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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
41

Catalytic Separation of Pure Hydrogen from Synthesis Gas by an Ethanol Dehydrogenation / Acetaldehyde Hydrogenation Loop

Chladek, Petr 20 September 2007 (has links)
A novel catalytic process for producing high-purity, elevated-pressure hydrogen from synthesis gas was proposed and investigated. The process combines the advantages of low investment and operating costs with the flexibility to adapt to a small-scale operation. The process consists of a loop containing two complementary reactions: ethanol dehydrogenation and acetaldehyde hydrogenation. In one part of the loop, hydrogen is produced by dehydrogenation of ethanol to acetaldehyde. Since acetaldehyde is a liquid under standard conditions, it can be easily separated and pure hydrogen is obtained. In the other part of the loop, hydrogen contained in synthesis gas is reacted with acetaldehyde to produce ethanol and purified carbon monoxide. Ethanol, also a liquid under standard conditions, is easily removed and purified carbon monoxide is obtained, which can be further water-gas shifted to produce more hydrogen. Various dimensionless criteria were evaluated to confirm there was no significant effect of heat and mass transfer limitations and thus the experimental results represent true kinetics. Furthermore, a thermodynamic study was conducted using a Gibbs free energy minimization model to identify the effect of reaction conditions on ethanol/acetaldehyde conversion and determine the thermodynamically favourable operating conditions. Various catalysts were synthesized, characterized and screened for each reaction in a down-flow, fixed-bed quartz reactor. A novel gas chromatography analysis method allowing for an on-line detection of all products was also developed. Unsupported copper in the form of copper foam and copper supported on three different high surface supports were evaluated in ethanol dehydrogenation. Copper foam provided the lowest activity, because of its low surface area. Cu/SiO2 was the most active catalyst for ethanol dehydrogenation. The effects of temperature, pressure, residence time, and feed composition on ethanol conversion and product composition were determined. While increasing temperature or residence time resulted in increased ethanol conversion, elevated pressure and water content in the feed had no effect on ethanol conversion. On the other hand, acetaldehyde selectivity decreased with increasing temperature, pressure and residence time, as acetaldehyde participated in undesirable transformations to secondary products, out of which the most dominant was ethyl acetate. The maximum operating temperature was limited by the stability of the copper catalyst, which deactivated by sintering at temperatures higher than 300°C. The range of temperatures investigated was from 200°C to 350°C, while pressures ranged from atmospheric to 0.5 MPa. For ethanol:water ratios <1, the addition of water to the ethanol feed improved the catalyst stability and acetaldehyde selectivity, but a detrimental effect was observed at higher ratios. The introduction of acetaldehyde into the feed always lowered the conversion, thus indicating a need for stream purification within the loop. An empirical kinetic model was used to determine the activation energy, the order of reaction and the frequency factor. Unsupported and SiO2-supported copper catalysts were compared in acetaldehyde hydrogenation. Pure copper was identified as the best catalyst. Effects of temperature, pressure, residence time, feed composition and catalyst promoter on acetaldehyde conversion and product composition were evaluated. The acetaldehyde hydrogenation was enhanced by increased temperature, pressure and residence time and suppressed in presence of Fe or Zn promoters. Once again, at elevated temperature and residence time, ethanol combined with acetaldehyde to produce undesired ethyl acetate. CO acted as an inert when testing with the pure copper catalyst, but slightly decreased conversion with the supported catalyst. A decrease in conversion was also observed with the introduction of water and ethanol in the feed, once again indicating a requirement for feed purity within the loop. A temperature range of 150-300°C was investigated with catalysts deactivating at temperatures exceeding 250°C. A pressure range identical to ethanol dehydrogenation was used: 0.1-0.5 MPa. Again, an empirical kinetic model allowed determination of the activation energy, the order of reaction and the frequency factor.
42

Catalytic Separation of Pure Hydrogen from Synthesis Gas by an Ethanol Dehydrogenation / Acetaldehyde Hydrogenation Loop

Chladek, Petr 20 September 2007 (has links)
A novel catalytic process for producing high-purity, elevated-pressure hydrogen from synthesis gas was proposed and investigated. The process combines the advantages of low investment and operating costs with the flexibility to adapt to a small-scale operation. The process consists of a loop containing two complementary reactions: ethanol dehydrogenation and acetaldehyde hydrogenation. In one part of the loop, hydrogen is produced by dehydrogenation of ethanol to acetaldehyde. Since acetaldehyde is a liquid under standard conditions, it can be easily separated and pure hydrogen is obtained. In the other part of the loop, hydrogen contained in synthesis gas is reacted with acetaldehyde to produce ethanol and purified carbon monoxide. Ethanol, also a liquid under standard conditions, is easily removed and purified carbon monoxide is obtained, which can be further water-gas shifted to produce more hydrogen. Various dimensionless criteria were evaluated to confirm there was no significant effect of heat and mass transfer limitations and thus the experimental results represent true kinetics. Furthermore, a thermodynamic study was conducted using a Gibbs free energy minimization model to identify the effect of reaction conditions on ethanol/acetaldehyde conversion and determine the thermodynamically favourable operating conditions. Various catalysts were synthesized, characterized and screened for each reaction in a down-flow, fixed-bed quartz reactor. A novel gas chromatography analysis method allowing for an on-line detection of all products was also developed. Unsupported copper in the form of copper foam and copper supported on three different high surface supports were evaluated in ethanol dehydrogenation. Copper foam provided the lowest activity, because of its low surface area. Cu/SiO2 was the most active catalyst for ethanol dehydrogenation. The effects of temperature, pressure, residence time, and feed composition on ethanol conversion and product composition were determined. While increasing temperature or residence time resulted in increased ethanol conversion, elevated pressure and water content in the feed had no effect on ethanol conversion. On the other hand, acetaldehyde selectivity decreased with increasing temperature, pressure and residence time, as acetaldehyde participated in undesirable transformations to secondary products, out of which the most dominant was ethyl acetate. The maximum operating temperature was limited by the stability of the copper catalyst, which deactivated by sintering at temperatures higher than 300°C. The range of temperatures investigated was from 200°C to 350°C, while pressures ranged from atmospheric to 0.5 MPa. For ethanol:water ratios <1, the addition of water to the ethanol feed improved the catalyst stability and acetaldehyde selectivity, but a detrimental effect was observed at higher ratios. The introduction of acetaldehyde into the feed always lowered the conversion, thus indicating a need for stream purification within the loop. An empirical kinetic model was used to determine the activation energy, the order of reaction and the frequency factor. Unsupported and SiO2-supported copper catalysts were compared in acetaldehyde hydrogenation. Pure copper was identified as the best catalyst. Effects of temperature, pressure, residence time, feed composition and catalyst promoter on acetaldehyde conversion and product composition were evaluated. The acetaldehyde hydrogenation was enhanced by increased temperature, pressure and residence time and suppressed in presence of Fe or Zn promoters. Once again, at elevated temperature and residence time, ethanol combined with acetaldehyde to produce undesired ethyl acetate. CO acted as an inert when testing with the pure copper catalyst, but slightly decreased conversion with the supported catalyst. A decrease in conversion was also observed with the introduction of water and ethanol in the feed, once again indicating a requirement for feed purity within the loop. A temperature range of 150-300°C was investigated with catalysts deactivating at temperatures exceeding 250°C. A pressure range identical to ethanol dehydrogenation was used: 0.1-0.5 MPa. Again, an empirical kinetic model allowed determination of the activation energy, the order of reaction and the frequency factor.
43

Applications of hydrogenation and dehydrogenation on noble metal catalysts

Wang, Bo 15 May 2009 (has links)
Hydrogenation and dehydrogenation on Pd- and Pt- catalysts are encountered in many industrial hydrocarbon processes. The present work considers the development of catalysts and their kinetic modeling along a general and rigorous approach. The first part deals with the kinetics of selective hydrogenation, more particularly of the C3 cut of a thermal cracking unit for olefins production. The kinetics of the gas phase selective hydrogenation of methyl-acetylene (MA) and propadiene (PD) over a Pd/γ-alumina catalyst were investigated in a fixed bed tubular reactor at temperatures 60 - 80 oC and a pressure of 20 bara. Hougen-Watson type kinetic equations were derived. The formation of higher oligomers slowly deactivated the catalyst. The effect of the deactivating agent on the rates of the main reactions as well as on the deactivating agent formation itself was expressed in terms of a deactivation function multiplying the corresponding rates at zero deactivation. Then, the kinetic model was plugged into the reactor model to simulate an industrial adiabatic reactor. In the second part the production of hydrogen from hydrocarbons was investigated. In both cyclohexane and decalin dehydrogenations, conversions higher than 98% could be obtained over Pt/γ-alumina catalyst at temperature of 320 and 340 oC, respectively, with no apparent deactivation for 30 h and with co-feed of H2 in the feed. Except for H2 and trace amounts of side cracking products, less than 0.01%, benzene was the only dehydrogenated product in cyclohexane dehydrogenation. In the case of decalin dehydrogenation, partially dehydrogenated product, tetralin, was also formed with selectivity lower than 5%, depending on operating conditions. A rigorous Hougen-Watson type kinetic model was derived, which accounted for both the dehydrogenation of cis- and trans- decalin in the feed and also the isomerization of the two isomers. Jet A is the logic fuel in the battlefields. The dehydrogenation of Jet A can produce H2 for military fuel cell application. Although the H2 production is lower than that of steam/autothermal reforming, it eliminates the needs of high temperature and product separation operation.
44

Ethylbenzene dehydrogenation into styrene: kinetic modeling and reactor simulation

Lee, Won Jae 25 April 2007 (has links)
A fundamental kinetic model based upon the Hougen-Watson formalism was derived as a basis not only for a better understanding of the reaction behavior but also for the design and simulation of industrial reactors. Kinetic experiments were carried out using a commercial potassium-promoted iron catalyst in a tubular reactor under atmospheric pressure. Typical reaction conditions were temperature = 620oC, steam to ethylbenzene mole ratio = 11, and partial pressure of N2 diluent = 0.432 bar. Experimental data were obtained for different operating conditions, i.e., temperature, feed molar ratio of steam to ethylbenzene, styrene to ethylbenzene, and hydrogen to ethylbenzene and space time. The effluent of the reactor was analyzed on-line using two GCs. Kinetic experiments for the formation of minor by-products, i.e. phenylacetylene, α-methylstyrene, β-methylstyrene, etc, were conducted as well. The reaction conditions were: temperature = 600oC ~ 640oC, a molar ratio of steam to ethylbenzene = 6.5, and partial pressure of N2 diluent = 0.43 bar and 0.64 bar. The products were analyzed by off-line GC. The mathematical model developed for the ethylbenzene dehydrogenation consists of nonlinear simultaneous differential equations in multiple dependent variables. The parameters were estimated from the minimization of the multiresponse objective function which was performed by means of the Marquardt algorithm. All the estimated parameters satisfied the statistical tests and physicochemical criteria. The kinetic model yielded an excellent fit of the experimental data. The intrinsic kinetic parameters were used with the heterogeneous fixed bed reactor model which is explicitly accounting for the diffusional limitations inside the porous catalyst. Multi-bed industrial adiabatic reactors with axial flow and radial flow were simulated and the effect of the operating conditions on the reactor performance was investigated. The dynamic equilibrium coke content was calculated using detailed kinetic model for coke formation and gasification, which was coupled to the kinetic model for the main reactions. The calculation of the dynamic equilibrium coke content provided a crucial guideline for the selection of the steam to ethylbenzene ratio leading to optimum operating conditions.
45

Characterisation of the NADH dehydrogenases associated with isolated plant mitochondria / Kathleen Lydia Soole

Soole, Kathleen Lydia January 1989 (has links)
Typescript (Photocopy) / Bibliography: leaves i-xii. (3rd paging sequence) / x, 157, xii, 13 leaves : ill ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Thesis (Ph.D.)--University of Adelaide, Dept. of Botany, 1990
46

Reaction and deactivation kinetics of isobutane, using a concentration-controlled internal-recycle reactor / by Andreas G. Zwahlen

Zwahlen, Andreas G. January 1989 (has links)
Bibliography: leaves 168-174 / ix, 225 leaves : ill ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Thesis (Ph.D.)--University of Adelaide, Dept. of Chemical Engineering, 1990
47

Iridium catalyzed alkane dehydrogenation, olefin isomerization and related chemistry

Ray, Amlan. January 2007 (has links)
Thesis (Ph. D.)--Rutgers University, 2007. / "Graduate Program in Chemistry and Chemical Biology." Includes bibliographical references.
48

Development of novel structured catalysts and testing for dehydrogenation of methylcyclohexane

Rallan, Chandni January 2014 (has links)
Hydrogen storage for stationary and mobile applications is an expanding research topic. Using liquid organic hydrides for hydrogen storage is one of the most promising alternatives as it provides simple and safe handling. Liquid organic hydrides are largely compatible with current transport infrastructure, whereas alternatives such as liquid and gaseous hydrogen and metal hydrides would require a completely new infrastructure. An attractive storage system is the so-called MTH system (Methylcyclohexane, Toluene and Hydrogen). The dehydrogenation of methylcyclohexane is a highly endothermic reaction. To improve the reaction kinetics, this research was to develop a structured catalyst with a conductive metal support (Fecralloy) which could hold an adherent catalytic washcoat (γ - Al2O3). The active phase was impregnated onto this support and the developed catalyst was tested for the dehydrogenation of methylcyclohexane. The catalyst preparation involved three key steps which were support oxidation, loading of an adherent washcoat and finally impregnation of the active phase. The oxidation and washcoat stages required significant optimisation. The optimum oxidation conditions were found to be 950 °C for 10 h. The washcoating procedure was optimised by modifying a one-step hybrid washcoating method suggested in patent literature. Characterization techniques including SEM, XRD and EDX were used to study each step of catalyst preparation. In addition the technique of STEM was used to study platinum dispersion on the catalytic washcoat. Finally the catalytic activity of the developed catalyst was compared with an in-house pelleted catalyst based on the material used to prepare the structured catalyst and commercially available platinum on γ - Al2O3. Three key factors: activity, selectivity and stability were evaluated. The activity and selectivity were studied at varied operating conditions of T = 340 °C - 400 °C, W/F = 7345 - 14690 g s/mol, H2/MCH molar ratio = 0 - 9 and P = 1.013 bar. The dehydrogenation reaction of methylcyclohexane was found to be very selective to toluene (above 99%). Compounds, which are considered coke precursors, were identified, to attempt to explain the mechanism of catalyst deactivation. By-product distribution was monitored and possible reaction pathways were postulated. To gauge the stability of the catalyst, long term life tests were also performed on the structured catalyst at 400 °C and W/F = 14690 g s/mol for approximately 400 h. The stability study investigated the different types of deactivation mechanisms. The catalyst evaluation study helped identify the effect of the alloy support, the alumina washcoat and platinum dispersion on the selectivity of the catalyst.
49

Studies on Syntheses and Reactivity of Coordination Polymers using Borohydride / ボロハイドライドを用いた配位高分子の合成と反応性

Kadota, Kentaro 23 March 2020 (has links)
京都大学 / 0048 / 新制・課程博士 / 博士(工学) / 甲第22461号 / 工博第4722号 / 新制||工||1737(附属図書館) / 京都大学大学院工学研究科分子工学専攻 / (主査)教授 SIVANIAH Easan, 教授 田中 庸裕, 教授 陰山 洋 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DGAM
50

Reversible Formic Acid Dehydrogenation to Hydrogen and CO2 Catalyzed by Ruthenium and Rhodium Complexes

Guan, Chao 09 1900 (has links)
Formic acid (FA) has been considered as one of the most promising materials for hydrogen storage today. The catalytic decarboxylation of formic acid ideally leads to the formation of CO2 and H2, and such CO2/H2 mixtures can be successfully applied in fuel cells. A large number of transition-metal based homogeneous catalysts with high activity and selectivity have been reported for the formic acid decarboxylation. In this presentation, we report ruthenium and rhodium complexes containing an N, N′-diimine ligand for the selective decomposition of formic acid to H2 and CO2 in water in the absence of any organic additives. Among them, the Ru complex could provide a TOF (turnover frequency) of 12 000 h–1 and a TON (turnover number) of 350 000 at 90 °C in the HCOOH/HCOONa aqueous solution. In addition to that, efficient production of high-pressure H2 and CO2 (24.0 MPa (3480 psi)) was achieved through the decomposition of formic acid with no formation of CO by this Ru complex. Moreover, well-defined ruthenium (II) PN3P pincer complexes were also developed for the reversible reaction-hydrogenation of carbon dioxide. Excellent product selectivity and catalytic activity with TOF and TON up to 13,000 h-1 and 33,000, respectively, in a THF/H2O biphasic system were achieved. Notably, effective conversion of carbon dioxide from the air into formate was conducted in the presence of an amine, allowing easy product separation and catalyst recycling.

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