Rapid Formation of Hydrogen-Enriched Hydrocarbon Gas Hydrates under Static Conditions

Abstract

This work introduces a "hydrate seed solution", 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 CH4-H-2 and C2H6-H-2 mixtures with the cyclopentane (CP) hydrate seed. The CP hydrate seed, which is immiscible with water, dominantly induces the growth of CH4-H-2 and C2H6-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 CH4-H-2 and C2H6-H(2 )hydrate, and the overall reaction was much slower than the CP hydrate seed case. For the C2H6-H-2 gas mixture, C2H6 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 C2H6-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.