Quantitative gas composition analysis method for a wide pressure range up to atmospheric pressure—CO2 plasma case study

Abstract

A mass spectrometer with a custom sampling system comprising one fixed and one variable orifice is presented. The custom sampling system allows the determination of the gas composition in the pressure range from 5 mbar to 1000 mbar, with low gas-demixing (<1.5%). A case study of mass spectrometer optimization and calibration for the measurement of relative concentration of CO2, CO, O2, and N2 gases is presented, together with an example of the CO2 conversion at a microwave plasma torch. The absolute error of the measured conversion of CO2 in CO is found to be less than 1.6% in the complete pressure range. The conversion determination routine presented here allows us to determine relative molar flows of CO2, CO, O2, and N2 and to distinguish between CO and N2 gases, which is important for the determination of the CO2 conversion in the case of air impurities or in the case of CO2/N2 mixtures.

Determination of the Conversion and Efficiency for CO2 in an Atmospheric Pressure Microwave Plasma Torch

“…D'Isa reported a maximal efficiency of around 25 % for the quasi‐atmospheric pressure measurements but a maximal conversion of about 15 % 20, 22. Hecimovic et al reported that the CO 2 conversion efficiency at a pressure of 200 mbar is independent of the measurement position along the exhaust gas tube and independent of the position of the heat exchanger 20. They noticed no decrease in the conversion and concluded that in their case, the quenching took place only in the first 4 cm above the resonator top (which, correspond to a downstream distance of z = 9 cm in this work).…”

“…The main differences are the absence of a tubular reactor for the incorporation of membranes for gas separation, a lower position of the heat exchanger and the presence at quasi atmospheric pressure of a pump to suck away the effluent gas. D'Isa reported a maximal efficiency of around 25 % for the quasi‐atmospheric pressure measurements but a maximal conversion of about 15 % 20, 22. Hecimovic et al reported that the CO 2 conversion efficiency at a pressure of 200 mbar is independent of the measurement position along the exhaust gas tube and independent of the position of the heat exchanger 20.…”

“…A torch similar to the one investigated in the current work, equipped with a different exhaust gas treatment, and that can be operated from 60 mbar up to a quasi-atmospheric pressure around 900 mbar, is located at the IPP Institute in Garching [20,22]. The main differences are the absence of a tubular reactor for the incorporation of membranes for gas separation, a lower position of the heat exchanger and the presence at quasi atmospheric pressure of a pump to suck away the effluent gas.…”

“…A plasma torch with the same resonator structure but different exhaust gas treatment has already been investigated in the pressure range from 60-900 mbar [20][21][22].…”

Trendbericht Technische Chemie 2021

“…Zum Verständnis zur Selektion des Plasmaprozesses und dessen Charakterisierung ist die Plasmadiagnostik essenziell und wird hier ebenfalls kurz angerissen. 34) Aus der entsprechenden Teilchendichte lassen sich die Konversion und -mit Hinzunahme des Gasflusses und der zugeführten Leistung zum Plasma -die Energieeffizienz quantifizieren. Für eine zuverlässige Bestimmung der Effizienz muss die Temperatur des entnommenen Gases allerdings nahe Raumtemperatur sein.…”