Premium
Homogeneous CO 2 conversion by microwave plasma: Wave propagation and diagnostics
Author(s) -
den Harder Niek,
van den Bekerom Dirk C. M.,
Al Richard S.,
Graswinckel Martijn F.,
Palomares Jose M.,
Peeters Floran J. J.,
Ponduri Srinath,
Minea Teofil,
Bongers Waldo A.,
van de Sanden Mauritius C. M.,
van Rooij Gerard J.
Publication year - 2017
Publication title -
plasma processes and polymers
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.644
H-Index - 74
eISSN - 1612-8869
pISSN - 1612-8850
DOI - 10.1002/ppap.201600120
Subject(s) - plasma , microwave , atomic physics , electron temperature , argon , materials science , analytical chemistry (journal) , afterglow , chemistry , physics , quantum mechanics , gamma ray burst , chromatography , astronomy
A suite of diagnostics is proposed to characterize microwave plasma dissociation of CO 2 : laser scattering, Fourier transform infrared spectroscopy, and passive emission imaging. It provides a comprehensive performance characterization as is illustrated on the basis of experiments in a 2.45 GHz, 1 kW microwave reactor with tangential gas injection. For example, two operating regimes are identified as function of pressure: the diffuse and constricted plasma mode. Their occurrence is explained by evaluation of microwave propagation, which changes with the electron‐heavy particle collision frequency v e−h . In the diffuse mode, gas temperatures of 1500–3500 K are determined. The measured conversion degree, specific energy input, and temperature are summarized in a two‐temperature thermal model, which is solved to obtain the gas temperature at the periphery of the reactor and the size of the hot zone. Solutions are found with edge temperatures of hundreds of K, and hot zone fractions which agree with the measured behavior. The agreement shows that non‐thermal processes play only a marginal role in the measured parameter space of the diffuse discharge. In the constricted mode, the radial plasma size is independent of power. A skin depth equal to the plasma size corresponds to electron densities of 10 18 –10 19 m −3 . Temperatures in the central filament are in the range 3000–5000 K. Both discharge modes are up to 50% energy efficient in CO production. Rayleigh signals increase in the afterglow, hinting at rapid gas cooling assuming that the gas composition remains unchanged.