Some new frontiers in chemical engineering thermodynamics

Abstract

The history of chemical engineering thermodynamics shows that its main concern has been development and extension of concepts and ideas that physicists and physical chemists have proposed in only general terms. For example, van der Waals proposed his theory of fluids in 1873 but its use for chemical engineering came only later, starting in the nineteen twenties, when MIT's Warren K. Lewis (and others) developed the generalized charts that we find today in Perry's Handbook and in undergraduate chemical engineering textbooks. Extension of van der Waals' theory remains a topic of active interest as indicated, for example, in the recent mixing rules of Wong and Sandler which significantly improve calculation of high-pressure phase equilibria for practical process design. A variety of recent concepts from physics and physical chemistry is now under active development by chemical engineering researchers. Examples include the integral theory of fluids, polymer equilibria, molecular simulation with computers, density functional theory, the theory of electrolytes, fluctuation theory and the properties of fluids under unusual conditions such as the critical region and the metastable state which contains supercooled fluids at negative pressures. Some of these topics are discussed at this symposium. In every case, remarkable progress has been made toward achieving a better understanding of the properties of matter. That understanding, in turn, is useful not only for better design of chemical processes, but also for discovering novel techniques for making new chemical products. Following a short introduction of these new developments, attention is given to an outline of progress in three areas under active investigation at Berkeley. The first area concerns phase equilibria in mixtures of polymers with solvents or with other polymers; the main focus is directed at liquid-liquid equilibria which are more difficult to describe than vapor-liquid equilibria. The basis of this description is a perturbation theory where the reference system is an equation of state for athermal chains based on a Percus-Yevick solution of the Ornstein-Zernike equation coupled with the restraint of chain connectivity. This perturbation theory can describe experimental data for systems with upper or lower consolute temperatures, or both, including closed-loop diagrams. The second area concerns the properties of polyelectrolyte hydrogels in contact with aqueous solutions. Here emphasis is on experimental studies of swelling properties with semi-quantitative description based on polymer-network elasticity and Donnan equilibria. The third area concerns selective precipitation of globular proteins from aqueous solution using a salt as the precipitating agent. A theoretical description, similar to that used for colloidal solutions, requires fundamental experimental data (e.g. osmotic virial coefficients) obtained by light-scattering and osmometry. For a given solution of proteins, this theory can identify not only the conditions that are required for precipitation (pH, concentration and nature of salt) but also the expected degree of protein separation.