Landfill gas upgrading using amine-functionalized silica sorbents

Separation of acid gases such as CO2 from biogas is a key step for its purification before biomethane is used in various applications such as injection into a pipeline or use as a vehicle fuel. In this study, the single step purification of real biogas (locally collected landfill gas) was demonstrated using (3-Aminopropyl) triethoxysilane (APTES)-grafted SBA-15. The sorbent was optimized between amine amount and accessibility to adsorption sites. In studies using a surrogate mixture of CH4/CO2 the sorbent recorded an adsorption capacity of 0.85 mmol(CO2)/g(ads) under dry conditions and this decreased to 0.72 mmol(CO2)/g(ads) when the surrogate biogas was saturated with steam. Even though the capacity was further decreased to 0.55 mmol(CO2)/g(ads) using real landfill gas, it remained fairly stable over 5 cycles despite the presence of impurities, namely hydrogen sulfide (68 ppm). In all cases, the capacity was regenerated with a thermal treatment in inert gas at 100 degrees C. The results suggested possibilities for a single step purification unit to remove acid gasses and water and provide potential for a streamlined operation for the separation of carbon dioxide from biogas. The enhanced economics should propel the move toward a green energy future.