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1.
Thermal pyrolysis of halon 1211 (CBrClF 2), diluted in nitrogen, in a tubular alumina reactor, has been studied over the temperature range of 773–1073 K at residence times from 0.3 to 2 s. At temperatures below 973 K, the major products were CCl 2F 2, CBr 2F 2, C 2Cl 2F 4, C 2BrClF 4, C 2F 4, and C 2Br 2F 4. Further increasing temperature resulted in the formation of CBrF 3, CClF 3, and many other species whose formation necessitated the rupture of C? F bonds. Coke formation was also observed on the surface of the reactor at high temperatures. A kinetic reaction scheme involving 16 species and 25 reaction steps was developed and applied to model the thermal pyrolysis of halon 1211 over the temperature range of 773–973 K. Sensitivity analysis suggests that the reaction CBrClF 2 + CClF 2→CCl 2F 2 + CBrF 2 constitutes the major pathway for the decomposition of halon 1211 under the conditions investigated. © 2005 Wiley Periodicals, Inc. Int J Chem Kinet 37: 134–146, 2005 相似文献
2.
An extensive set of measurements of the heats of solution of a number of fluorine-containing gases (CCl 2F 2, CClF 3, CBrF 3, CF 4) have been performed from 5 to 45°C. The temperature dependence allows accurate determination of the heat capacity change in the solution process as a function of temperature. To a first approximation these heat capacity results agree with the predictions of the simple two energy state model for water molecules in the first solvation shell. The further extension of the general applicability of this model, originally developed to account for the thermodynamic properties of solvation of hydrocarbon and other small apolar gases in water, suggests that the unique thermodynamic properties of hydrophobic solvation are largely determined by the water molecules in the first solvation shell. 相似文献
3.
The decomposition of carbon tetrachloride was investigated in an RF inductively coupled thermal plasma reactor in inert CCl 4–Ar and in oxidative CCl 4–O 2–Ar systems, respectively. The exhaust gases were analyzed by gas chromatography-mass spectrometry. The kinetics of CCl 4 decomposition at the experimental conditions was modeled in the temperature range of 300–7,000 K. The simulations predicted
67.0 and 97.9% net conversions of CCl 4 for CCl 4–Ar and for CCl 4–O 2–Ar, respectively. These values are close to the experimentally determined values of 60.6 and 92.5%. We concluded that in
RF thermal plasma much less CCl 4 reconstructed in oxidative environment than in an oxygen-free mixture. 相似文献
4.
Decomposition of dichlorodifluoromethane (CCl 2F 2 or CFC-12) in aradiofrequency (RF) plasma system is demonstrated. The CCl 2F 2decomposition fractions CCl
2
F
2 and mole fractionsof detected products in the effluent gas stream of CCl 2F 2/O 2/Ar andCCl 2F 2/H 2/Ar plasma, respectively, have been determined. The experimentalparameters including input power wattage, O 2/CCl 2F 2 or H 2/CCl 2F 2 ratio,operational pressure, and CCl 2F 2 feeding concentration wereinvestigated. The main carbonaceous product in the CCl 2F 2/O 2/Arplasma system was CO 2, while that in the CCl 2F 2/H 2/Ar plasma systemwas CH 4 and C 2H 2. Furthermore, the possible reaction pathways werebuilt-up and elucidated in this study. The results of the experimentsshowed that the highly electronegative chlorine and fluorine wouldeasily separate from the CCl 2F 2 molecule and combine with the addedreaction gas. This led to the reactions terminated with the CO 2,CH 4, and C 2H 2 formation, because of their high bonding strength. Theaddition of hydrogen would form a preferential pathway for the HCland HF formations, which were thermodynamically stable diatomicspecies that would limit the production of CCl 3F, CClF 3, CF 4, andCCl 4. In addition, the HCl and HF could be removed by neutral orscrubber method. Hence, a hydrogen-based RF plasma system provideda better alternative to decompose CCl 2F 2. 相似文献
5.
Reaction of CF 4, CBrF 3, and CBr 2F 2 with Silica CF 4 reacts with silica above 1200 K forming SiF 4 and CO 2. CBrF 3 and CBr 2F 2 yield SiF 4, Br 2, CO 2, and CO as well as products of pyrolysis, such as C 2BrF 5, C 2Br 2F 4, and others. The reaction starts at 900 K (CBrF 3) or 700 K (CBr 2F 2), resp. The CO 2/CO ratio is higher than expected. SiF 4 is absorbed at the surface of silica to a considerable extent. 相似文献
6.
Decomposition of carbon tetrachloride in a RF thermal
plasma reactor was investigated in argon atmosphere. The net
conversion of CCl 4 and the main products of its decomposition
were determined from the mass spectrometric analysis of outlet
gases. Flow and temperature profiles in the reactor were
calculated and concentration profiles of the species along the
axis of the reactor were estimated using a newly developed
chemical kinetic mechanism, containing 12 species and 34 reaction
steps. The simulations indicated that all carbon tetrachloride
decomposed within a few microseconds. However, CCl 4 was partly
recombined from its decomposition products. The calculations
predicted 70\% net conversion of CCl 4, which was close to the
experimentally determined value of 60\%. A thermodynamic
equilibrium model also simulated the decomposition. Results of the
kinetic and thermodynamic simulations agreed well above 2000 K.
However, below 2000 K the thermodynamic equilibrium model gave
wrong predictions. Therefore, application of detailed kinetic
mechanisms is recommended for modeling CCl 4 decomposition under
thermal plasma conditions. 相似文献
7.
Optical emission (180–800 nm) and mass spectroscopy have been used to study the CF 4, CF 4+O 2, C 2F 6, C 2F 6+H 2, CF 3Cl, and C 2F 4 decomposition in radio-frequency discharges. The analysis of the stable and unstable discharge products has allowed the suggestion of decomposition channels for the various gases and to classify the fluorinated gases according to their predominant etching or polymerizing characteristics on the basis of the active species present in the plasma. A new broad emission continuum centered at =290 nm (FWHM=66 nm) has also been identified and it has been tentatively assigned to CF +
2. 相似文献
8.
We examined the influence of the gas flow-rate, microwave power and trichloroethylene concentration on the destruction of
trichloroethylene with a system based on a microwave helium plasma operating at atmospheric pressure. Based on the experimental
results obtained, the proposed system allows input concentrations of C 2HCl 3 in the ppmv range to be reduced to output concentrations in the ppbv range (i.e. virtually quantitative destruction) by using
a microwave plasma power below 1000 W. High helium flow-rates and C 2HCl 3 concentrations allow energy efficiency values above 600 g/kW h to be obtained. Analyses of the output gases by gas chromatography
and species present in the plasma by optical emission spectroscopy confirmed the negligible presence of halogen compounds
resulting from the destruction of C 2HCl 3, and that of CCl 4 and C 2Cl 4 as the sole chlorine species exceeding levels of 30 ppbv. Gaseous by-products consisted mainly of CO 2, NO and N 2O in addition to Cl 2 traces. 相似文献
9.
Summary By means of cryogenic sampling and subsequent gas-chromatographic analysis vertical profiles of CCl 4, CCl 3F, CCl 2F 2, CClF 3, CF 4, C 2Cl 3F 3, C 2Cl 2F 4, C 2ClF 5, C 2F 6, CH 3Cl and CH 3CCl 3 were derived for stratospheric heights up to 35 km. Vertical profiles of halocarbons computed by means of one-dimensional and two-dimensional models fall off less rapidly in the stratosphere than the measured profiles, this systematic discrepancy being due to deficiencies in the radiation and transport schemes of present models. It is shown that measured profiles of fully halogenated hydrocarbons provide a tool for systematically studying these deficiencies and thus improving the models. Sources and sinks of halocarbons are discussed, and an assessment of past and future sources of organically bound chlorine in the atmosphere is made.
Die vertikale Verteilung halogenierter Kohlenwasserstoffe in der stratosphäre Zusammenfassung Die vertikalen Profile von CCl4, CCl3F, CCl2F2, CClF3, CF4, C2Cl3F3, C2Cl2F4, C2ClF5, C2F6, CH3Cl und CH3CCl3 wurden für stratosphärische Höhen bis zu 35 km mit Hilfe kryogener Probenahme und anschließender gas-chromatographischer Analyse bestimmt. Die mit Hilfe von ein- und zweidimensionalen Modellen berechneten Profile fallen in der Stratosphäre weniger schnell ab als die gemessenen. Dieser systematische Unterschied ist auf Mängel in den Strahlungs- und Transportmechanismen der gegenwärtigen Modelle zurückzuführen. Es wird gezeigt, daß die gemessenen Profile der vollhalogenisierten Kohlenwasserstoffe dazu dienen können, diese Mängel zu untersuchen und die Modelle zu verbessern. Ursprung und Verbleib der halogenierten Kohlenwasserstoffe werden beschrieben und vergangene und zukünftige Quellen organisch gebundenen Chlors in der Atmosphäre diskutiert. 相似文献
10.
A new reaction of MgCl 2·4H 2O with CCl 2F 2 is investigated by DTA and TG from room temperature to 350 °C. It is observed that MgF 2 was obtained between 252 and 350 °C, Below the temperature, MgCl 2·4H 2O dehydrates and hydrolyzes to MgCl 2 and Mg(OH)Cl, which are the real reactants of the reaction with CCl 2F 2. The formation of MgF 2 is ascribed to the reaction of MgCl 2 and Mg(OH)Cl with HF, which forms by decomposition of CCl 2F 2 with the taking part in of H 2O released from dehydration of hydrated magnesium chloride on the surface of MgCl 2 and Mg(OH)Cl, which catalyzes the decomposition of CCl 2F 2 in this case. Consequently, the reactions are tested in the fluid-bed condition. It is found that MgF 2 formed at temperatures down to 200 °C in a fluid-bed reactor. This reaction may be used as a method of disposing of the environmentally sensitive CCl 2F 2 (rather than release into the atmosphere). It is also a method for the preparation of MgF 2. 相似文献
11.
The reaction of tetrachloroethylene, C 2Cl 4, with O( 3P) atoms as well as the plasma decomposition of C 2Cl 4 and C 2Cl 4/O 2 mixtures have been investigated by combined application of electron paramagnetic resonance (EPR) and emission and mass spectroscopies. C 2Cl 4 plasma decomposition is shown to proceed primarily to the formation of CCl 3 radicals and chlorine-deficient products, which are ultimately involved in the formation of carbonaceous layers. A simple reaction model accounts for all the detected stable and radical species, encountered during the plasma decomposition. The model also enables order-of-magnitude estimates of decomposition rate constants to be made. The suppression of the formation of both carbonaceous layers and products C mCl n (m3) in C 2Cl 4/O 2 discharges is explained using results of an investigation of elementary reactions in the system C 2Cl 4/O( 3P)/O 2. The stable products of C 2Cl 4/O 2 discharges, i.e., COCl 2, CCl 4, and C 2Cl 6, respectively, are shown to originate from recombination of the peroxy radicals CCl 3OO and C 2Cl 5OO. 相似文献
12.
Molecular hydrogen production from ethanol decomposition by two microwave atmospheric pressure plasma sources (surfatron and Torche a Injection Axiale sur Guide d’Onde (TIAGO) torch) was studied by optical emission spectroscopy and mass spectrometry. In both cases ethanol was almost completely decomposed, thus giving place to molecular hydrogen. However, the atmosphere surrounding the discharge significantly influences the overall decomposition process. When the surfatron is used, C 2H 2 and CO are obtained as exhaust gases. Likewise, H 2O and HCN are also detected at plasma exit when sustained with the TIAGO torch. 相似文献
13.
Measurements of Ps yields in mixtures of CO 2 and Ar with the electron scavengers CCl 4 and CCl 2F 2 are reported. It is shown that the CO 2 mixtures provide direct evidence for Ps formation in spurs in this gas. Further, some support is also given to recent models which consider Ps formation in gases by both Ore and spur processes. The results obtained for the Ar mixtures are consistent with the Ore model of Ps formation. 相似文献
14.
To date, numerous studies have investigated the aftertreatment of exhaust gases from fossil-fueled combustors and combustion engines by plasmas as an environmental plasma application. Owing to the high power requirements of environmental plasma, it is difficult to use the plasma alone for aftertreatment; hence, a hybrid process that combines plasma processing with other techniques is required to reduce the overall power consumption. In developing countries, low-cost plasma hybrid processing has attracted considerable attention as an alternative to the selective catalytic reduction NOx decomposition (De-NOx) method and wet lime–gypsum SOx decomposition method. Moreover, reduced catalytic activity can be enhanced by the plasma because of the decreased exhaust gas temperature, owing to the increased combustion efficiency. This paper reviews studies on successful air pollutant decomposition processes using the plasma chemical process with scale-up reactors. First, experimental techniques and block diagrams of various environmental plasma systems are presented. Subsequently, real-world systems of scale-up plasma reactors are described in detail. Several experimental results suggest that the hybrid treatment of particulate matter and dry De-NOx is very promising from the viewpoint of energy consumption and material recycling. CO2 treatment is a very important direction for future work in environmental plasma. 相似文献
15.
Decomposition of carbon tetrachloride in a RF thermal plasma reactor was investigated in oxygen–argon atmosphere. The net conversion of CCl 4 and the main products of decomposition were determined by GC–MS (Gas Chromatographic Mass Spectroscopy) analysis of the exhaust gas. Temperature and flow profiles had been determined in computer simulations and were used for concentration calculations. Concentration profiles of the species along the axis of the reactor were calculated using a newly developed chemical kinetic mechanism, containing 34 species and 134 irreversible reaction steps. Simulations showed that all carbon tetrachloride decomposed within a few microseconds. However, CCl 4 was partly recombined from its decomposition products. Calculations predicted 97.9% net conversion of carbon tetrachloride, which was close to the experimentally determined value of 92.5%. This means that in RF thermal plasma reactor much less CCl 4 was reconstructed in oxidative environment than using an oxygen-free mixture, where the net conversion had been determined to be 61%. The kinetic mechanism could be reduced to 55 irreversible reaction steps of 26 species, while the simulated concentrations of the important species were within 0.1% identical compared to that of the complete mechanism. 相似文献
16.
Silicon nitride is an important material layer in various types of microelectronic devices. Because of continuous integration of devices, patterning of this layer requires a highly selective and anisotropic etching process. Reactive ion etching is one of the most simple and popular plasma processes. The present work is an experimental analysis of primary etch characteristics in reactive ion etching of silicon nitride using chlorine- and/or fluorine-based organic and inorganic chemistries (CCl
2
F
2+ O
2
, CHF
3+ O
2
, SiF
4
+O 2, SF 6+ O
2
, and SF
6+ He) in order to obtain a simultaneous etch selectivity against polysilicon and silicon dioxide. A recipe, in CCl
2
F
2
/O
2
plasma chemistry, which provides acceptable etch characteristics, along with a reasonable simultaneous selectivity against polysilicon and silicon dioxide, has been formulated. 相似文献
17.
The kinetics of the plasma-chemical conversion of a number of saturated, as well as of unsaturated, fluorocarbon compounds
is studied in an oxygen-based rf discharge by FTIR spectroscopy. Unsaturated fluorocarbons are rapidly converted into CF 4 and C 2F 6, which, in the presence of silica walls, are finally converted quantitatively into SiF 4 (etch reaction). The results of this investigation are used to design a plasma-chemical reactor for the conversion of fluorocarbon
exhaust gases into SiF 4 in the vacuum line of a technological low-pressure plasma reactor. Furthermore, it is shown that the primary conversion product
SiF 4 can be effectively converted into CaF 2 in a heterogeneous reaction with a CaO/Ca(OH) 2 absorber, also in the low-pressure line of the pumping system. 相似文献
18.
The rate coefficient for the reaction of CCl 3 radicals with ozone has been measured at 303 ± 2 K. The CCl 3 radicals were generated by the pulsed laser photolysis of carbon tetrachloride at 193 nm. The time profile of CCl 3 concentration was monitored with a photoionization mass spectrometer. Addition of the O 3–O 2 mixture to this system caused a decay of the CCl 3 concentration because of the reactions of CCl 3 + O 3 → products (5) and CCl 3 + O 2 → products (4). The decay of signals from the CCl 3 radical was measured in the presence and absence of ozone. In the absence of ozone, the O 3–O 2 mixture was passed through a heated quartz tube to convert the ozone to molecular oxygen. Since the rate coefficient for the reaction of CCl 3 + O 2 could be determined separately, the absolute rate coefficient for reaction ( 5 ) was obtained from the competition among these reactions. The rate coefficient determined for reaction ( 5 ) was (8.6 ± 0.5) × 10 ?13 cm 3 molecule ?1 s ?1 and was also found to be independent of the total pressure (253–880 Pa of N 2). This result shows that the reaction of CCl 3 with O 3 cannot compete with its reaction with O 2 in the ozone layer. © 2003 Wiley Periodicals, Inc. Int J Chem Kinet 35: 310–316, 2003 相似文献
19.
Reactions of Lanthanum Fluoride with Halogenoalkanes Reactions are reported on lanthanum fluoride as a fluorinating reagent and as a catalyst for the fluorination and dismutation of halogenoalkanes. Carbon tetrachloride, monofluorotrichlormethane, and chloroform are partially fluorinated by lanthanum fluoride. In the presence of HF, lanthanum fluoride acts as catalyst the fluorine transfer to CCl 4, CHCl 3 and C 2F 3Cl 3. Monofluorotrichloromethane, difluorodichloromethane, and trifluorotrichloroethane dismutate on lanthanum fluoride. Results on the thermal decomposition of the above-mentioned fluorochloroalkanes are communicated. 相似文献
20.
Energetic materials such as a mixture of guanidine nitrate (GN)/basic copper nitrate (BCN) are used as gas generators in automotive airbag systems. However, at the time of the airbag inflation, the gas generators release toxic combustion gases such as CO, NH 3, and NO x. In this study, we investigated the combustion and thermal decomposition behaviors of GN/BCN mixture, focusing primarily on their exhaust gas composition. As a result, when the exhaust gas of the combustion under constant pressure in an inert gas stream was analyzed using a detection tube, the amount of NO x (mainly NO) yielded greater decrease with increasing atmospheric pressure as compared to the amounts of CO and NH 3. Thus, provided GN/BCN is ignited in a closed container, a large amount of NO x is presumed to have been released during the initial stage of combustion, which yielded comparatively low pressure. Results of the thermogravimetry–differential scanning calorimetry–Fourier transform infrared spectroscopy (TG/DSC/FTIR) indicated that the GN/BCN mixture caused endothermic decomposition at 170 °C and exothermic decomposition at 208 °C, which was accompanied by 66% mass loss. The decomposition gases, CO 2, N 2O, and H 2O, were detected via FTIR spectrum. Because N 2O was not detected in the combustion gas, it was suggested that the detected N 2O was generated at a low temperature and decomposed in high-temperature combustion. 相似文献
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