chemical physics of discharges - Argonne National Laboratory

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HYDROCARBON-NITROGEN REACTIONS IN A TRERMAL INDUCTION PLASMA
Bary R. Bronfin
United Aircraft Research Laboratories
I East Hartford, ConneLticht 06108
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4, Gas temperatures anove l5,OOO K have been observed in plasma generateddby
radio-frequency induction coupling'. This high thermal erlergy regirre becon?es of
iqcerest to the chemist for the investigation of highly endothermic reactions.
I?. particular, this paper will report reactions between methane and nitrogen fed
to a thermal induction plasma ar,d subsequently quenched to yield hydrogen cyanide,
acetylene and hydrogen.
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PREVIOUS STUDIES OF THE E-C-N SYSTEM
Lar Pressure Discharges. Winkler and his co-workers2-5 have systematically
studied the reactions of nitrogen, activated by passage through a high-voltage
discharge, with various hydrocarbons. These studies were carried out at pressures
near 1 torr with very low reagent flow rates. Gas temperatures were also low,
typically 300 C. In this nonequilibrium system the reaction betw-een methane and
"active" nitrogen yielded hydrogen cyanide, acetylene and hydrogen2.
High Pressure Arcs. More recently high-power thermal arcs were used for the
study of the H-C-N system near atmospheric pressure. Leutrer' operated 2 nitrogen
plasma jet into which methane was mixed. In his briefly reported results, up to
LO percent conversion of the nitrogen to HCN was found'. -At this symposium
Freeman? has reported an extensive study of the synthesis of HCN, from EL nitrogen
plasma jet intermixed with methane. Typically, a 7 percent conversion of N2 to
HCN was observed. In both studies &, C2IJ2, and unreacted CHI, were also identified
as major constituents in the cooled product stream.
If the maximum mean temperature attainable in these previous studies is cal-
cdated, one finds that enthalpy input was insufficient to generate mean tempern-
f Caes greater than - 5000 K.
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Dissociating Plasmas. Upon considering the various species possible in.the
H-C-N system, the strongest bond found is N E N (226 kcal/g-mole). Thermal-dissociation
of N2 is essentiaU.y complete at temperatures in excess of 8000 K". Orv.
car. envision a high-pressure, stable plasma fed with any of e. variety of carbon,
hydrogen, or nitrogen compounds and supplied with sufficient erthalpy to reach
this high temperature range. The constituent species of srlch a plasma would be
prinarily atomic nitrogen, atornic hydrogen, and atomic carbon near lo1-( cm-3 concentration.
The result of rapidly quenching such! highly reactive atom mixture
nas been generally Lnexplored. &ann and TimminsJ,lO, however, did study the
rapid quenching of the simpler atonic-nitrogen/atormc-oxygen mixtures at 10,Oc)O K