Kinetic resolution of (R)- and (S)-mandelic acid by its transesterification with vinyl acetate catalysed by Burholderia cepacia lipase has been studied. The influence of the initial substrate concentration on the kinetics of process has been investigated. A modified ping-pong bi-bi model of enzymatic transesterification of (S)-mandelic acid including substrate inhibition has been developed. The values of kinetic parameters of the model have been estimated. We have shown that the inhibition effect revealed over a certain threshold limit value of the initial concentration of substrate.
The paper focuses on the modelling of bromate formation. An axial dispersion model was proposed to integrate the non-ideal mixing, mass-transfer and a kinetic model that links ozone decomposition reactions fromthe Tomiyasu, Fukutomi and Gordon (TFG) ozone decaymodelwith direct and indirect bromide oxidation reactions, oxidation of natural organicmatter and its reactionswith aqueous bromine. To elucidate the role of ammonia an additional set of reactions leading to bromamine formation, oxidation and disproportionation was incorporated in the kinetic model. Sensitivity analysis was conducted to obtain information on reliability of the reaction rate constants used and to simplify the model.
This paper presents an experimental study on Cochineal Red A dye adsorptive removal by yeast. Batch equilibrium and kinetic tests were conducted in constant temperature of 30 ◦C for the dye’s initial concentration range of 0.02–0.50 g/L (pH = 3 and 10) and 0.02–0.35 g/L (pH = 7:6). The equilibrium was reached after 105–120 min. Yeast demonstrated the adsorption capacity of 10.16 mg/g for acidic environment (pH = 3) and slightly lower values (8.13 mg/g and 8.38 mg/g respectively) for neutral (pH = 7:6) and alkaline environment (pH = 10). The experimental equilibrium results were fitted with Langmuir, Freundlich, Sips and Toth isotherm models. Most of them (Freundlich model being the exception) were proven sufficient for the experimental data correlation. The adsorption kinetic studies showed that the pseudo-second order model fits better the experimental data than the pseudo-first- order model. Results achieved from intra-particle diffusion model indicate that powdered yeast are a nonporous adsorbent. The percentage of solution discoloration reached a maximum value of 75% at pH = 3 for an initial dye concentration of 0.02 g/L.
The sorption isotherm and sorption kinetics of NH4+ by the Fen River reservoir sediment were investigated for a better understanding of the NH4+ sorption characteristics and parameters. The results showed that Q (adsorption content) increased with the increase of Ceq (equilibrium concentration), sorption isotherms could be described by Freundlich equation (R2 from 0.97 to 0.99). Cation exchange capacity (CEC) had a significant correlation with the parameters K and n (R2 was 0.85 and 0.95, respectively). The ENC0 (Ceq as Q was zero) of S1, S2, S3 and S4 was 1.25, 0.57, 1.15 and 1.14 mg L-1, respectively, and they were less than the NH4+ concentrations in reservoir water. The sediments released NH4+ to the Fen River reservoir water and acted as a pollution source, in the form of complex and heterogeneous adsorbents. The NH4+ adsorption kinetic process was composed of ‘fast’ and ‘slow’ reaction patterns and could be fitted using both Elovich equation and Pseudo second-equation. More than one-step may be involved in the NH4+ sorption processes, and interior diffusion was not dominant ion action.
The study was aimed to determine the hydrodynamic of water seepage through a porous bed saturated with different amounts of high viscosity liquids. An attempt was made to describe the process of seepage through beds saturated with oils using the theory of outflow of a liquid from the tank. It was assumed that the discharge coefficient will represent changes of flow resistance during the process. It was found that the dependence of this factor on time is linear. In the second part of this work kinetics of the seepage process was investigated. Dependence of oil concentrations, eluted from the deposit with the flowing water, on time has been evaluated. Thanks to these studies it was possible to determine the effectiveness of an elution of high viscosity liquids from porous beds using water as the washing out liquid.
Periodic adsorption in a perfect mixing tank of a limited volume was considered. It was assumed that the adsorption rate is limited by diffusion resistance in a pellet. The approximate model of diffusion kinetics based on a continued fraction approximation was compared with the exact analytical solution. For the approximate model an algorithm was developed to determine a temporal variation of the adsorbate concentration in the pellet. The comparison was made for different values of the adsorbent load factor. In the numerical tests different shapes of pellets were considered. Both the numerical tests as well as our own experimental results showed that the approximate model provides results that are in good agreement with the exact solution. In the experimental part of this work adsorption of p-nitrophenol and acetic acid from aqueous solutions on cylindrical pellets of activated carbon was conducted.
Balance, thermodynamic and mainly kinetic approaches using methods of process engineering enable to determine conditions under which iron technology can actually work in limiting technological states, at the lowest reachable fuel consumption (reducing factor) and the highest reachable productivity accordingly. Kinetic simulation can be also used for variant prognostic calculations. The paper deals with thermodynamics and kinetics of iron making process. It presents a kinetic model of iron oxide reduction in a low temperature area. In the experimental part it deals with testing of iron ore feedstock properties. The theoretical and practical limits determined by heat conditions, feedstock reducibility and kinetics of processes are calculated.
This study manufactured a SiC coating layer using the vacuum kinetic spray process and investigated its microstructure and wear properties. SiC powder feedstock with a angular shape and average particle size of 37.4 μm was used to manufacture an SiC coating layer at room temperature in two different process conditions (with different degrees of vacuum). The thickness of the manufactured coating layers were approximately 82.4 μm and 129.4 μm, forming a very thick coating layers. The SiC coating layers consisted of α-SiC and β-SiC phases, which are identical to the feedstock. Cross-sectional observation confirmed that the SiC coating layer formed a dense structure. In order to investigate the wear properties, ball crater tests were performed. The wear test results confirmed that the SiC coating layer with the best wear resistance achieved approximately 4.16 times greater wear resistance compared to the Zr alloy. This study observed the wear surface of the vacuum kinetic sprayed SiC coating layer and identified its wear mechanism. In addition, the potential applications of the SiC coating layer manufactured using the new process were also discussed.
Validation results of a theoretical model that describes the formation of bromate during ozonation of bromide-containing natural waters are presented. An axial dispersion model integrating the nonideal mixing, mass-transfer and a kinetic model that links ozone decomposition reactions from the Tomiyasu, Fukutomi and Gordon ozone decay model with direct and indirect bromide oxidation reactions, oxidation of natural organicmatter and reactions of dissolved organics and aqueous bromine was verified. Themodel was successfully validated with results obtained both at a laboratory and a full scale. Its applicability to different water supply systems was approved.
In this study a group of selected transformation kinetics equations is applied to describe the isothermal ferritic transformation in austempered ductile iron (ADI). A series of dilatometric tests has been carried out on ADI at different temperatures. The obtained experimental data are utilized to determine the parameter values of the considered kinetic equations. It is found that the transformation kinetics models by Starink, Austin and Rickett are substantially more effective at describing the ferritic transformation in ADI than the much celebrated Johnson-Mehl-Avrami-Kolmogorov (JMAK) equation. Furthermore, it is demonstrated that evaluating the kinetic parameters using the least squares method instead of calculating them from vastly used formulas can significantly improve the accuracy of the JMAK model’s predictions.
In this work, the spectrophotometric studies on the kinetics of redox reaction between gold(III) bromide complexes and sodium nitrite, were carried out. From the kinetic curves collected under different conditions of reactants concentration, addition of bromide ions, temperature, pH and ionic strength, corresponding rate constants have been determined. The obtained results suggest the complex path of the [AuBr4]– reduction consisting of two parallel, bimolecular reactions where different reductant species (HNO2 and NO2–) take place and consecutive step with the metallic gold production. The second-order rate constants at 20oC are equal to 2.948 and 0.191 M–1·s–1, respectively. The values of activation enthalpy and activation entropy for the first and the second parallel step of the reaction were found to be ΔH‡ = 29.18 kJ·mol–1 and ΔS‡ = –13.95 J·mol–1·K, and ΔH‡ = 40.75 kJ·mol–1 and ΔS‡ = –31.06 J·mol–1·K, respectively. It was found that the reaction accelerates significantly with the increase of pH and is inhibited with the increase of Br– concentration. The substitutive, inner-sphere mechanism of electron transfer in the studied system was also suggested.
The homogeneous stirred reactor designed for kinetic studies of the combustion of hydrocarbons with intensive internal recirculation in high temperature combustion chamber is described. The originality of our reactor lies in its construction which allows to intensively mix fuel and flue gases, measure gas temperature as well as obtain samples which can be used to investigate diffusion flames. The cylindrical construction enables to use the reactor in laboratory cylindrical electrically heated ovens. The CFD analysis of the reactors, the mixing parameters (turbulent Peclet number and mixing level) and the volume average temperature in the reactors were elaborated on the basis of the typical dimensions of classical reactors to kinetics research as well as the own reactor design. The results of the analysis allow to reveal advantages of our construction.
The demand for a net reduction of carbon dioxide and restrictions on energy efficiency make thermal conversion of biomass a very attractive alternative for energy production. However, sulphur dioxide emissions are of major environmental concern and may lead to an increased corrosion rate of boilers in the absence of sulfatation reactions. Therefore, the objective of the present study is to evaluate the kinetics of formation of sulphur dioxide during switchgrass combustion. Experimental data that records the combustion process and the emission formation versus time, carried out by the National Renewable Energy Institute in Colorado (US), was used to evaluate the kinetic data.
The combustion of switchgrass is described sufficiently accurate by the Discrete Particle Method (DPM). It predicts all major processes such as heating-up, pyrolysis, combustion of switchgrass by solving the differential conservation equations for mass and energy. The formation reactions of sulphur dioxide are approximated by an Arrhenius-like expression including a pre-exponential factor and an activation energy. Thus, the results predicted by the Discrete Particle Method were compared to measurements and the kinetic parameters were subsequently corrected by the least square method until the deviation between measurements and predictions was minimised. The determined kinetic data yielded good agreement between experimental data and predictions.
Nanoparticles are very fascinating area of science not only due to their unique properties but also possibility of producing new more complex materials, which may find an application in modern chemistry, engineering and medicine. In process of nanoparticles formation very important aspect is a rate of individual stage i.e. reduction, nucleation and autocatalytic growth, because this knowledge allows for proper materials design, morphology manipulation, stability. The last one aspect can be realized using proper electrostatic, steric and electrosteric stabilization. However until now nobody reports and measures kinetic rates of all stages during process of particles formation in the presence of steric stabilizers. Thus, the main contribution of this paper is determination of individual rate constants for nanoparticles formation in the presence of steric stabilizers and their comparison to the system without stabilizer. For this purpose, an aqueous solution of Au(III) and Pt(IV) ions were mixed with steric stabilizers like PVA and PVP, and reduced using L-ascorbic acid as a mild and sodium borohydride as a strong reductant. As a results stable nanoparticles were formed and process of their formation was registered spectrophotometrically. From obtained kinetic curves the values of observed rate constants for reduction metal ions, slow nucleation and fast autocatalytic growth were determined using Watzky-Finke model. It was found that the addition of polymer affects the rate of the individual stages. The addition of steric stabilizers to gold ions reduced with L-ascorbic acid causes that the process of nucleation and autocatalytic growth slows down and the value of observed rate constants for nucleation changes from 3.79·10–3 (without polymer) to 7.15·10–5s–1 (with PVA) and for growth changes from 1.15·103 (without polymer) to 0.48·102s–1M–1 (with PVA). However, the rate of the reduction reaction of Au(III) ions is practically unchanged. In case of using strong reductant the addition of polymer effects on the shape of kinetic curve for reduction of Au(III) and it suggests that mechanism is changed. In case of Pt(IV) ions reduction with L-ascorbic acid, the process speeds up a little when PVA was added. Determined values of observed rate constants for nucleation and growth platinum nanoparticles decrease twice comparing to the system without polymer. The reduction of Pt(IV) ions with sodium borohydride accelerates when PVP was added and slows down when PVA was used. Moreover, the size of obtained colloidal gold and platinum was also analysed using DLS method. Obtained results (rate constants) may be useful in the process of nanomaterials synthesis, in particular in microflow.