(212a) Taylor-Couette Flow and Multiphase Operations

Continuous multiphase processes will play a major role in process development for usage of sustainable and green raw material resources. Isolation of valuable materials from residuals and low grade resources, not yet economically feasible, requires stable and flexible operation of equipment to be able to manage changing raw material qualities. With its simple and effective design, the Taylor-Couette Disc Contactor (TCDC) offers a promising apparatus design, well suited for flexible use as multiphase contactor or reactor. The unique TCDC design allows continuous and intense contact of up to four phases (liquid-liquid-gas-solid). The contact mechanism is based on formation of Taylor-Couette vortices. The vorticity, adjusted by the rotor speed, provides the flexibility in establishing a specific hold up of dispersed liquid and/or solid and/or gaseous phases. Shear forces, induced by these vortices, help in adjusting the droplet or bubble size and the phase contact area.

Several multiphase operations in the TCDC have already been investigated. The column used for multiphase experiments has an inner diameter of 50 mm and an active height of 0.6 meters. The hydraulics in liquid-liquid extraction were performed and modeled with the test system kerosene/water. Application of continuous three phase (liquid-liquid-solid) contact was demonstrated with heterogeneous esterification of aqueous (2 mol/L) acetic acid with methanol combined with solvent extraction of the reaction product. The overall conversion of acetic acid was increased from 20% without solvent extraction to 30% [1]. Gas-liquid contact was investigated and modeled with continuous chemisorption of CO₂ for neutralization of 0.1 molar sodium hydroxide solution. The neutralization reaction of NaOH with a mixture of 30% CO₂ in nitrogen was performed at three different temperatures (25°C, 40°C, 60°C). The residence time distribution and the gas phase holdup were recorded. The neutralization reaction of CO₂ with NaOH in aqueous solution was modeled with the film theory and continuously stirred tanks in cascade. Concentration trajectories of the hydroxide and carbonate species along the reactor height were modeled with the reaction rate and pH value.

These examples confirm the flexible applicability of the TCDC in multiphase operations and demonstrate a one pot engineering solution, easily adjustable to different applications and phase systems. The operation principle of the TCDC also suggests advantages in leaching and in continuous precipitation, since driving force and residence time can be adjusted independently. Appropriate test systems are investigated at present.

[1] G. Rudelstorfer, M. Neubauer, M. Siebenhofer, S. Lux, A. Grafschafter, Chemie Ing. Tech. 2022. DOI: 10.1002/CITE.202100184.