二氧化碳和若干小分子气体置换天然气水合物的多尺度模拟

天然气水合物被视为未来石油天然气的替代能源，在我国南海其储量极为丰富。天然气水合物的赋存环境很复杂，影响水合物的形成和分解。利用温室气体二氧化碳及其混合气体置换天然气水合物中的甲烷是天然气水合物开采技术的研究热点，但置换水合物的特性和机理尚未阐明。界面和组成对水合物的形成分解很重要，本项目采用量子化学计算与分子动力学模拟，并结合温度积分抽样方法和转移路径理论，拟从界面到体相，研究二氧化碳分别与氮气、一氧化碳、一氧化氮、二氧化氮、二氧化硫、三氧化硫等组成混合气体在不同亲水性的二氧化硅表面上、体相水中置换天然气水合物中的甲烷。分析水合物的构象转变，筛选出能量较低的笼状物，从热力学上定义水合物的分解和形成状态，确定置换水合物的分解形成的主要路径。结果将有助于揭示二氧化碳混合气体置换天然气水合物的特性和机理，为深入理解置换天然气水合物提供新理论基础，为能源和环境的和谐发展提供新技术支持。

Natural gas hydrate is regarded as the alternative energy of oil and natural gas in future, and its reserves are abundant in the South China Sea. The occurrence environment of natural gas hydrate is very complex, which affects the formation and decomposition of hydrate. The replacement of methane in natural gas hydrate by using the greenhouse gas carbon dioxide and its mixed gases is a research hotspot in the research of natural gas hydrate. However, the properties and mechanism of replacement hydrate have not been clarified. Interface and composition are very important for the formation of hydrate. In this project, from interface to bulk phase, quantum mechanics calculation and molecular dynamics simulation, together with integrated tempering sampling method and transition-path theory, are applied to study the replacement of methane in natural gas hydrate by using mixed gases comprised of carbon dioxide and nitrogen, carbon monoxide, nitrogen monoxide, nitrogen dioxide, sulfur dioxide, sulfur trioxide on the surface of silica with different hydrophilicity and in bulk water. This project analyzes the conformational transformation of hydrate, and selects the cages with lower energy, and defines the states of hydrate decomposition and formation from thermodynamics, and determines the main paths of hydrate decomposition and formation. The results will help to reveal the properties and mechanism of replacement of natural gas hydrate with carbon dioxide mixture, and provide a new theoretical basis for deep understanding of replacement of natural gas hydrate, and provide new technical support for the harmonious development of energy and environment.