chemical physics of discharges - Argonne National Laboratory

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\ Frozen Compositior: Calcillation v5rsus Expcri;:icntally. 0bscrvt.d Ccwposition.
IC, indeed, the oriSinal assuption that important reactiotis occurrirg in the gas
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withdrawn from the plasma into the cold quenching tube are .frozen.in ths vicinity
1 1 ,of 3000 K is, valid, then agree'ment should be found betveeri the cc::!pssitions listed
in Tables I and 11. Ir. comparing the argon-fret coinposition listed in Table I with
PO~UIM 2 in Table 11, rciatively $cod agrement is found.
This comparison has been extended to thc' ikll ranee of stsichiomctries studied.
i)n Fig. 4, the maximum nitrogen'conversion, amar-l , and am0,-2, has been plotted
' against input CH)+/N2-molc ratio, 4,. The s.dlscript 1 refers to calculations includ-
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ing C(s); subscript 2, to excludine, C(s). Agrceinunt between the freezing mcdel and
crbserved results is very good over more than a two-decade range in stoichiometry
variation. These results strongly support .the freezing model in the overall reac-
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tion path. With the existing scatter of the data, a delineation between the
single-phase and two-phase equilibrium predictions of composition at Tf is not
possible. Additional sxperimental runs may lessen this ambiguity. The retarda-
/ tion of carbon solid fcrmation, however, accoiints fur Less than a 10 percent change
in predicted maximum nitrogen conversion, an the average.
Freezing Temperature. The data do not allow an t.xact determination of a frcczing
temperature appropriate to the quenching process. keferring back to Fig. 3a, a
change of a few hundred degrees in the assumed Tf could account for the data points
which indicate 10 to 20 percent less than the two-phase equilibrium predictions of
maximum nitrogen conversion. Fig. 3b shows the HCN concentration plateaus to be
quite broad. Hence the nitrogen conversion prediction would be relatively insensitive
to variation in freezing temperature over the range from 1500 to 3000 K.
Future experimental refinenents may allow a mvre exact determination of Tf .
Observed Compositions in Nitrile Experiments. An analysis of the maximum
nitrugen convcrsion predicted by tiiernochenical equilibrium has not been nlade fi.r
the different nitrile inputs desckibed in tne "Expcrirnental Conditions'' zectiuri.
The similarity cjf .product ciistri!iiition and uf the rxtio of. HCN to !Q in the prcduct
poitito to the same reaction mechanisms as iii tile CiU+/l\I2 studics.
Correlatiuri with Studies by Other Investigators
If the proposed reaction mechanism is correct, then the yields found in other
studies of the synthesis of HCN by thermal reactions of hydrocarbons with riitrogeri
should not exceed the predicted values of a . Some results of the production of
HCN in plasma jets have been reported, as was mentioned in the "fieviolis Studies"
section. While the differences in design between the plasma jet and induction
plasma reactors are not detailed here, sample results from these other studies are
plotted on Fig. 4. The maximum nitrogen conversion vdues observed 'in the nitrogen
plasma jet experiments of Leutnerll (designated XL) and FreemanE (designated xF )
appear. These experimental data points are seen to lie below the maximum nitrogen
conversion prediction.
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