Set Of Kinetic Parameters Research Articles

Activity Coefficients for Liquid Organic Reactions: Towards a Better Understanding of True Kinetics with the Synthesis of Jasmin Aldehyde as Showcase.

The aldol condensation of benzaldehyde and heptanal is taken as an example of reversible liquid phase organic reactions to show that inclusion of activity coefficients reveal distinct differences in conversion and product distribution when different solvents methanol, ethanol, n-propanol, or n-butanol are used. The purpose of this work is to show a pronounced solvent effect for a given set of identical kinetic parameters, i.e., the same liquid phase kinetics can result in different conversion and yield values, depending on the choice of solvent. It was shown that subsequent parameter estimation without inclusion of the activity coefficients resulted in a pronounced deviation from the ‘true’ kinetics, up to a factor of 30. It is proposed that the usage of average activity coefficients gives already a significant improvement, resulting in acceptable parameter estimates.

Reaction kinetic parameters for a distributed model of transport and reaction in Pd/Rh/CeZrO three-way catalytic converters

This paper presents a two-dimensional distributed model for the transport and reaction of combustion gases in channels of three-way catalytic converters, considering a detailed reaction kinetics with 16 chemical reactions in palladium and rhodium catalysts, and taking into account diffusive effects within the coating, to obtain a new set of reaction kinetic parameters that do not depend on the thickness of the coating. The model was solved using a finite volume method with a first order upwind scheme and simulations were conducted using computational fluid dynamics. The model with the new distributed reaction kinetic parameters, produced an excellent agreement with the experimental data of concentration at the end of the channels. Also, the model reproduced the most important concentration changes for the gas components in the specified temperature range and allowed simulations with excess oxygen and different thicknesses.

Rate Constant Approximation with Cubic Splines for Kinetic Analysis of Temperature-Programmed Reduction Data

Temperature-programmed reduction (TPR) is a widely used method for characterization of oxide-based catalysts, sorbents, and functional materials, but its results lack quantitative assessment. Here, we present a novel approach to kinetic analysis of the TPR that can be applied to a large variety of systems involving multiple limiting stages. Implementation of cubic splines to approximate rate constant vs. conversion dependencies obtained from several TPR curves recorded at different heating rates yields in a set of kinetic parameters (activation energy and preexponential factors) for all reduction stages. Relationship between preexponential factor of the first reduction stage and the specific surface area of the sample has been shown. Reduction of hematite has been studied to prove the performance of the developed kinetic analysis technique.

Kinetic ensemble model of gas fermenting Clostridium autoethanogenum for improved ethanol production

Developing autotrophic, acetogenic bacteria strains as gas fermentation platforms is a promising avenue for converting industrial waste gas streams into valuable chemical products. One such strain, Clostridium autoethanogenum, naturally converts CO, CO2, and H2 gases into ethanol and acetate. Currently, lowering the acetate to ethanol production ratio is a key strategy for accomplishing large-scale industrial application of C. autoethanogenum gas fermentation. Unfortunately, the limited availability and time-intensive implementation of genetic engineering tools for clostridia strains greatly hinders metabolic engineering efforts toward this goal. To alleviate the lack of sufficient mutant phenotype data interrogating the pathways of interest, computational tools are needed to resolve experimental observations and predict engineering targets to help minimize experimental characterization in the lab. While stoichiometric models of C. autoethanogenum metabolism are available, they are unable to provide insight into regulatory relationships, rate-limiting steps, or the effects of altering enzyme expression. In this work, we offer the first kinetic representation of C. autoethanogenum core metabolism developed using the Ensemble Modeling (EM) framework. We have adapted the existing method to enable the usage of non-genetic perturbation data, specifically the effects of changing biomass concentration, to sample and train our kinetic parameter sets. Our final kinetic parameter ensemble accurately predicts intracellular metabolite concentrations and engineering strategies for improved ethanol production.

Nanoscale structure of amorphous solid water: What determines the porosity in ASW?

AbstractThe pore structure of vapour deposited ASW is poorly understood, despite its importance to fundamental processes such as grain chemistry, cooling of star forming regions, and planet formation. We studied structural changes of vapour deposited D2O on intra-molecular to 30 nm length scales at temperatures ranging from 18 to 180 K and observed enhanced mobility from 100 to 150 K. An Arrhenius type model describes the loss of surface area and porosity with a common set of kinetic parameters. The low activation energy (428 K) is commensurate with van der Waals forces between nm-scale substructures in the ice. Our findings imply that water porosity will always change with time, even at low temperatures.

Determining stoichiometry and kinetics of two thermophilic nitrifying communities as a crucial step in the development of thermophilic nitrogen removal

Nitrification and denitrification, the key biological processes for thermophilic nitrogen removal, have separately been established in bioreactors at 50 °C. A well-characterized set of kinetic parameters is essential to integrate these processes while safeguarding the autotrophs performing nitrification. Knowledge on thermophilic nitrifying kinetics is restricted to isolated or highly enriched batch cultures, which do not represent bioreactor conditions. This study characterized the stoichiometry and kinetics of two thermophilic (50 °C) nitrifying communities. The most abundant ammonia oxidizing archaea (AOA) were related to the Nitrososphaera genus, clustering relatively far from known species Nitrososphaera gargensis (95.5% 16S rRNA gene sequence identity). The most abundant nitrite oxidizing bacteria (NOB) were related to Nitrospira calida (97% 16S rRNA gene sequence identity). The nitrification biomass yield was 0.20–0.24 g VSS g−1 N, resulting mainly from a high AOA yield (0.16–0.20 g VSS g−1 N), which was reflected in a high AOA abundance in the community (57–76%) compared to NOB (5–11%). Batch-wise determination of decay rates (AOA: 0.23–0.29 d−1; NOB: 0.32–0.43 d−1) rendered an overestimation compared to in situ estimations of overall decay rate (0.026–0.078 d−1). Possibly, the inactivation rate rather than the actual decay rate was determined in batch experiments. Maximum growth rates of AOA and NOB were 0.12–0.15 d−1 and 0.13–0.33 d−1 respectively. NOB were susceptible to nitrite, opening up opportunities for shortcut nitrogen removal. However, NOB had a similar growth rate and oxygen affinity (0.15–0.55 mg O2 L−1) as AOA and were resilient towards free ammonia (IC50 > 16 mg NH3-N L−1). This might complicate NOB outselection using common practices to establish shortcut nitrogen removal (SRT control; aeration control; free ammonia shocks). Overall, the obtained insights can assist in integrating thermophilic conversions and facilitate single-sludge nitrification/denitrification.

Kinetics mechanism and regulation of native human hepatic thymidine phosphorylase.

Thymidine phosphorylase (TP; EC 2.4.2.4) catalyzes the reversible phosphorolysis of thymidine, deoxyuridine, and their analogues to their respective nucleobases and 2-deoxy-α-d-ribose-1-phosphate (dRib-1-P). TP is a key enzyme in the pyrimidine salvage pathways. Activity of the enzyme is crucial in angiogenesis, cancer chemotherapy, radiotherapy, and tumor imaging, Nevertheless, a complete set of kinetic parameters has never been reported for any human TP. This study describes the kinetic mechanism and regulation of native human hepatic TP. The liver is a main site of pyrimidine metabolism and contains high levels of TP. Initial velocity and product inhibition studies demonstrated that the basic mechanism of this enzyme is a sequential random bi-bi mechanism. Initial velocity studies showed an intersecting pattern, consistent with substrate-enzyme-co-substrate complex formation, and a binding pattern indicating that the binding of the substrate interferes with the binding of the co-substrate and vice versa. Estimated kinetic parameters were KThymidine = 284 ± 55, KPi = 5.8 ± 1.9, KThymine = 244 ± 69, and KdRib-1-P = 90 ± 33 μM. Thymine was a product activator, but becomes a substrate inhibitor at concentrations eight times higher than its Km. dRib-1-P was a non-competitive product inhibitor of the forward reaction. It bounded better to the Enzyme●Pi complex than the free enzyme, but had better affinity to the free enzyme than the Enzyme●Thymidine complex. In the reverse reaction, dRib-1-P enhanced the binding of thymine. The enhancement of the thymine binding along with the fact that dRib-1-P was a non-competitive product inhibitor suggests the presence of another binding site for dRib-1-P on the enzyme.

Solute trapping in non-equilibrium solidification: A comparative model study

A sharp interface model and a diffuse interface model describing rapid solidification are compared. Both models are based on the assumption of two independent processes at the solid/liquid interface that together consume the available driving force. These two processes are (1) the interface motion and (2) the redistribution of atoms between the two phases. The sharp interface model is based on an interface thermodynamics model (Hillert and Rettenmayr, [3,4]) and derives its driving force for the phase transformation directly from Gibbs free energy formulations of the liquid and solid phases. In contrast, the Finite Interface Disspiation model (Steinbach et al., [10]), a diffuse interface model, is based on a grand potential formulation.The models are benchmarked against experimental data on solute trapping in the Al–Sn system (Smith and Aziz, [23]). The sharp interface model reproduces the experimental data with a single set of kinetic parameters, the diffuse interface model requires a velocity dependent interface permeability. It is concluded that due to the investigated high Péclet number regime the permeability in the diffuse interface model does not only describe the transport processes through the interface, but also the diffusion processes in the layer directly in front of it.

Investigation of the temperature dependence of lithium plating onset conditions in commercial Li-ion batteries

Fast charging is one of the main challenges in Lithium-ion battery applications. Especially at low temperatures and high C-rates, capacity loss due to lithium plating is identified as the main aging effect. Electrochemical models are able to predict the lithium plating onset conditions, as they provide information about the local potentials and lithium concentrations within the individual electrodes. Due to the narrow potential window of graphite, a precise determination of the sensitive parameters is needed for an accurate prediction of the plating onset. Experimental parameterization is needed as each cell has a specific geometry and the transport parameters are material and geometry-dependent. Literature values are scattered and often do not provide information on the electrode geometry. In this study, a non-isothermal electrochemical 3D model was experimentally parameterized and used to investigate the lithium plating onset at low temperatures. The whole set of geometrical, transport and kinetic model parameters were determined at different temperatures and states of charge and the results were validated against the individual potentials of a multi-layer pouch cell. Good predictions of lithium plating onset were obtained. The study shows that the model can be used to develop fast-charging strategies for commercial lithium-ion batteries at low temperatures.

Defining appropriate reaction scheme for hydrotreating of vegetable oil through proper calculation of kinetic parameters

Kinetic models reported in the literature were used to derive a new general kinetic model for the hydrotreating of vegetable oils. The proposed model includes ten reaction rate coefficients, three more than the literature models. Experimental data obtained at 360 °C with a CoMo/Al2O3 catalyst and at 420 °C with a NiW/SiO2-Al2O3 catalyst were used for model validations. A series of statistical tools and sensitivity analysis were applied to find the best set of kinetic parameters that assured the convergence to the global minimum of the objective function. To carry out a fair comparison of kinetic models due to the different number of parameters, the Akaike and Bayesian criteria were used. It was found that some reaction pathways that were omitted by the literature models have significant reaction rates, so that the proposed model exhibits better performance.

Atomic mobility in Titanium grade 5 (Ti6Al4V)

Titanium grade 5 (Ti6Al4V) is a modern material that can be found in a wide spectrum of applications, from medicine to aircraft industry. The commercial alloy is a mix of a body centered cubic structure (BCC_A2) and a hexagonal closed packed structure (HCP_A3). It is obvious, that heat treatment of the alloy will change a ratio between BCC_A2 and HCP_A3 and, as a consequence, properties of a material. Information about mobility of atoms in both crystal structures allows simulations and predictions of structures? behavior during the heat treatment and diffusion. In this work the atomic mobility in liquid, BCC_A2, and HCP_A3 phases of ternary alloy Al ? Ti ? V were obtained based on available literature information. Comparison between simulations and experiments shows a good agreement, hence it can be concluded that proposed set of kinetic parameters can be used for predictions and simulations of Titanium grade 5 heat treatment.

Kinetic Evaluation of the Charge Migration and H2O2 Transport Rates During the Electrocatalytic Reduction of H2O2 on Thin Prussian Blue Films

Kinetic analysis of the electrocatalytic reduction of H2O2 on electrodes modified with thin Prussian blue films was performed and a full set of kinetic parameters governing the rate of the electrocatalytic reaction was determined. Rate constant (κ·k') for the catalytic reaction between H2O2 and the reduced form of Prussian blue incorporating interstitial Cs+ and K+ ions was calculated to be equal to 3.1·106 and 2.3·106 cm3·mol–1 s–1, respectively. The diffusion coefficient of H2O2 and the apparent diffusion coefficient of electrons in the reduced form of Prussian blue were found to be κ·DS(H2O2) = 2.6·10–7 cm2/s and De = 2.8·10–12 cm2/s, respectively.

Sensitivity analysis of kinetic parameters for heavy oil hydrocracking

Sensitivity analysis is an important tool commonly used for confirming the achievement of the optimum set of parameter values obtained by regression analysis. To highlight this importance, two cases reported in the literature for the kinetic modeling of hydrocracking of heavy oils were selected, and sensitivity analysis was performed for the reported parameters. It was found that the values of the reported kinetic parameters do not reach the minimization of the objective function based on the sum of squares errors between predicted and experimental product yields, so that the reported set of kinetic parameters is not the optimal one. The calculated optimized reaction rate coefficients fitted better to experimental data than those reported in the literature. It was demonstrated that sensitivity analysis is of great relevance for determining the best set of parameters, and thus establishing proper reaction pathways, values of reaction rate coefficients, and activation energies, whereby reactor modeling, simulation, design and optimization can be done in an effective manner.

Experimental and kinetic analysis of hydrothermal aging effects on ammonia adsorption capacity over a commercial Cu-zeolite selective catalytic reduction catalyst

Ammonia/urea selective catalytic reduction is an efficient technology to control NOx emission from diesel engines. One of its critical challenges is the performance degradation of selective catalytic reduction catalysts due to the hydrothermal aging experienced in real-world operations during the lifetime. In this study, hydrothermal aging effects on the reduction of ammonia adsorption capacity over a commercial Cu-zeolite selective catalytic reduction catalyst were investigated under actual engine exhaust conditions. Ammonia adsorption site densities of the selective catalytic reduction catalysts aged at two different temperatures of 750°C and 850°C for 25 h with 10% H2O were experimentally measured and compared to that of fresh catalyst on a dynamometer test bench with a heavy-duty diesel engine. The test results revealed that hydrothermal aging significantly decreased the ammonia adsorption capacity of the current commercial Cu-zeolite selective catalytic reduction catalyst. Hydrothermal treatment at 750°C reduced the ammonia adsorption site to 62.5% level of that of fresh catalyst, while hydrothermal treatment at 850°C lowered the adsorption site to 37.0% level of that of fresh catalyst. Also, in this study, numerical simulation and kinetic analysis were carried out to quantify the impact of hydrothermal aging on the reduction of ammonia adsorption capacity by introducing an aging coefficient. The kinetic parameter calibrations based on actual diesel engine tests with a commercial monolith Cu-zeolite selective catalytic reduction catalyst provided a highly realistic kinetic parameter set of ammonia adsorption/desorption and enabled a mathematical description of hydrothermal aging effect.

Mango Firmness Modeling as Affected by Transport and Ethylene Treatments.

More and more, tropical fruit are subjected to accelerated ripening at receiving markets until “ready to eat.” We propose a kinetic model that incorporates the effects of temperature and ethylene on the firmness behavior of “Keitt” and “Kent” mangoes. Stiffness of individual mangoes, as measured by the acoustic firmness tester, was measured repeatedly over time. The firmness model assumes fixed levels of ethylene, established after the climacteric peak, that steadily induces production of softening enzymes that subsequently denaturalize. The initial level of these enzymes is assumed to be zero due to either the tree factor for freshly harvested mangoes, or due to chilling injury for reefer transported mangoes. The kinetic parameter set for “Keitt” mangoes was estimated based on a Spanish batch, freshly harvested and ripened under dynamic temperature scenarios, combined with a reefer transported Brazilian batch stored at four constant temperatures. Firmness data from reefer transported batches, from Brazil, Ivory Coast and Mali, stored at four constant temperatures were used to estimate a set of kinetic parameters for the “Kent” mangoes. Only a partial set of “Kent” kinetic parameters could be established due to the often already advanced stage of softening at the time of arrival. The effect of ethylene was investigated by applying external ethylene levels, varying from 0 to 100 μL L−1. The effect of external application of ethylene was modeled by estimating EF, the ethylene factor, being a reflection of the internal ethylene level and ethylene sensitivity. The effect of ethylene application on softening was sometimes huge. For an Israeli “Keitt” batch a fifty times higher EF was found when the firmness behavior of low- (without ethylene application) and high temperature (with ethylene application) stored sub-batches were compared. However, this effect was sometimes also small, especially for reefer transported mangoes. For commercial application, a reliable prediction of the time until “ready to eat” is not possible because of the current inability to assess EF. Nevertheless, the proposed model described mango softening accurately, irrespective of the sourcing area and includes the effects of storage temperature and ethylene application.

Identifying unified kinetic model parameters for thermal decomposition of polymer matrix composites

Predicting thermal responses of composite materials requires accurate input parameters derived from reliable thermal property characterization and kinetic models. Composite material properties and decomposition kinetics vary with temperature and heating rate. Typically, conventional kinetic models derived from thermogravimetric analysis data result in multiple sets of kinetic model parameters, which are difficult to implement into numerical simulations under widely varying temperature and heating rate conditions. Here, a methodology was developed to reliably predict decomposition processes of composite materials with a single (i.e., unified) set of kinetic model parameters. The unified kinetic model parameters for each of four different composite materials were used to accurately predict decomposition kinetics observed over the entire range of experimental temperatures and heating rates. Furthermore, this broadly applicable methodology may predict decomposition from limited data sets, and is expected to extrapolate reliably measurable data to experimentally challenging heating rates and temperatures.

Intradialytic kinetics of middle molecules during hemodialysis and hemodiafiltration.

The kinetics of β2-microglobulin during hemodialysis and hemodiafiltration is well described by a two-compartment model where clearance by the dialyzer is from a central compartment volume that approximates plasma volume and a total distribution volume that approximates extracellular fluid volume. The kinetics of middle molecules with molecular weights larger than β2-microglobulin have not been extensively studied. Intradialytic plasma concentrations and overall dialyzer clearances of β2-microglobulin (11.8 kD), myoglobin (16.7 kD) and complement factor D (24.4 kD) were used to estimate three kinetic parameters from a two-compartment model, namely intercompartmental clearance, central compartment volume and total distribution volume, in hemodialysis patients; these data were collected during two clinical trials of medium cut-off dialyzers (with extended middle molecule removal) during hemodialysis and high-flux dialyzers during hemodialysis and hemodiafiltration. In the current exploratory analyses, the kinetic parameters from all dialyzers were combined. Overall dialyzer clearance was evaluated by total mass removed in the dialysate. In total, 345 sets of kinetic parameters from 35 patients were determined. Intercompartmental clearance and central compartment volume for myoglobin and complement factor D were smaller (P < 0.001) than those for β2-microglobulin. Independent of middle molecule, intercompartmental clearance and central compartment volume were associated with overall dialyzer clearance (P < 0.001), but total distribution volume was not (P = 0.083). A two-compartment kinetic model can only describe intradialytic kinetics of middle molecules with molecular weights larger than β2-microglobulin if the central compartment is small and dependent on overall dialyzer clearance.

Characterization of receptor binding kinetics for vascular endothelial growth factor-A using SPR

Angiogenesis is a highly regulated process orchestrated, in large part, by the vascular endothelial growth factor-A (VEGF-A) system of ligands and receptors. Considerable effort has been invested in finding optimal ways to modulate VEGF-A activity to treat disease, however, the mechanisms by which the various components interact remain poorly understood. This is in part because of the difficulty of analyzing the various interactions in an intercomparable manner. In the present study, we established conditions to allow for the detailed characterization of the molecular interactions between VEGF and its receptors and the co-receptor NRP-1 using surface plasmon resonance (SPR). We found that VEGF dissociated 25-times faster from its major signaling receptor, VEGF receptor-2 (VEGFR-2) than from its “decoy” receptor, VEGF receptor-1 (VEGFR-1). Using a systematic approach, we obtained kinetic parameters for each individual interaction under a consistent set of experimental conditions allowing for comparison between various receptors. The set of quantitative kinetic parameters and experimental conditions reported herein will provide valuable tools for developing comprehensive models of the VEGF system.

Determination of intrinsic kinetic parameters in photocatalytic multi-tube reactors by combining the NTUm-method with radiation field modelling

In this work, we propose an adapted Number of Transfer Units (NTUm)-method as an effective tool to determine the Langmuir-Hinshelwood kinetic parameters for a photocatalytic multi-tube reactor. The Langmuir-Hinshelwood rate constant kLH and the Langmuir adsorption constant KL were determined from several experiments under different UV-irradiance conditions, resulting in irradiance depending values for kLH. In order to determine a unique, intrinsic empirical constant k0, valid for all irradiation conditions, we coupled the adapted NTUm-method with a radiation field model to predict UV-irradiance distribution inside the reactor. The final set of kinetic parameters were derived using a Generalized Reduced Gradient (GRG) nonlinear solving method in Matlab which minimizes the differences between model and experimental reactor outlet concentrations of acetaldehyde for various photocatalytic experiments under varying operating conditions, including inlet concentration, flow rate and UV-irradiance. An excellent agreement of the intrinsic empirical constant k0, derived from the coupled NTUm-radiation field model and an earlier published CFD approach was found, emphasizing its validity and reliability.

Molecular mechanistic insights into coupling of ion transport to ATP synthesis

A wealth of molecular mechanistic insights has been provided into the coupling of ion transport to ATP synthesis based on a two-ion theory of biological energy coupling. A kinetic scheme that considers the mode of functioning of a single F1FO-ATP synthase molecule with H+-A− cotransport and unidirectional rotation of the c-rotor in the membrane-bound FO-portion of the enzyme has been developed. Mathematical analysis leads to a detailed enzyme kinetic model applicable to a population of molecules which is compared with experimental data on the pH dependence of ATP synthesis. The model agrees well with the experimental data, and a single equation with a single set of standard enzymological kinetic parameters has been shown to explain the experimental data over the entire range of conditions for the chloroplast ATP synthase. The analysis gives novel insights into kinetic and mechanistic characteristics of ATP synthesis in FO. These include an order imposed on ion binding and unbinding events in FO, the essential role of the anion in direct activation of the ATP synthase (in addition to its role as a permeant ion), and the integration in a novel way of the functions of cooperativity and cotransport of dicarboxylic acid anions and protons during physiological ATP synthesis. Further, Wyman's pioneering classical work on the thermodynamics of linked functions has been shown to offer a new approach to distinguish between various models of energy coupling in ATP synthesis. All these results have been found to be inconsistent with Mitchell's chemiosmotic theory and are shown to be in agreement with Nath's torsional mechanism of energy transduction and ATP synthesis.