On-Line Full Molecular Characterization of Flashed Gases with a New Generation of NGD Detectors for Micro-GC

Abstract

Abstract Today, to get a full molecular characterization of gases, a gas chromatographic system hyphenated to both flame ionization (FID) and thermal conductivity (TCD) detectors is essential. However, for on-site, on-line analysis (mostly ATEX zone) FID are forbidden and TCD only allows quantification up to C7. A new universal detector (NGD for Nano Gravimetric Detector) covering a hydrocarbon range from C1 to C40+ has been developed and implemented in miniaturized and transportable system [1]. The first step is to evaluate the NGD response for different families of compounds present in the gas (synthetic and process gases) and develop different approaches to simplify the quantification. This one will be carried out in laboratories. To increase productivity and accuracy for PVT experiment, this detector will be implemented on a PVT unit. Once validated on fully controlled flashed gases, the system could be updated to work with batteries to be fully transportable for on-site or adapted for on-line analysis to be able to monitor any gas anywhere up to C11/ C12. All compounds were well separated and detected with the chromatographic resolution required for this study. Different standards gases have been used: from nC1 to nC10 with BTEX (benzene, toluene, ethylbenzene, m-xylene, p-xylene, and o-xylene). To achieve an external quantification, two approaches were carried out. A first approach based on the linear relationship that exists between the NGD response (as the logarithm of the peak area normalized by concentration) and the number of carbon atoms. These linear relationships are different depending on the family of compounds analyzed. The second approach uses a hyperbolic method based on the Langmuir model by applying an inverted Langmuir equation. This approach allows calibration of the NGD detector using a single linear relationship for all compounds regardless the family to which they belong. A quantification on diluted standards gases was carried out (4 levels) and the relative error was less than 10%. Moreover, a hyperbolic Langmuir approach improved the accuracy of the results with errors inferior at 5%. During 2023, the aim is to calibrate the NGD detector for the quantification of all compounds present in a process gas from a PVT unit and to proceed to the on-line monitoring. Today, only FID detector allows C5+ quantification on gaseous effluent, only present off-line. Tomorrow, thanks to the NGD detector, the gas analysis could be carried out on-line with a full molecular characterization of gases with a complete automatization of monitoring.