Formation Of Polycyclic Aromatic Hydrocarbons Research Articles

Marinades Based on Natural Ingredients as a Way to Improve the Quality and Shelf Life of Meat: A Review.

Marinating is a traditional method of improving the quality of meat, but it has been modified in response to consumer demand for "clean label" products. The aim of this review is to present scientific literature on the natural ingredients contained in marinades, the parameters of the marinating process, and certain mechanisms that bring about changes in meat. A review was carried out of publications from 2000 to 2023 available in Web of Science on the natural ingredients of meat marinades: fruit and vegetables, seasonings, fermented dairy products, wine, and beer. The review showed that natural marinades improve the sensory quality of meat and its culinary properties; they also extend its shelf life. They affect the safety of meat products by limiting the oxidation of fats and proteins. They also reduce biogenic amines and the formation of heterocyclic aromatic amines (HAAs) and polycyclic aromatic hydrocarbons (PAHs). This is possible due to the presence of biologically active substances and competitive microflora from dairy products. However, some marinades, especially those that are acidic, cause a slightly acidic flavour and an unfavourable colour change. Natural compounds in the ingredients of marinades are accepted by consumers. There are no results in the literature on the impact of natural marinades on the nutritional value and health-promoting potential of meat products, so it can be assumed that this is a future direction for scientific research.

Effects of Oil and Processing Conditions on Formation of Heterocyclic Amines and Polycyclic Aromatic Hydrocarbons in Pork Fiber.

Toxic compounds such as heterocyclic amines (HAs) and polycyclic aromatic hydrocarbons (PAHs) can be produced during food processing, especially meat products. This study aims to monitor the formation of HAs and PAHs in fried pork fiber, a common meat product in Taiwan, at different processing conditions. A total of six experimental groups, including raw pork tenderloin, dried pork filaments, sesame oil-stir-fried pork at 160 °C for 15 min, sesame oil-stir-fried pork at 200 °C for 6 min, lard-stir-fried pork at 160 °C for 15 min, and lard-stir-fried pork at 200 °C for 6 min, were prepared and analyzed for formation of HAs via UPLC-MS/MS and PAHs via GC-MS/MS in triplicate. Frying in sesame oil or lard showed a greater content of total HAs in fried pork fiber processed at 160 °C for 15 min than at 200 °C for 6 min. However, in the same heating conditions, pork fiber fried in sesame oil produced a higher level of total HAs than that fried in lard. Of the various HAs in fried pork fiber, both Harman and Norharman were generated in the highest amount. The precursors, including reducing sugar, amino acid, and creatine/creatinine, played a vital role in HAs formation in fried pork fiber. For total PAHs, the highest level was shown for pork fiber fried in lard at 200 °C/6 min, followed by frying in sesame oil at 200 °C/6 min and 160 °C/15 min, and in lard at 160 °C/15 min. Like HAs, at the same heating condition, a greater content of total PAHs was produced in pork fiber fried in sesame oil than in lard. Notably, the highly toxic benzo[a]pyrene was undetected in fried pork fiber. The PAH precursor benzaldehyde was shown to generate at a much higher level than 2-cyclohexene-1-one and trans,trans-2,4-decadienal in fried pork fiber, and it should play a more important role in PAH formation. Principal component analysis (PCA) also revealed that the formation mechanism of HAs and PAHs in fried pork fiber was different.

The Effect of Fatty Acids and Meat Oils Combustion on PAH Formation in Smoke during Grilling Process


 
 
 
 Background: Oil droplets from foods can cause the formation of Polycyclic Aromatic Hydrocarbons (PAHs) in smoke and contaminate grilled food. The aim of this research was to examine the effect of the number of carbon atoms, degree of double bonds, and types of fatty acids on the formation of PAHs in smoke during grilling process.
 Methods: Four fatty acids consisting of palmitic acid, stearic acid, linoleic acid, and oleic acid, and three animal oils consisting of chicken skin oil, beef oil, and striped catfish oil had been studied. The smoke obtained during the combustion of fatty acids and animal oils was collected in a PUF/XAD-2/PUF absorption tube, and the analysis of 16 major PAHs was done using Gas Chromatography-Mass Spectroscopy (GC-MS). The experiments were conducted in three replicates.
 Results: Linoleic acid and oleic acid generated relatively higher concentrations of PAHs in the smoke, at 48.53 and 46.81 ppm, while stearic acid and palmitic acid provided PAHs in the smoke at 6.15 and 3.87 ppm. The rank of the highest PAH concentration levels in order of decreasing in smoke included striped catfish oil, chicken skin oil, and beef loin oil, with values of 50.22, 35.07, and 33.62 ppm, respectively. A variety of fatty acids were found in animal oils, but some fatty acids, such as arachidic acid (20:0), mead acid (20:3), behenic acid (22:0), erucic acid (22:1), cervonic acid (DHA) (22:6), lignoceric acid (24:0), and nervonic acid (24:1), were not found in chicken skin oil or beef oil. Fatty acids in the striped catfish oil had longer carbon chains (20:0, 20:3, 22:0, 22:1, 22:6, 24:0, 24:1) compared to other animal oils and a higher degree of double bonds, thus giving a higher PAHs concentration.
 Conclusion: It can be concluded that PAH concentration present in the smoke of animal oils depends on the number of carbon atoms, the degree of double bonds in the molecules, and the types of fatty acids.
 
 
 

Comparison of PAHs behaviors in the pyrolysis products of oily sludge with different ash contents

Due to the presence of petroleum hydrocarbons, the production of polycyclic aromatic hydrocarbons (PAHs) is inevitable after oily sludge pyrolysis. The dispensation of PAHs in pyrolysis products was studied. The results indicated that PAHs were mainly enriched in liquid products, accounting for 97.97–99.88 %. Besides, the percentage of low-ring PAHs in products was the largest, subsequent to middle-ring PAHs. In the pyrolysis products of oily sludge with distinguishing ash contents, the impressions of pyrolysis temperature and residence time on the behaviors of PAHs were also compared. When pyrolysis temperature or residence time were variables, there were some similar characteristics in PAHs behaviors of oily sludge with different ash contents. The total concentration of PAHs in liquid products was positively correlated with pyrolysis temperature and residence time. The equal alteration was also exhibited in the concentration of high-ring PAHs in gas products with an increase in pyrolysis temperature. The formation of low-ring PAHs in liquid and gas products was improved by extended residence time. However, there were also differences in the evolution of PAHs in products of low-ash oily sludge (LOS) and high-ash oily sludge (HOS). The concentrations of low-ring and middle-ring PAHs in LOS gas products were positively correlated with pyrolysis temperature. Antithetically, the formation of low-ring and middle-ring PAHs in HOS gas products was inhibited by elevated pyrolysis temperature. Interestingly, the low-ring PAHs were converted into high-ring PAHs in HOS gas products with increasing pyrolysis temperature. As the residence time prolonged, the total concentrations of PAHs in LOS solid and gas products enlarged first and then reduced. Nevertheless, those of HOS were improved by continued residence time.

Gas-phase formation of the resonantly stabilized 1-indenyl (C9H7•) radical in the interstellar medium.

The 1-indenyl (C9H7•) radical, a prototype aromatic and resonantly stabilized free radical carrying a six- and a five-membered ring, has emerged as a fundamental molecular building block of nonplanar polycyclic aromatic hydrocarbons (PAHs) and carbonaceous nanostructures in deep space and combustion systems. However, the underlying formation mechanisms have remained elusive. Here, we reveal an unconventional low-temperature gas-phase formation of 1-indenyl via barrierless ring annulation involving reactions of atomic carbon [C(3P)] with styrene (C6H5C2H3) and propargyl (C3H3•) with phenyl (C6H5•). Macroscopic environments like molecular clouds act as natural low-temperature laboratories, where rapid molecular mass growth to 1-indenyl and subsequently complex PAHs involving vinyl side-chained aromatics and aryl radicals can occur. These reactions may account for the formation of PAHs and their derivatives in the interstellar medium and carbonaceous chondrites and could close the gap of timescales of their production and destruction in our carbonaceous universe.

Assessing the Formation of Polycyclic Aromatic Hydrocarbons in Grilled Beef Steak and Beef Patty with Different Charcoals by the Quick, Easy, Cheap, Effective, Rugged, and Safe (QuEChERS) Method with Gas Chromatography-Mass Spectrometry.

This study investigated the effects of different charcoals on the occurrence of 16 polycyclic aromatic hydrocarbons (PAHs) in grilled beef steaks and beef patties. Seven different charcoals were used as follows: from oak wood (C1), from orange wood (C2), from Valonia oak wood (C3), from Marabu wood (C4), extruded charcoal from beech wood (C5), from coconut shells (C6), and from hazelnut shells (C7). The grilling times for each charcoal type were 6 min for the beef patties and 7 min for the beef steaks, until the internal temperature reached at least 74°C. The total concentration of 16 PAHs (PAH16) in beef steaks grilled with C1 (35.75 μg/kg) and C7 (36.39 μg/kg) was higher than that of C3 (23.80 μg/kg) and C6 (24.48 μg/kg; p<0.05). The highest amounts of PAH16 (216.40 μg/kg) were determined in the beef patty samples grilled using C5 (p<0.05). The summation of benzo[a]anthracene, chrysene, benzo[b]fluoranthene and benzo[a]pyrene, referred to as PAH4, was not detected in any of the beef steaks, whereas it was determined in the beef patties grilled with C2 (7.72 μg/kg) and C5 (22.95 μg/kg; p<0.05). The PAH16 concentrations of the beef patty samples in each charcoal group were significantly higher compared to the beef steaks (p<0.05). To avoid the formation of high PAH levels, the use of extruded charcoal and hazelnut shell charcoal should therefore be avoided when charcoal grilling beef steaks and beef patties, and low-fat meat products should be preferred.

Reducing the Risk of Acrylamide and Other Processing Contaminant Formation in Wheat Products.

Wheat is a staple crop, consumed worldwide as a major source of starch and protein. Global intake of wheat has increased in recent years, and overall, wheat is considered to be a healthy food, particularly when products are made from whole grains. However, wheat is almost invariably processed before it is consumed, usually via baking and/or toasting, and this can lead to the formation of toxic processing contaminants, including acrylamide, 5-hydroxymethylfurfural (HMF) and polycyclic aromatic hydrocarbons (PAHs). Acrylamide is principally formed from free (soluble, non-protein) asparagine and reducing sugars (glucose, fructose and maltose) within the Maillard reaction and is classified as a Group 2A carcinogen (probably carcinogenic to humans). It also has neurotoxic and developmental effects at high doses. HMF is also generated within the Maillard reaction but can also be formed via the dehydration of fructose or caramelisation. It is frequently found in bread, biscuits, cookies, and cakes. Its molecular structure points to genotoxicity and carcinogenic risks. PAHs are a large class of chemical compounds, many of which are genotoxic, mutagenic, teratogenic and carcinogenic. They are mostly formed during frying, baking and grilling due to incomplete combustion of organic matter. Production of these processing contaminants can be reduced with changes in recipe and processing parameters, along with effective quality control measures. However, in the case of acrylamide and HMF, their formation is also highly dependent on the concentrations of precursors in the grain. Here, we review the synthesis of these contaminants, factors impacting their production and the mitigation measures that can be taken to reduce their formation in wheat products, focusing on the role of genetics and agronomy. We also review the risk management measures adopted by food safety authorities around the world.

Fire and Oil Led to Complex Mixtures of PAHs on Burnt and Unburnt Plastic during the M/V X-Press Pearl Disaster.

In May 2021, the M/V X-Press Pearl container ship burned for 2 weeks, leading to the largest maritime spill of resin pellets (nurdles). The disaster was exacerbated by the leakage of other cargo and the ship's underway fuel. This disaster affords the unique opportunity to study a time-stamped, geolocated release of plastic under real-world conditions. Field samples collected from beaches in Sri Lanka nearest to the ship comprised nurdles exposed to heat and combustion, burnt plastic pieces (pyroplastic), and oil-plastic agglomerates (petroplastic). An unresolved question is whether the 1600+ tons of spilled and recovered plastic should be considered hazardous waste. Due to the known formation and toxicity of combustion-derived polycyclic aromatic hydrocarbons (PAHs), we measured 20 parent and 21 alkylated PAHs associated with several types of spilled plastic. The maximum PAH content of the sampled pyroplastic had the greatest amount of PAHs recorded for marine plastic debris (199,000 ng/g). In contrast, the sampled unburnt white nurdles had two orders of magnitude less PAH content. The PAH composition varied between the types of spilled plastic and presented features typical of and conflicting with petrogenic and pyrogenic sources. Nevertheless, specific markers and compositional changes for burning plastics were identified, revealing that the fire was the main source of PAHs. Eight months after the spill, the PAH contents of sampled stray nurdles and pyroplastic were reduced by more than 50%. Due to their PAH content exceeding levels allowable for plastic consumer goods, classifying burnt plastic as hazardous waste may be warranted. Following a largely successful cleanup, we recommend that the Sri Lankans re-evaluate the identification, handling, and disposal of the plastic debris collected from beaches and the potential exposure of responders and the public to PAHs from handling it. The maritime disaster underscores pyroplastic as a type of plastic pollution that has yet to be fully explored, despite the pervasiveness of intentional and unintentional burning of plastic globally.

Emission characteristics of (halogenated) polycyclic aromatic hydrocarbons during printed circuit board combustion and estimated emission intensity of a typical e-waste dismantling site in South China

The pollution of polycyclic aromatic hydrocarbons (PAHs) and halogenated PAHs (Cl/Br-PAHs) caused by electronic waste dismantling activities have attracted considerable attention. The present study investigated the emissions and formation of PAHs and Cl/Br-PAHs based on the combustion of printed circuit boards simulating electronic waste dismantling process. The emission factor of ΣPAHs was 648 ± 56 ng/g, which was much lower than that of ΣCl/Br-PAHs (8.80 × 104 ± 9.14 × 103 ng/g). From 25 to 600 °C, the emission rate of ΣPAHs reached a sub-peak of 7.39 ± 1.85 ng/(g•min) at 350 °C, then increased gradually with the fastest rate of 19.9 ± 21.8 ng/(g•min) at 600 °C, whereas that of ΣCl/Br-PAHs was the fastest at 350 °C with a rate of 597 ± 106 ng/(g•min), then decreased gradually. The present study suggested that the formation pathways of PAHs and Cl/Br-PAHs are by de novo synthesis. Low molecular weight PAHs were readily partitioned into gas and particle phases, whereas high molecular weight fused PAHs were only detected in oil phase. However, the proportion of Cl/Br-PAHs in particle and oil phases were different from that of gas phase, whereas similar to that of the total emission. In addition, PAH and Cl/Br-PAH emission factors were used to estimate the emission intensity of pyrometallurgy project in Guiyu Circular Economy Industrial Park, and it was shown that approximately 1.30 kg PAHs and 176 kg Cl/Br-PAHs would be emitted annually. This study revealed that Cl/Br-PAHs would be formed by de novo synthesis, and for the first time provided the emission factors of Cl/Br-PAHs during the heat treatment process of printed circuit board, as well as estimated the contribution of pyrometallurgy, a new electronic waste recovery technology, to environmental Cl/Br-PAH pollution, which provides potential scientific information for governmental decision-making on the control of Cl/Br-PAHs.

Polycyclic Aromatic Hydrocarbons Occurrences in Biomass Char and Its Mitigation Approaches: A Mini Review

AbstractBiochar is a porous fine‐grained substance produced from the pyrolysis technology of biomass that can be commercially used as a soil conditioner to promote soil fertility. Biochar is characterized by high carbon content, stability, and porosity. However, organic pollutants residue of polycyclic aromatic hydrocarbons (PAHs) is also formed during the pyrolysis of biochar. The high concentration of PAHs adversely degrades the quality of biochar for soil amendment application. Meanwhile, highly toxic‐PAHs concentration may pose a potential threat to both human health and the environment. The total PAHs yield is mainly influenced by the pyrolysis condition and feedstock resource. This review aims to discuss the conversion pyrolysis technology of biochar and factors that may influence the PAHs formation. The key research findings from this literature will lead to some strategies to minimize the PAHs compound in biochar by controlling the pyrolysis conditions through higher pyrolysis temperature, carrier gas flow, and prolonged pyrolysis time or by selecting suitable feedstock with lower lignin content.

Polycyclic Aromatic Hydrocarbon Occurrence and Formation in Processed Meat, Edible Oils, and Cereal-Derived Products: A Review

The chemical group comprising polycyclic aromatic hydrocarbons (PAHs) has received prolonged evaluation and scrutiny in the past several decades. PAHs are ubiquitous carcinogenic pollutants and pose a significant threat to human health through their environmental prevalence and distribution. Regardless of their origin, natural or anthropogenic, PAHs generally stem from the incomplete combustion of organic materials. Dietary intake, one of the main routes of human exposure to PAHs, is modulated by pre-existing food contamination (air, water, soil) and their formation and accumulation during food processing. To this end, processing techniques and cooking options entailing thermal treatment carry additional weight in determining the PAH levels in the final product. With the background provided, this study aims to provide an improved understanding of PAH occurrence in meat, edible oils, and cereal products. The factors influencing PAH formation, including operational conditions and parameters, product composition, and storage settings, are described. The discussion also addresses reduction directions with respect to influencing factors informing the choice of the employed technique, fuel type, time–temperature settings, and ingredient variations. Considering the disparities caused by wide variations in PAH contamination, challenges associated with PAH control requirements are also outlined in the context of relevant preventive approaches during food processing.

Polycyclic aromatic hydrocarbons and food safety: A review

Polycyclic aromatic hydrocarbons (PAHs) are of petrogenic or pyrogenic origin. Of the known few hundred PAHs, 16 are identified to be toxic, of which 8 are teratogenic. Of the 8, 4 are carcinogens. Among them, Benzo[a]pyrene (BaP) possesses the highest carcinogenicity and is used as a marker in toxicity studies. PAHs of petrogenic origin contaminate soil, water and air. They may occur in air associated with dust particles. PAHs of pyrogenic origin are generated during burning of wood and other organic matter. They are also produced from lipids and carbohydrates during heating of foods. PAHs are mostly identified with grilling, smoking, frying, roasting and toasting of foods. Among the foods, formation of PAHs is studied mostly in association with grilling of fish and meat, where contacts occur between the dripping lipids and naked flames. The generated PAHs get deposited back on fish and meat muscles. PAHs in smoke are deposited on food surfaces on exposure to contaminated air from the vehicle fumes and smoke curing of foods. PAHs are formed during mechanical expulsion of edible oils. Presence of markers, carcinogenic PAHs and total PAHs in different foods and their extent of formation and deposition is discussed in relation to food safety hazards and health implications. Among the local foods and food preparation habits, the role of coconut oil, smoke curing of foods and formation of PAHs even under mild conditions of heat such as manufacture of black tea are reviewed. Recommendations for future actions, research and implementing food regulations to minimize PAHs in foods are presented.

Experimental and kinetic modeling study of polycyclic aromatic hydrocarbon formation pathways in fuel-rich oxidation of 2-methylfuran using an atmospheric flow reactor

2-Methylfuran is one of promising biofuels that is expected to be an alternative fuel or fuel additive to conventional fuels for reducing greenhouse gas emissions from internal combustion engines. Although oxidation experiments under a wide range of conditions are required for a better understanding of 2-methylfuran combustion, the fuel-rich oxidation of 2-methylfuran has not been studied extensively. In this study, the fuel-rich oxidation of 2-methylfuran was investigated using an atmospheric flow reactor at temperatures of 1000–1350 K, equivalence ratios of 3.0–12.0, and residence times of 0.2–1.5 s. Chemical species such as the polycyclic aromatic hydrocarbons (PAHs) with one to six aromatic rings formed in the oxidation were sampled and quantified using gas chromatography mass spectrometry, while small intermediate products from C1 to C5 were quantified using gas chromatograph equipped with flame ionization detector. A kinetic model was developed by combining the existing reaction mechanisms for 2-methylfuran oxidation and PAH growth, which were constructed separately. The developed model was validated against the experimental results obtained in this study, showing that the simulated concentration profiles of the chemical species were in reasonable agreement with the measured data under the present experimental conditions. Kinetic analyses using the model were conducted to unravel the reaction pathways of PAHs as well as the main consumption pathways of 2-methylfuran. These results showed that 2-methylfuran underwent ring cleavage and CO/CH3CO removal, resulting in production of C2–C4 species. It was also found that the resonantly stabilized radicals, particularly the propargyl radical, were the key species responsible for PAH growth reactions, and the hydrogen-abstraction carbon-addition mechanism was important for the formation of several PAHs.

Superacid-Assisted Degradation of Polystyrene

We report the degradation pathway of polystyrene in a low-temperature environment by superacid. Polystyrene is a thermoplastic resin widely used in packaging, disposable products, and structural materials. However, economically viable upcycling of polystyrene has yet to be established because of the high cost of chemical recycling and the low value of products. To understand the degradation pathway of polystyrene and establish competitive upcycling practices, we investigated the transformation of normal and deuterated polystyrene chains into small compounds by triflic acid at 20 °C. The degradation study of deuterated polystyrene showed the high stability of the hydrogens at the α carbons of polymerized styrene against triflic acid, which suggests the known β-scission degradation pathway of polystyrene by α-proton abstraction is unlikely. Rather, the polystyrene degradation proceeds through three distinct stages: (i) intrachain cross-linking that forms polymer nanoparticles and simultaneous transformation of polymerized styrene to indan units, (ii) degradation of the polymer nanoparticles into small molecular weight compounds, and (iii) formation of polycyclic aromatic hydrocarbons. The stepwise degradation pathway of polystyrene we report may enable the design of efficient and profitable upcycling processes for end-of-life polystyrene products in low-temperature environments.

Effects of pyrolysis conditions and heteroatom modification on the polycyclic aromatic hydrocarbons profile of biochar prepared from sorghum distillery residues

The formation of 2- to 6-ring polycyclic aromatic hydrocarbons (PAHs) in sorghum distillery residue-derived biochar (SDRBC) was evaluated under different thermochemical pyrolysis conditions of carbonization atmosphere (N2 or CO2), temperature (300–900 °C) and doping with nonmetallic elements, i.e., N, B, O, P, N + B, and N + S. The results indicated that without surface modification, PAHs formation was 944 ± 74 ng g–1, the highest level, and 181 ± 16 ng g–1, the lowest level, at 300 °C in N2 and CO2 atmosphere, respectively. Boron doping of SDRBC significantly reduced the PAHs content (by 97%) under N2 at 300 °C. Results demonstrated that boron modified SDRBC exhibited the highest degree of PAHs reduction. Combined pyrolysis temperature and atmosphere in addition to heteroatom doping is a robust and viable strategy for efficient suppression of PAHs formation and high-value utilization of pyrolysis products of low carbon footprint.

Occurrence, distribution, and toxicity assessment of polycyclic aromatic hydrocarbons in biochar, biocrude, and biogas obtained from pyrolysis of agricultural residues

Occurrence, distribution, and toxicity assessment of polycyclic aromatic hydrocarbons (PAHs) in pyrolysis steams (biochar, biocrude, and biogas) of three agricultural residues was investigated at pyrolysis temperatures of 400–800 °C. Increasing PAHs formation was observed in the narrow temperature range (500–600 °C) in all feedstocks due to temperature-induced dehydration, decarboxylation, and dehydrogenation reactions. Low molecular weight PAHs (naphthalene, phenanthrene) were dominant in all product streams while high molecular weight PAHs were found in negligible concentrations. Leaching studies showed that pyrolyzed biochars produced at lower temperatures are more prone to leaching due to the presence of hydrophilic amorphous uncarbonized structures, while the presence of hydrophobic carbonized matrix with denser and stronger polymetallic complex prevents the leaching of PAHs in the high temperature pyrolyzed biochar. Low leaching potential, low toxic equivalency, and permissible total PAHs values in biochar derived from all three feedstocks warrant the broader application and ensure ecological safety.

A kinetic modeling study on the effect of alkylbenzenes structure on PAH formation at elevated pressures

Alkylbenzene is one of the significant components of practical transport fuel, which is considered as the main reason leading to serious emissions of polycyclic aromatic hydrocarbon (PAH) from combustion processes. This work reports a kinetic modeling study on the impact of alkylbenzenes structure, i.e., the length and number of the alkyl side chain, on PAH formation at elevated pressures. A detailed kinetic model has been established and a large number of reactions concerning the PAH species formation have been updated according to the latest theoretical studies. The model is then verified by the previous experimental data containing the concentration profiles of PAH species. The fuel decomposition reactivity and the mole fraction curves of monocyclic aromatic hydrocarbon and polycyclic aromatic hydrocarbon can be well predicted by the present model. The kinetic analysis indicates that the dominant formation pathways of PAHs are barely influenced by the alkyl side chain length, especially at the high-temperature window. In the A1_C1-C4 linear alkylbenzenes pyrolysis system, the formation of benzene is mainly affected by the competition between the combination reaction of C5H3 with CH3 and the ipso-substitution reaction of A1CH3 by H. Unlike the A1_C1-C4 linear alkylbenzenes pyrolysis chemistry, fuel-related reactions associated with the formation of PAHs become more usual as the number of alkyl side chain increases, such as the formation pathway of C9 species in the pyrolysis chemistry of o-xylene and the formation pathway of phenanthrene in the oxidation chemistry of 1,3,5-trimethylbenzene.

Mass emissions of polycyclic aromatic hydrocarbons during fuel combustion in thermal power plant boilers

RELEVANCE of this study lies in the establishment of technological indicators of emissions of benz(a)pyrene into the atmosphere to assess the degree of negative impact of energy enterprises on the environment and the development on this basis of primary (air protection) measures, inventory of emissions ofpollutants, collection and preparation of initial environmental information for the effective implementation of the principles of technological regulation of emissions in the domestic thermal power industry. THE PURPOSE. The technological features of the formation of polycyclic aromatic hydrocarbons, in particular benz(a)pyrene, in the furnaces of power boilers burning organic fuel are considered. The regime factors significantly influencing the intensity of the formation of benz(a)pyrene as the most carcinogenic and mutagenic impurity influe gases have been determined. As part of the implementation of the principles of technological rationing of polluting marker substances, energy enterprises should determine the mass emission of highly toxic combustion products to improve the environmental performance of combustion processes and establish technological emission indicators. METHODS. Determination of mass emissions of polycyclic aromatic hydrocarbons was carried out using methods of mathematical statistics, processing of environmental information, system analysis of data and processing of the results obtained. RESULTS. Analytical expressions have been developed to determine the content of benz(a)pyrene in the combustion products of coal and anthracite. The values of mass emissions of benz(a)pyrene for inventory and justification of technological rationing of carcinogenic and mutagenic substances at energy enterprises have been determined. CONCLUSION. The results obtained are recommended to be used for a preliminary assessment of the content of benz(a)pyrene in the flue gases of boilers at power plants at the stage of collecting and preparing information for the introduction of technological rationing of highly toxic substances and the assessment of technological emission indicators.

Reaction Kinetics of CN + Toluene and Its Implication on the Production of Aromatic Nitriles in the Taurus Molecular Cloud and Titan’s Atmosphere

Reactions between cyano radicals and aromatic hydrocarbons are believed to be important pathways for the formation of aromatic nitriles in the interstellar medium (ISM) including those identified in the Taurus molecular cloud (TMC-1). Aromatic nitriles might participate in the formation of polycyclic aromatic nitrogen-containing hydrocarbons (PANHs) in Titan's atmosphere. Here, ab initio kinetic simulations reveal a high efficiency of ∼10−10 cm3 s−1 and the competition of the different products of the CN + toluene reaction at 30–1800 K and 10−7–100 atm. In the star-forming region of the TMC-1 environment, the product yields of benzonitrile and tolunitriles for CN reacting with toluene are approximately 17% and 83%, respectively. Detections of the main products, tolunitriles, can serve as proxies for the undetected toluene in the ISM due to their much larger dipole moments. Competition between bimolecular and unimolecular products is extremely intense in the warmer and denser PANH-forming region of Titan's stratosphere. Computational results show that the fractions of tolunitriles, adducts, and benzonitrile are 19%–68%, 15%–64%, and 17%, respectively, at 150–200 K and 0.0001–0.001 atm (Titan's stratosphere). Then, benzonitrile and tolunitriles may contribute to the formation of PANHs by consecutive C2H additions. The kinetic information of aromatic nitriles for the CN + toluene reaction calculated here helps to explain the formation mechanism of polycyclic aromatic hydrocarbons or PANHs under different interstellar environments and constrains corresponding astrochemical models.

Experimental and DFT study on the relationships between the evolution mechanism of PAHs and NOx precursors during coal pyrolysis

The evolution mechanism of coal carbon skeleton to polycyclic aromatic hydrocarbons (PAHs) with temperature has been researched by in-situ Raman and solid-state 13C NMR. A theoretical exploration with density functional theory at M06-2X/6-31G(d,p)//def-TZVP level was performed, in order to investigate the mutual conversion pathways among different functional nitrogen, and the relationships between their evolution to NOx precursors and PAHs. The aromatic nucleus radicals produced by homolysis reaction of aliphatic side chains can be connected by carbon-carbon single bonds to form PAHs remaining in char at medium pyrolysis temperature. The participation of olefin compounds cracked from aliphatic side chains is favorable to the conversion of pyrrolic and pyridinic (N-6) nitrogen to NOx precursors and PAHs, and the cyclopentadiene and butadiene obtained by the cleavage of different functional nitrogen in coal skeleton are important intermediates for the formation of PAHs. The conversion of pyridine oxide and quaternary nitrogen (N-Q) to N-6 around 440 °C can compensate for the own thermal decomposition of N-6, while the conversion of N-Q to N-6 is gradually dominated by the reverse reaction from around 690 °C.