Influence of propylene glycol on the thermodynamics and kinetics of methane hydrate formation

The formation of gas hydrates results in a major flow assurance challenge, as it can cause pipeline blockages, safety risks, and economic losses. Propylene glycol (PG) is a promising candidate for hydrate inhibition due to its low toxicity and low vapor pressure. In this study, methane hydrate dissociation conditions were experimentally determined at three PG concentrations (10, 15, and 25) mass% using the isochoric pressure-search method. The measurements were conducted in a high-pressure cell with an internal volume of 75 cm 3 . The average suppression temperatures of methane hydrate in PG aqueous solutions are 1.80 K, 3.01 K, and 5.90 K for (10, 15, and 25) mass% of PG, respectively, confirming the thermodynamic inhibition effect of PG. For thermodynamic modeling, different packages were employed: the van der Waals-Platteeuw (vdW-P) model for the hydrate phase, the Peng-Robinson equation of state (PR EoS) for the gas phase, and the UNIQUAC, NRTL, Wilson, and Flory-Huggins (FH) models for calculating water activity in the liquid phase. Among these, the combined (vdW-P + PR + FH) package gives the highest accuracy for the calculation of methane hydrate dissociation conditions in PG aqueous systems, with an average absolute deviation of 0.28 K. To evaluate the influence of PG on the kinetics of methane hydrate formation, induction times were measured. The results show that a 25 mass% PG aqueous solution can increase methane hydrate formation induction times by approximately 40% (128.64 min) compared to pure water (93.10 min) in the pressure range of (5 to 6) MPa, demonstrating the kinetic inhibition effect of PG.