Water content measurements for liquid propane in equilibrium with water or hydrates: New measurements & evaluation of literature data

Abstract

Propane is utilised primarily for industrial sector and domestic applications. However, propane is considered a hydrate former. Thus, it is necessary to establish pressure and temperature conditions that ensure a hydrate-free zone. This requires determining the minimum amount of water required for the formation of hydrates and providing a thermodynamic model capable of determining the water content and predicting pressure and temperature conditions for hydrate dissociation. Consequently this study investigated the water content of liquid propane in equilibrium with liquid water or hydrates at pressures up to 8.274 MPa and temperatures between 211.15 K and 313.15 K. Using three different methods: a quartz crystal microbalance (QCM), a silicon oxide-based hygrometer and the new method developed by Burgass et al. (2021). In general, water content measurements determined from the new method and QCM were found to be in good agreement. The fluid phase behaviour of the system (propane + water) was modelled using the simplified Cubic-Plus-Association (sCPA-SRK) and the Soave-Redlich-Kwong (SRK) equation of state combined with the van der Waals classical and non-density-dependent (NDD) mixing rules, respectively. Both models provided similar results, although the sCPA-SRK model used only one adjustable parameter in contrast with the SRK model, which used three adjustable parameters. The experimental measurements from the new method and QCM to the sCPA-SRK and SRK-NDD models presented 4.5% and 4.5% deviation, respectively over temperature range of 276.15–313.15 K. In all cases, the hydrate-forming conditions were modelled using the van der Waals and Platteeuw's solid solution theory. Additionally, the sCPA-SRK + van der Waals and Platteeuw model calculations were compared against hydrate dissociation conditions, using used two adjustable Kihara parameters and showed overall good agreement when compared to data from the literature.