Extraction of toluene, o-Xylene from Heptane and Benzyl Alcohol from Toluene with Aqueous Cyclodextrins

The separation of aromatic compounds (toluene and o-xylene) from heptane and of benzyl alcohol from toluene with aqueous solutions of cyclodextrins has been experimentally investigated, because cyclodextrins and its derivatives can selectively incorporate several organic compounds, whereas the separation of the aqueous solution of complexed cyclodextrins from the organic feed is simple. Cyclodextrins are not soluble in organic liquids, but cyclodextrin derivatives are highly soluble in water. Hydroxypropyl-β-cyclodextrins with different degrees of substitution and methylated β-cyclodextrin were selected for the extraction of toluene and o-xylene from heptane. Hydroxypropyl-β-cyclodextrin (two different substitution degrees) and hydroxypropyl-α-cyclodextrin were selected for the extraction of benzyl alcohol from toluene. The liquid–liquid distribution experiments were carried out at room temperature. Toluene and o-xylene form 1:1 complexes with different cyclodextrins and heptane can form 1:1 to 1:3 complexes. Benzyl alcohol forms 1:3 complexes with hydroxypropylated cyclodextrins. The models developed describe the experimental data reasonably well, considering the large deviations in the analyses. Aqueous cyclodextrin solutions are not feasible for the separation of aromatic components from aliphatic hydrocarbons, due to low distribution ratios of toluene (0.05) and o-xylene (0.023) between the aqueous and organic phase. With high distribution ratios of benzyl alcohol, between 0.3 and 2.2 depending on the CD concentration (at a solvent-to-feed ratio of 1) and a benzyl alcohol/toluene selectivity of at least 100, aqueous hydroxypropylated cyclodextrin solutions have sufficient potential for extracting benzyl alcohol from toluene.