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Hydrodynamics and Gas-Liquid Mass Transfer in a Horizontal Rotating Foam Stirrer Reactor

Leon, M. A.; Maas, R. J.; Bieberle, A.; Schubert, M.; Nijhuis, T. A.; van der Schaaf, J.; Hampel, U.; Schouten, J. C.


This paper describes a new multiphase reactor, the horizontal rotating foam stirrer reactor, which uses a donut-shaped foam block mounted on a horizontal shaft as a stirrer and as a catalyst support. The effect of different operating conditions such as stirring speed, reactor length, foam porosity, foam thickness and the presence of baffles on the gas-liquid mass transfer and the gas-liquid flow distribution is discussed for the systems water/air and glycerol/air. The gas-liquid mass transfer is measured spectrometrically while the hydrodynamics of the reactor is studied by gamma-ray computed tomography (CT). For a partially filled reactor, two flow states could be distinguished: the ‘trickle state’ and the ‘slosh state’. In the trickle state the liquid flows in a thin stream over the foam while in the slosh state the liquid is pushed upward by the stirrer and sprayed, leading to the formation of fine liquid droplets and fine gas bubbles. The transition between the trickle state and the slosh state occurs at approximately 200 rpm . When the stirring speed is constant, the ‘ring state ’, which results in a cylindrical liquid layer on the inside wall, appears with increasing the liquid content in the reactor (above 70%). Due to a large gas-liquid interface in the slosh state, a high gas-liquid mass transfer is achieved. kGLaGL values up to 0.35 s-1 are found which is three times higher than in a slurry reactor equipped with a Rushton stirrer and comparable to other types of multiphase reactors such as bubble columns and rotating packed beds. It is shown that mass transfer coefficients decreased with increasing viscosity, while the centrifugal force revealed to be effective in enhancing mass transfer in a viscous media. Conclusions on the optimal reactor configuration are drawn for the application in the fine chemical industry.

Keywords: multiphase reactors; solid foams; hydrodynamics; mass transfer; computed tomography