実験報告書様式（一般利用課題・成果公開利用）

MLF Experimental Report

提出日 Date of Report

課題番号 Project No.

装置責任者 Name of responsible person

2010B0039

Toru Ishigaki

実験課題名 Title of experiment

装置名 Name of Instrument/（BL No.）

Occupancy of guest molecules in hydrocarbon hydrate

iMATERIA / BL20

実験責任者名 Name of principal investigator

実施日 Date of Experiment

Akinori Hoshikawa

2011/2/16

所属 Affiliation
Ibaraki University
試料、実験方法、利用の結果得られた主なデータ、考察、結論等を、記述して下さい。（適宜、図表添付のこと）
Please report your samples, experimental method and results, discussion and conclusions. Please add figures andtables for better explanation.
1. 試料 Name of sample(s) and chemical formula, or compositions including physical form.
(1) mixed gas hydrate, 8(0.7 CH4 0.3CO2)・46(D2O)(2) ethane hydrate, 8(C2H6)・46(D2O)(3) propane hydrate, 8(C3H8)・136(D2O)

2. 実験方法及び結果 （実験がうまくいかなかった場合、その理由を記述してください。）
Experimental method and results.

If you failed to conduct experiment as planned, please describe reasons.

We prepared three samples which were mixed gas hydrate, ethane hydrate, and propane hydrate. Thesesamples were packed into the vanadium holder with an Al flange and an In-seal at liquid N2 temperature. The
samples were kept under 100 K. Each sample wasset to the cold head of the refrigerator and cooled
down. The neutron measurements were done at 10 K
with double frame mode. After measurement, thesample environment was changed. At the outside of
the vacuum chamber, the refrigerator was heated up
and another sample was set to the cold head and thesample was cooled down.
Figure 1 shows the Rietveld refinement pattern ofFigure 1. Powder neutron diffraction pattern of mixed

mixed gas hydrate. There are 5 phases, which aregas hydrate12. 実験方法及び結果（つづき） Experimental method and results (continued)
mixed gas hydrate, vanadium (holder), dry ice (CO2),Ice Ih, and Ice Ic. It was clarified that the mixed gas
hydrate had Structure I. There are two types of cage
structure in Structure I. One is dodecahedron andanother is tetrakaidecahedron. Usually, a guest
molecule occupies in each polyhedron. In our analysisof mixed gas hydrate, the guest molecules, whichwere mixed gas of CO2 and CH4, occupied in only
tetrakaidecahedra. Moreover, CO2 and CH4 occupied

Figure 2. Powder neutron diffraction pattern ofapproximately half and half. The carbon dioxide has aethane hydrate

lower freezing point than methane. It is possible thatthe carbon dioxide is selectively condensed when thesample is cooled down by liquid nitrogen in order topack into the holder. It is considered that the mixture
ratio was changed. Because the clathrate hydrate is
non-stoichiometricinclusion

compounds,

theoccupancy of the guest molecule can be variable.
Figure 2 shows diffraction pattern of ethanehydrate. In rough analysis, we could confirm that thecrystal structure of ethane hydrate was Structure I.

Figure 3. Powder neutron diffraction pattern ofThe guest molecule occupied in each polyhedral

propane hydrate

cage. It seems that there is no major impurity in thediffraction pattern. We succeeded in the synthesis of pure ethane hydrate.
Figure 3 shows diffraction pattern of propane hydrate. In rough analysis, it was confirmed that the crystal
structure of propane hydrate was Structure II as shown in the previous reports. There are two types of cage
structure in Structure II. One is dodecahedron and another is hexakaidecahedron. There are 16 dodecahedra
and 8 hexakaidecahedra in the unit cell of Structure II. The propane molecule cannot occupy in thedodecahedron because of large molecular size. The propane molecules as the guest molecule occupied in thehexakaidecahedra. It was successful that we synthesized pure propane hydrate because impurity peaks hardly
can be confirmed. Further, we need to analyze by improving structure model with hydrogen atoms. And wehave a plan for using maximum entropy method with developing software.
In summary, the crystal structure of hydrocarbon hydrate was investigated by powder neutron diffraction at
low temperature. We measured 3 samples (mixed gas hydrate, ethane hydrate, and propane hydrate) withpowder neutron diffractometer. We confirmed that the crystal structure of both mixed gas hydrate and ethane
hydrate was Structure I and that the one of propane hydrate was Structure II. Moreover, we succeeded in thesynthesis of both ethane hydrate and propane hydrate because the sample was high purity from powderneutron diffraction pattern.

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