The U.S. Environmental Protection Agency has endorsed biogas as an environment-friendly renewable energy source that can reduce reliance on fossil fuels. However, the energy potential and economic viability of biogas projects depend on different parameters, including the low-cost removal of ubiquitous impurities, namely CO2, H2S, and water vapor. Adsorption processes hold the promise of biogas purification in an efficient and cost-effective manner. The challenge, however, is to develop adsorbent materials that combine high uptakes, fast adsorption kinetics, and favorable stability during cyclic adsorption-desorption. The potential of amine-grafted silica (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 grafting of triamines onto mesoporous silica in the presence of different water and amine amounts. 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 1.5 mmol/g were chosen for further assessments in terms of CO2 adsorption kinetics. The highest-performing aminosilica achieved fast CO2 adsorption by reaching 80% of its equilibrium uptake in one minute. This material was subjected to rigorous 100-cycle testing and maintained 100% of its initial CO2 uptake throughout cycling. The final candidate also underwent column-breakthrough tests in the presence of different dry and humid gas streams containing CO2, H2S, and water vapor, and achieved concurrent and complete (100%) removal of all target impurities. The results suggest promising potential of aminosilicas as a viable method of biogas purification.
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