bluuebunny/crossref_metadata_2025 huggingface dataset:
Flow characteristics of large oscillating drops in liquid‐liquid systems
Authors: Al‐Hassan Tariq , Mumford Clive James , Jeffreys Geoffrey Vaughan
Published: August 2005

A study was made of the flow characteristics of large oscillating drops of pure liquid‐liquid systems, using a thermostatically‐controlled, rising drop column, 50 mm in diameter and 1000 mm in length. Mirrors in the jacket enabled front and side views of drops to be photographed simultaneously. Single drops in the size range 5–10 mm were investigated with both mutually‐saturated phases and when the solute was being transferred from the dispersed phase. The systems studied were (1) toluene and acetone (dispersed)‐water (continuous), and (2) n‐heptane and acetone (dispersed)‐water (continuous). Acetone concentrations were varied up to 3.75 kmol/m3. The oscillations of a travelling drop were asymmetrical; therefore, the amplitude cannot be expressed accurately in terms of only two axes. The area change of the drop compared to that of a sphere of equal volume ‘ε’, was shown to represent the amplitude accurately. The periods of droplet oscillation were uniform for the mutually saturated systems of constant physical and flow properties but changed when mass transfer was taking place. The interfacial tension exerted a marked effect on the amplitude, which also depended upon the oscillation frequency. The amplitude changed with droplet size in a similar manner to the terminal velocity, i.e. it increased with increasing size until it reached a maximum, subsequently decreasing less rapidly. The drag coefficient increased with increasing rate of mass transfer from the drop. Correlation of the results and the area eccentricity ‘ε’ by dimensional analysis embracing all possible parameters and physical properties affecting drop oscillation, resulted in the correlation ε = 0.22 Sr0.42 We−0.53 M0.13 with a mean deviation of ± 14%. This will facilitate more accurate prediction of the interfacial area for mass transfer calculations, relating to equipment containing droplets in the oscillating regime.
Decrease of diffusion coefficients near binodal states of liquid‐liquid systems
Authors: Hampe Manfred Josef , Schermuly Wolfgang , Blaß Eckhart
Published: August 2005

This work investigates the thermodynamically based assumption that diffusion at binodal states of unstable fluid systems vanishes. It is shown experimentally that a scaling law, which describes the fall in diffusion near critical points, may also be applied in an extended form to its abatement at the limits of solubility. These results may profoundly affect the modelling of mass transfer between phases whose bulks exhibit states of saturation.
Operation data of a directly fired absorption heating unit with periodically operating absorber
Authors: Knoche Karl‐Friedrich , Seitz Carl‐Werner , Zerres Hilarius
Published: August 2005

This contribution presents the layout, construction, and experimental investigation of operation behaviour of a directly fired absorption heating unit with periodically operating absorber. The working system is CH3OH‐LiBr/LiOH. The unit is designed to generate a maximum heat load of 10 kW. The field of application is mainly in domestic heatIng. A special feature of the absorption heating unit is the provision of the major part of required process heat in the heat pump mode of operation with high efficiency. At extremely low ambient air temperatures, heat is supplied in the direct mode. A numerical simulation routine is also described. The simulation program describes both steady‐state and dynamic processes in the unit. With models for each component, the performance of individual components can be studied and optimized. The results presented here consist of the first experimentally obtained efficiencies in direct heating mode, results of numerical simulation of the component generator, and a comparison of measured and predicted characteristic system temperatures.
Adaptive pole removal control for a batch polymerization reactor
Authors: Wang Feng‐Sheng , Lin Yunng‐Chin
Published: August 2005

A systematic method of controller design is introduced to determine the overall charcteristic behaviour developed on process pole removal. The time delay compensation is automatically incorporated in the proposed control law. The implemented tuning parameters in the law are confined to the range between 0 and 1 to guarantee the stability of the overall control system. Subsequently, the fixed and adaptive control strategies are implemented to simulate a batch PVC reaction system. The adaptive control scheme provides good, roubust control of this simulated reactor notwithstanding the wide range of operating conditions and non‐linear dynamics of the system. However, the fixed control scheme performs well only for a noise‐free system. In addition, two limiting control laws, derived from the proposed method, are also used to simulate the reactor. The results indicate that these laws are not suitable for this non‐linear reaction system.
Cocurrent vacuum de‐aeration of water for injection into oil reservoirs
Authors: Lydersen Aksel L.
Published: August 2005

Conventional vacuum stripping to reduce the oxygen content of injection water for secondary recovery of oil is carried out in packed columns with the released gases and water flowing countercurrently; hence large column diameters (normal liquid load circa 100 m3/(m2h)) and foaming that requires the addition of defoaming agents. Measurements with cocurrent and countercurrent flow at the same flow rate produced practically identical mass transfer coefficients. With flooding excluded in cocurrent flow, columns can be operated with higher liquid loads than in countercurrent flow. In addition, nitrogen released in the top part of the packing is better utilized as stripping gas, and foam is withdrawn as soon as it increases the pressure drop.
Electrochemical impedance spectroscopy of oxygen and hydrogen evolution on amorphous alloys in 1 M KOH
Authors: Kessler Teresita , Vilche Jorge R. , Ebert Michael , Jüttner Klaus , Lorenz Wolfgang J.
Published: August 2005

The mechanisms of oxygen and hydrogen evolution on amorphous alloys G 14 (Fe60Co20Si10B10) and G 16 (Co50Ni25Si15B10) in 1 M KOH at T = 298 K and 333 K were studied by electrochemical impedance spectroscopy (EIS). Comparative measurements were carried out on polycrystalline Pt electrodes. Impedance spectra in the frequency range 10−3 Hz ≤ f ≤ 104 Hz were analyzed to determine the kinetic behaviour of amorphous alloys by application of transfer function analysis, using non‐linear fit routines. The EIS‐data are interpreted in terms of consecutive reaction mechanisms for both oxygen and hydrogen evolution.
Absorption of nitric oxide in dilute nitric acid
Authors: Weisweiler Werner , Eidam Klaus , Thiemann Michael , Scheibler Erich , Wiegand Karl Wilhelm
Published: August 2005

This paper presents laboratory‐scale measurements on the absorption of nitric oxide in dilute nitric acid. The NO concentration in the gas feed varied from 250 to 10 000 ppm. Nitrogen was used as carrier gas. The concentration of nitric acid was between 30 and 60 mass‐%. Temperature during the measurements was set at 25 °C. In order to determine mass flow rates, experiments were performed in a double‐stirred cell. This type of absorber has a defined gas/liquid interface as the mass transfer area. The liquid phase is introduced periodically and the gas phase continuously. A well‐known model was used to describe the phenomenon of NO absorption. Several balance equations were established and solved. The calculated mass transfer rates were compared with those obtained experimentally. The empirical and theoretical data are in satisfactory agreement.
Photosensitive materials for use in velocity profile measurements in the water phase of air‐water systems and in single phase liquid systems
Authors: Douglas Peter
Published: August 2005

Those chemical and photochemical characteristics of a photochromic system which are necessary for successful application to flow visualization studies in water are identified. The properties of a number of photochromic and photosensitive systems are discussed, and critically examined, with regard to these requirements.
Simulation of a distillation column on an IBM PC, accounting for real behaviour of electrolyte solutions
Authors: Bosen André , Roth Manfred
Published: August 2005

This contribution demonstrates the possibility of using a thermodynamic description of electrolyte solutions directly for computer simulation of distillation columns. Coefficients are determined for a combination of a solvation model with a local composition equation for the activity coefficient. The use of one set of coefficients yields good results of calculation of vapour pressure, vapour phase composition and caloric data of hydrochloric acid. Solution of material and heat balance equations of distillation columns is achieved on an IBM PC with the above description. Two illustrative examples of an absorption and a rectification calculation are presented
Dynamic behaviour and simulation of a liquid‐liquid extraction column
Authors: Hufnagl Harry , McIntyre Michael , Blaß Eckhart
Published: August 2005

Dynamic behaviour of a stirred liquid‐liquid extraction column was studied experimentally. Various input variables of the column were varied stepwise and the resulting variations in the system and output variables were measured. In addition to experimental work, a computer model was developed on the basis of the dispersion model to simulate the dynamic behaviour of the extractor. This model forms a component program of the dynamic process simulator DIVA, developed at the TU Stuttgart. The experiments showed that the hydrodynamic parameters exhibit no significant dynamic behaviour of their own. Therefore, changes occurring in these parameters closely follow variations in input and system variables. As a result, steady‐state relationships for the calculation of flow parameters could be used in the simulation program. The simulator satisfactorily reproduced the experimental results for a number of disturbances. However, this was not always the case. As shown in the following, the model did not take into account the column level controller which, under certain conditions, exerts a very strong influence on the column's dynamic behaviour. As a result, larger differences occurred between experimental and simulated data. This influence on the extractor's dynamic behaviour can, however, be eliminated by a simple modification of the level controller arrangement.
Calculation methods for multicomponent adsorption equilibria
Authors: School Stephan , Schachtl Martin , Sievers Werner , Schweighart Peter , Mersmann Alfons
Published: August 2005

The knowledge of multicomponent adsorption equilibria is of great importance for the industrial design and application of adsorptive purification and separation processes. As the experimental determination of the required data is time‐consuming and costly, theoretical help is desirable. This contribution presents and assesses the most common theoretical approaches to the calculation of multicomponent adsorption equilibria. The models are based on the assumption of an adsorbed solution, extension of the volume filling of micropores theory or statistical thermodynamics. These models are applied to different adsorptive/adsorbent systems with ideal and non‐ideal equilibrium behaviour. It is established that, at low coverages of adsorbent surfaces, all theories provide good estimates of the adsorbed phase composition and total loading while, at high saturations, no model is completely satisfactory.
Simulation of fluidized‐bed reactors for catalytic oxidative coupling of methane to C2‐hydrocarbons
Authors: Mleczko Leslaw , Andorf Renato , Baerns Manfred
Published: August 2005

The “bubble assemblage model” of Kato and Wen was applied to simulate the catalytic oxidative coupling of methane to C2‐hydrocarbons in a fluidized bed reactor. Simulation results were compared to experimental data obtained in a laboratory‐scale fluidized bed reactor. To improve the accuracy of predictions, the influence of fluid bed hydrodynamic and kinetic submodels was investigated by applying a sensitivity analysis. It was shown that the most important element in the model is the applied reaction scheme; the consecutive reactions of C2 hydrocarbons occurring most probably in the gas phase should be considered.
Trichlorosilane chlorination in a multiphase multicomponent photoreactor
Authors: Schirmeister Reinhard , Hoffmann Ulrich
Published: August 2005

The photochemical reaction SiHCl3+Cl2→SiCl4+HCl is of industrial importance in the production of pure silicon for the semiconductor industry. The present paper deals with an experimental investigation of the kinetics of this purification step. The main reaction occurs in the liquid phase and is initiated by light. In this gas‐liquid reaction system, all components, which are present in both phases, were analyzed by gas chromatography. Reaction progress was monitored by recording the pressure rise. Apart from the influence of wavelength and radiation intensity on the above photoreaction, reactions in the absence of light and on the wall were also investigated.
Chemical reaction fouling of organic fluids
Authors: Watkinson A. Paul
Published: August 2005

Chemical reaction fouling of heat exchangers involves deposition that is caused by chemical reactions which occur in the fluid, or on the surface itself. The factors which influence fouling of organic fluids via autoxidation and thermal decomposition processes are described and the dependence of the rate of thermal fouling on chemical effects and process variables demonstrated. Mitigation techniques are outlined in brief.
A new method for determining the efficiency of tray columns with downcomers
Authors: Koziol Antoni , MaćKowiak Jerzy
Published: August 2005

A new method for determining the efficiency of columns with sieve, sieve‐valve, valve, bubble cap and tunnel trays is introduced, taking into consideration entrainment, weeping and mixing of liquid on the tray. The presented calculation concept is valid for any stripping factors and any quality of liquid mixing on the tray. A comparison of the new calculation concept with experimental data from literature resulted in an average relative deviation of approx. 8% between the sieve tray efficiencies. The comparison of calculated values with experimental data for sieve‐valve, valve and tunnel trays also produced a satisfactory agreement.
Thermodynamic conditions for the formation of dioxin
Authors: Spencer Philip John , Neuschütz Dieter
Published: August 2005

The thermodynamic data bank system THERDAS [1, 2] has been used in conjunction with the program ChemSage [3] to calculate the conditions necessary for the formation of 2,3,7,8‐TCDD (tetrachlorodibenzodioxin). The stability ranges of both gaseous and condensed dioxin are presented as functions of the chlorine content, C/H mole ratio, oxygen partial pressure and temperature of the system.
Adsorption of p‐nitrophenol from aqueous solution on activated carbon: Influence of pH and preozonization
Authors: Serrano Vicente G´mez , Beltrán Fernando J. , Segovia Antonio Durán
Published: August 2005

The adsorption of p‐nitrophenol (PNP) from an NaOH, H3PO4‐buffered, aqueous solution on activated carbon was studied at pH 2, 7, and 8.5. Comparative studies were then carried out on ozonized carbon and ozonized PNP solution. In the latter case, PNP adsorption was performed from an ozonized solution, and also after exposing the activated carbon to the ozonized PNP solution for 24 h. At acid pH, PNP adsorption was found to be markedly higher than at neutral and weakly basic pH's. Ozonization of carbon affects the results only at pH 7 and 8.5. Ozonization of PNP led to a small decrease in adsorption, irrespective of the method of contect between carbon and ozonization reaction products. The rate was faster at acid than at basic pH, and the ozonization speeded up the adsorption slightly but only at pH 8.5. Application of a mathematical model indicated that mass transfer in bulk solution controls the rate of adsorption.
Determination of intraparticle transport parameters for multicomponent adsorption
Authors: Carl Petra Sabine , Seidel‐Morgenstern Andreas
Published: August 2005

This paper is devoted to the problem of determining intraparticle transport coefficients for multicomponent adsorption from experimental kinetic curves. Due to thermodynamic and kinetic interactions between the mixture's components, this task is more difficult than for single component systems. As an example, the kinetics of adsorption on activated carbon of binary mixtures of phenol and indole from aqueous solutions was studied in a continuous stirred tank adsorber (CSTA). To describe the intraparticle transport of this system, the surface diffusion model using a linear driving force (LDF) was applied. For determining the matrix of the unknown kinetic parameters of the LDF‐model, the application of three independent mathematical methods is discussed. Firstly, a semi‐analytical calculation (SA) of the intraparticle transport parameters by solving a system of linear equations on the basis of an empirical description of experimental kinetic curves is put forward. Secondly, a non‐linear regression (NR) method for parameter estimation was applied. The third method is a non‐linear regression which, in contrast to the SA and NR methods, guarantees the stability of the system of differential equations in the steady state of the process (NRS).
Useful experimental technique for the study of heterogeneous reactions
Authors: Bjerle Ingemar , Xu Fuming , Ye Zhicheng
Published: August 2005

The heterogeneous CaO/SO2 reaction has been thoroughly investigated by developing a series of new experimental techniques including the TGA reactor, the volulmetric reactor and the entrained flow reactor. The heterogeneous system is designed in such a way that most of the gas film and pore diffusion resistances are reduced. The modelling of each step related to the reaction is discussed while the chemical reaction and product layer diffusion are emphasized as the main influences on the SO2removal. The unchanging size shrinking core model is used to describe the reaction progress with a two stage assumption which has been confirmed in the TGA reactor: first, a very fast surface reaction, followed by a product layer diffusion controlled reaction. It was found from the experiments that the SO2‐partial pressure aat the very beginning is very important for a high removal efficiency during the initial reaction period.
Estimation of dispersion coefficients in packed beds
Authors: Foumeny Esmail A. , Chowdhury Masrur A. , McGreavy Colin , Castro Jose A. A.
Published: August 2005

The design and performance of fixed beds are greatly influenced by fluid dispersion. Unfortunately, the existing design data do not provide an accurate picture of this phenomenon. This paper presents an attempt to characterize the dispersive features of packed beds by obtaining reliable estimates of the associated coefficients in the axial (DL) and radial (DR) directions. Such an objective is achieved by developing a representative two‐dimensional pseudo‐continuous dispersed flow model which is subsequently employed to compute the desired coefficients using data obtained from a refined experimental approach. The established values have been correlated to allow such coefficients to be reliably predicted under a variety of physical and operating conditions.
A study of mass transfer from single large oscillating drops
Authors: Al‐Hassan Tariq , Mumford Clive James , Jeffreys Geoffrey Vaughan
Published: August 2005

A study was made of mass trasfer rates from single large oscillating drops of pure liquid‐liquid systems, in the size range of 5 to 10 mm. A thrermostatically‐controlled, 50 mm in diameter, 1000 mm long, rising drop column was used, in which mirrors in the jacket enabled front and side views of drops to be photographed simultaneously. The systems studied were (1) toluene and acetone (dispersed)‐water (continuous), and (2) n‐heptane and acetone (dispersed)‐water (continuous). High concentrations of acetone (up to 3.75 kmol/m3) were used to examine the effect of different parameters on the mass transfer rate, frequency and amplitude of oscillation in countercurrent operation. Previous theories and empirical correlations [2–6, 12, 13, 15] for the prediction of overall mass transfer coefficients showed large deviations from measured values. These may have aarisen because the models do not represent droplet oscillation accurately, and/or apply only to oscillations of small droplets. Fair agreement was obtained for small oscillating droplets as low solute concentrations. The oscillations of a travelling drop were asymmetrical; the period of oscillation was uniform for mutually‐saturated systems but changed when mass transfer was taking place. The periods were longer than those predicted by the Lamb [7] and Shroeder and Kintner [37] correlations. Terminal velocities predicted from literature correlations [32, 34] did not give reasonable agreement with experimental data when there was mass transfer of solute. The drag coefficient increased with increasing mass transfer rate from the drop. Correlation of the results and the dispersed phase mass trasfer coefficients by dimensional analysis resulted in the correlation

List of symbols at the end of the paper.

with a mean deviation of ±23%, by insertion of experimental oscillation frequency data. This will facilitate more accurate prediction of the dispersed phase mass transfer coefficients relating to equipment containing droplets in the oscillating regime, e.g. pulsed columns or agitated tanks.
Development and start‐up of a fixed bed reaction column for manufacturing antiknock enhancer MTBE
Authors: Flato Jörg , Hoffmann Ulrich
Published: August 2005

A laboratory fixed‐bed reaction column is presented, in which a heterogeneouslyl catalyzed reversible fluid‐phase reaction and the separation of the reaction product from unreacted or inert components by distillation are performed simultaneously. The rection studied, the formation of methyl tertiary butyl ether (MTBE) from methanol and isobutylene, is catalyzed by strongly acidic macroreticular ion exchange resins. Packing elements are Raschig rings, manufactured for the first time from the above‐mentioned ion exchange resins. This in‐house made catalyst shows practically the same ion exchange capacity as the commercial products. The control system installed in the equipment is capable of correcting strong disturbances os the steady state. As shown by expwrimental results, the superimposed distillation process occurs in such a way that the chemical equilibrium of the MTBE synthesis does not limit isobutylene conversion.
Production of methylamines over ZK‐5 zeolite treated with tetramethoxysilane
Authors: Fetting Fritz , Dingerdissen Uwe
Published: August 2005

The reaction of methonol with ammonia over catalysts, used commercially today, to give methylamines, does not occur with the desired dimethylamine selectivity. Both a thermodynamically and kinetically controlled reaction over conventional catalysts permits a maximum dimethylamine selectivity (DMA selectivity) of only about 30 mol‐%. In addition to monomethylamine (MMA), a large amount of the undesirable trimethylamine (TMA) is formed. By using zeolites and taking advantage of their shap‐selective properties, it is possible to achieve high MMA and DMA selectivities. Shape‐selective catalysis can only take place at catalytically active centrs in the inteerior of the por system. The proportion of non‐shape‐selective catalysis at the active centres on the outer surfaces of zeolites is not negligible. Treatment of ZK‐5 zeolite with tetramethoxysilane deactivates the outer surface of the crystallite and increases the shape‐selectivity of the ZK‐5 zeolite with rgard to the amination reaction. Computer simulation of the zeolite skeleton in conjuction with investigations of the reaction leads to some conclusions with respect to the reaction mechanisms and reaction sites.
Design of vessels subjected to external pressure
Authors: Diwakar Chengalvala , Rao Yadavalli Bhaskar , Parlikar Ram Nagesh
Published: August 2005

An analytical procedure, developed to simulate the graphic method for the design of vessels subjected to external pressure or vacuum, suggested by the ASME Code, Section VIII, Division 1, is presented in this contribution. A comprehensive computer program based on this method is also presented. The program also covers the design of stiffener rings. The procedure can be easily extended to include other international standards such as the British and German codes, since the method is based on the concept of the number of lobes at collapse. The method produced reproducible results over the entire range of L/D0 and D0/t ratios of the code. The deviation observed at any point in this range is less than 0.5% for factor A. The variation in allowable pressure is less than 2%.
Sensitivity to phase equilibrium data in the simulation of a hydrogen purifying column
Authors: Campanella Enrique A.
Published: August 2005

The impact of phase equilibrium data on the simulation of a hydrogen purifying column has been evaluated. The analysis was performed in two stages. First, the most sensitive binary system was obtained. Then, it was verified if further experimental data were necessary for a reasonable simulation. The calculations were carried out using both rigorous and short‐cut methods.
Mixing characteristics in the torus reactor
Authors: Belleville Pascal , Nouri Lhadi , Legrand Jack
Published: August 2005

The hydrodynamic characteristics of propeller‐induced toroidal flow in a loop reactor were investigated by performing an RTD analysis. The experimental determination of circulation time allows the calculation of the mean axial velocity with respect to the rotational speed of the impeller. RTD measurements are interpreted with the aid of the dispersion plug flow model, and it is shown that axial dispersion is relatively weak in the torus reactor. The mixing time was also determined experimentally and related to the circulation time. A direct relationship between mixing time and axial dispersion coefficient has been established, leading to a correlation for the mixing time in a torus reactor.
Comparative studies of dehydrocyclization of n‐octane and iso‐octane on bifunctional and monofunctional Pt/Al2O3 catalysts
Authors: Ako Churchill T. , Susu Alfred A.
Published: August 2005

The dehydrocyclization of n‐octane and iso‐octane to ethyl benzene, and ortho‐, para‐, and meta‐xylenes was investigated on mono‐ and bifunctional platinum/alumina catalysts in a microcatalytic reactor with hydrogen as carrier at 1.8 atm pressure and between temperatures of 573 and 763 K, using pulse technique. On bifunctional Pt/Al2O3 catalyst, the total conversion of both n‐octane and iso‐octane was found to start from a high value and decrease with increasing temperature for all pulse volumes investigated. However, iso‐octane was found to be more reactive than n‐octane. There was only one primary product, namely iso‐octane, in the n‐octane reaction. As regards the iso‐octane reaction, two primary products, ethyl benzene and o‐oxylene were identified. For both reactions, these primary products decreased to a minimum as temperatures increased. On monofunctional (non‐acidic) Pt/Al2O3, the total conversion of n‐octane increased with temperature and passed through a maximum. The primary products of the reaction were ethyl benzene and o‐xylene.
A learning feedforward control strategy for the concentration control of recycle reactors. Part II: Disturbance control
Authors: Schnitzlein Klaus , Löwe Arno
Published: August 2005

A disturbance control scheme for the concentration control of differential recycle reactors is developed which is based on the learning feedforward control strategy. Steady‐state decoupling eliminates interactions between the closed loops of this non‐linear, multivariable control system, thereby significantly improving the response to disturbances. Since the process model is iteratively updated, the control strategy can be regarded as a model identification adaptive control. Simulation experiments show the performance of the overall control concept.
Binary ion exchange equilibrium for Ca2+, Mg2+, K+, Na+ and H+ ions on amberlite IR‐120
Authors: de Lucas Martínez Antonio , Cañizares Pablo , Díaz Jacinto Zarca
Published: August 2005

Experimental data are reported for ion exchange equilibria of binary systems on Amberlite IR‐120 resin, at different temperatures and total ionic concentrations in aqueous solutions. These systems exhibit non‐ideal behaviour in both phases, and the equilibrium characterization has been based on the law of mass action, using Wilson and Meisssner, and Kusik equations to correlate the activity coefficients in the resin and aqueous solutions, respectively. Equilibrium constants, standard thermodynamic properties (Gibbs free enthalpy changes, enthalpy and entropy) and Wilson binary parameters were obtained as functions of temperature.
Biocatalytic treatment of waste air
Authors: Wittorf Falko , Klein Joachim , Körner Klaus , Unterlöhner Othmar , Ziehr Holger
Published: August 2005

Biological processes are becoming increasingly popular in dealing with waste air problems. Compared to chemical and physical treatment methods, they offer several advantages, especially in handling of waste air contaminated with low concentrations of biodegradable organic and, occasionally, inorganic substances. Two types of commercial systems are currently in use: biofilters and bioscrubbers. The aim of our studies was to develop an innovative concept of reactor design and engineering called “biocatalyst” (Biokatalysator). Our biocatalytic three‐phase system lies in between the conventional biofilter and bioscrubber, using biomass immobilized on macroporous, tubiform supports installed in parallel to the air flow. In laboratory‐scale investigations, a bioreactor was continuously fed with solvent‐laden air, which produced a more cost‐effective mode of operation than the conventional bioscrubber systems.
Mass transfer in packed columns: The cylinder model
Authors: Bornhütter Klaus , Mersmann Alfons
Published: August 2005

In order to predict mass transfer in packed columns, it is necessary to know the interfacial area. The well‐known and often cited equation (Onda, Kolev, Zech, etc.) do not yield precise values for the mass transfer coefficient βL ae or the interfacial area ae, especially for modern packing elements. A new model will be presented which takes into account the structure of packing (cylinder model) as well as the structure of the liquid hold‐up. This model allows the separation of liquid flow through packings into its main constituents, i.e. rivulets and drops (freely falling). The determination of the structure of liquid flow allows the prediction of effective interfacial areas as well as of volumetric mass transfer coefficients for irrigated large packing elements manufactured from plastics, metals or ceramic. The applicability to novel future packings is one of the advantages of the new model.
Influence of recycling on mass transfer and reaction in a G‐L jet loop reactor with variable interfacial area
Authors: Warnecke Hans‐Joachim , Prüss Jan , Tamm Günter , Brinkmann Manfred
Published: August 2005

The effect of recycling on mass transfer, characterized by the volumetric mass transfer coefficient kLa, was investigated by absorbing CO2 into water in a laboratory jet loop reactor. Based on a mathematical model, which includes the correlation function kLa = kLa(rL), a first order chemical reaction and the variation of interfacial area, a = a(εG), caused by strong absorption effects, the interaction ‘recycling – mass transfer – reaction’ was simulated and its influence on the reactor performance is discussed.
A general method of designing gas and gas‐liquid injectors using laws of turbulent jet mixing
Authors: Rao Natti S. , Kremer Hans
Published: August 2005

Based on the equation for entrainment of a turbulent free jet, a simple method of designing gas and gas‐liquid injectors is presented. Using the formula for mass flow ratio of an injector consisting of a nozzle and a short cylindrical mixing tube open at both ends, a general equation for designing any injector with variable geometry and flow resistances is given. The optimization procedure is outlined. Compared to the conventional design of injectors, starting from macroscopic mass and momentum balances, the present method is much simpler, easily applicable and involves only one empirical entrainment coefficient. It is particularly advantageous in the case of variable density of the motive and entrained fluids since the density ratio appears explicitly in the relevant equations.
Gas and solids mixing in a commercial FCC regenerator
Authors: Wei Fei , Lin Shixiong , Yang Guanghua
Published: August 2005

Mixing of gas, solids and heat in a commercial FCC regenerator, 5.76 m in diameter, was investigated. This regenerator was operated at a high superficial gas velocity (>1.2 m/s) and high temperature (650–710°C). It is classified as a highly efficient regenerator. The profiles of coke content in the catalyst, gas composition, temperature and pressure were obtained by sampling and instrumental measurement. It was confirmed that a proposed axial dispersion model could be used for a satisfactory prediction of these experimental profiles. The values of gas and solids dispersion coefficients are also presented.
Quantitative rate equations for change of phase
Authors: Kasai Takeshi
Published: August 2005

A new set of rate equations for gas desorption has been derived from the laws of thermodynamics and motion and the kinetic theory of gases. The equations assume that gas desorption or absorption originally represents an isothermal change at the interface, similarly to condensation or vaporization. The mass transfer in gas desorption or absorption is initially caused by external work being done on the system and takes place as work done by the system which instantly develops a concentration gradient, increases in internal energy and temperature, and a deviation from the ideal gas behaviour inside MTZ in the process of mass transfer. After cessation of external work, these conditions disappear following the transfer of a small residual mass at a constant velocity and a decrease in internal energy inside the MTZ.
Experimental investigations of flow, turbulence and subspace formation on cold models of gas‐stirred reactors with a view to describing mixing processes by mathematical models
Authors: Jank Gerhard , Nonte Thomas , Steinmetz Eberhard , Wilhelmi Herbert
Published: August 2005

Theoretical and experimental investigations were performed with cold water models of bottom‐blown metallurgical ladles in order to develop a mathematical description of the mixing processes in such reactors. This analytical model is based on the subdivision of the reactor into interacting subspaces, whereby each subspace is regarded as an ideal mixer. The convective mass transfer between the subspaces is represented by constant coupling coefficients, and the mass balance for the material to be mixed in provides a homogeneous system of differential equations to determine the time dependence of concentration in the individual subspaces. Different combinations of interacting subspaces are represented. The flow field and the distribution of turbulence intensity measured by LDA in water models and the concentration profiles in mercury models measured by EMF cells show that a subdivision into five subspaces is adequate. Size, position and interaction coefficients are also determined by experiments. The calculated mixing times agree well with those measured.
Determination of operating characteristics of agitators in tubes
Authors: Rieger František , Weiserová Hana
Published: August 2005

Operating characteristics of an agitator in a tube are necessary for the calculation of its pumping capacity and power consumption in a given configuration. General dimensionless equations for pumping and power characteristics are presented which were derived by inspection analysis of basic equations. Experimental procedure for the determination of these characteristics is put forward. This procedure is based on the measurement of flow rate or pressure rise and power consumption for an agitator in a draft tube, calandria or closed tube. The measurements and their evaluation are illustrated on the example of a three‐blade screw agitator.
Kinetics of coal desulphurization by Acidianus brierleyi
Authors: Olsson Gunnel , Larsson Liselotte , Holst Olle , Karlsson Hans T.
Published: August 2005

Acidianus brierleyi was demonstrated to remove pyritic sulphur from coal. A. brierleyi was also found capable of catalyzing the removal of what is normally reported as organic sulphur from coal 171US34. A kinetic analysis was performed by assuming a first order reaction. The first order kinetics allowed a comparison with literature data for Thiobacillus ferrooxidans. Also, formation of jarosite was taken into account in the analysis. The simple first order kinetics was observed to fit the data on removal of sulphur satisfactorily.
A multi‐step kinetic model for phenol oxidation in high‐pressure water
Authors: Tufano Vincenzo
Published: August 2005

A kinetic model for the oxidation of phenol in high‐pressure water has been developed and compared with experimental data taken from literature. The model assumes a chain reaction propagated by O⋅ and OH⋅. Production of the hydroxyl radical by the reaction of atomic oxygen and water induces a chain‐branching effect, which is particularly effective at low temperatures and high pressures. The proposed model gives a fair correlation of the experimental data in the whole examined temperature and pressure range and appears significantly better than a simpler, power‐law kinetic model. The relibility of the model is strengthened by the consideration of values obtained for the kinetic parameters (in particular for the activation energies) which compare well with the literature.
A mathematical model of dehydroisomerization of methylcyclopentane using a bifunctional catalyst blend
Authors: Dittrich Joachim , Keil Frerich J. , Luus Rein
Published: August 2005

A mathematical model of dehydroisomerization of methylcyclopentane in presence of bifunctional catalysts under industrial operating conditions is presented. The model consists of six differential equations. The rate constants are expressed as polynomial functions of the catalyst blend, and coefficients of these polynomials were determined from numerous measurements, taken along the axis of a tubular reactor. The resulting polynomial coefficients led to reaction rate constants which yielded results close to the actual process.
Fluid phase equilibria in the system hydrogen sulphide‐water at high pressure. Application of an extended Henry's law
Authors: Carroll John J. , Mather Alan E.
Published: August 2005

Henry's law is often used to correlate the solubility of a gas in water. Such an approach is frequently employed to calculate the solubility of hydrogen sulphide in water. However, Wright and Maass [1] clearly demonstrated that the strict Henry's law did not apply to the solubility of hydrogen sulphide in water. That is, the solubility of hydrogen sulphide is not directly proportional to its partial pressure, even at seemingly low pressures. By accounting for the non‐idealities in the vapour phase, Carroll and Mather [2] showed how a simple modification of Henry's law could be used for moderate pressures (up to 1 MPa). In this paper, a further extension of Henry's law is used to model the vapour‐liquid equilibrium at higher pressures and temperatures. It is also applied to liquid‐liquid and vapour‐liquid‐liquid equilibria, areas where Henry's law is rarely used.
A learning feedforward control strategy for the concentration control of recycle reactors. Part III: Implementation and operation
Authors: Schnitzlein Klaus , Bolze Klaus , Löwe Arno
Published: August 2005

In order to verify its performance, the learning feedforward control strategy was applied to the catalytic methanation of CO‐rich synthesis gas. Details of the implementation in hardware as well as in software are discussed. The experimental results confirm the functionality of the learning feedforward control. Suggestions are given for further improvement of the control strategy.
Controlled precipitation
Authors: Mersmann Alfons , Angerhöfer Martin , Franke Jürgen
Published: August 2005

In a process of precipitation, two or more reactants form a product. In many cases, the solubility of this product is very low and high supersaturation is generated which leads to nucleation and crystal growth. The number of the formed nuclei and their growth govern the particle size distribution of the precipitate. As a rule, the precipitate is separated from the mother liquor in a centrifuge or on a filter. This separation and the subsequent drying process of very fine particles can be very expensive with respect to investment and energy costs. Therefore, it is desirable to produce as coarse a precipitate as possible with a narrow crystal size distribution.
Kinetic studies on high temperature desulphurization of synthesis gas with zinc ferrite
Authors: Karlegärd Åsa , Bjerle Ingemar
Published: August 2005

The desulphurization of synthesis gas with zinc ferrite was studied in a laboratory‐scale fixed‐bed reactor. Desulphurization efficiency of 97–99% was obtained. The inlet hydrogen sulphide concentration was about 2600 ppm. A flat breakthrough curve showed that diffusion through the sulphide layer controlled the rate of sulphidization. The degrees of utilization varied between 5 and 11%. Experimental data formed the basis of a kinetic evaluation with the fixed bed model and the unreacted core model. Rate constants, reaction orders, and effective diffusion constants were calculated. When chemical reaction controlled the rate, the order of reaction was between zero and unity. The rate of reaction increased with temperature. Effective diffusivities were of the order of 10−5 m2 s−1, increasing slightly in the temperature range between 500 and 600°C. The activation energy was determined as 54 kJ mol−1, which corresponds to an unexpectedly strong temperature dependence of the diffusion‐controlled reaction. The low degrees of utilization, and also the strong temperature dependence, are explained by sintering of the sulphidized zinc ferrite.
HCl formation via pyrolytic degradation of polyvinyl chloride (PVC): An empirical approach to kinetic modelling
Authors: Bisi Marco , Nicolella Cristiano , Palazzi Emilio , Rovatti Mauro , Ferraiolo Giuseppe
Published: August 2005

The pyrolysis of polyvinyl chloride (PVC) has been described in terms of a relatively simple kinetic model, based on a large number of laboratory tests. The model predictions are in a good agreement with experimental data, regarding hydrochloric acid and non‐condensable combustible gases. Therefore, the proposed model can be used to predict with good approximation the distributions of the above classes of compounds, in the whole range of applied experimental conditions.
Estimation of the drying rate and moisture profiles in an industrial spray dryer by means of experimental investigations and a simulation study
Authors: Fieg Georg , Wozny Günter , Buick Kurt , Jeromin Lutz
Published: August 2005

A spray dryer simulation program is described. It is based on the known conservation laws and permits determination of temperature and moisture profiles and droplet trajectories inside spray dryers. An industrial spray dryer used in the manufacture of detergents serves as an example to demonstrate the applicability of the program; this approach required prior experimental determination of the flow field and an axial temperature profile. On the basis of a rough estimate of the drying rate in the spray dryer, good agreement was observed between experiment and simulation.
Study of drop‐interface coalescence: Drainage time measurement
Authors: Kourio Maria Julia , Gourdon Christophe , Casamatta Gilbert
Published: August 2005

An automatic apparatus has been developed and set up for the study of drop‐interface coalescence. Most other studies have concentrated on events when the drop arrives at the interface with its terminal velocity. In our case, the drop is maintained fixed at the tip of a needle, and the interface is moved towards the drop at a controlled speed. The coalescence times are measured by means of a vectorial video camera focused on the drop. Several times are measured by means of a vectorial video camera focused on the drop. Several parameters have been investigated, such as the drop diameter, the relative drop‐interface velocity, the phase system, the presence and the direction of mass transfer.
A general simulation model of batch chemical reactors for thermal control investigations
Authors: Cabassud Michel , Lann Marie‐Véronique Le , Ettedgui Boaz , Casamatta Gilbert
Published: August 2005

This paper describes the development of a dynamic simulation model for stirred tank batch or semi‐batch chemical reactors fitted with an alternative heating‐cooling system. Heat and mass balances are established for the reactor and its jacket. Since the general purpose of our research is the thermal control of these reactors, special attention is devoted to the behaviour of the heating‐cooling system. In this article, we are particularly concerned with an alternative system, i.e. different fluids at a constant temperature can be alternatively delivered to the jacket. The computer simulation programme is flexible, enabling simulation of a batch or semi‐batch reaction vessel, ranging from a laboratory pilot plant to a full‐scale production plant. A control algorithm is included which allows reactor operation with open or closed‐loop temperature control. To demonstrate the good performance of the simulation model, experimental results are presented for both a pilot plant and an industrial reactor.
Crystallization process optimization using artificial neural networks
Authors: Woinaroschy Alexandru , Isopescu Raluca , Filipescu Laurentiu
Published: August 2005

This paper presents a new procedure for optimization of continuous mixed suspensionmixed product removal (MSMPR) crystallizing systems. Owing to the difficulties of theoretical modelling, simulation of the MSMPR crystallization process is based on the use of artificial neural networks (ANN). The optimization criterion is a compound objective function corresponding to an intended mean crystal size dimension and a minimal dispersion. The presence of multiple local minima has called for investigation by several optimization techniques. Ultimately, Luus' and Jaakola's random adaptive method proved to be most effective. The results obtained lend support to the general procedure proposed.
Unsteady two‐film model for mass transfer
Authors: Wang Jinfu , Langemann Horst
Published: August 2005

The classical two‐film model for mass transfer between two fluid phases can only be used to describe the steady state mass transfer mechanism. Both the penetration and the film‐penetration model are also valid solely when only one diffusion boundary layer exists at the interface between the phases. With a view to surmounting the limitations of the above models a new model has been developed for the mass transfer between two fluid phases with two diffusion boundary layers at the interface. The new model is based on the two‐film concept and the Danckwerts distribution function, and is also able to simulate the unsteady state mass transfer mechanism between two fluid phases with two different boundary layers.