Article Dans Une Revue Fluid Phase Equilibria Année : 2025

An optical microscopy method for determining stable and metastable phase equilibria involving gas hydrate and ice: Application to CO2 + water systems

Résumé

The temperatures and pressures of the three-phase equilibria between liq-uid water (Lw), gas hydrate (H) and a guest-rich phase (a vapor, V, or a condensed liquid, Lc) and between Lw, ice (I), and V, are determined experimentally by monitoring the disappearance of the hydrate or ice phases near the meniscus between the water-rich and guest-rich phases when temperature or pressure are varied slowly. This monitoring is carried out by optical microscopy used in the transmission mode with or without crossed polarizers, the latter serving to identify the presence or absence of hexagonal (birefringent) ice. The guest molecule (or hydrate-former) taken as an example is CO2. The triple lines corresponding to Lw-H-V, Lw-I-V and Lw-H-Lc equilib-ria are determined together with their intersections, i.e., the lower quadruple point Q1(Lw-I-H-V coexistence) and upper quadruple point Q2 (Lw-H-V-Lc coexistence). The metastable extension of the three-phase line Lw-H-V for temperatures and pressures below those of Q1is also determined. A Clausius-Clapeyron treatment of this line and its metastable extension shows that a similar dissociation process exists, whether the dissociation is to supercooled liquid water or not.
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hal-04955485 , version 1 (18-02-2025)

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Abdelhafid Touil, Daniel Broseta. An optical microscopy method for determining stable and metastable phase equilibria involving gas hydrate and ice: Application to CO2 + water systems. Fluid Phase Equilibria, In press, ⟨10.1016/j.fluid.2025.114369⟩. ⟨hal-04955485⟩
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