Separation of toluene from toluene/alkane mixtures with phosphonium salt based deep eutectic solvents

In this work, separation of aromatic hydrocarbons from aromatic/aliphatic mixtures by deep eutectic solvents (DESs) at room temperature was developed. It was found that DES formed by levulinic acid as hydrogen bond donor and tetrabutylphosphonium bromide (TBPB) as hydrogen bond acceptor could efficiently separate aromatic hydrocarbons from aromatic/aliphatic mixtures. Levulinic acid/TBPB mole ratio, DES/toluene mole ratio, toluene mole fraction , and extraction temperature had an influence on the selectivity and extraction rate of toluene. The extraction could be performed at optimal conditions of 6:1   mol ratio of levulinic acid to TBPB and 6.4:1   mol ratio of DES to toluene at room temperature. Toluene in DES could be recovered by distillation of toluene at 100   °C under reduced pressure and DES was reused four times without obvious decrease in weight, selectivity and extraction rate. The work may provide an environmentally friendly method to separate aromatic/aliphatic mixtures, which avoids using a large number of toxic organic solvents.