• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 632
  • 170
  • 81
  • 68
  • 36
  • 19
  • 14
  • 10
  • 7
  • 6
  • 5
  • 4
  • 3
  • 2
  • 2
  • Tagged with
  • 1276
  • 193
  • 181
  • 169
  • 118
  • 116
  • 113
  • 110
  • 106
  • 99
  • 95
  • 89
  • 86
  • 85
  • 84
  • 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.
401

Hydrodesulfurization of crude oil over Co-Mo catalysts in a slurry reactor

Porgar, S., Rahmanian, Nejat January 2015 (has links)
No / In this paper, hydrodesulfurization (HDS) of crude oil in the three-phase slurry reactor over cobalt – molybdenum catalyst (CoMo / ɣ- AL2O3) is studied. Effects of space velocity and length of reactor on the conversion rate and catalyst effectiveness for HDS process have been investigated. Kinetics of the reaction rate for this process is primarily and Arrhenius equation for the rate constant is used. The results show that the effectiveness factor for catalyst along the length of reactor is decreased about 83%. By increasing liquid velocity from 4 to 10 1/s, the conversion of sulfur components is decreased about 22% at the temperature of 523 K. At the same temperature, by increasing liquid velocity from 36 to 84 1/s conversion is reduced to 25%. The results of the variation of the dimensionless reaction rate against conversion show that with increasing conversion, the reaction rate decreases and the reaction is stopped when the conversion is 100%.
402

Design of Novel Synthetic Iron Oxide Nano-Catalyst Over Homemade Nano-Alumina for an Environmentally Friendly Fuel: Experiments and Modelling

Jarullah, A.T., Al-Tabbakh, B.A., Ahmed, M.A., Hameed, S.A., Mujtaba, Iqbal M. 04 July 2022 (has links)
No / Achieving an environmentally friendly fuel with respect to minimum sulfur compounds has recently became a significant issue for petroleum refining industries. This paper focuses on investigating oxidative desulfurization (ODS) process for removal of sulfur compounds found in light gas oil (LGO) in a batch reactor (at different reaction temperatures and batch time) using a novel nano-catalyst based on 4% iron oxide (Fe2O3) as an active component. Precipitation and Impregnation methods are used to prepare the nano-gamma alumina (γ-alumina) and to generate the new synthetic homemade nanocatalyst. A mathematical model is formulated for the ODS process to estimate the optimal kinetic parameters within gPROMS package. An excellent consistency with the experimental data of all runs with error less than 5% have obtained. The optimization results display that the new nanocatalyst prepared here is effective in removing more than 97% of the sulfur compounds from LGO resulting in a cleaner fuel. / The authors thank Petroleum Research and Development Center, The Iraqi Ministry of Oil /Baghdad, IRAQ for its financial support.
403

Production of Green Fuel: A Digital Baffle Batch Reactor for Enhanced Oxidative Desulfurization of Light Gas Oil Using Nano-Catalyst

Hameed, S.A., Nawaf, A.T., Mahmood, Q.A., Abdulateef, L.T., Jarullah, A.T., Mujtaba, Iqbal M. 04 July 2022 (has links)
Yes / A digital baffle batch reactor (DBBR) for oxidative desulfurization (ODS) reactions is designed and applied here in order to reduce the sulfur concentration presented in light gas oil (LGO) based on a novel homemade nano-catalyst (Copper Oxide (CuO)/Activated Carbon (AC)). With efficient impregnation, good pore size distribution, high activity and higher surface area, the designed nano-catalyst (CuO/AC) demonstrated excellent catalytic efficiency. To evaluate the effectiveness of nano catalyst (prepared experimentally), several experiments related to ODS reactions using the digital baffle batch reactor are carried out under moderate process conditions (reaction temperature (100, 120 and 140 °C), contact time (15, 30 and 45 min) and oxidant (H2O2) amount (2, 3 and 5 ml)). The experimental outcomes indicated that increasing the reaction temperature, batch time and oxidant amount lead to reduced sulfur concentration of oil feedstock leading to a greener fuel. The efficiency of sulfur conversion is reported to be 83.1 % using the modified nano-catalysts and new reactor (DBBR) at reaction temperature 140 oC, batch time 45 min and H2O2 amount of 5 ml. So, such new results using DBBR for ODS reactions based on CuO/AC as a new modified nano catalyst has not been reported in the public domain and it is considered as new results.
404

Investigation of the Effect of Catalyst Layer Composition on the Performance of PEM Fuel Cells

Russell, Jason Bradley 03 September 2003 (has links)
The catalyst layer of a proton exchange membrane (PEM) fuel cell is a porous mixture of polymer, carbon, and platinum. The characteristics of the catalyst layer play a critical role in determining the performance of the PEM fuel cell. In this research, sample membrane electrode assemblies (MEAs) are prepared using various combinations of polymer and carbon loadings while the platinum catalyst surface area is held constant. For each MEA, polarization curves are determined at common operating conditions. The polarization curves are compared to assess the effects of the catalyst layer composition. The results show that both Nafion and carbon content significantly affect MEA performance. The physical characteristics of the catalyst layer including porosity, thickness, active platinum surface area, ohmic resistance, and apparent Nafion film thickness are investigated to explain the variation in performance. The results show that for the range of compositions considered in this work, the most important factors are the platinum surface area and the apparent Nafion film thickness. / Master of Science
405

A Microscopic Continuum Model of a Proton Exchange Membrane Fuel Cell Electrode Catalyst Layer

Armstrong, Kenneth Weber 14 October 2004 (has links)
A series of steady-state microscopic continuum models of the cathode catalyst layer (active layer) of a proton exchange membrane fuel cell are developed and presented. This model incorporates O₂ species and ion transport while taking a discrete look at the platinum particles within the active layer. The original 2-dimensional axisymmetric Thin Film and Agglomerate Models of Bultel, Ozil, and Durand [8] were initially implemented, validated, and used to generate various results related to the performance of the active layer with changes in the thermodynamic conditions and geometry. The Agglomerate Model was then further developed, implemented, and validated to include among other things pores, flooding, and both humidified air and humidified O₂. All models were implemented and solved using FEMAP™ and a computational fluid dynamics (CFD) solver, developed by Blue Ridge Numerics Inc. (BRNI) called CFDesign™. The use of these models for the discrete modeling of platinum particles is shown to be beneficial for understanding the behavior of a fuel cell. The addition of gas pores is shown to promote high current densities due to increased species transport throughout the agglomerate. Flooding is considered, and its effect on the cathode active layer is evaluated. The model takes various transport and electrochemical kinetic parameters values from the literature in order to do a parametric study showing the degree to which temperature, pressure, and geometry are crucial to overall performance. This parametric study quantifies among a number of other things the degree to which lower porosities for thick active layers and higher porosities for thin active layers are advantageous to fuel cell performance. Cathode active layer performance is shown not to be solely a function of catalyst surface area but discrete catalyst placement within the agglomerate. / Master of Science
406

Preventing Oxidation of Dairy Powders Using Oxygen Removal Packaging

Mannon, Adria G. 09 January 2008 (has links)
Three types of dried milk (whole, nonfat, and buttermilk) were packaged in a modified atmosphere with a novel palladium-based oxygen removing catalyst and stored for eight weeks at 50°C. Powders stored in air with no catalyst and powders stored with the catalyst in an atmosphere modified to contain 5.7% hydrogen in nitrogen were evaluated by instrumental, chemical, and sensory methods. Hexanal concentrations were measured weekly using solid phase microextraction (SPME) and gas chromatography (GC) to compare the degrees of oxidation in the powders stored with the catalyst to those stored without it. Color changes were also monitored weekly using Hunter's L-, a-, and b-values. At the end of the eight-week period, a paired comparison sensory test was used to ascertain if the catalyst had an effect on odor. Anisidine values were also measured at this point to determine levels of oxidation in the powders. No significant difference was found in levels of oxidation between samples packaged with and without the catalyst in the modified atmosphere. At the end of eight weeks, the average hexanal concentration in the whole milk powder stored with the oxygen scavenger was 1.19 ± 0.20 ppm, while the average hexanal concentration in the air-packed whole milk powder was 1.06 ± 0.08 ppm. The average hexanal concentrations for the buttermilk stored with the catalyst and without were 0.84 ± 0.18 and 0.79 ± 0.15 ppm, respectively. In the nonfat milk powder, the sample stored with the catalyst had an average hexanal concentration of 0.91 ± 0.14 ppm and the sample stored in air without the catalyst had an average hexanal concentration of 0.83 ±0.20 ppm. Difference testing by volunteer sensory panelists also revealed no significant differences. It was expected that the milk powders stored with the catalyst in the modified atmosphere would have lower levels of oxidation and off-odors at the end of the eight weeks. However, the treatment ultimately resulted in no chemical or sensory differences. Thus, the catalyst proved ineffective in the given conditions. This could be due to a loss of the hydrogen required for the catalyst to function as time progressed or a lack of significant oxidation under the conditions employed. / Master of Science in Life Sciences
407

Combining In Situ Measurements and Advanced Catalyst Layer Modeling in PEM Fuel Cells

Regner, Keith Thomas 19 October 2011 (has links)
Catalyst layer modeling can be a useful tool for fuel cell design. By comparing numerical results to experimental results, numerical models can provide a better understanding of the physical processes occurring within the fuel cell catalyst layer. This can lead to design optimization and cost reduction. The purpose of this research was to compare, for the first time, a direct numerical simulation (DNS) model for the cathode catalyst layer of a PEM fuel cell to a newly developed experimental technique that measures the ionic potential through the length of the catalyst layer. A new design for a microstructured electrode scaffold (MES) is proposed and implemented. It was found that there is a 25%-27% difference between the model and the experimental measurements. Case studies were also performed with the DNS to compare the effects of different operating conditions, specifically temperature and relative humidity, and different reconstructed microstructures. Suggested operating parameters are proposed for the best comparison between numerical and experimental results. Recommendations for microstructure reconstruction, MES construction and design, and potential measurement techniques are also given. / Master of Science
408

Evaluation the performance of the tin (IV) oxide (SnO2) in the removal of sulfur compounds via oxidative-extractive desulfurization process for production an eco-friendly fuel

Humadi, J.I., Issa, Y.S., Aqar, D.Y., Ahmed, M.A., Ali Alak, H.H., Mujtaba, Iqbal M. 22 September 2022 (has links)
Yes / Catalysts play a vital role in petroleum and chemical reactions. Intensified concerns for cleaner air with strict environmental regulations on sulfur content in addition to meet economic requirements have generated significant interests for the development of more efficient and innovative oxidative catalysts recently. In this study, a novel homemade nano catalyst (manganese oxide (MnO2) over tin (IV) oxide (SnO2)) was used for the first time as an effective catalyst in removing dibenzothiophene (DBT) from kerosene fuel using hydrogen peroxide (H2O2) as oxidant in catalytic oxidative-extractive desulfurization process (OEDS). The catalyst was prepared by impregnation method with various amount of MnO2 loaded on SnO2. The oxidation step was carried out at different operating parameters such as reaction temperature and reaction time in batch reactor. The extractive desulfurization step was performed by using acetonitrile as solvent under several operating conditions (agitation speed and mixing time). The activity of MnO2/SnO2 catalyst in removing various sulfur compounds from kerosene fuel at the best operating conditions was investigated in this work. The results of the catalyst characterization proved that a high dispersion of MnO2 over the SnO2 was obtained. The experiments showed that the highest DBT and various sulfur compounds removal efficiency from kerosene fuel under the best operating conditions (oxidation: 5% MnO2/SnO2, reaction temperature of 75 0C, and reaction time of 100 min, extraction: acetonitrile, agitation speed of 900 rpm, and mixing time of 30 min) via the catalytic oxidative-extractive desulfurization process was 92.4% and 91.2%, respectively. Also, the MnO2/SnO2 catalyst activity was studied after six consecutive oxidation cycles at the best operating conditions, and the catalyst prove satisfactory stability in terms of sulfur compounds removal. After that, the spent catalyst were regenerated by utilizing different solvents (methanol, ethanol and iso-octane), and the experimental data explained that iso-octane achieved highest regeneration efficiency. / This study was supported by College of Petroleum Processes Engineering, Tikrit University, Iraq and Ministry of Oil, Iraq.
409

Synthesis and degradation of biobased polymers from plant oils incorporated with cellulose nanocrystals.

Elmore, Katherine 10 May 2024 (has links) (PDF)
Synthetic plastics are intrinsic to modern human existence. Unfortunately, many challenges exist related to the accumulation of plastic waste, including greenhouse gas emissions, contamination of natural environments, and entrance into the food chain through microplastics. Therefore, new polymers are being developed that both compete with the capabilities and costs of petroleum-based plastics and have assured biodegradability. Through decades of research, plant oils have emerged as one of the leading options for alternative starting materials because of their feasibility for use in polymerization reactions, wide availability, renewability, and cost-effectiveness. In this work, cottonseed oil (CSO) and soybean oil (SBO) are successfully utilized to synthesize polymers with a range of promising properties. A nanocomposite was produced by incorporating cellulose nanocrystals (CNCs) into an epoxidized CSO (ECSO) polymer matrix. A significant improvement in properties such as tensile stiffness and strength, without any substantial decrease in extensibility or thermal integrity has been observed. This demonstrated that CNCs can be used to tune the CSO- based polymer properties. Enzymes are excellent alternatives to traditional catalysts as they eliminate the necessity of elevated reaction temperatures and pressures. Epoxidized SBO (ESBO) was polymerized using immobilized candida antarctica lipase B (Novozyme N435). The resulting polymer was inhomogeneous, with soluble waxy and insoluble solid components. Analyses of the soluble component indicated the formation of a multi-branched polymer, showing that a greener system may be used to produce ESBO-based polymers. It is necessary to test the biodegradability of biobased polymers to confirm their validity as alternatives to traditional plastics. Degradation of the CNC-incorporated CSO-based network polymer was characterized by submersing specimens into various aqueous media, including artificial seawater and saltwater, to simulate realistic end-of-use scenarios. Decomposition occurred due to hydrolysis of the many ester linkages within the polymer structure. The presence of CNCs appeared to enhance the rate of degradation. Overall, the hydrolytic susceptibility of the CSO-based network polymer was observed as enhanced by incorporating CNCs. In summary, this work demonstrates the viability of using plant oils and CNCs to produce biodegradable polymers with a range of properties, thus aiding in the effort to replace traditional plastics.
410

Metodjämförelse av fenobarbital på Immulite 2000 versus Catalyst dx för hundar med epilepsi

Lönn, Rebecca January 2017 (has links)
Definitionen av epilepsi är ofrivillig förändring av den neurologiska funktionen i hjärnan. Sjukdomen uppkommer när det blir obalans i kommunikationen mellan hjärnans nervceller. Det är en störning/aktivering av impulsfrisättningen i hjärnan där orsakerna inte är fastställda. Fenobarbital är ett lugnande och sömngivande preparat, som motverkar kramper och begränsar retningens spridning i hjärnan genom att förstärka effekten av den hämmande transmittorsubstansen gammaaminosmörsyra (GABA). Syftet med studien var en metodjämförelse av fenobarbitalnivåer i serum uppmätta på Immulite 2000 versus Catalyst Dx hos hundar med epilepsi. Catalyst dx är ett veterinärmedicinskt instrument som använder torrkemisk analys. Immulite 2000 använder en våtkemisk metod och är ett instrument som fungerar på liknande sätt som sandwich ELISA metoden. Resultatet av de 14 prover som analyserades under april-maj 2017 visar på högre värden för samtliga prover analyserade på instrumentet Catalyst dx jämfört med Immulite 2000. Med ett P-värde på <0,0001 betyder det att nollhypotesen förkastas, dvs det förekommer en signifikant skillnad mellan instrumenten. / The definition of epilepsi is unintended change of neurological function in the brain. The disease occurs when there is imbalance in communication between the brains nerve cells. It is disorder/activation of pulse release in the brain where the causes are not determined. Phenobarbital is an appeasement and soporific preparation. It´s a drug that inhibits cramps and limit the spread of the direction in the brain by enhancing the effect of the inhibitory transmittor substance gamma aminobutyric acid (GABA). The aim of this study examine method comparison of the phenobarbital level measured on Immulite 2000 versus Catalyst Dx in dogs with epilepsy. Catalyst dx (IDEXX) is a veterinary instrument which uses dry chemical analysis. Immulite 2000 (Siemens) uses a wet chemical method and it´s an instrument that works similar to the sandwich ELISA method. The results from the 14 samples analyzed in april-may 2017 shows higher values for all samples on the instrument Catalyst dx comparison to Immulite 2000. With a P-value of <0,0001 it means that the zero hypothesis is rejected. There is a significant difference between the instruments.

Page generated in 0.0438 seconds