A Modified Hierarchy for Designing Chemical Processes

This paper presents a modified hierarchy for the design of chemical processes. The modified hierarchy differs from the hierarchy of Douglas [Conceptual Design of Chemical Processes; McGraw-Hill: New York, 1988] in two ways: (i) the design of a chemical reactor is considered as a separate, distinct step in the design exercise, and (ii) the implementation of a material recycle is considered to be part of the unit integration step, rather than a predetermined step in the design hierarchy. The advantage of the modified hierarchy is illustrated on a process to produce benzene by hydrodealkylation (HDA) of toluene (this is a benchmark case in teaching chemical process design). It is shown that, by applying the modified design hierarchy, a more economical process can be designed. The economic advantages are achieved mainly due to modifications in the reactor configuration and the elimination of the gas recycle stream.