Strategies for solids handling in microreactors
Solids are virtually unavoidable and generally difficult to be handled in microreactors. In this paper, we focus on solids handling in both feeding system and reaction channels of microreactors. In feeding systems, external actuation fields are usually required, and the corresponding dispersion effect depends on the particle sizes, densities, and concentrations. The behavior of solids in reaction channels is controlled by the interactions between particles, fluid, and reactor surface, and, if applicable, also applied external forces (e.g. acoustic fields). The management of solids can be achieved by managing these complex interactions and many strategies have been proposed to successfully handle solids in microreactors at the laboratory or small production scale. The purpose of this paper is to further analyze these strategies, point out remaining problems and discuss the feasibility of their industrial application.
Applications of microreactors in continuous flow chemistry are experiencing a period of rapid development, both in academia and industry (1-2). Due to their characteristically low total process fluid volumes and high surface to volume ratios, microreactors can become an appropriate choice to perform reactions that are difficult, dangerous, or even impossible when using conventional reactors in a safe, efficient, and sustainable way. A recent patent review by Hessel et al. (2) showed a decrease in the number of new micro devices, but an increase in the number of their applications and testing for various processes. According to the survey of Hessel et al. (3), micro-process technology has been introduced into pilot plants and at production scale by e.g. Uhde GmbH, Lonza, Sigma-Aldrich, for more than 20 different reactions until 2012. This clearly indicates that industry is becoming increasingly interested in applying micro-process technology in recent years. However, from an industrial perspective, the potential main drawback of using microfluidic reactors still exists: fouling, clogging, even breakage caused by the presence of solid material ...