Activity coefficient at infinite dilution measurements for organic solutes (polar and non-polar) in fatty compounds – Part II: C18 fatty acids

In this work, activity coefficients at infinite dilution (γ13∞) have been measured for 21 solutes (subscript 1) (alkanes, cycloalkanes, alkenes, aromatic compounds, alcohols, esters, ketones, and halogenated hydrocarbons), in four solvents (subscript 3), namely one saturated fatty acid and three unsaturated fatty acids: stearic (octadecanoic) acid – C18:0, oleic (cis-9-octadecenoic) acid – C18:1 9c, linoleic (cis,cis-9,12-octadecadienoic) acid – C18:2 9c12c, and linolenic (cis,cis,cis-9,12,15-octadecatrienoic) acid – C18:3 9c12c15c, by gas–liquid chromatography. The measurements were carried out at temperatures from (303.13 to 368.19) K and the partial molar excess Gibbs free energy (ΔG1E,∞), enthalpy (ΔH1E,∞), and entropy (ΔS1E,∞), at infinite dilution were calculated from experimental γ13∞ values obtained over the temperature range. The uncertainties in determination of γ13∞ and ΔH1E,∞ are 4% and 20%, respectively. The results for stearic acid obtained in this study have been compared to those available in the Dortmund Data Bank (DDB). The real behaviour of fatty systems could be better understood through the results obtained in this work.

► Limiting activity coefficients for 21 solutes in four C18 fatty acids were measured.
► Thermodynamic functions were derived for stearic, oleic, linoleic, and linolenic acids.
► Different trends for polar and nonpolar solutes could be identified.
► The cis  -double bonds in the fatty acid alkyl chain influence the γ13∞ values.