Structure-H hydrate of mixed gases: Phase equilibrium modeling and experimental validation

Clathrate hydrates are solid ice-like compounds that entrap the gas or liquid molecules into their cavities of hydrogen-bonded water molecules. As compared to commonly available sI and sII structures of clathrate hydrate, the sH-type is reported to possess more stability and gas uptake capacity. Despite copious implications of the sH-type hydrates of mixed gases in gas storage and separation, the phase equilibrium modeling to predict their formation condition is rarely available in the literature due to inaccurate estimation of the interactions between the guest components. In this view, we develop a novel methodology using the Wong-Sandler mixing rule extended for the three-parameter Patel-Teja equation of state, in association with the statistical thermodynamics based van der Waals and Platteeuw model to define the hydrate phase. This apart, the solubility of the help gases in water is estimated using the Patel-Teja model instead of the empirical correlations. It is observed that the proposed formulation is capable of predicting the experimental phase equilibrium data with a range of 1.389-2.812 %AARD for a variety of sH hydrates (i.e., neohexane, methylcyclopentane, isopentane, 2,2-dimethylpentane and a recently discovered first vapor phase heavy former tetrafluorocyclobutane) having methane, nitrogen or carbon dioxide as their co-guest. (C) 2021 Published by Elsevier B.V.

Automated summary

Clathrate hydrates, particularly the sH-type, are promising for gas storage and separation due to their stability and gas uptake capacity. However, accurate phase equilibrium modeling for their formation is lacking in literature. This study proposes a novel methodology using the Patel-Teja equation of state with statistical thermodynamics to predict experimental phase equilibrium data for various sH hydrates.