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Separation of Fischer-Tropsch Wax from Catalyst by Supercritical Extraction

Description: The proposed process of using supercritical fluid extraction in conjunction with the Fischer-Tropsch slurry bubble column reactor has been examined using the ASPEN Plus simulator by the research group at North Carolina State University. Qualitative results have been obtained for varying the following process parameters: solvent-to-wax ratio, solvent type (pentane or hexane), extraction temperature and pressure, and recovery unit temperature and pressure. The region of retrograde behavior was determined for pentane and hexane. Initial results show hexane to be the superior solvent; compared to pentane, hexane requires lower quantities of solvent makeup (the amount of solvent which needs to be added to account for solvent that cannot be recycled), and also results in a lower average molecular weight of slurry in the reactor. Studies indicate that increasing the extraction temperature, extraction pressure, recovery temperature, or solvent to wax ratio decreases the amount solvent makeup required. Decreasing the recovery pressure was found to decrease the makeup flowrate.
Date: January 31, 1997
Creator: Joyce, P.C. & Thies, M.C.
Partner: UNT Libraries Government Documents Department

Pentan isomers compound flame front structure

Description: The fuels (hexane, pentane, diethyl ether) and conditions investigated in this study are relevant to engine knock in spark- ignition engines. A review is provided of the field of low temperature hydrocarbon oxidation. Studies were made of radical and stable intermediate distribution in the front of cool flames: Maximum concentrations of H atoms and peroxy radicals were observed in the luminous zone of the cool flame front. Peroxy radicals appear before the luminous zone at 430 K due to diffusion. H atoms were found in cool flames of butane and hexane. H atoms diffuses from the luminous zone to the side of the fresh mixture, and they penetrate into the fresh mixture to a small depth. Extension of action sphear of peroxy radicals in the fresh mixture is much greater than that of H atoms due to their small activity and high concentrations.
Date: August 13, 1995
Creator: Mansurov, Z. A.; Mironenko, A. W.; Bodikov, D. U. & Rachmetkaliev, K. N.
Partner: UNT Libraries Government Documents Department

Assessing and Managing the Risks of Fuel Compounds: Ethanol Case Study

Description: We have implemented a suite of chemical transport and fate models that provide diagnostic information about the behavior of ethanol (denoted EtOH) and other fuel-related chemicals released to the environment. Our principal focus is on the impacts to water resources, as this has been one of the key issues facing the introduction of new fuels and additives. We present analyses comparing the transport and fate of EtOH, methyl tertiary butyl ether (MTBE), and 2,2,4 trimethyl pentane (TMP) for the following cases (1) discharges to stratified lakes, subsurface release in a surficial soil, (3) cross-media transfer from air to ground water, and (4) fate in a regional landscape. These compounds have significantly different properties that directly influence their behavior in the environment. EtOH, for example, has a low Henry's law constant, which means that it preferentially partitions to the water phase instead of air. An advantageous characteristic of EtOH is its rapid biodegradation rate in water; unlike MTBE or TMP, which degrade slowly. As a consequence, EtOH does not pose a significant risk to water resources. Preliminary health-protective limits for EtOH in drinking water suggest that routine releases to the environment will not result in levels that threaten human health.
Date: February 4, 2002
Creator: Layton, D.W. & Rice, D.W.
Partner: UNT Libraries Government Documents Department

Solvent Extraction of Chemical Attribution Signature Compounds from Painted Wall Board: Final Report

Description: This report summarizes work that developed a robust solvent extraction procedure for recovery of chemical attribution signature (CAS) compound dimethyl methyl phosphonate (DMMP) (as well as diethyl methyl phosphonate (DEMP), diethyl methyl phosphonothioate (DEMPT), and diisopropyl methyl phosphonate (DIMP)) from painted wall board (PWB), which was selected previously as the exposed media by the chemical attribution scientific working group (CASWG). An accelerated solvent extraction approach was examined to determine the most effective method of extraction from PWB. Three different solvent systems were examined, which varied in solvent strength and polarity (i.e., 1:1 dichloromethane : acetone,100% methanol, and 1% isopropanol in pentane) with a 1:1 methylene chloride : acetone mixture having the most robust and consistent extraction for four original target organophosphorus compounds. The optimum extraction solvent was determined based on the extraction efficiency of the target analytes from spiked painted wallboard as determined by gas chromatography x gas chromatography mass spectrometry (GCxGC-MS) analysis of the extract. An average extraction efficiency of approximately 60% was obtained for these four compounds. The extraction approach was further demonstrated by extracting and detecting the chemical impurities present in neat DMMP that was vapor-deposited onto painted wallboard tickets.
Date: October 29, 2009
Creator: Wahl, Jon H. & Colburn, Heather A.
Partner: UNT Libraries Government Documents Department

Molecular control of electron and hole transfer processes: Theory and applications

Description: Recent decades have seen remarkable advances in microscopic understanding of electron transfer (ET) processes in widely ranging contexts, including solid-state, liquid solution, and complex biological assemblies. The primary goal of this chapter is to report recent advances in the modeling, calculation, and analysis of electronic coupling in complex molecular aggregates, thereby allowing an assessment of current progress toward the goal of molecular-level control and design. The control of electron transfer kinetics (i.e., enhancing desired processes, while inhibiting others) involves, of course, system energetics (especially activation and reorganization energies) as well as electronic coupling, which is most directly relevant only after the system has reached the appropriate point (or region) along the reaction coordinate. Nevertheless, to focus the discussion in this chapter, the authors will consider such energetics, and the associated molecular and solvent coordinates which control then, only to the extent that they bear on the analysis of the electronic coupling. In the following sections they first discuss the formulation of basic ET models, including the definition of initial and final states, the role of orbitals and 1-particle models in a many-electron context, the utility of various effective Hamiltonians, and the role of vibronic as well as purely electronic effects. With these theoretical tools in hand, they then examine very recent applications to complex molecular systems using the techniques of computational quantum chemistry, followed by detailed analysis of the numerical results. They then conclude with some comments regarding the current ``state of the art`` and remaining challenges.
Date: February 1, 1996
Creator: Newton, M.D. & Cave, R.J.
Partner: UNT Libraries Government Documents Department

Fischer Tropsch synthesis in supercritical fluids. Quarterly technical progress report, April 1, 1995--June 30, 1995

Description: Our objective for this quarter was to study the effect of co-feeding a 1-olefin on the Ruhrchemie catalyst activity and selectivity, during-both conventional Fisher-Tropsch synthesis (FTS) and FTS under supercritical conditions. We used propane as the supercritical fluid and 1-dodecene (1-C{sub 12}H{sub 24}) in this test. Motivation for this study was the work of Fujimoto and co-workers who reported that suppression of methane and enhancement of high molecular weight hydrocarbons selectivities occurs with co-feeding of 1-olefins (1-heptene, 1-tetradecene, or 1-hexadecene) during FTS under supercritical conditions, but not during the conventional FTS (Co-La catalyst supported on silica in supercritical n-pentane).The diffusion coefficients of products in supercritical fluids is discussed.
Date: May 1, 1996
Creator: Akgerman, A. & Bukur, D.B.
Partner: UNT Libraries Government Documents Department

Extents of alkane combustion during rapid compression leading to single and two stage ignition

Description: Extents of reactant consumption have been measured during the course of spontaneous ignition following rapid compression of N-pentane and N-heptane and also of PRF 60 (N-heptane = i-octane, 2.2.4 trimethylpentane) in stoichiometric mixtures with air. Compressed gas temperatures of 720-750 K and 845-875 K were studied at reactant densities of 131 mol m{sup minus 3}. At the lower gas temperature there was no evidence of reactant consumption during the course of the compression stroke. Two-stage ignition occurred at these temperatures, but only modest proportions of n-pentane were consumed during the first stage (< 15%) whereas about 40% of proportions of n- heptane reacted under the same conditions. At the higher compressed gas temperature the oxidation of n-pentane began only after the piston had stopped, whereas more than 30% of the n-heptane had already been consumed in the final stage of the compression stroke. The behavior of the PRF 60 mixture differed somewhat from that of N- pentane despite the similarly of the research octane numbers. Although there was a preferential oxidation of n-heptane at T{sub c} = 850K, which persisted throughout the early development of spontaneous ignition during the post-compression period, oxidation of both components of the PRF 60 mixture began before the piston had stopped. Numerical simulations of the spontaneous ignition under conditions resembling those of the rapid compression experiments show that the predicted reactivity from detailed kinetics are consistent with the observed features. Insights into the kinetic interactions that give rise to the relative reactivities of the primary reference fuel components are established
Date: February 1, 1996
Creator: Cox, A.; Griffiths, J.F.; Mohamed, C.; Curran, H.; Pitz, W.J. & Westbrook, C.K.
Partner: UNT Libraries Government Documents Department

Chemical kinetic modelling of hydrocarbon ignition

Description: Chemical kinetic modeling of hydrocarbon ignition is discussed with reference to a range of experimental configurations, including shock tubes, detonations, pulse combustors, static reactors, stirred reactors and internal combustion engines. Important conditions of temperature, pressure or other factors are examined to determine the main chemical reaction sequences responsible for chain branching and ignition, and kinetic factors which can alter the rate of ignition are identified. Hydrocarbon ignition usually involves complex interactions between physical and chemical factors, and it therefore is a suitable and often productive subject for computer simulations. In most of the studies to be discussed below, the focus of the attention is placed on the chemical features of the system. The other physical parts of each application are generally included in the form of initial or boundary conditions to the chemical kinetic parts of the problem, as appropriate for each type of application being addressed.
Date: August 25, 1995
Creator: Westbrook, C.K.; Pitz, W.J.; Curran, H.J.; Gaffuri, P. & Marinov, N.M.
Partner: UNT Libraries Government Documents Department

Vapor space characterization of waste Tank 241-BY-106 (in situ): Results from samples collected on 5/4/94 and 5/5/94

Description: This report describes inorganic and organic analyses results from in situ samples obtained from the headspace of the Hanford waste storage Tank 241-BY-106 (referred to as Tank BY-106). The results described here were obtained to support safety and toxicological evaluations. A summary of the results for inorganic and organic analytes is listed in Table 1. Detailed descriptions of the results appear in the text. Quantitative results were obtained for the inorganic compounds NH{sub 3}, NO{sub 2}, NO, HCN, and H{sub 2}O. Sampling for sulfur oxides was not requested. Organic compounds were also quantitatively determined. Twenty-three organic tentatively identified compounds (TICS) were observed above the detection limit of (ca.) 10 ppbv, but standards for most of these were not available at the time of analysis, and the reported concentrations are semiquantitative estimates. In addition, the authors looked for the 41 standard TO-14 analytes. Of these, only a few were observed above the 2-ppbv detection limit. The 10 organic analytes with the highest estimated concentrations are listed in Table 1. The 10 analytes account for approximately 64% of the total organic components in Tank BY-106. Tank BY-106 is on the Ferrocyanide Watch List.
Date: April 1, 1995
Creator: Clauss, T.W.; Ligotke, M.W.; Pool, K.H.; Lucke, R.B.; McVeety, B.D.; Sharma, A.K. et al.
Partner: UNT Libraries Government Documents Department

Sensing liquid properties with shear-mode resonator sensors

Description: Liquid properties are measured from the changes they induce in the resonant frequency and damping of thicknessshear mode quartz resonators. A smooth-surfaced resonator viscously entrains the contacting fluid and responds to the density-viscosity product. Separation of density and viscosity is accomplished using two devices: one with a smooth surface and one with a corrugated surface that traps fluid. By observing the difference in stored and dissipated energies in the contacting fluid, its non-Newtonian characteristics can also be determined.
Date: June 1, 1995
Creator: Martin, S.J.; Cernosek, R.W. & Spates, J.J.
Partner: UNT Libraries Government Documents Department


Description: The molecular structure and microstructure of a suite of fine particulate matter (PM) samples produced by the combustion of residual fuel oil and diesel fuel were investigated by an array of analytical techniques. Some of the more important results are summarized below. Diesel PM (DPM): A small diesel engine test facility was used to generate a suite of diesel PM samples from different fuels under engine load and idle conditions. C XANES, {sup 13}C NMR, XRD, and TGA were in accord that the samples produced under engine load conditions contained more graphitic material than those produced under idle conditions, which contained a larger amount of unburned diesel fuel and lubricating oil. The difference was enhanced by the addition of 5% of oxygenated compounds to the reference fuel. Scanning transmission x-ray micro-spectroscopy (STXM) was able to distinguish particulate regions rich in C=C bonds from regions rich in C-H bonds with a resolution of {approx}50 nm. The former are representative of more graphitic regions and the latter of regions rich in unburned fuel and oil. The dominant microstructure observed by SEM and TEM consisted of complex chain-like structures of PM globules {approx}20-100 nm in mean diameter, with a high fractal dimension. High resolution TEM revealed that the graphitic part of the diesel soot consisted of onion-like structures made up of graphene layers. Typically 3-10 graphene layers make up the ''onion rings'', with the layer spacing decreasing as the number of layers increases. ROFA PM: Residual oil fly ash (ROFA) PM has been analyzed by a new approach that combines XAFS spectroscopy with selective leaching procedures. ROFA PM{sub 2.5} and PM{sub 2.5+} produced in combustion facilities at the U.S. EPA National Risk Management Research Laboratory (NRML) were analyzed by XAFS before and after leaching with water, acid (1N HCl), and pentane. Both water ...
Date: July 31, 2003
Creator: Huffman, Gerald P.; Huggins, Frank E.; Shah, Naresh; Braun, Artur; Chen, Yuanzhi; Robertson, J. David et al.
Partner: UNT Libraries Government Documents Department

Final Technical Report: Effects of Impurities on Fuel Cell Performance and Durability

Description: The main objectives of this project were to investigate the effect of a series of potential impurities on fuel cell operation and on the particular components of the fuel cell MEA, to propose (where possible) mechanism(s) by which these impurities affected fuel cell performance, and to suggest strategies for minimizing these impurity effects. The negative effect on Pt/C was to decrease hydrogen surface coverage and hydrogen activation at fuel cell conditions. The negative effect on Nafion components was to decrease proton conductivity, primarily by replacing/reacting with the protons on the Bronsted acid sites of the Nafion. Even though already well known as fuel cell poisons, the effects of CO and NH3 were studied in great detail early on in the project in order to develop methodology for evaluating poisoning effects in general, to help establish reproducibility of results among a number of laboratories in the U.S. investigating impurity effects, and to help establish lower limit standards for impurities during hydrogen production for fuel cell utilization. New methodologies developed included (1) a means to measure hydrogen surface concentration on the Pt catalyst (HDSAP) before and after exposure to impurities, (2) a way to predict conductivity of a Nafion membranes exposed to impurities using a characteristic acid catalyzed reaction (methanol esterification of acetic acid), and, more importantly, (3) application of the latter technique to predict conductivity on Nafion in the catalyst layer of the MEA. H2-D2 exchange was found to be suitable for predicting hydrogen activation of Pt catalysts. The Nafion (ca. 30 wt%) on the Pt/C catalyst resides primarily on the external surface of the C support where it blocks significant numbers of micropores, but only partially blocks the pore openings of the meso- and macro-pores wherein lie the small Pt particles (crystallites). For this reason, even with 30 wt% Nafion ...
Date: November 11, 2011
Creator: Goodwin, James G., Jr.; Colon-Mercado, Hector; Hongsirikarn, Kitiya & Zhang, Jack Z.
Partner: UNT Libraries Government Documents Department