High-Performance Carbon Molecular Sieves for the Separation of Propylene and Propane

High-performance
carbon molecular sieves (CMSs) for the separation
of propylene (C3H6) and propane (C3H8) were synthesized in this study by chemical vapor deposition
(CVD) of benzene on the pore entrances of activated carbon. The C3H6 and C3H8 separation characteristics
of the CMSs were controlled by altering the amount of carbon deposited
during CVD, and the resulting characteristic curve featuring the kinetic
selectivity of C3H6 over C3H8 as a function of the adsorption rate constant of C3H6 is considered to be the upper bound of the C3H6–C3H8 separation factor
for current CMSs because of the presence of previously reported CMS
data under this curve. Additionally, CMS models were constructed using
grand canonical molecular dynamics (GCMD) simulations mimicking the
process of CVD, which revealed that the kinetic selectivity of C3H6 over C3H8 strongly depended
on the size of the pore entrances at the level of 0.01 nm, and that
strict control of the pore-entrance size was crucial for obtaining
high-performance CMSs for C3H6–C3H8 separation. This was essentially achieved by
controlling the duration of CVD, which led to the experimental realization
of CMSs with a C3H6 selectivity over C3H8 of >2000 and a high uptake rate of C3H6. A design guideline for the development of high-performance
CMSs for C3H6–C3H8 separation was proposed based on theoretical calculations performed
using idealized carbon structures, which extracted the characteristics
of the CMS models obtained from the GCMD simulations.