Abstract
The presence of benzene and similar aromatic compounds in civil environments is due to anthropic actions but also to natural sources. Natural gas consists of a gas mixture where benzene and related compounds are usually presents. Thus, the detection of these compounds in natural gas pipelines is of the utmost importance as well as the control of the concentration level, which must remain below the limits consented by law. In this regard, it is of striking interest to engineer devices able to detect these compounds by automatic and continuous remote control. Here, we discuss the application of an optical device designed for the measurement of sulfured odorizing agents in natural gas pipelines aiming at the detection and the measurement of benzene, toluene, and xylenes (BTX) in the same contexts. The instrument consists of a customized UV spectrophotometer connected to an automatic control system able to provide in-field detections of BTX through a continuous and remote check of the gaseous mixture. Relatively to benzene, the instrument is characterized by values of LOD (level of detection) and LOQ (level of quantification) equal to 0.55 and 1.84 mg/Sm, respectively. Similar limits are found for toluene and xylenes (LOD of 0.81, 1.05, 1.41, and 1.00 mg/Sm for toluene, meta-, ortho-, and para-xylene, respectively).
Highlights
Natural gas pipelines are spread worldwide given that natural gas is a common fuel for civil purposes
Spectra is a UV–visible spectrophotometric instrument able to detect some components of a natural gas mixture in the range 200–280 nm; the choice of this range of analysis rules out the absorptions of aliphatic hydrocarbons, which fall at higher energies
UV–visible spectra in the established range of wavelengths whose absorbance profiles are compared with a database of spectra recorded for pure components; the comparison allows the qualitative recognition of the components of the gaseous mixture and, by taking the calibration line as reference (Figure 2), allows the quantitative measurements of selected components as, for example, sulfured odorants [18]
Summary
Natural gas pipelines are spread worldwide given that natural gas is a common fuel for civil purposes. The detection of benzene and its related compounds is a big issue in the field of environmental control and of safety in public and private areas or in workplace locations [4]. The presence of this kind of dangerous compound in the obtained gaseous fuel mixture may stiffly rise up and significant amounts may be dispersed in the atmosphere [5]. Most of the apparatus are based on electrochemical [7] and metal oxide sensors, micro-gas chromatographs (μGC) [8], or electronic noses [9,10] with variable limit of detection (generally quite low) but with significant problems in calibration and selectivity. Detection methods for the measurement of benzene and benzenoids have been based on AAS (atomic absorption spectroscopy) [11] or by applying infrared spectroscopy [12]
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