水合物/水/烃碳氢化合物三相共存系统中甲烷-乙烷混合物水合物的结构转变：气体浓度的影响,ACS Sustainable Chemistry & Engineering

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水合物/水/烃碳氢化合物三相共存系统中甲烷-乙烷混合物水合物的结构转变：气体浓度的影响
ACS Sustainable Chemistry & Engineering ( IF 8.4 ) Pub Date : 2020-11-03 , DOI: 10.1021/acssuschemeng.0c06432
Jiangtao Pang ₁ , Yunfeng Liang ₁ , Yoshihiro Masuda ₁ , Satoshi Takeya ₂

Affiliation

天然气混合物的水合物形成令人着迷。尽管纯甲烷和乙烷均形成结构I（sI）水合物，但它们的混合物在某些组成下可能形成结构II（sII）水合物。在这里，我们使用sII-水合物-水-烃三相界面系统研究了甲烷-乙烷混合物水合物结构转变的潜在机理。结果表明，sII水合物的形成是甲烷浓度的函数，摩尔浓度为83-90％时最大。相反，大量的sI水合物以低于75％或等于100％的浓度形成。此外，我们揭示了很少讨论的从sII到sI的结构转换的机制。15面体（主要是5 ¹² 6 ³）笼子可能来自水色和16面体（5 ¹² 6 ⁴）笼子过渡，在过渡界面处作为过渡的过渡桥起着至关重要的作用。由于15面体笼的特殊结构，14面体（5 ¹² 6 ²）笼子会生长，因此sI水合物也会生长。此外，基于甲烷和乙烷分子被困在内部的水合物的形成能，对14面体笼中的甲烷占有率和sII结构在能量上有利形成的浓度进行了定量。我们表明客体分子在界面或笼子上的吸附偏好可以归因于形成能预测和反应过程结果之间的差异。我们的发现对于具有混合气体水合物结构的储层中的流量保证，气体分离，气体运输和天然水合物开发的可持续化学具有学术和工程意义。

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Structural Transition of the Methane–Ethane Mixture Hydrate in a Hydrate/Water/Hydrocarbon Three-Phase Coexistence System: Effect of Gas Concentration

Hydrate formation of a natural gas mixture is fascinating. Whereas both pure methane and ethane form a structure I (sI) hydrate, their mixture may form a structure II (sII) hydrate at certain compositions. Here, we investigated the underlying mechanisms of the methane–ethane mixture hydrate structural transition using an sII-hydrate–water–hydrocarbon three-phase interface system. The results indicate that sII hydrate formation is a function of methane concentration with a maximum at a mole concentration of 83–90%. In contrast, a significant amount of the sI hydrate forms at concentrations below 75% or equal to 100%. In addition, we unveil the mechanism of the rarely discussed structure conversion from sII to sI. The 15-hedron (mainly 5¹²6³) cages, which may originate from both aqua and the 16-hedron (5¹²6⁴) cage transition, play a vital role as a transitional bridge in the conversion at the transition interface. Owing to the specific structure of 15-hedron cages, the 14-hedron (5¹²6²) cages can grow, and thus, the sI hydrate grows. Furthermore, the methane occupancy in the 14-hedron cages and the concentration for the energetically favorable formation of the sII structure were quantified based on the formation energies for hydrates with methane and ethane molecules trapped inside. We show that the adsorption preference of guest molecules at the interfaces or cages can be attributed to the difference between the formation energy prediction and the reaction process results. Our findings have both academic and engineering significance for sustainable chemistry related to flow assurance, gas separation, gas transportation, and natural hydrate development in reservoirs with mixed gas hydrate structures.

更新日期：2020-11-16

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