Consecutive Reaction Sequence

The first consideration in any design and optimization problem is to determine the boundaries of the system. A reactor can rarely be optimized without considering the upstream and downstream processes connected to it. This chapter attempts to integrate the reactor design concepts of Chapters 1-5 with process economics. The goal is an optimized process design that includes the costs of product recovery, recycling, and byproduct disposition. The reactions are 

Chemical Reactor Design, Optimization, and Scaleup, Second Edition. By E. B. Nauman Copyright 2008 John Wiley Sons, Inc. 

Few reactions are completely clean in the sense of giving only the desired product. There are some cases where the side products have commensurate value with the main products, but these cases are becoming increasingly rare even in the traditional chemical industry and are essentially nonexistent in fields like pharmaceuticals. Sometimes, C is a hazardous waste and has a large, negative value. 

The stmcture of the reactions in Equation 6.1 is typical of an immense class of industrially important reactions. It makes little difference if the reactions are all second order. Thus, the reaction set 

Show by example that it is generally necessary to inclnde the cost of recovering the prodnct and recycling nnnsed reactants in the reactor design optimization. 

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Consider the following first order consecutive reaction sequence... 

Thus to expand the potential dependence of the surface activity of the reactant (which is an intermediate) of the rds, and ultimately that of the forward, reductive reaction direction, we again build up progressively from the initial reactants. The potential dependence of Group I reaction steps would be exactly that which was evaluated previously (Section IV) for the simple consecutive reaction sequence, since there is no change in molecularity between [or stoichiometric coefficients (see footnote g) of] reactant and product for any of these reaction steps. Thus the potential dependence of the activity of the reactant of the dissociation step ] is given by Eq. (29) (but where i - 1 is used as the limit for the summation and product in that equation), i.e. 

Eind the optimal temperature profile T t) that maximizes the concentration of component B in the consecutive reaction sequence of Equation 6.6 for a PER subject to the constraint that f= 0.8 h. 

For a consecutive reaction sequence A=>B=>C when the rate equations are of first order and diffusional limitations can be neglected... 

Confronted with the need to develop a sustainable chemistry, we have witnessed an amazing increase in the efficiency and selectivity of synthetic methods in the last fifty years. In order to solve the problems associated with the traditional step-by-step procedures, such as the cumbersome, time-consuming, and expensive isolation of intermediates, several new criteria have been introduced atom, redox, step and pot economy or protecting-group-free synthesis. It is obvious that all variants of one-pot domino and cascade reactions or multicomponent consecutive reactions sequences may allow fulfilling these criteria. 

E. Quantitative Studies on the Consecutive Reaction Sequences between Cholesterol and Pregnenolone 316... 

The most commonly postulated mechanism for the desmolase reaction has been the suggestion of the enzymatic consecutive reaction sequence cholesterol 20a-hydroxycholesterol — (22R)-20a,22-dihydroxycholesterol pregnenolone (Shimizu et al., 1961, 1962 Constantopoulos and Tchen, 1961). This hypothetical scheme was actually advanced on the basis of three suppositions (1) cholesterol is cleaved between C-20 and C-22, as was discussed in a previous section, (2) 20a-hydroxycholesterol was formed from cholesterol-4- C by a cow adrenocortical homogenate in the presence of 20a-hy-droxycholesterol as a trapping agent (Solomon et al., 1956), and (3) both 20a-hydroxycholesterol and (22R)-20a,22-dihydroxycholesterol are much more efficiently transformed to pregnenolone than is cho-... 

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