The Gibbs–Helmholtz Equation and the Thermodynamic Consistency of Chemical Absorption Data

Abstract

The Gibbs–Helmholtz (G-H) equation connects vapor–liquid equilibrium (VLE) and calorimetric data. If experimental measurements for the heat of solution are not available, they may be estimated through the G-H equation. Further, if both VLE and heat-of-solution data are available, their mutual thermodynamic consistency can be evaluated through the G-H equation, to develop the most accurate and reliable model. This kind of analysis is particularly useful for chemical-absorption systems, such as the capture of CO2 using aqueous solutions of amines, where regeneration energies are significant. In this work, the G-H equation is derived to unambiguously relate the commonly used form to the rigorous and general form, including for systems where phase equilibrium is accompanied by chemical reactions in any phase. The effect of approximations and the range of applicability of the common G-H equation are first applied to data generated for a simple VLE system by an equation of state, with different reliability foun...