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Hydrodenitrogenation: An increasingly important part of catalytic hydroprocessing interlocking of thermodynamics and kinetics

Description: This report outlines a new use of thermodynamic property data. The Gibbs energies of reaction obtained from thermodynamic property measurements are used to estimate, with some success, relative reactivities for aromatic organonitrogen compounds. Calculated relative rates of reaction reproduce literature values within one power of ten. The relative rates of reaction are shown to be directly proportional to the concentration of hydrogenated species formed during hydrodenitrogenation (HDN). The production of completely saturated ring systems (overhydrogenation) in HDN reactions using conventional hydroprocessing is explained solely in terms of the thermodynamics in operation in the system. The results obtained show that the order of relative reactivity obtained is strongly dependence can account for some apparent contradictions when kinetic studies reported in the literature are compared. The results for a study of the hydroprocessing of a straight-run gas oil are reproduced in this report. The formation of anilines and the increase in indole concentration above that in the original gas oil sample are explained via the thermodynamics operating in the system.
Date: April 1, 1992
Creator: Steele, W.V. & Chirico, R.D.
Partner: UNT Libraries Government Documents Department

Correlation of Polarographic Walf-Wave Potentials With Nuclear Magnetic Resonance "Chemical Shifts." Parallel Correlation With Chemical Reactivity Parameters. Report No. 35

Description: Since nuclear magnetic resonance ''chemical shifts'' are considered to be good measures of electron densities in molecules, the extent to which they can be correlated with the polarographic half-wave potentials of organic compounds has been surveyed. To extend the applicability and interpretation of the proposed correlation, parallel correlatioan of E, with Hammett's sigma and Taft's sigma parameters were made, since both of the latter are also regarded as indication of electronic distrinution at the reactive center. The data in general support the view that changes in half-wave potential with structure are due to both electronic and steric effects, as well as perhaps to adsorption phenomena. Significantly, NMR data obtained with one type of substituent could be correlated with E/sub 1/2 data for a similar type of substituent. New NMR data for aliphatic nitro and halogen compounds are reported. (auth)
Date: July 14, 1958
Creator: Bennett, C. E. & Elving, P. J.
Partner: UNT Libraries Government Documents Department

6-Acetyldihydrohomopterin and sepiapterin affect some GTP cyclohydrolase I's and not others

Description: The first enzyme in pteridine biosynthesis, GTP cyclohydrolase I, is a likely site for regulation of pteridine biosynthesis to occur. GTP cyclohydrolase I responds to hormonal treatment and is found altered in a variety of mice with genetically based neurological and immunological disorders. Genetic loci can greatly modify the activity of GTP cyclohydrolase: Punch mutant in Drosophila hph-1 in mouse and atypical phenylketonuria in human. This report examines the ability of Ahp and sepiapterin to alter the activity of GTP cyclohydrolase I from mouse liver, rat liver and Drosophila head. 20 refs., 2 tabs.
Date: January 1, 1988
Creator: Jacobson, K.B. & Manos, R.E.
Partner: UNT Libraries Government Documents Department

Investigation of the triplet state of chlorophylls. Technical progress report, May 1, 1978--April 30, 1979

Description: The photoexcited triplet state properties of chlorophyll dimer systems in vitro were investigated by zero-field optically detected magnetic resonance (ODMR) spectroscopy at 2/sup 0/K. Measurements of the triplet state zero-field splittings, overall triplet lifetimes, and individual spin sublevel intersystem crossing rate constants were obtained for solutions of chlorophyll a and zinc-substituted chlorophyll a and for the covalently linked dimeric derivative of pyrochlorophyllide a. The triplet state properties found for these systems are interpreted within the framework of the triplet exciton model to assess the applicability of the exciton approach in determining the geometry of chlorophyll aggregate systems and to evaluate structural features of chlorophyll systems proposed as models for in vivo chlorophyll.
Date: January 1, 1979
Creator: Clarke, R.H.
Partner: UNT Libraries Government Documents Department

High load bearing flexible urethane foams

Description: The load bearing properties of flexible urethane foam as a function of the formulation variables were investigated. Varying levels of a polystyrene-acrylonitrile-polyol were added to the foam systems to increase the load-bearing capabilities of the resultant materials. The formulation water level and fluorocarbon blowing agent level were also varied to provide flexible urethane foams covering a wide range of density and compressive properties. The compression set/compression deflection properties, hydrolytic stability, and aging characteristics of these foam systems were determined.
Date: November 1, 1977
Creator: Parker, B.G.
Partner: UNT Libraries Government Documents Department

Photophysical processes of triplet states and radical ions in pure and molecularly doped polymers. Final report

Description: Both the past and current objectives are to learn how to control the rate and direction of triplet exciton migration in both pure and molecularly doped polymer systems. Since triplet excimers are efficient traps for migrating excitons, a secondary objective has been to characterize these excimers with a view toward their use as rate modifiers or excited state quenchers. Further objectives included those stated above as past and current objectives but with an additional goal. The authors learned that fluid solutions of many of the nitrogen containing chromophores with which they work produce both radical cations and anions upon excimer laser excitation. They also learned that a phosphorus analogue behaves similarly. At this time the mechanism of charge generation in these systems is not well established but they do know that the electronically excited states and radical ions can potentially interconvert. They wanted to find out whether or not the pure or molecularly doped polymer systems could be used in a step-wise sequence involving light absorption followed by charge generation. All of their activities are oriented toward the potential end use of polymeric systems in the conversion of light energy to perform various types of useful work.
Date: January 1, 1998
Creator: Burkhart, R.D.
Partner: UNT Libraries Government Documents Department

Accurate determination of pair potentials for a C{sub w}H{sub x}N{sub y}O{sub z} system of molecules: A semiempirical method

Description: Statistical mechanical chemical equilibrium calculations of the properties of high-pressure high-temperature reactive C,H,N,O mixtures are made to derive an accurate self-consistent set of inter-molecular potentials for the product molecules. Previous theoretical efforts to predict such properties relied in part on Corresponding States theory and shock wave data of argon. More recent high-pressure Hugoniot measurements on a number of elements and molecules allow more accurate determination of the potentials of these materials, and explicit inclusion of additional dissociation products. The present discussion briefly reviews the previous analysis and the method used to produce a self-consistent set of potentials from shock data on N{sub 2}, O{sub 2}, H{sub 2}, NO, an N{sub 2} + O{sub 2} mixture, carbon, CO{sub 2}, and CO, as well as some simple explosive product mixtures from detonation of hexanitrobenzene, PETN, and a mixture of hydrazine nitrate, hydrazine and water. The results are tested using the data from an HMX explosive formulations. The effect of the non-equilibrium nature of carbon clusters is estimated using data for TNT as a standard to determine a nonequilibrium equation of state for carbon. The resulting parameter set is used in a survey of 27 explosives. For the subset that contains no fluorine or two-phase carbon effects the rms deviation from experimental detonation velocity is 1.2%.
Date: March 1, 1995
Creator: Thiel, M. van; Ree, F.H. & Haselman, L.C.
Partner: UNT Libraries Government Documents Department

Some Physical and Chemical Properties of Scandium and the Rare Earths

Description: Conductances, densities, partial molal volumes, solubilities, and transference numbers were measured for scandium chloride, nitrate, and perchlorate. The stability constants of the chelates formed by the rare earths and scandium with ME(l,2-bis- STA2-di(carboxymethyl)aminoethoxy!ethane) and DE(2,2 -bis- STAdi(carboxymethyllaminoldiethyl ether) were measured polarographically. In addition, the stability constants of the scandium chelates of HEDTA (N -hydroxyethyl)-ethylenediamine-N,N,N -triacetic acid), EDTA- (ethylenediamine-N,N,N ,N -tetraacetic acid), DCTA (l,2-diaminocyclohexane-N,N,N ,N -tetraacetic acid), and DE TPA ((carboxymethyl)-bis- (2-di- (carboxymethyl)aminoethyllamine) were also measured. (auth)
Date: July 1, 1959
Creator: Hiller, M. A. & Powell, J. E.
Partner: UNT Libraries Government Documents Department

Development of a structure-property correlation for castable urethane elastomers

Description: A significant problem in electronic encapsulation is the poor load bearing performance of existing replacements for Adiprene-MOCA urethane elastomer. In response to this problem, this study defines the structural features that control the viscoelastic properties of the following liquid castable elastomers: Adiprene-MOCA, EN-7, and 3121-S. A review of previous investigations on a related class of materials suggests that viscoelastic properties may be more directly related to the physical structure or morphology of these elastomers, rather than their chemical structure. Accordingly, the morphology of the subject elastomers is characterized by means of electron microscopy and x-ray scattering measurements. These measurements reveal that within each elastomer incompatible chain segments cluster into separate domains, or microphases on a scale of 10 +- 1 nm. On this basis, it is concluded that the two major thermomechanical transitions present in each elastomer can be assigned to separate transitions within the two microphases. The above-ambient transition, which determines the upper use temperature of the elastomer, is specifically assigned to the glass transition of an amorphous microphase. The significance of this structure-property correltion for the liquid castable elastomers is twofold: (1) it permits generalization of mechanical property measurements on existing materials in order to predict their performance in unusual applications and (2) it leads to a rational strategy for developing improved elastomers for new, more demanding applications.
Date: January 1, 1978
Creator: Lagasse, R.R.
Partner: UNT Libraries Government Documents Department

Picosecond electron transfer in diporphyrin models of Photosystem II of green plants

Description: Green plants and photosynthetic bacteria efficiently transform the energy of an absorbed photon into redox products. Current in vivo and in vitro studies on Photosystem II (PS II) suggest the electron donor is a chlorophyll monomer, ligated to produce the high oxidation potential of P680, and the electron acceptor is pheophytin, a metal-free chlorophyll. This study probes the behavior of this PS II model in solvents of high dielectric constant and tests the sensitivity of its charge transfer reactions to increases in linking chain length as well as to changes in the relative orientation of the porphyrin subunits. (ACR)
Date: January 1, 1980
Creator: Netzel, T L; Fujita, I; Wang, C B & Fajer, J
Partner: UNT Libraries Government Documents Department

Tris(bis(trimethylsilyl)amido)uranium: Compounds with tri-, tetra-, and penta-valent uranium

Description: This trivalent uranium compound, serves as a precursor to new tri-, tetra-, and penta-valent uranium species. The geometry about the U atom is pyramidal. Lewis-base coordination compounds of U(N(SiMe/sub 3/)/sub 2/)/sub 3/ with a one-to-one- ratio of Lewis base to uranium were isolated with pyridine, 4-dimethylamino-pyridine, 2,6-Me/sub 2/-C/sub 6/H/sub 3/NC, and TPO. Two-to-one coordination compounds were obtained with t-butylnitrile and t-butylisocyanide. Compounds with more sterically demanding bases could not be isolated. The expected decrease in U-N(SiMe/sub 3/)/sub 2/ bond length with increase in oxidation state is not observed. Reaction of ClU(N(SiMe/sub 3/)/sub 2/)/sub 3/and Li(NH(p-tolyl)) yields the uranium (IV) dimer, U/sub 2/(N(SiMe/sub 3/)/sub 2/)/sub 4/(..mu..-N(p-tolyl))/sub 2/. Reaction with 2,4,6-triemethylaniline produces a dimer. Analogous substitution products could not be obtained with aniline or p-toluidine. t-Bu/sub 3/CO/sup /minus//, t-Bu/sub 2/CHO/sup /minus//, and t-Bu/sub 3/SiO/sup /minus// are used to synthesize new tetravalent, mononuclear uranium compounds. Reaction of ClU(tritox)/sub 3/ with alkyllithium reagents leads to isolation of RU(tritox)/sub 3/. The reaction of U(ditox)/sub 4/ with MeLi affords the addition product U(ditox)/sub 4/(Me)Li, whose crystal structure is described. Preparation of uranium silox compounds is reported. 97 refs., 26 figs., 39 tabs.
Date: April 1, 1988
Creator: Stewart, J.L.
Partner: UNT Libraries Government Documents Department

Physical properties of halthane series adhesives, part 2 of 2. Period covered: October--December 1976. [Urethanes: tensile adhesion; bulk viscosity; hardness]

Description: The Halthane series of urethane adhesives have sufficient adhesive strengths and cure times for most assembly processes at Pantex. The efficiency of preparation and handling of the three systems are nearly equal. Physical properties are more consistent between samples for the 87-1. The 73-18 system is ranked in the middle and 73-14 as the least consistent. The 87-1 system is high in viscosity and adhesive bond strength. The low viscosity of 73-18 and 73-14 allows more consistency in bond thickness control. The Halthane 73-18 system in this series of development tests is considered best for processing/assembly capability.
Date: January 1, 1976
Creator: Lichte, H.W.
Partner: UNT Libraries Government Documents Department

Improved bondability of molded rigid urethane form by plasma treatment

Description: Most mold releases, including so-called nontransferring releases, interfere with bonding of molded urethane foam. Water-washable mold releases are not readily removable from urethane foams cured at elevated temperatures. Plasma treatment in either argon or oxygen improves the bonding surfaces of molded urethane foam. Comparable bonding results can be obtained with RF (13.6 MHz), AC (20 kHz), or DC-plasma treatments. The plasma-treated foam surfaces will retain the improved bondability for a considerable length of time. Plasma treatment is effective for epoxy and RTV silicone adhesives. A primer recommended for metal bonding with RTV silicone, together with plasma treatment, produces superior bondability of molded urethane foam parts.
Date: unknown
Creator: DeGisi, S.L. & Smith, C.H.
Partner: UNT Libraries Government Documents Department


Description: A study into the use of sulfamic acld as a nitritedestroying reagent in the controlled-potentlal coulometrlc tltratlon method for uranlum(VI) was made. When nltrites are thus destroyed, the tltration ls much less subject to error from HNO/sub 3/. The results of titratlons of known amounts of uranlum(VI) in the presence of varlous amounts of HNO/sub 3/, Th(NO/sub 3/)/sub 4/, Al(NO/sub 3/ )/sub 4/, and LiNO/sub 3/ are given. (auth)
Date: January 17, 1962
Creator: Shults, W.D.
Partner: UNT Libraries Government Documents Department

Symmetry lowering in crystalline solid solutions: A study of cinnamamide-thienylacrylamide by x-ray and neutron diffraction and solid-state photochemistry

Description: Principles are outlined for symmetry lowering of a mixed crystal. A survey is given of methods used to detect reduced symmetry: changes in crystal morphology, detection of enantiomeric segregation of chiral additives in centrosymmetric'' crystals, generation of second harmonic optical signals, optical birefringence, asymmetric photoreactions in the crystalline state and X-ray and neutron diffraction. The last two methods are applied to mixed crystals of cinnamamide host and thienylacrylamide. Diffraction demonstrated that the mixed crystals are composed of six sectors of reduced symmetry, from monoclinic centrosymmetric P2[sub 1]/c to triclinic P1 in four sectors and possibly Pc in the remaining two. The X-ray diffraction data were not sufficiently accurate for assigning the absolute structures of the PI sectors of anomalous X-ray scattering. Thus, by this method one could not ascertain the absolute orientation of the guest molecules on the surface sites through which they were selectively occluded. This ambiguity was resolved by assignment of the absolute configuration of the chiral heterophotodimers, between host and guest, in enantiomeric excess in the PI sectors, after irradiation with UV light. This leads to the conclusion that the selective occlusion of thienylacrylamide arises from replacement of attractive C-H[pi] (electron) interactions between host molecules by a repulsive sulfur (lone pair electron)[pi](electron) interactions between guest and host at the crystal surfaces.
Date: January 1, 1993
Creator: Shimon, L.J.W.; Weissinger-Lewin, Y.; McMullan, R.K. (Brookhaven National Lab., Upton, NY (United States)); Vaida, M.; Frolow, F.; Lahav, M. et al.
Partner: UNT Libraries Government Documents Department

The effect of porous support composition and operating parameters on the performance of supported liquid membranes

Description: Factors, such as porous support composition and operating parameters, that influence the performance of supported liquid membranes (SLMs) were investigated. SLMs of varying porous support compositions and structures were studied for the transport of metal ions. A microporous polybenzimidazole support was synthesized and prepared in the form of an SLM. This SLM containing the selective extractant di-(2-ethylhexyl)phosphoric acid was evaluated for the transport of copper and neodymium. Dramatically improved performance over that of commercially available membranes was found in tests for removing the metal ions from solution. Metal ion transport reaches near completion in less than 3 hours, whereas Celgard-polypropylene and Nuclepore-polycarbonate reaches only 50% completion even after 15 hours. The transport driving force for acidic extractants is a pH gradient between the feed and strip solutions. Polybenzimidazole, an acid- and radiation-resistant polymer, has two protonatable tertiary nitrogens per repeat unit that may help sustain the pH driving force. Another factor may be the ability of the polybenzimidazole to hydrogen bond with the extractant. Transport through the flat-sheet SLMs were tested using a unique cell design. Countercurrent flow of the feed and strip solutions was established through machined channels in half-cell faceplates that are in a spiral, mirror-image pattern with respect to each other, with the flat-sheet SLM interposed between the two channeled solutions. 7 refs., 14 figs.
Date: February 1, 1991
Creator: Takigawa, D.Y.
Partner: UNT Libraries Government Documents Department

Molecular-orbital calculations for polynitropolyhedranes

Description: Various synthetic pathways to polyhedranes are being evaluated by using theoretical calculations. The results indicate that the synthesis of tetranitrotetrahedrane from tetralithiotetrahedrane is not a promising route. Alternatively, sequential base-promoted nitrations of cubanes seem a much more promising route for obtaining polynitrocubanes.
Date: January 1, 1982
Creator: Ritchie, J.P.
Partner: UNT Libraries Government Documents Department

Study of new materials for gun propellant formulations

Description: We are searching for new energetic materials to improve gun- propellant formulations. Theoretical calculations indicate that certain types of high nitrogen compounds produce lower average- molecular-weight gases than those with more carbon, and low average-molecular-weight by-products contribute to higher impetus. Therefore, our target compounds were chosen to contain only the elements C, H, N, and O, with a high percentage of nitrogen, be thermally stable and moderately insensitive to impact. The chemical preparations, impetus, flame temperatures, and heats of formation for the compounds are described.
Date: January 1, 1989
Creator: Lee, Kien-Yin & Stinecipher, M.M. (Los Alamos National Lab., NM (USA))
Partner: UNT Libraries Government Documents Department

Spectroscopy of the amide-I modes of acetanilide

Description: Raman measurements were made on acetanilide (N-phenyl-acetamide). Data are presented of the integrated intensity of the 1650 cm/sup /minus/1/ band as a function of temperature. The experimental procedures and data reduction were highly rigorous and are believed to be to most reliable data available. A concise theory of polaron states is presented and used to interpret the data. 22 refs., 4 figs., 1 tab.
Date: January 1, 1989
Creator: Bigio, I.J.; Scott, A.C. & Johnston, C.T.
Partner: UNT Libraries Government Documents Department

Uniform aluminum deposits on large nonplanar and planar polyimide substrates by physical vapor deposition

Description: The capability to deposit 10- to 12-..mu..m-thick aluminum films with less than 2 percent thickness uniformity (defined as standard deviation/average thickness) on large nonplanar and planar polyimide substrates has been developed using physical vapor deposition (PVD). A technique called shadow masking was developed to provide this consistent deposit uniformity over the entire substrate surfaces (greater than 2000 cm/sup 2/). The specific dimensions of a shadow mask for each substrate are generated from a computer-reduced plot of beta-backscatter thickness measurements of a previous deposit. With this developed method, initial thickness uniformities of 9.7 and 24.7 percent obtained for the nonplanar and planar deposits were improved to 1.07 and 1.80 percent, respectively.
Date: July 1, 1980
Creator: Hale, G.J.
Partner: UNT Libraries Government Documents Department

Stress relaxation of cellular silicone material

Description: Stress relaxation information for cellular silicone materials formed with urea leachable filler is being gathered. Two types of polymers are used in the test: equilibrium type (random copolymer) and condensation type (block copolymer). Each of these was compounded to provide finished materials with nominal apparent densities of 0.34 and 0.52 g/cm/sup 3/. Three sample variations of 1.17, 1.52, and 2.54 mm nominal thickness were prepared from the lower density product, and two sample variations higher density product. Each of the material/thickness combinations was compressed to nominal compressions of 20 and 40% with nine replicates at each condition. A compression fixture for aging is used to maintain a specific compression on the cellular sample at room temperature, and a test machine is used to acquire the load data. The load was recorded at initial assembly and at selected times thereafter. A total of 180 specimens are in test, 90 equilibrium type material samples that have been stored 4 years and 90 condensation type material samples that have been stored for 3 years. Each condition for each material type has nine replicates. Of these nine samples, two are 3 year controls, two more are 10 year controls, and five are tested regularly. Current data supports the statement that the time dependent loss of load bearing properties is approximately log-linear, with the major differences found to be between the material types and the two densities of each material type. Extrapolation indicates that at the end of the planned 10-year study, the load retention of all samples will be between 58 and 68% of original; the condensation type material is expected to be superior.
Date: May 1, 1980
Creator: Schneider, J.W.
Partner: UNT Libraries Government Documents Department

Production of super-smooth articles

Description: Super-smooth rounded or formed articles made of thermoplastic materials including various poly(methyl methacrylate) or acrylonitrile-butadiene-styrene copolymers are produced by immersing the articles into a bath, the composition of which is slowly changed with time. The starting composition of the bath is made up of at least one solvent for the polymer and a diluent made up of at least one nonsolvent for the polymer and optional materials which are soluble in the bath. The resulting extremely smooth articles are useful as mandrels for laser fusion and should be useful for a wide variety of other purposes, for example lenses.
Date: May 29, 1981
Creator: Duchane, D.V.
Partner: UNT Libraries Government Documents Department

Capacitance of edge plane of pyrolytic graphite in acetonitrile solutions

Description: The capacitance of the edge plane of pyrolytic graphite electrodes, in acetonitrile solutions, is measured by recording the current response to an applied triangular voltage sweep; TVS, and then fitting the current response with an appropriate function, (via a set of adjustable parameters). The pretreatment of the electrodes, the supporting electrolyte concentration used, and the frequency of the input TVS, were all found to affect the measured capacitance. In these experiments, a background current was also seen and the shape of the current output for the TVS; the charging/discharging curve, is shown to correlate with the magnitude of this background current. In addition, the size of the background current was found to have some dependence on the type of electrode pretreatment procedure used. 60 refs., 49 figs., 3 tabs.
Date: May 1, 1991
Creator: Minick, S.K. & Ishida, Takanobu.
Partner: UNT Libraries Government Documents Department