Helium Detection in Natural Gas Using Raman Spectroscopy.

Raman spectroscopy has great potential for quantitative analysis of natural gas. Helium is one of the components of natural gas and has a wide range of applications. It was believed that noble gases could not be detected using this technique due to the absence of their vibrational spectra. In this study, we demonstrated an approach to extracting the content of helium from the Raman spectrum of methane and carried out test measurements for the first time. The approach is based on the determination of changes in the ν₁ band of methane caused by the influence of helium and other components. The necessary spectroscopic parameters characterizing the effect of methane (CH₄), helium (He), nitrogen (N₂), carbon dioxide (CO₂), and ethane (C₂H₆) on the ν₁ band of methane at a resolution of 0.35 cm^-1 were obtained. The validation of the approach showed that the helium content in natural gas can be measured with an uncertainty of 1 mol% at a sample pressure of 50 bar. The measurement precision can be increased to 0.01 mol% by using a high-resolution spectrometer. The described method does not claim to replace helium detectors, but it can be considered a valuable addition to Raman gas analysis of natural gas in developing an all-in-one device. The possibilities for further improvement of the approach are also discussed.