Composition of Mixtures of Natural Gas Components Determined by Raman Spectrometry

The feasibility of using Raman spectrometry for determining the composition of mixtures of natural gas components was examined. Raman intensity measurements were carried out on eight, gravimetrically prepared, binary gas mixtures containing methane, nitrogen, and isobutane at ambient temperature and at pressures to 0.8 MPa. The repeatability of the molar intensity ratio, ( I2/ y2)/( I1/ y1), where y1 is the concentration of component 1 in the mixture, and I1 is the intensity of the related line in the mixture spectrum, was examined. The compositions of two gravimetrically prepared methane-nitrogen-isobutane gas mixtures were determined spectrometrically with an estimated precision of about 0.001 in the mole fraction. Typical differences from the gravimetric concentrations were less than 0.002 in the mole fraction. The Raman spectrum of a gravimetrically prepared, eight component, hydrocarbon gas mixture was obtained to show that the Raman spectrometric method has potential for being applicable to natural gas type mixtures.