No abstract

To investigate the effect of particle-based hydrate inhibitors on hydrate crystallization, molecular dynamics (MD) simulations were performed at the interface of hydrate-forming liquids where 2 nm sized silica nanoparticles are stabilized. The hydrophobic nanoparticles were prepared by functionalization of CH 3 groups on the amorphous SiO 2 surface, and the three-phase contact angle of the oil (CH 4 + decane), the aqueous phase (water + tetrahydrofuran (THF)), and the solid was 108.7°. Although the hydrates were not crystallized on the solid substrate, there was a trend that hydrate nucleation occurred on the side of the aqueous phase in the presence of nanoparticles. Through the four-body structural order parameter profiles, the formation of a low order parameter layer around the nanoparticles was observed, which originates from the reduced diffusivity by water binding. Adjacent to this layer, an elevation of the order parameter appeared in the same region where nucleation occurs because the less ordered layer acts as nucleation seeds. Indeed, a well of low free energy is formed in the presence of nanoparticles, in contrast to the nonnanoparticle system where no significant deviations were observed. Also, the driving force of hydrate nucleation is reduced with the increased nanoparticle injection. The nanoparticles prevented the diffusion of methane into the aqueous phase, resulting in a Vshape graph of induction time and delayed hydrate growth rate. These simulation results on the nanoparticle effect will provide a fundamental basis for improving the performance of particle-based inhibitors.

No abstract

No abstract

This work introduces a "hydrate seed solution", a surfactant solution containing pre-constructed structure II (sII) hydrate crystals, for the rapid formation of hydrogen-enriched hydrocarbon mixed hydrates. We observed the instantaneous nucleation and fast growth of mixed gas hydrates for both CH 4 − H 2 and C 2 H 6 −H 2 mixtures with the cyclopentane (CP) hydrate seed. The CP hydrate seed, which is immiscible with water, dominantly induces the growth of CH 4 −H 2 and C 2 H 6 −H 2 mixed gas hydrates with thermodynamically favorable sI structure. However, the THF hydrate seed, which is miscible with water, induced the formation of seed-templated sII CH 4 −H 2 or C 2 H 6 − H 2 hydrate, and the overall reaction was much slower than the CP hydrate seed case. For the C 2 H 6 −H 2 gas mixture, C 2 H 6 molecules could not occupy the small cage of hydrates, but H 2 mainly occupied the small cage. The THF hydrate seed provided a higher storage ratio of H 2 than the CP hydrate seed because the seed-templated sII C 2 H 6 −H 2 gas hydrates have a larger number of small cages than does the structure I (sI) hydrate. As the CP hydrate seed concentration decreased from 2.78 to 0.278 mol %, the growth of the mixed gas hydrates was extremely accelerated, and the overall conversion was completed within 1 h. The growth kinetics of hydrogen-enriched hydrocarbon mixed hydrates in the non-stirred system was much faster than that in prior agitation-applied studies. These findings suggest a way forward to an enhanced formation of hydrogen−natural gas clathrates for sustainable energy gas storage.