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Phase Equilibrium Diagrams

Abstract Phase equilibrium knowledge is required for the design of all sorts of chemical processes that may involve separations, reactions, fluids flow, particle micronization, etc. Indeed, different phase behavior scenarios are required for a rational conceptual process design. The aim of this chapter is to present the possible fluid mixture phase behavior that can be found in binary, ternary, and multicomponent systems. Moreover, representation of phase behavior in terms of phase diagrams is discussed. Dealing with phase diagrams of complex mixtures is not an easy task for beginners; however, very simple concepts are behind the rules for their construction. Phase diagrams are essential tools for phase equilibrium engineering as they provide valuable hints to understand the process and to assess the feasible and optimum operating regions. In this chapter, the “phenomenological” meaning of each phase behavior and its relation with molecular properties is discussed. A special attention is given to binary system phase behavior. Even though, in practice we rarely found such simple mixtures, they furnish a great deal of information for the understanding of multicomponent systems.

Phase Equilibrium Engineering Principles in Reactive Systems

Abstract The benefits of using SCF as reaction media have promoted an intense research and development activity in this field. In this chapter, several case studies demonstrate the advantages of working under supercritical conditions. In particular, gas–liquid catalyzed reactions are one of the areas where the use of supercritical fluids is very attractive. In general, these reactions are diffusion-controlled and the use of supercritical fluids increases the reaction rate by eliminating the gas–liquid interface. In this chapter also, the interesting properties of operation under near-critical conditions are analyzed: higher solubility of reactants and products in the supercritical phase, reduced deposition of reacting components on the catalyst pores, diffusion coefficients higher than in liquids, independent control of the concentration of permanent gases like H 2 , O 2 , or CO in the reaction mixture, higher thermal capacity, and low interfacial tension The hydrogenation of low volatile liquids, using solid–fluid heterogeneous catalysts, is presented to show the advantages of working under supercritical conditions. In this case study, the selection of the process conditions that guarantees operation under a supercritical single-phase state is discussed as a typical phase equilibrium engineering problem. Finally, for reactions in which the SCF plays a role not only as solvent but also as a reactant, the problem of phase condition design and cosolvent selection is addressed.

Separation of Azeotropic Mixtures

Abstract In this chapter, two well-known separation processes are introduced: homogeneous and heterogeneous azeotropic distillation. Since these technologies are reviewed in many separation process textbooks, the aim here is only to highlight the underlying phase equilibrium engineering principles of homogeneous and heterogeneous azeotropic distillation. Moreover, these types of distillations require the selection of a proper solvent to accomplish the mixture fractionation. Besides discussing the solvent functionality to make a proper selection, in the second part of the chapter we show how to design adequate solvents for liquid extraction and extractive distillation by computer-aided molecular design of solvents.

High Pressure Phase Equilibrium Engineering

Green Chemistry principles call for the use of renewable resources, less waste and environmentally friendly solvents (EFS). Among EFS increasing attention is given to supercritical fluids (SCF). A field that has numerous SCF applications is that related to natural products processing, which is growing driven by the fact that biomass is renewable and nature can produce many complex molecules in a highly efficient way. In the present chapter an introduction to SCF technologies applied to food additives and bioactive compounds is presented. Thereafter, the thermodynamic modeling of phase equilibrium of natural products with supercritical fluids is summarized. The effects of molecular size and molecular interactions on the type of binary phase equilibria is discussed on the basis of the classification of van Konynenburg and Scott as well as the phase scenarios found in processing of natural products with supercritical fluids. A phase equilibrium engineering approach is used to design the phase conditions that meet the separation process goal. This approach is illustrated with two case studies: fractionation of bioactive compounds and extraction of jojoba oil with near critical mixed-solvents.

Chapter 13:Equations of State in Chemical Reacting Systems

Phase and chemical equilibrium calculations are essential for the design of processes involving chemical transformations. Even in the case of reactions that cannot reach chemical equilibrium, the solution of this problem gives information on the expected behaviour of the system and the potential the...

Phase Equilibrium and Process Development

Abstract This volume on phase equilibrium engineering (PEE) aims to fill the gap between the books on reactors and separation process design and the textbooks on chemical engineering thermodynamics. The goal is to change the focus from the use of thermodynamic relationships to compute phase equilibria to the design and control of the phase conditions that a process needs. In this way, phase equilibrium thermodynamics is put to work. The main goal of PEE is the design of the system conditions to achieve the desired phase equilibrium scenario that the process at hand requires. In this chapter, the philosophy of phase equilibrium thermodynamic modeling is discussed in the context of process development and chemical plant operation. Typical phase scenarios that are encountered in separation, materials, and chemical process are presented as well as the problem of phase design and the PEE tools.

Chapter 2 - Intermolecular Forces, Classes of Molecules, and Separation Processes

Abstract The design of the phase scenario that meets the process needs defines a phase equilibrium engineering problem. The first step in the design of the phase scenario is to consider the mixture(s) to be handled in the process. What are the components, their chemical nature, composition, physical state, pressure, and/or temperature? This is a critical step and quite often one goes back to this step in the search of an answer to solve the phase design problem. The phase behavior of the mixture is closely determined by the molecular interactions of the components of the mixture. Therefore, an introduction to the different types of molecular interactions is provided in this chapter. Finally, a classification of molecules and families of separation problems is given, which shows the strong connection between the classes of molecules and the proper separation technologies.

Phase Equilibrium Engineering in Conceptual Process Design

Abstract The application of the principles of phase equilibrium engineering to the development of two innovative technologies for the production of biofuels is discussed in this chapter. The first technology is the production of biodiesel by transesterification of vegetable oils with supercritical methanol; the second, the extraction and dehydration of alcohols by near-critical dual effect solvents that exhibit good solvent power to extract alcohols and water entrainment effect to dehydrate the extracted alcohol. In the first case, the complexity of the reacting system, the large size asymmetry, and strong molecular interactions of the mixture components: methanol, vegetable oils, fatty esters, and glycerin precluded the design and analysis of the process conditions based on thermodynamic model predictions. Therefore, in this case, a systematic approach based on experimental studies was used to unveil the phase scenario and the physical properties required for the design and optimization of this technology. The conceptual design of extraction and dehydration of alcohols by near-critical solvents followed a different path. The process development was initially based on very limited experimental information. In this case, an equation of state for highly nonideal systems was the main tool for exploration of the process conditions over a wide range of pressures, temperatures, and compositions. This equation of state was based on a group contribution approach (GC-EOS) that allowed extrapolating the scarce experimental information available not only in pressure, temperature, and composition but also in molecular structure. The basic conceptual design was later confirmed by experimental information and pilot plant studies. In this case, the design of the experimental studies was guided by the process conceptual design. The experimental results provided key information for the upgrading of the thermodynamic model.

Green Processes and High-Pressure Solvents

Abstract In this chapter, the problem of sustainability of the chemical and pharmaceutical industries and the principles of green chemistry are outlined. In particular, the need for secure and environmentally safe solvents (ESSs) is pointed out. There are several ESS alternatives under study nowadays, like ionic liquids, polymeric solvents, and simple liquids like fatty esters; however, an increasing attention is being paid to supercritical fluids (SCFs) for a wide variety of applications in the chemical and pharmaceutical as well as in the materials and electronic industry. In the present chapter after an introduction to the fundamentals of SCF extraction, PEE principles are applied to several case studies of SCF—substrate mixtures of natural products with different types of phase behavior. Finally the application of SCF for supercritical micronization is reviewed and a case study is presented.

Chapter 6 - Phase Equilibrium Engineering Principles

Abstract In this chapter, the basic methodologies of phase equilibrium engineering are introduced through the systematic analysis of several case studies. Some of the thermodynamic tools that have been presented in the previous chapters are applied to illustrate how the phase and conceptual process design of complex engineering problems can be tackled from a phase equilibrium engineering approach. In all the case studies, the first step is to consider in great detail the properties of the process feed, the components, their physical properties, concentrations, and molecular interactions. This information is then used for the selection of thermodynamic models, a suitable technology, pressure, temperature, and compositional operating boundaries. It is shown how the mixture composition and the process goals and specifications determine the process scheme and the unit thermodynamic sensitivity. In addition, the importance of the mixture composition is highlighted in combination with the energy and material balance in the case study for the selection of the desirable natural gas cryogenic technologies. The use of a pressure versus temperature drawing board is used to plot the process trajectory and the mixture phase envelopes from the initial conditions to the key phase engineering design problem. Moreover, the phase design provides also a sound basis for the process initial specification and computer simulation. As another example of phase equilibrium engineering, the heat integration in a complex process is solved by the application of the Gibbs phase rule to the LLV equilibria of a ternary mixture.