Formation of the structure-II gas hydrate from low-concentration propane mixed with methane

It has been recognized that a small amount of propane mixed with methane can change greatly in not only the thermodynamics but also the structural properties of gas hydrate. However, its mechanism is still not well understood yet. In this research, structure-II (sII) hydrate is synthesized using a methane -propane gas mixture with an initial mole ratio of 99:1, and it is found that large (51264) cages are co -occupied by multiple gases based on the rigid structure analysis of neutron diffraction data. The first prin-ciples calculation and molecular dynamics simulation are conducted to uncover the molecular mecha-nism for sII methane-propane hydrate formation, revealing that the presence of propane inhibits the formation of structure-I (sI) hydrate but promotes sII hydrate formation. The results help to understand the accumulation mechanism of natural gas hydrate and benefit to optimize the condition for gas storage and transportation in hydrate form.& COPY; 2022 The Chemical Industry and Engineering Society of China, and Chemical Industry Press Co., Ltd. All rights reserved.

Automated summary

It is acknowledged that the addition of a small amount of propane to methane can greatly affect both the thermodynamics and structural properties of gas hydrates, although the exact mechanism is not well understood. In this study, structure-II (sII) hydrate was synthesized using a mixture of methane and propane, and it was observed that large cages were occupied by multiple gases. First-principles calculations and molecular dynamics simulations were performed to investigate the molecular mechanism of sII methane-propane hydrate formation, revealing that propane inhibits the formation of structure-I (sI) hydrates but promotes sII hydrate formation. These findings contribute to a better understanding of the accumulation mechanism of natural gas hydrates and have implications for optimizing gas storage and transportation in hydrate form.