(513d) Application of Taylor-Couette Flow in Continuous Multiphase Reaction/Separation Processes

Development and scale up of selective and flexible extraction processes requires customized and well investigated design of extraction columns. Ordinarily, industrial scale liquid-liquid extraction columns are not designed to process solid particle containing feed streams. They may suffer from solids deposition in hydraulic dead zones. Simplification of stirred column- extractor geometry lead to a resilient design suitable for harsh operation conditions. In this study multiphase Taylor Vortex flow (gas, liquid, solid) with a continuous liquid carrier phase in a Taylor-Couette Disc Contactor (TCDC) column setup was investigated. Taylor Vortex flow is induced and stabilized via discs mounted on a rotating shaft. The applicability of stable multiphase flow was demonstrated in three different applications. Firstly, the characterization of continuous gas-liquid flow was performed. The dispersed gas phase holdup and residence time distribution were evaluated and modelled. Practical application of gas-liquid flow in the Taylor-Couette Disc Contactor was tested by continuous neutralization of sodium hydroxide with gaseous CO₂. The 0.1 molar sodium hydroxide solution was neutralized with a mixture of 30 vol % CO₂ and 70 vol% N₂. The process parameters rotational speed, temperature, gas flow rate and sodium hydroxide flowrate were varied to achieve a fixed pH of 9 at the column outlet. The reaction was modelled based on the two film theory in order to provide a simple scale up algorithm. The outcome of this first study was used for implementing precipitation of lithium carbonate from aqueous lithium hydroxide solution with carbon dioxide in a second project phase. The solid lithium carbonate particles were collected in a sedimentation zone at the bottom of the column and continuously discharged with a peristaltic pump. Target of this study was the investigation of the effect of operation conditions on the particle size distribution. The results confirm applicability of continuous gas-liquid-solid flow in a TCDC column. In a next step liquid-liquid-solid operation by heterogeneously catalyzed esterification of acetic acid with methanol combined with in-situ solvent extraction of the reaction product methyl acetate was successfully performed and modeled. The hydraulic parameters were investigated in terms of residence time distribution, catalyst holdup and dispersed phase holdup [1]. The outcome of these investigations demonstrates applicability of the Taylor-Couette Disc Contactor for flexible continuous reactive and extractive operations. Based on this experience the continuous synthesis of 2-Methoxyhydroquinone (MHQ), which can be used as redox-active molecule for organic redox flow batteries [2], by oxidation of vanillin with hydrogen peroxide was applied. This synthesis reaction was performed with sodiumpercarbonate as hydrogen peroxide source. Conversion of vanillin leads to phase separation after reaction with the product acting as solvent phase. After optimization the process was operated in lab scale (50 mm diameter TCDC) for several hundred hours with a capacity of 0.6 kg/h MHQ. The outcome of these different processes confirms the great technological potential of the TCDC in multiphase reaction/separation processes.

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

[2] W. Schlemmer, P. Nothdurft, A. Petzold, G. Riess, P. Frühwirt, M. Schmallegger, G. Gescheidt‐Demner, R. Fischer, S. A. Freunberger, W. Kern, et al., Angew. Chemie Int. Ed. 2020, 59 (51), 22943–22946.
DOI: 10.1002/anie.202008253.