Experimental study of the effect of bubbles, drops and particles on the product distribution for a mixing sensitive, parallel-consecutive reaction system

Abstract

For stirred multiphase reactors the e!ect of a dispersed (gas, liquid or solid) phase on the product distribution for a mixing sensitive reaction was tested. Turbulence modi"cation due to the presence of dispersed-phase particles has been reported frequently in literature, but the extent of the e!ect in a stirred multiphase reactor was not clear. In this work the well-known mixing sensitive diazocoupling reaction system was selected to investigate the in#uence of the changes in the turbulent kinetic energy spectrum on the product distribution. This reaction system was found to be suitable to study the in#uence of a dispersed (gas, liquid or solid) phase. The Engulfment model could describe the single-phase experiments and describes reasonably well the multiphase experiments when the e!ective dispersion properties are implemented. For the liquid}liquid dispersions e!ects of de-localization of the reaction zone were encountered, due to Naphthol extraction by the dispersed phase. The Engulfment model was extended to incorporate mass transfer and the "rst experimental and simulation results are promising. Additional, experimental and theoretical, research studying the combined e!ects of the mass transfer rate and the mixing rate for the liquid}liquid dispersions is highly desired.

Micromixing in two‐phase (G‐L and S‐L) systems in a stirred vessel

“…In that thesis (Hilber, 1987), it was also shown that the micromixing near the upper surface was improved by sparging. On the other hand, a similar study (Brilman et al, 1999) in a 0.7 L vessel also using diazo‐coupling found a negligible effect of sparging from ∼0.5 to 10 vvm on micromixing, both near the impeller and half way between it and the liquid surface at constant impeller speed. This result is somewhat surprising as, at constant speed $({\bar {\varepsilon }}_{{\rm T}} )_{{\rm g}} < {\bar {\varepsilon }}_{{\rm T}} $ , and so are the equivalent local values.…”

“…For example, even when the same reaction scheme was used, Guichardon et al (1995) did not find any effect on micromixing of particles of 200 µm (or with the other sizes investigated) from 1 to 5 wt.%, while Unadkat et al (2009a) using similar sized (300 µm) particles found significant augmentation at concentrations for 1–1.3% but none at 750 µm. On the other hand, Brilman et al (1999) found essentially no effect with particles of 300 µm up to 15 wt.%.…”

“…They generally reported improved micromixing but most of the experiments were conducted under flooded conditions, especially at the higher rates, the specific energy dissipation rate from the sparged gas would have been greater than that from the impeller. The latter condition may also have applied to the work of Brilman et al (1999) at the higher sparge rate. For the non‐flooded conditions, Lin and Lee (1997) found that when feeding the closest to the impeller, the X s values were generally greater than the unsparged especially at the lower flow rate with little impact at the higher rates.…”

“…With the pitched blade turbine, cloud formation was found in every case and the selectivity was increased by about 20–50%. Brilman et al (1999) used azo‐coupling for investigating several feed positions but some very close to the impeller but none near the top surface where clear liquid would be found if “cloud” formation occurred. They used various sizes of glass beads from 30 to 700 µm and solid concentrations from about 2.5 up to 40 wt.% agitated by a Rushton turbine.…”

Gas–liquid–liquid reaction engineering: the Koch synthesis of pivalic acid from iso- and tert-butanol; Reaction kinetics and the effect of a dispersed second-liquid phase

“…This can be done either by transport of CO to the reaction zone near the feed inlet or, alternatively, by picking up reactant at the feed inlet and redistributing this throughout the whole vessel. An alternative explanation, assuming an increase of the local turbulence in the liquid}liquid dispersion, is not very likely (Brilman et al, 1999).…”