The Use of Multi-modal Tomography in the Study of Boehmite Precipitation

I. Edwards1,2, S. A. Axon1, M. Barigou2, R. Mann3, D. R. Stephenson3, E. H. Stitt1

1. Johnson Matthey Technology Centre, PO Box 1, Belasis Avenue, Billingham, Cleveland, TS23 1LB
   mail: hugh.stitt@matthey.com

2. Department of Chemical Engineering, University of Birmingham, Edgbaston, B15 2TT

3. School of Chemical Engineering and Analytical Science, The University of Manchester, Manchester, M60 1QD, UK

ABSTRACT

Multi-modal tomographic techniques have been applied to the in-situ study of the semi-batch precipitation of boehmite, an industrially important alumina precursor. For the first time Electrical Resistance Tomography (ERT) and Positron Emission Particle Tracking (PEPT) have been used concomitantly to study precipitation and hydrodynamics. This combination of techniques allows a step change in our ability to understand industrial precipitation processes.

ERT has previously been employed in the study of barium sulphate precipitation (Kagoshima and Mann, 2005), whilst PEPT is a well-established technique for studying the hydrodynamics of stirred vessels (Fangary et al., 2000; Fishwick et al., 2005). The macro-mixing characteristics can been analysed with PEPT and used to explain inhomogeneities observed within the vessel with ERT. ERT can provide an analysis of mixing times together with information of how the feed plume is dispersed under different mixing conditions. PEPT provides fluid velocities and recirculation times. Together the techniques can establish how the feed plume is dissipated into the bulk fluid.

The semi-batch precipitation of boehmite was investigated in a 154mm diameter vessel operated with different configurations. Mixing conditions during semi batch precipitation have been shown to determine particle properties (Peleka et al., 2004). Variables such as impeller design, power input, feed rate and feed location were used to provide different mixing conditions at the feed point where the reagents contact and precipitation takes place.

Keywords Electrical Resistance Tomography, Positron Emission Particle Tracking, Multimodality, Precipitation.