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Kinetic Modeling (kinetic + modeling)
Selected AbstractsKinetic Modeling of Non-Linear PolymerizationMACROMOLECULAR SYMPOSIA, Issue 1 2006Mário Rui P. F. N. Costa Abstract Recent developments of a method based upon population balances of generating functions of polymer chain length distributions (CLD) are presented. The calculation of the CLD and how to take into account chain length dependent reactivity are discussed. Prediction of polymer properties is also possible but only easily done for the average molecular radius of gyration; some results are presented for a radical polymerization including transfer to polymer and propagation with terminal double bonds. [source] Kinetic Modeling of Normal ATRP, Normal ATRP with [CuII]0, Reverse ATRP and SR&NI ATRPMACROMOLECULAR THEORY AND SIMULATIONS, Issue 7-8 2008Wei Tang Abstract The kinetics of various ATRP systems, including normal ATRP, normal ATRP in the presence of initially-added CuII, reverse ATRP and SR&NI ATRP were modeled using Predici software. The instantaneous kinetic chain length was introduced for ATRP and was used for the prediction of control over polymerization. Equations were derived to estimate the radical concentration at the quasi-steady-state. Normal ATRP experiences a continuous decrease of radical concentration leading to a decrease of polymerization rate; in contrast, SR&NI ATRP undergoes a continuous increase in radical concentration, leading to an increase of the polymerization rate. All of these ATRP methods can afford a relatively fast polymerization rate and retain good polymerization control. [source] Multi-Component Kinetic Modeling for Controlling Local Compositions in Thermosensitive PolymersMACROMOLECULAR THEORY AND SIMULATIONS, Issue 8 2006Todd Hoare Abstract Summary: An explicit terminal copolymerization kinetic model accounting for the copolymerization of up to four different comonomers is developed and applied to model the conversion profiles and local compositional gradients in functionalized PNIPAM-based polymer and hydrogel systems. The kinetics of the functional comonomer(s) have a large influence on both the mole fraction and chain distribution of functional groups in polymers. Strategies are developed to synthesize polymers with uniform compositions by applying semi-batch techniques or via copolymerization of multiple monomers with the same target functionality but with divergent reactivities relative to NIPAM. Synthetic protocols are also designed to maximize the compositional uniformity and randomness of ampholytic polymers. Instantaneous mole fractions of monomers in polymers as a function of the overall monomer conversion for the copolymerizations of NIPAM, MBA, and two functional monomers: MMA and acrylamide. [source] Kinetic Modeling of Thiol-Ene Reactions with Both Step and Chain Growth AspectsMACROMOLECULAR THEORY AND SIMULATIONS, Issue 4 2005Oguz Okay Abstract Summary: A kinetic model is presented for thiol-ene cross-linking photopolymerizations including the allowance for chain growth reaction of the ene, i.e., homopolymerization. The kinetic model is based on a description of the average chain lengths derived from differential equations of the type of Smoluchowski coagulation equations. The method of moments was applied to obtain average properties of thiol-ene reaction systems. The model predicts the molecular weight distribution of active and inactive species in the pre-gel regime of thiol-enes, as well as the gel points depending on the synthesis parameters. It is shown that, when no homopolymerization is allowed, the average molecular weights and the gel point conversion are given by the typical equations valid for the step-growth polymerization. Increasing the extent of homopolymerization also increases the average molecular weights and shifts the gel point toward lower conversions and shorter reaction times. It is also shown that the ratio of thiyl radical propagation to the chain transfer kinetic parameter (kp1/ktr) affects the gelation time, tcr. Gelation occurs earlier as the kp1/ktr ratio is increased due to the predominant attack of thiyl radicals on the vinyl groups and formation of more stable carbon radicals. The gel point in thiol-ene reactions is also found to be very sensitive to the extent of cyclization, particularly, if the monomer functionalities are low. Number-average chain length of carbon radicals (solid curves) and thiyl radicals (dashed curves) plotted against the vinyl group conversion, xM, during thiol-ene polymerization. Calculations were for six different kp/ktr ratios. [source] Adequacy Indices for Dialysis in Acute Renal Failure: Kinetic ModelingARTIFICIAL ORGANS, Issue 5 2010Malgorzata Debowska Abstract Many aspects of the management of renal replacement therapy in acute renal failure (ARF), including the appropriate assessment of dialysis adequacy, remain unresolved, because ARF patients often are not in a metabolic steady state. The aim of this study was to evaluate a system of adequacy indices for dialysis in ARF patients using urea and creatinine kinetic modeling. Kinetic modeling was performed for two different fictitious patients (A and B) with characteristics described by the average parameters for two patient groups and for two blood purification treatments: sustained low efficiency daily dialysis (SLEDD) in Patient A and continuous venovenous hemofiltration (CVVH) in Patient B, based on data from a clinical report. Urea and creatinine generation rates were estimated according to the clinical data on the solute concentrations in blood. Then, using estimated generation rates, two hypothetical treatments were simulated, CVVH in Patient A and SLEDD in Patient B. KT/V, fractional solute removal (FSR) and equivalent renal clearance (EKR) were calculated according to the definitions developed for metabolically unstable patients. CVVH appeared as being more effective than SLEDD because KT/V, FSR, and EKR were higher for CVVH than SLEDD in Patients A and B. Creatinine KT/V, FSR, and EKR were lower and well correlated to the respective indices for urea. Urea and creatinine generation rates were overestimated more than twice in Patient A and by 30,40% in Patient B if calculated assuming the metabolically stable state than if estimated by kinetic modeling. Adequacy indices and solute generation rates for ARF patients should be estimated using the definition for unsteady metabolic state. EKR and FSR were higher for urea and creatinine with CVVH than with SLEDD, because of higher K·T and minimized compartmental effects for CVVH. [source] Kinetic Modeling of Breweryapos;s Spent Grain AutohydrolysisBIOTECHNOLOGY PROGRESS, Issue 1 2005Florbela Carvalheiro Isothermal autohydrolysis treatments of breweryapos;s spent grain were used as a method for hemicellulose solubilization and xylo-oligosaccharides production. The time course of the concentrations of residual hemicelluloses (made up of xylan and arabinan) and reaction products were determined in experiments carried out at temperatures in the range from 150 to 190 °C using liquid-to-solid ratios of 8 and 10 g/g. To model the experimental findings concerning to breweryapos;s spent grain autohydrolysis several kinetic models based on sequential pseudo-homogeneous first-order reactions were tested. Xylan and arabinan were assumed to yield oligosaccharides, monosaccharides (xylose or arabinose), furfural, and other decomposition products in consecutive reaction steps. The models proposed provide a satisfactory interpretation of the hydrolytic conversion of xylan and arabinan. An additional model merging the two proposed models for xylan and arabinan degradation assuming that furfural was formed from both pentoses was developed and the results obtained are discussed. The dependence of the calculated kinetic coefficients on temperature was established using Arrhenius-type equations. [source] Kinetic Modeling of the Autotrophic Growth of Pavlova lutheri: Study of the Combined Influence of Light and TemperatureBIOTECHNOLOGY PROGRESS, Issue 4 2003Ana P. Carvalho The optimization and control of biochemical processes require the previous establishment of mathematical models that can describe the effect of process variables on their actual kinetics. Environmental temperature is a modulating factor to which the algal cells respond continuously by adjusting their rates of cellular reactions, their nutritional requirements, and, consequently, their biomass composition. Light intensity is an exhaustible resource, indispensable to autotrophic organisms. The effects of light intensity and temperature on growth of the microalga Pavlova lutheri, which have hardly been considered to date in a simultaneous fashion, were experimentally assessed using a factorial experimental design; in this way, the effects of each variable independently and their interactions could be quantified, using maximum biomass (Xmax) or maximum specific growth rate (,max) as objective functions. The preliminary results produced indicated that light intensity plays a more important role on ,max than temperature; in the case of Xmax, both temperature and, to a lesser extent, light intensity do apparently play a role. The highest values of Xmax were associated with low temperatures and high light intensities; a similar behavior could be observed for ,max concerning light intensity, although the dependency on temperature did not seem to be as important. A more complex mechanistic model was then postulated, incorporating light and temperature as input variables, which was successfully fitted to the experimental data generated during batch cultivation of P. lutheri. [source] Packed Bed Column Fermenter and Kinetic Modeling for Upgrading the Nutritional Quality of Coffee Husk in Solid-State FermentationBIOTECHNOLOGY PROGRESS, Issue 6 2001Débora Brand Studies were carried out to evaluate solid-state fermentation (SSF) for the upgradation of the nutritional quality of coffee husk by degrading the caffeine and tannins present in it. SSF was carried out by Aspergillus niger LPBx in a glass column fermenter using factorial design experiments and surface response methodology to optimize bioprocess parameters such as the substrate pH and moisture content and aeration rate. The first factorial design showed that the moisture content of the substrate and aeration rate were significant factors for the degradation of toxic compounds, which was confirmed by the second factorial design too. The kinetic study showed that the degradation of toxic compounds was related to the development of the mold and its respiration and also to the consumption of the reducing sugars present in coffee husk. From the values obtained experimentally for the oxygen uptake rate and CO2 evolved, the system determined a biomass yield (Yx/o) of 3.811 (g of biomass)·(g of consumed O2),1 and a maintenance coefficient (m) of 0.0031 (g of consumed O2)·(g biomass of biomass),1·h,1. The best results on the degradation of caffeine (90%) and tannins (57%) were achieved when SSF was carried out with a 30 mL·min,1 aeration rate using coffee husk having a 55% initial moisture content. The inoculation rate did not affect the metabolization of the toxic compounds by the fungal culture. After SSF, the protein content of the husk was increased to 10.6%, which was more than double that of the unfermented husk (5.2%). [source] Kinetic modeling of aqueous phenol degradation by UV/H2O2 processINTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 1 2008Maryam Edalatmanesh A dynamic kinetic model for the oxidation of phenol in water by an UV/H2O2 process is developed. The model is based on the elementary chemical and photochemical reactions, initiated by the photolysis of hydrogen peroxide into hydroxyl radicals. The model is validated by using experimental data obtained from the open literature for an actual UV/H2O2 process. Using those data and the developed kinetic model, kinetic rate constants for phenol intermediates, catechol and hydroquinone, are estimated. Moreover, the optimum initial hydrogen peroxide concentration is estimated by means of the validated model. © 2007 Wiley Periodicals, Inc. Int J Chem Kinet 40: 34,43, 2008 [source] The classical kinetic model for radical chain oxidation of hydrocarbon substrates initiated by bimolecular hydroperoxide decompositionINTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 11 2006X. Colin Kinetic modeling of the low-temperature (typically T , 200°C) thermal aging of polymers is a problem of great technological importance, owing to the continuously increasing needs of industry in terms of reliable methods for lifetime prediction. In the temperature domain under consideration, for most hydrocarbon substrates, oxidation proceeds by a radical chain reaction initiated by bimolecular hydroperoxide decomposition. In other words, the reaction generates its own initiator, which explains its strong autoaccelerated character. The most pertinent model is, to our opinion, the model elaborated by Tobolsky et al. (J Am Chem Soc 1950, 72, 1942) in the early 1950s. This model is, however, based on three questionable assumptions: the existence of a stationary state for radical concentrations (hypothesis S), the presence of oxygen in excess (hypothesis E), and the fact that the onset of steady state can be observed in the domain of low conversions, where the substrate consumption can be neglected (hypothesis L). One hypothesis (S) lacks consistency. A sounder alternative, which does not modify significantly the mathematical expressions of the model, will be proposed. The other hypotheses (E and L) can be justified in certain cases, but the limits of their domain of validity were never established to our knowledge. It is tried, here, to express these limits in function of fundamental parameters: rate constants and concentrations of reactants. © 2006 Wiley Periodicals, Inc. Int J Chem Kinet 38:666,676, 2006 [source] Kinetic modeling of esterification of cardanol-based epoxy resin in the presence of triphenylphosphine for producing vinyl ester resin: Mechanistic rate equationJOURNAL OF APPLIED POLYMER SCIENCE, Issue 4 2010Minakshi Sultania Abstract In this study, cardanol-based epoxidized novolac resins and methacrylic acid were used to produce cardanol-based epoxidised novolac vinyl ester resins. The reactions were conducted under nonstoichiometric condition using triphenylphosphine as catalyst in the temperature range of 80,100°C with an interval of 5°C. The first-order rate equation and mechanism based rate equation were examined. Parameters were evaluated by least square method. A comparison of mechnism based rate equation and experimental data showed an excellent agreement. Finally, Arrhenius equation and activation energy were presented. The specific rate constants, based on linear regression analysis, were found to obey Arrhenius equation. The values of activation energy, frequency factor, enthalpy, entropy, and free energy of the reaction revealed that the reaction was spontaneous and irreversible and produced a highly activated complex. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010 [source] Kinetic modeling of catalytic conversion of methylcyclohexane over USY zeolites: Adsorption and reaction phenomenaAICHE JOURNAL, Issue 6 2009Mustafa Al-Sabawi Abstract Catalytic conversion of cycloparaffins is a complex process involving competing reaction steps. To understand this process, FCC experiments using methylcyclohexane (MCH) on USY zeolite catalysts were carried out in the mini-fluidized CREC riser simulator. Runs were developed under relevant FCC process conditions in terms of partial pressures of MCH, temperatures (450,550°C), contact times (3,7 s), catalyst-oil mass ratios (5), and using fluidized catalysts. MCH overall conversions ranged between 4 to 16 wt %, with slightly higher conversions obtained using the larger zeolite crystallites. Moreover, it was found that MCH undergoes ring opening, protolytic cracking, isomerization, hydrogen transfer and transalkylation. A heterogeneous kinetic model for MCH conversion including thermal effects, adsorption and intrinsic catalytic reaction phenomena was established. Adsorption and kinetic parameters were determined, including the heat of adsorption (,40 kJ/mol), as well as thermal and primary catalytic intrinsic activation energies, which were in the range of 43,69 kJ/mol, and 50,74 kJ/mol, respectively. © 2009 American Institute of Chemical Engineers AIChE J, 2009 [source] Kinetic modeling of the photocatalytic degradation of air-borne pollutantsAICHE JOURNAL, Issue 5 2004H. Ibrahim Abstract The photocatalytic conversion of organic model pollutants (acetone, acetaldehyde, and isopropanol) in a novel Photo-CREC-Air unit is considered. This photocatalytic unit features: (1) external near-UV lamps placed in parabolic reflectors, (2) a basket supporting the irradiated glass mesh holding TiO2 loadings to achieve high photoconversion rates, and (3) a fluid flow pattern securing high gas velocities in the near-mesh region. Given the high quantum efficiencies observed in Photo-CREC-Air and, as a result, the high prospects for this novel design, rate equations and associated mechanistic formulations are investigated. With this goal, a Langmuir,Hinshelwood model, involving a one-site model pollutant mechanism, is considered. The associated kinetic parameters with the related statistical indicators are established, using least-square nonlinear regression. It is found that this model is adequate for describing the photodegradation of acetone on both Degussa P25 and Hombikat UV-100. It is also observed that the same type of reaction rate model is less adequate for the photodegradation of acetaldehyde and isopropanol, in particular, for predicting the formation of carbon dioxide. © 2004 American Institute of Chemical Engineers AIChE J 50: 1017,1027, 2004 [source] Transition from microemulsion to emulsion polymerization: Mechanism and final propertiesJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 20 2004Kevin D. Hermanson Abstract Microemulsion and emulsion polymerization can have some similarities in starting conditions and polymerization mechanisms, but the resulting latices are unalike in particle size and molecular weight. Here we show that polymerizations can be formulated that display the characteristics often separately associated with microemulsion or emulsion polymerization. Kinetic modeling and particle size measurements show that emulsion polymerizations with initial concentrations close to the microemulsion,emulsion phase boundary demonstrate relatively fast consumption of monomer droplets and produce smaller particles. Because of their high surfactant concentrations, none of the emulsion polymerizations examined demonstrate the classical Smith,Ewart kinetics usually associated with emulsion polymerization. Instead these emulsion polymerizations have a long period of particle nucleation that subsides only after the disappearance of monomer droplets. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 5253,5261, 2004 [source] Methyl methacrylate emulsion polymerization at low monomer concentration: Kinetic modeling of nucleation, particle size distribution, and rate of polymerizationJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 14 2001Jorge Herrera-Ordóñez Abstract The results of a mathematical model developed in the authors' previous work are discussed and compared against final number (N) and size distribution of particles (PSD) and the rate of polymerization (RP) experimental data of methyl methacrylate (MMA) emulsion polymerization above the critical micelle concentration (cmc) of the surfactant. On the basis of the model results, the hypothesis that the observed bimodal PSD can be ascribed to secondary nucleation as proposed in the literature is questionable. It is discussed that this PSD can also be caused by differences in the growing rate of different-size particles as predicted for styrene emulsion polymerization. Because of the small particle size obtained at low initial monomer concentration, the high rate of free-radical desorption reduces the accumulation of these species; therefore, the autoacceleration effect is less pronounced for the conditions under study compared with the usual behavior of the RP during MMA emulsion polymerization above cmc. Similarities and differences between model predictions and experimental data are discussed. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 2547,2556, 2001 [source] Kinetic modeling of lutein production by heterotrophic Chlorella at various pH and temperaturesMOLECULAR NUTRITION & FOOD RESEARCH (FORMERLY NAHRUNG/FOOD), Issue 8 2006Xianming Shi Abstract Kinetics of lutein production by heterotrophic Chlorella protothecoides was investigated with respect to pH and temperature. Flask cultures with initial pH 5.0,8.0 were carried out, and it was found that pH 6.0 was optimal for the algal growth. Further tests in fermentors showed that the highest biomass concentration, maximum cellular lutein content and lutein yield were achieved at pH 6. 6. In addition, it was shown that optimal biomass concentration and lutein yield were obtained at 28°C, while application of 35°C resulted in the highest cellular lutein content. A mathematical model was developed for the description of the processes under these cultivation conditions and the kinetic model fitted well to the experimental data. The obtained results may contribute to the commercial production of lutein by C. protothecoides. [source] Adequacy Indices for Dialysis in Acute Renal Failure: Kinetic ModelingARTIFICIAL ORGANS, Issue 5 2010Malgorzata Debowska Abstract Many aspects of the management of renal replacement therapy in acute renal failure (ARF), including the appropriate assessment of dialysis adequacy, remain unresolved, because ARF patients often are not in a metabolic steady state. The aim of this study was to evaluate a system of adequacy indices for dialysis in ARF patients using urea and creatinine kinetic modeling. Kinetic modeling was performed for two different fictitious patients (A and B) with characteristics described by the average parameters for two patient groups and for two blood purification treatments: sustained low efficiency daily dialysis (SLEDD) in Patient A and continuous venovenous hemofiltration (CVVH) in Patient B, based on data from a clinical report. Urea and creatinine generation rates were estimated according to the clinical data on the solute concentrations in blood. Then, using estimated generation rates, two hypothetical treatments were simulated, CVVH in Patient A and SLEDD in Patient B. KT/V, fractional solute removal (FSR) and equivalent renal clearance (EKR) were calculated according to the definitions developed for metabolically unstable patients. CVVH appeared as being more effective than SLEDD because KT/V, FSR, and EKR were higher for CVVH than SLEDD in Patients A and B. Creatinine KT/V, FSR, and EKR were lower and well correlated to the respective indices for urea. Urea and creatinine generation rates were overestimated more than twice in Patient A and by 30,40% in Patient B if calculated assuming the metabolically stable state than if estimated by kinetic modeling. Adequacy indices and solute generation rates for ARF patients should be estimated using the definition for unsteady metabolic state. EKR and FSR were higher for urea and creatinine with CVVH than with SLEDD, because of higher K·T and minimized compartmental effects for CVVH. [source] Simultaneous saccharification and co-fermentation of paper sludge to ethanol by Saccharomyces cerevisiae RWB222,Part I: Kinetic modeling and parametersBIOTECHNOLOGY & BIOENGINEERING, Issue 5 2009Jiayi Zhang Abstract A kinetic model was developed to predict batch simultaneous saccharification and co-fermentation (SSCF) of paper sludge by the xylose-utilizing yeast Saccharomyces cerevisiae RWB222 and the commercial cellulase preparation Spezyme CP. The model accounts for cellulose and xylan enzymatic hydrolysis and competitive uptake of glucose and xylose. Experimental results show that glucan and xylan enzymatic hydrolysis are highly correlated, and that the low concentrations of xylose encountered during SSCF do not have a significant inhibitory effect on enzymatic hydrolysis. Ethanol is found to not only inhibit the specific growth rate, but also to accelerate cell death. Glucose and xylose uptake rates were found to be competitively inhibitory, but this did not have a large impact during SSCF because the sugar concentrations are low. The model was used to evaluate which constants had the greatest impact on ethanol titer for a fixed substrate loading, enzyme loading, and fermentation time. The cellulose adsorption capacity and cellulose hydrolysis rate constants were found to have the greatest impact among enzymatic hydrolysis related constants, and ethanol yield and maximum ethanol tolerance had the greatest impact among fermentation related constants. Biotechnol. Bioeng. 2009; 104: 920,931. © 2009 Wiley Periodicals, Inc. [source] Kinetic modeling of a bi-enzymatic system for efficient conversion of lactose to lactobionic acidBIOTECHNOLOGY & BIOENGINEERING, Issue 5 2009Wouter Van Hecke Abstract A model has been developed to describe the interaction between two enzymes and an intermediary redox mediator. In this bi-enzymatic process, the enzyme cellobiose dehydrogenase oxidizes lactose at the C-1 position of the reducing sugar moiety to lactobionolactone, which spontaneously hydrolyzes to lactobionic acid. 2,2,-Azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) diammonium salt is used as electron acceptor and is continuously regenerated by laccase. Oxygen is the terminal electron acceptor and is fully reduced to water by laccase, a copper-containing oxidase. Oxygen is added to the system by means of bubble-free oxygenation. Using the model, the productivity of the process is investigated by simultaneous solution of the rate equations for varying enzyme quantities and redox mediator concentrations, solved with the aid of a numerical solution. The isocharts developed in this work provide an easy-to-use graphical tool to determine optimal process conditions. The model allows the optimization of the employed activities of the two enzymes and the redox mediator concentration for a given overall oxygen mass transfer coefficient by using the isocharts. Model predictions are well in agreement with the experimental data. Biotechnol. Bioeng. 2009;102: 1475,1482. © 2008 Wiley Periodicals, Inc. [source] Kinetic modeling of cellulosic biomass to ethanol via simultaneous saccharification and fermentation: Part I. Accommodation of intermittent feeding and analysis of staged reactorsBIOTECHNOLOGY & BIOENGINEERING, Issue 1 2009Xiongjun Shao Abstract The model of South et al. [South et al. (1995) Enzyme Microb Technol 17(9): 797,803] for simultaneous saccharification of fermentation of cellulosic biomass is extended and modified to accommodate intermittent feeding of substrate and enzyme, cascade reactor configurations, and to be more computationally efficient. A dynamic enzyme adsorption model is found to be much more computationally efficient than the equilibrium model used previously, thus increasing the feasibility of incorporating the kinetic model in a computational fluid dynamic framework in the future. For continuous or discretely fed reactors, it is necessary to use particle conversion in conversion-dependent hydrolysis rate laws rather than reactor conversion. Whereas reactor conversion decreases due to both reaction and exit of particles from the reactor, particle conversion decreases due to reaction only. Using the modified models, it is predicted that cellulose conversion increases with decreasing feeding frequency (feedings per residence time, f). A computationally efficient strategy for modeling cascade reactors involving a modified rate constant is shown to give equivalent results relative to an exhaustive approach considering the distribution of particles in each successive fermenter. Biotechnol. Bioeng. 2009;102: 59,65. © 2008 Wiley Periodicals, Inc. [source] Kinetic modeling of cellulosic biomass to ethanol via simultaneous saccharification and fermentation: Part II.BIOTECHNOLOGY & BIOENGINEERING, Issue 1 2009Experimental validation using waste paper sludge, anticipation of CFD analysis Abstract A kinetic model of cellulosic biomass conversion to ethanol via simultaneous saccharification and fermentation (SSF) developed previously was validated experimentally using paper sludge as the substrate. Adsorption parameters were evaluated based on the data obtained at various values for fractional cellulose conversion. The adsorption model was then combined with batch SSF data to evaluate the cellulose hydrolysis parameters. With the parameters evaluated for the specific substrate, the discrete model was able to predict SSF successfully both with discrete addition of cellulase only and with discrete feeding of substrate, cellulase, and media. The model tested in this study extends the capability of previous SSF models to semi-continuous feeding configurations, and invites a mechanistic interpretation of the recently observed trend of increasing conversion with decreasing feeding frequency [Fan et al. (2007a) Bioprocess Biosyst Eng 30(1):27,34]. Our results also support the feasibility and utility of determining adsorption parameters based on data obtained at several conversions, particularly when the model is to be applied to extended reaction times rather than only initial hydrolysis rates. The revised model is considerably more computationally efficient than earlier models, and appears for many conditions to be within the capability of simulation using computational fluid dynamics. Biotechnol. Bioeng. 2009;102: 66,72. © 2008 Wiley Periodicals, Inc. [source] Kinetic modeling of light limitation and sulfur deprivation effects in the induction of hydrogen production with Chlamydomonas reinhardtii: Part I. Model development and parameter identificationBIOTECHNOLOGY & BIOENGINEERING, Issue 1 2009Swanny Fouchard Abstract Chlamydomonas reinhardtii is a green microalga capable of turning its metabolism towards H2 production under specific conditions. However this H2 production, narrowly linked to the photosynthetic process, results from complex metabolic reactions highly dependent on the environmental conditions of the cells. A kinetic model has been developed to relate culture evolution from standard photosynthetic growth to H2 producing cells. It represents transition in sulfur-deprived conditions, known to lead to H2 production in Chlamydomonas reinhardtii, and the two main processes then induced which are an over-accumulation of intracellular starch and a progressive reduction of PSII activity for anoxia achievement. Because these phenomena are directly linked to the photosynthetic growth, two kinetic models were associated, the first (one) introducing light dependency (Haldane type model associated to a radiative light transfer model), the second (one) making growth a function of available sulfur amount under extracellular and intracellular forms (Droop formulation). The model parameters identification was realized from experimental data obtained with especially designed experiments and a sensitivity analysis of the model to its parameters was also conducted. Model behavior was finally studied showing interdependency between light transfer conditions, photosynthetic growth, sulfate uptake, photosynthetic activity and O2 release, during transition from oxygenic growth to anoxic H2 production conditions. Biotechnol. Bioeng. 2009;102: 232,245. © 2008 Wiley Periodicals, Inc. [source] Bacterial energetics, stoichiometry, and kinetic modeling of 2,4-Dinitrotoluene biodegradation in a batch respirometerENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 12 2004Chunlong Zhang Abstract A stoichiometric equation and kinetic model were developed and validated using experimental data from batch respirometer studies on the biodegradation of 2,4-dinitrotoluene (DNT). The stoichiometric equation integrates bacterial energetics and is revised from that in a previous study by including the mass balance of phosphorus (P) in the biomass. Stoichiometric results on O2 consumption, CO2 evolution, and nitrite evolution are in good agreement with respirometer data. However, the optimal P requirement is significantly higher than the stoichiometrically derived P, implying potentially limited bioavailability of P and the need for buffering capacity in the media to mitigate the adverse pH effect for optimal growth of DNT-degrading bacteria. An array of models was evaluated to fit the O2/CO2 data acquired experimentally and the DNT depletion data calculated from derived stoichiometric coefficients and cell yield. The deterministic, integrated Monod model provides the goodness of fit to the test data on DNT depletion, and the Monod model parameters (Ks, X0, ,max, and Y) were estimated by nonlinear regression. Further analyses with an equilibrium model (MINTEQ) indicate the interrelated nature of medium chemical compositions in controlling the rate and extent of DNT biodegradation. Results from the present batch respirometer study help to unravel some key factors in controlling DNT biodegradation in complex remediation systems, in particular the interactions between acidogenic DNT bacteria and various parameters, including pH and P, the latter of which could serve as a nutrient, a buffer, and a controlling factor on the bioavailable fractions of minerals (Ca, Fe, Zn, and Mo) in the medium. [source] Modeling complex decay profiles of hepatitis B virus during antiviral therapy,,HEPATOLOGY, Issue 1 2009Harel Dahari Typically, hepatitis B virus (HBV) decays in patients under therapy in a biphasic manner. However, more complex decay profiles of HBV DNA (e.g., flat partial response, triphasic, and stepwise), for which we have no clear understanding, have also been observed in some treated patients. We recently introduced the notion of a critical drug efficacy, ,c, such that if overall drug efficacy, ,tot, is higher than the critical drug efficacy (i.e., ,tot > ,c) then viral levels will continually decline on therapy, while if ,tot < ,c, then viral loads will initially decline but will ultimately stabilize at a new set point, as seen in flat partial responders. Using the idea of critical efficacy and including hepatocyte proliferation in a viral kinetic model, we can account for these complex HBV DNA decay profiles. The model predicts that complex profiles such as those exhibiting a plateau or shoulder phase, as well as a class of stepwise declines, occur only in patients in whom the majority of hepatocytes are infected before therapy. Conclusion: We show via kinetic modeling how a variety of HBV DNA decay profiles can arise in treated patients. (HEPATOLOGY 2009;49:32-38.) [source] Experimental measurements and kinetic modeling of CH4/O2 and CH4/C2H6/O2 conversion at high pressure,INTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 12 2008Christian Lund Rasmussen A detailed chemical kinetic model for homogeneous combustion of the light hydrocarbon fuels CH4 and C2H6 in the intermediate temperature range roughly 500,1100 K, and pressures up to 100 bar has been developed and validated experimentally. Rate constants have been obtained from critical evaluation of data for individual elementary reactions reported in the literature with particular emphasis on the conditions relevant to the present work. The experiments, involving CH4/O2 and CH4/C2H6/O2 mixtures diluted in N2, have been carried out in a high-pressure flow reactor at 600,900 K, 50,100 bar, and reaction stoichiometries ranging from very lean to fuel-rich conditions. Model predictions are generally satisfactory. The governing reaction mechanisms are outlined based on calculations with the kinetic model. Finally, the mechanism was extended with a number of reactions important at high temperature and tested against data from shock tubes, laminar flames, and flow reactors. © 2008 Wiley Periodicals, Inc. Int J Chem Kinet 40: 778,807, 2008 [source] Experimental measurements and kinetic modeling of CO/H2/O2/NOx conversion at high pressure,INTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 8 2008Christian Lund Rasmussen This paper presents results from lean CO/H2/O2/NOx oxidation experiments conducted at 20,100 bar and 600,900 K. The experiments were carried out in a new high-pressure laminar flow reactor designed to conduct well-defined experimental investigations of homogeneous gas phase chemistry at pressures and temperatures up to 100 bar and 925 K. The results have been interpreted in terms of an updated detailed chemical kinetic model, designed to operate also at high pressures. The model, describing H2/O2, CO/CO2, and NOx chemistry, is developed from a critical review of data for individual elementary reactions, with supplementary rate constants determined from ab initio CBS-QB3 calculations. New or updated rate constants are proposed for important reactions, including OH + HO2 , H2O + O2, CO + OH , [HOCO] , CO2 + H, HOCO + OH , CO + H2O2, NO2 + H2 , HNO2 + H, NO2 + HO2 , HONO/HNO2 + O2, and HNO2(+M) , HONO(+M). Further validation of the model performance is obtained through comparisons with flow reactor experiments from the literature on the chemical systems H2/O2, H2/O2/NO2, and CO/H2O/O2 at 780,1100 K and 1,10 bar. Moreover, introduction of the reaction CO + H2O2 , HOCO + OH into the model yields an improved prediction, but no final resolution, to the recently debated syngas ignition delay problem compared to previous kinetic models. © 2008 Wiley Periodicals, Inc. Int J Chem Kinet 40: 454,480, 2008 [source] Detailed chemical kinetic modeling of pyrolysis of ethylene, acetylene, and propylene at 1073,1373 K with a plug-flow reactor modelINTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 4 2008Koyo Norinaga This study examines the predictive capability of our recently proposed reaction mechanism (Norinaga and Deutschmann, Ind Eng Chem Res 2007, 46, 3547) for hydrocarbon pyrolysis at varying temperature. The conventional flow reactor experiments were conducted at 8 kPa, over the temperature range 1073,1373 K, using ethylene, acetylene, and propylene as reactants to validate the mechanism. More than 40 compounds were identified and quantitatively analyzed by on- and off-line gas chromatography. The chemical reaction schemes consisting of 227 species and 827 reactions were coupled with a plug-flow reactor model that incorporated the experimentally measured axial temperature profile of the reactor. Comparisons between the computations and the experiments are presented for more than 30 products including hydrogen and hydrocarbons ranging from methane to coronene as a function of temperature. The model can predict the compositions of major products (mole fractions larger than 10,2) in the pyrolysis of three hydrocarbons with satisfactory accuracies over the whole temperature range considered. Mole fraction profiles of minor compounds including polycyclic aromatic hydrocarbons (PAHs) up to three ring systems, such as phenanthrene, anthracene, and phenylnaphthalene, are also fairly modeled. At temperatures lower than 1273 K, larger PAHs were underpredicted and the deviation became larger with decreasing temperature and increasing molecular mass of PAHs, while better agreements were found at temperatures higher than 1323 K. © 2008 Wiley Periodicals, Inc. Int J Chem Kinet 40: 199,208, 2008 [source] Mechanisms and kinetics for preparing carbohydrazide by reacting dimethyl carbonate with hydrazine: A theoretical studyINTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 9 2008Jianguo Zhang Abstract The mechanism and kinetic modeling for preparing carbohydrazide from dimethyl carbonate and hydrazine has been declared. The geometries of all the stationary points (reactants, intermediates, transition states, and products) are optimized by using the B3LYP method with the cc-pVDZ basis set, and the harmonic vibrational frequencies as well as infrared intensities are predicted with the same method. The minimum-energy paths are obtained by using the intrinsic reaction coordinate (IRC) theory at the B3LYP/cc-pVDZ level of theory with the step length 0.02 (amu)1/2·bohr. The rate constants are evaluated by using the TST, TST/Eckart, and RRKM (T)/Eckart methods. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2008 [source] Accurate prediction of thermodynamic properties of alkyl peroxides by combining density functional theory calculation with least-square calibrationJOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 7 2009Cun-Xi Liu Abstract Owing to the significance in kinetic modeling of the oxidation and combustion mechanisms of hydrocarbons, a fast and relatively accurate method was developed for the prediction of ,fH of alkyl peroxides. By this method, a raw ,fH value was calculated from the optimized geometry and vibration frequencies at B3LYP/6-31G(d,p) level and then an accurate ,fH value was obtained by a least-square procedure. The least-square procedure is a six-parameter linear equation and is validated by a leave-one out technique, giving a cross-validation squared correlation coefficient q2 of 0.97 and a squared correlation coefficient of 0.98 for the final model. Calculated results demonstrated that the least-square calibration leads to a remarkable reduction of error and to the accurate ,fH values within the chemical accuracy of 8 kJ mol,1 except (CH3)2CHCH2CH2CH2OOH which has an error of 8.69 kJ mol,1. Comparison of the results by CBS-Q, CBS-QB3, G2, and G3 revealed that B3LYP/6-31G(d,p) in combination with a least-square calibration is reliable in the accurate prediction of the standard enthalpies of formation for alkyl peroxides. Standard entropies at 298 K and heat capacities in the temperature range of 300,1500 K for alkyl peroxides were also calculated using the rigid rotor-harmonic oscillator approximation. © 2008 Wiley Periodicals, Inc. J Comput Chem, 2009 [source] Optimization of multicomponent photopolymer formulations using high-throughput analysis and kinetic modelingAICHE JOURNAL, Issue 5 2010Peter M. Johnson Abstract While high throughput and combinatorial techniques have played an instrumental role in materials development and implementation, numerous problems in materials science and engineering are too complex and necessitate a prohibitive number of experiments, even when considering high throughput and combinatorial approaches, for a comprehensive approach to materials design. Here, we propose a unique combination of high throughput experiments focused on binary formulations that, in combination with advanced modeling, has the potential to facilitate true materials design and optimization in ternary and more complex systems for which experiments are never required. Extensive research on the development of photopolymerizable monomer formulations has produced a vast array of potential monomer/comonomer, initiator and additive combinations. This array dramatically expands the range of material properties that are achievable; however, the vast number of potential formulations has eliminated any possibility of comprehensive materials design or optimization. This limitation is addressed by maximizing the benefits and unique capabilities of high throughput experimentation coupled with predictive models for material behavior and properties. The high throughput experimentation-model combination is useful to collect a limited amount of data from as few as 11 experiments on binary combinations of 10 analyzed monomers, and then use this limited data set to predict and optimize formulation properties in ternary resins that would have necessitated at least 1000 high throughput experiments and several orders of magnitude greater numbers of traditional experiments. A data analysis approach is demonstrated, and the model development and implementation for one model application in which a range of material properties are prescribed, and an optimal formulation that meets those properties is predicted and evaluated. © 2009 American Institute of Chemical Engineers AIChE J, 2010 [source] | |||||||||||||||||||