bluuebunny/crossref_metadata_2025 huggingface dataset:
Relationship of squamosal suture to asterion on external skull surfaces versus endocasts of pongids: Implications for Hadar early hominid AL 162‐28
Authors: Falk Dean , Hildebolt Charles , Vannier Michael
Published: August 2005

The relationship between the squamosal suture and asterion was quantified in 15 hemispheres of eight chimpanzee endocasts that were aligned in the conventional lateral view (i.e., with frontal pole [FP]–occipital pole [OP] horizontal). Using a three‐dimensional digitizer, x, y, and z coordinates were collected for the highest and lowest points of the squamosal suture, and the most rostral point of the suture approximate to the coronal suture. Our results were compared to a similar study of the squamosal suture on the external surfaces of chimpanzee skulls that were oriented in the Frankfurt horizontal (Holloway and Shapiro, 1992). The relationship between the squamosal suture and asterion differs markedly between the outsides of skulls and endocasts. Whereas the squamosal suture is very rarely below asterion on the external skull, we found that most of the squamosal suture is located inferior to asterion on endocasts. We also found that the squamosal suture courses approximately 2.0 mm lower on the right side than the left. (An asymmetry of the same magnitude was reported for the external skull but, curiously, in the opposite direction.) It may be that a lowered right squamosal endosuture on chimpanzee endocasts is associated with earlier closure on that side. The discrepancy in results for the external skull versus endocast is partially attributable to orienting chimpanzee skulls in the Frankfurt horizontal, which usually results in the endocasts being tilted so that FP is above OP, i.e., FP‐OP is not parallel with the Frankfurt horizontal. Falk's (1985) orientation of the early hominid endocast from Hadar (AL 162‐28) is consistent with data determined from endocasts of chimpanzees. © 1994 Wiley‐Liss, Inc.
Genetic data on Alghero population (Sardinia): Contrast between biological and cultural evidence
Authors: Moral P. , Marogna G. , Salis M. , Succa V. , Vona G.
Published: August 2005

Data on 20 genetic polymorphisms (61 alleles) in the Algehero population on the northwestern coast of Sardinia are presented and discussed in relation to its linguistic peculiarity inside the island. Since the Aragonese (Spain) conquest of Sardinia in the 13th century, the Catalan language, the same as that spoken in Northeastern Spain and certain districts of Southern France, has been used in Alghero even until today. Analysis for heterogeneity of gene frequency distributions indicates that the genetic information obtained on Alghero is adequate to discriminate Sardinians from other neighbouring populations. Genetic variation between populations measured through genetic distances and principal‐component analysis shows that the present‐day population of Alghero is much closer genetically to Sardinians than to Catalonians. Our genetic results do not support any interpretation of the linguistic affinities between Alghero and Catalonia at present as indicative of biological kinship. © 1994 Wiley‐Liss, Inc.
Sexual dimorphism in canine shape among extant great apes
Authors: Kelley Jay
Published: August 2005

There have been numerous attempts to sex fossil specimens using the canine dentition. Whether focused on canine size or canine shape, most of these efforts share two deficiencies: lack of quantification of male‐female differences in the adopted criteria and a failure to adequately explore among extant species the discriminatory power of these criteria. Here, canine shape indices relating to relative canine height, upper canine root/crown proportionality, and relative length of the lower canine mesial ridge were calculated for males and females of all species and subspecies of extant great apes and two species of gibbons. The accuracy of these indices for identifying the sex of the extant ape specimens was investigated through discriminant analysis and the use of bivariate plots of the two upper and two lower canine indices. The indices were found to be highly accurate in identifying the sex of great ape individuals, not only in single‐species and subspecies samples but in mixed‐species samples as well; assignment error rates were mostly between 0 and 4%. Accuracy was lowest in Pan (error rates as high as 15%) and highest in Pongo (one error). In most cases, error rates were lower in the upper canines. The effectiveness of these shape indices for sexing might be related to the degree of absolute canine size dimorphism; the indices did not effectively segregate males and females among minimally canine‐dimorphic gibbons. The mixed‐species results reveal that same‐sex index values are remarkably concordant across great ape species, as are the patterns of spatial segregation of males and females in the bivariate plots. Results suggest that, while the indices can be used with some confidence to sex individual fossil specimens, their greatest utility will be for identifying the sex of groups of canines united by size and morphology. © 1995 Wiley‐Liss, Inc.
Titelbild: Nanoparticle PCR: Nanogold‐Assisted PCR with Enhanced Specificity (Angew. Chem. 32/2005)
Authors: Li Haikuo , Huang Jiehuan , Lv Junhong , An Hongjie , Zhang Xiaodong , Zhang Zhizhou , Fan Chunhai , Hu Jun
Published: August 2005

Bevorzugt gebunden werden Goldnanopartikel an Einzelstrang‐DNA. Ihre Anlagerung reduziert die Tendenz zur Fehlpaarung während des Annealing‐Prozesses und erhöht deutlich die Spezifität und Ausbeute der PCR, einer der wichtigsten Standardmethoden der Molekularbiologie. In ihrer Zuschrift auf S. 5230 ff. nehmen Z. Zhang, C. Fan, J. Hu und Mitarbeiter Bezug auf dieses vielversprechende Teilgebiet der Nanobiotechnologie. (Xiaobin Wang half beim Erzeugen der Abbildung.)
Borinium, Borenium, and Boronium Ions: Synthesis, Reactivity, and Applications
Authors: Piers Warren E. , Bourke Sara C. , Conroy Korey D.
Published: August 2005

Boron cations are elusive and highly electrophilic species that play a key role in the chemistry of boron. Despite early interest in the chemistry of boron cations, until recently they have largely remained chemical curiosities. However, hints at harnessing their potential as potent electrophiles have begun to appear and developments in weakly coordinating anion technology suggest that this is an area of research that is ripe for exploration. It has been nearly 20 years since the last major review on boron cations; herein we summarize the progress in the area since that time.
Adult and developmental myosin heavy chain isoforms in soleus muscle of aging Fischer Brown Norway rat
Authors: Snow Leann M. , Mcloon Linda K. , Thompson Ladora V.
Published: August 2005

Fiber type shifts in aging skeletal muscle have been studied with myofibrillar ATPase histochemistry and gel electrophoresis, but less commonly with immunohistochemistry. Immunohistochemical study of myosin heavy chains (MHCs) in single myofibers yields additional information about aged skeletal muscle. Furthermore, many studies of aging rodent skeletal muscle have been performed on fast‐MHC‐predominant muscle and in several different strains. The aim of this study was to evaluate immunohistochemically MHC characteristics in the slow‐MHC‐predominant soleus muscle in the Fischer Brown Norway F1 hybrid aging rat (FBN). Three age groups of FBN rats were studied: 12 months, 30 months, and 36 months. Soleus muscles were excised, quick‐frozen, and stained immunohistochemically for slow, fast, developmental, and neonatal MHC isoforms. Cross‐sections were evaluated for the number and cross‐sectional areas of fibers expressing each isoform. Single myofibers in soleus muscles of the aged rats showed significantly greater amounts of coexpression of slow and fast MHC than did younger animals. This change began by 30 months of age, but did not reach statistical significance until 36 months of age. The soleus from 36‐month‐old rats also expressed greater amounts of developmental MHC than did the other groups. These developmental MHC‐positive myofibers also coexpressed either slow or slow and fast MHC. The age‐related increase in MHC coexpression of slow with fast isoforms may indicate a fiber type shift suggestive of denervation that outpaces reinnervation. The developmental MHC‐positive fibers provide evidence of ongoing myofiber remodeling in the oldest rats in the midst of the fiber degeneration of aging. © 2005 Wiley‐Liss, Inc.
Vitamin A storage in hepatic stellate cells in the regenerating rat liver: With special reference to zonal heterogeneity
Authors: Higashi Nobuyo , Sato Mitsuru , Kojima Naosuke , Irie Toshiaki , Kawamura Koichi , Mabuchi Ayako , Senoo Haruki
Published: August 2005

Under physiological conditions, hepatic stellate cells (HSCs) within liver lobules store about 80% of the total body vitamin A in lipid droplets in their cytoplasm, and these cells show zonal heterogeneity in terms of vitamin A‐storing capacity. Vitamin A is essential for the growth and differentiation of cells, and it is well known that liver cells including HSCs show a remarkable growth capacity after partial hepatectomy (PHx). However, the status of vitamin A storage in HSCs in the liver regeneration is not yet known. Therefore, we conducted the present study to examine vitamin A storage in these cells during liver regeneration. Morphometry at the electron microscopic level, fluorescence microscopy for vitamin A autofluorescence, and immunofluorescence microscopy for desmin and α‐smooth muscle actin (α‐SMA) were performed on sections of liver from male Wistar strain rats at various times after the animal had been subjected to 70% PHx. The mean area of vitamin A‐storing lipid droplets per HSC gradually decreased toward 3 days after PHx, and then returned to normal within 14 days after it. However, the heterogeneity of vitamin A‐storing lipid droplet area per HSC within the hepatic lobule disappeared after PHx and did not return to normal by 14 days thereafter, even though the liver volume had returned to normal. These results suggest that HSCs alter their vitamin A‐storing capacity during liver regeneration and that the recovery of vitamin A homeostasis requires a much longer time than that for liver volume. © 2005 Wiley‐Liss, Inc.
The role of negative features in joint and separate evaluation
Authors: Willemsen Martijn C. , Keren Gideon
Published: August 2005

Separate and joint evaluations differ in the manner in which attribute information is processed. We propose that negative attributes weigh more in separate compared to joint ratings. To assess the relative weights of positive and negative attributes, stimuli were employed containing mixed attribute valence, with good and poor attributes. In three experiments it was demonstrated empirically that, using such mixed valence options, the negative attributes indeed weighed more than the positive ones in separate compared to joint ratings. Direct evidence for the increased weight of negative attributes in separate ratings was provided by showing preference shifts between joint and separate ratings for options with mixed attribute valence. Copyright © 2004 John Wiley & Sons, Ltd.
Mass transfer contributions of solid particles to gas permeation in viscous laminar tube flow
Authors: Haase Brigitte , Bauckhage Klaus
Published: August 2005

While two‐ and multiphase flows find more and more application in chemical engineering practice, and the demand for theoretical information about mass and heat transfer processes in such systems is increasing, such data or at least experimental results which could be generalized are still lacking. The following pages are concerned with mass transfer in laminar suspension tube flows normal to the main direction of flow due to the individual motions of small, inert spherical particles. On the basis of a large number of experimental data, an interpretation is attempted of the role of nearly neutrally‐buoyant particles in mass transfer enhancement, and a model for a semi‐empirical description is suggested. The experimental arrangement uses the mass transfer of carbon dioxide in laminar flow of salt water during the process of gas permeation through a permeable membrane tube wall.
Effect of enzyme inhibition on the performance of packed‐bed biological reactor ‐ a theoretical study
Authors: Hassan M. M. , Beg S. A.
Published: August 2005

The performance characteristic of a packed bed reactor has been analyzed by considering diffusional resistance of the biofilm. Model equations were solved by the method of orthogonal collocation for various classical enzyme inhibition kinetics, including partially non‐competitive, partially competitive, partially uncompetitive, partially mixed and fully mixed. For all considered modes of inhibition, an increase in the inlet substrate concentration decreases the steady state conversion in the reactor. However, an increase in the Peclet number has been found to improve the conversion. The effects of various other process variables of physical importance were also investigated parametrically.
A robust pole‐placement self‐tuning controller for chemical process control: Theoretical studies and simulation
Authors: Rohani Sohrab , Quail Douglas W.
Published: August 2005

A single variable pole‐placement self‐tuning controller (PPSTC) is used to simulate examples typical of chemical processes; i.e., open‐loop stable, unstable, and unstable non‐minimum phase systems with unknown varying process dead time. The PPSTC is shown to be effective in each case. Set‐point tracking and rejection of randomly occurring deterministic disturbances for all three types of processes are achieved. Simultaneous estimation of process parameters and process time delay is realized by using a recursive extended least squares method.
Experimental results from a plate‐column wet scrubber with gas‐atomized spray
Authors: Fan Xiaolun , Schultz Tilman , Muschelknautz Edgar
Published: August 2005

A pilot wet scrubber was examined experimentally. It is constructed like a plate column. Its plates are designed to set the gas into a whirling motion with tangential velocities of up to 25 m/s and to ensure a uniform distribution of the liquid throughout the gas flow. Particles suspended in the waste gas are collected by gas‐atomized droplets to yield cut diameters between one and two microns. Energy consumption is lower than in the case of other scrubbers. The scrubbing mechanisms are analyzed by examining the measured pressure drops. Finally, methods of determining the collection efficiency are discussed and an empirical approach to its calculation is presented.
The stability of crude oil residues and factors affecting their decomposition during mild thermal treatment
Authors: Pilcher Kenneth A. , Winterbottom John M.
Published: August 2005

A number of topped crude oil residues were subjected to mild thermal cracking in the temperature range between 613 and 673K at N2 pressure of one atmosphere. It was found that the thermal stability of the six topped crude oils decreased in the order Brent < Piper < Auk < Saudi Arabian < Romashkinskaya < Tia Juana Pesado. This was measured in terms of light end production (C1–C5 hydrocarbons). The asphaltene, sulphur and metal (nickel and vanadium) contents were also determined. The production of light ends, exemplified by methane, was found to be related to the metal asphaltene content of the crude oils, but the sulphur content exerted a moderating influence upon the extent of cracking. Hence, metal asphaltenes, probably as metal porphyrins, catalyse cracking but the presence of sulphur reduces that catalytic activity and can inhibit cracking. If cracking of long chain hydrocarbons is to be minimized, metal asphaltenes should be removed (preferably) or reduced in concentration or poisoned, in order to decrease their catalytic activity.
Kinetic analysis of the oxidation of isobutyraldehyde in liquid phase
Authors: Emig Gerhard , Haeberle Thomas , Höss Werner , Watzenberger Otto
Published: August 2005

The kinetics of non‐catalytic as well as catalytic oxidation of Isobutyraldehyde has been investigated. Reaction rate equations for the formation of the main product isobutyric acid and of the side products acetone, CO and CO2 were derived. Kinetic parameters, namely the order of reaction, preexponential factor and activation energy were estimated by non‐linear regression. The influence of selectivity and activity of the different type of catalysts employed was investigated quantitatively.
Measurement of temperature fields in mixing vessels using optical topography
Authors: Ostendorf Wilfried , Mewes Dieter
Published: August 2005

Experimental investigation of stirring processes require the measurement of temperature changes and concentration profiles in all the zones of the mixing volume. The conversion of simultaneous chemical reactions during the mixing process depends on the local temperature and concentration. The time‐dependent temperature and concentration fields can be recorded for the entire mixing volume with the use of optical tomography and correlated with time. This technique offers the possibility of continuous measurement of temperature and concentration changes during the mixing process throughout the measurement volume. In the described investigations, optical tomography is used to examine the transport and equalization processes during mixing in stirred vessels.
Scale‐up of bioreactors for fermentation of mammalian cell cultures with special reference to oxygen supply and microcarrier mixing
Authors: Vorlop Jürgen , Lehmann Jürgen
Published: August 2005

The increasing demand for products from mammalian cells has prompted the authors to develop a new type of bioreactor. Its significant features include the supply of oxygen, homogeneous distribution of microcarrier suspensions and process control. Media with high protein contents, required for mammalian cell cultures tend to generate foam. This causes the flotation of solid particles. The reactor was equipped with a system of porous hydrophobic Accurel hollow fibre membranes in order to prevent the formation of bubbles. The membrane is coiled in the form of a basket, or fixed on several carriers. If the liquid pressure is higher than that of the gas phase inside the membrane, a bubble ‐ free oxygen supply to the culture broth can be achieved. The problem of axial mixing of microcarier suspensions was solved by the use of a spiral agitator, attached underneath the aeration system at the bottom of the reactor. The combined aeration and mixing system, which is driven by an eccentric motor, undergoes a tumbling motion. Sufficiently homogeneous suspensions are produced in this system at low membrane velocities, i.e. in presence of low shear forces.
Influence of mechanical stress on the growth of Rhizopus nigricans in stirred bioreactors
Authors: Reuß Matthias
Published: August 2005

This investigation was undertaken in order to examine the factors affecting mechanical damage to micro‐organisms in stirred bioreactors. Growth of the mould Rhizopus nigricans was studied in stirred bioreactors at different geometrical and operating parameters. Since experimental results cannot be described by conventional key parameters, a new concept has been suggested. It is based on the analogy to processes of mechanical disintegration. It is shown that the same key parameter, i.e. the ratio of power input to flow rate, can be used for a satisfactory correlation of experimental data on mechanical damage to micro‐organisms, which is an important step in the recovery of intracellular products in biotechnology.
A model‐based control system for a distillation column
Authors: Rhiel Franz Ferdinand , Krahl Franz
Published: August 2005

A control concept which includes an adaptive multivariable control algorithm and an observer model has been put into practice in the operation of a distillation column which separates water from a solvent. The model yields predictions of solvent concentration in the waste water which forms the top product. Early detection of disturbances permits an adjustment of the process in time. This has resulted in an exceptionally smooth operation of the column, with a drastic reduction in solvent concentration fluctuations, observed with conventional control technology. Since the only measurements required are pressure, temperature and the rate of flow, this control system is largely free from disturbances. In addition to considerably reducing the burden on operating personnel, use of this control system has lowered the costs of waste water treatment, solvent losses, analysis expenditure and energy consumption.
Thermal deactivation of heterogeneous catalysts. Part 2: The compensation effect and the Catalytic Paradox
Authors: Kral Hans
Published: August 2005

The interpretation of the term “compensation” obscures a logical contradiction, the catalytic paradox, which is caused by inconsistent validity ranges of the Arrhenius parameters, the pre‐exponential factor and the activation energy. For this reason, a theory which contains the Arrhenius parameters cannot be established for the entire system (whole temperature range) on the basis of classical logic. Only the subsystems can be consistent and complete. One subsystem is the range of the topocatalytic concept which is relevant for thermal deactivation, thermal bistability and for all reactions with surface dependence of activity. The other is the range of the energetic concept which is preferred in fundamental research. In order to complete the subsystems, new consistent symbols are introduced. The change of particle size caused by thermal deactivation can result in four possible particle size effects, two of which have been discussed in the literature.
Effect of ethane addition on propane pyrolysis
Authors: Wami Emenike N.
Published: August 2005

Pyrolysis of propane/argon mixture in the presence of trace quantities (0.1% and 0.9%) of ethane was investigated at reflected shock wave temperatures between 1200 and 2000K. Traces of ethane accelerated propane decomposition at high temperature. However, increase in the quantity of ethane added to propane/argon mixture did not result in the same increase of its accelerating influence. Ethylene, methane and acetylene were the main hydrocarbon reaction products, with small quantities of propylene and ethane detected only at lower temperatures. Below 1500K, addition of ethane slightly enhanced the yields of ethylene and methane at the expense of propylene and ethane respectively. The selectivity for acetylene increased with increasing temperature and with the decline of those for the other products. For none of the products, did the presence of ethane alter the relationship between product formation rates and temperature. The influence of ethane addition on propane pyrolysis at high temperatures was explained in terms of increased radical concentrations, especially hydrogen atoms and vinyl radicals, formed at high conversions. These accounted for the rapid acceleration of propane decomposition and the high yield of acetylene at high temperatures.
Volumetric mass transfer coefficient in stirred reactors
Authors: Linek Václav , Vacek Václav
Published: August 2005

It is shown that the volumetric mass transfer coefficients, presented recently by Schmitz et al. [1] for viscous solutions of carboxymethyl cellulose (CMC) in aqueous sodium sulphite, are considerably underestimated as a result of unjustified neglect of the oxygen back pressure during oxygen absorption. Schmitz et. al. [1] found a decrease in the exponent n in the relationship between the oxygen mass transfer coefficient, kla, and the power dissipated per unit volume of the liquid phase, e (kla ∝ en), and ascribed it to viscosity effects. However, no such decrease is observed, provided that the actual oxygen back pressure is taken into account.
Parametric sensitivity of the ignition process to mass transfer in adiabatic tubular reactors with exothermic heterogeneous reactions
Authors: Quest Stefan , Mewes Dieter
Published: August 2005

The alternative effects of reaction kinetics, mass, heat and momentum transport on mass conversion by chemical reactions are examined theoretically for a reacot tube with laminar flow. The reaction enthalpy is considered. A heterogeneous reaction between several gaseous components takes place at the inner surface of this reactor tube. Strongly exothermic reactions lead to self‐acceleration of the reaction, unless reaction enthalpy is removed through the tube wall. Under certain conditions, there will be a sudden change from mass transfer controlled by the reaction to that controlled by diffusion. This phenomenon is known as ignition of the reaction. The effect of ignition and its sensitivity to reaction enthalpy, thermal conductivity and diffusivity of the fluid as well as activation energy of the first order heterogeneous wall reaction are investigated by a numerical solution of the transport equations. Axial conduction of heat and mass is neglected both in the fluid and in the tube wall. Non‐stoichiometric wall reactions of first order, with temperature dependent reaction rates and equilibrium constants, are considered. The results are presented in graphical form, as plots of the local mass flux at the reacting wall as functions of the dimensionless tube length.
Chemical engineering aspects of precipitation from solution
Authors: Mersmann Alfons , Kind Matthias
Published: August 2005

Precipitation is a rapid solidification. As a rule, it applies to substances which are sparingly soluble and is coupled with a chemical reaction or with a salting out process. The chemical engineer has to ensure that the product obtained has a constant and preferably coarse size distribution. This contribution compares the literature data on crystallization of soluble and sparingly soluble substances; it can be shown that, during precipitation processes, nuclei are formed, most probably by a primary mechanism. Analysis of the processes occurring during precipitation, such as chemical reaction, mixing and crystallization, leads to recommendations for the operation of precipitation processes.
Development of design charts for fixed‐bed adsorption
Authors: Otten Wilhelm , Kast Werner
Published: August 2005

A mathematical model of the dynamic behaviour of non‐isothermal fixed‐bed adsorbers has been developed which takes into account the various mass and heat transfer resistances. Comparison of experimental and simulated results confirms that the model can predict the adsorption and desorption breakthrough curves of an adiabatically operated column, using only equilibrium data and tortuosity factors obtained from single pellet experiments. A simplified model with a reduced number of parameters was derived by investigation of the dimensionless transfer parameters under industrial conditions. It becomes evident that the main transfer mechanisms are convective heat and mass transfer in the bulk flow and diffusion within the pores of the particle. Dimensionless effluent concentration is expresses in terms of dimensionless time, a transport parameter, a non‐isothermal parameter, the adsorption equilibrium and the inlet and initial concentrations and temperatures in the simplified model. For a chosen system of adsorbate and adsorbent, design charts can be developed by computer simulation, to determine graphically the breakthrough time as a function of significant process parameters, i.e. the dimensionless transfer parameter and the feed concentration.
The significance of fly ash in wet‐dry scrubbing of SO2
Authors: Petersen Tom , Karlsson Hans T.
Published: August 2005

A bench scale flue gas desulphurization spray dry scrubbing unit was employed to study the effect of fly ash on the removal of SO2. The equipment consisted of a spray dryer with and ultrasonic nozzle for atomization and a pulse jet baghouse. The flue gas rate was 1500 lN/h (dry gas). Four fly ashes, originating from different countries were investigated. The alkalinity and reactivity of the fly ashes were determined in a pH‐stat equipment. Pure fly ash removed SO2 in both the spray dryer and in the baghouse. An increase of humidity divided the fly ashes into two groups. The high calcium fly ash gave a considerably higher SO2 removal than the medium and low calcium fly ashes which showed similar SO2 removals. Fly ash did not enhance the removal of SO2 when added to a lime slurry because lime suppresses the dissolution of the alkali in the fly ashes. The pressure drop build‐up in the fabric filter showed a strong dependence on material properties.
Mass transfer in centrifugal extractors
Authors: Otillinger Franz , Blass Eckhart
Published: August 2005

This contribution presents the methods of measuring the mass transfer in centrifugal extractors and of determining it during the individual life stages of a fluid element of the dispersed liquid, i.e. drop formation, motion, coalescence and stay in the stationary layer of the dispersed phase. The experimental mass transfer coefficients of the dispersed and continuous phases are compared with well‐known theoretical models developed for extraction columns in gravitational field. Due to the fast motion and coalescence of the fluid particles at high centrifugal field intensities, mass transfer in centrifugal extractors takes place during short contact times. Nevertheless, this contribution shows that mass transfer in a centrifugal field can be calculated with selected theoretical models of the gravitational field. The investigations on mass transfer are completed by a classification of the strongly deformed fluid particles in centrifugal field into regimes of circulating and oscillating drops. In addition, data on the performance of centrifugal extractors, undergoing several exchange steps, are given.
Characteristics of solid suspensions in a bubble column without and with draft tube
Authors: Heck Joachim , Onken Ulfert
Published: August 2005

In order to investigate the suspension behaviour of solid particles in bubble columns without and with draft tube, minimum gas velocities for generating and maintaining complete solid suspension were determined. Experiments were carried out in a bubble column with a diameter of 200 mm and a height of 2 500 mm. The bubble column could be equipped with a draft tube with a diameter of 120 mm and a length of 1 500 mm. The state of suspension was determined by measuring the hydrostatic pressure as a result of suspended solid particles with an inductive pressure gauge. Solid content εs, solid density ϱs, particle size dp, particle shape, particle size distribution, and solid wettability were varied. Furthermore measurements of integral gas holdup were carried out.
Modelling of a pressure swing adsorption process for oxygen enrichment with carbon molecular sieve
Authors: Seemann Albert , Richter Ekkehard , Jüntgen Harald
Published: August 2005

Adsorptive separation of oxygen from nitrogen and argon is carried out during the desorption steps of a pressure swing adsorption (PSA) process which uses carbon molecular sieves developed by Bergbau‐Forschung GmbH. The adsorption isotherms of the three main components of air are very similar. On account of the pore size distribution of CMSN2, the diffusion coefficient of oxygen is more than eight times those of nitrogen and argon so that air separation occurs by adsorption kinetics. Experimental results for the individual steps and cyclic operation of the PSA process are presented and compared with the predictions of an isothermal plug‐flow model. Adsorption rate is represented by a linear driving force equation. If the diffusion coefficients are adapted separately to every step, a good agreement is observed between the model calculations and experimental results.
Modelling of activated carbon desorption by a circulated inert gas
Authors: Jedrzejak Andrzej
Published: August 2005

The adsorption solvent recovery process, known as Recursorb which involves desorption and cooling steps by a circulated inert gas, is analyzed in detail on the basis of equilibrium theory. Employing the method of characteristics, the model is solved for each step of the overall process. The estimations confirm that the process performance with respect to final gas purity, activated carbon useful capacity and operation times depends on condenser and heater temperatures. Simple expressions are derived for the calculation of adsorption, desorption and cooling times.
Decoking of fixed‐bed catalytic reactors
Authors: Westerterp K. Roel , Fontein H. Jan , van Beckum Frits P. H.
Published: August 2005

A mathematical model for the description of the non‐steady state process of decoking of a fixed bed catalytic reactor is presented. The relevant dimensionless groups are identified and their influence on the process discussed. Appropriate relationships are given for the estimation of the maximum temperature in the bed. Methods of monitoring the process and of controlling it in the case of unknown or variable coke contents are explained.
Two‐phase flow in porous media
Authors: Dullien Francis A. L.
Published: August 2005

Two‐phase flow in porous media depends on many factors, such as displacement vs steady two‐phase flow, saturation, wettability conditions, wetting fluid vs non‐wetting fluid is displacing, the capillary number, interfacial tension, viscosity ratio, pressure gradient, uniformly wetted vs mixed‐wet pore surface, uniform vs distributed pore throats, small vs large pores, well‐connected pores vs pores connected by small throats, etc. These parameters determine how the two fluids are distributed in the pores, e.g. whether they flow in seperate channels or side‐by‐side in the same channels, either with both fluids being continous or only one fluid being continous and the other discontinuous. In displacement, the capillary number and the viscosity ratio determine whether the displacement front is sharp, or if there is either capillary or viscous fingering.
Remarks upon the modelling of heterogeneous catalytic reactors – the single fluid‐solid cases
Authors: Carberry James J.
Published: August 2005

To our benefit, the modelling of fluid‐solid catalyzed reaction‐reactor systems has long been the keen concern of Hanns Paul Hofmann. In the light of his instruction we remark upon key aspects of modelling for the (a) fixed bed (b) fluid bed and (c) moving bed/transport line reactors. There emerges from such analyses a properly renewed awareness of the need for a more sophisticated respect for reliable physical‐chemical data. As Hanns has taught us, our models are no btter than our data.
Micromixing limits in an MSMPR crystallizer
Authors: Tavare Narayan S.
Published: August 2005

The effect of micromixing limits on a process of crystallization in an MSMPR crystallizer is studied with respect to power law growth and nucleation kinetics. Three limiting cases corresponding to maximum mixedness and complete segregation in an MSMPR crystallizer and plug flow configuration were analyzed for processes in which supersaturation is generated by conventional techniques. The sensitivity of these three limiting cases to the supersaturation generation term in each mode of operation was investigated using several numerical examples. The study demonstrates the effects of mixing on the overall crystallizer performance and, in particular, the enormous micromixing influence at high supersaturation generation rates. The difference in the product CSD arise from the variations of supersaturation profiles experienced by the elementary volumes throughout their sojourn. Characterization of mixing in a real crystallizer at some intermediate levels is emphasized with the aid of relevant industrial examples.
Performance of an RTL contactor for gas‐liquid systems: Effective interfacial area and volumetric mass transfer coefficient by oxidation of sodium sulphite solution
Authors: Alper Erdogan , Abu‐Sharkh Basel
Published: August 2005

Effective interfacial area a and volumetric liquid‐side mass transfer coefficient kLa of an RTL contactor were obtained at different stirring speeds by absorption of oxygen from air into 0.8 kmol/m3 sodium sulphite solution, in the presence of Co++ ions. The values of a and kLa ranged from 80 to 150 m2/m3 and 0.0003 to 0.00053 s−1, respectively, when stirrer speed was increased from 8 to 40 rpm. When kL alone was evaluated, it was found to be practically constant, irrespective of stirring speed.
IR study of chlorination of alumina employing mixtures of gaseous chlorine and carbon monoxide
Authors: Rohner Markus Ch. , Sharma Virendra K. , Richarz Werner
Published: August 2005

The chlorination of an alumina with BET surface area of 100 m2/g has been studied in situ by transmission IR measurements at about 670 K. The chlorinating gases consisting of Cl2 and CO were employed individually and in equimolar proportion. The IR results do not reveal the presence of a phosgene surface species which could support the only mechanism proposed so far to explain the chlorination. A detailed alternative reaction mechanism is suggested for the high temperature chlorination reaction, taking into account the IR results, together with the known electron donor‐acceptor properties of the activated alumina and the reaction gases: Cl2 molecules accept electrons from oxide ions with a lower coordination number on the alumina surface, leading to the formation of Cl−and Oad. While Cl− yields AlCl3, Oad reacts further with CO producing CO2.
Separation of liquid from vapour upon pressure relief
Authors: Muschelknautz Sebastian , Mayinger Franz
Published: August 2005

When a chemical reactor is depressurized or pressure in a vessel, filled with saturated liquid, has to be decreased, generally both vapour and liquid flow out through the relief valve. Since chemical reactors are usually operated with toxic and explosive fluids, the discharged liquid which vaporizes on the ground around the vessel may reach dangerous concentrations, causing explosions or accidents with the poisonous gas. During a research project, some fundamentals were developed for the design of separation systems which separate liquid from vapour and store it in a receiver. The requirement for a separation efficiency of a least 80% is related to the condition that the separated liquid should flow back into the reactor still during the pressure relief phase. For safety reasons, both separation and re‐storage are to be carried out without the supply of external energy. Theoretical and experimental investigations of pressure distribution within the piping to the relief valve and in an integrated separator show that re‐storage of the separated liquid in the vessel can be achieved under certain flow conditions. Therefore, the separator must be integrated in the pipe at a certain height above the vessel, so that the hydrostatic pressure of the separated liquid, corresponding to the difference in height, is sufficient to lead it back through another pipe against the internal pressure of the vessel. First, several separators were tested with air‐water mixtures. A swirl separator and a reversing separator have been developed to such an extent that they appear suitable for the set task. Experimental results with air‐water mixtures and refrigerant R12 upon pressure relief show separation efficiencies of between 90 and 100% at low pressure drops within the whole operating range. As an alternative to separation outside the vessel, a rotary separator was also developed which is fixed to the outlet opening in the vessel. A centrifugal field is produced by the separator rotor and the heavier liquid is largely separated from the vapour so that only drops in the range < 100 μm flow together with the vapour towards the central standpipe. The outflowing vapour leaves the separator via 4 tangentially arranged nozzles, under critical conditions. The vapour flow momentum drives the separator rotor. The arrangement was developed and tested during various series of experiments, under conditions or pressure relief with refrigerant R12. So far, separation efficiencies between 60 and 95% have been achieved at stirring speeds of up to 2500 min−1.
Increase in viscosity and its influence on polymerization processes
Authors: Moritz Hans Ulrich
Published: August 2005

In the course of polymerization in homogeneous systems, the viscosity of the reaction mass increases by several orders of magnitude. The viscosity increase is affected by reaction conditions, concentration and properties of the formed polymer. Empirical correlations for homogeneous and heterogeneous polymerizations are given. Viscosity significantly affects the polymerization kinetics as well as heat, mass and momentum balances of the polymerization reactor. The influence of viscosity and its increase on conductive heat transfer, stirrer power input and cooling capacity, molecular diffusion and mass transfer coefficients, mixing time and residence time distribution in homogeneous and heterogeneous polymerizations in stirred tank and tubular reactors is reviewed.
Simulation of sintering of model supported metal catalysts
Authors: Wanke Sieghard E. , Lynch David T.
Published: August 2005

During the past decade, the sintering of model supported metal catalysts, i.e. catalysts consisting of metal deposited on very thin and flat oxide films, has been intensively investigated by transmission electron microscopy. In the current paper, a mathematical model, based on an atomic migration mechanism, for the sintering of these catalysts is presented. The predictions of the model, based on Monte Carlo simulations, are in very good agreement with the experimental observations, i.e. phenomena such as ‘apparent’ particle migration, splitting and neck formation between particles are predicated by the model.
Combined process treatment of molasses fermentation waste water for biogas generation
Authors: Azzam Abdel Mouty , Abdel‐Shafy Hussein I. , Ibrahim Mohamend Z.
Published: August 2005

Anaerobic fermentation of molasses distillery slops to biogas was carried out with the aid of an adapted and selected anaerobic mixed culture. Two different types of fermenters were used, namely an agitated pretreatment fermenter and a column fermenter with glass rings as carriers for micro‐organisms. The production of biogas in both fermenters amounted to between 0.6 and 0.8 dm3/g COD. The aerobic pretreatment of distillery slops by T. fermentans, yeast during a 4 to 6 h period allows a high reduction of COD in the subsequent anaerobic phase of the process. After treatment of the distillery slops by T. fermentans, it was possible to convert between 85 and 93% of the organic matter to methane. Conversion was about 93% with loading rate of 25g COD/litre day.
Determination of size and stress intensity factors for leaks in nozzle attachments
Authors: Wiedemann Gerhard , Strohmeier Klaus
Published: August 2005

The prediction of leak areas in pressure vessels is an important objective in the safety analysis of chemical plants. Using suitable design rules, a leak‐before‐break behaviour can be achieved. This contribution outlines a procedure for the leak‐before‐break design of nozzle attachments and the determination of the size of the corresponding opening area. In addition, K1‐factors and leak areas for a number of nozzle geometries have been calculated and plotted.
Conversion of methanol to light olefins over zeolite H‐T
Authors: Gubisch Dietmar , Bandermann Friedhelm
Published: August 2005

The conversion of methanol over zeolite H‐T was investigated in a fixed bed reactor. H‐T was prepared from Na‐T by ion exchange with HCl and NH4Cl solutions. The HCl solution caused appreciable dealumination. High yields of ethene were obtained with NH4Cl exchangeed zeolites Na‐T with 45% decationization, high proprne yields with low HCl or NH4Cl Exchanged catalysts. Low methanol partial pressures and short residence times favoured the formation of lower olefins. Lowest coking rates were observed at a reaction temperature of 693 K. The catalytic activity decrased slowly with the number of reaction/regeneration cycles. The distribution of procucts > C2 could be described by the most probable distribution of Schulz and Flory.
Advances in modelling and design of multitubular fixed‐bed reactors
Authors: Stankiewicz Andrzej
Published: August 2005

This paper presents a method mathematical modelling of cocurrent multitubular fixed‐bed reactors. The method is adapted to the most widespread type of industrial reactor design, i.e. the system fitted with disk‐and‐doughnut baffles. The proposed model makes it possible to estimate the influence of non‐uniformity of the heat carrier flow on the reactor characteristics, taking into account the coolant streams by‐passing via the tube‐to‐baffle clearances. Based on the model, the effect of the operating parameters as well as of some more important geometrical parameters of the reactor on an exemplary highly exothermic process of partial benzene oxidation to maleic anhydride is discussed.
Effects of turbulence on heat and mass transfer in stagnation flows
Authors: Kottke Volker
Published: August 2005

The influence of turbulence on local heat and mass transfer is systematically analyzed. Essential prerequisite is the availability of measurement methods, based on convective mass transfer, which allow the visualization of heat and mass transfer distributions. The results show that, even at low turbulence intensities, the flow and transport phenomena are decisively influenced by the specific design of turbulence grids and the orientation of the grid wires with respect to the stagnation line. Thereby, two different flow mechanisms occur which may interact. The anisotropy of grid turbulence leads to the “wire‐gap effect” depending on the actual position of the grid wires in relation to the stagnation line. The other mechanism is based on the wavy wake velocity distribution behind screens and grid which, in conjunction with the centrifugal instability of stagnation flows, may lead to longitudinal vortices. The results indicate why turbulence has not been sufficiently considered in the available (semi‐) empirical correlations. Information needed for an accurate prediction of heat and mass transfer in turbulence flows is discussed.
Model concept of floc disintegration in centrifugal fields
Authors: Kleine Ulrich , Stahl Werner
Published: August 2005

A model of floc destruction resulting form mass forces in a centrifugal field is postulated and its validity examined. This model is to be regarded as a supplement to the existing shear‐loading disagglomeration models. In order to verify this additional floc disintegration mechanism, appropriate investigations were carried out with flocculated suspensions of silica and Hamburg dock sludge. As a result, in addition to floc disintegration by shear forces within a turbulent flow and in the centrifuge inlet, the existence of another mechanism was demonstrated. This consists in the floc destruction in a centrifugal field where particles in excess of a certain size, or specifically heavier components, are preferentially torn out of the floc. This floc disintegration by mass forces can lead to a classification effect in centrifuges which also subject the flocs to instant high centrifugal forces.
Dispersion behaviour of droplets in circular loop reactors
Authors: Tanaka Masato , Hosogai Kazuhiko , Sendai Takami
Published: August 2005

A circular loop reactor was built for application to a heterogeneous liquid‐liquid reaction. In order to investigate the dispersion behaviour of droplets in the reactor, basic experiments were performed using a number of liquid‐liquid dispersions. Droplets discharged form the impeller region were found to grow due to coalescence in the circulation region. Mean droplet diameter decreased exponentially with elapsing time. An expression correlating the steady‐state mean droplet diameter with the operating conditions was derived. Moreover, the transition time required for the droplet diameter to reach the equilibrium value was determined and correlated with the operating conditions.