bluuebunny/crossref_metadata_2025_split huggingface dataset:
A multiple state stochastic model for deep‐bed filtration
Authors: Tarafdar Suparna , Dey Avijit , Gupta Bhaskar Sen 
Published: August 2005

AbstractA one‐parameter stochastic model has been developed for the prediction of dynamic pressure drop in a deep‐bed filter. The model is based on a finite‐state and discrete‐time Markov chain method whereby the pressure drop in a deep‐bed filter can be estimated at discrete time intervals. The proposed model is simpler than the stochastic birth and death models available in literature. The bed is assumed to pass through different states of porosity during the filtration and it is spatially lumped in each state. For pressure drop calculation, the Carman‐Kozeny equation is used in conjunction with the Payatakes‐Tien‐Turian model. Model equations are simple and can be easily solved on a personal computer. The theoretical results agree well with the plant data as well as with the available experimental data.
Heat transfer mechanisms in gas fluidized beds. Part 3: Heat transfer in circulating fluidized beds
Authors: Molerus Otto , Mattmann Wolfgang 
Published: August 2005

AbstractPart 1 of this contribution reported on the effects of system properties on heat transfer between heating or cooling surfaces and bubbling fluidized beds. This investigation produced four correlations which define the respective maximum heat transfer. Part 2 of this study suggests that the heat transfer between exchanger surfaces and bubbling fluidized beds depends on superficial gas velocity, expressed as dimensionless excess gas velocity. The present paper shows that heat transfer coefficients in circulating fluidized beds can be predicted by evaluation of a state diagram, which combines three dimensionless groups: Nusselt number, Archimedes number and a dimensionless pressure gradient. A comparison of coal combustion experiments with own cold model measurements indicates that the radiative component of heat transfer coefficients is only evident at very low dimensionless pressure gradients.
Fatigue of thick‐walled pipes from soft martensitic and semi‐austenitic chrome‐nickel steels under pulsating internal pressure
Authors: Vetter Gerhard , Lambrecht Diethelm , Mischorr Gerhard 
Published: August 2005

AbstractThick‐walled components subjected to pulsating internal pressure are widely applied in high‐pressure technology and in manufacturing processes such as fluid‐jet cutting and high‐pressure cleaning, mainly in conjunction with reciprocating pumps. Corrosive fluids require high‐strength and tough chrome‐nickel steels with soft martensitic or semi‐austenitic structure. This contribution reports on the fatigue of thick‐walled plain and cross‐bored pipes made from high alloy chrome‐nickel steels such as X5 CrNiMoCu 21 8 and X5 CrNiMo 16 5. The speciments, uniaxial standard form and thick‐walled pipes, were cut from forged blocks in the three axial directions. For loading with pulsating pressure, a suitable, high‐frequency piston pulsation machine has been developed. The fatigue tests on pipe specimens show typical Woehler characteristics with only slight scatter and relatively good isotropy. The surprisingly large admissible pulsating pressure can be explained for the applied steels by dynamic generation of residual stresses as a result of shake‐down effects. Presentation in a Smith digram explains the occuring dynamic shake‐down and its favourable results in comparison to the more brittle highly tensile steels. It also reveals that heat treatment to higher tensile strength does not always yield an increase in the admissible pulsating pressure. It will be shown that static autofretting and shake‐down affect the fatigue strength of thick‐walled pipe specimens in the same way. Tests with internal liners in the tube specimens provide indications on the sensitivity of material failures towards fluids. The investigation aids the understanding of the fatigue behaviour and the design of components made of modern high‐strength corrosion resistant steels.
Physical properties of the NO‐absorbing system nitric acid‐tributyl phosphate
Authors: Pham Gia Hung , Gestrich Wolfgang 
Published: August 2005

AbstractFor water saturated tri‐n‐butyl phosphate (TBP) and for solutions of nitric or nitrous acid therein, the density, viscosity, physical solubility of nitric oxide (NO) and phase equilibria with aqueous phase, as distribution coefficients and water content of the TPB‐phase, were determined. The diffusion coefficient of nitric oxide was calculated, considering the solvent mixture to consist of one, two or, in the presence of nitric acid, three components.
Exergetic and engineering analyses of sulphuric acid decomposition process
Authors: Hammache Abdelaziz , Bilgen Earl 
Published: August 2005

AbstractThe purpose of this study was to evaluate the exergetic efficiency of the sulphuric acid decomposition process, which occurs in hydrogen producing thermochemical cycles and chemical energy storage systems. It is a process in which sulphuric acid is decomposed to a gaseous mixture consisting of water, sulphur dioxide and oxygen, using high temperature thermal energy, oxygen as a vector and mostly adiabatic equipment. Parts of the basic process with excessive exergy losses have been identified and a modified flow sheet has been developed and analyzed from thermodynamic and engineering points of view. Thermodynamic analysis of the modified flow sheet indicates that the overall exergetic efficiency of the decomposition process is 79.86%, which represents an improvement of 14.17% over the basic process. Engineering analysis of a plant producing 106 mol of SO2 per hour shows that the typical levelized cost of chemical exergy production was $ 2.25/GJ exergy from the basic process and $ 1.79/GJ exergy from the modified process.
Determination of process parameters and modelling of lipase‐catalyzed transesterification in a fixed bed reactor
Authors: Jung Hans Jürgen , Bauer Werner 
Published: August 2005

AbstractChemical transesterification is of major importance to the edible oil industry. While alkali catalysts randomize all the fatty acids in a triglyceride mixture, the use of a 1,3 specific lipase causes a more selective exchange of fatty acid residues. Basic process parameters for the development of a continuous solvent‐free process in a fixed bed reactor have been determined. The kinetics of the transesterfication reaction and the influence of particle diameter, substrate and water concentration on the effective reaction rate were examined in batchwise experiments. Residence time distribution and parameters of inter‐ and intraparticle mass transfer were determined by modelling of experiments carried out in a fixed bed reactor under transient conditions. Fixed bed reactors with side stream analysis were used for continuous transesterification. A kinetic model was developed for the enzyme catalyzed reaction, thereby showing the analogy between heterogeneous catalytic and enzyme catalyzed reactions. A one‐dimensional heterogeneous reactor model was formulated on the basis of the kinetic equation and different process parameters. For numerical calculations, an exponential enzyme distribution inside the carrier was assumed. The simulation of experimental results indicates that they are well described by the developed model. Water concentration and presence of other substances strongly influence the stability of the immobilized enzyme.
Propylene polymerization — a computer efficient algorithm with orthogonal collocation
Authors: Sarkar Priyabrata 
Published: August 2005

AbstractThis paper presents a new approach to the modelling of solid catalyzed Ziegler‐Natta polymerization of propylene, using orthogonal collocation technique. It is shown that this model can predict the width of the molar mass distribution (MWD) of the product polymer. Its computation time is much shorter compared to other models. An interesting feature of the model is that it considers the discrete nature of the microcatalyst particles and takes advantage of solving a smaller number of stiff differential equations by choosing the number of internal collocation points judiciously. In addition, pseudo‐steady state approximation (QSSA) is applied to some of the moment generating equations.
Multicomponent‐liquid‐membrane permeation of organic acids
Authors: Reisinger Hubert , Marr Rolf 
Published: August 2005

AbstractThe parameters of lactic acid separation from fermentation broths by Emulsion‐Liquid Membranes (ELMs) have been optimized. Using these parameters, lactic acid can be separated up to 90%, concentrated up to 3 times and cleared of most of its by‐products. Only about 1% of glucose and amino acids is permeated together with the lactic acid. With these parameters, not only lactic acid but also other monocarboxylic acids can be separated, the better and faster the lower the pKa‐value of the acid the fewer polar side groups it carries. When separating dicarboxylic acids, the mass transfer is hindered by the second carboxylic group. The smaller the distance between the two carboxylic groups, the slower is the separation of the acid. When several organic acids are separated from the same fermentation broth, their mutual influence is not very strong, at least when the concentrations of the acids are about 100 mmol/l. However, sulphuric acid which is added to the fermentation broth throughout permeation to maintain the broth at a constant pH, does exert a strong influence. In order to reduce the competition between the organic and sulphuric acids during permeation to a minimum, as little as possible sulphuric acid is used. However, a certain quantity of sulphuric acid is necessary to maintain the pH of the fermentation broth during permeation at 4.5, otherwise organic acid separation would become too slow.
Problems in use of supported liquid‐phase catalysts in fluidized bed reactors
Authors: Brüsewitz Rainer , Hesse Diethard 
Published: August 2005

AbstractSince SLP catalysts can become irreversibly deactivated due to evaporation of the solvent used to prepare the contacts, a saturation technique is proposed to stabilize the catalysts' activity. Application of this technique requires isothermal reaction conditions which can be achieved directly in fluidized bed reactors. Although the fluidization properties of SLP catalysts are mainly determined by interparticle forces, it can be shown that this type of reactor is suitable for an SLP‐catalyzed gas reaction provided that a number of prerequisites are fulfilled. Taking a hydroformylation reaction catalyzed by an Rh complex dissolved in dimethyl glycol phthalate as an example, it is demonstrated that the activity of the prepared SLP catalyst can, indeed, be stabilized by saturation of the reactant gas mixture with the employed solvent.
Gas‐phase properties in stirred tank bioreactors
Authors: Fischer Joachim , Brüring Stefan , Lübbert Andreas 
Published: August 2005

AbstractBubble properties in stirred tank bioreactors equipped with standard radial flow Rushton turbines have been investigated. Bubble velocity patterns within a stirred tank reactor were derived from measured local bubble velocity distributions. Local information on specific interfacial areas, bubble number densities and bubble diameters together with local gas hold‐ups, measured in a model medium at gas flow rates which are employed in practice, is presented. All measurements were performed with two new ultrasound pulse techniques which can be used in model as well as during real cultivation processes.
Fuzzy state estimator for a semibatch copolymerization reactor
Authors: Mahesh M. Muniram , Chidambaram Manickam 
Published: August 2005

AbstractThis work describes the development of a fuzzy estimator for determining copolymer composition (F1) in a semibatch solution copolymerization reactor. Membership functions, fuzzy ranges for input (ζ1 mole fraction of monomer 1 in polymerizing mass) and output (F1 mole fraction of monomer 1 in copolymer) are defined. A fuzzy rule base is constructed relating input to output, based on the operator's knowledge. A defuzzification method is selected and the non‐fuzzy values of F1 are obtained. The results are compared with the actual values of F1 which are obtained by rigorously solving the model equations of the system. The fuzzy ranges and limits for input and output are altered separately so as to test the estimator's performance. Thus obtained standard estimator is tested for other operating conditions. The developed estimator performed well also for wider operating conditions.
The concept of statistical molecular association and its application to reaction kinetics and chemical equilibria
Authors: Gestrich Wolfgang 
Published: August 2005

AbstractA simple statistical theory of molecular association has been developed, taking into account only the probability of residence of one or more molecules in an association volume. The result is a one parameter model which may be applied successfully to reaction kinetics and chemical equilibria of associated compounds. General concentration time profiles are presented and limiting cases discussed. Usefulness of the principle is demonstrated on experimental results.
Measurement of gas hold‐up in three‐phase systems by ultrasonic technique
Authors: Maezawa Akinori , Muramatsu Shingo , Uchida Shigeo , Okamura Seichi 
Published: August 2005

AbstractIt was established by using double impulse method that the transmission time of an ultrasonic wave, which passes near a bubble, is either shorter or longer than that in the liquid system. This is attributed to the fluid vortex originated by the bubble rising ahead of the wave. The longitudinal distribution of gas hold‐up in a three‐phase system, measured by analyzing wave shape and reduction of transmission time is in good agreement with that obtained by using the static pressure method. This indicates the possibility of application of ultrasonic techniques to the simultaneous measurement of phase hold‐ups in the three‐phase system.
Dynamics of the gas phase in bubble columns
Authors: Modak Shrikant Yadneshwar , Juvekar Vinay Anant , Rane Vishwanath Chango 
Published: August 2005

AbstractThe conventional two‐bubble‐class model for bubble column reactors has been modified to account for interactions between the two bubble classes. It is shown that the modified model is more consistent with the observed residence time distribution in the gas phase than the conventional model. The results indicate that there is an intensive cross‐mixing between the bubble phases. This study also reveals that the modified two‐bubble‐class model cannot be distinguished from the single‐bubble‐class model solely on the basis of the residence time distribution.
Flow regimes in circulating fluidized beds
Authors: Bai Dingrong , Jin Yong , Yu Zhiqing 
Published: August 2005

AbstractBased on a comprehensive hydrodynamic analysis, a practical definition of the circulating fluidized bed (CFB) regime has been proposed. It was established that two flow regimes are involved in a CFB: fast fluidization and dense phase conveying. By demonstrating the variation of pressure gradient in both the lower and the upper section of the bed versus superficial gas velocity, the criteria for the determination of transition velocities have been obtained. Literature data which over wider operating conditions, particle properties and bed diameters from the basis of the obtained generalized correlations of transition velocities. A quantitative flow diagram is presented.
Wall factor for acceleration and terminal velocity of falling spheres at high reynolds numbers
Authors: Bougas Athanasios , Stamatoudis Michael 
Published: August 2005

AbstractThe wall factor for spheres in the acceleration and terminal velocity ranges was determined experimentally for very high Reynolds numbers (13 500 < Re < 70 000). Experiments were performed with 12, 15, 18, 21, 25 and 31.75 mm spheres, falling in water inside cylinders 3.4, 4.9, 7, 10, 14 and 19 cm in diameter. A published empirical equation was found to yield good results for the terminal velocity wall factor in the range of studied Reynolds numbers.
Homogenization of liquids in tanks stirred by multiple impellers
Authors: Jahoda Milan , Machoň Václav 
Published: August 2005

AbstractThe process of homogenization of liquids in a tall vessel equipped with a multiple impeller was studied. Up to four standard Rushton turbines and/or six pitched‐blade turbines were used. The mixing time in the system was measured by the conductivity method. A continuous time history of the tracer concentration at several points in the system was recorded. The data were interpreted by means of an adapted cell model of the flow within the stirred vessel with several impellers based on the assumption of well mixed cells and intercellular flow of liquid. The liquid transfer flow rate between the cells, as a parameter of the model, was calculated from experimental data. A good agreement between the time dependence of concentration obtained experimentally and that calculated from theory was obtained. A direct relationship between the flow numbers between cells and those of impellers was established.
Influence of viscosity on product distribution of fast competitive chemical reactions
Authors: Gholap Raghuraj V. , Petrozzi Sergio , Bourne John R. 
Published: August 2005

AbstractThe objective of this study was to determine the influence of viscosity on micromixing in turbulent flow. It was first necessary to find a suitable viscosity‐raising additive. HEC (hydroxyethyl cellulose) proved to be better than previously studied additives [sorbitol and carboxymethylcellulose (CMC)]. In concentrations up to 1 wt‐%, HEC solutions are almost Newtonian with viscosities independent of pH over the range 2 to 10. HEC had no effect on the reaction rate constants and the spectrophotometric analysis of the fast, competing reactions used – the diazo coupling between 1‐naphthol and diazotized sulphanilic acid. The viscosity can then be raised by around an order of magnitude by adding less than 1 wt‐% HEC to this reaction system.Diazo couplings were conducted in a 20 1 semi‐batch tank reactor stirred by a Rushton turbine at two viscosity levels (0.9 and 6.2 mPa s). Long feed times ensured that micromixing was controlling. More bisazo dye was formed in the more viscous solution, all other conditions being unchanged, indicating more intense segregation and slower micromixing.This was also shown by visualizing the extent of neutralisation zones, with more spreading and slower micromixing being observed in viscous solution. Higher turbine speeds reduced this spreading. One feed point near and one far from the turbine were employed: the strong inhomogeneity of the turbulence led to smaller amounts of bisazo dye when the feed was added to the turbine suction, irrespective of the viscosity. All results agreed with the trends predicted by the engulfment model of micromixing. Its simplest form assigns an average energy dissipation rate to the reaction zone: the values obtained are of similar magnitude to those measured by physical techniques and were related to the spreading of the reaction zone.
Heterogeneous catalytic methylation of catechol
Authors: Porchet Stéphane , Su Shoujin , Doepper Ralf , Renken Albert 
Published: August 2005

AbstractIt has been shown that, after a partial deactivation, γ‐alumina (γ‐Al2O3) is a good catalyst for selective methylation of 1,2‐benzenediol in the temperature range of 260–310°C. The main products are the desired 3‐methyl‐1,2‐benzenediol and 2‐methoxyphenol, which may be converted in another step into 3‐methyl‐1,2‐benzenediol, giving an overall selectivity for the desired products of 80 to 90%. The catechol forms a strongly chemisorbed surface species on γ‐alumina and its steric adsorption model correlates with the kinetic data.
A mathematical model describing the ARI “autocirculation reactor” for low temperature conversion of H2S into sulphur
Authors: Abedinzadegan M. , Nasr M. R. Jaffari 
Published: August 2005

AbstractA prototype “autocirculation”‐type reactor has been designed and constructed at the N.I.O.C. Research Institute, Tehran and a mathematical model describing the concentration versus time profile subsequently developed. The model encompasses mass transfer considerations and kinetic studies of the regeneration reaction. For this purpose, the rate equation for iron complex oxidation, proposed by Japanese researchers, was modified and a new rate equation presented. This rate equation has been widely used in the above mentioned mathematical model. With this model, the vessel volume for a time‐dependent H2S feed has been calculated for a “ZDDP” production unit.
Conversion of ethanol over zeolite H‐ZSM‐5
Authors: Schulz Jürgen , Bandermann Friedhelm 
Published: August 2005

AbstractThe conversion of ethanol over H‐ZSM‐5 was studied as a function of ethanol partial pressure, reaction temperature, weight hourly space velocity and Si/Al ratio. The results obtained were in qualitative agreement with most of those in the literature. Combination with all published results to give a significant regression model was not possible due to the large scatter of the data from various scientific groups. In mechanistic investigations, temperature programmed reaction measurements of ethanol, diethyl ether and ethene were performed. The formation of ethene from ethanol via direct elimination or from diethyl ether as intermediate could be confirmed. In the conversion of ethanol/water mixtures, the product distribution did not change significantly up to a water content of 60 wt%. Then, a pronounced increase of ethene formation and a considerable decrease of the yields of aromatics was observed. When several reaction mixtures from syngas conversion to ethanol were converted over H‐ZSM‐5, the coking rate depended on the product distribution in the feed. Product mixtures from processes with higher amounts of compounds having an unfavourable C/H ratio led to rapid deactivation of the zeolite.
Kinetic modelling of zinc liberation from zinc sulphide‐containing sludges in the viscose industry
Authors: Hofmann Hanns , Glöckl Steffen 
Published: August 2005

AbstractLarge quantities of sludge containing considerable amounts of zinc are obtained on treatment of waste water from the production of viscose fibres for textiles and industrial applications. A process has been proposed [7, 10] for the recovery of zinc from one such sludge, in the first step of which zinc is transferred to the liquid phase with liberation of hydrogen sulphide. In connection with this work a model was developed which provides a kinetic description of zinc liberation from various sludges and the parameters of this model fitted to the measured data by means of linear regression.
Mass transfer effects on kinetics of nonideal liquid phase ethyl tert‐butyl ether formation
Authors: Sundmacher Kai , Zhang Rui‐Sheng , Hoffmann Ulrich 
Published: August 2005

AbstractEthyl tert‐butyl ether (ETBE) is an alternative fuel oxygenate that can be produced in the liquid phase by addition of ethanol to isobutene catalyzed by sulfonic acid ion exchange resins. A generalized Langmuir‐Hinshelwood rate expression is formulated in terms of the liquid phase activities of the reactants that is quasi‐autocatalytic due to ethanol. This microkinetic model is combined with the generalized Maxwell‐Stefan equations for a detailed investigation of the influence of multicomponent mass transfer limitations inside the macropores of the heterogeneous catalyst. The model is used for revision of experimental rate data for ETBE synthesis in the literature. The analysis reveals that reverse diffusion of isobutene can occur by strong interaction with ethanol and the catalyst effectiveness factor can exceed unity.