Liquid–Liquid Equilibria of Formic Acid and Furfural in a Biphasic Aqueous–Organic System: Optimization of Solvent and Amine Extractant

Liquid–liquid equilibria of formic acid (FA) and furfural in a biphasic aqueous–organic system were studied. Fourteen kinds of samples with a high boiling point and a large density difference with water were first screened to measure the distribution coefficient of furfural. Eight solvents with a high furfural distribution coefficient were further screened for FA extraction. Six solvents (1,2-dimethoxybenzene, 2,4-dimethyl-1-nitrobenzene, diethyl phthalate, tributyl phosphate, dibutyl phthalate, and dibutyl sebacate) with a low FA distribution coefficient were then selected to measure the mutual solubilities at 298.15 K. Furthermore, two amine extractants (tri-n-octylamine and amine N235) were diluted in six solvents for the extraction of FA and furfural from aqueous solutions to optimize the solvent and extractant. 2,4-Dimethyl-1-nitrobenzene or diethyl phthalate was proven to be more suitable for this system. Effects of the amine extractant concentration in solvents were evaluated to balance the furfura...