Operation and Optimization of an Oscillatory Flow Continuous Reactor

Abstract

Oscillatory flow reactors (OFRs) are a novel type of continuous reactor, in which tubes fitted with orifice plate baffles have an oscillatory motion superimposed upon the net flow of the process fluid. The combination of baffles and the oscillatory motion creates a flow pattern conducive to efficient heat and mass transfer while maintaining plug flow. Unlike conventional tubular reactors, where a minimum Reynolds number must be maintained, tube-side mixing is independent of the net flow, allowing long residence times to be achieved in a reactor of greatly reduced length-to-diameter ratio. We have evaluated a pilot-scale OFR as a method for continuous production of sterols in an ester saponification reaction. The OFR achieved the required product specification, in a residence time one-eighth that of a full-scale batch reactor. To better understand the effect of the process variables on the reactor performance, the OFR was modeled using a tanks-in-series residence time distribution, combined with the saponification reaction kinetics, giving a “flow-conversion” model which predicted conversion based on flow and feed parameters. This simple model has led to a number of insights into the optimal operation of the OFR, one of which was that the OFR could give desired conversion selectivity at a lower reaction temperature without significant alteration to other process variables. Also, the current product specification could be surpassed, if necessary. These predictions were verified by experiment. A full-scale OFR design based on these results would be less than one-hundredth the volume of a full-scale batch reactor, assuming the same production rate and product quality. The construction of such an industrial-scale OFR for the saponification reaction is now being considered by an industrial collaborator.