Synthesis of N₂-CH₄ and N₂-CO₂ Gas Mixtures as an Online Standard and Determination of Their Raman Quantification Factors of CH₄ and CO₂

Organic and/or inorganic gas composition can be measured quickly and accurately by using a Laser Raman Microprobe with an online standard of gas mixtures. The accuracy of the standard sample plays an important role in this method, but the commercial standard mixed gas cylinders are expensive with fixed composition that cannot be modified arbitrarily. A new method to synthesize the gas mixtures in different compositions under different pressures has been developed. The N₂-CH₄ and N₂-CO₂ gas mixtures with varied N₂ mol contents of 30%, 50% and 70% were synthesized. The pressure of these gas mixtures were increased to 5 and 10 MPa. Both the synthesized and commercial gas mixtures of 70% N₂ and 30% CO₂ have similar relative peak heights and peak areas of N₂ and CO₂. The error of this method is less than 4%. The Raman quantification factor of CH₄ and CO₂ are determined. In this study, the Raman quantification factor is insensitive to composition and pressure under 5 MPa and 10 MPa. This new method is relatively simple, easy and accurate, and only two or more kinds of pure gas cylinders are used to synthesize gas mixtures with different composition and under different pressure, which provides a new way for laser Raman calibration and gas composition measurement in situ.