Adsorption of Ternary Mixtures of Methane, Carbon Dioxide and Hydrogen Sulfide from Biogas through Single-Walled Carbon Nanotubes: Temperature, Pressure and Pore Size Effects

Biogas typically refers to a gas produced by the anaerobic digestion or fermentation of organic matter, including manure, sewage sludge, municipal solid waste, biodegradable waste or any other biodegradable feedstock. Biogas is comprised primarily of CH4, CO2 and amounts of H2S. Biogas has the same characteristics as Natural gas, if cleaned up sufficiently form the H2S. Molecular simulations are valuable methods to investigate the separation characteristics of gas mixtures. Separation of CO2/CH4 mixture using different types of membranes such as zeolites, nanoporous carbons, molecular sieves, polymeric membranes is simulated by both Monte Carlo and molecular dynamics (MD) methods [1, 2] but there is a little knowledge about the sorption and transport of H2S from the biogas through a carbon nanotube. In this work we simulated the ternary mixture of CO2/CH4/H2S in single-walled carbon nanotubes (CNTs) as adsorption media and investigate the adsorption selectivity of binary mixtures of H2S/CH4 and CO2/CH4 and also the ternary mixture of these gases that naturally found in the biogas in several pressures, temperatures and various nanotube diameters. In this work we are going to simulate any of pure CH4, CO2 and H2S adsorption in CNT as membrane at 298.0 K of temperature and pressures from 1 to 6 atmospheres. Then with same conditions adsorption of CH4/CO2 and CH4/CO2/H2S equimolar mixtures in CNT will be measured to realize the effect of presence of other gases on each gas adsorption. Finally adsorption selectivity of H2S and CO2 versus CH4 will be calculated.