Kinetics of carbon dioxide gas hydrates with tetrabutylammonium bromide and functionalized multi-walled carbon nanotubes

The effects of oxygen-functionalized multi-walled carbon nanotubes (MWCNTs) on tetrabutylammonium bromide (TBAB)-water-carbon dioxide semi-clathrate system was investigated. A system comprised of 9.5 ppmw MWCNTs and 40 wt % TBAB was chosen and the average gas consumption rate was calculated for different conditions. At 14 °C, the average gas consumption rate during growth decreased to a plateau with increasing induction time at 3.0 °C subcooling for systems with and without MWCNTs. The addition of MWCNTs increased the gas consumption rate during growth for induction times less than one hour but did not affect it at longer induction times. The maximum gas consumption enhancement from the added MWCNTs was 15%. Dissolution runs at equilibrium conditions indicated that the presence of MWCNTs improved the dissolution rate of carbon dioxide gas into the liquid by lowering the time constant τ by 5%. This suggests that the gas-liquid interfacial resistance of carbon dioxide gas mass transfer is not the limiting factor for hydrate growth in this TBAB semi-clathrate system with and without nanoparticles. At a lower subcooling of 1.5 °C, there was no significant difference in the gas consumption rates with the addition of MWCNTs, due to prolonged induction times.