Reactive Extraction of Picolinic Acid Using Tri-n-octylamine Dissolved in Different Diluents: Effect of Solvent Polarity

Picolinic acid is a useful intermediate for the synthesis of different pharmaceuticals, herbicides, and metal salts which is applied in the food supplements. Due to the rapid rise in the costs of fossil resources, efforts are made to synthesize this carboxylic acid from the renewable feedstock like biomass. The recovery of picolinic acid can be achieved by reactive extraction which is catching the attention of the researchers. For higher selectivity and efficient recovery of acid with high distribution, a proper combination and selection of extractant diluent system is required. Therefore, the current study is focused on the reactive extraction of picolinic acid [(0.01 to 0.10) mol.kg(-1) from aqueous solution by using tri-n-octylamine [TOA, (0.115 to 0.459) mol.kg(-1)] as extractant dissolved in five different diluents (cyclohexane, chlorobenzene, dichloromethane, 4-methylpentan-2-one, and octan-1-ol). The extraction results are interpreted and analyzed defining three terms like distribution coefficient (K-D), degree of extraction (%E), and loading ratio (Z). Highest value of the K-D (16.64) is obtained with 0.459 mol.kg-1 of TOA in DCM at 0.10 mol-kg(-1) of picolinic concentration. The solvent's ability to extract acid with TOA is observed as DCM >= MIBK > chlorobenzene > octan-1-ol > cydohexane. The number of TOA molecules (n) in the acid-TOA complex formed at equilibrium and equilibrium complexation constants (K-E) are estimated by developing a mathematical model using mass action law and regressing the experimental results.