Chemical Reactions in Multistage Separation

Chemical reactions and phase separation can occur simultaneously in multistage separation processes as in reactive distillation and absorption. This phenomenon is found in several operations in the petroleum, chemical, and petrochemical industries (Section 10.3). 

One or more reactions could take place in one or more stages in the column, and different reactions could take place in different stages. They could either be equilibrium or kinetically controlled reactions and could occur in either phase. The trays are assumed to act as continuous, well-mixed reactors as well as phase separation devices. Eor catalytic reactions, a catalyst is placed on the trays where reactions are intended to take place. 

To simulate multistage separation processes with reactions, the reaction equations must be included in the model equations. The component balances. Equation 13.2 or 13.49, will include an additional term that represents the rate of generation or disappearance of components by kinetic reactions. Another equation is included in the model to represent composition changes due to equilibrium reactions. The kinetic reaction rate is calculated by a power law expression. A holdup term is computed 

For a general reversible reaction, the reaction rate or the rate of disappearance of a reference reactant is expressed as 

A model for multistage separation accompanied by chemical reactions must include a term in the component material balance. Equation 13.2 or 13.49, to represent the change in the number of moles of component i on stage j due to chemical reaction. This term is expressed as 

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