Neat Operation Versus Use of Excess Reactant

The control of this system is fairly easy. The total flow is controlled by manipulating the fresh feed of B. The fresh feed of reactant A sets the production rate, and the set point of the total B flow controller is ratioed to the flow rate of A. The control scheme features reflux ratio control and temperature controllers in both columns. 

A commonly made mistake in these two-reactant feed systems is to assume that a control structure with one feed ratioed to the other will provide effective control. This scheme does not work because of inaccuracies in flow measurements and changes in feed compositions. Remember in neat operation the reactants must be balanced down to the last molecule. This can only be achieved by using some sort of feedback information from the process that indicates a buildup or depletion of reactant. 

The tert-amyl methyl ether (TAME) reactive distillation system considered in Section 9.3 has similar chemistry (two reactants and only one product), and an internal composition controller is required to balance the reaction stoichiometry. There is a recycle stream of one 

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