Effect of Molecular Weight of Polyethylene Glycol on the Equilibrium Dissociation Pressures of Methane Hydrate System

The experimental phase equilibrium data for methane (CH<inf>4</inf>) clathrate hydrates in the presence of polyethylene glycol (PEG) aqueous solutions with various number-average molecular weights of 200 kg/kmol (PEG-200), 400 kg/kmol (PEG-400), and 600 kg/kmol (PEG-600) for (0.077, 0.2, 0.4, 0.44 and 0.46) mass fractions at the temperature range (270.75 to 281.45) K and pressure range (4.60 to 7.05) MPa has been reported. The isochoric pressure-search method is used to generate the equilibrium data on the hydrate system. Comparative effects of PEG-200, PEG-400, and PEG-600 aqueous solutions at various concentrations (mass fraction and mole fraction basis) on the methane hydrate system have been studied. The inhibition effect using low molecular weight PEG-200 is observed to be more effective in suppressing the methane hydrate formation than PEG-400 and PEG-600 at the same mass fraction. On the mole fraction basis, at higher concentration, the inhibition effect of PEG-600 on the methane hydrate system at the same mole fraction is observed to be more than PEG-200. Surprisingly, at lower concentration (at the same mole fraction), PEG-200 is observed to inhibit the methane hydrate system more than PEG-600. The methane hydrate suppression temperature using PEG-200, PEG-400, and PEG-600 is also determined using Hammerschmidt's equation and are reported. The work also reports the values of enthalpy of dissociation determined using the Clausius-Clapeyron equation for a methane hydrate system in the presence of PEG-200, PEG-400, and PEG-600 aqueous solutions. The enthalpy of dissociation of methane hydrate is observed to increase with increasing molecular weight of PEG. The study shows the effectiveness of low molecular weight PEG in inhibiting methane hydrate as compared to higher molecular weight, thus indicating their possible use for effective design of drilling and completion fluids for hydrate bearing formation.