Thermodynamic Modeling of Solid–Fluid Equilibria: From Pure Solid Phases to Gas Semiclathrate Hydrates

In the field of gas hydrates, many thermodynamic models have been proposed to predict the state conditions under which gas hydrates can form or dissociate. This chapter presents the thermodynamic modeling of solid-liquid and solid-fluid equilibria with a focus on salt hydrates and semiclathrate hydrates. It discusses the expressions to solve a classical solid-liquid equilibrium problem by assuming that the solid phase is pure. The chapter then presents the modeling of solid-liquid phase equilibria in the presence of solid solutions and complex solids. It briefly explores the formalism used to write the chemical potential of species in electrolyte solutions, and discusses the phase equilibria of salt hydrates and semiclathrate hydrates. Finally, the chapter describes the working expressions of the van der Waals and Platteeuw (vdW-P) model and shows how it can be combined with the model of salt hydrate to describe the dissociation conditions of gas semiclathrate hydrates.