In this study, we investigate the crystal structures and phase equilibria of butanols+CH +H O systems to reveal the hydroxy group positioning and its effects on hydrate stability. Four clathrate hydrates formed by structural butanol isomers are identified with powder X-ray diffraction (PXRD). In addition, Raman spectroscopy is used to analyze the guest distributions and inclusion behaviors of large alcohol molecules in these hydrate systems. The existence of a free OH indicates that guest molecules can be captured in the large cages of structure II hydrates without any hydrogen-bonding interactions between the hydroxy group of the guests and the water-host framework. However, Raman spectra of the binary (1-butanol+CH ) hydrate do not show the free OH signal, indicating that there could be possible hydrogen-bonding interactions between the guests and hosts. We also measure the four-phase equilibrium conditions of the butanols+CH +H O systems.

Two isomers of C2H7N, dimethylamine (DMA) and ethylamine (EA), are known to be clathrate hydrate formers by themselves. Here we introduced methane gas as a secondary guest into both dimethylamine and ethylamine clathrate hydrates and identified their structural transitions using powder X-ray diffraction (PXRD) and solid-state NMR spectroscopy. We observed the structural transitions of amine clathrate hydrates from expanded structure I (cubic Pm3n) to structure II (cubic Fd3m). In addition, from experimental results obtained through neutron powder diffraction (NPD) and PXRD, we found that neither temperature nor pressure affected the hydrate structural transition. Raman spectroscopy was used to identify the structural transition occurring in these amine clathrate hydrate systems. In addition, we measured the hydrate equilibrium conditions for amine–water–methane hydrates. The DMA and EA act as hydrate inhibitors in DMA/EA + H2O + CH4 hydrate systems compared with pure methane hydrate over our experimental pressure and temperature ranges.

Investigations on the intrinsic properties of gas hydrates with multiple guests are essential to scientific and technological fields. In particular, even though evaluating and designing a hydrate phase process require isothermal phase equilibria, it is difficult to obtain extensive data with various components and compositions in a short period of time due to the static-analytic method. The present study introduces a new experimental determination on hydrate phase equilibria using continuous dissociation induced by extremely slow vapor volume expansion at a constant temperature. When a syringe pump is automatically operated at the microliter level during the dissociation process, the endothermic dissociation can be traced from the temperature readings. The validity and stability of the proposed technique were evaluated using pure CH 4 hydrates, and repeated measurements of three-phase (L W −H−V) equilibrium conditions are used to optimize the volumetric expansion rates. Then, an experimental approach is applied to incipient CH 4 + C 2 H 6 hydrates and identifies the structural transition behavior. This method is thought to provide extensive data and further improvements in terms of hydrate phase equilibria with multiple gas components.

In this study, we introduce a new structure-II hydrate former, 2-methylpropane-2-peroxol (tert-butyl hydroperoxide, TBHP), and identify the structure and guest distributions through spectroscopic tools including high-resolution powder diffraction (HRPD), 13 C solid-state NMR, and Raman spectroscopy. Here, the (H + L + V) phase equilibrium data of (TBHP + X) hydrates (X = CH 4 , N 2 , and O 2 ) were measured at (3.3 to 7.56) MPa and (282.2 to 288.5) K for CH 4 , (4.0 to 8.5) MPa and (271.6 to 277.5) K for N 2 , and (4.0 to 8.6) MPa and (273.8 to 279.6) K for O 2 . The (TBHP + X) hydrate phase equilibria showed that the addition of TBHP increased the structural stability with lower hydrate dissociation pressures when compared with those of pure CH 4 , N 2 , and O 2 hydrates. However, we noticed that the TBHP did not promote hydrate formation conditions as effectively as tetrahydrofuran.

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