Raman spectral behavior of N2, CO2, and CH4 in N2–CO2–CH4 gas mixtures from 22°C to 200°C and 10 to 500 bars, with application to other gas mixtures

Abstract

AbstractThe Raman spectral behavior of N2, CO2, and CH4 in ternary N2–CO2–CH4 mixtures was studied from 22°C to 200°C and 10 to 500 bars. The peak position of N2 in all mixtures is located at lower wavenumbers compared with pure N2 at the same pressure (P)–temperature (T) (PT) conditions. The Fermi diad splitting in CO2 is greater in the pure system than in the mixtures, and the Fermi diad splitting increases in the mixtures as CO2 concentration increases at constant P and T. The peak position of CH4 in the mixtures is shifted to higher wavenumbers compared with pure CH4 at the same PT conditions. However, the relationship between peak position and CH4 mole fraction is more complicated compared with the trends observed with N2 and CO2. The relative order of the peak position isotherms of CH4 and N2 in the mixtures in pressure–peak position space mimics trends in the molar volume of the mixtures in pressure–molar volume space. Relationships between the direction of peak shift of individual components in the mixtures, the relative molar volumes of the mixtures, and the attraction and repulsion forces between molecules are developed. Additionally, the relationship between the peak position of N2 in ternary N2–CO2–CH4 mixtures with pressure is extended to other N2‐bearing systems to assess similarities in the Raman spectral behavior of N2 in various systems.