Published: October 10, 2011 r2011 American Chemical Society 13526 dx.doi.org/10.1021/ie201228u | Ind. Eng. Chem. Res. 2011, 50, 13526–13537 ARTICLE pubs.acs.org/IECR Natural Nontoxic Solvents for Recovery of Picolinic Acid by Reactive Extraction Mangesh D. Waghmare, † Kailas L. Wasewar,* ,‡ Shriram S. Sonawane, ‡ and Diwakar Z. Shende ‡ † Department of Chemical Engineering, Priyadarshini Institute of Engineering and Technology, Nagpur, 440019, India ‡ Department of Chemical Engineering, Visvesvaraya National Institute of Technology, Nagpur, 440010, India ABSTRACT: Pyridine carboxylic acids and their derivatives are attracting considerable attention for their presence in many natural products. 2-Pyridinecarboxylic acid, also known as picolinic acid is widely used in the pharmaceutical industries. Compared to chemical methods, enzymatic oxidation of 3-hydroxyanthranillic acid is an advantageous alternative for the production of picolinic acid. Reactive extraction is a promising method to recover carboxylic acid but suffers from toxicity problems of the diluent and extractant employed, therefore there is a need for a nontoxic extractant and diluent or a combination of less toxic extractants in a nontoxic diluent that can recover acid efficiently. The present paper focuses on the reactive extraction of picolinic acid using tri-n-butyl phosphate (TBP) in sunflower oil and castor oil. Results were presented in terms of distribution coefficients (0.0066 to 0.664 for sunflower oil and 0.0099 to 0.94 for castor oil), loading ratio (<0.5), degree of extraction (0.65 to 42.9% for sunflower oil and 0.9 to 74.6% for castor oil), and equilibrium complexation constants. Relative basicity, mass action law, and Langmuir models were used to represent the reactive extraction equilibrium for picolinic acidTBPdiluent. Model results are close to experimental results. 1. INTRODUCTION Picolinic acid (2-pyridine carboxylic acid) (C 6 H 5 NO 2 ) is a white colored crystalline solid with a carboxyl side chain at the 2-position. Being the isomer of nicotinic acid, picolinic acid acts as a chelating agent of elements like chromium, zinc, manganese, copper, iron, and molybdenum in the human body. Its utility is in the quantitative detection of calcium and in the production of phenylalanine, tryptophan, and alkaloid. Commercially available picolinic acid is used as an intermediate to produce pharmaceu- ticals (especially local anesthetics) and metal salts for the application of nutritional supplements. 1 Pyridine-derived car- boxylic acids like picolinic acid are also important from the industrial point of view; for example, in nuclear reactor deconta- mination, where the low oxidation state metal ion (LOMI) decontamination process uses V(II)/V(III) picolinic acid com- plexes in the decontamination solutions. Picolinic acid contains two active groups: a carboxyl group and a pyridinic nitrogen atom, therefore its aqueous solutions are weakly acidic. 2 Picolinic acid is produced via either chemical synthesis or by a fermentation route following enzymatic oxida- tion of 3-hydroxyanthranilic acid. It is also produced by the catabolism of tryptophan through kynurenine to 3-hydroxyan- thranilic acid which is then further acted upon by the enzyme 3-hydroxyanthranilic acid oxygenase. 3 Because of the increased cost of petroleum products, it is preferred to produce the carboxylic acids by fermentation over chemical synthesis. 4 A major drawback in the use of fermentation to produce these acids is the difficulty in recovery from the dilute solutions in which they are produced. The main problem with fermentation technology is that, as the acid is generated, the pH of the system falls. The lowering of pH destroys the bacterial species which are respon- sible for the generation of acids. This leads to low acid product yield and concentration. The extractive fermentation, in situ application of the solvent extraction technique, keeps the pro- duct concentration in the broth at a desired level and suppresses product inhibition by continuously removing the product from the fermentation broth. A number of methods are available, such as adsorption, precipitation, distillation, membranes, ion exchange, dialysis, reactive extraction etc., to recover carboxylic acids from fermen- tation broths or aqueous streams. Most of these methods have inherent drawbacks. Calcium hydroxide precipitation has a few shortcomings such as consumption of large quantities of reagents (H 2 SO 4 and lime), a large amount of waste generation per ton of acid produced, disposal problems of waste, and very poor sustainability. Dialysis has good potential but has the drawbacks of a frequent cleaning requirement, membrane fouling, and a requirement of a larger dialysis unit as compared to a fermenter. Higher power consumption is the main problem with electro- dialysis, although it allows simultaneous separation and concen- tration of the acid. Ion-exchange requires a large amount of chemicals and generates a large amount of waste. The distillation method is a well-established technology, but its drawbacks are formation of high-boiling internal esters, dimers and greater power consumption. 510 Reactive extraction with the proper selection of diluents and extractants can provide high selectivity and extraction but suffers from toxicity problems of solvents toward microbial strains. Selection of an extractant and diluent for reactive extraction should be on the basis of minimal toxicity and maximum capacity. The problem is more important when recovery is carried out in situ from the reactor, where extractant Received: June 8, 2011 Accepted: October 10, 2011 Revised: October 10, 2011