Pyrolysis Environment Research Articles

Effect of the Pyrolysis Environment in a Complex Compound in the Synthesis of In0.6Ga0.4N Powders and their Characterization

In this work, the comparison between nitrogen and air synthesis environments in obtaining In0.6Ga0.4N powders is presented, and the effect of how the air environment can reduce the pyrolysis temperature of In0.6Ga0.4N powders to 271 °C using the thermal gravimetric analysis, and derivative thermogravimetry methods. X‐ray diffraction patterns demonstrate the presence of a cubic phase in nanocrystallites, in addition to less presence of the hexagonal phase. In contrast, scanning electron microscopy micrographs show a surface morphology of irregular agglomerates with a porous appearance and the presence of nonuniform plates. Energy‐dispersive spectroscopy and X‐ray photoelectron spectroscopy spectra demonstrate the presence of elemental contributions of gallium, indium, and nitrogen. At the same time, transmission electron microscopy shows the cubic structure and an interplanar distance of 2.7 Å for the (200) plane. Raman scattering shows the presence of E2(high) vibration mode for the hexagonal phase with a value of 560 cm−1. Finally, the photoluminescence spectrum shows an energy emission at 1.39 eV (886 nm), which is associated with the emission of the In0.6Ga0.4N powders.

Effect of H2O on macroscopic flame behaviors and combustion reaction mechanism of 1,1-difluoroethane (R152a)

1,1-difluoroethane (R152a) is one of the most prospective low GWP refrigerants but may trigger fires and explosions once it leaks. Understanding the flame propagation process and combustion mechanisms at different relative humidity conditions is essential to use flammable refrigerants safely. In this study, a high-speed camera has recorded the flame propagation of R152a combustion near the flammability limit. Combining with macroscopic experimental phenomena, we revealed the effect of H2O on the microscopic mechanism of R152a combustion by using reactive force field molecular dynamics simulations with a reliable force field. The promotion effects of H2O on the oxidation of R152a were revealed from an atomistic perspective. The differences of oxidation intermediates and products in different environments were analyzed for the first time. The H2O/O2 environment was the most potent promoter of R152a decomposition, followed by the O2 and the pyrolysis environment. The O2/H2O environment reduced the apparent activation energy of R152a, significantly enhanced the consumption rate of R152a, and enriched the number of species. O2 reacts with H2O or H to form OH to accelerate the reaction process. The H2O could provide more OH active fragments for the reaction. Moreover, it promotes the formation of HF and H2, H2O + F→HF + OH, H2O + H→H2 + HO. This study aims to provide a guiding theory for the safe application and disaster prevention of flammable refrigerants.

Effect of long reaction distance on gas composition from organic-rich shale pyrolysis under high-temperature steam environment

When high-temperature steam is used as a medium to pyrolyze organic-rich shale, water steam not only acts as heat transfer but also participates in the chemical reaction of organic matter pyrolysis, thus affecting the generation law and release characteristics of gas products. In this study, based on a long-distance reaction system of organic-rich shale pyrolysis via steam injection, the effects of steam temperature and reaction distance on gas product composition are analyzed in depth and compared with other pyrolysis processes. The advantages of organic-rich shale pyrolysis via steam injection are then evaluated. The volume concentration of hydrogen in the gas product obtained via the steam injection pyrolysis of organic-rich shale is the highest, which is more than 60%. The hydrogen content increases as the reaction distance is extended; however, the rate of increase changes gradually. Increasing the reaction distance from 800 to 4000 mm increases the hydrogen content from 34.91% to 69.68% and from 63.13% to 78.61% when the steam temperature is 500 °C and 555 °C, respectively. However, the higher the heat injection temperature, the smaller the reaction distance required to form a high concentration hydrogen pyrolysis environment (hydrogen concentration > 60%). When the steam pyrolysis temperature is increased from 500 °C to 555 °C, the reaction distance required to form a high concentration of hydrogen is reduced from 3800 to 800 mm. Compared with the direct retorting process, the volume concentration of hydrogen obtained from high-temperature steam pyrolysis of organic-rich shale is 8.82 and 10.72 times that of the commonly used Fushun and Kivite furnaces, respectively. The pyrolysis of organic-rich shale via steam injection is a pyrolysis process in a hydrogen-rich environment.

Gasification of municipal solid wastes with gypsum wastes under different gasifying environments

The global increase in population and rapid urbanization has been followed by a growing generation of municipal solid wastes and construction and demolition sector wastes. This has put increasing pressure on countries around the world to come up with sustainable ways to deal with issues related to waste generation, climate change, and social and environmental degradation. This paper investigates a novel means of co-utilization of municipal solid wastes (MSW) with gypsum wastes from the construction and demolition sector for energy recovery and materials recycling and explores synergistic improvement in their processed value. We investigated high-temperature pyrolysis and gasification under different gasifying environments of inert (N2), 10 % O2, 20 % CO2, and 70 % H2O at two different temperatures of 800 and 900 °C, in a semi-batch fixed bed reactor. Syngas obtained was analyzed for its composition and yield, while the solid residue obtained was analyzed for the crystalline phases of the inorganic content using powder-XRD (X-ray diffraction) diagnostics. These analyses revealed that increasing temperature as well as the addition of gypsum can significantly improve the carbon conversion and overall product gas yields.When comparing the gasifying environments, steam gasification provided increased syngas mass yields by up to 184 %, 425 % and 377 % respectively, as compared to CO2 gasification, O2 gasification, and pyrolysis environments. Adding gypsum at equal mass proportions (1:1) to MSW pyrolysis at 900 °C increased the syngas yield by 10 % compared to the non-catalytic case, while adding it at 800 °C reduced syngas yield by 6 % compared to the non-catalyzed pyrolytic case at 800 °C. Adding gypsum during O2 gasification increased the syngas yield by 25 % compared to the non-catalytic cases at 900 °C and increased by 12.5 % at 800 °C. However, the syngas yield was reduced by 84 % when gypsum was added at equal mass proportions (1:1) to steam gasification of MSW at 900 °C and 50 % for 800 °C. Adding gypsum to CO2 gasification also reduced the cumulative yield of syngas for both temperatures under investigation. However, the syngas quality was improved with gypsum addition as the yields of hydrocarbon were reduced. The char/solid residue was found to contain significant portions of CaS suggesting sulfur fixation capability of this process into the ash which can improve the ash characteristics in terms of metal recovery along with the improved waste conversion.

Experimental investigation on pyrolysis products and pore structure characteristics of organic-rich shale heated by supercritical carbon dioxide

The efficient pyrolysis and conversion of organic matter in organic-rich shale, as well as the effective recovery of pyrolysis shale oil and gas, play a vital role in alleviating energy pressure. The state of carbon dioxide (CO2) in the pyrolysis environment of shale reservoirs is the supercritical state. Its unique supercritical fluid properties not only effectively heat organic matter, displace pyrolysis products and change shale pore structure, but also achieve carbon storage to a certain extent. Shale samples were made into powder and three sizes of cores, and nitrogen (N2) and supercritical carbon dioxide (ScCO2) pyrolysis experiments were performed at different final pyrolysis temperatures. The properties and mineral characteristics of the pyrolysis products were studied based on gas chromatography analysis, X-ray diffraction tests, and mass spectrometry analysis. Besides, the pore structure characteristics at different regions of cores before and after pyrolysis were analyzed using N2 adsorption tests to clarify the impact of fracturing degree on the pyrolysis effect. The results indicate that the optimal pyrolysis temperature of Longkou shale is about 430 °C. Compared with N2, the oil yield of ScCO2 pyrolysis is higher. The pyrolysis oil obtained by ScCO2 extraction has more intermediate fractions and higher relative molecular weight. The ScCO2 can effectively improve the pore diameter of shale and its effect is better than that of N2. The micropores are produced in shale after pyrolysis, and the macropores only are generated in ScCO2 pyrolysis environments with temperatures greater than 430 °C. The pore structure has different development characteristics at different pyrolysis temperatures, which are mainly affected by the pressure holding of volatile matter and products blocking. Compared to the surface of the core, the pore development effect inside the core is better. With the decrease in core size, the pore diameter, specific surface area, and pore volume of cores all increase after pyrolysis.

Role of π-Radical Localization on Thermally Stable Cross-Links Between Polycyclic Aromatic Hydrocarbons.

The thermal stability of cross-links between polycyclic aromatic hydrocarbons (PAHs) is critical for understanding the formation of soot pollutants, graphite, and carbon blacks. Recently, a variety of different π-radicals have been directly imaged and suggested to enable thermally stable bonding; however, a systematic study of reactivity has been lacking. In this work, we use density functional theory to study the reactivity of PAH π-radicals. The Mulliken spin densities are initially used to categorize the different classes of localization, and the bond energy is computed to determine the degree of localization required for thermal stability. The results showed that the bond energies of PAHs are strongly correlated with the calculated spin densities, but bond energies do not exist with the bond lengths due to significant rearrangement and steric effects during bond formation. A threshold for π-radical localization is suggested that will be stable in combustion and pyrolysis environments of ρMα ≥ 0.5. Finally, the formation of multicenter bonds between localized and delocalized π-radicals was investigated using the nudge elastic band (NEB) scan, and it was found that only delocalized π-radicals provided local energy minima. These results show that the localization of π-radicals is critical for the formation of thermally stable single-center bonds between aromatic radicals.

Evolution of an Electrochemically Inactive Metal–Organic Framework to Reticulated Porous Carbon Particles with High Supercapacitance

An iron-containing porphyrin-based porous metal–organic framework (PPMOF) has been synthesized and subsequently pyrolyzed to obtain the carbon structure with homogeneous distribution of nitrogen. The pyrolysis is carried out at different temperatures and in the presence of two different environments; in argon to obtain PPMOF-Ar-700, PPMOF-Ar-800, and PPMOF-Ar-900, and in nitrogen to obtain PPMOF-N-800. The motivation here is to study the change in the electrochemical properties that take place on conversion of the metal–organic framework to its corresponding carbons. The materials have been characterized by powder X-ray diffraction, nitrogen adsorption/desorption, scanning electron microscopy, X-ray photoelectron spectroscopy, and Raman spectroscopy, among others. It was observed that PPMOF almost did not show any electrochemical response and was unstable, whereas the carbonized frameworks showed good supercapacitive behavior and stability. The surface area increases from 353 to 838 m2·g–1, when the pyrolysis gas is switched over from nitrogen to argon. It also results in the formation of uniform smooth spherical particles in PPMOF-Ar-800, in contrast to agglomerated broken particles in PPMOF-N-800. PPMOF-Ar-800 shows a remarkable specific capacitance value of 500 F·g–1 at a current density of 1 A·g–1 which is retained at a high value of 111 F·g–1 at a very high current density of 50 A·g–1 in galvanostatic charge/discharge studies, whereas for PPMOF-N-800, the specific capacitance is 400 F·g–1 at 1 A·g–1 and its discharge time is also shorter than that for PPMOF-Ar-800. This indicates that the pyrolysis environment plays a crucial role in the formation and stabilization of the carbon structures.

Thermodynamic Analysis of In Situ Underground Pyrolysis of Tar-Rich Coal: Primary Reactions.

In situ underground pyrolysis of tar-rich coal is significant for alleviating the scarcity of oil and gas resources and realizing the green and efficient development and utilization of coal in China. Tar-rich coal is often subjected to high axial pressure, surrounding pressure, and pore pressure in the in situ underground pyrolysis environment. Consequently, laboratory simulation conditions are difficult to meet the actual needs. This paper conducts a thermodynamic study of the pyrolysis characteristics of tar-rich coal under an in situ environment. Typical thermodynamic functions of tar-rich coal, including the standard enthalpy of formation, standard formation Gibbs free energy, and standard entropy, were determined. Ten representative primary reactions were constructed with typical tar-rich coal pyrolysis oil components as a guide. The Gibbs free energy and equilibrium constant change laws of the above reactions were analyzed for pyrolysis temperatures from 200 to 800 °C and pyrolysis pressures from atmospheric pressure to 10 MPa. The results showed that the standard enthalpy of formation of tar-rich coal was -72.27 kJ·mol-1, the standard entropy was -37.79 J·mol-1·K-1, and the standard formation Gibbs free energy was -60.01 kJ·mol-1. When the reaction pressure increased from atmospheric pressure to 10 MPa, the thermodynamically feasible initial temperature fractions of the primary reaction of tar-rich coal pyrolysis all showed different degrees of increase. In the underground environment, the initial temperature of the primary reaction of in situ underground pyrolysis of tar-rich coal moves to a higher-temperature gradient to some extent, so the adjustment of the reaction temperature and pressure could guide the directional regulation of the in situ underground pyrolysis products of tar-rich coal.

The Corrosion Behavior of WEDM Machined Stainless Steels in a Pyrolysis Environment

Pyrolysis represents one of the most convenient technologies for the chemical transformation of waste. The exposure to corrosion products and high temperatures does, however, require chemically resistant construction materials. This study was carried out to analyze the corrosion behavior of 1.4571 (AISI 316Ti) and 1.4305 (AISI 303) stainless steels machined with wire electric discharge machining (WEDM) in a pyrolysis environment. Different machining parameters were used for both materials tested to examine the influence of WEDM machining. The total testing time in the pyrolysis environment was 28 days, with the testing chamber being refilled 12 times. The surface topography was analyzed following the WEDM, cleaning, and corrosion test. The surface morphology and cross-section analyses were carried out using electron microscopy at all three stages of the process. An analysis of the chemical composition of the surfaces was carried out as well as of the pyrolysis environment to which the samples were exposed. It was established that the organic acids found in the pyrolysis chamber did not degrade the tested stainless steels to a meaningful degree. Minor fissures, that is, fine precipitated carbides, were observed on the surface of both the steel types and in their subsurface layer, as well as a significant presence of carbon. This presence was directly connected to the impurities found on the surface after the removal from the test furnace that were probably of a protective or passivation nature.

Steam Activation of Oil Shale to Enhance the Porosity of Produced Semicoke

ABSTRACT Finding a recycling method for waste materials is attracting increasing attention. In Estonia, semicoke from the shale oil industry is a material that can be used for adsorbent production. For this application, it is important to characterize the surface properties and enhance the porosity. In this study, different pyrolysis temperatures (from 500 to 800 °C) and steam activation parameters were applied to determine their influences on the surface properties of oil shale semicoke. It was found that pyrolysis at 700°C resulted in the highest Brunauer – Emmett–Teller surface area of 59 m2/g. To investigate the effect of activation, up to 70% vol of steam was added to the pyrolysis environment for different durations (15–60 min). Although the effect was relatively small, shorter activation times and less steam resulted in larger surface areas. The highest surface areas (68–69 m2/g) were achieved when activation was carried out for 15 to 30 min with 25–50% vol of steam in the environment after pyrolysis at 700°C. It can be concluded that longer activation and more steam causes widening and collapsing of some pore structures, resulting in a decrease in the surface area and total pore volume.

Effect of red mud-based additives on the formation characteristics of tar and gas produced during coal pyrolysis

Red mud (RM), an industrial solid waste, was introduced into the coal pyrolysis reaction system, and its effect on the formation characteristics of tar and gas products during coal pyrolysis was explored based on the regulation and characterization of RM structure along with a series of fixed-bed pyrolysis experiments. The results show that Fe2O3 in RM could react with reducing agents, e.g., solid carbon, H2 and CO, in coal pyrolysis environment, along with the gradual reduction process of Fe2O3→Fe3O4→FeO→Fe. As a result, coal conversion as well as release of light gas, such as CO and CO2, are both promoted. Influence tendency of RM after acid treatment (ARM) is consistent with that of the initial RM but the magnitude becomes greater. Compared with RM, ARM has a larger specific surface area and more developed mesoporous structure, thus providing a stronger regulation performance on tar composition. In the presence of ARM, contents of phenols, indenes and aliphatics in tar decrease, accompanied by the increase of monocyclic aromatic hydrocarbons, and the content of BTX and its yield increase by 76.25% and 47.90%, respectively. Furthermore, both the light components (boiling point, BP ≤ 360 °C) and light oil (BP ≤ 170 °C) in tar reach higher levels with addition of ARM. Therefore, ARM is an effective multifunctional catalyst for in-situ upgrading of tar during coal pyrolysis process.

Progress and challenges in sustainable pyrolysis technology: Reactors, feedstocks and products

Pyrolysis is a thermo-chemical decomposition process that converts organic or inorganic materials into solid, liquid and gaseous products. The pyrolysis process involves multiple complex chemical reactions, and the derived products are highly dependent on the pyrolysis operating parameters and type of feedstock. In the present review, progress on the state-of-the-art pyrolysis technology, feedstock and properties of the end products are thoroughly reviewed. The potential application of the pyrolysis products in the industries is discussed: solid leftover can be upgraded and used as a bio-adsorbant, soil amendment, fertilizer or solid fuel; pyrolysis liquid can be used as a bio-chemical source or upgraded into liquid fuel; gaseous products can be used as recirculating gas for the pyrolysis environment or burnt as fuel for heat and power generation. Despite the potential of pyrolysis in processing agricultural or industrial wastes, studies regarding the economic feasibility and environment sustainability of scaled-up pyrolysis plant are scarce. A comprehensive overview on the type of pyrolysis reactor technology, potential feedstock and the properties of the derived products is presented. Further, the sustainability of the technology is assessed from the aspects of energy balance, environment and economics. In spite of the potential benefits to the environment and recovery of valuable products, there are several challenges that need to be addressed to ensure the sustainability and commercialibility of the pyrolysis technologies.

Technical benefits of using methane as a pyrolysis medium for catalytic pyrolysis of Kraft lignin

Catalytic fast pyrolysis of low sulfonated Kraft lignin was performed under different atmospheric environments such as N2, CH4, and the gas derived from CH4 decomposition (CH4-D). The use of Zn- or Mo-loaded HZSM-5 as catalyst led to a higher pyrolytic oil yield compared to parent HZSM-5 in CH4 and CH4-D atmospheres. The yields of benzene, toluene, and xylenes were increased by the synergistic effects from metal loading, higher H/Ceff ratio, higher acidity, and CH4 activation. The enhanced CH4 activation via metal loading resulted in higher methylation of alkyl moieties and 33% increase in the total yield of benzene, toluene, and xylenes in comparison to parent HZSM-5. A higher H/Ceff ratio of 6 via CH4 decomposition led to the formation of a hydro-pyrolysis environment. Moreover, the CH4-D environment showed H2/CH4 ratio of 0.36 in the product gas which warranted the presence of more H2 under the CH4-D pyrolysis environment.

Research on a two-step pyrolysis-oxidation process of carbon fiber-reinforced epoxy resin-based composites and analysis of product properties

The recycling of carbon fiber is the focus of current research as carbon fiber-reinforced polymer (CFRP) waste have increased. Pyrolysis has been identified as an effective method for recycling CFRP. In this study, the surface resin of CFRP was first pyrolyzed, and then the residual carbon on the surface of the pyrolysis product was oxidized to recover carbon fiber. This work focused on the effect of various oxidation conditions on the recovery rate, mechanical properties, and electrical conductivity of RCFs. The results show that the carbon fibers recovered via pyrolysis at 600 ℃ for 30 min and oxidation at 450 ℃ for 15–20 min have better mechanical properties. The tensile strength can exceed 90.19% of the virgin carbon fiber (VCF), the tensile modulus can exceed 84.44% of the VCF, the electrical conductivity can exceed 70% of the VCF, and the recovery rate will exceed 95.22%. Furthermore, the results of simulating the high-temperature pyrolysis environment of CFRP showed that the high-temperature pyrolysis products mainly contained oxygenated aromatic compounds such as 3-Methyltetrahydrophthalic anhydride and Bisphenol-A.

Experimental Observation of Hydrocarbon Growth by Resonance-Stabilized Radical-Radical Chain Reaction.

Rapid molecular-weight growth of hydrocarbons occurs in flames, in industrial synthesis, and potentially in cold astrochemical environments. A variety of high- and low-temperature chemical mechanisms have been proposed and confirmed, but more facile pathways may be needed to explain observations. We provide laboratory confirmation in a controlled pyrolysis environment of a recently proposed mechanism, radical-radical chain reactions of resonance-stabilized species. The recombination reaction of phenyl (c-C6 H5 ) and benzyl (c-C6 H5 CH2 ) radicals produces both diphenylmethane and diphenylmethyl radicals, the concentration of the latter increasing with rising temperature. A second phenyl addition to the product radical forms both triphenylmethane and triphenylmethyl radicals, confirming the propagation of radical-radical chain reactions under the experimental conditions of high temperature (1100-1600 K) and low pressure (ca. 3 kPa). Similar chain reactions may contribute to particle growth in flames, the interstellar medium, and industrial reactors.

Experimental Observation of Hydrocarbon Growth by Resonance‐Stabilized Radical–Radical Chain Reaction

AbstractRapid molecular‐weight growth of hydrocarbons occurs in flames, in industrial synthesis, and potentially in cold astrochemical environments. A variety of high‐ and low‐temperature chemical mechanisms have been proposed and confirmed, but more facile pathways may be needed to explain observations. We provide laboratory confirmation in a controlled pyrolysis environment of a recently proposed mechanism, radical–radical chain reactions of resonance‐stabilized species. The recombination reaction of phenyl (c‐C6H5) and benzyl (c‐C6H5CH2) radicals produces both diphenylmethane and diphenylmethyl radicals, the concentration of the latter increasing with rising temperature. A second phenyl addition to the product radical forms both triphenylmethane and triphenylmethyl radicals, confirming the propagation of radical–radical chain reactions under the experimental conditions of high temperature (1100–1600 K) and low pressure (ca. 3 kPa). Similar chain reactions may contribute to particle growth in flames, the interstellar medium, and industrial reactors.

Rare earth insitu-doped ZIF-67 derived N doped C encapsulated Sm2O3/Co nanoparticles as excellent oxygen reduction reaction catalyst for Al-air batteries

A novel carbon coupled rare earth Sm doped zeolitic imidazolate framework-67 (ZIF-67) derived Sm2O3–Co/NEC300J electrocatalyst with an encapsulated structure was prepared via a composite synthetic strategy, which owns highly dispersed active sites and high conductivity. The introduction of Sm2O3 significantly improves the oxygen reduction reaction (ORR) electrocatalytic performance due to the strong synergistic effect between promoter Sm2O3 and guest Co species, in which the onset potential, half-wave potential and limiting current density are all improved compared to pristine ZIF-67 derived Co/NC. The introduction of Ketjen black EC300J (EC300J) brings high conductivity, so the precursor can be calcined under relative low temperature, and huge highly dispersed ORR active sites are created, meanwhile the EC300J offers a restricted pyrolysis environment to form carbon encapsulated structure. Therefore, Sm2O3–Co/NEC300J exhibits excellent activities and stability compared to Sm-doped ZIF-67 derived Sm2O3–Co/NC. For practical application, the designed Al-air battery with an air-cathode catalyst of Sm2O3–Co/NEC300J achieves the specific capacity of 1588 mAh·g-1Al at the discharge current density of 20 mA·cm−2, which almost equals to that of Pt/C. Furthermore, the peak power density and discharge voltage of Sm2O3–Co/NEC300J based Al-air battery are much higher than the Sm2O3–Co/NC, Co/NC and Pt/C counterparts.

Potassium-assisted carbonization of chlorobenzene in Ar/H2 to prepare porous carbon with low oxygen content for high withstanding voltage EDLCs

Low energy density is a fatal disadvantage of electric double-layer capacitor (EDLC). The improvement of the operation voltage of EDLCs is a more effective method to increase the energy density of EDLCs. When the operation voltage of EDLCs is higher than 2.7 V, the oxygen-containing functional groups on the surface of electrode materials (porous carbon) will decompose or chemically react with the electrolyte, causing significant deterioration of EDLC performance. In this paper, porous carbon with low oxygen content is prepared by using the potassium-assisted carbonization of chlorobenzene in Ar/H2 mixed gas to improve withstanding voltage characteristic of porous carbon. By constructing a relatively closed and stable pyrolysis environment (employing the nickel crucible with a lid), using the carbonaceous precursor without oxygen atoms (chlorobenzene) and selecting reasonable carbonization operation atmosphere (Ar/H2), the oxygen content of the as-prepared porous carbon (PC-KC-1000) is only 4.02 wt%. When the PC-KC-1000 sample is used as the electrode material of EDLCs, the operation voltage of EDLCs in the TEABF4/PC and EMIMBF4 electrolytes is respectively 3.3 and 3.5 V, and the maximum energy density is respectively 53.5 and 64.4 Wh kg−1. This strategy provides a new idea for the preparation of porous carbon with low oxygen content.

Reaction pathways of molecular growth for bay-region methyl-substituted polycyclic aromatic hydrocarbons during supercritical pyrolysis of n-decane, as determined from experiments with 4-methylchrysene dopant

To investigate the molecular-growth reactions of bay-region methyl-substituted polycyclic aromatic hydrocarbons (PAH) in the supercritical n-alkane-fuel pyrolysis environment, we have performed supercritical n-decane pyrolysis experiments with and without the dopant 4-methylchrysene (dopant concentration, 0.684 mg/g n-decane), in an isothermal, silica-lined stainless-steel flow reactor at 568 °C, 94.6 atm, and 133 s, conditions of rapid PAH growth. Analyses of the reaction products by high-pressure liquid chromatography with diode-array ultraviolet-visible absorbance and mass-spectrometric detection reveal that in the supercritical n-decane pyrolysis environment—where the aliphatic growth species methyl, ethylene, propene, and 1-butene are abundant—molecular growth of the four-ring 4-methylchrysene to high-ring-number PAH occurs chiefly through two routes, both of which take advantage of the bay-region position of 4-methylchrysene's methyl substituent. In the first route, 4-methylchrysene's resonance-stabilized arylmethyl radical 4-chrysenylmethyl attacks the aryl carbon just across the bay of 4-methylchrysene's structure to form the C19H12 methylene-bridged PAH 4H-cyclopenta[def]chrysene, whose resonance-stabilized radical 4-cyclopenta[def]chrysenyl reacts with methyl and ethylene in ring-expansion reactions that selectively produce the five-ring C20H12 benzo[a]pyrene and its derivatives 4- and 5-methylbenzo[a]pyrene. The arylmethyl radicals 4- and 5-benzo[a]pyrenylmethyl then undergo a series of reactions with n-decane's high-yield C2C4 1-alkenes to selectively produce particular six- to nine-ring peri‑condensed benzenoid PAH such as dibenzo[a,e]pyrene, benzo[a]naphtho[2,3-e]pyrene, dibenzo[e,ghi]perylene, benzo[a]coronene, and naphtho[8,1,2-abc]coronene—all of whose yields increase dramatically with 4-methylchrysene doping. In 4-methylchrysene's second major route of molecular growth, 4-chrysenylmethyl's attack of the aryl carbon across the bay is followed by an intramolecular rearrangement that produces 4H-benzo[cd]fluoranthene, a non-fully aromatic C19H12 PAH with an internal five-membered ring. Reactions of the resonance-stabilized benzo[cd]fluoranthenyl radicals with methyl, propene, and 1-butene selectively produce the six-ring C22H12 indeno[1,2,3-cd]pyrene and four particular seven-ring C26H14 benzindeno[1,2,3-cd]pyrenes—each of which contains an internal five-membered ring, evidencing the distinctive molecular-growth pathways of bay-region methyl-substituted PAH in the supercritical n-alkane-fuel pyrolysis environment.

Enhancement of aromatics from catalytic pyrolysis of yellow poplar: Role of hydrogen and methane decomposition

The present study examined the effects of the pyrolysis environment on BTEX (benzene, toluene, ethylbenzene, and xylenes) production in the catalytic upgrading of yellow poplar pyrolysis vapors. Three different gas environments, N2, CH4, and pre-decomposed CH4 stream (10 wt%-Ni/5 wt%-La2O3-5 wt% CeO2-Al2O3), which is a mixture of H2 (55.62%) and CH4, were studied using two types of zeolite catalysts, HZSM-5, and 1 wt% Ga/HZSM-5. The BTEX yields were enhanced linearly in the order N2 < CH4 < CH4 ex-situ decomposition. The highest BTEX yield of 9.58 wt% was obtained under the CH4 ex-situ decomposition environment over 1 wt% Ga/HZSM-5. The methane and hydrocarbons derived from biomass were activated on highly dispersed (GaO)+ sites and transformed smoothly to BTEX by aromatization on the BrØnsted acid sites of Ga/HZSM-5. The hydrogen produced from methane decomposition also assisted in aromatics production through the hydrodeoxygenation of methoxyphenols, guaiacols and catechols.