The separation performance of two-dimensional ZnPP-grid molecular sieve for C6 alkane molecules:A first-principles calculation

Abstract

Membrane separation technology plays a vital role in producing high-octane gasoline field. Based on the first-principles calculation, ZnPP-Grid molecular sieve with uniform intrinsic pore is used to systematically evaluate the separation performance of hexane isomers and cyclohexane. The difference of energy barriers indicates that ZnPP-Grid membrane allows linear hexane molecule to pass through the pore, but block di-branched 2,2-dimethylbutane molecule. The analysis of geometric and energy variation reveals that during penetration processes, the effect of molecular changes on the penetration barrier is greater than the effect of ZnPP-Grid membrane deformation on barrier, which is related to the size and structural flexibility of molecules and ZnPP-Grid molecular pore. Especially, when cyclic cyclohexane molecule travels to the pore area, the maximum geometric distortion of pore-rimmed atoms have not caused higher energy barrier than mono-branched 3-methylpentane, which also proves the flexibility of ZnPP-Grid membrane. The molecular sieve exhibits superior hexane/cyclohexane, hexane/branched isomers separation performance with high selectivity of 108–1080 within 150 K–400 K. More importantly, the hexane isomers mono-branched 3-methylpentane/di-branched 2,2-dimethylbutane can be discriminated with high selectivity ∼1029 at 300 K, which helps to obtain high-octane gasoline. The results demonstrate that the ZnPP-Grid molecular sieve is probably an excellent molecular sieve in petrochemical industry.