Hydrophobic carbon-based coating on metal tube with efficient and stable adsorption–desorption of CO2 from wet flue gas

In order to improve the heat transfer efficiency of the shaped activated carbon in CO2 adsorption, we proposed a rapid CO2 adsorption–desorption approach by coating the outer surface of the metal tube with a hydrophobic carbon layer. The coating layer was prepared by carboxylated cellulose nanofibers (CNF) as the binder, coconut shell-activated carbon as the carrier, and methyltrimethoxysilane (MTMS) as the hydrophobic modifier. The oxygenated groups can increase its surface polarity and adsorptivity for the weakly polar small molecules like carbon dioxide. The equilibrium adsorption capacity of SAC-6-1.0 for CO2 in dry (15 vol% CO2) and wet flue gas (15 vol% CO2 + 4.7 vol% H2O) is 39.4 mg/g and 34.3 mg/g, respectively, at 40 °C and 1.0 bar, which is 54.5% and 382.4% higher than that of the original activated carbon. After 10 cycled reuses, over 97% of its adsorption capacity can be retained. The CO2 adsorption performance of SAC-6-1.0 is better than most of the oxygenated and sulfur-doped activated carbons, albeit slightly worse than that of nitrogen-doped ones. The present hydrophobic carbon coating approach is of great industrial application in the field of CO2 capture and other gas separation.