Chemistry Reference
In-Depth Information
1E15
1E15
1E15
CH
4
adde
d
HCN
NH
3
NO
1E14
1E14
1E14
1E13
1E13
1E13
CH
4
CO
CO
2
H
2
O
OH
H
2
CO
1E12
1E12
1E12
1E11
1E11
1E11
0
5
10
15
20
0
5
10
15
20
Oxygen flow [sccm]
FIGURE 6.12
MostabundantmolecularspeciesandtheirconcentrationsinanAr/CH
4
/N
2
/O
2
plasma (420 sccm Ar, 10 sccm CH
4
,10sccmN
2
, 0-20 sccm O
2
; 1.5mbar). (From Welzel, S.
et al.,
J.Phys.Conf.Ser
., 86, 012012, 2007.)
which first leads to a conversion into CO and finally into CO
2
. Formaldehyde, as
the intermediate molecule is further converted leading to the observed maximum
in [H
2
CO] at lower oxygen flows. The more CO
2
is produced with higher oxygen
flows—as the final product of the CH
4
conversion path—the more the CO
2
selectivity
increases, i.e., the relative concentration of CO
2
over CO increases. However, all the
measurements were performed in a discharge regime which is still oxygen poor [133].
As a result CO remains the most abundant molecule due to an incomplete conversion
of CH
4
to CO [219].
The production of NO in combination with several other molecules in a planar
microwave plasma created from a mixture of Ar, CH
4
,N
2
, and O
2
has been studied by
Zijlmans et al. [220]. The molecules were detected by means of in-situ TDLAS and by
absolute mass spectrometry (MS). The time resolution of the TDLAS measurements
was in the range of 0.1-1 s. Three groups of molecules can be distinguished in terms
of their molecular abundances: CO is the main component, together with H
2
O, N
2
,
and H
2
. The molecules CH
4
and O
2
are significantly depleted, but still present in
finite amounts. The third group is formed by several other species like NH
3
, NO, and
HCN. The combination of both TDLAS and MS allowed a clear distinction to be
made between the etching and deposition modes of the microwave reactor [220].
6.3.4.2.2 On NO
x
Production and Volatile Organic Compound Removal
Recent concerns about air quality have led to increasing research in the field of
pollution abatement from gas exhausts. Apart from conventional techniques, such as
catalysis, scrubbers, and active carbon, the use of electric discharges is a promising
technique for toxic gas removal, especially when these gases are present in low
