Title : SiO2-amino adsorbents from geothermal silica waste with potential application in direct CO2 air capture
Abstract:
Direct CO2 air capture (DAC) has become a key strategy to address climate change as its implementation can contribute to a decrease in the concentration of this greenhouse gas in the atmosphere, which, until November 2024, had an upward trend of 423.85 ppm. Unlike other methods, such as post-combustion, direct capture aims to extract CO2 directly from ambient air, so working at low gas concentrations at atmospheric conditions is necessary. Most DAC techniques are based on sorption processes in which ambient air flows over a sorbent that selectively removes carbon dioxide. The sorbents used in DAC must have important characteristics, such as high adsorption capacity, good selectivity, easy regeneration, low energy penalty, adequate adsorption-desorption kinetics, excellent chemical stability and low cost. In this way, amine functionalization of porous materials has been proposed to improve the CO2 adsorption capacity and selectivity, while the use of waste to obtain economically viable adsorbents has been investigated. Thus, this research aims to develop an efficient SiO2-amine adsorbent material for direct CO2 air capture from geothermal silica waste. The wastes used as a source of silica come from two Mexican geothermal power plants (Cerro Prieto and Humeros). Once the silica samples were characterized by XRF, SEM and N2 adsorption, the functionalization with TEPA, PEHA and PEI (20 wt%) was carried out by impregnation. The obtained SiO2-amine materials were characterized by N2 adsorption, FT-IR and TG analysis. Moreover, CO2 capture tests were carried out with 400 ppm of CO2 and temperatures between 25 and 35 °C. The highest CO2 adsorption was 2.87 wt% (0.65 mmoles/g) obtained with the material prepared using Cerro Prieto silica waste treated with citric acid and impregnated with 20% TEPA (30 °C). Finally, the stability evaluation of this material over 10 consecutive adsorption-desorption cycles shows a mass loss of 2.24 %, which is mainly related to the decomposition of the amines with increasing temperature during desorption.
