Intensification of Propionic Acid Separation from Aqueous Solution using Reactive Extraction with Tri-n-butyl Phosphate (TBP) Dissolved in n-Decane and 1-Decanol

Over the last three decades, there has been a resurgence of interest in large-scale production of fermentation chemicals due to the sharp increase in petroleum cost. So the potential role of a new energy efficient fermentation technology is receiving growing attention. Propionic acid is widely used in the food, pharmaceutical and chemical industries. Fermentation technology for the production of this acid in particular has been known for more than a century. The importance to recover propionic acid effectively from fermentation broth and aqueous waste effluents has got more attention recently. Generally, the aqueous solutions, such as fermentation broth or wastewater stream has very low concentration of propionic acid (less than 10% (w/w). Also, these aqueous solutions have various impurities. Many separation processes in chemical industries have been employed to recover the organic acids from aqueous solutions. The conventional method for the recovery of propionic acid from fermentation broth is the calcium hydroxide precipitation method. This method of recovery is expensive and unfriendly to the environment as it consumes lime and sulphuric acid and also produces a large quantity of calcium sulphate sludge as solid waste. Among the all alternate, reactive extraction is found to be more efficient separation process, because of its high selectivity for desired compounds and low waste production. So, Separation of propionic acid from aqueous solutions (fermentation broth or wastewater stream) can be intensified through reactive extraction using phosphorus bonded oxygen bearing extractant (TBP) with diluents. The reactive extraction of propionic acid by tri-n-butylphospahte (TBP) in inert diluent (ndecane) and a modifier (1-decanol) is studied. The equilibrium experiments are carried out to investigate the effects of modifier composition (1-decanol), extractant (TBP) concentration, and initial acid concentration on extraction efficiency. The extraction efficiency is defined by distribution coefficient and degree of extraction. The extraction efficiency is found to be increased with increasing modifier composition and TBP composition, and decreased with increasing initial acid concentration. Mathematical modeling using mass action law approach is used to determine the number of extractant (TBP) molecules (n) involved in the acid:TBP complex formation. The extraction equilibrium constants (KE) is also estimated using same modeling approach.