Showing papers by "ExxonMobil published in 2015"

Redesigning photosynthesis to sustainably meet global food and bioenergy demand

Abstract: The world’s crop productivity is stagnating whereas population growth, rising affluence, and mandates for biofuels put increasing demands on agriculture. Meanwhile, demand for increasing cropland competes with equally crucial global sustainability and environmental protection needs. Addressing this looming agricultural crisis will be one of our greatest scientific challenges in the coming decades, and success will require substantial improvements at many levels. We assert that increasing the efficiency and productivity of photosynthesis in crop plants will be essential if this grand challenge is to be met. Here, we explore an array of prospective redesigns of plant systems at various scales, all aimed at increasing crop yields through improved photosynthetic efficiency and performance. Prospects range from straightforward alterations, already supported by preliminary evidence of feasibility, to substantial redesigns that are currently only conceptual, but that may be enabled by new developments in synthetic biology. Although some proposed redesigns are certain to face obstacles that will require alternate routes, the efforts should lead to new discoveries and technical advances with important impacts on the global problem of crop productivity and bioenergy production.

Catalyst Design with Atomic Layer Deposition

Abstract: Atomic layer deposition (ALD) has emerged as an interesting tool for the atomically precise design and synthesis of catalytic materials. Herein, we discuss examples in which the atomic precision has been used to elucidate reaction mechanisms and catalyst structure–property relationships by creating materials with a controlled distribution of size, composition, and active site. We highlight ways ALD has been utilized to design catalysts with improved activity, selectivity, and stability under a variety of conditions (e.g., high temperature, gas and liquid phase, and corrosive environments). In addition, due to the flexibility and control of structure and composition, ALD can create myriad catalytic structures (e.g., high surface area oxides, metal nanoparticles, bimetallic nanoparticles, bifunctional catalysts, controlled microenvironments, etc.) that consequently possess applicability for a wide range of chemical reactions (e.g., CO2 conversion, electrocatalysis, photocatalytic and thermal water splitting...

Mechanisms of antiwear tribofilm growth revealed in situ by single-asperity sliding contacts

Abstract: Zinc dialkyldithiophosphates (ZDDPs) form antiwear tribofilms at sliding interfaces and are widely used as additives in automotive lubricants. The mechanisms governing the tribofilm growth are not well understood, which limits the development of replacements that offer better performance and are less likely to degrade automobile catalytic converters over time. Using atomic force microscopy in ZDDP-containing lubricant base stock at elevated temperatures, we monitored the growth and properties of the tribofilms in situ in well-defined single-asperity sliding nanocontacts. Surface-based nucleation, growth, and thickness saturation of patchy tribofilms were observed. The growth rate increased exponentially with either applied compressive stress or temperature, consistent with a thermally activated, stress-assisted reaction rate model. Although some models rely on the presence of iron to catalyze tribofilm growth, the films grew regardless of the presence of iron on either the tip or substrate, highlighting the critical role of stress and thermal activation.

Capturing Key Attributes of Fine-Grained Sedimentary Rocks In Outcrops, Cores, and Thin Sections: Nomenclature and Description Guidelines

Abstract: An integrated nomenclature scheme is proposed to capture the inherent heterogeneity of fine-grained sedimentary rocks at the 102 to 10−3 mm scale and to assist the evaluation of these rocks as sinks of organic carbon, barriers to fluid flows, and reservoirs of oil and gas. This scheme incorporates previous knowledge and the latest field, petrographic, and laboratory observations. We propose to name fine-grained sedimentary rocks using a root term based on their texture (grain size), which is modified by description of bedding, composition, and grain origin. Regarding texture, we suggest the use of “mudstone” as a class name for the entire spectrum of fine-grained sedimentary rocks. We define mudstone as a rock in which more than fifty percent of its grains are mud (clay and silt) size (< 62.5 µm). Similar to the approach used for the description of sandstone texture, mudstone texture can be refined by a “coarse,” “medium,” or “fine” size-range term. Regarding bedding, we follow Campbell's (1967) genetic approach to define laminae, laminasets, and beds, and describe lamina geometry, continuity, and shape. Regarding composition, we propose terms such as “siliceous,” “calcareous,” “argillaceous,” and “carbonaceous” to capture differences in rock composition. The name of a mudstone can be further modified by additional attributes that detail the form and origin of the rock components. Application of this approach to the Cretaceous Eagle Ford Shale illustrates the variability typically present in mudstone successions and demonstrates how our detailed characterization can be used to decipher and predict rock properties of economic interest.

Aerosol characterization over the southeastern United States using high-resolution aerosol mass spectrometry: spatial and seasonal variation of aerosol composition and sources with a focus on organic nitrates

Abstract: . We deployed a High-Resolution Time-of-Flight Aerosol Mass Spectrometer (HR-ToF-AMS) and an Aerosol Chemical Speciation Monitor (ACSM) to characterize the chemical composition of submicron non-refractory particulate matter (NR-PM$_{1}$) in the southeastern USA. Measurements were performed in both rural and urban sites in the greater Atlanta area, Georgia (GA), and Centreville, Alabama (AL), for approximately 1 year as part of Southeastern Center for Air Pollution and Epidemiology study (SCAPE) and Southern Oxidant and Aerosol Study (SOAS). Organic aerosol (OA) accounts for more than half of NR-PM1 mass concentration regardless of sampling sites and seasons. Positive matrix factorization (PMF) analysis of HR-ToF-AMS measurements identified various OA sources, depending on location and season. Hydrocarbon-like OA (HOA) and cooking OA (COA) have important, but not dominant, contributions to total OA in urban sites (i.e., 21–38 % of total OA depending on site and season). Biomass burning OA (BBOA) concentration shows a distinct seasonal variation with a larger enhancement in winter than summer. We find a good correlation between BBOA and brown carbon, indicating biomass burning is an important source for brown carbon, although an additional, unidentified brown carbon source is likely present at the rural Yorkville site. Isoprene-derived OA factor (isoprene-OA) is only deconvolved in warmer months and contributes 18–36 % of total OA. The presence of isoprene-OA factor in urban sites is more likely from local production in the presence of NOx than transport from rural sites. More-oxidized and less-oxidized oxygenated organic aerosol (MO-OOA and LO-OOA, respectively) are dominant fractions (47–79 %) of OA in all sites. MO-OOA correlates well with ozone in summer but not in winter, indicating MO-OOA sources may vary with seasons. LO-OOA, which reaches a daily maximum at night, correlates better with estimated nitrate functionality from organic nitrates than total nitrates. Based on the HR-ToF-AMS measurements, we estimate that the nitrate functionality from organic nitrates contributes 63–100 % to the total measured nitrates in summer. Furthermore, the contribution of organic nitrates to total OA is estimated to be 5–12 % in summer, suggesting that organic nitrates are important components in the ambient aerosol in the southeastern USA. The spatial distribution of OA is investigated by comparing simultaneous HR-ToF-AMS measurements with ACSM measurements at two different sampling sites. OA is found to be spatially homogeneous in summer due possibly to stagnant air mass and a dominant amount of regional secondary organic aerosol (SOA) in the southeastern USA. The homogeneity is less in winter, which is likely due to spatial variation of primary emissions. We observe that the seasonality of OA concentration shows a clear urban/rural contrast. While OA exhibits weak seasonal variation in the urban sites, its concentration is higher in summer than winter for rural sites. This observation from our year-long measurements is consistent with 14 years of organic carbon (OC) data from the SouthEastern Aerosol Research and Characterization (SEARCH) network. The comparison between short-term measurements with advanced instruments and long-term measurements of basic air quality indicators not only tests the robustness of the short-term measurements but also provides insights in interpreting long-term measurements. We find that OA factors resolved from PMF analysis on HR-ToF-AMS measurements have distinctly different diurnal variations. The compensation of OA factors with different diurnal trends is one possible reason for the repeatedly observed, relatively flat OA diurnal profile in the southeastern USA. In addition, analysis of long-term measurements shows that the correlation between OC and sulfate is substantially stronger in summer than winter. This seasonality could be partly due to the effects of sulfate on isoprene SOA formation as revealed by the short-term intensive measurements.

Oil Spill Dispersants: Boon or Bane?

Abstract: Dispersants provide a reliable large-scale response to catastrophic oil spills that can be used when the preferable option of recapturing the oil cannot be achieved. By allowing even mild wave action to disperse floating oil into tiny droplets (<70 μm) in the water column, seabirds, reptiles, and mammals are protected from lethal oiling at the surface, and microbial biodegradation is dramatically increased. Recent work has clarified how dramatic this increase is likely to be: beached oil has an environmental residence of years, whereas dispersed oil has a half-life of weeks. Oil spill response operations endorse the concept of net environmental benefit, that any environmental costs imposed by a response technique must be outweighed by the likely benefits. This critical review discusses the potential environmental debits and credits from dispersant use and concludes that, in most cases, the potential environmental costs of adding these chemicals to a polluted area are likely outweighed by the much shorter residence time, and hence integrated environmental impact, of the spilled oil in the environment.

Pore Architecture and Connectivity in Gas Shale

Abstract: The pore size distribution and architecture in gas shales were studied using a combination of small-angle neutron scattering (SANS), mercury injection capillary pressure (MICP), and helium ion microscopy (HIM). SANS analysis shows that the pore size population is not a power-law distribution across many length scales, typical of sedimentary rocks, but contains an anomalous population of pores on-the-order ∼2 nm, housed primarily in the organic matter. A model is presented showing how a “foamy porosity” with such a characteristic size is a direct result of diagenetic evolution of kerogen. Cross-linking of the kerogen combined with phase separation of gas/oil, leads to arrested coarsening with a length scale set by the cross-length density. These pore populations determined by the scattering model are directly supported by HIM images. Pore connectivity determined through pore-size-to-pore-throat analysis, suggests that interpore connections are also distinct from typical sedimentary rocks. The pore/throat r...

The interaction of propagating opening mode fractures with preexisting discontinuities in shale

Abstract: Field observations show that hydraulic fracture growth in naturally fractured formations like shale is complex. Preexisting discontinuities in shale, including natural fractures and bedding, act as planes of weakness that divert fracture propagation. To investigate the influence of weak planes on hydraulic fracture propagation, we performed Semicircular Bend tests on Marcellus Shale core samples containing calcite-filled natural fractures (veins). The approach angle of the induced fracture to the veins and the thickness of the veins have a strong influence on propagation. As the approach angle becomes more oblique to the induced fracture plane, and as the vein gets thicker, the induced fracture is more likely to divert into the vein. Microstructural analysis of tested samples shows that the induced fracture propagates in the middle of the vein but not at the interface between the vein and the rock matrix. Cleavage planes and fluid inclusion trails in the vein cements exert some control on the fracture path. Combining the experimental results with theoretical fracture mechanics arguments, the fracture toughness of the calcite veins was estimated to range from 0.24 MPa m1/2 to 0.83 MPa m1/2, depending on the value used for the Young's modulus of the calcite vein material. Measured fracture toughness of unfractured Marcellus Shale was 0.47 MPa m1/2.

Natural hydraulic fracturing of tight-gas sandstone reservoirs, Piceance Basin, Colorado

Abstract: Natural fractures form preferred pathways for basinal fluid flow and associated heat and mass transport. In gas sandstone reservoirs with low matrix permeability, fractures provide flow pathways between organic-rich source and reservoir layers during gas charge, and between matrix pores, hydraulic fractures, and the well bore during production. While the formation of natural fractures has previously been associated with gas generation and pore-fluid pressure increase through a process referred to as natural hydraulic fracturing, other driving mechanisms such as stress changes by tectonic or exhumation processes remained viable alternatives. To test whether these mechanisms contributed to fracture development, we investigated the spatial and temporal distribution of fracture formation and its relationship to gas generation, migration, and charge in sandstone of the Cretaceous Mesaverde Group across the entire production interval on a basinwide scale. Using fluid inclusion microthermometry of crack-seal fracture cement formed concurrently with fracture opening, we observed temperature trends that, when compared with temperature evolution models of the formation, date fracture formation between 41 and 6 Ma in the northern and between 39 and 6 Ma in the southern Piceance Basin. The onset of fracture formation 20–30 m.y. prior to maximum burial eliminates changes in stress state associated with exhumation as a mechanism for triggering the onset of fracture formation. Instead, calculated paleo–pore-fluid pressures of 40–90 MPa (5800–13,000 psi) during fracture opening and the presence of methane-rich inclusions in fracture cement suggest that fracture formation was aided by high pore-fluid pressures during gas generation in organic-rich shales and coals and associated charging of adjacent and interlayered sandstone reservoirs. A 10–20 m.y. age progression in the onset of fracture formation from deeper to shallower horizons of the Mesaverde Group is consistent with gas generation and onset of fracture formation activated by burial temperature with limited upward migration of gas at this stage of reservoir evolution. This age progression with depth is inconsistent with fracture formation triggered by changes in stress conditions associated with tectonic or structural processes expected to affect the entire formation synchronously. Our observations are thus most consistent with fracture formation by natural hydraulic fracturing in response to gas generation in interbedded source layers and reservoir charge. Based on widespread observations of fractures with similar structural and diagenetic attributes, we consider natural hydraulic fracture formation in response to thermocatalytic gas generation to be a fundamental mode of brittle failure in otherwise structurally quiescent basins.

In Situ Nuclear Magnetic Resonance Mechanistic Studies of Carbon Dioxide Reactions with Liquid Amines in Aqueous Systems: New Insights on Carbon Capture Reaction Pathways

Abstract: A series of closely related primary, secondary, and tertiary alkanolamine model compounds were monitored in real time in aqueous solution via in situ nuclear magnetic resonance (NMR) spectroscopy while purging CO2-rich gas through the solution over a range of temperatures. The real-time in situ spectroscopic monitoring of this reaction chemistry provides new insight about reaction pathways through identification of primary products and their transformations into secondary products. New mechanistic pathways were observed and elucidated. The effects of CO2 loadings, relative absorption and desorption kinetics, pH, temperature, and other critical features of the amine/CO2 reaction system are discussed in detail. The effect of amine basicity and structure on these parameters was further elucidated by studying complementary electron-rich and -poor amines (pKa ∼ 4.5–11) and guanidines (pKa ∼ 14–15). While tertiary amines act only as simple proton acceptors, primary and secondary amines function as both bases an...

In Situ Nuclear Magnetic Resonance Mechanistic Studies of Carbon Dioxide Reactions with Liquid Amines in Non-aqueous Systems: Evidence for the Formation of Carbamic Acids and Zwitterionic Species

Abstract: In a previous study, we reported the use of in situ 1H and 13C nuclear magnetic resonance (NMR) to elucidate mechanistic pathways for the reaction of carbon dioxide with a broad range of amines (pKa ∼ 4.5–15.5), including alkanolamines of commercial interest, in water. In the aqueous systems of that study, water most importantly functions as a Bronsted acid/Lewis base and, as the amine is consumed and pH decreases, hydrolyzes the initially formed carbamate species (1:2 CO2/amine stoichiometry), into the alkyl ammonium bicarbonate with a more beneficial 1:1 CO2/amine stoichiometry. This study has been extended herein to amines, amidines, and guanidines dissolved in non-aqueous solvent systems, such as dimethyl sulfoxide, sulfolane, toluene, 1-methyl-2-pyrrolidinone, and the ionic liquid 1-ethyl-3-methyl-imidazolium acetate. The use of non-aqueous organic solvents shuts off some CO2 reaction pathways available in aqueous solution. However, more importantly, it opens up new possibilities and reaction pathway...

Fundamental Controls on Fluid Flow in Carbonates: Current Workflows to Emerging Technologies

Abstract: This volume highlights key challenges for fluid-flow prediction in carbonate reservoirs, the approaches currently employed to address these challenges and developments in fundamental science and technology. The papers span methods and case studies that highlight workflows and emerging technologies in the fields of geology, geophysics, petrophysics, reservoir modelling and computer science. Topics include: detailed pore-scale studies that explore fundamental processes and applications of imaging and flow modelling at the pore scale; case studies of diagenetic processes with complementary perspectives from reactive transport modelling; novel methods for rock typing; petrophysical studies that investigate the impact of diagenesis and fault-rock properties on acoustic signatures; mechanical modelling and seismic imaging of faults in carbonate rocks; modelling geological influences on seismic anisotropy; novel approaches to geological modelling; methods to represent key geological details in reservoir simulations and advances in computer visualization, analytics and interactions for geoscience and engineering.

A Universal Classification Scheme For the Microcrystals That Host Limestone Microporosity

Abstract: Microporosity is recognized as a significant concern in Phanerozoic-age limestone reservoirs throughout the world because its presence can severely complicate hydrocarbon evaluation and production. Numerous studies have documented the occurrence and abundance of micropores, their physical appearance, and diagenetic origins in specific reservoirs, but no published study has been systematic and global in its approach. Presented here is a global assessment of limestone microporosity that is based on scanning electron microscope, crystal size distributions, helium porosimetry, and mercury-injection capillary-pressure data collected from 12 microporous limestone reservoirs spanning a broad range of geologic ages, depositional facies, and burial depths. Results indicate that the vast majority of limestone microporosity is hosted within a framework of low-magnesium calcite microcrystals. In general, crystal size distributions are narrow and positively skewed. Compiled data indicate that > 99% of all microcrystals measure between 0.5 and 9.0 µm in diameter with a mode at ca. 2.0 µm. Based on microcrystal shape, packing, and edge density, microporous limestones can be classified into three major textural classes, which we term granular, clustered, and fitted. Granular textures, which include subhedral and euhedral subclasses, are characterized by a framework of unconsolidated rhombic to polyhedral microcrystals that exhibit straight to curvilinear boundaries and intermediate crystal edge densities. Clustered textures, which include loose and fused subclasses, are characterized by a framework of irregularly shaped microcrystals with relatively high densities of discontinuous, curvilinear crystal edges. Fitted textures, which include partial and fused subclasses, are characterized by a dense mosaic of slightly larger microcrystals with mostly curvilinear boundaries and relatively low edge densities. These textural classes have unique mean crystal sizes, average pore-throat radii, bulk porosities, and permeabilities. Furthermore, textural classes and their characteristic pore-throat radii fall along a single log-normal transform in porosity–permeability space. Based on these relationships, three petrophysical microporosity “types” are distinguished. Type 1 is associated with granular subhedral crystal fabrics and typically exhibit relatively large average pore throat radii (ca. 0.7 µm) as well as high porosity (> 20%) and permeability (1–20 mD). Type 2 includes granular euhedral and clustered fabrics, which most commonly exhibit intermediate average pore-throat radii (ca. 0.2 µm), porosity (10–20%), and permeability (0.1–1 mD). Type 3 includes fitted crystal fabrics, which are generally characterized by smaller average pore-throat radii (ca. 0.06 µm), and relatively low porosity (< 10%) and permeability (< 0.1 mD).

Characterizing the subsurface chlorophyll a maximum in the Chukchi Sea and Canada Basin

Abstract: Throughout the Arctic Ocean, subsurface chlorophyll a (Chl a) maxima (SCM) develop every summer after the water column stratifies and surface nutrients have been exhausted. Despite its ubiquity, the SCM׳s distribution, seasonal dynamics, and productivity remain uncertain. Here we present the first in-depth analysis of the SCM in the Chukchi Sea and adjacent Canada Basin, drawing on data collected during the field program Impacts of Climate on the EcoSystems and Chemistry of the Arctic Pacific Environment (ICESCAPE). The SCM was significantly shallower on the Chukchi shelf (30 m) than in the Canada Basin (56 m), and in both regions was correlated with the euphotic and nitracline depths, suggesting an actively growing community maintaining its optimal position within the water column, consistent with previous work. The SCM was located significantly deeper than the net primary productivity (NPP) maximum, which averaged 15 m depth. The development of the SCM on the Chukchi shelf appears tightly linked to under-ice blooms, beginning ~1 month prior to sea-ice retreat and reaching ~15 m depth by the time ice retreats, beyond the range of satellite ocean-color sensors. A seasonal analysis of historical data from the region shows that the SCM deepens to ~30 m by July and remains there throughout the summer, a depth that is consistent with previous studies across the pan-Arctic shelves. We employed a spectral model of light propagation through the water column to demonstrate that surface Chl a and CDOM play approximately equal roles in attenuating light, limiting euphotic depth, and therefore SCM depth, to ~30 m, thus greatly limiting new production. If surface Chl a and CDOM were reduced, allowing greater light penetration, new production on Arctic shelves could potentially be 40% greater.

Effect of Nonsolvent Treatments on the Microstructure of PIM-1

Abstract: The combination of appreciable swelling at unit activity sorption, weak polymer–penetrant interactions, and high vapor pressure allows methanol to be effective at restoring free volume to glassy polymers compared to similar organics. Polymers of intrinsic microporosity (PIMs) are often soaked in methanol and then dried before permeation and sorption analysis to improve reproducibility and eliminate processing history. Here, surface area, pore volume, thermogravimetric analysis, sorption, and diffusion data are used to demonstrate the effectiveness of methanol treatments at removing nonsolvent-induced changes to PIM-1, specifically using dimethylformamide (DMF) as a candidate conditioning molecule. DMF clearly plasticizes PIM-1 while methanol does not. In addition, diethyl ether-conditioned PIM-1 showed marked increases in surface area and free volume—higher than that found from methanol conditioning. Strongly plasticizing nonsolvents with low vapor pressures can be used as conditioning agents that promote...

Structural and stratigraphic evolution of the Iberia–Newfoundland hyper-extended rifted margin: a quantitative modelling approach

Abstract: Abstract We investigate the evolution of the Iberia–Newfoundland margin from Permian post-orogenic extension to Early Cretaceous break-up. We used a Quantitative Basin Analysis approach to integrate seismic stratigraphic interpretations and drill-hole data of two representative sections across the Iberia–Newfoundland margin with kinematic models for lithospheric thinning and subsequent flexural readjustment. We model the distribution of extension and thinning, palaeobathymetry, crustal structure, and subsidence and uplift history as functions of space and time. We start our modelling following post-orogenic extension, magmatic underplating and thermal re-equilibration of the Permian lithosphere. During the Late Triassic–Early Jurassic, broadly distributed, depth-independent lithospheric extension evolved into Late Jurassic–Early Cretaceous depth-dependent thinning as crustal extension progressed from distributed to focused deformation. During this time, palaeobathymetries rapidly deepened across the margin. Modelling of the southern and northern profiles highlighted the rapid development of crustal deformation from south to north over a 5–10 myr period, which accounts for the rapid change in Tithonian–Valanginian, deep- to shallow-water sedimentary facies between the Abyssal Plain and the adjacent Galicia Bank, respectively. Late-stage deformation of both margins was characterized by brittle deformation of the remaining continental crust, which led to exhumation of subcontinental mantle and, eventually, continental break-up and seafloor spreading.

Petroleum generation kinetics: Single versus multiple heating-ramp open-system pyrolysis

Abstract: Some recent publications promote one-run, open-system pyrolysis experiments using a single heating rate (ramp) and fixed frequency factor to determine the petroleum generation kinetics of source-rock samples because, compared to multiple-ramp experiments, the method is faster, less expensive, and presumably yields similar results. Some one-ramp pyrolysis experiments yield kinetic results similar to those from multiple-ramp experiments. However, our data for 52 worldwide source rocks containing types I, II, IIS, II/III, and III kerogen illustrate that one-ramp kinetics introduce the potential for significant error that can be avoided by using high-quality kinetic measurements and multiple-ramp experiments in which the frequency factor is optimized by the kinetic software rather than fixed at some universal value. The data show that kinetic modeling based on a discrete activation energy distribution and three different pyrolysis temperature ramps closely approximates that determined from additional runs, provided the three ramps span an appropriate range of heating rates. For some source rocks containing well-preserved kerogen and having narrow activation energy distributions, both single- and multiple-ramp discrete models are insufficient, and nucleation-growth models are necessary. Instrument design, thermocouple size or orientation, and sample weight likely influence the acceptable upper limit of pyrolysis heating rate. Caution is needed for ramps of 30–50°C/min, which can cause temperature errors due to impaired heat transfer between the oven, sample, and thermocouple. Compound volatility may inhibit pyrolyzate yield at the lowest heating rates, depending on the effectiveness of the gas sweep. We recommend at least three pyrolysis ramps that span at least a 20-fold variation of comparatively lower rates, such as 1, 5, and 25°C/min. The product of heating rate and sample size should not exceed ∼100 mg °C/min. Our results do not address the more fundamental questions of whether kinetic models based on multiple-ramp open-system pyrolysis are mechanistically appropriate for use in basin simulators or whether petroleum migration through the kerogen network, rather than cracking of organic matter, represents the rate-limiting step in expulsion.

Characterization of the toxicological hazards of hydrocarbon solvents

Abstract: Hydrocarbon solvents are liquid hydrocarbon fractions derived from petroleum processing streams, containing only carbon and hydrogen atoms, with carbon numbers ranging from approximately C5-C20 and boiling between approximately 35-370°C. Many of the hydrocarbon solvents have complex and variable compositions with constituents of 4 types, alkanes (normal paraffins, isoparaffins, and cycloparaffins) and aromatics (primarily alkylated one- and two-ring species). Because of the compositional complexity, hydrocarbon solvents are now identified by a nomenclature ("the naming convention") that describes them in terms of physical/chemical properties and compositional elements. Despite the compositional complexity, most hydrocarbon solvent constituents have similar toxicological properties, and the overall toxicological hazards can be characterized in generic terms. To facilitate hazard characterization, the solvents were divided into 9 groups (categories) of substances with similar physical and chemical properties. Hydrocarbon solvents can cause chemical pneumonitis if aspirated into the lung, and those that are volatile can cause acute CNS effects and/or ocular and respiratory irritation at exposure levels exceeding occupational recommendations. Otherwise, there are few toxicologically important effects. The exceptions, n-hexane and naphthalene, have unique toxicological properties, and those solvents containing constituents for which classification is required under the Globally Harmonized System (GHS) are differentiated by the substance names. Toxicological information from studies of representative substances was used to fulfill REACH registration requirements and to satisfy the needs of the OECD High Production Volume (HPV) initiative. As shown in the examples provided, the hazard characterization data can be used for hazard classification and for occupational exposure limit recommendations.

Clumped isotope thermometry in deeply buried sedimentary carbonates: The effects of bond reordering and recrystallization

Abstract: We utilize carbonate clumped isotope thermometry to explore the diagenetic and thermal histories of exhumed brachiopods, crinoids, cements, and host rock in the Permian Palmarito Formation, Venezuela, and the Carboniferous Bird Spring Formation, Nevada, USA. Carbonate components in the Palmarito Formation, buried to ∼4 km depth, yield statistically indistinguishable clumped isotope temperatures [ T (Δ47)] ranging from 86 to 122 °C. Clumped isotope temperatures of components in the more deeply buried Bird Spring Formation (>5 km) range from ∼100 to 165 °C and differ by component type, with brachiopods and pore-filling cements yielding the highest T (Δ47) (mean = 153 and 141 °C, respectively) and crinoids and host rock yielding significantly cooler T (Δ47) (mean = 103 and 114 °C). New high-resolution thermal histories are coupled with kinetic models to predict the extent of solid-state C-O bond reordering during burial and exhumation for both sites. Application of these models, termed “THRMs” (thermal history reordering models), suggests that brachiopods in the Palmarito Formation experienced partial bond reordering without complete equilibration of clumped isotopes at maximum burial temperature. In contrast, clumped isotope bonds of brachiopods from the Bird Spring Formation completely equilibrated at maximum burial temperature, and now reflect blocking temperatures achieved during cooling. The 40–50-°C-cooler clumped isotope temperatures measured in Bird Spring Formation crinoids and host rock can be explained by recrystallization and cementation during shallow burial combined with a greater inherent resistance to solid-state reordering than brachiopods.

Sevier belt exhumation in central Utah constrained from complex zircon (U-Th)/He data sets: Radiation damage and He inheritance effects on partially reset detrital zircons

Abstract: Thermochronologic dates of partially reset detrital grains are often difficult to interpret because of the potential for variation in inherited predepositional dates and kinetic behaviors of grains from diverse source terrains. In this study, we present several examples of complex detrital zircon (U-Th)/He date distributions from sedimentary rocks that have been heated to temperatures in or near the zircon He partial retention zone, leading to several types of date-eU correlations caused by variations in predepositional inherited age and radiation-damage–induced He diffusion kinetics. These examples are from three subvertical transects in mountain ranges in central Utah: the Wasatch Range near Provo, Utah, the Oquirrh Mountains, and the Stansbury Mountains. Each range lies in the hanging wall of one of three major thrust sheets that compose part of the Charleston-Nebo salient, a segment of the Cretaceous Sevier fold-and-thrust belt. Zircon grains from two of these transects (the Stansbury and Oquirrh Mountains) show large date variations that can be at least partially understood with a radiation-damage–based model for He diffusion in zircon. We combine the output from this model with a new approach for understanding partially reset data sets that relies upon the concept of an “inheritance envelope.” The transect from the Wasatch Range is relatively simple and does not require an inheritance-based interpretation. We document a pulse of 5 km of exhumation in this range at ca. 100 Ma. Time-temperature ( t - T ) constraints from inheritance envelopes in the Oquirrh Mountains transect suggest a pulse of exhumation beginning at either 110 or 100 Ma. Finally, for the Stansbury transect, the inheritance envelope approach yields inconclusive results; some aspects of the model generate inheritance envelopes that match the measured data set, whereas others do not. Despite their complexity, the t - T histories for these nonideal data sets represent some of the only in situ constraints on the timing of Cretaceous exhumation of Sevier-style deformation in the U.S. Cordillera. In the case of the Oquirrh and Wasatch Range data sets, these direct measurements of thrust sheet t - T histories offer some insight into the evolution of the Sevier fold-and-thrust belt of central Utah.

New High- and Low-Temperature Phase Changes of ZIF-7: Elucidation and Prediction of the Thermodynamics of Transitions

Abstract: We have found that the 3D zeolitic imidazolate framework ZIF-7 exhibits far more complex behavior in response to the adsorption of guest molecules and changes in temperature than previously thought. We believe that this arises from the existence of different polymorphs and different types of adsorption sites. We report that ZIF-7 undergoes a displacive, nondestructive phase change upon heating to above ∼700 °C in vacuum, or to ∼500 °C in CO2 or N2. This is the first example of a temperature-driven phase change in 3D ZIF frameworks. We predicted the occurrence of the high-temperature transition on the basis of thermodynamic arguments and analyses of the solid free-energy differences obtained from CO2 and n-butane adsorption isotherms. In addition, we found that ZIF-7 exhibits complex behavior in response to the adsorption of CO2 manifesting in double transitions on adsorption isotherms and a doubling of the adsorption capacity. We report adsorption microcalorimetry, molecular simulations, and detailed XRD ...

Binder Effects in SiO2- and Al2O3-Bound Zeolite ZSM-5-Based Extrudates as Studied by Microspectroscopy

Abstract: Microspectroscopic methods were explored to investigate binder effects occurring in ZSM-5-containing SiO2- and Al2O3-bound millimetre-sized extrudates. Using thiophene as a selective probe for Bronsted acidity, coupled with time-resolved in situ UV/Vis and confocal fluorescence microspectroscopy, variations in reactivity and selectivity between the two distinct binder types were established. It was found that aluminium migration occurs in ZSM-5-containing Al2O3-bound extrudates, forming additional Bronsted acid sites. These sites strongly influence the oligomer selectivity, favouring the formation of thiol-like species (i.e., ring-opened species) in contrast to higher oligomers, predominantly formed on SiO2-bound ZSM-5-containing extrudates. Not only were the location and distribution of these oligomers visualised by 3 D analysis, it was also observed that more conjugated species appeared to grow off the surface of the zeolite ZSM-5 crystals (containing less conjugated species) into the surrounding binder material. Furthermore, a higher binder content resulted in an increasing overall reactivity owing to the greater number of stored thiophene monomers available per Bronsted acid site.