(664e) From Simple Lubrication Models to Industrial Multiphase Monolith Reactors

We are interested in creating reactors that have a well-defined, precise laminar flow pattern over well-defined geometries. Many of today's industrial three-phase reactors are governed by chaotic processes such as turbulent flows, and by irregular and imprecise ?layering? of catalysts. In short, the local geometry and flow field immediately surrounding a catalyst particle is often ill-defined. In contrast, the monolith structure that is well known as automotive catalyst has a well defined geometry and can be operated with well-defined laminar multiphase flow.

The flow of elongated bubbles in channels of capillary dimensions can be described using a classical lubrication theory, pioneered by Bretheron [1] and Taylor [2]. Theory readily predicts variables like film thickness and pressure drop. Subsequently, engineering models for mass transfer, axial and radial mixing and stable flow distribution can be derived with relative ease [3]. In this talk, we take the simple scaling arguments that describe this flow to leading order and we confirm this analysis with experimental proof that laminar segmented flow in microchannels provides an excellent alternative to stirred slurry reactors and trickle beds alike.

Our experimental work begins with cold-flow experiments in a single microchannel and concludes with pilot-scale data under reacting conditions. We answer the question whether a monolith ensemble of microchannels can be modelled by considering a single channel using a hydrodynamic stability analysis. We show that multiphase laminar flow is an ideal alternative to turbulent contacting when high mass transfer rates are sought.

References

[1] F.P. Bretherton, The motion of long bubbles in tubes, Journal of Fluid Mechanics 10 (1961)

[2] G.I. Taylor, Deposition of a Viscous Fluid on the wall of a tube, Journal of Fluid Mechanics 10 (1961)

[3] M.T. Kreutzer, F. Kapteijn, J.A. Moulijn, J.J. Heiszwolf, Multiphase Monolith Reactors, Chemical Reaction Engineering of Segmented Flow in Microchannels. Chemical Engineering Science 60 (2005)