Methane Storage by Forming sII Hydrate in the Presence of a Novel Kinetic Promoter with the Function of Alleviating the Wall-Climbing Growth

Storing methane by forming structure II hydrate in the presence of thermodynamic hydrate promoters gains extensive attention due to the moderate operation conditions. Although the reaction rate and gas uptake can be improved by adding kinetic hydrate promoters (KHPs), the concomitant wall-climbing effect often leads to reactors and even pipelines being filled with hydrate. Therefore, in this study, a novel kind of KHPs [cocamidopropyl dimethylamine (CDA)] was developed to promote CH4/ tetrahydrofuran (THF, 5.56 mol %) hydrate formation and alleviate the hydrate wall-climbing growth. Results showed that the hydrate formation rate enhanced, and the induction time decreased as the CDA concentration increased. The largest CH4 storage capacity achieved was 107.78 +/- 1.89 v/v (the volume ratio of gas to hydrate, and the theoretical value is 115 v/v) at 283.15 K and at an initial pressure of 7.2 MPa, which was obtained at the CDA concentration of 0.2 wt %. The evolutionary morphologies of hydrate growth in the presence or absence of CDA were observed during the initial formation stage, confirming the great promotion effect of CDA on CH4/THF hydrate formation. The hydrate formed in the systems without CDA filled up the entire window, while the wall-climbing effect was significantly alleviated in the CDA-contained systems. As far as we know, this is the first time to report that a KHP (CDA) has the dual function of enhancing hydrate formation kinetics and alleviating its upward growth. In addition, the effect of CDA and L-tryptophan (L-Trp) on hydrate formation was compared at their optimal dosages under the currently experimental conditions, and the results indicated that CDA performed better in terms of hydrate induction time, formation rate, gas uptake, and wall-climbing height.

Automated summary

This study developed a novel type of kinetic hydrate promoters (CDA) to promote CH4/THF hydrate formation and alleviate the hydrate wall-climbing growth. Results showed that the hydrate formation rate enhanced, and the induction time decreased as the CDA concentration increased. The largest CH4 storage capacity achieved was 107.78 +/- 1.89 v/v at 283.15 K and at an initial pressure of 7.2 MPa, which was obtained at the CDA concentration of 0.2 wt %.