Photocatalytic degradation intrinsic kinetics of gaseous cyclohexane in a fluidized bed photocatalytic reactor

The special photocatalytic degradation intrinsic kinetics of gaseous cyclohexane were investigated in a designed fluidized bed photocatalytic reactor (FBPR). A series of photocatalytic kinetic reaction equations were developed to explore the relationship of degradation efficiency and operating variables based on photocatalytic mechanism and particle fluidization hydrodynamic characteristics. The corresponding results indicated that the initial concentration has influenced the photocatalytic degradation reaction conversion, and having a concentration inflexion point which theoretically divided the photocatalysis into a first-order apparent kinetic rate equation at low concentrations and a zero-order kinetic rate equation at high concentrations. Furthermore, these results were validated theoretically by the intrinsic kinetic models of photocatalytic degradation conversion developed according to variation of cyclohexane concentration and gas velocity. Based on the experimental results, the optimal operating gas velocity range was determined. The multi-factors synergy effect resulting from gas velocity on photocatalytic degradation efficiency was explored and proved by mass transfer, illumination transmission and adsorption models. Finally, the degradation pathways of the cyclohexane and deactivation mechanism of the photocatalyst were studied according to the intermediates degraded on TiO₂ surface, and a feasible method presented for catalyst regeneration.     

Kinetic model for hydrocarbon-assisted particulate boron combustion

A kinetic model is presented to describe the high temperature (1800 K < T < 3000 K) surface oxidation of particulate boron in a hydrocarbon combustion environment. The model includes a homogeneous gas-phase B/O/H/C oxidation mechanism consisting of 19 chemical species and 58 forward and reverse elementary reactions, multi-component gas-phase diffusion, and a heterogeneous surface oxidation mechanism consisting of ‘elementary’ adsorption and desorption reaction steps. Thermochemical and kinetic parameters for the surface reactions are estimated from available experimental data and/or elementary transition state arguments. The kinetic processes are treated using a generalized kinetics code, with embedded sensitivity analysis, for the combustion of a one-dimensional (particle radius), spherical particle. Model results are presented for the oxidation of a 200 μm boron particle in a JP-4/air mixture at ambient temperatures of 1400 K and 2000 K. These results include temperature and gas-phase species profiles as a function of radial distance and particle burning rates. © 1994 John Wiley & Sons, Inc.     

Acetylene‐Hydration Kinetics on Cadmium‐Exchanged Clinoptilolite Catalyst,Preliminary Communication

Hydration of acetylene under steady‐state conditions around 450 K proceeds on Cd‐clinoptilolite without catalyst deactivation and formation of by‐products. Reaction rates were determined under steady‐state conditions at different partial pressures of acetylene, water, and acetaldehyde. In relation with the results, rate equations for different kinetic models were evaluated. Langmuir‐Hinshelwood kinetics was established. According to this model, acetylene and water must adsorb on similar sites, and the surface reaction between the adsorbed reactants is the rate‐determining step, which is followed by equilibrated desorption of the produced acetaldehyde.     

Curing reaction of o-cresol novolac epoxy resin according to hardener change

The investigations of cure kinetics and glass transition temperature (T_g) versus reaction conversion (α) of o-cresol novolac epoxy resin with the change of hardener were performed. All kinetic parameters of the curing reaction such as the reaction rate order, activation energy, and frequency factor were calculated. The curing mechanisms were classified into two types. One was an autocatalytic mechanism and the other was a nth order kinetic mechanism. The constants related to the chain mobility of polymer segments were obtained by using the DiBenedetto equation. We have tried to correlate the relationships between curing mechanism and molecular structures of hardeners from these results. © 1993 John Wiley & Sons, Inc.     

Kinetics and mechanism of the oxidation of substituted benzaldehydes by hexamethylenetetramine‐bromine

The oxidation of thirty‐six monosubstituted benzaldehydes by hexa‐methylenetetramine‐bromine (HABR), in aqueous acetic acid solution, leads to the formation of the corresponding benzoic acids. The reaction is first order with respect to HABR. Michaelis‐Menten–type kinetics were observed with respect to aldehyde. The reaction failed to induce the polymerization of acrylonitrile. There is no effect of hexamethylenetetramine on the reaction rate. The oxidation of [²H]benzaldehyde (PhCDO) indicated the presence of a substantial kinetic isotope effect. The effect of solvent composition indicated that the reaction rate increases with an increase in the polarity of the solvent. The rates of oxidation of meta‐ and para‐substituted benzaldehydes showed excellent correlations in terms of Charton's triparametric LDR equation, whereas the oxidation of ortho‐substituted benzaldehydes correlated well with tetraparametric LDRS equation. The oxidation of para‐substituted benzaldehydes is more susceptible to the delocalization effect but the oxidation of ortho‐ and meta‐substituted compounds displayed a greater dependence on the field effect. The positive value of γ suggests the presence of an electron‐deficient reaction center in the rate‐determining step. The reaction is subjected to steric acceleration when ortho‐substituents are present. © 2000 John Wiley & Sons, Inc. Int J Chem Kinet 32: 615–622, 2000     

Effect of sucrose on BSA denatured aggregation at high concentration studied by the iso-conversional method and the master plots method

The kinetics of protein thermal transition is of a significant interest from the standpoint of medical treatment. The effect of sucrose (0–15 mass%) on bovine serum albumin denatured aggregation kinetics at high concentration was studied by the iso-conversional method and the master plots method using differential scanning calorimetry. The observed aggregation was irreversible and conformed to the simple order reaction. The denaturation temperature (T _m), the kinetic triplets all increased as the sucrose concentration increased, which indicated the remarkable stabilization effect of sucrose. The study purpose is to provide new opportunities in exploring aggregation kinetics mechanisms in the presence of additive.     

The effect of glucose on bovine serum albumin denatured aggregation kinetics at high concentration

The effect of glucose (0–15 mass%) on the kinetics of bovine serum albumin (BSA) denatured aggregation at high concentration in aqueous solution has been studied by differential scanning calorimetry. The observed denatured aggregation process was irreversible and could be characterized by a denaturation temperature (T _m), apparent activation energy (E _a), the approximate order of reaction, and pre-exponential factor (A). As the glucose concentration increased from 0 to 15 mass%, T _m increased, E _a also increased from 514.59409±6.61489 to 548.48611±7.81302 kJ mol⁻¹, and A/s⁻¹ increased from 1.24239E79 to 5.59975E83. The stabilization increased with an increasing concentration of glucose, which was attributed to its ability to alter protein denatured aggregation kinetics. The kinetic analysis was carried out using a composite procedure involving the iso-conversional method and the master plots method. The iso-conversional method indicated that denatured aggregation of BSA in the presence and absence of glucose should conform to single reaction model. The master plots method suggested that the simple order reaction model best describe the process. This study shows the combination of iso-conversional method and the master plots method can be used to quantitatively model the denatured aggregation mechanism of the BSA in the presence and absence of glucose.     

Temperature vs. time sequences to palliate deactivation in parallel and in series-parallel with the main reaction: parametric study

The calculation of temperature vs. time sequences to palliate catalyst deactivation in an integral reactor has been studied either by maintaining constant the conversion at the reactor outlet in a simple reaction or by maintaining constant the concentration of a given component at the outlet in a complex reaction system. The experimental systems studied, which are a simple one (dehydration of 2-ethylhexanol) and a complex one (isomerization of cis-butene), have kinetic models of the Langmuir-Hinshelwood-Hougen-Watson type for the main reaction and deactivation, with deactivation by coke dependent on the concentration of the reaction components. In the reaction of dehydration of 2-ethylhexanol deactivation occurs in parallel with the main reaction and in the isomerization of cis-butene deactivation occurs in series-parallel with the main reaction. A parametric study has been carried out for both reaction systems. The sequences calculated have been experimentally proven in an automated reaction apparatus.     

The solvent effects in the reactions of carboxylic acids with oxiranes. 1. Kinetics of the reaction of acetic acid with epichlorohydrin in butan‐1‐ol

Kinetics of the reaction of acetic acid with epichlorohydrin in the presence of chromium(III) acetate in butan‐1‐ol solution have been studied. The partial reaction orders with respect to reagents were found. The reactions were of first‐order with respect to both epichlorohydrin and catalyst and zeroth order with respect to acetic acid. A kinetic model for the overall process has been proposed. The reaction constants have been calculated along with the activation parameters. The effect of dilution on the rate of addition is discussed. In the equimolar mixture of acetic acid and epichlorohydrin the apparent rate constant of the addition k₁ initially decreases to increase again at the concentration of butan‐1‐ol exceeding 3 M. © 2000 John Wiley & Sons, Inc. Int J Chem Kinet 32: 378–387, 2000     

Synthesis of carboxy‐telechelic oligostyrene by dead‐end polymerization: Evaluation of primary radical termination by kinetic study and kinetic simulation model

Styrene was polymerized with azobiscyanovaleric acid (ACVA) to obtain carboxy‐telechelic polystyrene. Our aim was to synthesize an oligostyrene with a molecular weight of about 2000 g/mol. Thus, styrene was polymerized at 90 °C, where t_1/2ACVA is very short, and at very high initiator concentrations. In these conditions a new termination reaction appeared, known as the primary radical termination (PRT). At first, PRT was observed by a deviation from the simple kinetic law. Then, the constant of PRT was determined by several kinetic models to be more important than the constant of bimolecular termination. Finally, the PREDICI simulation program was used to confirm the predominance of PRT. This simulation program allowed the determination of the constant of primary radical deactivation k_rr and the influence of this reaction on the conversion rate. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 2740–2750, 2001     

Evaluation of the thermal degradation of PC/ABS/montmorillonite nanocomposites

Polycarbonate (PC)/acrylonitrile‐butadiene‐styrene (ABS) polymer alloy/montmorillonite (MMT) nanocomposites were prepared using a direct melt intercalation technique. The pyrolytic degradation and the thermo‐oxidative degradation of the polymer alloy and the nanocomposites were studied by thermogravimetric analysis (TGA). The kinetic evaluations were performed by the model‐free kinetic analysis and the multivariate non‐linear regression. Apparent kinetic parameters for the overall degradation were calculated. The results show that PC/ABS/MMT nanocomposites have high thermal stability and low flammability. Their pyrolytic degradation and the thermo‐oxidative degradation model are different. The pyrolytic degradation reaction of the polymer is a two‐step parallel reaction model: nth‐order reaction model, and ath‐degree autocatalytic reaction with an nth‐order reaction autocatalytic reaction, whereas the thermal oxidative degradation reaction of the polymer is a two‐step following reaction model: A → B → C of nth‐order reaction model, and autocatalytic reaction model. Copyright © 2005 John Wiley & Sons, Ltd.     

Modeling Investigation of Volume Variation Kinetics of Fast Response Hydrogels

Abstract

Fast response hydrogels have attracted great attention recently. Three kinds of models with different complexity are available in the literature to investigate their volume variation kinetics. A phenomenal model based on second‐order reaction kinetics provides a simple method to correlate the experimental kinetic data. A power law model can be employed to evaluate different volume variation mechanisms according to the diffusion exponential coefficient. The multi‐field model incorporates mechanical deformation with the diffusion of ion species. The volume variation rate is dependent on both hydrogel molecular design and operation conditions.     

Transport and kinetics at microheterogeneous electrodes: Part V. The methylviologen/platinum system

Results are reported for the reaction of methylviologen radical cation, MV⁺ with platinum colloidal particles, studied by stopped flow spectrophotometry. The rate of the reaction depends on the gaseous pretreatment of the particles. For particles reduced by hydrogen, the kinetics are usually first order with respect to MV⁺. The reaction is also first order in the concentration of platinum, and is inhibited in a first order manner by the product MV²⁺. This inhibition suggests that MV²⁺ is adsorbed on the particle surfaces, and this has been confirmed by ac, ring—disc electrode studies on macroscopic platinum electrodes. At high concentrations of MV⁺ some deviation from first order kinetics is observed. These results are all explained by a kinetic model in which either the desorption of MV²⁺ or the adsorption of MV⁺ is the rate limiting process. The rate of consumption of MV⁺ on an oxidised surface is an order of magnitude faster than that on the reduced surface. Ring—disc studies show that this is because the MV⁺ is not producing H₂ but is reducing the surface oxide. The results are shown to fit a simple model which takes into account this titration of the oxide layer. The model also explains why the rate on partially oxidised surfaces will appear to have an order greater than one in [Pt].     

Kinetics of catalyzed esterification of acetic acid with n-butanol using carbonized agro-waste

The objective of this research work was to investigate the kinetics of esterification of acetic acid with n-butanol through the variation of experimental parameters. The reaction mixture was catalyzed heterogeneously by a sulfonated catalyst in batch mode of operation. The catalyst was prepared from abundantly available agro-waste, Cajanus cajan husk by chemical activation process, which produces a carbon-based solid catalyst with high surface area. The catalyst was characterized by a Brunauer-Emmet-Teller surface analyzer and Fourier transform infrared spectroscopy to know the surface morphology. Process parameters such as contact time, reaction temperature, and catalyst loading, which can influence the extent of conversion of reactants, were studied. Furthermore, the kinetic investigation was also carried out to estimate the kinetic parameters for uncatalyzed and catalyzed reaction using the second-order pseudo-homogeneous (P-H), Eley-Rideal (E-R), and Langmuir-Hinshelwood (LH) kinetic models for this research work. The kinetic parameters such as activation energy, preexponential factor, and the thermodynamic parameters such as enthalpy and entropy were estimated for uncatalyzed and catalyzed reactions using these three models. The process conditions were optimized for catalyzed and uncatalyzed reactions to obtain the maximum product yield by minimizing root mean square error of each experimental data using the MS-excel solver tool. Thus, this study reveals the high potential of an agro-waste, Cajanus cajan husk as raw material for the synthesis of catalyst. The results show that the E-R model is more appropriate for predicting the dynamic data of an esterification reaction, as the forward rate of reaction estimated using the E-R model are more modified than P-H and L-H models.     

The Kissinger law and the IKP method for evaluating the non-isothermal kinetic parameters

The following problems concerning the apparent compensation effect (CE) (lnA=a+bE, where A is the pre-exponential factor, E is the activation energy, a and b are CE parameters) due to the change of the conversion function and on which the invariant kinetic parameters method (IKP method) is based, are discussed: (1) the explanation of this kind of CE; (2) the choice of the set of conversion functions that checks CE relationship; (3) the dependencies of CE parameters on the heating rate and the temperature corresponding to the maximum reaction rate. Using the condition of maximum of the reaction rate suggested by Kissinger (Kissinger law), it is pointed out that, for a certain heating rate, the CE relationship is checked only for reaction order (Fn) and Avrami-Erofeev (An) kinetic models, and not for diffusion kinetic models (Dn). Consequently, IKP method, which is based on the supercorrelation relationship between CE parameters, can be applied only for the set Fn+ An of kinetic models. The dependencies of a and b parameters on the heating rate and T _m (temperature corresponding to maximum reaction rate) are derived. The theoretical results are discussed and checked for (a) TG simulated data for a single first order reaction; (b) TG data for PVC degradation; (b) the dehydration of CaC₂O₄·H₂O.     

Photosensitized polymerization of methyl methacrylate with acriflavine dye

The kinetics of photopolymerization by ultraviolet-light with acriflavine as the sensitizer was studied in nonaqueous medium. The reducing agent used was alcohol. The rates of the photopolymerization were determined dilatometrically. The order of the reaction with respect to the sensitizer concentration was 0.14 while that with respect to the reducing agent concentration was 0.8 × 10^?1. These results are interpreted in terms of a kinetic scheme which involves a competitive ground-state deactivation of the dye triplet and photoreduction. A low initiator efficiency of the primary radicals (cage recombination) and bimolecular termination processes are assumed.     

Kinetic study of the reaction between a hydroxylated polybutadiene and isocyanates in chlorobenzene,III. Reaction with dimer diacid diisocyanate (DDI)

A kinetic study of the reaction of hydroxylated liquid polybutadiene (M?_n = 2400) R-45M and dimer diacid diisocyanate (DDI) was carried out in chlorobenzene solution. The kinetic data were compared with the data obtained in a previous work using toluene as solvent. This reaction presented an apparent second order rate law, and was faster in chlorobenzene than in toluene. The accelerating effect of chlorobenzene was higher at higher temperatures.     

The kinetic regularities, products, and mechanism of the thermal decomposition of dimethyldioxirane. The contribution of molecular and radical reaction channels

The products and kinetics of the thermal decomposition of dimethyldioxirane (DMDO) were studied. The reaction proceedsvia three parallel pathways: isomerization to methyl acetate, oxygen atom insertion into the C−H bond of a solvent molecule (acetone), and the solvent-induced homolysis of the O−O bond in the DMDO molecule. The contribution of the latter reaction channel isca. 23% at 56°C. The overall kinetic parameters of DMDO thermolysis in oxygen atmosphere were determined. The free radical-induced DMDO decomposition occurs in an inert atmosphere. The formal kinetics of this reaction was investigated. The mechanism of the DMDO thermolysis is discussed. Dedicated to Professor E. T. Denisov on the occasion of his 70th Birthday. Published inIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1344–1354, August, 2000.     

A study of the kinetics of the microwave cure of a phenylethynyl‐terminated imide model compound and imide oligomer (PETI‐5)

The kinetic mechanism of the microwave cure of a simple phenylethynyl‐terminated imide model compound, 3,4′‐bis[(4‐phenylethynyl)phthalimido]diphenyl ether (PEPA‐3,4′‐ODA) and a phenylethynyl‐terminated imide oligomer (PETI‐5, M_n 5000 g/mol) was studied. Dielectric properties of the model compound and PETI‐5 were measured in the microwave range from 0.4 GHz to 3 GHz. FTIR was used to follow the cure of the model compound (PEPA‐3,4′‐ODA), while thermal analysis (DSC) was used to follow the cure of the PETI‐5 oligomer. The changes in room temperature IR absorbance of phenylethynyl triple bonds at 2214 cm⁻¹ of PEPA‐3,4′‐ODA as a function of cure time were measured after cure temperatures of 300, 310, 320, and 330 °C. The changes in the glass‐transition temperature, T_g, of PETI‐5 as a function of cure time were measured after cure at 350, 360, 370, and 380 °C, respectively. The T_g 's were determined to calculated the relative extent of cure, x, of the PETI‐5 oligomer according to the DiBenedetto equation. For the model compound, the reaction followed first order kinetics, yielding an activation energy of 27.6 kcal/mol as determined by infrared spectroscopy. For PETI‐5, the reaction followed 1.5th order, yielding an activation energy of 17.1 kcal/mol for the whole cure reaction, as determined by T_g using the DiBenedetto method. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 2526–2535, 2000