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

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 Taylo r-Couette-Poiseuille apparatus, for low axial Reynolds numbers (REax 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-theta) close to th e critical value, downstream displacement of vortices was slower than the f luid's superficial velocity. One specific geometry was focused (radius rati o eta = 0.677 and aspect ratio Gamma = 18.30). This work presents a lumped- parameter model of this system that uses empirical values of the vortex dri ft velocity, V-d (the ratio between the speed of the vortex core and the fl uid's superficial velocity). The model has two mass transfer parameters, es timated after injections of a tracer. It is validated against the data of a n enzymatic test reaction, fructose-glucose isomerization, chosen in view o f the small changes of viscosity that occur along the VFR. Thus, no detecta ble alterations of flow patterns are caused by the progress of the reaction . The temperature is 40 degrees C, and the catalyst is glucose isomerase in soluble form. Mean residence times are approximately 2000 s, for a reactor volume of 1.5 x 10(-4) m(3). Two different models presented in the literat ure (the classical axial dispersion approach and a progressive vortices mod el, with V-d = 1.0) are compared with the empirical data and with the respo nse of the model proposed here. Re-theta ranges from 130 to 3700 (1.6 < Re- theta/Re-theta,Re-c < 46). The reactor's performance is close to a plug-flo w response for low rotations, but the by-pass Row, coupled with greater int er-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. (C) 2000 Elsevier Science Ltd. All rights reserved.