(578b) Heterogeneously Catalyzed Reactions with Solvent Extraction

Isolation of carboxylic acid from dilute pulping effluents has a huge energy demand. Target constituents do not show up in broths in appropriate concentration and composition for application of simple separation technologies. Via combination of chemical conversion (e.g. esterification) with simultaneous solvent extraction, economic isolation may become feasible. In dilute aqueous systems, the high water content shifts the chemical equilibrium composition of esterification reactions towards reactants. By extracting the reaction product, liquid-liquid separation of the product shifts conversion in the aqueous carrier. Slow chemical reactions, such as esterification reactions, require catalytic acceleration. For continuous operation, heterogeneous catalysts are very suitable since they can be separated from the reaction broth via sedimentation, simplifying downstream processing. Heterogeneously catalyzed esterification combined with solvent extraction requires adequate apparatus design. The Taylor-Couette Disc Contactor (TCDC) [1], a rotating liquid-liquid extraction column, is very suitable for multiphase flow since it has a simple design of internals and can withstand harsh operation conditions. The internals of the TCDC are similar to the Rotating Disc Contactor (RDC), but without stator rings and with increased shaft and rotor disc diameter.

For investigation of the hydraulics of multiphase flow as well as conversion efficiency, continuous liquid-liquid-solid flow has been implemented in a TCDC with 50 mm column diameter and 700 mm active mixing height. Acetic acid with equimolar amount of methanol was fed on top of the TCDC. Biodiesel was used as solvent for methyl acetate extraction, and it was fed at the bottom of the column. The esterification was accelerated with the solid cation exchanger Amberlyst15^®, which was fed on top of the column, separated after esterification from the continuous phase at the bottom, and recycled with a peristaltic pump. Due to the hydrophilic properties of the catalyst, it remains dispersed in the aqueous phase. Operation temperature was T = 65°C. For comparison, batch experiments were performed with the same operation conditions.

Beyond a critical rotational speed, the vorticity of the continuous phase overcomes sedimentation force of the dispersed phase and the solid phase and ensures intensive phase contact in the single compartment of the TCDC. The experimental results confirm applicability of the multiphase reactor TCDC for intensifying heterogeneously catalyzed chemical reactions such as esterification combined with liquid-liquid extraction.

[1] E. Aksamija, C. Weinländer, R. Sarzio, M. Siebenhofer, Sep. Sci. Technol. 2015, 50 (18), 2844–2852. DOI: 10.1080/01496395.2015.1085406