(76d) Multiphase Reaction/Separation Processes; Technologies and Apparatus Design

Industrial scale stirred liquid-liquid extraction columns are designed to provide perfect mixing of two immiscible liquid phases. Industrial scale reactors can’t be scaled up linearly from lab experiments. They often suffer from insufficient mixing caused by scale up errors. In recent time, high performance CFD simulations does help to understand the mixing in large size reaction vessels and multiphase contactors. In liquid-liquid extraction, high effort was spent on providing adequate rules for mixing from batch to industrial scale size. Scale up algorithms are available and proven. This knowledge has been applied in the design of perfectly mixed “multiphase reaction vessels” based on the design principle of extraction columns. Mixing units in extraction columns are divided in individual compartments. This compartments can be seen as multiple continuously stirred tanks, arranged vertically to obtain space and equipment savings for a cascade of reaction vessels. 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. 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 and gas flow rate were varied. To achieve a fixed pH of 9 at the column outlet the feed flowrate of sodium hydroxide was adjusted. 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. This paper presents the application of the TCDC as industrial scale reaction vessel. The concept is demonstrated in two environmentally friendly processes. The continuous synthesis of an organic electroactive molecule for redox flow batteries and the continuous recovery of lithium from battery scrap using CO2.

[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.