Equivalence between Minimum Entropy and Exergy Applied to Continuous Stirred-Tank Reactors

Minimum entropy and exergy concepts were applied to continuous stirred-tank reactors (CSTRs) to assess their effectiveness as analytical and optimization tools as well as to clarify some existing controversy regarding their practical applications. The second law of thermodynamics was used to establish in detail the concepts themselves or in the formulation of the exergy balance. Relevant information was extracted from both, in addition to which differences between them were revealed. By applying a commercial software package to the production of propylene glycol, the results of theoretical analysis and simulation showed that such concepts produced equivalent effects when applied to CSTRs and, due to the operating conditions, exergy proved to be independent of the so-called dead state. Therefore, it is concluded that both procedures lead to equivalent optimization strategies when applied to CSTRs and depending on the objectives, but the use of minimum entropy may be more advantageous for some approaches, as it does not depend on the dead state.