Thermodynamic consistency assessment and modeling of methane and carbon dioxide hydrates dissociation conditions in the presence of deep eutectic solvents as eco-friendly inhibitors

Abstract

The formation of gas hydrates in gas-dominated pipelines results in flow assurance challenges, potentially leading to blockages, production interruptions, equipment malfunctions, and financial losses. This study presents a comprehensive thermodynamic modeling framework to calculate methane and carbon dioxide hydrates dissociation conditions in the presence of deep eutectic solvent (DES) aqueous solution as promising thermodynamic hydrate inhibitor. A modified van der Waals-Platteeuw (vdW-P) model is utilized for the hydrate phase, combined with the Peng-Robinson (PR) equation of state for the gas/vapor phase. Water activity is calculated employing a combination of Flory-Huggins (FH), NRTL, or UNIQUAC models for short-range molecular interactions and the Pitzer model for long-range ionic effects. A database of 80 experimental hydrate dissociation conditions points across eight DES systems is then analyzed. All three modeling packages yield average absolute deviations (AAD) below 1 K, with the (vdW-P + PR + FH + Pitzer) model achieving the lowest AAD of 0.46 K after thermodynamic consistency screening. Thermodynamic consistency tests reveal that only 12 out of the 80 data points fully satisfy all three criteria (Clausius–Clapeyron linearity, enthalpy consistency, and water activity stability), which indicates potential limitations in experimental data reliability. The study presents a robust and validated modeling tool for calculating hydrate phase equilibrium in DES-containing systems, highlighting the importance of consistency tests in assessing experimental data quality.