The Modelling of Thermodynamically Difficult Systems

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9521406 Sandler Experimental measurements are very time consuming, and it is not practical to measure the thermodynamic properties and phase behavior of all substances and mixtures, that are of importance for chemical and pharmaceutical processing, for environmental and safety engineering, and for other aspects of chemical processing. Therefore, it is important to have accurate prediction or at least correlation methods. This proposal deals with research on the development of predictive models the thermodynamical properties and phase equilibria of industrially important, but complex mixtures. Three different types of mixtures will be considered: hydrogen-bonding fluids, protein solutions and colloidal systems. Hydrogen-bonding fluids are poorly described by current group contribution methods as documented in this proposal. The reason is that the extent and strength of hydrogen bonding is strongly influenced by functional groups on a molecule adjacent to the hydrogen-bonding groups. We have shown this both experimentally and from ab initio quantum mechanics calculations. We are now proposing to develop a new generation of prediction methods based on a combination of group contribution methods for the generalizable dispersive forces, and molecule-specific quantum chemistry calculations for hydrogen bonding. Protein solutions and their purification are important in many bio-processing applications. The research being proposed here involves the use of molecular thermodynamic and statistical mechanical modeling and computer simulation to develop predictive models for the partitioning of proteins in aqueous two-phase systems and for protein precipitation. Colloids lie between the macroscopic and microscopic regimes of matter, and are of interest because their behavior influences many emerging technologies in chemical, biochemical, and pharmaceutical processing. There are two scales of phase behavior in liquid-in-liquid colloidal systems. At the macroscale is liquid-liquid phase separation, or macroscopic phase equilibrium. The microscale behavior is the formation of microstructures in some (or all) of the separated phases. Many important characteristics of liquid colloids are dictated by the microstructures that form. However, to investigate the microstructure, one first needs to have an understanding of the macroscopic phase behavior as this identifies the phase boundaries within which microstructures are formed. Thermodynamic modeling of such systems has been rather simple, and has not captured the temperature and pressure dependence of the macroscopic phase boundaries of liquid colloidal systems. Here we are proposing research on the modeling of macroscopic phase behavior of liquid-in-liquid colloids using modern thermodynamic methods to provide a more accurate description of the changes in the macroscopic phase boundaries of colloidal systems with variations in temperature, pressure and composition. ***