434 research outputs found
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Linkages between aromatic structures in the Argonne Premium Coal Samples
The objective of this study is to elucidate the nature of the important linkages between aromatic clusters and variations of these links with coal rank. From studies using methods such as NMR and mass spectrometry, the authors have considerable information on the size and types of aromatic clusters in the Argonne coals. In this study, extracts, model polymers, extracted coals, and modified coals are examined by temperature resolved high resolution mass spectrometry. There is evidence that strong bond cleavage may be very important for volatile release in pyrolysis of higher rank coals
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Characterization of coals, other kerogens, and their extracts by thermal mass spectrometry
The objective of this study is to elucidate the nature of the medium size molecules derived from coals by a succession of stronger extraction conditions. The Argonne Premium Coals have been extracted with pyridine, binary solvents and with KOH/ethylene glycol at 250{degrees}C. Thermal desorption and pyrolysis mass spectrometry were the major approaches chosen to provide detailed information on structure and heteroatom composition. Soft ionization techniques including desorption chemical ionization (DCI) and fast atom bombardment (FAB) were combined with high resolution and tandem MS techniques. This paper will focus on the comparison of the nature of the unextracted coals, the pyridine extract and the extracted coal residue. With this approach the desorption-pyrolysis yields of the extracts and residues combined were greater than the yields from the starting material. Although molecule weight distributions had a monitor dependence on rank, the nature of molecules with the same nominal mass varied greatly with rank
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Structural elucidation of Argonne premium coals: Molecular weights, heteroatom distributions and linkages between clusters
The objective of this study is to create a statistically accurate picture of important structural features for a group of coals representing a broad rank range. Mass spectrometric techniques are used to study coals, coal extracts and chemically modified coals and extracts. Laser desorption mass spectrometry is used to determine molecular weight distributions. Desorption chemical ionization high resolution mass spectrometry provides detailed molecular information on compound classes of molecules is obtained using tandem mass spectrometry. These results are correlated with other direct studies on these samples such as solid NMR, XPS and X-ray absorption spectroscopy. From the complex sets of data, several general trends are emerging especially for heteroatom containing species. From a statistical point of view, heteroatoms must play important roles in the reactivity of all coals. Direct characterization of sulfur containing species in the Argonne coals has been reported from XANES analysis. Indirect methods used include: TG-FTIR and HRMS which rely on thermal desorption and pyrolysis to vaporize the samples. Both XANES and XPS data on nitrogen has been reported, but at this time, the XPS information is probably more reliable. Results from HRMS are discussed in this paper. Most other information on nitrogen is limited to analysis of liquefaction products. However, nitrogen can be important in influencing characteristics of coal liquids and as a source of NO{sub x}`s in coal combustion
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Molecular size and structure in pyridine extracts of upper Freeport coal as separated by M41S sieving.
The determination of the structure of coal has long been of interest due to its crucial importance in research on reactivity and processing. However, the chemically and physically heterogeneous nature of coals makes determination of the chemical nature of even the building blocks complicated, since the molecular structure and molecular weight distribution are not dependent on a single molecule or repeat unit as in technical polymers or biopolymers, but on a complex mixture of molecules and potential connections between them which may vary among coals. Coal extracts have long been used to obtain coal material in solution form that can readily be characterized. However, what part of the total coal structure these extracts represent is not completely known. Pyridine has been a particularly good solvent for coal; for example, the extractability of Upper Freeport has been shown to be as high 30%. Although pyridine extracts of coal have been referred to as solutions, there is good evidence that they are not truly solvated, but are dispersions which are polydisperse in particle size. The particle sizes may span the size range from clusters of small molecules (a few {angstrom}) to extended clusters of large particles (a few hundred {angstrom}), not unlike micelles, where the functional groups of molecules which interact favorably with the pyridine solvent lie at the surface of particles. Mesoporous silicates are attractive candidates for separations due to their high surface areas and porous nature. MCM-41 is one member of a new family of highly uniform mesoporous silicate materials introduced by Mobil, whose pore size can be accurately controlled in the range 1.5{angstrom}-10 nm. This recently discovered M41S class of zeolites should be useful to effect size separation, due to their large pore sizes and thus their potential for the separation of larger compounds or clusters. True molecular sieving on the size range of molecular and cluster types found in coal solutions should be possible with M41S materials by tuning the pore size. We have synthesized a mesoporous silicate material with a surface area of approximately 1100 m{sup 2}/g and pore sizes of approximately 25 {angstrom} and 33 {angstrom}. The results of a study on the ability of this mesoporous materials (M41S) to be used as stationary phases for separations of coal complexes in pyridine is the subject of this paper
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Small angle neutron and X-ray scattering studies of carbons prepared using inorganic templates
Small angle neutron (SANS) and X-ray (SAXS) scattering analyses of carbons derived from organic-loaded inorganic template materials, used as anodes in lithium ion cells, have been performed. Two clays were used as templates to load the organic precursors, pillared montmorrillonite (PILC), a layered silicate clay whose sheets have been permanently propped open by sets of thermally stable molecular props, and sepiolite, a natural channeled clay. Five different organic precursors were used to load the PILC: pyrene, styrene, pyrene/trioxane copolymer, ethylene and propylene, whereas only propylene and ethylene were used to load sepiolite. Pyrolysis took place at 700{degrees}C under nitrogen. Values such as hole radius, fractal dimension, cutoff length and density of the final carbons will be compared as a function of the clay and carbon precursors
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Novel carbonaceous materials for lithium secondary batteries
Carbonaceous materials have been synthesized using pillared clays (PILCs) as templates. The PILC was loaded with organic materials such as pyrene in the liquid and vapor phase, styrene in the vapor phase, trioxane, ethylene and propylene. The samples were then pyrolyzed at 700 C in an inert atmosphere, followed by dissolution of the inorganic template by conventional demineralization methods. X-ray powder diffraction of the carbons showed broad d{sub 002} peaks in the diffraction pattern, indicative of a disordered or turbostratic system. N{sub 2} BET surface areas of the carbonaceous materials range from 10 to 100 m{sup 2}/g. There is some microporosity (r < 1 nm) in the highest surface area carbons. Most of the surface area, however, comes from a mixture of micro and mesopores with radii of 2--5 nm. Electrochemical studies were performed on these carbons. Button cells were fabricated with capacity- limiting carbon pellets electrodes as the cathode a/nd metallic lithium foil as the anode. Large reversible capacities (up to 850 mAh/g) were achieved for most of the samples. The irreversible capacity loss was less than 180 mAh/g after the first cycle, suggesting that these types of carbon materials are very stable to lithium insertion and de-insertion reactions
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Anomalous small angle x-ray scattering study of layered silicate clays containing Ni(II) and Er(III)
These studies concern the synthesis of heterogeneous catalysts and the incorporation of heavy metals in trapping media. The Ni(II) containing clays were synthesized at 200{degree}C whereas those containing Er(III) were ion-exchanged natural clays. For the first system, ASAXS data were measured at 5 different energies near the K{alpha} edge of Ni at three different reaction times: unreacted, 4 hrs, and 15 hrs, when the crystallization is essentially complete. The data for the unreacted sample showed no correlations for a lamellar particle, while that reacted for 4 hrs indicated the evolution of lamella, and the crystallized sample (15 hrs) exhibits much larger lamellar correlations. Systematic variations are seen in the data for the 4 hr and 15 hr samples that are due to the anomalous scattering from the ordered Ni atoms in the layered silicates. The erbium study provides the first scattering measurements of heavy metal ion salvation and migration in clays, which has implications for both catalysis and environmental issues. Systematic energy-dependent variations in the signals near the L{sub III} edge of Er are observed for the hydrated sample, but not for the ``dry,`` as-prepared sample
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Model compound study of the pathways for aromatic hydrocarbon formation in soot.
To explore the mechanisms for formation of aromatic hydrocarbons as precursors to soot, a model system using combustion of biphenyl in a fuel rich flame is studied. The soots acquired at three different temperatures are solvent extracted and the extract characterized by both GCMS and high resolution mass spectrometry. A description of the NMR results for the whole soots has been published (1). The production of most products could be rationalized from the coupling of biphenyls and subsequent aromatic species and the addition of acetylenes to existing aromatic molecules. Early work by Badger on pyrolysis of hydrocarbons is used in developing these schemes (2). The reaction schemes to produce larger aromatic hydrocarbons will be discussed. Richter and Howard have discussed in detail potential reaction mechanisms in the formation of aromatics as precursors to soot (3)
Clinician Perspectives of an Intensive Comprehensive Aphasia Program
Background: Intensive comprehensive aphasia programs (ICAPs) have increased in number in recent years in the United States and abroad. Objective: To describe the experiences of clinicians working in an ICAP. Methods: A phenomenological approach was taken. Seven clinicians from 3 ICAPs were interviewed in person or on the phone. Their interviews were transcribed and coded for themes relating to their experiences. Results: Clinicians described 3 major themes. The first theme related to the intensity component of the ICAP that allowed clinicians to provide in-depth treatment and gave them a different perspective with regard to providing treatment and the potential impact on the person with aphasia. The second theme of rewards for the clinicians included learning and support, seeing progress, and developing relationships with their clients and family members. Third, challenges were noted, including the time involved in learning new therapy techniques, patient characteristics such as chronicity of the aphasia, and the difficulty of returning to work in typical clinical settings after having experienced an ICAP. Conclusions: Although there is a potential for bias with the small sample size, this pilot study gives insight into the clinician perspective of what makes working in an ICAP both worthwhile and challenging
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