Thermodynamic consistency test for isobaric experimental data of water content of methane

An important factor to predict the gas hydrate formation conditions is accurate estimation of water content of natural gas. The water content of natural gas (mostly methane as the main component) is very low and consequently its measurement is difficult and time consuming. The experimental data for water content of methane (or other natural gas components) in equilibrium with gas hydrates/ice/liquid water (at low temperatures) are scarce. The measurement difficulties may eventually result in generating unreliable experimental data or at least the data with high uncertainties. As a result, the available data should be checked for consistency prior to further applications. The goal of this work is to present a new consistency test method for investigation of the corresponding phase equilibrium data at constant pressure (isobaric data). The proposed method is based on the Gibbs–Duhem equation and the area test technique. In this method, HR (residual enthalpy) values are calculated at constant pressure. A thermodynamic model based on the Valderrama modification of the Patel–Teja equation of state along with non-density dependent mixing rules is applied for this purpose. The results show that the proposed consistency test can be applied with acceptable confidence, determining the quality of the investigated experimental data.

► An isobaric thermodynamic consistency test method is proposed and applied.
► The method is based on the Gibbs–Duhem equation and the area test technique.
► The experimental data for water content of methane are checked for their consistency.
► The results show that about 46% of the investigated data seem to be thermodynamically consistent.