Scaling-up multiphase monolith reactors: Linking residence time distribution and feed maldistribution

The scale-up of Taylor flow from a single capillary channel to a monolith is a critical step for the industrial application of microchannel reactors in general and monolith catalyst supports in particular. Characteristics of pressure drop in capillaries were used to identify the conditions under which all channels in a monolith behave essentially identically. This eliminated upflow as unstable and posed a criterion for the minimal stable gas and liquid velocity in downflow. The assumption that the pressure drop over all channels is the same allowed the transformation of feed maldistribution into a residence time distribution. The residence time of the bubble train was rather insentitive to feed maldistribution. Experiments confirmed the limited impact of maldistribution on the RTD for different distributors. The E curves in monoliths were described by a piston-dispersion-exchange (PDE) model, where the dispersion term quantified the maldistribution. Industrially relevant observations on distributor design and monoliths blocks stacking are reported. The most important practical conclusion was that monoliths can indeed be scaled-up using physically sound criteria.