Comparison of Equations of State and Langmuir Adsorption Models in the Thermodynamic Prediction of Hydrate Formation

In oil and gas production systems, the coexistence of water and hydrocarbon mixtures under high-pressure and low-temperature conditions creates a favorable environment for hydrate formation in pipelines, which can restrict the flow area. Hydrates are crystalline solids that emerge when gas molecules become trapped within cage-like structures formed by water molecules. The van der Waals-Platteeuw model has been a key reference for estimating hydrate formation conditions, relying on the calculation of the Langmuir adsorption constant (C_ki) and the fugacity of each component. The present work investigates the effects of two fugacity models (Peng–Robinson and SRK) and two C_ki models (Parrish–Prausnitz and Kihara) on hydrate formation calculations, aiming to identify the best combination for describing this phenomenon. To account for the CO₂ solubility in water, the Duan model was applied, while the hydrocarbons' solubility was neglected. Using an experimental database containing 2,162 pressure–temperature formation conditions for both pure gases and mixtures, the performance of the selected models was evaluated. The results demonstrate superior agreement with experimental data when the Parrish–Prausnitz adsorption model is combined with the SRK equation of state, yielding an average error below 0.3% and a coefficient of determination (R²) above 0.94. Conversely, the use of the Parrish–Prausnitz model with the Peng–Robinson equation, as well as formulations based on the Kihara potential, results in larger average errors of 0.8-1.5% and lower R² values, indicating reduced predictive capability for hydrate formation temperatures. Overall, within the scope of the analyzed data, the results suggest that the Parrish–Prausnitz–SRK combination provides the best agreement with the experimental data for both pure components and gas mixtures among the evaluated approaches.