Ultrarapid Formation and Direct Observation of Methane Hydrate in the Presence of l-Tryptophan

Environmentallyfriendly amino acids are promising candidates forthe application of hydrate-based gas solidification technology andothers. The formation kinetics and macroscopic morphology of methanehydrate in the presence of l-tryptophan were experimentallystudied by adopting an isothermal and isochoric method. The experimentalresults showed that l-tryptophan could not increase the nucleationrates of methane hydrates, but it had better kinetic promotion effectson the growth rates of methane hydrate than sodium dodecyl sulfate,and the minimum concentration required to be effective was 0.1 wt%. The promotion effects almost remained unchanged with the increaseof the concentration of l-tryptophan, even at a stirringrate of 200 rpm. For a 0.1 wt % l-tryptophan solution, theultimate gas consumption was increased by 46.52% and t (90) was decreased by 33.67% when the initial experimentalpressure was elevated from 7 to 11 MPa. Both ultimate gas consumptionand t (90) were increased when the temperaturewas increased from 273.65 to 277.15 K. From direct top view observation,methane hydrate tended to first nucleate at the gas-liquid-solidtriple phase lines, then stretched like a thin film along the surfaceof the solution. The hydrate continued to form at the edge of thefilm and even climbed on to the inner wall of the container. The solutionunder the hydrate film was continuously sucked, and the hydrate filmcould even be cracked by interfacial forces at higher pressure. Whenthe concentration of l-tryptophan was greater than 0.5 wt%, hydrates cropped out from several sites of the hydrate film andcontinued to grow upward. The formed hydrates were quite loose andporous which provided capillary forces and channels for the upwardtransportation of the solution. Ultrarapidformation kinetics and great gas-storage capacityof methane hydrate promoted by eco-friendly and biodegradable l-tryptophan and the evolution process.