Gas Solubility:  A Key to Estimating the Water Content of Natural Gases

Experimental water content data, at low temperatures, for hydrocarbons and non-hydrocarbon gases are scarce and often rather dispersed. This is partly due to the fact that water content of gases is indeed very low at low temperatures and high pressures and hence generally very difficult to measure. However, measuring gas solubility in water is easier than measuring water content of gases. In this work, we examine the need for water content data in the gas phase for tuning binary interaction parameters between water and gaseous components in an equation of state. We consider three cases for tuning: (1) gas solubility in the liquid-phase only, (2) water content of the gas phase, and (3) mutual solubilities. The Valderrama modification of the Patel−Teja equation of state with the nondensity dependent mixing rules is used for modeling the fluid phases. These results show that using only gas solubility data in tuning the thermodynamic model leads to accurate predictions of water content data, and, therefore, experimental gas-phase water contents are not indispensable. Furthermore, we report new experimental data on the water content of the gas phase for a gas mixture consisting of 94% methane, 4% ethane, and 2% n-butane at low temperatures. The data were measured in the 277.82−292.88 K temperature range and at pressures up to 3.028 MPa, using a static-analytic technique taking advantage of a Rolsi sampling device. To examine the consistency of the new experimental data they are compared with the results of a previously reported semi-empirical approach and the developed thermodynamic model. The agreements between the experimental and predicted data are good, demonstrating the reliability of the data and the techniques used in this work.