Correlations between local conversion and hydrodynamics in a 3-D fixed-bed esterification process: An MRI and lattice-Boltzmann study

In situ magnetic resonance (MR) visualisation techniques are used to study chemical conversion within a fixed-bed reactor. The reaction chosen for study is the esterification of acetic acid by methanol, catalysed by an acidic ion exchange catalyst. MR visualisation shows that fractional variations in steady-state conversion within slice sections of the bed, perpendicular to the direction of superficial flow, are of order 20%. The origin of this heterogeneity in conversion lies in the heterogeneity in the fluid flow field within the bed as is seen directly from MR flow visualisation. A lattice-Boltzmann code is validated for the prediction of the flow field within this fixed bed of porous resin packing. The lattice-Boltzmann predictions of the flow field are then used to explore any dependence of local conversion within the bed with locally averaged fluid velocity, over varying length-scales within the bed. These data report a first demonstration that MR visualisation techniques can be used to gain insight into the true rate-limiting processes influencing the performance of fixed-bed reactors.