Hydrate Research‐From Correlations to a Knowledge‐based Discipline: The Importance of Structure

This contribution gives a short historical perspective on the development of fundamental knowledge about gas hydrates, and how such fundamental knowledge is important for a variety of problems related to hydrate prevention (pipelines), hydrate formation (CO2 sequestration), or hydrate decomposition (permafrost or marine natural gas hydrates). It is shown that early correlations derived from measurements on hydrates, many of which were made as early as the 1800s, could not be understood properly until around 1950 when X‐ray diffraction measurements gave a structural understanding of the materials we now know as clathrates, or host‐guest materials. In turn, this led to a statistical mechanical description and a thermodynamic model that has considerable predictive power. Recently, it has become apparent that there is considerable complexity and subtlety in the relationship between structure and the size of the hydrate formers once more than a single species is present. This emphasizes the need to obtain structural information together with thermodynamic measurements, especially in multicomponent systems. Such developments have encouraged the adoption of additional structural techniques such as NMR and vibrational spectroscopy. Current interest in hydrate formation and decomposition requires the adaptation and development of new approaches that allow the acquisition of time‐resolved structural information. Furthermore, an understanding of the morphology of hydrate crystals and how to modify this morphology, as well as understanding of interfacial properties, are all key to learning how to control hydrates. Although a great deal of progress has been made, much remains to be learned.