Reactive extraction of caproic acid using tri n-octylamine + 2 octanol system

Abstract

Recovery of dilute caproic acid from waste streams by reactive extraction using tri n-octyl amine (TOA) as an extractant and 2 octanol as a diluent is attempted in this work. 0.005–0.0572 mol/lit concentration of caproic acid found in aqueous streams of fermentation broth is left untreated or found too expensive to recover by conventional methods. Reactive extraction is an intensified technology implemented for maximum recovery of acid. An identical concentration range of caproic acid was used for batch experiments using toluene, benzyl alcohol, 2 octanol, and decanol as diluents in independent experimental runs. A comparative experimental study was made by adding TOA as an extractant. The results revealed 2 octanol to be the suitable diluent among selected diluents for extraction of very dilute acid concentrations of 0.005 mol/lit. Hence, 2 octanol was selected for further study of reactive extraction experiments. Nearly 54–87 % degree of extraction was observed in physical extraction when 2 octanol alone was used as a diluent. However, reactive extraction using TOA in 2 octanol exhibited a synergetic effect on the recovery of the acid. The degree of extraction enhanced nearly by 30% and is reported in the range 86 to 98.60 % whereas the distribution coefficient is in the range 6.5–67. Encouraging results were achieved in a continuous counter-current extraction experiment, extraction efficiency was found to be 91% for very dilute acid (0.005 mol/lit). The novelty of the work is in exploring the TOA + 2 octanol system for extraction of caproic acid in batch and continuous mode of operation. Experimental work on reactive extraction of carboxylic acid using counter-current packed column is rarely reported and hence we have explored this technology in a continuous mode of operation.