The extraction equilibria of the type 2 ternary systems containing (water + isovaleric acid + solvent) have been investigated at T = (298.2 +/- 0.1) K and P = (101.3 +/- 0.7) kPa. Aromatic solvents xylene, chlorobenzene and benzyl ether give the largest distribution ratios and separation factors, as compared to 1-phenyl ethanol, cyclohexanol and 1-decanol. The distribution data have been subjected to formulation of an optimization structure for an effective acid separation. The optimization approach uses a derivative variation method to efficiently identify the optimization range through analyzing the first order derivatives of the optimized quantity and the non-linear deviation profile of the derivative value. Some aspects of selection of an appropriate criterion for designing optimum extraction are discussed. Modeling efforts based on the LSER (linear solvation energy relation) principles have shown considerable success. The proposed SERLAS model using six physical descriptors of the components has provided relatively reliable fits with a mean relative error of 10.1% and satisfies have established limiting behavior of the physical event. As well, the tie-lines of relevant systems have been predicted by the UNIFAC-original model. (C) 2015 Elsevier Ltd. All rights reserved.