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

MOLINA, MATÍAS JOSÉ ; PORRAS GIRALDO, ANDRÉS FELIPE; ESCOBAR GARCÍA, DAVID J.; RODRIGUEZ REARTES, SABRINA BELÉN; ZABALOY, MARCELO SANTIAGO

La Pineda, Tarragona

Conferencia; 16th International Conference on Properties and Phase Equilibria for Product and Process Design; 2023

Universitat Rovira i Virgili and Khalifa University

Plugging of pipelines in the oil and gas industry may be caused by precipitation of Clathrate hydrates (CHs). Knowledge of the conditions that promote the CH formation is in such application useful to avoid the CH precipitation. On the other hand, the formation of CHs may be exploited in applications such as the fractionation of mixtures of gases. CHs are nonstoichiometric ice-like solid materials (solid solutions) made of water (host) and another component (guest), such as methane. Actually, more than one guest may be present in the CH, e.g., the CH may contain ethane and propane. Conventionally, in the literature, two different models are combined for describing the CH formation: one to represent the fluid phases, and another one for the CHs, being the van der Waals-Platteeuw model the more frequently 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 particular unified form is a 4-parameter equation of state (EoS) (and its mixing rules). Yokozeki’s approach 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 a modelling approach (SSA) for the description of the thermodynamic properties of multi-component solid phases, i.e., of solid solutions, which is also applicable, as a limiting case, to pure-component solids. The SSA has the following features: [a] it is in principle a unified approach for describing the thermodynamic properties of molecular solids, [b] it is analogous in many respects to the equation of state approach for fluids, [c] it does not describe the micro-structures of the solid state, and [d] in its application the occurrence of equilibrium between multicomponent phases and strictly pure-component solids is not allowed, i.e., the frequently used assumption of precipitation in pure state from a multicomponent phase is never adopted in the SSA. This work focuses on the application of the SSA to the formation of CHs. The case study here is the one of methane hydrates. The parameterization strategy is described, in particular how to fulfill the need for making the model predict an acceptable variation range for the concentration of methane in the hydrate. Three-phase lines and quadruple points were computed in this work for the system water-methane. The obtained results, together with results of previous works for systems having solid phases which are not CHs [2], suggest that the engineering oriented SSA is in principle able to unify the representation of molecular solids of widely varying nature (e.g., CHs, wax containing solids, etc)