ISSN:0010-2202    

DOI:10.1080/00102209808924122

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

The dehydrochlorination of poly(vinyl chloride) is of interest from several points of view, e.g., the evolution of harmful substances during fires or waste incineration, reclaiming chemical raw materials from plastic waste, electronic scrap management and recycling of plastic waste mixtures. In this work some new mechanistic aspects of the decomposition of poly(vinyl chloride) are investigated by the combined application of TG-MS, isothermal experiments in a gradient-free reactor and DSC.Poly(vinyl chloride) degrades in two steps. At lower temperature (220-350°C) HCl and small amounts of benzene are formed. At higher temperature ( > 400°C) the residue decomposes into mostly aromatic compounds. Dehydrochlorination at moderate temperatures consists of an endothermic and exothermic path. The benzene formation is identified to be a second order reaction.The kinetic data for decomposition confirm that in mixtures of different plastics the dehydrochlorination of poly(vinyl chloride) can be conducted at moderate temperature and prior to the thermal degradation of most other plastics. This has been demonstrated in this work in a cascade of well stirred reactors at laboratory scale. The degree of conversion of chlorine from PVC into hydrogen chloride in the first reactor is about 99.6% at 330°C after a residence time of 26 min.Similar results are obtained during the thermal degradation of electronic scrap. The hydrogen chloride evolution from poly(vinyl chloride) occurs in the same way as in mixtures of commodity plastics. Brominated flame retardants are decomposed or evolve at higher temperatures ( > 300°C). The conversion of bromine into copper salts by means of copper from copper wires is observed as well.

ISSN:0010-2202    

DOI:10.1080/00102209808924123

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Thermal decomposition results for CCl4, CHCl3CH2Cl2, CH3Cl, C3H3Cl, CFCl3CF2Cl2, CF3Cl, CF2HCl, CF3I, CH3I, C2H5I, C6H5I, and CCl2O are reviewed and summarized. The results were obtained by shock tube techniques coupled with optical spectroscopic detection of transient species formed from dissociation. The method is illustrated with the CH3I (+ Kr) → CH3+ 1(+ Kr) reaction where decomposition was monitored using l-atorn atomic resonance absorption spectrometry CARAS). Modern unimolecular rate theoretical analysis has been carriedout on the present cases, and the conclusions from these calculations are discussed. Lastly, the possible destruction of halo-organics by incineration is considered and some implications are discussed.

ISSN:0010-2202    

DOI:10.1080/00102209808924124

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

ISSN:0010-2202    

DOI:10.1080/00102209808924125

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

This paper presents an experimental study that focuses on the formation of perfluoroisobutene (i-C4Fg). Experiments were carried out at atmospheric pressure in a quartz flow tube reactor over the temperature range of 823 to 1273K and an initial reactant feed concentration of 2% with the balance nitrogen. Reactants studied include chlorodifluoromethane (CHF2Cl), 1,1,1,2-tetrafluoro-2-chloroethane (CF3CHFCl), trifluoromethane (CHF3), perfluoropropene (C3F6), and mixtures of these species. Effluent gas concentrations were obtained using a water cooled gas sampling probe, and analysis of products was performed via on line gas chromatography with flame ionization detection and gas chromatography with mass selective detection. C3F6pyrolysis produced more than 22% i-C.F, yield, while mixtures with CHF2Cl and CHF3resulted in i-C4Fgyields of 14% and 28%, respectively. The pyrolysis of CF3CHFCI resulted in slightly greater than 6% i-C4Fgyield, and CHF2Cl decomposition produced up to 6% i-C4Fgyield, while CHF2Cl/CF3CHFC1 copyrolysis produced 8% yield of i-C4Fg. These results show that the addition of a difluoromethylene (iCF2) source increases i-C4Fgproduction. This suggests that a major pathway to i-C4Fgproduction may be C3F6isomerization to singlet perfluorodimethylcarbene (l:C(CF3)2) and subsequent collisional stabilization to the triplet carbene (3:C(CF3)2) followed by either 1:CF2addition or further reaction with C3F6. This work focuses on an experimental study. Detailed modeling work is ongoing.

ISSN:0010-2202    

DOI:10.1080/00102209808924126

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

The combination of laser induced Resonance-Enhanced Multi-Photon Ionization and Time-Of-Flight Mass Spectrometry (REMPI-TOFMS) represents a highly selective and sensitive analytical technique ideal for real-time determination of organic trace components. For example, aromatic hydrocarbons can be continuously monitored in industrial off gases. Weintroduce a new mobile REMPI-TOFMS instrument, which is robust and easy to operate, even under industrial conditions.

ISSN:0010-2202    

DOI:10.1080/00102209808924127

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Laser-Induced Breakdown Spectrometry (L1BS) can meet the U.S. Environmental Protection Agency/s (EPA) proposed Maximum Achievable Control Technology (MACT) rules requirements for Be, Cd, Cr, Pb, and Sb. However, L1BS’ current limits of detection (LODs) for As and Hg are significantly higher than the LODs that EPA is seeking. The current Laser Optogalvanic Spectrometry (LOGS) laboratory LODs for airborne metal particles are comparable to or lower than the desired EPA MACT LODs for Cd, Cr, Hg, Pb, and Sb. We report our efforts to combine LOGS with LIBS to produce a near real-time metal emissions monitor that is capable of monitoring the volatile toxic metals that are regulated by EPA. During a field simulation test, LIBS, LOGS, and EPA Method 29 simultaneously determined the concentration of airborne metals in the off-gas. The LIBS results are found to be in reasonably good agreement with those of EPA Method 29. The LOGS real-time determinations were higher than those reported by either L1BS or EPA Method 29; this discrepancy is due (a) to a spectral interference with a two-photon sodium transition, and (b) to oversampling of large particles.

ISSN:0010-2202    

DOI:10.1080/00102209808924128

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

A new method to measure and examine ignition delays for hypergolic acid-organic reactants is described, Methods of previous investigations will be critically compared by mixing techniques, sensing devices, repeatability, and chemical composition for the influence of these parameters on ignition delay measurements, The time delay for hypergolics to react from initial contact to the appearance of flame is classically termed the ignition delay. This technique. as a result of its resolution, is the first to measure the chemical reaction time just prior to ignition, This new chemical performance measurement defines the time during which free radicals generated by the reaction should be analyzed by spectroscopic techniques, Unsymmetrical dimethylhydrazine, hydrazine, and furfuryl alcohol were individually reacted with various nitric acid mixtures. For the furfuryl alcohol-white fuming nitric acid system, this technique is the first to show that an initiation-propagation step is required for complete hypergolic combustion, This method also is the first to quantitatively measure the chemical performance of the hypergolic reactants, The technique clearly identifies the chemical delay time within the classical definition of the ignition delay time. The chemical delay time permits direct comparison of chemical performance of hypergolic acid-organic reactions.

ISSN:0010-2202    

DOI:10.1080/00102209808924129

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Resonance-enhanced multiphoton ionization/time-of-flight mass spectrometry (REMPI/TOFMS) has been employed for detection limit measurements of dibenzodioxin, dibenzofuran, 2,8-dichloro-dibenzodioxin, biphenyl, anthracene, phenanthrene and pyrene. REMPI/TOFMS detection limit data are currently available for 28 molecules. Nineteen of these, with detection limits at or below the part-per-billion level, are recommended for use as surrogates for continuous real-time monitoring of hazardous emissions from incinerators. The excellent spectral selectivity of the REMPl/TOFMS tecbnique, exhibited by single ring phenyl compounds, may be substantially reduced for many of the higher aromatics. Additional studies are needed of the one- and two-color spectral signatures for resonance two-photon ionization of PCBs and chlorinated polycyclic aromatics.

ISSN:0010-2202    

DOI:10.1080/00102209808924130

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

We have developed and are employing a broadly tunable, KCI:Li color center laser (CCL) measurement apparatus to make line-or-sight absorption measurements on combusting systems. Our CCL offers a tuning range of 0.4μm, which permits spectral access to several combustion products and byproducts, and a linewidth of ∼ 0.01cm−1, which is sufficiently narrow to resolve spectral features of interest to the experiment. Measurements in a cell containing an absorbing gas at room temperature have demonstrated our ability to determine both temperature and gas number density. We are presently using the laser system on a uniform, flat-flame burner apparatus with the goal of determining temperature and species concentrations in a flame. Results of measurements both on the cell and on the flame ace presented.

ISSN:0010-2202    

DOI:10.1080/00102209808924131

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor