Single-ring Aromatics Research Articles

Obscured Contribution of Oxygenated Intermediate-Volatility Organic Compounds to Secondary Organic Aerosol Formation from Gasoline Vehicle Emissions.

Secondary organic aerosol (SOA) formation from gasoline vehicles spanning a wide range of emission types was investigated using an oxidation flow reactor (OFR) by conducting chassis dynamometer tests. Aided by advanced mass spectrometric techniques, SOA precursors, including volatile organic compounds (VOCs) and intermediate/semivolatile organic compounds (I/SVOCs), were comprehensively characterized. The reconstructed SOA produced from the speciated VOCs and I/SVOCs can explain 69% of the SOA measured downstream of an OFR upon 0.5-3 days' OH exposure. While VOCs can only explain 10% of total SOA production, the contribution from I/SVOCs is 59%, with oxygenated I/SVOCs (O-I/SVOCs) taking up 20% of that contribution. O-I/SVOCs (e.g., benzylic or aliphatic aldehydes and ketones), as an obscured source, account for 16% of total nonmethane organic gas (NMOG) emission. More importantly, with the improvement in emission standards, the NMOG is effectively mitigated by 35% from China 4 to China 6, which is predominantly attributed to the decrease of VOCs. Real-time measurements of different NMOG components as well as SOA production further reveal that the current emission control measures, such as advances in engine and three-way catalytic converter (TWC) techniques, are effective in reducing the "light" SOA precursors (i.e., single-ring aromatics) but not for the I/SVOC emissions. Our results also highlight greater effects of O-I/SVOCs to SOA formation than previously observed and the urgent need for further investigation into their origins, i.e., incomplete combustion, lubricating oil, etc., which requires improvements in real-time molecular-level characterization of I/SVOC molecules and in turn will benefit the future design of control measures.

Balancing the Components of Biomass and the Reactivity of Pyrolysis Gas: Biomass-Assisted Recycling of Spent LiCoO2 Batteries.

Waste biomass is one of the promising feedstocks to supply syngas that can be used as fuels, chemicals, reductants, etc. However, the relationship between the component of biomass and the constituent of pyrolysis gas remains unclear. Here, we study the pyrolysis behaviors of various biomasses and reveal the relationship between the biomass components and gas compositions. Further, different pyrolysis gases are applied for the reduction of spent lithium cobalt oxide (LiCoO2) below 500 °C. The pyrolysis gas with a higher concentration of CO has a higher reductivity to convert LiCoO2 to CoO and Li2CO3 with a conversion rate close to 100% in 1 h at 500 °C. The biomass rich in cellulose and with a lower content of lignin tends to produce pyrolysis gas with a high concentration of CO, which comes from the deliberate breakdown of carboxyl, carbonyl, ether, and ester linkages. Moreover, LiCoO2 exerts catalytic functions over the deoxygenation and enhancement of oxygenates and single-ring aromatics. Overall, this paper offers a tailored approach to regulating biomass pyrolysis gases, enabling highly efficient battery recycling and syngas production.

Floating reactive barriers to mitigate secondary organic aerosol formation from oil sands tailings ponds

Oil sands operations to recover bitumen in Alberta, Canada generate large volumes of contaminated water which are stored in tailings ponds. These ponds emit large quantities of intermediate / semi- volatile organic compounds (IVOC/SVOCs) which upon emission can react or partition to form secondary organic aerosols (SOAs), a significant issue concerning human and environmental health. These ponds are one of the largest sources of SOAs in North America, and the responsible VOCs (polycyclic aromatic hydrocarbons (PAHs), alkanes, single ring aromatics) are difficult to treat. Passive technologies that can reduce aqueous emissions and degrade volatiles in-situ are desired. A promising technology is buoyant photocatalysts (BPCs), which float on the surface of water bodies and absorb sunlight to oxidize contaminants. In this work, a glass microsphere TiO2-coated BPC is studied, which forms a semi-porous floating reactive barrier on the surface of water, intercepting VOC emissions and photocatalytically oxidizing them in water before they can be released to air. Based on a group of F2 – F3 hydrocarbons, 16 PAHs (C10 – C22) and 8 alkanes (C11-C18), this BPC technology reduced 89% of these SOA precursor emissions while degrading 84% of the compounds in the system under 2 days of simulated sunlight. In a synthetic tailings pond environment, BPCs were demonstrated to block and treat VOCs of particular concern well (phenanthrene, pyrene, chrysene), while further preventing emissions from free phase hydrocarbons. In context of tailings pond SOA precursor emissions, application of this floating reactive barrier technology to all ponds could reduce the environmental impact of oil sands operations by preventing release of between 2400 to 11000 tonnes of SOAs per year. The proven ability to intercept and treat VOCs in water extends the potential of this technology past the oil sands industry, providing one of the first options for passive fugitive emission management for various industrial water bodies. SynopsisBuoyant Photocatalysts permanently prevent aqueous gas emissions and likely subsequent secondary organic aerosol formation by preventing release while oxidizing aqueous volatiles.

Secondary Organic Aerosol Formation from Volatile Chemical Product Emissions: Model Parameters and Contributions to Anthropogenic Aerosol.

Volatile chemical products (VCP) are an increasingly important source of hydrocarbon and oxygenated volatile organic compound (OVOC) emissions to the atmosphere, and these emissions are likely to play an important role as anthropogenic precursors for secondary organic aerosol (SOA). While the SOA from VCP hydrocarbons is often accounted for in models, the formation, evolution, and properties of SOA from VCP OVOCs remain uncertain. We use environmental chamber data and a kinetic model to develop SOA parameters for 10 OVOCs representing glycols, glycol ethers, esters, oxygenated aromatics, and amines. Model simulations suggest that the SOA mass yields for these OVOCs are of the same magnitude as widely studied SOA precursors (e.g., long-chain alkanes, monoterpenes, and single-ring aromatics), and these yields exhibit a linear correlation with the carbon number of the precursor. When combined with emissions inventories for two megacities in the United States (US) and a US-wide inventory, we find that VCP VOCs react with OH to form 0.8-2.5× as much SOA, by mass, as mobile sources. Hydrocarbons (terpenes, branched and cyclic alkanes) and OVOCs (terpenoids, glycols, glycol ethers) make up 60-75 and 25-40% of the SOA arising from VCP use, respectively. This work contributes to the growing body of knowledge focused on studying VCP VOC contributions to urban air pollution.

Soot nucleation in diffusion flames and the role of aromatic hydrocarbons

We perform spatially resolved measurements of light scattering of soot in atmospheric pressure counterflow diffusion flames to complement previously reported data on soot pyrometry, temperature and gaseous species up to three-ring polycyclic aromatic hydrocarbons (PAHs). We compare two flames: a baseline ethylene flame and a toluene-seeded flame in which an aliquot of ethylene in the feed stream is replaced with 3500 ppm of pre-vaporized toluene. The goal is twofold: directly adding an aromatic fuel to bypass the formation of the first aromatic ring, widely regarded as the main bottleneck to soot formation from aliphatic fuels, and assessing the impact of a common component of surrogates of transportation fuels on soot formation. The composition of the fuel and oxidizer streams are adjusted to ensure invariance of the temperature-time history, thereby decoupling the chemical effects of the fuel substitution from other factors. The doping approach enables the comparison of very similar flames with respect to combustion products, radicals and critical precursors to aromatic formation (C2–C5 species), in addition to the temperature-time history. Doping with toluene boosts the aromatic content and soot volume fraction relative to the baseline ethylene flame, but, surprisingly, the soot number density and nucleation rate are affected modestly. As a result, the observed difference in volume fraction in the toluene-doped flame is reflective of larger initial particles at the onset of soot nucleation. The nucleation rate when soot first appears near the flame is of the same order as the dimerization rate of single-ring aromatics, in contrast with the expectation that the dimerization of larger PAHs initiates the process. Even though in and of itself nucleation contributes modestly to the overall soot loading, nucleation conditions the overall soot loading by affecting the size of the initial particle, which ultimately affects subsequent growth.

Adsorbing Volatile Organic Compounds within Bitumen Improves Colloidal Stability and Air Quality

The mass loss of bitumen due to volatilization is one of the deterioration mechanisms through which the chemical composition of bitumen deviates from its original condition, leading to change in the physical and rheological properties of bitumen. The emissions from bitumen not only accelerate its aging but also negatively impact air quality and consequently human health. Here, we characterized the molecular compositions of the volatiles emitted from bitumen in an isothermal aging process (150 °C for 24 h). We also investigated the impact of losing these compounds on the association behavior of asphaltene stacks. Based on the GC-MS results, the main mass loss of SARA (saturates, aromatics, resins, asphaltenes) fractions is attributed to the emission of lightweight nonpolar aromatic and aliphatic compounds. The most dominant volatiles are single-ring aromatics carrying short side chains, followed by saturated and unsaturated aliphatic compounds including short-chain n-alkanes, iso-alkanes, cyclic alkenes, alkenes, and dienes. Using molecular modeling in the framework of density functional theory (DFT), we showed how the reduction in aromatics and saturates can impact the colloidal stability of asphaltenes in the matrix of bitumen. Based on the DFT results, the surface adsorption of aromatics and saturates on asphaltene planes provides the steric repulsion required to maintain the asphaltene planes at a distance sufficient to inhibit their agglomeration. In addition, aromatic molecules with the least hindrance repulsion can disturb the π–π interfacial interactions between asphaltene planes, facilitating their deagglomeration. Therefore, a direct consequence of the mass loss of bitumen due to volatilization is disturbing the asphaltene distribution within the bitumen and stimulating the aggregation of asphaltenes. We also studied the merits of incorporating biochar into the bitumen surface to reduce bitumen’s mass loss. Modification of bitumen separately with each of six biochars derived from biomass feedstocks (walnut shell, peanut shell, Douglas fir, pine bark, birch, and algae) showed the efficacy of each biochar to reduce the volatiles emitted from bitumen, thereby reducing the changes in the composition of maltene with consequent colloidal stability losses. The study outcomes highlight the importance of reducing emissions from bitumen to delay its aging and minimize negative impacts on air quality and human health.

Influence of coal bottom ash additives on catalytic reforming of biomass pyrolysis gaseous tar and biochar/steam gasification reactivity

This work investigated the effect of CBA additives as bed material in gasification process on gaseous tar catalytic reforming characteristic and biochar/steam gasification reactivity adopting a lab-scale dual-stage fixed bed furnace and a thermogravimetric analyzer equipped with water vapor furnace. Results showed that CBA additive exhibited good catalytic performance for tar cracking and gas upgrading effect on the basis of larger specific surface area as well as higher content of metallic matters. Particularly, tar conversion efficiency and syngas acquired peaking at 92.39% and 594.3 mL/g adopting mixing biochar (PSC) with CBA at ratio of 1:15 (PSC-15CBA) as catalyst at reforming temperature of 900 °C, respectively, in which the main components of syngas are H2, CO and CH4. It is noted that PSC-nCBA exhibited higher deoxygenation extent and single-ring aromatics and aliphatic selectivity in tar, and the polycyclic aromatics selectivity evidently decreased. The CBA additive has a beneficial impact on the biochar/steam gasification reactivity. Interestingly, a relatively high proportion of CBA additive has a negative impact on promoting reactivity. Result from kinetics analysis that CBA additive had ability to reduce the activation energy of PSC gasification process.

The role of temperature profile during the pyrolysis of end-of-life-tyres in an industrially relevant conditions auger plant

Pyrolysis is a chemical recycling process of interest as a means to achieve a sustainable circular economy for end-of-life tyres (ELTs). In the pyrolysis process, ELTs are converted into tyre pyrolysis gas (TPG), tyre pyrolysis oil (TPO) and raw recovered carbon black (RRCB). This work investigates for the first time the effect of different temperature profiles by using a single-auger pyrolysis reactor in an industrially relevant scale (TRL-5). Since the development of this process at this representative scale is quite limited and the temperature profile has not been previously studied, the results achieved in this work can provide a useful database for the development of this process at industrial scale. For this purpose, two different sources of ELTs, commercial truck tyres (CTTs) and passenger car tyres (PCTs), were used. Accordingly, the experimental campaign was conducted using two different incremental temperature profiles (425-550-775 °C and 600-700-800 °C) based on those that can be replicated in an industrial-scale auger pyrolysis plant. For the sake of comparison, two isothermal heating conditions (500-500-500 °C and 600-600-600 °C) were also tested. The results confirmed the remarkable influence of temperature profile on both the distribution and properties of products. The 425-550-775 °C temperature profile was found to enhance limonene production, which is associated with the minimisation of secondary reactions in the first heating zone of the reactor. Additionally, there were very low carbonaceous deposits found in the RRCB because of the high severity of devolatilisation conditions in the third heating zone of the reactor. On the other hand, when the temperature profile was raised, the production of single-ring aromatics, particularly benzene, toluene, ethylbenzene and xylenes (BTEX) significantly increased in the TPO at the expense of limonene. Thus, from this strategy, it is possible to tune the properties of the products depending on the requirements of the application in a single step, getting closer for circular economy in the ELT recycling domain.

Highly Selective Conversion of CO2 or CO into Precursors for Kerosene-Based Aviation Fuel via an Aldol–Aromatic Mechanism

The extensive emission of CO2 into the atmosphere due to the burning of fossil fuels has urged many countries to move toward decarbonized energy. Based on the concept of carbon neutrality, the European Union Emissions Trading System implemented the aviation carbon tax (ACT), which stimulated the rapid transformation in aviation fuels. To cope with the ACT and mitigate the CO2 emissions from the aviation industry, here, we present a promising route for the synthesis of precursors such as aromatics, alkyl benzenes, and naphthenes, which account for 40–50 vol % fraction of the kerosene-based aviation fuel, from waste CO2 or biomass-derived syngas. The ultra-high selectivity of single-ring aromatics (precursors for the kerosene-based aviation fuel) with a selective range of carbon chain numbers (C8–C12) was achieved (>80% in hydrocarbons at a reaction temperature of 275 °C) via the catalytic hydrogenation of CO2 or CO over a bifunctional catalyst (nano-sized ZnCr2O4/Sbx-H-ZSM-5). In situ diffuse reflectance infrared Fourier transform spectroscopy, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, gas chromatography–mass spectrometry, and reaction analysis revealed that the product distribution was controlled by thermodynamics and the formation of the aromatics followed an “aldol–aromatic” mechanism. The high selectivity of aromatics at the low reaction temperature (i.e., 275 °C) was attributed to the catalyst topology, the closed carbon chain aromatization reaction, and the presence of highly active oxygenated species in the hydrocarbon pool. For the first time, an asymmetric desorption behavior between the active oxygenate species and aromatic hydrocarbons over the ZnCr2O4/Sbx-H-ZSM-5 catalyst is reported with the help of integrated differential phase contrast scanning transmission electron microscopy, which made the reaction highly selective toward aromatics. This strategy gives a carbon-neutral route for the synthesis of kerosene-based aviation fuel precursors and will reduce the burden of the carbon tax on the aviation industry.

Oxidation Flow Reactor Results in a Chinese Megacity Emphasize the Important Contribution of S/IVOCs to Ambient SOA Formation

Oxygenated volatile organic compounds (OVOCs) and secondary organic aerosol (SOA) formation potential of ambient air in Guangzhou, China was investigated using a field-deployed oxidation flow reactor (OFR). The OFR was used to mimic hours to weeks of atmospheric exposure to hydroxyl (OH) radicals within the 2-3 min residence time. A comprehensive investigation on the variation of VOCs and OVOCs as a function of OH exposure is shown. Substantial formation of organic acids and nitrogen-containing OVOC species were observed. Maximum SOA formation in the OFR was observed following 1-4 equiv days' OH exposure. SOA produced from known/measured VOC/IVOC precursors such as single-ring aromatics and long-chain alkanes can account for 52-75% of measured SOA under low NOx and 26-60% under high NOx conditions based on laboratory SOA yield parametrizations. To our knowledge, this is the first time that the contribution (8-20%) of long-chain (C8-C20) alkane oxidation to OFR SOA formation was quantified from direct measurement. By additionally estimating contribution from unmeasured semivolatile and intermediate volatility compounds (S/IVOCs) that are committed with C8-C20 alkanes, 64-100% of the SOA formation observed in the OFR can be explained, signifying the important contribution of S/IVOCs such as large cyclic alkanes to ambient SOA.

Product distribution from oil sludge and waste tires under high pressure pyrolysis

Oil sludge (OS) and waste tires were studied widely with pyrolysis technology. However, the influence and characteristics of OS and waste tires were not studied with the pressurized co-pyrolysis technology. The pressurized pyrolysis of OS, combined with pressurized co-pyrolysis of side wall rubber (SWR), and catalytic cracking over bottom ash (BA) and SWR char (SWRC), were studied. First, the influence of pressure and temperature on the product distribution of OS pyrolysis was investigated. Then, the effect of the SWR/OS ratio on the pressurized co-pyrolysis product distribution was tested. Finally, the influence of BA on the product distribution of SWR/OS co-pyrolysis under high pressure was evaluated. The OS char obtained under high pressure exhibited serious melting phenomena, whose catalytic effect on the SWR pyrolysis in the pressurized co-pyrolysis process was investigated with TG-FTIR and SEM. The high activity and CO2 adsorption effect of bottom ash were confirmed. The CH4 content in the SWR/OS5/5 gas reached 45.55 vol%. The single ring aromatics concentration reached 57.11% in the SWR/OS6/4 oil. The naphthalene concentration reached 39.31% with the SWRC catalyst.

Characteristics and sources of non-methane VOCs and their roles in SOA formation during autumn in a central Chinese city

Volatile organic compounds (VOCs) are essential in secondary organic aerosol (SOA) formation due to their dual roles as precursors and oxidant producers. In order to explore the dominant contributions of SOA formation from VOCs in central China, 53 VOC species were observed with proton transfer reaction-mass spectrometry (PTR-MS) and canister grab samples in Xinxiang, a mid-sized city located in Henan Province, from November 5th to December 3rd, 2018. The result showed that anthropogenic emissions were intensive compared with many studies in the world. Among the observed VOCs, benzene and toluene had the largest SOA formation potential (SOAFP), and their contributions in SOA formation kept stable with the aggravation of pollution. Among VOCs, formaldehyde was the strongest radical contributor, and the contribution of acetaldehyde was also found significant in this study, especially in polluted periods. Based on the positive matrix factorization (PMF) model, benzenoids (mainly single-ring aromatics) were majorly emitted from chemical process, solvent evaporation, and residential heating, with a total fraction of 75%, and these sources were estimated to have largest SOAFP. However, thermal power generation, chemical process, and solvent evaporation had highest radical contribution rates. According to the backward trajectory analysis, the VOC concentrations were dominated by local emissions. Emissions in the surrounding provinces occupied fractions of 33%–42% in the five sources. Therefore, regional collaborative emission reduction is also important.

Ambient naphthalene and methylnaphthalenes observed at an urban site in the Pearl River Delta region: Sources and contributions to secondary organic aerosol

Naphthalene (Nap) and methylnaphthalenes (MN) are among important intermediate volatility organic compounds (IVOCs) that contribute substantially to the formation of secondary organic aerosols (SOA), yet studies about their ambient levels, source contributions and SOA productions are quite limited. In this study a field campaign was conducted from September 23rd to October 4th, 2019 at an urban site in the megacity Guangzhou in south China for characterizing ambient Nap and MN. Measured Nap, 2-MN, and 1-MN concentrations were 94.0 ± 23.1, 25.3 ± 4.5, and 11.8 ± 2.1 ng m−3 (mean ± 95% C.I.), respectively. Initial levels and chemical losses of Nap and MN were estimated using a photochemical age-based parameterization method, and results demonstrated that on average ~60% of Nap + MN were degraded during photochemical ageing. During the photochemically active period (12:00–15:00), Nap and MN could contribute 12.4% of estimated SOA formed from single-ring aromatics, Nap and MN altogether, while their initial levels were less than 2% of single-ring aromatics. Source apportioning by the positive matrix factorization (PMF) coupled with the photochemical age-based parameterization revealed that gasoline exhaust was the largest source, accounting for 39.1% of Nap and MN, followed by biomass/coal burning (29.9%), diesel exhaust (26.3%) and industrial emission (4.7%).

Measurements of higher alkanes using NO<sup>+</sup> chemical ionization in PTR-ToF-MS: important contributions of higher alkanes to secondary organic aerosols in China

Abstract. Higher alkanes are a major class of intermediate-volatility organic compounds (IVOCs), which have been proposed to be important precursors of secondary organic aerosols (SOA) in the atmosphere. Accurate estimation of SOA from higher alkanes and their oxidation processes in the atmosphere is limited, partially due to the difficulty of their measurement. High-time-resolution (10 s) measurements of higher alkanes were performed using NO+ chemical ionization in proton transfer reaction time-of-flight mass spectrometry (NO+ PTR-ToF-MS) at an urban site in Guangzhou in the Pearl River Delta (PRD) and at a rural site in the North China Plain (NCP). High concentrations were observed in both environments, with significant diurnal variations. At both sites, SOA production from higher alkanes is estimated from their photochemical losses and SOA yields. Higher alkanes account for significant fractions of SOA formation at the two sites, with average contributions of 7.0 % ± 8.0 % in Guangzhou and 9.4 % ± 9.1 % in NCP, which are comparable to or even higher than both single-ring aromatics and naphthalenes. The significant contributions of higher alkanes to SOA formation suggests that they should be explicitly included in current models for SOA formation. Our work also highlights the importance of NO+ PTR-ToF-MS in measuring higher alkanes and quantifying their contributions to SOA formation.

The Uniqueness of Tryptophan in Biology: Properties, Metabolism, Interactions and Localization in Proteins.

Tryptophan (Trp) holds a unique place in biology for a multitude of reasons. It is the largest of all twenty amino acids in the translational toolbox. Its side chain is indole, which is aromatic with a binuclear ring structure, whereas those of Phe, Tyr, and His are single-ring aromatics. In part due to these elaborate structural features, the biosynthetic pathway of Trp is the most complex and the most energy-consuming among all amino acids. Essential in the animal diet, Trp is also the least abundant amino acid in the cell, and one of the rarest in the proteome. In most eukaryotes, Trp is the only amino acid besides Met, which is coded for by a single codon, namely UGG. Due to the large and hydrophobic π-electron surface area, its aromatic side chain interacts with multiple other side chains in the protein, befitting its strategic locations in the protein structure. Finally, several Trp derivatives, namely tryptophylquinone, oxitriptan, serotonin, melatonin, and tryptophol, have specialized functions. Overall, Trp is a scarce and precious amino acid in the cell, such that nature uses it parsimoniously, for multiple but selective functions. Here, the various aspects of the uniqueness of Trp are presented in molecular terms.

Pressure dependence of sooting characteristics of m-xylene and n-octane doped laminar methane diffusion flames from 2 to 10 bar

The work reported here contributes to a wider effort that focuses on the issue of whether single ring aromatics and their same carbon number alkane counterparts have the same pressure dependence of their sooting characteristics. Influence of doping methane base fuel with either m-xylene or n-octane in laminar high-pressure co-flow diffusion flames was studied from 2 to 10 bar pressure in current work. Two liquid hydrocarbons added to the base fuel methane contributed 3% of the total carbon mass flow in the fuel stream, which was kept fixed at 0.524 mg/s at all pressures considered, to have tractable measurements. The methane flames doped with either m-xylene or n-octane were stabilized on a co-flow diffusion burner installed inside of a high pressure combustion chamber with optical access. Temperatures and soot volume fractions were inferred from spectrally-resolved measurements of soot radiation. Line of sight soot emission intensities were inverted at each measurement plane along the flame axis to obtain radially-resolved temperature and soot volume fraction. Soot yields, calculated from soot volume fractions, of m-xylene doped flames were found to be higher than those of n-octane doped flames in the pressure range of 2–10 bar; however, the ratio of soot yields of m-xylene to n-octane decreased with pressure, from 2.9 at 2 bar to 1.2 at 10 bar. This finding implies that m-xylene and n-octane, both with eight carbons in their molecular structure, do not have the same sooting propensity with increasing pressure; m-xylene’s pressure dependence is weaker than that of n-octane within the pressure range of 2–10 bar.

Testing of formulated fuel with variable aromatic type and contents in a compression-ignition engine

Fuels used in various combustion engines necessitate deep understanding of the fuel components before being used as a feedstock with present engine technology. Fuel components impact the efficiency of the engine along with the formation of pollutant emissions. Aromatics are important component of the fossil-based diesel fuel, which highly affects the tailpipe emissions. Therefore, the study of aromatics has a great significance for diesel engine. A comprehensive study with a total of 13 different aromatics was performed to investigate the impact of their structure and content on diesel engine characteristics. Diesel, pure higher chain alkanes and single added aromatics were blended as ternary mixture. Detailed spray investigations were carried out at an injection pressure of 200 bar using a three-hole nozzle of diesel engine. The aromatic structure and content highly influenced the emission and performance characteristics. A blending ratio of 10% aromatics in base fuel shows promising results compared to 5% and 15% blending content of aromatics in the base fuel. Higher aromatics blending in ternary mixture led to higher particulate matter, carbon monoxide, and unburnt hydrocarbon emissions. Due to higher degree of unsaturation, polycyclic single and double ring aromatics produce higher pollutant emissions compared to single ring monocyclic aromatics.

Catalytic fast pyrolysis of cellulose over Ce0.8Zr0.2-xAlxO2 catalysts to produce aromatic hydrocarbons: Analytical Py-GC × GC/MS

Analytical pyrolysis-comprehensive two-dimensional gas chromatography/mass spectrometry (Py-GC × GC/MS) was employed for the on-line analysis of cellulose via catalytic pyrolysis with different catalysts and catalytic temperatures to study the products and aromatic hydrocarbons selectivity. The catalysts were subjected to characterization methods, including XRD, TEM, NH3-TPD, to investigate the effects of the physicochemical properties of the catalyst on the product distribution. Results showed that the Ce0.8Zr0.2-xAlxO2 could significantly promote the formation of aromatic hydrocarbons under 400–550 °C. A lower catalytic temperature (≤350 °C) favored the formation of furan compounds, and a higher catalytic temperature (≥450 °C) supported the formation of aromatic hydrocarbons. The relative peak area of the aromatics prepared by using the Ce0.8Zr0.15Al0.05O2 catalyst was the highest being 85.24% at 550 °C. Moreover, the selectivity of the single-ring aromatics, such as benzene, toluene and xylene, were significantly affected by the presence of the Ce0.8Zr0.2-xAlxO2 catalysts. The higher total acidity of Ce0.8Zr0.15Al0.05O2 favored the formation of benzene and toluene. Additionally, the Ce0.8Zr0.15Al0.05O2 catalyst had a great thermal stability. The catalyst recycling tests showed that the Ce0.8Zr0.15Al0.05O2 catalyst can be reused five times to produce aromatic-rich bio-oil via catalytic fast pyrolysis.

Simulation of organic aerosol formation during the CalNex study: updated mobile emissions and secondary organic aerosol parameterization for intermediate-volatility organic compounds.

We describe simulations using an updated version of the Community Multiscale Air Quality model version 5.3 (CMAQ v5.3) to investigate the contribution of intermediate-volatility organic compounds (IVOCs) to secondary organic aerosol (SOA) formation in southern California during the CalNex study. We first derive a model-ready parameterization for SOA formation from IVOC emissions from mobile sources. To account for SOA formation from both diesel and gasoline sources, the parameterization has six lumped precursor species that resolve both volatility and molecular structure (aromatic versus aliphatic). We also implement new mobile-source emission profiles that quantify all IVOCs based on direct measurements. The profiles have been released in SPECIATE 5.0. By incorporating both comprehensive mobile-source emission profiles for semivolatile organic compounds (SVOCs) and IVOCs and experimentally constrained SOA yields, this CMAQ configuration best represents the contribution of mobile sources to urban and regional ambient organic aerosol (OA). In the Los Angeles region, gasoline sources emit 4 times more non-methane organic gases (NMOGs) than diesel sources, but diesel emits roughly 3 times more IVOCs on an absolute basis. The revised model predicts all mobile sources (including on- and off-road gasoline, aircraft, and on- and off-road diesel) contribute ~ 1 μgm-3 to the daily peak SOA concentration in Pasadena. This represents a ~ 70% increase in predicted daily peak SOA formation compared to the base version of CMAQ. Therefore, IVOCs in mobile-source emissions contribute almost as much SOA as traditional precursors such as single-ring aromatics. However, accounting for these emissions in CMAQ does not reproduce measurements of either ambient SOA or IVOCs. To investigate the potential contribution of other IVOC sources, we performed two exploratory simulations with varying amounts of IVOC emissions from nonmobile sources. To close the mass balance of primary hydrocarbon IVOCs, IVOCs would need to account for 12% of NMOG emissions from nonmobile sources (or equivalently 30.7 t d-1 in the Los Angeles-Pasadena region), a value that is well within the reported range of IVOC content from volatile chemical products. To close the SOA mass balance and also explain the mildly oxygenated IVOCs in Pasadena, an additional 14.8% of nonmobile-source NMOG emissions would need to be IVOCs (assuming SOA yields from the mobile IVOCs apply to nonmobile IVOCs). However, an IVOC-to-NMOG ratio of 26.8% (or equivalently 68.5 t d-1 in the Los Angeles-Pasadena region) for nonmobile sources is likely unrealistically high. Our results highlight the important contribution of IVOCs to SOA production in the Los Angeles region but underscore that other uncertainties must be addressed (multigenerational aging, aqueous chemistry and vapor wall losses) to close the SOA mass balance. This research also highlights the effectiveness of regulations to reduce mobile-source emissions, which have in turn increased the relative importance of other sources, such as volatile chemical products.

Low-pressure two-stage catalytic hydropyrolysis of lignin and lignin-derived phenolic monomers using zeolite-based bifunctional catalysts

In the present study, a two-stage catalytic hydropyrolysis of lignin was investigated by converting lignin extracted from corn stover, loblolly pine and red oak using HZSM-5, MoO3/ZSM-5 and Ni/ZSM-5 as catalysts. Compared to the catalytic pyrolysis with inert gas, the presence of atmospheric-pressure hydrogen significantly enhanced the formation of hydrocarbon from lignin whereas dramatically reducing coke yield. In comparison to HZSM-5, MoO3/ZSM-5 increased the production of aromatic hydrocarbons, while Ni/ZSM-5 enhanced the formation of aliphatic hydrocarbons. Coke yields decreased with both MoO3/ZSM-5 and Ni/ZSM-5, which corresponds to the suppression of polyaromatic formation and increased selectivity to single ring aromatics. Corn stover lignin produced the highest yield of aromatic hydrocarbons with all three catalysts, followed by loblolly pine and red oak lignins. Particularly, up to 42.24 C% of corn stover lignin was converted into aromatic and aliphatic hydrocarbons with MoO3/ZSM-5. In this study, reaction pathways of lignin-derived pyrolysis vapor during catalytic hydropyrolysis were further studied using phenol, guaiacol, and syringol as the model compounds. Results suggest that demethoxylation followed by the hydrodeoxygenation of methoxyl radicals and subsequent alkylation of the phenolic ring to produce cresol, and dimethyl phenol as intermediates prior to the intermediate phenolics were further hydrodeoxygenated to produce benzene and alkylated benzene. MoO3/ZSM-5 showed strong ability for both demethoxylation and hydrodeoxygenation. In comparison, the ability of Ni/ZSM-5 for phenolic-hydroxyl removal was much inferior. Based on the results obtained from the conversions of lignin and the model compounds, a negative correlation between the total yields of aromatic hydrocarbons from lignin and the abundancy of phenolic methoxyls in the lignin-derived pyrolysis vapor was found. It was also found that the pyrolysis vapors of simple H, G, or S-based monomers tend to produce more aromatic hydrocarbons than the vapors composed of more complex monomers and oligomers from their corresponding H, G or S group. However, the yield differences were less significant among G and S-based monomers and oligomers.