Direct hydrocarbon fuel cells are fuel cells than use hydrocarbons directly as fuel instead of the most commonly used fuel in a fuel cell, hydrogen. Studies are being done on direct hydrocarbon fuel cells because they have the potential to be energetically more efficient than hydrogen fuel cells. There are many different hydrocarbons that are available to use as a feed stock and each one reacts at different reaction rates. As the current density of a fuel cell is linked to the reaction rate, it is important to know the energetics of an oxidation reaction that is occurring. Density Functional Theory (DFT) is a technique that can be used to predict the energy states of intermediate reaction steps in a given mechanism. The focus of this study is the using DFT to explore the energetics of the oxidation of ethane to ethylene in a nickel-anode catalyst fuel cell. DFT was used in adsorption runs to optimize the geometries beginning (adsorbed ethane) and end (adsorbed ethylene) of the oxidation reaction. DFT was then used to calculate the energy of transition states by varying bond lengths. It was determined the removal of the second hydrogen from the ethyl radical is the most energy intensive step and, thus, the rate limiting step. Hydrogen, ethane, and ethylene were all explored in this study. The heats of adsorption varied from largest to smallest in the order of ethylene, hydrogen, and ethane. It was determined that the heat of adsorption of hydrogen is sufficient to meet the energy requirements for the dissociation reaction. This may help explain why hydrogen reacts so readily in fuel cells. Conversely, the heats of adsorption for the hydrocarbons did not meet the energy requirements for the dissociation reactions. This may help explain why ethane and ethylene react more slowly in a fuel cell as compared to hydrogen. Also, the oxidation of ethane to ethylene requires two large activation energies. These two additional activation energies may help explain why ethylene reacts more readily than ethane in a fuel cell.

Complex reaction kinetics of the solid acid alkylation of isobutane with butenes over a proton-exchanged Y-zeolite has been modeled at the elementary step level. Starting with a computer algorithm that generated the reaction network based on the fundamentals of the carbenium ion chemistry, the formation of over 100+ product species has been modeled in order to gain understanding of the underlying phenomena leading to rapid catalyst deactivation and product selectivity shifts observed in experimental runs. An experimental investigation of the solid acid alkylation process was carried out in a fixed bed catalytic reactor operating with an excess of isobutane under isothermal conditions at moderate temperatures (353-393 K) in liquid phase. Experimental data varying with run-time for a set of butene space-times and reaction temperatures were collected for parameter estimation purposes. A kinetic model was formulated in terms of rate expressions at the elementary step level including a rigorous modeling of deactivation through site coverage. The single event concept was applied to each rate coefficient at the elementary step level to achieve a significant reduction in the number of model parameters. Based on the identification of structural changes leading to the creation or destruction of symmetry axes and chiral centers in an elementary step, formulae have been developed for the calculation of the number of single events. The Evans-Polanyi relationship and the concept of stabilization energy were introduced to account for energy levels in surface-bonded carbenium ions. A novel functional dependency of the stabilization energy with the nature of the carbenium ion and the carbon number was proposed to account for energy effects from the acid sites on the catalyst. Further reductions in the number of parameters and simplification of the equations for the transient pseudohomogeneous one-dimensional plug-flow model of the reactor were achieved by means of thermodynamic constraints. Altogether, the single event concept, the Evans-Polanyi relationship, the stabilization energy approach and the thermodynamic constraints led to a set of 14 parameters necessary for a complete description of solid acid alkylation at the elementary step level.

Multi-walled carbon nanotubes (MWCNTs) are a potential alternative to commonly used catalyst support structures in hydrotreating processes. Synthesis of MWCNTs with specific pore diameters can be achieved by chemical vapor deposition (CVD) of a carbon source onto an anodic aluminum oxide (AAO) template. AAO films consist of pore channels in a uniform hexagonal arrangement that run parallel to the surface of the film. These films are created by the passivation of an aluminum anode within an electrolysis cell consisting of certain weak acid electrolytes. Changing the concentration of the electrolyte (oxalic acid) and the electrical potential of the electrolysis cell altered the pore channel diameter of these AAO films. Controlling the pore diameter of these templates enabled the pore diameter of MWCNTs synthesized by CVD to be controlled as well. The produced MWCNTs were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), thermogravimetric analysis (TGA), Raman spectroscopy, and N2 adsorption analysis. Anodizing conditions of 0.40 M oxalic acid concentration and 40.0 V maximum anodizing potential were found to produce AAO films that resulted in MWCNTs with optimum surface characteristics for a catalyst support application. CVD parameter values of 650°C reaction temperature and 8.00 mL/(min·g) C2H2-to-AAO ratio were found to produce the highest yield of MWCNT product.<p> The MWCNTs were synthesized for the purpose of supporting hydroprocessing catalysts, with several grades of NiMo/MWCNT sulfide catalysts being prepared to determine the optimum pore size. These catalysts were characterized by techniques of TEM, CO chemisorption, N2 adsorption, and H2 temperature programmed reduction (TPR). A MWCNT grade with 67 nm inner diameters (found from TEM analysis) was found to offer the best hydrodesulfurization (HDS) and hydrodenitrogenation (HDN) activities for the treatment of coker light gas oil (CLGO). After determining the most suitable pore diameter, the optimum catalyst metal loadings were found to be 2.5 wt.% for Ni and 19.5 wt.% for Mo. The optimum catalyst was found to offer HDS conversions of 90.5%, 84.4%, and 73.5% with HDN conversions of 75.9%, 65.8%, and 55.3% for temperatures of 370°C, 350°C, and 330°C, respectively. An equal mass loading of commercial NiMo/ã-Al2O3 catalyst offered HDS conversions of 91.2%, 77.9%, and 58.5% with HDN conversions of 71.4%, 53.2%, and 31.3% for temperatures of 370°C, 350°C, and 330°C, respectively.<p> A kinetic study was performed on the optimum NiMo/MWCNT catalyst to help predict its HDS and HDN activities while varying the parameters of temperature, liquid hourly space velocity (LHSV), pressure, and gas-to-oil flow rate ratio. Rate expressions were then developed to predict the behavior of both the HDS and HDN reactions. Power law models were best fit with reaction orders of 2.6 and 1.2, and activation energies of 161 kJ/mol and 82.3 kJ/mol, for the HDS and HDN reactions, respectively. Generalized Langmuir-Hinshelwood models were found to have reaction orders of 3.0 and 1.5, and activation energies of 155 kJ/mol and 42.3 kJ/mol, for the HDS and HDN reactions, respectively.

In 1957 Vroom presented an article that dealt with the kinetics of the sulphate cook. He showed that the lignin dissolution exhibited a temperature/time dependency that could be explained by the Arrhenius equation and that the reaction was of first order with respect to lignin. However, even before Vroom introduced the H-factor all wood components were assumed to react according to a first order reaction. In recent years progresses in this area have been made. Lignin for example is nowadays considered to dissolve during three parallel first order reactions, all with differences in activation energies. When the kinetics are evaluated, several cooking series at different temperatures and concentrations of active cooking chemicals are needed. The data points obtained are then fitted into some equation. If the concentration of the active cooking chemicals is constant, the activation energies and the chemical dependency for the dissolution of wood components can easily be found. In order to simplify the evaluations of the kinetics, very high liquor-to-wood ratios are sometimes used, often as high as 50:1 or even 75:1. In this manner, the chemical concentrations are almost constant during the cook. The problem is that in the normal industrial cook where the liquor-to-wood ratio is about 4:1, the chemical concentration is not constant. This is due mostly to the alkali consumption that takes place in the cook for example when neutralising the acidic groups in the hemicelluloses. A disadvantage with high liquor-to-wood ratios is the high dilution of the dissolved organic matter. A high concentration of dissolved lignin boosts the dissolution of the remaining lignin in the wood residue and xylan can redeposit on the fibres when its concentration in the cooking liquor is high. The aim of this project was to describe how different liquor-to-wood ratios influence the kinetics during sulphate cooking of spruce.

Multi-walled carbon nanotubes (MWCNTs) are a potential alternative to commonly used catalyst support structures in hydrotreating processes. Synthesis of MWCNTs with specific pore diameters can be achieved by chemical vapor deposition (CVD) of a carbon source onto an anodic aluminum oxide (AAO) template. AAO films consist of pore channels in a uniform hexagonal arrangement that run parallel to the surface of the film. These films are created by the passivation of an aluminum anode within an electrolysis cell consisting of certain weak acid electrolytes. Changing the concentration of the electrolyte (oxalic acid) and the electrical potential of the electrolysis cell altered the pore channel diameter of these AAO films. Controlling the pore diameter of these templates enabled the pore diameter of MWCNTs synthesized by CVD to be controlled as well. The produced MWCNTs were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), thermogravimetric analysis (TGA), Raman spectroscopy, and N2 adsorption analysis. Anodizing conditions of 0.40 M oxalic acid concentration and 40.0 V maximum anodizing potential were found to produce AAO films that resulted in MWCNTs with optimum surface characteristics for a catalyst support application. CVD parameter values of 650°C reaction temperature and 8.00 mL/(min·g) C2H2-to-AAO ratio were found to produce the highest yield of MWCNT product.<p> The MWCNTs were synthesized for the purpose of supporting hydroprocessing catalysts, with several grades of NiMo/MWCNT sulfide catalysts being prepared to determine the optimum pore size. These catalysts were characterized by techniques of TEM, CO chemisorption, N2 adsorption, and H2 temperature programmed reduction (TPR). A MWCNT grade with 67 nm inner diameters (found from TEM analysis) was found to offer the best hydrodesulfurization (HDS) and hydrodenitrogenation (HDN) activities for the treatment of coker light gas oil (CLGO). After determining the most suitable pore diameter, the optimum catalyst metal loadings were found to be 2.5 wt.% for Ni and 19.5 wt.% for Mo. The optimum catalyst was found to offer HDS conversions of 90.5%, 84.4%, and 73.5% with HDN conversions of 75.9%, 65.8%, and 55.3% for temperatures of 370°C, 350°C, and 330°C, respectively. An equal mass loading of commercial NiMo/ã-Al2O3 catalyst offered HDS conversions of 91.2%, 77.9%, and 58.5% with HDN conversions of 71.4%, 53.2%, and 31.3% for temperatures of 370°C, 350°C, and 330°C, respectively.<p> A kinetic study was performed on the optimum NiMo/MWCNT catalyst to help predict its HDS and HDN activities while varying the parameters of temperature, liquid hourly space velocity (LHSV), pressure, and gas-to-oil flow rate ratio. Rate expressions were then developed to predict the behavior of both the HDS and HDN reactions. Power law models were best fit with reaction orders of 2.6 and 1.2, and activation energies of 161 kJ/mol and 82.3 kJ/mol, for the HDS and HDN reactions, respectively. Generalized Langmuir-Hinshelwood models were found to have reaction orders of 3.0 and 1.5, and activation energies of 155 kJ/mol and 42.3 kJ/mol, for the HDS and HDN reactions, respectively.

No description available.

No description available.

Complex reaction kinetics of the solid acid alkylation of isobutane with butenes over a proton-exchanged Y-zeolite has been modeled at the elementary step level. Starting with a computer algorithm that generated the reaction network based on the fundamentals of the carbenium ion chemistry, the formation of over 100+ product species has been modeled in order to gain understanding of the underlying phenomena leading to rapid catalyst deactivation and product selectivity shifts observed in experimental runs. An experimental investigation of the solid acid alkylation process was carried out in a fixed bed catalytic reactor operating with an excess of isobutane under isothermal conditions at moderate temperatures (353-393 K) in liquid phase. Experimental data varying with run-time for a set of butene space-times and reaction temperatures were collected for parameter estimation purposes. A kinetic model was formulated in terms of rate expressions at the elementary step level including a rigorous modeling of deactivation through site coverage. The single event concept was applied to each rate coefficient at the elementary step level to achieve a significant reduction in the number of model parameters. Based on the identification of structural changes leading to the creation or destruction of symmetry axes and chiral centers in an elementary step, formulae have been developed for the calculation of the number of single events. The Evans-Polanyi relationship and the concept of stabilization energy were introduced to account for energy levels in surface-bonded carbenium ions. A novel functional dependency of the stabilization energy with the nature of the carbenium ion and the carbon number was proposed to account for energy effects from the acid sites on the catalyst. Further reductions in the number of parameters and simplification of the equations for the transient pseudohomogeneous one-dimensional plug-flow model of the reactor were achieved by means of thermodynamic constraints. Altogether, the single event concept, the Evans-Polanyi relationship, the stabilization energy approach and the thermodynamic constraints led to a set of 14 parameters necessary for a complete description of solid acid alkylation at the elementary step level.

We study particle production and its density evolution and equilibration in hot dense medium, such as hadronic gas after quark gluon plasma hadronization and relativistic electron positron photon plasma. For this study we use kinetic momentum integrated equations for particles density evolution with Lorentz invariant reaction rates. We extend these equations, used before for two-to-two particles reactions (1 + 2 ↔ 3 + 4), to the case of two-to-one and backward reactions (1 + 2 ↔ 3). One type of hot dense medium, which we study, is hadronic gas produced at quark gluon plasma hadronization in heavy ions collisions in SPS, RHIC and LHC experiments. We study hadron production at quark gluon plasma hadronization and their evolution in thermal hadronic gas phase. We consider non-equilibrium hadronization model, for which the yields of the light quark hadrons are defined by entropy conservation. Yields of hadrons containing heavier (strange, charm, bottom) quarks are mainly controlled by flavor conservation. We predict yields of charm and bottom hadrons within this non-equilibrium statistical hadronization model. Then we use this non-equilibrium hadronization as the initial condition in the study of hadronic kinetic phase. During this time period some hadronic resonances can be produced in lighter hadrons fusion. This reaction is opposite to resonance decay. Production of resonances is dominant over decay if there is non-equilibrium excess of decay products. Within this model we explain apparently contradictory experimental results reported in RHIC experiments: ∑(1385) yield is enhanced while ∧(1520) yield is suppressed compared to the statistical hadronization model expectation obtained without kinetic phase. We also predict Δ(1232) enhancement. The second type of plasma medium we consider is the relativistic electron position photon plasma (EP³) drop. This plasma is expected to be produced in decay of supercritical field created in ultrashort laser pulse. We study at what conditions this plasma drop is opaque for photons and therefore may reach thermal and chemical equilibrium. Further we consider muon and pion production in this plasma also as a diagnostic tool. Such heavy particles can be diagnostic tool to study the properties of EP³ plasma, similar to the role taken by heavy hadrons production in heavy ions collisions. Finally all these theoretical developments can be applied to begin a study of particles evolution in early universe in temperatures domain from QGP hadronization (160 MeV) to nucleosynthesis (0.1 MeV). The first results on pion equilibration are presented here.

No description available.