(472b) Intensified Liquid-Liquid Extraction with Chemical Reaction By Emulsification

Authors: 
Toth, A., Graz University of Technology
Macher-Ambrosch, R., Graz University of Technology
Painer, D., Graz University of Technology
Lux, S., Graz University of Technology
Siebenhofer, M., Graz University of Technology
Biobased effluents are commonly defined by undesirable characteristics, such as a low concentration of the target constituent in aqueous solution or separation barriers like azeotropes. The isolation of the constituents from such effluents challenges standard unit operations to their limits. To accomplish this task liquid-liquid extraction has been widely used, but for an increase of efficiency and operability further improvement is necessary. Improvement can be obtained through intensification of the extraction step by combination with chemical conversion of the target constituent. Thus, the separability of the constituent as well as economics can be significantly increased.

Effluents from biorefinery processes like pulping serve as representative separation task. Such effluents often contain a significant amount of carboxylic acids like acetic acid or formic acid. Through spiking an appropriate solvent with an aliphatic alcohol, the extraction rate of the carboxylic acids can be increased by chemical conversion via esterification which yields a favorable change of the physio-chemical properties of the constituents. Admixture of homogeneous catalysts to the solvent provides an additional benefit by increasing the reaction rate of the esterification step. 4-dodecylbenzenesulfonic acid (4DBSA) is a suitable catalyst. This highly potent catalyst, which additionally acts as a strong anionic surfactant, offers access to two different process routes.
The first route focuses on the prevention of emulsification by adjusting the hydrophilic-lipophilic balance value (HLB value) through adding a second surfactant to the system. Admixture of nonionic surfactants (e.g. SPAN®85) significantly enhances primary phase separation.
The second process route makes use of emulsification in order to increase the interaction between reactants and catalyst, thus increasing the reaction rate although splitting of the emulsion must be applied prior to product isolation. This technology is a promising alternative to state of the art isolation of carboxylic acids from aqueous effluents by liquid-liquid extraction.