Recovery of furfural from aqueous solution by ionic liquid based liquid-liquid extraction

Liquid-liquid extraction with imidazolium based ionic liquids ([C(4)mim][PF6], [C(6)mim][PF6], and [C(8)mim][PF6]) is proposed for the separation of furfural or 5-methylfurfural from aqueous solution. Factors affecting the extraction of furfural or 5-methylfurfural have been studied. It was shown that the extraction equilibria can be achieved within 30min and the process was less affected by the factors such as volume ratio and feed concentration. The partition coefficients of furfural and 5-methylfurfural decreased with increasing temperature. [C(6)mim][PF6] was found to have the best extraction ability among the three ionic liquids studied. Presence of small amount of NaCl or Na2SO4 in the aqueous phase results in the considerable increase in the partition coefficients of furfural because of the competitive hydration of the salts with furfural. A thermodynamic study revealed that the extraction process was driven mainly by hydrophobic interactions. Further experimental results indicated that furfural can be separated selectively from aqueous furfural/acetic acid mixtures.