Separation of Biogas Components with Single Wall Carbon Nanotubes: a GCMC Simulation.

Biogas is a green energy source that mainly contains CH4, CO2 ,traces of H2S and fractions of H2O vapor. One of the effective methods in biogas treatment from its pollutants is adsorptive separation. Here, enrichment of methane using (10, 10) and (6, 6) carbon nanotubes (CNTs) in modelled biogas consisting CH4, CO2 and H2S is studied. Simulations were carried out using Grand Canonical Monte Carlo (GCMC) method. Adsorption isotherms obtained at various temperatures and pressures for two single wall carbon nanotubes (SWCNTs). To quantify the separation ability of the nanotubes the adsorptive separation factors for H2S/CH4 and CO2/CH4 were calculated. For studding temperature effect, simulations at two (0.1 and 1 MPa) pressures and four temperatures: 288, 298, 318 and 338 K have been performed. In all studied conditions, CO2 is preferentially adsorbed by CNTs. Results have shown that the two separation factors are considerable, particularly for (10, 10) CNT. Additionally, the adsorption and selectivity behaviour of studied gases were considered in (6,6), (8,8) and (10,10) CNT hexagonal bundles for comparison. The results for single nanotubes were confirmed with the bundles. Hence, despite lower concentration of CO2 than CH4 and trace amount of H2S in biogas, they can be separated from methane effectively by CNTs as adsorbents. Our results showed that the CNTs can be remarkable tools in methane separation from biogas.