Recovery of Propionic Acid using Reactive Extraction

Propionic acid is a carboxylic acid produced by fermentation and widely used in chemical, pharmaceutical and food industries. It is used primarily for animal feed preservation, including hay, silage, and grains, and in human foods (mainly in baked goods and cheeses). The growing demand of this acid draws attention towards a more economical energy efficient technology. The conventional methods for the recovery of propionic acid from fermentation broth are expensive and unfriendly to the environment. Reactive extraction with specified extractant giving a higher distribution coefficient has been emerged as a promising technique for the recovery of acids. For the design of extraction process, equilibrium data of extractant is required to select a proper extractant for reactive extraction. In the present work equilibrium study for the reactive extraction of propionic acid is carried out. Various diluents and extractants are used for equilibrium studies and data are presented in terms of distribution coefficient and equilibrium complexation constant. On the basis of higher distribution coefficient and equilibrium complexation constant, the best combination of diluent extractant is suggested. In physical equilibria, distribution coefficient (KD = 2.14) with 1-octanol is maximum at concentration of 5% (v/v). Distribution coefficient(KD = 2.3) is enhanced with Aliquat 336 (10%) in 1-octanol for the reactive extraction of propionic acid. Presented data can be used for the design of reactive extraction process for the recovery of propionic acid. INTRODUCTION Over the last 3 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. The current economic impact of fermentation chemicals, however, is still limited, in large part because of difficulties of product recovery. Thus, for fermentation products to penetrate the organic chemicals industry, substantial improvements in the existing recovery technology are needed. Organic acids are widely used in the food, pharmaceutical and chemical industries. Fermentation technology for the production of organic acids in particular has been known for more than a century and acids have been produced in aqueous solutions. Propionic acid is used in the manufacture of herbicides, chemical intermediates, artificial fruit flavors, pharmaceuticals, cellulose acetate propionate, and preservatives for food, animal feed, and grain [1]. Commercial production of propionic acid is chiefly carried out by chemical synthesis from petroleum feedstocks [1], but fermentation is an attractive alternative to produce this acid from renewable resources. Several carbon sources have been used for this fermentation such as glucose [2], xylose [3], maltose [4], sucrose [5] and whey lac-tose [6]. 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. Thus there is a need to look at other methods of producing propionic acid. Reactive extraction with specified extractant giving a higher distribution coefficient has been proposed as a promising technique for the recovery of carboxylic and hydroxycarboxylic acids. This method is advantageous for alcohol and organic fermentations [7]. Some of the advantages include increased reactor productivity, ease in reactor pH control without requiring base addition, and use of a high-concentration substrate as the process feed to reduce process wastes and production costs. This method may also allow the process to produce and recover the fermentation