Interaction of oxalate with ß-glucan: Implications for the fungal extracellular matrix, and metabolite transport.

ß-glucan is the major component of the extracellular matrix (ECM) of many fungi, including wood degrading fungi. Many of these species also secrete oxalate into the ECM. Our research demonstrates that ß-glucan forms a novel, previously unreported, hydrogel at room temperature with oxalate. Oxalate was found to alter the rheometric properties of the ß-glucan hydrogels, and modeling showed that ß-glucan hydrogen bonds with oxalate in a non-covalent matrix. Change of oxalate concentration also impacted the diffusion of a high-molecular-weight protein through the gels. This finding has relevance to the diffusion of extracellular enzymes into substrates and helps to explain why some types of wood-decay fungi rely on non-enzymatic degradation schemes for carbon cycling. Further, this research has potential impact on the diffusion of metabolites in association with pathogenic/biomedical fungi.

Machine Learning Predictions of Oil Yields Obtained by Plastic Pyrolysis and Application to Thermodynamic Analysis.

Chemical recycling via thermal processes such as pyrolysis is a potentially viable way to convert mixed streams of waste plastics into usable fuels and chemicals. Unfortunately, experimentally measuring product yields for real waste streams can be time- and cost-prohibitive, and the yields are very sensitive to feed composition, especially for certain types of plastics like poly(ethylene terephthalate) (PET) and polyvinyl chloride (PVC). Models capable of predicting yields and conversion from feed composition and reaction conditions have potential as tools to prioritize resources to the most promising plastic streams and to evaluate potential preseparation strategies to improve yields. In this study, a data set consisting of 325 data points for pyrolysis of plastic feeds was collected from the open literature. The data set was divided into training and test sub data sets; the training data were used to optimize the seven different machine learning regression methods, and the testing data were used to evaluate the accuracy of the resulting models. Of the seven types of models, eXtreme Gradient Boosting (XGBoost) predicted the oil yield of the test set with the highest accuracy, corresponding to a mean absolute error (MAE) value of 9.1%. The optimized XGBoost model was then used to predict the oil yields from real waste compositions found in Municipal Recycling Facilities (MRFs) and the Rhine River. The dependence of oil yields on composition was evaluated, and strategies for removing PET and PVC were assessed as examples of how to use the model. Thermodynamic analysis of a pyrolysis system capable of achieving oil yields predicted using the machine-learned model showed that pyrolysis of Rhine River plastics should be net exergy producing under most reasonable conditions.

Dimensionally reduced machine learning model for predicting single component octanol-water partition coefficients.

MF-LOGP, a new method for determining a single component octanol-water partition coefficients ([Formula: see text]) is presented which uses molecular formula as the only input. Octanol-water partition coefficients are useful in many applications, ranging from environmental fate and drug delivery. Currently, partition coefficients are either experimentally measured or predicted as a function of structural fragments, topological descriptors, or thermodynamic properties known or calculated from precise molecular structures. The MF-LOGP method presented here differs from classical methods as it does not require any structural information and uses molecular formula as the sole model input. MF-LOGP is therefore useful for situations in which the structure is unknown or where the use of a low dimensional, easily automatable, and computationally inexpensive calculations is required. MF-LOGP is a random forest algorithm that is trained and tested on 15,377 data points, using 10 features derived from the molecular formula to make [Formula: see text] predictions. Using an independent validation set of 2713 data points, MF-LOGP was found to have an average [Formula: see text] = 0.77 ± 0.007, [Formula: see text] = 0.52 ± 0.003, and [Formula: see text] = 0.83 ± 0.003. This performance fell within the spectrum of performances reported in the published literature for conventional higher dimensional models ([Formula: see text] = 0.42-1.54, [Formula: see text] = 0.09-1.07, and [Formula: see text] = 0.32-0.95). Compared with existing models, MF-LOGP requires a maximum of ten features and no structural information, thereby providing a practical and yet predictive tool. The development of MF-LOGP provides the groundwork for development of more physical prediction models leveraging big data analytical methods or complex multicomponent mixtures.

Hydroxyapatite catalyzed hydrothermal liquefaction transforms food waste from an environmental liability to renewable fuel.

Food waste is an abundant and inexpensive resource for the production of renewable fuels. Biocrude yields obtained from hydrothermal liquefaction (HTL) of food waste can be boosted using hydroxyapatite (HAP) as an inexpensive and abundant catalyst. Combining HAP with an inexpensive homogeneous base increased biocrude yield from 14 ± 1 to 37 ± 3%, resulting in the recovery of 49 ± 2% of the energy contained in the food waste feed. Detailed product analysis revealed the importance of fatty-acid oligomerization during biocrude formation, highlighting the role of acid-base catalysts in promoting condensation reactions. Economic and environmental analysis found that the new technology has the potential to reduce US greenhouse gas emissions by 2.6% while producing renewable diesel with a minimum fuel selling price of $1.06/GGE. HAP can play a role in transforming food waste from a liability to a renewable fuel.

Thermodynamic feasibility of shipboard conversion of marine plastics to blue diesel for self-powered ocean cleanup.

Collecting and removing ocean plastics can mitigate their environmental impacts; however, ocean cleanup will be a complex and energy-intensive operation that has not been fully evaluated. This work examines the thermodynamic feasibility and subsequent implications of hydrothermally converting this waste into a fuel to enable self-powered cleanup. A comprehensive probabilistic exergy analysis demonstrates that hydrothermal liquefaction has potential to generate sufficient energy to power both the process and the ship performing the cleanup. Self-powered cleanup reduces the number of roundtrips to port of a waste-laden ship, eliminating the need for fossil fuel use for most plastic concentrations. Several cleanup scenarios are modeled for the Great Pacific Garbage Patch (GPGP), corresponding to 230 t to 11,500 t of plastic removed yearly; the range corresponds to uncertainty in the surface concentration of plastics in the GPGP. Estimated cleanup times depends mainly on the number of booms that can be deployed in the GPGP without sacrificing collection efficiency. Self-powered cleanup may be a viable approach for removal of plastics from the ocean, and gaps in our understanding of GPGP characteristics should be addressed to reduce uncertainty.

Rational design of solid-acid catalysts for cellulose hydrolysis using colloidal theory.

Solid-acid catalysts functionalized with catalytic groups have attracted intense interest for converting cellulose into soluble products. However, design of solid-7 acid catalysts has been guided by molecular level interactions and the actual mechanism of cellulose-solid-acid catalyst particles adsorption remains unknown. Here, colloidal stability theory, DLVO, is used to rationalize the design of solid acids for targeted cellulose adsorption. In nearly all cases, an energy barrier, arising from electrostatic repulsion and much larger than the energy associated with thermal fluctuations, prevents close contact between the solid acid and cellulose. Polymer-based solid-acid substrates such as polystyrene and Nafion are especially ineffective as their interaction with cellulose is dominated by the repulsive electrostatic force. Carbon and metal oxides have potential to be effective for cellulose-solid-acid interaction as their attractive van der Waals interaction can offset the repulsive electrostatic interaction. The effects of reactor temperature and shear force were evaluated, with the finding that reactor temperature can minimize the catalyst-cellulose interaction barrier, promoting coagulation, but that the shear force in a typical laboratory reactor cannot. We have evaluated strategies for enhancing cellulose-catalyst interaction and conclude that raising reaction temperature or synthesizing acid/base bifunctional catalysts can effectively diminish electrostatic repulsion and promote cellulose-catalyst coagulation. The analysis presented here establishes a rational method for designing solid acid catalysts for cellulose hydrolysis.

Rapid Depolymerization of Decrystallized Cellulose to Soluble Products via Ethanolysis under Mild Conditions.

Efficient cellulose depolymerization is a major bottleneck for economical production of second-generation biofuels. In this work, crystalline cellulose was subjected to sequential ball milling and ethanolysis as a mild and selective depolymerization approach. Ball milling and ethanolysis resulted in 38±1 % cellulose conversion, with 24 % ethyl-glucopyranoside as the main identified and quantified product and negligible side reaction of the ethanol solvent to form diethyl ether. In comparison, ethanolysis of the original cellulose resulted in only 3±1 % conversion. Additional soluble products from cellulose ethanolysis included carbohydrate isomers and oligomers, differing from the products obtained from hydrolysis. X-ray diffraction and nuclear magnetic resonance spectroscopy revealed increased crystallinity post-reaction, retarding further depolymerization. Hot liquid water extracted soluble oligomers from the ethanolyzed cellulose, suggesting formation of a nanoscale barrier of crystalline cellulose that traps soluble products during ethanolysis. Use of cellulose-swelling co-solvents and repeated mechanical decrystallization both proved effective at increasing cellulose conversion and soluble product yields. Repeated ball milling and ethanolysis resulted in 62±1 % cellulose conversion. Ethanolysis of decrystallized cellulose has potential for rapid (<2 h) de-polymerization at mild conditions.

Critical Role of Tricyclic Bridges Including Neighboring Rings for Understanding Raman Spectra of Zeolites.

Raman spectroscopy of network solids such as zeolites is critical for shedding light on collective vibrations of medium-range structures such as rings that exist in crystals and that form during crystallization processes. Despite this importance, assignments of Raman spectra are not completely understood, though it is often assumed that Raman bands can be assigned to individual rings. We report a systematic zeolite synthesis, spectroscopy, and periodic DFT study of several all-silica zeolites to test this assumption and to determine the fundamental structural motifs that explain Raman spectral features. We have discovered from normal-mode analysis that Raman bands can be assigned to tricyclic bridges-three zeolite rings that share a common Si-O-Si bridge. Furthermore, we have found that the vibrational frequency of a given Raman band can be correlated to the smallest ring of its tricyclic bridge and not to the ring that is actually vibrating. Finally, we have discovered a precise anticorrelation between Raman frequency and Si-O-Si angle. These discoveries open new ways to investigate structures of network materials made of corner-sharing tetrahedra and to study crystallization from amorphous gels where structural information is limited.

Binary Liquid Mixture Contact-Angle Measurements for Precise Estimation of Surface Free Energy.

Surface free energy remains a fundamental material property to characterize the interfacial interactions between liquid and solid. Here, we developed a precise approach to determine surface energy by using contact angles of binary mixtures of water-dimethyl sulfoxide (DMSO), water-formamide, water-ethylene glycol, and water-glycerol and analyzed using the Owens-Wendt method. A mixing equation was developed to estimate liquid-dispersive surface tension (γL,mixd) and polar surface tension (γL,mixp) parameters for binary mixtures. To test the approach, two hydrophobic surfaces, flat polydimethylsiloxane (PDMS), and silane-derivatized glass were prepared and the contact angle of mixtures on the surfaces were obtained. Surface energy of PDMS determined by three binary mixtures agrees with that from pure solvents, but the uncertainty decreases to less than 13%; remarkably, the uncertainty drops to around 5% once we combined measured contact angles from all the mixtures, namely, water-DMSO, water-formamide, and water-ethylene glycol. Surface energies of silane-derivatized glass bearing ethyl (C2), hexyl (C6), and octadecyl (C18) alkyl chains were determined with water-formamide and water-glycerol mixtures. Measured contact angles fit the Owens-Wendt model, and surface energy value determined from different binary mixtures agree with each other within error. Contact angle measurement of liquid mixtures is a simple method for determination of surface energy that improves the precision of surface energy determined by measurements of multiple pure solvents.

ZSM-5 decrystallization and dealumination in hot liquid water.

Zeolites have recently attracted attention for upgrading renewable resources in the presence of liquid water phases; however, the stability of zeolites in the presence of liquid-phase water is not completely understood. Accordingly, the stability of the ZSM-5 framework and its acid sites was studied in the presence of water at temperatures ranging from 250 to 450 °C and at pressures sufficient to maintain a liquid or liquid-like state (25 MPa). Treated samples were analyzed for framework degradation and Al content and coordination using a variety of complementary techniques, including X-ray diffraction, electron microscopy, N2 sorption, 27Al and 29Si NMR spectroscopy, and several different types of infrared spectroscopy. These analyses indicate that the ZSM-5 framework retains >80% crystallinity at all conditions, and that 300-400 °C are the most aggressive. Decrystallization appears to initiate primarily at crystal surfaces and share many characteristics in common with alkali promoted desilication. Liquid water treatment promotes ZSM-5 dealumination, following a mechanism analogous to that observed under steaming conditions: initiation by Al-O hydrolysis, Al migration to the surface, and finally deposition as extra framework Al or possibly complete dissolution under some conditions. As with the framework, dealumination is most aggressive at 300-400 °C. Several models were evaluated to capture the non-Arrhenius effect of temperature on decrystallization and dealumination, the most successful of which included temperature dependent values of the water auto-ionization constant. These results can help interpretation of previous studies on ZSM-5 catalysis in hot liquid water and suggest future approaches to extend catalyst lifetime.

Detailed kinetic model for hexyl sulfide pyrolysis and its desulfurization by supercritical water.

A detailed reaction network is proposed for the pyrolysis and desulfurization of hexyl sulfide in the presence or absence of both supercritical water (SCW) and hexadecane, but without any added H2 or catalyst, for T = 400-450 °C. The new kinetic model is developed using the Reaction Mechanism Generator (RMG) software where most of the rate coefficients are derived from quantum chemical calculations. We previously reported that pentane, carbon monoxide and carbon dioxide are major products of hexyl sulfide desulfurization in SCW, but not in the anhydrous pyrolysis of hexyl sulfide. The observation of CO and CO2 in the reaction products indicates that water effectively acts as a hydrogen source; presumably this assists in sulfur reduction to H2S. Kinetic parameters for several of the important reactions are calculated using transition state theory and quantum chemical calculations at the CBS-QB3 level of theory and then further refined using CCSD(T)-F12//cc-pVTZ-F12 single point energies. Predictions from the new kinetic model agree with factor-of-2 accuracy with new and previously published experimental data for hexyl sulfide conversion and for yields of most major products, either neat or in a hexadecane solvent, both in the presence and absence of SCW. Flux analysis was then used to identify the most important reaction steps, and sensitivity analysis was used to propose reactions that should be studied further in the future to decrease the model's uncertainty. This study establishes the molecular role of water as diluent, hydrogen bond donor, and reductant in the decomposition of hexyl sulfide. Future work to add molecular weight growth pathways to the model would lead to a more complete mechanism, resulting in improved predictions of product yields.

Engineered microbial biofuel production and recovery under supercritical carbon dioxide.

Culture contamination, end-product toxicity, and energy efficient product recovery are long-standing bioprocess challenges. To solve these problems, we propose a high-pressure fermentation strategy, coupled with in situ extraction using the abundant and renewable solvent supercritical carbon dioxide (scCO2), which is also known for its broad microbial lethality. Towards this goal, we report the domestication and engineering of a scCO2-tolerant strain of Bacillus megaterium, previously isolated from formation waters from the McElmo Dome CO2 field, to produce branched alcohols that have potential use as biofuels. After establishing induced-expression under scCO2, isobutanol production from 2-ketoisovalerate is observed with greater than 40% yield with co-produced isopentanol. Finally, we present a process model to compare the energy required for our process to other in situ extraction methods, such as gas stripping, finding scCO2 extraction to be potentially competitive, if not superior.

Combining experiment and theory to elucidate the role of supercritical water in sulfide decomposition.

The cleavage of C-S linkages plays a key role in fuel processing and organic geochemistry. Water is known to affect these processes, and several hypotheses have been proposed, but the mechanism has been elusive. Here we use both experiment and theory to demonstrate that supercritical water reacts with intermediates formed during alkyl sulfide decomposition. During hexyl sulfide decomposition in supercritical water, pentane and CO + CO2 were detected in addition to the expected six carbon products. A multi-step reaction sequence for hexyl sulfide reacting with supercritical water is proposed which explains the surprising products, and quantum chemical calculations provide quantitative rates that support the proposed mechanism. The key sequence is cleavage of one C-S bond to form a thioaldehyde via radical reactions, followed by a pericyclic addition of water to the C[double bond, length as m-dash]S bond to form a geminal mercaptoalcohol. The mercaptoalcohol decomposes into an aldehyde and H2S either directly or via a water-catalyzed 6-membered ring transition state. The aldehyde quickly decomposes into CO plus pentane by radical reactions. The time is ripe for quantitative modelling of organosulfur reaction kinetics based on modern quantum chemistry.

Identification of lubrication oil in the particulate matter emissions from engine exhaust of in-service commercial aircraft.

Lubrication oil was identified in the organic particulate matter (PM) emissions of engine exhaust plumes from in-service commercial aircraft at Chicago Midway Airport (MDW) and O'Hare International Airport (ORD). This is the first field study focused on aircraft lubrication oil emissions, and all of the observed plumes described in this work were due to near-idle engine operations. The identification was carried out with an Aerodyne high-resolution time-of-flight aerosol mass spectrometer (HR-ToF AMS) via a collaborative laboratory and field investigation. A characteristic mass marker of lubrication oil, I(85)/I(71), the ratio of ion fragment intensity between m/z = 85 and 71, was used to distinguish lubrication oil from jet engine combustion products. This AMS marker was based on ion fragmentation patterns measured using electron impact ionization for two brands of widely used lubrication oil in a laboratory study. The AMS measurements of exhaust plumes from commercial aircraft in this airport field study reveal that lubrication oil is commonly present in organic PM emissions that are associated with emitted soot particles, unlike the purely oil droplets observed at the lubrication system vent. The characteristic oil marker, I(85)/I(71), was applied to quantitatively determine the contribution from lubrication oil in measured aircraft plumes, which ranges from 5% to 100%.

Determination of the emissions from an aircraft auxiliary power unit (APU) during the Alternative Aviation Fuel Experiment (AAFEX).

The emissions from a Garrett-AiResearch (now Honeywell) Model GTCP85-98CK auxiliary power unit (APU) were determined as part of the National Aeronautics and Space Administration's (NASA's) Alternative Aviation Fuel Experiment (AAFEX) using both JP-8 and a coal-derived Fischer Tropsch fuel (FT-2). Measurements were conducted by multiple research organizations for sulfur dioxide (SO2, total hydrocarbons (THC), carbon monoxide (CO), carbon dioxide (CO2), nitrogen oxides (NOx), speciated gas-phase emissions, particulate matter (PM) mass and number, black carbon, and speciated PM. In addition, particle size distribution (PSD), number-based geometric mean particle diameter (GMD), and smoke number were also determined from the data collected. The results of the research showed PM mass emission indices (EIs) in the range of 20 to 700 mg/kg fuel and PM number EIs ranging from 0.5 x 10(15) to 5 x 10(15) particles/kg fuel depending on engine load and fuel type. In addition, significant reductions in both the SO2 and PM EIs were observed for the use of the FT fuel. These reductions were on the order of approximately 90% for SO2 and particle mass EIs and approximately 60% for the particle number EI, with similar decreases observed for black carbon. Also, the size of the particles generated by JP-8 combustion are noticeably larger than those emitted by the APU burning the FT fuel with the geometric mean diameters ranging from 20 to 50 nm depending on engine load and fuel type. Finally, both particle-bound sulfate and organics were reduced during FT-2 combustion. The PM sulfate was reduced by nearly 100% due to lack of sulfur in the fuel, with the PM organics reduced by a factor of approximately 5 as compared with JP-8.

Characterization of lubrication oil emissions from aircraft engines.

In this first ever study, particulate matter (PM) emitted from the lubrication system overboard breather vent for two different models of aircraft engines has been systematically characterized. Lubrication oil was confirmed as the predominant component of the emitted particulate matter based upon the characteristic mass spectrum of the pure oil. Total particulate mass and size distributions of the emitted oil are also investigated by several high-sensitivity aerosol characterization instruments. The emission index (EI) of lubrication oil at engine idle is in the range of 2-12 mg kg(-1) and increases with engine power. The chemical composition of the oil droplets is essentially independent of engine thrust, suggesting that engine oil does not undergo thermally driven chemical transformations during the ∼4 h test window. Volumetric mean diameter is around 250-350 nm for all engine power conditions with a slight power dependence.

Speciation and chemical evolution of nitrogen oxides in aircraft exhaust near airports.

Measurements of nitrogen oxides from a variety of commercial aircraft engines as part of the JETS-APEX2 and APEX3 campaigns show that NOx (NOx [triple bond] NO + NO2) is emitted primarily in the form of NO2 at idle thrust and NO at high thrust. A chemical kinetics combustion model reproduces the observed NO2 and NOx trends with engine power and sheds light on the relevant chemical mechanisms. Experimental evidence is presented of rapid conversion of NO to NO2 in the exhaust plume from engines at low thrust. The rapid conversion and the high NO2/NOx emission ratios observed are unrelated to ozone chemistry. NO2 emissions from a CFM56-3B1 engine account for approximately 25% of the NOx emitted below 3000 feet (916 m) and 50% of NOx emitted below 500 feet (153 m) during a standard ICAO (International Civil Aviation Organization) landing-takeoff cycle. Nitrous acid (HONO) accounts for 0.5% to 7% of NOy emissions from aircraft exhaust depending on thrust and engine type. Implications for photochemistry near airports resulting from aircraft emissions are discussed.

Manipulation of slow molecular beams by static external fields.

Deflection by magnetic or electric field gradients has long been used to analyze or to alter the translational trajectories of neutral gas-phase atoms or molecules. Recent work has developed sources of slow, cold molecular beams that offer means to enhance markedly the attainable deflections, which are inversely proportional to the translational kinetic energy. The sensitivity and resolution can thus be much increased, typically by factors of 10(2)-10(4). We illustrate ways to exploit this enhanced deflection capability, particularly when balancing electric and magnetic deflections. Chemical scope can be greatly extended by utilizing feeble but ubiquitous interactions, especially the induced electric dipole due to the molecular polarizability and magnetic moments resulting from molecular rotation or nuclear spins. We also examine the effect of non-Maxwellian velocity distributions produced by supersonic expansions or by quantum statistics (pertinent for ultracold beams). Generic plots are provided, employing dimensionless variables, to facilitate the design and interpretation of experiments with deflections amplified by low kinetic energy.

Solvophobic acceleration of Diels-Alder reactions in supercritical carbon dioxide.

The rate of the Diels-Alder reaction between N-ethylmaleimide and 9-hydroxymethylanthracene in supercritical carbon dioxide (scCO(2)) was determined by following the disappearance of 9-hydroxymethylanthracene with in situ UV/vis absorption spectroscopy. The reaction conditions were 45-75 degrees C and 90-190 bar, which correspond to fluid densities (based on pure carbon dioxide) ranging between approximately 340 and 730 kg m(-3). The measured reaction rate at low scCO(2) fluid densities was nearly 25x faster than that reported in acetonitrile at the same temperature (45 degrees C). An inverse relationship between reaction rate and fluid density/pressure was observed at all temperatures in scCO(2). The apparent activation volumes were large and positive (350 cm(3) mol(-1)) and only a weak function of reduced temperature. A solvophobic mechanism analogous to those observed in conventional solvents is postulated to describe (a) the rate acceleration observed for this reaction in scCO(2) relative to that in acetonitrile, (b) the observed relationship between reaction rate and pressure/temperature/density, and (c) the large, positive activation volumes. Solubility measurements in scCO(2), rate measurements in conventional solvents, and an empirical correlation are used to support this theory. Our results advance the general understanding of reactivity in supercritical fluids and provide a rationale for selecting reactions which can be accelerated when conducted in scCO(2).