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2372 results in Chemical engineering

Page 53 of 119

  • 2 - Description of separation in open separators

  • Kamalesh K. Sirkar, New Jersey Institute of Technology
  • Book:
    Separation of Molecules, Macromolecules and Particles
    Published online:
    28 May 2018
    Print publication:
    16 January 2014, pp 39-75

  • Summary

    Separations for preparative or analytical purposes are often carried out batchwise in a closed vessel. On the other hand, industrial-scale separations are commonly achieved in a continuous manner with open vessels into which feed streams enter and from which product streams leave. In this chapter, we consider the available methods of describing separation in such open separators. The quantities, fluxes and mass balances necessary for such descriptions are presented first in Section 2.1. Section 2.2 describes the available indices of separation and their interrelationships for binary separation with a single feed stream entering the separator. In Section 2.3, we briefly introduce indices for binary separation with two feed streams entering a separator. The complications encountered in describing multicomponent separations with a single-entry or double-entry separator are presented in Section 2.4. This section provides also an introduction to the description of systems of continuous chemical mixtures and size-distributed population of particles. Separation by any of the separators considered in these sections presupposes that the output streams have different compositions. There are separation processes, e.g. chromatography, in which the separator has only one output stream, but that has a time-varying composition. The description of separation in such a separator with the help of various indices has been considered in Section 2.5. Triple-entry separators etc. have not been dealt with here. Further, except for Section 2.5, steady state operation is assumed throughout.

  • Preface

  • Kamalesh K. Sirkar, New Jersey Institute of Technology
  • Book:
    Separation of Molecules, Macromolecules and Particles
    Published online:
    28 May 2018
    Print publication:
    16 January 2014, pp xi-xii

  • Summary

    This is an introductory textbook for studying separation. Primarily, this book covers the separation of mixtures of molecules; in addition, it provides a significant treatment of particle separation methods. Separation of macromolecules has also received some attention. The treatment and coverage of topics are suitable for chemical engineering students at undergraduate and graduate levels. There is enough material here to cover a variety of introductory courses on separation processes at different levels.

    This book is focused on developing a basic understanding of how separation takes place, and of how the resulting separation phenomenon is utilized in a separation device. The role of various forces driving molecules or particles from a feed mixture into separate phases/fractions/regions is basic to such an approach to studying separation. The separation achieved is then amplified in an open separator via different patterns of bulk-phase velocities vis-à-vis the direction(s) of the force(s). The forces are generated by chemical potential gradient, electrical field, rotational motion, gravity, magnetic field, etc. The resulting separation is studied under three broad categories of separation processes.

  • 3 - Physicochemical basis for separation

  • Kamalesh K. Sirkar, New Jersey Institute of Technology
  • Book:
    Separation of Molecules, Macromolecules and Particles
    Published online:
    28 May 2018
    Print publication:
    16 January 2014, pp 76-204

  • Summary

    The preceding chapters introduced first the notion of separation and then a variety of indices to describe separation. These indices were used to characterize quantitatively the amount of separation achieved in a closed or an open separation vessel. The quantitative description included systems at steady or unsteady state involving chemical or particulate systems. Systems studied were either binary or multicomponent or a continuous mixture. Not considered in these two chapters was the fundamental physicochemical basis for these separations; appropriately, this is the focus of our attention in this chapter.

    In Section 3.1, we distinguish between bulk and relative displacements and describe the external and internal forces that cause separation-inducing displacements. This section then identifies species migration velocities and the resulting fluxes as a function of various potential gradients. Section 3.2 is devoted to a quantitative analysis of separation phenomena and multicomponent separation ability in a closed vessel as influenced by two basic types of forces. The criteria for equilibrium separation in a closed separator vessel and individual species equilibrium between immiscible phases are covered in Section 3.3. Section 3.4 treats flux expressions containing mass-transfer coefficients in multiphase systems. Flux expressions for transport through membranes are also introduced here.

  • 6 - Open separators: bulk flow parallel to force and continuous stirred tank separators

  • Kamalesh K. Sirkar, New Jersey Institute of Technology
  • Book:
    Separation of Molecules, Macromolecules and Particles
    Published online:
    28 May 2018
    Print publication:
    16 January 2014, pp 346-484

  • Summary

    Chapter 4 described the extent of separation that can be achieved in a closed vessel under three basic categories of separation: phase equilibrium based separations; external force based separations; membrane based separations. Beginning with Chapter 6, we focus on separation achieved in an open vessel: fluid streams and/or solid streams may flow into and/or out of the vessel. Thus, we have bulk flow/s in and/or out of this device. A broad variety of bulk flow patterns can exist in a separation vessel. We will, however, mostly study separations under three general categories of bulk flow configurations defined with respect to the direction of the force which is the source of the basic separation phenomenon. The three general categories of bulk flow–force combinations are:

  • (a) bulk flow of phase(s) parallel to the force direction;

  • (b) bulk flow of feed-containing fluid phase/region perpendicular to the force direction;

  • (c) bulk flow of two fluid phases/fractions/regions perpendicular to the force direction.

    • In the bulk flow–force combination of (c), there can be cases where, instead of two fluid phases, one can have one fluid phase and another solid phase. Categories (b) and (c) provide a broader and more useful framework than the category of bulk flow perpendicular to the force direction illustrated by Giddings (1991) using a few examples.

  • 10 - Energy required for separation

  • Kamalesh K. Sirkar, New Jersey Institute of Technology
  • Book:
    Separation of Molecules, Macromolecules and Particles
    Published online:
    28 May 2018
    Print publication:
    16 January 2014, pp 827-846

  • Summary

    Energy is needed to separate a mixture into pure compounds. Some separation operations are highly energy consuming; others are less so. But all separations require a minimum amount of energy. Section 10.1 introduces the concept of minimum energy required for separation, independent of the process employed. This section then illustrates the minimum energy required in various separation processes such as membrane gas permeation, distillation, extraction and adsorption. How to reduce the amount of energy needed for a given separation by particular separation processes is the general topic of Section 10.2. The specific separation processes and topics covered in this section include: evaporation of water for desalination by multiple-effect evaporation, multistage flash evaporation, vapor-compression evaporation; distillation based separation of mixtures by multieffect and heat pump configuration. The role of free energy of mixing in influencing the energy requirement for separation is briefly considered here. Finally, the special considerations needed for processing dilute solutions of solutes of interest are discussed in the context of reducing the total energy required.

  • 7 - Separation in bulk flow of feed-containing phase perpendicular to the direction of the force

  • Kamalesh K. Sirkar, New Jersey Institute of Technology
  • Book:
    Separation of Molecules, Macromolecules and Particles
    Published online:
    28 May 2018
    Print publication:
    16 January 2014, pp 485-669

  • Summary

    Separations in which the feed phase or feed-containing phase has a bulk motion parallel to the direction of the force causing separation have been studied in Chapter 6. In many separation techniques/processes/operations, the feed phase or feed-containing phase has a bulk motion perpendicular to the direction of the driving force. In a number of situations, the feed is introduced in small amounts in a carrier fluid whose bulk motion is perpendicular to the force direction. Such separations will be studied in this chapter.

    For separations based on distribution of species between two phases in equilibrium, we study in Section 7.1 primarily those two-phase systems where the second phase (e.g. adsorbent particles in a packed adsorbent bed) is stationary; the first phase, which is more often the feed solution/mixture, moves perpendicular to the direction of chemical potential driving force between the two immiscible phases (Figure 7.0.1(a)). This first phase (the mobile phase) bulk motion is generally in one direction. The benefits of such bulk motion in terms of extreme purification achievable in two-component systems and multicomponent separation capability will be illustrated. In the cyclic processes studied next, the direction of motion of the mobile phase is periodically reversed; the direction of force is also reversed, except it remains perpendicular to the bulk-phase flow direction (Figures 7.0.1(b) and (c)). The mobile phase is sometimes generated by the separation operation, as in the case of the blowdown phase of pressure swing adsorption (PSA). The elution chromatographic process considered next involves injection of a sample to be separated into a carrier fluid flowing perpendicular to the direction of the force between the fluid and the stationary adsorbent phase (Figure 7.0.1(d)); this and other related chromatographic processes are also studied in Section 7.1.5. The imposition of an electrical force parallel to the direction of flow in a packed chromatographic column is studied in Section 7.1.6 in what is called counteracting chromatographic processes.

  • 9 - Cascades

  • Kamalesh K. Sirkar, New Jersey Institute of Technology
  • Book:
    Separation of Molecules, Macromolecules and Particles
    Published online:
    28 May 2018
    Print publication:
    16 January 2014, pp 812-826

  • Summary

    We have studied in Section 8.1 how a number of double-entry separation stages can be connected together in a countercurrent fashion. We have also learnt that such an arrangement achieves a far greater extent of separation in separation processes such as distillation, extraction, absorption and adsorption compared to what can be achieved in a single stage. Such multistage configurations are generally identified as “cascades,” and in the case of configurations of an overall countercurrent flow as “countercurrent cascades.” Such countercurrent cascades can have significant variations, for example ideal cascades, squared off cascades, tapered cascades, etc. Further, there can be novel countercurrent cascades with single-entry separation stages. In addition, there can be other types of connections between a number of single stages, resulting in, for example, crosscurrent cascades, two-dimensional cascades, etc.

    We will briefly focus in Section 9.1 of this chapter on many such configurations of cascades, beginning with countercurrent cascades. Special attention will be paid to single-entry separation stages in, for example, the configuration of an ideal cascade. These cascades are generally employed to enhance substantially the separation achieved in a single stage for a binary mixture. Such cascades can also reduce the amount of energy or mass-separating agent needed for the separation of a binary mixture. In the separation of a multicomponent mixture by distillation, a number of such cascades may be joined together in particular ways – Section 9.2 will provide a brief introduction to this topic. Section 9.3 briefly considers cascades for multicomponent mixture separation involving other separation processes.

  • Postface

  • Kamalesh K. Sirkar, New Jersey Institute of Technology
  • Book:
    Separation of Molecules, Macromolecules and Particles
    Published online:
    28 May 2018
    Print publication:
    16 January 2014, pp 856-856

  • Summary

    The area of separations is extremely broad. Most separation processes/techniques have an extensive literature. Each process has its own universe. Yet there are a few common principles and characteristics that are shared by many separation techniques/processes. This book has provided an elementary introduction to such principles and characteristics, even as it provides some details of many of the most commonly used separation processes. It is hoped that this book will help the reader to be prepared to undertake more extensive studies of individual processes/techniques or of a certain class of techniques or certain sequences of separation processes/techniques.

    An important goal of this book is to develop an appreciation that separation processes/techniques may be understood on the basis of a few key features/concepts: the nature of the force causing the selective movement of molecules, macromolecules and particles; the nature of the various regions/phases in the separation system; the four types of bulk flow pattern of the regions/phases vis-à-vis the direction(s) of the forces causing selective movement of species/particles to be separated; the method of feed introduction. Further, for relatively simple systems, one could develop the governing equations that describe the separation achievable from the set of basic governing equations provided in Section 6.2 for most systems described in the book. In addition, a useful introduction to the role played by chemical reactions of certain types for a variety of separations has been provided.

  • 5 - Effect of chemical reactions on separation

  • Kamalesh K. Sirkar, New Jersey Institute of Technology
  • Book:
    Separation of Molecules, Macromolecules and Particles
    Published online:
    28 May 2018
    Print publication:
    16 January 2014, pp 280-345

  • Summary

    Chemical reactions occur in many commonly practiced separation processes. By chemical reactions, we mean those molecular interactions in which a new species results (Prausnitz et al., 1986). In a few processes, there will be hardly any separation without a chemical reaction (e.g. isotope exchange processes). In some other processes, chemical reactions enhance the extent of separation considerably (e.g. scrubbing of acid gases with alkaline absorbent solutions, solvent extraction with complexing agents). In still others, chemical reactions happen whether intended or unintended; estimation of the extent of separation requires consideration of the reaction. For example, in solvent extraction of organic acids, the extent of acid dissociation in the aqueous phase at a given pH should be taken into account (Treybal, 1963, pp. 38–41). Chemical equilibrium has a secondary role here, yet sometimes it is crucial to separation.

    Familiarity with the role of chemical reactions in separation processes will be helpful in many ways. This is especially relevant since a few particular types of chemical reactions occur repeatedly in different separation processes/techniques. These include ionization reactions, acid–base reactions and various types of complexation reactions. The complexation reactions also include the weaker noncovalent low binding energy based bonding/interactions identified in Section 4.1.9. A better understanding and quantitative prediction of separation in a given process is possible, leading to better process and equipment design. In processes where a chemical agent is used, different agents can be evaluated systematically. On occasions, it may facilitate the introduction of reactions to processes for enhancing separation.

  • 8 - Bulk flow of two phases/regions perpendicular to the direction(s) of the force(s)

  • Kamalesh K. Sirkar, New Jersey Institute of Technology
  • Book:
    Separation of Molecules, Macromolecules and Particles
    Published online:
    28 May 2018
    Print publication:
    16 January 2014, pp 670-811

  • Summary

    In this chapter, we cover those separation processes/techniques where two bulk phases or regions flow through the separation device such that the force(s) driving the separation act perpendicular to the directions of flow of both phases/regions. Section 8.1 describes those separation devices where the two phases or regions have bulk motions countercurrent to each other in the separation device. This section also covers those larger multistage separation devices where the overall pattern of flow vs. force corresponds to countercurrent flow, even through the local flow configurations in a stage may utilize other flow vs. force arrangements for the two flowing phases. Invariably, these separations will be studied under continuous flow of two phases/regions and steady state conditions. The focus will be primarily on phase equilibrium based processes driven by chemical potential gradient such as gas absorption, distillation, solvent extraction, melt crystallization and adsorption. Limited attention has been paid to membrane based processes such as dialysis, electrodialysis, liquid membrane processes, gas permeation and external force driven processes of gas centrifuge (thermal diffusion and mass diffusion are also considered here). Section 8.2 will be concerned with separations where the two phases or regions flow in a cocurrent fashion. Continuous flow of two phases/regions as well as discontinuous flow of one of the phases will be covered. Section 8.3 will focus on those configurations where the two bulk phases are in crossflow in the device. The force(s) will continue to act perpendicular to the flow directions of the two bulk phases in both Sections 8.2 and 8.3.

  • Introduction to the book

  • Kamalesh K. Sirkar, New Jersey Institute of Technology
  • Book:
    Separation of Molecules, Macromolecules and Particles
    Published online:
    28 May 2018
    Print publication:
    16 January 2014, pp 1-18

  • Summary

    The basic objective of this chapter is to describe the organization of this book vis-à-vis separations from a chemical engineering perspective. Separation, sometimes identified as concentration, enrichment or purification, is employed widely in large industrial-scale as well as small laboratory-scale processes. Here we refer primarily to physical separation methods. However, chemical reactions, especially reversible ones, can enhance separation and have therefore received significant attention in this book. Further, we have considered not only separation of mixtures of molecules, but also mixtures of particles and macromolecules.

    The number of different separation processes, methods and techniques is very large. Further new techniques or variations of older techniques keep appearing in industries, old and new. The potential for the emergence of new techniques is very high. Therefore, the approach taken in this book is focused on understanding the basic concepts of separation. Such an approach is expected not only to help develop a better understanding of common separation processes, but also to lay the foundation for deciphering emerging separation processes/techniques. The level of treatment of an individual separation process is generally elementary. Traditional equilibrium based separation processes have received considerable but not overwhelming attention. Many other emerging processes, as well as established processes dealing with particles and external forces, are not usually taught to chemical engineering students; these are integral parts of this book. To facilitate the analysis of processes over such a broad canvas, a somewhat generalized structure has been provided. This includes a core set of equations of change for species concentration, particle population and particle trajectory. These equations are expected to be quite useful in general; however, separation systems are quite often very complicated, thereby limiting the direct utilization of such equations.

  • 4 - Separation in a closed vessel

  • Kamalesh K. Sirkar, New Jersey Institute of Technology
  • Book:
    Separation of Molecules, Macromolecules and Particles
    Published online:
    28 May 2018
    Print publication:
    16 January 2014, pp 205-279

  • Summary

    In Section 3.3, we illustrated the thermodynamic relations that govern the conditions of equilibrium distribution of a species between two or more immiscible phases under thermodynamic equilibrium. In Section 4.1, we focus on the value of the separation factor or other separation indices for two or more species present in a variety of two-phase separation systems under thermodynamic equilibrium in a closed vessel. The closed vessels of Figure 1.1.2 are appropriate for such equilibrium separation calculations. There is no bulk or diffusive flow into or out of the system in the closed vessel. The processes achieving such separations are called equilibrium separation processes. Separations based on such phenomena in an open vessel with bulk flow in and out are studied in Chapters 6, 7 and 8. No chemical reactions are considered here; however, partitioning between a bulk fluid phase and an individual molecule/macromolecule or collection of molecules for noncovalent solute binding has been touched upon here. The effects of chemical reactions are treated in Chapter 5. Partitioning of one species between two phases is an important aspect ever present in this section.

    The criteria for thermodynamic equilibrium in a single-phase system in a closed vessel subjected to an external force field were also developed in Section 3.3. Based on these criteria, we develop in Section 4.2 estimates of the separation achieved in a single phase in the closed vessel. These estimates are also developed in a closed vessel when an additional property gradient, e.g. density gradient, pH gradient, etc., exists across the vessel length. Focusing is the term often used to characterize the latter separation techniques. In this section, we cover in addition the extent of separation achieved when a temperature gradient is imposed on a single-phase system in a closed vessel not subjected to any external force field.

Separation of Molecules, Macromolecules and Particles
  • Principles, Phenomena and Processes
  • Kamalesh K. Sirkar
  • Published online:
    28 May 2018
    Print publication:
    16 January 2014
  • Providing chemical engineering undergraduate and graduate students with a basic understanding of how separation of a mixture of molecules, macromolecules or particles is achieved, this textbook is a comprehensive introduction to the engineering science of separation.Students learn how to apply their knowledge to determine the separation achieved in a given device or processReal-world examples are taken from biotechnology, chemical, food, petrochemical, pharmaceutical and pollution control industriesWorked examples, elementary separator designs and chapter-end problems are provided, giving students a practical understanding of separation.The textbook systematically develops different separation processes by considering the forces causing the separation and how this separation is influenced by the patterns of bulk flow in the separation device. Readers will be able to take this knowledge and apply it to their own future studies and research in separation and purification. Online resources include solutions to the exercises and guidance for computer simulations.

Page 53 of 119