absolute average deviation of the concentrations of the phase-forming components obtained by ePC-SAFT is 2.25 wt%. Moreover, it could be shown that by applying ion-specific model parameters, ePC-SAFT is even capable of predicting ATPS which were not used for the parameter estimation.
[show abstract][hide abstract] ABSTRACT: This work focuses on modeling and experimental investigation of temperature dependent interfacial properties of binary DMF/n-alkane (C7, C10, C12) mixtures. The systems consisting of solvents with very different polarity show azeotropic behavior. New experimental vapor–liquid and liquid–liquid interfacial tension data are provided between 298.15 and 328.15 K using the drop volume method. The Perturbed Chain Polar Statistical Associating Fluid Theory (PCP-SAFT) equation of state was combined with the Density Gradient Theory (DGT) to calculate phase equilibria and interfacial properties. Modeling results are in good agreement with the corresponding experimental data. Thereby, the binary parameter βij within the DGT framework does not equal one. Investigating density and concentration profiles in the interface revealed characteristic trends which are related to the azeotropic behavior of the mixtures.
[show abstract][hide abstract] ABSTRACT: Biorefining processes using ionic liquids (ILs) require proper solubility data of biomass-based compounds in ILs, as well as an appropriate thermodynamic approach for the modeling of such data. Carbohydrates and their derivatives such as sugar alcohols represent a class of compounds that could play an important role in biorefining. Thus, in this work, the pure IL density and solubility of xylitol and sorbitol in five different ILs were measured between 288 and 339 K. The ILs under consideration were 1-ethyl-3-methylimidazolium dicyanamide, 1-butyl-3-methylimidazolium dicyanamide ([bmim][DCA]), Aliquat dicyanamide, trihexyltetradecylphosphonium dicyanamide, and 1-ethyl-3-methylimidazolium trifluoroacetate. Comparison with the literature data was performed, showing good agreement. With the exception of [bmim][DCA], the solubility of these sugar alcohols in the other ILs is presented for the first time. The measured data as well as previously published solubility data of glucose and fructose in these ILs were modeled by means of PC-SAFT using a molecular-based associative approach for ILs. PC-SAFT was used in this work as it has shown to be applicable to model the solubility of xylitol and sorbitol in ILs ( Paduszyński ; et al. J. Phys. Chem. B 2013 , 117 , 7034 - 7046 ). For this purpose, three pure IL parameters were fitted to pure IL densities, activity coefficients of 1-propanol at infinite dilution in ILs, and/or xylitol solubility in ILs. This approach allows accurate modeling of the pure IL data and the mixture data with only one binary interaction parameter kij between sugar and the IL or sugar alcohol and the IL. In cases where only the pure IL density and activity coefficients of 1-propanol at infinite dilution in ILs were used for the IL parameter estimation, the solubility of the sugars and sugar alcohols in the ILs could be predicted (kij = 0 between sugar and the IL or sugar alcohol and the IL) with reasonable accuracy.
The Journal of Physical Chemistry B 08/2013; · 3.61 Impact Factor
[show abstract][hide abstract] ABSTRACT: Molecular interactions in 1-butanol + ionic liquid (IL) solutions have been investigated by measuring and modeling activity-coefficient data. The activity coefficients in binary solutions containing 1-butanol and an IL were determined experimentally: the ILs studied were 1-decyl-3-methyl-imidazolium tetracyanoborate ([Im10.1]+[tcb]-), 4-decyl-4-methyl-morpholinium tetracyanoborate ([Mo10.1]+[tcb]-), 1-decyl-3-methyl-imidazolium bis(trifluoromethylsulfonyl)imide ([Im10.1]+[ntf2]-), and 4-decyl-4-methyl-morpholinium bis(trifluoromethylsulfonyl)imide ([Mo10.1]+[ntf2]-). The methods used to determine the activity coefficients included vapor-pressure osmometry, headspace-gas chromatography, and gas-liquid chromatography. The results from all of these techniques were combined to obtain activity-coefficient data over the entire IL concentration range, and the ion-specific interactions of the ILs investigated were identified with 1-butanol. The highest (1-butanol)-IL interactions of the ILs considered in this work were found for [Im10.1]+[tcb]-; thus, [Im10.1]+[tcb]- showed the highest affinity for 1-butanol in a binary mixture. The experimental data were modeled with the Perturbed-Chain Statistical Associating Fluid Theory (PC-SAFT). PC-SAFT was able to accurately describe the pure IL and (1-butanol)-IL data. Moreover, the model was shown to be predictive and extrapolative with respect to concentration and temperature.
The Journal of Physical Chemistry B 03/2013; · 3.61 Impact Factor
[show abstract][hide abstract] ABSTRACT: The Gibbs energy of reaction (Δ(R)g) is the key quantity in the thermodynamic characterization of biological reactions. Its calculation requires precise standard Gibbs energy of reaction (Δ(R)g(+)) values. The value of Δ(R)g(+) is usually determined by measuring the apparent (concentration-dependent) equilibrium constants K, e.g., the molality-based Km. However, the thermodynamically consistent determination of Δ(R)g(+) requires the thermodynamic (activity-based) equilibrium constant Ka. These values (Km and Ka) are equal only if the ratio of the activity coefficients of the reactants to the activity coefficients of the products (Kγ) is equal to unity. In this work, the impact of Kγ on the estimation of Ka for biological reactions was investigated using methyl ferulate (MF) hydrolysis as a model reaction. The value of Kγ was experimentally determined from Km values that were measured at different reactant concentrations. Moreover, Kγ was independently predicted using the thermodynamic model ePC-SAFT. Both the experimentally determined and the predicted Kγ values indicate that this value cannot be assumed to be unity in the considered reaction. In fact, in the reaction conditions considered in this work, Kγ was shown to be in the range of 3<Kγ<6 for different reactant molalities (2<mmol MF kg(-1)<10). The inclusion of Kγ and thus the use of the thermodynamically correct Ka value instead of Km lead to remarkable differences (almost 40%) in the determination of Δ(R)g(+). Moreover, the new value for Δ(R)g(+) increases the concentration window at which the reaction can thermodynamically occur. The influence of additives was also investigated both experimentally and theoretically. Both procedures consistently indicated that the addition of NaCl (0 to 1molkg(-1) water) moderately decreased the value of Kγ, which means that the values of Km increase and that a higher amount of products is obtained as a result of the addition of salt. Additionally, Km was found to strongly depend on pH. A ten-fold increase in the Km values was observed in the pH range of 6 to 7; this increase corresponds to a change of more than 100% in the value of Δ(R)g(+).
[show abstract][hide abstract] ABSTRACT: The experimental determination and modeling of osmotic coefficients in electrolyte solutions requires knowledge of the stoichiometric coefficient ν(i). In contrast to strong electrolytes, weak electrolytes exhibit a concentration-dependent stoichiometric coefficient, which directly influences the thermodynamic properties (e.g., osmotic coefficients). Neglecting this concentration dependence leads to erroneous osmotic coefficients for solutions of weak electrolytes. In this work, the concentration dependence of the stoichiometric coefficients and the influence of concentration on the osmotic coefficient data were accounted for by considering the dissociation equilibria of aqueous sulfuric and phosphoric acid systems. The dissociation equilibrium was combined with the ePC-SAFT equation of state to model osmotic coefficients and densities of electrolyte solutions. Without the introduction of any additional adjustable parameters, the average relative deviation between the modeled and the experimental data decreases from 12.82% to 4.28% (osmotic coefficients) and from 2.59% to 0.89% (densities) for 12 phosphoric and sulfuric systems compared to calculations that do not account for speciation. For easy access to the concentration-dependent stoichiometric coefficient, estimation schemes were formulated for mono-, di-, and triprotic acids and their salts.
The Journal of Physical Chemistry B 05/2012; 116(25):7479-91. · 3.61 Impact Factor
[show abstract][hide abstract] ABSTRACT: In an earlier study, biocatalytic carbon oxyfunctionalization with water serving as oxygen donor, e.g., the bioconversion of quinaldine to 4-hydroxyquinaldine, was successfully achieved using resting cells of recombinant Pseudomonas putida, containing the molybdenum-enzyme quinaldine 4-oxidase, in a two-liquid phase (2LP) system (Ütkür et al. J Ind Microbiol Biotechnol 38:1067-1077, 2011). In the study reported here, key parameters determining process performance were investigated and an efficient and easy method for product recovery was established. The performance of the whole-cell biocatalyst was shown not to be limited by the availability of the inducer benzoate (also serving as growth substrate) during the growth of recombinant P. putida cells. Furthermore, catalyst performance during 2LP biotransformations was not limited by the availability of glucose, the energy source to maintain metabolic activity in resting cells, and molecular oxygen, a possible final electron acceptor during quinaldine oxidation. The product and the organic solvent (1-dodecanol) were identified as the most critical factors affecting biocatalyst performance, to a large extent on the enzyme level (inhibition), whereas substrate effects were negligible. However, none of the 13 alternative solvents tested surpassed 1-dodecanol in terms of toxicity, substrate/product solubility, and partitioning. The use of supercritical carbon dioxide for phase separation and an easy and efficient liquid-liquid extraction step enabled 4-hydroxyquinaldine to be isolated at a purity of >99.9% with recoveries of 57 and 84%, respectively. This study constitutes the first proof of concept on an integrated process for the oxyfunctionalization of toxic substrates with a water-incorporating hydroxylase.
Journal of Industrial Microbiology 03/2012; 39(7):1049-59. · 1.80 Impact Factor
[show abstract][hide abstract] ABSTRACT: Liquid densities, osmotic coefficients, and mean ionic activity coefficients (MIAC) at 25 °C of single-salt alcohol (methanol and ethanol) solutions containing univalent ions were measured and modeled with the ePC-SAFT equation of state. In accordance with our previous work [Held, C., Cameretti, L.F., Sadowski, G., Fluid Phase Equlilib. 270 (2008) 87–96], only two solvent-specific ion parameters were adjusted to experimental solution densities and osmotic coefficients: the solvated ion diameter and the dispersion-energy parameter. ePC-SAFT was able to reproduce experimental data of the respective alcohol/salt systems with reasonable accuracy. Based on the solvent-specific ion-parameter sets, it is possible to predict densities and MIACs in ternary and quaternary water/alcohol(s)/salt solutions by introducing appropriate mixing rules that do not contain any additional fitting parameters.
Chemical Engineering Science. 01/2012; 68(1):328–339.
[show abstract][hide abstract] ABSTRACT: Activity coefficients of solvents and solutes in different aqueous solutions of alcohols and polymers are determined by molecular dynamic simulations. These data are often not accessible by simulation due to unacceptably high computational demands. Therefore, we applied a combination of two methods: water activity coefficients were determined directly via Overlapping Distribution Method, while counter-component activity coefficients were calculated indirectly by Gibbs-Duhem integration of the respective water activities. Results are in good agreement with experimental data. The method can easily be applied to determine activity coefficients of very complex components in water or other simple solvents.
[show abstract][hide abstract] ABSTRACT: The pure-component parameters of the Perturbed Chain Polar-Statistical Associating Fluid Theory (PCP-SAFT) equation of state are usually fitted to experimental data over broad temperature ranges. Against a background of limited experimental data, this article examines the amount and type of experimental data that are minimally required for safe parameter estimation. For nonassociating components, a minimal data set containing three data points is sufficient. For associating components, five data points are sufficient. The influence of vapor-pressure data on parameter estimation and the modeling results is larger than that of liquid-volume data. The temperature ranges of the experimental data can be chosen to be as small as 5 K for all of the data, except for the vapor pressures of associating components. These data require a range of at least 20 K. Application of the parameters fitted to the minimal experimental data set led to convincing results for the modeling of pure-component properties and binary mixtures.
[show abstract][hide abstract] ABSTRACT: This work considers aqueous two-phase systems (ATPS) containing one polymer–polyelectrolyte as well as one salt. To model the liquid–liquid equilibria (LLE) of these systems, the recently presented model pePC-SAFT has been employed. ATPS containing poly(acrylic acid) of different degrees of neutralization or poly(vinyl pyrrolidone), respectively, were considered. The binary interaction parameters used between water–poly(acrylic acid) and water–poly(vinyl pyrrolidone) were adjusted to vapor–liquid equilibrium (VLE) data of these systems. ATPS consisting of poly(vinyl pyrrolidone)–water–sodium sulfate were predicted as function of temperature as well as of molar mass of the polymer. For poly(acrylic acid) systems, ATPS were predicted as function of charge density (degree of neutralization) for different types of salt. For these calculations, the polyelectrolyte model parameters were determined from the non-charged polymer whereas the effect of increasing charge density has been purely predicted by the model. Using this approach, it is possible to predict the shrinking of the liquid–liquid equilibrium region with increasing charging of the polyelectrolyte.
[show abstract][hide abstract] ABSTRACT: The solubility of amino acids is highly depending on the prevailing pH value. However, this dependency is neglected in the state-of-the-art modeling of solubilities in multisolute solutions. In order to describe the pH-dependency of the solubilities, the PC-SAFT model is applied to aqueous solutions containing two amino acids accounting for their dissociation/association equilibria. This approach is applied to four ternary mixtures with pronounced pH-dependent solubility behavior allowing for a good description of experimental amino acid solubilities depending on temperature, cosolute concentration, and pH value. The systems considered within this work each contain two amino acids which show big differences in pI, i.e., l-glutamic acid or l/dl-aspartic acid on the one hand and glycine or l-serine on the other hand, respectively.
[show abstract][hide abstract] ABSTRACT: New force fields for molecular dynamics (MD) simulation of aqueous zwitterionic amino acid simulations were developed. These were especially designed to calculate activity coefficient of water in amino acid solutions with high accuracy. For example, aqueous solutions of the following amino acids were considered: glycine, alanine, α-aminobutyric acid, α-aminovalerianic acid, valine and leucine. The force fields were obtained by quantum chemical calculations using B3LYP/6-31G and MP2/6-311(d,p) model theories in combination with the Merz–Kollmann–Singh scheme. To further increase the accuracy of the force field, a polarised continuum was considered in all quantum chemical calculations. Water activity coefficients obtained from MD using different all-purpose literature force fields, namely, OPLS, AMBER ff03 and GROMOS 53A6 as well as experimental data are compared with the results utilising the new force field. The new force field is shown to give better results compared with experimental data than existing force fields.