Investigating the influence of solvent molecular structure on the separation of α-olefins in Fischer-Tropsch naphtha.

The rapid expansion of high-end polyolefin and photovoltaic industries has pushed the annual demand for C6C8 α-olefins to million tons. Fischer-Tropsch naphtha contains over 50 % α-olefins, yet their boiling points differ very little from those of the corresponding alkanes, rendering conventional distillation unfeasible. Extractive distillation is regarded as a viable industrial separation approach. Using the n-hexane/1-hexene, we combine quantum-chemical calculations with vapor-liquid equilibrium experiments to systematically evaluate four solvents-2-pyrrolidone (2-P), dimethyl sulfoxide (DMSO), N,N-dimethylformamide (DMF) and γ-butyrolactone (GBL)-and establish a quantitative "solvent structure-interaction energy-separation efficiency" relationship. Molecular polarity index and electrostatic surface potential are introduced for rapid solvent pre-screening; weak interaction analysis and interaction-energy computations clarify the selective recognition of 1-hexene. Experimental data are in agreement with theoretical predictions: solvents containing S/N heteroatoms-DMSO, 2-P and DMF-augment the negative charge on oxygen via inductive effects. Among them, the oxygen atom of DMSO exhibits the highest electron density and thus delivers the most efficient separation, whereas GBL, bearing only oxygen atoms with lower electron density, shows the poorest performance. The greater the number of electronegative functional groups and the tighter their spatial arrangement, the stronger the solvent-1-hexene interaction and the higher the separation efficiency. The proposed model provides a robust theoretical and experimental basis for the rational design of high-performance extractants and it can also be extended to the separation of other systems with polarity differences.