bluuebunny/crossref_metadata_2025 huggingface dataset:
Agriculture wastes. A source of bulk products?
Authors: Schügerl Karl
Published: August 2005

Biotechnological production processes for low‐molecular bulk chemicals can only compete with their petrochemical counterparts on using inexpensive raw materials, e.g., agricultural by‐products or wastes, otherwise requiring disposal. The upgrading of by‐products/wastes of potato starch production and the use of potato protein liquor and potato pulp for the production of bulk chemicals were investigated. It transpired that the economy of these processes depends on the waste disposal costs of the upgrading processes. In addition, it is shown that specialty chemicals can be produced economically from wastes. However, since they are produced in a large quantities, the upgraded product cannot be put on the market without ruining existing prices.
Comparison of the dynamic behaviour of packed and plate distillation columns
Authors: Fieg Georg , Wozny Günter , Jeromin Lutz , Kruse Christopher
Published: August 2005

The results of experimental investigations on distillation columns operating on a lab and on a production scale are presented and compared with the results obtained by simulation. There is good agreement between experiment and simulation. On the basis of these results a dynamic analysis was carried out. It compares the dynamic behaviour of packed and plate distillation columns of the same diameter and same number of theoretical plates. This reflects the influence of the different hold‐ups of the two columns.
On the para/ortho product ratio of phenol and anisole hydroxylation over titanium silicalite‐1
Authors: Vetter Sabina , Schulz‐Ekloff Günter , Kulawik Kornelia , Jaeger Nils I.
Published: August 2005

Titanium silicalite‐1 samples of different particle size are synthesised and characterised by X‐ray diffraction (XRD), photoelectron spectroscopy (XPS), diffuse reflectance spectroscopy (DRS), Raman and infrared spectroscopy. Size histograms are taken from transmission electron micrographs. Temporal changes of activity and selectivity for the hydroxylation of phenol and anisole are monitored. It is postulated that the p/o product ratios are due to the greater chemisorption of the ortho molecule.
Process for production of pure 4‐methyl‐1‐pentene
Authors: Yankov Marin , Ninov Jordan , Petrov Peter
Published: August 2005

A process for the manufacture of pure 4‐methyl‐1‐pentene by catalytic dimerization of propylene has been developed in three stages. The first stage involves preparation of a new process catalyst, which contains metallic sodium and potassium deposited on a Bulgarian natural zeolite, the support having been passivated previously by potassium carbonate. The experimental results demonstrate the advantages of the resulting catalyst over exisisting technology, namely 36% conversion and 92% selectivity relevant to liquid isomers. The second development stage concerns the technological regime of chemical reaction for production of 4‐methyl‐1‐pentene. In the third stage, the regime conditions and equipment ensuring desired quality of the product and utilization of the unreacted propylene returned to the reactor are determined. Based on the studies of all stages, a flowsheet is proposed for synthesis and separation of the reaction mixture of isomeric hexenes to give pure 4‐methyl‐1‐pentene.
Hydrogen consuming anodes for energy saving in sodium sulphate electrolysis
Authors: Holze Stephan , Jörissen Jakob , Fischer Christian , Kalvelage Heinrich
Published: August 2005

Gas diffusion electrodes, made of PTFE‐bonded carbon with precious metal catalysts, were investigated as hydrogen consuming anodes in sodium sulphate electrolysis. The catalysts used were platinum and palladium and mixtures of both metals, prepared by two different methods. Various metal meshes were used as current collector. The electrodes performed well in pure sulphuric acid (5–15 wt‐%) and in mixtures with sodium sulphate (10 wt‐%) at temperatures of 30 to 70°C and current densities up to 5 kA/m2. In long‐term experiments, at a current density of 2.6 kA/m2, the electrodes were stable over three months. The electrodes were characterised by stationary current density/potential curves and by galvanostatic current interruption measurements.
Hydrogenation of carbon dioxide on cobalt catalysts – activation, deactivation, influence of carbon monoxide
Authors: Kestel Ulrich , Fröhlich Gerd , Borgmann Dieter , Wedler Gerd
Published: August 2005

A batch reactor directly combined with an ultrahigh vacuum apparatus, which is equipped with facilities for catalyst preparation and Auger electron spectroscopy, was used to answer some questions which had arisen in recent studies concerning carbon dioxide hydrogenation on pure metallic and supported Co catalysts. Both oxygen incorporated during oxidation/reduction cycles and carbon deposited when CO2 is hydrogenated penetrate deep into the bulk. This kind of carbon can easily be hydrogenated. CO strongly hinders the reduction of the oxidized Co surface in the H2/CO2 reaction mixture (4 : 1). CO hydrogenation is favoured over CO2 hydrogenation and leads to a higher percentage of C2 to C4 hydrocarbons as compared with CH4 formation.
Gas mixing in the cocurrent downflow circulating fluidised bed
Authors: Wei Fei , Jin Yong , Yu Zhiqing , Liu Jinzhong
Published: August 2005

An experimental study on the gas dispersion behaviour of a cocurrent downflow gas‐solids suspension in a 140 mm i.d. circulating fluidised bed (CDCFB) using the steady‐state tracer method is presented. The influence of gas velocity, solids circulating rate and particle density on radial gas dispersion has been examined. Gas dispersion can well be described by an eddy diffusion mechanism and a proposed two dimensional dispersed plug‐flow model can fit the experimental data very well. Correlations of the radial diffusion coefficient were obtained. It is found that the axial diffusion coefficient obtained in the CDCFB is much lower than that in conventional circulating fluidised beds.
Recommended operating range for a rotating disc contactor
Authors: Niedzialkowski Włodzimierz , Kaczmarski Krzysztof
Published: August 2005

Influences of different parameters on diameter and height of RDC column and on mass transferred from unit column volume were investigated. The results of the calculation can assist designers in making proper choice for the operating range of RDC columns.
Influence of hydrodynamics of rotary dynamic filters on separation processes
Authors: Rudniak Leszek , Wroński Stanisław
Published: August 2005

The fluid flow in a filter chamber, consisting of a rotating disk and a stationary plate, has been numerically investigated. A proposed model provided acceptable predictions for shear rate and frictional torque in laminar and turbulent flow regimes. Owing to the pronounced effect of the shear stress on the filtration rate, the data obtained were used in analysis of the influence of hydrodynamics on the shear stress field in the filter chamber.
Modelling of pressures and flow in silos
Authors: Schwedes Jörg , Feise Hermann
Published: August 2005

The modelling of pressures in silos has been attempted by numerous researchers using a variety of different methods. Starting with the work of Janssen, the slice element method, the method of characteristics, the finite element method and the method of granular dynamics are reviewed. Every model needs constitutive parameters which have to be found from experiments. A method to calibrate the more recent – and highly complex – constitutive models from general tests is presented. Besides the models for silo pressures, several models of flow in silos are considered.
CO hydrogenation over supported cobalt catalysts: FTIR and gravimetric studies
Authors: Fredriksen Geir R. , Blekkan Edd A. , Schanke Dag , Holmen Anders
Published: August 2005

The hydrogenation of CO over supported cobalt catalysts has been studied using in situ FTIR spectroscopy and gravimetry at P = 6 bar, T = 473–723 K and H2/CO = 2–3. On both silica‐ and alumina‐supported catalysts IR absorption bands corresponding to linearly adsorbed CO on metallic cobalt were observed. On alumina an additional pair of bands at lower frequencies was attributed to bridge‐bonded CO. Absorption bands corresponding to adsorbed hydrocarbons (3050–2700 cm−1) and to oxygen containing species (1800–1200 cm−1) were found to correspond to adsorbed products or unreactive species. The gravimetric studies showed a significant difference between the supports. On the silica‐supported catalyst the weight uptake decreased with increasing temperature (473–573 K). The weight increase during reaction was attributed to adsorbed hydrocarbon reaction products. On the alumina‐supported catalyst the weight uptake increased with increasing temperature, and there was also a significant weight increase with the support alone. Most of the weight uptake can be attributed to the formation of stable formate and carbonate species on the alumina support. At 723 K the deposits formed were stable in H2, and the shape of the curves indicated different mechanisms for deposition of material. In particular the Co/Al2O3 sample showed a very high and linear rate of weight gain, which was an order of magnitude higher than for the other samples.
Kinetic modelling of the oxidative coupling of methane over lanthanum oxide in connection with mechanistic studies
Authors: Lacombe Sylvie , Durjanova Zuzana , Mleczko Lezlaw , Mirodatos Claude
Published: August 2005

A kinetic model of the oxidative coupling of methane (OCM) over lanthanum oxide is developed on the basis of mechanistic conclusions obtained elsewhere. A reaction scheme is proposed, and the kinetic parameters corresponding to the different kinetic equation are optimized. Experimental and calculated reaction rates are compared with the aim of testing the proposed scheme and validating the basic mechanistic assumptions.
Modeling of sulphur retention in atmospheric fluidized bed combustors. Sensitivity analysis and simulation
Authors: Adánez Juan , García‐Labiano Francisco
Published: August 2005

For the design, simulation and optimization of sulphur retention in atmospheric fluidized bed coal combustors, a mathematical model is needed that would be able to predict the behaviour of the combustor in a wide range of operating conditions. In this work, a sensitivity analysis of the sulphur retention predictions of the different hypotheses, equations and parameters, which define the different submodels and phenomena occurring in the combustor, has been carried out. It has been found that the hypotheses related to the gas flow, devolatilization type and sulphur distribution in the pyrolysis products imply an important division among models. The greatest effect on sulphur retention predictions is exercised by the parameters defining the fines elutriation and sorbent sulphation capacity. However, those corresponding to the bed hydrodynamics (minimum fluidization velocity and bed expansion) do not have a significant effect on the sulphur retention predictions.

The sulphur retentions obtained in the combustion of high sulphur lignites with eight different limestones were used for model validation. A good fit of the experimental sulphur retentions was found, without using any adjustable parameter. Finally, a simulation of the process was made. The great effect of the bed height, air velocity and the particle size distribution of the limestone must be pointed out, as well as the effect of its reactivity through the maximum conversion attainable by each particle size.
Crystallization of potassium chloride: The additives ZnCl2, Na6 [(PO3)6] and K4 [Fe(CN)6]
Authors: Behrens Marcus A. H. , Lacmann Rolf , Schröder Wolfgang
Published: August 2005

The batch crystallization of potassium chloride from aqueous solution is investigated without impurities, with zinc chloride I (30, 100, 1000 ppm), with sodium hexametaphosphate II (100 ppm) and potassium hexacyanoferrate (II) III (100, 500, 1000, 16 × 25 ppm). The dominant particle size of the pure system LN, D = 427 μm increases by 40% by addition of I and by 250% by addition of II. While I does not affect the habit II changes it from cubes to octahedrons. In cases of low concentration, III leads to dendrites.

It is shown that addition of III decelerates growth and increases the metastable zone width. Hence a high supersaturation is formed, the solution impoverishes fast while III gets incorporated and therefore a strong nucleation starts in a relatively pure solution. By quasi‐continuously adding 16 × 25 ppm of III the dominant particle size increases by 160% with little fines. In this case the content of III in the product is relatively low.
Latex characterization by atomic force microscopy
Authors: Nick Leo , Lämmel Ralf , Fuhrmann Jürgen
Published: August 2005

Ways, benefits and limitations of extracting the form and size of single latex particles or particle size distributions out of the surface topography of non‐coalesced latex films obtained by atomic force microscopy (AFM) are discussed. The general ways to generate the desired information out of topographical information in terms of height, surface curvature and lateral extensions are shown for idealized particles and measurement conditions. The different sources of information are evaluated for practical use and the analysis of particle size distributions is demonstrated by practical examples. The information content in lateral particle dimensions is shown to be the most advantageous for practical use.

Determination of latex particle size distributions by AFM is shown to be an interesting alternative to the arsenal of available methods with respect to exactness of results, time consummation and instrumentation costs.
Circulating fluid‐bed reactor for coal pyrolysis
Authors: Ścia̧żko Marek , Zieliński Henryk
Published: August 2005

A high temperature coal pyrolysis reactor was developed and its operation demonstrated on a scale of 8 t/h. Pyrolysis is performed in a circulating fluidized bed reactor at 850–950°C. The developed process was integrated into smokeless fuel production technology and tested. Experimental data and reactor performance are presented.
Fluid dynamics and mass transfer in the total capacity range of packed columns up to the flood point
Authors: Billet R. , Schultes M.
Published: August 2005

Up to now, the only equations that were known for calculating mass transfer during two‐phase countercurrent flow in packed columns were those that apply to the range extending up to the loading point. The gas and liquid streams flow separately through the column below but not above this point. Above it, the shear stress in the gas stream supports an increasing quantity of liquid in the column, with the result that the liquid holdup greatly increases. Finally, at the flood point, the liquid accumulates to such an extent that column instability occurs. Mass transfer in this upper loading range can be described if these fluid dynamic relationships are taken into consideration. The algorithm that is presented here for its prediction is based on theoretical and experimental studies.
Mass‐ and momentum transfer in hydrogen/air and methane/air mixtures
Authors: Metz Stefan W. , Aretz Wilfried , Wilhelmi Herbert
Published: August 2005

In this article we present results for the viscosity and the mass transfer rates of hydrogen/air, hydrogen/oxygen, methane/air and methane/oxygen mixtures in the temperature range from 1000 to 7000 K and a pressure range from 103 to 106 Pa. In addition, the combustion ratio is varied from 0 to ∞. The transport properties are calculated from the first order solution of the Chapman Enskog approach to the Boltzmann equation, assuming chemical equilibrium composition. An extensive literature study was performed to derive experimental and/or theoretically based data for the respective binary interaction potentials. The values of the collision integrals, as derived from a complex numerical integration procedure, are correlated to an approximation formula. In addition, the exact solutions of the kinetic theory are compared to frequently used empirical mixture rules. For the mixture viscosity an easy approximation formula is deduced from the gas‐kinetic theory.
A model for the rate of hydrodesulfurization of thiophene in a continuous catalytic fixed bed reactor
Authors: Sohrabi Morteza , Zahedi Marganeh
Published: August 2005

Hydrodesulfurization of thiophene in n‐heptane, using a mixture of cobalt and molybdenum oxides as catalyst, has been studied in a fixed bed integral reactor, 200 mm long, 30 mm outer diameter and 20 mm inner diameter. It has been shown that, under experimental conditions employed in this study, neither external nor internal diffusion had been effective in the process and isothermal conditions prevailed in both gas and solid phases. A three step mechanism has been proposed for the hydrodesulfurization of thiophene. According to such a mechanism the diluent (n‐heptane) acts as an inhibitor by occupying free active sites. In further steps, thiophene is adsorbed on the catalyst surface and then undergoes reaction with hydrogen gas. Based on this scheme a rate model has been derived and verified by experimental results.
Agglomeration of alumina powders: A turbidimetric study
Authors: Masy Jean‐Claude , Cournil Michel , Lance Michel
Published: August 2005

Turbidimetry has proved to be an efficient method for the quantitative study of powder agglomeration for particle sizes in the region of 1 μm. This work presents a new application of the technique for the agglomeration of α‐alumina in water and in n‐heptane. The method of determining the kinetic parameters of agglomeration from the initial time‐evolution of turbidity is explained.

Turbulent flow in the reactor has also been characterised by laser anemometry. From the turbulence intensity, the number of collisions per unit time is calculated and the agglomeration rate can therefore be determined.

Good agreement is found between the values obtained respectively from turbidimetric and hydrodynamic measurements. Addition of KOH modifies the zeta potential of alumina in water and influences the agglomeration kinetics. This can also be quantitatively characterised by turbidimetry. The experimental results obtained for alumina particles of diameter 0.3 μm and 1 μm are interpreted according to the DLVO model of interaction between particles.
Vertical motion of spherical particles
Authors: Michalski Jacek A.
Published: August 2005

A theoretical analysis is presented for the time‐dependent vertical motion of spherical particles in a gas stream. Laminar, transitional and turbulent flows are considered, and equations are developed to predict particle velocity and distance travelled as functions of time in both stagnant and slowly‐moving gases. In both cases the equations are shown not to be universally applicable, and algorithms for estimating the limits within which they remain valid are briefly presented.
Design of conical and toriconical shells under internal pressure based on finite‐elements‐analyses
Authors: Weiß Eckart , Lietzmann Andreas , Rudolph Jürgen
Published: August 2005

Existing design codes propose different methods for the analysis for the junction region of conical and toriconical shells (limit analysis, shake down analysis, Kellog design approach, area replacement method) submitted to internal pressure load. However, now it is possible to develop generally valid an very precise guidelines based on linear and nonlinear Finite Elements‐Analyses. A clear difference is made between design with respect to fatigue strength and design according to load carrying capacity criteria. A. Major advantage of the Finite‐Elements‐Method(FEM) is the opportunity of its adaptation to given design criteria such as a strain limit or a plastification limit. It shown how design curves can be directly derived from the FE‐analysis with respect to fatigue strength (stress concentration factors) and load carrying capacity (design factors for the calculation of a required wall thickness). The materials behavior in the plastic region is considered with an without strain hardening. Large deformation effects as geometric nonlinearities can be involved in the analysis. The method can easily be applied for the analysis of other pressure vessel components.
Prediction of maximum stable diameter of viscous drops in a turbulent dispersion
Authors: Das Parichay K.
Published: August 2005

A new Paradigm has been developed fro the prediction of maximum stable diameter of viscous drops in turbulent dispersions using the Voigt model. The model assumes that a drop would break if its deformation reaches unity. The prediction from the model compares quite well with the available experimental results.
Kinetic of a liquid/liquid/solid fine chemicals reactions – modelling of a continuous pilot plant reactor
Authors: Chamayou Alain , Delmas Henri , Casamatta Gilbert
Published: August 2005

In the field of fine chemicals batch process the implementation of synthesis paths results most often in the determination of the optimal operating conditions on a bench scale apparatus; successive scale‐ups are then handled in an empirical way.

For multi‐phase reactions, this approach can be limited due to the coupling between the chemical kinetics and the physical kinetics of the mass transfer. This work proposes a more rational approach for the overall synthesis of Amiodarone, a widely used anti‐arrhythmic drug produced by a liquid/liquid/solid reaction. After analysing the reaction scheme and identifying the limiting steps of the process, a simplified model is proposed to describe the overall process kinetics. The latter is used to model a continuous pilot loop‐reactor packed with static mixers.
Biotechnological H2S gas treatment with Thiobacillus ferrooxidans
Authors: Pagella Claudio , Perego Patrizia , Zilli Mario
Published: August 2005

In this paper a novel process for biotechnological abatement of hydrogen sulphide is presented which details the fundamentals of chemical and biological phenomena involved. The process is based on the combination of two steps to form a closed cycle which has special enviornmental advantages. The chemical step corresponds to the abatement reaction itself with absorption of the gas in a ferric solution. The biological step is related to the regeneration of the absorbing solution by means of specific bacterial strains. Particular interest is devoted to the biological kinetics of the regeneration stage, where several inhibition phenomena appear, and are also related to parameters such as temperature and pH. Results of experimental runs of gas absorption in a laboratory scale plant are also described.
Membrane reactors in chemical production processes and the application to the pervaporation‐assisted esterification
Authors: Waldburger Raoul M. , Widmer Fritz
Published: August 2005

When appropriate membrane was used for the assistance of chemical and biochemical equilibrium reactions, it is possible to enhance the yield and the purity of the reaction product by selectively adding educts or selectively removing products and to a lower the energy input and the reaction time compared to conventional process.

In this paper a review on membrane reactors with special emphasis on membrane‐assistance of esterification reactions and a continuous tube membrane reactor for the pervaporation‐assistance of the esterification are presented. The heterogeneously catalyzed esterification of ethanol and acetic acid to ethyl acetate and water was investigated as a typical chemical equilibrium reaction.

The selective and simultaneous water separation from the reaction mixture of the esterification with polyvinyl alcohol pervaporation membranes is considered to be an interesting process alternative to the conventional distillation process. Compared to the distillation process, for the pervaporation‐assisted process a decrease of the energy input of over 75% and of the investment and operating coasts of over 50% each was calculated.
Systems engineering approach for chemical process energy optimization
Authors: Koehler Jürgen , Schadler Norbert
Published: August 2005

Process energy integration and continuous improvement of process technology are everlasting issues to ensure profitability of chemical productions. And both objectives become increasingly important due to long‐term environmental effects of energy degradation, such as resource depletion, emissions and the release of “waste” heat. The key success factor for process improvement lies in combining up‐to‐date expertise from different areas in an overall approach. One such approach is the systems engineering concept. It helps to structure and to organize problem‐solving process. We strongly believe that the increasing complexity of large and interlinked chemical production system and the tightening of global economic pressure force us to use more than ever systematic analysis and design methods to guarantee optimality throughout the entire product life. First we present a brief introduction to systems engineering in general. Then, in the main part of the paper, we give examples for optimizing the use of energy in chemical plants in order to illustrate advantages of the systems engineering concept. The examples range from improving the performance of individual pieces of equipment over changes in the process structure up to optimizing process clusters.
Exergoeconomics: Is it only a new name?
Authors: Tsatsaronis George
Published: August 2005

The paper briefly reviews the historical development of exergoeconomics, the existing methodologies, and their application. Particular emphasis is placed on the optimization of the design of new energy‐conversion systems.
General criteria to analyze the role of mass transfer and hydrodynamics in trickle‐bed reactors
Authors: Cassanello Miryan C. , Cukierman Ana L. , Martinez Osvaldo M.
Published: August 2005

General simple criteria to predict and analyze the influence on trickle‐bed reactors behavior of three phenomena, namely, plug flow deviations, external wetting efficiency and external mass transfer resistance, are developed. Criteria predictions are compared with results arising from a comprehensive mathematical model widely employed to describe trickle‐bed reactors behavior and with other particular criteria reported in the literature. Present criteria applications to different sets of experimental data exemplify their practical utility for various actual situations and verify their validity. Besides, they constitute simple tools to diagnose detrimental on trickle‐bed reactors operation.
Power consumption of multiple shaft agitators
Authors: Pahl Manfred H. , Brenke Andreas , Luo Yining
Published: August 2005

For highly viscous products, multiple shaft agitators represent an interesting alternative to expensive special mixers. A triple shaft agitator with a volume of 250 liters is used to determine the powder consumption of the impellers and its relationship with the process parameters. The result shows that the power consumption of a single impeller running in multiple shaft mode is significantly smaller than of one running in single shaft mode. But the power required for the whole multiple shaft machine is much higher than that for a single shaft machine. A model is presented for detailed description of the interactions between the individual agitators in multiple shaft mode.
Numerical simulation of influence of mass transfer on phase transfer catalytic reaction
Authors: Wu Ho‐Shing
Published: August 2005

Mass transfer with chemical reaction by liquid/liquid phase tranfer catalysis (LLPTC) for an isothermal batch reactor was analyzed. The results for the phase transfer catalyzed reaction system can be generally described by a pseudo first‐order hypothesis, whereas the reaction system can be controlled by simultaneous mass transfer of the catalysts between two liquid phases and chemical reaction in the organic phase. The mass transfer limitation is mainly from the mass transfer step of QX from the organic phase to the aqueous phase. The concept of catalyst‐effectiveness vs. physically meaningful parameters in a liquid/liquid phase transfer catalyzed reaction is introduced. The catalyst effectiveness is increased as the mass transfer factors increase, the ratio of reaction rate coefficients of aqueous forward reaction to organic increases, and the equilibrium constant in the aqueous solution increases.
Analytical study of type‐1 facilitated transport through liquid surfactant membrane
Authors: Bhowal Avijit , Datta Siddhartha
Published: August 2005

In the present study, a mass transfer model for Type‐1 facilitated transport in liquid surfactant membrane is developed by taking into consideration a size distribution of emulsion drops, and analytical solution of the model equations has been presented. The model takes into account the continuous phase and outer liquid membrane phase resistances along with diffusion through composite emulsion drop. Effort has been made to highlight the effect of the various system parameters on the extraction rate including computation of reaction front position. The results of this work are found to be in good agreement with the published experimental results on batch extraction of phenol using NaOH as internal reagent. The model would thus provide an insight of the separation mechanism involved in the mass transfer processes in this type of system.
The effect of mannitol and pH of the solution on the properties of sintered magnesium oxide obtained from sea water
Authors: Petric Nedjeljka , Martinac Vanja , Labor Miroslav
Published: August 2005

In order to reduce the B2O3 content in sintered magnesium oxide as much as possible, in precipitation with 80% of the stoichiometric quantity of dolomite lime, the effect of the pH of the agent used for rinsing the magnesium hydroxide precipitate was examined, as well as the effect of mannitol in sea water before precipitation. Mannitol binds orthoboric acid present in sea water into a weakly dissociated complex acid HB(OC)4. Experiments have shown that the B2O3 content in the sintered magnesium oxide samples is satisfactorily low. The lowest B2O3 content is obtained when mannitol is added; no B2O3 was found in these samples after sintering. Magnesium oxide samples were sintered at 1500°C; duration of isothemal sintering was one hour. Values for density and porosity of individually sintered samples are listed. The ratio CaO/SiO2 indicates that forsterite (Mg2SiO4), monticellite (CaMgSiO4) and mervinite (Ca3MgSi2O8) are formed during sintering of the samples.
Kinetics of liquid‐phase cyclohexanone ammoximation over a titanium silicate
Authors: Kul'kova Natal'ya V. , Kotova Valentina G. , Kvyathovskaya Marina Yu. , Murzin Dmitry Yu.
Published: August 2005

Liquid‐phase cyclohexanone ammoximation over titanium silicate was carried out in a batch reactor. The influence of the solvent, duration of kinetic run, catalyst amount and reactant concentrations was investigated. Byproducts were formed in considerable amounts, leading to catalyst deactivation by pore blocking. The values of initial reaction rates were calculated taking into account deactivation phenomenon. Theses values indicated that within the range of studied concentration (Ccyclohexanone = 0.4 to 1.70 mol/l; Cammonia = 1 to 4 mol/l; Chydrogen peroxide = 0.4 to 1.8 mol/l) the reaction rates plotted as a function of all the reagent concentrations go through a maximum. Special experiments on hydrogen peroxide decomposition and cyclohexanone oximation by hydroxylamine demonstrated that the rates of these reactions are essentially higher than the ammoximation rates.

A kinetic equation for initial ammoximation rates was developed on the basis of a mechanistic model. The advanced model permits description of the observed kinetic regularities.
Economic process optimization strategies
Authors: Buskies Ulrich
Published: August 2005

The following deliberations are concerned with the application of economy criteria to the optimization of process‐engineering plants. We are therefore not concerned here with criteria for investment decisions, i.e., decisions on the implementation orabandonment of an investment project, nor with criteria for the selection of the most profitable investment options from a series of alternatives. Instead, we are interested here in the question of how a plant, while at the planning stage, can best be designed, i.e., the most rational method of selecting process parameters, such as throughputs, pressures, temperatures, concentrations, etc. The problem of plant optimization only occurs, however, when there are design parameters which can be selected at will or can, at least, be varied within certain limits. This is however, virtually always the case. There is then a need for an optimization strategy in the form of an objective function which is either reduced to a minimum, where lowest possible production costs are the target, for instance, or advanced to a maximum, where high profitability is the aim. The inclusion of engineering economy functions, in the form, namely, of the net present value function and the internal rate of return function for definition of such objective functions, provides better defined information on the best possible choice of process parameters than was possible with methods previosly used, such as the annuity method, for instance. One obtains different values for the process parameters to be optimized, depending on the objective functionused, and therefore different investment costs and utility consumptions. These differences are delineated and quantified using a process‐engineering example in the course of the following discussion. The example selected is a gas scrubber, the function of which is to remove and recover useful components from a flow of gas. The specific problem examined is one of heat recovery.
Bubble emissions from submerged orifices – a critical review
Authors: Ponter Anthony B. , Surati Ashini I.
Published: August 2005

A comparative study of reported theoretical and experimental investigations evaluating the numbers and sizes of bubbles emerging from submerged orifices reveals that the lack of consistency can be attributed largely to faulty experimental techniques. Errors are attributed to an inadequate knowledge of the influence of the surface properties of the solid and liquid media on the emission process and to the lack of standardization of the equipment geometries especially regarding the pressure chambers and orifice plates. The analyses provide guidance to designing standardized equipment to produce reproducible bubbles.
A vapor pressure equation for heavy compounds
Authors: Campanella Enrique A.
Published: August 2005

A vapor pressure calculation procedure based on a lattice equation is applied to several compounds. Originally, the method was used to predict low vapor pressures of heavy hydrocarbons. In this work, the method is used at low vapor pressure for nonhydrocarbons, and a modified version is employed at high vapor pressure for n‐alkanes. As the procedures require the knowledge of one vapor pressure datum only, they work in a predictive mode. Prediction for hydrocarbons is good and for nonhydrocarbons is poor. Prediction of n‐alkanes high vapor pressure is good with an overall average relative absolute deviation under 6 percent.
Effect of fasting condition on multi‐substrate carbon oxidation and nitrification system in an upflow packed‐bed biofilm reactor
Authors: Beg Shafkat Ali , Hassan Mirza Manirul , Chaudhry Muhammad Arshad Saeed
Published: August 2005

The performance of an upflow packed‐bed biofilm reactor has been analyzed under multisubstrate limitation by considering simultaneous carbon oxidation and nitrification reactions. The fasting shock load of inlet methanol concentration has a much more pronounced effect on the response of the system compared to that of inlet NH4+ ‐nitrogen concentration. The exit concentration of NH4+ ‐nitrogen drops very close to zero, thereby showing essentially complete nitrification during methanol fasting condition. Further, the concentration profiles of oxygen within the biofilm show significant variation during methanol fasting and nonfasting conditions whereas during NH4+ ‐nitrogen fasting conditions the oxygen concentration profile in the biofilm remains essentially unaffected.
Effect of laminar flow on the rate of mass transfer inside cubical cavities
Authors: Zaki M. M. , Nirdosh I. , Sedahmed G. H.
Published: August 2005

An electrochemical technique which involved measuring the limiting current of the cathodic reduction of potassium ferricyanide was used to study the rate of mass transfer inside a cubical cavity machined in the wall of a vertical rectangular duct. Variables studied were side length, physical properties of the solution and flow rate of the solution. The mass transfer coefficient was found to decrease with increasing cavity size; in all cases, the mass transfer coefficient inside the cavity was less than that at the duct wall. Mass transfer data inside the cavity were correlated by the equation Shc = 0.525 (Sc Re de/L)0.33. Comparison of the present results with the results obtained using other cavity geometries shows that cavity geometry plays an important role in determining the rate of mass transfer inside the cavity.
Bioheat equation of the human thermal system
Authors: Xuan Yimin , Roetzel W.
Published: August 2005

As an alternative to the existing bioheat transfer models a new system of two energy equations is proposed by considering the human body as a deformable porous medium. One equation is developed for the blood and the other for the peripheral skeletal tissue. It includes such significant factors as the vascular geometry and size, the blood flow and direction, thermal diffusion and the local thermal nonequilibrium between the blood and peripheral tissue. Discussion and application of both equations are given.
Reaction kinetics of the CO2 reforming of methane
Authors: Mark Michael F. , Maier Wilhelm F. , Mark Franz
Published: August 2005

The kinetics of the CO2 reforming of methane was investigated in the temperature range 700–850°C at normal pressure with a 1:1 mixture of CH4 and CO2 on Ir/Al2O3 catalysts. The feed composition was kept constant to avoid a change in mechanism associated with composition changes. Various rate models were fitted to the experimental data by numerically integrating the rate equations. All rate models included the reverse water gas shift reaction as the most important side reaction at these reaction conditions. The best agreement was obtained with a rate model based on the stepwise mechanism, where in the rate‐determining step methane is decomposed to hydrogen and active carbon followed by the direct and fast conversion of this active carbon with CO2 to 2 CO. This model is also the first and only one containing a complete subset of reactions necessary to describe the network of reactions known to occur at these reaction conditions. Comparable fit quality was obtained with a simple first order model and with a model based on a Langmuir‐Hinshelwood rate expression, where the latter provided physically meaningless parameters. Values of the reaction parameters are given for the 5 best rate models studied.
Fuzzy logic control of an unstable biological reactor
Authors: Inamdar Satish R. , Chiu Min‐Sen
Published: August 2005

In the present work, we employ a fuzzy logic controller (FLC) to control the unstable state of a nonlinear biological reaction. The state variable vectors consist of cell density and substrate concentration. The dilution rate is used as a manipulated variable to control the reaction dynamics. An analytic form of FLC employing Zadeh AND logic along with Center of Mass defuzzification method is considered. Simulations reveal that for servo response test, the FLC shows satisfactory performance for natural unsteady states for which a conventional PI controller is known to fail. Further simulations also show that the FLC gives satisfactory regulatory response and is relatively insensitive to the deviations in model parameters.
A new correlation for the two‐phase pressure recovery downstream from a sudden enlargement
Authors: Attou A. , Bolle L.
Published: August 2005

By applying the macroscopic conservation laws to a simplified jet downstream from a sudden enlargement, a new correlation of the two‐phase subcritical pressure recovery is obtained. Comparisons with the set of existing data (air‐water and steam‐water subcritical flows) show that the predictions obtained by means of this formula are more accurate than the ones given by available analytical models. The proposed correlation presents an important improvement of the pressure recovery predictions in the case of small mass velocities. However, it can not be applied in the conditions of quality too close to one.
Caprolactam production: A comparison of different layouts of the liquid‐liquid extraction section
Authors: Alessi Vanni , Penzo Renzo , Slater Michael J. , Tessari Roberto
Published: August 2005

Two different layouts for the liquid‐liquid extraction section of an industrial caprolactam process are evaluated. Laboratory mass transfer measurements on streams obtained from an industrial and a demonstration plant with different extraction sections are interpreted by a model describing the effect of surface contaminants on mass transfer coefficients. Indications of the impact of these layouts on the complexity of the extraction section, quality of products and efficiency of the extraction processes are given.
Comparison of two‐phase upflow and downflow fixed bed reactors performance: Catalytic SO2 oxidation
Authors: Iliuta Ion , Iliuta Maria C.
Published: August 2005

A time‐ and space‐dependent model based on the piston‐dispersion‐exchange model for liquid flow was developed to analyze the performance of two‐phase upflow and downflow fixed bed reactors and was applied to the catalytic SO2 oxidation. The hydrodynamic parameters were determined from residence time distribution measurements, using an imperfect pulse method for time‐domain analysis of nonideal pulse tracer response. A transient diffusion model of the tracer in the porous particle coupled with the PDE model was used to interpret the obtained RTD curves. Gas‐liquid mass transfer parameters were determined by a stationary method based on the least square fit of the calculated concentration profiles in gas phase to the experimental values. It is shown that two‐phase downflow fixed bed reactor performs better at low liquid flow rates, while two‐phase downflow fixed bed reactor performs better at low liquid flow rates, while two‐phase upflow performs better at high liquid flow rates.
Three‐dimensional vibrational mixing
Authors: Pahl Manfred H. , Wittreck Hubert
Published: August 2005

When working with disperse solid matter systems, one uses the effect of vibration in numerous processes. Solid matter mixing with vibration has only occurred in very simple units up to now. By means of the 3D‐vibrational mixer from the company Kuston, Kleve, the influence of vibration on bulk materials and new mixing techniques are demonstrated. The 3D‐vibrational mixer is suitable for liquids and solids, does not require mixing tools that need to be cleaned, and does not carry out rotary motions which would hinder incoming lines. It is used for mixing small amounts, where the mixing tank can be used simultaneously as the transportation container, so that a transfer is unnecessary.

With the aid of 4 linear motors, the vibrational amplitudes and the frequencies can be varied within wide boundaries in all three spatial directions. By analyzing the vibrational system by means of Lissajous figures, it can be demonstrated that the optimal mixing effect occurs in the case of small frequency differences between the three axes. For freeflowing bulk materials, the best possible mixing state, the uniform coincidence mixing, is achieved after 2 min.
High shear rheology of paper coating colors – more than just viscosity
Authors: Willenbacher Norbert , Hanciogullari Haryutum , Wagner Hans G.
Published: August 2005

Capillary viscometry is used to characterize viscosity, entrance pressure loss and apparent wall slip of paper coating colors at high shear rates. Special emphasis is laid on the dependence of these phenomena on solids content in order to account for changes in the rheology due to the dewatering of the color during the coating process. Coating colors with substantially different runnability have been investigated. Differences in apparent wall slip and high shear viscoelasticity (manifesting itself in extremely high entrance pressure losses) are observed at increased concentration, even if these phenomena do not show up at the initial solids content. Poor runnability is observed when viscosity, entrance pressure loss and wall slip increase strongly with increasing solids content. But all rheological features change simultaneously with the coating color recipe and it is not possible to separate out the contribution of the particular rheological features on the runnability of the coating colors or to correlate the runnability to a single rheological prorameter. Future work will have to focus on a numerical analysis of the blade coating process taking into account all the rheological features described here. First simulations including slip at the color/blade interface indicate that wall slip may cause severe runnability problems, at least when the apparent slip velocity exceeds the web velocity.
Calculation of equilibrium composition in combustion products
Authors: Rashidi Manoochehr
Published: August 2005

For a specific combustion problem involving calculations of several species at equilibrium, it is much simpler to write a special computer program and calculate the concentrations, rather than to use a generalized computer program. To calculate these concentrations, one must solve a set of non‐linear algebraic equations. This work describes a procedure in which the Newton‐Raphson method and the successive substitution method are combined. It is was found that for these types of problems the value of unknowns and the nature of the equations are such that by adopting the two procedures simultaneously a much faster and reliable convergence is achieved. This study also shows what possible species should be considered for these calculations.
Numerical determination of the three‐dimensional velocity distribution in a baffled pitched blade impeller stirred vessel
Authors: Götz Sven , Sperling Reinhard , Liepe Friedrich , Jembere Solomon
Published: August 2005

The objective of the work presented here was the development of a method of modeling the effect of an impeller on the velocity distribution in a stirred vessel. The developed model makes it possible to numerically investigate the flow field almost independently of any experimental data. The starting point was a force balance around an impeller blade, which took into consideration the lift and drag forces. The obtained volume forces were circumferentially averaged in the impeller region. The calculations were carried out time‐averaged for the case of a pitched blade impeller. The results were compared with experimental data which were obtained by laser Doppler anemometry. The comparison of the axial velocity components shows a good agreement between numerical and experimental data. Furthermore some characteristic integral values were calculated, which demonstrate the efficiency of the impeller.