A review on the solid–liquid–vapor phase equilibria of acid gases in methane

In spite of the increasing levels of greenhouse gases in the atmosphere, and their impact on the environment, the demand for natural/biogas will increase significantly in the coming few decades. To cover this demand, the global energy industry is continuously exploiting sour gas reserves located around the world. Nonetheless, sour gas has to be sweetened before the practical utilization of natural or biogas. The cryogenic separation technologies have emerged as a new technology to separate carbon dioxide (CO₂) and hydrogen sulfide (H₂S gases) from natural/biogas. The cryogenic separation produces less harmful gases, and can be less expensive to operate and maintain in comparison to the conventional technologies. To design cryogenic separation equipment, vapor–liquid equilibrium (VLE), solid–liquid equilibrium (SLE), solid–vapor equilibrium (SVE), and solid–liquid–vapor equilibrium (SLVE) data for the corresponding binary systems (of CH₄-CO₂, CH₄-H₂S, and H₂S-CO₂) and ternary system (of CH₄-H₂S-CO₂) are required. The main target of this article is to review the SLVE data for the acid gases (CO₂ and H₂S) in methane (CH₄) as the main constituent of natural/biogas. It will address SLVE data for the binary systems of CH₄-CO₂, CH₄-H₂S and H₂S-CO₂ as well as the ternary system of CH₄-H₂S-CO₂. It will not only address the available laboratory data, but it will also discuss, compare and evaluate the different models used to correlate/predict these data.