First-order Reaction Mechanism Research Articles

Kinetic study on pyrolytic process of oil-palm solid waste using two-step consecutive reaction model

Pyrolysis of oil-palm ( Elaeis guineensis Jacq.) shell, a cheap and abundantly available solid waste from palm oil producing process, was carried out using thermogravimetric analysis. The effects of raw material particle size and heating rate on the pyrolytic properties and kinetic parameters (activation energy, frequency factor and reaction order) were investigated. A one-step global model and a two-step consecutive reaction model were used to simulate the pyrolytic process and predict the weight loss during pyrolysis. The two-step model fitted the experimental data much better than the one-step model as the softening effect and formation of an intermediate during the pyrolytic process were taken into account. This two-stage reaction characteristic was confirmed by two obvious maxima in the derivative thermogram for pyrolysis of palm shells under different heating rates. The pyrolytic reactions at the low- and high-temperature regimes were found to be based on a first-order reaction mechanism and a contracting volume mechanism, respectively.

NO adsorption and dissociation on Co{1010}

Nitric oxide adsorption and dissociation on Co{101̄0} have been studied using reflection absorption infrared spectroscopy (RAIRS), low energy electron diffraction (LEED) and thermal programmed desorption (TPD). At 100 K, NO is found to absorb molecularly on the Co{101̄0} surface with an estimated 0.5 ML coverage at saturation. At low coverages, three adsorption sites, on-top, twofold and threefold, are occupied, while from moderate coverage to saturation, bridge-bonded NO becomes dominant. A sharp c(2×4) LEED pattern is observed at saturation, and a corresponding surface structure is proposed for the pattern. For all precoverages of NO, dissociation is complete on heating the surface, but the temperature at which dissociation occurs depends critically on NO coverage and on the presence of the dissociation products. TPD spectra indicate that no species other than N 2 desorbs below 630 K; c(2×6) and p(2×3) LEED patterns are observed after annealing to 600 K, and removal of O adatoms by H 2 shows that these are due to N adsorption. A first-order unimolecular reaction mechanism is proposed for NO dissociation on Co{101̄0}, with a strong dependence of the activation energy for surface dissociation on both NO coverage and the coverage of the dissociation products, N and O.

Phytotransformation of Perchlorate and Identification of Metabolic Products in Myriophyllum aquaticum

ABSTRACT The uptake and transformation of perchlorate in the presence of Myriophyllum aquaticum (parrot-feather) were examined in sand and aqueous treatments with concentrations between 0.2 to 20 ppm. Controls were included without plants to confirm the uptake of perchlorate by parrot-feather. The kinetic data followed a first-order reaction mechanism with rate constants ranging from 0.004 to 0.090, resulting in half-lives between 7 to 173 days. Uptake rates were five times higher in aqueous treatments than in sand treatments. The intermediates detected in the plant tissue suggest that perchlorate transformed in a step-wise fashion to form chloride. Accumulation of perchlorate in the plant tissues (1.2 g/kg) suggests that parrot-feather has a high capacity for accumulating this contaminant.

Emissions of odorous aldehydes from alkyd paint

Aldehyde emissions are widely held responsible for the acrid after-odor of drying alkyd-based paint films. The aldehyde emissions from three different alkyd paints were measured in small environ-mental chambers. It was found that, for each gram of alkyd paint applied, more than 2 mg of aldehydes (mainly hexanal) were emitted during the curing (drying) period. Since no measurable hexanal was found in the original paint, it is suspected that the aldehydes emitted were produced by autoxidation of the unsaturated fatty acid esters in the alkyd resins. The hexanal emission rate was simulated by a model assuming that the autoxidation process was controlled by a consecutive first-order reaction mechanism. Using the emission rate model, indoor air quality simulation indicated that the hexanal emissions can result in prolonged (several days) exposure risk to occupants. The occupant exposure to aldehydes emitted from alkyd paint also could cause sensory irritation and other health concerns.

Reductive transformations of halogenated aromatics in anaerobic estuarine sediment: kinetics, products and pathways

The transformation of different classes of halogenated aromatic compounds in sulfidogenic sediment slurries was examined in laboratory incubation experiments. The results indicated that several processes were shown to occur, leading to the formation of a number of intermediate metabolites. The kinetics of transformation followed a first-order reaction mechanism, with k values in the range of 1.67 and 0.0005 day −1 or half-lives of 0.4 and 1386 days. The order of transformation rates among different classes of compounds was: phenols > anilines > benzenes > pesticides. The pathway of transformation among single-ring aromatic compounds indicated that ortho and para halogen removal was the predominant compared to meta halogen removal.

Benztropine mesylate: crystal structure and kinetics of dehydration

The crystal structure of benztropine mesylate has been determined. It is orthorhombic, Pbca, with a = 12. 885(8)A, b = 32.012(9)A, and c = 10.027(3) A. It exhibits similar packing to that seen in the previously reported crystal structure of benztropine mesylate monhydrate. X-ray powder diffraction patterns have been used to identify the anhydrous and monohydrate forms. The dehydration of the monohydrate follows a first-order reaction mechanism with activation energy of 92(8) kJ mol−1.

Transformations of chloronitrobenzenes in anaerobic sediment

The transformations of chloronitrobenzenes (CNBs) in anaerobic estuarine sediment were examined. The sediment had been preexposed to various anthropogenic chemicals from the surrounding industries. The sulfate content of the interstitial and overlaying waters was approximately 20 mmole/1 indicating that the sediment was sulfidogenic. All the CNBs tested transformed without any lag period. The kinetic data followed a first-order reaction mechanism with rate constants ranging from 0.216 to 0.866 day −1 or half-lives from 0.8 to 3.2 days. The intermediates detected in the experiment indicated that the reduction of the nitro group was the first stage in the transformation of chloronitro aromatic compounds, resulting in the formation of corresponding chloroanilines (CAs). The CAs further transformed via ortho and para dechlorination pathways.

Determination of Initial Concentration of an Analyte by Kinetic Detection of the Intermediate Product in Consecutive First-Order Reactions Using an Extended Kalman Filter

Many analytical reagents react with analytes according to a rate law described by a consecutive first-order reaction mechanism, A [yields][sup k(1)] B [yields][sup k(2)] C, where a product formation step is followed by a product degradation step. In many cases, consecutive first-order reactions are used to determine the initial concentration of analyte A by kinetic detection of the intermediate product B. In this work, the factors that affect the determination of the initial concentration of analyte and the kinetic parameters for this class of reactions have been investigated by computer simulations using an extended Kalman filter. The flip-flop phenomenon exhibited by this kinetic model is discussed, and a unique approach for the determination of the initial concentration of analyte is proposed. Empirical and residual methods for obtaining initial estimates for the rate constants and the initial concentration from the kinetic data, based on the model for consecutive first-order reactions, the initial concentration of analyte, the mismatch between the measured time and the real time, the data density, the fitting range, and the initial estimate for the background signal have been evaluated by using synthetic data with Gaussian-distributed noise. 15 refs., 6 figs.

Chromatographic reactions of three components: application to separations

Consider three chemical components in a chromatographic system that interact according to A 1 ⇌ A 2 ⇌ A 3 or the cyclic reaction A 1 ⇌ A 2 ⇌ A 3 ⇌ A 1 and move with different velocities . This problem has application in a variety of chromatographic reaction systems, including the case of three interacting isomers undergoing separation by electrophoresis or sedimentation. A particular example is the separation of proteins that fold and unfold. A mathematical model consisting of three partial differential equations, accounting for convection, longitudinal dispersion and chemical reaction, describes these chromatographic reactions. For the unsteady-state case, Fourier transformation with symbolic and numeric manipulations by computer allow the determination of the spatial moments and their asymptotic behavior, which provide the shape characteristics of the pulse responses. The concentration profiles are constructed using the moment expressions in a polynomial expansion. In addition, generalization to any number of components interacting according to a first-order reaction mechanism is discussed for large and small time asymptotes. At short times (relative to the reaction time), the components move independently; at long times, the interacting components move as a group. For the steady-state reactor with adsorption, similar computer techniques provide concentration distributions and show entrance and exit discontinuities (in the absence of diffusion and longitudinal dispersion).

Synthesis of Substituted Phenyl Esters of Amino Acids and Polycondensation in Langmuirblodgett Films

Abstract Long-alkyl-chain phenyl esters of β-alanine, glycine, and L-valine were prepared, and their monolayer properties were correlated with their molecular structures. These compounds formed stable monolayers on acidic subphases. In particular, the p-hexadecylphenyl esters of β-alanine and glycine were remarkably stable, and their monolayers could be deposited on calcium fluoride plates as Y-type film by Blodgett's technique. The polycondensation of multilayers under an atmosphere saturated with triethylamine was investigated by changes in the IR spectra. It was determined that the polycondensation proceeded by a first-order reaction mechanism in the initial stage and that the rate in multilayers was faster than that in the bulk crystalline powder. These results suggest that the polycondensation is accelerated by a regular arrangement of the monomer in the multilayers, where the active sites are concentrated and located better for the polycondensation. In the case of the polycondensation in multilayers...

A model for baculovirus production with continuous insect cell cultures

A model, suitable for reactor-design purposes, is presented for the infection process of insect cells with baculovirus in a continuous bioreactor system. The infection process can be described by a first-order reaction mechanism if the viable, non-infected, insect cells are regarded as substrate, and the resulting polyhedra as product. Experimental results from continuous systems, consisting of a series of mixed reactors in which growth of Spodoptera frugiperda cells takes place in the first reactor and infection with Autographa californica nuclear polyhedrosis virus in the other reactors in the series, show typical values for the reaction rate constant of 0.7–1.0 10-5 s-1.

Effects of temperature on lactose hydrolysis by immobilized β‐galactosidase in plug‐flow reactor

The hydrolysis of lactose using immobilized beta-galactosidase (from Aspergillus niger) on phenol-formaldehyde resin was studied at temperatures between 8 and 60 degrees C and initial lactose concentrations ranging from 2.5 to 20.0%. A model involving enzyme-galactose complex similar to Michaelis-Menten kinetics with competitive product (galactose) inhibition is suitable to describe the lactose hydrolysis reaction. A small degree of lack of fit between the model and the data was found to be due to the formation of oligosaccharides. Thermal deactivation of lactase follows first-order reaction mechanism. The effect of temperature on the reaction and the deactivation rate constants follows the Arrhenius relationship. The Oligosaccharide formation was not significantly affected by the temperature when the initial lactose concentration was 5%. A design equation for the plug-flow immobilized lactase reactor was developed from the reaction and the deactivation kinetics and was used to find the optimal operating temperature. The optimal temperature was found to be dependent on the operating time but not on the lactose concentration or the conversion. The optimal operating temperature is 60 degrees C when operating time is short but is close to 35 degrees C for a long operating time. A preliminary economic analysis indicates that the optimal operating temperature is 43, 38.5, and 33 degrees C when the operating time is 300 days, 1000 days, and infinity, respectively.

A model for the dissolution behaviour of a graphite overlayer

A model based on a two-step first-order reaction mechanism is proposed to explain the dissolution behaviour of a graphite overlayer into the substrate. The two steps are (a) the decomposition of the graphite layer on and (b) the dissolution of the individual atoms into the substrate. The model was used to successfully explain some results from the literature.

The variation of β R with probe in inelastic hadron scattering and the adequacy of first-order calculations

The predicted probe dependence of the collective parameter δ = βR, obtained from distorted wave analyses of inelastic scattering data, is shown to have been observed for a variety of hadrons from low to intermediate energies for 0 + → 2 + transitions in single-closed-shell nuclei. These results, when compared to electromagnetic data, show an internal consistency which provides both a check of the validity of the first-order reaction mechanism as well as a determination of the relative neutron to proton transition matrix elements to ≈15% accuracy. The empically determined systematically variation of neutron and proton transition strenghts are in agreement with a schematic calculation of core polarization.

The Activation and Inactivation of Human Factor VIII by Thrombin:Effect of Inhibitors of Thrombin

The activation and inactivation of human factor VIII by thrombin have been investigated by the use of thrombin inhibitors. The addition of inhibitors to nonactivated factor VIII blocks activation by thrombin. In contrast, their addition to factor VIII activated with thrombin does not block inactivation, but causes an initial period of decay that is more rapid than in the absence of inhibitor. This effect was seen only with protease inhibitors that inhibit thrombin. After the initial decay, low levels of factor VIII coagulant activity persist in the presence of inhibitors, but an assay specific for activated factor VIII showed this to be largely a result of the persistence of nonactivated factor VIII. Only in the case of reversible inhibition is activated factor VIII present in this plateau phase. Possible mechanisms that would account for these observations were studied by iterative computer simulation of model reactions. Two classes were considered: (formula: see text). The experimental results are inconsistent with the first mechanism, which predicts that thrombin indicators should stabilize activated factor VIII (VIIIt). Alternative mechanisms were studied where activation is thrombin-dependent, but inactivation is a first-order reaction (mechanism 2). This family of mechanisms includes those where VIIIt is an VIII. thrombin complex. Simulation of the addition of thrombin inhibitors to such model systems shows the initial rapid decay of activity characteristic of the experimental observations and predicts qualitatively the different effects of reversible and irreversible inhibitors that are observed in the plateau phase. These results argue strongly against a two-cleavage model for the activation and inactivation of factor VII by thrombin and support a one-cleavage model in which inactivation is due to first-order decay. In addition, they provide a plausible mechanistic explanation for the fact that serine protease inhibitors appear to inhibit thrombin-activated factor VIII.

Kinetic Characteristics of a Solid Photochromic Film

Analytical or numerical solutions are given for the kinetic equations describing the time behavior of a solid photochromic film for the cases of photocoloration, photobleaching, and thermal bleaching. A procedure to evaluate relative quantum yields and absorption cross sections from the comparison of experimental results with theoretical solutions is demonstrated by an example using 6-nitro-8 piperidinomethyl-1', 3', 3'-trimethylspiro-[1H-benzopyran-2, 2'-indoline] as a photochromic compound. The theoretical results are presented in a suitably normalized form to be applicable to a broad range of experimental situations. The agreement between calculated and measured results is good as long as strictly first-order reaction mechanisms are obeyed.

Kinetic constants of polymeric materials from thermogravimetric data

The thermal decomposition of polytetrafluoroethylene (TFE, Teflon), high and low density polyethylene (HDP and LDP), Delrin Acetal (DA), AVCO Phenolic Fiberglass (APFG), and carbon phenolic (CP), were studied by a thermogravimetric technique which utilized a constant heating rate. Loss in sample weight was recorded as a function of time or temperature from room temperature to approximately 700°. Reaction orders were established from logarithmic rate versus temperature plots. Arrhenius frequency factors and overall activation energies were determined from computerized integrations of the appropriate rate equations in which the results were treated on the basis of first-order reaction mechanisms for specific temperature regions. Zero-order mechanisms were estimated by the usual graphical methods.