(441d) Extractive Recovery of Low Molecular Weight Fatty Acids from Aqueous Effluents

Wastewater from biobased industries is frequently laden with low molecular weight fatty acids. Separation of the fatty acids from the aqueous effluents is vital due to environmental reasons and for the exploitation of valuable byproducts. Pulp and paper industries for instance may produce effluents containing formic acid and acetic acid. Liquid/liquid extraction is perfectly suited to remove the acids from the aqueous solution and beneficiate them in the extract phase. The extraction of carboxylic acids with organophosphorus solvents i.e. Cyanex^®923 is state of the art.

By means of the ternary system acetic acid/formic acid/water the simultaneous extraction of the carboxylic acids with Cyanex^®923 was investigated. The organic phase consists of 70 wt% Cyanex^®923 and 30 wt% non-reactive diluent undecane. The acid concentration was varied between 10 – 50 g/L. The temperature influence on the carboxylic acid extraction was investigated.

From the economic point of view recovery and isolation of the acids is challenging. Distillative recovery of the solvent will end up in a mixture of the ternary system water/acetic acid/formic acid with a total acid content of about 90 wt%. Isolation of the pure substances from these mixtures by distillation is impossible because of the binary high boiling azeotrope formic acid – water and a ternary saddle point azeotrope. Esterification may help improve separation properties. Selective esterification of formic acid or nonselective catalytic esterification of both acids offers different separation and isolation routes by distillation as well as combination with membrane separation. Several separation routes and isolation routes were investigated and tested for their technological potential.