Phase Equilibria of the CH4-CO2 Binary and the CH4-CO2-H2O Ternary Mixtures in the Presence of a CO2-Rich Liquid Phase

Ludovic Legoix,Matthias Haeckel,Livio Ruffine,Jean-Pierre Donval

doi:10.3390/en10122034

Ludovic Legoix, Matthias Haeckel + Show 2 more

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https://doi.org/10.3390/en10122034

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Abstract

The knowledge of the phase behavior of carbon dioxide (CO2)-rich mixtures is a key factor to understand the chemistry and migration of natural volcanic CO2 seeps in the marine environment, as well as to develop engineering processes for CO2 sequestration coupled to methane (CH4) production from gas hydrate deposits. In both cases, it is important to gain insights into the interactions of the CO2-rich phase—liquid or gas—with the aqueous medium (H2O) in the pore space below the seafloor or in the ocean. Thus, the CH4-CO2 binary and CH4-CO2-H2O ternary mixtures were investigated at relevant pressure and temperature conditions. The solubility of CH4 in liquid CO2 (vapor-liquid equilibrium) was determined in laboratory experiments and then modelled with the Soave–Redlich–Kwong equation of state (EoS) consisting of an optimized binary interaction parameter kij(CH4-CO2) = 1.32 × 10−3 × T − 0.251 describing the non-ideality of the mixture. The hydrate-liquid-liquid equilibrium (HLLE) was measured in addition to the composition of the CO2-rich fluid phase in the presence of H2O. In contrast to the behavior in the presence of vapor, gas hydrates become more stable when increasing the CH4 content, and the relative proportion of CH4 to CO2 decreases in the CO2-rich phase after gas hydrate formation.

Highlights

CO2 is ubiquitous in geological systems, and is encountered in geofluids in multiple phases (e.g., Lewicki et al [1], Boiron et al [2])
For temperatures below Q2, or a richer CH4 mole fraction, the area is well described and several stability points of mixed gas hydrates with vapor and aqueous phase, the hydrate-vapor-liquid equilibrium (HVLE), monitoring have been published as reviewed by Kastanidis et al [41]
Mixtures of CH4-CO2 and CH4-CO2-H2O involving a CO2-rich liquid phase are investigated under p–T conditions typical for marine environments, such as CO2-rich seeps of volcanic origin and Mixtures of CH4 -CO

Summary

Introduction

CO2 is ubiquitous in geological systems, and is encountered in geofluids in multiple phases (e.g., Lewicki et al [1], Boiron et al [2]). It is either generated by the degradation of organic matter, decomposition of carbonate rock, or post-genetic mantle processes. As society is increasingly concerned about mitigating CO2 emissions into the atmosphere, understanding the phase behavior of CO2 -rich mixtures becomes more important for the design and conception of reliable carbon storage processes. Amongst the processes under investigation, the storage of CO2 in solid gas hydrates by replacing the CH4 from natural accumulations seems to be very promising, since it helps to meet the global energy demand, while reducing net global carbon emissions. CH4 production from gas hydrates coupled to CO2 sequestration has been investigated

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