Clathrate phase behavior of the phenolmethane, phenolcarbon dioxide and phenolnitrogen systems
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Clathrate hydrate
Density functional theory calculation has been carried out to elucidate the thermodynamic properties of the methane clathrate hydrate(51262 and 512).At the B3LYP/6-31G**level,methane clathrate hydrate is fully optimized and the potential energy curves are scanned.The theoretical calculations showed that one methane molecule encaged in the 51262 cavity is most stable.The preserved condition for safely storing methane hydrate is 190 K,200 MPa.The calculated values of symmetric C—H stretching frequencies of the methane molecule in the two cluster cavities are agreed with the experimental data.The narrow potential wall in the 512 cavity leads to restricting the motion of the methane molecule in the small cavity.
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Clathrate hydrate
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The adsorption of phenol on flat and stepped Pt and Rh surfaces and the dissociation of hydrogen from the hydroxyl group of phenol on Pt(111) and Rh(111) were studied by density functional calculations. On both Pt(111) and Rh(111), phenol adsorbs with the aromatic ring parallel to the surface and the hydroxyl group tilted away from the surface. Furthermore, adsorption on stepped surfaces was concluded to be unfavourable compared to the (111) surfaces due to the repulsion of the hydroxyl group from the step edges. Transition state calculations revealed that the reaction barriers, associated with the dissociation of phenol into phenoxy, are almost identical on Pt and Rh. Furthermore, the oxygen in the dissociated phenol is strongly attracted by Rh(111), while it is repelled by Pt(111).
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The paper presents measurement results of methane and carbon dioxide emission in Western Carpathians. The investigations were carried out with application of static chamber method in 10 stations. An emission and dynamics of changes within methane and carbon dioxide concentrations were examined by measuring the emission directly from the land surface as well as after drilling an additional hole. In total, 40 gas samples were taken, which were then subjected to chromatographic analysis. The measurements of methane and carbon dioxide emission have not shown significant emission values of these gases. The average value of methane emission from soil to the atmosphere at selected measurement sites was -0.451 mg * m -2* d -1 , while the average methane emission with the use of the hole, equalled to -0.361 mg * m -2* d -1 . The changes of carbon dioxide concetration were opposite. Higher emission of this gas was showed due to its natural escaping to the atmosphere with an average concetration of 1829,3 mg * m -2* d -1 . Conducted studies show that methane and carbon dioxide emission are low in the studied area. It does not confirm the elevated values of light hydrocarbons and associated components which were previously recorded in the soil gas samples.
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The exchange of methane between clathrate phase and gas phase on artificial methane hydrate was studied. Artificial methane hydrate samples were formed in a pressure cell from methane gas with stable carbon isotope composition δ13C of －42.3‰（ methane A）. Methane A remaining in the gas phase was removed from the cell at 77 K and methane gas with stable carbon isotope composition δ13C of －66.9‰（ methane B） was introduced into the cell. The carbon isotope compositions of both clathrate phase and gas phase methane gases were measured after the samples had been maintained at 274.7 K for 7-50 days. The δ13C of the clathrate phase methane was smaller than the initial value of －42.3‰ and that of the gas phase methane was larger than its initial value of －66.9‰. These results suggest that the exchange between the clathrate phase and gas phase methane proceeded in the period of the scale for several weeks.
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Clathrate hydrate
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clathrate compound란 호스트 분자가 수소 결합에 의하여 3차원 골격구조를 만들고, 이 격자 내부의 동공으로 저분자량의 기체 게스트 분자가 포집되며 형성되는 고체 결정 화합물이다. 현재까지 다양한 호스트 분자가 clathrate 화합물을 형성하는 것으로 보고되어 있으며, 이 중 유기물인 hydroquinone 역시 clathrate compound를 형성할 수 있는 것으로 알려져 있다. clathrate compound는 작은 고체 부피 내부에 막대한 양의 기체 분자를 저장할 수 있는 특성을 지니고 있기 때문에, 에너지 가스의 저장/수송이나 혼합 가스의 선택적 분리와 같은 다양한 응용을 위한 연구가 활발히 진행되고 있다. 본 연구에서는 clathrate compound를 형성하는 유기 호스트 분자인 hydroquinone을 이용하여 다양한 기체분자들에 대한 포집 거동을 파악하였다. 순수 기체로는 N₂, H₂, CO₂, CH₄의 4종류를 가지고 고압 반응기에서 50bar의 압력, 상온에서의 반응 조건으로 반응을 시켰다. 이렇게 형성된 반응 샘플들은 clathrate 형성 여부(기체의 포집 여부)를 확인하기 위하여 x-ray 회절을 통한 고체 결정 구조 분석을 수행하였다. 또한 순수 기체 이외에 다양한 비율(20%, 40%, 60%, 80%)의 조성을 갖는 CO₂+N₂ 혼합가스를 이용하여 clathrate compound의 형성과 조성 분석을 수행하였는데, x-ray 회절 분석과 13C 고체 NMR 분석을 통해 미세 구조 분석 연구를 수행하였고, Raman분석을 통하여 그 조성을 확인하였다. 본 연구에서 얻어진 결과는 기체의 저장/수송이나 혼합 가스의 선택적 분리와 같은 응용 분야에서 중요한 정보를 제공할 수 있을 것으로 기대된다.
Clathrate hydrate
Hydroquinone
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Clathrate hydrate
Powder Diffraction
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Termites may emit large quantities of methane, carbon dioxide, and molecular hydrogen into the atmosphere. Global annual emissions calculated from laboratory measurements could reach 1.5 x 10(14) grams of methane and 5 x 10(16) grams of carbon dioxide. As much as 2 x 10(14) grams of molecular hydrogen may also be produced. Field measurements of methane emissions from two termite nests in Guatemala corroborated the laboratory results. The largest emissions should occur in tropical areas disturbed by human activities.
Atmospheric methane
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Atmospheric carbon cycle
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