Kinetics and Reaction Engineering

75 Reaction Kinetics K. H. Lin Fundamentals • Analysis of Kinetic Data 76 Chemical Reaction Engineering H. S. Fogler The Algorithm • Pressure Drop in Reactors • Multiple Reactions • Heat Effects • Summary 77 The Scaleup of Chemical Reaction Systems from Laboratory to Plant J. B. Cropley General Considerations in the Rational Design of Chemical Reactors • Protocol for the Rational Design of Chemical Reactors CHEMICAL REACTORS ARE THE MOST IMPORTANT PART of a chemical plant. In most cases, multiple reactions take place, multiple reactors are required, and catalysts are used to obtain sufficient rates and desired selectivities. Improvements in reaction rates and selectivities to desired products can have significant influences on other parts of the chemical plant such as the separations processes. Thus, design of the chemical reactor can control the economics of a plant even though the reactor is not the most expensive part. The chemical reactor also determines the amounts of waste products that form and thus the plant's effect on the environment. Because highly exothermic reactions are often carried out in chemical reactors on a large scale, the reactor is also the biggest safety hazard in the plant. The first chapter of Section X is concerned with chemical kinetics and the analysis of kinetic data. The most important aspect of chemical kinetics is the rate at which a chemical reaction takes place and the selectivity to reaction products. Also of interest is how the rate and selectivity depend on concentrations, temperature, and other reaction conditions. Reaction rates and the products that form for a given set of reactants and reaction conditions cannot be predicted; such kinetic information must be measured. These measurements are particularly sensitive to temperature because most chemical reactions exhibit an exponential dependence on temperature. They also must be made in the absence of transport effects such as diffusion and mass transfer. Moreover, many large-scale chemical processes use catalysts, and the composition and preparation of the catalyst can have a large influence on both the rate of reaction and the product distribution. The basic methods for analyzing laboratory kinetic data to determine rate expressions are presented in this section, and the mechanisms by which reactions occur on a molecular scale are also discussed. The second chapter discusses the design and analysis of chemical reactors. Reaction engineering involves determining how the type of reactor, its size, and its operating conditions affect production rates and distribution of products. Industrial processes almost always involve multiple reactions taking place simultaneously, and the desired product is often not the more favored