title: Structural transformation and tuning behavior induced by the propylamine concentration in hydrogen clathrate hydrates.
abstract: The structures and the guest-host distributions of iso-propylamine (i-PA) and n-propylamine (n-PA) hydrates with hydrogen as a secondary guest were identified by powder X-ray diffraction and Raman spectroscopic analysis. The structure of 11.1 mol% i-PA + H2 hydrate was identified to be hexagonal (space group P63/mmc) with a few unindexed diffraction peaks, while 5.6 mol% i-PA + H2 hydrate had a cubic structure (space group Fd3¯m). Similarly, the structure of 13.3 mol% n-PA + H2 hydrate was found to be monoclinic (space group P2(1)/n), while 5.6 mol% n-PA + H2 hydrate had a cubic structure (space group Fd3¯m). The 'tuning' phenomenon, multiple occupancy of hydrogen in the large cage at the pressure and temperature regions outside of pure hydrogen hydrate stability, was observed in the i-PA + H2 hydrate only when the amine concentration was lower than the stoichiometric value of structure II hydrate. The three-phase (H-L(w)-V) equilibria for alkylamine + H2 + water mixtures were also measured to investigate their thermodynamic stability.
authors.affiliation: Department of Chemical and Biomolecular Engineering (BK21+program), Korea Advanced Institute of Science and Technology (KAIST), 291 Daehak-ro, Yuseong-gu, Daejeon 305-701, Republic of Korea. hlee@kaist.ac.kr.
authors.forename: Seongmin
authors.initials: S
authors.lastname: Park
authors.forename: Hyery
authors.initials: H
authors.lastname: Kang
authors.forename: Kyuchul
authors.initials: K
authors.lastname: Shin
authors.forename: Yutaek
authors.initials: Y
authors.lastname: Seo
authors.forename: Huen
authors.initials: H
authors.lastname: Lee