Performance of dry water- and porous carbon-based sorbents for carbon dioxide capture

Carbon dioxide is the primary greenhouse gas that has a strong impact on global warming. Several technologies have been developed for capturing CO₂ to mitigate the greenhouse effect. The objective of this research was to investigate the performance of several sorbents based on dry water and porous carbon materials for capturing CO₂. Seven sorbents were prepared and comparatively evaluated for their CO₂ capture capabilities: (i) Conocarpus biochar (CBC); (ii) commercial activated carbon (CAC); (iii) normal dry water (NDW); (iv) K₂CO₃-treated CBC (TCBC); (v) K₂CO₃-modified dry water (MDW); (vi) MDW and 2% TCBC (MDWTCBC); and (vii) MDW and 2% activated carbon (MDWCAC). The sorption process was carried out with initial CO₂ concentration of 5.7%, temperature of 25 °C, feed gas flow rate of 0.5 l min^-1 and a pressure of 1.0 bar. The pure CO₂ was mixed with O₂ or N₂ to achieve the desired inlet concentration of CO₂. The CO₂ adsorption capacity and partition coefficient (PC) of the tested sorbents were evaluated at 5% and 100% breakthrough (BT). The results showed a longer breakthrough and equilibrium adsorption times for CO₂ when mixed with N₂ than with O₂. Among all sorbents, both CAC and CBC showed enhanced CO₂ capture performance with equilibrium (100% BT) adsorption capacities of 239 and 197 mg g^-1, respectively (in terms of PC: 1.0 × 10^-3 and 7.9 × 10^-4 mol kg^-1 Pa^-1, respectively). In contrast, the performance of TCBC and the dry water-based sorbents was far lower than CAC or CBC. The CO₂ adsorption data fitted well to the non-linearized form of the pseudo-first-order kinetic model. The Fourier-transform infrared spectral patterns indicated that the reaction of CO₂ molecules with the hydroxyl groups of sorbents is possible through the formation of chemisorbed CO₂ species. It could be concluded that the activation process did not play a role in increasing the CO₂ capture performance in order to form new active sorption sites. However, Conocarpus biochar can be used as efficient sorbent for CO₂ capture with a better performance than other materials tested previously (e.g., activated carbon).