Thermal oxidation of HCN by NO$_2$ at high ... - Chemistry

Thermal oxidation of HCN by NO 2 3Figure 2. Comparison of typical H2O concentration profilewith modeled values: H2O formed at 2182.6 K (mixture C,P = 0.531 atm).Figure 4. Arrhenius plots for N02 +M=O+NO+M(1).A: Eq.(I). B.k1 = 1016.0 exp(-33,000/T) cm3 mole-1 s-1 (ref.20). Data points: P, modeling of NO profiles; o, modeling ofNO2 decay rates by Filter and Holmes.reactions (1) and (2), respectively, with a noticeable dependenceon reaction (6), HCN + O, which generatesNCO+H.4. Discussion4.1. Decomposition of NO 2Figure 3. Comparison of typical NO concentration profilewith modeled values: NO formed at 2005.6 K (X, mixture C,P = 0.614 atm.); 1893.5 K(o , mixture B, P = 0.598 atm);1695.6 K (D , mixture A, P = 0.648 atm).and H 2 O increased steadily until they reached plateauvalues. The agreement between experimental and modeledconcentration-time profiles is reasonable.The results of kinetic sensitivity analyses reveal therelative importance of various reactions to NO, CO, andH 2 O formation at different times. For NO, the initiationreaction, NO 2 +M=NO+O+M,(1), was foundto be the dominant reaction controlling its concentrationduring the early stage. Several reactions could beresponsible for CO production and removal; the decompositionof NO 2 and the reaction of HCN with O arethe key processes for its concentration increase, whereasO+NO 2 =O 2 +NO(2)andCO+OH=CO 2 +H(17) lead to its concentration decrease. H 2 O formationis controlled by oxygen atom production and removal byPrior to our recent measurement by simultaneously monitoringthe rates of NO 2 decay and NO production (SeeWang et al. (1988)), the unimolecular decomposition ofNO 2 at high temperatures had been studied by severalgroups (See Tsang and Herron (1991)). The Arrheniusparameters obtained by the earlier studies withAr as diluent have been recommended as k 1 =10 16.0exp (-33,000/T) cm 3 mol −1 s −1 . They differ substantiallyfrom our values given by the expression (SeeWang et al. (1988)):k 1 =10 14.83±0.12 exp(−26, 600 ± 750/T )cm 3 mol −1 s −1 (I)as also illustrated in Fig. 4. The data (points) shown inthe figure are the modeled values based on the rates ofNO formation measured in the present HCN-NO 2 systemand in the HNCO + NO 2 reaction (which had not beenreported previously (See He et al. (1992)) on account ofspace limitations). In addition, the modeled results ofFifer and Holmes’ NO 2 decay rates (vide infra) are alsoincluded in the figure. These results agree closely withthose computed by Eq. (I).Although the absolute values of k 1 given by Eq. (I)and by the recommended literature expression givenabove do not differ very much in the temperature rangestudied by shock-heating, the extrapolated value at 1000Paper 8880 21st International Symposium on Shock Waves, Great Keppel Island, Australia, July 20-25, 1997