Basis for Current Thermodynamic Models

With the determination of hydrate structure, more rigorous predictive methods were formulated for hydrate thermodynamic property predictions. Barrer and Stuart (1957) initially suggested a statistical thermodynamic approach to determining gas hydrate properties. In a similar yet more successful approach, 

The advantage of the method in addition to accuracy is that, in principle, it enables the user to predict properties of mixtures from parameters of single hydrate formers. Since there are only eight natural gas components (yet an infinite number of natural gas mixtures) that form hydrates, the method represents a tremendous saving in experimental effort for the natural gas industry. The modified van der Waals and Platteeuw method is detailed in Chapter 5. 

McKoy and Sinanoglu (1963) and Child (1964) refined the van der Waals and Platteeuw method using different intermolecular potentials such as the Kihara potential. Workers at Rice University, such as Marshall et al. (1964) and Nagata and Kobayashi (1966a,b), first fit simple hydrate parameters to experimental data for methane, nitrogen, and argon. Parrish and Prausnitz (1972) showed in detail how this method could be extended to all natural gases and mixed hydrates. 

Efforts to improve the original assumptions by van der Waals and Platteeuw were detailed in a review by Holder et al. (1988). Erbar and coworkers (Wagner et al., 1985) and Anderson and Prausnitz (1986) presented improvements to inhibitor prediction. Robinson and coworkers introduced guest interaction parameters into their prediction scheme, as summarized by Nolte et al. (1985). At Heriot-Watt University, the group of Tohidi and Danesh generated another prediction extension, with emphasis on systems containing oil or condensate (Avlonitis et al., 1989 Avlonitis, 1994 Tohidi et al., 1994a). 

The van der Waals and Platteeuw method has been extended to flash programs by a number of researchers (Bishnoi et al., 1989 Cole and Goodwin, 1990 Edmonds et al., 1994, 1995 Tohidi et al., 1995a Ballard and Sloan, 2002). These flash calculations predict the equilibrium amount of the hydrate phase relative to associated fluid phases. 

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