A novel technique based in a cylindrical microwave resonator for high pressure phase equilibrium determination

Highlights: • Phase equilibria data were performed using a novel cylindrical microwave resonator. • Dew and bubble points were detected by dielectric constant changes. • Experimental data were compared with GERG-2008 and Peng-Robinson EoS. • CO₂ + CH₄ mixtures are of interest to model reference EoS natural gas-like mixtures. -- Abstract: The development of a novel technique based on a cylindrical microwave resonator for high pressure phase equilibrium determination is described. Electric permittivity or dielectric constant is a physical property that depends on temperature and pressure ε(p,T). Based on this property, a measuring technique consisting of a cylindrical resonant cavity that works in the microwave spectrum has been developed. Equilibrium data of fluid mixtures are measured at high pressure using a synthetic method, where phase transition is determined under isothermal conditions due to the change of the dielectric constant. This technique may be a more accurate alternative to conventional visual synthetic methods. The technique was validated measuring pure CO₂, and phase behaviour was then determined for two binary mixtures {CO₂ (0.6) + CH₄ (0.4)} and {CO₂ (0.4) + CH₄ (0.6)}, results for which are presented. These systems are interesting for the study of biogas-like mixtures. In addition, data were compared with the equation of state used for natural gas GERG-2008, and also, they were modelled using Peng-Robinson equation of state and Wong-Sandler mixing rules, which are widely employed in chemical industries and which give good results.