Amine-grafted mesoporous silica materials for single-stage biogas upgrading to biomethane

The potential of amine-grafted silica materials (i.e., aminosilicas) was investigated for single-stage biogas purification via simultaneous removal of CO2, H2S, and water vapor. Custom aminosilicas were synthesized by covalent tethering of primary amines onto commercially available mesoporous silica. Screening adsorption experiments were completed at 40 degrees C in the presence of dry 30 vol% CO2 in N-2, and performance was measured using thermogravimetric analysis. Selected materials with equilibrium CO2 uptakes greater than 6 wt% were chosen for additional assessments in terms of CO2 adsorption kinetics. The highest-performing aminosilica achieved fast CO2 uptake by reaching 82% of its equilibrium CO2 uptake in one minute. This material was subjected to rigorous 100-cycle testing and retained stable performance as evidenced by maintaining 99% of its initial CO2 uptake throughout cycling, regardless of using air or N-2 as desorption purge gas. The final candidate also underwent column-breakthrough tests in the presence of humid 24% CO2, 200 ppmv H2S, balance N-2, at 40 degrees C, and achieved concurrent and complete (100%) removal of all target impurities, namely CO2, H2S, and water vapor, prior to their respective breakthrough times. The results suggest promising potential of aminosilicas as a viable method of biogas purification, particularly in remote areas where access to other purge gases such as steam or N-2 is not practical.