Molecular Simulations on Tuning the Interlayer Spacing of Graphene Nanoslits for C₄H₆/C₄H₁₀ Separation

There
are great challenges in developing efficient membranes to
replace the currently energy-intensive cryogenic distillation processes
for purifying C4H6 from C4H6/C4H10 mixtures due to their similar physical
and chemical properties. Here, we investigated the performance of
graphene slits with different interlayer spacings for C4H6/C4H10 separation via molecular
simulations. The results demonstrate that the 3.4-Å-interlayer-spacing
graphene slit only allows the penetration of C4H6 due to the size sieving effect and the permeance of C4H6 is up to 2.09 × 106 GPU. When the interlayer
spacing increases to 3.6–6.8 Å, the graphene slits still
exhibit the preferential penetration for C4H6 over C4H10 due to the π–π
adsorption interaction between graphene sheets and C4H6. Surprisingly, the graphene slits (>10.2 Å) exhibit
the preferential penetration for C4H10 over
C4H6 owing to the diffusivity of C4H10 being much larger than that of C4H6 under confined conditions. In conclusion, by fine-tuning
the interlayer spacing of graphene slits, the dominant separation
mechanism is switched in the order of size sieving, thermodynamic
adsorption, and dynamic diffusion, thereby achieving the controllable
regulation of the preferential permeation from C4H6 to C4H10. C4H10-selective membranes are of great significance for energy saving.
The tuning strategy is expected to be applied in different paraffin/olefin
separation scenarios such as high-content and low-content olefin feedstocks.