The recovery of hydrocarbon based valuables from industrial effluents is crucial from the point of view of pollution control and exploitation of the valuable constituents. Treatment of waste water laden with low molecular weight carboxylic acids, such as formic acid and acetic acid, is expensive and a waste of useful constituents with a wide range of applications.
However, isolation of carboxylic acids from dilute aqueous solutions is a challenging task. Reactive separations via esterification of the carboxylic acid provide an efficient tool for their isolation from aqueous effluents. Whereas conventional esterification in aqueous solution is virtually impossible due to the aqueous environment and an unfavorable chemical equilibrium, the combination with liquid/liquid extraction exhibits process-intensifying effects.
Our approach is to extract the carboxylic acids and directly esterify them with an alcohol in the solvent phase. Due to their high affinity to water carboxylic acids cannot be separated with conventional solvents. Extractability may be enhanced by reactive extractants, for instance with organophosphorus compounds. Long chain aliphatic alcohols starting with butanol and higher also show beneficial distribution properties in the solvent phase. Sulfonic acids provide catalytic acceleration of esterification.
Liquid/liquid extraction of dilute acetic acid with the solvent Cyanex 923 was investigated. Prior to extraction the solvent was laden with n-butanol and spiked with dodecybenzenesulfonic acid to form butyl acetate during extraction.
Experimental lab scale validation in batch mode confirmed the potential of the proposed concept. Esterification of acetic acid during continuous countercurrent operation provides a permanent driving force maximum for mass transfer which gives access to complete removal of carboxylic acids from aqueous feed.