Hydrate Decomposition Conditions for Liquid Water and Propane

Abstract

Because of the industrial importance of C 3 H 8 and because C 3 H 8 hydrate is a reference material for other sII hydrates, the C 3 H 8 hydrate dissociation conditions were independently measured using the phase boundary dissociation and isochoric methods for T = 273.63–278.75 K and p = 0.1887–18.2622 MPa. Along the liquid water Lw–H–C 3 H 8 ( g ) phase boundary, two different purities of 99.5 and 99.999 mol % C 3 H 8 were studied. Data have been used to optimize two semiempirical correlations for rapid calculation of the phase dissociation conditions for p < 20 MPa. For a more rigorous model, the highest purity data have been fit using the van der Waals and Platteuw model and reference quality reduced Helmholtz equations-of-state (EOSs) for the hydrate phase and fluid phases, respectively. The optimized thermodynamic-based model agrees with the experimental data to within the estimated uncertainty of δ T = ±0.1 K. The results were also compared to the highly variant literature data for the Lw–H–C 3 H 8 ( l ) phase boundary, where the deviations can be attributed to measurement difficulties when a hydrate is less dense than the liquid hydrate former in the liquid region.