Introduction and Overview

Biotransformation deals with use of natural and recombinant microorganisms (e.g., yeast, fungi, bacteria), enzymes, whole cells, etc., as catalysts in organic synthesis. Biotransformation plays a key role in the area of foodstuff, chiral drug industry, vitamins, specialty chemicals, and animal feed stock (Fig. 1.1). Scaling up a bioprocess from the lab to a commercial scale is challenging and needs several innovations. Nevertheless, more and more industries are moving toward developing processes based on biocatalysis because of their inherent advantages. In the year 2000 biotechnology stocks traded in the Nasdaq exchange outperformed the overall index by 24% (outperformed the Internet stocks by 17%)! This observed general buoyancy is due to the successful applications of biotransformations in the field of pharmaceuticals, environmental bioremediation, textiles, plastics, and agriculture. Biopolymers made from dextrose and plastics made from corn sugar beet and other biomass compete with polymers made from hydrocarbons. Breakthroughs in the area of optimization, reactor design, separation techniques, and molecular modeling are a few of the underlying reasons for these successes.

The design and operation of industrial reactors for bioprocesses are inherently different from the conventional reactors. This book deals not only with how a biocatalyst could be used for synthesis of an organic molecule but also with the steps involved in the scale-up of a process from the bench scale to

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Figure 1.1 Role of biotransformation.

the full commercial scale and the reaction engineering aspects of the manufacturing technology, with an in-depth analysis of bioreactor design.

As shown in Fig. 1.2 the field of biotransformation and bioprocess is interdisciplinary in nature. As the process moves from the lab scale to full-scale commercial production, it requires the expertise of biochemist, molecular biologist, synthetic chemist, physical chemist, biotechnologist, and chemical and instrument engineers. All the aspects listed in Fig. 1.2 are dealt in the various chapters of this book. At times the process as it is scaled up may have to go back to the lab because of issues not foreseen earlier.

A biochemical process generally consists of five sections; they are catalyst and raw material preparation, reaction, biocell recovery for reuse or destruction, product recovery and purification, and waste disposal (Fig. 1.3). The book is divided into four parts. The first part deals with the fundamentals, namely chemistry of biotransformation and the associated areas such as synthetic chemistry, enzyme chemistry, frontiers in biotransformations, and enzyme and biocell kinetics. The second part deals with bioreactors selection, types of bioreactors and their design including fermen-tors, and aspects of biochemical engineering. The third part touches on the downstream separation techniques, and the fourth part, on industrial examples of biotransformations, waste treatment, and scale-up of bioreactions.

The book is written for practicing biochemists and pharmacists who would like to understand the reaction engineering aspects and to chemical engineers who wish to understand the synthetic techniques and organic chem-

Figure 1.2 Biocatalysis and bioprocess: an interdisciplinary field.
Figure 1.3 General flow sheet of a biocatalytic manufacturing process.

istry aspects of this vast field. A large number of problems are given in the end of many of the chapters for students to sharpen their knowledge they would have acquired. This book is not intended to be an encyclopedia for biotransformations or bioreactors, but a ready reference to the practioners relating the science and engineering.

Chapter 2 gives an introduction to molecules, structures and their relationships, quantum mechanical approach, and different types of reactions starting from small to supra molecules. This explanation is then extended to enzymes and proteins.

Chapter 3 describes the structure and activity of enzymes and proteins, differences between enzymes and conventional heterogeneous catalysts and the thermodynamic aspects of the biocatalytic reaction.

Chapter 4 deals in detail with the reactions catalyzed by enzymes, whole cells, and microbes. Mechanistic aspects of these reactions are also discussed.

Chapter 5 deals with various experimental techniques and analytical techniques a bioorganic chemist will employ in the lab. These techniques are very specific to biocatalytic reactions.

Chapter 6 briefly describes the frontier research areas in the area of biotransformation that includes cross-linked enzymes, designer enzymes, ab-

zymes, site-selective modification of enzymes, etc., all aimed toward improving their stability, activity, and specificity.

Chapter 7 deals with enzyme kinetics, inhibition, Michaleis-Menten approach to modeling biocatalytic reactions, and cell growth. Rate equation for different types of reactions is listed.

Chapter 8 deals with biochemical reactor selection, different types of reactor and their salient features. Basic design equations for various types of reactors and Monod equation are also described here.

Chapter 9 deals with fermentation, namely fermentation classification, issues in fermentation, modeling of molds, and four stages of biocell growth. Details of reactor and process control design are also described here.

Chapter 10 gives an overview of reaction engineering principles such as mass and heat transfers and how they are estimated for design purposes.

Chapter 11 deals with stirred bioreactors in detail, since they are used in general because of simple construction and ease of operation. Several correlations for gas-liquid mass transfer that are needed for design are described here.

Chapter 12 gives a detailed analysis of tower bioreactors including the gas, solid, and liquid mixing and heat transfer issues.

Chapter 13 is an introduction to biochemical separation and downstream processing and purification. The various traditional chemical engineering separation processes such as distillation, extraction, filtration, etc., and separations that are very specific to biochemical processes, namely, chro-matography, membrane, electrophoresis, etc. are discussed here.

Chapter 14 deals with industrial examples of where biocatalyst is used successfully including chiral synthesis, pharmaceuticals, specialty chemicals, etc. This chapter is an eye opener to chemists and biologists, giving the industrial world scenario.

Chapter 15 deals with in situ and ex situ waste treatment procedures for solid, liquid, and gas. Different types of reactors used in waste treatment are also discussed. The current chemical methods available in waste treatment are also listed with their advantages and disadvantages over the biochemical approach.

Chapter 16 deals with a large number of scale-up rules which need to be followed for successfully translating a process from bench to commercial scale. They relate to mixing, heat transfer, solid suspension, etc. Several scale-up rules are listed depending upon the criteria one would like to select. A list of innovative techniques reported in literature for scaling up biochemical processes is also tabulated.

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