A Method for the Accurate Quantification of Gas Streams by On-Line Mass Spectrometry

The accuracy of the online quantification of gaseous effluents from catalytic reactors by mass spectrometry (MS) is rarely addressed by researchers, despite the extensive use of the technique. MS results are strongly sensitive to both the operation conditions of the reactor and to the state of the instrument. Therefore, most studies use them as qualitative descriptors of the performance of catalytic reaction systems. The purpose of this work was to develop an accurate method for the quantification of gaseous effluents from catalytic reactors. For this purpose, the mathematical expressions from the so-called external and internal standard calibration methods for MS were coupled to the typical metrics used for studying catalytic reactions; namely, conversion, selectivity, and carbon mass balances. The catalytic combustion of methane was selected as a model reaction to test the developed approach. The accuracy of the developed method was validated by comparison with results obtained in a separated reaction system coupled online to a gas chromatograph. The closure of the carbon mass balance was used as a control metrics allowing for the assessment of the physical meaning of the method. In general, the internal standard method of calibration was found to be best for the accurate quantification of gaseous streams by on-line mass spectrometry. In general, the results of this investigation may be of use to researchers in the field of catalysis as well as to research workers using mass spectrometry for various purposes.