Assessment of Hydrate Formation, Storage Capacity, and Transport Properties of Methane and Carbon Dioxide through Functionalized Carbon Nanotube Membranes

The present work investigates the gas hydrates, storage, and transport properties of methane (CH4) and carbon dioxide (CO2 ) across carbon nanotubes (CNTs) designed by CONH2 (aquaporin, AQP selective filter), H2O2, and COOH functional groups via molecular dynamics (MD) simulations. Two separate systems of water-CH4 and water-CO2 at different mole fractions have been considered. The main goal is to discuss, for the first time, the gas hydrate formation mechanism in the membrane technology framework as a promising approach to mitigate the drawbacks in traditional hydrate technologies. Our model membranes offer very high CH4 storage capacity concerning available experiments. The hydrate cages decrease since the mole fraction increases (or water loading decreases), suggesting a significant contribution of water hydrogen-bonded in the hydrate formation process. The CNT-CONH2 and CNT-H2O2 model membranes provide higher hydrate cage numbers compared to CNT-COOH, suggesting a better performance for CNT-CONH2. The CNT-CONH2 shows a higher hydrate cage in the presence of CO, particularly at the small mole fraction, while CNT-COOH and CNT-H2O2 are good at the large mole fraction. Regardless of the gas type (CH4 or CO2), both CNT-CONH2 and CNT-H2O2 model membranes suggest better performance in gas hydrate formation. Moreover, our simulated model membranes indicate better efficiency in the formation of gas hydrates concerning available experiments. An enhancement in hydrate formation in the presence of CH4 was also found in the CNT-CONH2 and CNT-H2O2 model membranes concerning the bulk system, suggesting a better performance for CNT-CONH2. This finding could reflect the potential of the membrane-based hydrate formation over the bulk system. The transport properties of water/CH4/CO2 across the model membranes have also been discussed.