Thermodynamic and Transport Excess Properties of Binary Mixture: Ethyl Benzoate and 2-Butanol

Abstract

Excess thermodynamic and transport properties provide critical insight into non-ideal interactions in liquid mixtures. In this work, experimental data for the binary system ethyl benzoate (X₁) + 2-butanol (X₂) were analyzed at four temperatures (303.15, 308.15, 313.15, and 318.15 K) across the entire composition range. Excess molar volume (V^E), excess isothermal compressibility (Δβ_ad), viscosity deviations (Δη), excess free length (L_f^E), excess surface tension (π^E), excess acoustic impedance (Z^E), excess enthalpy (H^E), excess Gibbs energy (G^E), and excess sound velocity (U^E) were derived from measured densities, viscosities, surface tensions, and sound velocities. The results show predominantly negative V^E and Δη across the composition range, indicating strong molecular interactions and structural rearrangements due to unlike molecular attraction and hydrogen bonding between the hydroxyl group of 2-butanol and the ester group of ethyl benzoate. With increasing temperature, magnitudes of excess functions decrease, reflecting the weakening of intermolecular interactions at higher thermal energy. All excess quantities were fitted to Redlich–Kister polynomials, providing correlation coefficients suitable for modelling and process design. Trends were discussed in terms of mixture molecular size disparity and association effects, compared to similar ester-alkanol systems reported in previous literature. Overall, the results contribute valuable data to the literature on ester–alcohol mixtures and offer deeper insight into molecular interaction mechanisms. The findings are expected to be useful for process design, solvent formulation, and theoretical modelling in chemical and pharmaceutical industries.