Phase equilibrium for clathrate hydrate formed in methane plus water plus urea system

We performed phase equilibrium measurements in a methane + urea + water system for three phases (gas-hydrate-liquid) and four phases (gas-hydrate-liquid-solid urea). The data ranged from 262 K to 277 K for temperature, 2 to 4.5 MPa for pressure, and 0.05 to 0.50 for mass fraction (0.0159 to 0.231 for mole fraction) for aqueous urea composition. Urea, even in small dosages, shifted the methane hydrate formation conditions to lower temperature. The equilibrium state achieved a four-phase equilibrium, i.e., gas-hydrate-liquid-solid urea, when the aqueous feed composition was above a mass fraction of 0.40. The difference in equilibrium temperature between the urea + methane + water and methane + water systems expanded to approximately 10 K. The effect of urea on methane hydrate formation conditions was compared with that of alcoholic substances. (C) 2015 Elsevier B.V. All rights reserved.