Volume 55

A preliminary study of C@Fe3O4 for gas separation of CH4 and CO2 Longlong Lei,Hang Yuan,Hongguang Zhu,Fanghui Pan,Fulu Lu

Abstract

Biogas, produced through the anaerobic digestion (AD) process of biomass, is one of the most promising renewable energy sources. Besides CH4, biogas contains other components that negatively impact its direct application, such as H2S, CO2, NH3, and siloxanes. Among these, CO2 has the most significant effect on reducing the calorific value of biogas, with its content reaching 30%-45%. Therefore, the separation of CO2 from biogas using solid adsorbents for biogas upgrading has been a widely studied topic in recent years. Previous theoretical studies have found strong interactions between Fe3O4 and CO2, indicating a high CO2-specific adsorption capacity. However, the low specific surface area of Fe3O4 limits its CO2 loading capacity. Coating the surface of Fe3O4 with a carbon layer to form carbon-coated magnetite (C@Fe3O4) can significantly increase its specific surface area, making Fe3O4 a promising new CO2 adsorption material. In this study, a novel C@Fe3O4 material was prepared using concentrated organic matter from biogas effluents and iron oxide through a hydrothermal-carbonization process. This material achieved a specific surface area of up to 187.50 m²/g. Under conditions of 1 bar and 37 °C, the material demonstrated a selectivity for CO2 over CH4 of up to 10.5, outperforming most adsorbent materials. Its CO2 adsorption capacity was measured at 0.56 mmol/g (0.99 mmol/cm³).This material supports the development of a new, efficient, low-energy, and low-cost pressure swing adsorption (PSA) process for CO2 and CH4 purification.

Keywords C@Fe3O4, gas separation, CO2 adsorption, biogas purification