Model-based Design of optimal chemical reactors

The core of most chemical processes is the reactor, and therefore optimal reactor design has a large potential to enhance the energy and rawmaterial efficiency of today’s chemical processes. In order to make breakthroughs in chemical reactor technology and to overcome the limitations of existing reactors, process intensification (PI) needs to be applied systematically in the reactor design task. Hence, the scope of this thesis is to create amodel-based designmethodologywhich includes PI options and enables the design of innovative tailor-made reactors. In the first part of this work, the fundamentals for the reactor design task are provided and the design framework is explained. The general idea of the design method is based on the conceptual framework of elementary process functions; a fluid element is tracked on its way through the reactor and manipulated by optimal flux profiles to obtain the best reaction conditions over the entire residence time. In order to resolve the complex reactor design task, a three step methodology is developed. On the first level, the optimal heat and mass flux profiles, which provide the best route in the thermodynamic state space, are determined independent of existing apparatuses. On the second level, it is investigated if the desired flux profiles are attainable. For this purpose, the best principle reactor set-up including the catalyst support, the exchange areas and the control variables which can be manipulated by the reactor design are identified. On the third level, a technical approximation of the best reaction route is developed giving rise to superior chemical reactors. The approach is rigorously based on the equations of change, thermodynamic relationships, and the reaction kinetics including PI options by modeling their physico-chemical effects. In the second part of this thesis, several industrially important examples of increasing complexity are considered. The SO2 oxidation, the air and oxygen based ethylene oxide (EO) process, and the hydroformylation of long chain linear alkenes are investigated demonstrating the wide applicability of the method. For the SO2 oxidation, a new reactor design is proposed based on the optimal heat flux profile reducing the residence time in the reactor by 69% compared to an optimized reference case. This result illustrates the large potential of realizing the optimal reaction route and is an example for exothermic equilibrium reactions. For the air based EO process several dosing and removal concepts were investigated showing the potential of the method for screening complex reaction concepts. In addition, the derived reactor is investigated in detail using a two-dimensional reactor model taking non-idealities in the flow, temperature, and concentration field into account. For the oxygen based EO process the overall process is modeled and simultaneously optimized giving rise to the best reaction concept from the overall process point of view. Furthermore, a sensitivity analysis for the critical model assumptions is performed investigating the robustness of the derived optimal reaction concept. For the hydroformylation of long chain linear alkenes the design approach is extended for the design of optimal multiphase reactors. Here, an innovative reactor design including static mixers, advanced cooling, and distributed dosing of alkene and synthesis gas is developed giving rise to a selectivity increase of 9.1% based on an optimized reference case. In summary, the developed reactor design methodology enables the design of optimal tailor-made chemical reactors, which is a first step on the way to more economical, greener, and more sustainable chemical processes. The potential of the method is exemplified on three industrially important processes.