Amide solvents for extraction and separation of 1-hexene from n-heptane: Effect of the amount of methyl groups

In this work, the influence mechanism of methyl group in the structure of amide solvent on the extraction and separation of alkene (1-hexene or 1-octene) from n-heptane has been studied by a combination of liquid-liquid equilibrium (LLE) experiments and quantum chemical calculations. For LLE experiments, as the number of methyl groups in the extractant structure increases, its selectivity for alkene (1-hexene or 1-octene) gradually decreases, and the distribution coefficients of alkene (1-hexene or 1-octene) and n-heptane gradually increase. In the interaction between 1-hexene and extractant, the amount and intensity of C-H & ctdot;O interactions, as well as the presence or absence of N/C-H & ctdot;pi interactions and their intensities, are all affected by the amount (0,1,2,3) of methyl group introduced into the amide solvent. The existence of the C-H & ctdot;O and N-H & ctdot;pi interactions were verified by the infrared spectroscopy. With increasing methyl group amounts in the extractant structure, the dispersion interaction strengthens, while the contribution percentage of electrostatic interaction and Delta Eelst/Delta E declines, leading to the increase of distribution coefficient and decrease of selectivity for alkene (1-hexene or 1octene) respectively.