CO Separation from H2 via Hydrate Formation in Single-Walled Carbon Nanotubes.

Abstract

Hydrogen is an alternative fuel without generating greenhouse gas or other harmful emissions. Industrial hydrogen production, however, always contains a small fraction of carbon monoxide (CO) (∼0.5-2%) that must be removed for use in fuel cells. Here, we present molecular dynamics simulation evidence on facile separation of CO from H2 at ambient pressure via the formation of quasi-one-dimensional (Q1D) clathrate hydrates within single-walled carbon nanotubes (SW-CNTs). At ambient pressure, Q1D CO (or H2) clathrates in SW-CNTs are formed spontaneously when the SW-CNTs are immersed in CO (or H2) aqueous solution. More interestingly, for the CO/H2 aqueous solution, highly preferential adsorption of CO over H2 occurs within the octagonal or nonagonal ice nanotubes inside of SW-CNTs. These results suggest that the formation of Q1D hydrates within SW-CNTs can be a viable and safe method for the separation of CO from H2, which can be exploited for hydrogen purification in fuel cells.