The use of NIR spectroscopy for the quantification of water content and compositional analysis in compressed gas-systems

The use of Near Infrared Spectroscopy (NIRS) has a significant potential to enable the detection and quantification of natural gas components (e.g., CH₄, CO₂, moisture). It offers a quick, non-invasive, and non-destructive approach, eliminating the challenges associated with traditional sampling methods. Here, we investigated the applicability of the NIR technique to perform accurate quantification of water content and compositional analysis regarding CH₄ and CO₂ in compressed systems. The system’s pressure is also considered a response variable. The spectra collection was made at room temperature (298.15 K), with pressures up to 120 bar and CO₂ concentrations varying from 0 % to 50 % of the total composition. The Partial Least Squares (PLS) was used as the regression method, and the Quartz Crystal Microbalance (QCM) as the reference technique for water content. The PLS models yielded high accuracy, with R² values of 0.990 for CH₄, 0.993 for CO₂, and 0.947 for H₂O, with RMSEP values of 4.43 %, 3.55 %, and 8.35 %, respectively. Although water estimation showed slightly higher deviation, it remained within the experimental uncertainty range of the QCM reference. These results confirm the feasibility of applying NIRS for real-time, multi-component gas analysis in industrial settings