Temperature- and Pressure-induced Structural Transition of Binary Clathrate Hydrates |
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Authors: | Dr. Yun-Ho Ahn Seungjun Baek Juwon Min Prof. Dr. Minjun Cha Prof. Dr. Jae W. Lee |
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Affiliation: | 1. Department of Chemical and Biomolecular Engineering (BK21+Program), Korea Advanced Institute of Science and Technology (KAIST), 291 Daehak-ro, Yuseong-gu, Daejeon, 34141 Republic of Korea;2. Department of Energy and Resources Engineering, Kangwon National University, 1 Kangwondaehak-gil, Chuncheon-si, Gangwon-do, 24341 Republic of Korea |
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Abstract: | We discover new structure II (sII) hydrate forming agents of two C4H8O molecules (2-methyl-2-propen-1-ol and 2-butanone) and report the abnormal structural transition of binary C4H8O+CH4 hydrates between structure I (sI) and sII with varying temperature and pressure conditions. In both (2-methyl-2-propen-1-ol+CH4) and (2-butanone+CH4) systems, the phase boundary of the two different hydrate phases (sI and sII) exists at the slope change of the phase-equilibrium curve in the semi-logarithmic plots. We confirm the crystal structures of two hydrates synthesized at low (278 K and 6 MPa) and high (286 K and 15 MPa) temperature and pressure conditions by using high-resolution powder diffraction and Raman spectroscopy. 2-Methyl-2-propen-1-ol and 2-butanone can occupy the large cages of sII hydrate at low temperature and pressure conditions; however, they are excluded from the hydrate phase at high temperature and pressure conditions, resulting in the formation of pure sI CH4 hydrate. |
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Keywords: | clathrate hydrates host-guest chemistry hydrate structure analysis phase equilibria structural transition |
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