bluuebunny/crossref_metadata_2025_split huggingface dataset:
Activity evaluation of a catalytic distillation packing for MTBE production
Authors: Sundmacher Kai , Hoffmann Ulrich 
Published: August 2005

AbstractThe octane enhancer methyl tertiary butyl ether (MTBE) can be produced very efficiently from methanol and isobutene in a reactive distillation column where the heterogeneous catalyst also acts as distillation packing. Some mathematical models have been published for the simulation of such a process but they focus on the physical transport processes between the vapour and liquid phases. However, the aim of this paper is to analyze the importance of the internal and external multicomponent mass and heat transfer phenomena on the catalyst under boiling conditions. Therefore, experiments were carried out in a reactive distillation column at different compositions of feed, column pressures and reflux ratios using a Raschig ring shaped acidic ion exchange resin as the catalyst. The temperature and composition of the liquid phase entering and leaving the catalytic column section were measured. These data were used to evaluate the effectiveness factor of the catalyst with a rigorous macrokinetic model. It is shown that the effectiveness factor varies significantly along the column length. Under certain operating conditions, decomposition of MTBE can occur accompanied by boiling processes inside the catalyst macropores.
Transient behaviour of shell and tube heat exchangers
Authors: Roetzel Wilfried , Xuan Yimin 
Published: August 2005

AbstractBased on the dispersion model rather than on the conventional pluf‐flow model, a method of predicting the transient behaviour of parallel and counterflow heat exchangers is developed, whereby the effects of shell‐side flow maldistribution and the finite heat capacities of both fluids, tube bundle and shell are considered. The final solution has been obtained by numerical inversion of the Laplace transform, to determine the transient responses to arbitrary inlet temperature variations. The experiment was carried out in a one pass tube heat exchanger. The comparison between therotical and experimental results is presented and the feasibility of this method is discussed.
Industrial fires and explosions due to electrostatic ignition
Authors: Mittal Manju , Guha Barun K. 
Published: August 2005

AbstractStatic electricity is a frequent source of fires and explosions in industry. A variety of operations may generate static electricity leading to such fires and explosions. This requires adequate preventive and protective measures against this hazard. The present paper describes the theory and mechanism of electrostatic sparking, parameters needed to assess the respective hazard in a plant, safety measures to combat electrostatic problems, common operations where such problems exist and measures to eliminate or mitigate these problems.
Estimation of kinetic parameters of benzene hydrogenation in a trickle bed reactor
Authors: Sharma Sunil Dutt , Gadgil Kasturi , Sarkar Manoj Kumar 
Published: August 2005

AbstractA high pressure and high temperature catalytic hydrocracking unit based on trickle‐bed reactors was constructed. Data obtained under conditions simulating those of industrial processes, were evaluated. Partial wetting characteristics of trickle beds were especially taken into account in the interpretation of results together with combined contributions of gas and liquid phase reactions.
The cyclone scrubber – a high efficiency wet separator
Authors: Krames Jörg , Büttner Helmut 
Published: August 2005

AbstractDue to induced turbulent interactions between particles to be separated and the scrubbing liquid present as droplets, very good collection efficiency down to submicron particle size can be achieved as shown by detailed studies [1]. Assumed are suitable flow conditions, a long residence time and a certain droplet size distribution or a special liquid dispersion system. As the name implies, the cyclone scrubber basically consists of a cyclone. This cyclone serves as a contact space in which the interaction between dust particles and scrubbing liquid droplets takes place, and as a droplet separator. Thus, under normal conditions, a water saturated but dust‐ and droplet‐free gas stream leaves the cyclone. The droplets are generated by a pneumatic atomization nozzle, arranged at the cyclone inlet in the direction of flow. A complete theoretical description of the three‐dimensional, three‐phase, non‐steady turbulent flow in the cyclone scrubber has not been possible up to now. The detailed experimental investigations presented in this work, and covering multiple parameters, led to physically based conclusions about the dominant interactions and separation mechanisms involved. Grade efficiencies which did not fall below 0.75, down to a particle size of 0.5 μm, could be measured by an optical particle counter. Collection efficiency of 99.2% was determined by gravimetric analysis of the dust load, according to VDI‐guideline 2066, in the raw and clean gas sections of the dust load, according to VDI‐guideline 2066, in the raw and clean gas sections of the cyclone scrubber.
A rotating two‐phase gas/liquid flow regime for pressure reduction in underwater plasma arc welding
Authors: Steinkamp Helmut , Mewes Dieter 
Published: August 2005

AbstractPlasma arc welding processes are used in the off‐shore industry for construction and maintenance of underwater structures and pipelines in a wet environment. At greater water depths the density of the plasma gas increases because of the greater hydrostatic pressure. This causes conductive heat losses to the wet environment to increase. To maintain the energy flux to the workpiece to be welded, the plasma arc has to burn in a local dry area with an inside pressure of 1 bar. This requirement can be fulfilled by a rotating cylinder with a liquid film flowing down the inner wall. The flow around the rotating cylinder is experimentally investigated. The rotating cylinder is placed above the work surface which is simulated by a flat plate. Because of the centrifugal forces of the rotating flow inside the gap between the lower end of the cylinder and the flat plate the water is forced out of the cylinder. The velocity distribution in the flow is measured by laser Doppler anemometry. The phase distribution in the two‐phase flow in the gap is measured by local electrical probes. The static pressure inside the gaseous atmosphere is reduced in comparison to the hydrostatic pressure of the surrounding water. The pressure reduction is given by the void fraction, the phase distribution and the volume flow rates of both phases in the gap as well as by the speed of revolution and the design of the cylinder and the work surface. The influence of these parameters on heat transfer from the workpiece to the two‐phase flow regime is also investigated.
Deactivation of a vinyl acetate catalyst
Authors: Abel Roland , Prauser Günther , Tiltscher Helmut 
Published: August 2005

AbstractKinetic studies as well as morphological and physico‐chemical surface studies have been carried out on the deactivation of a palladium carrier catalyst for vinyl acetate synthesis in the ethylene gas phase process. The experiments cover concentration and temperature ranges of technical interest at a total pressure of 900 kPa. The deactivation rate depends on the temperature and the oxygen and acetic acid concentrations. The decline in activity is best described by a rate law of second order relative to the activity number. This behaviour is attributed to the observed aggregation of finely dispersed palladium. It can be concluded that palladium(II) acetate acts as a transport species in a chemically assisted sintering mechanism. At temperatures T ≤ 438 K the more advantageous final texture of the catalyst will only be formed on reaction.
Modelling of coadsorption of different‐sized molecules by using methods of statistical thermodynamics
Authors: Meyer Carsten , Hesse Diethard 
Published: August 2005

AbstractUsing methods of statistical thermodynamics, adsorption isotherms for the description of multicomponent chemisorption of different‐sized molecular species are derived by assuming the adsorbing surface to be energetically homogeneous and by neglecting lateral interactions between the adsorbed particles. In the first part of this contribution, the adsorption equilibria for a mixture of different‐sized chain molecules adsorbed on a lattice of coordination number z are discussed supposing each unit of a given chain to bind to one adsorption site only. In the second part, the coadsorption of molecular species consisting of a different number of segments on a continuous surface is treated. A comparison of the predicted to the measured isotherms for the coadsorption of two freon species on activated carbon shows that the proposed equations describe the results of the coadsorption measurements sufficiently well, provided the adsorption data for the pure components have been determined experimentally.
Applications of computational fluid dynamics in the chemical industry
Authors: Bode Jürgen 
Published: August 2005

AbstractIn order to illustrate the use of CFD in providing an understanding of mixing processes, three examples, mixing in a pipe, homogenization with a static mixer and flow in a mixing vessel with a Rushton turbine, are discussed and compared with experimental results. Special attention is focussed on the resultant concentration distribution, which is closely linked to turbulent properties. A semi‐empirical model is presented for a quantitative prediction of the initial turbulent conditions. Using special numerical techniques a mixing vessel with wall‐separated baffles, which represents a problem generally regarded as beyond the capabilities of numerical analysis, can be simulated.
Investigations on precious metal/alumina interactions on three‐way automotive emission control catalysts, BMA catalysts and model samples
Authors: Albers P. , Engler B. , Leyrer J. , Lox E. , Prescher G. , Seibold K. 
Published: August 2005

AbstractCombined XPS and SIMS measurements, partly supplemented by XRD investigations, were utilized to detect precious metal/support interactions on catalysts containing various precious metals. The Klemm‐Bronger reaction between Pt and α‐Al2O3 on methane/ammonia catalysts was used as a standard reference. Evidence was found for different stages of Pt/Al interactions and changing electronic properties of Pt on the surfaces of these Pt/α‐Al2O3 catalysts by means of XPS and SIMS, and in the bulk material by XRD. The SIMS investigations on Pt and Rh on γ‐Al2O3 showed that, even at temperatures around 500 °C, Rh/Al interactions can appear to a small extent in the topmost atomic layers, whereas the Pt/γ‐Al2O3 specimens did not show any measurable effects. After on‐road operation, enhanced SIMS cluster‐ion signals as well as anomalous XPS signal contributions were measured on the surfaces of used three‐way automotive emission control catalysts. These signals did not appear for the fresh catalysts. By analogy with the related results reported on the methane/ammonia catalysts, the ion signals were used as qualitative surface probes indicating the presence of precious metal/support interactions, especially between Rh and Al.
Liquid phase oxidation of α‐pinene initiated by ozone. 2: Formation of verbenol, verbenone and acid products
Authors: Encinar José María , Beltrán Fernando J. , Frades Jesus María 
Published: August 2005

AbstractThe formation of verbenol, verbenone and acids during liquid phase ozone‐initiated oxidation of α‐pinene has been investigated; temperature, ozone partial pressure and ozone initiation time were the variables studied. While increasing temperature promotes the formation of secondary products, the other two variables affect mainly the selectivity. Thus, an ozone partial pressure and ozone initiation time of 1014 Pa and 10 min, respectively, lead to the highest selectivities. Kinetic expressions for the formation of verbenol and verbenone, which are consistent with experimental data, have also been developed from a free radical mechanism.
Kinetic study of the synthesis of n‐octyl octanoate using cobalt chloride as catalyst
Authors: Urteaga Laura , Sánchez Nieves , Martinez Mercedes , Aracil José 
Published: August 2005

AbstractThe kinetics of the pseudohomogeneous liquid phase synthesis of a high molecular weight ester in a stirred tank reactor using cobalt chloride as catalyst has been studied at various temperatures, catalyst concentrations, and acid/alcohol molar ratios. A kinetic model has been determined that predicts the experimental results quite well.
Pbs‐field‐effect‐transistor for heavy metal concentration monitoring
Authors: Kullick Thomas , Quack Ralf , Röhrkasten Cornelia , Pekeler Thomas , Scheper Thomas , Schügerl Karl 
Published: August 2005

AbstractA simple and inexpensive Pbs‐FET with high sensitivity and short response time was developed which consists of a PbS layer on a pH‐sensitive gate of a field effect transistor. The PbS‐layer was prepared with simple wet precipitations technique. The PbS‐FET has about the same selectivities for Pb2+ ‐and for Cu2+ ‐ions, but only slight sensitivity for Cd2+ ‐and Zn2+ ‐ions. The sensor was integrated in a FIA system. By variing the injection time the measuring range varied between 10−1‐10−6 and 10−2‐10−8 mol Pb2+/1. The PbS‐FET‐FIA system is suitable for monitoring of Pb2+ concentrations in drinking water.
Interfacial area of mellapak packing: Absorption of 1,1,1‐trichloroethane by Genosorb 300
Authors: Brunazzi Elisabetta , Nardini Giuliano , Paglianti Alessandro , Petarca Luigi 
Published: August 2005

AbstractIn this work a Sulzer structured packing, Mellapak 250Y, was studied for applications in the field of absorption. A new model was proposed which makes it possible to estimate the packing surface that actually takes part in the process. In the course of these studies, new experimental data were obtained relating to the absorption of 1,1,1‐trichloroethane using Genosorb 300, a mixture of polyethylene glycol dimethyl ethers produced by Hoechst S.p.A., as absorption liquid. The results obtained with the proposed model are in agreement both with the experimental measurements made in the course of the work and with experimental absorption measurements reported by other authors on water systems.
Continuous enzyme‐catalyzed production of 6‐aminopenicillanic acid and product concentration by reverse osmosis
Authors: Danzig Joachim , Tischer Wilhelm , Wandrey Christian 
Published: August 2005

AbstractThe efficiency of 6‐aminopenicillanic acid (6‐APA) production by enzyme‐catalyzed hydrolysis of penicillin G using penicillin G amidase (E. C. 3.5.1.11) immobilized in polyacrylamide gel can be improved by using a lower substrate concentration and an optimized low buffer concentration. In a continuous process the combination of a stirred‐tank reactor and a plug‐flow reactor gives optimum productivity. Since precipitation of 6‐APA is the crucial step in downstream processing, the product concentration has to be as high as possible. This can be achieved by concentrating the product solution by reverse osmosis.
Deactivation kinetics and modelling of coke removal under supercritical conditions for the example of ethylbenzene disproportionation
Authors: Niu Fenghui , Kolb Gunther , Hofmann Hanns 
Published: August 2005

AbstractDeactivation kinetics and coke removal kinetics were derived from experimental studies on the disproportionation of ethylbenzene with a protonated Y‐faujasite (Z‐14) in a loop reactor under supercritical conditions. Derivation of the steady state kinetics of ethylbenzene disproportionation permitted determination of the catalyst activity. At small educt mole fractions of ethylbenzene, owing to the modest removal of coke the deactivation kinetics can be described by a power relationship. The rate of coke removal can be correlated with the activity and the deactivation rate of the catalyst.
An efficient method for the calculation of chemical equilibrium composition in multicomponent gas mixtures
Authors: Metz Stefan W. , Aretz Wilfried , Wilhelmi Herbert 
Published: August 2005

AbstractThe determination of the composition of multi‐component mixtures is the basis by which a number of technical and physical problems in the field of power and process engineering are modelled. In order to calculate chemical states of equilibrium in the gas phase, a calculation method will be presented which is founded on a minimization of the Gibbs enthalpy. This method is characterized by a high reliability in convergency, considerable independence of starting vectors and by a moderate requirement for programming. These characteristics are achieved by a transformation of variables which results in numerically more favourable solutions to the non‐linear equation system. Calculated equilibrium compositions (including dissociation and ionisation) for a stochiometric mixture of hydrogen and oxygen in a temperature range of 300–12000 K and a pressure of 105 Pa as well as the application of the method will be demonstrated.
Simplified transient model of an upflow cocurrent packed bed bioreactor
Authors: Samb Falilou M. , Benthack Christina , Deront Marc , Adler Nevenka , Péringer Paul 
Published: August 2005

AbstractA dynamic model incorporating biomass growth and liquid hold‐up evolution is developed to describe a fixed bed bioreactor operation with cocurrent upflow of water and air flows. The model permits to predict cycle time and optimal operation conditions for high substrate removal and long cycle times. Simulation results are compared with published experimental results and show good model accuracy.
A new continuous‐flow recycle microwave reactor for homogeneous and heterogeneous chemical reactions
Authors: Chemat Farid , Poux Martine , de Martino Jean‐Louis , Berlan Jacques 
Published: August 2005

AbstractA new continuous‐flow recycle microwave reactor suitable for organic synthesis has been developed to handle 0.51 quantities of reagents. The apparatus, which is designed for laboratory use, operates at atmospheric pressure in open‐ or closed‐loop mode. It is fitted with a temperature control system. We describe this novel reactor and illustrate its efficiency with examples of organic syntheses carried out using both homogeneous and heterogeneous reactions.
Mass transfer studies in pneumatic reactors
Authors: Benyahia Farid , Jones Lynn , Petit Silvain , Plantaz David 
Published: August 2005

AbstractLocal mass transfer studies have been carried out in an external loop airlift reactor and indicated the existence of significant non‐uniformities in aeration capacity in the various sections of the reactor. The traditional assumption of a single well mixed unit with a single kL a value for external loop airlift reactors was found to be poor and cannot represent adequately the reactor as a whole. The liquid head in the gas/liquid separator was found to have a significant negative negative effect on the local mass transfer coefficient kL a. Visualization of flow patterns showed the existence of strong vortices in the riser and downcomer which contributed to a reduction in local aeration capacity. Mass transfer experiments in an aerated tank showed that the aeration capacity can be reduced by half in viscous media but improved significantly in the presence of salts.
A new method for the characterisation of the wettability of powders
Authors: Link Kersten Christoph , Schlünder Ernst‐Ulrich 
Published: August 2005

AbstractThe wetting characteristics of fine powders play an important role in a variety of processes. The most important way of characterising the wettability of a fluid/fluid/solid system is to measure the contact angle. This paper describes a relatively simple method for the determination of the contact angle on powdery materials. The technique involves the measurement of the dynamic contact angle which is formed when a liquid drop is placed on a horizontal porous surface. On the basis of the measured dynamic contact angle as a function of time an “apparent” static contact angle has been defined, which gives a measure of the wettability of porous solid systems by analogy with the wetting of non‐porous solids. Determinations with glass beads and NaCl‐powders as the test materials indicate that the measured value depends on the particle size of the powder, the porosity and the temperature. It was concluded that the capillary penetration of the liquid droplet into the porous media itself influences the wetting characteristics.
The use of statistical properties of transmission signals for particle characterization
Authors: Wessely Benno , Altmann Justus , Ripperger Siegfried 
Published: August 2005

AbstractThe measurement of transmission is an often used measuring principle in technology. The evaluation algorithms of fluctuating transmission signals are well known in the case of single particle measurement. By evaluating fluctuating transmission signals the particle characterization is also possible at high particle concentrations (0.01 to 30 vol.‐%). In comparison with conventional photometers a significant gain of information can be received. Fluctuating signals are caused by the statistical probability of a limited number of particles being present in a defined measuring volume. The evaluation of such signals allows the determination of particle concentration, particle size of monodisperse particles (extinction diameter) and information about structure of agglomerates independent from each other. Mathematical fundamentals and practical ways to measure these parameters are shown. Experimental results are examplarily presented for monodisperse, polydisperse and agglomerated suspensions.
EXSENSEL – a rule‐based approach to selection of sensors for process variables
Authors: Barua Alok , Sengupta Sumit 
Published: August 2005

AbstractA novel expert‐system‐based method for selection of sensors for process variables is presented. EXSENSEL (expert system based sensor selection) deals with 12 process variables and currently has 94 rules in its knowledge base. Despite its large knowledge base, users have to answer a set of only a few questions regarding a particular process variable, which is selected from a menu of 12 variables. A general description of the chosen process variable can be viewed before invoking the rules. Once a sensor has been selected, a brief write up on that particular sensor is also available on user's request. EXSENSEL is the successor to TRANSELEX, which is a single expert system for selection of transducers in the area of temperature, pressure, and flow measurement.
Performance of a three‐phase fluidized bed as a reactive distillation device
Authors: Liang Wugeng , Wang Zhanwen , Jin Yong , Yu Zhiqing , Yang Sheng 
Published: August 2005

AbstractA new reactive distillation device, the multistage gas/liquid/solid three‐phase fluidized bed, has been developed. The flow regimes of the multistage three‐phase fluidized bed have been studied and the regimes can be divided into the liquid leakage regime, the dispersed bubble regime, and the coalesced bubble regime. Liquid velocity has a much smaller effect on phase holdups in this device than in conventional three‐phase fluidized beds. The three phase fluidized bed is used as a reactive distillation device for the hydrolysis of methyl acetate. Much higher reaction conversion than the equilibrium value and high catalyst‐contacting efficiency are obtained. Different methods of feeding the water into the reactive distillation section are studied.