Windowed Carbon Nanotubes for Efficient CO2 Removal from Natural Gas

TL;DR

This study uses molecular dynamics simulations to show that windowed carbon nanotubes can selectively and efficiently remove CO2 from natural gas mixtures, outperforming traditional polymeric membranes in permeance and selectivity.

Contribution

The paper introduces a novel design of windowed carbon nanotubes that achieve high CO2 selectivity and permeance for natural gas purification, demonstrated through detailed molecular dynamics simulations.

Findings

CO2 permeance ranges from 10^5 to 10^7 GPU.

CO2/CH4 selectivity is approximately 10^8.

Complete rejection of CH4 in all simulated conditions.

Abstract

We demonstrate from molecular dynamics simulations that windowed carbon nanotubes can efficiently separate CO2 from the CO2/CH4 mixture, resembling polymeric hollow fibers for gas separation. Three CO2/CH4 mixtures with 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 timescale, while maintaining a fast diffusion rate along the tube. The estimated time-dependent CO2 permeance ranges from 107 to 105 GPU (gas permeation unit), compared with ~100 GPU for typical polymeric membranes. CO2/CH4 selectivity is estimated to be ~108 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.