Coexistence of sI and sII in methane-propane hydrate former systems at high pressures

• Published in: Chemical engineering science 2019-11, Vol.208, p.115149, Article 115149
• Main Authors: de Menezes, Davi Éber Sanches, Sum, Amadeu K., Desmedt, Arnaud, Pessôa Filho, Pedro de Alcântara, Robustillo Fuentes, Maria Dolores
• Format: Article
• Language: English
• Subjects: Chemical and Process Engineering; Chemical Sciences; Engineering Sciences; High pressure calorimetry; Isochoric method; Material chemistry; Metastable structure; Methane propane hydrate; or physical chemistry; Theoretical and
• ISSN: 0009-2509; 1873-4405
• DOI: 10.1016/j.ces.2019.08.007

•New equilibrium data up to 100 MPa are presented for CH4-C3H8 gas hydrates.•Influence of experimental factors on HP-µDSC and isochoric results were evaluated.•Both sI and sII are found in CH4-C3H8 hydrate-former systems above 10 MPa.•Fractions of sI and sII depend on gas phase compositions and the methodology applied.•Mixing and high subcooling may favor the methane hydrate (sI) formation. The hydrate-former system composed of methane-propane-water was studied through HP-µDSC and a PVT cell. New equilibrium data were obtained. Results reveal evidence of the simultaneous formation of structures I and II, although only sII is expected at such conditions at equilibrium. Most of sI is present as a metastable structure, but a small fraction of it seems to provide a more stable system, mainly at excess methane conditions. The effect of heating rate, mixing, multiple cycles and initial gas phase composition on the formation of both structures was evaluated. These factors affect the formation kinetics, the type and the proportion of each hydrate structure and hence the thermodynamic profile during dissociation. Raman spectroscopy was applied for studying ex situ single and double hydrates, suggesting a higher fraction of sII than sI for all gas phase compositions studied, and higher occupancy of large cavities by methane molecules as methane content increases.