Analysis of a Taylor–Poiseuille vortex flow reactor — II: reactor modeling and performance assessment using glucose-fructose isomerization as test reaction

Abstract

In a previous work, Giordano, Giordano, Prazeres and Cooney (1998, Chemical Engineering Science, 53(20), 3635–3652) reported experimental evidence of a significant by-pass stream around toroidal vortices that occur in a Taylor–Couette–Poiseuille apparatus, for low axial Reynolds numbers ( Re ax from 0.172 to 1.067, corresponding to mean residence times between 30 min and 5 h). With the exception of rotational Reynolds numbers ( Re θ ) close to the critical value, downstream displacement of vortices was slower than the fluid's superficial velocity. One specific geometry was focused (radius ratio η=0.677 and aspect ratio Γ=18.30). This work presents a lumped-parameter model of this system that uses empirical values of the vortex drift velocity, V d (the ratio between the speed of the vortex core and the fluid's superficial velocity). The model has two mass transfer parameters, estimated after injections of a tracer. It is validated against the data of an enzymatic test reaction, fructose–glucose isomerization, chosen in view of the small changes of viscosity that occur along the VFR. Thus, no detectable alterations of flow patterns are caused by the progress of the reaction. The temperature is 40°C, and the catalyst is glucose isomerase in soluble form. Mean residence times are approximately 2000 s, for a reactor volume of 1.5×10 −4 m 3. Two different models presented in the literature (the classical axial dispersion approach and a progressive vortices model, with V d =1.0) are compared with the empirical data and with the response of the model proposed here. Re θ ranges from 130 to 3700 (1.6< Re θ / Re θ, c <46). The reactor's performance is close to a plug-flow response for low rotations, but the by-pass flow, coupled with greater inter-vortex mixing, have a detrimental effect at higher rotations. A careful assessment of these features is essential, therefore, when the VFR is used in the manufacture of high-valued products.