E.D. Sloan

Experimental determination and modeling of structure II hydrates in mixtures of methane+water+1,4-dioxane

Abstract Hydrate phase equilibrium conditions were measured with a Cailletet apparatus in the pressure range 2

The next generation of hydrate prediction: II. Dedicated aqueous phase fugacity model for hydrate prediction

Abstract The van der Waals and Platteeuw [Adv. Chem. Phys. 2 (1959) 1] hydrate equation of state (EoS), coupled with the classical thermodynamic equation for hydrates, has been used in the prediction of hydrate formation for over 40 years. In Part I of this series [Fluid Phase Equilib. 194 (2002) 371] , we proposed an alternative derivation of these equations using a different standard state. The new hydrate equations were shown to be simpler to use. The new approach allows for a full description of each phase via fugacity models. This is the second article in a series of four, providing a description of an aqueous phase fugacity model tailored specifically for the presence of mixed hydrate inhibitors such as salts and methanol in the aqueous phase. There are several fugacity models that can adequately describe the aqueous phase for systems of hydrocarbons and water. However, when salts, alcohols, and glycols are added to the system, most fugacity models fail to account for proper interactions. In this work, we present an aqueous phase fugacity model using a modified Helgeson [Geochim. Cosmochim. Acta 52 (1988) 2009] equation of state combined with a Bromley [AIChE J. 19 (1973) 313] activity model. The Helgeson equation of state describes hydrocarbon–water systems, while the Bromley activity model accounts for interactions within the aqueous phase when salts and methanol are added. The advantage of this model is that the aqueous phase fugacity can be described more accurately than with the approach of using cubic equations of state intended for hydrocarbons, so that, for example, salting out can be predicted.

A first order method of hydrate equilibrium estimation and its use with new structures

Abstract First order correlations are presented for phase equilibria of two clathrate hydrates which have been known for the last half century. The correlations are shown to apply to equilibria for a hydrate discovered in 1987. Extrapolations to newer, relatively unknown hydrates (which have been found only with unusual guests) suggest equilibrium conditions for hydrocarbon components.

A Model for Systems with Soluble Hydrate Formers

Abstract: The objective of this study was to measure and model hydrate phase equilibria in a system containing a water‐soluble hydrate former. The system investigated is methane + water + 1,4‐dioxane in the pressure range between 2 and 14 MPa. Experimental results show that the stability of hydrates is a strong function of 1,4‐dioxane concentration in the water phase. The hydrate phase equilibria data are modeled using the van der Waals and Platteeuw theory assuming that 1,4‐dioxane is a soluble sII former. Activity coefficients of the liquid phase can be calculated from water + 1,4‐dioxane vapor liquid equilibria. Under these assumptions, the predicted equilibrium pressures are within 5% of the experimental data up to a concentration of 20 mol% 1,4‐dioxane relative to water.