Phase Equilibrium Engineering

Abstract

It is with pleasure that I introduce the third volume in the Elsevier Book Series on Supercritical Fluid Science and Technology, Phase Equilibrium Engineering, which has been authored by Drs. Esteban Brignole and Selva Pereda from Universidad National del Sur, Argentina, with one chapter also contributed by Drs. Martin Cismondi and Marcelo S. Zabaloy from Universidad National de Co´rdoba and Universidad National del Sur, Argentina, respectively. They are all well-recognized names in the supercritical fluids and phase equilibria community. The book reflects and benefits from their many years of accumulated knowledge and practical expertise. Phase equilibrium is at the heart of chemical processes, and phase equilibrium at high pressures is a central theme in any application involving supercritical fluids. The topic becomes even more relevant when systems under consideration involve chemical transformations along a reaction coordinate which continually alter the compositional make up and thereby alter the phase equilibrium conditions. This book starts out with a clear statement of the significance of phase equilibrium in process development where there is a critical need to fill the gap between reaction and separation stages by designing and controlling the phase conditions that are essential for the success of the process. The book emphasizes the importance and the need for effective information flow along the pathways connecting the chemical plant or process to the laboratory, to the thermodynamics and phase equilibria, and to modeling and simulations. This four-node grid and their interplay form the essence of Phase Equilibrium Engineering. To provide a pedagogical development of the relevant engineering concepts, the authors start in Chapter 2 with a brief review of intermolecular forces (attractive and repulsive) and molecular interactions (dispersive, polar, electrostatic, induced dipole) that are important in phase equilibria and separation processes. Chapter 3 provides the background on thermodynamics of phase equilibrium and reviews the phase diagrams for pure substances and binary fluid mixtures within the framework of the van Konynenburg and Scott classification of the different types of phase behavior. The authors provide a clear and elegant graphical description of the changes in the binary mixture phase diagrams and the behavior of the critical lines from Type I to Type VI with changes in the size of the molecules and the nature of the molecular interactions and the energy asymmetries encountered. This chapter further provides a classification for ternary mixture phase diagrams that are based on the partial miscibility in one, two, or three of the binary pairs, which are graphically described in Gibb’s triangles. Multicomponent systems are also discussed in terms of pseudocomponents that are used to represent similar molecules. Chapter 4 is devoted to thermodynamic models and provides guidelines for selecting the appropriate model from among the various options, ranging from cubic equations of state to SAFT (Statistical Associating Fluid Theory) for different scenarios which are accomplished by using real case studies for separations of different levels of complexity. A comprehensive treatment of a methodology for general phase equilibrium calculations and generation of phase diagrams is provided in Chapter 5. Chapter 6 shifts the focus to engineering and provides a practical perspective on how the fundamental thermodynamics and phase equilibrium calculations and predictions are used in addressing complex separation processes using several case studies such as the supercritical biodiesel production process. These are continued in Chapter 7 by demonstrating how phase equilibrium engineering comes into play in distillation processes by an elegant description that makes the connections to the Type I to Type VI phase descriptions. The ethylene plant recovery section is used as a case study. In Chapter 8, discussions are extended to azeotropic mixtures and to the synthesis of solvents by computer-aided molecular design (MOLDES) to break up the azeotropes. As case studies, solvent design for recovery of aromatic fractions of reforming naphtha and high-pressure azeotropic separation of ethaneþCO2 mixtures by extractive distillation using n-butane as solvent are presented. Chapter 9 is devoted to green processes and high-pressure supercritical fluid solvents. Solvent tuning for systems displaying Type V (propaneþvegetable oil) and Type III (carbon dioxideþnatural oil) phase behavior are discussed in detail. Chapter 10 continues the discussions on the use of supercritical fluids in high-pressure fractionation and extraction of natural oils using orange oil deterpenation as a case study. Chapter 11 is devoted to reactive systems and supercritical reactors, and the phase behavior of reactive mixtures and solvents. Solvent selection strategies are discussed according to the reaction pathway using case studies such as selective hydrogenation of fatty acid methyl esters or hydrogenation of vegetable oils. Feasible or unfeasible operational regions are discussed in terms of the prevailing phase diagrams. Finally, Chapter 12 discusses how phase equilibrium engineering is used in the conceptual process design using production of biodiesel via transesterification of vegetable oil with methanol and alcohol extraction and dehydration as examples. I trust you will find this volume with its application-oriented engineering approach to be of great value and interest.