Aromatic Formation Research Articles

Plasmon-mediated dehydrogenation of the aromatic methyl group and benzyl radical formation

A plasmon-driven deprotonation reaction of the aromatic methyl group can occur in aqueous solution under the illumination of red light. The reaction produces a benzyl radical and anion, and dimers through a self-reaction.

Influence of Mo modification on coaromatization coupling methanol with n-hexane over [Zn,Mo]/HZSM-5 catalysts

Zn and Mo modified HZSM-5 catalyst benefits the formation of aromatics and the yield of BTX reached 64%. The influence of Mo content on the catalytic performance and carbon deposit were investigated in detail.

Sensory acceptability of antioxidant-based formulations dedicated to mitigate heterocyclic aromatic amines in cooked meat

In a previous work, we studied the inhibition of heterocyclic aromatic amine formation by natural ingredients rich in antioxidants: caper, oregano, wine and green tea. This present work aimed to assess the sensory impact of the addition of these ingredients in ground beef patties. The best liked formulations were determined by a hedonic scoring. Caper and oregano were not significantly different from the standard, the most appreciated, due to their congruency with cooked meat. Direct dissimilarity assessment was performed to evaluate the overall, gustative and odor differences between formulations. Olfactive differences were evidenced as key drivers of these differences. Standard and caper were close while oregano was found significantly different from them. A fast sensory profiling permitted to evidence that aromatic plant note was discriminant for oregano formulation. Gas chromatography-mass spectrometry/multibooth olfactometry identified the distinctive odor-active compounds of the formulations as pyrazines and sulfide for oregano formulation and ester for caper formulation.

Co-torrefaction of corncob and waste cooking oil coupled with fast co-pyrolysis for bio-oil production

Lignocellulosic biomass is a rich source of fixed renewable carbon and a promising alternative to fossil sources. However, low effective hydrogen to carbon ratio limits its applications. This work studied the influence of oil-bath co-torrefaction of corncob and waste cooking oil for co-pyrolysis. It was compared with dry torrefaction and hydrothermal wet torrefaction firstly. Residual of oil-bath co-torrefaction were the highest of 97.01 %. Oil-bath co-torrefaction could maximize hydrogen atoms retention in corncob, which has a positive significance for deoxygenation during pyrolysis. Oil-bath co-torrefaction could also reduce the average activation energy required for corncob decomposition, while it was increased with dry torrefaction. Oil-bath co-torrefaction coupled with co-pyrolysis was more suitable for hydrocarbon-rich bio-oil production. Oil-bath co-torrefaction temperature had the greatest influence on bio-oil composition. High pressure promoted formation of the CC double bond and degradation of lignin, which further promoted the formation of monocyclic aromatics in bio-oil.

Roles of Molecular Structure in the Catalytic Cracking of n‐Heptane, Methylcyclohexane and Cyclopentene over HZSM‐5 Zeolites

AbstractCatalytic cracking technology is an important candidate for the crude‐to‐chemicals, which is promising to convert oil into chemicals by a clean and efficient way. n‐Heptane, methylcyclohexane and cyclopentene catalytic cracking over HZSM‐5 zeolites were studied at 320–550 °C under atmosphere, and a particular attention was paid to the effects of reaction temperature and time on stream. The cracked gas was analyzed by an online gas chromatograph, and the spent HZSM‐5 zeolites were characterized by TG, N2 physisorption and NH3‐TPD. It provided detailed information about the conversion, product distribution, coke formation and catalyst deactivation. Furthermore, the roles of molecular structure in the reaction network were discussed based on the carbenium ion mechanism. It was found that the protolytic cracking and hydride transfer was favored by n‐heptane due to the linear structure; the demethylation, protolytic ring‐opening and protolytic dehydrogenation was favored by methylcyclohexane due to the methyl group and cyclic structure; the protonation and oligomerization was favored by cyclopentene due to the cyclic and C=C structure. This made a significant difference on the catalytic performance: The activity was in a descending order of n‐heptane≈cyclopentene>methylcyclohexane. Alkane formation was in a descending order of n‐heptane>methylcyclohexane>cyclopentene. Aromatic and coke formation were in a descending order of cyclopentene>methylcyclohexane>n‐heptane.

Detailed Study of the Formation of Soot Precursors and Soot in Highly Controlled Ethylene(/Toluene) Counterflow Diffusion Flames

We perform spatially resolved measurements of temperature, gaseous species up to three-ring Polycyclic Aromatic Hydrocarbons (PAHs), and soot in atmospheric pressure counterflow diffusion flames. First, we characterize fully a baseline ethylene flame and then a toluene-seeded flame in which an aliquot of ethylene in the feed stream is replaced with 3500 ppm of prevaporized toluene. The goal is twofold: to investigate the impact of a common reference fuel component of surrogates of transportation fuels and bypass the main bottleneck to soot formation from aliphatic fuels, that is, the formation of the first aromatic ring. The composition of the fuel and oxidizer streams are adjusted to maintain a constant stoichiometric mixture fraction and global strain rate, thereby ensuring invariance of the temperature-time history in the comparison between the two flames and decoupling the chemical effects of the fuel substitution from other factors. Major combustion products and critical radicals are fixed by the baseline flame, and profiles of critical C2-C5 species precursors to aromatic formation are invariant in both flames. On the other hand, doping with toluene boosts the aromatic content and soot volume fraction, increasing the mole fraction of benzenoid structures and soot volume fraction by a factor of 2 or 3, relative to the baseline ethylene flame. This finding is consistent with the expectation that the formation of the first aromatic ring is no longer a bottleneck to soot formation in the doped flame. In addition, toluene bypasses completely benzene formation, opening a radical recombination pathway to soot precursors through the production of C14H14 (via dimerization of benzyl radical) and pyrene (through dimerization of indenyl radical).

A detailed kinetic model for aromatics formation from small hydrocarbon and gasoline surrogate fuel combustion

This work develops a detailed chemical kinetic model for Polycyclic Aromatic Hydrocarbon (PAH) chemistry that builds on a chemical model for gasoline surrogates by Cai et al. [Proc. Combust. Inst. 37 (2019) 639–647]. Informed by ab-initio and experimental studies, the model development emphasizes the prediction of soot precursors starting from C3H4 isomers up to the size of acepyrene. The proposed model was validated against experimental measurements from 79 publications, including ignition delay times, laminar burning velocities, and speciation data for several fuels in various conditions. A validation against measured peak mole fractions from 31 counterflow flames demonstrates an average prediction error of aromatic species up to the size of acenaphthalene below a factor of three. Additionally, the effects of experimental uncertainty are quantitatively discussed by computing confidence intervals for the true model prediction error. The formation of two-ring aromatic species is often still considered poorly understood. Accordingly, special attention is given to the formation of indene and naphthalene. Reaction flux analyses based on rigorously defined species selection criteria reveal that indene formation pathways are initiated by reactions of phenyl and benzyl and described by the reaction kinetics from theoretical calculations. In contrast, naphthalene formation is dominated by more uncertain pathways relying on estimated rates that are initiated by reactions of benzene and fulvenallenyl. Five-member rings on the periphery of PAH species and soot particles play a crucial role in recent experimental and theoretical studies. Therefore, this work investigates acenaphthene and other C12H8 isomers. The most abundant C12H8 isomers are acenaphthene, 1-ethynylnaphthalene, and 2-ethynylnaphthalene, and their respective concentrations are predicted to be similar in many flames. Furthermore, reaction flux analyses show that their formation is dominated by HACA routes starting from naphthalene.

The construction of garlic diallyl disulfide nano-emulsions and their effect on the physicochemical properties and heterocyclic aromatic amines formation in roasted pork

Garlic diallyl disulfide (DAD) nano-emulsions consisting of soy proteins were constructed, and their effects on physicochemical properties and heterocyclic aromatic amines (HAAs) formation in roasted pork were investigated. DAD was well encapsulated by soy proteins with a mean particle of 400–700 nm. Applying DAD nano-emulsions to pork patties significantly altered the color and texture of roasted pork, with a slight increase in brightness and decreases in redness and yellowness. The flavor determination demonstrated that sulfur-containing compound levels in encapsulated DAD were significantly reduced, particularly 7S group compounds, indicating an effective shielding effect on the irritating odor of garlic oil by protein. The levels of three HAAs (MeIQx, PhIP, and Harman) were significantly reduced by DAD nano-emulsion exposure (51.84 %, 76.80 %, and 48.70 %, respectively). This study provides a new method for inhibiting HAA formation and improving the sensory qualities of meat products.

Catalytic upgrading of cow manure pyrolysis vapors over zeolite/carbon composites prepared from coal gasification fine slag: High quality bio-oil obtaining and mechanism investigation

The resource utilization of solid waste not only reduces the environmental pollution, but also reduces the use of fossil energy. In this study, three low-cost zeolite/carbon composites, including Y-type zeolite/carbon, Beta zeolite/carbon and ZSM-5 zeolite/carbon, were prepared from coal gasification fine slag (CGFS), which were used for catalytic upgrading of pyrolysis vapors of cow manure (CM). The composition and distribution of products from the catalytic pyrolysis of CM over different types composites were explored, and the relationship between catalysts structure and product selectivity was clarified. The results show that different types of catalysts have virous effects on the composition and distribution of products due to different physiochemical structures such as pore size and acid site. Among them, ZSM-5 zeolite/carbon is more conducive to the formation of monocyclic aromatics due to its shape selective catalysis, Beta zeolite/carbon has relatively large pore size and has high selectivity for polycyclic aromatics, and Y-type zeolite/carbon is more conducive to the removal of nitrogen and oxygen-containing compounds. Moreover, vanillin, glucose and valine, which are the main components of lignin, cellulose and protein in CM were selected as model compounds to reveal the reaction mechanism of catalytic upgrading. The results of this study can provide reference and theoretical guidance for the comprehensive utilization of solid waste and the development of low-carbon green industry.

Highly stable Mo-based bimetallic catalysts for selective deoxygenation of oleic acid to fuel-like hydrocarbons

To develop efficient, economical and environmentally friendly Mo-based bimetallic Al/MCM-41 catalysts for catalytic oleic acid pyrolysis into hydrocarbon-like upgrading biofuel, a series of metal-modified Mo-based catalysts was successfully synthesized. The effects of different metal oxide types (Zr, Zn, Pt, Cu, Co, Ce, Ni) and Ce to Mo mixed ratios were compared and characterized by XRD, BET, NH3-TPD, XPS, SEM and TEM technologies. Simultaneously, the deoxygenation effect and reusability properties were also evaluated by Py-GC/MS and TGA. The results showed that the molybdenum-based bimetallic catalyst exhibited superior deoxygenation activity (Ce>Cu>Zn>Ni>Zr∼Pt>Co) in the decarbonylation and decarboxylation pathways. Higher deoxygenation activity was related to rich surface Ce-□-Mo synergistic oxygen vacancies, suitable metal-Lewis and Brønsted acidity and excellent textural properties. A higher Ce content was beneficial to HC and aromatic formation due to a higher specific surface area and mesoporous volume, and a higher Mo content facilitated olefin and alkane conversion due to a higher Brønsted acid intensity and smaller pore size. The 3Ce-1Mo/Al-MCM-41 exhibited excellent catalytic activity and promising reusability by yielding 97.72% hydrocarbons, 75.33% aromatic content and 57.92% MAHs due to the synergistic effect between Ce and MoOx, rich surface Ce-□-Mo synergistic oxygen vacancies and suitable metal-Lewis and Brønsted acid intensities that contributed to better reaction activity and coke resistance and activated the CO of oleic acid. The slight reduction in HCs was mainly due to the loss of active metal sites and coke deposition. Furthermore, the synergistic effect of Ce and MoOx species obviously advanced the reaction activity and coke resistance.

The effects of pore structures and functional groups on the catalytic performance of activated carbon catalysts for the co-pyrolysis of biomass and plastic into aromatics and hydrogen-rich syngas

The catalytic co-pyrolysis of Douglas fir and low-density polyethylene over different activated carbons (AC) was conducted using a fixed bed reactor, and the roles of AC pore structures and active functional groups in product yields and compositions was explored. While the liquid yield varied in the range of 36.7%–50.0%, the maximum yield was obtained using an H3PO4 activated AC catalyst. The AC catalysts activated by steam had well-developed micro-mesoporous structures dominated by micropores, which displayed high selectivity towards mono-aromatics. Whereas, the AC catalysts activated by H3PO4 exhibited additional mesoporous properties and P-containing functional groups, providing adequate space and reactive sites for converting bulky co-pyrolytic intermediates into double-ring aromatics, which were accompanied by the release of hydrogen (up to 80.6 vol%). A synergistic catalytic effect during co-pyrolysis promoted gas production at the expense of liquid. All the AC catalysts enhanced aromatics formation and reduced the yield of oxygenates and > C16 aliphatic hydrocarbons. In contrast to H3PO4 activated AC catalysts, steam activated AC catalysts exhibited a negative effect on hydrogen production, indicating different synergistic pathways during co-pyrolysis. These findings provide a reference for improving the catalytic activity of AC catalysts by regulating the pore structure and functional groups.

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.

Synthesis of unsymmetrical, Symmetrical Schiff bases by Ultrasonic Assisted Technique and Biological Evaluation of their Metal-Complex

A mild and efficient method has been reported for preparation of Schiff base ligands through condensation reaction of aromatic aldehydes and keton with different aromatic amines and formation of metal complex through the use of ultrasonic assisting technique. The advantages of this friendly, economically, environmentally and mild method are such as; simple work-up, high product yields and very short reaction times.

Role of formaldehyde in promoting aromatic selectivity during methanol conversion over gallium-modified zeolites

Gallium-modified HZSM-5 zeolites are known to increase aromatic selectivity in methanol conversion. However, there are still disputes about the exact active sites and the aromatic formation mechanisms over Ga-modified zeolites. In this work, in situ synchrotron radiation photoionization mass spectrometry (SR-PIMS) experiments were carried out to study the behaviors of intermediates and products during methanol conversion over Ga-modified HZSM-5. The increased formaldehyde (HCHO) yield over Ga-modified HZSM-5 was found to play a key role in the increase in aromatic yields. More HCHO was deemed to be generated from the direct dehydrogenation of methanol, and Ga2O3 in Ga-modified HZSM-5 was found to be the active phase. The larger increase in aromatic production over Ga-modified HZSM-5 after reduction‒oxidation treatment was found to be the result of redispersed Ga2O3 with smaller size generating a larger amount of HCHO. This study provides some new insights into the internal driving force for promoting the production of aromatics over Ga-modified HZSM-5.

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.

Acidity regulation for improved activity of Mo/HZSM-5 catalyst in methane dehydroaromatization

The Mo/HZSM-5 is a widely studied bifunctional methane dehydroaromatization (MDA) catalyst, and the acid site of zeolite is essential to the reaction process. In this study, the relationship between acid site control and MDA reaction performance is investigated. The Brønsted/Lewis acid sites have been toned by introducing promoters to the ZSM-5 zeolite. It shows that proper strong Brønsted acid sites are conducive to aromatic formation, while excessive Brønsted acid sites will lead to serious coke deposition. Thus, the MDA catalytic stability is further improved by passivation of partial Brønsted acid sites of Mo/HZSM-5 via coating Silicalite-1 on the catalyst surface. The optimized catalyst shows 95 % aromatic selectivity at initial with only 0.06 h−1 deactivation rate constant. The surface of HZSM-5 is reconstructed after hydrothermal treatment and the surface aluminum content is reduced. Moreover, the Silicalite-1 layer is beneficial to Mo species dispersion for preventing its aggregation and stabilizing the Mo-C active sites.

Изотопия углерода индивидуальных ароматических соединений нефти для понимания их геохимии

The article analyzes published and original data related to the carbon isotopic composition of individual aromatic compounds of fossil organic matter and oil. It has been shown that there is reliable evidence of the intramolecular isotopic heterogeneity of a number of molecules. For example the isotopically depleted carbon of the methyl group of alkylnaphthalenes and the terminal methyl of n-alkanes. The 13C inheritance from the biochemical precursor during the aromatization is also well documented in the example of diterpenes in the series abietic acid — dehydroabietane — simonellite — retene, as well as in the other terpene and steroid series. At the same time, there is evidence of carbon isotopic fractionation during the formation of several aromatic compounds from a single precursor. The increasing aromatization of the prebuild polycyclic structure does not change the 13C value of the molecule, and the formation of aromatic compounds with different numbers of aromatic rings in competing reactions leads to isotope differentiation in accordance with the thermodynamically determined distribution of carbon isotopes. If the suggestion is correct, it is the key to the understanding of specific petroleum aromatic hydrocarbons formation mechanism. It is possible that a comparison of 13C values for pairs of compounds formed during the transformation of one precursor will also provide information on the temperature conditions for the occurrence of the corresponding reactions.

Inhibitory effects of 25 spices on heterocyclic aromatic amines formation in cooked pork patties

Inhibitory effects of 25 spices on heterocyclic aromatic amines formation in cooked pork patties

Construction of an Axially Chiral Fluorene Nitrile-Based Framework via Benzannulation of Indene Diene with Benzoylacetonitrile

The methodology for the synthesis of fluorene-based atropisomers was developed via the strategy of aromatic ring formation. By this strategy, an efficient benzannulation of indene-based diene with benzoylacetonitrile divergently promoted by DABCO and a chiral organocatalyst was established, and various atropisomeric fluorene-based skeletons were generated in good yields, which not only provide a new strategy for the construction of atropisomeric biaryls but also offer a new member to the atropisomeric family.

Characteristics and Evolution Mechanism of Three Phase Products of Lignite by Hydrothermal Treatment Dewatering.

Baiyinhua lignite was treated by hydrothermal treatment dewatering (HTD). The production characteristics of the gas, solid, and liquid were studied. Results show that HTD is an effective means to decrease water content and water-holding capacity. When the treatment temperature was increased to 310 °C, the moisture was reduced from 26.55% to 5.27%, and the dehydration rate reached 80.20%. At the same time, the carbon content and calorific value increased during the HTD process, which increased energy density. The H/C atomic ratio increased first, then decreased with the increasing temperature. The increase in the H/C atomic ratio was due to the breakdown of aromatic ether and formation of phenolic compounds at the low temperature. The phenolic compounds started to break at the high temperature, which resulted in the decrease in the H/C atomic ratio. These results can be proven by 13C NMR analysis. Combined with the analyses of calorific value, dehydration ratio, recovery of combustible product, and heat loss, the relative balance dehydration and deoxidation efficiency were evaluated, and 250 °C is a suitable temperature for the HTD process in lignite upgrading. The HTD process promoted the breakage and decomposition of weak chemical bonds in lignite, which resulted in many organic compounds in wastewater after the HTD process. The chemical oxygen demand and biochemical oxygen demand continually increase, and the biodegradability of the wastewater is relatively good. The index of biodegradability for wastewater is greater than 0.3 even at a hydrothermal treatment temperature of 310 °C. This indicates that wastewater can be subjected to biochemical treatment at a low treatment cost. At the same time, the metal ions and nonmetallic ions in wastewater and the gas component were studied. These research results aim to provide theoretical guidance for the industrialization of lignite hydrothermal modification.