(597a) Apparatus Design for Liquid-Liquid Extraction Combined with Heterogeneously Catalyzed Esterification

In biorefinery processes downstream processing often suffers from poor economics. Target constituents do not turn up in broths in appropriate concentration for simple separation technologies. For instance, black liquor evaporation condensate from pulping contains carboxylic acids at low concentration. Isolation of these constituents from the aqueous effluent fails because economic feasibility cannot be achieved by state of the art downstream processes. The gap between expectations and needs may be solved by combining simple solvent extraction with proper chosen chemical conversion by esterification due to changes in the substance properties. The esterification of carboxylic acids is a well investigated chemical reaction, and esters have a wide applicability. Unfavorably esterification reactions are slow chemical equilibrium reactions and catalytic acceleration is recommended. High water content of the reaction broth shifts the chemical equilibrium composition to the reactant side. Via liquid-liquid extraction the carboxylic acids can be transferred into the solvent phase prior to or after esterification, and the limitation of conversion because of high water load is avoided. Due to the limited solubility in the solvent phase the byproduct water is transferred to the aqueous phase. Conversion of the carboxylic acids is either accelerated by catalysis of esterification in the carrier phase or in the solvent phase.

However, the application of reactive separation processes accelerated with heterogeneous catalysis does induce new demands to apparatus design, when implemented in a continuous process. The Taylor-Couette Disc Contactor (TCDC), a hybrid of the Rotating Disc Contactor (RDC) and the Taylor-Couette Reactor (TCR) satisfies the requirements necessary for intensive liquid-liquid-solid phase contact. In operation the main advantage of the TCDC over the RDC is, that the TCDC does not need stator rings to provide sufficient phase contact. Accumulation of the catalyst in dead zones of stator rings along the reactor can therefore be avoided. Shaft and rotor discs induce a similar flow pattern to banded two phase flow in Taylor-Couette reactors. Banded two phase flow provides proper mixing and sufficient residence time for solid catalysts in the rotor compartments.

Several experiments were carried out to quantify liquid-liquid flow in presence of a solid phase in the TCDC. Beyond the critical rotational speed the catalyst is dragged by the toroidal vortexes. Even in the presence of the dispersed solvent phase the catalyst particles remain within the single compartment for a reasonable residence time. The results confirm applicability of the three-phase reactor TCDC in intensification of mass transfer unit operations by chemical conversion of phase transfer constituents.