Recovery of propionic acid from an aqueous stream by reactive extraction: effect of diluents Original Research Article

Reactive extraction is a promising technique for the recovery of carboxylic acid from dilute aqueous solutions. Reactive extraction requires a proper combination of extractant and diluent which provides higher capacity and selectivity. The recovery of propionic acid by reactive extraction (present in concentration range of 0.05–0.4 kmol/m3 in the aqueous phase) was studied using tri-n-butyl phosphate (TBP) in different diluents (n-heptane, petroleum ether and toluene). Extraction using pure diluents was found to be poor. Using the mixtures of extractant-diluents the extraction was significantly improved. Results are presented in terms of distribution coefficient, equilibrium complexation constant, loading ratio and extraction efficiency. Propionic acid—TBP was found to form a 1:1 complex with no overloading in any case. Though the TBP—toluene system was found to provide the highest distribution coefficient of the three diluents tested, when extraction is to be done from a fermentation broth where a toxicity problem is the main consideration factor for selection of solvent, TBP + n-heptane is preferred.