Dispersion in open tubular reactors of various geometries

A study comparing the band dispersions observed in tubular conduits of diff erent overall geometry is described. Straight, coiled and various types of serpentine and superserpentine geometries of open tubular reactors (OTRs) w ere studied in two different tube diameters (300 mum i.d., 110 cm active le ngth, residence volume 80 mul and 750 mum i.d., 75 cm long, residence volum e 330 mul) as a function of flow rate. Dispersion is presented in terms of the observed bandwidth of the peak, as measured photometrically by using an injection of slightly acidic bromthymol blue into a dilute base carrier. V ery small injection volumes (200 nl) and an on-tube detector were used to m inimize extra reactor contributions to the observed dispersion. Some result s are expected: the dispersion observed in a straight tube increases steepl y with increasing flow rate. For many of the more complex designs, the incr ease in absolute dispersion with increasing flow rate tapers off rapidly, r eaching a virtual plateau value. The dispersion observed in identically mad e devices are reproducible. However, dimensional changes (e.g. grid spacing ) within a given geometry can have a very major effect on the observed disp ersion. While there is no unique "best reactor" geometry, a knotted reactor with knots of alternating flow directions and a serpentine II design with greater horizontal than vertical spacing performed well over a large range of flow rates. The caveat on the knotted design is that such a reactor is d ifficult to precisely reproduce manually. (C) 2001 Elsevier Science B.V. Al l rights reserved.