Yields Of Polycyclic Aromatic Hydrocarbons Research Articles

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

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

Tailoring the impact of synthetic strategies on the catalytic upgrading of crude glycerol to produce bio-based aromatics in hierarchical HZSM-5

The catalytic upgrading of renewable biomass derived crude glycerol to generate bio-based aromatics is a promising alternative to petroleum route for the synthesis of valuable and versatile aromatics. The effects of synthetic strategies on the physicochemical property of hierarchical HZSM-5 as well as their corresponding catalytic upgrading performances of crude glycerol to bio-based aromatics were systematically investigated in this work. HZSM-5/0.3M NaOH catalyst exhibited smaller improvement in aromatic yields than microporous HZSM-5, which could be ascribed to the uncontrollable large intra-mesopore diameter and less increment in the amounts of acid sites during the introduction of mesoporosity via destructive alkali treatment. The soft templated HZSM-5/TPOAC catalyst produced more BTX and C9+ monocyclic aromatics, which could be attributed to its larger crystal sizes, higher external surfaces, luxuriant L acid amounts, uniform and small mesopore sizes. However, the hard templated HZSM-5/CNT-OH catalyst exhibited higher yields of polycyclic aromatic hydrocarbons and coke during the crude glycerol upgrading process, which could be assigned to its smaller crystal sizes, abundant B acid quantities, uniform and large mesopore diameters. The reusability of desilicated HZSM-5/0.3M NaOH was also deteriorated than the templated HZSM-5/CNT-OH and HZSM-5/TPOAC due to the inferior stability of incorporated mesoporosity via desilication. Finally, plausible reaction pathway involved catalytic upgrading of crude glycerol to produce aromatics was proposed in detail.

Suppression of polycyclic aromatic hydrocarbon formation during pyrolytic production of lignin-based biochar via nitrogen and boron co-doping

Polycyclic aromatic hydrocarbons are toxic byproducts of biochar production. The effects of pyrolysis atmosphere (i.e., N2 and CO2) and temperature (i.e., 300–900 °C) and element doping (i.e., N, B, O, and S) on the production of sixteen high priority polycyclic aromatic hydrocarbons in lignin-based biochar was investigated. N2 atmosphere at 300 °C produced the highest total polycyclic aromatic hydrocarbon content (1698 ± 50 ng/g). Polycyclic aromatic hydrocarbon formation decreased with increase in temperature (31 ± 15 ng/g at 900 °C). CO2 atmosphere significantly decreased yield of polycyclic aromatic hydrocarbons. The effects of heteroatom doping on polycyclic aromatic hydrocarbon formation were investigated for the first time in the pyrolysis synthesis of lignin-based biochar. N-, B-, O, N–B-, and N–S-doping of biochar reduced polycyclic aromatic hydrocarbon formation by 90, 85, 87, 97, and 89%, respectively. Results bring new insights into the role of heteroatom-doping and pyrolysis conditions in controlling polycyclic aromatic hydrocarbon formation in biochars.

Polycyclic aromatic hydrocarbons in biochar originated from pyrolysis of aseptic packages (Tetra Pak®)

Determination of the total yield of polycyclic aromatic hydrocarbons (PAHs) and their derivatives in a Tetra Pak® biochar was the leading target of this study. It was also evaluated the toxicity of Tetra Pak® biochars originated from pyrolysis performed at different temperatures. The relationship between the pyrolysis temperature and the yield of PAHs contained in Tetra Pak® biochars was also investigated. The material (Tetra Pak® packages, aseptic type) was decomposed in a laboratory pyrolysis reaction unit at different temperatures (400 °C, 500 °C, 600 °C, 700 °C). The concentrations of PAHs in Tetra Pak® biochars were determined using the method of pyrolysis gas chromatography combined with mass spectrometric detection. The toxicity of Tetra Pak® biochars was evaluated by Sinapis alba test and calculating of toxic equivalents.The total PAHs concentration in Tetra Pak® biochars oscillated between 79.6 mg/kg and 173.0 mg/kg. The measured concentrations of 16 priority PAHs U.S. Environmental Protection Agency (US EPA) reached the range from 38.4 mg/kg to 73.7 mg/kg. The yields of methylated derivatives of Tetra Pak®-biochar-borne PAHs varied from 5.2 mg/kg to 77.1 mg/kg. A phytotoxicity index of Sinapis alba has shown that biochar produced at temperatures above 500 °C is more likely to have a stimulating effect, supported by the leaching of Ca after the thermal decomposition of calcite and water extractable organic carbon. The stimulating effect of the addition of Tetra Pak® biochar increases with the decreasing concentration of biochar-borne PAHs. Given the financial cost and the minimisation of environmental risk, the addition of biochar in the range of 5–10% can be recommended.

Biomass:polystyrene co-pyrolysis coupled with metal-modified zeolite catalysis for liquid fuel and chemical production

Biomass and waste polystyrene plastic (ratio 1:1) were co-pyrolysed followed by catalysis in a two-stage fixed bed reactor system to produce upgraded bio-oils for production of liquid fuel and aromatic chemicals. The catalysts investigated were ZSM-5 impregnated with different metals, Ga, Co, Cu, Fe and Ni to determine their influence on bio-oil upgrading. The results showed that the different added metals had a different impact on the yield and composition of the product oils and gases. Deoxygenation of the bio-oils was mainly via formation of CO2 and CO via decarboxylation and decarbonylation with the Ni–ZSM-5 and Co–ZSM-5 catalysts whereas higher water yield and lower CO2 and CO was obtained with the ZSM-5, Ga–ZSM-5, Cu–ZSM-5 and Fe–ZSM-5 catalysts suggesting hydrodeoxygenation was dominant. Compared to the unmodified ZSM-5, the yield of single-ring aromatic compounds in the product oil was increased for the Co–ZSM-5, Cu–ZSM-5, Fe–ZSM-5 and Ni–ZSM-5 catalysts. However, for the Ga–ZSM-5 catalyst, single-ring aromatic compounds were reduced, but the highest yield of polycyclic aromatic hydrocarbons was produced. A higher biomass to polystyrene ratio (4:1) resulted in a markedly lower oil yield with a consequent increased yield of gas.

Synergistic sorption/photo-Fenton removal of typical substituted and parent polycyclic aromatic hydrocarbons from coking wastewater over CuO-Montmorillonite

Polycyclic aromatic hydrocarbons (PAHs) and substituted PAHs (SPAHs) are commonly persistent organic pollutants that are found in different industrial and agricultural wastewaters. In the present research study, we investigated the purification of coking wastewater containing mixed 16 PAHs and 18 SPAHs using CuO decorated montmorillonite (CuO-M) under solar light. For better removal efficiency, H2O2 was added to make the photo-Fenton reaction into action. Due to the complexity of this coking wastewater, the purification was carried out in two runs. The results showed that, by using CuO-M/H2O2/light, 66% of the total yield of PAHs and SPAHs was removed from coking wastewater within 4 h. The second treatment run led to a further increase in the removal rate up to 91% of total pollution. Different synergetic mechanistic pathways such as the adsorb & shuttle process, generation of reactive oxygen species (ROSs) by photoactive CuO on the montmorillonite surface, and photo-Fenton ROSs generation in bulk water catalyzed by CuO and H2O2 are responsible for the effective removal of PAHs and SPAHs. Even though the study was established under well-controlled lab conditions, we should say that the CuO-M/H2O2/light system showed excellent performance in removing a significant part of PAH and SPAH compounds that might make it a potential alternative/cooperative to be involved in wastewater treatment plant (WWTP) to purify the same coking wastewater.

Comparative study on the two-step and one-step pyrolysis of lignin: effects of pyrolysis temperature and residence time on the product distribution

To explore a new way of utilizing lignin and deepen the understanding of mechanism of two-step pyrolysis (TSP) of biomass, the effects of the first step pyrolysis temperature (T1) and residence time (RT1) on TSP of lignin were studied by using pyrolysis gas chromatography/mass spectrometry (Py-GC/MS). TSP of lignin was also compared with one-step pyrolysis (OSP) of lignin. The results indicated that higher pyrolysis temperature promoted the break of ether linkage among the structural elements of lignin and the removal of side chains. With T1 increasing, the contents of monophenols (MPs), catechols (CPs), monocyclic aromatic hydrocarbons (MAHs), and polycyclic aromatic hydrocarbons (PAHs) increased in the first step, while the contents of methoxyphenols with double bond in the side-chain (MPBSs) and methoxyphenols with no double bond in the side-chain (MPSs) increased firstly and then decreased. In the second step, with T1 increasing the contents of MPs and CPs increased firstly and then decreased, the contents of MAHs and PAHs increased significantly, and the contents of MPBSs and MPSs decreased. Higher T1 increased the yields of the most identified compounds of the first step, but decreased the yields of MPs, CPs, MPBSs, and MPSs in the second step. RT1 had great effects on the pyrolysis behaviors and product distribution of TSP of lignin, and the content of MAHs and PAHs in the second step increased significantly with RT1 increasing. Compared with OSP, the yields of MAHs and PAHs could increase in the second step. TSP of lignin could improve the selectivity of value-added chemicals remarkably, such as guaiacol, vanillin, acetovanillone in the first step, and the selectivity of benzene, toluene, m-xylene, phenol, o-cresol, and p-cresol in the second step.

Polycyclic aromatic hydrocarbons in the Mukundpura (CM2) Chondrite

Soluble polycyclic aromatic hydrocarbons (PAHs) have been measured in Mukundpura (MK) CM2 carbonaceous chondrite using Gas Chromatography-Mass Spectrometry (GC-MS). The data show high yields of PAHs with the presence of 2, 3, and 4 ring polycyclic aromatic hydrocarbons along with heterocyclic nitrogen and sulfur-containing compounds. MK also shows the presence of significant amount of alkylation products. The distribution and relative abundances of PAHs in the MK are discussed in context of its petrographic grade and correlation with aqueous alteration.

Distribution and toxicity of polycyclic aromatic hydrocarbons during CaO-assisted hydrothermal carbonization of sewage sludge

Hydrothermal carbonization (HTC) of sewage sludge (SS) with and without calcium oxide (CaO) introduction was conducted at 160–240 °C, and the yield and distribution of polycyclic aromatic hydrocarbons (PAHs) were evaluated for the first time. PAHs (2972.99 μg/kg) and toxic equivalent quantity (TEQ) (373.09 μg/kg) yields in SS decreased by 13.61% and 14.65%, respectively, after treatment at 160 °C and substantially increased as temperatures increased. More PAHs were distributed in the hydrochar than in the aqueous products. Hydrochar yields decreased linearly with temperature, thus increasing PAH concentration in hydrochar; 6221.98 μg/kg of PAHs in hydrocar at 240 °C exceeded agricultural use standard limits. PAH and TEQ yields at 200 °C decreased by 5.55–15.98% and 2.88–3.54%, respectively, when 3–9% CaO was added, which could be ascribed to CaO inhibition in the free radical reaction for PAH generation. Additionally, 6% CaO addition substantially weakened the acceleration effect of high temperatures on PAH formation; the decrease of PAH yield at 240 °C was 22.14%, which is higher than that at other temperatures. Consequently, the PAH concentration in hydrochar declined by 2.33–22.37%. PAH content in hydrochar obtained from CaO-assisted HTC of SS fell within agriculture use standard limit and exhibits potential for use as a soil conditioner. However, condition with a CaO amount of 15% would significantly increase TEQ yields. Considering both PAH and TEQ yields and the ecological risks of PAHs in hydrochar derived from HTC of SS, the appropriate reaction conditions were found to be 200 °C with 3–6% added CaO.

Catalytic Fast Pyrolysis of Biomass into Aromatic Hydrocarbons over Mo-Modified ZSM-5 Catalysts

Mo-modified ZSM-5 catalysts were prepared and used to produce aromatic hydrocarbons during catalytic fast pyrolysis (CFP) of biomass. The composition and distribution of aromatics were investigated on pyrolysis–gas chromatography/mass spectrometry (Py-GC/MS). The reaction factors, such as the Mo content, the reaction temperature and the catalyst/biomass mass ratio, were also optimized. It was found that the 10Mo/ZSM-5 catalyst displayed the best activity in improving the production of monocyclic aromatic hydrocarbons (MAHs) and decreasing the yield of polycyclic aromatic hydrocarbons (PAHs) at 600 °C and with a catalyst/biomass ratio of 10. Furthermore, according to catalyst characterization and the experiment results, the aromatics formation mechanism over Mo/ZSM-5 catalysts was also summarized and proposed.

Pollutant emissions during the pyrolysis and combustion of starch/poly(vinyl alcohol) biodegradable films

The massive use of petroleum-based polymers and their improper waste treatment has brought on significant global environmental problems due to their non-biodegradable nature. Starch/poly(vinyl alcohol) (PVA) bioplastics are suitable substitutes for conventional polymers, such as polyethylene, due to their full biodegradability and excellent mechanical properties. Knowledge of the pollutant emissions during pyrolysis and combustion of starch/PVA films is important because they can arrive at landfills mixed with conventional polymers and be thermally degraded in uncontrolled fires. On the other hand, controlled thermal treatments could result in thermal valorization of the waste. Pyrolysis and combustion experiments were carried out at 650, 750, 850 and 950 °C in a laboratory furnace. The analysis of carbon oxides, light hydrocarbons, and semivolatile compounds, including polycyclic aromatic hydrocarbons (PAHs), is shown. Experiments showed lower pollutant emissions than those found with conventional polymers, such as polyethylene and polyester, in the same equipment. Nevertheless, the pyrolysis run at 950 °C showed the highest light hydrocarbon yield (123013 mg kg−1), but this is considerably lower than the values found for polyethylene. The main semivolatile compounds (not PAHs) emitted, with maximum yields ranging from 1351 to 4694 mg kg−1, were benzaldehyde, phenol, indene, and acetophenone. Specifically, the total semivolatile compounds emitted after pyrolysis and combustion of starch/PVA samples represent only 38 and 50%, respectively, of those emitted with polyethylene. Further, the main PAHs were naphthalene, acenaphthylene, and phenanthrene with maximum values of 4694, 2704 and 1496 mg kg−1, respectively. The PAH yield was considerably higher in experiments with low oxygen content.

Formation and inhibition of polycyclic aromatic hydrocarbons from the gasification of cyanobacterial biomass in supercritical water

Polycyclic aromatic hydrocarbons (PAHs) formation and inhibition from supercritical water gasification (SCWG) of cyanobacterial biomass were investigated. High reaction temperature, long residence time, and low feedstock concentration favoured higher molecular weight (HMW) PAH formation. The total PAH yield reached 34.80 μg g−1 at 500 °C, 22.5 MPa, and 10 min. The main PAHs formed in the liquid phase and the solid residue were 3-ring and 4-ring PAHs, which were generated from the cycloaddition reaction of lower molecular weight (LMW) PAHs. In addition, 2-ring PAHs were produced from the Diels-Alder reaction of phenols and unsaturated hydrocarbons. The possible control methods for PAH formation during the SCWG of cyanobacterial biomass were proposed. H2O2 addition effectively inhibited the reaction pathways underlying PAH formation, and the addition at more than 1.0% concentration suppressed H2 production. The work revealed that the inhibition of PAHs was achieved in terms of improving the oxidisation condition during the SCWG process for converting wet biomass or organic wastes to energy sources.

Catalytic Pyrolysis of Guaiacol over Ni/La–Modified Hierarchical HZSM‐5

AbstractCatalytic pyrolysis of guaiacol as a model compound of lignin was conducted to explore the lignin pyrolysis mechanism in this study. The effects of catalyst and temperature on product distribution were studied. Five catalysts were tested including HZSM‐5, hierarchical HZSM‐5, metal‐modified hierarchical HZSM‐5 catalysts. And the Ni/La bimetallic hierarchical HZSM‐5 (NiLa/HZ‐SH) contributes to the achievement of high conversion and selectivity in catalytic pyrolysis of guaiacol. we obtained the yields of monocyclic aromatic hydrocarbons over NiLa/HZ‐SH (550°C): Phenol (23.01%), Benzofuran (6.68%), Salicylaldehyde (1.54%), 2‐Methylphenol (31.48%), 4‐Methylphenol (6.54%), 2‐Ethylphenol (14.89%), 4‐Vinylphenol (1.45%) and Catechol (8.67%), and the maximal yields of these monocyclic aromatic hydrocarbons is 94.26%. Moreover, the yield of polycyclic aromatic hydrocarbons (PAH) as the non‐target product reached a minimum of 1.46% over NiLa/HZ‐SH, while it was 16.88% without catalyst. In addition, catalyst stability was investigated, the reason that led to the decrease of target products could be the acidity and surface area of catalysts decreased as the coke blocked the pore channels, spent catalyst can be successfully regenerated through calcination treatment. Finally, based on the experiment results in this work and other published studies, a guaiacol pyrolysis mechanism was summarized and proposed aiming to understand the lignin pyrolysis process.

The Sonodegradation of a Petrochemical Industry Wastewater

In this study, the effects of increasing sonication times (0 min, 60 min, 120 and 150 min), sonication temperatures (25oC, 30oC and 60oC), increasing titanium dioxide (TiO2) (0.1 mg/L, 0.5 mg/L, 10 and 20 mg/L), sodium chloride (NaCl) (1 g/L, 2.5 and 15 g/L), ferrous ion (Fe+2) (2 mg/L, 8 and 20 mg/L) and ferric ion (Fe+3) (10 mg/L, 20 and 50 mg/L) concentrations on the dissolved chemical oxygen demand (CODdis), total organic carbon (TOC) and total polycyclic aromatic hydrocarbons (PAH) removal efficiencies were monitored at a sonication frequency of 35 kHz and a sonication power of 640 W for a raw petrochemical industry wastewater (PCI ww). As the sonication time and temperature were increased from 60 to 120 and 150 min, and from 25 oC to 30 oC and to 60 oC, the CODdis, total PAH and TOC yields increased from around 52-58% and 69%-72% to 80-87% and 78%-90%. The maximum CODdis, total PAH and TOC yields were obtained with 20 mg/l TiO2, 15 mg/l NaCl, 20 mg/L Fe+2 and with 50 mg/L Fe+3, particularly after 150 min sonication at 60 oC. However, it is important to note that after 150 min sonication in the samples free of the chemicals mentioned above, in other words, in the samples with only sonication exhibited high yields as is the samples added the chemicals. After sonication with the chemicals, the EC50 values decreased significantly versus sonication times. The maximum Daphnia magna acute toxicity removal yield was 99.91% at NaCl=1 g/L at 60oC after 150 min sonication.

Pressurized entrained-flow pyrolysis of lignite for enhanced production of hydrogen-rich gas and chemical raw materials

This paper reports the enhanced production of H2 and polyaromatics during lignite pyrolysis under pressurized entrained-flow conditions. The pyrolysis temperature and pressure ranged between 600−900 °C and 0.1–4.0 MPa, respectively, and were found to greatly influence the yield and composition of pyrolysis products. The results showed that the concentration of H2 in the light gas fraction increased drastically with pyrolysis temperature and pressure, reaching 91.69 vol% at 900 °C and 4.0 MPa, which corresponded to H2 generation of 0.27 m3/kg coal. The yield of polycyclic aromatic hydrocarbons (PAHs) such as naphthalene, biphenylene, fluorene, phenanthrene, pyrene, and fluoranthene was also promoted at elevated pyrolysis temperatures and pressures. The highest PAHs concentration of 90.4 area% in the pyrolysis oil was obtained at 900 °C and 4.0 MPa. It was also found that the changes in the hydrogen distribution under pressurized entrained-flow conditions mainly took place during the secondary pyrolysis reactions. It was postulated that hydrogen was formed via aromatization, condensation, aromatic ring growth mechanism, and direct cleavage reactions. The findings of this study showed that lignite could be efficiently converted to H2-rich gas, PAHs as chemical raw materials, and energy-dense lignite char via a novel poly-generation system based on pressurized entrained-flow pyrolysis.

Selective preparation of monocyclic aromatic hydrocarbons from ex-situ catalytic fast pyrolysis of pine over Ti(SO4)2-Mo2N/HZSM-5 catalyst

To selectively produce monocyclic aromatic hydrocarbons (MAHs) with low amount of polycyclic aromatic hydrocarbons (PAHs), modified HZSM-5 catalysts (Mo2N/HZSM-5, Ti(SO4)2/HZSM-5 and Ti(SO4)2-Mo2N/HZSM-5) were prepared and employed for ex-situ catalytic fast pyrolysis (CFP) of pine wood. Both analytical pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS) and lab-scale pyrolysis experiments were conducted to investigate the effects of catalyst, pyrolysis temperature and catalyst-to-pine ratio on the distribution of aromatic hydrocarbon products. Py-GC/MS results showed that the maximal MAHs yields from the HZSM-5, Mo2N/HZSM-5, Ti(SO4)2/HZSM-5 and Ti(SO4)2-Mo2N/HZSM-5 catalysts were 7.57 wt%, 8.11 wt%, 8.71 wt% and 12.53 wt% at 650 °C and catalyst-to-pine ratio of 7. Corresponding PAHs yields from the four catalysts were 2.55 wt%, 0.97 wt%, 1.47 wt% and 1.10 wt%, which clearly indicated that the Ti(SO4)2-Mo2N/HZSM-5 significantly increased MAHs formation and decreased PAHs formation as compared with HZSM-5. Furthermore, lab-scale experiments were conducted to quantitatively determine the pyrolytic product distribution. Results showed that Ti(SO4)2-Mo2N/HZSM-5 catalyst increased the yield of liquid and gas products, and decreased solid products as compared with HZSM-5. Under optimal conditions of 650 °C and catalyst-to-pine ratio of 4/3, the actual yields of MAHs and PAHs from Ti(SO4)2-Mo2N/HZSM-5 catalyst were 9.71 wt% and 1.45 wt%, respectively. In addition, stability tests confirmed that the Ti(SO4)2-Mo2N/HZSM-5 catalyst possessed better effects on MAHs production as well as anti-deactivation than the HZSM-5.

Synergetic effects during co-pyrolysis of biomass and waste tire: A study on product distribution and reaction kinetics

The synergetic effects during co-pyrolysis of biomass and waste tire (WT) were investigated concerning the product distribution and reaction kinetics. Two biomass feedstocks were separately mixed with WT at different effective hydrogen/carbon ratio (H/Ceff), and analytical co-pyrolysis of mixtures was conducted using pyrolysis gas chromatography/mass spectroscopy at 500 °C. Product distributions were similar between different biomass feedstocks but varied significantly at different H/Ceff values. The percentage of hydrocarbons increased significantly when increasing H/Ceff, and the optimal H/Ceff was determined considering the correspondingly higher yield of polycyclic aromatic hydrocarbons and char residuals at higher percentage of WT. The experimental derivative thermogravimetric curves of mixtures at the optimal H/Ceff were compared with the calculated results based on kinetic analysis of three individual components using the distributed activation energy model. Significant synergetic effects were observed at the initial and final stages of the pyrolysis process.

Production of biochar and bioenergy from rice husk: Influence of feedstock drying on particulate matter and the associated polycyclic aromatic hydrocarbon emissions

This study investigates the effect of feedstock drying on the emissions of polycyclic aromatic hydrocarbons (PAHs) associated with the particulate matter (PM) produced during the co-generation of biochar and bioenergy. Raw pyrolysis volatile mixtures were generated from the pyrolysis of rice husk at 400, 500, 600, 700, and 800 °C using a laboratory-scale continuous pyrolysis-combustion system and combusted at 850 °C. PM samples from the combustion were collected and analysed for 15 priority PAH species with a gas chromatography/mass spectrometer (GC/MS). It was found that the utilization of the as received (AR) rice husk resulted in significantly greater energy-based yields of PM10 (1.2 times at 400 °C and 1.6 times at 800 °C) than the dried rice husk. The majority of the increase was of the PM2.1-10 size fraction. The PM-bound PAH concentration was found to be 2.1 and 2.8 times higher for the AR rice husk at 400 and 800 °C, respectively. This resulted in a significant increase in the energy-based yield of PAHs over the entire volatile production temperature range for the AR rice husk. Nevertheless, the majority of the PM-bound PAH species generated from the AR rice husk consisted of 2 and 3 ring PAHs (naphthalene, acenapthylene, and acenaphthene) with relatively low toxicity. The concentration of 4, 5, and 6 ring PAHs was generally lower than that generated from the dried rice husk. This resulted in the benzo(a)pyrene-equivalent toxicity of the PM generated from the AR rice husk being lower than the dried counterpart.

Nanocage-Confined Synthesis of Fluorescent Polycyclic Aromatic Hydrocarbons in Zeolite.

Polycyclic aromatic hydrocarbons (PAHs) attract much attention for applications to organic light-emitting diodes, field-effect transistors, and photovoltaic cells. The current synthetic approaches to PAHs involve high-temperature flash pyrolysis or complicated step-by-step organic reactions, which lead to low yields of PAHs. Herein, we report a facile and scalable synthesis of PAHs, which is carried out simply by flowing acetylene gas into zeolite under mild heating, typically at 400 °C and generates the products of 0.30 g g-1 zeolite. PAHs are synthesized via acetylene polymerization inside Ca2+-ion-exchanged Linde type A (LTA) zeolite, of which the α-cage puts a limit on the product molecular size as a confined-space nanoreactor. The resultant product after the removal of the zeolite framework exhibits brilliant white fluorescence emission in N-methylpyrrolidone solution. The product is separated into four different color emitters (violet, blue, green, and orange) by column chromatography. Detailed characterizations of the products by means of various spectroscopic methods and mainly mass spectrometric analyses indicate that coronene (C24H12) is the main component of the blue emitter, while the green emitter is a mixture of planar and curved PAHs. The orange can be attributed to curved PAHs larger than ovalene, and the violet to smaller molecules than coronene. The PAH growth mechanism inside Ca2+-exchanged LTA zeolite is proposed on the basis of mass spectral analyses and density functional theory calculations.

Monocyclic aromatic hydrocarbons production from catalytic cracking of pine wood-derived pyrolytic vapors over Ce-Mo2N/HZSM-5 catalyst

A series of Mo2N/HZSM-5 and transition metal modified Mo2N/HZSM-5 catalysts were prepared for the catalytic upgrading of pine wood-derived pyrolytic vapors for the selective production of monocyclic aromatic hydrocarbons (MAHs), while restraining the formation of polycyclic aromatic hydrocarbons (PAHs). Pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS) experiments were performed to determine the effects of several factors on selective MAHs production, including Mo2N loading on HZSM-5, transition metal (Fe, Ce, La, Cu, Cr) modification of Mo2N/HZSM-5, pyrolysis temperature, and catalyst-to-biomass ratio. In addition, quantitative experiments were conducted to determine the actual yields of major aromatic hydrocarbons and the source of aromatic hydrocarbons from basic biomass components. Results indicated that among the various catalysts, the Ce-10%Mo2N/HZSM-5 exhibited the best performance on promoting the formation of MAHs and restraining the generation of PAHs. Under the optimal conditions, the actual yields of MAHs and PAHs from Ce-10%Mo2N/HZSM-5 catalytic process were 99.8mg/g and 7.5mg/g, while those from HZSM catalyst were only 77.2mg/g and 23.7mg/g respectively. Furthermore, the possible catalytic mechanism of the Ce-Mo2N/HZSM-5 catalyst was proposed based on the catalyst characterization.