Thermodynamic modeling of aqueous systems containing amines and amine hydrochlorides: Application to methylamine, morpholine, and morpholine derivatives

Abstract A comprehensive thermodynamic model has been developed for calculating phase equilibria and speciation in aqueous mixtures containing neutralizing amines and corresponding amine hydrochlorides. The model has been designed to simulate the behavior of refinery overhead environments, in which the presence of amines in combination with hydrogen chloride may lead to the formation of potentially corrosive solid or concentrated aqueous amine hydrochloride phases. For this purpose, the previously developed Mixed-Solvent Electrolyte (MSE) model has been extended to calculate simultaneously solid–gas, solid–liquid, and vapor–liquid equilibria, liquid-phase chemical equilibria, and caloric properties. In the model, standard-state properties of individual species are calculated from the Helgeson–Kirkham–Flowers equation of state whereas the excess Gibbs energy includes a long-range electrostatic interaction term expressed by a Pitzer–Debye–Huckel equation, a virial coefficient-type term for interactions between ions and a short-range term for interactions involving neutral molecules. This framework accurately represents the properties of systems that range from weak electrolytes, such as amine – water mixtures, to strong electrolytes such as amine hydrochloride – water solutions. For amine hydrochlorides, the model is applicable up to the limit of solid or fused liquid hydrochloride phases. Model parameters have been developed for methylamine, morpholine, N-methylmorpholine, N-ethylmorpholine and their hydrochlorides. The model offers the possibility of understanding the formation of amine hydrochlorides in multicomponent mixtures containing amines, water, hydrogen chloride, and carbon dioxide.