Study on formation characteristics of carbon dioxide hydrate in modified carbon microtube system

Abstract

The slow formation rate and low nucleation rate of carbon dioxide hydrate were common problems in current research. Many scholars focused on the promotion of gas hydrates by carbon nanotubes, whereas they ignored carbon microtubes, which were similar in structure and properties to carbon nanotubes and had more structural advantages. In this article, the effects of system temperature (1, 2, and 3 °C), pressure (3, 3.5, and 4 MPa), gas–liquid ratio (3:2, 4:1, and 5:1) and different types of carbon microtube concentration (0.01, 0.05, and 0.1 mg/mL) on the growth kinetics of carbon dioxide hydrate were investigated using orthogonal experiment method in a high-pressure reactor. The results revealed that compared to the pure carbon microtube system, amination, carboxylation, and hydroxylation carbon microtube systems improved the probability of carbon dioxide hydrate generation by 11–22%, with the shortest induction time of 0.23 hour. The highest gas storage capacity was 31.71 V/V under the carboxylated carbon microtube system. In the pure carbon, aminocarbon, carboxylated carbon and hydroxylated carbon microtube systems, the primary factors affecting the induction time were temperature, gas–liquid ratio, pressure and concentration. The gas–liquid ratio was the primary factor influencing the gas storage capacity of the carboxylated carbon microtubes; however, temperature was the primary factor affecting the gas storage capacity of the remaining three systems. Finally, we compared the effects of modified hydrophilic groups on the formation of carbon dioxide hydrate and made a conjecture.