Influence of Water Vapor on CO2 Adsorption Using a Biomass-Based Carbon

Adsorption processes can be used for removing the CO2 present in flue gas streams, contributing to reduce greenhouse gas emissions. To evaluate adsorbents for this application, many studies focus on the adsorption capacity of pure CO2 or, in the best cases, on binary mixtures of N-2 and CO2. However, the role of water vapor, which is one of the main components of flue gas and is strongly adsorbed by many adsorbents, is less explored. Carbon materials are selective toward CO2 and have an intrinsic hydrophobic nature, being appealing candidates for postcombustion CO2 capture. In this work, the influence of water vapor on CO2 adsorption is evaluated under postcombustion conditions using a biomass-based microporous carbon produced from olive stones by single-step activation with carbon dioxide. The adsorption isotherms of water vapor at 25, 50, and 70 degrees C present a type V topology that will facilitate the desorption of H2O compared to other adsorbents with type I or II isotherms, reducing the energy consumption of the adsorption process. Multicomponent adsorption experiments carried out under dynamic conditions with the main flue gas components, N-2, CO2, O-2, and H2O, showed that CO2 and H2O are preferentially adsorbed over N-2 and O-2. However, although water vapor is coadsorbed with CO2, no significant decrease in the adsorbent CO2 capture capacity was observed. Moreover, the adsorbent can be easily regenerated by temperature swing adsorption (TSA) or vacuum and temperature swing adsorption (VTSA), recovering its full adsorption capacity. These characteristics, added to their low cost and environmentally friendly character, make these adsorbents appealing adsorbents for postcombustion applications.