Enrichment of ventilation air methane by adsorption with displacement chromatography technology: Experiment and numerical simulation

Using the principles of displacement chromatography, a cost-effective adsorption separation method for the recovery of ventilation air methane (VAM) is developed. A fixed bed with activated carbon beads (ACBs) is used to adsorb low-concentration methane from VAM gas. The stronger adsorption component CO2 passes through the column to displace the adsorbed CH4. This displacement step generates a product with highly pure CH4 gas. Adsorption equilibrium isotherms of CH4, N2 and CO2 have been measured gravimetrically at different temperatures up to 10 bar. These isotherms are fitted to the Sips model. Diluted breakthrough results are analyzed using a bi-pore diffusion model to obtain the micropore diffusivities of CH4, N2 and CO2 in the ACBs. Mixture breakthrough results have been employed to validate the applicability of the IAST-Sips model to predict mixture adsorption equilibria. A rigorous mathematical model is used to investigate the evolution curves of CH4, N2 and CO2 along the fixed bed during the CO2 displacement step, where it is found that the enrichment of the low concentration CH4 is improved significantly. Furthermore, the CO2 displacement experiments in the fixed bed for methane recovery from CH4/N2 mixtures with 1% and 10% CH4 content are performed and compared with the simulated results. It is found that 10% CH4 gas is concentrated to 89% CH4 purity and 1% CH4 gas can be concentrated to 53.5% CH4 purity, demonstrating that CO2 displacement is a promising technology for the enrichment of ventilation air methane.