Production Of Aromatic Hydrocarbons Research Articles

Catalyst-Free Oxidation Reactions in a Microwave Plasma Torch-Based Ion/Molecular Reactor: An Approach for Predicting the Atmospheric Oxidation of Pollutants.

The atmospheric oxidation of chemicals has produced many new unpredicted pollutants. A microwave plasma torch-based ion/molecular reactor (MPTIR) interfacing an online mass spectrometer has been developed for creating and monitoring rapid oxidation reactions. Oxygen in the air is activated by the plasma into highly reactive oxygen radicals, thereby achieving oxidation of thioethers, alcohols, and various environmental pollutants on a millisecond scale without the addition of external oxidants or catalysts (6 orders of magnitude faster than bulk). The direct and real-time oxidation products of polycyclic aromatic hydrocarbons and p-phenylenediamines from the MPTIR match those of the long-term multistep environmental oxidative process. Meanwhile, two unreported environmental compounds were identified with an MPTIR and measured in the actual water samples, which demonstrates the considerable significance of the proposed device for both predicting the environmental pollutants (non-target screening) and studying the mechanism of atmospheric oxidative processes.

Co-pyrolysis characteristics of waste tire and maize stalk using TGA, FTIR and Py-GC/MS analysis

Co-pyrolysis technology is an important pathway to realize efficient utilization of waste tires and biomass resources, solve environmental problems and help mitigate the energy supply issues. Results are presented on the pyrolysis behavior of waste tire, maize stalk and their mixtures using thermogravimetric analysis (TGA), Fourier transform infrared (FTIR) spectroscopy, and gas chromatography/mass spectrometry (GC/MS). The results showed synergistic effects in the co-pyrolysis of waste tire and maize stalk. The co-pyrolysis results showed increased weight loss. The pyrolysis of waste tire and maize stalk was relatively independent in the co-pyrolysis process. The FTIR results showed that the waste tire and maize stalk had similar functional groups, and that the co-pyrolysis products not only included ketones, aldehydes and acids, but also H2O and SO2. The GC/MS analysis data showed that co-pyrolysis helps to inhibit polycyclic aromatic hydrocarbons (PAHs) production and improve products yield of hydrocarbons and alcohols. The results presented here provide a fundamental basis of the co-pyrolysis technology for the disposal of waste tire and agricultural biomass for cleaner energy conversion and greener environment.

Formation of c-C6H5CN Ice Using the SPACE TIGER Experimental Setup

Benzonitrile (c-C6H5CN) has been recently detected in cold and dense regions of the interstellar medium, where it has been used as a signpost of a rich aromatic organic chemistry that might lead to the production of polycyclic aromatic hydrocarbons. One possible origin of this benzonitrile is interstellar ice chemistry involving benzene (c-C6H6) and nitrile molecules (organic molecules containing the −C≡N group). We have addressed the plausibility of this c-C6H5CN formation pathway through laboratory experiments using our new setup SPACE TIGER. The SPACE TIGER experimental setup is designed to explore the physics and chemistry of interstellar ice mantles using laser-based ice processing and product detection methods. We have found that c-C6H5CN is formed upon irradiation of c-C6H6:CH3CN binary ice mixtures with 2 keV electrons and Lyα photons at low temperatures (4−10 K). Formation of c-C6H5CN was also observed when c-C6H6 and CH3CN were embedded in a CO ice matrix, but it was efficiently quenched in a H2O ice matrix. The results presented in this work imply that interstellar ice chemistry involving benzene and nitrile molecules could contribute to the formation of the observed benzonitrile only if these species are present on top of the ice mantles or embedded in the CO-rich ice layer, instead of being mixed into the H2O-rich ice layer.

Preparation of aromatic hydrocarbons from fast pyrolysis of waste medical mask catalyzed by modified HZSM-5

The safe and efficient utilization of waste medical masks has attracted worldwide attention. Fast pyrolysis with the catalysis of zeolites can provide a promising route for the production of value-added aromatic hydrocarbons from waste medical masks. Herein, HZSM-5 was employed and modified by metal loading (Ga, Mo) and alkali treatment for the ex-situ catalytic pyrolysis of mask filters. The non-catalytic pyrolysis of mask filters only led to a low yield of aromatics. When HZSM-5 catalysts were employed, the liquid long-chain olefins, cycloalkanes, and alcohols, as well as gaseous light hydrocarbons were mainly converted into aromatics. According to the micro-scale pyrolysis experiments, the alkali treatment as well as Ga and Mo loading further promoted the generation of aromatics, with aromatic yields of 52.8 wt%, 54.1 wt%, and 46.3 wt%, respectively. For alkali treatment, the NaOH concentration of 0.3 mol/L was most effective for aromatic production, due to the moderate change in the pore size. For metal loading, Ga loading had better performance than Mo loading because the former resulted in a higher specific surface area while the two modified catalysts possessed similar acid activity. When the two modification methods were combined, the yields of aromatics increased to 56.7 wt% and 60.3 wt% under the catalysis of Mo/Na-HZSM-5 and Ga/Na-HZSM-5. Based on the lab-scale experiments, the aromatic yield could reach 63.0 wt% with the catalysis of Ga/Na-HZSM-5, accompanied by a high selectivity of 87.6% for monocyclic aromatic hydrocarbons (MAHs). In summary, both MAHs and polycyclic aromatic hydrocarbons (PAHs) were promoted with these catalyst modification methods by expanding the mesopore size and adjusting acid site distribution, with greater promotion on the formation of MAHs.

Formation Mechanism of Monocyclic Aromatic Hydrocarbons during Pyrolysis of Styrene Butadiene Rubber in Waste Passenger Car Tires.

The production of aromatic hydrocarbons from the waste tire pyrolysis attracts more and more attention because of its tremendous potential. Based on styrene-butadiene rubber (SBR), which is the main rubber in the waste passenger car tires, this work studies the temperature influence on primary pyrolysis product distribution by experimental techniques (Py-GC/MS, TG-MS), and then, the formation mechanism of monocyclic aromatic hydrocarbons (MAHs) observed in the experiment was analyzed by first-principles calculations. The experimental results show that the MAHs during the pyrolysis mainly include styrene, toluene, and xylene, and subsequent calculations showed that these compounds were formed through a series of primary and secondary reactions. The formation pathways of these typical MAHs were studied via the reaction energy barrier analysis, respectively. It shows that the MAHs were not only derived from the benzene ring in the SBR chain but also generated from short-chain alkenes through the Diels-Alder reaction. The obtained pyrolysis reaction mechanism provides theoretical guidance for the regulation of the pyrolysis product distribution of MAHs.

Corrigendum to “Production of aromatic hydrocarbons by co-cracking of bio-oil and ethanol over Ga2O3/HZSM-5 catalysts” [Chin. J. Chem. Eng. 46 (2022) 126–133

Corrigendum to “Production of aromatic hydrocarbons by co-cracking of bio-oil and ethanol over Ga2O3/HZSM-5 catalysts” [Chin. J. Chem. Eng. 46 (2022) 126–133

Enhancing high selectivity production of light aromatics from in-situ catalytic upgrading of cellulose pyrolysis vapors by regulating hierarchical core-shell ZSM-5@MCM-41

The catalytic upgrading of cellulose pyrolysis vapors is one of the effective methods to realize its high value utilization. Tuning the pore structure and acid sites of ZSM-5 (Z5) is a necessary strategy to develop effective catalysts for the production of light aromatics and the inhibition of carbon formation. In this study, a core-shell structure ZSM-5 @MCM-41 was developed and used for the first time in catalytic fast pyrolysis (CFP) of cellulose to prepare light aromatic hydrocarbons. The successful synthesis of the hierarchical core-shell ZSM-5 @MCM-41 was confirmed by nitrogen physisorption, X-ray diffraction (XRD), and transmission electron microscope (TEM) analysis. In aromatic hydrocarbon production, 1.0SH-Z5 @ M41 (1.0 mol/L, ZSM-5 @MCM-41) has the highest relative content of 98.76%. The relative content of BTEX (benzene, toluene, ethylbenzene, and xylene) is up to 89.83%, which is 2.39 times that of traditional microporous Z5. The quadratic polynomials were developed to correlate the Brønsted-to-Lewis acid site strength ratio (BLR) and mesopore-to-micropore volume ratio (MMR) with the relative content of BTEX. The mechanism of in-situ catalytic upgrading of cellulose pyrolysis vapor over ZSM-5 @MCM-41 was revealed. Due to high selectivities and low coke formation, ZSM-5 @MCM-41 offers an improved option for making monocyclic aromatics from cellulosic biomass.

Catalytic fast pyrolysis of herbal medicine wastes over zeolite catalyst for aromatic hydrocarbons production

Catalytic pyrolysis is an effective method to upgrade biomass pyrolytic bio-oil. In this study, catalytic fast pyrolysis (CFP) of licorice residue (LR) over ZSM-5 was conducted using pyrolysis–gas chromatography/mass spectrometry. The effects of temperature, Si/Al atomic ratio (SAR) and catalyst to feedstock (C/F) ratio on the formation of aromatic hydrocarbons (AHs) were investigated. The results indicated that ZSM-5 effectively converts oxygenates into AHs. Specifically, benzene, toluene, ethylbenzene, p-xylene and naphthalene (BTEXN) were the dominant components. The pyrolysis temperature and acidity of zeolite exert a greater influence on the formation of BTEXN. The maximum content of BTEXN was 73.45 % at 500 °C and 72.21 % at lower SARs (27 and 36). Coke can be formed and deposited on the zeolite during CFP of LR, which cause the deactivation of catalyst. A higher pyrolysis temperature and C/F ratios inhibits the coke formation, while a higher SAR is beneficial to coke formation. The large oxygenated molecules and aliphatic hydrocarbons (AHCs) was the precursors of coke during catalytic pyrolysis. The coke was tended to disperse on the surface of catalyst at low temperature. However, it was largely deposited in the channels of zeolite catalyst at high temperatures. This study reveals that ZSM-5 is an effective catalyst for the utilization of herbal medicine wastes. The pyrolytic bio-oil has high potential for use in fuels or renewable chemical production.

Application of low-cost natural zeolite catalyst to enhance monoaromatics yield in co-pyrolysis of wheat straw and waste tire

This study explored the impacts of low-cost natural zeolite (NZ) catalyst application on production of aromatic hydrocarbons during co-pyrolysis of wheat straw (WS) and waste tire (WT). Various blend ratios of WS and WT (1:0,3:1,1:1,1:3 and 0:1) were investigated to determine the optimum ratio in the terms of oil quantity and quality. The blend ratio of WS:WT 1:3 was observed to be optimum combination with oil, char and gas yields of 45, 36 and 19 wt% respectively. The catalyst was found to have silicon to aluminum ratio (SAR), surface area and pore size of 7.39, 4.2 m2/g and 23.10 Å respectively. The incorporation of NZ catalyst into WS, WT and their blend ratio of 1:3 improved the quality of oil in the terms of hydrocarbons and physiochemical properties compared to their respective ratios in non-catalyst pyrolysis. The total hydrocarbons content was increased from 72.00 area% in case of non-catalytic pyrolysis of WS:WT (1:3) to 86 area% with addition of NZ while oxygenates were reduced from 20.20 to 10.50 area% respectively. The contents of desired aromatic hydrocarbons such as benzene, toluene and xylene (BTX) were increased to 61.0 area% in catalytic pyrolysis for WS:WT 1:3 compared to 45.59 area% in non-catalytic pyrolysis of the same combination. Moreover, the higher heating value (HHV) of 42.15 MJ/kg was observed in catalytic pyrolysis of WS:WT (1:3) compared to 40.70 MJ/kg in non-catalytic pyrolysis. Besides, Kinematic viscosity and density of the oil also improved with addition of catalyst.

Highly Selective Production of Valuable Aromatic Hydrocarbons/Phenols from Forestry and Agricultural Residues Using Ni/ZSM-5 Catalyst

The aim of this research is to design and synthesize an efficient catalyst to enhance high value-added products, such as aromatic hydrocarbons and phenols, from the catalytic fast pyrolysis (CFP) of different types of forestry and agricultural residues. All three biomasses (rape straw, wheat straw, and bamboo powder) had no aromatic production via thermal pyrolysis alone; however, the aromatic selectivity and monocyclic aromatic selectivity were largely enhanced using ZSM-5, with suitable silica-alumina ratios and Ni loadings. Specifically, for rape straw, the optimum catalyst was 15 wt.% Ni/ZSM-5 (silica-aluminum ratios = 85), and the selectivity of aromatic hydrocarbons was achieved at 39%, of which 71% were monocyclic aromatic hydrocarbons. For wheat straw, the optimum catalyst was 10 wt.% Ni/ZSM-5 (silica-aluminum ratios = 18), and the selectivity of aromatic hydrocarbons was 67%, of which 55% were monocyclic aromatic hydrocarbons. For bamboo powder, the optimum catalyst was 10 wt.% Ni/ZSM-5 (silica-aluminum ratios = 18), and the selectivity of aromatic hydrocarbons was achieved at 21%, of which 80% were monocyclic aromatic hydrocarbons. Meanwhile, biomass types have significant effects on the pyrolyzed product distribution due to their different components. Cellulose and hemicellulose promoted the production of aromatic hydrocarbons, while lignin enhanced the production of phenols. The promotion of phenol by Ni was better and more efficient than that by the molecular sieve.

Selective production of monocyclic aromatic hydrocarbon from agricultural waste wheat straw for aviation fuel using Ni/ZSM-5 catalyst

Aromatic is a vital chemical raw material and product as well as an essential component for aviation fuel. Bio-based aromatics, especially the monocyclic aromatic hydrocarbon, are beneficial for the green chemical process and aviation fuel development. In this research, firstly, the effects of different kinds of metal catalysts (Pt/C, Rh/C, Ru/C, Pd/C, 65 wt% Ni/SiO2–Al2O3) on the pyrolysis behavior and aromatic hydrocarbons selectivity of four kinds of agricultural and forestry waste biomass (wheat straw, rape straw, poplar sawdust, and bamboo powder) were systematically investigated. The research results showed that the selectivity of aromatics has been largely increased in the presence of 65 wt% Ni/SiO2–Al2O3 while the carbon-based noble catalysts had few impacts on aromatics production. Furtherly, zeolite with different Si/Al ratios (5:18, 5:50, 5:85, 5:300, and 5:470) and the Ni loading amounts (5, 10, 15, 20, 25 wt%) were systematically studied. The series of Ni/ZSM-5 catalyst reduced the phenolic components in the pyrolysis products, and significantly increased the relative content of the target product aromatics, and the proportion of monocyclic aromatic hydrocarbons in the aromatic. The research results showed the ZSM-5 with the Si/Al ratio of 5:18 had the best catalytic properties for aromatic production. The loading of 10 wt% of Ni (10 wt% Ni/ZSM-5, Si/Al = 5:18) further boosted the catalytic performance for wheat straw, achieving the highest relative concentration of aromatic at 67%, of which the ratio of monocyclic aromatic hydrocarbon was 55%.

Selective recycling of BTX hydrocarbons from electronic plastic wastes using catalytic fast pyrolysis

Non-catalytic and catalytic pyrolysis of two waste electrical and electronic equipment (WEEE) fractions, with two different copper contents (low- and medium-grade WEEE named as LGE and MGE, respectively), were performed using micro- and lab-scale pyrolyzers. This research aimed to fundamentally study the feasibility of chemical recycling of the WEEE fractions via pyrolysis process considering molecular interactions at the interfaces of catalyst active sites and WEEE pyrolyzates which significantly influence the chemical functionality of surface intermediates and catalysis by reorganizing the pyrolyzates near catalytic active sites forming reactive surface intermediates. Hence, Al2O3, TiO2, HBeta, HZSM-5 and spent FCC catalysts were used in in-situ micro-scale pyrolysis. Results indicated that HBeta and HZSM-5 zeolites were more suitable than other catalysts for selective production of aromatic hydrocarbons and BTX. High acidity and shape selectivity of zeotype surfaces make them attractive frameworks for catalytic pyrolysis processes aiming for light hydrocarbons like BTX. Meanwhile, the ex-situ pyrolysis of LGE and MGE were carried out using HZSM-5 in micro- and lab-scale pyrolyzers to investigate the effect of pyrolysis configuration on the BTX selectivity. Although the ex-situ pyrolysis resulted in higher formation of BTX from LGE, the in-situ configuration was more efficient to produce BTX from MGE.

Catalytic pyrolysis of bamboo residue and its extracted three main components over copper modified ZSM-5 for the production of aromatic hydrocarbons

In this study, the product distribution from the catalytic pyrolysis of bamboo residue and its three main extracted components (cellulose, hemicellulose, and lignin) over Copper (Cu) modified ZSM-5 with different loading rates was conducted using pyrolysis-gas chromatography/mass spectroscopy. The addition of Cu modified ZSM-5 reduced the relative content of phenols, while that of monocyclic aromatic hydrocarbons (MAHs) increased significantly. The relative content of MAHs for the bamboo residue without catalyst was 2.10%, which increased considerably by 66.67% over Cu(2)/ZSM-5. The MAHs yield in cellulose is 3.03 times as that of the bamboo residue during catalytic pyrolysis over Cu(2)/ZSM-5. Phenolic compounds are mainly produced by lignin, whereas cellulose and hemicellulose are the primary producers of ketones and aldehydes. This study is crucial for understanding the pyrolytic product distribution of the bamboo residue and its three main extracted components.

Enhancement of the production of aromatics and bio-syngas from microwave ex-situ pyrolysis based on Zn/Zr modified biochar and multi-catalysts

The main purpose of this work was to explore the effect of metal modified biochar and multi-catalysts on improving the quality of products by microwave pyrolysis (MVP) of biomass. Single-component catalysts and multi-catalysts were prepared by Zn/Zr impregnation methods. The prepared catalysts were evaluated by XRD, BET, FT-IR and SEM. The properties, composition and product distribution of bio-oil and bio-syngas were analyzed. The results showed that ZSM-5 obtained more bio-oil (42.16 wt%) at the expense of gas product yield, and BC obtained the highest gas yield (43.10 wt%). Zn promoted the selectivity of aromatic hydrocarbons in bio-oil, Zr could effectively improve the yield of syngas and upgrading bio-oil, respectively. Zr-modified multi-catalyst was prepared, and the highest syngas yield (91.54 vol%) and aromatic hydrocarbon products were obtained. Among them, the selectivity of monocyclic aromatic hydrocarbons (MAHs) reached 21.82%. The mechanism of MVP of biomass under the effect of Zn/Zr modified different catalysts was proposed. The study has successfully demonstrated an approach for producing high-value bio-oil and bio-syngas from microwave multi-catalyst pyrolytic system.

Catalytic pyrolysis of cotton stalk to produce aromatic hydrocarbons over Fe modified CaO catalysts and ZSM-5

In this study, a novel method for the enhanced production of aromatic hydrocarbons by biomass pyrolysis with Fe modified CaO and ZSM-5 was proposed. The feasibility of aforementioned method and related reaction mechanism for the formation of aromatic hydrocarbons were investigated in Py-GC/MS. The results showed that Fe modification of CaO increased its specific surface area and generated Ca2Fe2O5. As a result, 5Fe/CaO and 10Fe/CaO (CaO modification by 5 wt% and 10 wt% Fe, respectively) promoted the cracking of lignin oligomer to phenols, ketonization of acetic acid to acetone, and dehydration of levoglucosan to furfural. Therefore, the addition of 5Fe/CaO or 10Fe/CaO in cotton stalk catalytic pyrolysis with ZSM-5 favored the formation of BTX obviously. The peak area % of BTX obtained by dual-catalyst of 10Fe/CaO and ZSM-5 can reached up to 67.5%, boosting 10.94% and 2.94% than ZSM-5 alone and dual-catalyst of CaO and ZSM-5, respectively. Meanwhile, the peak area of BTX obtained by dual-catalyst of 5Fe/CaO and ZSM-5 boosts 9.59% and 7.11% than ZSM-5 alone and the dual-catalyst of CaO and ZSM-5, respectively.

Improving catalytic production of aromatic hydrocarbons with a mesoporous ZSM-5 modified with nanocellulose as a green template

ZSM-5 is an important class of acid catalyst for producing bio-oil rich in petrochemicals; however, continuous efforts are required to improve the conversion efficiency of the biomass-derived oxygenates with large molecular sizes. The mesoporous ZSM-5 (N-ZSM-5) was prepared in a post-treatment method with nanocellulose as a green template in this study to induce additional surface and porous features. The post-treatment promoted the mesoporous properties in N-ZSM-5, which effectively converted lignocellulosic biomass to deoxygenated aromatic products in catalytic pyrolysis. Moreover, compared to the conventional or alkali-treated mesoporous ZSM-5, higher selectivity of monocyclic aromatic hydrocarbons (MAHs) was attained in catalytic pyrolysis of lignin while mitigating the coke accumulation. The product distribution was evaluated using the response surface methodology with reaction temperature (°C) and catalyst loading (g/g feedstock). The compositions of upgraded volatile products measured MAHs (~46.55 area%) and monophenols (~98.09 area%) depending on the process conditions.

Enhanced production of monocyclic aromatic hydrocarbons by catalytic pyrolysis of rape straw in a cascade dual-catalyst system of modified red mud and HZSM-5

Catalytic pyrolysis of rape straw was carried out on a dual-catalyst system to produce benzene, toluene, xylene (BTX), realized by promoted cracking of large-molecule pyrolysis vapor over red mud (RM) and followed by selectively catalytic conversion over HZSM-5. With the pyrolysis temperature of 550 °C and the catalyst/biomass mass ratio of 2:1, the yield of BTX in bio-oil reached the maximum of 10.27 wt%. The coking resistance of HZSM-5 in the cascade catalytic system was obviously better than pure HZSM-5. The pretreatment of RM by calcination and acid washing was also performed. The unstable components of RM like cancrinite were decomposed during the calcination. Besides, the content of active metal oxides in RM after acid washing increased by removing Na2O and CaO. Its specific surface area was promoted, due to the new micropores caused by the dispersion of dissolved metal oxides. RM treated with 3 mol/L hydrochloric acid presented the highest specific surface area of 55.24 m2/g while the maximized yield of BTX of 12.91 wt%. Therefore, the dual-catalyst system might be an effective method to dispose and high valued use of rape straw and RM as solid wastes with significant environmental impact to promote carbon neutrality.

Incipient sooting tendency of oxygenated fuels doped in ethylene counterflow diffusion flames

The incipient sooting tendencies of oxygenated fuels in counterflow diffusion flames were systematically assessed by doping selected oxygenate fuels into the baseline fuel of ethylene with various mixing ratios. Laser light scattering and planar laser-induced fluorescence (PLIF) techniques were adopted. The critical oxygen mole fractions at different mixing ratios were identified with the use of laser scattering. It is found that the critical oxygen mole fraction varies with oxygenates, suggesting that the effect of mixing ethylene with oxygenates is highly sensitive to the types of oxygenate. While the doping of acetone moderately promoted the incipient sooting tendency, the doping of methanol, acetic acid, formic acid, and diethyl carbonate suppressed the formation of incipient soot. On the other hand, the doping of ethanol, dimethyl carbonate, diethyl ether, and dimethoxymethane had weak influences on the incipient sooting tendency. The production of polycyclic aromatic hydrocarbons (PAHs) of different sizes were measured by PLIF. The results show there was a strong correlation between the incipient sooting tendency and the production of large PAHs. One important finding is that, at their sooting limits, the total oxygen-to-carbon ratio of a stoichiometric fuel/oxygen mixture is linearly correlated with the mixing ratio of the ethylene-oxygenate mixture. This slope of these two quantities can be defined as an incipient sooting index (ISI) of oxygenated fuels for ranking their tendency of incipient sooting formation. Having the slopes correlated well with the oxygenates’ hydrogen/oxygen ratio, a reasonably accurate prediction of critical oxygen mole fractions from the molecule information of oxygenated fuels can be achieved.

Prediction of •OH-Initiated and •NO3-Initiated Transformation Products of Polycyclic Aromatic Hydrocarbons by Electronic Structure Approaches.

The abiotic reaction products of polycyclic aromatic hydrocarbons (PAHs) with hydroxyl radicals (•OH) and nitrate radicals (•NO3) are nitro-, oxygen-, and hydroxyl-containing PAHs (NPAHs, OPAHs, and OHPAHs). Four methods of the highest occupied molecular orbital (HOMO), Fukui function (FF), dual descriptor (DD), and population of π electrons (PP-π) are selected to predict the chemical reactivity of PAHs attacked by •OH and •NO3 in this study. The predicted •OH-initiated and •NO3-initiated transformation products are compared with the main PAH transformation products (PAH-TPs) observed in the laboratory. The results indicate that PP-π and DD approaches fail to predict the transformation products of fused PAHs containing five-membered rings. By predicting the PAH-TPs of 13–14 out of the 15 parent PAHs accurately, HOMO and FF methods were shown to be suitable for predicting the transformation products formed from the abiotic reactions of fused PAHs with •OH and •NO3.

Study Of Soot Aggregate Formation And Oxidation In A Swirled Stratified Premixed Ethylene/Air Flame

Soot particles are one of the main causes of today's pollution because of their negative contribution to global warming and human health. Aviation is one of the domains dealing with soot reduction as the new engine concepts are developed to reduce fuel consumption and global emissions. Despite the fact that most combustion devices used for air transportation operate at high pressure (e.g., aircraft gas turbines up to 40 bar), our understanding of soot formation and oxidation in such conditions is not yet at an appropriate level, as there is still a fundamental lack of experimental data and corresponding predictive models in the literature. Thus, the objective of the current study is to evaluate soot formation and oxidation processes in stratified, swirled, premixed ethylene/air flames examined with a variety of laser diagnostics designed to simultaneously measure soot particle and soot precursor 2D-distributions, as well as the flame structure and the aerodynamic field. For that, the SIRIUS burner was selected because of its ability to produce flames with topologies similar to those encountered in aircraft combustors. Soot particle distributions are measured by Planar Laser-induced incandescence (PLII) diagnostic. The flame structure is obtained by detecting the hydroxyl radicals (OH) with Planar laser-induced fluorescence (PLIF). A second PLIF diagnostic is also used to investigate the production of polycyclic aromatic hydrocarbons (PAH) with the detection of two benzene rings molecules which are recognized as good precursors of soot nucleation and growth. Finally, the particle Image Velocimetry (PIV) diagnostic is used for measuring the velocity distributions. These laser diagnostics are coupled together in order to obtain cross-correlations between several scalar parameters playing a determining role in the soot formation/consumption processes. The experimental results collected at atmospheric pressure are reviewed and critically assessed. A scenario describing the link between the soot inception, growth, aggregation and oxidation processes is proposed by analyzing velocity, OH, PAHs and soot distributions. In particular, the data reveal the presence of distinct regions for these processes. Incipient soot production zone is strongly function of specific local conditions of velocity, PAH concentration, and strain rate encountered at the interface of the internal recirculation zone and the fuel/air jet. The central part of the inner recirculation zone in which large structures move at low velocities provides suitable conditions for the aggregation of nascent soot particles while an oxidation region located in the upper zone of the internal recirculation zone favors the consumption of soot.