Preface

Mass transfer refers to processes involving transport of one or more components in a multicomponent mixture across two locations in a single-phase system or from one phase to another in a two-phase system. Examples are encountered in practically all fields of engineering and in biological systems. Production of chemicals starts with reactions often carried out in systems with two or more phases. The transport of reactants from one phase to a second reacting phase and the counter-transport of products play an important role in determining the rate of production, the reactor type to be used, and design of such equipment. The products formed in the reactor in turn have to be separated and purified. This is accomplished by various unit operations, most of which essentially involve mass transfer from one phase to another. Hence the study of fundamental principles of mass transfer and its application to reactors and separators is an essential skill set of the chemical engineering profession.

The study of principles of modeling of mass transfer processes is also essential to understand many other processes in biomedical engineering, environmental transport, dopant profiling in semiconductors, metallurgical processes, and so on. The underlying phenomena behind all these seemingly diverse applications is mass transfer and hence the analysis and modeling of this phenomena followed by computations of the developed model is an essential element in the analysis of all these systems. The central theme of this book is, therefore, to provide a basic introduction to modeling and computation of mass transfer processes, show their application to the design of reactors and separation systems, and also present some applications in environmental and biomedical areas. There is a need for a single volume textbook that embraces a wide range of topics in mass transfer and this book fulfills that need.

Mass transfer effects are quite important in heterogeneous reactor analysis and design. But books on reaction engineering place emphasis mainly on the chemical kinetics and study of homogeneous reactions, which are obviously and important part of the subject. However, heterogeneous reactions are more common in industrial practice and the coupling of mass transfer with reaction is the most significant issue in design of these systems. The book shows how fundamental mass transport theory can be applied to simulation and design of these reactors.

Chemical reactors are followed by separation units in industrial production; mass transfer is underlying phenomena in most of the industrially important separation processes. The traditional books on unit operations deal mainly with equilibrium-based separation processes and do not provide adequate coverage of rate-based processes and some recent advances such as reactive separations, membranes, pervaporation, electrodialysis, electrophoresis, and so on. Hence it is reasonable to conclude that there is no text that is comprehensive enough to cover the fundamentals, and at the same time show the applications of mass transfer in reacting systems and in separations. This book meets that need and includes the fundamentals; the methodology of modeling mass transport processes; setting up the governing model equations; finding solutions through analytical methods for classic problems and through numerical methods using some simple MATLAB snippets; application examples for both heterogeneous reactions and separation; and some illustrative design examples.

Some novel topics and features of the current book are:

• An early introduction to models at three hierarchy levels and the connection between them.

• Solutions to illustrative problems using both numerical and analytical methods.

• Sample code in MATLAB for help in development of numerical problem-solving skills.

• Sample code using CHEBFUN methods, which is a powerful tool for solution of common ODEs and PDEs of importance in mass transfer. This is optional material but students may find it useful to study these tools.

• Detailed discussion on analysis of transport with chemical reactions. Coupling of local differential models with reactor models for macroscopic and mesocopic models is clearly illustrated.

• Detailed analysis of multicomponent diffusion using the Stefan-Maxwell model with many worked examples.

• Three chapters on electrochemical systems and ionic transport with illustrative application examples.

• A chapter on the role of mass transfer in illustrative biomedical problems.

• Introductory treatment of reactive separation processes and process intensification concepts.

• Sample MATLAB codes for many common mass transfer and separation processes so that students learn basic simulation and sensitivity analysis.

A brief description of the contents and the scope of each part is presented here.

Chapter 1 introduces the basic methodology for modeling of mass transport processes and indicates three hierarchical levels of models, namely differential, macroscopic, and mesoscopic models. Chapters 2 to 4 take up introductory examples of modeling at these three levels, respectively, and you will learn the basic skills to model mass transport processes. Differential-level models are treated in further detail starting from Chapter 5, which develops the general differential equations for mass transfer. Application of the differential equations is then treated progressively in Chapters 6 to 12. Chapter 6 introduces the film model of mass transfer and shows how it is used to calculate the local rate of mass transfer. Chapter 7 provides the physical chemistry aspects of diffusion phenomena. Chapter 8 shows the application of differential equations for transient diffusion. Convective mass transfer is treated in detail in the next four chapters; empirical correlation in Chapter 9, internal laminar flows in Chapter 10, external laminar flows in Chapter 11, and turbulent flows in Chapter 12. Chapters 13 and 14 provide more details on macroscopic and mesoscopic models, respectively. Chapters 15 and 16 provide treatments of mass transfer in multicomponent systems and electrochemical systems, respectively.

Overall these chapters provide the foundations over which mass transfer models are built and provide the basics and the fundamentals needed in modeling of such processes. Reaction followed by separation forms the backbone of chemical industries. Mass transfer applications for reacting systems and separation systems are taken up in Parts II and III.

Chapters 25 and 26 deal with processes where the simultaneous analysis of heat and mass transfer is needed and provides design calculations for humidification, drying, and condensation systems. Chapters 27 and 28 focus on membrane-based separations for gas and liquid systems, respectively. Chapter 29 deals with adsorption processes and chromatographic separations. Chapter 30 deals with separation processes where electrochemical mass transport effects are important. Overall Part III presents applications of the basic modeling tools introduced in Part I to these processes and also supplements the traditional books on separation processes.

The book has more material than can be covered in one semester and can be used in the following manner in teaching:

• For an integrated course for mass transfer fundamentals, Chapters 1 to 12 can be covered in one semester. Additional topics from Chapters 13 to 16 and Parts II and III may be selected and assigned as reading material or used in supplementary lectures. The chapters in these parts are written in a modular fashion and are more or less written in a stand-alone style. Hence these need not be followed in a sequential manner.

• For a course focused mainly on heterogeneous reactions, Chapters 1 to 4, 12, and 13 provide the needed foundation and can be followed by Part II of the book, which deals with applications of mass transfer to reacting systems.

• For a course focused mainly on unit operations, Chapters 1 to 4 provide the foundation and can be followed with Part III of the book. Chapters 25 to 30 supplement traditional books on equilibrium-stage models and provide a nice one-semester textbook for this.

Washington University in St. Louis provided me an academic home and I express my gratitude for all the support and encouragement they provided throughout my long career of research and teaching. I would like to thank many colleagues with whom I worked on several projects and learned from, in particular Professors M. P. Dudukovic, A. Muthanna, and P. L. Mills. Working with graduate students in the Chemical Reaction Engineering Laboratory of Washington University and training them was a unique experience for me. I feel delighted that most of them are doing well in industrial practice.

Many summers were spent at Kasetsart University at Bangkok where I got an opportunity to teach some of these materials and interact with students on many projects, and I thank the university and Professors Limtrakul and Terdthai for their hospitality and interaction on many topics.

This is also an opportunity to thank many colleagues with whom I had a chance to interact and learn from. Close interactions with Professors L. K. Doraiswamy, R. A. Mashelkar, R. V. Chaudhari, R. Hughes, J. M. Smith, R. Krishna, S. Limtrakul, M. P. Dudukovic, P. L. Mills, A. Muthanna, and Bala Subramanian are acknowledged.

On the publishing side, I would like to thank Laura Lewin, executive editor at Pearson/IT Professional Group, who gave me the opportunity to publish this book, and Michael Thurston, development editor, who helped to review all chapters and gave me valuable suggestions on the content presentation.

I would also like to thank all the technical reviewers for identifying errors and for providing valuable feedback to this book. Special thanks to Professor A. K. Suresh, who encouraged me throughout the writing and offered valuable suggestions. Many thanks also to Professor R. V. Chaudhari for reading through several chapters in the book.

On the editing side many thanks are due to Vaibhav Kedar and Angela Weatherspoon for helping me with the preparation of many figures in the text.

Book writing is a difficult task and is not possible without the support of family and friends. I would like to express my appreciation to my immediate family in the USA, Nima, Josh, Maya, and Gabe, and my extended family in India and other parts of the world, particularly my brothers, sisters, and sisters-in-law for all their support and encouragement. Much appreciation is due to my friends in University City, Missouri, who encouraged me when the going got tough.