Binary Adsorption Equilibria Measurement for Biogas Separation Using a Zero Length Column Method

Biogas is a promising alternative to natural gas as the global energy sources shift from fossil fuels to renewables. The main components in biogas are CH₄ (35-70%), CO₂ (15-60%), and N₂ (15-50%), with trace impurities such as NH₃, H₂O, and H₂S. Release of biogas into the atmosphere causes rising levels of greenhouse gases, and flaring biogas produces SO_X due to the H₂S present in biogas. It’s critical to remove H₂S and CO₂ in biogas as H₂S causes equipment corrosion and poisons catalysts for downstream processes, and CO₂ reduces the heating value. Purifying biogas for electricity generation or biomethane production has gained interest among researchers. Many are exploring less energy-intensive separation processes compared to traditional methods involving liquid scrubbing. Adsorption using microporous materials such as zeolites, metal-organic frameworks (MOFs), and porous organic cages (POCs) is a promising technology as it provides tuned selectivity and requires less regeneration energy. However, the majority of research is on single-component adsorption, which does not well predict the competitive interaction in gas mixtures. This work focuses on the design of a Zero Length Column (ZLC) for rapid binary adsorption equilibria measurement. The binary adsorption equilibria are studied in both pristine and acid-gas exposed MOFs and zeolites such as MIL-125-NH₂, ZIF-8, mmen-Mg₂(dobpdc), and zeolite 13X. With a better understanding of competitive adsorption behavior, sorption materials for complex gas separation can be screened more rapidly, and processes such as pressure swing adsorption (PSA) can be modeled with better accuracy.