Screening analysis of natural gas with respect to methane content by near-infrared spectrometry

This paper proposes a method for fast, non-destructive screening analysis of natural gas (NG) with respect to methane content by using near-infrared (NIR) spectrometry. A total of 55 NG samples were collected from vehicle fueling stations in north-eastern Brazil by using a lab-made high-pressure sampling cylinder with a purpose-built admission system. In addition, a gas mixing system was specifically developed for use in this investigation in order to simulate NG samples with methane content smaller than 85.0% mol/mol, which is the lower limit specification established by the Brazilian National Fuel Authority. A total of 23 simulated samples were prepared by mixing NG with nitrogen, compressed air, lighter fluid (commercial propane-butane mixture) and ethane. The NIR screening analysis was then carried out by using a SIMCA (soft independent modelling of class analogies) model. For this purpose, samples with methane content above and below the 85.0% mol/mol specification were considered negative and positive cases, respectively. At a confidence level of 95%, all test samples were correctly classified, i.e. no false positives or false negatives were obtained. These findings indicate that the use of NIR spectrometry can be of value for routine quality control of NG with respect to methane content.