Thermal decomposition of gaseous ammonium nitrate at low pressure: Kinetic modeling of product formation and heterogeneous decomposition of nitric acid

J. Park*, Ming-Chang Lin

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

24 Scopus citations

Abstract

The thermal decomposition of ammonium nitrate, NH4NO3 (AN), in the gas phase has been studied at 423-56 K by pyrolysis/mass spectrometry under low-pressure conditions using a Saalfeld reactor coated with boric acid. The sublimation of NH4NO3 at 423 K was proposed to produce equal amounts of NH3 and HNO3, followed by the decomposition reaction of HNO3, HNO3 + M → OH + NO2 + M (where M ) third-body and reactor surface). The absolute yields of N2, N2O, H2O, and NH 3, which can be unambiguously measured and quantitatively calibrated under a constant pressure at 5-6.2 torr He are kinetically modeled using the detailed [H,N,O]-mechanism established earlier for the simulation of NH 3-NO2 (Park, J.; Lin, M. C.Technologies and Combustion for a Clean Environment. Proc. 4th Int. Conf. 1997, 34-1, 1-5) and ADN decomposition reactions (Park, J.; Chakraborty, D.; Lin, M. C. Proc. Combust. Inst. 1998, 27, 2351-2357). Since the homogeneous decomposition reaction of HNO3 itself was found to be too slow to account for the consumption of reactants and the formation of products, we also introduced the heterogeneous decomposition of HNO3 in our kinetic modeling. The heterogeneous decomposition rate of HNO3, HNO3 + (B2O 3/SiO2) → OH + NO2 + (B2O 3/SiO2), was determined by varying its rate to match the modeled result to the measured concentrations of NH3 and H 2O; the rate could be represented by k2b ) 7.91 × 107 exp(-12 600/T) s-1, which appears to be consistent with those reported by Johnston and co-workers (Johnston, H. S.; Foering, L.; Tao, Y.-S.; Messerly, G. H. J. Am. Chem. Soc. 1951, 73, 2319-2321) for HNO 3 decomposition on glass reactors at higher temperatures. Notably, the concentration profiles of all species measured could be satisfactorily predicted by the existing [H,N,O]-mechanism with the heterogeneous initiation process.

Original languageEnglish
Pages (from-to)13556-13561
Number of pages6
JournalJournal of Physical Chemistry A
Volume113
Issue number48
DOIs
StatePublished - 1 Jan 2009

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