The thermal reaction of HNCO at moderate temperatures

Abstract

The thermal reaction of HNCO has been studied in a static cell at temperatures between 873 and 1220 K and a constant pressure of 800 torr under highly diluted conditions. The reaction was measurable above 1000 K by FTIR spectrometry. The products detected include CO, COZ, HCN, NH3, and the unreacted HNCO. In this moderate temperature regime, the rates of product formation and HNCO decay cannot be accounted for by a previously established hightemperature mechanism, assuming HNCO + NH + CO (1) as the initiation process. Instead, a new bimolecular reaction, 2HNCO -Con + HNCNH (2), has been invoked to interpret the disappearance of HNCO as well as the formation of various products, most importantly COZ.The concentration profiles of all measured species can be quantitatively modeled, throughout the temperature range analyzed, by varying kz using a modified mechanism. The kinetically modeled values of kz can be effectively represented by exp( -21,240 2 1,96O/T) cm3/mol s .

Modeling nitrogen chemistry in combustion

“…The importance of a secondary product channel to NH 2 + CO 2 has been in discussion, but the theoretical study of Sengupta and Nguyen [172] indicates that this channel is 2.0E13 0.000 48500 [173,174], est 51. HNCO + HNCO HNCNH + CO 2 6.9E11 0.000 42100 [164] Reaction R51 has been studied both experimentally [164] and theoretically [164,175] and data are in good agreement. The reaction is too slow to contribute 51 to HNCO consumption under most conditions of interest.…”

Detailed modeling of the evaporation and thermal decomposition of urea‐water solution in SCR systems

“…As can be noticed on Figure 11, a slight impact of gas-phase kinetics can be noticed at the higher edge of the temperature range investigated. HNCO spontaneous decomposition kinetics is rather slow in the temperature range investigated [67,68]. Therefore, the thermal decomposition of HNCO should be triggered by an active species produced by ammelide decomposition.…”

“…HNCO spontaneous decomposition kinetics is rather slow in the temperature range investigated. 68,69 Therefore, the thermal decomposition of HNCO should be triggered by an active species produced by ammelide decomposition. The slight decrease in HNCO concentration is found to be quasi exclusively due to the following reaction:…”

Theoretical and experimental studies of the diketene system: Product branching decomposition rate constants and energetics of isomers

“…was proposed to account for the production of CO 2 and nitrogen-containing products, such as HCN and NH 3 [12]. Employing the same mechanism and similar transition state geometries as in (5), we can conveniently explain (1) and (2).…”