Yeobum Youn

Spectroscopic Observation of the Hydroxy Position in Butanol Hydrates and Its Effect on Hydrate Stability

In this study, we investigate the crystal structures and phase equilibria of butanols+CH4 +H2 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+CH4 ) 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+CH4 +H2 O systems.

One-dimensional approaches for methane hydrate production by CO2/N2 gas mixture in horizontal and vertical column reactor

The recovery of methane gas from methane hydrate bearing sediments was investigated by using a continuous stream of a CO2 and N2 gas mixture. A long cylindrical high-pressure reactor was designed to demonstrate the recovery of methane from methane hydrate bearing sediments, and the injection rate of the gas mixture was controlled to monitor the amount of recovered methane from methane hydrates. The recovery efficiency of methane gas from methane hydrates is inversely proportional to the flow rate of the CO2 and N2 gas mixture. Methane hydrates were synthesized by using two different sediments, having particle size distributions of 75 to 150 μm and 45 to 90 μm with the same porosity, and the recovery efficiency of methane from methane hydrates was also monitored. We confirmed that there is no significant difference in the replacement characteristics by using these two different sediments. Horizontal and vertical flows of the CO2 and N2 gas mixture were applied to monitor the effect of flow direction on replacement characteristics. We also confirmed that a similar amount of methane was recovered in horizontal and vertical flows of the CO2 and N2 gas mixture at the same flow rate. The present study may help in establishing the process variables for recovering methane gas from methane hydrate bearing sediments in offshore conditions.

Abnormal thermal expansion of clathrate hydrates induced by asymmetric guest molecules.

We investigated for the first time the abnormal thermal expansion induced by an asymmetric guest structure using high-resolution neutron powder diffraction. Three dihydrogen molecules (H(2), D(2), and HD) were tested to explore the guest dynamics and thermal behavior of hydrogen-doped clathrate hydrates. We confirmed the restricted spatial distribution and doughnut-like motion of the HD guest in the center of anisotropic sII-S (sII-S=small cages of structure II hydrates). However, we failed to observe a mass-dependent relationship when comparing D(2) with HD. The use of asymmetric guest molecules can significantly contribute to tuning the cage dimension and thus can improve the stable inclusion of small gaseous molecules in confined cages.

Spectroscopic and thermodynamic investigations of clathrate hydrates of methacrolein

This study characterized new structure II (sII) clathrate hydrates, consisting of 136 H2O molecules with 8 large 51264 cages and 16 small 512 cages, with methacrolein for the first time. The crystal structure and guest distributions of binary (methacrolein + gaseous guests) clathrate hydrates were identified using spectroscopic tools, namely powder X-ray diffraction (PXRD) and Raman spectroscopy. The PXRD and Raman results showed that the inclusion of methacrolein and gaseous guests including CH4, N2, O2 or CO2 could be monitored in the large and small cages of sII hydrates, respectively. The conformation of methacrolein in the large cages of sII hydrates was also analyzed via Raman spectroscopy, revealing an s-trans conformer of methacrolein in the large cages of sII hydrates. High-resolution powder diffraction (HRPD) and Raman spectroscopy were also used to identify the dissociation of binary (methacrolein + CH4) clathrate hydrate, showing that it was almost completely dissociated at 200 K. Finally, we measured the equilibrium conditions of four phases, clathrate hydrates, liquid water, liquid methacrolein, and the vapour phase, to check the thermodynamic stability of binary (methacrolein + gaseous guest) clathrate hydrates. The phase equilibria of binary (methacrolein + CH4, N2, or O2) clathrate hydrates showed that the addition of methacrolein to the hydrate phase increased the hydrate stability with a higher hydrate dissociation temperature when compared to the hydrate stability of pure (CH4, N2, or O2) clathrate hydrates. The thermodynamic stability of binary (methacrolein + CO2) clathrate hydrate exhibits a higher hydrate dissociation temperature when compared with that of the pure CO2 clathrate hydrate below 279 K.