Improving energy efficiency of process of direct adipic acid synthesis in flow using pinch analysis

Together with transport and chemical intensification, process-design intensification is situated under the umbrella of Novel Process Windows and heads for integrated and simplified smart-scaled (micro/meso) flow process design in a holistic picture. As a demonstration example, the direct oxidation of cyclohexene with hydrogen peroxide for adipic acid synthesis is considered. It provides an innovative alternative to the two-step industrial process currently used. It is aimed to design an energy efficient process for this novel route. For systematically and holistically analyzing the process and, in particular, its heat integration, pinch analysis is employed. With the use of the software Aspen Energy Analyzer, the available energy recovery potential is determined, and a heat exchanger network is designed that gives a minimum total annual cost. Compared with the initial heat exchanger network where energy requirements are supplied with utility streams, the improved heat exchanger network designed enables 70% saving in operating cost which enables to pay back the extra capital cost requirement in 8 months. The heat exchanger selection is also a very important design consideration. The utilization of compact heat exchangers (including microchannel-based), which have proven advantages in thermal effectiveness, safety, and reduced size, can enable further benefits in terms of total plant cost and plant complexity. The opportunity to have lower operable temperature approach gives the possibility to lower the utility requirement by 20%. For the case of temperature cross, the additional capital cost requirement can be halved. As a consequence, for operation of flow processes using micro/meso-reactors at large scale, the utility/energy support and heat exchanger selection should be taken into consideration. Such holistic thinking has not been detailed and justified so far for micro- or similar smart-scale flow reactors, to our best knowledge.