Characterization of Carbon Dioxide Hydrate Growth Kinetics in Carbon Micron Tube Oil–Water System

Abstract

Carbon nanotubes have a significant impact on hydrate formation. However, the effect and mechanism of carbon micrometer tubes, which have a similar structure to carbon nanotubes, on the promotion of hydrate growth is not yet clear. Therefore, in this paper, experiments on the growth kinetics of CO2 hydrate in oil–water systems under the effect of multiwalled carbon microtubes (MWCMTs) were carried out. The effects of pressure, temperature, and oil–water ratio on the induction period and gas consumption of CO2 hydrate were investigated. It also revealed the hydrate growth promotion mechanism of MWCMTs. The conclusions were as follows: (1) MWCMTs could significantly improve the hydrate gas storage capacity in an oil–water system by up to 80.3% over the pure water system. (2) Pressure and temperature had a large effect on the storage capacity and induction time of CO2 hydrate, and the results showed that the induction time decreased significantly with increasing pressure and decreasing temperature. At the same time, the hydrate growth time was significantly shortened, but the gas storage capacity first increased and then decreased. One reason for this was that the hydrate film hindered gas–water mass transfer, and the other was that the gas dissolved by the oil droplets rapidly generated hydrates and could not continue to transfer gas molecules. (3) In the oil–water system, lipophilic MWCMTs carried adsorbed CO2 to contact water, at the same time providing a large number of hydrate nucleation sites to promote hydrate formation.