Although lots of spectroscopic data exist for free solid CO2 and ice in extra‐terrestrial space, no sign of CO2 hydrate has been found, see Chapters 3 and 13 for possible reasons.
The large gas capacity and water as cheap working fluid make gas hydrates interesting materials for industrial applications. Gas hydrates are generally selective for guest molecule adsorption which allows the separation of gas mixtures. Much as salt is excluded when brine is frozen in desalination processes, gas hydrates have the same ability, but now the properties of the solid phase can be adjusted. For example, depending on the choice of guest, the hydrate freezing point can be well above the ice point, so saving on refrigeration costs. The same principle applies to cool energy storage where the freezing point of the hydrate can be tuned to minimize operational costs. Further applications include dewatering of fruit juices, sewage sludge and wood pulp, and the storage of unstable molecules such as ozone and chlorine dioxide. A more exotic application was the separation of radioactive radon gas from a gas mixture.
The gentler conditions required for the formation and storage of methane in solid hydrate form as compared to the low temperature required for liquid nitrogen storage of liquefied methane has resulted in the evaluation of transport by these two means. Indeed, some cost advantages become apparent for solid hydrate transport if methane has to be transported from stray fields where construction of a liquid natural gas (LNG) plant is not cost effective. Other applications for storage have been explored, e.g. for hydrogen as fuel gas and CO2 for greenhouse gas separation and storage.
Gas hydrates, because of their unique properties, have demonstrated some entertainment value. The “burning snowball” results when methane from decomposing methane hydrate is ignited and this phenomenon has been admired by many, both live and in print. In the early 1980s, it was proposed that sudden, massive decomposition of marine methane hydrates could be the cause of disappearances of ships and planes in mythically mysterious areas such as the Bermuda triangle. It appears the mystery novel “Death by gas hydrate” still needs to be written: hydrates have great potential as difficult to track murder weapons. The media also have frequently given news coverage of “burning ice” which is rediscovered every 10 years or so.
From the earlier examples, it is clear that gas hydrates are interesting and unusual materials partly because nature makes them and partly because there are many potential uses which unfortunately remain largely prospective. This book will emphasize the molecular chemical, physical, and material aspects of clathrate hydrates, that is, the many details needed to understand the macroscopic properties and processes mentioned earlier. Engineering and geological aspects of the gas hydrates have been covered admirably in a number of previous books mentioned later.
In Section 1.2 of this chapter, we highlight milestones of clathrate hydrate science up to the present. The history and context of some of these earlier developments are discussed in greater detail in Chapter 2 and in chapters that follow and the relevant references can be found there. From their beginning and in the decades that followed, many centers of clathrate hydrate research emerged in different parts of the world. From the early 1960s with the work of Don Davidson and coworkers, the National Research Council (NRC) of Canada in Ottawa emerged as one of the active centers of research in this field. In Section 1.3, we give a summary of the contributions to clathrate hydrate science made in the NRC of Canada during this time period. Contributors to the clathrate hydrate research at the NRC are acknowledged in Section 1.4. Some influential books and review articles on clathrate hydrates that appeared during this period and up to the current time are introduced in Section 1.5. International conferences focusing on clathrate hydrate science are listed in Section 1.6.
1.2 Selected Highlights of Clathrate Hydrate Science Research Up to the Present
In this section, we summarize selected highlights of clathrate hydrate research, emphasizing contributions to molecular science. Not all engineering and geological discoveries are covered in detail in this selection. Full author names and references for most of these highlights are given in the following chapters.
| 1810 | Sir Humphrey Davy correctly identified a solid material, previously thought to be solid chlorine, as a compound of chlorine and water and called it “gas hydrate.” |
| 1823 | Faraday determined the composition of chlorine hydrate to be Cl2·10H2O. |
| 1823 | Faraday acting upon a suggestion by Davy, used decomposition of gas hydrates in confined vessels as a method of liquefying gases. |
| 1828 | Löwig prepared bromine hydrate and determined the formula Br2·10H2O for the compound. |
| 1829 | de la Rive prepared SO2 hydrate, SO2·14H2O, and proposed that all common gases form hydrates. |
| 1840 | Wöhler prepared H2S hydrate. |
| 1843 | Millon prepared chlorine dioxide hydrate, the first example of the preservation of an unstable chemical species, ClO2, an explosive‐free radical. |
| 1852 | Loir prepared solid binary hydrates from water, H2S, or H2Se and halogenated hydrocarbons like chloroform, their composition remained unknown for some 30 years. |
| 1856 | Berthelot prepared the first pure hydrates of organic compounds, namely, those of methyl chloride and methyl bromide. He also claimed that CS2 formed a hydrate, starting a controversy about its existence that lasted 40 years. |
| 1863 | Wurtz prepared ethylene oxide (EO) hydrate, the first example of a water‐soluble guest. Its composition and melting point diagram were not determined until 1922. |
| 1878 | Isambard showed that the equilibrium pressure of chlorine hydrate is univariant. |
| 1878 | Cailletet designed and built apparatus suitable for working at high pressure and low temperature. This was of great value for the preparation of new gas hydrates and the determination of phase equilibria. He illustrated this by preparing new hydrates of acetylene and phosphine. |
| 1882 | Wróblewski prepared CO2 hydrate. |
| 1882 | de Forcrand prepared and characterized 33 double hydrates of H2S with a variety of guests and established similarities of composition, M·2H2S·23H2O. Studies were extended to double hydrates with H2Se as well as a simple hydrate of H2Se. |
| 1882 | Cailletet and Bordet showed that mixed hydrates of CO2 and PH3 were not simply physical mixtures of simple CO2 and PH3 hydrates but hydrates with unique properties. |
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