Representation of clathrate hydrates through a solid-solution engineering modeling approach

MATÍAS J MOLINA; ANDRÉS F. PORRAS GIRALDO; S. BELÉN RODRIGUEZ-REARTES; MARCELO S. ZABALOY

LA PINEDA, COSTA DORADA, TARRAGONA

Conferencia; 16TH INTERNATIONAL CONFERENCE ON PROPERTIES AND PHASEEQUILIBRIA FOR PRODUCT AND PROCESS DESIGN; 2023

Universitat Rovira i Virgili, Khalifa University and Texas and Texas A&M University

Plugging of pipelines in the oil and gas industry may be caused by precipitation of Clathratehydrates (CHs). Knowledge of the conditions that promote the CH formation is in suchapplication useful to avoid the CH precipitation. On the other hand, the formation of CHsmay be exploited in applications such as the fractionation of mixtures of gases. CHs arenonstoichiometric ice-like solid materials (solid solutions) made of water (host) and anothercomponent (guest), such as methane. Actually, more than one guest may be present in theCH, e.g., the CH may contain ethane and propane. Conventionally, in the literature, twodifferent models are combined for describing the CH formation: one to represent the fluidphases, and another one for the CHs, being the van der Waals-Platteeuw model the morefrequently used for CHs. A third model is used for representing ice. In contrast, Yokozeki [1]used unified functional forms for the PVT behavior of the three states of matter. A particularunified form is a 4-parameter equation of state (EoS) (and its mixing rules). Yokozeki’sapproach is in principle applicable to CHs because of their solid solution nature. However,such approach has a number of drawbacks [2]. Recently, Porras et al [2] proposed amodelling approach (SSA) for the description of the thermodynamic properties of multicomponentsolid phases, i.e., of solid solutions, which is also applicable, as a limiting case, topure-component solids. The SSA has the following features: [a] it is in principle a unifiedapproach for describing the thermodynamic properties of molecular solids, [b] it is analogousin many respects to the equation of state approach for fluids, [c] it does not describe themicro-structures of the solid state, and [d] in its application the occurrence of equilibriumbetween multicomponent phases and strictly pure-component solids is not allowed, i.e., thefrequently used assumption of precipitation in pure state from a multicomponent phase isnever adopted in the SSA. This work focuses on the application of the SSA to the formationof CHs. The case study here is the one of methane hydrates. The parameterization strategyis described, in particular how to fulfill the need for making the model predict an acceptablevariation range for the concentration of methane in the hydrate. Three-phase lines andquadruple points were computed in this work for the system water-methane. The obtainedresults, together with results of previous works for systems having solid phases which arenot CHs [2], suggest that the engineering oriented SSA is in principle able to unify therepresentation of molecular solids of widely varying nature (e.g., CHs, wax containing solids,etc).