PAH Formation Research Articles

ReaxFF molecular dynamics study of N-containing PAHs formation in the pyrolysis of C2H4/NH3 mixtures

The reactive force field molecular dynamics (ReaxFF MD) simulations are performed to depict the whole process including fuel pyrolysis, the formation and growth of PAHs/NPAHs and soot formation in the pyrolysis of C2H4 and C2H4/NH3 mixtures. NH3 doping increases the concentration of H radicals through the decomposition of NH3. These H radicals then promote the consumption of C2H4 by participating in H-abstraction reactions. The formation of C-N species (mainly HCN, H2CN, C2N, CH3CN, NCCN, and HC3N) removes the C atoms participating in the formation of PAHs and soot, thus inhibiting the formation of soot. And such inhibitory effect is strengthened with increasing temperature due to the promoted formation of C-N species. Most importantly, the structure, formation and evolution paths of N-containing PAHs (NPAHs) are identified based on the experimental and simulation results for the first time, revealing that N atoms in the NPAHs are almost always present in the carbon chains attached to the aromatic rings while barely enter the rings to form heterocyclic structure. The simulations further reveal that when the temperature is less than 2500 K, the first N-containing aromatic ring is formed through the reaction of phenyl with small C-N species (such as HCN and CN radicals), followed by the increase of new rings primarily via the HACA mechanism. At temperatures greater than 2500 K, the formation and growth of NPAHs are dominated by the continuous attachment of N-containing carbon chains and cyclic polycondensation-cyclization reactions. The identification of new C-N species especially NPAHs would help improve the kinetic mechanisms for ammonia blending combustion.

Catalytic co-pyrolysis of cabbage waste and plastics with Ni/ZSM-5 catalysis to produce aromatic-rich oil

This study investigates the selective production of aromatics through the co-pyrolysis of cabbage waste and plastics followed by catalytic reforming with Ni-modified ZSM-5. Co-pyrolysis significantly improves the inflection point (a parameter for determining thermal stability) to 251.3 °C from 232.7 °C. This process also enhances the relative yield of olefins and phenols, which are precursors for aromatic production to 25.46 and 17.23 respectively, up from 13.87 to 12.05. Furthermore, catalytic pyrolysis elevates the relative yield of aromatics to 53.4, as confirmed by Thermogravimetric Analysis (TGA) and Thermogravimetric-Fourier Transform Infrared Spectroscopy (TG-FTIR) analyses. GC-MS confirms the enhanced formation of valuable chemical precursors via co-pyrolysis such as phenols and olefines to 18.67 % and 22.13 % leading to a 63.81 % selective yield of aromatics in the final oil with 10Ni/ZSM-5. Ni modification of ZSM-5 is influential in decreasing PAH formation (7.26 % from 20.37 %), indicating that this two-step process is an effective method for transforming waste into high-quality bio-oil with enriched aromatic content.

Numerical study on kinetics of tar production and mechanism of benzene formation during corn straw gasification

Tar production is a key factor hindering the industrialization of biomass gasification technology. Understanding the mechanisms of tar formation can help predict and reduce tar yield. A gasification model was proposed to investigate the effects of oxygen ratio (OR) and temperature on products formation. Its accuracy was validated using experimental data. The relative content of PAHs from corn straw gasification decreased from 95 % to 53 % with OR and temperature increasing, indicating PAHs relative content could be decreased by increasing OR and temperature. The concentrations of phenanthrene from cellulose and corn straw gasification at 900 °C were 0.85 and 378 ppm, separately. The concentrations of pyrene were 52 and 558 ppm, respectively. The content of PAHs from cellulose gasification was much less than that from corn straw gasification. However, the contribution of cellulose to PAHs formation increased with temperature increasing. Furthermore, the mechanism of benzene formation was analyzed qualitatively and quantitatively. C2H2, C3H3, and C4H6 were main precursors and exhibited a considerable role in benzene formation. H, OH, CH3, and C6H5 were the key radicals. The analysis results indicated that CH3→C2H2→C3H3→benzene and C2H3/C2H4→C4H6→n-C4H5→benzene were two main paths for benzene formation during corn straw gasification.

Formation mechanism of polycyclic aromatic hydrocarbons in grilled beef and the mitigative effect of flavonoids

AbstractPolycyclic aromatic hydrocarbons (PAHs) are found in many common foods and increase the risk of cancer in humans. This study systematically screened the components that may be related to the formation of PAHs by an excessive addition of 19 amino acids and glucose in the beef patties. Phenylalanine and glucose exhibited the potential as promoters of PAHs, while lysine, aspartic acid, glutamic acid, valine, and methionine exhibited excellent potential as inhibitors of PAHs. Subsequently, a chemical model containing phenylalanine and glucose was established to confirm their roles as precursors of PAHs. The formation mechanism of PAHs showed that naphthalene was first formed as a basic structure, and then, PAHs with more rings were further formed through substitution, addition reactions, or intramolecular cyclization reactions. The mitigative effects of four flavonoids on total PAH contents were in the order: kaempferol > naringenin (better for individual PAH) > myricetin > quercetin (contradictory), which suggested that the antioxidant ability or radical scavenging capacity of flavonoids may be one of the pathways for PAH inhibition.

Reaction mechanism and light gas conversion in pyrolysis and oxidation of dimethyl ether (DME): A ReaxFF molecular dynamics study

To uncover the microscopic reaction mechanisms of dimethyl ether (DME) pyrolysis and oxidation, reactive molecular dynamics simulations were employed to investigate the reaction processes under various O2/DME ratios and impurity environments at 2200 K–3200 K. The results show that DME pyrolysis begins with a decomposition reaction of CH3OCH3 → CH3O + CH3, ultimately leading to the formation of CO, H2 and PAHs. The reaction pathways of DME oxidation contain light gas conversion and combustion. In fuel rich conditions, the oxidation produces mainly H2 and CO, while in fuel lean conditions, the oxidation products tend to be H2O and CO2. The carbon components of DME are completely converted into CO2 and CO regardless of O2 content. In the presence of impurities H2O or CO2, the oxidation reaction pathway is altered, causing consumption and transformation of these impurities into active radicals such as OH, further promoting the progress of the reaction. The top three light gases produced are hydrogen, methanol and methane, and increasing H2 production in the DME oxidation process can be achieved through both oxygen subtraction and water addition. The rate of formaldehyde generation during pyrolysis is higher than that during oxidation. However, a higher oxygen content leads to increased formaldehyde production.

Prediction of soot for pressurized turbulent kerosene-air diffusion flames using method of moments

ABSTRACT A comprehensive CFD model is developed to predict soot for a turbulent kerosene-air diffusion flame. The method of moments (MOM) soot model has better prediction capability with meaningful soot behavioral predictions than semi-empirical models. The coupled model is primarily validated with experimental measurements from the literature in the form of major species concentration, flame temperature, and soot volume fraction. A surrogate mix comprising 80% n-decane and 20% toluene on a liquid volume basis constitutes kerosene fuel. The 20% aromatic content is able to reproduce the sooting behavior with considerable accuracy. The model can replicate CO, CO2, CH4, C2H2, C2H4, and C6H6 concentrations, flame temperature, soot volume fraction, and soot aggregation parameters for a laminar JetA-1 flame at atmospheric pressure. The reproduction of flame temperature and major species concentrations for a laminar kerosene flame validates the applicability of the gas-phase kinetic mechanism and PAH formation pathway for the reacting flow system. The model also performs appreciably for measurements of a turbulent kerosene flame at higher operating pressures up to 6.44 bar. The peak soot volume fraction matches significantly well with the measurements for all the flames. The predicted peak soot volume fractions are 8.8, 27.3, 68, and 82 ppm compared to measured values of 9.3, 28.3, 63, and 67 ppm at pressures 1, 2.7, 4.81, and 6.44 bar, respectively. However, the location of the peak soot has a slight discrepancy at low pressures till 2.7 bar, showing the predicted peak earlier compared to a later appearance in the measurements. The simulated peak flame temperatures are 1377, 1393, 1412, and 1477 K as operating pressure increases from 1 to 2.7, 4.81, and 6.44 bar. The thermal absorbance from soot and species radiation plays a vital role in predicting the flame temperature. Soot radiation reduces flame temperature by ~ 500 K compared to gaseous radiation (CO2, H2O, CO, CH4, etc.), reducing approximately 100 K. The predictive soot number density, mean diameter, surface area, primary particle count in soot aggregates, and primary particle diameter carry a substantial dependency on the operating pressure.

Experimental and kinetic modeling investigation on the co-pyrolysis of benzene, acetylene, and dimethyl ether: Insights into the fuel component interactions

The addition of dimethyl ether (DME) to hydrocarbons is proposed to be a feasible strategy to reduce carbon dioxide emissions in engines. In order to unravel the interaction between hydrocarbons and oxygenated fuels, the co-pyrolysis of benzene, acetylene, and dimethyl ether (DME) is investigated in a flow reactor at 880–1250 K and 1 atm using gas chromatography in this work. Additionally, pyrolysis of pure benzene and co-pyrolysis of benzene and acetylene are also performed. It is observed that the pyrolysis of pure hydrocarbon components and co-pyrolysis of benzene and acetylene can hardly happen in the investigated temperature region, while the addition of DME to the pyrolysis of benzene and acetylene significantly accelerate their decompositions and enhance the formation of key aromatics, such as toluene and indene, showing remarkable synergistic effects on pyrolysis reactivity and aromatics growth. A kinetic model describing the combustion of the three components is developed and used to perform numerical investigation on fuel decomposition and PAH formation. Modeling analysis shows that the addition of DME can effectively activate the pyrolysis system through fast C-O bond dissociation reactions, thereby reducing the decomposition temperatures of benzene and acetylene. The phenyl radical produced from the H-abstraction of benzene can react with acetylene to produce phenylacetylene, while phenylacetylene can further combine with another phenyl radical to form b-phenyl-a-styryl radical which can readily convert to phenanthrene. The addition of DME also generates abundant methyl radical, which further reacts with benzene or other aromatics to form large aromatics such as toluene and methylated PAHs.

Exploration on the combustion chemistry of p-xylene: A comprehensive study over wide conditions and comparison among C8H10 isomers

Pyrolysis and oxidation of p-xylene over wide conditions were studied in this work in order to provide a comprehensive insight into the combustion chemistry of p-xylene. Concerning this goal, the pyrolysis of p-xylene was investigated in a flow reactor at pressures from 0.04 to 1 atm over the temperature range of 1000–1600 K. Key radicals, isomers and PAH products including three xylyl isomers, benzyl, xylylene isomers, styrene, benzene, fulvene, indene, naphthalene and phenanthrene, were identified and quantified using synchrotron vacuum ultraviolet photoionization mass spectrometry. The oxidation of p-xylene was studied in a jet-stirred reactor at 10 atm, 800–1300 K and equivalence ratios of 0.5–2.0 with a residence time of 0.5 s. Oxidation products were quantified by using gas chromatography combined with mass spectrometry and Fourier transform infrared spectrometry. A kinetic model for p-xylene combustion over wide conditions was developed based on our previously proposed p-xylene oxidation model and validated against the new experimental measurements in this work and literature reported experimental data, including flow reactor oxidation, laminar premixed flame, ignition delay time and laminar burning velocity. In the flow reactor pyrolysis, p-xylene mainly undergoes unimolecular decomposition to yield p-xylyl, which mainly suffers the H-loss reaction to form p-xylylene and isomerization reaction to form o-xylyl. The resonantly stabilized fulvenallenyl and benzyl radicals play an important role in the formation of bicyclic and tricyclic PAHs including indene, naphthalene, and phenanthrene. In the JSR oxidation, p-xylene is predominantly consumed via H-abstraction by oxygenated radicals such as OH, O, and HO2 forming p-xylyl, which can be oxidized by HO2 and eventually converted to p-methylbenzaldehyde. As the most abundantly produced oxygenated aromatics, further consumption of p-methylbenzaldehyde results in the formation of other observed oxygenated aromatics such as cresol, benzofuran, and benzaldehyde. The combustion chemistry of three C8H10 isomers, i.e., p-xylene, o-xylene, and ethylbenzene, were also compared in terms of pyrolysis and oxidation fuel reactivity, and PAHs formation and growth, showing remarkable fuel isomeric effects.

Analysis of Polycyclic Aromatic Hydrocarbons via GC-MS/MS and Heterocyclic Amines via UPLC-MS/MS in Crispy Pork Spareribs for Studying Their Formation during Frying.

This study aims to explore the effects of frying conditions on the formation of HAs and PAHs in crispy pork spareribs, a popular meat commodity sold on Taiwan's market. Raw pork spareribs were marinated, coated with sweet potato powder, and fried in soybean oil and palm oil at 190 °C/6 min or 150 °C/12 min, followed by an analysis of HAs and PAHs via QuEChERS coupled with UPLC-MS/MS and GC-MS/MS, respectively. Both HAs and PAHs in pork spareribs during frying followed a temperature- and time-dependent rise. A total of 7 HAs (20.34-25.97 μg/kg) and 12 PAHs (67.69-85.10 μg/kg) were detected in pork spareribs fried in soybean oil and palm oil at 150 °C/12 min or 190 °C/6 min, with palm oil producing a higher level of total HAs and a lower level of total PAHs than soybean oil. The content changes of amino acid, reducing sugar, and creatinine played a vital role in affecting HA formation, while the degree of oil unsaturation and the contents of precursors including benzaldehyde, 2-cyclohexene-1-one, and trans,trans-2,4-decadienal showed a crucial role in affecting PAH formation. The principal component analysis revealed that HAs and PAHs were formed by different mechanisms, with the latter being more liable to formation in pork spareribs during frying, while the two-factorial analysis indicated that the interaction between oil type and frying condition was insignificant for HAs and PAHs generated in crispy pork spareribs. Both CcdP (22.67-32.78 μg/kg) and Pyr (16.70-22.36 μg/kg) dominated in PAH formation, while Harman (14.46-17.91 μg/kg) and Norharman (3.41-4.55 μg/kg) dominated in HA formation in crispy pork spareribs during frying. The outcome of this study forms a basis for learning both the variety and content of HAs and PAHs generated during the frying of pork spareribs and the optimum frying condition to minimize their formation.

Evaluation of Sources of Polycyclic Aromatic Hydrocarbons in Thermally Treated Meat and Fish: A Food Pollutant Study

This study assessed the sources of PAH in cooked meat and fish. Gas Chromatography-Mass Spectrometry (GC-MS) performed the sample analysis. The total PAH concentrations (mg/kg) ranged from 0.911 to 2.763. Levels of low-molecular-weight (LMW) PAHs varied from 0.353 mg/kg to 1.786 mg/kg, while high-molecular-weight (HMW) PAHs ranged from 0.516 to 0.977 mg/kg. The study detected 2 to 6-ring PAHs, the 3-ring PAHs were the most prominent. PAHs diagnostic ratios, their plots and principal component analysis (PCA) were used to assess the origin of PAHs in the samples. Values of diagnostic ratios, such as Phenanthrene/Anthracene (1.84–3.58), Anthracene/(Anthracene + Phenanthrene) (0.21–0.35), Fluoranthene/Pyrene (0.00-1.79), Fluoranthene /(Fluoranthene + Pyrene) (0.00-0.64), Indeno[123-cd-]pyrene/(Indeno[123-cd-]pyrene + Benzo[ghi]perylene) (0.00–43), LMW-PAH/HMW-PAH (0.59–1.83) and Benzo[a]pyrene/(Benzo[a]pyrene + Chrysene) (0.00–0.50) indicated that the PAHs in the samples were from mixed sources, with greater contributions from pyrogenic sources. They show that the barbecued samples were contaminated primarily by pyrogenic PAHs (biomass (wood/charcoal) burning, liquid fuel combustion, or automobile exhaust emissions). The grilled and smoked samples were mostly contaminated from different combustion sources (traffic and non-traffic, biomass burning, automobile exhaust and liquid fuel), with little input from petrogenic sources. The combination plots of the ratios also show that PAH was from mixed sources (petrogenic and pyrogenic), but mostly from a pyrogenic source (wood/charcoal burning, liquid fuel combustion, and automobile exhaust emissions) with minor inputs from petrogenic origin, as shown by the value of LMW-PAH/HMW-PAH ratios > 1 in a few samples. PCA equally showed that four factors accounted for 82.47% of the total variability and separated the PAHs into identifiable source groups, comprising mixed sources, combustion of liquid fossil fuel, automobile/diesel engine exhaust, gasoline and oil combustion and biomass burning. The study showed that contamination from the natural habitats of the animals contributed to the PAHs in them in addition to the cooking process. This therefore underscored the impacts of anthropogenic pyrogenic activities on PAHs formation and levels in meat and fish, hence adequate control/reduction of these activities will promote a healthier and safer food environment for all.

Study of HAA and PAH accumulation in meat products during its heat treatment using different types of oils

Heat treatment of meat inevitably leads to the formation of chemical compounds non characterized for it. New chemical compounds formed in meat during its heat treatment are responsible not only for changing the organoleptic properties of the product, but can also be potential carcinogens and mutagens. One type of such compounds is HAA, the carcinogenic and mutagenic potential of which has been proven in a number of studies on laboratory animals and microorganisms. Concern about consuming of HAA led to a number of studies devoted to searching the ways to reduce the amount of HAA formation. In such studies it was found that the most powerful inhibitors in the formation reaction of HAA are antioxidants, vitamin E in particular. Such studies determined the aim of this work - research the influence of various types of vegetable oils (a rich sources of vitamin E) used during heat treatment of meat on the amount of carcinogens formed in meat products. The research results showed that the greatest reduction in the amount of HAA was achieved in samples with avocado oil - the total reduction relative to the control sample was about 54%. Also, the use of avocado oil led to the formation of fewer PAH. In samples with sunflower oils it was observed the reduction of the HAA amount by 43, 44 and 51%. The lowest inhibitory effect in the reaction of HAA formation was observed in samples with coconut and flaxseed oils - 22 and 9.5% respectively. On the contrary, the use of butter during heat treatment of meat increased the HAA amount - about 15% relative to the control sample. Studies have shown that the use of vegetable oils during heat treatment of meat products can significantly reduce the amount of carcinogens formed in it.

Relationship between PAH4 formation and thermal reaction products in model lipids and possible pathways of PAHs formation

Lipids are closely related to the generation of PAHs during food thermal processing. During heating, lipids mainly triglycerides undergo hydrolysis, oxidation and decomposition. The relationship between the various products and the formation of PAHs is still unclear. This paper investigated the effect of different lipid standards on PAH4 production, and explored their thermal stability and reaction products to delve into nature of the differences in PAH4 production. Fatty acids were more prone to generate PAH4 than glycerides. The higher the degree of esterification of glycerides, the higher its thermal stability and the lower the content of PAH4 generated, implying that hydrolysis of glycerides promoted the generation of PAH4. In addition, there was a positive correlation between unsaturation in lipids and the PAH4 production. After heat treatment, hydroperoxides, unsaturated fatty alcohols and aldehydes, alkenes and aromatic substances were abundant in oleic acid and linoleic acid which produced the most PAH4. Thermal decomposition of lipid hydroperoxides was the pathway for the generation of conjugated hydrocarbon radicals, alcohols, aldehydes, and alkenes. The intramolecular cyclization and Diels-Alder reaction acted as ring-forming reactions, with consequent dehydrogenation, decarboxylation, side-chain breaks and radical reorganization, ultimately facilitating the amplification of the aromatic rings and the formation of PAHs.

Experimental and kinetic modeling study of C5 cyclic hydrocarbons pyrolysis at elevated pressures: Effect of unsaturation on the reactivity and PAH formation

To further explore the decomposition behaviors of C5 cyclic hydrocarbons, important components in the transportation fuels and pivotal intermediates in high-density liquid fuels, the pyrolysis of cyclopentane, cyclopentene and cyclopentadiene with different unsaturation degrees were investigated. The experiments of cyclopentane and cyclopentene were performed at 1.0, 30.0 atm and 773–1173 K in a flow tube reactor. The mole fraction profiles of pyrolysis species, involving C1-C5 small hydrocarbons and monocyclic, bicyclic as well as polycyclic aromatic hydrocarbons (MAHs, BAHs and PAHs), were provided. A universal kinetic model for three C5 cyclic fuels pyrolysis chemistry was proposed and reasonably predicted the speciation profiles newly reported in this work and literature, where rate coefficients of the crucial reactions were compared and upgraded. The differences among three fuels specific pathways were evaluated and the effects of unsaturation on the pyrolysis characteristics of intrinsic reactivity and aromatics formation were revealed. Cyclopentene has the highest pyrolysis reactivity, followed by cyclopentane and cyclopentadiene. Simultaneously formed fuel radicals and key intermediates in three C5 cyclic fuels influence the formation channels of small products, MAHs and BAHs. The saturated cyclopentane is easily occur the ring-opening reaction to generate more C2 and C3 species, whereas the increase in unsaturation promotes MAHs and BAHs formation in cyclopentene and cyclopentadiene pyrolysis, especially the toluene, styrene, indene and naphthalene. The rate of production analysis shows the formations of these MAHs and BAHs are strongly dependent on the concentration levels of cyclopentadienyl resonance stabilized radical (RSR). Differently, the dominated growth pathways of three- and four-ring PAHs are barely influenced by the specific fuel chemistry and indenyl plays a crucial role via the typical RSR chain reactions at high pressures.

Recent Research Progress on Black Carbon Emissions from Marine Diesel Engines

Black carbon (BC) emissions from shipboard diesel engines are the next potentially important issue of interest to the International Maritime Organization (IMO) and are considered to have a significant impact on the climate environment and human health. However, theories and technologies regarding the mechanisms of black carbon formation, oxidizing and influencing factors, emission detection methods, and abatement techniques are still missing in science and engineering. This paper provides a comprehensive overview of relevant advances in international maritime regulations, the frontier theory on formation mechanisms, comprehensive physical and chemical properties, and the potential reduction measures and control measures of emissions. These results suggest that BC is produced in the combustion flame of fuel and is related to the nucleation as well as the formation of PAHs. It helps to understand the initial generation process of black carbon and reduce its emission by studying it in detail and revealing some key factors, including micromorphology, nanostructural features, surface functional groups, oxidizing activity, size distribution, and elemental composition. Further, an in-depth understanding of the complex characteristics of BC can also help to identify viable BC measurement techniques and instrumentation for marine engines, thereby enhancing emission regulation. Overall, extensive technology can reduce BC emissions from marine diesel engines by approximately 50%. The information contained in this report can be used as a significant reference to further explore the BC formation mechanism and develop exclusive BC emission control strategies.

Polycyclic aromatic hydrocarbons in exoplanet atmospheres

Context. Polycyclic aromatic hydrocarbons, largely known as PAHs, are widespread in the Universe and have been identified in a vast array of astronomical observations, from the interstellar medium to protoplanetary disks. They are likely to be associated with the chemical history of the Universe and the emergence of life on Earth. However, their abundance on exoplanets remains unknown. Aims. We aim to investigate the feasibility of PAH formation in the thermalized atmospheres of irradiated and non-irradiated hot Jupiters around Sun-like stars. Methods. To this aim, we introduced PAHs in the 1D, self-consistent forward modeling code petitCODE. We simulated a large number of planet atmospheres with different parameters (e.g., carbon to oxygen ratio, metallicity, and effective planetary temperature) to study PAH formation. By coupling the thermochemical equilibrium solution from petitCODE with the 1D radiative transfer code, petitRADTRANS, we calculated the synthetic transmission and emission spectra for irradiated and non-irradiated planets, respectively, and explored the role of PAHs in planet spectra. Results. Our models show strong correlations between PAH abundance and the aforementioned parameters. In thermochemical equilibrium scenarios, an optimal temperature, elevated carbon to oxygen ratio, and increased metallicity values are conducive to the formation of PAHs, with the carbon to oxygen ratio having the largest effect.

An Experimental and Kinetic Study of Phenylacetylene Ignition at High Temperatures

ABSTRACT Phenylacetylene plays a critical role as an intermediate in PAH formation in hydrocarbon flames. In this work, the autoignition characteristics of phenylacetylene were investigated behind reflected shock waves. Ignition delay times were measured at temperatures ranging from 1228 to 1813 K, pressures of 2, 4, and 10 atm, equivalence ratios of 0.5, 1.0, and 2.0, as well as fuel mole fractions of 0.1% and 0.2%. The effects of temperature, pressure, equivalence ratio, and mole fractions on ignition delay time were investigated, and quantitative relationships were obtained by regression analysis of the experimental data. A detailed oxidation mechanism of phenylacetylene based on NUIGMech1.1 was proposed and verified using ignition data. Reaction pathway and sensitivity analyses have been carried out to investigate the significant reaction pathways in the ignition process and key reactions that affect the ignition delay time. The addition reactions by O and OH species contribute significantly to phenylacetylene consumption and promote fuel ignition. Finally, a comparison of the ignition delay times of ethylbenzene, styrene, and phenylacetylene was conducted in this study, and kinetic analyses have been conducted to investigate the impact of different side chains attached to aromatic rings on the ignition of these C8 aromatics.

Comprehensive study on particle size distribution, MAH and PAH profiles during alkylbenzene pyrolysis

The 5 linear alkylbenzenes, i.e., toluene, ethylbenzene, n-propylbenzene, n-butylbenzene, and n-pentylbenzene as fuels underwent pyrolysis at temperatures from 950 to 1450 °C in a flow reactor. Measurements of particle number size distribution, 11 monocyclic aromatic hydrocarbons, and 3 groups of polycyclic aromatic hydrocarbons (20 unsubstituted PAHs, 5 aliphatic-bridged PAHs, and 10 methyl PAHs) during the pyrolysis of linear alkylbenzenes were conducted. Results showed that the increase in side chain length suppressed the formation of particles, but ethylbenzene produced the highest particle mass and most extensive particle number size distribution. Total particle peak number concentrations exhibited a rise-then-fall trend (peaking at a critical temperature of 1050 °C) with increasing temperature regardless of the side chain length, indicating that high temperature promoted a transition from nucleation to agglomeration and coagulation. Total PAH mass concentrations were ranked in the same order with the variation of side-chain length as particle mass and peak number concentrations, indicating that soot nucleation was highly related to total PAH mass concentrations. Unsubstituted PAHs accounted for most PAHs while substituted·PAHs, including aliphatic-bridged PAHs and methyl PAHs presented 1–2 orders of magnitude less than the corresponding unsubstituted PAHs, probably distinct thermal stability and reactivity led to different growth routes between unsubstituted and substituted PAHs. Increasing the temperature from 950 to 1250 °C, the formation of high molecular weight PAHs was promoted. while a drop of high molecular weight fractions was observed above 1350 °C, which is attributed to the suppression of the formation, as well as their conversions of high molecular weight PAHs to heavier unidentified PAHs or soot. Among the test alkylbenzene fuels, the fuels with a long side chain benefit from the reduction of particles and PAHs. Furthermore, carbon atoms in aromatic rings are dominant sources of large PAHs and particles, while the carbon atoms in aliphatic side chains mainly form gas species.

Formation of pyrolysis-affected PAHs, oxygenated PAHs and MCPDs in home smoked meat

Traditional American home smoking of meat is becoming more and more popular also in Europe due to the positive characteristics of home smoked meat such as flavor, taste and texture. However, the long and intensive smoke exposure leads to the formation of pyrolysis-affected contaminants. Here, the contents of eight oxygenated polycyclic aromatic hydrocarbons (OPAHs), six PAHs, and free 3- and 2-MCPD were investigated in home smoked meat. The meat was prepared under seven different conditions (four replicates, each) defined by smoking device (offset smoker or kettle grill), heating material (beech wood logs or charcoal), smoking material (logs or chips) and sample pretreatment (unsalted and salted). The highest median contents were observed for salted meat prepared on an offset smoker using logs (OPAH4: 31 μg/kg; PAH4: 68 μg/kg; 3-MCPD: 98 μg/kg; 2-MCPD: 7 μg/kg), exceeding the PAH4 EU maximum level for barbecued meat of 30 μg/kg. Salting of meat before smoking had a great effect on the 3- and 2-MCPD content, but not on the OPAHs and PAHs. 3- and 2-MCPD noticeably penetrated the smoked product in contrast to the PAHs and OPAHs. An approximate prediction of the OPAH4 content on the basis of the PAH4 content is possible.

PAH laser diagnostics and soot particle dynamics in gasoline co-flow flames doped with n-butanol

As a carbon-neutral fuel, bio-butanol mixed with gasoline has become a potential decarbonization method in transportation field. In this work, the effects of n-butanol addition to gasoline on PAH and soot formation were investigated experimentally and numerically. As n-butanol ratio increases, flame lift-off height, flame height and OH/CH chemiluminescence intensity decrease gradually. The n-butanol addition has inhibitory effect on PAH with different sizes, and the inhibitory effect increases with the increasing aromatic-ring size. As ring size increases, the high concentration region gradually evolves from the center of upper flame to the two wings of downstream flame. The primary particle size and number density show a monotonically decreasing trend with n-butanol ratio, attributing to the significant decrease of nucleation and surface growth rate. For particle surface growth, the decreasing trend of PAH condensation is higher than that of HACA with the n-butanol ratio. The contribution of HACA to particle growth increases with n-butanol ratio, and replaces PAH condensation as the main mechanism when n-butanol ratio exceeds 60%. For particle oxidation, n-butanol addition leads to a slight increase in OH oxidation rate and a significant decrease in O2 oxidation rate, while O2 oxidation is always the dominant mechanism for particle oxidation.

Studying the impact of anti-oxidant extract of different vegetables on the formation of PAHs in rabbit meat

Studying the impact of anti-oxidant extract of different vegetables on the formation of PAHs in rabbit meat