Liquid–liquid equilibrium extraction of ethanol with mixed solvent for bioethanol concentration

The extraction of ethanol with the solvents of aldehydes mixed with m-xylene was studied for the bioethanol concentration process. Furfural and benzaldehyde were selected as extraction solvents, with which the solubility of water is small, expecting large distribution coefficient of ethanol. The liquid–liquid two-phase region was the largest with m-xylene solvent, followed by benzaldehyde and furfural. The region of two liquid–liquid phase became larger with the mixed solvent of m-xylene and furfural than that with furfural solvent. The NRTL model was applied to the ethanol–water–furfural–m-xylene system, and the model could well express the liquid–liquid equilibrium of the system. For any solvent used in this study, the separation selectivity of ethanol relative to water decreased as the distribution coefficient of ethanol increased. The separation selectivity with m-xylene was the largest among the employed solvents, but the distribution coefficient was the smallest. The solvent mixture of furfural and m-xylene showed relatively high distribution coefficient of ethanol and separation selectivity, even in the higher mass fraction of m-xylene in the solvent phase.The ethanol extraction with a countercurrent multistage extractor by a continuous operation was simulated to evaluate the extraction performance. The ethanol content could be concentrated in the extract phase with relatively small number of extraction stages but low yield of ethanol was obtained.

Triangular diagrams of liquid–liquid equilibrium for ternary and quaternary systems.Figure optionsDownload as PowerPoint slide