(120d) Using Porous Carbon Nanotube Membranes for Separation of CH4/CO2 and CH4/H2 Mixtures

Although separations are typically expensive and energy-intensive, membranes have the potential to separate gases both economically and efficiently. However, conventional polymeric membranes exhibit a tradeoff between selectivity and permeance. Carbon nanotubes (CNTs) exhibit very different transport behavior compared with other nanoporous materials, having transport diffusivities orders of magnitude higher than other matierals. Theoretically, gas mixtures could be separated by pores in a CNT membrane via a size-sieving mechanism. This means that nanoporous CNT membranes have the potential to be both selective and permeable, overcoming the limitations of conventional membranes.

We modeled a theoretical porous carbon nanotube (PCNT) membrane by generating pores on the wall of a CNT. We used molecular dynamics simulations to study fluid transport across the PCNT membrane, comparing models with rigid and flexible bonds. We also calculated the potential energy surfaces of each fluid molecule passing through the PCNT. Our simulations of both rigid and flexible PCNTs showed high selectivity for CH4/H2 and CH4/CO2 mixtures. Separations of N2/CO2 mixtures were also studied.