Thermal expansivity for sI and sII clathrate hydrates
Thermal expansivity for sI and sII clathrate hydrates
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DOI：
10.1021/jp0715880
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发表时间：
2007-08-02
影响因子：
3.3
通讯作者：
Sloan, E. D.
中科院分区：
文献类型：
--
作者：
Hester, K. C.;Huo, Z.;Sloan, E. D.
热膨胀系数的知识可以帮助理解笼形水合物的微观和宏观行为。衍射研究表明，水合物的体积变化显着（高达1.5%，超过50 K）作为温度的函数。先前已经通过统计力学证明，水合物体积的微小变化（例如，1.5%的体积变化或0.5%的晶格参数变化）可导致预测的水合物形成压力的主要变化（例如，对于甲烷，在> 100 MPa下> 15%）。由于这种敏感性，水合物的热膨胀率测量，为结构I和II与各种客人，需要帮助量化水合物晶格中的体积畸变，以确保准确的水合物相平衡预测。除了宏观相平衡，不同水合物的热膨胀可以提供关于客体分子和主体晶格之间的相互作用的信息。在这项工作中，四个结构I的水合物晶格参数（C2H6，CO2，47%C2H6 + 53%CO2，和85%CH4 + 15%CO2）和7个结构II（C3H8、60%CH4 + 40%C3H8、30%C2H6 + 70%C3H8、18%CO2 + 82%C3H8、87.6%CH4 + 12.4%i-C4H10、95%CH4 + 5%C5H10O和天然气混合物）体系作为温度的函数进行测量。晶格参数的测量与现有的文献值相结合。SI和SII水合物，有几个例外，有一个共同的热膨胀，独立的水合物客人。已经提出了许多依赖于客人的线性热膨胀系数的关联式。然而，我们提出了两个客人独立的，结构相关的sI和sII晶格，这已被开发来表达归一化的水合物晶格参数（因此体积）作为温度的函数。
Knowledge of thermal expansivity can aid in the understanding of both microscopic and macroscopic behavior of clathrate hydrates. Diffraction studies have shown that hydrate volume changes significantly (as much as 1.5% over 50 K) as a function of temperature. It has been demonstrated previously via statistical mechanics that a minor change in hydrate volume (e.g., a 1.5% change in volume or 0.5% change in lattice parameter) can lead to a major change in the predicted hydrate formation pressure (e.g., > 15% at > 100 MPa for methane). Because of this sensitivity, hydrate thermal expansivity measurements, for both Structures I and II with various guests, are needed help quantify volume distortions in hydrate lattices to ensure accurate hydrate phase equilibria predictions. In addition to macroscopic phase equilibria, the thermal expansion of different hydrates can give information about the interactions between the guest molecules and the host lattice. In this work, the hydrate lattice parameters for four Structure I (C2H6, CO2, 47% C2H6 + 53% CO2, and 85% CH4 + 15% CO2) and seven Structure II (C3H8, 60% CH4 + 40% C3H8, 30% C2H6 + 70% C3H8, 18% CO2 + 82% C3H8, 87.6% CH4 + 12.4% i-C4H10, 95% CH4 + 5% C5H10O, and a natural gas mixture) systems were measured as a function of temperature. The lattice parameter measurements were combined with existing literature values. Both sI and sII hydrates, with a few exceptions, had a common thermal expansivity, independent of hydrate guest. Many guest-dependent correlations for linear thermal expansivity have been proposed. However, we present two guest-independent, structure-dependent correlations for sI and sII lattices, which have been developed to express the normalized hydrate lattice parameters (and therefore volume) as a function of temperature.