UNIFAC Dortmund Research Articles

Extension of modified UNIFAC (Dortmund) matrix to piperidinium ionic liquids

In this contribution, modified UNIFAC (Dortmund) matrix for ionic liquids reported by Nebig and Gmehling [Fluid Phase Equilib. 302 (2011) 220–225] is extended. New parameters, determined on the basis of thermodynamic data extracted from literature, enable to apply the model to calculate various thermodynamic properties (limiting activity coefficients, liquid–liquid and solid–liquid equilibrium phase diagrams, and excess enthalpies) of binary systems formed by 1,1-dialkylpiperidinium ionic liquids based on bis[(trifluoromethyl)sulfonyl]imide anion and different organic solvents (n-alkane, cycloalkane, 1-alkene, benzene, thiophene, 1-alcohol), or water. It is demonstrated that the modified UNIFAC (Dortmund) group contribution method is capable of capturing those different properties with a very good accuracy.

Biofuels and additives: Comparative kinetic study of Amberlite IR 120-catalyzed esterification of ethanol with acetic, propanoic and pentanoic acids to produce eco-ethyl-esters

The effect of reaction time and operating parameters like temperature, catalyst loading and feed ratios on Amberlite IR 120-catalyzed esterification of ethanol with acetic, propanoic and pentanoic acids is studied. All three esterifications are slightly endothermic. The kinetic results are presented in the form of surface response plots. Relative increase in initial rates with increase in temperature depends on the steric hindrance around the carboxylic group. Ethanol feed ratios ranging from 0.3 to 0.6 exhibit the fastest initial rates. Catalyst efficiency is found to decrease significantly with increase in carboxylic acid chain length. Modified UNIFAC (Dortmund) model is used to predict system non idealities. An Eley Rideal mechanism, with surface reaction between adsorbed ethanol and acid in the bulk as the limiting step, best correlates the kinetic data.

Isothermal (vapour+liquid) equilibria for binary mixtures of diisopropyl ether with (methanol, or ethanol, or 1-butanol): Experimental data, correlations, and predictions

Abstract A glass dynamic recirculating still was employed for the measurement of isothermal (vapour + liquid) equilibrium (VLE) data for the binary mixtures of diisopropyl ether (DIPE) + alcohol, viz. (DIPE + methanol), (DIPE + ethanol), and (DIPE + 1-butanol) at T = (305.15, 315.15, and 325.15) K, T = (313.15, 323.15, and 333.15) K and T = (318.15, and 338.15) K, respectively. The combined standard uncertainties in the reported system pressures, temperatures and phase compositions are ±0.2 kPa, ±0.1 K and ±0.003, respectively. Maximum pressure azeotropes were observed for all isotherms of the (DIPE + methanol) and (DIPE + ethanol) systems. The experimental results were correlated using both the γ–ϕ and ϕ–ϕ approaches. For the correlation of the VLE data with the γ–ϕ approach, the Wilson, NRTL and UNIQUAC GE models with the truncated two-term virial equation of state (Hayden and O’Connell correlation for second virial coefficient computation) were used. In the ϕ–ϕ correlation approach, the Peng–Robinson equation of state was used with the Wong–Sander mixing rules incorporating the same GE models used in the γ–ϕ approach. Comparisons between the experimental values and predictions using UNIFAC (Dortmund) and the Predictive Soave–Redlich–Kwong (PSRK) model were performed to test the predictive capabilities of these models for the experimental data measured here. The thermodynamic consistency of the experimental data was checked with the Herington area test.

Isothermal vapor–liquid equilibria and excess Gibbs free energies in some binary nitroalkane + chloroalkane mixtures at temperatures from 298.15 K to 318.15 K

The vapor pressures of binary mixtures of cloroalkane (1-chlorobutane, 1-chloropentane)+nitromethane or nitroethane were measured at temperatures between 298.15K and 318.15K. The vapor pressures vs. liquid phase composition data have been used to calculate the activity coefficients of the two components, and the excess molar Gibbs energies GE for the mixtures, using Barker's method. Redlich–Kister, Wilson, NRTL and UNIQUAC equations, taking into account the vapor phase imperfection in terms of the 2-nd virial coefficient, have represented the GE values. No significant difference between GE values obtained with these equations has been observed. The results indicate that all the systems show positive deviations from Raoult's law. The experimental VLE data were analyzed in terms of the modified UNIFAC (Dortmund) model.

Ternary liquid–liquid phase equilibria of (water–carboxylic acid–1-undecanol) systems at 298.15 K

Liquid–liquid equilibrium (LLE) data for the ternary systems of (water–formic acid–1-undecanol), (water–acetic acid–1-undecanol), (water–propionic acid–1-undecanol), (water–butyric acid–1-undecanol), and (water–valeric acid–1-undecanol) were investigated at 298.15K and atmospheric pressure. Complete phase diagrams were obtained by determining solubility and tie-line data. The tie-line data were compared with the results predicted by the UNIFAC, modified UNIFAC (Dortmund), and modified UNIFAC (Lyngby) methods and correlated by means of UNIQUAC model. The reliability of the experimental tie-line data was confirmed by using the Othmer–Tobias correlation. Distribution coefficients and separation factor values were evaluated for the immiscibility region.

Product Separation after Chemical Interesterification of Vegetable Oils with Methyl Acetate. Part I: Vapor–Liquid Equilibrium

Chemical interesterification of triglycerides with methyl acetate yields biodiesel and triacetin. This reaction is highly reversible, which implies the presence of intermediate compounds such as diacetinmonoglycerides. In addition, the use of methanolic potassium methoxide as the catalyst causes the appearance of diacetin, monoacetin, and glycerol. Vacuum distillation becomes an interesting alternative for the separation of biodiesel and triacetin. Vapor–liquid equilibrium (VLE) determination requires information related to the vapor pressures of the different compounds and the nonideality of the liquid phase (activity coefficients). The lack of literature information for some compounds was supplemented with experimental data and predictive models for vapor pressure and activity coefficients (UNIFAC and UNIFAC Dortmund). The suitability of using vacuum distillation was evaluated using the Fenske equation and experimental results from a structured packed distillation column. According to the results, removal of diacetinmonoglycerides can be easily accomplished, unlike the elimination of diacetin, monoacetin, and glycerol, which form azeotropes with triacetin.

Thermodynamic Modeling of Ionic Liquid Systems: Development and Detailed Overview of Novel Methodology Based on the PC-SAFT

We present the results of an extensive study on a novel approach of modeling ionic liquids (ILs) and their mixtures with molecular compounds, incorporating perturbed-chain statistical associating fluid theory (PC-SAFT). PC-SAFT was used to calculate the thermodynamic properties of different homologous series of ILs based on the bis(trifluormethylsulfonyl)imide anion ([NTf2]). First, pure fluid parameters were obtained for each IL by means of fitting the model predictions to experimental liquid densities over a broad range of temperature and pressure. The reliability and physical significance of the parameters as well as the employed molecular scheme were tested by calculation of density, vapor pressure, and other properties of pure ILs (e.g., critical properties, normal boiling point). Additionally, the surface tension of pure ILs was calculated by coupling the PC-SAFT equation of state with density gradient theory (DGT). All correlated/predicted results were compared with literature experimental or simulation data. Afterward, we attempted to model various thermodynamic properties of some binary systems composed of IL and organic solvent or water. The properties under study were the binary vapor-liquid, liquid-liquid, and solid-liquid equilibria and the excess enthalpies of mixing. To calculate cross-interaction energies we used the standard combining rules of Lorentz-Berthelot, Kleiner-Sadowski, and Wolbach-Sandler. It was shown that incorporation of temperature-dependent binary corrections was required to obtain much more accurate results than in the case of conventional predictions. Binary corrections were adjusted to infinite dilution activity coefficients of a particular solute in a given IL determined experimentally or predicted by means of the modified UNIFAC (Dortmund) group contribution method. We concluded that the latter method allows accurate and reliable calculations of bulk-phase properties in a totally predictive manner.

Phase equilibrium properties of the ternary mixture dibutyl ether + toluene + heptane at 313.15 K

New accurate vapour liquid equilibrium data for the ternary mixture formed by dibutyl ether (DBE), toluene and heptane at 313.15K have been measured. A static method using an isothermal total pressure cell (Van Ness’ technique) has been employed. The system studied presented a slight deviation from ideal behaviour. Reduction of the experimental data has been done by Barker's method using Wohl expansion, NRTL, Wilson and UNIQUAC equations. Moreover, experimental results have been compared to predictions for the ternary system obtained from the Wilson, NRTL, UNIQUAC and UNIFAC (Dortmund) models.

Analysis of Predictive Thermodynamic Models for Estimation of Polycyclic Aromatic Solid Solubility in Hot Pressurized Water

The ability of two thermodynamic approaches to predict the solubility of solid compounds in hot pressurized water is studied and compared. The Regular Solution Theory, based on the solubility parameter concept, and UNIFAC- based models were applied to calculate the solute activity coefficient and then, solubility predictions were compared with experimental data reported in the literature. The analysis was carried out considering polycyclic aromatic hydrocarbons as model substances, i.e. substances which contain only the aromatic AC and ACH groups, and for which reliable pure physical properties such as melting point, fusion enthalpy and molar volume are available in the literature. The solubility values predicted with the UNIFAC-based models were considerably better than those obtained with the solubility parameter approach. Particularly, the modified Dortmund UNIFAC model presented an appropriate functionality of solubility with temperature, and the extension of this model to other type of aromatic compounds also provided a satisfactory prediction of solubility data.

Thermodynamics and transport properties of citral

In this work, transport and thermodynamic properties of mixtures of n-hexane with the aldehydes citral, citronellal and dihydrocitronellal, important to the fine chemicals industry, were determined experimentally and compared to theoretical predictions. Liquid binary diffusion coefficients were measured using the Taylor dispersion technique at various temperatures. The Wilke-Chang correlation gave precise approximations. The second part of this work is concerned with the gas-liquid phase equilibrium of citral/n-hexane. The mixture is slightly nonideal and may be sufficiently described by applying the modified UNIFAC (Dortmund) group contribution method. © 2011 American Institute of Chemical Engineers AIChE J, 58: 2557–2562, 2012

Introduction of the amine group at cycloaliphatic hydrocarbon (c-CHNH 2) for the modified UNIFAC (Dortmund) model and validation in multicomponent systems containing cyclohexylamine

The group interaction parameters for modified UNIFAC (Dortmund) of the newly defined amine group at cycloaliphatic hydrocarbon occurring for example in cyclohexylamine with six established groups were determined using binary data available from literature and new experimental data presented in this paper. The calculations of binary and ternary systems are compared to the predictions using the amine group at aliphatic hydrocarbon. The liquid–liquid and vapour–liquid equilibria of the quaternary system water + toluene + aniline + cyclohexylamine were determined at two temperatures, each, and predicted with mod. UNIFAC (Do) using the new group interaction parameters. Furthermore, the predictions for the ternary and quaternary systems with mod. UNIFAC (Do) are compared to the predictions with NRTL, UNIQUAC, and Elliott–Suresh–Donohue equation of state using binary interaction parameters.

Solid–liquid equilibrium data for the binary system methacrylic acid + methanol in the high methacrylic acid concentration range

Experimental solid–liquid equilibrium (SLE) data for the binary system methacrylic acid–methanol in the high concentration range of methacrylic acid were obtained and correlated using several methods. The heat of solution of methacrylic acid was obtained from the results. Several methods of determination of SLE categorized into two kinds of activity coefficient treatments were also studied. The former methods were the modified UNIFAC (Dortmund) model and the calculation from solubility parameters under regular solution assumption using predicted activity coefficients. The later were the NRTL equation and the λ h equation estimating the heat of solution and activity coefficients directly by fitting the experimental SLE data. Based on the results, the recommended method of determination for this system was discussed.

Selection of entrainers for the separation of the binary azeotropic system methanol + dimethyl carbonate by extractive distillation

The objective of this study is the selection of a suitable entrainer for the separation of the binary azeotropic mixture, namely methanol + dimethyl carbonate (DMC) by extractive distillation. In this study, 2-ethoxyethanol and 4-methyl-2-pentanone were considered as entrainer candidates for the separation of methanol and DMC. Isobaric vapor–liquid equilibria (VLE) were measured for the ternary mixtures methanol + DMC + 2-ethoxyethanol and methanol + DMC + 4-methyl-2-pentanone, and for their constituent binary mixtures, under reduced pressures of 66.66 kPa and 93.32 kPa. Experimental VLE data for the constituent binary mixtures were represented by the Wilson and the NRTL model. The VLE predictions for two ternary mixtures were compared with the experimental VLE data on the basis of the Wilson or NRTL parameters obtained from the constituent binary VLE data. The modified UNIFAC (Dortmund) model was also used for the prediction of the binary and ternary mixtures. The solvent effects of the two entrainer candidates investigated are discussed using the predicted results for the ternary mixtures and both 2-ethoxyethanol and 4-methyl-2-pentanone were found to be suitable entrainers for the separation of methanol and DMC. When the selectivity of 2-ethoxyethanol and 4-methyl-2-pentanone are compared, it could be concluded from the separation factors that 4-methyl-2-pentanone shows a higher selectivity.

Ebulliometric determination and prediction of (vapor + liquid) equilibria for binary and ternary mixtures containing alcohols (C 1–C 4) and dimethyl carbonate

(Vapor + liquid) equilibrium (VLE) data for a ternary mixture, namely {methanol + propan-1-ol + dimethyl carbonate (DMC)}, and four binary mixtures, namely an {alcohol (C 3 or C 4) + DMC}, containing the binary constituent mixtures of the ternary mixture, were measured at p = (40.00 to 93.32) kPa using a modified Swietoslawski-type ebulliometer. The experimental data for the binary systems were correlated using the Wilson model. The Wilson model was also applied to the ternary system to predict the VLE behavior using parameters from the binary mixtures. The modified UNIFAC (Dortmund) model was also tested for the predictions of the VLE behavior of the binary and ternary mixtures. In addition, the experimental VLE data for the ternary and constituent binary mixtures were correlated using the extended Redlich–Kister (ERK) model, which can completely represent the azeotropic points. For the ternary system, a comparison of the experimental and the predicted or correlated boiling points obtained using the Wilson and ERK models showed that the ERK model is more accurate. The valley line, i.e., the curve which divides the patterns of vapor–liquid tie lines, was found in the (methanol + propan-1-ol + DMC) system. This valley line could be represented by the ERK model. Finally, the composition profile for simple distillation of this ternary mixture was obtained by analysis of the residue curves from the estimated Wilson parameters of the constituent binary mixtures.

Experiment based model development for the enzymatic hydrolysis in a packed-bed reactor with biphasic reactant flow

A systematic experiment based development of a kinetic model for the immobilized lipase (Novozym 435) catalyzed hydrolysis of a short-chain fatty acid methyl ester mixture in a biphasic organic–aqueous system was conducted. It included kinetic experiments to find the influence of the operating conditions on the reaction rate, the examination of the catalyst wetting and of the liquid–liquid phase behavior, as well as the formulation of an integral mathematical model for the used packed-bed reactor assembly. From experiments it was found that the initial reaction rate was independent of the total water content and directly proportional to the catalyst to organic phase mass ratio. The produced fatty acids and methanol reduced the reaction rate reversibly. During the experiments no negative impact on the enzyme activity was observed for temperatures <65 °C. The organic phase retained in the particle pores and around the particle prevented the aqueous phase from penetrating it. The influence of the aqueous phase pH-value on the reaction rate was negligible. A good description of the liquid–liquid phase behavior was obtained from a UNIFAC (Dortmund) and literature data based UNIQUAC model. For the reaction rate and the chemical equilibrium activity based expressions were chosen. The very good consistency of the resulting kinetic model with the experimental data confirmed the ability of the chosen approach to elucidate the relationships between the singular effects simultaneously occurring in the reaction system.

Vapor–liquid equilibria of ternary systems with 1-ethyl-3-methylimidazolium ethyl sulfate using headspace gas chromatography

Vapor–liquid equilibria (VLE) for two binary systems 1-propanol + water and methyl acetate + methanol, and the ternary mixtures with the ionic liquid 1-ethyl-3-methylimidazolium ethyl sulfate [EMIM] +[EtSO 4] − as entrainer were measured by headspace gas chromatography. From the experimental VLE data, the influence of the ionic liquid on the separation factors was investigated. The experimental results for the ternary systems show that [EMIM] +[EtSO 4] − has a great influence on the separation factors of the systems investigated. Furthermore, the experimental separation factors were compared with the predicted ones of other ionic liquids and conventional selective solvents using modified UNIFAC (Dortmund).

The solid–liquid phase diagrams of binary mixtures of even saturated fatty alcohols

This study is part of a work developed in the author's research group on the solid–liquid equilibrium of fatty substances. The phase diagrams of the following fatty alcohol systems were determined by differential scanning calorimetry (DSC): 1-octanol+1-dodecanol, 1-octanol+1-tetradecanol, 1-decanol+1-tetradecanol, 1-decanol+1-hexadecanol and 1-dodecanol+1-octadecanol. The liquidus lines of three of these systems were previously reported in the literature but the other two systems were never published. Moreover other transitions, in addition to the eutectic temperature, were also detected in all the systems. A region of solid solution at the extreme left of the phase diagrams was observed for all the binary mixtures. Polarized light microscopy was used to complement the characterization of the systems for a full grasp of the phase diagrams. The solid–liquid equilibrium was modeled using the Margules 2-suffix, Margules 3-suffix, NRTL and UNIFAC Dortmund equations.

Phase equilibria of (water–carboxylic acid–diethyl maleate) ternary liquid systems at 298.15 K

Liquid–liquid equilibrium (LLE) data for the ternary systems of (water–formic acid–diethyl maleate), (water–acetic acid–diethyl maleate), (water–propionic acid–diethyl maleate), (water–butyric acid–diethyl maleate), and (water–valeric acid–diethyl maleate) were investigated at 298.15K and atmospheric pressure. Complete phase diagrams were obtained by determining solubility and the tie-line data. The tie-line data were compared with the results predicted by the UNIFAC and the modified UNIFAC (Dortmund) methods and correlated by means of UNIQUAC model. The reliability of the experimental tie-line data was confirmed by using the Othmer–Tobias correlation. Distribution coefficients and selectivity were evaluated for the immiscibility region.

Liquid−Liquid(−Liquid) Equilibria in Ternary Systems of Aliphatic Hydrocarbons (Heptane or Octane) + Phenols + Water

The liquid−liquid equilibria (LLE) and liquid−liquid−liquid equilibria (LLLE) in eight ternary systems were determined by photometric turbidity titration at atmospheric pressure. Additionally, the compositions of coexisting phases were determined with analytic methods. The measurements in the systems heptane or octane + phenol + water were realized at temperatures of (313.15 and 333.15) K. The equilibrium data in the systems heptane + 2-cresol or 3-cresol or 4-cresol + water and octane + 2-cresol or 3-cresol or 4-cresol + water were estimated at temperatures of (298.15 and 323.15) K. The excess Gibbs energy nonrandom two-liquid (NRTL) and universal quasichemical (UNIQUAC) activity coefficient models as well as the Elliott−Suresh−Donohue equation of state (ESD EoS) were used to predict the LLE or LLLE in the investigated ternary systems. The binary interaction parameters were calculated using vapor−liquid and LLE data from the literature or data predicted with the modified universal quasichemical functional-group activity coefficient (UNIFAC Dortmund) model.

Thermodynamics of mixtures containing oxaalkanes. 5. Ether + benzene, or +toluene systems

Linear or cyclic ether + benzene or +toluene mixtures have been investigated in terms of the DISQUAC and UNIFAC (Dortmund version) models as well as using the Kirkwood–Buff formalism. The corresponding DISQUAC interaction parameters are reported. The QUAC interaction parameters are independent of the aromatic compound, and those for l = 1 (Gibbs energy) and l = 3 (heat capacity) are also independent of the ether. DISQUAC correctly describes a whole set of thermodynamic properties of these systems: vapour–liquid equilibria, VLE, solid–liquid equilibria, SLE, molar excess enthalpy, H m E , molar excess isobaric heat capacity, C pm E , and Kirkwood–Buff integrals. DISQUAC improves meaningfully UNIFAC H m E results, which remarks that the accurate description of this property is difficult when proximity effects or cyclization are present. From values of the molar excess enthalpies at infinite dilution obtained from H m E data available in the literature, it is concluded that the increase of the number of –O– atoms in the ether or cyclization leads to stronger interactions between unlike molecules. Values of the Kirkwood–Buff integrals and of linear coefficients of preferential solvation reveal that the structure of the investigated systems is close to random mixing.