Reactive extraction of butyric acid from effluent streams and fermentation broth by using tri-n-octyl amine in decanol/natural oils

In this work, the reactive extraction of butyric acid (BA) from very dilute aqueous solutions in effluent stream and fermentation broth by using tri-octyl amine (TOA) at different temperatures (298-318 K) in various diluents was investigated. To reduce the toxic effect of TOA and to avoid the harmful effect of decanol on the living microorganism in the bioreactor, nontoxic and green solvents, sunflower and soybean oils were tested as the diluents. The obtained K-D(dil) was 2.8-4.2 for decanol, 2.0-4.0 for sunflower oil and 1.3-3.8 for soybean oil. The extraction capacity of the solvents was decreased in the order of decanol > sunflower oil > soybean oil. In chemical extraction, the extraction efficiencies were 85-92% for decanol, 81-91% for sunflower oil and 78-89% soybean oil. The experimentally determined K-D(overall) was 4.8-9.5 for decanol, 4.6-8.8 for sunflower oil and 4.5-8.3 for soybean oil. In terms of distribution coefficient and extraction efficiency, decanol showed better recovery of BA than sunflower oil and soybean oil. Overall, the recovery efficiencies using both the edible oils were at per with decanol. Thus, edible oils are suggested to use in the biorefinery industries. The obtained K-D(chem)/K-D(phy) greater than 1.0 has justified the use of TOA as the reactive extractant. The order of the complex concentration, [(HA)(m)S-n](org), in different diluents was decanol > sunflower oil > soybean oil. Other important parameters like acid extractant, free acid and dimer concentration at chemical equilibrium state were determined and analysed. The estimated enthalpy change due to mass transfer, (Delta H)(masstr), showed the easiest mixing of the phases in soybean oil. Reaction equilibrium constant, (K-E(m:n)), also followed the above trend of the effects of the diluents with highest for decanol (8.7-4347), intermediate for sunflower oil (6.6-3222) and lowest for soybean oil (5.5-2018). It also diminished with temperature.