The knowledge of activity coefficients at infinite dilution (γ ∞ ) are of particular importance for the synthesis, design, and optimization of separation processes because the largest separation effort is required to remove the last traces of impurities. Furthermore, reliable γ ∞ values are required to select selective solvents (entrainers) for separation processes such as extractive distillation, extraction, and so forth or to check for separation problems (azeotropic points and miscibility gaps). Various experimental techniques for the determination of limiting activity coefficients in pure solvents have been developed. In this paper γ ∞ values for different hydrocarbons (n-hexane, cyclohexane, 1-hexene, and benzene) for NMP/water mixtures measured with the help of the dilutor technique in the temperature range between 30 and 60 °C are reported, which can be used to select and to optimize the selectivity and capacity for the separation of aliphatics from aromatic or alkanes from alkenes using NMP/water mixtures as the entrainer.

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.

This paper reports experimental activity coefficients at infinite dilution for 16 solutes (benzene, toluene, ethanol, esters, ketones, and ethers) at different temperatures (308 e T/K e 343) measured with the help of a dilutor technique (inert gas stripping). The activity coefficients obtained are in good agreement with data derived from LLE data. Furthermore, the partial molar excess enthalpies derived from these data are in agreement with the values derived from enthalpy of mixing data.

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