Aromatic Fuels Research Articles

Catalysis and chemistry of lignin depolymerization in alcohol solvents - A review

The second-generation biofuel strategy aims to fully utilize lignocellulose, which is the major component of the plant cell wall and the most abundant form of renewable organic resources. Among three major components of lignocellulose, i.e. cellulose, hemicellulose and lignin, lignin has been the least utilized one up to now. Nevertheless, lignin depolymerization (LD) to produce aromatic chemicals and fuels has been intensely explored in the recent decade. Alcohols have been the mostly employed solvents in LD reaction, and are also involved into the LD reaction. This review provides an overview of the catalysis and chemistry of LD reaction in alcohols, especially in methanol, ethanol and isopropanol. The recent advances are firstly summarized, and then the roles of alcohol in LD reaction are outlined. The alcohol self-conversions are firstly discussed, and then the roles of alcohol are discussed in four subtopics: supplying hydrogen, depolymerizing lignin, hindering repolymerization and affecting monomer structure. Alcohol and alcohol-derived intermediates provide active hydrogen for reductive catalytic LD reaction carried out without hydrogen input, effectively break ether linkages but not C-C linkages in lignin, and also react with active intermediates and monomers, suppressing the repolymerization side reactions. In addition, alcohol also inhibits the hydrogenation of benzene rings and involves in the formation of products, affecting the structure of monomers. With these understandings, the challenges and opportunities of LD are proposed.

Advances in the application of molecular sieves as catalysts for lignin depolymerization—HZSM‐5 as an example

AbstractAt present, mankind faces the problem of increasingly serious global environmental crisis and growing shortage of petrochemical resources, making it more and more necessary to seek renewable substitute for petroleum. Biomass resources, which have received widespread attention and worldwide research, are the most common source of renewable carbon. Moreover, they are considered to be the major source of renewable green carbon today. Biomass resources contain three main aggregates, which are cellulose, hemicellulose, and lignin, as well as small amounts of other additional materials. Notably, the aromatic ring ethers linkage inside lignin molecules enables it to serve as a renewable and suitable feedstock for the production of aromatic chemicals and fuels. However, the recognition that lignin is the most difficult lignocellulosic biomass to degrade makes it much less valuable for practical applications. Therefore, in order to achieve high‐value conversion and utilization of lignin and replace non‐renewable fossil resources, the targeted conversion of lignin into chemicals and materials has become one of the major hot research areas. To this end, this article reviews research results on the use of molecular sieves (HZSM‐5) as catalysts for lignin degradation and conversion, providing an outlook on future research directions.

Influence of alternative fuel properties and combustor operating conditions on the nvPM and gaseous emissions produced by a small-scale RQL combustor

Non-volatile Particulate Matter (nvPM) from aircraft gas turbine engines are harmful to both human health and the environment, but can be significantly reduced by using low aromatic Sustainable Aviation Fuel (SAF). As part of the Horizon 2020 funded JETSCREEN (JET fuel SCREENing and optimisation platform for alternative fuels) project, nvPM and gaseous emissions were characterised using regulatory compliant sampling and measurement methodologies for a small-scale (<250kW) non-proprietary RQL combustion rig, at pressures ranging from 1.0 to 2.4 bara. The impact of flow conditions, air to fuel ratio and fuel composition was investigated for a selection of conventional aviation Jet-A1 fuels, SAFs, and blended fuels. Measured concentrations were corrected for particle-size-dependant system losses using particle size measurements, to be representative of combustor exit concentrations.Across the range of fuels (hydrogen contents 13.51%-15:31%), system-loss-corrected nvPM mass, number, and size were shown to decrease with increasing fuel hydrogen content, in agreement with previous studies. Inverse power law correlations are proposed as the best descriptors of these trends. Average reductions in nvPM mass, number, and sizes of 73%, 54% and 17% respectively, were observed for a near-zero aromatic ATJ fuel compared to a reference Jet A1 fuel, with minimal changes to measured gaseous pollutants. It is noted that without size-dependant system loss corrections, nvPM number reductions were overreported (∼6% for the ATJ fuel) due to the smaller particle sizes with increasing fuel hydrogen content. It was hypothesised that observed nvPM deviations from the fuel hydrogen content trends were due to fuel physical properties affecting atomisation, however no correlations were found greater than the measurement uncertainty and combustor rig variability.This study provides a unique dataset intended to facilitate combustion model validation, providing full details of combustor geometry, flow conditions and rig conditions, along with the representative combustor exit nvPM and gaseous data.

Effect of alkyl substituent for cyclohexane on pyrolysis towards sooting tendency from theoretical principle

The fuel structure is an important controlling factor during the process of soot formation. Alkylated cyclohexane is a typical surrogate fuel with more complex structure than alkanes or aromatic fuels. Five alkylated cyclohexanes (i.e., cyclohexane, methylcyclohexane, ethylcyclohexane, 1,3-dimethylcyclohexane, 1,3,5-trimethylcyclohexane) and the n-alkane were selected to investigate the effect of the alkyl substituent on sooting tendency during the pyrolysis process from the theoretical principle. The reaction energy barriers profiles of alkylated cyclohexanes obtained by the density functional theory (DFT) illustrate the length and number of the alkyl substituent will affect the production of alkenes fragments which finally decompose to C2H2 and C3H3 species. The molecular dynamics simulations show the abundance of C2H2 and C3H3 fragments from the initial pyrolysis of fuels will accelerate the sooting tendency, which follow the trend of cyclohexane < methylcyclohexane < ethylcyclohexane ≈ 1,3-dimethylcyclohexane < 1,3,5-trimethylcyclohexane, in agreement with experimental findings. We hope this study can provide a more comprehensive understanding of the effect of fuel structure on sooting tendency and ideas for soot inhibition.

Low-Emission Alternative Energy for Transport in the EU: State of Play of Research and Innovation

The 2030 Climate target plan of the European Commission (EC) establishes a greenhouse gases (GHG) emissions reduction target of at least 55% by 2030, compared to 1990. It highlights that all transport modes—road, rail, aviation and waterborne—will have to contribute to this aim. A smart combination of vehicle/vessel/aircraft efficiency improvements, as well as fuel mix changes, are among the measures that can reduce GHG emissions, reducing at the same time noise pollution and improving air quality. This research provides a comprehensive analysis of recent research and innovation in low-emission alternative energy for transport (excluding hydrogen) in selected European Union (EU)-funded projects. It considers the latest developments in the field, identifying relevant researched technologies by fuel type and their development phase. The results show that liquefied natural gas (LNG) refueling stations, followed by biofuels for road transport and alternative aviation fuels, are among the researched technologies with the highest investments. Methane-based fuels (e.g., compressed natural gas (CNG), LNG) have received the greatest attention concerning the number of projects and the level of funding. By contrast, liquefied petroleum gas (LPG) only has four ongoing projects. Alcohols, esters and ethers, and synthetic paraffinic and aromatic fuels (SPF) are in between. So far, road transport has the highest use of alternative fuels in the transport sector. Despite the financial support from the EU, advances have yet to materialize, suggesting that EU transport decarbonization policies should not consider a radical or sudden change, and therefore, transition periods are critical. It is also noteworthy that there is no silver bullet solution to decarbonization and thus the right use of the various alternative fuels available will be key.

Enhancement of the production of chemicals and liquid fuels from grass biowaste via NaOH-Fenton pretreatment coupled with fast pyrolysis

Biomass waste pyrolysis has taken an increasing interest in producing biofuels and bio-based chemicals, but the complex compositions of pyrolytic liquid hinder its development and utilization. To address these challenges and improve the yield of target chemicals (levoglucosan) and aromatics, a novel two-stage process based on NaOH-Fenton pretreatment coupled with fast pyrolysis is firstly proposed. Firstly, rice straw was pretreated by dilute alkali to separate lignin fractions, and then the residue was further treated via Fenton reaction at room temperature to obtain cellulose-rich substrate. The fast pyrolysis of raw rice straw produced the complex compositions in the pyrolytic liquid. After NaOH-Fenton pretreatment, the target platform chemicals in the pyrolysate were effectively concentrated. The cellulose-rich substrate exhibited a very high absolute yield of levoglucosan (201.9 mg/g) as compared to raw rice straw (not detected). The lignin fractions recovered from this process were catalytically fast pyrolyzed for preparing aromatic fuels. Furtherly, the maximum removal rates of nitrogen (76.5%) and sulfur (93.3%) were achieved by the coupled process. A short-chain cellulose-rich substrate with similar dissociation energy of glycosidic bonds was formed by the NaOH-Fenton process based on the analytical results of the DFT calculation and mechanism. The similar dissociation energy of C–O bonds from the short-chain cellulose-rich substrate favors the formation of high-yield levoglucosan in subsequent fast pyrolysis. This work introduces a simple and highly efficient strategy to convert grass biowaste into value-added chemicals and liquid fuels.

Experimental investigation and correlation development for engine emissions with polycyclic aromatic blended formulated fuels

Higher engine out emissions are the challenges and need to be addressed for better environmental health. One of the leading emitters of harmful pollutants is the transportation sector. These harmful emissions are highly affected by fuel components and properties. Investigating the influence of dominant fuel composition such as aromatics can help reform diesel fuel with better aromatic types. Therefore, polycyclic aromatics with single and double ring structure were blended with a base fuel in 5, 10 and 15% by mass. The blended aromatics were then tested in direct injection combustion engine on variable load conditions. The results revealed that aromatic percentage in tested fuels promote engine out emissions. Methylnaphthalene blended fuel promotes CO, UHC, PM and smoke emission to the higher extent among different investigated aromatics. The efficacy of the aromatics on engine performance is also assessed experimentally and discussed. Engine performance deteriorates with the aromatic content in blends due to their low cetane number and heating value. The present study contributes knowledge towards better fuel formulation for lower emissions, improved performance and better engine compatibility with a particular type of single added aromatic.

Petroleum Pitch from Highly Aromatic Fuel Oil for Nonferrous Metallurgy

Petroleum Pitch from Highly Aromatic Fuel Oil for Nonferrous Metallurgy

Cleaner burning aviation fuels can reduce contrail cloudiness

Contrail cirrus account for the major share of aviation’s climate impact. Yet, the links between jet fuel composition, contrail microphysics and climate impact remain unresolved. Here we present unique observations from two DLR-NASA aircraft campaigns that measured exhaust and contrail characteristics of an Airbus A320 burning either standard jet fuels or low aromatic sustainable aviation fuel blends. Our results show that soot particles can regulate the number of contrail cirrus ice crystals for current emission levels. We provide experimental evidence that burning low aromatic sustainable aviation fuel can result in a 50 to 70% reduction in soot and ice number concentrations and an increase in ice crystal size. Reduced contrail ice numbers cause less energy deposition in the atmosphere and less warming. Meaningful reductions in aviation’s climate impact could therefore be obtained from the widespread adoptation of low aromatic fuels, and from regulations to lower the maximum aromatic fuel content.

Highly Dispersed Rh/NbOx Invoking High Catalytic Performances for the Valorization of Lignin Monophenols and Lignin Oil into Aromatics

As fossil fuels are constantly depleted, valorization of lignocellulosic biomass into valuable aromatic compounds is of great significance but exceedingly challenging. In this work, the structure and catalytic performance of various Rh/Nb₂O₅ catalysts were studied in detail via the catalytic hydrodeoxygenation of a representative lignin monophenol compound 2-methoxy-4-propylphenol. The best catalytic performance was obtained over Rh/Nb₂O₅-400 (Nb₂O₅ calcined at 400 °C) with an exceptional 98% yield of propylbenzene under 0.5 MPa H₂, which was mainly due to the cooperation between highly dispersed Rh metals and NbOₓ species, in which Rh was responsible for dissociation of H₂ and NbOₓ for breaking of C–O bonds at the metal–support interface. Besides, the lignin oil obtained in depolymerization of raw pine wood was directly used as the substrate in the catalytic hydrodeoxygenation reaction over the Rh/Nb₂O₅-400 catalyst under 0.5 MPa H₂. Encouragingly, the liquid products were identified and found that lignin oil was completely converted into C₆–C₁₀ hydrocarbons (>99% selectivity) with an 80.1 mol % yield of aromatics. The results achieved in this work highlighted that high-value utilization of lignocellulosic biomass feedstocks to produce aromatic chemicals and liquid fuels could be achieved over Rh/Nb₂O₅ under a low hydrogen pressure.

Exploring pyrolysis and oxidation chemistry of o-xylene at various pressures with special concerns on PAH formation

This work reports an experimental and kinetic modelling investigation on flow reactor pyrolysis and jet-stirred reactor oxidation of o-xylene. The flow reactor pyrolysis experiments were conducted over 1050–1600 K at 0.04 and 1.0 atm. Key products related to fuel decomposition such as o-xylyl radical, o-xylylene, benzocyclobutene and styrene, as well as polycyclic aromatic hydrocarbons (PAHs), were detected by using synchrotron vacuum ultraviolet photoionization mass spectrometry. The jet-stirred reactor oxidation experiments were performed at 10 atm, 800–1200 K, a residence time of 0.5 s and equivalence ratios of 0.5, 1.0 and 2.0. Speciation were conducted by using gas chromatography and Fourier transform infrared spectrometry. A kinetic model of o-xylene was developed from our previous models of aromatic fuels and validated against both present data and experimental data in literature. Styrene is observed as the dominant product in the pyrolysis of o-xylene and it is mainly produced from the isomerization of o-xylylene directly or via benzocyclobutene as an intermediate species. C9 PAHs (indenyl, indene and indane), phenanthrene and its methyl derivatives were observed as the abundantly produced bicyclic and tricyclic PAHs. The main formation pathways of bicyclic and tricyclic PAHs are found to be different at low and atmospheric pressures, depending on the major precursors produced. Particularly, the self-combination reactions of o-xylyl and the addition reaction of o-xylyl with benzyl and subsequent stepwise H-loss/cyclization reactions are found to be the main sources of methylphenanthrene and dimethylphenanthrene. In the JSR oxidation of o-xylene, toluene and benzene were observed as the abundantly produced aromatic products, while o-methylbenzaldehyde was among the most abundantly produced oxygenated aromatics. modelling analysis reveals that o-xylyl radical is also the dominant fuel consumption product. Its consumption mainly proceeds through the oxidation by HO2 and finally produces o-methylbenzaldehyde. Further decomposition reactions of o-methylbenzaldehyde contribute to the formation of other major oxygenated aromatics such as cresol and benzofuran. Indene and naphthalene were also observed in the oxidation of o-xylene, which are mainly produced from the stepwise H-loss/cyclization reaction sequence of o-methylethylbenzene and decomposition of dibenzofuran, respectively.

Investigations on Combustion and Emissions Characteristics of Aromatic Fuel Blends in a Distributed Combustor

The present article reports the combustion and emission characteristics of different monocyclic and polycyclic aromatics in a distributed combustion regime. Fuel blends based on five different arom...

Catalytic Hydrodeoxygenation of Lignin-Derived Feedstock Into Arenes and Phenolics

lignin, as the only most abundant aromatic source in nature, shows great potential to address environmental and energy problems. Hydrodeoxygenation (HDO) as a useful way of converting lignin and its-derived compounds into value-added aromatic chemicals and fuels is able to transform the vision “fueling the future” into reality, thus garnering considerable attention in the past decade. The purpose of this minireview is to specifically address the removal of phenolic hydroxyl groups and/or methoxy groups within lignin, mainly focusing on the core questions and challenges of catalytic systems. Our own insights into future studies and recommendations for future research in this promising field are also provided.

Evaluating the relationships between aromatic and ethanol levels in gasoline on secondary aerosol formation from a gasoline direct injection vehicle

While the effects of fuel composition on primary vehicle emissions have been well studied, less is known about the effects on secondary aerosol formation and composition. The propensity of light-duty gasoline engines to form secondary aerosol and contribute to regional air quality burdens are of scientific interest. This study assessed secondary aerosol formation and composition due to photochemical aging of exhaust emissions from a light-duty vehicle equipped with gasoline direct injection (GDI) engine. The vehicle was operated on eight fuels with varying ethanol and aromatic levels. Testing was performed over the LA92 cycle using a chassis dynamometer. The aging studies were performed using a mobile environmental chamber. Diluted exhaust emissions were introduced to the mobile chamber over the course of the LA92 cycle and subsequently photochemically reacted. It was found that secondary aerosol mass exceeded the primary particulate matter (PM) emissions. Secondary aerosol was primarily composed of ammonium nitrate due to the elevated tailpipe ammonia emissions. The high aromatic fuels produced greater total carbonaceous aerosol and secondary organic aerosol (SOA) compared to the low aromatic fuels. A clear influence of ethanol for the high aromatic fuels on SOA formation was observed, with greater SOA formation for the fuels with higher ethanol contents. Our results suggest that more SOA formation is expected from current GDI vehicles when operated with gasoline fuels rich with heavier aromatics and blended with higher ethanol levels.

Photocatalytic Conversion of Lignin into Chemicals and Fuels.

Lignin, an underutilized component of lignocellulosic biomass, is regarded as a rich reservoir for the production of aromatic chemicals and fuels. Despite extensive research in recent years, lignin's potential is far from being fully unlocked. Photocatalysis that uses sustainable solar energy to drive lignin conversion under mild conditions has been identified as a promising strategy and received growing research interest. This review aims to present a critical introduction to the photocatalytic conversion of lignin, including a summary of lignin conversion pathways and mechanisms, as well as the latest cutting-edge innovations on photocatalyst design and reactor construction. Moreover, the screening of solvents and regulation of other key factors that are involved in photocatalytic lignin conversion are also elucidated and future perspectives and challenges for photocatalytic conversion of lignin into valuable products are discussed.

Successive organic solvent fractionation and structural characterization of lignin extracted from hybrid poplar by deep eutectic solvent for improving the homogeneity and isolating narrow fractions

Deep eutectic solvent (DES) treatment emerged as an efficient way to separate lignin at a moderate condition via acidolysis and hydrophobic interaction. In the attempt to realize lignin’s upgrading, this work employs successive organic solvent fractionation in DES-extracted lignin to obtain fragments with a narrow molecular weight distribution and relatively homogeneous structure. The polydispersity was decreased from 2.26 to 1.35. Purity and thermal stability were enhanced. Ethyl acetate-extracted lignin possessed the highest content of phenolic hydroxyls (3.23 mmol/g) but the lowest content of aliphatic hydroxyls of 1.10 mmol/g β-O-4 linkages were partly cleaved during DES separation and fragments containing more C–C bonds tended to be dissolved in ethyl acetate through hydrophobic interaction. The successive fractionation performed effectively in obtaining lignin fragments with diversity in main linkages and functional groups. This approach provided lignin fractions with versatility in preparation and application in thermos-plastics, lignin-derived carbon materials, antioxidants and aromatic fuels and chemicals.

Study of PAH formation in laminar premixed toluene and C8H10 aromatics flames

Toluene and C8H10 aromatic fuels are widely proposed as components of surrogate mixtures and usually employed as the prototypical fuels to investigate the combustion properties of aromatic fuels. In this study, the PAH formation of pure C8H10 aromatics (xylenes and ethylbenzene) and toluene was studied in a laminar premixed flame at atmospheric pressure using laser-induced fluorescence (LIF) diagnostic. The experimental results indicated the aromatic structure has a significant influence on the PAH tendency, and the observed LIF intensities were sequenced by toluene < xylenes < ethylbenzene. A detailed kinetic model was employed to validate against the experimental results based on the ROP analysis. The predicted mole fraction profiles of PAHs were consistent with the measured PAH tendency for toluene, o-xylene, and ethylbenzene. The chemical kinetic analysis indicated that benzyl is the most dominant intermediate product in toluene decomposition and precursor in PAH formation, corresponding to methylbenzyl in o-xylene flame, styrene and benzyl in ethylbenzene flame. In the comparison of o-xylene and toluene, the increased methylated groups on the benzenoid ring make the yield of benzylic radicals (mostly methylbenzyl) enhanced, increasing the probability of radical–radical recombination on PAH formation. In the ethylbenzene flame, two secondary CH bonds in the ethyl site are much easier to be abstracted than primary CH bonds in methyl sites of o-xylene. The different bond dissociation energies (BDEs) depended on the aromatic structure can change the distribution of the intermediate species in fuel decomposition, which can result in either an increase or decrease of PAH formation. Additionally, the weak benzylic CC bond makes the initiation of ethylbenzene decomposition easier, which could also explain the fated PAH formation in contrast with toluene and o-xylene. The experimental and kinetic analysis for C8H10 aromatics and toluene conducted in the present study contributed a deep insight into the PAH formation of aromatics fuels.

Phenomenological soot modeling with solution mapping optimization of biodiesel-diesel blends in diesel engines

It is widely accepted that the particulate matter emissions of a diesel engine may be substantially reduced when a blend of diesel and biodiesel fuels is used. Here we propose a phenomenological model aimed at evaluating the extent of soot formation and oxidation in a diesel engine fueled with diesel–biodiesel blends and providing a better understanding of these processes. These blends are represented by three hydrocarbon functional groups: aromatic, aliphatic, and ester fuels, in different proportions.In a previous study, the phenomenological soot model of Foster and Reitz and colleagues was modified to capture the influence of the diesel–biodiesel molecular composition on soot formation and emissions. In the present work, this model was implemented in computational fluid dynamics (CFD) diesel engine combustion simulations. These CFD simulations were performed using the finite volume method commercial code ANSYS Fluent 16.1. The solution mapping optimization method developed by Frenklach and colleagues was used to calibrate this model for the engine. Validation was performed by comparing the following simulated variables with experimental results: pressure, heat release rate, averaged soot density inside the piston bowl, maximal temperature inside the piston bowl, and exhaust soot emissions. Reasonable agreement was obtained between our computational results and the published experimental results of Mancaruso and colleagues. The soot evolution in the piston bowl in these simulations was to a certain extent qualitatively and quantitatively similar to that in the experiments. The maximal experimental in-cylinder two-color soot density was 44 g/m3 and its computational equivalent was 60 g/m3. The maximal space-averaged two-color soot densities in the experiments and the computations were 9.3 and 7.73, respectively. The experimental soot reduction potentials of biodiesel blending for B20, B50, and biodiesel were 12.0%, 27.3%, and 47.2%, respectively. The respective computational soot reduction potentials were 34.8%, 36.2%, and 43.4%.

Influence of gasoline olefin and aromatic content on exhaust emissions of 15% ethanol blends

This research focused on the determination of relationships between aromatic and olefins in fuels with constant concentration of ethanol compared with blends without the oxygenate compound. Nine fuels were used for testing prepared by match blending, four of them were non-oxygenate with high and low levels of aromatics and olefins, another four were fuels with 15% volume of ethanol and similar levels of aromatic and olefins. The ninth fuel was oxygenated with 7% volume ethanol to monitor differences in vehicle performance. This study evaluated the tailpipe emissions of four-model year 2017–2018 light-duty gasoline vehicles subjected to the EPA protocol related to FTP-75. During cold start period CO contribution to emissions increase in the ethanol blends, being greater with the low olefins blends, while, NOx emissions are reduced in the low aromatic fuels without ethanol compared with the high aromatic blends. Principal components analysis was used to investigate the relationship between formulated fuels. Non-oxygenated fuels with high aromatic and olefin content shows higher values of the ozone formation. The aromatic content is positively related with hydrocarbons and CO2 emissions. Additionally the aromatic content is related with 3-methylpentane and the BTEX compounds. NOx emissions are related with ethanol content, but inversely associated with the carbon fraction of fuels.

A review on influence of injection timing and injection pressure on DI diesel engine fuelled with low viscous fuel

It is necessary to search for new fuel in an energy crisis considering fuel replacement of diesel fuel considering the emission norms. Also, the rise in demand for fuel is due to the rapid increase of automation in industry and also transportation. At the same time, the disposal of plastic waste is causing serious environmental problems. Waste Plastic Oil (WPO) and renewable energy are getting more attention in this modern world as a source, non-biodegradable alternative. It is observed that most of alcoholic and aromatic fuels are low viscous in nature. The waste plastic oil is associated with gasoline and petroleum products. It is proven that Ethanol and Waste Plastic Oil (WPO) in the compression ignition engines can be used as a supplementary fuel. However, the direct injection diesel engine is designed for diesel fuel, it is necessary to modify the injection pressure and injection timing for low viscous fuel. Thus, consequence of the injection pressure and timing on the Direct Injection Diesel engine was experimentally investigated with low viscous fuel. Tests were carried out at various injection timings like (25°, 23°, 20° and 17° bTDC) and also at reduced injection pressures to find out the least possible emissions and better performance characteristics. Many researchers revealed that retarded injection timing (17°bTDC) and lower injection pressure (180 bar) the low viscous fuel perform well in performance, combustion and emission characteristics.