Chemical Engineering and Processing 50 (2011) 1017–1026 Contents lists available at ScienceDirect Chemical Engineering and Processing: Process Intensification jo u rn al hom epage: www.elsevier.com/locate/cep Scale-up concept for modular microstructured reactors based on mixing, heat transfer, and reactor safety Norbert Kockmann a,∗ , Dominique M. Roberge b a TU Dortmund University, BCI, Equipment Design, D-44227 Dortmund, Germany b Lonza AG, CH-3930 Visp, Switzerland a r t i c l e i n f o Article history: Received 15 January 2011 Received in revised form 18 April 2011 Accepted 31 May 2011 Available online 7 July 2011 Keywords: Microreactor Mixing Heat transfer Parametric sensitivity Reaction runaway Scale-up a b s t r a c t Microstructured reactors are characterized by rapid mixing processes and excellent temperature control of chemical reactions. These properties allow the safe operation of hazardous chemistry in intensified processes. Problems occur during scale-up of these processes, where heat transfer becomes the limiting effect. With high flow rates and transitional or even turbulent flow regimes in small channels, rapid mixing and excellent heat transfer can be maintained up to high production rates. For exothermic reactions, limits for parametric sensitivity and safe operation are shown from literature and combined with convective heat transfer for consistent scale-up. Good knowledge of reaction kinetics, thermodynamics and heat transfer is essential to determine runaway regions for exothermic reactions. From these correlations, consistent channel design and continuous-flow reactor setup is shown. © 2011 Elsevier B.V. All rights reserved. 1. Introduction Process Intensification and Green Chemistry are currently two main drivers in chemical engineering development. Microstruc- tured reactors and devices are playing a vital role in this development for chemical synthesis and production [1,2]. Organic chemical synthesis is investigated in lab-on-chip devices with very tiny channels [3] and often nano-structured elements for detec- tion or catalytic purpose [4,5]. A recent paper of Valera et al. [6] shows a nice comparison of flow reactors with flasks for homogeneous catalyzed reactions. A flow reactor is recommended mainly when the adiabatic temperature rise of the reaction is high. Continuous-flow reactors with micro-structured elements have found their place in laboratory process research and develop- ment [7,8] as well as in pilot-scale production [9,10]. In fine chemistry and pharmaceutical production, the pilot scale is often also production scale, while bulk chemicals are produced on a much larger scale. Here, applications of microstructured equip- ment are still rare, but for gas phase processes first applications are reported [11]. Microreactors constitute a confined, continu- ously operated system, where complex chemical reactions are ∗ Corresponding author. Tel.: +49 0 231 755 8077. E-mail address: norbert.kockmann@bci.tu-dortmund.de (N. Kockmann). performed in tiny, highly adapted channels allowing improved process conditions [12]. Chemical and biochemical transforma- tions can be carried out with dramatically enhanced mixing and heat transfer with controlled residence time. Typical reac- tions are rapid or hazardous [13] or with unstable intermediates under intensified process conditions [14]. A key point is the consistent scale-up of the synthetic route and process from lab- oratory on gram or even milligram scale to ton and multi-ton scale. Mixing and transport of species and energy over short dis- tance is rapid and controlled by diffusion, advection [15] and convection [7] in homogeneous systems. Mixing by diffusion in aqueous solutions is well below 1 s for a distance smaller than 100 m, while the characteristic time for heat transfer is already below 1 millisecond for the same distance in liquids. Heteroge- neous systems are determined by droplet generation [16] and further coalescence and dispersion [17]. Here, we focus on homo- geneous flow, which is a good starting point for multiphase flow [18]. Excellent heat transfer is a main advantage of microstructured channels due to high surface-to-volume ratio and low volume for processing highly exothermic reactions or temperature sensitive material. This argument is often extended to statements of isother- mal reactor operation and inherent safe reactors [19]. The first statement can easily be refuted for exothermic reactions, where the heat transfer needs a driving temperature difference. The second 0255-2701/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.cep.2011.05.021