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

TL;DR

This paper introduces a new microwave resonator technique for high-pressure phase equilibrium measurement, offering potentially more accurate data compared to traditional visual methods, validated on CO2 and methane mixtures relevant to biogas studies.

Contribution

A novel microwave resonator method for high-pressure phase equilibrium determination is developed and validated, providing an alternative to conventional visual techniques with improved accuracy.

Findings

Validated with pure CO2 measurements.

Determined phase behavior of CO2-methane mixtures.

Compared results with GERG-2008 and Peng-Robinson models.

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 $\epsilon$($p$,$T$). 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 $CO_{2}$, and phase behaviour was then determined for two binary mixtures [$CO_{2}$ (0.6) + $CH_{4}$ (0.4)] and [$CO_{2}$ (0.4) + $CH_{4}$ (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.