Ethanol-treated eggshell-derived sorbents for direct air capture

Eggshell is a cheap and environmentally friendly waste stream from the food industry, which could be potentially used for different applications in a circular economy scenario. Carbonation of eggshell derived sorbents has been investigated for calcium looping high temperature applications. Nevertheless, the application of these sorbents for direct air capture is yet to be explored in detail. In this work, waste eggshell (ES) and three different ethanol/water treated eggshell samples (E70, E80 and E90) are assessed for direct air capture and compared to limestone. These samples are exposed to ambient air in two distinct conditions. Namely, i) ambient air at 25 degrees C in a laboratory and ii) refrigerator conditions at 4 degrees C in order to simulate how these sorbents might perform in different climatic scenarios for varying geographic areas. Carbonation and hydration conversions were calculated for times of similar to 3000 h. It was found that treating the eggshells with ethanol was key in order to obtain a suitable material for this application. Two of the ethanol-treated samples obtained similar conversions in comparable amounts of time for ambient air conditions, while limestone still performed better in refrigerator conditions.