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The kinetics of sulfation of calcium oxide

Description: The rate of sulfation of a CaO surface is rapid at first, limited by the intrinsic kinetics, but slows down with increasing conversion as a consequence of the increased resistance to diffusion through the product layer. The objectives of this study are to determine the intrinsic kinetics and the product layer diffusion pate by minimizing the resistances to gas-phase pore diffusion, and eliminating complications due to pore filling. This is achieved by the use of nonporous CaO. A wide range of particle sizes are used to change the relative importance of the regimes in which the intrinsic kinetics and product layer diffusion control. The assumption of constant product layer diffusivity can then be tested and the variables that determine this diffusivity independently studied. Information on product layer diffusion can also be obtained from studies of porous particles after the pore mouths are all plugged and a uniform surface coating is obtained. This information on diffusion rate and intrinsic reactivity can then be combined with a geometrical model to describe the rate of reaction over the entire range of conversions and is particularly useful in treating the effect of particle size on conversion history.
Date: January 1, 1990
Creator: Sarofim, A.F. & Longwell, J.P.
Partner: UNT Libraries Government Documents Department

Identification of nitriding mechanisms in high purity reaction bonded silicon nitride

Description: The rapid, low-temperature nitriding results from surface effects on the Si particles beginning with loss of chemisorbed H and sequential formation of thin amorphous Si nitride layers. Rapid complete conversion to Si[sub 3]N[sub 4] during the fast reaction can be inhibited when either too few or too many nuclei form on Si particels. Optimally, [approximately] 10 Si[sub 3]N[sub 4] nuclei form per Si particles under rapid, complete nitridation conditions. Nitridation during the slow reaction period appears to progress by both continued reaction of nonpreferred Si[sub 3]N[sub 4] growth interfaces and direct nitridation of the remaining Si/vapor interfaces.
Date: March 1, 1993
Creator: Haggerty, J.S.
Partner: UNT Libraries Government Documents Department

Slurry phase Fischer-Tropsch synthesis: Cobalt plus a water-gas shift catalyst

Description: This report details experiments performed on three different copper-based catalysts: Cu/Cr[sub 2]O[sub 3], Cu/MnO/Cr[sub 2]O[sub 3] and Cu/ZnO/Al[sub 2]O[sub 3]. Of these three catalysts, the Cu/ZnO/Al[sub 2]O[sub 3] exhibits the greatest stability when slurried in octacosane. More than 1000 hours-on-stream indicate that the catalyst activity is not detrimentally affected by high pressure, high H[sub 2]/CO ratio, or the presence of alkenes. All of these are necessary stability characteristics for the water-gas shift catalyst, if it is to be used in combination with a cobalt Fischer-Tropsch catalyst. A review of documented reduction procedures for cobalt-based Fischer-Tropsch catalysts is presented.
Date: January 1, 1988
Creator: Yates, I.C. & Satterfield, C.N.
Partner: UNT Libraries Government Documents Department

Slurry phase Fischer-Tropsch synthesis: Cobalt plus a water-gas shift catalyst

Description: Experiments on cobalt-catalyzed reactions of light 1-alkenes added to synthesis gas were performed. Data have been collected at 220C, 0.45 to 1.48 MPa and a synthesis gas flow rate between 0.015 and 0.030 Nl/(gcat[center dot]min) with H[sub 2]/CO of 1.45 to 2.25. Ethylene, propene, and butene were added to synthesis gas feed from 0.5 to 1.2 mole% of total feed. For each material balance in which 1-alkenes were added, a material balance was performed at similar process conditions without 1-alkenes added, as base case''. Material balances without added 1-alkenes were also repeated to verify of catalyst selectivity stability. 49 material balances were performed during a single run lasting over 2,500 hours-on-stream. The hydrocarbon data have been completely analyzed; data correlations are still being made. Since C[sub 3]/C[sub 1] ratios by ethene addition, C[sub 4]/C[sub 1] ratios by propene addition, and C[sub 5]/C[sub 1] ratios by 1-butene addition, it appears that 1-alkenes may incorporate into growing chains on the surface of the catalyst. Further evidence for incorporation can be seen by comparing selectivity to n-alcohol one carbon number higher than added 1-alkene. Yield of this n-alcohol increases when alkenes are present. Sensitivity of hydrocarbon distribution to process variables seems to be greater on Co than on Fe catalysts.
Date: January 1, 1990
Creator: Yates, I.C. & Satterfield, C.N.
Partner: UNT Libraries Government Documents Department

Slurry phase Fischer-Tropsch synthesis: Cobalt plus a water-gas shift catalyst

Description: A cobalt Fischer-Tropsch catalyst (CO/MgO/silica) was reduced and slurried in combination with reduced Cu/ZnO/Al[sub 2]0[sub 3] water-gas-shift catalyst. Combined catalyst system was run at fixed process conditions for more than 400 hours. The system showed stable selectivity. The Cu/ZnO/Al[sub 2]0[sub 3] water-gas-shift catalyst remained reasonably active in the presence of the cobalt catalyst. Hydrocarbon selectivity of the cobalt and Cu/ZnO/Al[sub 2]0[sub 3] catalyst system compared favorably to selectivity of iron-based catalysts. Methane selectivity was slightly higher for the cobalt-based system, but C[sub 5][sup +] selectivity was essentially the same. The hydrocarbon product distribution appeared to exhibit a double-a behavior. a[sub 1] was near 0.80 which is higher than that of iron catalysts, while a[sub 2] was calculated to be 0.86 which is somewhat lower than would be typical for an iron-based catalyst.
Date: January 1, 1988
Creator: Yates, I.C. & Satterfield, C.N.
Partner: UNT Libraries Government Documents Department

Slurry phase Fischer-Tropsch synthesis: Cobalt plus a water-gas shift catalyst

Description: The rate of synthesis gas consumption over a cobalt FischerTropsch catalyst was measured in a well-mixed, continuous-flow, slurry reactor at 220 to 240[degrees]C, 0.5 to 1.5 MPa, H[sub 2]/CO feed ratios of 1.5 to 3.5 and conversions of 7 to 68% of hydrogen and 11 to 73% of carbon monoxide. The inhibiting effect of carbon monoxide was determined quantitatively and a Langmuir-Hinshelwood-type equation of the following form was found to best represent the results: -R[sub H[sub 2+Co]] = (a P[sub CO]P[sub H[sub 2]])/(1 + b P[sub CO])[sup 2]. The apparent activation energy was 93 to 95 kJ/mol. Data from previous studies on cobalt-based Fischer-Tropsch catalysts are also well correlated with this rate expression.
Date: January 1, 1989
Creator: Yates, I.C. & Satterfield, C.N.
Partner: UNT Libraries Government Documents Department

Slurry phase Fischer-Tropsch synthesis: Cobalt plus a water-gas shift catalyst

Description: A Co/MgO/SiO[sub 2] Fischer-Tropsch catalyst was operated simultaneously with a Cu/ZnO/Al[sub 2]O[sub 3] water-gas-shift catalyst in a slurry reactor for over 400 hours. The process conditions were held constant at a temperature of 240[degrees]C, a pressure of 0.79 MPa, and a 1.1 H[sub 2]/CO feed of 0.065 Nl/min-g.cat. The Fischer-Tropsch activity remained constant at the level predicted by the operation of the Co/MgO/SiO[sub 2] catalyst alone. The water-gas-shift reaction was near equilibrium. The hydrocarbon product distribution of the combined catalyst system was stable and matched that of the CO/MgO/SiO[sub 2] operating alone under similar conditions. The combined catalyst system exhibited a high selectivity to n-alkanes. Neither catalysts's operation appeared to have a detrimental effect on that of the other, showing promise for future option.
Date: January 1, 1990
Creator: Chanenchuk, C.A.; Yates, I.C. & Satterfield, C.N.
Partner: UNT Libraries Government Documents Department

Comparative mutagenesis of human cells in vivo and in vitro

Description: This report discusses measuring methods of point mutations; high density cell cultures for low dose studies; measurement and sequence determination of mutations in DNA; the mutational spectra of styrene oxide and ethlyene oxide in TK-6 cells; mutational spectrum of Cr in human lymphoblast cells; mutational spectra of radon in TK-6 cells; and the mutational spectra of smokeless tobacco. (CBS)
Date: May 1, 1992
Creator: Thilly, W.G.
Partner: UNT Libraries Government Documents Department

Cryotribology: Development of cryotribological theories and application to cryogenic devices

Description: High-performance superconducting solenoids are susceptible to premature quenches, or superconducting to normal state transitions, due to abrupt conductor movements within the winding. Abrupt motions involving 5{approximately}10{mu}m conductor displacements dissipate sufficient energy to trigger a quench. Sliding and mechanical behaviors of materials at cryogenic temperatures have been experimentally examined. After accounting for changes in the sliding materials' low-temperature strength properties, we have found that the adhesion theory of friction and wear remains applicable at cryogenic temperatures. The adhesion friction theory suggests two methods for controlling unsteady sliding motions. The first involves the selection of sliding materials whose friction coefficients increase with increasing sliding speed. A number of material pairs have been examined for positive friction-velocity characteristics. This materials-based approach to frictional stabilization does not seem a viable option at 4.2 K. The second altemative is to preprogram the force conditions within high-risk regions of the winding to regulate the occurrence of unsteady sliding motions. Structural models are proposed to account for unsteady conductor motions on a variety of dimensional scales. The models are used to design a small superconducting solenoid. Performance of this solenoid suggests that force-based motion control is a potentially viable design approach for achieving successful dry-wound magnets.
Date: September 15, 1992
Creator: Iwasa, Y.; Michael, P. (Massachusetts Inst. of Tech., Cambridge, MA (United States)) & Rabinowicz, E. (Massachusetts Inst. of Tech., Cambridge, MA (United States) Massachusetts Inst. of Tech., Cambridge, MA (United States). Francis Bitter National Magnet Lab.)
Partner: UNT Libraries Government Documents Department

A comparison of radioactive waste from first generation fusion reactors and fast fission reactors with actinide recycling

Description: Limitations of the fission fuel resources will presumably mandate the replacement of thermal fission reactors by fast fission reactors that operate on a self-sufficient closed fuel cycle. This replacement might take place within the next one hundred years, so the direct competitors of fusion reactors will be fission reactors of the latter rather than the former type. Also, fast fission reactors, in contrast to thermal fission reactors, have the potential for transmuting long-lived actinides into short-lived fission products. The associated reduction of the long-term activation of radioactive waste due to actinides makes the comparison of radioactive waste from fast fission reactors to that from fusion reactors more rewarding than the comparison of radioactive waste from thermal fission reactors to that from fusion reactors. Radioactive waste from an experimental and a commercial fast fission reactor and an experimental and a commercial fusion reactor has been characterized. The fast fission reactors chosen for this study were the Experimental Breeder Reactor 2 and the Integral Fast Reactor. The fusion reactors chosen for this study were the International Thermonuclear Experimental Reactor and a Reduced Activation Ferrite Helium Tokamak. The comparison of radioactive waste parameters shows that radioactive waste from the experimental fast fission reactor may be less hazardous than that from the experimental fusion reactor. Inclusion of the actinides would reverse this conclusion only in the long-term. Radioactive waste from the commercial fusion reactor may always be less hazardous than that from the commercial fast fission reactor, irrespective of the inclusion or exclusion of the actinides. The fusion waste would even be far less hazardous, if advanced structural materials, like silicon carbide or vanadium alloy, were employed.
Date: April 1, 1991
Creator: Koch, M. & Kazimi, M.S.
Partner: UNT Libraries Government Documents Department

Coal plasticity at high heating rates and temperatures. Y

Description: This report presents the Ph.D. Thesis Proposal of Mr. Sarakorn Gerjarusak to the MIT Department of Chemical Engineering on the topic: Plasticity Kinetics of Different Coal Types.'' A theoretical approach to the study of coal plasticity is described. Previous work relating the viscosity of molten coal to the inventory of metaplast employed a single chemical reaction model. In order to be able to use the kinetics parameters such as the activation energy obtained at one temperature-time history to predict the plasticity of molten coal at other temperature-time histories, a multiple independent parallel reaction model will be used to interpret our plastometer data. In addition, key plastic properties of different coals such as maximum fluidity and duration of plasticity will be correlated to a coal-type specific parameter formulated by Ko, and requiring only the elemental composition of the parent coal. Finally, the plastic properties of each coal will be correlated to the tar yield from that coal to test a model which assumes metaplast to be the precursor of tar. 24 refs., 8 figs., 1 tab.
Date: August 1, 1991
Creator: Gerjarusak, S.; Peters, W.A. & Howard, J.B.
Partner: UNT Libraries Government Documents Department

Coal plasticity at high heating rates and temperatures

Description: The rapid-heating, fast response plastometer has been reassembled and restored to its working condition. The plastometer was calibrated with various viscosity standards. The ratio of the observed viscosity to the actual viscosity was found to range from 1.2 to 2.8. The higher observed viscosity values were attributed to friction and misalignment of the shearing disk. In addition, the viscosity readings varied from one run to another because the distance between the moving disk and the stationary plate could not be maintained constant. Use of a low friction bearing for the shearing disk's shaft and the cone-and-plate configuration have been suggested as remedies to these problems.
Date: December 1, 1990
Creator: Gerjarusak, S.; Peters, W. A & Howard, J. B.
Partner: UNT Libraries Government Documents Department

Conversion of light hydrocarbon gases to metal carbides for production of liquid fuels and chemicals

Description: Light hydrocarbon gases could be reacted with low cost alkaline earth metal oxide (CaO, MgO) in high-temperature plasma reactor to achieve very high ([le]100%) gas conversion to H[sub 2], CO, and the corresponding metal carbides. These carbides could be stored, transported, and hydrolyzed to acetylene or methyl acetylene, which in turn could be upgraded to a wide range of chemicals and premium liquid hydrocarbon fuels. An electric arc discharge reactor was built for converting methane. Literature reviews were made.
Date: February 1, 1993
Creator: Diaz, A.F.; Modestino, A.J.; Howard, J.B. & Peters, W.A.
Partner: UNT Libraries Government Documents Department

Slurry phase Fischer-Tropsch synthesis: Cobalt plus a water-gas shift catalyst, January 1, 1990--March 30, 1990

Description: Experiments to study cobalt-catalyzed reactions of light 1-alkenes added to synthesis gas feed have been performed. Data have been collected at 220{degrees}C, 0.45 to 1.48 MPa and a synthesis gas flow rate between 0.015 and 0.030 Nl/(gcatmin) with H{sub 2}/CO of 1.45 to 2.25. C{sub 2}H{sub 4}, C{sub 3}H{sub 6}, and C{sub 4}H{sub 8} were added to the synthesis gas feed in concentrations ranging from 0.5 to 1.2 mole% of total feed. For each material balance in which 1-alkenes were added, a material balance was performed at similar process conditions without 1-alkenes added. This use of base case'' process conditions should make data analysis and interpretation easier. Material balances without 1-alkenes were also repeated to allow verification of catalyst selectivity stability. A total of 49 balances were performed during a single run which lasted over 2500 hours-on-stream. The hydrocarbon data have not yet been completed analyzed.
Date: January 1, 1990
Creator: Yates, I.C. & Satterfield, C.N.
Partner: UNT Libraries Government Documents Department

The kinetics of sulfation of calcium oxide

Description: The objectives of this study are to determine the intrinsic kinetics and the product layer diffusion rate by minimizing the resistances to gas-phase pore diffusion, and eliminating complications due to pore filling. In the report, a grain model was used to introduce the various potentially rate-limiting processes. It was compared with results obtained with a distributed pore model by Bhatia Perlmutter (1981). Comparing the predicted behavior of the surface areas with conversion, it was even possible to compare experimental results with other models. The conclusion of this study was that, even thought the kinetic parameters obtained with different samples differed much more if product layer diffusion assumed rate-limiting rather than the surface reaction, the shape of the predicted curve approached the experimental findings so much better, that product layer diffusion is indeed most likely to be rate-limiting. (VC)
Date: March 28, 1990
Creator: Sarofim, A. F. & Longwell, J. P.
Partner: UNT Libraries Government Documents Department

A two-photon fluorescence autocorrelator for a Nd:YLF modelocked laser

Description: In this thesis, I discuss the design and implementation of an autocorrelator for an actively modelocked ND:YLF laser at wavelength 1.054{mu}m. A dye is used to generate a broadband two-photon fluorescence (TPF) signal at 570nm which is the autocorrelation of the laser pulses. Two different techniques are discussed. A colliding pulse scheme can be used to generate a TPF autocorrelation signal as a function of distance, or an interferometer technique can be used to generate an autocorrelation signal as a function of the delay in an interferometer arm. Experimental results are discussed, but they are inconclusive because of difficulties in interpreting the signal.
Date: May 1, 1991
Creator: Kner, P. A.
Partner: UNT Libraries Government Documents Department

The kinetics of sulfation of calcium oxide

Description: Studies of the sulfation rate behavior show an initial fast rate followed by a rate decrease. It is generally agreed that product layer diffusion limitations are the explanation for this behavior. Many investigators tried to model this observed rate change, more or less successfully. No agreement has been reached, however, as to the value of the produce layer diffusivity. Hence, in this work we want to investigate the mechanism of this process. In addition to understanding the initial kinetics, two questions will be focused on. First, we should understand what is diffusing. It appears that the driving force for this diffusion phenomenon is not first order with the SO{sub 2} concentration in the gas. This would indicate that some other, intermediary step is occurring. The second question concerns the composition of the product layer. Different conditions at the start of the reaction were observed to produce different diffusion rates at a later stage. The microscopic appearance of the product layer also appeared to be different.
Date: January 1, 1989
Creator: Sarofim, A. F. & Longwell, J. P.
Partner: UNT Libraries Government Documents Department

Harvard-MIT research program in short-lived radiopharmaceuticals

Description: This report presents research on radiopharmaceuticals. The following topics are discussed: antibody labeling with positron-emitting radionuclides; antibody modification for radioimmune imaging; labeling antibodies; evaluation of technetium acetlyacetonates as potential cerebral blood flow agents; and studies in technetium chemistry. (CBS)
Date: January 1, 1991
Creator: Adelstein, S.J.
Partner: UNT Libraries Government Documents Department

Coal plasticity at high heating rates and temperatures

Description: The results of the multiple independent parallel reaction (MIPR) kinetics model are reported and discussed. The MIPR model's results agree well with the data. The effects of holding temperature, heating rate, and coal type on plasticity are displayed by the model. However, the model does not address the secondary reactions forming higher molecular weight liquid hypothesized to be responsible for the initial rise in viscosity during solidification. The average standard error of estimates for the plastic period and maximum plasticity are 0.13 s and 317 Pa-s, respectively. These values are comparable to the measurement resolution of the plastometer (0.1 s and [plus minus] 200 Pa[center dot]s).
Date: April 1, 1993
Creator: Gerjarusak, S.; Peters, W.A. & Howard, J.B.
Partner: UNT Libraries Government Documents Department

Control of catalytic hydrotreating selectivity with ammonia. [Hydrodeoxygenation]

Description: The hydrogenation of naphthalene in the presence of 0, 24, or 48 kPa of ammonia derived from propyl amine was studied during the hydrodeoxygenation (HDO) of dibenzofuran (DBF). A new sample of sulfided NiMo/Al{sub 2}O{sub 3} catalyst at 360{degrees}C, 6.9 MPa total H{sub 2} pressure in a vapor phase tubular reactor was used. As a base-line the HDO of DBF was also studied in the absence of both naphthalene and ammonia. Ammonia inhibited both the HDO of dibenzofuran and the hydrogenation of naphthalene. The addition of ammonia may not be suitable if a high conversion of HDO is desired. 12 figs.
Date: January 1, 1992
Creator: Satterfield, C.N. & Lee, C.M.
Partner: UNT Libraries Government Documents Department

The kinetics of sulfation of calcium oxide

Description: Studies of the sulfation rate behavior show an initial fast rate followed by a rate decrease. This behavior has generally been interpreted as product layer diffusion limitations taking over after an initial kinetic rate regime. Many investigators tried to model this observed rate change, more or less successfully. No agreement has been reached, however, as to the value of the product layer diffusivity. In this work we want to investigate the mechanism of this process. During the last quarter, most attention has been paid to analyzing the results obtained earlier. In the light of some unexpected results, we returned to the most fundamental question: what is the rate-limiting mechanism It appeared that whatever the mechanism is, no rate constant'' could be used, since the rate is a function of the product layer composition, which changes during the reaction. When comparing the results obtained with different samples, however, it appeared that the best correlation was found if one assumes the limiting rate to occur at the CaSO{sub 4} interphase. This point of view has never been presented before and requires therefore a more attentive analysis.
Date: January 1, 1989
Creator: Sarofim, A.F. & Longwell, J.P.
Partner: UNT Libraries Government Documents Department

Water hammer due to the sudden stopping of a flashing flow

Description: Measurements of the peak pressure occurring when a valve at the end of a pipe passing a flashing flow is slammed shut have been made. Scatter is considerable. The pressure trace indicates that condensing of the vapor occurs at essentially constant pressure after which a single phase liquid water hammer occurs. A simplified hand calculation and a more elaborate computer calculation are both shown to bound the data. For designing pipe supports, the peak pressure can be conservatively estimated assuming the flow is pure liquid. Before the spike is experienced, however, a delay, while the pipe is being filled, ensues. What constitutes a rapid valve closure in this problem, compared to single phase liquid rapid valve closure, is quite different. To avoid the waterhammer, a much slower stroking of the valve is needed.
Date: August 1, 1991
Creator: Sweeney, E.J. & Griffith, P.
Partner: UNT Libraries Government Documents Department

Forces on a pipe bend resulting from clearing a pool of liquid upstream

Description: The forces experienced by a bend in a pipe when a pool of water upstream is cleared by a rush of air have been measured. These forces are found to be negligible as long as a transition to slug flow does not occur. This transition does not occur as long as the maximum liquid fraction in the pool is less than 20%. The forces experienced at the bend are greatly reduced if the slug has traveled more than 6 L/D's, a distance which is more than sufficient to insure that the slug has entrained air. The effect of an upstream expansion on the force experienced by the bend as a cleared air-water plug passes through it has also been measured. A conservative estimate of the maximum force can be made by assuming that the plug is composed entirely of liquid and moves at the mixture velocity characteristic of the small pipe. The measured maximum force decreases rapidly with increasing distance. These measurements will help in designing piping supports for lines which cannot be properly sloped or are downstream of a pressure relief valve. 2 refs.
Date: January 1, 1991
Creator: Neumann, A. (Schlumberger Technology Corp., New York, NY (United States)) & Griffith, P. (Massachusetts Inst. of Tech., Cambridge, MA (United States))
Partner: UNT Libraries Government Documents Department

The kinetics of sulfation of calcium oxide

Description: Studies of the sulfation rate behavior show an initial fast rate followed by a rate decrease. This behavior has generally been interpreted as product layer diffusion limitations taking over after an initial kinetic rate regime. Many investigators tried to model this observed rate change. As pore diffusion was a limiting phenomenon in most of the experiments, authors have used several pore models to described this complication, more or less successfully. Product layer diffusivity has been assumed to be constant as conversion increased; however, there is no general agreement as to its value. In this work we are investigating the mechanism of this process with emphasis on measurement of product layer diffusivity and the surface reaction rate. Some additional experimental work was done to investigate the order and activation energy of the sulfation under different conditions. The effect of additives was studied again, by sprinkling some KCl or NaCl salt on top of partially reacted synthetic lime, in an effort to change the surface reaction rate rather than the diffusion rate.
Date: December 29, 1989
Creator: Sarofim, A. F. & Longwell, J. P.
Partner: UNT Libraries Government Documents Department