Дисертації з теми "Chemical kinetic modeling"
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1
Jalan, Amrit. "Predictive kinetic modeling of low-temperature hydrocarbon oxidation." Thesis, Massachusetts Institute of Technology, 2014. http://hdl.handle.net/1721.1/91059.
Анотація:
Thesis: Ph. D., Massachusetts Institute of Technology, Department of Chemical Engineering, 2014.Cataloged from PDF version of thesis.
Includes bibliographical references (pages 221-235).
Low temperature oxidation in the gas and condensed phases has been the subject of experimental investigations for many decades owing to applications in many areas of practical significance like thermal stability, combustion, atmospheric chemistry and industrial syntheses. Owing to several practical limitations it has proven difficult to understand these processes at a mechanistic level from experiments alone. Developments in scientific computing have opened up computational chemistry and cheminformatics based tools as an attractive option for exploring and elucidating the kinetics of these complex processes through detailed kinetic modeling and requires efforts in three key areas: single reaction kinetics, reaction networks and coupling kinetics with mass/momentum/energy balance models. This thesis presents several contributions employing high-level electronic structure calculations, reaction rate theory, automated kinetic modeling and empirical correlations to further our mechanistic understanding of low-temperature oxidation in the gas and liquid phase. First, an extensible framework for automatic estimation of species thermochemistry in the solution phase is presented and validated. This framework uses the Linear Solvation Energy Relationship (LSER) formalism of Abraham/Mintz and co-workers for high-throughput estimation of [delta]G°solv(T) in over 30 solvents using solute descriptors estimated from group additivity. The performance of scaled particle theory (SPT) expressions for enthalpic-entropic decomposition of [delta]G°solv(T) is also discussed along with the associated computational issues. Second, the importance of solvent effects on free-radical kinetics is explored using tetralin oxidation as a case study. The solvent dependence for the main propagation and termination reactions are determined using the Polarizable Continuum (PCM) family of solvation models. Incorporating these kinetic solvent effects in detailed kinetic models suggest oxidation rates increase with solvent polarity, consistent with experiment. Following this, electronic structure methods and reaction rate theory are used elucidate mechanistic details of new pathways in liquid-phase and atmospheric oxidation. The first of these studies focuses on pathways that establish [gamma]-ketohydroperoxides (KHP), well-known products in low-temperature alkane oxidation, as precursors to acids through a two-step process. Ab initio calculations are used to identify pathways leading from KHP to a cyclic peroxide isomer which decomposes through novel concerted reactions into carbonyl and carboxylic acid products. High-level gas phase rate coefficients are obtained using DFT/WFT methods coupled with VTST/SCT calculations and multi-structural partition functions (QMs-T). Solvent effects are included using continuum dielectric solvation models and the predicted rate coefficients found to be in excellent agreement with experiment lending theoretical support to the 30-year old Korcek hypothesis. Next, insights from the Korcek reaction are extended to atmospheric chemistry where similar cyclic peroxides are formed by reactions of the Criegee Intermediate (*CH₂OO*) with double bonds. More specifically, the role of chemical activation in reactions between *CH₂OO* and C=O/C=C species is explored using master equation calculations to obtain phenomenological rate coefficients k(T,P). In the case of reactions with C=O, the yield of collisionally stabilized SOZ at atmospheric pressure was found to increase in the order HCHO < CH₃CHO < CH₃COCH₃ - At low pressures, chemically activated formation of organic acids was found to be the major product channel in agreement with recent direct measurements. Epoxide and CH₂=CHOH are predicted to be the major products for *CH₂OO* + C₂H₄ under atmospheric conditions. Finally, as a case study in coupling detailed chemical and physical models, the improved understanding of liquid phase oxidation developed above is used to build multi-physics models of diesel injector deposit formation that adversely affects fuel spray characteristics and engine efficiency. Octane is used as a model liquid fuel for detailed kinetic modeling of oxidative aging leading to deposit precursors. In addition to fuel chemistry, the immiscibility of polar oxidation products leading to 'soft deposit' is modeled using linear solvation energy relationships. The chemistry and phase separation models are coupled with physical processes like washing. The resulting framework is used to explore the sensitivity of deposit formation to various model parameters.
by Amrit Jalan.
Ph. D.
2
Moore, Jason Stuart. "Kinetic modeling and automated optimization in microreactor systems." Thesis, Massachusetts Institute of Technology, 2013. http://hdl.handle.net/1721.1/79195.
Анотація:
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemical Engineering, 2013.Cataloged from PDF version of thesis.
Includes bibliographical references (p. 127-138).
The optimization, kinetic investigation, or scale-up of a reaction often requires significant time and materials. Silicon microreactor systems have been shown advantageous for studying chemical reactions due to their small volume, rapid mixing, tight temperature control, large range of operating conditions, and increased safety. The primary goal of this thesis is to expand the capabilities of automated microreactor systems to increase their scope and efficiency. An automated optimization platform is built utilizing continuous inline IR analysis at the reactor exit, and a Paal-Knorr reaction is chosen as the first example chemistry. This reaction, where both the first and second reaction steps affect the overall rate, leads to a more complex conversion profile. A steepest descent algorithm is first used to optimize conversion and production rates. The steepest descent algorithm tends to move slowly up the production rate ridge, significantly reducing efficiency. This issue is overcome by using a Fletcher-Reeves conjugate gradient method, which finds the constrained optimum in much fewer experiments. The conjugate gradient algorithm is then further improved upon by incorporating a hybrid Armijo line search and bisection contraction method. However, the conversion is only about 40% at the maximum in production rate. A further optimization is performed using a quadratic loss function to penalize conversions of less than 85%. This optimization of production rate led to an optimum at higher residence time, where a conversion of 81% is achieved. In the conventional view of reaction analysis, batch reactions are thought to be significantly more efficient in generating time-course reaction data than flow reactions, which are generally limited to steady-state studies. By taking advantage of the low dispersion in microreactors, successive fluid elements of the reactor may be treated as separate batch reactors. By continuously manipulating the reaction flow rate and tracking the total reaction time of each fluid element, time-course data analogous to that conventionally derived from batch reactors are generated and shown to be in agreement with steady-state results. Palladium-catalyzed carbonylation and CN-coupling reactions are used extensively in laboratory synthesis and industrial processes. The primary reaction studied involves the coupling of bromobenzene and morpholene with the addition of one or two carbonyl groups. The dependence of reaction conversion and selectivity on temperature, CO pressure, and Pd concentration are investigated using GC and IR analysis. A temperature ramp method is employed to rapidly investigate temperature effects on reaction rate and selectivity. The experiments reveal a change in the rate determining step at approximately 120 °C and corresponded well with GC data taken at several setpoints. In addition, the activation energy of the lower temperature regime as determined by this IR analysis is found to be very similar to that found by GC analysis, the experiments for which took significantly longer both to perform and analyze. Furthermore, the data collected from these experiments are used to fit a kinetic model. Multicomponent reactions (MCRs) are important to drug discovery by affording complex products in only a single step. By linking two of these MCRs, a Petasis boronic acid-Mannich reaction and an Ugi reaction, six different components could be incorporated in a relatively short time. The kinetics of each reaction are investigated with online UPLC analysis, allowing for quantification of a number of reaction components, including monitoring the formation of side products that were unknown prior to experimentation. A simple microcalorimeter is built using thermoelectric elements and a silicon microreactor to experimentally determine the heats of reaction during flow to allow for understanding the heat transfer needs for scale up. The result from the nitration of benzene, which has a heat of reaction of -117 kJ/mol, is -118.6 +/- 2.4 kJ/mol. The experimentally determined values are close to the known values; however, there is significant noise in the output during the reaction due to the two-phase nature of the reaction. The Paal-Knorr reaction is further investigated to determine the limits of sensitivity of the microcalorimetry system. A continuous concentration ramp experiment is performed with online IR analysis, enabling the thermoelectric output to be adjusted for reaction rate to determine the sensitivity to the heat of reaction. Below approximately 2 M, the sensitivity decreases rapidly, largely due to noise in the temperature control and concentration. To attempt to correct for the former, a calorimetry system with larger thermal mass is constructed and shown to decrease the sensitivity limit to 1 M, corresponding to a heat flow of approximately 0.05 W.
by Jason Stuart Moore.
Ph.D.
3
Akih, Kumgeh Benjamin. "Shock tube studies and chemical kinetic modeling of oxygenated hydrocarbon ignition." Thesis, McGill University, 2011. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=103701.
Анотація:
As a contribution towards understanding, modeling and controlling the combustion of oxygenated hydrocarbons such as biofuels, the high-temperature ignition of a series of relevant molecules has been investigated behind reflected shock waves at pressures ranging from 1 atm to 13 atm. Short chain biodiesel surrogates, methyl and ethyl esters, have been investigated. Methyl esters of formic to butanoic acids have been investigated in order to uncover the trends in their ignition delay times. The trends have further been explored by means of computational quantum chemical calculations. While most of these surrogates portray similar ignition behavior, the influence of structure with respect to terminal methyl groups and the presence or absence of secondary C–H bonds have been observed as in the case of methyl acetate with longer ignition delay times. The role of the alkyl group on the ester reactivity has been investigated by comparing methyl and ethyl esters, with the result that ethyl esters are generally more reactive. Apart from these biodiesel surrogates, selected C3 oxygenates, relevant to combustion have been investigated. A chemical kinetic mechanism for the high-temperature oxidation of propanal is developed and tested. Propanal, like other aldehydes, belongs to the group of intermediate species which occur in the combustion of almost all hydrocarbons, but their accurate prediction in combustion modeling is challenging. Targeted studies of the submodels of these compounds are expected to contribute towards predictive chemical kinetic modeling. The developed mechanism also shows encouraging performance in the prediction of acetaldehyde (ethanal) ignition. Ethanol is another biofuel widely used in spark-ignition engines. There is also interest in using this fuel in diesel and Homogeneous Charge Compression Ignition (HCCI) engine concepts. This is in line with the need for tailor-made, flexible fuels for wide range applications in energy conversion. Ethanol ignition modification by isopropyl nitrate (IPN), isopropyl formate (IPF) and water has been investigated. It is found that whereas IPN improves the ignition performance of ethanol (shorter ignition delay times), IPF increases its ignition resistance (longer ignition delay times), so that it can be used as an anti-knock agent. It is further observed that at temperatures above 1400 K, IPN addition ceases to improve the ignition of ethanol. Wet ethanol ignition reveals that at the same post-shock temperature water has an ignition promoting effect. The feasibility of igniting wet ethanol raises the prospect of reducing ethanol production cost (distillation) by using ethanol with allowable water content, albeit with a lower specific energy content. The ignition behavior of the biodiesel surrogate, methyl butanoate, and the diesel surrogate, n-heptane, is compared. Similar behavior is observed under stoichiometric conditions, with slight differences under rich conditions. A skeletal mechanism is proposed for the combustion of blends of the two surrogates. The skeletal mechanism is derived from reduced skeletal mechanisms of literature mechanisms for n-heptane and methyl butanoate obtained on the basis of extensive ignition sensitivity analyses and chemical kinetic insight. These reduced skeletal models have been found to perform reasonably well when compared to predictions by their original detailed mechanisms with respect to ignition, flame propagation and the structure of an opposed flow flame in the mixture fraction space. A systematic approach has been taken in this work to compare the reactivity of fuels, which leads to insight on trends, similarities and differences in global ignition behavior. The combination of experiments, analyses, computations and modeling demonstrates the synergy required to address problems in modern combustion science and technology.En tant que contribution à la compréhension, la modélisation et le contrôle de la combustion des hydrocarbures oxygénés tels que les biocarburants, l'auto-allumage à haute température d'une série de molécules a été étudiée avec la méthode de tube a onde de choc pour les pressions entre 1 atm et 13 atm. Les molécules représentatives du biodiésel, c'est à dire des esters méthyliques et éthyliques, ont été étudiées. Les esters méthyliques d'acide formique jusqu'à butanoique ont été étudiés afin de découvrir l'influence de leurs structures sur l'auto-allumage. Cette relation a aussi été examinée avec les calculs de la chimique quantique. Alors que la pluparts de ces esters sont marqués par des délais d'auto-allumage similaires, les influences des groupes méthyliques terminales, et la présence ou absence des liaisons secondaires de C-H, ont été identifiées, comme dans le cas d'acétate de méthyle, caractérisé par les plus longs délais. Le rôle du groupe alkyle sur la réactivité d'ester a été étudié en comparant des esters méthyliques avec les esters éthyliques. Les esters éthyliques sont généralement plus réactifs que les esters méthyliques du même acide. De la même manière, sont investigués quelques hydrocarbures oxygénés, dont leur cinétique d'oxydation est impliquée dans la combustion des biocarburants et carburants pétrolifères. Un mécanisme de la cinétique chimique pour la combustion du propanal à haute température a été développé et validé. Le propanal, comme d'autres aldéhydes, appartient au groupe des espèces intermédiaires qui se forment pendant la combustion de presque tous les hydrocarbures, mais leur modélisation reste imprécise. Des études consacrées à la compréhension des sous-modèles de ces molécules devraient contribuer à la modélisation avancée de la cinétique chimique de la combustion. Le mécanisme proposé prédit aussi les délais d'auto-allumage d'acétaldéhyde, dont le sous-mécanisme est inclus. L'éthanol est un biocarburant largement utilisé dans les moteurs à allumage commandé. Il y a également intérêt à utiliser ce carburant dans les moteurs à allumage par compression. Ceci est en accord avec la nécessité de développer des carburants flexibles pour des moteurs divers. La modification de l'auto-allumage de l'éthanol par des additifs chimiques comme le nitrate d'isopropyle (IPN), le formiate d'isopropyle (IPF) et l'eau a été investiguée. Il se trouve que, alors que l'IPN améliore la tendance à l'auto-allumage de l'éthanol (délais plus courts), l'IPF augmente sa résistance à l'autoallumage, de sorte que ce dernier peut être utilisé comme additif pour supprimer l'autoallumage. Pour une même température, l'auto-allumage de l'éthanol contenant de l'eau se révèle accélérée. Un mécanisme pour la combustion des mélanges de diesel et du biodiesel est également proposé. Le mécanisme est dérivé de la réduction des mécanismes détaillés pour le n-heptane et le butanoate de méthyle obtenus sur la base de l'analyse de sensitivité de l'auto-allumage. Cette méthode comparative systématique et innovatrice cherche à caractériser les propriétés des carburants oxygénés en vue de révéler les similitudes et les différences. Les résultats servent à l'optimisation des modèles cinétiques chimiques ainsi qu'à la compréhension de la cinétique de combustion d'une série d'espèces oxygénées. Des corrélations de délais d'auto-allumage sont également proposées pour l'application pratique. Le mécanisme proposé pour les mélanges diesel et biodiesel se prête à l'étude de la combustion dans les écoulements turbulents.
4
Alecu, Ionut M. Marshall Paul. "Kinetic studies and computational modeling of atomic chlorine reactions in the gas phase." [Denton, Tex.] : University of North Texas, 2009. http://digital.library.unt.edu/ark:/67531/metadc12071.
5
Alecu, Ionut M. "Kinetic studies and computational modeling of atomic chlorine reactions in the gas phase." Thesis, University of North Texas, 2009. https://digital.library.unt.edu/ark:/67531/metadc12071/.
Анотація:
The gas phase reactions of atomic chlorine with hydrogen sulfide, ammonia, benzene, and ethylene are investigated using the laser flash photolysis / resonance fluorescence experimental technique. In addition, the kinetics of the reverse processes for the latter two elementary reactions are also studied experimentally. The absolute rate constants for these processes are measured over a wide range of conditions, and the results offer new accurate information about the reactivity and thermochemistry of these systems. The temperature dependences of these reactions are interpreted via the Arrhenius equation, which yields significantly negative activation energies for the reaction of the chlorine atom and hydrogen sulfide as well as for that between the phenyl radical and hydrogen chloride. Positive activation energies which are smaller than the overall endothermicity are measured for the reactions between atomic chlorine with ammonia and ethylene, which suggests that the reverse processes for these reactions also possess negative activation energies. The enthalpies of formation of the phenyl and β-chlorovinyl are assessed via the third-law method. The stability and reactivity of each reaction system is further rationalized based on potential energy surfaces, computed with high-level ab initio quantum mechanical methods and refined through the inclusion of effects which arise from the special theory of relativity. Large amounts of spin-contamination are found to result in inaccurate computed thermochemistry for the phenyl and ethyl radicals. A reformulation of the computational approach to incorporate spin-restricted reference wavefunctions yields computed thermochemistry in good accord with experiment. The computed potential energy surfaces rationalize the observed negative temperature dependences in terms of a chemical activation mechanism, and the possibility that an energized adduct may contribute to product formation is investigated via RRKM theory.
6
Castaneda-Lopez, Luis Carlos. "Kinetic modeling of the hydrotreatment of light cycle oil/diesel." [College Station, Tex. : Texas A&M University, 2006. http://hdl.handle.net/1969.1/ETD-TAMU-1061.
7
Wu, Kuo-chʻun 1968. "Chemical kinetic modeling of oxidation of hydrocarbon emissions in spark ignition engines." Thesis, Massachusetts Institute of Technology, 1994. http://hdl.handle.net/1721.1/35377.
8
Boddapati, Aparna. "Modeling cure depth during photopolymerization of multifunctional acrylates." Thesis, Georgia Institute of Technology, 2010. http://hdl.handle.net/1853/33934.
Анотація:
The photopolymerization of multifunctional acrylates leads to the formation of a complex and insoluble network due to cross-linking. This characteristic is a useful property for stereolithography applications, where solid parts of the desired shape are cured using a pre-determined energy exposure profile. Traditionally, the required energy exposure is determined using a critical energy--depth of penetration, or Ec--Dp, model. The parameters Ec and Dp, are usually fit to experimental data at a specific resin composition and cure intensity. As a result, since the Ec--Dp model does not explicitly incorporate cure kinetics, it cannot be used for a different set of process conditions without first obtaining experimental data at the new conditions. Thus, the Ec--Dp model does not provide any insight when a new process needs to be developed, and the best processing conditions are unknown.
The kinetic model for multifunctional acrylate photopolymerization presented here is based on a set of ordinary differential equations (ODE), which can be used to predict part height versus exposure condition across varying resin compositions. Kinetic parameter information used in the model is obtained by fitting the model to double bond conversion data from Fourier Transform Infrared Spectroscopy (FTIR) measurements. An additional parameter, the critical conversion value, is necessary for determining the formation of a solid part of the desired height. The initial rate of initiation, Ri, combines all the factors that impact part height, and therefore, it is an important quantity that is required in order to find the critical conversion value. The critical conversion value is estimated using the Ri and Tgel value from microrheology measurements.
Information about network connectivity, which can be used to get properties such as molecular weight, cannot be derived from models using traditional mass-action kinetics for the cross-linking system. Therefore, in addition to modeling the reaction using the ODE based model, the results from a statistical model based on Kinetic Monte Carlo (KMC) principles are also shown here. The KMC model is applicable in situations where the impact of chain length on the kinetics or molecular weight evolution is of interest. For the present project, the detailed information from network connectivity was not required to make part height predictions, and the conversion information from the ODE model was sufficient.
The final results show that the kinetic ODE model presented here, based on the critical conversion value, captures the impact of process parameters such as initiator concentration, light intensity, and exposure time, on the final part height of the object. In addition, for the case of blanket cure samples, the part height predictions from the ODE model make comparable predictions to the Ec--Dp model. Thus, the ODE model presented here is a versatile tool that can be used to determine optimum operating conditions during process development.
9
Lee, Chuang-Chung. "Kinetic modeling of amyloid fibrillation and synaptic plasticity as memory loss and formation mechanisms." Thesis, Massachusetts Institute of Technology, 2008. http://hdl.handle.net/1721.1/49893.
Анотація:
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Chemical Engineering, 2008.Includes bibliographical references (p. 141-150).
The principles of biochemical kinetics and system engineering are applied to explain memory-related neuroscientific phenomena. Amyloid fibrillation and synaptic plasticity have been our focus of research due to their significance. The former is related to the pathology of many neurodegenerative diseases and the later is regarded as the principal mechanism underlying learning and memory. Claimed to be the number one cause of senile dementia, Alzheimer's disease (AD) is one of the disorders that involve misfolding of amyloid protein and formation of insoluble fibrils. Although a variety of time dependent fibrillation data in vitro are available, few mechanistic models have been developed. To bridge this gap we used chemical engineering concepts from polymer dynamics, particle mechanics and population balance models to develop a mathematical formulation of amyloid growth dynamics. A three-stage mechanism consisting of natural protein misfolding, nucleation, and fibril elongation phases was proposed to capture the features of homogeneous fibrillation responses. While our cooperative laboratory provided us with experimental findings, we guided them with experimental design based on modeling work. It was through the iterative process that the size of fibril nuclei and concentration profiles of soluble proteins were elucidated. The study also reveals further experiments for diagnosing the evolution of amyloid coagulation and probing desired properties of potential fibrillation inhibitors. Synaptic plasticity at various time ranges has been studied experimentally to elucidate memory formation mechanism. By comparison, the theoretical work is underdeveloped and insufficient to explain some experiments. To resolve the issue, we developed models for short-term, long-term, and spike timing dependent synaptic plasticity, respectively.
(cont.) First, presynaptic vesicle trafficking that leads to the release of glutamate as neurotransmitter was taken into account to explain short-term plasticity data. Second, long-term plasticity data lasting for hours after tetanus stimuli has been matched by a calcium entrapment model we developed. Model differentiation was done to demonstrate the better performance of calcium entrapment model than an alternative bistable theory in fitting graded long-term potentiation responses. Finally, to decipher spike timing dependent plasticity (STDP), we developed a systematic model incorporating back propagation of action potential, dual requirement of NMDA receptors, and calcium dependent plasticity. This built model is supported by five different types of STDP experimental data. The accumulation of amyloid beta has been found to disrupt the sustainable modification of long-term synaptic plasticity which might explain the inability of AD patients to form new memory at early stage of the disease. Yet the linkage between the existence of amyloid beta species and failure of long-term plasticity was unclear. We suggest that the abnormality of calcium entrapment function caused by amyloid oligomers is the intermediate step that eventually leads to memory loss. Unsustainable calcium level and decreased postsynaptic activities result into the removal or internalization of alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors. The number of AMPA receptors as the indicators of synaptic strength may result into disconnection between neurons and even neuronal apoptosis. New experiments have been suggested to validate this hypothesis and to elucidate the pathology of Alzheimer's disease.
by Chuang-Chung (Justin) Lee.
Ph.D.
10
Bandstra, Joel Zachary. "Kinetic modeling of heterogeneous chemical reactions with applications to the reduction of environmental contaminants on iron metal." Full text open access at:, 2005. http://content.ohsu.edu/u?/etd,280.
11
Kumar, Hans. "Mechanistic kinetic modeling of the hydrocracking of complex feedstocks." [College Station, Tex. : Texas A&M University, 2006. http://hdl.handle.net/1969.1/ETD-TAMU-1063.
12
Bongartz, Dominik. "Chemical kinetic modeling of oxy-fuel combustion of sour gas for enhanced oil recovery." Thesis, Massachusetts Institute of Technology, 2014. http://hdl.handle.net/1721.1/92224.
Анотація:
Thesis: S.M., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2014.Cataloged from PDF version of thesis.
Includes bibliographical references (pages 135-147).
Oxy-fuel combustion of sour gas, a mixture of natural gas (primarily methane (CH 4 )), carbon dioxide (CO 2 ), and hydrogen sulfide (H 2 S), could enable the utilization of large natural gas resources, especially when combined with enhanced oil recovery (EOR). Chemical kinetic modeling can help to assess the potential of this approach. In this thesis, a detailed chemical reaction mechanism for oxy-fuel combustion of sour gas has been developed and applied for studying the combustion behavior of sour gas and the design of power cycles with EOR. The reaction mechanism was constructed by combining mechanisms for the oxidation of CH4 and H2S and optimizing the sulfur sub-mechanism. The optimized mechanism was validated against experimental data for oxy-fuel combustion of CH4, oxidation of H2S, and interaction between carbon and sulfur species. Improved overall performance was achieved through the optimization and all important trends were captured in the modeling results. Calculations with the optimized mechanism suggest that increasing H2 S content in the fuel tends to improve flame stability through a lower ignition delay time. Water diluted oxy-fuel combustion leads to higher burning velocities at elevated pressures than CO 2 dilution or air combustion, which also facilitates flame stabilization. In a mixed CH4 and H2S flame, H25 is oxidized completely as CH4 is converted to carbon monoxide (CO). During CO burnout, some highly corrosive sulfur trioxide (SO3 ) is formed. Quenching of SO 3 formation in the combustor can only be achieved at the expense of higher CO emissions. The modeling of a gas turbine cycle showed that oxy-fuel combustion leads to SO 3 concentrations that are one to two orders of magnitude lower than in air combustion and will thus suffer much less from the associated corrosion problems. Slightly fuel-rich operation is most promising for achieving the low CO and oxygen (02) concentrations required for EOR while further minimizing SO 3. Carbon dioxide dilution is better for achiving low 02 in the EOR stream while H20 gives the better combustion efficiency.
by Dominik Bongartz.
S.M.
13
Pope, Christopher James. "A chemical mechanism for fullerenes C₆₀ and C₇₀ formation with kinetic modeling of their synthesis in flames." Thesis, Massachusetts Institute of Technology, 1993. http://hdl.handle.net/1721.1/12663.
14
Tripathi, Rupali [Verfasser]. "Detailed Chemical Kinetic Modeling of Biofuels and their Blends with Conventional Fuel Components / Rupali Tripathi." Düren : Shaker, 2020. http://d-nb.info/1213471850/34.
15
Foster, Michael Scott. "Design, synthesis, kinetic analysis, molecular modeling, and pharmacological evaluation of novel inhibitors of peptide amidation." Diss., Atlanta, Ga. : Georgia Institute of Technology, 2008. http://hdl.handle.net/1853/31816.
Анотація:
Thesis (Ph.D)--Chemistry and Biochemistry, Georgia Institute of Technology, 2009.Committee Chair: Dr. Sheldon W. May; Committee Member: Dr. James C. Powers; Committee Member: Dr. Nicholas Hud; Committee Member: Dr. Niren Murthy; Committee Member: Dr. Stanley H. Pollock. Part of the SMARTech Electronic Thesis and Dissertation Collection.
16
Giramondi, Nicola. "Multi-energy well kinetic modeling of novel PAH formation pathways in flames." Thesis, KTH, Kraft- och värmeteknologi, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-183558.
Анотація:
Polycyclic Aromatic Hydrocarbons (PAHs) are harmful by-products formed during combustion of hydrocarbons under locally fuel-rich conditions followed by incomplete combustion. PAHs act as precursors during the formation of soot. PAHs and soot are harmful for human health and legislation limits the emission of unburned hydrocarbons and soot. Consequently, other measures are necessary in order to limit the production of PAHs and soot in internal combustion engines applications, entailing a possible decrease of fuel efficiency and higher technical requirements for automotive manufactures. The combustion chemistry of PAHs is not fully understood, which prompts the need of further investigations. The chemical dynamics shown by novel pathways of PAH formation involving vinylacetylene addition to the phenyl radical opens up new horizons for the potential contribution to PAH formation through this class of reactions. In the present work novel pathways of the formation of naphthalene and phenanthrene are investigated for a laminar premixed benzene flame and a laminar ethylene diffusion flame. The purpose is to improve the prediction of the aromatic species concentration in the flames. A pathway chosen due the high potential aromatic yield is assessed through preliminary flame calculations relying on simplifying assumptions concerning reaction rates. Certain isomerisation steps of the pathway occur within a time-scale characteristic of thermal relaxation processes. Therefore, the solution of the energy grained master equation is necessary in order to calculate the phenomenological reaction rates resulting from a non-equilibrium kinetic modeling. Quantum chemical calculations are performed in order to calculate molecular properties of the species involved. These properties are subsequently processed to determine the rate constants of the sequence of multi-energy well reactions. Moreover, the chemical dynamics of the pathway is analyzed and the effect of temperature and pressure on the kinetic parameters is investigated. Despite of the potential yield demonstrated through the preliminary flame calculations, the computed rate constants show that the studied reactions are insignificant for the formation of naphthalene and phenanthrene in the studied flames. An effort is put on evaluating if the non-equilibrium kinetic modeling adopted for the calculation of the kinetic parameters is consistent with the kinetic modeling used in the flame calculations. The current work provides an efficient method to compute rate constants of multi-energy well reactions at different thermodynamic conditions, characteristic of flames and of combustion in commercial devices or in internal combustion engines. Pathways with a slightly different chemical dynamics should be tested applying the current methodology. Moreover, further studies should be aimed at overcoming possible limits of the kinetic modeling of multi-energy well reactions occurring in combustion environments.
17
Sriramulu, Suresh. "Rates of the surface reactions in methanol and carbon monoxide electrooxidation : experimental measurements and kinetic modeling /." Thesis, Connect to this title online; UW restricted, 1999. http://hdl.handle.net/1773/9904.
18
Davidson, Jeffrey E. "Combustion Modeling of RDX, HMX and GAP with Detailed Kinetics." BYU ScholarsArchive, 1996. https://scholarsarchive.byu.edu/etd/6531.
Анотація:
A one-dimensional, steady-state numerical model of the combustion of homogeneous solid propellant has been developed. The combustion processes is modeled in three regions: solid, two-phase (liquid and gas) and gas. Conservation of energy and mass equations are solved in the two-phase and gas regions and the eigenvalue of the system (the mass burning rate) is converged by matching the heat flux at the interface of these two regions. The chemical reactions of the system are modeled using a global kinetic mechanism in the two-phase region and an elementary kinetic mechanism in the gas region. The model has been applied to RDX, HMX and GAP. There is very reasonable agreement between experimental data and model predictions for burning rate, temperature sensitivity, surface temperature, adiabatic flame temperature, species concentration profiles and melt-layer thickness. Many of the similarities and differences in the combustion of RDX and HMX are explained from sensitivity analysis results. The combustion characteristics of RDX and HMX are similar because of their similar chemistry. Differences in combustion characteristics arise due to differences in melting temperature, vapor pressure and initial decomposition steps. A reduced mechanism consisting of 18 species and 39 reactions was developed from the Melius-Yetter RDX mechanism (45 species, 232 reactions). This reduced mechanism reproduces most of the predictions of the full mechanism but is 7.5 times faster. Because of lack of concrete thermophysical property data for GAP, the modeling results are preliminary but indicate what type of experimental data is necessary before GAP can be modeled with more certainty.
19
Leamen, Michael. "Kinetic Investigation and Modelling of Multi-Component Polymer Systems with Depropagation." Thesis, University of Waterloo, 2005. http://hdl.handle.net/10012/885.
Анотація:
The phenomenon of depropagation or reverse polymerization for multicomponent polymerizations has been studied in detail. The monomer Alpha-Methyl Styrene (AMS) has been copolymerized with Methyl Methacrylate (MMA) and Butyl Acrylate (BA) at temperatures ranging from 60oC to 140oC and the kinetics have been studied in the form of propagation/cross propagation and depropagation parameters. There have been multiple attempts with varying amounts of success in the past to determine the kinetic parameters for depropagating systems including work by Lowry and Wittmer as well as other modelling methodologies that are not as mechanistic. The most recent development of the mechanistic terminal model is that of the Kruger model. The model is robust and can take into account all special cases as well as all reactions being reversible. The kinetic parameters have been estimated for each of the three binary systems using the Kruger model (MMA/AMS, MMA/BA, BA/AMS). The Alfrey-Goldfinger model is inadequate to describe depropagating terpolymer systems and in order to study them, a new model was developed based upon the binary Kruger model. This new model takes into account a fully depropagating terpolymer system leading to a total of 15 parameters to be estimated. These 15 parameters have the same definitions as those estimated from the binary Kruger model, thus making accurate analysis of the binary systems crucial since these will be used as first estimates for the terpolymer system. Extensive experimental data (composition, conversion and molecular weights) was collected and analysed for the MMA/AMS and BA/AMS systems. For the BA/AMS system both the bulk and solution copolymerizations were studied in detail with the results from the Kruger model not showing a significant difference in the reactivity ratios between the two types of polymerization. For the MMA/AMS system, a bulk study only was done which revealed an interesting phenomenon that points toward a break down of the long chain approximations used for all of the models being studied. For both of these systems, extensive 1H NMR analysis was done to determine the copolymer composition. Data collected in previous research for the MMA/BA system was reanalysed using the Kruger model and it was found that the parameter estimates did not differ significantly from the published values. Extensive benchmarking was done with the newly developed terpolymer model on non-depropagating systems using data from the literature to ensure it worked for the simplest cases. It was found that the model matched the parameter estimates from the literature and in some cases improving upon them to fit the data better. Along with the benchmarking a sensitivity analysis was done which revealed some interesting information. For the MMA/BA/AMS terpolymer system a set of experiments (based upon practical considerations) were performed and the composition of the polymer was determined using 13C NMR instead of the usual 1H NMR due to the difficulty of peak separation for the complex terpolymer. Using the depropagating terpolymer composition data in conjunction with the parameter estimates from the three binary systems allowed for estimation of the 15 kinetic parameters, which showed only minor variation from the binary estimates.
20
Shen, Xiaozhou. "Electrostatic Charging of Solid and Gas Phases and Application to Controlling Chemical Reactions." Case Western Reserve University School of Graduate Studies / OhioLINK, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=case1499941952140625.
21
Kim, Youngseob. "Air quality modeling : evaluation of chemical and meteorological parameterizations." Phd thesis, Université Paris-Est, 2011. http://pastel.archives-ouvertes.fr/pastel-00667777.
Анотація:
The influence of chemical mechanisms and meteorological parameterizations on pollutant concentrations calculated with an air quality model is studied. The influence of the differences between two gas-phase chemical mechanisms on the formation of ozone and aerosols in Europe is low on average. For ozone, the large local differences are mainly due to the uncertainty associated with the kinetics of nitrogen monoxide (NO) oxidation reactions on the one hand and the representation of different pathways for the oxidation of aromatic compounds on the other hand. The aerosol concentrations are mainly influenced by the selection of all major precursors of secondary aerosols and the explicit treatment of chemical regimes corresponding to the nitrogen oxides (NOx) levels. The influence of the meteorological parameterizations on the concentrations of aerosols and their vertical distribution is evaluated over the Paris region in France by comparison to lidar data. The influence of the parameterization of the dynamics in the atmospheric boundary layer is important ; however, it is the use of an urban canopy model that improves significantly the modeling of the pollutant vertical distribution
22
Shiraiwa, Manabu [Verfasser]. "Kinetic modeling and experiments on gas uptake and chemical transformation of organic aerosol in the atmosphere / Manabu Shiraiwa." Mainz : Universitätsbibliothek Mainz, 2011. http://d-nb.info/1025263596/34.
23
Adhikari, Shreya. "EXPERIMENTAL AND KINETIC ANALYSIS OF CATALYTIC GASIFICATION." Cleveland State University / OhioLINK, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=csu1406058470.
24
Champion, Wyatt. "Development of a Chemical Kinetic Model for a Fluidized-bed Sewage Sludge Gasifier." Master's thesis, University of Central Florida, 2013. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/5922.
Анотація:
As the need for both sustainable energy production and waste minimization increases, the gasification of biomass becomes an increasingly important process. What would otherwise be considered waste can now be used as fuel, and the benefits of volume reduction through gasification are seen in the increased lifespan of landfills. Fluidized-bed gasification is a particularly robust technology, and allows for the conversion of most types of waste biomass.
Within a fluidized-bed gasifier, thermal medium (sand) is heated to operating temperature (around 1350°F) and begins to fluidize due to the rapid expansion of air entering the bottom of the reactor. This fluidization allows for excellent heat transfer and contact between gases and solids, and prevents localized “hot spots” within the gasifier, thereby reducing the occurrence of ash agglomeration within the gasifier. Solids enter the middle of the gasifier and are rapidly dried and devolatilized, and the products of this step are subsequently oxidized and then reduced in the remainder of the gasifier. A syngas composed mainly of N2, H2O, CO2, CO, CH4, and H2 exits the top of the gasifier.
A computer model was developed to predict the syngas composition and flow rate, as well as ash composition and mass flow rate from a fluidized-bed gasifier. A review of the literature was performed to determine the most appropriate modeling approach. A chemical kinetic model was chosen, and developed in MATLAB using the Newton-Raphson method to solve sets of 18 simultaneous equations. These equations account for mass and energy balances throughout the gasifier. The chemical kinetic rate expressions for these reactions were sourced from the literature, and some values modified to better fit the predicted gas composition to literature data.M.S.Env.E.
Masters
Civil, Environmental, and Construction Engineering
Engineering and Computer Science
Environmental Engineering
25
Tripathi, Rupali [Verfasser], Heinz Günter [Akademischer Betreuer] Pitsch, and S. Mani [Akademischer Betreuer] Sarathy. "Detailed chemical kinetic modeling of biofuels and their blends with conventional fuel components / Rupali Tripathi ; Heinz Pitsch, S. Mani Sarathy." Aachen : Universitätsbibliothek der RWTH Aachen, 2019. http://nbn-resolving.de/urn:nbn:de:101:1-2020080423315879685573.
26
Tripathi, Rupali Verfasser], Heinz Günter [Akademischer Betreuer] [Pitsch, and S. Mani [Akademischer Betreuer] Sarathy. "Detailed chemical kinetic modeling of biofuels and their blends with conventional fuel components / Rupali Tripathi ; Heinz Pitsch, S. Mani Sarathy." Aachen : Universitätsbibliothek der RWTH Aachen, 2019. http://d-nb.info/1215171676/34.
27
Zhang, Fan. "A NEW PARADIGM OF MODELING WATERSHED WATER QUALITY." Doctoral diss., University of Central Florida, 2005. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/2387.
Анотація:
Accurate models to reliably predict sediment and chemical transport in watershed water systems enhance the ability of environmental scientists, engineers and decision makers to analyze the impact of contamination problems and to evaluate the efficacy of alternative remediation techniques and management strategies prior to incurring expense in the field. This dissertation presents the conceptual and mathematical development of a general numerical model simulating (1) sediment and reactive chemical transport in river/stream networks of watershed systems; (2) sediment and reactive chemical transport in overland shallow water of watershed systems; and (3) reactive chemical transport in three-dimensional subsurface systems. Through the decomposition of the system of species transport equations via Gauss-Jordan column reduction of the reaction network, fast reactions and slow reactions are decoupled, which enables robust numerical integrations. Species reactive transport equations are transformed into two sets: nonlinear algebraic equations representing equilibrium reactions and transport equations of kinetic-variables in terms of kinetically controlled reaction rates. As a result, the model uses kinetic-variables instead of biogeochemical species as primary dependent variables, which reduces the number of transport equations and simplifies reaction terms in these equations. For each time step, we first solve the advective-dispersive transport of kinetic-variables. We then solve the reactive chemical system node by node to yield concentrations of all species. In order to obtain accurate, efficient and robust computations, five numerical options are provided to solve the advective-dispersive transport equations; and three coupling strategies are given to deal with the reactive chemistry. Verification examples are compared with analytical solutions to demonstrate the numerical accuracy of the code and to emphasize the need of implementing various numerical options and coupling strategies to deal with different types of problems for different application circumstances. Validation examples are presented to evaluate the ability of the model to replicate behavior observed in real systems. Hypothetical examples with complex reaction networks are employed to demonstrate the design capability of the model to handle field-scale problems involving both kinetic and equilibrium reactions. The deficiency of current practices in the water quality modeling is discussed and potential improvements over current practices using this model are addressed.Ph.D.
Department of Civil and Environmental Engineering
Engineering and Computer Science
Civil Engineering
28
Visneski, Michael J. "Modeling of the low temperature reaction of sulfur dioxide and limestone using a three resistance film theory instantaneous reaction model." Ohio : Ohio University, 1991. http://www.ohiolink.edu/etd/view.cgi?ohiou1173741863.
29
Diaz, Aldana Luis A. "Mathematical Modeling of Ammonia Electro-Oxidation on Polycrystalline Pt DepositedElectrodes." Ohio University / OhioLINK, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1395077873.
30
Dmitriev, Artëm. "Kinetic study of ester biofuels in flames." Electronic Thesis or Diss., Université de Lorraine, 2020. http://www.theses.fr/2020LORR0238.
Анотація:
Le progrès partout dans le monde nécessite une variété de sources d'énergie propre. Les biocarburants liquides de type ester semblent être très efficaces dans ce contexte, car ils sont faciles à utiliser dans les véhicules modernes, ils peuvent être produits à partir de diverses ressources renouvelables et ils offrent des caractéristiques de combustion respectueuses de l'environnement. À cet égard, les esters éthyliques d'acides gras (EEAG) sont considérés comme une classe prometteuse de biocarburants. L'objectif principal de cette thèse était de développer un mécanisme cinétique chimique actualisé de la combustion des EEAG légers jusqu'au pentanoate d'éthyle et de le valider par rapport aux nouvelles données expérimentales sur la structure de flammes laminaires prémélangées à basse pression et pression atmosphérique. Les flammes alimentées par trois EEAG, l'acétate d'éthyle, le butanoate d'éthyle et le pentanoate d'éthyle, ont été étudiées au moyen de la spectrométrie de masse avec faisceau moléculaire et de la chromatographie en phase gazeuse. Plus de 40 espèces stables et intermédiaires comprenant des radicaux ont été détectées et quantifiées dans les flammes. Une analyse complète du mécanisme développé a été réalisée. La thèse se compose de 3 chapitres. Le premier chapitre présente une revue bibliographique. Les études expérimentales et théoriques les plus importantes sur la combustion des EEAG sont discutées. Le deuxième chapitre présente un aperçu des méthodes expérimentales et de simulation utilisées dans la thèse. Des détails sur le développement du mécanisme sont également fournis dans cette partie. Le dernier chapitre présente des résultats expérimentaux et de modélisation sur les esters étudiés en comparaison avec les mécanismes cinétiques de la littératureGlobal progress all over the world requires a variety of clean energy sources. Liquid ester-based biofuels seem to be very effective in this context since they are easy to use in modern vehicles, they can be produced from a variety of renewable resources, and they provide environmentally friendly combustion characteristics. In this regard, fatty acid ethyl esters (FAEEs) are considered as a promising class of biofuels. The main goal of this thesis was to develop an updated chemical kinetic mechanism of combustion of light FAEEs up to ethyl pentanoate and validate it against the new experimental data on chemical speciation in low and atmospheric pressure premixed laminar flames. The flames fueled by three FAEEs, ethyl acetate, ethyl butanoate and ethyl pentanoate, were investigated by means of molecular-beam mass-spectrometry and gas-chromatography. More than 40 stable and intermediate species including radicals were detected and quantified in the flames. A comprehensive analysis of the developed mechanism was performed. The thesis consists of 3 chapters. In the first chapter a review of literature is presented. The most important experimental and theoretic studies on FAEEs are discussed. The second chapter presents an overview of experimental and simulation methods used in the work. Details on the mechanism development are also provided in this part. The last chapter present experimental and modeling results on the esters studied in comparison with the literature kinetic mechanisms
31
JALADI, HEMACHAND. "EFFECTS OF MASS-TRANSFER AND KINETIC PARAMETERS ON BURKHOLDERIA CEPACIALIPASE IMMOBILIZED IN ORDERED MESOPOROUS SBA-15 HOSTS IN A PACKED-BED REACTOR." University of Cincinnati / OhioLINK, 2006. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1155788046.
32
Critchfield, Brian L. "Statistical Methods For Kinetic Modeling Of Fischer Tropsch Synthesis On A Supported Iron Catalyst." Diss., CLICK HERE for online access, 2006. http://contentdm.lib.byu.edu/ETD/image/etd1670.pdf.
33
Guo, Xufeng. "Evaluating the thermal-mechanical coupling effect on rubber aging: a combined experimental and modeling approach." University of Akron / OhioLINK, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=akron1586791964476118.
34
Ambati, Jyotrhirmai. "STUDIES ON SILICON NMR CHARACTERIZATION AND KINETIC MODELING OF THE STRUCTURAL EVOLUTION OF SILOXANE-BASED MATERIALS AND THEIR APPLICATIONS IN DRUG DELIVERY AND ADSORPTION." UKnowledge, 2011. http://uknowledge.uky.edu/gradschool_diss/203.
Анотація:
This dissertation presents studies of the synthetic processes and applications of siloxane-based materials. Kinetic investigations of bridged organoalkoxysilanes that are precursors to organic-inorganic hybrid polysilsesquioxanes are a primary focus. Quick gelation despite extensive cyclization is found during the polymerization of bridged silane precursors except for silanes with certain short bridges. This work is an attempt to characterize and understand some of the distinct features of bridged silanes using experimental characterization, kinetic modeling and simulation. In addition to this, the dissertation shows how the properties of siloxane- materials can be engineered for drug delivery and adsorption.
The phase behavior of polymerizing mixtures is first investigated to identify the solutions that favor kinetic characterization. Microphase separation is found to cause gradual loss of NMR signal for certain initial compositions. Distortionless Enhancement by Polarization Transfer 29Si NMR is employed to identify the products of polymerization of some short-bridged silanes under no signal loss conditions. This technique requires knowing indirect 29Si-1H scalar coupling constants which sometimes cannot be measured due to second-order effects. However, the B3LYP density functional method with 6-31G basis set is found to predict accurate 29Si-1H coupling constants of organoalkoxysilanes and siloxanes. The scalar coupling constants thus estimated are employed to resolve non-trivial coupled NMR spectra and quantitative kinetic modeling is performed using the DEPT Si NMR transients. In order to investigate the role of the organic bridging group, the structural evolution of bridged and non-bridged silanes are compared using Monte Carlo simulations. Kinetic and simulation models suggest that cyclization plays a key role right from the onset of polymerization for bridged silanes even more than in non-bridged silanes. The simulations indicate that the carbosiloxane rings formed from short-bridged precursors slow down but do not prevent gelation.
The tuning of siloxane-based materials for adsorption technologies are also discussed here. In the first example, antioxidant enzyme loading is investigated as a means to reduce oxidative stress generated by silica nanoparticle drug carriers. Materials are engineered for promising enzyme loading and protection from proteolysis. Second, the potential of copper sulfate impregnation to enhance adsorption of ammonia by silica is explored by molecular simulation.
35
Paul, Uchenna Prince. "Microkinetic Model of Fischer-Tropsch Synthesis on Iron Catalysts." Diss., CLICK HERE for online access, 2008. http://contentdm.lib.byu.edu/ETD/image/etd2535.pdf.
36
Celik, Akdur Eda. "Bioprocess Development For Therapeutical Protein Production." Phd thesis, METU, 2008. http://etd.lib.metu.edu.tr/upload/3/12610236/index.pdf.
Анотація:
In this study, it was aimed to develop a bioprocess using the Pichia pastoris expression system as an alternative to the mammalian system used in industry, for production of the therapeutically important glycoprotein, erythropoietin, and to form stoichiometric and kinetic models.
Firstly, the human EPO gene, fused with a polyhistidine-tag and factor-Xa protease target site, in which cleavage produces the native termini of EPO, was integrated to AOX1 locus of P. pastoris. The Mut+ strain having the highest rHuEPO production capacity was selected. The glycosylation profile of rHuEPO was characterized by MALDI-ToF MS and Western blotting. The native polypeptide form of human EPO was obtained for the first time in P. pastoris expression system, after affinity-purification, deglycosylation and factor-Xa protease digestion.
Thereafter, effects of medium components and pH on rHuEPO production and cell growth were investigated in laboratory-scale bioreactors. Sorbitol was shown to increase production efficiency when added as a co-substrate. Moreover, a cheap alternative nutrient, the byproduct of biodiesel industry, crude-glycerol, was suggested for the first time for P. pastoris fermentations. Furthermore, methanol feeding strategy was investigated in fed-batch pilot-scale bioreactors, producing 70 g L-1 biomass and 130 mg L-1 rHuEPO at t=24h.
Moreover, metabolic flux analysis by using the stoichiometric model formed, which consisted of m=102 metabolites and n=141 reactions, proved useful in further understanding the P. pastoris metabolism. Finally, the first structured kinetic model formed for r-protein production with P. pastoris successfully predicted cell growth, substrate consumption and r-product production rates, where rHuEPO production kinetics was associated with AOX production and proteolytic degradation.
37
Hallac, Basseem Bishara. "Kinetic Experimental and Modeling Studies on Iron-Based Catalysts Promoted with Lanthana for the High-Temperature Water-Gas Shift Reaction Characterized with Operando UV-Visible Spectroscopy and for the Fischer-Tropsch Synthesis." BYU ScholarsArchive, 2014. https://scholarsarchive.byu.edu/etd/4271.
Анотація:
The structural and functional roles of lanthana in unsupported iron-based catalysts for the high-temperature water-gas shift reaction and Fischer-Tropsch synthesis were investigated. The performance of the catalysts with varying lanthana contents was based on their activity, selectivity, and stability. With regard to the former reaction, extent of reduction of the iron in Fe2O3/Cr2O3/CuO/La2O3 water-gas shift catalysts is a key parameter that was characterized using UV-visible spectroscopy. Minor addition of lanthana (<0.5 wt%) produces more active and stable catalysts apparently because it stabilizes the iron-chromium spinel, increases the surface area of the reduced catalysts, enhances the reduction of hematite to the magnetite active phase, and facilitates the adsorption of CO on the surface of the catalyst modeled by an adsorptive Langmuir-Hinshelwood mechanism. Statistical 95% confidence contour plots of the adsorption equilibrium constants show that water adsorbs more strongly than CO, which inhibits the reaction rate. A calibration curve that correlates the oxidation state of surface iron domains to normalized absorbance of visible light was successfully generated and applied to the water-gas shift catalysts. UV-visible studies indicated higher extent of reduction for surface Fe domains for the catalysts promoted with 1 wt% of lanthana and showed potential to be a more convenient technique for surface chemistry studies than X-ray absorption near edge spectroscopy (XANES). Lanthana addition to iron-based Fischer-Tropsch catalysts enhances the olefin-to-paraffin ratio, but decreases their activity, stability, and selectivity to liquid hydrocarbons. Adding lanthana at the expense of potassium reduces the water-gas shift selectivity and enhances the activity and stability of the catalysts. Finally, a model that simulates heat and mass transfer limitations on the particle scale for the Fischer-Tropsch reaction applicable at lab-scale suggests optimal operating and design conditions of 256°C, 30 bar, and 80 mirons are recommended for higher selectivity to liquid hydrocarbons. The model considers pressure drop, deactivation, pore diffusion, film heat transfer, and internal heat transfer when solving for the optimal conditions, and maps them as functions of design variables. This model can be up-scaled to provide guidance for optimal design of commercial-size reactors.
38
Dutta, Ashim. "Cavity Ignition and Flameholding of High Speed Fuel-Air Flows by a Repetitively Pulsed Nanosecond Discharge." The Ohio State University, 2011. http://rave.ohiolink.edu/etdc/view?acc_num=osu1313179906.
39
Yu, Jing. "A THREE-DIMENSIONAL BAY/ESTUARY MODEL TO SIMULATE WATER QUALITY TRANSPORT." Master's thesis, University of Central Florida, 2006. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/2434.
Анотація:
This thesis presents the development of a numerical water quality model using a general paradigm of reaction-based approaches. In a reaction-based approach, all conceptualized biogeochemical processes are transformed into a reaction network. Through the decomposition of species governing equations via Gauss-Jordan column reduction of the reaction network, (1) redundant fast reactions and irrelevant kinetic reactions are removed from the system, which alleviates the problem of unnecessary and erroneous formulation and parameterization of these reactions, and (2) fast reactions and slow reactions are decoupled, which enables robust numerical integrations. The system of species transport equations is transformed to reaction-extent transport equations, which is then approximated with two subsets: algebraic equations and kinetic-variables transport equations. As a result, the model alleviates the needs of using simple partitions for fast reactions. With the diagonalization strategy, it makes the inclusion of arbitrary number of fast and kinetic reactions relatively easy, and, more importantly, it enables the formulation and parameterization of kinetic reactions one by one. To demonstrate the general paradigm, QAUL2E was recasted in the mode of a reaction network. The model then was applied to the Loxahatchee estuary to study its response to a hypothetical biogeochemical loading from its surrounding drainage. Preliminary results indicated that the model can simulate four interacting biogeochemical processes: algae kinetics, nitrogen cycle, phosphorus cycle, and dissolved oxygen balance.M.S.
Department of Civil and Environmental Engineering
Engineering and Computer Science
Civil Engineering
40
Marsano, Flavio. "Chemical kinetic modelling of hydrocarbon combustion." Thesis, Cardiff University, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.402067.
41
Peng, Zhe, Douglas A. Day, Amber M. Ortega, Brett B. Palm, Weiwei Hu, Harald Stark, Rui Li, Kostas Tsigaridis, William H. Brune, and Jose L. Jimenez. "Non-OH chemistry in oxidation flow reactors for the study of atmospheric chemistry systematically examined by modeling." COPERNICUS GESELLSCHAFT MBH, 2016. http://hdl.handle.net/10150/614743.
Анотація:
Oxidation flow reactors (OFRs) using low-pressure Hg lamp emission at 185 and 254 nm produce OH radicals efficiently and are widely used in atmospheric chemistry and other fields. However, knowledge of detailed OFR chemistry is limited, allowing speculation in the literature about whether some non-OH reactants, including several not relevant for tropospheric chemistry, may play an important role in these OFRs. These non-OH reactants are UV radiation, O(1D), O(3P), and O3. In this study, we investigate the relative importance of other reactants to OH for the fate of reactant species in OFR under a wide range of conditions via box modeling. The relative importance of non-OH species is less sensitive to UV light intensity than to water vapor mixing ratio (H2O) and external OH reactivity (OHRext), as both non-OH reactants and OH scale roughly proportionally to UV intensity. We show that for field studies in forested regions and also the urban area of Los Angeles, reactants of atmospheric interest are predominantly consumed by OH. We find that O(1D), O(3P), and O3 have relative contributions to volatile organic compound (VOC) consumption that are similar or lower than in the troposphere. The impact of O atoms can be neglected under most conditions in both OFR and troposphere. We define “riskier OFR conditions” as those with either low H2O (< 0.1 %) or high OHRext ( ≥ 100 s−1 in OFR185 and > 200 s−1 in OFR254). We strongly suggest avoiding such conditions as the importance of non-OH reactants can be substantial for the most sensitive species, although OH may still dominate under some riskier conditions, depending on the species present. Photolysis at non-tropospheric wavelengths (185 and 254 nm) may play a significant (> 20 %) role in the degradation of some aromatics, as well as some oxidation intermediates, under riskier reactor conditions, if the quantum yields are high. Under riskier conditions, some biogenics can have substantial destructions by O3, similarly to the troposphere. Working under low O2 (volume mixing ratio of 0.002) with the OFR185 mode allows OH to completely dominate over O3 reactions even for the biogenic species most reactive with O3. Non-tropospheric VOC photolysis may have been a problem in some laboratory and source studies, but can be avoided or lessened in future studies by diluting source emissions and working at lower precursor concentrations in laboratory studies and by humidification. Photolysis of secondary organic aerosol (SOA) samples is estimated to be significant (> 20 %) under the upper limit assumption of unity quantum yield at medium (1 × 1013 and 1.5 × 1015 photons cm−2 s−1 at 185 and 254 nm, respectively) or higher UV flux settings. The need for quantum yield measurements of both VOC and SOA photolysis is highlighted in this study. The results of this study allow improved OFR operation and experimental design and also inform the design of future reactors.
42
Potter, Mark Lee. "Detailed chemical kinetic modelling of propulsion fuels." Thesis, Imperial College London, 2004. http://hdl.handle.net/10044/1/7995.
43
Rizos, Konstantinos-Athanassios. "Detailed chemical kinetic modelling of homogeneous systems." Thesis, Imperial College London, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.407143.
44
Binns, Michael John. "Kinetic modelling of chemical and biochemical networks." Thesis, University of Manchester, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.496236.
Анотація:
The modelling of chemical and biochemical systems is highly dependent on the reaction network of the system. A reaction network should contain all the reactions which can occur in addition to the species involved. However in many cases there will be reactions occurring which are missing from the network. These are called gaps (Reed et al., 2003; Duarte et al, 2004) and occur because the databases of reactions used to build them are incomplete. The main aim of this work is to identify all the reactions which can occur in a given system including the unknown ones. This is accomplished through a new procedure which will be called metabolic network development and is aimed at constructing reaction networks for biochemical systems.
45
Johansson, David. "Kinetic modelling of autoignition phenomena." Licentiate thesis, Stockholm : Kemiteknik, Kungliga Tekniska högskolan, 2007. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-4516.
46
Mével, Rémy. "Etude de mécanismes cinétiques et des propriétés explosives des systèmes hydrogène-protoxyde d'azote et silane-protoxyde d'azote : application à la sécurité industrielle." Phd thesis, Université d'Orléans, 2009. http://tel.archives-ouvertes.fr/tel-00517364.
Анотація:
La présente étude s'inscrit dans le cadre d'une évaluation des risques liés d'une part au stockage des déchets nucléaires et d'autre part à la production des semi-conducteurs. L'ojectif est d'obtenir des paramètres fondamentaux sur les propriétés explosives des mélanges hydrogène-protoxyde d'azote et silane-protoxyde d'azote. Pour le système hydrogène-protoxyde d'azote, les temps caractéristiques de réaction derrière une onde de choc réfléchie, les vitesses fondamentales de flamme et les largeurs des cellules de détonation ont été mesurées expérimentalement sur une large gamme de composition et de condition. Un mécanisme cinétique détaillé a été développé et validé sur les données de la présente étude et de la littérature. Des mécanismes cinétiques réduits ont été obtenus par une méthode de réduction automatique et inclus dans un code de simulation numérique bi-dimensionnelle d'onde de détonation. Pour le système silane-protoxyde d'azote, l'évolution temporelle des atomes d'oxygène derrière une onde de choc réfléchie et les vitesses fondamentales de flammes ont été étudiées expérimentalement. Une étude préliminaire d'analyse des produits solides de combustion formés en bombe sphérique a également été réalisée. Un mécanisme cinétique réduit de la littérature a été modifié afin de reproduire les profils des atomes d'oxygène.
47
Wallin, Peter John. "The mathematical modelling of flotation kinetics." Thesis, University of Manchester, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.314632.
48
Tomlin, Alison Sarah. "Bifurcation analysis for non-linear chemical kinetics." Thesis, University of Leeds, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.255345.
49
Khan, Ahmed Faraz. "Chemical kinetics modelling of combustion processes in SI engines." Thesis, University of Leeds, 2014. http://etheses.whiterose.ac.uk/7554/.
Анотація:
The need for improving the efficiency and reducing emissions is a constant challenge in combustion engine design. For spark ignition engines, these challenges have been targeted in the past decade or so, through ‘engine downsizing’ which refers to a reduction in engine displacement accompanied by turbocharging. Besides the benefits of this, it is expected to aggravate the already serious issue of engine knock owing to increased cylinder pressure. Engine knock which is a consequence of an abnormal mode of combustion in SI engines, is a performance limiting phenomenon and potentially damaging to the engine parts. It is therefore of great interest to develop capability to predict autoignition which leads to engine knock. Traditionally, rather rudimentary skeletal chemical kinetics models have been used for autoignition modelling, however, they either produce incorrect predictions or are only limited to certain fuels. In this work, realistic chemical kinetics of gasoline surrogate oxidation has been employed to address these issues. A holistic modelling approach has been employed to predict combustion, cyclic variability, end gas autoignition and knock propensity of a turbocharged SI engine. This was achieved by first developing a Fortran code for chemical kinetics calculations which was then coupled with a quasi-dimensional thermodynamic combustion modelling code called LUSIE and the commercial package, GT-Power. The resulting code allowed fast and appreciably accurate predictions of the effects of operating condition on autoignition. Modelling was validated through comparisons with engine experimental data at all stages. Constant volume chemical kinetics modelling of the autoignition of various gasoline surrogate components, i.e. iso-octane, n-heptane, toluene and ethanol, by using three reduced mechanisms revealed how the conversion rate of relatively less reactive blend components, toluene and ethanol, is accelerated as they scavenge active radical formed during the oxidation of n-heptane and iso-octane. Autoignition modelling in engines offered an insight into the fuel-engine interactions and that how the composition of a gasoline surrogate should be selected. The simulations also demonstrated the reduced relevance of research and motor octane numbers to the determination of gasoline surrogates and that it is crucial for a gasoline surrogate to reflect the composition of the target gasoline and that optimising its physicochemical properties and octane numbers to match those of the gasoline does not guarantee that the surrogate will mimic the autoignition behaviour of gasoline. During combustion modelling, possible deficiencies in in-cylinder turbulence predictions and possible inaccuracies in turbulent entrainment velocity model required an optimisation of the turbulent length scale in the eddy burn-up model to achieve the correct combustion rate. After the prediction of a correct mean cycle at a certain engine speed, effects of variation in intake air temperature and spark timing were studied without the need for any model adjustment. Autoignition predictions at various conditions of a downsized, turbocharged engine agreed remarkably well with experimental values. When coupled with a simple cyclic variability model, the autoignition predictions for the full spectrum of cylinder pressures allowed determination of a percentage of the severely autoigniting cycles at any given spark timing or intake temperature. Based on that, a knock-limited spark advance was predicted within an accuracy of 2° of crank angle.
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Jenkins, Robert. "Deterministic and stochastic modelling of chemical and biochemical reaction kinetics." Thesis, University of Nottingham, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.495585.
Анотація:
We analyse various chemical reaction schemes both deterministically and stochastically. The reactions are considered to demonstrate the rich, mathematical behaviour apparent in the systems, rather than to represent realistic chemical reactions. The deterministic analysis is carried out to provide insights into the behaviour of the systems that we can then consider stochastically.