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Abstract: In the first three papers of this series, it has been shown that strengthening internal heat integration within a reactive distillation column involving reactions with high thermal effect is really effective for the reduction of utility consumption and capital investment besides the improvement in process dynamics and operation. One important issue that remains unstudied so far is the influences of reaction selectivity upon the reinforcement of internal heat integration, since the reaction operation is often accompanied by side-reactions and the maintenance of a high selectivity is extremely necessary in process synthesis and design. A reactive distillation column synthesizing high-purity ethylene glycol through the hydration of ethylene oxide is chosen and studied in this work. Because of the unfavorable physicochemical properties of the reacting mixture separated (e.g., the fairly large volatility between the reactants and the existence of a consecutive side-reaction), the process represents a challenging problem for the reinforcement of internal heat integration. Intensive comparison is conducted between the process designs with and without the consideration of further internal heat integration between the reaction operation and the separation operation involved, and it has been found that seeking further internal heat integration still leads to a substantial reduction of energy requirement, in addition to a further abatement in capital investment. Moreover, a favorable effect is again observed upon the process dynamics and operability. These striking outcomes manifest evidently that seeking further internal heat integration should be considered in process synthesis and design irrespective of what a reaction selectivity has been assigned. [Copyright &y& Elsevier]

Abstract: Process intensification calls for the combination of two or more conventional unit operations within one framework, thus giving rise to a challenging coordination problem in process synthesis and design. Seeking synergistic effect among all the conventional unit operations involved is found to be an important principle for process development. Three cases of process intensification are studied to evaluate the principle, including: (i) a hypothetical reactive distillation system; (ii) a reactive distillation column for the hydration of ethylene oxide; (iii) an ideal heat-integrated distillation column. It is demonstrated that simply combining two or more conventional unit operations together does not necessarily tap out the full potentials of capital investment reduction and energy saving. Only after the synergistic effect has been deliberately considered in process synthesis and design, can process intensification be carried out in the most effective manner. Furthermore, seeking synergistic effect appears frequently to yield improved process dynamics and provide additional redundancy to process operation because the underlying conflicts could be attenuated among all the conventional unit operations involved. [Copyright &y& Elsevier]