Conversion Of Polycyclic Aromatic Hydrocarbons Research Articles

In situ visualization of polycyclic aromatic hydrocarbon hydrothermal decomposition process utilizing planar induced fluorescence: A mechanistic analysis

Hydrothermal decomposition of coal or biomass for hydrogen production is a clean and efficient technology. Comprehending the hydrothermal decomposition mechanism of Polycyclic Aromatic Hydrocarbons (PAHs) is pivotal for advancing biomass or coal hydrothermal reaction technology. Traditional non-in situ measurement methods present challenges in thoroughly exploring the intricacies of PAHs’ hydrothermal reaction mechanisms. To address this issue, this study establishes an in situ visualization platform leveraging planar laser-induced fluorescence (PLIF) technology. Fluorescence signals emanating from naphthalene are meticulously measured in situ across diverse temperature conditions (450 °C-650 °C). The decomposition rate characteristics of PAH in hydrothermal process are thereby elucidated. A proportional increase in the reaction rate of naphthalene with elevated temperatures, concomitant with an augmented risk of coking. Moreover, the generation of hydroxyl radicals (OH) during the hydrothermal decomposition process was observed in the in situ visualization platform. Afterwards, to promote the generation of OH radicals and improve the conversion of PAHs, small molecule additives (formic acid, acetic acid, methanol, and ethanol) were added into the reactions. The experimental results indicate that the addition of small molecules increases the conversion rate of PAH and significantly reduces coking. These radicals effectively occupy reactive sites on naphthalene, thereby suppressing the coking proclivity of PAHs. This work provides a novel method to investigate the mechanism of hydrothermal process and offers a potential way to improve the conversion efficiency.

Regulate the mesopores and acidic structure of Pt/USY zeolite catalyst for improved performance in the hydroisomerization of phenanthrene to alkyl-adamantane

Adamantane-based high energy density fuels (HEDFs) play a key role in military and aerospace applications due to their high volumetric calorific value and high density. In the preparation of adamantane-based HEDFs by hydroisomerization of polycyclic aromatic hydrocarbons (PAHs) in coal tar, there is competition between cracking and ring-opening reactions. Therefore, USY zeolites were etched with NaOH solution to expand the mesoporous and regulate the acidity, inhibit the cracking reaction, and promote the ring-shift isomerization of perhydrophenanthrene (PHP) to alkyl-adamantane (AlA), increasing the yield of AlA from 19% to 32%. There are two processes in the conversion of PAHs to AlA, hydrogenation and ring-shift isomerization. Phenanthrene was first hydrogenated to PHP, then isomerized to alkyl-adamantane, the product distribution of alkyl-adamantanes with different side chains was discovered, part of the C14 alkyl-adamantanes cracked, and the hydroisomerization reaction of PHP occurred only on the outer surface or pore mouth of USY zeolite. It provides a new perspective for the hydroconversion of PAHs to HEDFs.

Study on thermochemical conversion of triglyceride biomass catalyzed by biochar catalyst

This study investigates the fast catalytic pyrolysis of rubber seed oil over a CO2-activated biochar catalyst in the temperature range of 600–800 °C, producing high-value products. The effect of activation time on the catalytic performance and the possibility of using the deactivated catalyst as fuel are also examined. The results indicate that extending the activation time can increase the specific surface area and oxygen active sites of biochar catalyst, thereby improving the catalytic performance. At optimum temperature (800 °C), the biochar catalysts increase the syngas yield from 507.90 mL/g to 634.51 mL/g while facilitating the conversion of polycyclic aromatic hydrocarbons to monocyclic aromatic hydrocarbons. Consequently, the yield of monocyclic aromatic hydrocarbons is increased from 3.72 wt% to 55.77 wt%. Out of the monocyclic aromatic hydrocarbons, benzene and its derivatives are important chemicals, with a yield of 46.80 wt%. Besides, microporous channels in biochar catalysts inhibit the generation of coke, reducing the coke yield from 13.57 to 5.59 wt%; the coke deposit on biochar catalyst is pyrolytic coke. The high heating value of the deactivated biochar catalyst reach 28.605 MJ/kg, and it can be used as a solid fuel. Finally, a mechanism for converting polycyclic aromatic hydrocarbons to monocyclic aromatic hydrocarbons during the fast catalytic pyrolysis of the rubber seed oil is proposed.

Effects of different carbon substrates on PAHs fractions and microbial community changes in PAHs-contaminated soils

Different types of carbon substrates were widely used in soil remediation. However, differences of their impacts and related mechanisms on degradation of polycyclic aromatic hydrocarbons (PAHs) and microbial community structures in contaminated soil still remain unclear. Here, we investigated the effects of corn straw (S), glucose (G), straw combined with glucose (SG), and sodium azide (N, as an abiotic control) on PAHs fractions and bacterial communities in soil. After 70 days’ microcosm experiments, total PAHs concentrations were significantly reduced by 30.9%, 19.5% and 44.6% under S, G and SG treatments. Water soluble, acid soluble and residual PAHs under all treatments were significantly decreased after 70 days of incubation, while organically bound PAHs were increased by 11.4%, 22.7% and 36.1% under G, S and SG treatments. Additionally, straw and glucose application increased relative abundance related PAHs-degrading bacteria and the copy numbers of gram-negative (PAHs-RHDα GN) and gram-positive genes (PAHs-RHDα GP) in the contaminated soil. Redundancy analysis (RDA) and Random Forest (RF) indicated that PAHs fractions are crucial factors for biodegradation of PAHs in PAHs-contaminated soils amended with carbon substrates. These suggested that carbon substrates contributed to PAHs conversion from residual PAHs (nonlabile fractions) to organically bound PAHs and thus increased the potential for PAHs conversion to water-soluble and organic acid-soluble PAHs, which were more easy to be utilized by soil microorganisms. This study revealed the new insights of different carbon substrates on degradation and dynamic changes of PAHs fractions and the better potential of combined application of straw and glucose in enhancing degradation of PAHs in PAHs-contaminated soils.

Comparative insights into flue gas-to-ash characteristics on co-combustion of walnut shell and bio-oil distillation sludge under atmospheric and oxy-fuel condition

The clean recovery of bio-oil distillation sludge (DS) is a pivotal sector to perfect the biomass refinery system in responses to effective waste management and environmentally friendly consensus. This work aimed to comparatively characterize atmospheric and oxy-fuel co-combustion of walnut shell (WS) and DS in terms of (co-)combustion performance, distributed kinetics, flue gas evolution and ash characteristics. The results indicated co-combustion of WS and DS significantly increased the allocated proportion of char combustion stage and improved co-combustion performance, which was reflected in the enhanced four quantitative combustion indices. The fourth pseudo component, corresponded to the char combustion stage, continuously dominated the whole combustion process by adding more fraction of DS to co-combust with WS, whose activation energy was diminished, thereby optimizing the initial reaction energy barrier. In addition, oxy-fuel combustion promoted the recovery and sequestration of CO2, facilitated the formation of CO, and further endowed the conversion of polycyclic aromatic hydrocarbons into phenols rather than aromatics. Although the composition for mixed molten ash presented the decreased contents for easy-slagging minerals, the co-combustion process was still with potential ash fouling risk owing to basically unchanged ash configuration consistent with WS ash. However, the addition of DS to some extent strengthened anti-slagging performance, consequently optimizing the empirical indices of slagging and fouling for mixed ashes. Also, a higher ash content was yielded in oxy-fuel combustion than that in atmospheric combustion owing to the reducibility of CO2, in which the presence of CO2 contributed to the formations of carbonates and low melting-temperature potassium-containing silicates.

Catalytic conversion of asphaltenes to BTXN using metal-loaded modified HZSM-5

HZSM-5 zeolites with Si/Al ratios of 20, 35, 50 and 65 were prepared by the directing crystallization process of silicalite-1 seeds. The influence of Si/Al ratios on the production of benzene, toluene, xylene and naphthalene (BTXN) originated from asphaltenes catalytic pyrolysis was explored by adopting Py-GC/MS. Modified Z5-50 zeolites were prepared by various metal ions (Ni 2+ , Mo 6+ , Fe 3+ , and Co 2+ ) with different loading rates (3% (mass), 5% (mass), 7% (mass), and 9% (mass)) and the physical and chemical properties of these zeolites were characterized by XRD, SEM, ICP-OES, XPS, NH 3 -TPD, FTIR, Py-IR and N 2 adsorption−desorption isotherm. In addition, they were employed to catalyze the conversion of asphaltenes pyrolysis production to BTXN using Py-GC/MS. Results show that the highest relative content of aromatics has been obtained over HZSM-5 with Si/Al ratio of 50 (Z5-50), reaching 61.87%. Besides, the loading of Ni, Mo, Fe, and Co on Z5-50 leads to an increase of acid strength and provides new active sites. The relative content of BTXN increases by 3.17% over 3Ni-Z5, which may be ascribed to that Ni promoted the conversion of polycyclic aromatic hydrocarbons (PAHs) to monocyclic aromatics due to the cracking of aliphatic side chains of PAHs and the decrease of phenolic activation energy. While under the catalysis of 5Mo-Z5, the relative content of aromatics and BTXN augmented by 5.75% and 4.02%, respectively. In addition, the highest relative content of aromatics reaches 70.09% when the loading rate of Fe was 7% (mass), and the relative content of BTXN increases from 25.87% to 29.42%. The results demonstrate that the active sites provided by different metal species expressed diverse effects on BTXN. Although the Brønsted/Lewis acid ratios of HZSM-5 modified by metal decreased, the acid strength and the relative content of BTXN both increased, which illustrated that there is a synergistic catalysis with the Brønsted acid sites and Lewis acid sites provided by metal species. In general, the performance of the catalyst is affected by the pore structure, acidity and metal active sites. Moreover, the possible formation mechanism of BTXN derived from asphaltenes catalytic pyrolysis was proposed on the basis of structural features and catalytic performances of a series of zeolites.

Hydrogenation of polycyclic aromatic hydrocarbons over Pt/γ-Al2O3 catalysts in a trickle bed reactor

This work aims to investigate the effect of the amount of platinum loading on the hydrogenation of polycyclic aromatic hydrocarbons (PAHs) included in pyrolysis fuel oil (PFO) over Pt/γ-Al2O3 catalysts for the production of jet fuel. Catalyst characterizations were conducted by means of nitrogen adsorption, temperature-programmed desorption of ammonia, and temperature-programmed reduction under a hydrogen flow. The catalytic performance of bead-type Pt/γ-Al2O3 catalysts during the hydrogenation of PAHs included in PFO-cut was evaluated in a trickle-bed reactor. The main components produced by the hydrogenation reaction are decalin derivatives, alkylated cyclohexane, hexahydroindan derivatives, and bicyclohexyl. The cracking reaction was accelerated at the same time as the hydrogenation reaction over the Pt(1.0 wt%)/γ-Al2O3 and Pt(2.0 wt%)/γ-Al2O3; hence, the carbon number distribution shifted to the lighter side. The Pt(1.0 wt%)/γ-Al2O3 catalyst showed the highest activity during the hydrogenation of PFO-cut, which is attributed not only to the highest mesoporosity but also to the highest Pt dispersion. Catalyst deactivation could be ignored over the Pt(1.0 wt%)/γ-Al2O3 catalyst during ten hours of time-on-stream. The optimal reaction temperature and space velocity of PFO-cut to maximize the conversion of PAHs were determined to be 300 °C and 1.0 h−1, respectively.

Effective regulation of Ga active species in mesoporous ZSM-5 for catalytic upgrading of coal pyrolysis volatiles

Quality improvement of pyrolysis tar with yield increasing of high value-added components is highly desired for coal utilization. Herein, Ga-impregnated mesoporous ZSM-5 (Ga/MZ5) directed by organosilane surfactant of [3-(trimethoxysilyl) propyl] octadecyldimethylammonium chloride (TPOAC) is used as a catalyst for the catalytic upgrading of coal pyrolysis volatiles. Effective regulation by reduction and reduction/reoxidation promotes a secondary dispersion of gallium species from external surface deposition to micropore permeation. The comprehensive evaluation of catalytic upgrading performance indicates that the designedly regulated gallium species (mainly Ga+, GaH2+ and GaO+), feasible balance of Brønsted and Lewis active sites and mesopore diffusion superiority effectively contribute the yield increasing of both light-fraction (MLF/MTar) and target products of BTEXN (benzene, toluene, ethylbenzene, xylene and naphthalene). The optimal catalyst of Ga/MZ5_R/O exhibited the highest value of MLF/MTar (88 %) and highest yield of BTEXN (31.84 mg.g−1), which are 173 and 589 % higher than non-catalytic single pyrolysis and 133 and 280 % higher than those over the conventional Ga-impregnated ZSM-5 (Ga/Z5). Moreover, the possible reaction networks towards high value-added products of BTEXN based on the positive conversion of polycyclic aromatic hydrocarbons (PAHs), phenols, and other oxygen-containing compounds (abbreviated as PPO) is further proposed.

AHR gene expression and the polymorphism rs2066853 are associated with clinicopathological parameters in colorectal carcinoma

The relationship between red and processed meat and its risk towardcolorectal carcinoma (CRC) is not fully explored in literature. Polycyclic aromatic hydrocarbons (PAHs) are procarcinogenic molecules that are ingested with meat cooked at high temperatures. The metabolic conversion of PAHs to carcinogenic diol epoxides is in part mediated by the aryl hydrocarbon receptor (AhR)-dependent induction of CYP1A1. This study aims to examine the expression profiles and polymorphisms of the AHR (aryl hydrocarbon receptor) gene which is involved in the metabolic conversion of PAHs in patients with CRC. Genetic analysis was done in matched cancer and non-neoplastic tissues from 79 patients diagnosed with CRCs. Low AHR mRNA expression was associated with mucinous colorectal adenocarcinoma. Exon 10 of AHR showed that 27% of patients had the rs2066853 single-nucleotide polymorphism resulting in an arginine-to-lysine change at codon 554. This variant was significantly associated with a lower likelihood of perineural invasion, presence of synchronous cancer, and multiple colorectal polyps. Furthermore, rs2066853 individuals were significantly more likely to be of more advanced age and have a more favorable tumor grade and pathological stage. These results imply the pathogenic roles of AHR in PAH-associated colorectal carcinogenesis.

Anaerobic oxidation of petroleum hydrocarbons in enrichment cultures from sediments of the Gorevoy Utes natural oil seep under methanogenic and sulfate-reducing conditions.

This article presents the first experimental data on the ability of microbial communities from sediments of the Gorevoy Utes natural oil seep to degrade petroleum hydrocarbons under anaerobic conditions. Like in marine ecosystems associated with oil discharge, available electron acceptors, in particular sulfate ions, affect the composition of the microbial community and the degree of hydrocarbon conversion. The cultivation of the surface sediments under sulfate-reducing conditions led to the formation of a more diverse bacterial community and greater loss of n-alkanes (28%) in comparison to methanogenic conditions (6%). Microbial communities of both surface and deep sediments are more oriented to degrade polycyclic aromatic hydrocarbons (PAHs), to which the degree of the PAH conversion testifies (up to 46%) irrespective of the present electron acceptors. Microorganisms with the uncultured closest homologues from thermal habitats, sediments of mud volcanoes, and environments contaminated with hydrocarbons mainly represented microbial communities of enrichment cultures. The members of the phyla Firmicutes, Chloroflexi, and Caldiserica (OP5), as well as the class Deltaproteobacteria and Methanomicrobia, were mostly found in enrichment cultures. The influence of gas-saturated fluids may be responsible for the presence in the bacterial 16S rRNA gene libraries of the sequences of "rare taxa": Planctomycetes, Ca. Atribacteria (OP9), Ca. Armatimonadetes (OP10), Ca. Latescibacteria (WS3), Ca. division (AC1), Ca. division (OP11), and Ca. Parcubacteria (OD1), which can be involved in hydrocarbon oxidation.

Global distribution of oxygenated polycyclic aromatic hydrocarbons in mineral topsoils.

Hazardous oxygenated polycyclic aromatic hydrocarbons (OPAHs) originate from combustion (primary sources) or postemission conversion of polycyclic aromatic hydrocarbons (PAHs) (secondary sources). We evaluated the global distribution of up to 15 OPAHs in 195 mineral topsoils from 33 study sites (covering 52° N-47° S, 71° W-118 °E) to identify indications of primary or secondary sources of OPAHs. The sums of the (frequently measured 7 and 15) OPAH concentrations correlated with those of the Σ16EPA-PAHs. The relationship of the Σ16EPA-PAH concentrations with the Σ7OPAH/Σ16EPA-PAH concentration ratios (a measure of the variable OPAH sources) could be described by a power function with a negative exponent<1, leveling off at a Σ16EPA-PAH concentration of approximately 400 ng g-1 . We suggest that below this value, secondary sources contributed more to the OPAH burden in soil than above this value, where primary sources dominated the OPAH mixture. This was supported by a negative correlation of the Σ16EPA-PAH concentrations with the contribution of the more readily biologically produced highly polar OPAHs (log octanol-water partition coefficient<3) to the Σ7OPAH concentrations. We identified mean annual precipitation (Spearman ρ=.33, p<.001, n=143) and clay concentrations (ρ=.55, p<.001, n=33) as important drivers of the Σ7OPAH/Σ16EPA-PAH concentration ratios. Our results indicate that at low PAH contamination levels, secondary sources contribute considerably and to a variable extent to total OPAH concentrations, whereas at Σ16EPA-PAH contamination levels>400 ng g-1 , there was a nearly constant Σ7OPAH/Σ16EPA-PAH ratio (0.08±0.005 [SE], n=80) determined by their combustion sources.

Effect of Ring-Configuration on Pyrolysis and V2O5Catalyzed Oxidation of Polycyclic Aromatic Hydrocarbons

Conversion of polycyclic aromatic hydrocarbons (PAHs) through oxidative ring-opening can be used as a potential strategy for upgrading of aromatic-rich fractions of heavy oil and bitumen. At the core of such a process is the oxidation of PAHs to produce quinonoids, further oxidation of quinonoids to form ring-opened carboxylic acids, and finally decarboxylation of the carboxylic acids. The fused ring systems in PAHs include linear and angular ring-configurations, which affect pyrolysis and oxidation selectivity. This study evaluated the effect of the ring-configuration of PAHs on pyrolysis and on oxidation over a metal oxide catalyst (V₂O₅). Pyrolysis takes place in parallel with catalytic oxidation, and so it has an effect on the observed conversion chemistry. Liquid-phase pyrolysis and V₂O₅-catalyzed conversion of anthracene, phenanthrene, anthraquinone, and phenanthrenequinone were studied individually. All experimental work was conducted under a nitrogen atmosphere to avoid autoxidation. Results from high-pressure differential scanning calorimetry (HP-DSC) as well as from batch oxidation reactions indicated differences in reactivities due to the ring-configurations of both PAHs and their corresponding quinonoids. The reactivity sequence over V₂O₅ for PAHs was anthracene > phenanthrene as the increase in π-sextets in anthracene provided additional driving force toward oxidation. On the contrary, the reactivity over V₂O₅ of the corresponding quinonoids was phenanthrenequinone > anthraquinone. The angular configuration of phenanthrenequinone led to the carbonyl groups to be adjacent and to the carbons participating in that C–C bond to have an aliphatic nature, which increased the reactivity of the bond. The angular ring-configuration of phenanthrenequinone favored intramolecular ring-closing reactions, while the linear ring-configuration of anthraquinone exhibited higher stability toward oxidation. Conversion of anthraquinone led to products of oxygen removal via anthrone as well as to some ring-opened products. Compared to pyrolysis, V₂O₅ accelerated the conversion of PAHs and their corresponding quinonoids. Regardless of the ring-configuration, catalytic oxidation of PAHs over V₂O₅ did not favor production of ring-opened products. The study highlighted the importance of a hydrogen source, possibly water, for a successful ring-opening.

Enhancing the Conversion of Polycyclic Aromatic Hydrocarbons from Naphthenic Heavy Oil: Novel Process Design, Comparative Techno-Economic Analysis, and Life Cycle Assessment

Enhancing the deep processing of naphthenic heavy oil and selective hydrogenated saturation combined with ring opening of polycyclic aromatic hydrocarbons (PAHs) have extremely important industrial...

A molecular dynamics simulation investigation on the solubility of polycyclic aromatic hydrocarbons in supercritical water

Polycyclic aromatic hydrocarbons (PAHs) are typical chemical pollutants from coal or organic matters. The solubility and conversion of PAHs in water phase are the prerequisite of complete gasification of organic matter or coal and the rate-determining step. This paper is supposed to provide a theoretical basis of restraining coking for ensuring efficient gasification. In this work, molecular dynamics (MD) simulation investigations focused on dissolution of macromolecules including PAHs were summarized and relevant problems were outlined. MD simulations on the solubility of PAH mixtures in supercritical water were carried out for the purpose of illuminating the behaviors of oil droplets containing PAHs under the extreme hydrothermal circumstances. Water densities were ranging from 0.1 g/cm3 to 0.3 g/cm3 in this study. The calculation results indicated that the solubility of light PAHs such as naphthalene was complete and thorough in supercritical water, while heavy PAHs such as benzo[ghi]perylene were sensitive to the thermodynamic state of water solvent. As for PAHs mixtures, light PAHs were inclined to be dissolved, while heavy PAHs were more likely to form PAH aggregates. Furthermore, effects of pressure on solubility were not significant. The increase in temperature and density was primarily beneficial to enhance the solubility of PAH mixtures in supercritical water.

A density functional theory study on the conversion of polycyclic aromatic hydrocarbons in hydrogen plasma

Tar is the byproduct of fuel in the pyrolysis or gasification process. Hydrogen plasma could effectively promote the decomposition of tar into acetylene and hydrogen, but the detailed cracking mechanism is difficult to detect. The DMol3 calculations, based on density functional theory (DFT), have been employed to explore the pyrolysis pathways of naphthalene. Naphthalene is chosen as the model compound for polycyclic aromatic hydrocarbons (PAHs), which are the main components of tar. Our calculations investigate that the energy barriers required for the reactions are greatly reduced due to the participation of active hydrogen atoms. Naphthalene is easily converted into acetylene, hydrogen and carbon black through two main routes. This is in good agreement with the experiment results.

Effects of carbon dioxide addition to fuel on soot evolution in ethylene and propane diffusion flames

The influence of carbon dioxide addition to the fuel on soot evolution in ethylene and propane diffusion flames was studied by optical diagnostics. The mole fraction of CO2 addition ranged from 0 to 0.5, while the flow rate of the fuel gas was kept constant for these two sets of flames. Spatial distributions of polycyclic aromatic hydrocarbons (PAHs), temperature, as well as volume fraction, primary particle size and number density of soot were observed by the methods of laser-induced fluorescence (LIF), ratio pyrometry and laser-induced incandescence (LII), respectively. It was found that the flame height decreased for ethylene flames while it was nearly constant for propane flames with increasing addition of CO2. The measurements showed a temperature reduction in the lower part but an increase in the upper part in the ethylene-based flames. By contrast, a slight temperature decrease was observed in overall propane-based flames with the addition of CO2. Similar suppression effects were observed in the total soot/PAHs loading, percentage of carbon conversion to soot, and the total number of primary soot particles regardless of the fuel type. Comparison between the total loading of soot and PAHs indicated that addition of CO2 inhibited the conversion of PAHs to soot. The results also showed that the addition of CO2 in the fuel had a small effect on the specific growth rate of soot regardless of the fuel type. Relative changes of particle surface area could reasonably well explain the shift in the peak volume fraction from the wings to the centerline with the addition of CO2 to the ethylene flames.

Effects of H2S and phenanthrene on the activity of Ni and Rh-based catalysts for the reforming of a simulated biomass-derived producer gas

A series of Rh and Ni-based catalysts were tested for the reforming of methane and phenanthrene using a feed composition similar in terms of main components to that of the producer gas obtained from wood gasification. The objective was to identify formulations that would enable reforming methane and tars without the need to purify the producer gas. Phenanthrene was chosen as a representative tar because this compound is produced in significant concentrations during low-temperature gasification of woody biomasses and its three-ring structure favors coke formation. The concentration of H2S used was set at the higher range of typical values, i.e. 200ppm, to make these tests more challenging. At 900°C, 200ppm of H2S induced a significantly higher activity loss for methane reforming than that induced by 200ppm of phenanthrene. The rate of methane consumption in the presence of both poisons varied linearly with the Rh metal surface area. The slight deviation observed at higher loading was in part due to heat and mass transport limitations. The rate of methane consumption per unit of metal surface area was about 5-fold higher on Rh than that on Ni. No information could be derived from the measure of apparent activation energies, due to changes in adsorption coverages of reactants and poisons with temperature. Incomplete conversion of polycyclic aromatic hydrocarbons, well-known coke precursors, was obtained at 875°C and 850°C.

Distribution and Conversion of Polycyclic Aromatic Hydrocarbons during the Hydrothermal Treatment of Sewage Sludge

In this paper, the solid residue and liquid residue were obtained via the hydrothermal processing of sewage sludge. The effect of reaction temperature (180–260 °C), retention time (30–90 min), and cosolvent (ethanol volume proportion) (0%–100%) on the polycyclic aromatic hydrocarbons (PAHs) distribution and formation were investigated. The results showed that the concentration of total polycyclic aromatic hydrocarbons (TPAHs) in the solid phase slightly decreased as the temperature increased, while, in the liquid phase, the TPAHs concentration increased; the TPAH concentration decreased from 3.862 μg/g to 2.808 μg/g in solid residue, and, in liquid residue, it increased from 2.755 μg/mL to 2.974 μg/mL and then decreased to 1.961 μg/mL. There was no tremendous influence by retention time, since the TPAHs concentration in solid residue decreased from 3.020 μg/g to 2.808 μg/g, and, in liquid residue, slightly increased from 1.80 μg/mL to 1.961 μg/mL. The concentrations of TPAHs showed the minimum level at 26...

Use of different kinds of persulfate activation with iron for the remediation of a PAH-contaminated soil

Contamination of soils by persistent pollutants is considered an important matter of increasing concern. In this work, activated persulfate (PS) was applied for the remediation of a soil contaminated with polycyclic aromatic hydrocarbons (PAHs), such as anthracene (ANT), phenanthrene (PHE), pyrene (PYR) and benzo[a]pyrene (BaP). PS activation was performed by different ways; where ferric, ferrous sulfate salts (1–5mmol·L−1) and nanoparticles of zerovalent iron (nZVI) were used as activators. Moreover, in order to improve the oxidation rate of contaminants in the aqueous phase, the addition of sodium dodecyl sulfate (SDS), as anionic surfactant, was tested. On the other hand, it was also studied the role of humic acids (HA), as reducing agent or surfactant, on PAHs conversion. Removal efficiencies near 100% were achieved for ANT and BaP in all the runs carried out. Nevertheless, remarkable differences on removal efficiencies were observed for the different techniques applied in case of PHE and PYR. In this sense, the highest conversions of PHE (80%) and PYR (near 100%) were achieved when nZVI was used as activator. Similar results were obtained when activation was carried out either with Fe2+ or Fe3+. This can be explained by the presence of quinone type compounds, as 9,10-anthraquinone (ATQ), that can promote the reduction of Fe3+ into Fe2+, permitting PS radicals to be generated. On the other hand, the addition of HA did not produce an improvement of the process while surfactant addition slightly increases the PAHs removal. Furthermore, a kinetic model was developed, describing the behavior of persulfate consumption, and contaminants removal under first order kinetics.

Catalytic cracking of polycyclic aromatic hydrocarbons with hydrogen transfer reaction

With the aim of enhancing oil refining processes based on fluid catalytic cracking (FCC), the catalytic cracking of polycyclic aromatic hydrocarbons (PAHs) was investigated using an FCC catalyst consisting of a rare earth ion exchanged USY zeolite. In these trials, model PAHs were dissolved in n-hexadecane and were fed into a fixed bed microactivity test reactor operating at 516°C. Reaction product analysis indicated very little cracking of the 2-ring PAH over the FCC catalyst, while in contrast the 3-ring PAH was highly reactive, and was rapidly converted into monocyclic aromatic hydrocarbons, 2-ring PAHs and coke. Tests using FCC catalysts with different rare earth loadings revealed that the loading amount has little effect on the conversion of the 3-ring PAH. In addition, catalysts containing USY zeolites with comparable unit cell sizes, and thus having comparable hydrogen transfer activities, exhibited similar catalytic activities for 3-ring PAH conversion, even though they contained different amounts of the rare earth metal oxide. This result suggests that the hydrogen transfer reaction plays an important role in 3-ring PAH conversion and that the main effect of rare earth loading is to maintain the hydrogen transfer activity of the catalyst by stabilizing the USY zeolite against steam deactivation. In summary, this study successfully demonstrated a potential FCC process for converting PAHs into useful light fractions without the necessity of employing a pressurized hydrogen atmosphere.