Monday, February 10, 2014

Bourne reactions for vessel characterization

Many are familiar with the term 'solvent test' as a means of characterizing vessel heat transfer and sometimes also gas-liquid mass transfer.  Another type of characterization test addresses the turbulent energy distribution in a vessel and uses experiments with Bourne reactions (mixing-sensitive) together with a mathematical model.

These techniques enable a quantitative estimate of the local power per unit mass (or volume) at a specific feed location.  That is useful when scaling processes that are mixing-sensitive, such as some fast / dosing-controlled reactions and some antisolvent crystallizations.

XQ (or XS) from the Bourne chemistry depends on the mixing rate near the feedpoint.  When the experiments are micromixing-controlled, XQ is independent of feed time; this occurs at longer feed times.  In those circumstances, the local epsilon (W/kg) may be estimated directly from the Engulfment frequency that corresponds with the measured XQ:

(Equation 1)

An example model-generated curve relating XQ and epsilon is shown in Figure 1 below: given a measured XQ under micromixing-controlled conditions, epsilon can be read from the x-axis:

Figure 1: Example plot of XQ versus epsilon (W/kg) under micromixing-controlled conditions.

The value of experiments to measure XQ depends on running the chemistry under mixing-sensitive conditions.  If you are planning experiments like these, you should first use a model with estimated epsilon to identify both chemical (concentrations) and mixing conditions (e.g. rpm) that will lead to sensitivity in your case.  Our utilities provide good estimates of the parameters you need.  Then when you have your measured XQ results, you can back-calculate epsilon.

DynoChem is the only software that contains these readymade tools for characterizing your equipment and handling micromixing and mesomixing limited systems during process development and scale-up.  Sign up to find out more.

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