UNIFAC Dortmund Research Articles

Solid−Liquid Equilibria of Viscous Binary Mixtures with Alcohols

Solid−liquid equilibria of the following 11 alcohol systems have been measured by the visual method: cyclohexanol + dodecane, cyclohexanol + cyclohexane, cyclohexanol + benzene, cyclohexanol + tetrachloromethane, 1-butanol + water, 2-butanol + water, 2-methyl-1-propanol + water, 2-pentanol + tetrachloromethane, 1-pentanol + cyclohexane, 2-pentanol + cyclohexane, and 3-pentanol + cyclohexane. For all systems, with the exception of the system cyclohexanol + cyclohexane, eutectic behavior is assumed. With the visual technique not all systems can be determined over the whole concentration range because the mixtures become very viscous at low temperatures and high alcohol concentrations. Therefore the systems cyclohexanol + benzene, 2-butanol + water, and 2-pentanol + cyclohexane were also studied by an analytical method, which is introduced in this paper. The experimental data of the eutectic systems were compared with predicted values using the modified UNIFAC (Dortmund) group contribution method.

Estimation of Enthalpies of Fusion, Melting Temperatures, Enthalpies of Transition, and Transition Temperatures of Pure Compounds from Experimental Binary Solid−Liquid Equilibrium Data of Eutectic Systems

This paper presents a procedure for the estimation of enthalpies of fusion, melting temperatures, enthalpies of transition, and transition temperatures using experimental binary solid−liquid equilibrium data of eutectic systems and the group contribution method modified UNIFAC (Dortmund) for the calculation of the required activity coefficients. Additionally, experimental solid−liquid equilibrium data of the system tetrachloromethane + m-xylene are presented.

Measurement and Prediction of Ternary Solid−Liquid Equilibria

Solid−liquid equilibria (SLE) and liquidus lines for the ternary systems cyclohexane + benzene + 2-heptanone and acetonitrile + benzene + chloroform were determined by means of the synthetic visual method. The phase diagrams are represented in different graphical forms. The experimental SLE data were compared with results obtained by the modified UNIFAC (Dortmund) method. The prediction of ternary solid−liquid equilibria with the help of a reliable group contribution method is a suitable way for choosing selective solvents for extractive crystallization processes. A model comparison (original UNIFAC, modified UNIFAC (Dortmund), modified UNIFAC (Lyngby), and ASOG) for the prediction of about 325 ternary SLE systems taken from the Dortmund Data Bank shows superior results for mod. UNIFAC (Do) in comparison to the other methods.

Measurement of Activity Coefficients at Infinite Dilution Using Gas−Liquid Chromatography. 6. Results for Systems Exhibiting Gas−Liquid Interface Adsorption with 1-Octanol

Activity coefficients at infinite dilution provide a useful tool for solvent selection in extractive distillation or extraction processes. In this work activity coefficients at infinite dilution for various solutes (alkanes, cycloalkanes, alcohols, aromatic hydrocarbons, xylenes and alkenes) in the solvent 1-octanol were measured at four temperatures, (293.44, 303.45, 313.55, and 323.43) K, with the help of gas−liquid chromatography. The adsorption at the gas−liquid interface between the solutes and the solvent was examined by varying the solvent liquid loading in the columns. Corrected retention values taking adsorption effects into account are determined and are used to calculate the activity coefficients at infinite dilution. These values compare well with various activity coefficients taken from the literature using different techniques and the predicted values using the modified UNIFAC (Dortmund) method. An important application of the present data can be seen in the use of 1-octanol as a solvent for processes such as extractive distillation or extraction. It is sufficient to know the separation factor at infinite dilution of the components to be separated in order to determine the applicability of 1-octanol as a selective solvent.

Solubility of long-chain n-alkanols in dipropyl and dibutyl ether

Solubility of the following 1-alkanols (1-dodecanol, 1-tridecanol, 1-tetradecanol, 1-pentadecanol, 1-hexadecanol and 1-octadecanol) in dipropyl ether or dibutyl ether are reported. They have been measured by the dynamic method from a temperature close to 0°C up to the melting point. All systems exhibit positive deviations from ideal solubility. For all the alcohols, two transition points close to the melting temperature have been observed. The abilities of the Modified UNIFAC (Dortmund) and the DISQUAC models to predict these data have been tested.

Application of the extended real associated solution model to predict thermodynamic properties of n-alcohol + linear monoether mixtures

Applicability of the extended real associated solution (ERAS) model to describe and predict properties of n-alcohol + unbranched monoether mixtures has been tested. Two versions of the model have been applied: its original, developed by Heintz [1] and a modified form, reported recently by Hofman and Casanova [2]. The basic assumption states that the purely physical contribution to the model should be meaningless. The model has three adjustable parameters which are common for all the mixtures considered. It has been applied to predict H E, V E and VLE data. The modified version gives acceptable results which for the non-volume properties are similar to those predicted by the Modified UNIFAC (Dortmund) using six parameters. The original ERAS model turned out to be inadequate.

Isothermal Vapor−Liquid Equilibria of 2-Methoxy-2-methylbutane (TAME) + n-Alcohol (C1−C4) Mixtures at 323.15 and 333.15 K

Ether mixtures containing oxygen in their body such as 2-methoxy-2-methylbutane (tert-amyl methyl ether; TAME) and 2-methoxy-2-methylpropane (methyl tert-butyl ether; MTBE) are used as octane boosters for lead-free or low-leaded gasoline because of their octane-enhancing and pollution-reducing capabilities. In this work, isothermal vapor−liquid equilibrium was measured by headspace gas chromatography, one of the static methods, for TAME + n-alcohol (C1−C4) binary mixtures at 323.15 and 333.15 K. The binaries showed positive deviations from Raoult's law and have minimum boiling azeotropes, except for TAME + 1-butanol. Results were correlated with GE model equations and also compared with the values predicted by modified UNIFAC (Dortmund).

Fluid phase equilibria modified UNIFAC application to thermodynamic properties of binary mixtures containing sulfolane

The data available in the literature and our new experimental data of vapour-liquid equilibrium (VLE), molar excess enthalpies, H E, solid-liquid equilibrium (SLE) and activity coefficients at infinite dilution, γ i ∞, for mixtures of different organic solvents with sulfolane are examined on the basis of the group contribution model, modified UNIFAC (Dortmund). New interchange coefficients for various groups/sulfolane contacts, a mn and a nm , of the modified UNIFAC were optimized. The model describes consistently the excess functions G E, H E and ln γ i ∞ of most of the experimental data (VLE and SLE).

Solid-liquid equilibria in binary mixtures of organic compounds

Solid-liquid phase equilibria for the systems idane/nitrobenzene, indane/1,2-dichloroethane, indane/1,4-dioxane, ndane/dodecane, acenaphthene/1,4-xylene, tetrachloromethane/2-dodecanone, tetrachloromethane/2-undecanone, 1,2-xylene/1,3-xylene, 1,4-xylene/1,3-xylene, and 1,2-xylene/1,4-xylene were measured visually using the synthetic method. The measured systems were calculated by means of the group contribution method UNIFAC and modified UNIFAC (Dortmund). If necessary, solid-solid transitions were taken into account in the calculations. The systems selected are of technical interest and can also be used for checking and the further development of the group contribution method modified UNIFAC (Dortmund).

Infinite-dilution activity coefficients by comparative ebulliometry: Measurements and group contribution calculations for some binary mixtures ether + n-alkane and ether + alcohol

Infinite-dilution activity coefficients γ i ∞ were measured for 33 solute-solvent pairs of the type ether + n-alkane and ether + alcohol using the comparative ebulliometry technique. The experimental results were compared with the values obtained by two group contribution models, DISQUAC and modified UNIFAC (Dortmund).

Excess enthalpies and excess heat capacities of the ternary system ethanol + N,N-dimethylformamide + tetrahydrofuran at 298.15 K

Excess enthalpies and excess heat capacities at 298.15 K for the ternary system ethanol + dimethylformamide + tetrahydrofuran were determined by means of a flow calorimetric apparatus built in our laboratory. Experimental data were described with a Redlich-Kister type equation and compared with those of other ternary systems previously studied (ethanol + tetrahydrofuran + cyclohexane, ethanol + dimethylformamide + cyclohexane, dimethylformamide + tetrahydrofuran + cyclohexane). A peculiar behaviour was observed for mixtures containing dimethylformamide, namely the negative values of both H E and C p E ternary contributions. A satisfactory prediction of experimental H E data is provided by the UNIQUAC model, while UNIFAC (Dortmund, Germany) clearly fails probably owing to an unsufficient definition of interaction parameters involving dimethylformamide.

A modified UNIFAC model. 2. Present parameter matrix and results for different thermodynamic properties

Several years ago a modified UNIFAC (Dortmund, FRG) method was proposed, which shows various advantages when compared with the group contribution methods UNIFAC or ASOG; the latter are used worldwide for the synthesis and design of rectification processes. These advantages were reached by using a modified combinatorial part and by using a large data base to fit temperature-dependent group interaction parameters simultaneously to vapor-liquid equilibrium (VLE), liquid-liquid equilibrium (LLE), h E , and γ ∞ data. The main advantages of the modified UNIFAC method are a better description of the temperature dependence and the real behavior in the dilute region and that it can be applied more reliably for systems involving molecules very different in size. To increase the range of this applicability, the temperature-dependent group interaction parameters of the modified UNIFAC has been fitted for 45 main groups using phase equilibrium information (VLE, h E , γ ∞, LLE) stored in the Dortmund Data Bank. A comprehensive comparison with the results of other group contribution methods confirms the high reliability of the modified UNIFAC (Dortmund) method