Design of Extraction Processes

For an ideal ternary system where practically only the solute is soluble in both phases, the design of an extraction process is straightforward. As shown by 

Example 3.3.7, the McCabe-Thiele approach - already examined for distillation (Section 3.3.2) and absorption (Section 3.3.3) - is the common technique used to design an extraction process  

The actual number of extraction stages required is given by the ratio of the theoretical number of stages to the stage efficiency  

For packed columns or columns with rotating or pulsating internals, the height equivalent to one stage HETS) is commonly used, and the total column height is determined by  

The value of HETS must be determined experimentally and depends both on the apparatus and the ternary system used for the extraction. 

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Computer programs are available for the design of extraction processes and would normally be included in the various commercial process simulation packages available see Chapter 4. 

Design of extraction processes and equipment is based on mass transfer and thermodynamic data. Among such thermodynamic data, phase equilibrium data for mixtures, that is, the distribution of components between different phases, are among the most important. Equations for the calculations of phase equilibria can be used in process simulation programs like PROCESS and ASPEN. 

Another consideration affecting the design of extraction processes is the extraction rate as it determines the residence time of the phases in the... 

For the design of extraction processes of mostly high boiling liquid or solid compounds with the help of supercritical fluids, for example, the extraction of caffeine from coffee beans using carbon dioxide the phase equilibrium behavior as a function, of the pressure without or in the presence of co-solvents is required. As in the case of all other phase equilibria, the isofugacity condition has to be fulfilled ... 

Four major principles must be considered in a study of the factors which have a bearing upon the design of extraction processes ... 

Whilst such a classification [1, 9] is useful because it indicates the different types of chemical changes which can occur at the metal centres during phase transfer, it oversimplifies the situation in many cases and fails to indicate the importance of the outer sphere coordination chemistry and of solvation effects in general on the free energies of extraction. Alternative classifications of extraction processes which take better account of these have been presented recently by the Moyer Group. [22] The importance of such supramolecular effects in the design of reagents will be stressed in the examples below. 

When extracting chondroitin sulfate from salmon head cartilage, collagen inevitably accompanies it. In this extraction process, from a pharmaceutical point of view, collagen is considered as an impurity. This is a kind of contradiction because if we administrate chondroitin sulfate and collagen simultaneously, the result will be beneficial and effective. Most marine bioresources contain many health beneficial compounds even in the same tissues. For this reason, we should design sequential extraction processes of those useful compounds from the most value added to the poorly valued compounds. For example, the first step for pharmaceutical use should be the mild extraction of compounds. And the final step should extract materials for fertilizers. 

The use of digital computers to carry out complete calculations in the design of separation processes has been the goal of many. To do this effectively, suitable methods for phase equilibria and tray-to-tray distillation calculations are required. Results calculated by the application of such methods to dehydrate aqueous ethanol mixtures using ethylene glycol as the extractive distillation solvent is discussed below. A brief review of the methods used for phase equilibria and enthalpies is followed by a discussion of the results from distillation calculations. These are compared for extractive distillation with corresponding results obtained by azeotropic distillation with n-pentane. 

The design of any process has to be supported by a proper understanding of the system behavior. Next, the kinetics of the simultaneous extraction and back-extraction processes of two metallic ions by membrane-assisted solvent extraction is analyzed theoretically. 

For the right choice of the selective solvent and for the development and design of separation processes, a reliable knowledge of the phase equilibrium behavior (extractive distillation vapor-liquid equilibrium (VLE) extraction liquid-liquid equilibrium (LLE), absorption gas-liquid equilibrium (GLE)) is required. This information is available from phase equilibrium thermodynamics. 

Successful approaches to designing an extraction process begin with an appreciation of the fundamentals (basic phase equilibrium and mass-transfer principles) and generally rely on both experimental studies and mathematical models or simulations to define the commercial technology. Small-scale e3q)eriments using representative feed usually are needed to accurately quantify physical properties and phase equilibrium. Additionally, it is common practice in industry to perform... 

The use of process simulation software for process design is discussed by Seider, Seader, and Lewin [Product and Process Design Principles Synthesis, Analysis, and Evaluation, 2d ed. (Wiley, 2004)] and by Turton et al. [Analysis, Synthesis, and Design of Chemical Processes, 2d ed. (Prentice-Hall, 2002)]. Various computational procedures for extraction simulation are discussed by Steiner [Chap. 6 in Liquid-Liquid Extraction Equipment, Godfrey and Slater, eds. (Wiley, 1994)]. In addition, a number of authors have developed specialized methods of analysis. For example, Sanpui, Singh, and Khanna [AlChE J., 50(2), pp. 368-381 (2004)] outline a computer-based approach to rate-based, nonisothermal modeling of extraction processes. Harjo,... 

This chapter is mainly concerned with the performance analysis of extraction processes and the estimation of design and operating parameters using graphical techniques. 

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