Sonic Velocity Based Experimental and Modeling Approach to Determine Fluid Properties of Greenhouse Gases and Mixtures

Abstract Climate-related concerns from rising CO2 emissions, along with geopolitical pressures, have prompted the chemical, manufacturing, and energy industries to urgently tackle the issue by developing/adopting emission-reduction technologies. To address this, various decarbonization pathways are being explored, including carbon capture and storage (CCS), enhanced geothermal, electrification, and hydrogen. In all these pathways, an accurate estimation of thermodynamic properties of fluids are essential for process design and scaleups. In this work, we focus primary on greenhouse gases (especially CO2, CH4 and their mixtures) for the applications of CCS and enhanced geothermal and develop an equation-of-state (EOS)based modeling approach,coupled with sonic velocity based experimental validation,to estimate several fluid properties (such as heat capacities, enthalpy, entropy, sonic velocity, density, compressibility, and Joule-Thomson coefficient). A pulse-echo technique was used to measure the sonic velocity in CO2, methane, and their mixtures (containing 5 - 30 mol% CO2) in the pressure range of 1 – 200 bar and in temperaturerange of 300 – 323K. The corresponding density was measured using a PVT cell. The modeling is based on PR78 EOS with Peneloux shift, where the ideal part of the isobaric heat capacity (obtained from correlations available in literature) is used to determine the residual part of all fluid properties fromthe EOS model atextended pressure and temperature conditions.The main results are as follows: Experimentally measured sonic velocity and density data for CO2, methane, and their mixture are aligned with that available in literature.The modeling framework leads to a very good match with the in-house and available literature data, within the relative error of 1 – 3%, which is acceptable for most practical applications.The compressibility of the fluid is derived directly from the sonic velocity, leading to much better estimation as compared to traditional approach (which is based on the derivative of density and leads to significant noise in the estimation)Most importantly, the framework is general and can utilize any other EOS model. Additionally, it can easily be extended to any fluid system as long as the EOS parameters and ideal part of isobaric heat capacity are known a priory. Novelty of this work includes (i) experimental measurements of sonic velocity and density of a fluid system containing CO2 and methane at high pressures, and (ii) development of a modeling framework to accurately determine the thermodynamic properties (such as density, sonic velocity, heat capacities, enthalpy, entropy, compressibility, and Joule-Thomson coefficient) for any fluid mixtures.