Selective and Efficient Separation of Levulinic, Acetic and Formic Acids From Multi-Acid Solutions by Adjusting Process Parameters

Abstract

This investigation focuses on the recovery of levulinic-(LA), acetic-(AA) and formic acids (FA) from aqueous mixed-acid solutions by reactive extraction using tri-n-octylamine (TOA). Alcohols were found to be the most efficient solvents tested. Recoveries increased with shorter alcohol chain length and higher TOA concentrations. Yields decreased with pH and maximum efficiencies were obtained at the unadjusted pH (1.83) of the ternary -acid solutions for all acids; with LA, maximum selectivity occurred at pH 5. Higher TOA levels enhanced efficiency in mixtures but slightly reduced selectivity. For LA recovery, efficiency and selectivity using 0.5 M TOA in 1-hexanol were 92 % and 23.8 %, respectively. Co-extraction of AA ceased at consecutive extractions (from 2nd to 10th) and 93.6 % of LA was recovered with a selectivity of 98 % after ten subsequent steps. LA in the organic phase was stripped with an efficiency of-91 % with aqueous 1.0 M NaNO3. Selective extraction of AA and FA from binary-acid solutions was achieved at pH 5. The selectivity and separation factor decreased at higher TOA concentrations; however, 94.2 % of the AA was recovered with a selectivity of 93 % after seven successive extractions, followed by-93 % recovery by back extraction. The remaining FA (94.2 %) in the aqueous solution had a selectivity of-95 %. The data show that multi-stage reactive extraction can selectively separate LA, AA and FA from ternary-and binary-acid solutions.