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Studies of transition states and radicals by negative ion photodetachment

Description: Negative ion photodetachment is a versatile tool for the production and study of transient neutral species such as reaction intermediates and free radicals. Photodetachment of the stable XHY{sup {minus}} anion provides a direct spectroscopic probe of the transition state region of the potential energy surface for the neutral hydrogen transfer reaction X + HY {yields} XH + Y, where X and Y are halogen atoms. The technique is especially sensitive to resonances, which occur at a specific energy, but the spectra also show features due to direct scattering. We have used collinear adiabatic simulations of the photoelectron spectra to evaluate trail potential energy surfaces for the biomolecular reactions and have extended the adiabatic approach to three dimensions and used it to evaluate empirical potential energy surfaces for the I + Hl and Br + HI reactions. In addition, we have derived an empirical, collinear potential energy surface for the Br + HBr reaction that reproduces our experimental results and have extended this surface to three dimensions. Photodetachment of a negative ion can be also used to study neutral free radicals. We have studied the vibrational and electronic spectroscopy of CH{sub 2}NO{sub 2} by photoelectron spectroscopy of CH{sub 2}NO{sub 2}{sup {minus}}, determining the electron affinity of CH{sub 2}NO{sub 2}, gaining insight on the bonding of the {sup 2}B{sub 1} ground state and observing the {sup 2}A{sub 2} excited state for the first time. Negative ion photodetachment also provides a novel and versatile source of mass-selected, jet-cooled free radicals. We have studied the photodissociation of CH{sub 2}NO{sub 2} at 270, 235, and 208 nm, obtaining information on the dissociation products by measuring the kinetic energy release in the photodissociation.
Date: December 1, 1991
Creator: Metz, R. B.
Partner: UNT Libraries Government Documents Department

Diosmacycloalkanes as models for the formation of hydrocarbons from surface methylenes

Description: We are making progress on our investigation of the mechanism of olefin exchange with Os{sub 2}(C{sub 2}H{sub 4})(CO){sub 8}. We are probing this system by kinetic study of the reaction of Os{sub 2}(C{sub 2}H{sub 4})(CO){sub 8} with butyl acrylate (BA) under various pressures of ethylene.
Date: May 1, 1992
Creator: Norton, J.R.
Partner: UNT Libraries Government Documents Department

One carbon metabolism in anaerobic bacteria: Regulation of carbon and electron flow during organic acid production

Description: This reporting period, progress is reported on the following: metabolic pathway of solvent production in B. methylotrophicum; the biochemical mechanism for metabolic regulation of the succinate fermentation; models to understand the physiobiochemical function of formate metabolism in anaerobes and; models for understanding the influence of low pH on one carbon metabolism. (CBS)
Date: January 1, 1992
Creator: Zeikus, J.G. & Jain, M.K.
Partner: UNT Libraries Government Documents Department

Variational transition state theory calculations of tunneling effects on concerted hydrogen motion in water clusters and formaldehyde/water clusters

Description: The direct participation of water molecules in aqueous phase reaction processes has been postulated to occur via both single-step mechanisms as well as concerted hydrogen atom or proton shifts. In the present work, simple prototypes of concerted hydrogen atom transfer processes are examined for small hydrogen-bonded water clusters -- cyclic trimers and tetramers -- and hydrogen-bonded clusters of formaldehyde with one and two water molecules. Rate constants for the rearrangement processes are computed using variational transition state theory, accounting for quantum mechanical tunneling effects by semiclassical ground-state adiabatic transmission coefficients. The variational transition state theory calculations directly utilize selected information about the potential energy surface along the minimum energy path as parameters of the reaction path Hamiltonian. The potential energy information is obtained from ab ignite electronic structure calculations with an empirical bond additivity correction (the BAC-MP4 method). Tunneling is found to be very important for these concerted rearrangement processes -- the semiclassical ground-state adiabatic transmission coefficients are estimated to be as high as four order of magnitude at room temperature. Effects of the size of the cluster (number of water molecules in the cyclic complex) are also dramatic -- addition of a water molecule is seen to change the calculated rates by orders of magnitude. 36 refs., 10 figs.
Date: August 1, 1990
Creator: Garrett, B.C. (Pacific Northwest Lab., Richland, WA (USA)) & Melius, C.F. (Sandia National Labs., Livermore, CA (USA))
Partner: UNT Libraries Government Documents Department

The role of the resid solvent in co-processing with finely divided catalysts

Description: Goal this quarter was to evaluate the reactivity of an anthracene (H-deficient aromatic) and perhydropyrene (H-rich cycloalkane) system to determine if this system is the one desired for the parametric evaluation. Idea was to determine if hydrogen could be transferred from cycloalkane to aromatic in a hydrogen atmosphere, which is always present in coprocessing. This quarter's work established procedures for performing thermal and catalytic reactions without a solvent, and for analysis of reaction products. Individual thermal and catalytic reactions using anthracene and perhydropyrene were the primary reactions performed this quarter.
Date: January 1, 1992
Creator: Curtis, C.W.
Partner: UNT Libraries Government Documents Department

Photoinitiated electron transfer in multichromophoric species: Synthetic tetrads and pentads featuring diquinone moieties

Description: This project involves the design, synthesis and photophysical study of complex molecular systems engineered to achieve long lived charge separated states by a biomimetic, photoinitiated multistep electron transfer process. The use of these artificial systems to investigate different electron and energy transfer strategies will allow the evolution of more efficient molecular devices for the gathering of light energy and its transformation into chemical potential energy. The three major aspects of the work emphasized in the initial proposal are: design and synthesis of molecular devices incorporating new quinone moieties, synthesis and spectroscopic studies of molecular tetrads and pentads featuring modified porphyrin-diquinone linkages, and new photochemical and photophysical investigations of tetrads and pentads, including the development of methods for harvesting the energy stored in long-lived charge separated states.
Date: April 30, 1992
Partner: UNT Libraries Government Documents Department

Organometallic chemistry of bimetallic compounds

Description: This report consists of six sections: heterobimetallic dihydrides, early-late transition metal heterobimetallic compounds, amphiphilic carbene complexes and hydroxycarbene complexes, diiron compounds with bridging hydrocarbon ligands, diphosphine chelates with natural bite angles near 120 degrees, and synthesis and reactions of M=M compounds. (WET)
Date: July 1, 1991
Creator: Casey, C.P.
Partner: UNT Libraries Government Documents Department

Magnetic resonance studies of photo-induced electron transfer reactions. Final report, June 1, 1990--May 31, 1993

Description: Fourier Transform Electron Paramagnetic Resonance (FT EPR) is useful in study of photochemical reactions: a microwave pulse rotates the electron spin magnetization vector from z (magnetic field) into xy plane ({pi}/2 pulse); the time evolution of magnetization in xy plane, the free induction decay (FID), is sampled. Fourier transform of FID gives the frequency domain EPR spectrum of the free radicals, and the method is ideal for time-resolved studies of free radicals produced by pulsed-laser excitation. Investigations of electron transfer reactions focused on porphyrin (donor) - quinone (acceptor) systems. First, two hydrogen abstraction reactions were studied with FT EPR: photoreduction of acetone with 2-propanol, yielding the acetone ketyl radical, and the reaction of 2-propanol with t-butoxy radicals. Then, the FT EPR study of benzoquinone or duroquinone anion radicals generated by pulsed-laser induced electron transfer from zinc tetraphenylporphyrin (ZnTPP) or tetrasulfonated Zn(TPP), was carried out in homogeneous solution, micellar solutions, and silica gel. Finally, FT EPR was used to study electron transfer quenching of triplet C{sub 60} by electron donors.
Date: November 1, 1992
Creator: van Willigen, H.
Partner: UNT Libraries Government Documents Department

The role of the resid solvent in co-processing with finely divided catalysts. Quarterly report, January--March 1993

Description: The overall objective of this project is to evaluate the role of the resid in coprocessing. The primary purpose of this initial work was to establish under thermal and catalytic reaction conditions whether hydrogen transfer occurred between cycloalkane type structures that are present in resids and aromatics that are present in coal and liquefied coal. The research this quarter focused upon evaluating different reaction systems for performing model donor and model acceptor studies. The first system that was evaluated involved anthracene (ANT) as the model acceptor. Previous results had shown that ANT did not convert substantially in a thermal reaction at 380{degrees}C (Wang 1992); however, more was converted (about 50%) at 440{degrees}C. The results from the reactions performed last quarter indicated that substantial hydrogenation of ANT occurred thermally at 440{degrees}C; more than had been observed previously. The reactors that were used, though, had contained substantial amounts of catalysts prior to the performance of the thermal reactions. Hence, the passivity of the reactors was questioned and new reactors were fabricated. Some of the reactions using ANT were performed again and are reported herein. The second part of the work performed this quarter was to evaluate hydrogen transfer from the cycloalkane, perhydropyrene (PHP), to the aromatic phenanthrene (PHEN). Reactions were performed at a 1:1 PHP to PHEN weight ratio and with a 5:1 PHP to PHEN ratio. The reactions were performed thermally and catalytically at 400 and 425{degrees}C using molybdenum naphthenate and nickel octoate as catalysts. Reactions were also performed with added sulfur either as elemental sulfur or benzothiophene.
Date: August 1, 1993
Creator: Curtis, C. W.
Partner: UNT Libraries Government Documents Department

Selective solvent absorption in coal conversion

Description: The objectives of this research are: (1) to determine the importance of the presence of added hydrogen donor compounds within the coal in the first stage of direct liquefaction processes; and (2) to determine the composition of the solvent absorbed by and present within the coal in the first stages of direct coal liquefaction. Scope of work study the conversion of Argonne Premium coals in tetralin and 2-t-butyltetralin and compare the following: conversion to soluble products and product composition. Hydrogen donated by both solvents will be measured by gas chromatography and the same technique will be used to establish the amount of dealkylation of 2-t-butyltetralin. Reactions will be performed at several different temperatures for varying amounts of time.
Date: June 1, 1992
Creator: Larsen, J.W. & Amui, J.
Partner: UNT Libraries Government Documents Department

The effect of selective absorption on coal conversion. [2-t-butyltetralin]

Description: Scope of work: (1) Importance of hydrogen donors in the coal, prepare highly pure 2-t-butyltetralin. Study the conversion of Argonne coals in tetralin and 2-t-butyltetralin and compare the following: conversion to soluble products, product molecular weight distributions, and product structure. Hydrogen donated by both solvents will be measured by gas chromatography and the same technique will be used to establish the amount of dealkylation of 2-t-butyltetralin. Reactions will be run at several temperatures for varying times. (2) Selective recycle solvent absorption. Argonne coals will be exposed to recycle solvents at several elevated temperatures and the non-absorbed portion of the solvent will be separated by filtration. The composition of the whole oil and non-absorbed portion will be analyzed spectroscopically and chromatographically and compared to determine the composition of the recycle oil dissolved in the coal. 6 figs., 1 tab.
Date: July 1, 1991
Creator: Larsen, J.W. & Lazarov, L.
Partner: UNT Libraries Government Documents Department

High conversion of coal to transportationn fuels for the future with low HC gas production. Progress report No. 7, April 1--June 30, 1994

Description: The objective is to produce a Synthetic crude from coal at a cost lower than $30.00 per barrel (Task A). A second objective is to produce a fuel which is low in aromatics, yet of sufficiently high octane number for use in the gasoline-burning transportation vehicles of today. To meet this second objective, research was proposed, and funding awarded, for conversion of the highly-aromatic liquid product from coal conversion to a product high in isoparaffins, which compounds in the gasoline range exhibit a high octane number (Task B). Experimental coal liquefaction studies conducted in a batch microreactor in our laboratory have demonstrated potential for high conversions of coal to liquids with low yields of hydrocarbon (HC) gases, hence small consumption of hydrogen in the primary liquefaction step. Ratios of liquids/HC gases as high as 30/1, at liquid yields as high as 82% of the coal by weight, have been achieved. The principal objective of this work is to examine how nearly we may approach these results in a continuous-flow reactor system, at a size sufficient to evaluate the process concept for production of transportation fuels from coal. Accomplishments for this period are described.
Date: July 1, 1994
Creator: Wiser, W. H. & Oblad, A. G.
Partner: UNT Libraries Government Documents Department

Low severity coal liquefaction promoted by cyclic olefins

Description: The naphthalene hydrogenation performed thermally at 350 and 400[degrees]C showed no reactivity of the naphthalene. The Molyvan L catalyst precursor promoted a small amount of hydrogenation of naphthalene at 400[degrees]C as shown in Table 1. Reaction at the higher initial pressure of 1250 psi resulted in slightly more conversion of naplithalene and a higher production of tetralin but no decalin was observed. The naphthalene hydrogenation reactions with Molyvan L without sulfur yielded a slightly higher % HYD of naphthalene than did the reactions with sulfur. Likewise, the reactions with an initial hydrogen pressure of 1250 psi yielded a higher % HYD of naphthalene than did the reaction with 1000 psi, regardless of whether sulfur was present. The Molyvan 822 catalyst precursor was substantially more active at 400[degrees]C than at 350[degrees]C as presented in Table 2. The presence of sulfur also promoted the activity of Molyvan 822 as a catalyst. Tetralin was the product and was produced in substantial quantities at 400[degrees]C. Molyvan 822 was much more active for naphthalene hydrogenation than was Molyvan L under equivalent conditions. For example, at 400[degrees]C with sulfur the reactions with Molyvan 822 produced 33.5% HYD while Molyvan L yielded 1.8% HYD. With Molyvan L, the less active catalyst, the effect tile mode of agitation (vertical or horizontal) was minimal.
Date: January 1, 1992
Creator: Curtis, C.W.
Partner: UNT Libraries Government Documents Department

The Wilsonville Advanced Coal Liquefaction Research and Development Facility, Wilsonville, Alabama

Description: This reports presents the operating results for Run 252 at the Advanced Coal Liquefaction R D Facility in Wilsonville, Alabama. This run operated in the Close-Coupled Integrated Two-Stage Liquefaction mode (CC-ITSL) using Illinois No. 6 bituminous coal. The primary run objective was demonstration of unit and system operability in the CC-ITSL mode with catalytic-catalytic reactors and with ash recycle. Run 252 began on 26 November 1986 and continued through 3 February 1987. During this period 214.4 MF tons of Illinois No. 6 coal were fed in 1250 hours of operation. 3 refs., 29 figs., 18 tabs.
Date: May 1, 1990
Partner: UNT Libraries Government Documents Department

Applied research and evaluation of process concepts for liquefaction and gasification of western coals. Final report

Description: Fourteen sections, including five subsections, of the final report covering work done between June 1, 1975 to July 31, 1980 on research programs in coal gasification and liquefaction have been entered individually into EDB and ERA. (LTN)
Date: September 1, 1980
Creator: Wiser, W. H.
Partner: UNT Libraries Government Documents Department

General quantitative model for coal liquefaction kinetics: the thermal cleavage/hydrogen donor capping mechanism. [59 references]

Description: A mechanism for coal liquefaction, based on the concept of thermal cleavage-hydrogen capping donor complexes, is proposed and the quantitative agreement between the derived rate laws and the kinetic data obtained from fifteen publications is presented. The mechanism provides rate laws which describe the preasphaltene, asphaltene, oil and gas time/yield curves for the coal liquefaction process. A simplistic dissolution model is presented and used to relate the proposed mechanism to the experimentally observed products. Based on the quality of the mechanistic fit to the reported coal liquefaction systems, which cover a diverse range of reaction conditions, coal types and donor solvent compositions, it is proposed that the donor solvent/thermal bond cleavage/hydrogen capping mechanism provides a good, quantitative description of the rate limiting process. Interpretation of the rate constant/temperature dependencies in terms of transition state theory indicates formation of the activated complex can involve either physically or chemically controlled steps. A uniform free energy of activation of 52 kcal was found for the diverse liquefaction systems indicating a common transition state describes the reactions. Thus the proposed mechanism unifies the diverse liquefaction kinetic data by using a set of uniform reaction sequences, which have a common transition state, to describe the conversion chemistry. The mechanism thereby creates a common base for intercomparison, interpretation and evaluation of coal conversion for the broad range of processes currently being investigated in the liquefaction field.
Date: January 1, 1980
Creator: Gangwer, T
Partner: UNT Libraries Government Documents Department

Solvent tailoring in coal liquefaction. Quarterly report, February 1982-May 1982. [In many cases the simple organic compounds listed were hydrogenated]

Description: Twenty-three model donor solvents were used to rank their efficacy for the dissolution of Western Kentucky No. 9/14 coal. The transfer of hydrogen from the solvent to the coal fragments, as measured by coal conversion, was examined at three levels of available hydrogen. The hydrogen donors are ranked according to their ability to convert coal to THF solubles. Aromatic analogs of the model donors showed little ability to convert coal to THF solubles. Factors which influence hydrogen donation include the presence of heteroatoms or substituents both internal and external to the aromatic or hydroaromatic rings, the degree of hydrogenation, the aromaticity or nonaromaticity of the hydroaromatics, and the presence of five-membered rings. A relationship between heats of formation and hydrogen donor ability was shown for hydroaromatics within two ring or three ring homologous series. A model hydrogen acceptor, benzophenone, was also used to rank model donors and a comparison was made with the model donor ranking by coal conversion. The ranking of hydrogen donors at the same donatable hydrogen level for their ability to convert coal to THF solubles demonstrates that different donors have different abilities to liquefy coal. The presence of donatable hydrogen constitutes a necessary and important factor in coal conversion as evidenced by comparison with the conversion aromatic analogs. However, properties of the model donors other than the concentration of available hydrogen can affect THF solubles. The ease with which hydrogen is abstracted from a particular donor, as well as the functional groups and heteroatoms present, are significant factors affecting reactivity of the hydrogen donors during liquefaction. Ranking of hydrogen donor reactivity by coal conversion and by model acceptor experiments shows no direct correlation between the two.
Date: January 1, 1982
Creator: Tarrer, A.R.; Guin, J.A.; Curtis, C.W. & Williams, D.C.
Partner: UNT Libraries Government Documents Department

Fundamental reaction pathways during coprocessing

Description: The objective of this research was to investigate the fundamental reaction pathways in coal petroleum residuum coprocessing. Once the reaction pathways are defined, further efforts can be directed at improving those aspects of the chemistry of coprocessing that are responsible for the desired results such as high oil yields, low dihydrogen consumption, and mild reaction conditions. We decided to carry out this investigation by looking at four basic aspects of coprocessing: (1) the effect of fossil fuel materials on promoting reactions essential to coprocessing such as hydrogen atom transfer, carbon-carbon bond scission, and hydrodemethylation; (2) the effect of varied mild conditions on the coprocessing reactions; (3) determination of dihydrogen uptake and utilization under severe conditions as a function of the coal or petroleum residuum employed; and (4) the effect of varied dihydrogen pressure, temperature, and residence time on the uptake and utilization of dihydrogen and on the distribution of the coprocessed products. Accomplishments are described.
Date: December 1, 1992
Creator: Stock, L.M. & Gatsis, J.G. (Chicago Univ., IL (United States). Dept. of Chemistry)
Partner: UNT Libraries Government Documents Department

Solvent tailoring in coal liquefaction. Quarterly report, October 1983-December 1983

Description: The contribution of transferable hydrogen in coal-derived solvents to coal conversion was investigated in a two-step process. Initially, the amount of transferable hydrogen in the coal-derived solvents was analyzed by spectroscopic methods and by catalytic dehydrogenation. The spectroscopic methods included carbon magnetic resonance, proton magnetic resonance as well as a combination of these two methods. Three of the methods gave nearly equivalent quantities for the amount of transferable hydrogen present in the complex coal liquids. Coal conversion determined in each of the coal-derived solvents was correlated to the amount of transferable hydrogen present. The contribution of transferable hydrogen is a significant factor in coal dissolution and the presence of saturates and hexane insolubles compounds in these solvents may have a detrimental effect on coal dissolution. 20 references, 9 figures, 2 tables.
Date: July 1, 1983
Creator: Tarrer, A. R.; Curtis, C. W.; Guin, J. A. & Williams, D. C.
Partner: UNT Libraries Government Documents Department

Studies in coal liquefaction with application to the SRC and related processes. Quarterly report, November 1981-January 1982

Description: The concentration of hydroaromatics in a coal liquefaction solvent is regarded as a significant factor in the determination of solvent quality. An analytical method is described based on catalytic solvent dehydrogenation (CSD) for the measurement of transferable hydrogen, including hydroaromatic sources, in a solvent. The dehydrogenation of several model compounds in the presence of Pd/CaCO/sub 3/ was conducted under batch conditions. Hydroaromatics containing six-member rings were found to dehydrogenate effectively. Lesser degrees of dehydrogenation were found for alkyl-substituted aromatics and saturated compounds. CSD was applied to a series of hydrogenated creosote oils plus several light recycle oils. The normalized H/sub 2/ volumes obtained by CSD could be correlated with the coal-dissolution ability of the creosote oils. It was not possible to include the light recycle oils in the same correlation. /sup 13/C-NMR was used to measure the transferable hydrogen of selected hydrogenated creosote oils and light recycle oils. Values of transferable hydrogen determined by /sup 13/C-NMR were generally larger than the corresponding values obtained by CSD. A smooth correlation was found between coal conversion and transferable hydrogen as measured by /sup 13/C-NMR. The light recycle oils could not be fitted to the curve defined by the creosote oils. Minerals indigenous to coal provide an internal but weak source of catalytic activity during liquefaction reactions. A sensitive probe reaction, cyclohexene hydrogenation/isomerization, was used to compare the catalytic activity of several clay minerals, oxides used as catalyst supports, pyrite and liquefaction residue ashes.
Date: January 1, 1982
Creator: Tarrer, A.R.; Guin, J.A. & Curtis, C.W.
Partner: UNT Libraries Government Documents Department

Coal-derived promoters for the liquefaction of Illinois coal

Description: The objective of this program is to investigate the use of liquids derived from coal either by mild gasification or supercritical extraction (SCE) to promote direct liquefaction of Illinois coal. Some organic sulfur-, nitrogen-, and oxygen-containing compounds have been found to enhance liquefaction reactions. The use of Illinois coal to produce liquid fractions rich in these types of compounds could increase the rates of liquefaction reactions, thus improving the process economics. An integrated process combining direct liquefaction with mild gasification or SCE of coal is being developed by IGT. The approach taken in this two-year program is to use recently developed molecular probe techniques to assess the reactivity of three coal-derived liquids with respect to (A) hydrogen transfer rate, (B) carbon-carbon bond cleavage rate, (C) free radical flux, and (D) hydrocracking activity. Sample liquids from Illinois Basin Coal IBC-106 are prepared by three methods: mild gasification in an isothermal free-fall reactor (IFFR), steam treatment followed by mild gasification in a fixed-bed reactor (ST/FBR), and SCE using toluene in a batch autoclave. During the first year of the program, the IFFR and ST/FBR coal liquids were produced and characterized, and the IFFR liquid was assessed by the four molecular-probe methods. During the first quarter of the second year, reactivity testing and data analysis on the ST/FBR coal liquid was completed. For the ST/FBR liquid, hydrogen transfer rate showed a mean increase of 7%, C-C bond cleavage selectivity increased by 27%, free radical flux increased 101%, and data indicated a 227% increase in hydrocracking activity. 12 refs., 5 figs., 7 tabs.
Date: January 1, 1991
Creator: Carty, R.H.
Partner: UNT Libraries Government Documents Department

Resonance Raman and photophysical studies of transition metal complexes in solution and entrapped in zeolites

Description: We have obtained convincing evidence for localization of the optical electron on a single-ring fragment of a chelated bipyridine-like'' ligand (ie., pyridylpyrazine or 4-Methyl-bipyridine). In addition we have completed studies of Ru(bipyrazine){sub 3}{sup 2+} in aqueous sulfuric acid (0--98% by weight) and find clear evidence for sequential addition of six-protons to the six peripheral nitrogen atoms. Studies of zeolite-entrapped complexes are continuing and a series of homo- and heteroleptic complexes have been prepared and characterized. Finally, the synthesis of zeolite-entrapped metallophthalocyanines has now been developed and the copper and cobalt analogues synthesized. The characterization of these materials is now in progress.
Date: March 31, 1992
Creator: Kincaid, J.R.
Partner: UNT Libraries Government Documents Department