Gas-Phase Simulated Moving Bed for Methane/Nitrogen Separation Using a Commercial Activated Carbon

This work focuses on designing and developing a simulated moving bed (SMB) process for the separation of methane and nitrogen mixtures, using a commercial activated carbon (BPL) as the adsorbent material and two potential desorbent gases: argon and carbon dioxide. As such, the material performance was evaluated by measuring the adsorption equilibrium data and the dynamic behavior of single and multicomponent adsorption through fixed-bed experiments. The pure component isotherms of N2, CH4, Ar, and CO2 were measured at 303, 323, and 343 K in a pressure range of 0–2.5 bar using a volumetric apparatus, with CO2 exhibiting the highest affinity to the stationary phase and Ar the lowest. The data was regressed against the dual-site Langmuir (DSL) model. Single, binary, and ternary breakthrough curves were also assessed, allowing the validation of the proposed mathematical model. Two SMB cycles were employed to separate an equimolar CH4/N2 mixture using each desorbent gas to evaluate the impact of the desorbent strength in the process. The respective separation regions were drawn. Both cycles were capable of producing a high-purity methane stream (96.2 and 97.4% for the Ar and CO2 experiment, respectively) with high recovery (>92%). When argon is used as the desorbent gas, the extract product stream is obtained with productivity of 14.1 kg·m–3ads·h–1.