Liquid-liquid extraction of isovaleric acid using Alamine 308/diluent and conventional solvent systems: Effect of diluent and acid structure

Distribution of isovaleric (3-methyl butanoic) acid between water and Alamine 308 (triisooctylamine) dissolved in C-5 and C-6-ring included diluents of proton-donating and -accepting (cyclopentanol, cyclohexanone), polar (chlorobenzene) and inert (toluene) types, as well as a comparison with the extraction equilibria of pure diluent alone (chloroform) have been studied at 298 K. Among the tested C-6 ring-containing and aliphatic diluents, cyclic alcohol/amine system yields the highest synergistic extraction efficiency. The strength of the complex solvation was found to be reasonably large for halogenated aromatics favoring mainly the formation of acid(1)-amine(2) structure. The influence of the acid structure over distribution has been interpreted through comparing the extractabilities of seven acids containing different functional groups, i.e., isovaleric, formic, levulinic, acetic, propanoic, pyruvic and nicotinic acids. The results were correlated using a modified linear solvation energy relation (METLER) and versions of the mass action law, i.e., a chemodel approach and a modified Langmuir equilibrium model comprising the formation of one or two acid-multiple amines complex formation