Water Content of Liquid Hydrocarbon in Equilibrium with Hydrates

2 Water Content of Liquid Hydrocarbon in Equilibrium with Hydrates 

In the H-Lhc two-phase region there is a severe paucity of both data and a simple calculation scheme. These data find applications in condensate pipelines, which may have hydrates. The only data available are from this laboratory 

Because there are so few data for water content of the fluid hydrocarbon in either of the two-phase (H-V or H-Lhc) regions, their accuracy cannot be determined. These data are very difficult to obtain due to the low concentrations (typically 100 ppm mol). The inaccuracies in normal experimental data in other phase regions are frequently greater than the absolute values of the water content in the H-Lhc region. 

With low concentrations of water a substantial amount of time may be required before the water molecules can agglomerate into a hydrate structure. Experimental time to acquire each data point is normally on the order of days or weeks, rather than hours. Appreciable metastability is observed, and long times are required for the formation of critical hydrate nuclei. Nevertheless, the long time involved should not be taken as an indication that hydrates are not thermodynamically stable in the two-phase region. The phase diagram analyses presented in Section 4.1 indicate the thermodynamic validity of this region. 

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