Assistant Professor Florida Atlantic University Dania Beach, FL
The U.S. Environmental Protection Agency (EPA) has endorsed Landfill Gas (LFG) as an environment-friendly renewable energy source that can reduce our reliance on fossil fuels. In addition to CH4, LFG is rich in water vapor and CO2, which comprise 40-50% of the gas. LFG collection and use as a source of Renewable Natural Gas (RNG) is not only beneficial for the environment by minimizing uncontrolled Greenhouse Gas (GHG) and odor emissions, but also provides a source of revenue for landfill facilities. However, the energy potential and economic feasibility of LFG recovery projects depend on certain parameters, the most significant being the removal of impurities at a minimal cost. Adsorption processes hold the promise of LFG purification efficiently and cost-effectively. The challenge, however, is to develop adsorbent materials that combine such attributes as high CO2 and water vapor uptakes, fast adsorption kinetics, high selectivity for CO2, and favorable stability during cyclic adsorption-desorption. Amine-grafted silica materials, also known as aminosilicas, can effectively remove CO2 over a wide range of concentrations. Unlike zeolites, the presence of water vapor in the feed gas increases the CO2 uptake of aminosilicas. Interestingly, aminosilicas not only tolerate water vapor in the gas feed, but humidity is required to prevent premature deactivation of the adsorbent, maintaining performance and stability over thousands of adsorption-desorption cycles. To investigate aminosilica potential for LFG purification, several aminosilicas were synthesized via covalent bonding of primary amines onto commercially available mesoporous silica. The performance of the synthesized adsorbents was analyzed using Thermogravimetric Analysis (TGA). Screening adsorption experiments were completed at 40 °C in the presence of dry 30 vol.% CO2 in N2 to mimic LFG specifications. The best-performing material with the highest CO2 uptake and fastest CO2 adsorption kinetics was chosen for testing under humid conditions as well as rigorous 100-cycle testing under the aforementioned adsorption conditions, followed by regeneration at 120 °C in the presence of N2. The results indicated stable performance as evidenced by maintaining 100% of the initial CO2 uptake throughout cycling. These results suggest the high potential of aminosilicas for single-stage LFG purification through simultaneous removal of CO2 and water vapor.
