Modelling of chemical processes and materials by free energy minimisation: Additional constraints and work terms: Dissertation

Chemical equilibrium thermodynamics has found numerous application areas in diverse fields such as pyrolysis and combustion, metallurgy, petrochemistry, the pulp and paper industry, the study of advanced inorganic materials, environmental science and biochemistry. As many of the cases of interest are not actually in equilibrium, there is a need for methods that extend the application area of multiphase chemical equilibrium solvers to non-equilibrium systems. Likewise, there is a demand for efficient handling of systems that are described by thermodynamic parameters other than those most commonly associated with Gibbs energy, namely temperature, pressure and fixed elemental (and charge) balances. In this thesis computational methods and related theory are presented that can be used with a standard Gibbs energy minimiser to solve advanced thermochemical problems. The extensions developed enable handling of systems with multiple kinds of thermodynamic work, systems with constrained reaction extents and other systems with linear constraints on composition. The actual calculations have been performed using the ChemSheet software, but the presentation has aimed to be generic and applicable with other thermochemical codes that allow the user to define thermodynamic data and the stoichiometries of the constituent species in the system. The examples discussed include the electrochemical Donnan equilibrium (particularly applied to aqueous pulp suspension), surface and interfacial energies, systems affected by external magnetic fields and systems with time-dependent reaction extents. The greatest practical success has been achieved with the models that combine reaction kinetics with partial thermodynamic equilibrium calculation and ion exchange models based on Donnan equilibrium, both of which have been applied with success in real-life industrial design and development work with multicomponent, multiphase systems. The method has also been successfully applied to liquid surface energies in systems with multiple components and complex non-ideality data.