Modeling and Scale-Up of Mixing- and Temperature-Sensitive Chemical Reactions

Abstract

A review of published measurements of yield for complex chemical reactions in mixed reactors of various types and methods of modeling and simulating such reactions for the purpose of reactor scale-up shows the extent of progress that has been made. Reaction kinetics for very fast competitive reactions are usually difficult and expensive to determine. Many reaction processes must be scaled up from bench-and/or pilot-scale experiments that produce yield data under various mixing conditions. The variables that strongly affect the yield results are the reaction types and their rates, feed point in the reactor, feed injection velocity and scale, mixing reactor type, and intensity of mixing induced. Because temperature affects the rates of many chemical reactions, the effects of exothermic reactions are examined. Simulation methods that aim at accounting for all these variables, as well as more approximate methods that are easier and quicker to use, are reviewed. An approach to scale-up is proposed that involves a series of yield calculations for conditions ranging from perfectly mixed to full simulation of the mixed vessel or flow mixer. These may be progressively compared with experimental yields, and the ratios of rate constants and their absolute values are adjusted to give yields close to those of bench and pilot experiments. The rate constant ratios and absolute values may in this way be bracketed (maximum and minimum values) for use in doing the scale-up computations. General conclusions based on the current knowledge of mixing effects on chemical reactions and a correlation based on dimensional analysis that incorporates most of the above variables are presented.

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