Comparative computational study of the binary vapor liquid equilibria of methane and thermodynamic inhibitors at hydrate formation conditions using the Soave-Redlich Kwong and Peng-Robinson equations of state

Thermodynamic inhibitors like methanol, monoethylene glycol and triethylene glycol are frequently used for mitigating gas hydrate formation. They operate by changing the composition of the system so that the conditions under which gas hydrate would otherwise form would not lead to hydrate formation in the changed system. Simulation software packages are used to determine computationally whether gas hydrates might form in a pipeline. The Soave-Redlich-Kwong (SRK-EOS) and the Peng-Robinson (PREOS) are the two most commonly used equations of state for simulating vapor-liquid equilibria (VLE) for many process fluids. Four binary systems were studied at conditions close to those at which hydrate can form: methane + water, methane + methanol, methane + monoethylene glycol (MEG), and methane + triethylene glycol (TEG). Conditions selected were those at which methane and water can form clathrates: 283.89K to 323.56K and 5.01MPa to 18.48MPa. Computing the VLE behavior of methane + water failed for both the PR-EOS and the SRK-EOS. The equations of state are ill suited for water because of its high polarity and strong hydrogen bonding. Both equations of state overestimate the pressure of methane + methanol by a factor of two. The SRK-EOS model overestimates more than the PR-EOS model. In the methane + MEG system, the predicted pressures for both models are generally less than experimental pressure except for the highest concentration of methane in MEG calculated by the SRK-EOS. In the methane + TEG system, the predictions of both models are close and trend similarly. Because of the lack of suitable methane + TEG data for comparison, the similarity of the methane + TEG computed results can be used as a basis for further study of this system experimentally.