Wayne A. Rubey

High-temperature degradation of polybrominated flame retardant materials

Abstract This experimental study examined gas-phase oxidative and pyrolytic thermal degradation of three brominated flame retardant materials in a high-temperature flow reactor. Br-benzenes, Br-phenols, PBDDs and PBDFs were formed at intermediate temperatures and subsequently destroyed by 800°C.

Detailed Modeling of the Pyrolysis of Trichloroethene: Formation of Chlorinated Aromatic Species

Comprehensive product yield determinations from the high-temperature, gas-phase pyrolysis of trichloroethene (C 2 HCl 3 ) using two fused silica tubular flow reactors coupled to in-line gas chromatographic-mass spectrometric analyses are reported. Initial decomposition was observed at 1000 K with formation of HCl and C 2 Cl 2 . Pronounced molecular growth was observed at higher temperatures as evidenced by the formation of C 2 Cl 4 , C 4 Cl 4 , and C 6 Cl 6 (cy) as major (≤5 mole%) products and C 4 Cl 2 , C 4 Cl 6 , C 6 HCl 5 (cy), C 8 Cl 6 (cy), C 8 Cl 8 (cy), C 10 Cl 8 (cy), and C 12 Cl 8 (cy) as minor (≤5 mole %) products. The effects of reactor surface area to volume (S/V) ratio were evaluated by conducting detailed product analyses with 0.1 cm i.d. and 1.0 cm i.d. reactors. Under the higher S/V ratio, C 2 HCl 3 decomposition was increased by an order of magnitude and product distributions suggested that radical-radical and radical-atom recombination rates were enhanced. Product yields under reduced S/V ratio indicated that yields of perchlorinated aromatic and perchlorinated PAH species were a factor of 10 larger than observed for higher S/V ratios. A detailed reaction mechanism is presented for the 1 cm i.d. reactor data describing molecular growth up to the formation of C 8 Cl 6 (cy) and C 8 Cl 8 (cy). Comparison of predicted versus experimental major and minor species profiles are presented, with generally good agreement. Important radical-molecule addition reactions leading to molecular growth are identified using sensitivity analysis and production rate calculations

Design aspects of a modular instrumentation system for thermal diagnostic studies

A laboratory instrumentation system has been developed which provides flexibility for conducting an extensive range of thermal investigations of organic materials. Test samples can be of gaseous, liquid, solid, polymeric, composite, or even multiphase nature. This modular system uses an interchangeable test‐cell assembly concept for performing laboratory experiments and physical simulations. Incorporated in‐line instrumental analysis techniques provide sensitive and comprehensive effluent analyses of the thermal‐related degradation behavior.

Evidence for a unified pathway of dioxin formation from aliphatic hydrocarbons

Acetylene is readily converted to perchlorinated gas-phase intermediates including hexachlorobenzene, hexachlorobutadiene, and tetrachloroethylene and heavier perchlorinated species via heterogeneous gas-solid reactions with HCl and cupric oxide on borosilicate under postcombustion conditions. Experiments were conducted using an integrated gas-solid flow-reactor and analytical system at temperatures ranging from 150 to 500°C for gas-phase residence times of 2.0 s and total reaction times of 60 min. Chlorine addition and chlorine net substitution mechanisms mediated by the conversion of Cu(II)Cl2 to Cu(I)Cl are proposed to account for the observed or inferred C2 reaction products including tetrachloroethylene, trichloroethylene, and dichloroacetylene. The formation of condensation products including tetrachlorovinylacetylene, hexachlorobutadiene, and hexachlorobenzene are proposed to be catalyzed by copper chloride species and involve the following steps: (1) chemisorption of a chlorinated ethylene or acetylene by HCl elimination or 1,2-Cu−Cl addition, respectively: (2) physisorption of additional chlorimated ethylenes or acetylenes followed by cis-insertions: and (3) carbon-to-copper chlorine transfer followed by desorption of the molecular growth product. The mechanism accounts for product isomer distributions and branching desorption of the higher molecular weight products, and regeneration of the copper chloride catalyst.

High-temperature gas-phase formation and destruction of polychlorinated dibenzofurans☆

The high-temperature gas-phase decomposition of a PCB isomer was studied using a tubular flow reactor. The formation and destruction of various PCDFs were investigated in atmospheres containing different concentrations of O2.

Design of a tubular reactor instrumentation assembly for conducting thermal decomposition studies

A thermal instrumentation assembly which uses a high‐temperature tubular reactor for conducting gas‐phase thermal decomposition studies of organic substances has been designed. This thermal reactor assembly uses a counterflow heat exchanger in conjunction with a narrow‐bore quartz tubular reactor to obtain precise control over physical factors, such as exposure temperature, mean residence time, and gas‐phase residence‐time distribution. By virtue of the design of this quartz‐ware assembly, gaseous species are subjected to essentially a square‐wave thermal pulse as they pass through the thermal reactor.

Trace-level measurement of complex combustion effluents and residues using multidimensional gas chromatography-mass spectrometry (MDGC-MS)

The identification and quantitation of non-method-specific target analytes have greater importance with respect to EPAs current combustion strategy. The risk associated with combustion process emissions must now be characterized. EPA has recently released draft guidance on procedures for the collection of emissions data to support and augment site-specific risk assessments (SSRAs) as part of the hazardous waste incineration permitting process. This guidance includes methodology for quantifying total organic (TO) emissions as a function of compound volatility. The ultimate intent is to compare the amount of organic material identified and quantified by target analyte-specific methodologies to organic emissions quantified by the TO methodology. The greater the amount accounted for by the target analyte-specific methodologies, the less uncertainty may be associated with the SSRAs. A limitation of this approach is that the target analyte-specific methodologies do not routinely quantify compounds of low toxicological interest; nor do they target products of incomplete combustion (PICs). Thus, the analysis can miss both toxic and non-toxic compounds. As a result, it is unknown whether the uncharacterized fraction of the TO emission possesses toxic properties. The hypothesis that we propose to test is that organic emissions and organics extracted from particulate matter (PM) are more complex than standard GC-MS-based instrumentation can currently measure. This complexity can affect quantitation for toxic compounds, thereby potentially affecting risk assessments. There is a pressing need to better characterize these organic emissions from hazardous waste incinerators and PM extracts from various other combustion sources. We will demonstrate that multidimensional gas chromatography-mass spectrometry (MDGC-MS) procedures significantly improve chromatographic separation for complex environmental samples. Sequential repetitive heart-cutting MDGC, with coupled mass spectrometry will be shown to be a complete analysis technique. The ability of this technique to disengage components from complex mixtures taken from hazardous and municipal waste incinerators will be shown.

Speciation of Organic By-Products from the Thermal Decomposition of Alternative Automotive Fuels

The high-temperature thermal degradation of four alternative automotive fuels (methanol, ethanol, natural gas, and liquefied petroleum (LP) gas) have been examined as a function of fuel-oxygen equivalence ratio and exposure temperature using fused silica flow reactor instrumentation coupled to in-line GC-TCD and GC-MS detection. Organic speciation for methanol, natural gas, and LP gas were consistent with previous measurements. However, several previously undetected organic by-products were observed from ethanol oxidation and pyrolysis. Organic speciation was found to vary significantly between methanol and ethanol and less so between natural gas and LP gas. Non-methane organic gases (NMOG) and specific reactivities of the respective fuels were measured, and trends with respect to proposed reactivity adjustment factors are discussed. A qualitative comparison of NMOG quantified in the flow reactor tests with the results of recent vehicle tests is also reported. The most significant differences in the comparisons were observed for toxic compounds, including the lack of detection of acetalde-hyde, 1,3-butadiene, and benzene from flow reactor experiments of methanol degradation, and the lack of detection of 1,3-butadiene from flow reactor experiments of ethanol combustion. Possible sources for the formation of these compounds in vehicle tests are discussed.

AN INSTRUMENTATION ASSEMBLY FOR STUDYING OPERATIONAL BEHAVIOR OF THERMAL GRADIENT PROGRAMMED GAS CHROMATOGRAPHY

Extensive laboratory experiments and measurements are required for the operational evaluation and optimization of thermal gradient programmed gas chromatography (TGPGC). To accommodate these numerous laboratory investigations, an instrumentation assembly has been designed and constructed which possesses the needed built‐in experimental flexibility or adaptability. This system has been configured to test a variety of column sheath assembly designs and their associated open tubular separation columns. It is also used for performance testing many other special TGPGC components, including devices needed for the different types of sample introduction. The major application area of TGPGC is the rapid analysis of complex organic mixtures which cover a broad volatility range. Consequently, this system has been designed to permit exploratory investigations over a temperature range of −100 to 500 °C, while using programmed flows of a variety of inert transport gases. With the use of this instrumentation assembly, o...