Chapter Summary and Relationship to Following Chapters

The statistical thermodynamic method and the Gibbs energy minimization presented in this chapter represents the state-of-the-art for the prediction of the following types of phase equilibria  

By comparing the program predictions with data, along with those of three current commercial hydrate programs, the conclusion is reached that the current state-of-the-art programs can predict the uninhibited, incipient hydrate formation temperature and pressure to within an average of 0.65 K and 10% of overall pressure, respectively. The equivalent inhibited inaccuracies for incipient temperature and pressure are 2 K and 20% in overall pressure, respectively. 

The chapter also examined three molecular methods (1) ab initio quantum mechanical calculations, which are typically used to get better interatomic potentials, (2) MC calculations, and (3) molecular dynamic calculations. The latter two molecular methods are most useful to probe the behavior of a small number of molecules, in which experimental capability is constrained by either space or time. 

Chapter 6, which immediately follows, presents experimental methods and data for comparison with predictions in the present chapter. Such data will form the foundation for future modifications of theory in hydrate phase equilibria. However, the above thermodynamic prediction accuracies are usually satisfactory for engineering calculations, so that the state-of-the-art in hydrates is turning from thermodynamic (time-independence) to kinetics (time-dependence) phenomena, 

Chapter 7 then considers the formation of hydrates in nature, such as in the permafrost and deep oceans of the earth. In such situations geologic time mitigates the necessity for kinetic formation effects and allows the use of thermodynamic conditions, such as those in the three-phase portions of the present chapter, for identification, exploration, and recovery. 

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