A vast source of methane is found in gas hydrate deposits, which form naturally dispersed throughout ocean sediments and arctic permafrost. Methane may be obtained from hydrates by exchange with hydrocarbon byproduct carbon dioxide. It is imperative for the development of safe methane extraction and carbon dioxide sequestration to understand how methane and carbon dioxide co-occupy the same hydrate structure. Pair distribution functions (PDFs) provide atomic-scale structural insight into intermolecular interactions in methane and carbon dioxide hydrates. We present experimental neutron PDFs of methane, carbon dioxide and mixed methane-carbon dioxide hydrates at 10 K analyzed with complementing classical molecular dynamics simulations and Reverse Monte Carlo fitting. Mixed hydrate, which forms during the exchange process, is more locally disordered than methane or carbon dioxide hydrates. The behavior of mixed gas species cannot be interpolated from properties of pure compounds, and PDF measurements provide important understanding of how the guest composition impacts overall order in the hydrate structure.

在天然气水合物沉积物中发现了大量的甲烷来源，这些沉积物自然分散在海洋沉积物和北极永久冻土中。甲烷可以通过与烃副产物二氧化碳交换而从水合物中获得。必须了解甲烷和二氧化碳如何共同占据相同的水合物结构，才能开发安全的甲烷提取和二氧化碳封存。对分布函数 (PDF) 提供了对甲烷和二氧化碳水合物中分子间相互作用的原子级结构洞察。我们展示了 10 K 下甲烷、二氧化碳和混合甲烷-二氧化碳水合物的实验中子 PDF，并通过补充经典分子动力学模拟和反向蒙特卡罗拟合进行了分析。在交换过程中形成的混合水合物，比甲烷或二氧化碳水合物更局部无序。混合气体物种的行为不能从纯化合物的性质中推断出来，PDF 测量提供了重要的理解来宾组成如何影响水合物结构中的整体秩序。