水合物CH4-CO2置换的双重机理:空位辅助与竞争

过去的CO2置换甲烷水合物的微观机理研究,主要集中在客体分子(CH4、CO2)之间的交换、占据状态,孤立地研究分解过程或生成过程,忽视主体-客体之间的作用、主体分子(H2O)的空位辅助和客体分子的多重竞争通道。本文基于水合物分解的过冷水及其水空位辅助,以及水合物生成的串滴链及其客体分子竞争的研究,进一步评论水合物CH4-CO2置换的双重机理。然后,对微观机理的动态性和未来研究的相关问题进行讨论。通过综述和评论,文章得出以下初步结果:过冷水通过水空位推动客体分子的跳跃、扩散,实现置换过程的自组装;CO2分子在分解前沿形成一个有序结构的CO2串滴链,其动态性伴随水的组织到获取包合物笼的结构,以及非晶形包合物转变成晶形包合物的生长过程;CO2和CH4在中晶穴中必然产生竞争,并且存在多种竞争类型;成核过程中,不稳定簇导致竞争结构,且有多重竞争通道。最后,结果表明水合物的CH4-CO2置换机理具有双重性,即主体分子的空位辅助和客体分子的竞争,是分解过程和生成过程的自然统一。

Double Mechanism of CH4-CO2 Replacement in Hydrate:Vacancy Assistance and Competition

Previous studies on the microcosmic mechanism of CO2 replacing methane hydrate(CH4·H2O) mainly focus on the exchanged and occupied state between the guest molecules(CH4 and CO2),and examine decomposition process or formation process alone,ignoring the interactions of host-guest molecules and vacancy assistance of host molecule(H2O) and multiple competing path of guest molecules.Based on researches about supercooled water and water-vacancy assistance of hydrate decomposition,and blobs of hydrate formation and competition of guest molecules,this article further reviewed double mechanism of CH4-CO2 replacement in hydrate.Then,dynamic of microcosmic mechanism and related issues of future research were discussed.Through the reviews and comments,the following preliminary conclusions were drawn: self-assembly of replacing process is carried out through hop and diffusion of the guest molecules pushed by water vacancy in supercooled water;CO2 blobs of ordered structure is formed in decomposition frontier,and its dynamic is followed by organization of water and acquisition of the clathrate cages structure,as well as the developing process of the amorphous clathrate transforming into crystalline clathrate;CO2 and CH4 produce competition are inevitable in the medium cavity,and there are many types of competition;labile clusters results in formation of competing structure,with multiple competition paths,in formation process of critical nucleus.Finally,the results show that mechanism of CH4-CO2 replacement in hydrate is of dual nature—the vacancy assistance of host molecule and competition of guest molecules are the natural unity of decomposition and formation processes.