The synergy of spiral agitation and nano-promoters significantly enhances hydrate formation under mild conditions

Abstract

Sluggish hydrate kinetics and low methane storage capacity, especially under mild conditions, limit the application of hydrate-based solidified natural gas (SNG) technology. Here, we prepared two nano-promoters of -SO3−@PSNS and –COO−@PSNS, with which, methane hydrate formation in a spiral-agitated reactor under mild conditions was evaluated. Spiral agitation enhances hydrate nucleation and initial growth kinetics, while the nano-promoters improve hydrate later growth kinetics, and the synergy of them results in extraordinary hydrate formation kinetics under mild conditions. In pure water systems, a small methane storage capacity of 79.58 V/V was obtained at 3.8 MPa and 45°, but it was significantly improved by the nano-promoters. The larger methane storage capacity of 147.28 V/V and 141.33 V/V were obtained under the mild condition in the systems of -SO3−@PSNS and –COO−@PSNS separately, which increase by 85.07 % and 77.59 %, respectively. The synergistic promotion mechanisms were finally proposed, and it was found that hydrate growth is mass transfer-limited and kinetic-limited at high and low driving force, respectively. The presence of nano-promoters increases the ductility and porosity of hydrates, improving the accessibility of inner interstitial water, so large water-to-hydrate conversion and methane storage capacity under mild conditions are anticipated.