Long-Term Effect of Steam Exposure on CO2 Capture Performance of Amine-Grafted Silica

This study investigates the hydrothermal stability of triamine-grafted CO2 adsorbent based on a commercial-grade silica (CARiACT, P10). Grafting was conducted in dry and wet conditions at 85 °C. At optimum grafting conditions using 0.2 cm3 water and 1.5 cm3 aminosilane per gram of silica, the highest CO2 uptake of 1.93 mmol/g at 50 °C was obtained. This material was exposed to steam at 120 °C for up to 360 h. It was observed that increasing the duration of steam exposure from 3 to 24 h reduced adsorption uptake at 25 °C by 56%. However, the CO2 uptake reduction was much less severe at higher adsorption temperatures, reaching 21% at 50 °C and only 4% at 75 °C. Conducting steam treatment for 360 h reduced adsorption uptake at 25, 50, and 75 °C by 83, 61, and 26%, respectively. For this extreme steaming experiment, the decrease in CO2 uptake at all adsorption temperatures was attributed to the reduction of the sorbent average pore width, increasing diffusional mass transfer resistance. The results revealed that steam exposure did not reduce the amine loading or deactivate the amine groups; however, increasing exposure time decreased the average pore width, until partial collapse of material structure. Nevertheless, the large average pore width (21 nm) of the P10 silica led to higher hydrothermal stability of the amine-grafted sorbent compared to those with ordered pore structure supports, such as SBA-15 silica.