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).