An investigation of saturated vapor pressure regarding low-volatility organophosphorus extractants Di-(2-ethylhexyl) phosphoric acid and tributyl phosphate: Correlation and thermodynamics study

New saturated vapor pressure (psat) data of organophosphorus extractants, di-(2-ethylhexyl) phosphoric acid (D2EHPA) and tributyl phosphate (TBP), were investigated in T = (383.8-546.2) K and psat = (0.13-6.67) kPa using vacuum distillation method. The data was found to be a good fit with Antoine, August, Riedel and Wagner equation. Regression constants prove to be very useful in estimating psat at operating temperature. Intermolecular hydrogen bonding affected D2EHPA having lower psat in comparison with TBP. Thermodynamic properties of both molar enthalpy and molar entropy of vaporization were obtained using the Clausius-Clapeyron equation. As temperature increased, molar enthalpy and molar entropy of vaporization decreased showing a positive deviation from Trouton's rule. Using the relations of molar enthalpy and temperature, saturated liquid heat capacity was obtained. All data can be usefully employed for the design of a distillation column or evaporator for recycling of both extractants from organic wastewater.