In silico synthesis of carbon molecular sieves for high-performance air separation

Abstract

We performed nonequilibrium molecular dynamics simulations of the chemical vapor deposition (CVD) of hydrocarbons on a precursor-activated carbon model with a slit-like pore (in silico CVD simulation) to explore design guidelines for the synthesis of high-performance carbon molecular sieves (CMSs) for air-separation purposes. The dependence of the CVD process on gas species was investigated using “united-atom” hydrocarbons mimicking ethylene, benzene, toluene, and mesitylene. The obtained CMS models were then used to evaluation the diffusion rate constants of O2 and N2 using the transition state theory. We also constructed idealized carbon pore structures that extracted the characteristics of the CMS models obtained via the in silico CVD simulations to understand the relation between the size and geometry of pore mouths, diffusion rate constants, and kinetic O2 selectivity. We found that most of the simulated results were supported by experimental evidence. Furthermore, we conclude that a high-performance CMS for air separation requires the development of thin amorphous carbon at the pore mouths of the precursor-activated carbon by CVD, which provides a single energy barrier for O2 diffusion and effectively prevents the formation of multiple energy barriers.