Halpern Y, Thieu V, Henning R W, Wang X, Schultz A J
Energy Systems Division, Argonne National Laboratory, Argonne, Illinois 60439, USA.
J Am Chem Soc. 2001 Dec 26;123(51):12826-31. doi: 10.1021/ja010280y.
We report the in situ observation from diffraction data of the conversion of a gas hydrate with the structure II (sII) lattice to one with the structure I (sI) lattice. Initially, the in situ formation, dissociation, and reactivity of argon gas clathrate hydrate was investigated by time-of-flight neutron powder diffraction at temperatures ranging from 230 to 263 K and pressures up to 5000 psi (34.5 MPa). These samples were prepared from deuterated ice crystals and transformed to hydrate by pressurizing the system with argon gas. Complete transformation from D(2)O ice to sII Ar hydrate was observed as the sample temperature was slowly increased through the D(2)O ice melting point. The transformation of sII argon hydrate to sI hydrate was achieved by removing excess Ar gas and exposing the hydrate to liquid CO(2) by pressurizing the Ar hydrate with CO(2). Results suggest the sI hydrate formed from CO(2) exchange in argon sII hydrate is a mixed Ar/CO(2) hydrate. The proposed exchange mechanism is consistent with clathrate hydrate being an equilibrium system in which guest molecules are exchanging between encapsulated molecules in the solid hydrate and free molecules in the surrounding gas or liquid phase.
我们报告了通过衍射数据对具有结构II（sII）晶格的气体水合物向具有结构I（sI）晶格的气体水合物转变的原位观察结果。最初，通过飞行时间中子粉末衍射在230至263 K的温度范围和高达5000 psi（34.5 MPa）的压力下研究了氩气笼形水合物的原位形成、分解和反应性。这些样品由重水冰晶体制备，并通过用氩气对系统加压转化为水合物。当样品温度缓慢升高至重水熔点以上时，观察到从D₂O冰完全转变为sII氩水合物。通过去除过量的氩气并通过用二氧化碳对氩水合物加压使水合物暴露于液态二氧化碳，实现了sII氩水合物向sI水合物的转变。结果表明，由氩sII水合物中的二氧化碳交换形成的sI水合物是一种混合的Ar/CO₂水合物。所提出的交换机制与笼形水合物作为平衡系统一致，在该系统中客体分子在固体水合物中的包封分子与周围气相或液相中的自由分子之间进行交换。
