Novel Porous Carbon Nanotube Membranes for Separation of CH4/CO2 and CH4/H2 Mixtures

Separation of gas mixtures is important for a wide range of applications. Membrane separators have the potential to operate at high energy efficiency. However, it has long been noted that there is a fundamental trade-off between selectivity and permeance for polymeric membranes, i.e., the larger the selectivity, the smaller the permeability and vice versa. Carbon nanotubes (CNTs) exhibit very different transport behavior compared with other nanoporous materials, having transport diffusivities that orders of magnitude higher than other materials. Coupling this high diffusivity with high selectivity would lead to a membrane that transcends the limits of traditional membranes. We have theoretically designed a porous carbon nanotube (PCNT) by generating pores on the wall of CNTs. Our simulations show that hypothetical PCNT membranes exhibit high selectivities for CH₄/H₂ and CH₄/CO₂ mixtures, accompanied by high permeance.