bluuebunny/crossref_metadata_2025 huggingface dataset:
Rear surface deposition of fine particles on spheres — eddy deposition or electrostatic effects?
Authors: Dau Güunter
Published: August 2005

The aim of this investigation is to show the demarcation of two possible mechanisms for surface deposition of fine particles on the rear surface of single spheres. By means of single particle trajectory computation, based on numerically determined flow fields (Remax = 103), it is shown that the mere existence of a wake is not in itself sufficient to produce eddy deposition. In addition, the particle's motion must undergo a lateral transfer promoted by fluid trubulence, in order to effect eddy deposition commencing at a Reynolds number of about 100. On the other hand, rear deposition, influenced by electrostatic forces, especially by the Coulomb force, is possible at any Reynolds number. Consequently, for Reynolds numbers of less than 100, only electrostatic effects can produce rear surface deposition. In the range of high Reynolds numbers, the coexistence of both mechanisms is possible. Very high Reynolds numbers (Re > 103) and low Stokes numbers indicated the predominance of the electrostatic effect over eddy deposition, whereas at very high Reynolds numbers and medium to high Stokes numbers the electrostatic effect is only predominant in presence of high electrostatic charges.
Theory and application of an alternative correlation flowmeter
Authors: Braun Hans , Füg Michael , Schneider Georg
Published: August 2005

Correlation flowmeters have been used in the scientific field for many years and are actually gaining greater commercial importance due to an increasing number of applications in industrial plants. The importance of the correlation method is based on the fact that essentially no alternatives exist for measuring velocity and mass flow rate in pneumatic conveyors. However, the hitherto employed transit time correlation method leads to results which are clouded by uncertainties. The commonly used theoretical model of the measurement process does not explain these effects satisfactorily. Therefore, the theory of non‐intrusive flow sensors is reinvestigated from a physical standpoint. The derived model permits a discussion of the transit time correlation method in some detail. Furthermore, this model leads to an alternative sensor arrangement and signal processing scheme which makes it possible to measure the true mean velocities. Examples of experimental results are given.
Calo‐visco‐densimeter: A multipurpose apparatus
Authors: Zech Helmut , Knapp Helmut
Published: August 2005

A multipurpose apparatus was designed, built and operated with the aim of a simultaneous determination of enthalpy of mixing, heat capacity, kinematic viscosity and density of liquid mixtures at 240 < T < 370 K and 1 < p < 25 bar. Its operation was monitored by a PC. Details of design and the first experimental results are presented.
Effect of some operating variables on the flotation of aluminium particles
Authors: Abdo Mohamed S. E. , Darwish Amina M.
Published: August 2005

The effects of impeller speed, air flow rate, cell concentration, agitator size and cell volume on the recovery of aluminium particles have been studied in a KHD Humboldt Wedge AG machine, using alkyl benzene sodium sulphonate paste as collector and pine oil as frother. The recovery yield increased with increasing impeller speed, air flow rate, cell concentration and cell volume, up to a certain range, whereafter it decreased. A decrease in the recovery yield was observed on increasing the agitator size. A mathematical model has been developed to correlate percentage recovery with the above variables.
An automatic laboratory reactor for homogeneous polymerization of methyl methacrylate
Authors: Budde Uwe , Reichert Karl‐Heinz
Published: August 2005

An automatic stirred tank reactor of laboratory scale has been developed for on‐line measurement of conversion, viscosity, and molar mass distribution of homogeneous polymerizations. For these on‐line measurements, a fraction of the reaction mixture is bypassed through a densimeter and a viscometer. Samples are taken at intervals of 15 min, diluted semi‐automatically, and then injected into a high performance gel permeation chromatograph for determination of the molar mass distribution of the polymers. A microcomputer collects the measured data, calculates the monomer conversion and the output data for different control units. In this study, methyl methacrylate is polymerized batch‐ and semi‐batchwise with ethyl acetate as solvent and in the presence of different initiators. The semi‐batch polymerizations are carried out at constant reaction rate by feeding the initiator and at a given increase in viscosity by feeding the solvent.
Two‐phase flow and mass transfer in scrubbers
Authors: Schmidt Burkhard , Stichlmair Johann
Published: August 2005

Experimental investigations were carried out in spray scrubbers of different sizes with cocurrent flow of gas and liquid. Of special interest were the local processes in the mass transfer zone. The scrubber was operated with warm water/air system (cooling tower) to obtain detailed information about mass transfer. Air is being humidified with water vapour, which in turn leads to a temperature drop in the liquid. The liquid temperatures are relatively easy to measure and are shown as liquid isotherms. In the case of plug flow, the liquid isotherms should be straight horizontal lines. In reality, significant deviations from plug flow are caused by the transfer of liquid to the walls. A large part of the liquid forms a film flow at the wall. Furthermore, nearly all the mass transfer is completed in the zone of liquid atomization immediately beneath the nozzle. The number of measured transfer units was between 0.5 and 2.0 and was significantly influenced by the liquid flow rate. Based on the improved knowledge of the proceses inside the scrubber, a simplified model has been developed. Since the model simulates all the essential processes inside the mass transfer zone, liquid distribution and mass transfer efficiency can be approximately predicted.
Thermally safe operation of a semibatch reactor for liquid‐liquid reactions–fast reactions
Authors: Steensma Metske , Westerterp K. Roel
Published: August 2005

Accumulation of the reactant supplied to a cooled semibatch reactor (SBR) will occur if the mass transfer rate across the interface is insufficient to keep pace with the supply rate. Then, due to a low starting temperature or supercooling, the reaction temperature does not rise fast enough to the desired value. This accumulation may eventually lead to a temperature runaway. We investigated the possibility of such an event for reactions of the type “chemically enhanced mass transfer” or “fast” and found that only low distribution coefficients, i.e. 10−4 or lower, can lead to accumulation. At higher distribution coefficients, the mass transfer rate across the interface of a well‐mixed dispersion is generally sufficient to prevent accumulation. A thermal runaway in the fast regime exerts a moderate effect, because the effective activation energy is halved. Calculations for the “instantaneous” reaction regime, regarded as a special case of fast reactions, show that there is no runaway possible.
Mass transfer during the removal of dissolved heavy metals from wastewater flows in fluidized beds of ion exchange resins
Authors: Zarraa Mahmoud A.
Published: August 2005

A fluidized bed of cation exchange resin was used for the removal of cupric ions from a simulated wastewater effluent consisting of copper sulphate solution. Variables investigated were: superficial liquid velocity, particle diameter, bed height and copper sulphate concentration. These variables were studied with respect to their effect on the solid‐liquid mass transfer coefficient. The coefficient was found to increase with increasing superficial liquid velocity. Increasing particle diameter, bed height and copper sulphate concentration were found to reduce the mass transfer coefficient. The experimental data can be correlated by the equation

equation image

valid for the following conditions: 0.23 < Re1 < 2.27; 0.52 < ϵ < 0.87; 0.0127 < dp/d < 0.0417 and 0.0095 < dp/L < 0.125.
Experimental studies on parametric sensitivity of a batch reactor
Authors: Haldar Raghunath , Rao Damaraju Phaneswara
Published: August 2005

Runaway behaviour of exothermic reactions in a batch reactor has been studied experimentally on the example of acetic anhydride hydrolysis catalyzed by sulphuric acid, in a 700 ml batch reactor. High parametric senstivities of peak reactor temperature with respect to initial reactor temperature and catalyst concentration were obtained.
Experimental studies on semibatch reactor parametric sensitivity
Authors: Haldar Raghunath , Rao Damaraju Phaneswara
Published: August 2005

Runaway behaviour of an exothermic reaction in a semibatch reactor was studied experimentally on the example of hydrolysis of acetic anhydride catalyzed by sulphuric acid, in a 700 cm3 thinwalled stainless steel stirred reactor, 10.2 cm in diameter and 13.0 cm high. The reactor was partially immersed, to a depth of 2.1 cm, in a thermostatic bath, in order to obtain sufficiently rapid cooling of its contents. A reaction run was performed by first introducing water, acetic acid and sulphuric acid into the reactor. After the contents attained bath temperature, acetic anhydride at room temperature was fed to the reactor for a fixed time period, at a constant flow rate. When water was present in excess of the stoichiometric requirement and addition of acetic anhydride completed before the reactor attained peak temperature, the system showed sensitivity to coolant temperature and sulphuric acid concentration. When the reactants were present in stoichiometric quantities and addition of acetic anhydride was completed after the reactor attained peak temperature, the system did not exhibit any significant parametric sensitivity.
Experimental and analytical study of countercurrent flow limitation in vertical gas/liquid flows
Authors: Stephan Martin , Mayinger Franz
Published: August 2005

An experimental and analytical study of adiabatic countercurrent flow limitation (flooding) in single vertical ducts is reported. The experiments were carried out in a rectangular channel using saturated liquid and vapour of Refrigerant 12 (CCl2F2). The steady‐state liquid delivery (flooding) curves as well as local pressure drop and void fraction distributions in the countercurrent flow were measured in a range of system pressures from p/pcrit = 0.16 to p/pcrit = 0.31, and for various total liquid injection rates and locations. The measured flooding curves j1 = f(jg) as well as pressure drop and void fraction during partial liquid delivery (j1 < j1in) were not affected either by the axial liquid feed location or by the excess liquid rate carried upwards by the vapour. Moreover, for given flow conditions during flooding pressure drop and void fraction were essentially the same at different axial positions. Radial void fraction distributions evaluated from optical fibre probe data indicate an annular‐type flow pattern. Based on this experimental evidence, a mechanistic core/film flow model was developed for the calculation of flooding. The analytical results are compared with the present high pressure and with comparable atmospheric pressure experimental data, showing reasonable overall predictions not only of the flooding curves, but also of the pressure drop in countercurrent flow.
Design algorithm for rotating disc contactors
Authors: Kłeczek Fryderyk , Niedziałkowski Włodzimierz , Kaczmarski Krzysztof
Published: August 2005

An algorithm is presented for computing the diameter and length of RDC columns, based on the analysis of literature data and the results of author's own investigations.
Mass transfer improvements in single phase in regular packings
Authors: Colazo Jorge A. , Böhm Ursula
Published: August 2005

Two ways of enhancing liquid to solid mass transfer in regular packings are proposed and investigated: the introduction of a fluidized bed of inert particles and of turbulence promoters by constructing the packing from expanded metal. It is shown that both systems can be of considerable benefit in improving the mass transfer performance: up to 200% in the first case and up to 130% in the second case. However, the energy dissipated by fluidized particles is excessive in comparison to that consumed by turbulence promoters.
Physical properties of the NO‐absorbing system cupric chloride‐tributyl phosphate
Authors: Yavuz Ömer Nafi , Gestrich Wolfgang
Published: August 2005

For pure tri‐n‐butyl phosphate (TBP) as well as solutions of cupric chloride in TBP and for mixtures of TBP with n‐decane or solutions of cupric chloride therein, the density, viscosity, physical solubility of nitric oxide (NO) and its diffusion coefficient have been determined and a discussion is presented
Crystallization of potash alum in an MSMPR crystallizer
Authors: Synowiec P. , Sangl R. , Mersmann A.
Published: August 2005

New data are presented on the crystallization of potash alum (KAl(SO4)2·12H2O) from solution, in a continuously operating MSMPR cooling crystallizer, 61 in volume. Population density distributions were determined by sieve analysis. Highly polydispersed product was obtained, with median crystal size, L50, in the range between 264 and 607 μm. Suspension density was varied between mT = 7 and 98 kg/m3. The results were evaluated according to an attrition model and the obtained kinetic efficiency should be valid for other types of crystallizers.
Experimental validation of a packed bed distillation model
Authors: Karlström Anders , Breitholtz Claes
Published: August 2005

A mathematical model of a packed bed distillation column is presented and applied to a binary system in a full scale industrial distillation column with structured packings. The model is reduced by orthogonal collocation to sets of ordinary differential and algebraic equations. A linearized large state space model is then obtained and further reduced by the optimal Hankel norm method in order to obtain a model of manageable size. The model is studied under three different operating conditions in order to cover the feasible operating ranges during the experiments. The experiments carried out with a monoethanolamine‐diethanolamine system show a good agreement with the model implying that a control design based on the model is satisfactory. It is also shown that the control configuration to be used can be easily analyzed by the model, since different input and output structures can be studied. Furthermore, models based on one‐film and two‐film theories are compared in the frequency domain and show that, due to its simplicity, the one‐film theory should be used in control design.
Local heat transfer and heat flux distributions in finned tube heat exchangers
Authors: Schüz Gerhard , Kottke Volker
Published: August 2005

A detailed analysis of the effect of local heat transfer distributions, which were determined experimentally, on temperature distributions in the fins and in the fluid between two adjacent fins of finned tube heat exchangers is presented. The heat transfer distributions, obtained by a mass transfer technique, prove to be very inhomogeneous over the fin surface, leading to variable results for fin efficiency calculated by the conventional method. In addition, the effect of temperature variation in the fluid, which is usually neglected in fin analysis, is shown in many cases to exert a very strong influence on fin efficiency and total heat flux. For the optimization of fin designs, a combined analysis of local heat transfer, conduction resistance in the fin and temperature variation in the passage is indispensable.
Xanthan production in stirred tank fermenters: Oxygen transfer and scale‐up
Authors: Herbst Holger , Schumpe Adrian , Deckwer Wolf‐Dieter
Published: August 2005

The microbial polysaccharide xanthan was produced by cultivation of Xanthomonas campestris in four stirred tanks with volumes ranging from 0.072 to 3 m3. Many of the previously suggested correlations for the volumetric mass transfer coefficient described the present data very unsatisfactorily. When Rushton turbines were employed as stirrers, the experimental results agreed well with a correlation suggested by Kawase and Moo‐Young; for the more energy‐efficient INTERMIG impellers, this correlation was modified by a factor of three. Constant specific oxygen transfer rate was found to be the appropriate scale‐up criterion for constant space‐time yield and constant product quality, specifically, the molar mass which determines the viscosity yield.
Modelling of mass transfer phenomena of associated systems in packed distillation columns
Authors: Savkovic‐Stevanovic Jelenka
Published: August 2005

Mass transfer between liquid and vapour phases in packed distillation columns has been investigated by the two‐film theory for binary associated systems. The effects of association reaction in systems with the association of one component in both phases, taking into account a concentration‐dependent liquid‐phase association constant, were examined. The mass transfer coefficients are modelled, taking into account the association constant. The experiments were carried out at atmospheric pressure with acetic acid‐benzene and acetic acid‐toluene systems in a column packed with Rasching rings.
Liquid homogenization in agitated tanks
Authors: Rzyski Edward
Published: August 2005

This paper presents a very simple model of liquid homogenization in a mixing tank. The model, based on the pumping capacity of impellers and the degree of homogeneity, is valid for turbulent mixing; however, it has been extended to transient regime of mixing (Re = 100 to 1000).
Comparison of single and double inert tracer fluctuation measurements in a continuous stirred tank
Authors: David René , André Christophe
Published: August 2005

A comparison is made between two different methods using laser induced fluorescence spectroscopy for measuring local concentration fluctuations in the same stirred tank. The first method using a single inert fluorescent tracer yields a segregation index quite different from that determined by the second method, which requires two inert tracers, a fluorescent one and a fluorescence quencher. By recalling the theoretical background, it is demonstrated that the characteristic segregation indices should be equal for the experiments under consideration. According to the discussion, it is likely that the double tracer method gives more reliable results.
Targeting for CO2emissions for Total Sites
Authors: Linnhoff Bodo , Dhole Vikas R.
Published: August 2005

This paper describes an approach based on the concepts of Pinch Technology for Total Site targeting for fuel and power. If specific CO2emissions for fuel and power are known, the approach will also target for CO2emissions for any given site in the industry. The approach takes account of the trade‐offs between process fuel and steam, between steam, site fuel and cogeneration, and of fuel mix. A case study is described where an 18% reduction in global CO2emissions is possible through the correct use of these trade‐offs.
Fuzzy sets. Introduction to theory and applications in process engineering
Authors: Kraslawski Andrzej , Nyström Lars
Published: August 2005

Fuzziness is quite a different notion from probability. Probability describes the objective uncertainty obtained on the basis of a large number of observations. Fuzziness describes the uncertainity that has a subjective meaning. Fuzzy notions describe the degrees of possession of a given property. The popularity of fuzzy set theory in solving control problems results from its ability to treat some situations which are difficult to deal with by the classical control theory. Fuzzy sets are used to control ill‐defined, complex, non‐linear systems. There are two aspects of this phenomenon. The first aspect concerns the descriptive ability of fuzzy sets. The second important feature is the applicability of fuzzy sets to work with incomplete, contradictory and subjective information. Fuzzy set theory is becoming increasingly important tool in the new fast developing disciplines of artificial intelligence: expert systems and neural networks. It creates completely new opportunities for the application of fuzzy sets in chemical engineering.
Studies on parametric sensitivity and safe operation criteria of batch processes
Authors: Papayannakos Nikos G. , Koufopanos Charalambos A. , Karetsou Ageliki
Published: August 2005

Heat accumulation in batch reactors may eventually lead to a temperature runaway. Critical values of process parameters were used to investigate process safety. Parameter sensitivity is discussed for a wide range of operating conditions. Two criteria for safe operation are presented, based on critical values of process parameters.
Conversion of ethanol over metal‐exchanged zeolites
Authors: Schulz Jürgen , Bandermann Friedhelm
Published: August 2005

The effects of metal exchange between zeolites and alkali metals (Li, Na, K; zeolite Y, ZSM‐5, T), alkaline earths (Mg, Ca, Sr, Ba; ZSM‐5), transition metals (La, Ce, Cr, Mn, Fe, Co, Ni, Pd, Cu, Zn; ZSM‐5) and aluminium (ZSM‐5) on the conversion of ethanol were studied. Activities of the catalysts and selectivities for ethene, C3+ olefins, paraffins and arenes strongly depended on the cation, chosen for the modification. Only ethene was formed by alkali exchanged zeolites, the most active being Li‐Y. This could be confirmed by a long‐term ageing test with Li‐Y pellets under semi‐industrial conditions. The exchange of ZSM‐5 with alkaline earths or transition metals permitted the formation of a wide variety of products, raning from high ethene to high aromatic yields. A correlation between certain product selectivities and electronegativity was only possible in a rough approximation.
A study of phase equilibria sensitivity in the 1,1,1‐trichloroethane–1,2‐dichloroethane separation by distillation
Authors: Quiroga Mónica E. , Campanella Enrique A.
Published: August 2005

The sensitivity of the plate number and reflux ratio to the description of vapour‐liquid equilibria in the 1,1,1‐trichloroethane–1,2‐dichloroethane separation was calculated via case studies. Published experimental data are not sufficiently accurate to satisfy an adequate overdesign of the distillation column. On the other hand, the data are suitable for the design of an extractive distillation.
Defect structure of metal oxides at high temperatures
Authors: Paladino Ombretta
Published: August 2005

High temperature oxidation of some metals contained in special alloys has been studied. Defect models for pure an doped CoO and pure NiO were developed and fitted to electrical conductivity data. The models involve different kinds of theoretically possible complex defects with different numbers of vacancies and interstitials forming a cluster. Equilibrium constants for defects formation have been estimated using an algorithm based on the constrained variation method that allows fitting of data to implicit models involving errors in all the measured variables. Results indicate the presence of a significant concentration of complex defects in CoO at high temperatures, while confirming the rather small concentration of these defects in NiO.
Inertial impaction of aerosol particles on single and multiple spherical targets
Authors: Hähner Frank , Dau Günter , Ebert Fritz
Published: August 2005

Inertial deposition of aerosol droplets (diameter: 1–14 μm) on steel spheres (diameter: 3–9 mm) was investigated. Air velocity was varied between 7 and 28 m/s (corresponding sphere Reynolds numbers: 1400–17000). The impaction on single spheres as well as that on linear arrays of eight spheres was measured. Theoretical results, based on potential flow investigations were verified by single sphere experiments. Of special interest was the range of lower Stokes numbers, where the theoretically predicted limit of deposition cannot be verified. The experiments on sphere arrays were for the first time performed in the low Stokes number range. Deposition on the leading sphere, relative to that on the shielded spheres, exhibits a maximum in the high Stokes number range, but this changes drastically in the low Stokes number range. Here, maximum deposition can be found on the shielded spheres while the leading sphere shows a markedly lower deposition.
Continuous computer controlled production of formate dehydrogenase (FDH) and isolation on a pilot scale
Authors: Weuster‐Botz Dirk , Paschold Holger , Striegel Bernd , Gieren Holger , Kula Maria‐Regina , Wandrey Christian
Published: August 2005

A continuous production process has been developed up to pilot scale (300 l) for FDH production with the methylotrophic yeast Candida boidinii. A high cell mass specific FDH activity (50 U/g) is achieved by process computer controlled supply of pure methanol to operate the reactor at an optimum methanol concentration of 10 g/l. The maximum FDH spacetime yield achievable with this process control involves a residence time of 7 h. The FDH space‐time yield (STY) and FDH concentration are a function of the oxygen transfer rate (OTR) of the fermenter (maximum STY = 255 U/(l h) at kLa = 870 l/h). For a reasonable compromise between high FDH space‐time yield and high FDH concentration, an optimum residence time is adjustable by regulating the supply of nutrient salt solution in relation to the OTR of the fermenter. On a pilot scale (200 l continuously stirred tank reactor) roughly 4 million U of FDH were produced within 10 days at a residence time of 14.3 h. Isolation of intracellular FDH enzyme was performed using extraction with an aqueous two‐phase system (PEG/K2HPO4). A technical product quality of 1.2 U/mg FDH was achieved without any chromatographic purification step.
Kinetics and mechanisms of reaction between carbon disulphide and morpholine in aqueous solutions
Authors: Alper Erdogan , Bouhamra Walid
Published: August 2005

The reaction in aqueous solutions between carbon disulphide and morpholine has been studied experimentally at 303 K using a conductimetric stopped‐flow technique. The observed pseudo‐first order rate constant does not vary linearly with amine concentration but follows the equation:

.

This equation is compatible both with (i) zwitterion intermediate and (ii) single‐step termolecular reaction mechanisms which were previously proposed for the corresponding reactions of CO2 and COS. Values of rate constants kAm and kw at 303 K are also reported.
Reduction of diesel particulate emissions by catalytic filtration
Authors: Hoffmann Ulrich , Rieckmann Thomas
Published: August 2005

Several kinds of diesel soot filters and filter materials of high melting points with eleven different catalytic coatings were prepared. They were calcined at a maximum temperature of 1000°C. The reaction rate and the kinetic parameters of the combustion of diesel soot were determined in a closed loop laboratory reactor. A packed bed of alumina particulates was the most active filter in soot combustion. Catalytic coatings with oxides of vanadium, copper or cerium accelerated the reaction. In each case the effect of the coating was dependent on specific interactions between the catalyst and the filter material. The manner of filtration and the nature of the soot filter are found to be more important for the overall result than the nature of the catalytic coating.
Reaction engineering simulations of a fluidized‐bed reactor for selective oxidation of fluorene to 9‐fluorenone
Authors: Mleczko Leslaw , Pannek Ulrich , Baerns Manfred
Published: August 2005

The catalytic oxidation of fluorene to 9‐fluorenone in a fluidized‐bed reactor was investigated by modeling of the reactor and simulation of its performance. The “Bubble Assemblage Model” of Kato and Wen, the “Bubbling Bed Model” of Kunii and Levenspiel and the “Countercurrent Backmixing Model” of Potter were applied. From a comparison of simulation results obtained by the various fluidized‐bed models and a fixed‐bed model conclusions were drawn about the influence of interphase mass transfer and gas backmixing on the conversion of fluorene and slectivity of 9‐fluorenone formation. Furthermore, the dependence of conversion and selectivity on temperature and hydrodynamic conditions was investigated. In particular, the implications of a change of hydrodynamic conditions for scale‐up were analysed. The highest yield of 9‐fluorenone predicted for a bench‐scale fluidized bed amounted to 88% (XF = 97%, SNON = 91%). This yield was lower than in a fixed‐bed reactor (YNON = 92%, XF = 99%, SNON = 93%). A further drop of the yield was predicted when scaling‐up from a bench‐scale reactor to a commercial size unit (YNON = 54%, XF = 86%, SNON = 63%).
Pyrolysis of propane at reflected shock‐wave temperatures from 1300 to 2700 K
Authors: Wami Emenike N.
Published: August 2005

Shock tube pyrolysis of propane at temperatures between 1300 K and 2700 K at reflected shock pressures of 500 to 1500 kN/m2 has been investigated. The reaction is of 1st order with a rate constant K = 1.79 × 108 exp (‐176.2 kJ/RT) s−1. The major reaction products were acetylene, ethylene and methane, while traces of propylene and ethane were only detected at temperatures below 1500 K. At higher temperatures, propane conversion to acetylene increased at the expense of the other products. Optimum conversions to ethylene and methane, in contrast to that to acetylene, were more sensitive to changes in temperature than to variations in reaction time. However, at reaction pressures above 550 kN/m2, extension of reaction time beyond 0.5 ms did not favour the formation of acetylene. A simple kinetic model which confirmed the experimental optimum product selectivity conditions is put forward.
Mass transfer and reaction behaviour of a circulating fluidized bed reactor
Authors: Vollert Joachim , Werther Joachim
Published: August 2005

This contribution presents a chemical reactor model of a circulating fluidized bed (CFB) which takes into account adsorption effects and provides a description of the vertical profiles of gas concentration in the riser. The oxidation of NO is used as an example of a heterogeneous catalytic reaction. Mass transfer between the gas phase and solid particles in the CFB was investigated at various temperatures and solids mass flow rates. The measurements show that the mass transfer coefficient decreases with increasing solids mass flux and that the CFB resembles a bubbling fluidized bed as regards gas‐solid contacting.
Optimal experimental procedures in a combined TPR/TPO apparatus
Authors: Jouguet Bernadette , Gervasini Antonella , Auroux Aline
Published: August 2005

The apparatus described allows successive TPR/TPO experiments on the same sample. A calibration method for the reducing or oxidizing gas mixture is described. The best operating conditions for optimal results and sensitivity are discussed. We have studied the application of TPR/TPO to bulk V2O5 and to the redox behaviour of CuII ions on silica‐alumina. The procedure resulted in reproducible TPR/TPO profiles.
Rotational particle separator: A new method for separating fine particles and mists from gases
Authors: Brouwers Bert
Published: August 2005

An account is given of the patented technique of the rotational particle separator for separating solid and liquid particles of diameter 0.1 μm and larger from gases. Attention is focused on the working principle, fluid mechanical constraints, particle design, separation performance, power consumption, dimensions, filter cleaning and costs. Furthermore, an overview is given of current developments to introduce this technique in industrial dust removal, in electricity generation and in the consumer goods market. The article concludes with a summary of the feature which distinguish this technique from existing filtering methods.
Sulzer BX gauze: Fluid dynamics and absorption of acid gases
Authors: Nardini Giuliano , Paglianti Alessandro , Petarca Luigi , Viviani Elena
Published: August 2005

The aim of this work is a fluid dynamics study of the structured packing Sulzer BX gauze. A new model is proposed which, on the basis of a knowledge of the dynamic component of the liquid holdup, permits calculation of the fraction of the geometric area of the packing that effectively participates in the mass transfer. Both the metal and plastic versions of the packing are studied. Experimental data are supplied on the absorption of pollutants such as HCl and SO2 by aqueous solutions of NaOH in columns in cocurrent operation. The results obtained by the proposed model are in good agreement with experimental data obtained by the present authors as well as with experimental data published in the literature.
A review of some parameters involved in fluidized bed bioreactors
Authors: Wright Phillip C. , Raper Judy A.
Published: August 2005

Three‐Phase fluidized bed bioreactors have advantages over conventional chemical reaction systems. There is a lack of agreement over most major operational conditions, and a wide range of design variables are open to question. A large body of recent work in the field has been reviewed, with a degree of historical comparison and discussion.

It has been found that aspects of fluidized bed biofilm reactors of vital importance include: choice of solid media, gas and liquid loadings, bacterial type and reactor mechanical design. A large proportion of the work in the field of three‐phase fluidization is non‐biologically specific, or not tested on a bacterially inoculated system.

The majority of three‐phase fluidized bed bioreactor work is in the field of water treatment. Although this work has highlighted the potential for use of bio‐fluidized beds for this application, there are still specific problems hindering the large scale industrial acceptance of three‐phase fluidized bed bioreactors.
An investigation of the phase transformations in a CaSO4/(NH4)2SO4/H2O system, directed at the preparation of a fine dispersed purified phosphogypsum
Authors: Bojinova Darinka , Gruncharov I.
Published: August 2005

The process of recrystallization of apatite phosphogypsum (PHG) in a solution ammonium sulphate (AS) with the subsequent decomposition of the binary salt was investigated and the resulting highly dispersed products with a low P2O5 content have been discussed. The following effects were examined: (NH4)2SO4 concentration, the quantity of ammonium sulphate, the reaction temperature of phosphogypsum with (NH4)2SO4 solution, the time of treatment of phosphogypsum with (NH4)2SO4 solution and the decomposition of the binary salt, as well as the liquid/solid ratio for the binary salts, Based on the results of the chemical and X‐ray analysis, it was established that, depending on the technological conditions of the process of recrystallization, binary salts of (NH4)2SO4·CaSO4·H2O and of (NH4)2SO4·CaSO4·H2O and of (NH4)2SO4·5 CaSO4·H2O were formed. As a result of the investigations carried out, a product with a low P2O5 content, suitable for direct processing to secondary products has been prepared.
Behavior of three‐way catalyst in a hybrid drive system
Authors: Padeste Lukas , Tagliaferri Sergio , Baiker Alfons
Published: August 2005

The dynamic behavior of a Pt‐Rh/CeO2‐Al2O3 three‐way catalyst (TWC) under pulsed flow operation conditions (intermittent mode), such as occur in a newly developed hybrid drive system, has been studied experimentally in a laboratory apparatus with simulated exhaust gas. The parallel hybrid system is based on the combination of an Otto‐cycle engine with an electric motor and a flywheel providing a short‐term energy storage. This configuration permits intermittent charging of the flywheel by the combustion engine which runs only during about 10% of the driving time. Each exhaust gas pulse (duration typically ca. 3 s) is proceeded by an air pulse, which results from the filling of the engine cylinders with air at start up and shut off. Experimental studies indicated that the air pulses have a negative impact on the performance of the catalytic converter, reducing the inherent benefits resulting from the intermittent operation mode of the combustion engine.

Forced asymmetric λ‐cycling during exhaust pulse was found to be most beneficial for improving catalyst performance. A simple reduced kinetic model derived from a Langmuir‐Hinshelwood model for CO oxidation, which was extended by introducing CO and O2 equivalents to mimic the complex exhaust gas, was used to describe the dynamic behavior of the TWC. The model proved to be useful for finding the optimal λ‐cycling conditions. Experiments with the real Otto‐cycle engine exhaust proved that the reduced kinetic model is suitable for use in a closed loop λ‐control.
Simulation and design of membrane plants with AspenPlus
Authors: Rautenbach Robert , Knauf Rüdiger , Struck Alexander , Vier Jens
Published: August 2005

In this paper the simulation of hybrid processes containing membrane units will be discussed. For this purpose a user‐defined module for simulation and design of membrane processes was implemented into the simulation program AspenPlus.

The advantages can be summarized as follows:

–any combination of membrane processes with all other units already implemented in AspenPlus is possible, including internal recycle streams

–utilization of the physical property models and data bases of AspenPlus is possible

– cost and sensitivity analysis can be performed.

These benefits are demonstrated in detail for a membrane vapor recovery unit for the treatment of tank farm off ‐gas, for a two‐stage reverse osmosis plant for organic/‐organic separations and for a combination of distillation and pervaporation for the separation of a dimethylcarbonate/methanol mixture.
Design of affinity membrane bioseparations
Authors: Sridhar P.
Published: August 2005

Affinity separations rely on the highly specific binding between a protein in solution and an immobilized ligand to achieve a high degree of protein purification. A mathematical model including convection, diffusion, and rate kinetics is formulated to analyze the design and operation of affinity membrane bioseparation. The model equations are solved by orthogonal collocation method. Danckwerts' boundary conditions are used. The results obtained from model simulation show that the breakthrough of the protein is significantly influenced by Péclet number, feed protein concentration, Ligand number, Damköhler number, membrane thickness, and flow rate. Breakthrough profiles are quantitatively discussed in terms of protein recovery efficiency, ligand utilization efficiency, thickness of unused membrane, and width of the mass transfer zone.
Mathematical modeling and experimental validation of an absorption‐driven multiple‐effect evaporator
Authors: Yanniotis Stavros , Pilavachi Peter A.
Published: August 2005

A mathematical model has been developed to simulate the operation of an absorption‐driven multiple‐effect evaporator. The model is based on mass and enthalpy balances and heat transfer rate equations of the various components of the system. The model has been validated by comparing model predictions to experimental results from the operation of a four effect absorption‐driven falling film evaporator coupled with a two‐effect regenerator which operated using solutions of sodium hydroxide as an absorptive medium. The model predictions are in satisfactory agreement with the experimental results.
Interfacial tension measurements between α‐tocopherol and carbon dioxide at high pressures
Authors: Moser Micro , Pietzonka Werner , Trepp Christian
Published: August 2005

The interfacial tension of the binary system α‐tocopherol/carbon dioxide was measured using the pendant drop method in the pressure range between 10 and 37 MPa at nine different temperatures: 313, 333, 343, 353, 363, 373, 383, 393, and 402 K. At every interfacial tension measurement, densities of both the liquid and the supercritical gas phase were also determined as the knowledge of these values is essential for calculating interfacial tension from the shape and size of drops. The interfacial tension decrease with rising pressure at a constant temperature and increases with increasing temperature at a constant pressure. The interfacial tension was found to be mainly a function of the mutual solubility of the two system components and of the density of pure carbon dioxide.
Heat consumption and irreversibilities in rectification processes
Authors: Knoche Karl Friedrich
Published: August 2005

Chemical engineering analysis using entropy production has been proven to be an essential tool to identify areas in chemical plants, where degradation of energy occurs. Though, applied very extensively in the area of heat exchanger networks in the form of “pinch technology”, the method is rarely used with respect to processes with mass energy. Entropy productions in destillation columns have been evaluated and discussed with respect to feed introduction, sequences of columns and other technically important features.
Adaptation of hydrocyclone to varying solid load by air injection
Authors: Mittal Manju
Published: August 2005

In the Chemical and Process Industry, liquid streams having a variable concentration solids are not uncommon. The hydrocyclone has been found to be a useful unit for the removal of particulate matter from these streams. The function of a hydrocyclone gets disturbed by an increase in the solid load concentration beyond a specified limit, and it may even overload the underflow opening. A variation of the solid load calls for a change in the split ratio of the hydrocyclone, which in turn requires an adjustment to the diameter of the underflow opening. A new technique has been developed which can automatically adjust to the change in the solid load without changing the underflow opening diameter. The split ration of a hydrocyclone can be changed by varying the pneumatic injection rate at the hydrocyclone's axis. Experiments were conducted using three geometrically similar hydrocyclones, and equations have been evolved to size the underflow opening.
Models describing the behavior of new carbon fiber packings inn rectification processes
Authors: Becker Oliver , Steiner Rudolf
Published: August 2005

Many rectification processes are used to separate corrosive substances with high boiling points. This reports deals with a new type of structured column pacing mode of corrosion‐resistant carbon fiber material. These column internals allows for low pressure drop at high throughput rated with reasonable column efficiency. Experiments in columns of 50 and 100 mm diameter have been carried out to investigated separation efficiency, pressure drop and liquid holdup of the packing even at low operation pressures. In the respective columns twp geometrical different types of packing have been tested using binary mixtures of chlorobenzene/ethylbenzene with a packing geometry similar to the Sulzer EX packing, the 100 mm diameter column was filled with elements of rougher structure and smaller specific surface. Basing on the experimental results, model equations are presented, which allow the calculation of the investigated performance characteristics.
Characterization of small‐ and intermediate‐pore zeolites by means of temperature‐programmed desorption of amines
Authors: Christoph Merz , Fetting Fritz
Published: August 2005

This paper presents results of temperature‐programmed desorption (TDP) as a method for studying the acid and shape‐selective properties of small‐ and intermediate‐pore zeolites.

A combination of an in situ infrared spectrometer and a downstream gas chromatograph for analyzing the desorption products is used to detect the desorption process. This is followed by a separate, newly installed microbalance facility.

The studies shows that a part of the amines, esp. dimethylamine (DMA) and trimethylamine (TMA), adsorbed on the zeolites undergo decomposition, disproportionation and carbonization reaction during the TDP measurements at elevated temperatures. Comparison of the microbalance measurements and the gas chromatographic results give a good picture of the extent of these reaction.
Tailor‐made additives to influence the habit of barite (BaSO4) obtained by precipitation
Authors: Kipp Stephan , Lacmann Rolf , Reichelt Michael , Schröder Wolfgang
Published: August 2005

In order to influence the habit of barite (BaSO4) single crystals obtained by precipitation, the tailor‐made additives 2‐aminomethanol, 3‐aminoproponal, 5‐aminopentanol, 4‐aminobutane sulfonic acid, and several other growth inhibitors have been tested. The crystallization experiments have been carried out in a fully automated crystallizer with reproducible educt feed rates. The kinetics of the reaction has been measured by means of the conductivity. Scanning electron microscopic analysis of the obtained crystal habits led to the raesult that most of the additives tested did not influence the growth form of the crystals, but the predicted, tailor‐made additives resulted in a more isometric crystal form.
Simulation of removal of HCI gas in a spray dry tower
Authors: Meazawa Akinori , Suzuki Harunobu , Seno Tadachika , Uchida Shigeo
Published: August 2005

A mathematical model of the absorption of HCI gas in a spray dry tower has been proposed. The proposed model describes the mechanism of HCI removal talking into account atomized droplet size distribution and the change in the droplet state from “slurry droplet” to “dry particle”. It is found that the removal efficiency can be simulated by using the model with the constant mean diameter of droplet from the simulation results. Simulation results of the removal of HCI gas are in good agreement with the experimental data in a spray dry tower.
Relation of mechanical power to gas holdup and mass transfer in an agitated vessel
Authors: Benadda Belkacem , Ismaili Samir , Otterbein Michel
Published: August 2005

Two devices were developed, mechanical and electrical, to measure the mechanical power relative to superficial gas velocity and stirring speed in a mechanically agitated reactor. Two bubble regimes were demonstrated. The study of gas holdup, obtained from the residence time distribution, and the bubble size, determined by interfacial area measurement, confirm these two regimes of flow. Our results show that the gas holdup, the interfacial area, and the liquid‐side mass transfer coefficient are increasing functions of the energy dissipated in the solution.
The determination of multiple steady‐states for a family of catalytic reactions in an isothermal CFSTR
Authors: Li Hsing‐Ya
Published: August 2005

The Subnetwork Corollary provides some sufficient conditions for which a complex reaction network could be determined to have capacity of admitting multiple positive steady‐states, if it contains a subnetwork that also admit multiple positive steady‐states. A family of reaction networks, involving catalytic reactions in an isothermal continuous flow stirred tank reactor (CFSTR), is determined to have the capacity to exhibit steady‐state multiplicity by implementation of the Deficiency One Algorithm and the Subnetwork Corollary. A set of rate constants and two corresponding positive steady‐states are constructed for several cases.
A contribution to the evaluation of mass transfer trays
Authors: Billet Reinhard
Published: August 2005

To review mass transfer trays from a process point of view, the dependence of efficiency on the loadings, the loading range and the maximum loadings with an acceptable tray efficiency have to be known. Comparing the results taken from experiments on Dualflex trays and from other types of trays which have been in industrial applications for many years and which are recognized as “industrial standard”, has been evaluated in this review.