Shock Tube Experiments on Nitromethane and Promotion Of
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Report no. 2002:09 Classification The Norwegian University of Science and Technology Open Norges teknisk-naturvitenskapelige universitet POSTAL ADDRESS TELEPHONE TELEFAX NTNU Switchboard NTNU: +47 73 59 40 00 Department office: +47 73 59 83 90 DEPARTMENT OF THERMAL Department office: +47 73 59 27 00 Hydropower section: +47 73 59 38 54 ENERGY AND HYDROPOWER Hydropower section: +47 73 59 38 57 Kolbjørn Hejes vei 1A N-7491 TRONDHEIM Title of report Date Shock tube experiments on nitromethane and 03.06.2002 Promotion of chemical reactions by non- No. of pages/appendixes thermal plasma 328 Author Project manager Morten Seljeskog Otto K. Sønju Division Project no. Faculty of Engineering Science and Technology Department of Thermal Energy and Hydropower ISBN nr. Price group 82-471-5464-1 Client/sponsor of project Client’s ref. The Norwegian Defense Construction service, TOTAL Norge AS, Elf Petroleum Norge AS Abstract This dissertation was undertaken to study two different subjects both related to molecular decomposition by applying a shock tube and non-thermal plasma to decompose selected hydrocarbons. The first approach to molecular decomposition concerned thermal decomposition and oxidation of highly diluted nitromethane (NM) in a shock tube. Reflected shock tube experiments on NM decomposition, using mixtures of 0.2 to 1.5 vol% NM in nitrogen or argon were performed over the temperature range 850-1550 K and pressure range 190-900 kPa, with 46 experiments diluted in nitrogen and 44 diluted in argon. By residual error analysis of the measured decomposition profiles it was found that NM decomposition (CH3NO2 + M -> CH3 + NO2 + M, where M = N2 /Ar) corresponds well to a 17.011 law of first order. Arrhenius expressions corresponding to NM diluted either in N2 or in Ar were found as kN2 = 10 ×exp(-182.6 3 17.574 3 kJ/mole / R×T ) <cm /mole×s> and kAr = 10 ×exp(-207 kJ/mole / R×T ) <cm /mole×s>, respectively. A new reaction mechanism was then proposed, based on new experimental data for NM decomposition both in Ar and N2 and on three previously developed mechanisms. The new mechanism predicts well the decomposition of NM diluted in both N2 and Ar within the pressure and temperature range covered by the experiments. In parallel to, and following the decomposition experiments, oxidative experiments on the ignition delay times of NM/O2/Ar mixtures were investigated over high temperature and low to high pressure ranges. These experiments were carried out with eight different mixtures of gaseous NM and oxygen diluted in argon, with pressures ranging between 44.3-600 kPa, and temperatures ranging between 842-1378 K. The oxidation experiments were divided into different categories according to the type of decomposition signals achieved. For signals with and without emission, the apparent quasi-constant activation energy was found from the correlations, to be 64.574 kJ/mol and 113.544 kJ/mol, respectively. The correlations for the ignition delay for time signals with and without emission were deduced as -2 -1.02 -1.08 1.42 -2 -0.28 0.12 -0.59 τemission = 0.3669×10 ×[NM] [O2] ×[Ar] ×exp(7767/T) and τno emission = 0.3005×10 ×[NM] [O2] ×[Ar] ×exp(13657/T), respectively. The second approach to molecular decomposition concerned the application of non-thermal plasma to initiate reactions and decompose/oxidize selected hydrocarbons, methane and propane, in air. Experiments with a gliding arc discharge device were performed at the university of Orléans on the decomposition/reforming of low-to-stoichiometric concentration air/CH4 mixtures. The presented results show that complete reduction of methane could be obtained if the residence time in the reactor was sufficiently long. The products of the methane decomposition were mainly CO2, CO and H2O. The CH4 conversion rate showed to increase with increasing residence 3 time, temperature of the operating gas, and initial concentration of methane. To achieve complete decomposition of CH4 in 1 m of a 2 vol% mixture, the energy cost was about 1.5 kWh. However, the formation of both CO and NOx in the present gliding discharge system was found to be significant. The produced amount of both CO (0.4-1 vol%) and NOx (2000-3500 ppm) were in such high quantities that they would constitute an important pollution threat if this process as of today was to be used in large scale CH4 decomposition. Further experimental investigations were performed on self-built laboratory scale, single- and double dielectric-barrier discharge devices as a means of removing CH4 and C3H8 from simulated reactive inlet mixtures. The different discharge reactors were all powered by an arrangement of commercially available Tesla coil units capable of high-voltage high-frequency output. The results from each of the different experiments are limited and sometimes only qualitative, but show a tendency that the both CH4 and C3H8 are reduced in a matter of a 3-6 min. retention time. The most plausible mechanism for explaining the current achievements is the decomposition by direct electron impact. Indexing Terms: English Indexing Terms: Norwegian Group 1 Nitromethane decomposition Nitrometane dekomponering Group 2 Non-thermal plasma Kaldt plasma Selected Nitromethane reaction mechanism Nitrometane reaksjonsmekanisme by author Hydrocarbon decomposition Hydrokarbon dekomponering URN:NBN:no-3311 URN:NBN:no-3311 SHOCK TUBE EXPERIMENTS ON NITROMETHANE AND PROMOTION OF CHEMICAL REACTIONS BY NON-THERMAL PLASMA By Morten Seljeskog A dissertation submitted for the degree of doktor ingeniør Department of Thermal Energy and Hydropower Norwegian University of Science and Technology Submitted June 2002 URN:NBN:no-3311 URN:NBN:no-3311 - iii - SUMMARY This dissertation was undertaken to study two different subjects both related to molecular decomposition by applying a shock tube and non-thermal plasma to decompose selected hydrocarbons. The first approach to molecular decomposition concerned thermal decomposition and oxidation of highly diluted nitromethane in a shock tube. The basic physical and chemical properties for nitromethane are reported together with some theory on nitromethane detonation structure, ignition process and the effect of additives on these parameters. The experimental part covered the calibration of experimental apparatus, UV spectrum analysis and shock tube experiments. Reflected shock experiments on nitromethane decomposition were studied. The experiments were performed in the transient region, which is in the region between pressure dependent and independent rate constants. By residual error analysis of the measured decomposition profiles, it was found that nitromethane decomposition corresponds well enough to a law of first order. In this work, a new reaction mechanism is proposed, based on new experimental data for NM decomposition both in Ar and N2. The new mechanism was based on three previously developed mechanisms. Arrhenius expressions were derived for the nitromethane decomposition at different wavelengths and diluents. These were derived from the plot of the best exponential fit of the experimental k-values versus the inverse of the temperature in the reflected shock. By comparing the experimental against the calculated results it was indeed clarified that decomposition of highly diluted nitromethane at higher temperature conditions could be explained by the unimolecular third body dissociation reaction alone. Computer simulations of the thermal nitromethane decomposition were used to verify that the reaction mechanism indeed initiates through the third body decomposition of the nitromethane molecule as stated by previous authors. Three previously proposed reaction mechanisms were compared against the experimental data and used as basis for the simulations. After the decomposition of the nitromethane molecule the reaction proceeds by two major and parallel pathways, which both include radical reactions, to produce CH2O. The latter acting as a source for further radicals when attacked by existing OH and H radicals, producing HCO radicals that will carry the reactions to completion. The simulated profiles corresponded well with those obtained experimentally. SUMMARY URN:NBN:no-3311 - iv - Following the decomposition experiments, oxidative experiments on the ignition delay times of CH3NO2/O2/Ar mixtures were investigated over high temperature and low to high pressure ranges. These experiments were carried out with eight different mixtures of gaseous nitromethane and oxygen diluted in argon. The oxidation experiments were divided into three different types according to the type of decomposition signals achieved. For signals with emission and for slightly or non-diluted mixtures the apparent quasi- constant activation energy was found from experimental correlations. When the molar fraction of argon tends to unity and for slightly diluted mixtures, a different correlation was derived. A quasi-constant activation energy (∆E) was also deduced from these correlations. The second approach to molecular decomposition concerned the application of non- thermal plasma to initiate reactions and decompose/oxidize selected hydrocarbons, methane and propane, in air and was sectioned into one theoretical and two experimental parts. In such discharges, chemical change is driven by a variety of processes including ionization, molecular excitation, ion-electron recombination, fragmentation of ions and excited molecules, and reactions of radicals, atoms, and ions. The first experimental section on non-thermal plasma was performed at the university