(294d) Revisiting the Tubular Flow Reactor Experiment

Revisiting
the Tubular Flow Reactor Experiment

Yanir
Maidenberg and J. Patrick Abulenicia

Abstract

The
tubular flow reactor experiment is a common reaction kinetics example in the
unit operations laboratory sequence. In this experiment, students are typically
tasked to examine reaction conversion as a function of both volumetric flow
rate and residence time. More specifically, students evaluate if the fluid-flow
regime (i.e. laminar or turbulent flow) or the time in the reactor plays a more
effective role in generating the desired products.

The
chemical reaction that has been traditionally used at our institution, as well
as many other institutions, is the saponification of
ethyl acetate to form ethanol. Briefly, solutions of sodium hydroxide and ethyl
acetate are prepared in separate vessels and then introduced simultaneously at
prescribed flow rates into the tubular flow reactor. Students can calculate the
degree of conversion for the reaction by either monitoring the conductivity -
either at the inlet or outlet - or by performing a titration against
hydrochloric acid to calculate uncreacted sodium
hydroxide. This process would be repeated over several volumetric flow rates to
cover the laminar and turbulent regimes. Although this is a robust reaction,
the authors began exploring ways to improve some areas of the tubular flow
reactor experiment. First, the conductivity measurements from this setup
exhibited great fluctuation as the reactants flowed,
which made it difficult for students to reliably collect data. Second,
variations among different groups were found due to the bias inherent in
determining start point and end point of titrations. Third, sodium hydroxide is
a strong base, and can be dangerous if handled improperly (it has a health
rating of 3). Last, it was found the reaction proceeded too slowly to discern
any statistically meaningful variations.

To
this end, the authors began to explore other possible chemical reactions for
this experiment, with the following criteria: 1) it had to be safe, 2) conversion should be easily measured, and 3)
relatively inexpensive. A fourth (but less important) criterion is that the reaction undergo a color change, so that visual confirmation
of the reaction conversion could be observed in the clear glass reactor at the
institution. In this presentation, the authors will outline several alternative
reactions for the tubular flow reaction experiment, as well as a summary of
past work by chemical engineering educators on this topic.