(609d) Investigations of Use of Ionic Liquid in Extraction of Picolinic Acid From Aqueous Solutions

Abstract

Picolinic acid (C₆H₅NO₂₎ is an isomer of nicotinic acid, a pyridine compound with a carboxyl side chain at the 2-position. It is involved in the manufacturing of amino acids like tryptophan and phenylalanine etc. To improve the biological production of picolinic acid and its derivatives by fermentation, it is necessary to develop new environment friendly and efficient separation methods that improve the productivity of the acid (1, 2). The reactive extraction by a suitable extractant has been found to be a most promising alternative to the conventional separation processes to recover this acid from the fermentation broth and aqueous solution (3-5). Phosphorus bonded oxygen bearing extractants such as tri-n-butyl phosphate (TBP) and tri-n-octyl phosphine oxide (TOPO), and long chain aliphatic amines such as tri-n-octylamine (TOA), tri-octyl methyl ammonium chloride (Aliquat 336) and Amberlite LA-2 are effectively used for the reactive extraction of different carboxylic acids (3-8). The increasing emphasis on cleaner and environmentally benign extraction procedures has led to the systematic investigation of systems containing ionic liquids (ILs) - a new class of non-volatile alternative solvents. The unique physicochemical properties of  ILs and the relative ease with which these properties can be fine-tuned by altering the cationic or anionic moieties comprising the IL have led to intense interest in their use as alternatives to conventional organic solvents in a wide range of synthetic, catalytic, and electrochemical applications. In this study we have investigated the use green solvents, ionic liquids with for the extraction of picolinic acid along with the amine based extractant, tri-n-octylamine (TOA).

The extraction equilibrium experiments are carried out with aqueous (acid + water) and organic (IL + TOA) solutions in conical flasks of 25 ml and shaken at 100 rpm for 12 hours in a temperature controlled magnetic stirrer water bath at constant temperature (298.15 K). The aqueous solutions of picolinic acid are prepared in the concentration range of 0.01 to 0.18 M using doubled distilled water. The organic solutions are prepared by dissolving ionic liquid and TOA. After attaining equilibrium, the mixture of aqueous and organic phases is kept for separation in a separating funnel (60 ml) for 2 hrs at 298.15 K. After the separation of both phases, the aqueous phase acid concentration is analyzed with titration using NaOH solution of 0.008 N and phenolphthalein as an indicator. The acid concentration in the organic phase is calculated by mass balance. The experimental data are analyzed by calculating distribution coefficient (K_D = C_org/C_aq) and degrees of extraction [E = K_D / (1 + K_D)].

The equilibrium experiments are carried out for the extraction of picolinic acid using two ionic liquids (1-butyl,3-methylimidazolium hexafluorophosphate, C4MIMPF6 and 1-octyl,3-methylimidazolium hexafluorophosphate, C8MIMPF6) with and without TOA. The effect of different parameters such as type of IL, volume phase ratio, composition of IL in organic phase and concentration of acid in aqueous phase on the extraction is also determined.  The extraction efficiency is found to be increased by increasing the TOA concentration in IL upto a maximum value and after that it is showing the decrease in degree of extraction. Due to high viscocity and very low quantity of IL, pure IL is not found better extractant for the extraction. 1-octyl,3-methylimidazolium hexafluorophosphate, C8MIMPF6 containing higher alkyl chain showed less extractability as compared to C4MIMPF6. The aqueous phase concentration is also affecting the extraction efficiency of IL and TOA. It is found to increase the degree of extraction with an increase in acid concentration at constant organic phase concentration. The highest degree of extraction is achieved 94% at acid concentration of 0.18 mol/L and organic phase composition (TOA:IL = 2:3 v/v).

It can be seen from data presented by Datta et al, 2012, Very high amount of TOA (equal molar solution and 1:1 volume phase ratio) is required to achieve the degree of extraction more than 90%.  The present investigations on the use of IL for extraction of picolinic acid show that small amount of IL can replace the huge amount of TOA to give same or better degree of extraction.

Keywords: Green Solvent; Ionic liquid; Equilibria; Reactive extraction; Tri octyl amine.

Refernces:

1. Wang, L.R.; Fang, Y. (2005) UV-Raman study and theoretical analogue of picolinic acid in aqueous solution. J. Molec. Spect., 234: 137.
2. Gonzalez, J.M.; Fernandez, M.A.; Pizarro, C. (1997) Application of weakly basic copolymer polyacrylamide (acrylamide-co- N,Ndimethylaminoethyl methacrylate) gels in the recovery of citric acid. J. Euro. Poly., 33: 475.
3. Kumar, S.; Babu B.V. (2009) Process intensification of nicotinic acid production via enzymatic conversion using reactive extraction. Chem. Biochem. Eng. Q. 23: 367.
4. Kertes, A. S.; King, C. (1986) Extraction chemistry of fermentation product carboxylic acids. J. Biotechnol. Bioeng., 28: 269.
5. Kumar, S.; Babu, B.V. (2008) Process intensification for separation of carboxylic acids from fermentation broths using reactive extraction. J. Fut. Eng. Technol., 3 (3): 19.
6. Kumar, S.; Wasewar, K. L.; Babu, B. V. (2008) Intensification of nicotinic acid separation using organophosphorous solvating extractants by reactive extraction. Chem. Eng. Tech. 31 (11): 1584.
7. Datta, D., Kumar, S. Reactive Extraction of Pyridine Carboxylic Acids with N, N-Dioctyloctan-1-amine Dissolved in Five Different Diluents. Sep.Sci.Technol. 2013, 48(6), 898-908.
8. Datta, D., Kumar, S., Wasewar K.L., Babu B.V.  Comparative Study on Reactive Extraction of Picolinic Acid with Six Different Extractants (Phosphoric and Aminic) Dissolved in Two Different Diluents (Benzene and Decane-1-ol). Sep.Sci.Technol. 2012, 47(7), 997-1005.