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Visualisation of chemistry in flow

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Keywords
  • Qd Chemistry
Disciplines
  • Chemistry

Abstract

This research project investigated the pattern-producing Belousov- Zhabotinsky (BZ) reaction under flow using a combination of optical and magnetic resonance (MRI) imaging techniques. The coupling between reaction-diffusion and advection was studied in three distinct systems. Stationary flow-distributed oscillation (FDO) patterns, previously only observed in packed bed reactors, were produced in alternative flow fields for the first time. The two systems studied have allowed greater insight into the structure, dynamics and stability of the patterns. Plug-like flow was produced with an agar gelling agent and in a vortex flow reactor (VFR). The agar system allowed the production of FDO patterns in the absence of a packing material and could be forced by a periodic change in reaction temperature. Synchronisation was found in space-time but not time. This was in contrast to previous investigations, where periodic illumination resulted in the observation of synchronous behaviour. The VFR provided a flow field which was able to produce stationary and travelling patterns. The complex structure of the stationary bands was explained by the flow, in which Taylor vortices translate axially up the tube in an approximation of plug flow. The rotation rate of the inner cylinder was identified as a new parameter for control of both the stability and wavelength of FDO patterns. Optical imaging was able to probe the bulk behaviour of propagating waves through three-dimensional Taylor vortices but was unable to probe the wave propagation mechanisms. It was found however, that magnetic resonance imaging was able to visualise the behaviour of the chemical waves within the Couette cell in order to elucidate the wave behaviour. In conjunction with this MR velocity and diffusion imaging were able to characterise the flow within the Taylor vortices. The combination of these two methods uniquely allowed the behaviour of these travelling waves to be explained in terms of the flow within the system.

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