Windowed Carbon Nanotubes for Efficient CO2 Removal from Natural Gas
HJ Liu and VR Cooper and S Dai and DE Jiang, JOURNAL OF PHYSICAL CHEMISTRY LETTERS, 3, 3343-3347 (2012).
We show from molecular dynamics simulations that windowed carbon nanotubes can efficiently separate CO2 from the CO2/CH4 mixture, resembling polymeric hollow fibers for gas separation. Four CO2/CH4 mixtures with 10, 30, 50, and 80% CO2 are investigated as a function of applied pressure from 80 to 180 bar. In all simulated conditions, only CO2 permeation is observed; CH4 is completely rejected by the nitrogen- functionalized windows or pores on the nanotube wall in the accessible time scale, while maintaining a fast diffusion rate along the tube. The estimated time-dependent CO2 permeance ranges from 10(7) to 10(5) GPU (gas permeation unit), compared with similar to 100 GPU for typical polymeric membranes. CO2/CH4 selectivity is estimated to be similar to 10(8) from the difference in free-energy barriers of permeation. This work suggests that a windowed carbon nanotube can be used as a highly efficient medium, configurable in hollow-fiber-like modules, for removing CO2 from natural gas.
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