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• Two steps of CH 4 hydrate formation in the presence of CP were observed. • Gas uptake as high as 131.80 mmol/molH 2 O was obtained in this work. • The stability of methane hydrates was characterized in this work. • A new strategy for methane hydrate storage and transportation was proposed. The work systematically investigates the kinetic of methane(CH 4) hydrate formation in the presence of cyclopentane（CP）by measuring induction time, hydrate formation rate, and gas uptake. The results showed that there are two steps for CH 4 hydrate formation in the presence of CP: Step 1, pure CP hydrate formation. Step 2, gas enters the empty cages of pure CP hydrates to form CP/CH 4 mixed hydrates. Besides, the rapid hydrate formation rate and high CH 4 uptake are observed from hydrate formation in this work. At the optimum conditions of 288.15 K and CP mole fractions of 5.6 mol%, the gas uptake and the time required for completion of hydrate formation are 131.80 mmol/mol H 2 O and 138 min, respectively. Relative to the highest reported gas uptake obtained in the presence of thermodynamic promoter (72.0 mmol/mol H 2 O), the value increased by 83%. More strikingly, the work shows that high gas uptake hydrates formed at relatively low temperatures can be stored and transported at relatively high temperatures, as high as 298.15 K, without significantly reducing the gas uptake, thereby providing one of the cost-effective methods for hydrate storage and transportation, that is forming hydrates at relatively low temperatures and storing and transporting hydrates at relatively high temperatures. Further, we proposed a schematic of the process chain of SNG(storing natural gas via solid hydrate) technology in vehicular and detailed discuss the current status of SNG technology development. It can be concluded that using the strategy that storage and transportation hydrates at a low-pressure condition instead of at ambient pressure (1.0 atm) may be a more realistic choice to industrialize SNG technology. [ABSTRACT FROM AUTHOR]

• Morphologies of hydrate formation in the CH 4 + THF + CP system are characterized. • The mechanism of hydrate layer rupture is determined in this study. • The kinetics of hydrate formation in the CH 4 + THF + CP system are studied. • Three stages of hydrate formation are obtained from the CH 4 + THF + CP system. The morphologies of methane (CH 4) hydrate formation in the system containing different mole ratios of tetrahydrofuran (THF) and cyclopentane (CP) at two different temperatures are systematically studied in this work. The results showed that for all cases conducted at 274.2 K, a hydrate film quickly covers the entire interface between the oil (CP) and the THF solution phase after gas loading, and then a hydrate layer forms, thereby significantly decreasing the following gas-liquids mass transfer efficiency. Raman spectrum shows this hydrate layer is caused mainly by pure THF hydrate. Interestingly, as the temperature increase to 278.2 K, the hydrate layer breaks. This is because, after hydrate layer formation, hydrate still grows at the contact interface of the metal, gas, and liquid phase, and then moves upward. In this process, liquids are gradually transported to the reaction front to form hydrate by capillary force and the hydrate layer's downward curvature gradually increases as the consumption of liquid until rupture. Besides, typical reaction kinetics shows that there are three stages of hydrate formation in the THF + CP + CH 4 system at 278.2 K. (1) hydrate layer formation (pure THF hydrate formation); (2) CP-CH 4 hydrate formation; (3) large amount of THF-CH 4 hydrate formation (after hydrate layer rupture). Further, this work also confirmed that after the hydrate layer rupture, the CH 4 occupancy in 512 cages of sII at the same temperature and promoter's mole fractions is independent of the type of promoters (CP, THF, and CP + THF) used in the system. [ABSTRACT FROM AUTHOR]

• Promoter-CH 4 hydrate formation in a high-pressure microcalorimeter is studied. • The CH 4 hydrate formation thermodynamic behavior depends greatly on the promoter. • The hydrate structure has little effect on its formation thermodynamic behavior. To understand the thermodynamic characteristics of CH 4 hydrate formation in a high-pressure microcalorimeter under different reaction kinetics, five typical systems including CH 4 -H 2 O, CH 4 -Tetrahydrofuran (THF)–H 2 O, CH 4 -Cyclopentane (CP)–H 2 O, CH 4 -Methyl cyclohexane (MCH)–H 2 O, and CH 4 - tert -Butyl methyl ether (TBME)–H 2 O are adopted to conduct experiments in this work. The results show that their hydrate formation thermodynamic characteristics depend greatly on the promoter. For the CH 4 -H 2 O system, a hydrate crystals film will form quickly at the beginning of the reaction, hindering the mass transfer between gas and liquid, thereby presenting an extremely slow hydrate formation kinetics. After adding the water-soluble promoter that cannot form an oil phase, like THF, a rapid hydrate formation process is observed from the cooling stage. However, if the promoter can form an oil phase (CP, MCH, and TBME), regardless of whether the promoter is soluble in water, only a slow hydrate formation kinetics can be observed. This is because the oil phase can separate the water and gas phase, reducing their mass transfer efficiency, thereby restricting the hydrate growth. Interestingly, a rapid hydrate formation process can be obtained during their heating stage. These indicate that high driving force cannot always lead to a rapid hydrate formation kinetics. It is worth mentioning that a similar hydrate formation and dissociation behavior in high-pressure microcalorimeter is observed for water-insoluble promoters (CP, MCH), indicating the hydrate structure will not significantly affect their thermodynamic behavior except for the intensity of the peaks. [ABSTRACT FROM AUTHOR]