Effect of heating rate on the accuracy of measuring equilibrium conditions for methane and argon hydrates

This work examined the effect of the heating rate (from 0.2 K/h (5.56 . 10(-5) K/s) to 10 K/h (277.78 . 10-5 K/s)) on the accuracy of measuring the three-phase equilibrium conditions for gas-liquid water-hydrate systems. The H(2)On+CH4 (CS-I) system was studied over the temperature range of 274.2-285.2 K and the pressure range of 3.0-9.0 MPa. Additionally, the H2O+Ar (CS-II) system was studied over the temperature and pressure ranges of 273.7-280.2 K and 9.5-18.5 MPa, respectively. The hydrate formation/dissociation experiments were performed in a Sapphire Rocking Cell RCS6 under isochoric conditions. Gas hydrates were formed using a 0.1% (w/w) solution of sodium dodecyl sulfate. It was found that the dissociation of the methane and argon hydrates (CS-I and CS-II, respectively) proceeds under conditions close to equilibrium at heating rates up to 0.5 K/h (13.89. 10-5 K/s). Significant deviations of the P,T-curve from the equilibrium line are observed at higher heating rates for methane hydrate ( > 281.2 K) and argon hydrate ( > 2772 K). Our data on the equilibrium conditions of argon hydrate complement previous published data over the temperature range of 273.7-2802 K and the pressure range of 9.5-18.5 MPa. (C) 2015 Elsevier Ltd. All rights reserved.