(399g) Thermally Stable Amine-Impregnated Mesoporous Silica Materials for Direct Air Capture

The concentration of CO₂, the primary anthropogenic greenhouse gas (GHG) responsible for global warming and climate change, has experienced a rapid increase since the Industrial Revolution. The present levels of CO₂ reached a global average concentration of 425 parts per million by volume (ppmv) in 2024, as opposed to 315 ppmv in 1958. This increase in emissions has caused a nearly 2-degree Fahrenheit rise in global temperatures since the pre-industrial era. CO₂ capture from the ambient air, also known as direct air capture (DAC), is a possible solution to this problem. The U.S. Department of Energy has endorsed DAC as one of the helpful strategies to achieve net-zero emissions by 2050. Owing to their superior performance, DAC applications involving cyclic adsorption-desorption of CO₂ by amine-modified silica materials (i.e., “aminosilica”) have gained momentum in recent years. To that end, this project aims to develop thermally stable aminosilicas materials suitable for DAC applications. This research involves the synthesis of amine-impregnated mesoporous silica materials using tetraethylenepentamine (TEPA) and TEPA modified with the following epoxides: 1,2-epoxybutane (EB), 1,2-epoxyoctane (EO), 1,2-epoxydodecane (ED), and 1,2-epoxyhexadecane (EH). CARiACT G-10 silica (Fuji Silysia Chemical Ltd.) was used as support for the synthesis of aminosilicas. G-10 silica is commercially available at a low cost and has a high pore volume (1.2 cm³/g), large surface area (300 m²/g), small particle size (5 µm), and wide pores (20 nm), enabling it to attain high amine loadings and CO₂ uptakes, without compromising adsorption kinetics. Using thermogravimetric analysis (TGA), the materials were screened for equilibrium CO₂ uptake, amine efficiency, and adsorption kinetics in the presence of dry CO₂ (400 ppmv, balance nitrogen) at 25 °C. Multiple performant materials with high CO₂ uptake and fast CO₂ adsorption kinetics were chosen for rigorous 50-cycle testing under the above adsorption conditions, followed by regeneration at 100 °C in the presence of N₂. Using column-breakthrough testing, the performance of one final candidate was also evaluated in the presence of humid CO₂. The preliminary results suggest the high potential of aminosilicas for DAC applications.