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1
Jansson, Stina. « Thermal formation and chlorination of dioxins and dioxin-like compounds ». Doctoral thesis, Umeå universitet, Kemi, 2008. http://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-1881.
Texte intégralRésumé :
This thesis contributes to an increased understanding of the formation of dioxins and dioxin-like compounds in combustion processes. Although emissions to air from waste incineration facilities have been greatly reduced by the use of efficient air pollution control measures, the resulting residues (ashes and filters) are highly toxic and are classified as hazardous waste. The main objective of the work underlying this thesis was to elucidate the formation and chlorination pathways of dioxins and dioxin-like compounds in waste combustion flue gases in the temperature range 640-200°C in a representative, well-controlled laboratory-scale reactor using artificial municipal solid waste. This could contribute to the reduction of harmful emissions to air and also reduce the toxicity of waste incineration residues, thus reducing or even eliminating the need for costly and potentially hazardous after-treatment. A comparison of four different quenching profiles showed that the formation of polychlorinated dibenzo-p-dioxins (PCDD) and dibenzofurans (PCDF) was rapid and mainly occurred in the 640-400°C temperature region, with high dependency on sufficient residence time within a specific temperature region. Prolonged residence time at high temperatures (450/460°C) reduced the PCDD yields, even at lower temperatures along the post-combustion zone. PCDD, PCDF and PCN (polychlorinated naphthalene) isomer distribution patterns indicated contributions from chlorophenol condensation as well as chlorination reactions for all three classes of compounds. The formation of PCDDs was largely influenced by chlorophenol condensation and to some extent by chlorination reactions. For the PCDFs, chlorine substitution adjacent to the oxygen bridges was unfavoured, as demonstrated by the notably lower abundance of 1,9-substituted congeners. This was supported by bidirectional orthogonal partial least squares (O2PLS) modelling. The variable with the greatest influence on the distribution of PCDD congeners was the relative free energy (RΔGf). The O2PLS models displayed distinct clusters, dividing most of the homologues into two or three sub-groups of congeners which seemed to correspond to the probability of origination from chlorophenol condensation. The effects of injection of aromatic structures into the flue gas differed for each class of compounds. Injection of naphthalene increased the formation of monochlorinated naphthalene but the remaining homologues appeared to be unaffected. This was probably due to insufficient residence time at temperatures necessary for further chlorination. Injected dibenzo-p-dioxin was decomposed, chlorinated and re-condensated into PCDDs and PCDFs, whereas injection of dibenzofuran and fluorene reduced the PCDD levels in the flue gas.Denna avhandling fokuserar på olika aspekter som kan bidra till en ökad förståelse av bildning av dioxiner och dioxin-lika föreningar i förbränningsprocesser. Även om utsläppen till luft från sopförbränningsanläggningar har minskat kraftigt tack vare effektiva rökgasreningsmetoder, så återstår problemet med mycket giftiga rökgasreningsprodukter (askor och filter), vilka klassificeras som farligt avfall. Det huvudsakliga syftet med arbetet bakom denna avhandling var att klarlägga bildnings- och kloreringsvägarna för dioxiner och dioxin-lika föreningar i temperaturintervallet 640-200°C i rökgaser från sopförbränning. Detta kan möjliggöra lösningar för ytterligare emissionsminskningar och en avgiftning av biprodukterna från avfallsförbränning, vilket minskar eller till och med eliminerar behovet av kostsam och riskfylld efterbehandling. Realistiska och välkontrollerade försök har utförts i en lab-skalereaktor där en artificiell hushållssopa har förbränts. En jämförelse av fyra olika temperatur- och uppehållstidsprofiler visade att bildning av polyklorerade dibenso-p-dioxiner (PCDD) och dibensofuraner (PCDF) sker snabbt och huvudsakligen inom temperaturintervallet 640-400°C. Bildningen var starkt beroende av en tillräckligt lång uppehållstid inom ett visst temperaturområde. En förlängd uppehållstid vid höga temperaturer (>450°C) resulterade i minskade halter av PCDD, vilka förhöll sig låga även senare i efterförbränningszonen. Isomermönstren av PCDD, PCDF och PCN (polyklorerade naftalener) visade alla tecken på att härröra från både klorfenolkondensation och kloreringsreaktioner. PCDD-mönstret visade tydliga indikationer på bildning från klorfenoler, och till mindre grad bildning via klorering. För PCDF var klorsubstitution i positioner angränsande till syrebryggan missgynnad, vilket bekräftades av multivariat modellering (O2PLS). Den variabel som starkast påverkade bildningen av PCDD var relativa fria energin (RΔGf). Modellerna visade på en distinkt gruppering av PCDD- och PCDF-kongenerna i två eller tre grupper för varje kloreringsgrad, och föreslås vara relaterad till sannolikheten för respektive kongen att bildas via klorfenolkondensation. Injektion av aromatiska kolstrukturer i rökgaskanalen gav upphov till skilda effekter. Injektion av naftalen ökade bildningen av monoklorerad naftalen medan resterande homologer inte verkade påverkas, sannolikt på grund av för kort uppehållstid för ytterligare klorering. Dibenso-p-dioxin spjälkades sannolikt till fenoliska fragment som klorerades och sedan återkondenserades till PCDD och PCDF, medan dibensofuran och fluoren kraftigt reducerade PCDD-koncentrationerna.
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Gao, Qiuju. « Dioxins and dioxin-like compounds in thermochemical conversion of biomass : formation, distribution and fingerprints ». Doctoral thesis, Umeå universitet, Kemiska institutionen, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-118861.
Texte intégralRésumé :
In the transition to a sustainable energy supply there is an increasing need to use biomass for replacement of fossil fuel. A key challenge is to utilize biomass conversion technologies in an environmentally sound manner. Important aspects are to minimize potential formation of persistent organic pollutants (POPs) such as dioxins and dioxin-like compounds. This thesis involves studies of formation characteristics of polychlorinated dibenzo-p-dioxins (PCDDs), dibenzofurans (PCDFs) and naphthalenes (PCNs) in microwave-assisted pyrolysis (MAP) and torrefaction using biomass as feedstock. The research focuses are on their levels, distributions, fingerprints (homologue profiles and isomer patterns) and the underlying formation pathways. The study also included efforts to optimize methods for extracting chlorinated aromatic compounds from thermally treated biomass. The overall objective was to contribute better understanding on the formation of dioxins and dioxin-like compounds in low temperature thermal processes. The main findings include the following: Pressurized liquid extraction (PLE) is applicable for simultaneous extraction of PCDDs, PCDFs, PCNs, polychlorinated phenols and benzenes from thermally treated wood. The choice of solvent for PLE is critical, and the extraction efficiency depends on the degrees of biomass carbonization. In MAP experiments PCDDs, PCDFs and PCNs were predominantly found in pyrolysis oils, while in torrefaction experiments they were mainly retained in solid chars with minor fractions in volatiles. In both cases, highly chlorinated congeners with low volatility tended to retain on particles whereas the less chlorinated congeners tended to volatize into the gas phase. Isomer patterns of PCDDs, PCDFs and PCNs generated in MAP were more selective than those reported in combustion processes. The presence of isomers with low thermodynamic stability suggests that the pathway of POPs formation in MAP may be governed not only by thermodynamic stabilities but also by kinetic factors. Formation of PCDDs, PCDFs and PCNs depends not only on the chlorine contents in biomass but also the presence of metal catalysts and organic/metal-based preservatives. Overall, the results provide information on the formation characteristics of PCDDs, PCDFs and PCNs in MAP and torrefaction. The obtained knowledge is useful regarding management and utilization of thermally treated biomass with minimum environmental impact.
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Ryu, Jae-Yong. « Dioxin formation on copper (II) chloride from chlorinated phenol, dibenzo-p-dioxin and dibenzofuran precursors ». Diss., Georgia Institute of Technology, 2002. http://hdl.handle.net/1853/19050.
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Akki, Umesh. « Gas phase formation pathways and mechanisms of polychlorinated dibenzo-p-dioxins and dibenzofurans ». Diss., Georgia Institute of Technology, 1998. http://hdl.handle.net/1853/23157.
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JAMSHAID, ASHIQ MUHAMMAD. « Influence of alternative fuels on the formation of dioxins in a cement production plant ». Thesis, Umeå universitet, Kemiska institutionen, 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-89026.
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Arnoldsson, Kristina. « Polybrominated dibenzo-p-dioxins : Natural formation mechanisms and biota retention, maternal transfer, and effects ». Doctoral thesis, Umeå universitet, Kemiska institutionen, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-50887.
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Polybrominated dibenzo-p-dioxins (PBDD) and dibenzofurans (PBDF) are a group of compounds of emerging interest as potential environmental stressors. Their structures as well as toxic responses are similar to the highly characterized toxicants polychlorinated dibenzo-p-dioxins. High levels of PBDDs have been found in algae, shellfish, and fish, also from remote areas in theBaltic Sea. This thesis presents studies on PBDD behavior in fish and offspring, and natural formation of PBDDs from naturally abundant phenolic precursors. The uptake, elimination, and maternal transfer of mono- to tetraBDD/Fs were investigated in an exposure study reported in Paper I. The effects of PBDDs in fish were examined in a dose-response study (Paper II). It was shown that fish can assimilate PBDD/Fs from their feed, although non-laterally substituted congeners were rapidly eliminated. Laterally substituted congeners were retained as was congeners without vicinal hydrogens to some extent. PBDD/Fs were transferred to eggs, and congeners that were rapidly eliminated in fish showed a higher transfer ratio to eggs. Exposure to the laterally substituted 2,3,7,8-TeBDD had significant effects on the health, gene expression and several reproduction end-points of zebrafish, even at the lowest dose applied. The geographical and temporal variations of PBDD in biota samples from the Baltic Seasuggest biogenic rather than anthropogenic origin. In Paper III, bromoperoxidase-mediated coupling of 2,4,6-tribromophenol yielded several PBDD congeners, some formed after rearrangement. The overall yield was low, but significantly higher at low temperature, and the product profile obtained was similar to congener profiles found in biota from the Swedish West Coast. In Paper IV, photochemically induced cyclization of hydroxylated polybrominated diphenyl ethers under natural conditions produced PBDDs at percentage yield. Rearranged products were not detected, and some abundant congeners do not seem to be formed this way. However, the product profile obtained was similar to congener profiles found in biota from the Baltic Proper. Since the PBDD congeners found in biota have a high turn-over in fish, the exposure must be high and continuous to yield the PBDD levels measured in wild fish. Thus, PBDDs must presumably be formed by common precursors in general processes, such as via enzymatic oxidations, UV-initiated reactions or a combination of both. The presented pathways for formation of PBDDs are both likely sensitive to changes in climatic conditions.
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PICCINELLI, ELSA. « Environmental impact of industrial plants combustion processes : kinetic and formation/destruction mechanisms of PolichlorinatedDibenzo-p-Dioxins and PolichlorinatedDibenzoFurans ». Doctoral thesis, Università degli Studi di Milano-Bicocca, 2009. http://hdl.handle.net/10281/10060.
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The aim of the project was to study the mechanism of formation and degradation of PolyChlorinatedDibenzo-p-Dioxins (PCDDs) and PolyChlorinatedDibenzoFurans (PCDFs) in combustion processes. Today the challenge is to demonstrate that the conclusion based on laboratory scale experiments and the models coming from the results are useful tools to estimate emissions and to prevent or reduce PCDD/F (sum of PCDDs and PCDFs) formation in the flue gas cleaning system of plants. Following this, the study was developed at two different scales:
Laboratory scale. The native carbon oxidation and PCDD/F formation were simultaneously studied at different temperatures (230-350 °C) and times (0-1440 min) in order to establish a direct correlation between the disappearance of the reagents and the formation of the products. The kinetic runs were conducted in a experimental set up where conditions were chosen to gain information on the role of fly ash deposits in cold zone of the plant in PCCD/F formation reaction
Real plant scale. An extensive experimental study of a secondary aluminium casting plant flue gas cleaning system was performed. In particular, on the strength of the knowledge obtained by laboratory studies and the results of the samplings, the best strategies to prevent PCDD/F formation were identify and Air Pollution Control Device (APCD) performance was improved.
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Saeed, Anam. « Studies on the Decomposition of Selected Brominated Flame Retardants (BFRs) and Formation of Polybrominated Dibenzo-p-dioxins and Dibenzofurans (PBDD/Fs) and Mixed Halogenated Dibenzo-p-dioxins and Dibenzofurans (PXDD/Fs) ». Thesis, Saeed, Anam (2016) Studies on the Decomposition of Selected Brominated Flame Retardants (BFRs) and Formation of Polybrominated Dibenzo-p-dioxins and Dibenzofurans (PBDD/Fs) and Mixed Halogenated Dibenzo-p-dioxins and Dibenzofurans (PXDD/Fs). PhD thesis, Murdoch University, 2016. https://researchrepository.murdoch.edu.au/id/eprint/35843/.
Texte intégralRésumé :
Brominated flame retardants (BFRs) are bromine-bearing hydrocarbons added or applied to materials to increase their fire resistance. As thermal treatment or recycling activities are common disposal methods for BFR-laden objects, it is essential to determine the precise decomposition chemistry of BFRs at elevated temperatures, and their transformation pathways into hazardous pollutants. Sunlight can trigger the photodecomposition of BFRs, either during the life cycle of treated objects, or when emitted to the environment after disposal. Therefore, knowledge of the geometric and electronic structures of BFRs is of chief importance when tracking their fate in the ambient environment.
Although BFR decomposition mainly occurs in a condensed phase, gas phase reactions also contribute significantly to their overall decay and subsequent fragmentation into brominated pollutants. Thermal degradation of BFRs often proceeds in the presence of bromine atoms which inhibit complete combustion. Therefore, under thermal conditions such as smouldering, municipal waste incineration, pyrolysis, thermal recycling, uncontrolled burning and fires, BFRs degrade to form brominated products of incomplete combustion (BPICs). Thermal degradation of BFRs produces potent precursors to polybrominated dibenzo-p-dioxins and dibenzofurans (PBDD/Fs). Co-combustion of BFR-containing objects with a chlorine source (e.g., polyvinyl chlorides) results in the emission of significant concentrations of mixed halogenated dibenzo-p-dioxins and dibenzofurans (i.e., PXDD/Fs; X = Br, Cl).
In this thesis, we investigated the thermochemical parameters of bromochlorophenols (BCPhs) and the photodecomposition properties of major BFRs and their derived brominated phenols (BPhs). We scrutinised the formation of brominated and non-brominated products that evolved during the thermal decomposition of major BFR i.e., tetrabromobisphenol A (TBBA), through experimental measurements coupled with accurate quantum chemical calculations. We acquired thermo-kinetic parameters as well as mechanistic routes pertinent to the destruction of TBBA. We illustrated reaction networks for the synthesis of PXDD/Fs from BPhs and chlorinated phenols (CPhs). Similarly, we described pathways leading to the formation of PBDFs and polybrominated diphenylethers (PBDEs) from brominated benzenes (BBzs). We critically reviewed the literature on BFR thermal decomposition with specific foci on underlying mechanisms, decomposition products, the influence of the polymeric matrix, metallic content and operational conditions.
As BCPhs are direct building blocks for the formation of PXDD/Fs, we computed the thermochemical parameters of their complete series. We calculated standard enthalpies of formation, entropies, heat capacities and bond dissociation enthalpies (BDHs) of O-H bonds for the complete series of BCPhs. Values of the acid dissociation constant (pKa) were estimated based on an accurate thermodynamic cycle incorporating solvation and protonation energies. Calculated values of BDHs of O-H bonds in BCPhs vary slightly with the change in degree and pattern of halogenation. Gibbs energies of solvation of BCPhs in water are highly exergonic, with their values increasing with the degree of halogen substitution. Values of pKa dictate that BCPhs characterised by high degrees of halogenation display stronger acidity and dissociate more easily in aqueous media (i.e., they are stronger acids than lower substituted phenols).
Photolysis and photochemical decomposition are important channels for the degradation of halogenated organic pollutants in the environment. Therefore, we performed density functional theory (DFT) and time-dependent density functional theory (TDFT) calculations in order to derive the photodecomposition properties of major deployed BFRs and congeners of BPhs in both gaseous and aqueous media. We clarified the effect of degree and pattern of bromination on the photodebromination of selected brominated aromatic compounds based on several molecular descriptors; namely, geometries of the ground (S0) and electronically first excited (S1) states, values of the HOMO-LUMO energy gap (EH-L) and atomic charges on bromine atoms (qBr). Molecules exhibit different geometries in the S0 and S1 states and C-Br bonds elongate upon S0 → S1 transitions. In agreement with the recent findings on PBDEs, we found that the photoreactivity of bromine atoms in investigated BFRs and BPhs followed the sequence of ortho > meta > para. The bromine atom connected to the ortho-position holds the highest positive atomic charge and, thus, experiences the greatest lengthening of C-Br bonds in the S1 state, in both gaseous and an aqueous media, prompting their reductive debromination. Excitation energies decrease linearly with increasing numbers of bromine substituents, and congeners with a high degree of bromination photodecompose more readily than lower brominated isomers. Computed values of EH-L for major BFRs and their non-brominated molecules inferred that the number of bromine substituents and the nature of the structure (aromatic/non-aromatic) contributes significantly towards the photoreactivity of molecules.
We conducted gas phase thermal decomposition of TBBA using a laboratory-scale tubular reactor. Our main focus was to identify pollutants arising in the temperature range of 673 – 1123 K following evaporation of TBBA in the gas phase. The identification and quantitation involved the use of a gas chromatograph – triple quadrupole mass spectrometer (GC-QQQMS) instrument, functioning in multiple reaction monitoring (MRM) and total ion current (TIC) modes. Product analysis revealed that thermal decomposition of TBBA commenced at 723 K. The major decomposition products were HBr, di-tribrominated bisphenols, benzene, phenol, mono-tribrominated congeners of benzene and phenol, brominated and non-brominated alkylated benzenes, benzofuran, bromobenzofuran, dibenzofuran, bromine substituted polyaromatic hydrocarbons (PAHs), biphenyl and biphenylene. We observed that, most of the decomposition products evolved in trivial concentrations at a temperature of 773 K and peaked at around 923 – 973 K. Higher temperatures favour the generation of non-brominated products. In this chapter, we have performed quantum chemical calculations to derive the degradation pathways of TBBA and to illustrate routes for the formation of brominated and non-brominated species.
We constructed formation mechanisms related to the emission of PBDD/Fs in systems involving BFRs. In particular, we investigated formation corridors of (i) PXDD/Fs from the coupling reactions of 2-chlorophenoxy (2-CPhxy) and 2-bromophenoxy (2-BPhxy) radicals, (ii) PBDFs and PBDEs synthesis from the condensation reaction of monobromobenzene (MBBz) and a 2-BPhxy radical. The coupling reactions of 2-BPhxy and 2-CPhxy radicals produce keto-ether (through the additions of a phenoxy O at ortho C(H), C(Cl) and C(Br) sites) and diketo (at ortho positions to C–C bridges) structures. Keto-ethers act as direct intermediates for the formation of dioxin moieties such as dibenzo-p-dioxin (DD), 1-monochlorodibenzo-p-dioxin (1-MCDD), 1-monobromodibenzo-p-dioxin (1-MBDD), 1-bromo-6-chlorodibenzo-p-dioxin (1-B,6-CDD) and 1-bromo-9-chlorodibenzo-p-dioxin (1-B,9-CDD) molecules. Diketo adducts initiate the formation of furan species, i.e., 4-monochlorodibenzofuran (4-MCDF), 4-monobromodibenzofuran (4-MBDF) and 4-bromo-6-chlorodibenzofuran (4-B,6-CDF) compounds, through interconversion and rearrangement reactions. We found that, these mechanisms of formation, commencing from halogenated phenoxy radicals, are largely insensitive to patterns and degrees of halogenation on meta and para sites. It follows that, our developed mechanistic and kinetic factors of reactions involving 2-BPhxy and 2-CPhxy should also apply to higher halogenated phenoxy radicals.
We explored the initial oxidative decomposition pathways of monobromobenzene (MBBz) in the generation of BPhxy radicals and examined the possible dimerisation reactions of MBBz and 2-BPhxy. It was found that, the coupling of MBBz and 2-BPhxy results in the generation of twelve pre-PBDF intermediates, of which four can also serve as building blocks for the synthesis of PBDEs. The resonance-stabilised structure of the o-BPhxy radical accumulates more spin density character on its phenoxy O atom (30.9 %) in reference to ortho-C and para-C sites. Thus, the formation of the pre-PBDE/pre-PBDF structures via O/o-C couplings advances faster, as it requires lower activation enthalpies (79.2 – 84.9 kJ mol-1) than the pre-PBDF moieties, which arise via pairing reactions involving o-C(H or Br)/o-C(H or Br) sites (97.2 – 180.2 kJ mol-1). Kinetic analysis indicates that the O/o-C pre-PBDE/pre-PBDF adducts self-eject the out-of-plane H atoms to produce PBDEs, rather than undergo a three-step mechanism that forms PBDFs. Since the formation mechanisms of PBDFs and PBDDs are typically only sensitive to the bromination at ortho positions, the results reported herein also apply to higher brominated isomers of BBzs.
Overall, this thesis provides novel and comprehensive information on the thermochemical properties of the complete series of BCPhs (potential precursors to PXDD/Fs) and the electronic/structural characteristics of BFRs and their derived BPhs, with regards to their photodecomposition. To gain an insight into the degradation of TBBA once it has evaporated, this thesis examines the pure gas phase decomposition of TBBA and suggests mechanisms by which the experimentally-detected volatile organic compounds (VOCs) and semi-volatile organic compounds (SVOCs) are generated. Furthermore, this thesis explores the role of BPhs and CPhs as building blocks for the formation of PXDD/Fs, and computes their parameters. We also elucidate reaction pathways and thermo-kinetic parameters for PBDFs and PBDEs produced by the oxidation of BBzs.
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CARLE, AXEL BJORN. « A Mechanistic Investigation of the Photochemical and Thermal Activation of 2,2- and 2,3-Diaryl- and 2,2,3-Triaryl-2,3-dihydro-phenanthro[9,10-b]-1,4-dioxins, a New Class of 1,4-Dioxene Based DNA Cleaving Agents ». University of Cincinnati / OhioLINK, 2002. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1016478287.
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Phan, Duong Ngoc Chau. « The relationship between fly ash chemistry and the thermal formation of polychlorinated pollutants during waste incineration ». Doctoral thesis, Umeå universitet, Kemiska institutionen, 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-80186.
Texte intégralRésumé :
The thermal formation of polychlorinated dibenzo-p-dioxins (PCDDs), dibenzofurans (PCDFs), biphenyls (PCBs), and naphthalenes (PCNs) is a major problem in waste incineration. Ideally, rather than relying on air cleaning systems and treatment techniques, their formation should be minimized or, if possible eliminated. The work presented in this thesis was conducted to obtain a deeper understanding of the thermal formation of PCDDs, PCDFs, PCBs, and PCNs during incineration using a 5 kW laboratory scale incinerator and two artificial wastes that were designed to reflect regional differences in waste composition. The first part of the thesis focuses on the validation of a recently-developed flue-gas sampling probe with enhanced cooling capabilities. Artifact formation of PCDDs and PCDFs can occur during the sampling of hot flue gases if the cooling is insufficient. The new probe was successfully used to collect samples at 700 °C without biasing the measured POP levels. The thermal formation of PCDDs, PCDFs, PCBs, and PCNs in the post-combustion zone of the incinerator was then studied by collecting flue gas samples at 400 °C, 300 °C, and 200 °C during the incineration of the two artificial wastes. Highly chlorinated POPs were formed in larger quantities when burning the waste with the higher content of metals and chlorine, which suggests that high metal levels in the waste favor the chlorination of less chlorinated POPs or otherwise facilitate the formation of highly chlorinated polyaromatics, possibly via the condensation of highly chlorinated phenols. The concentrations of these pollutants and the abundance of highly chlorinated homologues increased as the flue gas cooled. Fly ash particles play an important role in thermal POP formation by providing essential elements (carbon, chlorine, etc.) and catalytic sites. The chemical and mineralogical properties of fly ash samples were studied by X-ray diffraction (XRD), Fourier Transform Infrared (FTIR), Scanning Electron Microscopy/Energy Dispersive X-ray (SEM/EDX), and X-ray photoelectron spectroscopy (XPS) to determine their impact on thermal POP formation. Orthogonal Partial Least Squares (OPLS) modeling was used to identify correlations between the observed POP distributions and the physicochemical data. This investigation provided new insights into the impact of fly ash chemistry on thermal POP formation. In addition, the POP isomer distribution patterns generated during waste combustion were examined. These patterns are used to “fingerprint” mechanisms of POP formation. It was found that wastes containing large quantities of metals and chlorine favored the formation of highly chlorinated homologues including the very toxic 2,3,7,8-congeners. The data suggest that reducing fly ash emissions might increase the SO2 content of the flue gas and thereby suppress the Deacon process and the formation of harmful highly chlorinated aromatic species.
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Wörner, Ralf. « Oxydation du dibenzofurane : application à l'abattement des dioxines ». Vandoeuvre-les-Nancy, INPL, 1997. http://www.theses.fr/1997INPL063N.
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La plupart des procédés thermiques conduisent à la formation de dioxine (PCDD/F) à l'état de traces. Leur toxicité et leur faible biodégradabilité nécessitent de minimiser ces rejets par tous les moyens disponibles (modification du procédé, traitement des émissions, etc. ). Dans le cas des incinérateurs, notre étude bibliographique révèle que la zone de refroidissement des fumées joue un rôle particulièrement important sur la formation des PCDD/F. Des études approfondies effectuées sur des micropilotes ont permis d'identifier trois voies indépendantes conduisant à la formation de ces produits : une formation en phase gazeuse vers 600°C, une formation catalytique en présence de poussières de 300°C à 500°C et finalement la réaction de-novo par gazéification des poussières à 300°C. Nous en avons conclu que seule une amélioration de la combustion permettait de réduire la quantité de PCDD/F émis mais également celle d'autres produits imbrulés indésirables. Nos résultats expérimentaux sur l'oxydation du dibenzofurane en phase gazeuse et à des températures relativement élevées (> 900°C) prouvent que la teneur en oxygène ainsi que le régime d'écoulement sont les paramètres primordiaux et qu'une richesse d'environ 0,8 conduit à une combustion totale des imbrulés. Enfin, nous avons construit un mécanisme détaillé appliqué à l'oxydation du dibenzofurane qui permet d'expliquer qualitativement nos observations expérimentales et qui semble être en bon accord avec les hypothèses faites par d'autres équipes de recherche sur l'oxydation des produits aromatiques à haute température
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Fernandes, M. H. R. « Formation of diazopeptides by nitrogen dioxide ». Thesis, Imperial College London, 1986. http://hdl.handle.net/10044/1/38006.
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Lian, Zhuoyang. « Biodegradable polymer particle formation using supercritical carbon dioxide ». Access to citation, abstract and download form provided by ProQuest Information and Learning Company ; downloadable PDF file 2.84 Mb., 293 p, 2006. http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&res_dat=xri:pqdiss&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&rft_dat=xri:pqdiss:1435248.
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Visez, Nicolas. « Étude des processus hétérogènes de formation et de destruction des "dioxines" ». Lille 1, 2005. https://pepite-depot.univ-lille.fr/LIBRE/Th_Num/2005/50376-2005-Visez.pdf.
Texte intégralRésumé :
L'objectif de ce travail est l'apport d'une meilleure compréhension des mécanismes hétérogénes de formation et de destruction des dioxines dans les procédés de combustion industriels. Les deux voies hétérogènes de formation des dioxines ont èté étudiées. La synthèse par précurseurs (voie I) et la synthèse de novo (voie II). Concernant la voie I, les processus de dégradation thermique du 2-chlorophénol (précurseur) ont été étudiés en présence de CuCl2, ou de CuCI par la technique des tubes scellés. Les principaux produits formés ont èté identifiés et quantifiés en fonction de la température (250-400'C) et du temps de séjour (1-120 min. ), en présence de différents oxydes (Al2O3, MgO et SiO2) et avec un ajout d'urée (inhibiteur de la fonnation des dioxines). Les paramètres influents ont été identifiés et des corrélations entre divers produits formés établies. En particulier, les réactions de chloration du précurseur et de dégradation des composés organiques chlorés sont les facteurs influençant fortement les concentrations des dioxines. Les polychlorobenzènes ont notamment été observés en tant que produits de dégradation thermique des "dioxines". Pour la voie II, la combustion de carbone activé en présence de CuCI, a été étudiée à 350'C dans un réacteur ouvert à lit fixe. L'analyse cbromatograpbique des produits formés a mis en évidence deux phases réactionnelles successives. Une première phase rapide d'oxydation du carbone activé suivie d'une phase lente de dégradation thermique du résidu de combustion. La concentration maximale en dioxines a été obtenue pour des temps de séjour longs, suggérant leur formation à partir du résidu de la combustion du carbone.
15
Visez, Nicolas Sawerysyn Jean-Pierre. « Étude des processus hétérogènes de formation et de destruction des "dioxines" ». Villeneuve d'Ascq : Université des sciences et technologies de Lille, 2007. https://iris.univ-lille1.fr/dspace/handle/1908/302.
Texte intégralRésumé :
Reproduction de : Thèse de doctorat : Structure et dynamique des systèmes réactifs : Lille 1 : 2005.N° d'ordre (Lille 1) : 3724. Résumé en français et en anglais. Titre provenant de la page de titre du document numérisé. Bibliogr. p. 227-250.
16
Stamp, Louise Michelle. « Alkene synthesis and polycarbonate formation in supercritical carbon dioxide ». Thesis, University of Cambridge, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.619690.
Texte intégral
17
Chawla, Sandeep Kumar. « Film formation on copper in moist air-sulfur dioxide ». Case Western Reserve University School of Graduate Studies / OhioLINK, 1990. http://rave.ohiolink.edu/etdc/view?acc_num=case1059053796.
Texte intégral
18
Yates, Matthew Zachariah. « Latex formation and steric stabilization in supercritical carbon dioxide / ». Digital version accessible at:, 1999. http://wwwlib.umi.com/cr/utexas/main.
Texte intégral
19
Webb, Kimberly F. « Formation of electrically condution polymer blends using supercritical carbon dioxide ». Thesis, Georgia Institute of Technology, 1998. http://hdl.handle.net/1853/10121.
Texte intégral
20
Chen, Hsiao-Hui. « Formation of low temperature silicon dioxide films using chemical vapor deposition / ». Online version of thesis, 1991. http://hdl.handle.net/1850/11160.
Texte intégral
21
Gultekin, Cagdas. « Feasibilty Study Of Sequestration Of Carbon Dioxide In Geological Formations ». Master's thesis, METU, 2011. http://etd.lib.metu.edu.tr/upload/12612756/index.pdf.
Texte intégralRésumé :
Although there are some carbon capture and storage (CCS-CO2 sequestration) projects in all over the world, feasibility problems exist due to the high economical issues. The aim of this study is to evaluate the feasibility of a potential CCS project where the source of CO2 is Afsin Elbistan Thermal Power Plant. Selection of candidate sites in the vicinity of Diyarbakir, Batman and Adiyaman regions depends on sequestration criteria. According to sequestration criteria, CCS can be applied to Çaylarbasi mature oil field, Midyat saline aquifer and Dodan CO2 gas field. Disposing of CO2 from the source of Afsin Elbistan Thermal Power Plant is analyzed by pipeline and tanker. CO2 capturing technologies are determined from published literature. CO2 transportation can be applied by pipeline or tanker. CO2 transportation cost by pipeline and tanker are compared. It has been calculated that, transportation by pipeline is more economical compared to tanker transportation. It is further found that the number of boosting pump stations, the length of the pipeline and CO2 mass flow rate are the issues that alter the economical aspect in the pipeline transportation. The transportation costs by tankers depend on fuel cost, distance, tanker storage capacity, pin-up cost and CO2 storage facilities. The final part of CCS project is injection and storage of CO2 to the candidate areas. Reservoir parameters which are reservoir temperature, viscosity, permeability, reservoir pressure, reservoir thickness, CO2 density mass flow rate and injection pipe diameter determine the number and cost of the injection wells.
22
Rawlins, Charles Henry. « Geological sequestration of carbon dioxide by hydrous carbonate formation in steelmaking slag ». Diss., Rolla, Mo. : Missouri University of Science and Technology, 2008. http://scholarsmine.mst.edu/thesis/pdf/Rawlins_09007dcc804d4f95.pdf.
Texte intégralRésumé :
Thesis (Ph. D.)--Missouri University of Science and Technology, 2008.Vita. The entire thesis text is included in file. Title from title screen of thesis/dissertation PDF file (viewed April 18, 2008) Includes bibliographical references.
23
Flett, Matthew Alexander. « Subsurface re-injection of carbon dioxide for greenhouse gas control : influence of formation heterogeneity on reservoir performance ». Thesis, Curtin University, 2008. http://hdl.handle.net/20.500.11937/1802.
Texte intégralRésumé :
The injection of carbon dioxide (CO2) into saline formations for the purpose of limiting greenhouse gas emissions has been proposed as an alternative to the atmospheric venting of carbon dioxide. In the evaluation process for selecting a potential target saline formation for the disposal of carbon dioxide, flow characterisation of the disposed plume should be undertaken by reservoir simulation of the target formation. The movement of injected carbon dioxide in the saline formation is influenced by many factors including the physics of carbon dioxide at deep formation depths and pressure, physical interactions with formation rock and pore water and variations in the rock flow pathways through changes in formation heterogeneity. This thesis investigates the roles of physical interactions on the disposal of carbon dioxide and the ability to contain the injected gas through evaluation of trapping mechanisms such as dissolution of CO2 in formation water and residual gas trapping through the process of gas-water relative permeability hysteresis. Variable formation heterogeneity is evaluated for its impact on the migration of injected CO2 plume movement and the role of formation heterogeneity in impeding or accelerating the immobilisation of injected carbon dioxide. Multiple reservoir simulation studies were conducted to evaluate, initially, the role of different trapping mechanisms in immobilising the movement of injected carbon dioxide and subsequently, the role of variations in formation rock in the migration and trapping of and injected plume of carbon dioxide. The major simulation study shows that the selection process for identifying appropriate saline formations should not only consider their size and permeability but should also consider their degree of heterogeneity endemic to the formation.A set of reservoir performance metrics were developed for the CO2 disposal projects. The metrics were applied to compare plume migration of injected CO2 (both vertically and laterally) and containment (through dissolution and residual phase trapping) in these studies. The findings demonstrate how formation heterogeneity has a significant impact on the subsurface behaviour of the carbon dioxide. Formation dip influences the rate of migration, with low formation dipping reservoirs having slower rates of vertical migration. Increasing the tortuousity of the migration flow path by either increasing the shale (non-reservoir) content or lengthening the shale baffles in the formation (corresponding to a gradual decrease in reservoir quality), can progressively inhibit the vertical flow of the plume whilst promoting its lateral flow. The increase in the tortuosity of the CO2 migration pathway delays the migration of CO2 and increases the residence time for the CO2 in the formation. Thus, formation heterogeneity impedes the onset of residual gas trapping through hysteresis effects. Ultimately less carbon dioxide is likely to collect under the seal in heterogeneous formations due to increased reservoir contact and long residence times, thereby reducing the risk of seepage to overlying formations.Given sufficient permeability for economic injection of CO2, then low to mid net-to-gross heterogeneous saline formations with low formation dip and lengthy intra-bedded shales are desirable for selection for the geological disposal of CO2. Detailed reservoir characterisation of any potential geological disposal saline formations is required in order to accurately predict the range of outcomes in the long term flow characterisation of injected CO2 into those formations.
24
Parthasarathy, Hariprasad. « Arsenic Dissolution from Sedimentary Formations under Geologic Carbon Dioxide Storage Conditions ». Research Showcase @ CMU, 2014. http://repository.cmu.edu/dissertations/488.
Texte intégralRésumé :
The overall goal of this Ph.D. study was to investigate the mobilization of arsenic (As) from sedimentary formations under conditions representative of geologic carbon dioxide storage (GCS) i.e., high pressure, temperature, and salinity. GCS is a promising technology for the mitigation of increasing CO2 emissions in the atmosphere. It primarily involves the capture of CO2 from point sources, followed by transport and injection into deep subsurface formations for long-term storage. Of the potential subsurface formations under consideration in the United States, saline formations, characterized by the presence of high salinity brines, are estimated to have the largest storage capacity. Potential for leakage of injected CO2, native brines, and CO2- saturated brines from these reservoirs exists and may lead to an increase in mineral dissolution from reservoir formations, and leakage pathways. Of particular interest in the risk assessment of GCS is the dissolution and mobilization of toxic metals such as arsenic (As) and lead. The primary mineral source of As in high and low permeability sedimentary formations is arsenopyrite (FeAsS (s)). While the oxidative dissolution of FeAsS (s) has been reported in the literature, the dissolution of FeAsS (s) under anoxic, high salinity conditions of GCS remains unexplored. To conduct dissolution experiments at high pressure, temperature, and salinity, a small-scale plug-flow system capable of measuring dissolution rates without mass transfer limitations was designed and constructed. The capacity of the system in measuring dissolution rates under GCS conditions was validated. The plug-flow system is capable of accurate and rapid measurement of dissolution rates for minerals with slow and moderate dissolution rates, with a maximum rate limitation of 5 x10-5 mol/m2s at a flow rate of 10 ml/min. To enable accurate determination of reaction rates, a method for preparation of uniformly sized arsenopyrite particles free of surface oxides was developed. The method involves sonication of crushed minerals with ethanol, washing with 12N HCl, and 50% ethanol, followed by drying in N2. Analysis of the arsenopyrite surface with X-ray photoelectron spectroscopy revelealed that the method was successful in removing all the oxides of As and S on the surface, while only 12% of Fe was left oxidized. Subsequently, the dissolution of arsenopyrite, galena, and pyrite in low-concentration alkali and alkaline metal chloride solutions under anoxic conditions was investigated. Further, the effect of Na-Ca-Cl brines on the release of arsenic was determined under ambient as well as GCS conditions. The result of these experiments revealed that electrolytes traditionally considered inert, such as NaCl, CaCl2, and MgCl2 are capable of effecting sulfide mineral dissolution. In particular, the dissolution of As increased with increasing cation activity, and the dissolution of sulfur decreased with an increase in chloride ion activity in solution. Dissolution experiments with 1.5M Na-Ca-Cl brines resulted in arsenic dissolution rates in the range of 10-10 to 10-11 mol/m2 s under anoxic conditions. The rate of As release was found to be dependent on the CaCl2 content of these Na-Ca-Cl brines. Upon the introduction of CO2 into the system, the dissolution rate of As decreased and was determined to be in the range of 10-11 to 10-12 mol/m2s. For comparison, the rate of As release from arsenopyrite under oxic conditions is in the range of X to Y mol/m2 s. Finally, dissolution experiments aimed at understanding the release of As from naturally occurring seal rocks of a GCS formation were conducted. A primary seal rock and two secondary seal rocks were obtained from the Cranfield oil field CO2- EOR site in Mississippi. The rock samples were characterized by micro Xray adsorption near edge structure analysis, which revealed that multiple sources of As exist in the reservoir seal rocks studied. Dissolution experiments with seal rocks and anoxic brines of 105g/L NaCl resulted in the dissolution of arsenic in concentrations of 70 to 80 ppb at steady state. Dissolution of CO2 in the brine had no discernible effect on the steady state release concentration of As.
25
Adeyemo, Adebola. « Post combustion capture of carbon dioxide through hydrate formation in silica gel column ». Thesis, University of British Columbia, 2008. http://hdl.handle.net/2429/531.
Texte intégralRésumé :
Carbon dioxide CO₂capture through hydrate formation is a novel technology under consideration as an efficient means of separating CO₂from flue/fuel gas mixtures for sequestration and enhanced oil recovery operations. This thesis examines post-combustion capture of CO₂from fossil-fuel power plant flue-gas streams through hydrate formation in a silica gel column. Power plant flue-gas contains essentially CO₂and nitrogen (N2) after suitable pre-treatment steps, thus a model flue-gas comprising 17% co₂and 83% N2 was used in the study. Previous studies employed a stirred-tank reactor to achieve water-gas contact for formation of hydrates; recent microscopic studies involved using water dispersed in silica gel to react with gas, showing potential for improved hydrate formation rates without the need for agitation. This study focuses on macroscopic kinetics of hydrate formation in silica gel to evaluate hydrate formation rates, CO₂separation efficiency and determining optimal silica gel properties as a basis for a CO2 capture process.
Spherical silica gels with 30.0 and 100.0 nm pore sizes and 40-75 and 75-200 μm particle sizes were studied to determine pore size and particle size effects on hydrate formation. 100.0 nm pores achieved higher gas uptake and CO₂recovery over the 30.0 nm case. Improved CO₂separation was obtained when 75-200 μm particles with 100.0 nm pores were used. The two effects observed are due to improved gas diffusion occurring with larger pore and particle size, favouring increased hydrate formation. Compared to stirred-tank experiments, results in this study show a near four-fold increase in moles of gas incorporated in the hydrate per mole of water, showing that improved water-to-hydrate conversion is obtained with pore-dispersed water. At similar experimental conditions, CO₂recovery improved from 42% for stirred-tank studies to 51% for the optimum silica (100.0 nm 75-200 μm) determined in this study. Finally, effects of tetrahydrofuran (THF) - an additive that reduces operating pressure were evaluated. Experiments with 1 mol% THF, the optimum determined from previous stirred tank studies, showed improved gas consumption in silica but reduced CO₂recovery, indicating that the optimum concentration for use in silica is different from that in stirred-tank experiments.
26
Indu, Bhart. « Kinetics and mechanism of methanol-chlorate reaction in the formation of chlorine dioxide ». Diss., Georgia Institute of Technology, 1993. http://hdl.handle.net/1853/10956.
Texte intégral
27
Burke, Michael A. « Kinetics of the chlorate-hydrogen peroxide reaction in the formation of chlorine dioxide ». Thesis, Georgia Institute of Technology, 1993. http://hdl.handle.net/1853/11817.
Texte intégral
28
Sirokman, Gergely. « (N-heterocyclic-carbene)Copper(I)-catalyzed carbon-carbon bond formation using carbon dioxide ». Thesis, Massachusetts Institute of Technology, 2007. http://hdl.handle.net/1721.1/39584.
Texte intégralRésumé :
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemistry, 2007.Vita.
Includes bibliographical references.
This thesis presents work towards the development of a new catalytic C-C bond forming reaction. Alkynes and olefins insert into [(IPr)CuH]2 (IPr = N,N-bis-(2,6-diisopropylphenyl)-1,3-imidazol-2-ylidene) to give copper vinyl and copper alkyl complexes. These copper complexes insert CO2 into the Cu-C bond to form copper acrylate and copper carboxylate complexes. Acrylic and carboxylic acids can be isolated by hydrolysis. A catalytic cycle based on (IPr)copper(I) was developed. Alkynes undergo reductive carboxylation to give acrylic acids in moderate yields. Unexpected interactions between several components of the catalytic system led to a number of side reaction, most importantly between [(IPr)CuH]2 and the product silyl acrylate. The use of silylcarbonate salts to desylilate the product enhanced yield. In addition, silylcarbonates can also serve as a source of CO2.
by Gergely Sirokman.
Ph.D.
29
Tsang, Melanie Wing-Sze. « Pd-catalysed carbon-heteroatom bond formation and urea synthesis in supercritical carbon dioxide ». Thesis, University of Cambridge, 2006. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.614105.
Texte intégral
30
Hajizadeh, Yaghoub. « Influence of PAH, SO2 and NH3 on Dioxin Formation, and the Effectiveness of Waste Derived Activated Carbons on Control of Dioxin Emissions from Waste Incineration ». Thesis, University of Leeds, 2011. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.534431.
Texte intégral
31
Flett, Matthew Alexander. « Subsurface re-injection of carbon dioxide for greenhouse gas control : influence of formation heterogeneity on reservoir performance ». Curtin University of Technology, Dept. of Petroleum Engineering, 2008. http://espace.library.curtin.edu.au:80/R/?func=dbin-jump-full&object_id=18597.
Texte intégralRésumé :
The injection of carbon dioxide (CO2) into saline formations for the purpose of limiting greenhouse gas emissions has been proposed as an alternative to the atmospheric venting of carbon dioxide. In the evaluation process for selecting a potential target saline formation for the disposal of carbon dioxide, flow characterisation of the disposed plume should be undertaken by reservoir simulation of the target formation. The movement of injected carbon dioxide in the saline formation is influenced by many factors including the physics of carbon dioxide at deep formation depths and pressure, physical interactions with formation rock and pore water and variations in the rock flow pathways through changes in formation heterogeneity. This thesis investigates the roles of physical interactions on the disposal of carbon dioxide and the ability to contain the injected gas through evaluation of trapping mechanisms such as dissolution of CO2 in formation water and residual gas trapping through the process of gas-water relative permeability hysteresis. Variable formation heterogeneity is evaluated for its impact on the migration of injected CO2 plume movement and the role of formation heterogeneity in impeding or accelerating the immobilisation of injected carbon dioxide. Multiple reservoir simulation studies were conducted to evaluate, initially, the role of different trapping mechanisms in immobilising the movement of injected carbon dioxide and subsequently, the role of variations in formation rock in the migration and trapping of and injected plume of carbon dioxide. The major simulation study shows that the selection process for identifying appropriate saline formations should not only consider their size and permeability but should also consider their degree of heterogeneity endemic to the formation.A set of reservoir performance metrics were developed for the CO2 disposal projects. The metrics were applied to compare plume migration of injected CO2 (both vertically and laterally) and containment (through dissolution and residual phase trapping) in these studies. The findings demonstrate how formation heterogeneity has a significant impact on the subsurface behaviour of the carbon dioxide. Formation dip influences the rate of migration, with low formation dipping reservoirs having slower rates of vertical migration. Increasing the tortuousity of the migration flow path by either increasing the shale (non-reservoir) content or lengthening the shale baffles in the formation (corresponding to a gradual decrease in reservoir quality), can progressively inhibit the vertical flow of the plume whilst promoting its lateral flow. The increase in the tortuosity of the CO2 migration pathway delays the migration of CO2 and increases the residence time for the CO2 in the formation. Thus, formation heterogeneity impedes the onset of residual gas trapping through hysteresis effects. Ultimately less carbon dioxide is likely to collect under the seal in heterogeneous formations due to increased reservoir contact and long residence times, thereby reducing the risk of seepage to overlying formations.
Given sufficient permeability for economic injection of CO2, then low to mid net-to-gross heterogeneous saline formations with low formation dip and lengthy intra-bedded shales are desirable for selection for the geological disposal of CO2. Detailed reservoir characterisation of any potential geological disposal saline formations is required in order to accurately predict the range of outcomes in the long term flow characterisation of injected CO2 into those formations.
32
Psathas, Petros. « Relationship between interfacial properties and formation of microemulsions and emulsions of water and supercritical carbon dioxide ». Access restricted to users with UT Austin EID, 2001. http://wwwlib.umi.com/cr/utexas/fullcit?p3035167.
Texte intégral
33
Nafday, Omkar A. « Film formation and CO₂ corrosion in the presence of acetic acid ». Ohio : Ohio University, 2004. http://www.ohiolink.edu/etd/view.cgi?ohiou1103226118.
Texte intégral
34
Lee, Charles Ted. « Water-in-carbon dioxide microemulsions and emulsions : formation, stability, and media for chemical reactions / ». Full text (PDF) from UMI/Dissertation Abstracts International, 2000. http://wwwlib.umi.com/cr/utexas/fullcit?p3004317.
Texte intégral
35
Rushing, Charles W. Rushing Charles W. « Part A, Indoaniline dye formation ; Part B, Chlorite redox chemistry / ». free to MU campus, to others for purchase, 2000. http://wwwlib.umi.com/cr/mo/fullcit?p9999311.
Texte intégral
36
Naidoo, Jacinth. « Investigation of the Pressure Dependence of SO3 Formation ». Thesis, University of North Texas, 2003. https://digital.library.unt.edu/ark:/67531/metadc4403/.
Texte intégralRésumé :
The kinetics of the pressure dependent O + SO2 + Ar reaction have been investigated using laser photolysis resonance fluorescence at temperatures of 289 K, 399 K, 581 K, 699 K, 842 K and 1040 K and at pressures from 30-665 torr. Falloff was observed for the first time in the pressure dependence. Application of Lindemann theory yielded an Arrhenius expression of k(T) = 3.3 x 10-32exp(-992/T) cm6 molecule-1 s-1 for the low pressure limit and k(T) = 8.47 x 10-14exp(-468/T) cm3 molecule-1 s-1 for the high pressure limit at temperatures between 289 and 842 K. The reaction is unusual as it possesses a positive activation energy at low temperature, yet at higher temperatures the activation energy is negative, illustrating a reaction barrier.
37
Grandelli, Heather Eilenfield. « Formation of Cyclodextrin-Drug Inclusion Compounds and Polymeric Drug Delivery Systems using Supercritical Carbon Dioxide ». Diss., Virginia Tech, 2013. http://hdl.handle.net/10919/23891.
Texte intégralRésumé :
New methods for the preparation of porous biomedical scaffolds have been explored for applications in tissue engineering and drug delivery. Scaffolds with controlled pore morphologies have been generated which incorporate cyclodextrin-drug inclusion complexes as the drug delivery component. Supercritical CO2 was explored as the main processing fluid in the complex formation and in the foaming of the polymer scaffold. The co-solvents, ethanol, ethyl acetate and acetone, were explored in each stage, as needed, to improve the solvent power of CO2.
The first goal was to promote cyclodextrin-drug complex formation. Complex formation by traditional methods was compared with complex formation driven by processing in supercritical CO2. Complex formation was promoted by melting the drug in supercritical CO2 or in CO2 + co-solvent mixtures while in the presence of cyclodextrin. Some drugs, such as piroxicam, are prone to degradation near the drug's ambient melting temperature. However, this approach using CO2 was found to circumvent drug thermal degradation, since drug melting temperatures were depressed in the presence of CO2.
The second goal was to produce porous polymeric matrices to serve as tissue engineering scaffolds. Poly(lactide-co-glycolide) and poly(ε-caprolactone) were investigated for foaming, since these biomedical polymers are already commonly used and FDA approved. Polymer foaming with CO2 is an alternative approach to conventional solvent-intensive methods for porosity generation. However, two major limitations of polymer foaming using CO2 as the only processing fluid have been reported, including the formation of a non-porous outer skin upon depressurization and limited pore interconnectivity. Approaches to circumvent these limitations include the use of a co-solvent and controlling depressurization rates. The effect of processing parameters, including foaming temperatures and depressurization rate, as well as co-solvent addition, were examined in polymer foaming using CO2. Drug release dynamics were compared for foams incorporated with either pure drug, cyclodextrin-drug physical mixture or cyclodextrin-drug complex. Pore morphology, polymer choice and drug release compound choice were found to alter drug release profiles.Ph. D.
38
Jin, Yichao. « Listeria innnocua Biofilm Formation on Food Contact Surfaces and Its inactivation by Chlorine Dioxide Gas ». The Ohio State University, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=osu1502966404221271.
Texte intégral
39
Aurell, Johanna. « Effects of Varying Combustion Conditions on PCDD/F Formation ». Doctoral thesis, Umeå universitet, Kemi, 2008. http://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-1795.
Texte intégralRésumé :
Polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs) are by-products emitted from combustion sources such as municipal solid waste (MSW) incineration plants. These organic compounds are recognized as toxic, bioaccumulative and persistent in the environment. PCDD/Fs are removed from flue gases before released from MSW incineration. However, the PCDD/Fs are not destroyed but retained in the residues, thus in the environment. Understanding the pathways that lead to their formation is important in order to develop ways to suppress their formation and prevent their release into the environment. Suppressing the formation can also allow less expensive air pollution control system to be used, and/or the costs of thermally treating the residues to be reduced. The main objective of the studies underlying this thesis was to elucidate process, combustion and fuel parameters that substantially affect the emission levels and formation of PCDD/Fs in flue gases from MSW incineration. The experiments were conducted under controllable, realistic combustion conditions using a laboratory-scale reactor combusting artificial MSW. The parameter found to most strongly reduce the PCDD/F emissions, was prolonging the flue gas residence time at a relatively high temperature (460°C). Increasing the sulfur dioxide (SO2) to hydrogen chloride (HCl) ratio to 1.6 in the flue gas was also found to reduce the PCDF levels, but not the PCDD levels. Fluctuations in the combustion process (carbon monoxide peaks), high chlorine levels in the waste (1.7%) and low temperatures in the secondary combustion zone (660°C) all tended to increase the emission levels. The PCDD/PCDF ratio in the flue gas was found to depend on the chlorine level in the waste, fluctuations in the combustion process and the SO2:HCl ratio in the flue gas. The formation pathways were found to be affected by the quench time profiles in the post-combustion zone, fluctuations in the combustion process and addition of sulfur. In addition, increased levels of chlorine in the waste increased the chlorination degrees of both PCDDs and PCDFs. A tendency for increased SO2 levels in the flue gas to increase levels of polychlorinated dibenzothiophenes (sulfur analogues of PCDFs) was also detected, however the increases were much less significant than the reduction in PCDF levels.
40
Su, Lusheng. « Formation Mechanism and Thermoelectric Energy Conversion of Titanium Dioxide Nanotube Based Multi-Component Materials and Structures ». University of Toledo / OhioLINK, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=toledo1370793126.
Texte intégral
41
Briois, Christelle. « Étude expérimentale et modélisation des processus de dégradation thermique du 2-chlorophénol : mécanisme de formation de "dioxines" en phase gazeuse ». Lille 1, 2002. https://pepite-depot.univ-lille.fr/LIBRE/Th_Num/2002/50376-2002-267.pdf.
Texte intégralRésumé :
L'oxydation thermique en phase gazeuse du 2-chlorophenol (1000 ppmV dans l'air) a été étudiée à 1 atm entre 500 et 900°C de 1 à 3 s. Les principales espèces moléculaires intermédiaires et finales ont été identifiées et quantifiées en fonction de la température et des temps de séjour. 4 dioxines sont observées dans nos conditions expérimentales. Un mécanisme chimique détaillé comportant 837 réactions réversibles et 161 espèces est proposé. Un accord relativement bon est obtenu entre les profils de concentration calculés et mesurés pour un certain nombre d'espèces. Ce mécanisme doit être complété et affiné pour rendre compte de toutes les espèces détectées. La formation hétérogène des dioxines à partir du 2-chlorophénol a également été examinée en utilisant deux types de réacteurs (lit fixe et tubes scellés). De nombreux isomères de dioxines et d'espèces précurseurs ont été identifiés. Les résultats obtenus sont discutés sur les plans qualitatif et semi-quantitatif.
42
Payyapilly, Jairaj Joseph. « Formation And Growth Mechanisms of a High Temperature Interfacial Layer Between Al and TiO2 ». Diss., Virginia Tech, 2008. http://hdl.handle.net/10919/29733.
Texte intégralRésumé :
The product of interaction between Al and TiO2 at elevated temperature has a wide range of applications in refractory, structural and electronics industries (refractory tiles, tank armor, fuel cells, and microelectronic devices). This research attempts to understand the extent of interaction between Al and TiO2 when the reactant surfaces are in contact at elevated temperature and normal atmospheric pressure. The interfacial region between the reactant compounds is examined using analytical techniques; and the formation of TiAl as the interfacial compound is described. The thermodynamics of the Al â Ti â O system is explained as it relates to the particular conditions for the Al â TiO2 reaction research. Thermodynamic principles have been used to demonstrate that the formation of TiAl is favored instead of other TixAly compounds for the set of conditions outlined in this thesis. A study of the mechanism of interactions in the interfacial region can help towards being able to determine the reaction kinetics that lead to the control of microstructure and thus an improvement in the material performance. An appropriate model that describes the formation of TiAl at the interface is described in this study. The formation of TiAl at the interface is a result of the reduction reaction between TiO2 and Al. The O released during the reduction of TiO2 has been investigated and demonstrated to partly remain dissolved in TiAl at the interfacial region. Some O reacts with Al as well to form crystalline Al2O3 in the interfacial layer.Ph. D.
43
Harris, Charissa Larine. « The Effect of Predisinfection with Chlorine Dioxide on the Formation of Haloacetic Acids and Trihalomethanes in a Drinking Water Supply ». Thesis, Virginia Tech, 2001. http://hdl.handle.net/10919/34518.
Texte intégralRésumé :
In an effort to maintain compliance with current and future United States Environmental Protection Agency regulations governing haloacetic acids (HAAs) and trihalomethanes (THMs), the Blacksburg, Christiansburg, VPI (BCVPI) Water Authority in Radford, Virginia elected to eliminate prechlorination and replace it with preoxidation using chlorine dioxide (ClO2). Prior to full-scale application at the BCVPI Water Treatment Plant, jar testing was done to determine the effects of ClO2 on the formation of HAAs and THMs.
Jar testing results showed a significant reduction in THM formation potential when 2.0 mg/L ClO2 was applied to raw water and chlorination was delayed. Chlorine dioxide doses less than 2.0 mg/L were statistically insignificant in the reduction of THM formation potentials below samples that were prechlorinated according to the BCVPI Water Treatment Plant's current practice. Likewise, ClO2 did not alter HAA formation potentials in such a way that statistical differences could be detected between ClO2 pretreatment and prechlorination, even at a dose of 2.0 mg/L ClO2.
The two inorganic byproducts of ClO2, chlorite and chlorate, were also measured following jar tests. Chlorite concentrations increased with an increased ClO2 dose, but remained below 1.0 mg/L. Chlorate was formed in all jar-test samples.Master of Science
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Peters, Teresa Baker 1981. « Clathrate hydrates in frozen confections : formation by carbon dioxide flash freezing and behavior during distribution and consumption ». Thesis, Massachusetts Institute of Technology, 2009. http://hdl.handle.net/1721.1/54872.
Texte intégralRésumé :
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2009.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Cataloged from PDF version of thesis.
Includes bibliographical references (p. 113-117).
Carbonated frozen foods are not common on the market due to the limited liquid water available to dissolve CO₂ . CO₂ clathrate hydrates can change this because CO₂ is trapped in crystalline water. The CO₂ flash-freezing process developed in this thesis forms CO₂ hydrates directly in a confection as it freezes. In this process, the confection mixture is dispersed in liquid CO₂; then the combined fluids are flashed to 10-20 bars. The mixture breaks up into small fragments, which rapidly crystallize into CO₂ hydrate (instead of ice) due to the intimate contact between mixture and evaporating CO₂ . This CO₂ hydrate formation results in a frozen, carbonated confection. CO₂ hydrates have a significant impact on packaging and storage requirements for the confection. This study shows that the minimum storage pressure is determined by the ice- CO₂ hydrate-gas equilibrium (IHG) curve, which does not change with the concentration of solutes in the aqueous phase. The minimum CO₂ content in a storage vessel is determined by the amount of CO₂ needed to avoid ice; in the presence of ice CO₂ can redistribute quickly, leading to an inhomogeneous product. Packaging must therefore be designed considering the significant CO₂ evolution from dissociating CO₂ hydrates during heat shock. Warming of a confection causes CO₂ hydrates to dissociate, even at pressures greater than the IHG pressure due to the requirement of chemical equilibrium between water in aqueous and crystalline phases. In packaging with limited heads pace, this CO₂ release increases the pressure significantly.
(cont.) When CO₂ hydrate confections are consumed CO₂ is strongly perceived both through tingling caused by carbonic acid and through tactile stimulation caused by bubbles. A higher concentration of CO 2 is required in CO₂ hydrate confections than in carbonated beverages for similar fizziness perception because a significant fraction of the CO₂ escapes when a consumer exhales. The CO₂ concentration in the melted confection does not exceed the solubility of CO₂ at atmospheric pressure, but ingredients in the recipe can modulate the growth of bubbles as the confection melts. Consumer testing is needed to define the form and style of CO₂ hydrate confection that should be pursued.
by Teresa Baker Peters.
Ph.D.
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Solovyova, A. E. « Simulation of the Mechanism of Formation of Solid Solutions in the System In2О3 – ТіO2 When Heated in Air ». Thesis, Sumy State University, 2013. http://essuir.sumdu.edu.ua/handle/123456789/35393.
Texte intégralRésumé :
On the basis of mathematical models of the formation of solid solutions in the In2O3 – ТіО2 calculated ionic radius of the cations: indium, titanium, anion and anionic vacancies on the scale of Templeton and Deben. A phase transformation in the oxide of indium was related with disorder of anionic vacancies in the lattice type C. The formation of solid solutions in this system proceeds on the basis of the disordered phase of type С1. The system formed limited solid solutions such as: subtraction – substitution – inculcation of a range of concentrations (0 – 2% ТіО2), subtraction – substitution of concentrations (0.5 – 2% іО2), higher concentrations of these compounds present in the mixture of In2TiO5-х – rhombic modification, which is formed during sintering the samples at 1100 ·C in air. The type solid solution systems in the In2O3 – ТіО2, depend on the size of cation bases and additives. The energies of formation: solid solution subtraction – substitution – introduction, solid solution subtraction – substitution were determined and shows that the conductivity of the current, concentration and mobility of the charge carriers depends on the type of the solid solution and not on the valence of the dissolved additive.
При цитуванні документа, використовуйте посилання http://essuir.sumdu.edu.ua/handle/123456789/35393
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Liu, Kun. « Miscibility, Viscosity, Density, and Formation of Polymers in High-Pressure Dense Fluids ». Diss., Virginia Tech, 2007. http://hdl.handle.net/10919/29787.
Texte intégralRésumé :
This thesis is an experimental investigation of the phase behavior, volumetric properties, and viscosity of poly (methyl methacrylate) (PMMA), poly (ε-caprolactone) (PCL) and their blends. Homopolymerization and copolymerizations of methyl methacrylate (MMA) and 2-methylene-1,3-dioxepane (MDO) in mixtures of acetone + CO2 have also been explored.
The viscosities and densities of acetone + CO2 mixtures were measured in the temperature range 323-398 K at pressures up to 35 MPa. This is the first study in which viscosity of acetone + CO2 mixtures have been measured and the mixtures have been evaluated as solvents for PCL. It is shown that PCL can be readily dissolved in these fluid mixtures at modest pressures even at high carbon dioxide levels. Investigations have been conducted over a temperature range from 323 to 398 K at pressures up to 50 MPa for polymer concentrations up to 20 wt %, and CO2 concentrations up to 60 wt %. It is shown that in these mixtures PCL is dissolved at pressures that are much lower than the pressures reported for miscibility in the mixtures of carbon dioxide with other organic solvents. It is shown that PMMA also readily dissolves at modest pressures. Blends of PMMA and PCL require higher pressures than for the individual polymers for complete miscibility.
Free-radical polymerizations of MMA in acetone at 343 K were followed using in-situ measurements of viscosity and density at different pressures from 7- 42 MPa. This is the first time viscosity has been used as a real-time probe of high pressure polymerizations. Two distinct kinetic regimes were identified. Homopolymerizations of MDO were conducted in carbon dioxide at 323 and 343 K at pressures up to 42 MPa. For the first time it is shown that high molecular weight PCL can be produced from MDO in high pressure CO2. Ring-opening free-radical copolymerizations of MDO with MMA, styrene and acrylonitrile were conducted for the first time in carbon dioxide and have been shown to lead to polymers with high molecular weights.Ph. D.
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Masuda, Yuusuke. « Development of New C-C Bond Forming Reactions Utilizing Light as Energy Source ». 京都大学 (Kyoto University), 2017. http://hdl.handle.net/2433/225634.
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Lee, David Robert. « Genesis of fault hosted carbonate fracture cements in a naturally high CO2 province, South Viking Graben, UK North Sea ». Thesis, University of Edinburgh, 2013. http://hdl.handle.net/1842/7817.
Texte intégralRésumé :
The Late Jurassic Brae oilfields in the South Viking Graben of the northern North Sea contain naturally high concentrations of carbon dioxide (up to 35 mol %). Fields immediately adjacent to the graben bounding fault display the highest concentrations, with CO2 content decreasing eastward into the basin. It is thought the CO2 was introduced into the region via this fault. This thesis examines the possible source of the high CO2 present in the region, focusing on the graben margin fault as a potential conduit for CO2 flux from depth Investigation of cored sections penetrating the graben bounding fault revealed numerous carbonate cemented fracture arrays. The morphology of the fractures and cements is attributed to hydraulic fracturing induced by episodic release of overpressured fluids up the margin fault from depth. Periods of rapid subsidence omnipresent throughout the tectonic history of the graben are conducive to the generation of overpressure; a feature commonly reported in the region. Samples from the carbonate fracture cements were analysed using a host of techniques, including SEM, EMPA, fluid inclusion, and stable δ13C ‐ δ18O analyses. Using SEM analysis, at least five generations of dolomite cement with concomitant iron sulphide were observed. Cement chemistry and textures indicate precipitation from concentrated CO2–rich fluids. A reported high salinity basinal influx from depth concomitant with proposed CO2 charge into the region ~70 Ma is a probable source for the dissolved solids subsequently precipitated as carbonate in the fracture networks. Fluid inclusion analysis provided sufficient evidence to suggest the influx of hot fluids into the region, presumably sourced from deep in the margin fill. Two distinct δ13C vs. δ18O trends are observed in the isotope data from four wells studied. The trends are interpreted as differential mixing between ascending basinal fluids rich in dissolved inorganic carbon and in situ formation waters dominated by organically derived carbon following the onset of thermal decarboxylation in the Kimmeridge Clay Formation. Dissolution of Zechstein carbonates underlying the region is a credible source for the isotopically heavy CO2 found adjacent to the graben margin (δ13CCO2 = ‐2 to ‐5 ‰) and incorporated into the carbonate cements. Inferred variations in fluid mixing from well to well have implications on the variability of fluid flow along the graben margin with respect to contrasting fault morphologies. A Rayleigh fractionation model accommodating CO2 degassing from a hot ascending isotopically heavy fluid can be invoked to explain the observed carbon‐oxygen isotopic covariations in the fracture cements. Geochemical modelling simulating the ascent of CO2‐rich waters suggests degassing has limited impact on precipitation volumes, with fluid‐rock reactions the most likely driver for extensive carbonate mineralisation observed.
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Frogneux, Xavier. « Transformations réductrices du CO2 pour la formation de liaisons C-N et C-C ». Thesis, Paris 11, 2015. http://www.theses.fr/2015PA112136/document.
Texte intégralRésumé :
Dans le monde actuel, le dioxyde de carbone (CO2) est le déchet majoritaire issu de l’utilisation des ressources fossiles mais il est encore peu utilisé dans les applications à grande échelle. Afin de tirer parti de son abondance, le développement de nouvelles transformations chimiques du CO2 pour accéder à des produits de chimie fine connait un intérêt croissant au sein de la communauté scientifique. Tout particulièrement, la formation de liaison(s) C-N à partir du CO2 et d’un substrat azotés permet d’accéder à des produits à hautes valeurs énergétiques et commerciales. Un second type de transformation désirable est la formation de liaison C-C à partir du CO2 afin de synthétiser des dérivés d’acides carboxyliques comme des esters. L’utilisation d’hydrosilanes, réducteurs doux, permet de travailler sous 1 bar de CO2 avec des catalyseurs à base de métaux peu coûteux et abondants tels que le fer et le zinc ou bien avec des organocatalyseurs. Les synthèses de formamides, de méthylamines ou d’aminals à partir du CO2 ont ainsi été développées par hydrosilylation. Enfin, la carboxylation des carbosilanes à partir du CO2 a été développée pour la première fois avec un catalyseur à base de cuivre. Dans le cas des 2-pyridylsilanes, l’utilisation de sels de fluorures pentavalents permet d’activer le substrat efficacement sans catalyseurIn the current world, carbon dioxide (CO2) is the major waste of the massive utilization of fossil resources but only few applications have been developed using this compound. In order to take advantage of its abundancy, the development of novel chemical transformation of CO2 to produce fine chemicals is of high interest in the scientific community. In particular, the formation of C-N bond(s) from CO2 and amine compounds unlocks a new way to access high energy and value-added. A second type of highly desirable transformation is the formation of C-C bonds with CO2 so as to synthesize carboxylic acid derivatives. The utilization of hydrosilanes as mild reductants allows the reactions to proceed under 1 bar of CO2 with abundant and cheap metal-based catalysts (iron, zinc) or with organocatalysts. The synthesis of formamides, methylamines and aminals from CO2 are described herein. Ultimately, the catalytic carboxylation of carbosilanes has been achieved for the first time using copper-based complexes. In the specific case of 2-pyridylsilanes, the use of pentavalent fluoride salts allowed us to perform the reaction without catalyst
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Stein, Antoinette Weil. « Investigation of the Chemical Pathway for Gaseous Nitrogen Dioxide Formation during Flue Gas Desulfurization with Dry Sodium Bicarbonate Injection ». Cincinnati, Ohio : University of Cincinnati, 2001. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=ucin997940666.
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