Benzene Formation Research Articles

Benzoic Acid Based Beverages: Health Implications

Soft drinks nowadays are becoming an important part of the modern diet consumed in many communities worldwide and are available in the market virtually in the same form almost anywhere around the globe. Additives such as antioxidants and preservatives are usually added to soft drinks to increase their shelf life. Several acids such as benzoic and ascorbic acid are used in beverages to prevent oxidation and degradation of matrix. Literature documented that combination of these preservatives in soft drinks results in benzene formation. Moreover, benzene has long been reported to inflict many public health problems. This review elucidated different health consequences such as hematological, neurological, reproductive and carcinogenic effects of exposure to benzene. Liver and kidney derangements were also reported from different epidemiological and experimental studies. Therefore, we suggest that combination of ascorbic acid and benzoic acid in beverages should be avoided by small scale and industrial manufactures. A closer monitoring of these preservatives in beverages by regulatory agencies is highly needed.

Aromatics and Cyclic Molecules in Molecular Clouds: A New Dimension of Interstellar Organic Chemistry.

Astrochemistry lies at the nexus of astronomy, chemistry, and molecular physics. On the basis of precise laboratory data, a rich collection of more than 200 familiar and exotic molecules have been identified in the interstellar medium, the vast majority by their unique rotational fingerprint. Despite this large body of work, there is scant evidence in the radio band for the basic building blocks of chemistry on earth-five- and six-membered rings-despite long-standing and sustained efforts during the past 50 years. In contrast, a peculiar structural motif, highly unsaturated carbon in a chainlike arrangement, is instead quite common in space. The recent astronomical detection of cyanobenzene, the simplest aromatic nitrile, in the dark molecular cloud TMC-1, and soon afterward in additional prestellar and possibly protostellar sources, establishes that aromatic chemistry is likely widespread in the earliest stages of star formation. The subsequent discovery of cyanocyclopentadienes and even cyanonaphthalenes in TMC-1 provides further evidence that organic molecules of considerable complexity are readily synthesized in regions with high visual extinction but where the low temperature and pressure are remarkably low. This review focuses on laboratory efforts now underway to understand the rich transition region between linear and planar carbon structures using microwave spectroscopy. We present key features, advantages, and disadvantages of current detection methods, a discussion of the types of molecules found in space and in the laboratory, and approaches under development to identify entirely new species in complex mixtures. Studies focusing on the cyanation of hydrocarbons and the formation of benzene from acyclic precursors are highlighted, as is the role that isotopic studies might play in elucidating the chemical pathways to ring formation.

Identifying Barrierless Mechanisms for Benzene Formation in the Interstellar Medium Using Permutationally Invariant Reaction Discovery.

Complex chemical reaction environments, such as those found in combustion engines, the upper atmosphere, or the interstellar medium, can contain large numbers of different reactive species participating in similarly large numbers of different chemical reactions. In such settings, identifying the most-likely multistep reaction mechanisms which lead to the production of a particular defined product species is an extremely challenging problem, requiring search and evaluation over a large number of different possible candidate mechanisms while also addressing the permutational challenges posed when considering a large number of reaction routes available to sets of identical molecular species. In this article, the problem of generating candidate reaction mechanisms which form a defined product from a diverse set of reactive molecules is cast as a discrete optimization of a permutationally invariant cost function describing similarity between the target product and the product generated by a trial reaction mechanism. This approach is demonstrated by generating 2230 candidate reaction mechanisms which form benzene from diverse sets of reactive molecules which have been experimentally identified in the interstellar medium. By screening this set of autogenerated mechanisms, using dispersion-corrected DFT to evaluate reaction energies and activation barriers, we identify several candidate barrierless reaction mechanisms (both previously proposed and new) for benzene formation which may operate in the low temperatures found in the interstellar medium and could be investigated further to supplement existing microkinetic models.

Production of light hydrocarbons from organosolv lignin through catalytic hydrogenation and subsequent fast pyrolysis

Valorization and utilization of lignin have been drawing increasing attention recently. Hydroprocess is one of the main technologies, which can reduce organic compounds and partially depolymerize the macromolecular structure of lignin. The mechanism of lignin hydroprocess has been extensively discussed focusing on hydrogenolysis. In contrast, the solid residue regarded as unreacted or depolymerized lignin has drawn less attention so far. This study proposes an integrated process that consists of catalytic hydrogenation and subsequent fast pyrolysis for valorizing lignin. The results showed that 48−87 wt.% of solid product could be recovered as hydrogenated lignin (H-EOL) after hydrogenation at 200–250 ℃ for 1−7 h. Chemical structure of H-EOL was comprehensively investigated by means of elemental analysis, FTIR, 13C &1H NMR, and TGA. Furthermore, behavior of fast pyrolysis of H-EOL was detected here for the first time. H-EOL has higher hydrogen to carbon atomic effective ratio(H/Ceff ratio) and achieves the increasing reactivity of thermal decomposition. H-EOL yields light olefins double as much as raw ethanol organosolv lignin (EOL). And the formation of alkanes (C1-C4), benzene, and toluene was promoted to various degrees, while the yield of carbon monoxide, carbon dioxide, and vapor decreased. A novel and efficient pretreatment method has been provided to valorize lignin, which is instructive for subsequent research.

Direct evidence for a single-step radiation-induced assembling of benzene ring from acetylene trimer at cryogenic temperatures

The discovery of carbon-rich species, including polycyclic aromatic hydrocarbons (PAH) and fullerenes, in the space environment is among the most intriguing findings in molecular astrophysics and astrochemistry of the recent decades. The mechanism of their formation remains unclear and the one of the key issues is related to making “first ring”, i.e., formation of benzene from simple small molecules abundant in the outer space. Different routes involving C2, C3 and C4 hydrocarbons are considered in literature. Here we report the first direct evidence for a single-step radiation-induced formation of benzene from pre-existing isolated acetylene trimer occurring in frozen inert environment at very low temperature (6 K). The finding is based on the correlation between trimer decay and build-up of benzene as monitored by FTIR spectroscopy. This concerted pathway may be applicable to acetylene aggregates trapped in the bulky ices or in the grain pores and it emphasizes the importance of concept of molecular organization in the chemical history of the Universe.

Different chemical effect of hydrogen addition on soot formation in laminar coflow methane and ethylene diffusion flames

Previous studies showed that adding hydrogen (H2) can have an opposite chemical effect on soot formation: its chemical effect enhances and suppresses soot formation in methane (CH4) and ethylene (C2H4) diffusion flames, respectively. Such opposite chemical effect of H2 (CE-H2) remains unresolved. The different CE-H2 is studied numerically in the two laminar coflow diffusion flames. A detailed chemical mechanism with the addition of a chemically inert virtual species FH2 is used to model the gas-phase combustion chemistry in this study. Particularly, a reaction pathway analysis was performed based on the numerical results to gain insights into how H2 addition to fuel affects the pathways leading to the formation of benzene (A1) in CH4 and C2H4 flames. The numerical results show that the CE-H2 in CH4 diffusion flame to prompt soot formation is ascribed that the higher mole fraction of H atom promotes the formation of A1 and Acetylene (C2H2) and leads to higher nucleation rate and eventually higher soot surface growth rate. In contrast, adding H2 to C2H4 diffusion flames decreases soot nucleation and surface growth rate. The lower soot nucleation rate is due to the lower mole fractions of pyrene (A4), while the lower soot surface growth rate is due to the lower mole fractions of H atom and C2H2, higher mole fraction of H2 and lower soot nucleation rate. Furthermore, the CE-H2 in C2H4 diffusion flames promotes the formation of A1, but suppresses the formation of A4.

Atmospheric and high pressures pyrolysis study of n-decane in a flow reactor with online GC-MS/FID analysis: Experiments and modeling

The atmospheric and high-pressure pyrolysis of n-decane was studied in a flow tube reactor combined with online GC–MS/FID at 723−1123 K, 0.1–3.0 MPa (highly diluted in helium). Compared with 0.1 MPa, the conversion of n-decane and mole fraction of alkenes clearly increased at 3.0 MPa at the fixed temperature, and more aromatics were observed including toluene, styrene, ethylbenzene, indene and naphthalene, suggesting that the secondary reactions are more intense under high pressure. To account for these differences, a detailed kinetic model with 191 species and 1117 reactions was constructed by incorporating the aromatics subset to a n-decane model developed in previous low-pressure work, and further validated against literature data covering a wide pressure range (0.004–7.2 MPa) with reasonable reproducibility. The current model was compared against three literature kinetic models (LLNL, JetSurf 2.0 and Rev1stGen) and showed a better accordant with the conversion of n-decane and the selectivity of major products. Based on the rate of production and sensitivity analysis using the current model, the results show that although the total consumption of n-decane is weakly pressure-dependent at fixed temperature and residence time under the investigated conditions, the formation and consumption pathways of primary products change significantly attributed to the enhanced bimolecular abstraction and combination reactions at higher pressures. For the formation of benzene, the combination of 1,3-butadien-2-yl with ethylene is the main pathway at both 0.1 and 3.0 MPa, while the additional combination reactions: propargyl with allyl and cyclopentadienyl (c-C5H5) with CH3 become dominant at 0.1 MPa and 3.0 MPa, respectively. For the formation of larger aromatic naphthalene, the self-recombination of c-C5H5 is the most important channel at all investigated pressures.

Insights into coke location of catalyst deactivation during in-situ catalytic reforming of lignite pyrolysis volatiles over cobalt-modified zeolites

HZSM-5, Co-incorporated HZSM-5 (3Co/Z5) and Co-incorporated hierarchical HZSM-5 (3Co/DZ5) were employed in catalytic reforming of volatiles from lignite pyrolysis in a drop bed reactor aiming at high yields of light aromatics. The co-effect of hierarchical pores and metallic sites on 3Co/DZ5 promoted the formation of benzene, toluene, xylene and naphthalene, and improved the service lifespan by decreasing coke formation. The influence of hierarchical pores and metallic sites on the deposition and nature of coke and on its location in the channels or/and the outer surface of zeolites was investigated. For 3Co/DZ5, the hierarchical pores retarded its deactivation by preventing internal coke formation while facilitating the external coke formation, owing to the reduced diffusion resistance of coke precursors (aromatic species) out of channels. The introduction of metallic sites brought the suppression of O-containing species depositing on zeolite. After continuous operation, the skeleton structures of both spent and regenerated catalysts were seriously damaged by coke deposition and sintering. The main causes of catalyst deactivation were assigned to two deactivating carbonaceous species with aromaticity and aliphaticity located on the inner pores and outer surface. The soluble long-chain aliphatics from coke extracts located on the outer surface were attributed to the decomposition of inherent aliphatic chain structure in lignite. The residual coke trended to graphite-like structure. The coking behavior was revealed by means of some technologies that the internal coke mainly had impact on the catalyst performance, especially for the insoluble aromatics with high polycondensation, whereas the external coke consumes the surface active sites, resulting in uninterrupted accumulation of coke precursors, eventually blocking the accessibility to channels.

Upcycling of waste teabags via catalytic pyrolysis in carbon dioxide over HZSM-11

Disruptive impact of everyday waste on the environment makes it a serious growing concern. Even though disposal and reclaim strategies are firstly considered to overcome this problem, upcycling of the waste via thermochemical transformations (e.g., pyrolysis) will eventually be essential to reconvert massive quantities of waste materials. Here, to seek a method to valorize everyday waste, the effects of CO2 and HZSM-11 catalyst on pyrolytic products produced via pyrolysis of waste teabag were investigated. For non-catalytic pyrolysis of waste teabag, CO2 increased the yield of pyrolytic gases and suppressed the formation of benzenes, phenolics, and polycyclic aromatic hydrocarbons, compared to N2. For catalytic pyrolysis of waste teabag over HZSM-11 more CO2 was transformed to CO than non-catalytic pyrolysis. The extent of CO2 conversion into CO was greater in CO2 environment than in N2 environment. A synergistical use of CO2 and HZSM-11 in pyrolysis of waste teabag enhanced the production of caprolactam (6.8 wt% yield), a value-added nylon monomer. The char derived from waste teabag via the pyrolysis in CO2 over HZSM-11 had higher heating value of 26 MJ kg−1 comparable to HHV of coal. The synergistical employment of HZSM-11 catalyst and CO2 pyrolysis medium has a significant feature of upcycling everyday waste such as waste teabag.

Catalytic Process in Producing Green Aromatics through Fast Pyrolysis of Wood of Five Tropical Fast Growing Trees Species

The generation of liquid fuels and chemicals is potential through a catalytic fast pyrolysis (CFP) which is a rapid, inexpensive, and promising method utilizing tropical wood biomass as starting material. There is a little known in the potential of wood biomass from tropical fast-growing trees as starting materials for the production of liquid fuel and chemicals. In this study the formation of aromatics by pyrolytic-gas chromatography/mass spectroscopy (Py-GC/MS) is evaluated on the effect of wood species with different characteristics and its cellulose component to the formation of aromatics. Fast pyrolysis of eucalyptus wood characterized with low content of ash and high percentages of hollocellulose and α-cellulose produced much high relative peaks of levoglucosan and small relative peaks of lignin derived products. Meanwhile high content of vollatile matter and high crystallinity of cellulose attributed balsa and jabon woods as feedstock for fast pyrolysis. The catalytic process in fast pyrolysis of eucalyptus decomposed the most of oxygenated compound such as levoglucosan and furfural into aromatics in the presence of ZSM-5. Coke formation on the surface catalyst might lead partly of decomposition of levoglucosan and furfural to form aromatics in the catalytic fast pyrolysis of balsa wood. Cellulose component determined on the formation of benzene, toluene, styrene, p-xylene, indane, indene, and naphthalene in catalytic fast pyrolysis of wood.

Detailed gas-phase kinetics and reduced reaction mechanism for methane pyrolysis involved in CVD/CVI processes

A detailed gas-phase kinetic model consisting of 37 species and 318 reactions is developed for methane pyrolysis involved in the chemical vapour deposition/infiltration (CVD/CVI) processes. The model was used to perform the simulations of CH4 pyrolysis in a hot-wall CVD reactor over a wide range of operating conditions and validated against the experimental data. The overall trend of the concentration profiles of notable species is in good agreement with experimental results. The sensitivity analysis and reaction path flux diagram revealed that CH4 pyrolysis directly proceeds without any induction period. C2 species are the primary intermediates for the formation of acetylene, ethylene, and benzene. Besides, the accuracy of the present model is better than the models available in the literature. The detailed kinetic model was then systematically reduced to a small mechanism comprising 13 species and 29 reactions. The predictions of reduced mechanism also agreed well with the detailed mechanism at low inlet partial pressure (<10 kPa). Although the error in the mole fraction of light species was minimal, the relatively large error for C6H6 species was observed at high inlet partial pressure of CH4.

Trapping AsPh3 via reaction with NiS/γ-Al2O3 in the presence of H2: Reaction mechanism and kinetics

Removal of As from petroleum feedstocks is an important process which can be realized using As trapping mass containing supported nickel sulfide. In order to understand the mechanism of the trapping we studied the reaction of AsPh3 with NiS/γ-Al2O3 in the presence of H2 in a batch reactor in toluene solution at 230 °C. This reaction results in formation of NiAs, benzene and H2S. Also, the intermediate species, thiophenol and diphenylsulfide, were observed. Despite formation of NiAs layer in the course of reaction, the rate of AsPh3 decomposition is not affected by the solid state diffusion up to ∼ 50 % of nickel conversion. The rate determining step in these conditions appears to be the hydrogenolysis of As-C bonds. It was found that the reaction order changes in the course of reaction from zero to one. This trend is described by a kinetic model assuming adsorption of AsPh3 molecules followed by decomposition.

An experimental and modeling study on sooting characteristics of laminar counterflow diffusion flames with partial premixing

The effects of partial premixing on soot formation were investigated both experimentally and numerically in counterflow diffusion flames (CDFs) of ethylene, propane and ethylene/propane binary mixtures. The partial premixing ratio was maintained at relatively low levels so as to minimize the hydrodynamic effects; while the chemical effects of partial premixing on soot formation can be highlighted. The experimental results and simulations consistently showed that partial premixing notably increased soot formation in ethylene flames; while it slightly reduced the soot formation in propane flames, suggesting that partial premixing played different chemical roles in the soot formation process of ethylene and propane flames. Kinetic analyses revealed that partial premixing showed opposing effects on propargyl formation of ethylene and propane flames; this in turn led to the opposing effects on the formation of benzene and polycyclic aromatic hydrocarbons (PAH), and finally on the soot inception process. For partial premixing in propane/ethylene mixtures, the observed synergistic effects with propane added to ethylene CDFs disappeared, indicating a chemical cross-linking effect between partial premixing and ethylene/propane mixture. In addition, the present soot model showed satisfactory performance in reproducing the mismatch between PAH and soot formation tendencies in ethylene and propane CDFs. This result implies that great care is needed when using PAH concentration as an indicator of sooting tendency of different fuels. The present modeling results provided new insights into the chemical role of partial premixing in the soot evolution process of ethylene, propane and their blends. Further investigations towards the partial premixing effects on soot formation of larger liquid hydrocarbons such as diesel surrogates are required.

Experimental and kinetic modeling study of ammonia addition on PAH characteristics in premixed n-heptane flames

Due to concerns over pollutant emissions and ever-increasing energy crisis, ammonia is being considered as a promising alternative fuel to control soot particles and their precursors (polycyclic aromatic hydrocarbons, PAHs) emissions in combustion for diesel engines. This paper aims to investigate the chemical effects of NH3 addition on PAH formation in n-heptane laminar premixed flames. The laser-induced fluorescence (LIF) technique was used to measure the relative PAH fluorescence intensities qualitatively. A kinetic modeling study was performed to predict PAH concentrations by comparing with the experimental results, and then clarify the underlying effects of NH3 on PAH formation. Both experimental and numerical results revealed that PAH concentrations decreased monotonically as ammonia fraction increased, suggesting a PAHs-inhibiting role for NH3 in n-heptane baseline flames. Reaction pathway analysis revealed that the suppression of NH3 on PAH formation could be attributed to the competition for H, OH and O radicals in fuels' decomposition, and chemical interactions of amine radicals with the C1-C2 species. For this reason, the NH3 addition produced a relatively decreased C2H2, thereby inhibiting the formation of propargyl. As a result, benzene formation was inhibited through C3H3 self-recombination reaction, resulting sequentially in the suppression of PAH formation and growth. Besides, the decreased C2H2 yield in the post-flame region of NH3 doping flames also inhibited the formation of PAHs through the hydrogen-abstraction-acetylene-addition (HACA) mechanism.

Evaluation of zeolite catalysts on product distribution during sweet sorghum bagasse catalytic pyrolysis

The catalytic fast pyrolysis (CFP) of sweet sorghum bagasse was carried out in a three-stage tube furnace to achieve high value utilization of sweet sorghum bagasse. The effects of zeolite catalysts (hierarchical HZSM-5, HBeta, HY and HUSY) and pyrolysis temperature (450 °C, 500 °C, 550 °C and 600 °C) were investigated to obtain the relationship between the product distribution of bio-oil and the zeolite properties. The results showed that the relative contents of monocyclic aromatics followed the order: hierarchical HZSM-5 (DS-HZSM-5) > HBeta > HUSY > HY, and the relative contents of polycyclic aromatics followed the order DS-HZSM-5 < HY < HUSY < HBeta. DS-HZSM-5 contributed to the formation of benzenes, obtaining the highest relative content (80.8%), whereas HUSY and HBeta facilitated the formation of naphthalenes with relative contents of 7.4% and 11.2%, respectively. Furthermore, 550 °C was the optimum pyrolysis temperature for the catalysis of DS-HZSM-5, and 450 °C was the most suitable pyrolysis temperature for the catalysis of HBeta, HY and HUSY. The results of this research are important for the utilization of sweet sorghum wastes in view of obtaining high-value chemicals.

A mid-infrared diagnostic for benzene using a tunable difference-frequency-generation laser

Benzene is a very important molecule in a variety of industrial, environmental, and chemical systems. In combustion, benzene plays an essential role in the formation and growth of polycyclic aromatic hydrocarbons and soot. In this work, a new laser-based diagnostic is presented to make quantitative, interference-free, and sensitive measurements of benzene in the mid-infrared (MIR) region. The diagnostic is based on a widely tunable difference-frequency-generation (DFG) laser system. We developed this laser source to emit in the MIR between 666.54 cm−1 and 790.76 cm−1 as a result of the DFG process between an external-cavity quantum-cascade-laser and a CO2 gas laser in a nonlinear, orientation-patterned GaAs crystal. Benzene measurements were carried out at the peak (673.94 cm−1) of the Q-branch of the ν11 vibrational band of benzene. The absorption cross-section of benzene was measured over a range of pressures (4.44 mbar to 1.158 bar) at room temperature. The temperature dependence of the absorption cross-section was studied behind reflected shock waves over 553–1473 K. The diagnostic was demonstrated in a high-temperature reactive experiment of benzene formation from propargyl radicals. The new diagnostic will prove highly beneficial for high-temperature studies of benzene formation and consumption kinetics.

Catalysis of water molecules acting as Brönsted acids at Lewis acid sites on niobium oxide

The effects of water addition on cumene cracking over niobium oxide and H-ZSM-5 are investigated in order to clarify the behavior of water molecules on solid acid catalysts. The activity of niobium oxide was improved in the presence of water vapor although H-ZSM-5 showed constant activity. When heavy water was introduced into the reaction over niobium oxide, the hydrogen atoms were substituted with the deuterium atoms in about 85 % of the produced benzene. The heavy water molecule on niobium oxide acts as the catalyst for cumene cracking, resulting in the formation of benzene containing D atoms. In addition, the Lewis acid on the niobium oxide was observed to change reversibly to the Brönsted acid in the presence of water using IR of adsorbed pyridine. We propose a mechanism that water behaves as Brönsted acid, which was clarified by repeating adsorption and desorption on Lewis acid sites of niobium oxide.

Kinetics and thermochemistry of cyclohexadienes reactions with hydroxyl radicals

Cyclohexadienes (CHDs) are important intermediates in the pyrolysis and oxidation of many C6 cyclic hydrocarbons. Under combustion relevant conditions, these dienes may either eliminate H2 directly or lose H atoms sequentially to produce the first aromatic ring, i.e., benzene. This is one of the major reaction pathways for the formation of benzene from C6 cyclic hydrocarbons. Despite its importance in PAH and soot formation process, the chemistry of CHD has attracted less attention from the scientific community. In this work, we have investigated hydrogen abstraction reactions of 1,3- and 1,4-CHD by OH radicals using a shock tube and UV laser absorption over the temperature range of 900 – 1100 K and pressures of ∼ 1 – 3 atm. Reaction kinetics was followed by monitoring OH radicals near 307 nm. At high temperatures, both isomers of CHDs are found to exhibit comparable reactivity with OH radicals. These reactions show a weak positive temperature dependence. Measured rate coefficients can be represented by the following Arrhenius expressions in units of cm3 molecule−1s − 1:k1(1,3−CHD+OH)=1.76×10−10exp(−1761KT)k2(1,4−CHD+OH)=2.23×10−10exp(−1813KT) To gain further insights into these reactions, various ab initio methods were employed to compute relevant thermochemical data. This study reports the first high-temperature kinetic data for cyclohexadienes which will be beneficial to improve the performance of the oxidation kinetic models of C6 cyclic hydrocarbons.

Reforming of toluene as a tar model compound over straw char containing fly ash

The present work focuses on confirming that straw char containing fly ash (SCFA) produced from steam–oxygen gasification (SOG) of straw pellets has the potential to be reused as a tar–reforming catalyst in the original process. The catalytic activity and reforming selectivity of SCFA was evaluated with toluene as a tar model compound in the presence of steam and hydrogen in a lab–scale fixed bed reactor at high temperature up to 900 °C. The kinetic results showed that SCFA was effective in toluene reforming with a complete toluene conversion at a space time of 0.05 kg h m−3 under 850 °C and a steam volume fraction of 15%. On the other hand, when hydrogen was present, the significant effect of hydrogen on toluene reforming was demonstrated by the formation of benzene through hydrodealkylation reaction. The volumetric ratio of H2O to H2 was an essential parameter that decided the selectivity of toluene reforming. Although the coexist of toluene and hydrogen would inhibit the gasification, SCFA was proved to be gasified during toluene reforming. The surface migration and agglomeration of inorganics due to gasification also resulted in the change of catalytic activity and reforming selectivity through time. In conclusion, this study demonstrated the potential utilization of SCFA derived from the SOG process as a tar–reforming catalyst to enhance the overall performance of the SOG process.

Effects of pressure on soot formation in laminar coflow methane/air diffusion flames doped with n-heptane and toluene between 2 and 8 atm

There is currently a lack of adequate understanding of soot formation in flames fueled with liquid hydrocarbons at elevated pressures. In this study, laminar coflow n-heptane and toluene doped CH4/air diffusion flames were numerically investigated under a constant carbon mass flow rate at pressures between 2 and 8 atm to understand how pressure affects the sooting propensity of these two main components of surrogate fuels mimicking gasoline. Numerical simulations were performed using a detailed reaction mechanism containing 175 species and 1175 reactions and a sectional soot model. Soot inception is modeled by collisions among pyrene, BAPYR and BGHIF. Soot surface growth and oxidation are modeled using the hydrogen abstraction acetylene addition (HACA) mechanism as well as PAH surface condensation. The predicted sensitivity of soot production to pressure is in better agreement with the measurements of Daca and Gülder (2017) when the soot aging effect is considered in HACA surface growth. The predicted soot concentrations are in overall good agreement with measurements. Propargyl recombination and propargyl reaction with propyne are important pathways for the formation of benzene. In methane+toluene flames, attack of toluene by H radical is an effective benzene formation pathway low in the flame, but the relative importance of benzene formation from toluene is reduced with increasing pressure. Although all the soot formation processes are enhanced with increasing pressure, PAH condensation is enhanced the most, followed by HACA and inception. At 6 and 8 atm, PAH condensation becomes comparable to HACA. The pressure dependence of the sooting propensity follows the order of methane+toluene < methane+n-heptane < methane, consistent with measurements. This result can be explained by the pressure dependence of benzene formation pathways, the kinetic effect of pressure, and the scrubbing effect of soot production on the gas-phase species involved in soot formation.