Chapter 2 - Microstructured Catalytic Reactors

Abstract

Abstract This chapter is a summary of recent advances in microreactors, which have become increasingly important in process development and chemical research. Microstructured chemical reactors are characterized by dimensions in the submillimeter range and, thus, surface-to-volume ratios are roughly two orders of magnitude greater than those of conventional reactors. The fundamentals of design and operation of microreactors are explained, and the necessary heat and mass transfer considerations are presented. Various designs are discussed, their key features are illustrated, and examples of successful applications are given. Emphasis is placed on the methods of introducing a catalyst into a microstructured reactor (MSR). The advantages of microreactor technology—and also the difficulties in development—are highlighted. Because of the small reactor dimensions, diffusion times are short, and the influence of mass transfer on the rate of reaction can be efficiently reduced or even be avoided. Because the heat transfer is greatly improved relative to that in conventional reactors, higher reaction temperatures, pressures, and reactant concentrations are attainable, leading to reduced reactor volumes and amounts of catalyst. Therefore, MSRs are particularly advantageous for fast reactions that are highly exothermic or highly endothermic. Isothermal conditions combined with short residence times and narrow residence time distributions allow optimization of the contact time in the reactor and avoidance of unwanted consecutive reactions. The rational design of catalytic microreactors requires the simultaneous development of the catalyst and the reactor. The catalyst design should be closely integrated with the reactor design, with consideration taken of the intrinsic reaction kinetics and transport phenomena. The accurate tuning and control of the reaction conditions lead to impressively high product selectivity and energy efficiency. Thus, MSRs are versatile tools for the development of sustainable processes. Further objectives of the application of miniaturized reactors concern the generation of chemical information, facilitation of catalyst development, optimization, and characterization of reaction kinetics.