(429a) Thermodynamics, Chemical Process Stability and Control

The basic geometric structure of the thermodynamic phase space is based on the idea that the second law of thermodynamics characterizes concave (differentiable) equilibrium manifold. The primary coordinates in phase space are determined by extensive variables, such as energy, volume and mol-numbers. The secondary variables are given by the tangent space and these correspond to intensive variables such as temperature, pressure and chemical potentials. In the past decade this geometric structure has led to different developments that relate to modeling control and optimization of chemical process systems. These include nonlinear geometric control, passive based adaptive control, energy shaping control and control of process networks using circuit theory or port-Hamiltonian descriptions.  These theories all describe how systems evolve on equilibrium manifold and the theory thereby provides a generalization of Gibbs stability theory for isolated to thermodynamically open systems. The theory has been used to show that multi-component, multi-phase and reactive equilibrium systems have stable dynamics provided suitable control strategies are applied. It has been applied to non-equilibrium reactive systems, networked systems and more generally a class of distributed parameter systems satisfying the hypothesis of local equilibrium.  Such systems include, distillation and absorption columns, tubular reactors, particulate systems and even chemical plants. The purpose of the paper is to review the basics of the theory, provide an overview of potential application domains and list outstanding problems.