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All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

Laboratory-Scale Coal-Derived Graphene Process (Final Report)

The Energy & Environmental Research Center (EERC) conducted a laboratory-scale coal-derived graphene (CDG) project focused on developing a technological process for making graphene from four U.S. domestic coal or coal wastes, including lignite from North Dakota, subbituminous coal from Wyoming, bituminous coal from Utah, and anthracite from Pennsylvania. The project was divided into two performance or budget periods (BPs), with BP1 comprising the up-front laboratory experiments to make graphene materials from coal beginning on May 1, 2020, to April 30, 2022. BP2 was conducted from May 1, 2022, to April 30, 2023, and was focused on analyzing the CDG process economic feasibility and the technical gaps for technological scale-up and commercialization. During this project, a few different coal-derived high-value products have been demonstrated, including graphite, graphene oxide (GO), reduced graphene oxide (rGO), and graphene quantum dots (GQDs). A new graphite microstructure was discovered and named “croissant graphite” because of the exterior morphological and textural resemblance to croissant food items sold in commercial groceries stores. The new graphite structure and the associated preparation from coal or coal waste feedstocks has been the subject of a U.S. patent application. The systematic experimental processes involving coal cleaning, upgrading, and conversion to high-value carbon products culminated into a developed upgraded coal-to-products (UCP) technology that is being pursued for potential fast-track commercialization, if funding is available. It is envisioned that commercialization of the UCP technology would increase consumption of U.S. domestic coals or coal wastes to make environmentally sustainable high-value products for the electronics industry, high-energy-storage applications, and clean energy technologies such as electric vehicle (EV) lithium-ion batteries (LIBs), for which graphite has become a critical mineral commodity. Croissant graphite microstructures, when observed by field emission scanning electron microscopy (FESEM), display wavy surface morphology and often grow from a base that is made of graphitized particles with honeycomb-like layers, which are believed to be graphene layers. While more studies are needed to fully ascertain the mechanisms of the croissant graphite microstructure formation, it is postulated that their growth may begin from curling of the graphene sheets into ribbon-like structures, and continuous growth and densification of the ribbon-like structures forms croissant microstructures. Additional studies are ongoing to evaluate the electrochemical performance of croissant graphite for LIB applications and to determine the experimental conditions necessary to tune on/off croissant formation so that it can be either optimized or suppressed depending on performance evaluation results. In addition to the discovery of croissant graphite, the graphitization process from the four coal ranks in general was successful. X-ray diffraction (XRD) analysis showed that the degree of graphitization (DoG) ranged from 12% to 80% in an early sample set, and further optimization on lignite coal produces a DoG of about 92%, which was spectacular to see as lignite is the lowest-rank coal. Thus, it is expected that the graphitization performance for higher-rank coals will be similar or better when optimized as well. The coal-derived graphite was used to make GO and rGO. Analytical characterization, e.g., by methods such as Raman spectroscopy, XRD, Fourier transform infrared (FTIR) spectroscopy and FESEM, showed that the sequence of converting the coal to graphite, exfoliating it to GO, and then chemically reducing the GO to rGO was successful. Although coal naturally contains aromatic compounds and some relatively small-sized condensed aromatic units, it does not contain graphene sheets. In the UCP process, the aromatic domains in the coals, particularly low-rank coals, are concentrated and condensed further into graphene sheets, which are ordered into a 3D stack during graphitization. The synthesized graphite is then unpacked by methods such as exfoliation to various graphene products. GQDs were synthesized from all four coal types, and their optical properties were demonstrated to be tunable by the coal precursor preprocessing treatments. In all four coal types, enhanced optical properties were observed for the produced GDQs with incremental improvements made to the coal precursors. GQDs produced from raw coal samples displayed lower ultraviolet–visible (UV–Vis) spectroscopy absorbance intensity compared to those obtained from cleaned and upgraded coal residues. The photoluminescence (PL) intensities also varied with pretreatment conditions and with the concentration of GQDs in aqueous solutions. GQDs obtained from anthracite show longer emission wavelengths and can be excited by visible light as opposed to GQDs derived from the other coal ranks. UV fluorescence 3D maps and spectra revealed that the emission wavelength at which the GQDs solutions display the highest intensity was slightly redshifted based on the coal precursor pretreatments. In low-rank coal (lignite and subbituminous) samples, two clusters were observed in the maps for GQDs, which may suggest that there are potentially two types of fluorophores in solution or two main size populations. The ability to tune the properties of GQDs based on processing methods can be exploited to make GQDs for various optical display or optoelectronics applications. The results also highlight the importance of removing coal-borne impurities to improve the quality of the coal precursor for preparation of graphene products. Coal and/or coal wastes preprocessing methods were developed and applied to clean and upgrade the coal precursors prior to graphitization and subsequent conversion to graphene products. The preprocessing methods involve high specific-gravity separations, mineral acid cleaning (no hydrofluoric acid), and subsequent upgrading by reducing the coal-borne heteroatom (nitrogen, sulfur, and oxygen) content using proprietary chemical agents. Analytical characterization revealed that the preprocessing steps were successful, with ash reductions that range from 38% to 80% and residual ash content that was below the 5 wt% initial target. Based on proximate and ultimate analysis, the heteroatom reduction reactions produced upgraded coal residues with the oxygen content reduced by 8% to 24%, with additional reductions in the nitrogen and sulfur contents. An initial assessment of the waste streams from the UCP process shows very small to negligible environmental impact due to CO 2 , NO x , and SO x because most process steps are performed under inert atmosphere with argon. Consequently, reactive oxygen environments that tend to create these species are avoided. The inorganic and potentially hazardous species are released into aqueous waste streams that are easy to handle for proper disposal. The liquid waste streams were found to contain low-level concentrations of rare-earth elements (REEs), which could be concentrated and recovered as value-added by-products. Additionally, the volatile and gaseous fractions from carbonization and heat treatment contain useful organic compounds that can also be recovered as potential valuable by-products. Thus, the UCP technology is considered an environmentally sustainable and promising emerging technology for making high-value products from coal and coal wastes, with potential additional value-added by-products. Analysis of potential markets for the coal-derived carbon products shows a strong demand in both niche market sectors and across a wide variety of other industrial sectors. Graphite is currently considered a critical mineral commodity that has a large and growing demand in the LIB industry for EV applications. Based on data from Fortune Business Insights (2022) and Marketwatch (2023) reports, the average global graphite market is projected to reach about 33 billion by 2028, growing at a compound annual growth rate (CAGR) of about 7%, with much of this growth expected to be in the LIB industry. GO and rGO have strong market potentials in various application areas, such as coatings for anticorrosion, anti-icing, and antimicrobial protection, thermal barriers, wear resistance, sensors, additive manufacturing such as 3D inks, and others. GQDs are the emerging key player in the bioimaging, photovoltaics, and light-emitting diodes (LEDs) applications, with the potential to replace traditional semiconductor quantum dots (SQDs), which are based on metallic systems that are more toxic and more expensive. Biomedical applications of GQDs are becoming more attractive because of low to no toxicity and extremely low cost compared to SQDs. The major challenges for scale-up and commercialization of coal-derived carbon products such as graphene vary from the inherent attributes of graphene itself to reluctance to accept graphene in new manufacturing processes because of the uncertainty of the unknown. The 2D nature of graphene materials with a thickness of one atom presents significant challenges to proper handling/processing, and process scale-up becomes difficult because it requires high-end, expensive equipment, even for routine handling and analysis for quality assurance and control. Pristine graphene can also be extremely difficult to work into other matrices, thus hindering downstream processibility, especially at large scale. Currently, the cost of graphene and graphene products is still high and presents an economic risk that tends to slow down investment in scaling up emerging technologies. The lack of a standard for graphene materials for quality assurance and quality control poses a great challenge not only for the markets but also for commercialization efforts. A first-look economic feasibility analysis of the UCP technology provided valuable information that suggests the UCP process would be feasible, especially when it is scaled to a pilot scale and could be more competitive at the full scale. Graphitization was found to be the most energy-consuming and most capital-intensive step in the overall process. In small laboratory- and bench-scale experiments, labor is a significant contributor to the total process costs. Although these energy, capital, and labor constraints contribute to a higher selling price for the product, a preliminary economic model suggests that the process would be feasible at large scale when the process is fully integrated, optimized, and automated.

01 COAL, LIGNITE, AND PEAT↗
DOE OSTI2026

Flow Reactor Study and Kinetic Model Development of HEFA-SPK and its Surrogate

In this work, we formulate a two-component surrogate for HEFA-SPK, incorporating aromatic or cycloalkane components, and develop reduced kinetic models for the surrogates to be used in high-performance computing simulations. The HEFA-SPK surrogate was selected and optimized based on the fuel's physical and combustion properties, including ignition delay times and flame speeds. The resulting surrogate consists of 40% n-undecane and 60% 2-methylnonane. The surrogate was confirmed by flow reactor experiments for both the HEFA-SPK fuel and the suggested two-component surrogates, where excellent agreement was observed. To meet aromatic requirements, 1,2,4-trimethylbenzene (8%) was selected, and we determined that incorporating 30% propylcyclohexane into the HEFA-SPK will achieve a volume swell equivalent to 8% aromatics. The properties of the surrogates were measured, and a new reduced kinetic model was developed based on the semi-decoupling methodology, using a reduced CH4 chemistry from NUIG 1.0 as base chemistry. Kinetic models will be employed in combustor simulations to enable a comprehensive understanding of the effect of SAF fuel properties on aviation combustor performance.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Particle Matter Index and Fuel Wall-wetting Relations on Stochastic Pre-ignition

This works explores the effect of the particle matter index (PMI) and aromatic content on fuel wall impingement and associated stochastic pre-ignition (SPI) propensity. Statically significant measurements of SPI rates are directly coupled with laser induced florescence (LIF) measurements of fuel dilution from spray-linear impingement. Literature suggests that PMI is could be correlated with the number of SPI events, but the root cause(s) of PMI and SPI are directly causational or are a predicator of SPI. Three fuels have been used in this study with 3 different PMI and two different aromatic contents. These fuels are direct injected at two different injection timings, an earlier injection timing which targets the piston crown, 310°CA bTDC, and a later injection timing that the linear, 220°CA bTDC start of injection timings (SOI) respectively. The earlier 310 SOI injection increases soot, whereas the later 220°CD SOI targets the linear and increases wall-wetting. The findings of this work highlight that the SPI activity has a weak correlation with the soot promoted by the combustion process and increased PMI. However, SPI activity shows a strong dependency with high levels of oil dilution and aromatic content, suggesting that PMI might be an indicator of fuel chemistry conducive to SPI and the soot form increased PMI fuels is not a strong source of SPI relative to fuel wall wetting.

42 ENGINEERING↗
DOE OSTI2021

A Full Spectrum of Characterization for Insight into Carbon Speciation and Removal on a Cu/BEA Catalyst During Renewable High-Octane Hydrocarbon Synthesis

Conversion of methanol and dimethyl ether to high-octane gasoline catalyzed by beta zeolite (BEA) provides an opportunity for the production of high-quality fuels from renewable carbon sources (e.g., gasified biomass). Recent research demonstrated that a Cu-modified BEA zeolite catalyst (Cu/BEA) offered advantages over the unmodified BEA catalyst due to multifunctional Cu species that enabled incorporation of co-fed H2, reactivation of light alkanes, and reduction of products from the aromatic hydrocarbon pool. The shift in hydrocarbon pool chemistry has the potential to influence the identity and relative composition of surface carbon species that are often linked to deactivation. A detailed understanding of these carbon species is important to develop an effective and efficient regeneration procedure that can enable the transition from fundamental catalyst development to commercial application. Here, we applied complementary ex situ and in situ characterization techniques to compare the structures of surface carbon species on post-reaction Cu/BEA and unmodified BEA catalysts. Both catalysts contained acyclic and aromatic hydrocarbons along with graphitic carbon species. However, the post-reaction Cu/BEA catalyst had a lower polycyclic aromatic content, and further, the graphitic species were more hydrogenated and defective. It was also found that the presence of Cu promoted carbon removal at lower temperatures than for unmodified BEA through activation of O2 by Cu during thermal oxidation. The fundamental insight into the composition of surface carbon species enabled the design of an effective and efficient regeneration strategy for the DME homologation reaction over Cu/BEA, resulting in full recovery of the catalyst activity.

29 ENERGY PLANNING, POLICY, AND ECONOMY↗
DOE OSTI2021

Polycarboxylated compounds and compositions containing same

Methods of selectively modifying lignin, polycarboxylated products thereof, and methods of deriving aromatic compounds therefrom. The methods comprise electrochemically oxidizing lignin using stable nitroxyl radicals to selectively oxidize primary hydroxyls on β-O-4 phenylpropanoid units to corresponding carboxylic acids while leaving the secondary hydroxyls unchanged. The oxidation results in polycarboxylated lignin in the form of a polymeric β-hydroxy acid. The polymeric β-hydroxy acid has a high loading of carboxylic acid and can be isolated in acid form, deprotonated, and/or converted to a salt. The β-hydroxy acid, anion, or salt can also be subjected to acidolysis to generate various aromatic monomers or oligomers. The initial oxidation of lignin to the polycarboxylated form renders the lignin more susceptible to acidolysis and thereby enhances the yield of aromatic monomers and oligomers obtained through acidolysis.

Stahl, Shannon S.↗
DOE OSTI2023

2.3.2.100 - Biological Lignin Valorization (BLV)

The Biological Lignin Valorization (BLV) project develops microbial strains and associated bioprocesses to convert lignin-derived aromatic compounds into value-added bioproducts. Our main objective in the BLV project is to achieve industrially relevant bioproduction metrics that can directly contribute to the economic viability and improved sustainability of the integrated lignocellulosic biorefinery, in collaboration with complementary BETO-funded lignin valorization projects. Specifically, the BLV project works closely with the BETO-funded Lignin Utilization project, which provides bio-available aromatic compounds from chemo-catalytic lignin depolymerization. We use the robust soil bacterium, Pseudomonas putida, as our primary microbial host for the conversion of lignin-derived compounds to bioproducts. To date, we have focused on atom-efficient bioproducts that can be used as either direct replacement chemicals or performance-advantaged bioproducts, including cis,cis-muconic acid, beta-ketoadipic acid, and 2-pyrone-4,6-dicarboxylic acid. From model aromatic substrates, we have achieved titers of each of these compounds approaching 40 g/L and productivity values ranging from 0.5 to over 1 g/L/hr, all at 90% molar yield or higher. From real lignin streams, we have thus far achieved 24 g/L, 0.66 g/L/hr, and theoretical yield of beta-ketoadipic acid. A major pursuit now is to reach industrially relevant performance metrics on an expanded slate of lignin-derived streams.

BIOMASS FUELS↗
DOE OSTI2021

SPRUCE Compositional Stability of Peat in Ecosystem-Scale Warming Mesocosms, 2014 and 2019

This dataset contains measurements of carbohydrate and aromatic compounds in peat samples subjected to various levels of deep peat heating (DPE) and whole ecosystem warming (WEW). Samples were collected in August 2014 and August 2019 at the Spruce and Peatland Responses Under Changing Environments (SPRUCE) experimental site within the Marcell Experimental Forest in northern Minnesota, USA. These data serve to identify chemical changes occurring within peatland soils following five years of warming. Samples were analyzed in the uppermost 2m of peat using Fourier Transform Infrared Spectroscopy (FT-IR) to quantify the relative abundance of carbohydrate and aromatic compounds in the peat. The peat soils were subjected to DPH beginning in June of 2014 followed by WEW in August of 2015. This dataset contains one data file in comma-separated values (.csv) format. Additional metadata are provided: one data dictionary and a file-level metadata file in comma-separated values (.csv) format and a user guide in PDF (*.pdf) format.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2020

A Free-Radical Prompted Barrierless Gas-Phase Synthesis of Pentacene

A representative, low-temperature gas-phase reaction mechanism synthesizing polyacenes via ring annulation exemplified by the formation of pentacene (C 22 H 14 ) along with its benzo[ a ]tetracene isomer (C 22 H 14 ) is unraveled by probing the elementary reaction of the 2-tetracenyl radical (C 18 H 11 . ) with vinylacetylene (C 4 H 4 ). The pathway to pentacene—a prototype polyacene and a fundamental molecular building block in graphenes, fullerenes, and carbon nanotubes—is facilitated by a barrierless, vinylacetylene mediated gas-phase process thus disputing conventional hypotheses that synthesis of polycyclic aromatic hydrocarbons (PAHs) solely proceeds at elevated temperatures. This low-temperature pathway can launch isomer-selective routes to aromatic structures through submerged reaction barriers, resonantly stabilized free-radical intermediates, and methodical ring annulation in deep space eventually changing our perception about the chemistry of carbon in our universe.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Stringing the Perylene Diimide Bow

This study explores a new mode of contortion in perylene diimides where the molecule is bent, like a bow, along its long axis. These bowed PDIs were synthesized through a facile fourfold Suzuki macrocyclization with aromatic linkers and a tetraborylated perylene diimide that introduces strain and results in a bowed structure. By altering the strings of the bow, the degree of bending can be controlled from flat to highly bent. Through spectroscopy and quantum chemical calculations, it is demonstrated that the energy of the lowest unoccupied orbital can be controlled by the degree of bending in the structures and that the energy of the highest occupied orbital can be controlled to a large extent by the constitution of the aromatic linkers. The important finding is that the bowing results not only in red-shifted absorptions but also more facile reductions.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

Synergy of Oxygen Vacancies and Base Sites for Transfer Hydrogenation of Nitroarenes on Ceria Nanorods

CeO 2 nanorod based catalysts for the base-free synthesis of azoxy-aromatics via transfer hydrogenation of nitroarenes with ethanol as hydrogen donor have been synthesized and investigated. The oxygen vacancies (O v ) and base sites are critical for their excellent catalytic properties. The O v , i.e., undercoordinated Ce cations, serve as the sites to activate ethanol and nitroarenes by lowering the energy barrier to transfer hydrogen from α–C sp3 –H in ethanol to the nitro group coupling it to the redox reactions between Ce 3+ and Ce 4+ . At the same time, the base sites catalyze the condensation step to selectively produce azoxy-aromatics. Finally, the catalytic route opens a much improved way to use non-noble metal oxides without additives for the selective functional group reduction and coupling reactions.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Molecular dynamics analysis of the binding of human interleukin-6 with interleukin-6 α-receptor

Human interleukin-6 (hIL-6) is a multifunctional cytokine that regulates immune and inflammatory responses in addition to metabolic and regenerative processes and cancer. hIL-6 binding to the IL-6 receptor (IL-6Rα) induces homodimerization and recruitment of the glycoprotein (gp130) to form a hexameric signaling complex. Anti-IL-6 and IL-6R antibodies are clinically approved inhibitors of IL-6 signaling pathway for treating rheumatoid arthritis and Castleman's disease, respectively. There is a potential to develop novel small molecule IL-6 antagonists derived from understanding the structural basis for IL-6/IL-6Rα interactions. In this work, we combine homology modeling with extensive molecular dynamics (MD) simulations to examine the association of hIL-6 with IL-6Rα. A comparison with MD of apo hIL-6 reveals that the binding of hIL-6 to IL-6Rα induces structural and dynamic rearrangements in the AB loop region of hIL-6, disrupting intraprotein contacts and increasing the flexibility of residues 48 to 58 of the AB loop. In contrast, due to the involvement of residues 59 to 78 in forming contacts with the receptor, these residues of the AB loop are observed to rigidify in the presence of the receptor. The binary complex is primarily stabilized by two pairs of salt bridges, Arg181 (hIL-6)- Glu182 (IL-6Rα) and Arg184 (hIL-6)- Glu183 (IL-6Rα) as well as hydrophobic and aromatic stacking interactions mediated essentially by Phe residues in both proteins. An interplay of electrostatic, hydrophobic, hydrogen bonding, and aromatic stacking interactions facilitates the formation of the hIL-6/IL-6Rα complex.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2021

Lipid production from non-sugar compounds in pretreated lignocellulose hydrolysates by Rhodococcus jostii RHA1

Valorization of all carbon sources from biorefinery wastes to biofuels and bioproducts is an attractive but challenging strategy to improve the carbon efficiency of the entire biorefinery process for economic competitiveness. Rhodococcus jostii RHA1 is considered as a promising candidate for conversion of non-sugar compounds in pretreated lignocellulose hydrolysate, which contain aromatic monomers, furans and acids derived from biomass. However, the insufficient understanding of the strain’s complex metabolism network limits its application. In this study, furans (furfural, 5-hydroxymethylfurfural), phenols (vanillin, vanillate), and organic acids (acetic acid), which mimic the complex components of the non-sugar compounds in pretreated biomass hydrolysate, were mixed with benzoate or used individually as carbon sources to investigate the growth and lipid accumulation of R. jostii RHA1. Fermentation kinetics, specific growth rates (h-1) and lipid yield (g(g) -1, g(mmol)-1), for each selected biomass-derived compound were compared for lipid production. The order of the specific growth rates (h-1) was benzoate > acetic acid > vanillate > vanillin. Higher consumption rate of benzoate than that of vanillate, as well as different lipid yield from them, suggested the preference of strain employing two branches of ß-ketoadipate pathway and plausibly distinct carbon routing to lipid biosynthesis. And acetic acid showed the lowest lipid yield (g(mmol)-1) indicating less carbon contributed to lipid production. The highest lipid content (0.46 g lipid/g CDW) was achieved using benzoate as a main carbon source in the presence of 5-hydroxymethylfurfural (5-HMF). The generated lipids predominantly contained C16:0 and C17:0 fatty acids. The concentration of furfural and 5-HMF in fermentation broth decreased individually or simultaneously with benzoate catabolism. NMR results revealed the oxidation of furfural and 5-HMF by R. jostii RHA1. This study provides new insights into the catabolism and metabolism of non-sugar compounds derived from biomass by Rhodococcus in terms of growth and lipid production, facilitating its application to 2nd generation biofuel production.

Li, Xiaolu↗
DOE OSTI2020

An integrated methane dehydroaromatization and chemical looping process

Most of the natural gas co-produced in oil wells is flared due to the high transportation costs of bringing it to market. Onsite upgrading of natural gas to liquid products could address this issue but there are few processes for effective direct conversion of natural gas to liquid products. Methane dehydroaromatization (DHA) over Mo/HZSM- 5 offers a potential route to a value-added liquid product, however, DHA conversion is severely limited by thermodynamics at most industrially relevant temperatures. Here we propose an integrated process coupling methane DHA, chemical looping for selective hydrogen oxidation, and subsequent water removal to achieve higher yields of aromatic products limited by the thermodynamics in one-pass systems. Here, we validate this process via the construction and operation of a one-of-a-kind multibed recirculating reactor, and achieve a combined aromatics yield of 42%. Detailed technoeconomic analysis of the process for mobile applications show that such a process could be economically viable under certain circumstances.

03 NATURAL GAS↗
DOE OSTI2024

Biochemical and structural characterization of enzymes in the 4-hydroxybenzoate catabolic pathway of lignin-degrading white-rot fungi

White-rot fungi (WRF) are the most efficient lignin-degrading organisms in nature. However, their capacity to use lignin-related aromatic compounds, such as 4-hydroxybenzoate, as carbon sources has only been described recently. Previously, the hydroxyquinol pathway was proposed for the bioconversion of these compounds in fungi, but gene- and structure-function relationships of the full enzymatic pathway remain uncharacterized in any single fungal species. Here, we characterize seven enzymes from two WRF, Trametes versicolor and Gelatoporia subvermispora, which constitute a four-enzyme cascade from 4-hydroxybenzoate to β-ketoadipate via the hydroxyquinol pathway. Furthermore, we solve the crystal structure of four of these enzymes and identify mechanistic differences with the closest bacterial and fungal structural homologs. Overall, this research expands our understanding of aromatic catabolism by WRF and establishes an alternative strategy for the conversion of lignin-related compounds to the valuable molecule β-ketoadipate, contributing to the development of biological processes for lignin valorization.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2023

Fuel-rich oxidation of gasoline surrogate components in an atmospheric flow reactor

Fuel-rich oxidation of three typical gasoline surrogate components, toluene, isooctane, and n-heptane, was investigated in an atmospheric-pressure flow reactor at mean gas temperatures from 1050 to 1350 K, equivalence ratio of 9.0, and residence times of 0.45 and 1.2 s. Not only polycyclic aromatic hydrocarbons (PAHs) up to 3 ring structure but also small intermediate products from C 1 to C 5 were quantified by a gas chromatograph mass spectrometry coupled with photon ionization and gas chromatograph with flame ionization detector, respectively. The kinetic model recently developed by Lawrence Livermore National Laboratory was revised to reflect the results of many recent investigations. Basically, the updated model could satisfactorily reproduce the experimental mole fractions of many species. The experimental and simulated results showed that PAH mole fractions produced were in the order of toluene, isooctane, and n-heptane. The kinetic analysis using the model was carried out to explore PAH formation pathways, especially focusing on naphthalene, acenaphthylene, and phenanthrene. Through rate of production analysis, it was found that the main formation pathways of many PAHs were affected by the fuels. Although resonantly stabilized radicals, such as benzyl and fulvenallenyl radicals, played a crucial role in the formation pathways of many PAHs in every fuel, they were produced through hydrogen elimination of toluene in toluene fuel, while they were formed from small intermediate products in isooctane and n-heptane fuels. Sensitivity analysis revealed the difference and similarity of the reactions with large positive coefficients according to the fuels studied here. In conclusion, the molecular growth reactions of aromatic species were influential in PAH production in every fuel, whereas the ring formation reactions from small species and the reactions involving toluene had large positive sensitivity coefficients in isooctane/n-heptane and toluene fuels, respectively.

32 ENERGY CONSERVATION, CONSUMPTION, AND UTILIZATI↗
DOE OSTI2022

Syntheses of gold supported on metal oxides and their application in organic transformations

Herein, we report a general and straightforward synthesis method for gold supported on mesoporous and microporous metal oxides. Supported materials, in general, show higher crystallinity compare to unsupported systems as verified through powder X-ray diffraction (XRD). Also, through XRD, most of the metal is observed to be in its oxide form, whereas the gold support was found to be in its metallic state, which has been further confirmed from TEM. In terms of surface area, the catalyst was not found to follow any trend. Morphology wise, there are no changes observed after doping except in few cases. Combined results from XRD, X-ray fluorescence spectroscopy, Auger, and X-ray photoelectron spectroscopy suggest that gold is mainly in the bulk and very little (0.04% in case of gold doped calcium oxide) or non (in case of gold doped mixed manganese-cerium oxide) on the surface. The presence of Au (0) 4f peaks in XPS further confirms the metallic state of the gold. Oxides of indium, magnesium and calcium have been studied for the organic transformation reactions. An enhancement in activity and product selectivity was observed in the case of the gold supported catalysts. Indium serves as a great catalyst for C–C coupling and electrophilic aromatic substitution reactions and gives >99% conversion. Interestingly, 88% selectivity for C–C coupling and >99% selectivity for aromatic substitution have been achieved at 100 °C and room temperature respectively. Magnesium and calcium give Knoevenagel condensation products. At room temperature with very low catalyst loading, >99% conversion and selectivity were observed for the Knoevenagel reaction with as high as 35.30 TOF. Finally, a mechanism for the C–C coupling reaction has been proposed based on these results.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Biological upgrading of pyrolysis-derived wastewater: Engineering Pseudomonas putida for alkylphenol, furfural, and acetone catabolism and (methyl)muconic acid production

While biomass-derived carbohydrates have been predominant substrates for biological production of renewable fuels, chemicals, and materials, organic waste streams are growing in prominence as potential alternative feedstocks to improve the sustainability of manufacturing processes. Catalytic fast pyrolysis (CFP) is a promising approach to generate biofuels from lignocellulosic biomass, but it generates a complex, carbon-rich, and toxic wastewater stream that is challenging to process catalytically but could be biologically upgraded to valuable co-products. Here, we implemented modular, heterologous catabolic pathways in the Pseudomonas putida KT2440-derived EM42 strain along with the overexpression of native toxicity tolerance machinery to enable utilization of 89% (w/w) of carbon in CFP wastewater. The dmp monooxygenase and meta-cleavage pathway from Pseudomonas putida CF600 were constitutively expressed to enable utilization of phenol, cresols, 2- and 3-ethyl phenol, and methyl catechols, and the native chaperones clpB, groES, and groEL were overexpressed to improve toxicity tolerance to diverse aromatic substrates. Next, heterologous furfural and acetone utilization pathways were incorporated, and a native alcohol dehydrogenase was overexpressed to improve methanol utilization, generating reducing equivalents. All pathways (encoded by genes totaling ~30 kilobases of DNA) were combined into a single strain that can catabolize a mock CFP wastewater stream as a sole carbon source. Further engineering enabled conversion of all aromatic compounds in the mock wastewater stream to (methyl)muconates with a ~90% (mol/mol) yield. Biological upgrading of CFP wastewater as outlined in this work provides a roadmap for future applications in valorizing other heterogeneous waste streams.

(methyl)muconates↗
DOE OSTI2025

Flow Reactor Study of the Soot Precursors of Novel Cycloalkanes as Synthetic Jet Fuel Compounds: Octahydroindene, p -Menthane, and 1,4-Dimethylcyclooctane

Sustainable aviation fuels (SAFs) or Synthetic aviation turbine fuels (SATFs) derived from nonpetroleum sources are essential for energy security and a strong rural and agricultural economy. Airplanes operating on SAF can have lower particle emissions compared to those of conventional jet fuel, reducing air quality impacts near airports. Processing biobased isoprene or wood and agricultural waste can produce cycloalkane-rich fuels with properties meeting ASTM International’s SATF requirements. The unique structures of these cycloalkanes yield lower soot emissions because of their lack of aromatic rings. We measured the soot formation tendency as yield sooting index (YSI) and used laminar flow reactor experiments to evaluate soot precursors formed for isoprene-derived compounds p-menthane and 1,4-dimethylcyclooctane (DMCO), and octahydroindene (OHI)─ produced from woody biomass via catalytic fast pyrolysis. The combustion chemistry of the OHI and DMCO has not been previously studied. Experiments were conducted at 10 bar from 800 to 1200 K, equivalence ratios of 1.0 and 3.0, and residence times of 1.0 and 0.6 s, respectively. Experimentally detected species were used to elucidate the mechanisms of soot precursor formation. OHI exhibited the highest YSI (94.5) and formed a high concentration of benzene primarily by direct dehydrogenation of the six-membered ring. p-Menthane (YSI 92.0) and DMCO (YSI 85.0) oxidation products included fewer aromatic components but higher benzene precursors, including 1,3-butadiene, propyne, and allene. This suggests that the ring-opening pathway is dominant over the dehydrogenation pathway in the benzene formation for these compounds. This experimental speciation provides insight into the influence of the cycloalkane structure on the sooting tendencies of potential SAF blend components, thereby aiding in fuel design processes.

09 BIOMASS FUELS↗