Dataset for the phase equilibria and PXRD studies of urea as a green thermodynamic inhibitor of sII gas hydrates

The equilibrium conditions of sII methane/propane hydrates have been experimentally determined for the C(3)H(8)/CH(4)-H(2)O-urea system. The equilibrium dissociation temperatures and pressures of sII hydrates span a wide P,T-range (266.7–293.9 K; 0.87–9.49 MPa) and were measured by varying the feed mass fraction of urea in solution from 0 to 50 mass%. The experimental points at feed urea concentration ≤ 40 mass% correspond to the V-L(w)-H equilibrium (gas-aqueous urea solution-gas hydrate). A four-phase V-L(w)-H-S(u) equilibrium (with an additional phase of solid urea) was observed because the solubility limit of urea in water was reached for all points at a feed mass fraction of 50 mass% and for one point at 40 mass% (266.93 K). Gas hydrate equilibria were measured using a high-pressure rig GHA350 under isochoric conditions with rapid fluid stirring and slow ramp heating of 0.1 K/h. Each measured point represents complete dissociation of the sII hydrate. The phase equilibrium data was compared with the literature reported for the C(3)H(8)/CH(4)-H(2)O and CH(4)-H(2)O-urea systems. A comprehensive analysis of the thermodynamic inhibition effect of urea to sII C(3)H(8)/CH(4) hydrates on pressure and concentration of the inhibitor was carried out. The phase composition of the samples was analyzed by powder X-ray diffractometry at 173 K.