The same courtesy and help are being extended by the present chair, Charles Glatz, and I am equally grateful to him. I am deeply appreciative of their interest. I would like specially to thank the late Maurice Larson for his professional collaboration the results of which are presented in one of the chapters of the book and for his many personal kindnesses.
My grateful thanks are also due to Ed Lightfoot, a true friend of over three decades, who has helped me in many ways, particularly since my arrival in this country over ten years ago, and to Rutherford Aris from whom I have learned much.
The typing of this manuscript must have been a nightmare for Linda Edson, what with my ceaseless corrections, changes of format, and endless additions, modifications, and deletions of figures and tables. I am grateful to her for her patience, and most of all for making sense out of my scribblings, often unintelligible even to me. The writing of this book has been plagued by delays arising largely from bouts of temporary ill health.
I am sincerely grateful to Bob Rogers, senior editor of Oxford University Press during that period, for putting up with these delays and encouraging me with expressions of continued interest in the completion of this book.
I am also thankful to Cynthia Garver for her patience and help during the production of the book. My biggest source of strength has been my family: son Deepak, daughter Sandhya, son-in-law Sankar, and grandchildren Rahul and Priya.
Their care and affection have sustained me through the protracted evolution of this book. Well, what's new about that? It is being done without much fuss over the years.
In the words of Stephen Jay Gould: "If these paeans and effusions were invariably true, I could compose my own lyrical version of the consensus and end this book forthwith. It has been expressed and occasionally illustrated in articles and books, but there has always been a gulf between the expression and the thematic demonstration of many of the strategies in a single consolidated effort. And it is in the strength of such a connected demonstration of these strategies superimposed on a canvas of CRE principles that this book will, one hopes, find its greatest appeal.
Had this book been a hastily written one, the inevitable errors might have been brazenly attributed to time and condoned by an understanding readership. As things are, time and those who assisted me are blameless. I bear the full responsibility for any errors and would be glad to have them brought to my attention.
A large part of the chemical industry is concerned with organic chemicals from simple to highly complex structures. In dealing with relatively simple structures, there does not appear to be any need usually for a deeper understanding of chemistry than that to which an engineer is normally exposed. Most reaction engineering texts are written with this basic assumption. Catalysis, which is invariably an integral part of the reaction engineer's arsenal, has been limited to the production of large volume chemicals which are often relatively simple in structure.
Increasing attempts by chemists today to extend the use of catalysis to the production of medium and small volume chemicals has triggered a change in perspective that augers well for a closer liaison between chemists and engineers.
We examine this a little further below by defining an organic chemicals ladder, and the merging roles of the two in exploiting this ladder, particularly for chemicals stacked on its intermediate rungs. Another change that is taking place is the increasing role of process intensification, nowhere more evident than in the production of organic chemicals.
Process intensification means improvement of a process, mainly the reaction, by any possible means, to increase the overall productivity. This usually takes the form of reaction rate enhancement by extending known or emerging laboratory techniques to industrial scale production. These techniques can be engineering intensive, chemistry intensive, or both. Examples are the use of ultrasound sonochemistry , light photochemistry , electrons electrochemistry , enzymes biotechnology , agents for facilitating a reaction between immiscible phases phase-transfer catalysis , microparticles microphase engineering , membranes membrane reactor engineering , a second phase biphasing , combinations of 3 4 Organic Synthesis Engineering reactions with different techniques of separation multifunctional or combo reactor engineering , and mixing.
Their use in the production of medium and small volume chemicals like pesticides, drugs, Pharmaceuticals, perfumery chemicals, and other consumer products is being increasingly explored both by industry and academe. Some of these techniques have progressed little beyond the laboratory stage, although they have been a part of the synthetic organic chemist's repertoire for a number of years.
All of these techniques and operational innovations will be overlaid on a canvas of reaction engineering principles for both homogeneous and heterogeneous systems.
Of these, petroleum continues to be the dominant resource, followed by biomass. Coal-to-chemicals has always been a subject of debate, marked by sporadic justifications of neglect to perceptions of possible use, depending on such imponderable factors as international politics, economics, and the energy crunch.
Taking petroleum as the source, the first step is to convert it to aromatics, alkenes, and paraffins. Their production usually involves the use of solid catalysts in vapor-phase reactions producing several hundred tons of each per day.
They are chemically simple molecules such as ethylene, propylene, butylene, benzene, toluene, and naphthalene. These chemicals are then converted to next level chemicals such as ethylene oxide, propylene oxide, chlorobenzene, nitrobenzene, and benzenesulfonic acid.
These second level chemicals are converted to the next third level chemicals, lower in volume of production but even more complex in structure. This is repeated over a few more stages to obtain a series of higher order chemicals known as organic intermediates, till finally the penultimate intermediate in each case is converted to a consumer product.
Thus an organic chemicals ladder is established. Two such ladders leading to a number of drugs and Pharmaceuticals are shown in Tables 1. Two main features of these ladders are noteworthy. As already noted, the molecules become progressively more complex as one goes down the ladder, and except in rare cases such as thermal cracking, processes for first level chemicals of the ladder are usually catalytic. A large fraction of the second level processes are also catalytic, but those at the lower end tend to be largely noncatalytic.
A great change is taking place now in which the chemicals in the lower rungs of the ladder are also sought to be made catalytically because of the many advantages of catalytic processes such as the avoidance of corrosive reagents, easy separation of product, greater safety, and often greater selectivity particularly where zeolites or asymmetric catalysts are used.
Several serial publications such as Heterogeneous Catalysis and Fine Chemicals and Catalysis of Organic Compounds regularly report on the development of catalysts for making known or occasionally new organic molecules. There is, indeed, a Table 1. This trend has spurred research on the engineering aspects of catalytic processes for intermediate and small volume chemicals.
Thus the earlier concept of catalysis as the bedrock of large volume productions is slowly but definitely giving place to a much broader role for catalysts in organic synthesis.
This trend is qualitatively depicted in Figure 1. In some cases reactions can be initiated, in some just facilitated, and in many enhanced. They can be used individually, in various combinations usually binary , or as supplements to catalysis. A list of these techniques was mentioned in the introduction. Unfortunately, although almost all of them are known to perform very well in the chemist's lab, their scale-up to industrial size remains a daunting issue.
As an example, the use of light for enhancing or initiating a reaction is well known, but the rational scale-up of reactors for carrying out such reactions has, ironically, reentered the zone of uncertainty from one of fair certainty, thanks mainly to a better understanding of the principles of photoreaction engineering.
In the case of ultrasound, the uncertainty has never left, so that today we are still groping for reasonable methods of scale-up. The situation is more encouraging in some of the other areas of enhancement, such as the use of enzymes, membranes, or a second liquid phase.
Intensive research in the area of multifunctional reactors has brought their design from first principles within reach. In this book we attempt to cover the use of many of these techniques for facilitating organic reactions or enhancing their rates. The structural details of the treatment are given in the next section. The latter is necessary because many organic reactions occur in the liquid phase and our ability to predict the behavior of liquid-phase reactions is severely limited.
In this approach, enough microscopic detail is added to the macroscopic approach of conventional thermodynamics, thus enabling a certain degree of prediction. The chemical engineer is usually not exposed to these methods. Following logically from the extrathermodynamic approach, we move on to Chapter 3 in which the most useful feature of this approach, the method of group contributions, is considered; we construct procedures for estimating the thermodynamic properties of a variety of organic compounds.
The need for knowledge of these properties in reactor design is obvious enough and beyond question, but the need for methods to estimate them in light of their direct availability from computer programs and databases can be a matter of debate. I firmly believe that inclusion of these methods in a book of this kind is neither a superfluous nor an outdated exercise but a necessary one, and hence a brief description of these is presented in Chapter 3. The properties include the thermodynamic properties of relevance to design and also the major transport properties of fluids.
Chapter 4 outlines the elements of stoichiometry, rates, and reaction and reactor analysis. The reader is introduced to the concept of ideal reactors and the principles of their design for simple reactions. Extensions of these ideal reactors form the subject matter of Part III but are anticipated at this stage as an introductory setting for that part.
Chapter 5 extends the analysis to complex reactions, but the design of reactors for complex reactions is deferred to Part III. Catalysis in Organic Synthesis and Technology This part constitutes a significant and rather extensive departure from other books on chemical reaction engineering. Because catalysis is emerging as an important component of organic synthesis, several aspects of catalysis are described in this part: catalysis by solids in the production of organic chemicals in general Chapter 6 ; homogeneous liquid-phase catalysis Chapter 8 ; and asymmetric catalysis used specifically for the selective production of biologically active isomers Chapter 9.
In addition, it is important to recognize that catalysis by solids involves diffusion of reactants from fluid bulk to the catalyst surface, as well as diffusion within the solid matrix. The latter invariably occurs simultaneously with the reaction, and the former is usually but not necessarily rigorously treated as an independent precursor to it. Thus any analysis of catalysis by solids is based on understanding its action under the physical influence of the microenvironment in which it functions.
Catalysis by solids actually occurs on the catalyst surface and constitutes the surface field problem, which is the core of its action. Diffusion of reactant within its matrix is an internal or intraparticle field problem, and its transport from bulk to surface is an external or interphase field problem.
Introduction and Book Structure 11 Figure 1. All of these occur within the microenvironment of a single particle or pellet and constitute the contents of Chapter 7.
Consideration of the various field problems just described provides the groundwork for the design of catalytic reactors in Part III. Within the reactor, the happenings in the microenvironment of a pellet translate into the overall behavior of a bed of pellets, fixed or fluidized.
In other words, the consequences of reaction in a given microenvironment are transferred to a neighboring microenvironment and the process is continued till an integrated effect is realized in a flowing stream of reactant s at the exit of the bed.
This is basically an interparticle field problem and constitutes the core of reactor design. Thus the complete design of a catalytic reactor involves all of these considerations which are schematically shown in Figure 1. Chapter 7 of Part II is concerned with the surface, internal, and external field problems, and the interparticle field problem is considered in Part III devoted to reactor design. Note that these observations are restricted to the use of solid catalysts, which constitutes only a part of the much wider scope of the book.
Reactor Design for Homogeneous and Fluid-Solid Catalytic Reactions This part is basically an extension of the methods of reactor analysis and design introduced in Chapter 4 and covers the design of homogeneous reactors for both simple and complex reactions Chapters 10 and Considerable attention is 12 Organic Synthesis Engineering given to semibatch reactors because of their importance in industrial organic synthesis. Further, these reactors are not normally dealt with in adequate detail in many formal texts on reaction engineering.
In view of the growing importance of catalysis in organic synthesis, the design of catalytic reactors assumes considerable significance. Although published work and industrial practice seem to indicate that catalytic reactors are largely restricted to large scale production, they can also be used for medium and small volume production. The design of fluidized bed reactors, in particular, is aimed at very large scale production, but my personal experience has shown that the procedures apply equally to intermediate-scale production.
Therefore, the treatment of catalytic reactors in Chapter 12 follows that of many existing books but is structured differently to fit into the pattern of presentation adopted in this book. The treatment of reactors in the preceding chapters was based on the assumption of ideality with respect to mixing and the existence of a single solution for a given set of operating conditions i. Although deviations from these assumptions are usually not severe, they can be, and hence a separate chapter Chapter 13 is devoted to a brief description of mixing and multiple steady states.
Another kind of unsteady-state operation, one in which the direction of reactant flow within a reactor is reversed in cycles, is referred to as forced unsteady-state operation FUSO. Although such forced cycling increases the conversion and therefore can be regarded as a strategy for process intensification, it is included in Chapter 13 because it is also a form of unsteadystate operation.
The analysis of these situations tends to be highly mathematical. Thus only a qualitative treatment is attempted with minimal resort to mathematics. Fluid-Fluid and Fluid-Fluid-Solid Reactions and Reactors Heterogeneous reactions involving more than one phase are a common feature of organic synthesis.
Among them are gas-liquid reactions, liquid-liquid reactions, solid-liquid reactions, and gas-liquid-solid reactions e. The main features of various two-phase reactions are covered in Chapters 14 and 15, and Chapter 16 discusses reactors for such systems.
Chapter 17 covers the analysis of three-phase reactions and reactors. Strategies for Enhancing the Rates of Organic Reactions Parts I and II provide material with which both chemist and chemical engineer should be comfortable. Parts III and IV are aimed more toward the chemical engineer, although the text itself excluding the many equation-laden tables provided should offer no great hurdles to the chemist.
Part V is unique in the sense that it is never a part of any conventional reaction engineering book, except by way of brief excursions to illustrate applications. In this part of the book we cover several strategies for reaction rate enhancement.
Many of these have reached a stage where they merit consideration as Introduction and Book Structure 13 special chapters. Chapters 18 to 25 belong to this category. Chapter 26 includes a number of strategies that are being increasingly explored, but seem currently to lack the potential of the others. The strategies covered in these chapters are all written in practically the same format: a brief introduction followed by references to major works and texts; an outline of principles; methods of reactor design with illustrative problems where considered necessary; and a listing of examples of their use, accompanied sometimes by brief descriptions of a few important ones.
The lists are quite extensive in many cases; consequently, the literature cited is also extensive. With this objective in mind, the various chapters are organized so that some of them have a chemistry focus and the rest an engineering focus.
By the mid sixties, Starks had formulated the principles of phase transfer catalysis and had applied for patents on many reactions that others were later to examine in somewhat greater detail. His mechanistic model of phase transfer catalysis still stands up well today and is a model for much of the thinking in this area.
It is fitting that Starks suggested the name "phase transfer catalysis" by which the whole field is now known. We wish to thank a number of people who have aided us in many ways in the preparation of this volume. We very much appreciate the helpful discussions and insights provided by Drs. We also thank Dr.Chapters 18 to 25 belong to this category. These second level chemicals are converted to the next third level chemicals, lower in volume of production but even more complex in structure. Thus an organic chemicals ladder is established. The same courtesy and help are being extended by the present chair, Charles Glatz, and I am equally grateful to him. As an example, the use of light for enhancing or initiating a reaction is well known, but the rational scale-up of reactors for carrying out such reactions has, ironically, reentered the zone of uncertainty from one of fair certainty, thanks mainly to a better understanding of the principles of photoreaction engineering.
Some of the chapters might serve as refreshers to the chemical engineer and others to the chemist. Thus any analysis of catalysis by solids is based on understanding its action under the physical influence of the microenvironment in which it functions. Keywords Alkene Amine Ether Phenol Weber aromatic carbon catalysis nucleophile organic synthesis oxygen polymer rearrangement synthesis Authors and affiliations. Naik phase transfer catalysis and miscellaneous strategies , P.
Consideration of the various field problems just described provides the groundwork for the design of catalytic reactors in Part III.
In the words of Stephen Jay Gould: "If these paeans and effusions were invariably true, I could compose my own lyrical version of the consensus and end this book forthwith.