Calculations of NMR properties for sI and sII clathrate hydrates of methane, ethane and propane
نویسندگان
چکیده
Calculations of NMR parameters (the absolute shielding constants and the spin-spin coupling constants) for 5(12), 5(12)6(2) and 5(12)6(4) cages enclathrating CH4, C2H6 and C3H8 molecules are presented. The DFT/B3LYP/HuzIII-su3 level of theory was employed. The (13)C shielding constants of guest molecules are close to available experimental data. In two cases (the ethane in 5(12) and the propane in 5(12)6(2) cages) the (13)C shielding constants are reported for the first time. Inversion of the methyl/methylene (13)C and (1)H shielding constants order is found for propane in the 5(12)6(2) cage. Topological criteria are used to interpret the changes of values of NMR parameters of water molecules and they establish a connection between single cages and bulk crystal.
منابع مشابه
A Fugacity Approach for Prediction of Phase Equilibria of Methane Clathrate Hydrate in Structure H
In this communication, a thermodynamic model is presented to predict the dissociation conditions of structure H (sH) clathrate hydrates with methane as help gas. This approach is an extension of the Klauda and Sandler fugacity model (2000) for prediction of phase boundaries of sI and sII clathrate hydrates. The phase behavior of the water and hydrocarbon system is modeled using the Peng-Robinso...
متن کاملApplication of Gas Hydrates as an Alternative Dehydration Method
Gas hydrates were first discovered by Sir HumphryDavy in 1810 [1]. Clathratehydrates are crystalline compounds, formed by the smaller molecules (guest), entrapped within the cavities of a rigid “cage-like” lattice of water molecules (host) at low temperature (typically less than 300K) and high pressure (typically more than 0.6MPa) conditions [2]. The small molecules of gasses, such as methane (...
متن کاملPrediction of Structural Changes in Gas Hydrate for Methane and Ethane Mixture by Using Tangent Plane Distance Minimization
Abstract: Â In this study, the change in the crystalline structure of gas hydrate was predicted for ternary mixture of methane-ethane-water. For this purpose, the tangent plane distance (TPD) minimization method was used. First, the calculations were performed for the binary mixtures of methane-water and ethane-water as the gas and liquid phases. The results show that for a binary mixture of th...
متن کاملRaman spectroscopic measurements of synthetic gas hydrates in the ocean
A Raman spectrometer extensively modified for deep ocean use was used to measure synthetic hydrates formed in an ocean environment. This was the first time hydrates formed in the ocean have been measured in situ using Raman spectroscopy. Gas hydrates were formed in situ in the Monterey Bay by pressurizing a Pyrex cell with various gas mixtures. Raman spectra were obtained for sI methane hydrate...
متن کاملChanges in structure and preferential cage occupancy of ethane hydrate and ethane-methane mixed gas hydrate under high pressure
Structural changes and preferential cage occupancies were examined for ethane hydrate and ethane-methane mixed gas hydrates with five compositions in a pressure range of 0.2 to 2.8 GPa at room temperature. X-ray diffractometry and Raman spectroscopy showed the following structural changes. The initial structure, structure I (sI), of ethane hydrate was retained up to 2.1 GPa without any structur...
متن کامل