Equilibrium and Kinetic Studies of the Reactive Extraction of Nicotinic Acid with Tri-n-octylamine Dissolved in MIBK

The design of an extraction process requires equilibrium and kinetic data for the acid (solute)-amine (solvent) system used. In this study, equilibrium and kinetic experiments on the recovery of nicotinic acid (0.02-0.10 kmol-m(-3)) were performed using tri-n-octylamine (TOA; 0.115-0.459 kmol.m(-3)) dissolved in methyl isobutyl ketone (MIBK) as a diluent. The chemical equilibrium of acid and amine is interpreted as a result of the formation of both 1:1 and 2:1 complexes with an equilibrium constant (K-E) of 37.11 (kmol.m(-3))(-1.21). The mass-transfer coefficient (k(L) = 2.03 x 10(-5) m.s(-1)) of nicotinic acid in MIBK was determined in a stirred cell. Based on the values of Hatta number (0.089-0.123) and the criterion proposed by Doraiswamy and Sharma (Heterogeneous Reactions: Analysis, Examples, and Reactor Design; John Wiley & Sons: New York, 1984), the reaction was found to be a very slow chemical reaction occurring in the bulk of the organic phase. The reaction was found to have orders of 0.8 with respect to nicotinic acid and 0.5 with respect to TOA with a forward rate constant of 3.19 x 10(-3) (kmol. m(-3))(-0.3).s(-1) and a backward reaction rate constant of 8.6 x 10(-5) (kmol.m(-3))(0.91).s(-1).