Formation Of Polycyclic Aromatic Hydrocarbons Research Articles

Numerical simulation study on the effect of different oxygen-enrichment atmospheres on diesel combustion

Oxygen-rich combustion technology can improve fuel combustion efficiency and reduce pollutant emissions. It is one of the effective technical means to solve energy shortages and environmental pollution problems caused by rapid development of industry. In this paper, the combustion thermodynamic characteristics and pollutant emission of diesel fuel in different oxygen-rich atmospheres (oxygen-enriched air and fuel oxygen-rich atmosphere, and ethanol and biodiesel were selected in fuel oxygen-rich atmosphere) were investigated by numerical simulation. The results show that both oxygen-rich atmospheres increase the combustion temperature, flame temperature gradient, combustion heat release rate and flame propagation speed. The effect of oxygen-rich atmosphere on combustion is more severe, and the promotion effect of low oxygen-rich air on combustion process is more obvious. The flame thickness decreased in the two oxygen-rich atmospheres, and the flame thickness decreased significantly in the oxygen-enriched air atmosphere. Ethanol could reduce the flame thickness of diesel combustion more than biodiesel. The flame thickness was reduced from 0.03890 cm to 0.03214 cm with the addition of 20% ethanol. Oxygen-rich atmosphere can significantly inhibit the formation of soot precursor polycyclic aromatic hydrocarbons (PAHs) during diesel combustion, thereby reducing the amount of soot. However, the two oxygen-rich atmospheres have different effects on the formation of PAHs. The oxygen-rich atmosphere in the air mainly enhanced the oxidation reaction of PAHS with OH, O, H and other free radicals, resulting in a significant reduction in the production of PAHS. The fuel oxygen-rich atmosphere reduced the content of C2–C4 and other small molecules substances, hindered the formation process of PAHS, and strengthened the oxidation reaction of PAHS. The smoke reduction effect of ethanol is better than that of biodiesel. By analyzing the reaction rate of PAHs formation path, it is determined that the main path of A1 affecting PAHs is R45 and R58.

A ReaxFF molecular dynamics study of polycyclic aromatic hydrocarbon oxidation assisted by nitrogen oxides

Fossil fuel-derived soot poses a persistent problem. A joint reduction is conducted via the reaction between NOx and soot. The underlying reaction mechanisms of large polycyclic aromatic hydrocarbons (PAHs), as well as the interactions between O2, NO and NO2, have been extensively investigated by ReaxFF molecular dynamics simulations for the first time. The pyrolysis and oxidation of coronene are conducted at 2500 K and 50 atm. Coronene in the pyrolysis system first experiences dehydrogenation reactions and subsequently undergoes recombination reactions, leading to the formation of large PAHs. Among the three oxidizers, NO2 is the strongest in coronene oxidation, followed by NO and O2. Meanwhile, the O radical is identified as the key species for PAH oxidation. In the presence of O2, the formation of O radicals requires the assistance of H radicals that are formed by the dehydrogenation of PAHs, which retards the oxidation process. In the presence of NO, O radicals can be directly formed via reactions of NO → N+O and N + NO ⇌ N2 + O. NO2 first undergoes a decomposition reaction: NO2 → NO + O, followed by NO decomposition. O-addition and N-addition, as well as subsequent fragmentation reactions including the generation of COx and (H)CN are important routes in PAH oxidation. Furthermore, compared to NO, NO2 provides more O radicals that significantly accelerate PAH oxidation. This study provides fundamental insight into PAH oxidation that may help to design strategies to inhibit soot and NOx emissions at the source.

Effect of n-Butanol Addition to Diesel Fuel on Reduction of PAH Formation and Regulated Pollutants

The primary motivation of this paper is to report the effects of n-butanol addition (5, 20 and 35% by volume) to diesel fuel on regulated and polycyclic aromatic hydrocarbon (PAH) emissions of a diesel engine. PAH samples were quantified using rigorous analytical chemistry procedures to determine total PAHs, PAH dispersion and PAH toxicity. In comparison with diesel fuel, all n-butanol blends (DBu5, DBu20, and DBu35) reduced nitrogen oxides (NOx) emissions by 6.77%, 9.59%, and 20.08% and total PAH emissions by 66.86%, 75.33%, and 80.98%. In terms of the relative distribution of PAHs, a significant decrease was recorded in higher cyclic PAHs such as Pyrene, Benzo[a]anthracene, Chrysene, Benzo[k]floranthene, Benzo[a]pyrene for all blends. Similarly, the amount of the toxicity of the PAH emissions also decreased by 11.66%, 87.53%, and 67.28% with DBu5, DBu20 and DBu35 blends, respectively. With the addition of n-butanol to the diesel fuel, total PAH emissions were detected below the Occupational Safety and Health Administration’s (OSHA)-Permissible Exposure Level. Overall, it was demonstrated that n-butanol addition to diesel fuel significantly reduced PAH formation which is helpful to prevent wet stacking, and prolong the operating time of the diesel engine especially at low loads or cold operating conditions.

High-risk meat and fish cooking methods of polycyclic aromatic hydrocarbons formation and its avoidance strategies

According to recent research, human exposures to polycyclic aromatic hydrocarbons (PAHs) are mainly through the food route. Food such as meat and fish are two primary sources of dietary protein. However, a certain level of unawareness and poor cooking education leads to the formation of PAHs in cooked meat and fish meals. PAHs are classified as human carcinogens that poses a risk of cancer and related diseases. This review studied high-quality published articles on cooked meat and fish, emphasizing the level of PAHs contaminations, cooking methods, and related parameters. Additionally, verities of easy-feasible PAHs avoidance strategies for meat and fish cooking are summarized. Meat and fish cooking methods such as smoking, grilling, barbecuing, roasting, and traditional frying amalgamated with the risk of PAHs contamination. In accordance with expectations, there are some strategies to avoid PAHs contamination in cooked meat and fish up to 100%, including low-fat content, fuel/wood types, smoking filters, and different types of marination. This study comprehensively identified the manner in which PAHs avoidance strategies aligned with present safety guidelines.

Upgrading and PAHs formation during used lubricant oil pyrolysis at different heating modes

Recycling used lubricant oil (ULO) to produce valuable products through pyrolysis is a flexible and efficient method. Presently, the mechanisms of oil conversion and polycyclic aromatic hydrocarbons (PAHs) formation during ULO pyrolysis at different thermal conditions were poorly explored. In this study, ULO pyrolysis at different heating modes (slow: 10 °C min−1, medium: ∼10,00 °C min−1, fast: >10000 °C min−1) were conducted at the temperature range of 400–700 °C. Extensive analyses on the chemical compositions and carbon number distributions of pyrolytic products were conducted to illustrate the mechanisms of ULO evolution and the formation of PAHs. Increasing temperature or heating rate can lead to more gas but less liquid production. The high temperature at fast heating mode can greatly promote the aromatization of pyrolytic oil. Various types of valuable products, such as base oil, fuel, and chemical feedstock, can be obtained at different heating rate conditions. More than 98% of PAHs produced from ULO pyrolysis were gathered in the liquid phase. Naphthalene, phenanthrene, and pyrene were the primary PAH species in both the liquid and gaseous products. Elevating the heating rate can lead to more PAH production and the enrichment of more toxic (5-/6-ring) PAHs in pyrolytic oil. Comparatively, distillation dominated in the slow pyrolysis, and chemical reactions of cracking and recombination occurred markedly at the medium and fast heating modes for both the ULO evolution and PAHs formation.

Inhibiting Effects of Ginger and Rosemary on the Formation of Heterocyclic Amines, Polycyclic Aromatic Hydrocarbons, and Trans Fatty Acids in Fried Pork Balls

The preparation of fried meat products is prone to the formation of large amounts of heterocyclic amines (HCAs), polycyclic aromatic hydrocarbons (PAHs), and trans fatty acids (TFAs), which are potential risks to human health. Spices contain natural antioxidants that can inhibit the oxidation of fats and oils and the formation of hazardous substances. In this experiment, the effect of adding different levels (0.25%, 0.75%, 1.25%) of ginger or rosemary during meatball preparation on the formation of HCAs, PAHs and TFAs in fried pork balls was investigated. The results showed that the addition of ginger and rosemary reduced the content of HCAs in fried pork balls compared to the control group (no added spices). The inhibition of total HCAs was 63% when 0.25% ginger was added, while the total HCA content was reduced to 59% when 0.25% rosemary was added. The addition of 0.25% and 0.75% rosemary reduced the PAH content in fried pork balls by 30% and 35%. In addition, ginger and rosemary showed significant inhibition of C20:1 11t in TFAs, with a maximum inhibition rate of 40%. Therefore, adding appropriate levels of ginger or rosemary to fried pork balls could simultaneously inhibit the formation of HCAs, PAHs, and TFAs.

Inhibitory effect of coriander (Coriandrum sativum L.) extract marinades on the formation of polycyclic aromatic hydrocarbons in roasted duck wings

Coriander (Coriandrum sativum L.) is recognized for its antioxidant property, as a kind of natural phenolic-rich ingredient. Polycyclic aromatic hydrocarbons (PAHs) present a class of heat-driven hazards in foods, especially the processed meat. In this study, the effect of coriander root and leaf extract on the formation and inhibition of PAH8 in roasted duck wings was firstly investigated. Coriander root extract (CRE) and coriander leaf extract (CLE) with five concentration groups (200, 400, 600, 800, 1000 mg/L) were prepared respectively to marinate the duck wings. CRE marinade exhibited greater inhibitory effect on PAH8 formation in roasted duck wings that ranged from 65.0 %–87.4 %. The electron spin resonance study indicated a significantly positive correlation between PAH8 and free radical level, suggesting the participation of radicals in PAHs formation. Also, it was speculated that the inhibitory effect on PAH8 was related to the phenolic compounds identified in coriander marinades. CRE made greater inhibitory effect on the formation of PAH8 and could be considered as a kind of natural source to mitigate PAHs in heat-processed meat products.

An experimental and modeling study of tetramethyl ethylene pyrolysis with polycyclic aromatic hydrocarbon formation

Iso-olefins, in the C5–C8 range can potentially be blended with renewable gasoline fuels to increase their research octane number (RON) and octane sensitivity (S). RON and S increase with the degree of branching in iso-olefins and this is a desirable fuel anti-knock quality in modern spark-ignited direct-injection engines. However, these iso-olefins tend to form larger concentrations of aromatic species leading to the formation of polycyclic aromatic hydrocarbons (PAHs). Thus, it is important to understand the pyrolysis chemistry of these iso-olefins. In this study, a new detailed chemical kinetic mechanism is developed to describe the pyrolysis of tetramethyl ethylene (TME), a symmetric iso-olefin. The mechanism, which includes the formation of PAHs, is validated against species versus temperature (700–1160 K) measurements in a jet-stirred reactor at atmospheric pressure and in a single-pulse shock tube at a pressure of 5 bar in the temperature range 1150–1600 K. Synchrotron vacuum ultraviolet photoionization mass spectrometer (SVUV-PIMS) and gas chromatography (GC) systems were used to quantify the species in the jet-stirred reactor and in the single-pulse shock tube, respectively. The mechanism derives its base and PAH chemistry from the LLNL PAH sub-mechanism. The predictions are accurate for most of the species measured in both facilities. However, there is scope for mechanism improvement by understanding the consumption pathways for some of the intermediate species such as isoprene. The formation of 1, 2, and 3-ring aromatic species such as benzene, toluene, naphthalene and phenanthrene measured experimentally is analyzed using the chemical kinetic mechanism. It is found that the PAH formation chemistry for TME under pyrolysis conditions is driven by both propargyl addition reactions and the HACA mechanism.

Comparative Assessment of Polycyclic Aromatic Hydrocarbons and Toxicity in a Diesel Engine Powered by Diesel and Biodiesel Blends with High Concentrations of Alcohols

Higher carbon alcohols such as n-propanol, n-butanol, and n-pentanol that can be produced from biomass can be used as alternative fuels in diesel engines. These alcohols can mix with both diesel fuel and biodiesel without any phase separation. Currently, unregulated emissions such as toxicity and total polycyclic aromatic hydrocarbon (PAH) from the use of these alcohols are not monitored. Investigating the effects of increasing the alternative fuel concentration for use in a diesel engine on PAH emissions will contribute to the protection of the environment and extend the engine’s operating life. In this study, the effects of adding 35% (by volume) n-propanol, n-butanol and n-pentanol to diesel and biodiesel on unregulated emissions in a diesel engine were compared. In the total PAH emission of biodiesel, the mixture containing n-pentanol stood out compared to other mixtures with a decrease of 39.17%. In higher alcohol-diesel mixtures, the highest reduction was observed in the n-butanol mixture as 80.98%. With respect to toxic emissions, very close values were obtained in biodiesel blends up to 94.15%, although n-butanol showed a maximum reduction of 84.33% in diesel blends. All these reductions also prevented the formation of high-cycle PAHs. The results obtained showed that the use of high carbon alcohols in a high mixing ratio contributed to the improvement of the fuel properties of biodiesel and to an increase in the alternative fuel mixing ratio with the reduction of PAH emissions from diesel fuel.

Blending effect of methanol on the formation of polycyclic aromatic hydrocarbons in the oxidation of toluene

Methanol has been considered as a potential renewable liquid fuel and blending it with gasoline and diesel is an effective way to reduce greenhouse gas emissions from the transport sector. To understand the mixing effect of methanol on the formation of polycyclic aromatic hydrocarbons (PAHs) and oxygenated PAHs (OPAHs), the fuel-rich oxidation of toluene with and without methanol was studied using a flow reactor at atmospheric pressure, temperatures from 1050 to 1350 K, equivalence ratio of 9.0, and residence time of 1.2 s. The blending ratio of methanol was varied as 0% and 50% on a molar basis. Gas chromatograph mass spectrometer was employed to identify and quantify PAHs and OPAHs in gaseous products. A kinetic model on PAH growth up to five ring structures was used to investigate the blending effect on PAH and OPAH formation. Both experiment and modeling showed that PAH and OPAH production at lower temperatures was unexpectedly promoted in toluene/methanol oxidation compared with toluene oxidation, while their production in toluene oxidation was identical with or larger than that in toluene/methanol oxidation at elevated temperatures. In methanol oxidation, no PAHs were produced under the current experimental conditions. Kinetic analysis indicated that high methanol reactivity produced several radicals, such as OH, H, and HO2, which promoted toluene reactivity at lower temperatures, resulting in the enlargement of PAH and OPAH formation in toluene/methanol oxidation compared to neat toluene oxidation. When the temperature was increased, the effect of methanol blending was diminished based on the kinetic analysis. These results suggest that oxygenated fuels do not necessarily reduce PAH production, but promote it under some conditions.

Effect of diesel and propanol blends on regulated pollutants and polycyclic aromatic hydrocarbons under lean combustion conditions

AbstractAlcohols such as n‐propanol and diesel fuel can be mixed to increase the rate of bioalcohol utilization while reducing harmful pollutants. Examination of exhaust emissions from diesel engines, in terms of both regulated pollutants and unregulated polycyclic aromatic hydrocarbons (PAHs), is very important to the environment, public health, and engine durability. For this purpose, in this study, diesel blends with various n‐propanol concentrations (5%, 20%, and 35% by volume) were evaluated in a diesel engine. Regulated emissions were measured using a standard 5‐gas analyzer and polycyclic aromatic hydrocarbons were detected and quantified using gas chromatography–mass spectrometry (GC–MS). The effect of blended fuels on PAH formation (total PAHs, PAH distribution, and PAH toxicity) was examined in detail and compared with baseline diesel. Nitrogen oxide (NOx) emissions were reduced by 18.30% with higher n‐propanol concentrations. The addition of n‐propanol to diesel decreased total PAHs by as much as 71.20%. The fuel blend with a 20% n‐propanol concentration stood out with a maximum reduction of 91.23% in the toxicity of PAHs. In addition, n‐propanol led to a substantial decrease in the distribution of high ring aromatic compounds. Overall, it was demonstrated that n‐propanol is an effective additive to not only reduce the total PAH emissions and toxicity but also heavier PAHs which are more carcinogenic and cause a greater risk of the wetstacking issues for engines under cold operating or low load conditions.

The contamination, formation, determination and control of polycyclic aromatic hydrocarbons in meat products

Polycyclic aromatic hydrocarbons (PAHs) are aromatic compounds with two or more benzene rings composed of carbon and hydrogen, which are potential hazard substances produced by food thermal processing. However, the toxicological effects differ due to their varieties, causing many countries to have inconsistent standards. Also, the formation mechanism of PAHs in meat products is still controversial, and the detection methods and influencing factors are diverse, resulting in food control challenges. Therefore, this work reviewed PAHs in food, especially meat products from the perspectives of their classification, toxicological evaluation, formation mechanism, methods for extraction and detection, influencing factors, and control strategies. This paper provides some perspectives on the control of food PAHs in research and industrial production.

Benchmark Thermochemistry of Polycyclic Aromatic Hydrocarbons.

The DLPNO-CCSD(T1)/CBS method in conjunction with isodesmic-type reactions was used to calculate the enthalpies of formation of 30 polycyclic aromatic hydrocarbons (PAHs). The small reference species with well-determined experimental enthalpies of formation were used in these reactions. From comparison with available experimental data and other recently published high-level quantum chemical calculations, the reference values of the standard enthalpy of formation are recommended for 13 PAHs. The difference between the calculated and experimental values for these compounds does not exceed 2 kJ/mol and their experimental data can be considered as benchmark values for use in calculation of enthalpies of formation of various large PAHs and testing the accuracy of theoretical methods. The use of isodesmic-type reactions involving reference PAHs conserves the structural features of these compounds on both sides of the reaction which leads to a better error compensation. As a result, as shown in the example of coronene, a less-expensive DLPNO-CCSD(T)/CBS method can be used in this case for accurate prediction of enthalpies of formation of large PAHs.

Synergistic effects in toluene/C3H4 isomers co-pyrolysis: Formation of indene and naphthalene

A combination of experimental and kinetic modeling study is performed to explore synergistic effects between toluene and C3H4 isomers on the formation of polycyclic aromatic hydrocarbons (PAHs) and pyrolysis reactivity. Co-pyrolysis of toluene-allene and toluene-propyne is investigated in a flow reactor employing synchrotron vacuum ultraviolet photoionization mass spectrometry (SVUV-PIMS) at 0.04 bar and 1 bar. Mole fraction profiles of fuels and intermediates up to two-ring PAHs are obtained. A kinetic model for co-pyrolysis of toluene-C3H4 isomers is established and examined against the present data. Sampled mass-specific photoionization efficiency (PIE) curves are employed to identify the presence of aliphatic aromatic species, favoring specific perception into interactions between phenyl/benzyl radicals and C3 species. The synergistic effects observed in this work are not sensitive to the molecular structure of allene and propyne but quite sensitive to the experimental pressures. The reason being that the interactions between phenyl/benzyl radicals and small molecules like CH3, C2H2 and C3H3 are pressure dependent. Both experimental and simulation results indicate the essential role of the aliphatically substituted aromatic in the growth reactions. Indene and naphthalene are identified as the predominant C9H8 and C10H8 products respectively, in all cases studied. Channels leading to the formation of indene and naphthalene vary with pressure, according to rate-of-production (ROP) analyses. The phenyl + C3H4/C3H3 channel and benzyl + C2H2 channel make comparable contributions to the formation of indene at 0.04 bar, while the latter channel dominates the formation of indene at 1 bar. Both C7H5 + C3H3 channel and benzyl + C3H3 channel can lead to the formation of naphthalene at 0.04 bar, while the latter channel is more competitive at 1 bar.

Investigation of cyclohexene thermal decomposition and cyclohexene + OH reactions

Cyclohexene is a common intermediate in the oxidation of cyclohexane and alkyl-substituted cyclohexanes. It also plays an important role in the formation of polycyclic aromatic hydrocarbons (PAHs) by providing a route for the first aromatic ring. Two types of reactions are highly important in cyclohexene kinetics, i.e., H-abstraction by OH radicals and cyclohexene thermal decomposition. In this work, we have investigated these two reactions experimentally by employing sensitive UV diagnostics of OH radicals and 1,3-butadiene. We conducted rate coefficient measurements of cyclohexene + OH reaction (k1) over 933–1259 K and 1–4 bar using a narrow-linewidth UV absorption diagnostic of OH radicals near 306.67 nm. The carefully designed test conditions minimized the influence of secondary reactions such as cyclohexene thermal decomposition. Our determined OH + cyclohexene high-temperature rate coefficients show a positive temperature dependence and a negligible pressure dependence. Our rate values may be fitted with a two-parameter Arrhenius expression (units of cm3molecule−1s−1):k1=1.28×10−10e(−1225T)We also investigated channel-specific competition in OH + cyclohexene reaction. H-abstraction by OH from allylic (kc), alkylic (kb), and vinylic (ka) CH bonds contributes roughly 60%, 35%, and 5% over our temperature range. Our determined kc agrees excellently with literature rate coefficient of H-abstraction from the allylic site of 1-butene.We studied cyclohexene thermal decomposition reaction (k2) by tracing the product 1,3-butadiene near 212.5 nm over 1092–1361 K and 0.82–1 bar. Compared to literature works, our highly sensitive UV diagnostic of 1,3-butadiene enabled time-resolved measurements with low cyclohexene concentration, which guaranteed nearly isothermal conditions despite reaction endothermcity. Our measured rate coefficients may be expressed as (unit of s−1):k2=3.68×1014e(−31,562T)We implemented our determined rate coefficients (k1 and k2) in a literature cyclohexene kinetic model and also updated the 1,3-butadiene sub-mechanism. The updated model shows improved predictions of measured ignition delay times of cyclohexene.

Probing the influence of hydrogen cyanide on PAH chemistry

Hydrogen cyanide (HCN) is an important and highly toxic intermediate in coal, nitrogen-rich biomass, and ammonia combustion. It may play an important role in polycyclic aromatic hydrocarbons (PAH) and soot reduction, but the influence of HCN on PAH chemistry is unclear due to the lack of experimental data. With this motivation, the experimental and numerical investigations were performed in this work. Key intermediates were detected, identified, and quantified by the combination of Linear Trap Quadropole (LTQ) Velos Orbitrap mass spectrometer and gas chromatography-mass spectrometer in a jet-stirred reactor fueled by C2H2/HCN/N2 in the temperature range of 800-1200 K. The results reveal that the formation of benzene increases with the addition of HCN, but the PAH formation decreases. PAH reduction can be attributed to the formation of N-containing PAH (NPAH) via HCN-PAH interaction reactions, which were investigated by quantum chemistry and the Rice–Ramsperger–Kassel–Marcus theory with solving the master equation (RRKM-ME). Reaction rate comparison suggests that the HCN addition pathways to NPAH compete with the C2H2 addition pathways to PAH. The product yields in the systems of 1-naphthyl radical + C2H2 and 1-naphthyl radical + HCN were evaluated (T=800-2500 K and p=0.1-100 atm). The results indicate that the increasement of a new aromatic ring via cyclization is difficult in the 1-naphthyl radical + HCN system due to the high energy barrier, and the growth of larger NPAH is limited since the saturated N atoms in the heterocycle rings and CN functional group inhibit further carbon addition.

Effect of diesel and pentanol blends on PAH formation and regulated pollutants

The necessity of using oxygenated fuel blends in diesel engines has become apparent in recent years as one of the leading emission reduction approaches. Among such fuels, high-carbon alcohols, including n-pentanol, may serve as potential additives to reduce regulated and unregulated emissions. The aim of this study is to understand the effects of diesel fuel and n-pentanol blends (5%, 20% and 35% by volume: DPen5, DPen20, DPen35) on regulated emissions and polycyclic aromatic hydrocarbons (PAHs). These blends were tested in a diesel engine under three different load conditions and regulated emissions were determined. The PAH emissions of the exhaust gases were collected at idle and quantified using the gas chromatography–mass spectrometry (GC-MS) technique. Compared to neat diesel, the blended fuels, with their addition of n-pentanol, showed a significant reduction of up to 16.52% in nitrogen oxides (NOx) emissions. Additionally, decreases of up to 42.02% in total PAH emissions were obtained with 35% pentanol addition. For all blends, a significant reduction in higher cyclic PAHs was noted. Overall, diesel-pentanol blends were effective in reducing nitrous oxides, carcinogenic pollutants, and further, the possibility of engine malfunction operating at low load or cold operating conditions.

Formation and Inhibition of Heterocyclic Amines and Polycyclic Aromatic Hydrocarbons in Ground Pork during Marinating.

This study aims to simultaneously extract heterocyclic amines (HAs) and polycyclic aromatic hydrocarbons (PAHs) from ground pork for respective analysis by UPLC-MS/MS and GC-MS/MS, and study the effects of different flavorings and marinating time length on their formation and inhibition. Results showed that both HA and PAH contents followed a time-dependent increase during marinating, with HAs being more susceptible to formation than PAHs. The total HA contents in unmarinated pork and juice was, respectively, 61.58 and 139.26 ng/g, and rose to 2986.46 and 1792.07 ng/g after 24-h marinating, which can be attributed to the elevation of reducing sugar and creatinine contents. The total PAH contents in unmarinated pork and juice were, respectively, 34.56 and 26.84 ng/g, and increased to 55.93 and 44.16 ng/g after 24-h marinating, which can be due to the increment of PAH precursors such as benzaldehyde, 2-cyclohexene-1-one and trans,trans-2,4-decadienal. Incorporation of 0.5% (w/v) cinnamon powder or 0.5% (w/v) green tea powder was effective in inhibiting HA formation with the former showing a more pronounced effect for marinated pork, while the latter was for marinated juice. However, their addition was only effective in inhibiting PAH formation in marinated pork. Principle component analysis revealed the relationship between HA and PAH formation in ground pork and juice during marinating.

Combined effects of engine characteristics and fuel aromatic content on polycyclic aromatic hydrocarbons and toxicity

ABSTRACT Polycyclic aromatic hydrocarbons (PAHs) are harmful compounds because of their toxicity, adverse effects on human health, and threats to engine components (i.e. wetstacking). With the increased use of renewable fuels, it is imperative that the formation of PAHs be examined, in detail, with respect to the combustion characteristics and aromatic content of biofuels used in diesel engines. Since biodiesel is free of aromatic content in its chemical structure, this study provides comparative assessments of the PAHs, toxicity and regulated emissions of biodiesel (B100) and diesel fuel (D100), based on the fuel aromaticity and engine characteristics when used in two diverse engines. Results indicate that the use of B100 in both engines reduced total PAH emissions by 48.02% − 49.36% and PAH toxicity by 83.49% − 84.8% as compared to diesel fuel, which is a clear indication of the importance of the aromatic content of the base fuel on PAH formation and toxicity (i.e. aromatic-free fuel produces less PAH than diesel with high aromaticity). The aromatic ring distribution associated with B100 exhaust consisted of 50% two, 34% three and 16% four aromatic rings for the Onan engine, and 53% two, 32% three and 15% four aromatic rings for the Kubota engine. Benzo[a]pyrene, a five-ring PAH with great carcinogenic threat, was eliminated in both engines as a result of using B100. To demonstrate the significance of combustion processes on PAH formation, performances of the engines were compared and it was determined that the Kubota engine performed better for both fuels in reducing PAH emissions, due to such features as its injection system and combustion chamber design as compared to the Onan engine. Therefore, it has been concluded that PAH emissions and toxicity strongly depend on both the aromatic content and the combustion processes, as aromatic-free biodiesel significantly decreased PAHs along with additional reduction in PAHs and toxicity depending on the structural specifications of the diesel engine. Based on this study, aromaticity has been determined to be more effective than the type of engine in use for PAH reduction.

Pahs emission characteristics and the mitigation in the valuable products from used mineral oil thermolysis recycling

Pyrolysis of used mineral oil (UMO) to produce various valuable products is a flexible and efficient way for UMO recycling. Along with the preferred pyrolytic products, toxic polycyclic aromatic hydrocarbons (PAHs) may also be generated. To mitigate the PAHs emission during UMO pyrolysis, an understanding of emission characteristics and formation mechanism of PAHs is needed. In this work, four used minerals (engine, hydraulic, turbine, transformer) oil and three base oil were pyrolyzed at 600 °C at different heating modes (slow: 10 °C min−1, medium: ∼1000 °C min−1, fast: greater than10000 °C min−1) under N2/CO2 atmosphere. The results show that a higher heating rate can lead to more gas but less oil production. At different heating modes, PAHs emission factors change markedly and are in the range of 34.63–1492.85 ug g−1, among which more than 92 % of PAHs are enriched into pyrolytic oil. Naphthalene, phenanthrene and pyrene are the first three PAHs species in the gaseous product. The mechanism of evaporation and chemical evolution control PAHs formation for the SP process and FP process, respectively. PAHs formation is related to both the naphthene and aromatic contents of UMO, and the contribution of aromatics is about fourfold of the naphthenes. In the CO2 atmosphere, more liquid product and ∼ 33 % less PAHs formation can be realised due to the depressed dehydrogenation reaction.