Measurements of activity coefficients at infinite dilution in vegetable oils and capric acid using the dilutor technique

• Limiting activity coefficients in three refined vegetable oils were measured.
• The γi∞ data were obtained using the inert gas stripping method.
• Excess thermodynamic functions were evaluated at infinite dilution.
• Different trends for polar and nonpolar solutes could be identified.
• Experimental γi∞ data were compared with the orig. and mod. UNIFAC (Dort.) results.

This paper reports experimental activity coefficients at infinite dilution, γi∞, for methanol, ethanol and n-hexane in three refined vegetable oils (soybean, sunflower, and rapeseed oils) measured using the dilutor technique (inert gas stripping method). The measurements were carried out in the temperature range between 313.15 and 353.15 K. Furthermore, activity coefficients at infinite dilution for various solutes (acetone, methanol, ethanol, n-hexane, cyclohexane and toluene) were measured in capric (decanoic) acid using the same technique in the temperature range from 313.13 to 353.30 K. The new data obtained for capric acid and soybean oil were compared with already published experimental data. Additionally, densities of the investigated vegetable oils were measured in the temperature range from 293.15 to 353.15 K. Using the experimental γi∞ values obtained over the temperature range, the partial molar excess Gibbs energy (ΔGiE,∞), enthalpy (ΔHiE,∞) and entropy (ΔSiE,∞) at infinite dilution were determined. The relative error for the γi∞ measurements carried out using the dilutor technique is approximately ±2.5%. The measured γi∞ data in the investigated refined vegetable oils were also compared with the results of the group contribution methods original UNIFAC and modified UNIFAC (Dortmund) and an extension of the latter method to triacylglycerols was proposed.