(225m) Amine-Impregnated Mesoporous Silica Materials for Biogas Upgrading

The U.S. Environmental Protection Agency (EPA) has endorsed biogas as a cleaner renewable energy source that can reduce our reliance on fossil fuels. In addition to CH₄, biogas is rich in water vapor and CO₂.Biogas production is beneficial for the environment by minimizing uncontrolled Greenhouse Gas (GHG) and odor emissions. However, biogas should be purified to produce grid-quality Renewable Natural Gas (RNG). 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 the impurities, and favorable stability during cyclic adsorption-desorption. Amine-impregnated 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 many adsorption-desorption cycles. To test their potential for biogas purification, twenty aminosilicas were synthesized by utilizing (i) mesoporous silica that is commercially available (G-10, Fuji Silycia), (ii) four polyamines, specifically tetraethylenepentamine (TEPA), and three branched polyethylenimines (PEI) with different molecular weights (600, 1200, and 1800), and (iii) five levels of amine loadings (ranging from 20 to 60 wt.%). Thermogravimetric analysis (TGA) was performed on all the materials to quantify amine loading, equilibrium CO₂ uptake, amine efficiency, and CO₂ adsorption kinetics in the presence of dry CO₂ (30%, balance nitrogen) at 40 °C. Selected performant materials were further investigated in terms of cyclic adsorption-desorption performance, long-term thermal stability, and column-breakthrough experiments in the presence of dry and humid gas streams. The final candidate achieved concurrent and complete (100%) removal of all target impurities. The results suggest promising potential of aminosilicas as a viable adsorbent material for biogas purification.