bluuebunny/crossref_metadata_2025_split huggingface dataset:
A general integral method for the determination of empirical reaction rates and parameters
Authors: Neuhaus Gerd W. , Maier Wilhelm F. 
Published: August 2005

AbstractA general procedure for the determination of empirical rates and kinetic parameters of irreversible, constant volume reactions is presented which is clearly superior to the conventional methods of kinetic analysis. By nonlinear regression of the integrated potential rate equation for stoichiometrically independent reactions of n the order, the empirical pre‐exponential factor, activation energy, and reaction order are obtained. The regression equation relates explicitly the final concentration of the reference component not only to the time parameter of the reaction but also to the initial concentration. This includes an integral method for the determination of reaction orders in concentration. Two limiting cases are treated ‐ the stoichiometric mixture of reactants and a mixture with one reactant in large excess. By analysis of standard Hougen‐Watson rate models the dependence of empirical reaction orders on experimental conditions and simulated rate parameters is evaluated. By grouping the data into ranges of monotonous concentration change, conversion rates and rate parameters of reactions with changing volumes are calculated in a less rigorous deduction. The simplified interpretation of published experimental data is demonstated for the total oxidation of methane on Pd‐catalysts and the dehydrogenation of cyclohexanol on ZnO.
On the activity and stability of platinum/alumina catalyst during multiple deactivation and regeneration
Authors: Manga Ngomo H. , Susu Alfred A. 
Published: August 2005

AbstractCatalyst surface characterizations have been carried out to investigate the role of dispersion on catalyst activity and to probe the occurrence of oscillations in coking levels with cycle number generally observed during multiple deactivation and regeneration schemes. The titrations were done, cycle by cycle, at 430°C after oxidation and at the same temperature (430°C) after reduction at 500°C. Results show the usually observed trend ‐ that the dispersions after oxidation are higher than those after reduction. The average decline in dispersion from oxidation to reduction was calculated to be 39.25%. It was observed that the cycles with high toxic coke removal were characterised by high deactivation times. The deactivation times were still high even for cycles subsequent to those with low dispersion. At high dispersions the catalyst had short deactivation times, that is the small crystallites deactivate faster than large ones. The nature of reducebale coke and the efficiency of its removal is a much more determinant factor of catalyst activity than the level of metal disperision. Thus prolonged toxic coke reduction at the high temperature of 500°C, though resulting in an apparent lowering of dispersion, does not affect the quality of the catalyst. The dispersion before reduction could be retained on oxidation. Hence reduction at 500°C did not introduce sintering.
A model for primary and heterogeneous secondary reactions of wood pyrolysis
Authors: Ahuja Pradeep , Kumar Surendra , Singh Prem Chand 
Published: August 2005

AbstractA chain growth model for heterogeneous secondary reactions is developed for the pyrolysis of large wood particles and the parameters determined by nonlinear optimization. The model takes both the volatile retention time and cracking and repolymerization reactions of the vapours with the decomposing solid as well as sutocatalysis into consideration. The extent of the secondary reactions is strongly influenced by the time and the ratio of the autocatalytic (propagation) reaction rate to noncatalytic (initiation) reaction rate. The wood which has a higher value of the autocatalytic/noncatalytic ratio also has a higher exothermic heat of reaction and yields a higher amount of final char residue. This fact confirms the heterogeneous secondary reactions lead to carbon enrichment of the final residue and are accompanied with an exothermic heat of reaction. The lower activation energies of the initiation and propagation reactions as compared to primary reactions (competitive reaction model consisting of weight loss and char forming reactions) confirm autocatalysis in large particles. The sealed reactor studies of small quantities of fine wood samples show that heterogeneous secondary reactions and not lower heating rates in large particles are the main source of char formed during the thermal decomposition of large wood particles. The model predictions are in agreement with the weight loss and temperature versus time curves over a wide range of particle size and furnace temperatures.
Distributed control suboptimal operating policies for ethane thermal cracking reactors
Authors: Bozga Grigore , Tsakiris Cristian 
Published: August 2005

AbstractA nonlinear unsteady state optimal control problem for a classical, constant diameter ethane thermal cracking reactor is formulated and solved. The process is represented by a pseudo steady state mathematical model, consisting of mass and heat balance, pressure drop, and coking equations. The performance index is of an economical nature, representing the global benefit of reactor operation over a constant operating time. As control variables, the space and time dependent skin tube temperature, the time dependent steam to hydrocarbon ratio, and the time dependent feed flow rate were considered. The results are in agreement with the process physicochemical and technological fundamentals.
Does the fluid elasticity influence the dispersion in packed beds?
Authors: Westerterp K. Roel , Wijngaarden Ruud J. , Nijhuis Niek B. G. 
Published: August 2005

AbstractReasons are given why the axial dispersion in a gas flowing through a packed bed may be influenced by the elasticity ‐ or compressibility ‐ of the fluid. To support this hypothesis, experiments have been done in a packed column at pressures from 0.13 to 2.0 MPa. The elasticity E of a gas is proportional to the pressure P and the compressibility to 1/P. The axial dispersion coefficients as determined were found to be a function of the pressure in the packed bed in the turbulent flow region of 3 < Rep < 150 if the Bodenstein number is plotted as a function of the particle Reynolds number. This is shown to be an artifact. The pressure influence is eliminated, if Bom, ax is plotted versus the ratio of the kinetic forces over the elastic forces ϱu2/E. Regrettably, Bom, ax seems to be independent of ϱu2/E. For the moment we only can conclude that Bom, ax in the turbulent region is a unique function of the velocity of the gas which flows through the packed bed. Although the fact that a constant Bo value is obtained when plotted against ϱu2/E, the experimental results are so intriguing we wanted to make them public already now. The experimental work proceeds.
Energy transfer in hydrogen/air and methane/air mixtures
Authors: Aretz Wilfried , Metz Stefan W. , Wilhelmi Herbert 
Published: August 2005

AbstractThis article presents gas kinetic calculation methods for the energy transport in hydrogen/ air and methane/ air mixture. The total molecular heat conductivity as well as its various shares are calculated and discussed for a temperature range of 400 to 3500 K and for a pressure of 105 Pa. The variation of the air/ fuel ratio under the conditions of chemical equilibrium is also investigated. As opposed to our previous article, an extension of the Chapman‐Knskog method which goes beyond the classical 1st approximation for elastic collisions is applied for the evaluation of suitable calculation methods. This is carried out following the method for strong relaxing thermal nonequilibrium according to Brun. The equations applied in this work are simplified formulations for the proximity to equilibrium. The method for the evaluation of the parameters of the inelastic collision and some chosen results are presented. A discussion of the various shares of the molecular heat conductivity emphasizes the considerable influence of the diffusion and the thermal diffusion processes in fuel/ air mixtures compared to the Fourier heat conductivity.
Modelling of affinity separation by batch and fixed bed adsorption – a comparative study
Authors: Sridhar P. 
Published: August 2005

AbstractAffinity separation can be achieved by batch and fixed bed modes. Mathematical models including film mass transfer, intraparticle diffusion, and reversible reaction are formulated for both fixed bed and batch adsorption processes. Orthogonal collocation method is used to numerically evaluate the performance of batch and fixed bed adsorption. The efficiencies are evaluated in terms of both the solute recovery and adsorbent utilization. The effect of the following parameters is simulated for the comparison purpose: solute concentration, reaction kinetics, ligand content, and particle size. Fixed bed mode is found to be efficient.
Kinetics of calcium carbonate decomposition
Authors: Rao T. Rajeswara 
Published: August 2005

AbstractExperiments on thermal decomposition of calcium carbonate were carried out in a thermogravimetric analyser under non‐isothermal conditions of different heating rates (10 to 100°C/ min). A new technique for determining the kinetic parameters from non‐ isothermal thermogravimetric data was described. The activation energy and frequency factors were determined from the proposed method and also by the widely used Coats and Redfern method. The kinetic compensation effect between the activation energy and frequency factors obtained from both the methods were found to be very consistent and are in very good agreement with the literature values. The activation energy and frequency factors were also determined from isothermal experiments in the temperature range from 680 to 875°C. The activation energy and frequency factors determined from isothermal data using initial rate method were also found to be in very good agreement with the above results. It is also found that the kinetic parameters determined by isothermal analysis were consistent with the values determined by non‐isothermal analysis.
Numerical simulation of contraction flow of a dilute polymer solution
Authors: Bschorer Sabine , Brunn Peter O. 
Published: August 2005

AbstractNumerical results are presented for a contraction flow of a non‐Newtonian fluid. In this work a new finite‐volume algorithm was used and various non‐Newtonian fluid models (with and without elasticity) were studied. The results are discussed and compared to experimental results obtained with a dilute polymer solution.
Dual substrate limitations in upflow packed‐bed biofilm reactors — a theoretical study
Authors: Beg Shafkat Ali , Hassan Mirza Manirul , Chaudhry Muhammad Arshad Saeed 
Published: August 2005

AbstractThe performance of an upflow packed‐bed biofilm reactor has been analyzed under dual substrate limitation conditions. The numerical solution of the proposed equations defining the system has been obtained for a wide range of operating conditions for a case of practical significance involving glucose and oxygen as dual substrates. The results show that the inlet glucose concentration defines the limiting substrate at a position near the inlet of the reactor. For inlet glucose concentrations up to 300 mg/l, glucose acts as the limiting substrate. However, for inlet concentrations of 400 mg/l of glucose or higher, oxygen assumes the role of the limiting substrate at that position. For all other positions in the reactor, glucose acts as the limiting substrate, irrespective of its inlet concentration. Extensive computations were performed in order to define regions where glucose, oxygen or both are limiting. The predicted results have been found to be in agreement with the theoretical criteria, proposed in the literature, of determining the limiting substrate.
Reaction engineering studies in a polytropic fixed‐bed reactor over a highly active and selective catalyst for oxidative methane coupling
Authors: Mleczko Leslaw , Gayko Guido , Niemi Vesa M. , Hiltunen Jyrki 
Published: August 2005

AbstractThe oxidative coupling of methane (OCM) was carried out in a polytropic fixed‐bed reactor applying a Zr/La/Sr catalyst developed by the Neste company. Over this catalyst the OCM reaction follows a complex reaction scheme which includes primary parallel reaction steps to CO, CO2 and C2H6 and consecutive reactions of ethane to ethylene or COx. Yield of higher hydrocarbons C2+ obtained with this catalyst strongly depended on reaction conditions, i.e. low partial pressures of methane and oxygen obtained by diluting the feed gas with nitrogen and high reaction temperatures promoted C2+ selectivity and yield. The maximum yield amounted to 21.4% (20 Vol.‐% CH4, 9 Vol.‐% O2, 71 Vol.‐% N2, T = 860°C; XCH4 = 41.8%, S = 52.5%). This result belongs to the highest yields reported in the open literature.
Measurement of solids concentration by an ultrasonic transmission technique
Authors: Soong Yee , Gamwo Isaac K. , Harke Fred W. , Blackwell Arthur G. , Schehl Richard R. , Zarochak Michael F. 
Published: August 2005

AbstractAn ultrasonic transmission technique is under development to determine the concentration of solids in a three‐phase slurry reactor by measuring the velocity of ultrasound in slurries. Preliminary measurements have been made on slurries consisting of water, glass beads, and air bubbles. The data show that both the sound speed and attenuation are well‐defined functions of both the solid and gas concentrations in the slurries. A simple model is proposed to correlate the concentration of solids with the measured ultrasonic signals.
The development of chemical engineering in german industry and universities
Authors: Onken Ulfert 
Published: August 2005

AbstractChemical engineering is taught at German universities in three different types of curricula: chemical engineering proper, process engineering (“Verfahrenstechnik”), and industrial chemistry (“Technische Chemie”). Independent departments resp. faculties of chemical engineering exist at four universities. At other universities process engineering is offered as a complete curriculum with a smaller amount of chemistry than chemical engineering curricula, mostly by the departments of mechanical engineering. Industrial chemistry is an essential component of chemistry courses at most technical universities and optional subject at several classical universities. The cause of this diversity of approaches to chemical engineering can be traced back to the beginning of the production of high‐value organics (dyes, pharmaceuticals) in Germany in the second half of the 19th century.
Effect of surfactants on the rate of solid‐liquid mass transfer in packed bubble columns
Authors: Nosier Shaaban Ali Attia , El‐Khaiary Mohammad Ibrahim , Zaki Magdy Mohammad 
Published: August 2005

AbstractThe effect of sodium lauryl sulphate (anionic) and Triton X‐100 (nonionic) on the solid‐liquid mass transfer at a gas‐sparged fixed bed of copper Raschig rings was studied by measuring the diffusion‐controlled dissolution of copper rings in acidified chromate solution. The variables studied were the nitrogen flow rate, the type of surfactant, and the surfactant concentration. It was found that an increase occurs in the solid‐liquid mass transfer coefficient with increasing the nitrogen flow rate. Increasing the surfactant concentration was found to decrease the mass transfer coefficient. For a given surfactant concentration, it was found that Triton X‐100 reduces the mass transfer coefficient more than sodium lauryl sulphate.
Minimum energy demand of distillation columns with multiple feeds
Authors: Glanz Stephan , Stichlmair Johann 
Published: August 2005

AbstractDistillation columns with multiple feeds are often used in processes for the separation of multicomponent mixtures. The minimum energy demand of such columns is determined via the minimum reflux and reboil, respectively.A novel method for directly calculating the minimum reflux ratio is presented in this paper. Applicable to ideal, nonideal and azeotropic mixtures the method is based merely on the knowledge of vapor‐liquid equilibrium of the feed mixtures. This knowledge allows the determination of the internal concentration profile near the feed entry and, in turn, the calculation of both minimum reflux and optimal sequence of feeds. This sequence of feeds depends on feed compositions and product compositions, as well. Surprisingly, sometimes a multiple feed entry requires a higher energy demand than premixing the feed streams.
Kinetics of buta‐1,3‐diene hydrogenation over 0.5% Pd/γ‐Al2O3 catalyst
Authors: Goetz Jessie , Touroude Raymonde , Murzin Dmitry Yu. 
Published: August 2005

AbstractThe gas‐phase hydrogenation of buta‐1,3‐diene to but‐1‐ene, trans‐ and cis‐but‐2‐ene and butane has been performed over 0.5% Pd/γ‐Al2O3 catalyst. The reaction has been investigated at atmospheric pressure and 0°C over a wide range of conversions. The kinetic model based on the present day knowledge of reaction mechanism has been advanced. The parameters of the kinetic model have been estimated through statistical data fitting. The kinetic model provides a fairly good description of selectivity in the whole range of conversions.
Kinetics of 4‐tert‐butylphenol hydrogenation over rhodium
Authors: Konuspaev Sapar R. , Zhanbekov Khairulla N. , Kul'Kova Natalya V. , Murzin Dmitry Yu. 
Published: August 2005

AbstractThe kinetics of the liquid phase hydrogenation of 4‐tert‐butylphenol to form cis‐ and trans‐ 4‐tert‐butylcyclohexanol at 1.0–10.0 MPa and 40°C in isopropanol over a Rh catalyst has been studied. The kinetic behavior of this parallel system is described by a proposed reaction network. Keto‐enol tautomeric transformation of adsorbed 4‐tert‐butyltetrahydrophenol and 4‐tert‐butylcyclohexanone is thought to be a key step, which governs the stereoselectivity of the overall complex reaction of alkylphenol hydrogenation.
A study of gain scheduling control applied to an exothermic CSTR
Authors: Lagerberg Adam , Breitholtz Claes 
Published: August 2005

AbstractThis paper describes how gain scheduling control is applied to a continuous stirred tank reactor model. The CSTR process, equipped with a cooling system, is modelled. Based on the resulting nonlinear model, a gain scheduling controller is designed. The gain scheduling follows a scheme denoted bias compensation. Compared to earlier reported gain scheduling schemes, the proposed scheme results in a controller that is less complex, which is advantageous in the controller implementation stage. Numerous simulations are performed, using the gain scheduling controller and two choices of control input to the reactor model. The simulation results indicate that a gain scheduling controller performs better than a linear controller. Simulations using different choices of control input to the reactor model indicate that proper process design is crucial for the controlled process performance.
Oxidation of aqueous sulfide solutions by dioxygen Part I: Autoxidation reaction
Authors: Fischer Holger , Schulz‐Ekloff Günter , Wöhrle Dieter 
Published: August 2005

AbstractThe autoxidation of aqueous sulfide solutions by dioxygen is studied at pH 9 and 14 and at initial sulfide concentrations between 1 and 100 mM. Disulfide as a primarary intermediate is proposed to enhance the sulfide oxidation by autocatalytically forming polysulfies. The postulate is supported by the observed acceleration of the process at increasing pH favoring the presence of disulfide rather than that of sulfur. The final reaction products thiosulfate and sulfate are proposed to result from the hydrolysis of the highly instable intermediate polythiosulfite in parallel parallel reaction pathways, assuming probabilities for breaking the sulfur chain at the α (sulfate) and β (thiosulfate) positions to be responsible for the selectivity. A reaction scheme is proposed, considering all experimental observations.
Influence of dust particles on the hydrodynamic behavior and mass transfer in droplet column
Authors: Muller Nathalie , Benadda Belkacem , Otterbein Michel 
Published: August 2005

AbstractBubble columns are commonly used in industry for polluted gas treatment. Based on the same principle, the droplet column which is not widely known in the literature, uses much higher gas velocities, up to 14 m/s. This study concerns the hydrodynamics and mass transfer in this apparatus, in presence or absence of solid particles. Our results have demonstrated the impact of dusts on mass transfer performance giving rise to an increase in the kL aL coefficient with decreasing particle size. However, no influence of dust on the hydrodynamics of the column has been demonstrated within the studied particle size range.A study of liquid holdups obtained by three different methods is also carried out. Our results are comparable, thus validating the methods used.
Modeling of multi‐solid liquid fluidized bed
Authors: Asif Mohammad 
Published: August 2005

AbstractA dynamic model of the liquid fluidized bed containing two or more solid particle species of different size and density is presented. The model incorporates the particle mass transport mechanisms of the convection and the dispersion. The movement of the upper interface of the bed subject to a change in the liquid velocity is specified using the mass balance constraint. The particle velocities and dispersion coefficients are evaluated using correlations. The model is capable of describing the bed expansion, concentration profiles of the individual particle species, the bulk density profile, and the occurrence of layer inversion.
Slip velocity characteristics in the riser of circulating fluidised bed
Authors: Subramanian N. Bala , Kannan C. Srinivasa 
Published: August 2005

AbstractExperiments were carried out in a conventional circulating fluidised bed to measure the axial pressure profile and total pressure drop, which covered a wide range of operating conditions. Material belonging to the Geldart A (fine material) as well as the Geldart B (course material) categories have been used in the present work. Slip velocity is determined from the total pressure drop and noticed that the slip velocity is much higher than the free fall velocity of single particle for Geldart A type material, while it is approximately equal to the free fall velocity of single particle for the Geldart B type materials.A model is developed for slip velocity taking into account all the hindrance effects: particle‐particle, and particle‐wall, and particle agglomeration. Predictions of the present model are validated with the data due to present study and the data reported in the literature.
Intermixing of fluidizing gas streams in a compartmented circulating fluidized bed
Authors: Bhattacharya B. , Sathiyamoorthy D. , Rao V. Govardhana , Mahajan S. P. 
Published: August 2005

AbstractThe intermixing of fluidizing gas between the compartments of a compartmented circulating gas fluidized bed fitted with a V‐valve and riser combination has been experimentally studied. The intermixing of fluidizing gas that flows co‐current (cross flow) as well as counter‐current (back flow) to the circulating solids has been investigated. At low aerations, gas cross flow increased proportionally with the increase in solid circulation rate. But at high aerations, gas cross flow increased with aeration even when solid circulation decreased. Studies on back flow of gas revealed some interesting observations. At high fluidizing bed height on upstream side back flow of V‐valve, gas has been negligible. But at low upstream bed heights and low aeration in V‐valve and riser back flow of V‐valve, gas has been substantial.