Improving Methane Hydrate Formation Kinetics and Gas Storage Capacity with a Promoter

Solidified natural gas (SNG) has been viewed as a promising method for the storage and transportation of natural gas, while a primary challenge for this technology remains how to effectively enhance the hydrate formation kinetics as well as its storage capacity. In this study, a natural soil organic matter fulvic acid (FA) was used as the hydrate promoter, and the effect of the FA concentration and experimental pressure and temperature on CH4 hydrate formation kinetics and gas uptake was systematically investigated. The findings revealed that the presence of FA significantly reduced the CH4 hydrate induction time and accelerated its gas uptake rate. The CH4 storage capacity in the 0.25 wt % FA solution reached 105.8 +/- 1.1 V/VH at 274.15 K and 5.5 MPa, which was much higher than that of pure water (19.8 +/- 0.9 V/VH) and increased by 18% compared to that of the 500 ppm sodium dodecyl sulfate (SDS) solution (89.8 +/- 0.7 V/VH) under the same conditions. A high initial pressure and low temperature were favorable to obtain a high gas uptake, and the CH4 storage capacity reached 158.5 +/- 0.6 V/VH (volume ratio of gas to hydrate, with the theoretical value being 172 V/V-H) in the 0.5 wt % FA solution at 274.15 K and 8.5 MPa. Morphological observations showed that the CH4 hydrate formed in the FA solutions was in a small-grained form, suggesting that FA presented the anti-agglomerant effect in the pure water system. No foam was generated during CH4 hydrate formation in the FA solutions. In comparison to the SDS system, much less foam was observed during the CH4 hydrate decomposition in the FA solutions, and the foam completely disappeared after hydrate decomposition.