bluuebunny/crossref_metadata_2025 huggingface dataset:
Modelling of Fluidized Bed Reactors
Authors: Werther Joachim , Hartge Ernst-Ulrich
Published: October 2005

The fluidized bed reactor has a lot of advantages: excellent gas-solid contacting, no hot spots even with highly exothermal reactions, good gas-to-particle and bed-to-wall heat transfer and the ease of solids handling which is particularly important if the catalyst is quickly ageing. However, the list of disadvantages is as long: broad residence time distribution of the gas due to dispersion and gas-bypass in the form of bubbles, broad residence time distribution of solids due to intense mixing, erosion of bed internals and the attrition of the catalyst particles. A particular disadvantage of the fluidized bed reactor is its difficult scale-up. The historical experience with the FCC process is that in the early 40's of the last century this process was successfully scaled up from a 5 cm dia. pilot-scale unit to a 4.5 m dia. bed in the production unit. On the other hand, around 1950 the scale up of the Fischer-Tropsch synthesis in the fluidized bed failed completely. Modern process design should be able to avoid such disasters by making use of modeling and simulation tools. However, a modeling tool which is really helpful in planning and designing of an industrial fluidized bed reactor has to fulfill a lot of requirements. It should be able to describe the influence of the several changes which are typical for the scale-up process, for example enlargement of bed diameter, bed height and fluidizing velocity, changes of gas distributor design, introduction of in-bed heat exchanger tubes and baffles. In the present work a modelling approach is presented which is able to handle the most important aspects of industrial fluidized bed reactors. A particular focus is to describe the relationship between catalyst attrition, solids recovery in the reactor system and chemical performance of the fluidized bed reactor. The competing influences of attrition of the catalyst particles and efficiency of the solids recovery lead to the establishment of a catalyst particle size distribution (PSD) in the bed inventory which in turn influences via the hydrodynamic characteristics of the fluidized bed the performance of the chemical reactor. The usefulness of this approach is illustrated with model calculations for a fictituous first order reaction where the fluidized bed is equipped with different solids recovery systems including one single stage cyclone, several cyclones in parallel, two- and three-stage cyclone systems, respectively. Model calculations illustrate the significance of a high efficiency of the solids recovery in order to keep the fines in the system which is decisive for a high performance of the reactor. The calculations reveal that it may take months until a quasi steady state of the bed particle size distribution is obtained.
A Hybrid Methodology For On-Line Process Monitoring
Authors: Kumar Rakesh , Jade Avinash M. , Jayaraman Valadi K. , Kulkarni Bhaskar D.
Published: October 2005

A hybrid strategy of using (i) locally linear embedding for nonlinear dimensionality reduction of high dimensional data and (ii) support vector machines for classification of the resultant features is proposed as a robust methodology for process monitoring. Illustrative examples substantiate the methodology vis-à-vis current practice.
Enhancement of the Distribution of a Liquid Sprayed Into a Fluidized Bed
Authors: Zhou David , Saberian Mohammad , Briens Cedric , Berruti Franco , Chan Edward W , McDougall Steven L
Published: October 2005

In the fluid coking process, bitumen and steam are sprayed into a fluidized bed of coke particles. The liquid reacts on the surface of the hot particles to give distillate products, light gases and coke. A good primary particle/liquid mixing in the spray jet is required in order to achieve high yields of valuable products and minimize operability problems due to particles agglomeration or loss of bed fluidity.An Enhanced Solids Entrainment (ESE) device has been proposed to improve the mixing of droplets and particles during injection. It consists of a cylindrical tube mounted co-axially downstream of the spray nozzle. The objective of this study is to develop an effective and convenient non-invasive technique to quantify the improvements in liquid distribution on the particles that results from the use of ESE device.A slug of 30 vol% ethanol in water solution is sprayed into a fluidized bed of sand. The bed is defluidized shortly after the start of the ethanol water injection. Then, the gas-solid contacting pattern is changed to fixed bed, with downward airflow. The evaporation rate can be obtained from the measured concentration of ethanol in the gaseous effluent. The evaporation rate depends on the wetted area that is exposed to the gas. Good primary dispersion of the liquid on particles yields a large exposed wetted area and, hence, a high evaporation rate. A model is used to estimate the distribution of liquid on the particles from the measured evaporation rate.The experimental results show that the ESE device produces a more uniform primary liquid distribution on the particles, increasing by 7 to 21 % the mass of solids contacted by the injected liquid.
Entrainment and Stability of a Horizontal Gas-Liquid Jet in a Fluidized Bed
Authors: Hulet Craig , Briens Cedric , Berruti Franco , Chan Edward W , Ariyapadi Siva
Published: October 2005

Fluid coking is a non-catalytic process where heavy hydrocarbon feed, sprayed using jets into a fluidized bed reactor, cracks upon contacting hot coke particles and produces valuable volatile fractions. It is estimated that the Alberta tar sands contain 1.7 trillion barrels of oil, equivalent to 35% of the worlds crude oil reserves, of which the majority is processed using fluid cokers. Important parameters that affect the yield of fluid cokers include the feed jet stability and therefore its ability to entrain and mix the injected feedstock with the fluidized coke particles. To this purpose, this study investigated the effect of the use of various types of draft tubes, placed downstream of the feed jet to enhance mixing, on solids entrainment and jet stability.Specifically, it has been demonstrated with the use of a gas-liquid and gas-only jet that an optimum distance exists between the nozzle and draft tube for entrainment of solids. For both cases, this optimal distance occurs as the jet touches the draft tube wall. However, for a gas-only jet this occurs at a shorter distances due to the increased angle of expansion. The angles of expansion were confirmed using triboelectric probe measurements. It has also been shown that the shape of the inlet to the draft tube will have an effect on the rate of solids entrainment as will the presence of pulsations in the jet.
Influence of the Preparation Method and Metal Precursor Compound on Alumina-Supported Pd Catalysts
Authors: Tonetto Gabriela M , Damiani Daniel E
Published: October 2005

Supported palladium catalysts were prepared by two different methods: wet impregnation and incipient-wetness impregnation. Commercial gamma-Al2O3 and sol-gel derived alumina were used as support. The synthesis of alumina xerogel was carried out by hydrolysis of aluminum isopropoxide (AIP) in 2-propanol solution. Organometallic -Pd(C5H7O2)2- and inorganic precursor -Pd(NH3)4Cl2.H2O- were used for the synthesis of the catalytic systems.Samples were characterized by BET surface area measurement, atomic absorption spectroscopy (AAS), X-ray diffraction (XRD), temperature-programmed reduction (TPR), and hydrogen chemisorption. The activity of these catalysts was studied for the stoichiometric reduction of NO by methane. The decomposition of NO and methane oxidation were also used as a test reaction. Catalyst prepared by wet impregnation method using Pd(C5H7O2)2 and alumina xerogel presented the best performance for the studied reaction. The activity of Pd/alumina catalysts for NO-CH4 reaction is related to the facility for reduction/oxidation of the metal. This property is affected by the nature of the support as well as the metal precursor.
Characterization of Fluidization Quality in Fluidized Beds of Wet Particles
Authors: McDougall Steven L , Saberian Mohammad , Briens Cedric , Berruti Franco , Chan Edward W
Published: October 2005

Monitoring the fluidization quality represents an operating challenge for many processes in which a liquid is sprayed into a gas-fluidized bed, such as fluid coking, fluid catalytic cracking, gas-phase polymerization, agglomeration and drying. Although the presence of liquid will generally have an adverse effect on fluidization, there are often strong incentives in operating with high liquid loadings. For the fluid coking process, for example, operating at lower reactor temperature increases yield and reduces emissions but increases the bed wetness, which may lead to local zones of poor mixing, local defluidization and a reduction in fluidization quality, compromising the reactor performance and stability. The objective of this study is to develop reliable methods to quantify the effects of liquids on fluidized beds.This study examined several methods to evaluate the fluidization quality. Each method was tested in a 3 m tall column, 0.3 m in diameter. Bed wetness was achieved with an atomized spray of various liquids, spanning a wide range of liquid properties.The introduction of liquid in a fluidized bed may result in the formation of wet agglomerates that settle at the bottom of the bed. The liquid may also spread on the particles, increasing their cohesivity and reducing the bed fluidity.Several experimental methods were developed to characterize the effect of liquids on fluidization. Some methods such as the falling ball velocity or the detection of micro-agglomeration from the entrainment of fine particles, are unaffected by agglomerates and detect only the change in bed fluidity. Other methods, such as deaeration or the determination of bubble size from the TDH, are affected by agglomerate formation and changes in bed fluidity.
A Review of Short Residence Time Cracking Processes
Authors: Hulet Craig , Briens Cedric , Berruti Franco , Chan Edward W
Published: October 2005

This review examines the key features and configurations of short residence time cracking processes from a diverse range of industries that have been developed over the past 25 years. These industries include: bitumen or heavy oil upgrading, biomass pyrolysis, olefin production, catalytic cracking, and coal gasification. Characterization of the gas, liquid, and solid products and feedstock is provided wherever possible. In addition, a description of the source and mechanism of heat transfer, and how the feedstock is brought into contact with and separated from  this source is also given.There is a strong economic incentive for considering short residence time cracking processes. Not only do such processes increase the yields of the more valuable liquid and gaseous products, but more compact designs would also decrease capital costs. Careful control of the vapour residence times appears to be crucial in order to prevent secondary cracking and yet allow for maximum cracking of the feedstock. Rapid and thorough mixing of the feedstock with the heat source, not just creating a uniform dispersion, is also a key design aspect to consider. Finally, rapid and complete separation must also be carefully considered; again, to help control product residence time and avoid secondary cracking but also from a heat balance point of view.
Enhanced Reactor Performance with Pressure and Vacuum Swing Reaction
Authors: Gomes Vincent G
Published: October 2005

Product separation and regeneration of sorbent was accomplished in a novel pressure swing reactor through pressurisation, adsorption, blowdown and purge steps. The switching from sorption to reaction to regeneration was tested in a two bed sorption/reaction apparatus. Models developed for the mass and momentum transfer in the catalyst bed and sorber, were solved using orthogonal collocation within the method of lines. The effects of operating conditions and cycle configurations on performance were assessed. The results from dynamic experiments with propene metathesis to produce ethene and 2-butene in a fixed-bed catalytic reactor were in agreement with model predictions. Both pressure and vacuum swing demonstrated that conversion and product quality can be enhanced by periodic cycling with greater separation obtained with vacuum swing. The separation of products help reduce the downstream processing costs of exit mixtures, enable reactant utilisation by recycling and improve product handling at subsequent stages. The efficacy of the periodic separating reactor in terms of conversion, product purity and recovery were investigated.
A Local Model for Gas-Liquid Mass Transfer in a Gas-Liquid-Solid Circulating Fluidized Bed
Authors: Liu Zhengliang , Zheng Ying
Published: October 2005

A local mass transfer model which details the local gas-liquid mass transfer phenomenon in a gas-liquid-solid circulating fluidized bed (GLSCFB) is discussed and tested in this work. It is observed that the local mass transfer model with consideration of the axial liquid dispersion can appropriately address the gas-liquid mass transfer at every radial position in the riser; however, that without consideration of the axial liquid dispersion can only deal with the mass transfer near the wall where the axial liquid dispersion is negligible. The effects of gas flow rates, liquid velocities, particle circulating rates, and particle sizes on gas-liquid mass transfer in GLSCFBs have also been examined systematically. Based on the experimental data, a correlation is obtained to predict the gas-liquid mass transfer coefficients in GLSCFBs for the first time.
Modeling, Simulation and Optimal Control of Ethylene Polymerization in Non-Isothermal, High-Pressure Tubular Reactors
Authors: Yao Fred Z , Lohi Ali , Upreti Simant R. , Dhib Ramdhane
Published: October 2005

Low-density polyethylene (LDPE) is a very important polymer, which is usually produced through a free radical polymerization process in high-pressure tubular reactors. In this study, the mathematical model of this process is developed on the basis of a comprehensive reaction mechanism to accurately determine polymerization rate, and polymer properties under extreme temperature conditions. The model comprises of (i) the mass balances of monomer, initiator, solvent, live radicals and dead polymer chains, and (ii) the energy balances of a tubular LDPE reactor, and its jacket under steady state condition. The model considers the variations in the density and viscosity of reactants along reactor length. Computer simulation of the model is successfully carried out to accurately describe the performance of a non-isothermal, high-pressure, industrial LDPE reactor with multiple initiator injections. Based on the developed non-linear model, the optimal control of the industrial reactor is carried out using genetic algorithms to maximize monomer conversion using jacket temperature as a control function of reactor length. The application of optimal control leads to significant improvements in the final monomer conversion, and capacity utilization of the reactor.
A Parametric Study of the Oxygen Elimination Process in a Packed Bed
Authors: Natarajan Shankar , Zhang Chao , Briens Cedric
Published: October 2005

This study is concerned with an industrial application involved in the manufacture of the polymer Nylon12, which is polymerised from solid monomer particles. There exists interstitial air among those particles. Oxygen in the air is a strong inhibitor of the polymerization reaction and has to be eliminated from the packed bed of monomer particles before they are introduced into the polymerization reactor. This is done by injecting nitrogen into the packed bed from the bottom of the bed. The nitrogen spreads into the packed bed displacing the air inside. This process is already being employed in the polymer processing industries. The present research focuses on how to make this oxygen elimination process more effective.The information from a parametric study can be used to improve the design and operation of the packed bed to have a more effective oxygen elimination process. Conducting the parametric study numerically saves a lot of time and cost. The numerical model used to simulate the fluid flow in packed beds was successfully validated against experimental and analytical results in previous work. This model is used to carry out a numerical parametric study. It is found that having a single jet at the centre of the packed bed is better than having 4 jets closer to the wall. Having an inclined jet instead of a jet parallel to the wall also improves the oxygen elimination process. Simulations are also done with helium as the carrier gas; though economically, it is better to use nitrogen, the purpose of using helium is to investigate the effect of the properties of the carrier gas on the oxygen elimination process.
Modeling and Simulation of a Multistage Agitated Contactor for Hydrogenation of Nitrile Butadiene Rubber
Authors: Zhang Lifeng , Pan Qinmin , Rempel Garry L.
Published: October 2005

The dynamic behavior of a multistage agitated contactor has been numerically studied for its potential use for catalytic hydrogenation of nitrile butadiene rubber. A model consisting of stirred tanks in series with back flow is applied to describe the flow behavior in the presence of hydrogenation within a multistage agitated contactor of six stages. The coupled behavior between kinetics and mass transfer is analyzed by manipulating parameters involved in the model. The model predicted that the performance of the reactor is completely governed by the ability of the catalyst in activating hydrogen, the loading level of C=C double bonds, the relative capacity of the reaction to mass transfer, and the backmixing. Mass transfer and backmixing are important factors for the hydrogenation process and enhancing mass transfer and minimizing backmixing helps in increasing hydrogenation conversion. The effects of backmixing and the number of stages for the hydrogenation are discussed, and optimal operation conditions are suggested.
Chemical Reaction Engineering, the Environment, Pollution Prevention and Sustainable Development
Authors: Dudukovic Milorad P.
Published: October 2005

This presentation attempts to illustrate the links between chemistry, the environment, multiphase reaction engineering, pollution prevention and sustainable development. The choice of process chemistry impacts not only the atom efficiency but also the degree of environmental damage caused by the manufacture of the choisen product. The execution of this chemistry requires multi-phase reaction engineering and, depending on the contacting scheme used, leads to different degrees of product yield, energy efficiency and formation of unwanted products. As a consequence, the number and type of separation units used and the recycling burden created is a function of the reactor choice and operating conditions. Clearly, understanding the principles of multiphase reaction engineering and their application are very important for proper execution of truly environmentally benign processes.Advances in understanding the phase contacting and mixing in reactors with moving and stagnant catalysts, and proper use of appropriate CFD codes are reviewed. Two powerful techniques for evaluation of holdup distribution (Computer Tomography - CT) and assessment of velocity profiles and mixing (Computer Aided Radioactive Particle Tracking - CARPT) are introduced. The data gathered is used for validation of CFD multiphase codes and for the establishment of appropriate engineering models for a variety of multiphase reactors such as risers, bubble columns, stirred tanks, etc.
Ultrasonic Investigation of Hydrodynamics and Mass Transfer in a Gas-Liquid(-Liquid) Stirred Vessel
Authors: Cents A.H.G. , Brilman D.W.F. , Versteeg G.F.
Published: October 2005

The rate of gas-liquid mass transfer is very important in several industrial chemical engineering applications. In many multi-phase reaction systems, however, the mechanism of mass transfer is not well understood. This is for instance the case in Gas-Liquid-Solid (G-L-S) and Gas-Liquid-Liquid (G-L-L) systems. To obtain more knowledge of the mechanism of mass transfer, the mass transfer coefficient, kL, and the interfacial area, a, should be studied separately. In this work an ultrasonic measurement technique is used to study the local interfacial area in a standard sized vessel, equipped with a Rushton type impeller. This is done in combination with experimental determination of the volumetric mass transfer coefficient, kLa, using the dynamic oxygen method, to obtain values for kL. The gas hold-up is determined additionally to obtain values for the Sauter mean bubble diameter at different positions in the vessel. In a coalescing air-water system the bubble size was non-uniform throughout the vessel and increased from small bubbles at the impeller along with the flow pattern to larger sizes in the bulk of the vessel. In a non-coalescing electrolyte system the vessel was much more uniform and the bubbles were smaller when compared to the air-water system. To obtain overall values of the mass transfer parameters the local values were integrated according to their volume fraction in the reactor. In both coalescing and non-coalescing systems the overall values for the mass transfer parameters were in good agreement with literature correlations. The addition of small volume-fractions of toluene to an air-water system caused a strong decrease in both the volumetric mass transfer coefficient and in the gas hold-up. The interfacial area increased, however, but it was shown that this was due to the presence of microbubbles in the solution, which do not take part in the mass transfer process. The enhancing effect on gas-liquid mass transfer due to the addition of larger volume-fractions of toluene could be described reasonably well by a homogeneous model of the shuttle mechanism.
A Computational Study of Gas-solid Flow in an Enhanced Solid Entrainment (ESE) Nozzle System
Authors: Cui Maopei , Straatman Anthony G , Zhang Chao
Published: October 2005

A numerical study has been undertaken to explore the influence of geometry and flow parameters on the entrainment of solid in an ESE nozzle system immersed in a fluidized riser. A fully three-dimensional computational model of the nozzle system has been developed and all appropriate approximations and simplifications are described. A multi-phase Eulerian-Eulerian model incorporating the kinetic theory for solid particles is used. Numerical results are obtained using the commercial Computational Fluid Dynamics software FLUENT. The results indicate that solid entrainment in the ESE system is a strong function of both geometry and flow. The optimal entrainment is seen to occur when the ratio of the draft tube diameter D to separation distance I is approximately unity. At this value, the jet of injected gas is seen to spread fully into the opening of the draft tube causing the highest transport of solid particles through the tube. The entrainment is shown to increase with increasing jet velocity across the full range of flows considered. The results are consistent with similar experimental results. The results of this study should find immediate application in the design and implementation of ESE nozzle systems.
Dodecane Decomposition in a Radio-Frequency (RF) Plasma Reactor
Authors: Merlo-Sosa Laura , Soucy Gervais
Published: October 2005

The research outlined here includes a study of the production of carbon black (CB) in an inductive plasma reactor, using dodecane (C12H26) as the starting material. Thermodynamic and kinetic studies were carried out to predict the species concentrations likely to be obtained in the pyrolysis process at plasma temperatures. A thorough statistical experimental design was undertaken to investigate the influence of the different operational conditions such as: the feed rates of dodecane, the reactor pressure, the plate power applied to the plasma torch and the composition of the plasma gas, on the production of carbon black and gaseous acetylene-like compounds. Thermodynamic and kinetic models were compared with experimental results, a kinetic reaction model best representing the experimental results. Morphological analysis of the solid product using Transmission Electron Microscopy (TEM) indicates that a high plasma temperature is the most important factor affecting the final morphology of the carbon black formed during the reaction. Carbon black with average particle size of 10-30 nm and specific surface of 130 m2/g was obtained. Morphological analyses also demonstrated the presence of new structures ranging from carbon black to fullerenes and including certain graphitized carbon molecules.
Mixing Time Studies in Bubble Column Reactor with and without Internals
Authors: Pandit A. B. , Doshi Yogesh K.
Published: October 2005

Sectionalized bubble columns are finding a wide use in the case of FT synthesis, petroleum refining, wastewater treatments, extraction, absorption, leaching, ion exchange etc., due to their superiority in terms of reduced liquid phase back-mixing. The present work covers a mixing aspect in a 0.41 m id. sectionalized bubble column over a wide range of superficial gas velocity, liquid height to column diameter ratio, percent free area of the sectionalizing plates and electrolyte concentration for Air-water system. The acquired conductivity data was optimized using a compartmental and axial dispersion models and the model parameters have been estimated. For a given Hc/D ratio; mixing time was found to decrease with an increase in gas superficial velocity and free area of the sectionalizing plate. The compartmental model successfully predicts the tracer concentration profile and the longitudinal dispersion coefficient. The mixing time in a sectionalized bubble column was also compared with a non-sectionalized bubble column and was found to be order of magnitude higher.
Heat Transfer in a Membrane Assisted Bubbling Fluidized Bed with Immersed Horizontal Tubes
Authors: Deshmukh Salim A.R.K. , Volkers Sander , van Sint Annaland Martin , Kuipers Hans
Published: October 2005

The effect of gas permeation through horizontally immersed membrane tubes on the heat transfer characteristics in a membrane assisted fluidized bed operated in the bubbling fluidization regime was investigated experimentally. Local time-averaged heat transfer coefficients from copper tubes arranged in a staggered formation with the membrane tubes to the fluidized bed were measured in a square bed (0.15 m x 0.15 m x 0.95 m). Glass particles (75-110 micrometer) were fluidized with air distributed via a porous plate, where the ratio of gas fed or removed through the membrane bundles and the porous plate distributor was varied. The experimental results revealed that high gas permeation rates through the membranes strongly decreased the heat transfer coefficient at high superficial gas velocities for tubes at the top of the tube bundle, which was attributed to the reduced mobility and increased bubble hold up and/or dilution of the emulsion phase, reducing overall heat capacity.In the design of membrane assisted fluidized beds care must be taken to include the effect of gas addition or withdrawal through the membranes on the required heat transfer surface area.
Simulation of the Storage of Molten Poly(Ethylene Terephthalate)
Authors: Yamada Toshiro , Hao Lifei , Tada Kaoru , Konagaya Shigeji
Published: October 2005

In order to decrease the manufacturing cost, the molten poly(ethylene terephthalate)(PET) produced by batch process is stored in a large tank named Pool Tank for after treatment to bring about a continuous manufacture. The alterations of quality happened during the storage should be precisely controlled. In this paper, a method for prediction of fluctuation of molten PET properties with computer simulation only was designed. First of all, a new reaction model which could present the mechanism of polycondensation occurred in Pool Tank was proposed. Then, reaction rate constants were determined by experiments according to the optimization procedure and subsequently, applied to the simulation of storage of molten PET. The fluctuation of intrinsic viscosity and concentration of carboxyl terminal groups of molten PET was predicted. Meanwhile, some useful information for the design of storing tank could be obtained.
Comparative Study of Two-Phase Gas-Liquid Flow in the Ejector Induced Upflow and Downflow Bubble Column
Authors: Mandal Ajay , Kundu Gautam , Mukherjee Dibyendu
Published: October 2005

A comparative study has been made on the hydrodynamics and gas-liquid mass transfer performances of upflow and downflow bubble columns. Gas-liquid distributions in the column are made by an ejector system using liquid as motive fluid and gas is used as secondary fluid for both the cases. The two-phase hydrodynamic studies have been done with water and aqueous solutions of carboxy methyl cellulose at different concentrations and air as gas phase. The volumetric mass transfer coefficients have been measured by absorbing air-carbon dioxide mixture in aqueous solutions of sodium carbonate and bicarbonate. For downflow system, experiments are carried out at natural suction of air through the ejector; whereas for upflow system, air is forced through the secondary entrance of the ejector from a high pressure tank at any desired rate. The effect of gas and liquid flowrates on gas holdup, frictional pressure drop and mass transfer coefficients have been investigated. All the experiments have been performed in the homogeneous flow regime for a stable operation.
Mixing Characteristics of an Axial-Flow Rotor: Experimental and Numerical Study
Authors: Kerdouss Fouzi , Kiss Laszlo , Proulx Pierre , Bilodeau Jean-Francois , Dupuis Claude
Published: October 2005

In the metallurgical industry, various types of rotors are used for the injection and distribution of gas and for homogenizing molten metal. In the present work, the liquid-gas two-phase flow around an axial type impeller is studied in a water model, in order to analyze the bubble break-up and coalescence and metal mixing. Details like primary and secondary vortex structure, gas flooding between the blades and gas dispersion are recorded by using high speed photography.A mathematical model that takes into account the combined effect of bubble break-up and coalescence is implemented in the commercial computational fluid dynamics (CFD) software FLUENT. In the proposed work, the impeller is explicitly described in three dimensions using Multiple Reference Frame Model. Dispersed gas and bubbles dynamics in the turbulent water are modeled using an Eulerian-Eulerian approach with dispersed k-epsilon turbulent model. The model predicts spatial distribution of gas hold-up, average bubble size and flow structure. Good qualitative agreement between physical model and simulation is achieved when comparing the bubble size distribution, flow structure and mixing.
First Steps in the Adsorption of C5H8 on Pt(111)
Authors: Simonetti Sandra , Brizuela Graciela
Published: October 2005

The adsorption of C5H8 on Pt(111) has been studied using a semiempirical theoretical method implemented with the YAeHMOP package. The energetic calculations show that the adsorption is weak. The adsorbate-surface interaction requires that both C-H and Pt-Pt bonds be weaken. The main interaction comes from the C and H nearest to the metal surface. The tilted geometrical configuration adopted by the molecule facilitates this interaction. The Pt-C and Pt-H interactions are mainly due to overlaps between the dz2 and pz metal orbitals and the C pz and H s orbitals, respectively.
Solvent Effects During Oxidation-Extraction Desulfurization Process of Aromatic Sulfur Compounds from Fuels
Authors: Gomez Bernal Hilda , Cedeño Caero Luis
Published: October 2005

Benzothiophene, Dibenzothiophene (DBT), 4-methyldibenzothiophene, and 4,6-dimethyldibenzothiophene are typical thiophenic compounds prevailing in diesel fuels. Using a hexadecane solution of these model compounds, experiments were carried out to compare the reactivity of the different benzothiophenes in oxidesulfurization (ODS) with several polar solvents. V2O5/Al2O3 catalyst, hydrogen peroxide as oxidant and the solvents: N,N-dimethylformamide (DMF), 2-ethoxyethanol (EEOH), acetonitrile (MeCN) and gamma-butyrolactone (BuL) were used. The experimental results showed that removal of benzothiophenes contained in diesel can be carried out efficiently in conditions here studied, with a yield to sulfones higher than 80%, depending on the reactivity of each S-compound and solvent used. DBT was completely removed but the yield to DBT sulfone with MeCN was only 95%. According to the solvent used, benzothiophenes reactivities decrease in the order: MeCN > BuL > EEOH > DMF. It was found that an important fraction of the eliminated compounds in the diesel phase, is not totally transformed to its corresponding sulfone, it is only removed as sulfur compound by extraction, without undergoing ODS reaction. Depending on the thiophenic compound, it was possible to remove about 70-85% of benzothiophenes by physical extraction process, using the best solvent (DMF) and only close to 30-60% with MeCN.
The Influence Of The Support On The Deactivation Behaviour of Pt-Sn Reforming Catalysts
Authors: Contreras Ignacio , Pérez Gustavo , Viveros Tomás
Published: October 2005

The effect of Al2O3-ZrO2, Al2O3-TiO2 and Al2O3-La2O3 mixed oxides on the deactivation of bifunctional Pt-Sn/ Al2O3 reforming catalysts has been investigated. The n-heptane reforming at 500°C was used as a test reaction. Changes in the catalytic behavior due to differences of the acidity and the support-metal interaction were observed. Levenspiel´s and Beltramini´s deactivation models were developed assuming a series fouling for the carbonaceous deposits. Through the Beltraminis model it was possible to distinguish the amount of acidity that participates in the deactivation processes. Both models successfully correlated with the experimental profiles of n-heptane activity decay. The following deactivation decreasing order, Al2O3-TiO2-1>Al2O3-ZrO2-25>Al2O3-TiO2-2> Al2O3>Al2O3-La2O3-10 was found with both deactivation models. A quasi-linear correlation between the deactivation order and the coke formation kinetic constant (Levenspiels parameters) was observed. The catalyst acidity and the n-heptane conversion were correlated with Beltraminis model. It was found that a high acidity (12 X 10-17 acid sites/g cat.) or metal dispersion (83%) increases the catalyst deactivation and it is necessary to have a balance of active sites in order to have a catalyst working as a bifunctional catalyst. On the other hand, the auto-regeneration Beltraminis parameter suggests that the lowest deactivation of the Pt-Sn/ Al2O3-La2O3-10 catalyst is attributed to the cleaning capacity of the active sites. It was observed that the highest deactivation (80-92%) of the platinum-tin catalysts supported in alumina-titania mixed oxides were a result of the strong metal-support interaction (SMSI) effect. The Pt-Sn/Al2O3-La2O3-10 showed the best catalytic behavior with high initial and residual conversions (70 and 48%, respectively) and low deactivation (17 %) at a 50-minute reaction time. Furthermore, in the Pt-Sn/Al2O3 catalyst, the benzene yield was 1%, while the Pt-Sn/Al2O3-La2O3-10 showed a total inhibition of benzene production yield at residual conversions.
Effect of Temperature on Solids Mixing in a Bubbling Fluidized Bed Reactor
Authors: Radmanesh Ramin , Mabrouk Rachid , Chaouki Jamal , Guy Christophe
Published: October 2005

Solid mixing in fluidized bed reactors has a great impact on the transport phenomena in the reactor. Most studies, concerning solid behavior and hydrodynamic correlations of fluidized bed reactors, have been done at ambient temperature. Industrially, however, fluidized bed reactors operate at high temperatures. The lack of studies at higher temperatures is due to difficulties associated with measuring techniques under these conditions. In extrapolating hydrodynamic parameters derived at ambient temperature to higher temperatures, only the physical property changes of gas and solid phases, such as density and viscosity are taken into consideration. On a microscopic scale, however, change of temperature strongly affects the interaction between particles, which in turn has a substantial impact on the hydrodynamics of a fluidized bed.In this study and for the first time, the Radioactive Particle Tracking (RPT) is used to investigate the effect of temperature on the fluidization of silica sand particles (Geldat-B) in a bubbling fluidized bed reactor. Experiments have been carried out at different temperatures (25-400oC) and superficial gas velocities (0.17-0.75 m/s). The effect of temperature on the global mixing is studied in conjunction with the changes found in the dynamic of the ascending and descending phases. A two-phase countercurrent back-mixing model (CCBM) was used to investigate global solid mixing at different temperatures. The wake exchange coefficient, in the CCBM model, is calculated and compared with the values obtained from different correlations. For various experiments, the exchange coefficient is found to be in the range of 0.6-1.7 sec-1. The correlations can predict the trend of the wake exchange coefficient change with temperature, but they all overestimate it. The correlations developed by Hoffmann et al. (1993) and Lim et al. (1993) were found to give a better agreement with the results at high temperatures.
The Optimisation of Pressure Measurements for the Control of Bubbling Fluidised Beds
Authors: Croxford Anthony J , Harrison Andrew J.L. , Gilbertson Mark A
Published: October 2005

A common form of chemical reactor is the bubbling fluidised bed where gas is introduced into a free bed of particles at a rate exceeding that necessary to support their weight. The behaviour of the reactor is dependent on the distribution and characteristics of the bubbles within the bed. Information about these can be inferred from pressure measurements within the bed, which can also be used to characterise the dynamics of a bed and therefore to control it and the reaction.It is necessary to understand what the pressure signals are measuring, how many of them are necessary, and where they should be placed for them to be used to characterise the state of the bed. Pressure measurements are made at single points within a bed, and it is not immediately clear whether the measurements are local (owing to some sort of wall effect, for example), characterise the region close to the sensor, or the whole bed. It is shown how the dynamics of the bed can be characterised from the pressure signals, and that these signals are sensitive to the state of the bed. It is also necessary to evaluate where the sensors should be placed and how many of them should be used. Important considerations here are the extent to which the measurements of pressure are axisymmetrical, and whether in some circumstances and positions the local dynamics mask the overall bed dynamics. Axisymmetry is shown to exist under many conditions and that a single transducer can be sufficient. Furthermore, the depth of the bed is also shown to have a significant effect on its dynamics.It is also shown how the characterised pressure measurements can be used to control the state of the fluidised bed and used to enhance the performance of a fluidised bed reactor.
Carbon Nanotube Synthesis: A Review
Authors: Baddour Carole E , Briens Cedric
Published: October 2005

Discovered in 1991, carbon nanotubes (CNTs) have reached the forefront of many industrial research projects. Carbon nanotubes are tubular carbon molecules with remarkable mechanical, chemical, thermal and electrical properties, which make them useful in various applications. This paper reviews three methods of synthesizing the nanomaterial, namely arc-discharge, laser-ablation and fixed bed/fluidized bed catalytic. These methods have generated a large interest in many industrial companies to date. At the moment, the most critical issue faced by industrial companies is determining the best synthesis method, which will give the most economical large-scale production of CNTs. Compared to the other two methods, the catalytic technique to synthesize CNTs is simple, inexpensive, energy-efficient and can produce large CNTs quantities of high yield and purity.
Hydrogen Production in Fluidized Beds with In-Situ Membranes
Authors: Grace John , Elnashaie Said S.E.H. , Lim C. Jim
Published: October 2005

Fluidized Bed Membrane Reactors (FBMR) offer significant advantages for steam reforming and the production of hydrogen. Potential advantages include higher yields by reducing thermodynamic equilibrium limitations, process intensification by combining three vessels into one, reduced temperatures of operation, countering the adverse effects of pressure, virtually eliminating catalyst diffusional limitations, high productivity per unit volume of reformer, and flexibility in using alternative feedstocks. Realization of the FBMR process for hydrogen production requires that a number of unusual challenges in reactor design be met. This paper discusses the technical challenges and outlines key factors which are being addressed in providing the membranes, reactor configuration and integrity, catalyst, energy integration and operating conditions needed to establish an economically viable FBMR process.
Mechanochemical Degradation of Aromatic Sulfonic Acids
Authors: Caschili Silvia , Delogu Francesco , Cao Giacomo
Published: October 2005

Sulfonic acids and sulfonates are widely used as surfactants in various industrial processes. Although partial biodegradation occurs, their release in the environment has determined a widespread pollution problem due to their remarkable tendency towards accumulation. For this reason, various methodologies to effectively degrade sulfonic acids and sulfonates in real matrices are currently under investigation. In this study, we focused our attention on the mechanochemical degradation of the 1,5‐naphthalene disulfonic acid using strongly reducing agents such as pure Mg and Ca metals. The mechanochemical processing induced either a gradual degradation of the organic compound or a combustion‐like reaction depending upon the experimental conditions. A partial degradation of the sulfonic acid was observed as a result of gradual reactions. An almost complete removal of the pollutant was instead observed after combustion‐like reactions.
Characterization of Raw and Stabilized Waste in Relation to Toxic Metals Mobility in Realistic Landfilling Scenarios
Authors: Buondonno Andrea , Cioffi Raffaele , Santoro Luciano
Published: October 2005

Toxic metal release in simple leaching tests has been studied in this paper to assess waste behaviour in realistic landfilling scenarios. The waste is a galvanic sludge, raw or cement stabilized. Six different leachants were taken into account: distilled water, CO2‐saturated solution, Olsen solution, Mehlich No. 3 solution, acid or alkaline soil circulating solution. Dynamic leaching tests of different duration were used for raw and stabilized waste. The results have shown that, with the exception of Mehlich No. 3 solution, when the waste comes into contact with waters of composition similar to that of the solutions studied, the potential environmental contamination should not be of concern.
Detection of breastfeeding and weaning in modern human infants with carbon and nitrogen stable isotope ratios
Authors: Fuller B.T. , Fuller J.L. , Harris D.A. , Hedges R.E.M.
Published: October 2005

Carbon (13C/12C) and nitrogen (15N/14N) stable isotope ratios were longitudinally measured in fingernail and hair samples from mother‐infant pairs where infants were exclusively breastfed (n = 5), breast‐ and formula‐fed (n = 2), or exclusively formula‐fed (n = 1) from birth. All exclusively breastfed infants had a dual enrichment in carbon (≈1‰) and nitrogen (≈2–3‰) when compared to maternal values. In contrast, breast‐ and formula‐fed subjects had reduced enrichments compared to exclusively breastfed subjects, and the exclusively formula‐fed infant showed no increase in δ13C or δ15N values. This finding of a carbon trophic level effect in breastfeeding infants suggests that 13C‐enrichments of approximately 1‰ in archaeological populations are not necessarily the result of the consumption of C4‐based weaning foods such as maize or millet. During the weaning process, the δ13C results for breastfed infants declined to maternal levels more rapidly than the δ15N results. This suggests that δ13C values have the potential to track the introduction of solid foods into the diet, whereas δ15N values monitor the length of time of breast milk consumption. These findings can be used to refine the isotopic analysis of breastfeeding and weaning patterns in past and modern populations. Am J Phys Anthropol, 2006. © 2005 Wiley‐Liss, Inc.
Experiencing and detecting happiness in humans: The role of the supplementary motor area
Authors: Krolak‐Salmon Pierre , Hénaff Marie‐Anne , Vighetto Alain , Bauchet Françoise , Bertrand Olivier , Mauguière François , Isnard Jean
Published: October 2005

Understanding emotions in others may involve neural structures implicated in both perception and action.1 Laughter is a socially important behavior and its neural correlates are poorly understood. Depth electrode electrophysiological techniques offer a rare opportunity to both record and stimulate neural structures involved in emotion processing.2, 3 This kind of direct electrophysiological investigation in humans is particularly determinant because laughter processing cannot be studied in animals. Ann Neurol 2005
Titelbild: Mass Spectrometric Profiling of Intact Biological Tissue by Using Desorption Electrospray Ionization (Angew. Chem. 43/2005)
Authors: Wiseman Justin M. , Puolitaival Satu M. , Takáts Zoltán , Cooks R. Graham , Caprioli Richard M.
Published: October 2005

Die Desorptions‐Elektrospray‐Ionisierung wird für die massenspektrometrische Analyse von Phospholipiden genutzt. In ihrer Zuschrift auf S. 7256 ff. beschreiben R. G. Cooks, R. M. Caprioli et al. die schnelle Analyse von unbehandelten biologischen Geweben, darunter der Tumorregion von Lebergewebe. Im Titelbild sind das Auftreffen geladener Liquidmikrotröpfchen auf Lebergewebe an Luft und die Freisetzung von Lipiden und anderen Molekülen als Ionen für die Analyse dargestellt. (Das Bild stammt von Z. Ouyang, J. Wiseman und R. Shreve.)
Insights into the Role of the Liquid–Liquid Interface in Biphasic Reactions: The Reaction of Vitamin B12s(aq) with Vicinal Dibromides(oil)
Authors: Davies Trevor J. , Garner A. Christopher , Davies Stephen G. , Compton Richard G.
Published: October 2005

Electrocatalytic processes can take place either homogeneously in a single liquid phase or heterogeneously at the liquid–liquid interface formed in emulsions. This Article addresses the question as to whether a change in rate and/or mechanism can occur between the two possibilities. Specifically, cyclic voltammetry and electrosynthetic experiments are used to demonstrate that for the vitamin B12 mediated reduction of vicinal dibromides producing olefins, electric field effects likely operate at the liquid–liquid interface which can change the populations of different conformers relative to the single homogeneous‐phase experiment, leading to significant changes in rate.