(285d) Optimization of Salting-out Extraction of Butyric Acid Using Non-Ionic Surfactant Ecosurf EH-3

Carboxylic acids like butyric acid, often synthesized through fermentation, are important precursors for various industrial applications. However, a major challenge in the bioproduction of butyric acid lies in the recovery from the fermentation broth. Hence, in this study, a novel separation technology is presented based on aqueous two-phase extraction with inorganic salts using the non-ionic surfactant Ecosurf EH-3. This process is termed salting-out extraction (SOE). The addition of salts into the system alters the structure and properties of the liquids in equilibrium through ionic forces. By similarity-intermiscibility theory, the salt dissociates and directly interacts with water molecules while the surfactant precipitates from the aqueous solution along with the weakly polar butyric acid. To verify this phenomenon, the salting-out effect of modified Savin’s medium nutrients (KH₂PO₄, (NH₄)₂SO₄, MnSO₄∙H₂O, FeSO₄∙7H₂O, and MgSO₄∙7H₂O) at varying concentrations (0.01M, 0.0.5M, 1M) was initially examined on extraction of pure butyric acid from aqueous solution. Findings of this section of the study specified FeSO₄·7H₂O and KH₂PO₄ as most significant influencing factors and recommended to maximize the concentrations of the salts to 0.33M and 0.64M, respectively to achieve the optimum butyric acid recovery of 98.4% and a partition coefficient of 7.2. These concentrations of FeSO₄·7H₂O and KH₂PO₄ were adopted as the maximum levels, while their concentrations in modified Savin’s medium were set as minimum for optimizing the SOE of the acid from the actual fermentation broth using Clostridium tyrobutyricum. Aside from salt concentrations, glucose (5, 15, 25 g/L) and surfactant concentrations (0, 20, 40% w/w) were also varied. By applying response surface methodology on a central composite design matrix, the recommended surfactant concentration was 20% w/w for every 25 g/L of initial glucose concentration, and with introduction of 0.17M FeSO₄·7H₂O and 0.33M KH₂PO₄. This combination of conditions established the highest butyric acid yield of 66% at a reaction time of 48h and using the agitation rate of 60 rpm which were determined in preliminary parametric studies before optimization runs. As compared to control run of fermenting 25 g/L glucose using the same optimum concentrations of the salts (i.e., without addition of Ecosurf EH-3), the % butyric acid yield was doubled by SOE using the non-ionic surfactant, Ecosurf EH-3. Overall, the SOE process was found effective in extraction of butyric acid from fermentation broth, and these results can be utilized by the industrial set-up to improve their production rate of butyric acid.