Isobaric Vapor–Liquid Equilibrium Data of Binary Mixtures of [Water + 2,3-butanediol] and [Water + 1,4-butanediol] at 40, 50, 60, 66.7, 80, and 101 kPa

Isobaric vapor–liquid equilibrium (VLE) data for two binary systems, water + 2,3-butanediol (2,3-BDO) and water + 1,4-butanediol (1,4-BDO), were gathered using a customized Othmer still VLE apparatus at various pressures (40, 50, 60, 66.7, 80, and 101 kPa). In addition, the NRTL and UNIQUAC activity coefficient models were applied to correlate the data obtained experimentally, and the parameters for these binary models were derived. The average absolute deviation of temperature (AAD_T), AAD of vapor-phase composition (AAD_y), and root-mean-square deviation values were employed to assess the agreement between the experimental results and the values calculated using the two modeling methods. The total AAD_y values for the water + 2,3-butanediol system were calculated to be 6.4 × 10^–3 (NRTL) and 2.2 × 10^–3 (UNIQUAC), and for the water + 1,4-butanediol system, the values were 2.7 × 10^–3 (NRTL) and 2.5 × 10^–3 (UNIQUAC). The reliability of the models was confirmed by the close match between the calculated and experimental data. The Van Ness-Byer-Gibbs test was conducted to evaluate the validity and thermodynamic consistency of the experimental results. The calculated values for ΔP and Δy in all systems were below 1.0, satisfying the thermodynamic consistency requirements. The information gained from this study on the vapor–liquid equilibrium behavior of the water + 2,3-butanediol and water + 1,4-butanediol systems is crucial for optimizing and designing their separation processes.