On the Structure Selectivity of Clathrate Hydrates
On the Structure Selectivity of Clathrate Hydrates
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DOI：
10.1021/jp203478z
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发表时间：
2011-06-30
影响因子：
3.3
通讯作者：
Tanaka, Hideki
中科院分区：
文献类型：
--
作者：
Matsumoto, Masakazu;Tanaka, Hideki
我们提出了一个战略方法来寻找一个新的笼形水合物通过调查其晶体结构的选择性，这已被预期主要取决于客体物种和热力学条件少。各种形态之间的相对稳定性检查在与客体气体平衡的笼形水合物的水的化学势。该评估通过根据标准统计力学理论计算笼占据的自由能来进行，并借助于关于Frank-Kasper型合金的Yarzenuk和Kripyakevich规则来估计各种类型的笼的数量。因此，晶体结构的选择性的综合解释是成功的。我们解释了为什么两个主要的结构是稳定的，在大多数的热力学条件下，并建立了笼形水合物的多晶型和客体的大小和其他参数之间的关系，从而提出了一种方法来找到一个新的笼形水合物通过适当的选择的客体物种和/或热力学性质。研究发现，在上述参数空间中，有一个小的空间，比主要的两个结构是最稳定的，包括一个新的结构。此外，对溴水合物中优先形成TS-Ⅰ结构的现象给出了简单而透彻的解释。
We propose a strategic method to search for a new clathrate hydrate by investigating the selectivity of its crystalline structure, which has been expected to depend mostly on the guest species and less on the thermodynamic conditions. Relative stability among various morphologies is examined in terms of the chemical potential of water of clathrate hydrates in equilibrium with guest gases. This evaluation is performed by calculating the free energy of cage occupancy according to the standard statistical mechanical theory with the aid of the Yarmolyuk and Kripyakevich's rule on the Frank-Kasper type alloys to estimate the numbers of cages of various types. Thus, a comprehensive interpretation of the selectivity of crystalline structures is successfully made. We explain why two major structures are stable in most of the thermodynamic conditions and establish a relation between polymorphism of clathrate hydrate and the guest size and other parameters, thereby suggesting a way to find a new clathrate hydrate by appropriate choice of the guest species and/or the thermodynamic properties. It is found that there is a small room in the above parameter space for the other structure than the major two to be the most stable, including a new structure. In addition, simple but thorough elucidation is given for preferential formation of TS-I structure in bromine hydrate.