Biogas--Purification

The potential of plastic waste-derived activated carbon was investigated for the removal of carbon dioxide and hydrogen sulfide from biogas. Activated carbon materials were prepared by carbonizing plastic waste followed by activation via microwave heating after mixing with potassium hydroxide. Samples were tested using thermogravimetric analysis to determine the equilibrium uptake of carbon dioxide. Samples were modified with tetraethylenepentamine and diethanolamine however, sample texture produced was deemed unusable for further testing due to operational concerns. Adsorbent screening was conducted in conditions mimicking that of biogas at a temperature of 40 °C and 30% carbon dioxide in nitrogen. Performant samples were identified as those achieving uptakes greater than 3 wt.%. The best performing sample achieved an uptake of 3.57 wt.% and maintained 99% of its uptake during cycling. Column breakthrough experiments demonstrated that the final candidate achieved complete removal of both carbon dioxide and hydrogen sulfide, suggesting viability for larger scale biogas purification.

The potential of amine-grafted silica materials (i.e., aminosilicas) was investigated for single-stage biogas and landfill gas 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°C in the presence of dry 30 vol.% CO2 in N2, 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. The final candidate also underwent multicomponent column-breakthrough tests and achieved complete (100%) removal of all target impurities. The results suggest promising potential of aminosilicas as a viable method of biogas and landfill gas purification.