Activity coefficients of C5 to C8 hydrocarbons in squalane and dinonyl phthalate at 30°C determined by a vacuum micro-balance technique

The activity coefficients of benzene, cyclohexane, n-pentane, n-hexane, n-heptane and n-octane in the involatile solvents, dinonyl phthalate and squalane, have been determined over a solute mole fraction range 0.05 to 0.4 at 30°C using a vacuum microbalance. The results are analysed in terms of the Flory-Huggins equation by regarding the interaction parameter as an empirical quantity dependent on the composition of the solution. Values of the solute activity coefficient at infinite dilution in the solvent are derived from the analysis for comparison with values from gas-liquid-chromatographic determinations. The technique is relatively quick compared to classical methods of determining activity coefficients of such systems and shown to be capable of good precision.