Engineering, 2011, 3, 829-835 doi:10.4236/eng.2011.38101 Published Online August 2011 (http://www.SciRP.org/journal/eng) Copyright © 2011 SciRes. ENG Equilibrium Study for Reactive Extraction of Caproic Acid in Mibk and Xylene Kailas L. Wasewar*, Diwakar Z. Shende Department of Chemical Engineering, Visvesvaraya National Institute of Technology, Nagpur, India E-mail: k_wasewar@rediffmail.com Received November 19, 2010; revised June 8, 2011; accepted June 20, 2011 Abstract The recovery of caproic acid from the aqueous stream is of practical relevance due to its market value and the stringent environmental standards. The profound success of reactive extraction has been noted in the re- covery of carboxylic acids from dilute solutions. In present paper, equilibrium of caproic acid with ali- quat-336, a quaternary amine compound, in xylene and Methyl Isobutyl Ketone (MIBK) has been studied. Equilibrium parameters such as distribution coefficients, loading ratio, degree of extraction and equilibrium complexation constants have been presented. The data obtained is useful in understanding the equilibrium characteristics and efficient design of the recovery process of caproic acid by reactive extraction. Keywords: Caproic Acid, Reactive Extraction, Aliquat-336, Xylene, MIBK 1. Introduction The recovery of caproic acid from an aqueous stream is of considerable commercial importance from an envi- ronmental point of view. Caproic acid impart finite chemical oxygen demand (COD) and biochemical oxy- gen demand (BOD) to the aqueous waste [1]. Caproic acid is formed during the air oxidation of cyclohexane in the manufacture of cyclohexanone/nol in a caprolactam plant. Caproic acid is a by-product and conventionally separated from the reaction mixture by extraction with an aqueous caustic to form water-soluble, sodium salt of respective acids [2]. The resulting aqueous stream (after extraction with aqueous caustic) is then neutralized with H 2 SO 4 to liberate the caproic acid. Thus, this method of recovery is expensive and unfriendly to the environment as it consumes sodium hydroxide and sulphuric acid and also produces a large quantity of sodium sulphate sludge as solid waste. Caproic acid is a carboxylic acid and it can be pro- duced by the fermentation route [3]. Carboxylic acids are promising intermediates, because the oxygen of the bio- mass is placed in a form that is useful for further reaction with many other products. Low concentrations of car- boxylic acids (<10%) are achieved in fermentations. Chemical reaction combined with extraction can be con- sidered as an alternative to the conventional calcium salt precipitation techniques for the recovery of carboxylic acids from aqueous stream. Reactive extraction with specified extractant giving a higher distribution coeffi- cient has been proposed as a promising technique for the recovery of carboxylic and hydroxycarboxylic acids [4,5]. Reactive liquid-liquid extraction has the advantage that caproic acid can be removed easily from aquesous str- eam. Further, the caproic acid can be re-extracted and the extractant recycled to the process. When selecting an extractant, along with other considerations such as price, availability, ease of regeneration, very high distribution coefficients, and low toxicity, one must ensure that the extractant is environment friendly [1]. In other words, the extractant should have as low solubility in water as possible, so that it does not add substantially to COD of the aqueous raffinate. Methyltricaprylammonium chlo- ride (Aliquat-336) is one such solvent that process envi- ronmental engineers can use in their process [6-8]. Long-chain aliphatic amines are effective extractants for the separation of carboxylic acids from dilute solu- tion [6-8]. The amines are been favored because of lower cost and generally higher distribution coefficient. Among different amines, extraction with primary amines is cha- racterized by a large mutual solubility of the aqueous and organic phase. The secondary amines have the highest reported distribution coefficient, but tend to form amides is the downstream regeneration by distillation. The qua- ternary amines extract carboxylic acids at both acidic and basic pH via an anoin exchange mechanism [7]. Conse-