Modelling of carbon dioxide: methane separation using titanium dioxide nanotubes

摘要

The separation of carbon dioxide (CO2) and methane (CH4) mixture is of considerable interest in order to purify natural gas, and one suggestion is that titanium dioxide (TiO2) nanotubes might be exploited to separate a gaseous mixture of methane and carbon dioxide. In this study, we employ both Coulomb’s law and the Lennard–Jones potential to determine the total energy of adsorption CO2 and CH4 into a TiO2 nanotube. The CH4 is a nonpolar molecule, and therefore the Coulombic interaction may be neglected. The total energy of the systems is evaluated utilizing the continuous approximation, which assumes that the two gas molecules are spheres of certain radii, while the tube is modelled as a cylinder. Further, both electrostatic and van der Waals potentials are determined and expressed in the exact analytical formulae. The numerical results predict that a single molecule of CO2 or CH4 can be encapsulated into the tube. On assuming both gases may form clusters with the same proportion of atom species, a cluster of CO2 will not be adsorbed into the tube when its radius exceeds 3.32Å. On the other hand, a cluster of CH4 can be encapsulated into an appropriate radius of TiO2 nanotube. These results indicate that TiO2 nanotubes may be useful in the purification of CH4.