Preventive approach for a reduction of Polycyclic Aromatic Hydrocarbons (PAHs) in pyrolysis furnaces : Application to low-pressure gas carburizing

La cémentation gazeuse à basse pression est un procédé de traitement de surface qui consiste à renforcer des pièces en acier par diffusion d’atomes de carbone provenant de la pyrolyse d’hydrocarbures gazeux. Une partie de l’hydrocarbure craqué est adsorbée sur le métal mais une autre partie réagit en phase gazeuse et conduit, entre autres, à la formation de HAP. Or, de nombreux HAP sont toxiques, voire cancérigènes, et les salariés en charge du nettoyage ou de la maintenance des fours de cémentation peuvent y être exposés. Des expériences de pyrolyse d’acétylène ont été réalisées à 900°C et 8 kPa, conditions proches de celles des procédés de cémentation gazeuse à basse pression. Un réacteur auto-agité par jets gazeux et des réacteurs tubulaires ont été utilisés. A la sortie de la zone réactionnelle, les produits de la pyrolyse ont été analysés. Entre autres, 16 HAP considérés comme des polluants prioritaires par l’Agence de Protection de l’Environnement aux Etats-Unis (US EPA) ont été observés. L’influence du taux de dilution du réactif en entrée et du temps de passage dans le réacteur a été étudiée. Les résultats expérimentaux ont été comparés à ceux obtenus avec un modèle cinétique détaillé. Ce modèle a été développé dans le but de décrire la formation des HAP lors de la pyrolyse d’hydrocarbures légers. Une attention particulière a été portée aux voies de formation des premiers cycles aromatiques et des 16 HAP de la liste de l’EPA. En plus des données expérimentales obtenues dans le cadre de cette étude, le modèle a été validé à partir de données expérimentales de la littérature. Le but de l’étude est de comprendre les phénomènes de formation et de croissance des HAP afin de trouver des conditions opératoires permettant de rendre plus surs les procédés de cémentation gazeuse à basse pressionLow-pressure gas carburizing is a heat treatment process used to harden surface of steel by enriching the metal with carbon atoms coming from pyrolysis of hydrocarbons. At the same time, a wide variety of molecules and radicals are also formed in the gas phase. They react together, leading to the formation of PAHs. PAHs are toxic and even carcinogenic, and activities such as furnace maintenance may thus represent a risk to workers. Experiments of acetylene pyrolysis were carried out in conditions close to low-pressure gas carburizing processes, at 900°C and 8 kPa. Two kinds of reactors were used: a jet stirred reactor and tubular reactors. At the outlet of the reaction zone, products of pyrolysis were analyzed. Among other products, 16 PAHs classified as priority pollutants by the United States Environmental Protection Agency (US EPA) were observed. Influence of residence time and of reactant dilution was studied. Experimental results were compared to those obtained with a detailed kinetic model. This model was developed in order to describe PAH formation during light hydrocarbon pyrolysis. The focus was placed on formation pathways of the first aromatic rings and of the 16 EPA-PAHs. In addition to the experimental data obtained in this study, the model was validated using experimental data from the literature. The aim of the study is to understand the phenomena of PAH formation and growth in order to find operating conditions to make safer the low-pressure gas carburizing processe

Approche préventive pour une réduction des Hydrocarbures Aromatiques Polycycliques (HAP) dans les fours à pyrolyse : application à la cémentation gazeuse à basse pression

Low-pressure gas carburizing is a heat treatment process used to harden surface of steel by enriching the metal with carbon atoms coming from pyrolysis of hydrocarbons. At the same time, a wide variety of molecules and radicals are also formed in the gas phase. They react together, leading to the formation of PAHs. PAHs are toxic and even carcinogenic, and activities such as furnace maintenance may thus represent a risk to workers. Experiments of acetylene pyrolysis were carried out in conditions close to low-pressure gas carburizing processes, at 900°C and 8 kPa. Two kinds of reactors were used: a jet stirred reactor and tubular reactors. At the outlet of the reaction zone, products of pyrolysis were analyzed. Among other products, 16 PAHs classified as priority pollutants by the United States Environmental Protection Agency (US EPA) were observed. Influence of residence time and of reactant dilution was studied. Experimental results were compared to those obtained with a detailed kinetic model. This model was developed in order to describe PAH formation during light hydrocarbon pyrolysis. The focus was placed on formation pathways of the first aromatic rings and of the 16 EPA-PAHs. In addition to the experimental data obtained in this study, the model was validated using experimental data from the literature. The aim of the study is to understand the phenomena of PAH formation and growth in order to find operating conditions to make safer the low-pressure gas carburizing processesLa cémentation gazeuse à basse pression est un procédé de traitement de surface qui consiste à renforcer des pièces en acier par diffusion d’atomes de carbone provenant de la pyrolyse d’hydrocarbures gazeux. Une partie de l’hydrocarbure craqué est adsorbée sur le métal mais une autre partie réagit en phase gazeuse et conduit, entre autres, à la formation de HAP. Or, de nombreux HAP sont toxiques, voire cancérigènes, et les salariés en charge du nettoyage ou de la maintenance des fours de cémentation peuvent y être exposés. Des expériences de pyrolyse d’acétylène ont été réalisées à 900°C et 8 kPa, conditions proches de celles des procédés de cémentation gazeuse à basse pression. Un réacteur auto-agité par jets gazeux et des réacteurs tubulaires ont été utilisés. A la sortie de la zone réactionnelle, les produits de la pyrolyse ont été analysés. Entre autres, 16 HAP considérés comme des polluants prioritaires par l’Agence de Protection de l’Environnement aux Etats-Unis (US EPA) ont été observés. L’influence du taux de dilution du réactif en entrée et du temps de passage dans le réacteur a été étudiée. Les résultats expérimentaux ont été comparés à ceux obtenus avec un modèle cinétique détaillé. Ce modèle a été développé dans le but de décrire la formation des HAP lors de la pyrolyse d’hydrocarbures légers. Une attention particulière a été portée aux voies de formation des premiers cycles aromatiques et des 16 HAP de la liste de l’EPA. En plus des données expérimentales obtenues dans le cadre de cette étude, le modèle a été validé à partir de données expérimentales de la littérature. Le but de l’étude est de comprendre les phénomènes de formation et de croissance des HAP afin de trouver des conditions opératoires permettant de rendre plus surs les procédés de cémentation gazeuse à basse pressio

Acetylene pyrolysis in a jet-stirred-reactor for low pressure gas carburizing process- Experiments, kinetic modeling and mixing intensity investigations by CFD simulation

International audienceLow-pressure gas carburizing is used to harden steel, it has been shown to be a source of considerable PAH (Polycyclic Aromatic Hydrocarbon) pollution. Some PAH, like benzo[a]pyrene, are carcinogenic, and activities such as furnace maintenance and cleaning operations may thus represent a risk to workers. Occupational exposure during these operations should therefore be reduced. Benzene is a specific chemical marker of PAH, and the aim of the study was to understand its formation. Acetylene pyrolysis was experimentally performed in a jet-stirred-reactor in the laboratory, in conditions close to those encountered in industrial processes (1173 K and 8 kPa). Products of pyrolysis were analyzed by gas chromatography (TCD, FID) at the outlet from the reaction zone. The influence of residence time in the reactor was studied. A detailed kinetic model assuming an ideal continuous stirred tank reactor was used to describe the formation of chemical compounds and validate experimental data. CFD simulations were performed to characterize the reactor’s hydrodynamics by applying the theory of the free jet. They allowed putting forward one explanation to understand the deviation between experiments and the kinetic model

Hydrothermal liquefaction and partial oxidation of microalgae : influence of lipid content

International audienceMicroalgae allow the production of third generation bio-fuels through various conversion routes. Because of the high amount of water in this biomass, hydrothermal liquefaction is particularly appropriate for the conversion of microalgae into liquid fuels. Microalgae mainly consist of proteins, lipids and carbohydrates. Lipids are easily recoverable and often extracted by different methods. Some do not need to dry the biomass, such as some solvent extraction (with dimethyl ether, 1,2-dimethoxyethane, etc.). Thus, the valorization described here can follow a first step of lipid extraction

Hydrothermal liquefaction and partial oxidation of microalgae : influence of lipid content

International audienceMicroalgae allow the production of third generation bio-fuels through various conversion routes. Because of the high amount of water in this biomass, hydrothermal liquefaction is particularly appropriate for the conversion of microalgae into liquid fuels. Microalgae mainly consist of proteins, lipids and carbohydrates. Lipids are easily recoverable and often extracted by different methods. Some do not need to dry the biomass, such as some solvent extraction (with dimethyl ether, 1,2-dimethoxyethane, etc.). Thus, the valorization described here can follow a first step of lipid extraction

2019 FIRE RETARDANCY ODYSSEY: A JOURNEY THROUGH THE MECHANISMS

Mechanisms of action are revisited through two case studies: (i) soot morphology released from EVA and EVA/ATH and (ii) anisotropy of heat gradient in intumescent PP

Modeling of Polycyclic Aromatic Hydrocarbon (PAH) formation during hydrocarbon pyrolysis

International audienceHydrocarbon pyrolysis in low-Pressure gas carburizing conditions drives to gas phase reactions which lead to the production of Polycyclic Aromatic Hydrocarbons (PAHs). These PAHs are afterwards responsible for soot formation. The aim of the study is to predict the formation of mainly sixteen PAHs considered as priority pollutants by the Environmental Protection Agency in the United States (US EPA). Some of them, like benzo(a)pyrene, are carcinogens. A model has been implemented in order to describe the reaction pathways leading to these PAHs. The model was validated using experimental data from the literature, obtained in the case of pyrolysis of different hydrocarbons. Results for ethylene pyrolysis are more specifically presented in this paper. Flux analyses were realized in order to determine the main reaction pathways leading to benzene

INTUMESCENT POLYOLEFINS: A JOURNEY FROM FIRE BEHAVIOR TO MECHANISTIC ASPECTS

International audienc

Polycyclic aromatic hydrocarbon (PAH) formation during acetylene pyrolysis in tubular reactor under low pressure carburizing conditions

International audienceLow-pressure carburizing involves hydrocarbon pyrolysis, which leads to a fast gas-phase formation of polycyclic aromatic hydrocarbons (PAHs), some of which, such as benzo[a]pyrene, are carcinogenic. Workers can be exposed to these PAHs during maintenance and cleaning operations of carburizing furnaces. Experiments of acetylene pyrolysis were carried out in conditions close to low-pressure gas carburizing processes, at 1173 K and 8 kPa, in tubular reactors. At the outlet of the reaction zone, the reactant and the reaction products were analyzed by gas chromatography (TCD, FID and MS). Amongst other products, 16 PAHs classified as priority pollutants by the United States Environmental Protection Agency (US EPA) were observed and quantified. The study of the influence of residence time and of inlet reactant concentration shows that amounts of PAHs increase with residence time at low acetylene concentration but slightly decrease with pure acetylene due to the conversion of PAHs into soot. Results were compared to simulation results obtained with a detailed kinetic model of light hydrocarbon pyrolysis

Intumescent polypropylene: Interactions between physical and chemical expansion

International audienceTo decrease the reaction to fire of a highly flammable plastic, polypropylene (PP), theconcept of intumescence was applied. Two intumescent systems were designed onthe basis of different mechanisms: physical expansion with expandable graphite (EG)and chemical expansion with modified ammonium polyphosphate (AP). Fire behaviorof PP containing EG, AP, or an AP/EG mixture with a total loading of 10 wt% wasevaluated by cone calorimetry at 35 kW m−2. Thermocouples allowed measuring thetemperature at the backside or inside samples over time and evaluating the thermalbarrier of these intumescent materials. Two grades of AP (difference in composition)and several grades of EG (difference in expansion characteristics) were compared.Mixing AP and EG does not create a synergistic effect in studied conditions. Contrarily,the incorporation of small amount of EG in PP-AP modifies heat transfer inthe coating, creating a strong anisotropy. Graphite worms are trapped vertically intothe expanded AP, which increases the transverse heat conductivity (lower efficiencyof the thermal barrier) and decreases the fire performance. This phenomenon disappearsin thicker specimens. While a higher expansion volume of graphite wormsimproves fire performances of PP with only small amount of EG (1 wt%), this effect isnot noticeable with AP/EG mixtures