bluuebunny/crossref_metadata_2025 huggingface dataset:
The influence of baffle off‐bottom clearance on the solids suspension performance of pitched‐blade and high‐efficiency impellers
Authors: Myers Kevin J. , Fasno Julian B.
Published: March 2009

An innovative video technique indicates that the solids suspension performance of pitched‐blade impellers in flat‐bottomed tanks is improved by using a baffle off‐bottom clearance in the range of one‐fourth to one‐half of the baffle width (standard baffle width being one‐twelfth of the tank diameter). The solids suspension performance of high‐efficiency impellers is relatively unaffected by baffle off‐bottom clearances in the range of zero to one‐half of the baffle width. A baffle off‐bottom clearance equal to the baffle width is detrimental to the solids suspension performance of both pitched‐blade and high efficiency impellers.
The selective non‐catalytic reduction of nitric oxide using ammonia at up to 15% oxygen
Authors: Caton J. A. , Narney J. K. , Cariappa H. C. , Laster W. R.
Published: March 2009

Selective non‐catalytic reduction of nitric oxide (NO) using ammonia was studied with up to 15% (by volume) oxygen at 102 kPa. The experiments were conducted in an electrically heated laminar‐flow, quartz reactor using mixtures of N2, O2, NO, and CO to simulate exhaust gas. The base case condition included 330 ppmv of NO, 495 ppmv of NH3, and 15% O2. At a reactor temperature of 1050 K, 77% of the NO was removed. For a lower oxygen concentration of 1%, the NO removal was as high as 98% at 1100 K. The degraded performance at high oxygen concentrations is attributed to increases in the oxidation reactions.

A major result of this work was the quantification of the amount of N2O in the treated gases. For the base case conditions, 21 ppmv of N2O was measured for a reactor temperature of 1075 K. Increasing the ratio of NH3 to NO (by increasing the NH3 concentration) increased the maximum NO removal and decreased the temperature at which this level of NO removal was achieved. For the higher NH3 concentrations, however, the N2O concentration increased to as high as 54 ppmv. The oxidation products of ammonia (in the absence of NO) for these conditions were found to include first N2O beginning at 900 K and then NO beginning at 1050 K. Comparisons between these experimental results and predictions from the Miller and Bowman (1989) model indicate that further enhancements of the model may be necessary to incorporate the features of high oxygen conditions.
Equation of state representation of aqueous mixtures using an association model
Authors: Shinta Ali A. , Firoozabadi Abbas
Published: March 2009

A previously proposed association equation of state (AEOS) (Anderko, 1991) for aqueous mixtures is modified to extend its applicability to a wider range of temperatures and pressures. In the AEOS, the compressibility factor is subdivided into two parts; physical and chemical. The physical part, in this work, is represented by the Peng‐Robinson (PR) (1976a) EOS for nonpolar compounds. Other cubic EOS can be used for this purpose with little effect on results. The chemical part is expressed by an empirical association model. The improved association model enables the AEOS to reproduce accurately the total compressibility of pure liquid water along the saturation line. Incorporation of the new association model in the PR‐EOS allows the combined model to calculate accurately the phase behavior of water/hydrocarbons and water/nonhydrocarbons in VLE, LLE, and VLLE regions.
Revisiting the maximum conversion of substrate in an enzymatic cstr with micromixing considerations
Authors: Malcata F. Xavier
Published: March 2009

The balance equations pertaining to an enzyme undergoing first order thermal deactivation and a substrate undergoing enzyme‐catalyzed transformation following Michaelis‐Menten kinetics in a CSTR are solved for the two limits of micromixing. The maximum conversions of substrate are obtained under the assumption that the space time of the reactor is infinite. The range of the maximum conversion of substrate is wider at intermediate values for the dimensionless Michaelis‐Menten constant and becomes narrower as the ratio of the time scales of the enzyme‐catalyzed reaction and the enzyme deactivation increases.
Particle cross‐flow, lateral momentum flux and lateral velocity in a circulating fluidized bed
Authors: Zhou J. , Grace J. R. , Lim C. J. , Brereton C. M. H. , Qin S. , Lim K. S.
Published: March 2009

Lateral and axial profiles of solids cross‐flow flux were measured in a circulating fluidized bed riser of square cross‐section with a sampling probe. The solids cross‐flow flux was found to be higher near the wall, especially near the corners, and lower in the core of the riser. The net solids horizontal flux was outwards in the lower part of the riser and inwards near the top.

The lateral solids momentum flux, measured by means of a piezoelectric probe, increased with height and then decreased near the top of the riser. The lateral solids momentum flux first increased with distance from the axis and then decreased towards the wall. It was especially low near the corners.
On‐Line control of supersaturation in a continuous cooling KCL crystallizer
Authors: Redman T. P. , Rohani S. , Strathdee G.
Published: March 2009

Control of supersaturation in a 1‐L continuous cooling KC1 crystallizer was investigated. The supersaturation was determined from on‐line measurements of the density and temperature of clear liquor samples. A cascade control scheme was used to control the supersaturation through the manipulation of the co‐saturated feed temperature set‐point while maintaining the crystallizer temperature at 303.2 K. Experimental results showed that due to the suppression of spontaneous nuclearion, a decrease in the measured supersaturation resulted in a 23% increase in the mean crystal size and a 12% decrease in the amount of NaCl impurity in the KCI crystals.
Video analysis of submerged jet microencapsulation using HEMA‐MMA
Authors: Stegemann Jan P. , Sefton Michael V.
Published: March 2009

Video and digital image analysis were used to understand the limiting steps in a submerged jet microencapsulation process for mammalian cells. Hydroxyethylmethacrylate‐methylmethacrylate copolymer (HEMA‐MMA) two phase droplets with an aqueous core are formed by coextrusion at a needle tip and fall through a layer of hexadecane prior to precipitation in an aqueous medium. Initial eccentricity was lowest when the capsule cores contained 20% (w/v) Ficoll and the inner needle protruded 100 m̈m past the outer needle. Capsule morphology was refined in the hexadecane over‐layer, and was strongly affected by crossing the hexadecane‐precipitation bath interface.
On the clean and efficient thermal treatment of de‐inking solid residues
Authors: Kozinski Janusz A. , Zheng Guohui , Saade Raafat , Di Lalla Sergio
Published: March 2009

Thermal treatment of contaminated de‐inking sludge in a low‐high‐low (LHL) temperature reactor was investigated. Experiments were conducted in a Cahn TGA‐171 furnace coupled with a Mattson Galaxy 5020 FTIR. Sludge samples (70 g) were heated up to 1770 K (50 K/min.), kept at that temperature for 5 min. and were then quenched (60 K/min.). During the LHL process the sludge underwent structural transformations from a mixture of fibers, through skeleton‐like structures (45–110 μm), porous particles, to compact spheres (5–30 μm). It was shown that the LHL treatment results in a safe encapsulation of heavy metals (Pb, Cd) inside the ash and in a 78.2% decrease in the amount of mutagenic polycyclic aromatic hydrocarbons. The LHL method developed could help to solve waste management and environmental protection problems.
Modelling and simulation of commercial catalytic naphtha reformers
Authors: Vathi Garimella Padma , Chaudhuri Kumar K.
Published: March 2009

A simulation model for catalytic reforming has been developed to monitor commercial plant performance. The model consists of various modules to predict temperature and concentration profiles, catalyst deactivation and cycle length, inter stage heater duties, recycle gas composition and octane number. The lumping details of the feed and reaction scheme, parameter estimation and model validation details are given. The model numerically integrates the component and energy balance equations for the combined feed and recycle gas in each reactor and then simulates flash separator for recycle gas composition. The results of the model validated for four different commercial reactors performance are presented.
Axial and lateral dispersion of fine particles in a binary‐solid riser
Authors: Wei Fei , Cheng Yi , Jin Yong , Yu Zhiqing
Published: March 2009

Axial and lateral mixing of fine particles in a binary‐solid riser have been investigated using a phosphor tracer method. The measured bimodal residence time distribution (RTD) demonstrated two types of axial dispersions of the fines: the dispersion of discrete particles and that of clusters. A proposed one‐dimensional, bimodal dispersion model describes the bimodal RTDs very well. The axial Peclet number of the fines is not sensitive to the fraction of coarse particles, gas velocity and solids circulation rate. Lateral solids dispersion was determined by measuring the solids RTD at different radii using a point source tracer injection. A two‐dimensional dispersion model describes the measured RTDs satisfactorily. Lateral solids mixing decreased as coarse particles were added into the riser. Correlations of the axial and lateral Peclet numbers obtained fit the experimental data well.
Representation of the concentric spherical powder reaction model in the form of linear regression analysis
Authors: Shimizu Akira , Hao Yu‐Jun , Tanaka Tatsuo
Published: March 2009

To perform the linear regression analysis of the powder reaction rate, some kinetic equations are derived on the basis of the Hao and Tanaka's concentric spherical model (Intern. Chem. Eng. 30, 244 (1990) and Can. J. Chem. Eng. 68, 81 (1990)) assuming monodisperse particles. The applicability of the kinetic equations is examined by using the experimental data of both counterdiffusion system and uni‐directional diffusion system. This linear regression analysis enables us to decide rapidly about the suitability of the model, to predict the diffusion mode and to determine the diffusivity.
The dissolution kinetics of sand as function of particle size
Authors: Jendoubi Ferida , Mgaidi Arbi , Maaoui Mohamed El
Published: March 2009

The initial dissolution rate of sand into sodium hydroxide solution (12.5 mol/L) over a wide range of temperatures (150 to 220°C) and pressures (0.47 to 2.29 MPa) has been determined. A semi‐empirical equation was found to fit the dissolution data obtained at different temperatures and at different particle sizes. The influence of temperature on the reaction extent led to the activation energy of the dissolution, Ea = 74.41 kJ/mol. Six samples of sieved silica having narrow particle size distribution 38–40, 100–125, 212–200, 400–500 and 850–1000 μm were reacted with 12.5 mol/L sodium hydroxide solution at 220°C. The effect of particle size, i.e., surface area of the grains, on the initial rate of dissolution (denoted v0) has been described by an empirical equation. Evidence is given here showing that the general assumption of the simple proportionality between the rate of reaction and the exposed surface of solid is not always confirmed.
Use of velocity of sound in predicting thermodynamic properties of dense fluids from cubic equations of state
Authors: Shabani Mohammad R. , Riazi Mohammad R. , Shaban Habib I.
Published: March 2009

In this paper it has been shown that velocity of sound data may be used to obtain constants of a cubic equation of state and then thermodynamic properties can be accurately calculated through the constants extracted from sonic velocity data. Results are presented for estimation of heat capacities, enthalpies, vapor pressures and compressibility factors of some pure vapor and liquid compounds as well as some binary mixtures for pressures up to 100 MPa and temperatures up to 600 K for hydrocarbons from methane to hexadecane. The method will be useful for those mixtures containing heavy compounds for which accurate data on critical constants are not available, but for which the sonic velocity can be measured.
Determination of correlations to predict the minimum agitation speed for complete solid suspension in agitated vessels
Authors: Armenante Piero M. , Nagamine Ernesto Uehara , Susanto Jessyca
Published: March 2009

Experiments were conducted to determine the effects of impeller clearance, impeller diameter, and other operating variables on the minimum agitation speed for off‐bottom solid suspension in agitated vessels, Njs, for disc turbines (DTs) and flat‐blade turbines (FBTs). Only data for which the impellers produced recirculation flows above and below the impeller (the so‐called “double‐eight” flow pattern) were considered. Regression equations for Njs were obtained, in which explicit terms for impeller clearance and vessel diameter‐to‐impeller diameter ratio (T/D) were included. Modified Zwietering equations (Zwietering, 1958) were also obtained, in which Zwietering's parameter S was mathematically expressed as a function of vessel diameter‐to‐impeller clearance ratio and T/D ratio. When used together with the correlations of Armenante and Uehara Nagamine (1998) for impellers close to the vessel bottom, the equations presented here can be used to calculate Njs for DTs and FBTs for any typical impeller clearance.
Stresses on immobilized phanerochaete chrysosporium hyphae in submerged cultures for ligninase production
Authors: Zhen Zhonming , Yu Jian
Published: March 2009

Effects of hydraulic shear stress and oxygen starvation stress on immobilized white‐rot fungus Phanerochaete chrysosporium in submerged cultures for ligninase production were studied. The immobilized fungal hyphae formed an even mycelial mat on a rotating cylindrical stainless steel net showing little sensitivity to the shear stress. The average activity of ligninase over 24 h during a peak production period was 389 U/L at a tip velocity of 0.44 m/s and 369 U/L at a doubled tip velocity of 0.88 m/s. When the dissolved oxygen level dropped below 1 mg/L, the fungal cells responded to the oxygen starvation stress and released a considerable amount of protease. The proteolytic denaturation of ligninase was the major reason that a negligible ligninase activity was detected at a low aeration rate.
Noncatalytic and catalytic pyrolysis of toluene
Authors: Pant Kamal K. , Kunzru Deepak
Published: March 2009

Noncatalytic and catalytic pyrolysis of toluene has been studied at atmospheric pressure in the temperature range of 1043 to 1153 K using steam or nitrogen as the diluent. The catalyst used was potassium carbonate impregnated calcium aluminate. Compared to noncatalytic pyrolysis, the conversions were significantly higher in the presence of the catalyst although the product selectivities were not affected. With nitrogen as the diluent the main products were hydrogen, methane, benzene, bibenzyl and higher hydrocarbons. When steam was used as the diluent, in addition to the above products appreciable amounts of carbon monoxide and carbon dioxide were also produced. The overall reaction of toluene could be represented by two parallel paths; one for toluene decomposition and the other for the toluene‐steam reaction. The kinetic constants of these two reactions for catalytic as well as noncatalytic pyrolysis were determined by nonlinear optimization. In the presence of the catalyst, the activation energy for toluene decompostion was significantly reduced, whereas there was only a marginal reduction in the activation energy of the toluene‐steam reaction.
Collapse of dilute suspension in different circulating fluidized bed risers with respect to different particles
Authors: Xu Guangwen , Nomura Kousuke , Nakagawa Nobuyoshi , Kato Kunio
Published: March 2009

The collapse of dilute suspension was studied in three different circulating fluidized bed (CFB) risers with two types of particles. The risers had the same height of 3.0 m but different inner diameters of 66 mm, 97 mm and 150 mm, respectively. FCC particles (Geldart A) and silica sand particles (Geldart B) were used. It was found that the collapse of dilute suspension is characterized by rapid accumulation of particles at the riser bottom, independent of the riser diameter and the types of particles. In accordance with the observation, an approach was developed to determine the collapsing point from experimental measurements. Then, the dilute suspension collapse was found to be dominated by an identical differential pressure drop at the riser bottom. This critical pressure drop is independent of gas velocity and riser diameter, whereas varies with the properties of particles. Riser diameter has different influences for FCC and silica sand particles upon the saturation carrying capacity, the solids circulation rate at the dilute suspension collapse. Under a given gas velocity, the collapse in a larger riser is observed to take place at a larger solids circulation rate for FCC, but at a smaller solids circulation rate for silica sand. This diversified dependence on riser diameter of the saturation carrying capacity was identified as a result of the different influences of the riser diameter on the bed density for those two types of particles.
Modeling of biomass devolatilization in a fluidized bed reactor
Authors: Difelice Renzo , Coppola Gianfilippo , Rapagna Sergio , Jand Nader
Published: March 2009

A simple model that simulates a single biomass particle devolatilization is described. The model takes into account the main physical and chemical factors influencing the phenomenon at high temperatures (>700 K), where the production of gaseous components far outweighs that of liquids. The predictions of the model are shown to be in good agreement with published data. The model is then applied to the devolatilization of biomass in a fluidized bed, in which attention is focused on heat transfer, particle mixing and elutriation, and gas production. Predictions on the overall devolatilization time for a biomass particle are compared with experimental results obtained in a fluidized bed reactor in which the process was monitored by continuous measurement of the bed pressure. Good correspondence of predicted with calculated values was obtained, supporting the validity of the many approximations made in the derivation of the governing relationships for the pyrolysis process.
Modeling of an internally circulating fluidized bed reactor for thermal treatment of industrial solid wastes
Authors: Mukadi Lukanda , Guy Christophe , Legros Robert
Published: March 2009

A predictive mathematical model is developed to describe and characterize the key design variables of a novel Internal Circulating Fluidized Bed Combustor. The model is based on fundamental principles of heat transfer, mass transfer, hydrodynamics and reaction kinetics. Under justifiable assumptions unsteady state mathematical equations are written and solved. The input parameters of the model are gas and solid flowrates, solid circulation flux, as well as physical properties of gas and solids. The model allows to predict and to investigate the temperature, the combustible conversion, the oxygen concentration, the residence time, the voidage and the solid velocity in the riser. Experiments with spent foundry sand are undertaken in order to assess the validity of the model. The predictions for the transition period of heating clean sand and the treatment of waste compare satisfactorily to the experimental data.
Leaching of uranium and 226ra from low‐level radioactive waste from port hope, ontario
Authors: Nirdosh Inderjit
Published: March 2009

Uranium and radium were leached from a low‐level radioactive soil sample neutralized with limestone from Port Hope, ON, in single stage and multistage leaching tests. The leachants used were alkaline EDTA, sodium citrate, sodium potassium tartrate, acidic ferric chloride, hydrochloric acid, nitric acid and hydrochloric or nitric acid plus boric acid mixtures. All leaching tests except the two‐stage acid leachings proved ineffective in yielding leach residues with low residual 226Ra concentrations of < 100 pCi/g. Leaching with 4 mol/L HNO3 in the first stage followed by treatment with 4 mol/L HNO3 plus 0.05 mol/L boric acid in the second stage proved effective and gave a leach residue with 85 pCi/g 226Ra and 16 ppm uranium.
Influence of geometry and solids concentration on the hydrodynamics and mass transfer of a rectangular airlift reactor for marine sediment and soil bioremediation
Authors: Tobajas Montserrat , Siegel Marc H. , Apitz Sabine E.
Published: March 2009

Hydrodynamics and mass transfer characteristics of a three‐phase airlift reactor were studied in a rectangular split‐vessel reactor and using an air‐seawater‐marine sediment system. Experiments were conducted over a range of downcomer to riser cross‐sectional area ratios (AD/AR = 0.65 to 1.0) for two‐phase systems and for five sediment concentrations (5 to 25% w/v) using marine sediments. The influence of higher sediment concentrations (30 to 50% w/v) was examined for AD/AR = 1. The presence of fine sediment particles in the system had little effect on hydrodynamic and mass transfer parameters compared to the two‐phase systems up to 25% loading, decreasing at higher loadings. The airlift reactor was found to meet the dissolved oxygen demand needed for a contaminated sediment treatment process. Axial distribution of the particles was uniform along the riser and the downcomer. Correlations were developed that described the hydrodynamic and mass transfer behaviour for all experimental conditions examined.
Onset of pulsing in trickle beds: Evaluation of current tools and state‐of‐the‐art correlation
Authors: Larachi F. , Iliuta I. , Chen M. , Grandjean B. P. A.
Published: March 2009

The transition between trickle flow and pulse flow regimes in cocurrent trickle‐bed reactors is not properly predicted by existing phenomenological, semi‐theoretical and empirical tools. Based on the most complete flow regime transition data base (700 measurements, 30 gas–liquid systems, 18 columns diameters, 38 packing materials, high pressure conditions, coalescing, non‐coalescing and pseudoplastic non‐Newtonian aqueous and organic liquids), a state‐of‐the‐art explicit correlation of trickle‐to‐pulse flow changeover was derived relying on neural network modeling. Robustness of the proposed correlation was verified, and the limitations of the literature correlations and models were demonstrated through systematic statistical testing over the constructed data base. The overall result was a net improvement in predicting the trickle‐to‐pulse flow regime transition.
Numerical correlation for thermal conduction in packed beds
Authors: Lund Kurt O. , Nguyen Huy , Lord Stephen M. , Thompson Chrystal
Published: March 2009

The numerical conduction of heat in packed beds of particles is investigated, including the effects of inter‐particle microasperity gaps and deformation contacts. A detailed numerical model of two half spheres in contact with interstitial fluid is constructed, including asperity (roughness) gaps and deformation contacts on the respective orders of 5 μm and 100 μm for 1 mm particle diameters. The resulting heat flux distributions at the diametrical planes of the particles are integrated to yield the overall thermal conductance, K, or resistance, R = 1/K, between the two diametrical planes. The results show K to be strongly dependent on the interstitial fluid gap and the deformation contact diameter, as well as on fluid and solid conductivities. The effective bed conductivity, ke, is determined as a function of K and the void fraction, and correlated in terms of bed parameters. The resulting ke correlation agrees well with published experimental data over a wide range of substances and temperatures.
Mass transfer properties of bubble columns suspending immobilized glucose oxidase gel beads for gluconic acid production
Authors: Nakao Katsumi , Harada Tsuyoshi , Furumoto Keiji , Kiefner Andreas , Popovic Milan
Published: March 2009

The volumetric gas‐liquid oxygen transfer coefficient, kL a, and the liquid–solid coefficient, kS, were measured in a 6.7 L external loop airlift bubble column (ELBC), a 2.5 L internal loop airlift (ILBC) and a 2.5 L normal bubble column (NBC) by the steady state method proposed previously using the oxidation of glucose with air catalyzed by glucose oxidase, GO. For an improved and simultaneous determination of kL a and kS, GO was entrapped in calcium alginate gel beads together with fine palladium particles instead of catalase to decompose the hydrogen peroxide produced. The gas holdup, ϵG, in each type of bubble column and the liquid circulation velocity, uL, governing ϵG in the ELBC were also measured to correlate the data on kLa according to the previous correlations proposed for a larger scale of the ELBC, ILBC and NBC. The data on kL a, kS, ϵG and uL (only for the ELBC) in the reaction system were compared to each other for the three types of bubble columns. The results are well predicted by the previous correlations.
Bioremediation of contaminated air using an external‐loop airlift bioreactor
Authors: Wei Vicky Q. , Hill Gordon A. , Macdonald Douglas G.
Published: March 2009

Biological air treatment methods are gaining popularity in the chemical industries due to their low cost and ability to convert many hazardous volatile organic compounds (VOCs) into harmless byproducts. An external loop, airlift bioreactor (ELAB) is used to separately bioremediate two prototype, water‐soluble VOC compounds: p‐cresol and ethanol. In both cases, the effluent air was cleansed and bioremediated to below detectable limits (beyond 99.7% removal) due to the efficient scrubbing action of the ELAB. The bioreactor continued to provide this removal efficiency up to maximum air p‐cresol concentration of 0.6 g/m3 and ethanol concentration of 110 g/m3 and at bioreactor loading rates up to 8 g/m3 h for p‐cresol and 220 g/m3 h for ethanol. A dynamic and quasi‐steady state, biokinetic model is shown to predict the transient bioremediation process very well using batch growth biokinetic parameters.
Steady incompressible fluid flow over a bundle of cylinders at moderate reynolds numbers
Authors: Satheesh V. K. , Chhabra Raj P. , Eswaran V.
Published: March 2009

The complete Navier‐Stokes equations describing the steady flow of incompressible Newtonian fluids normal to an array of long cylinders have been solved numerically using the finite difference method in terms of the stream function and vorticity variables. The inter‐cylinder interactions have been mimicked using the well known free surface cell model. Extensive information on the detailed structure of the flow field in terms of the surface vorticity distribution, stagnation pressure, stream line and iso‐vorticity line plots, as well as on the values of the integral quantities, such as pressure, friction and total drag coefficients, have been obtained under wide ranges of conditions as follows: 0.3 ≤ ϵ 0.99 and 0.01 ≤ Re ≤ 100. The numerical results presented herein have been validated using the appropriate theoretical and experimental results available in the literature; the match between the present predictions and the scant experimental results is good.
Modeling the effect of drop charge on coalescence in turbulent liquid—liquid dispersions
Authors: Tobin Thomas , Ramkrishna Doraiswami
Published: March 2009

In this work, a mechanistic model of drop coalescence based upon a stochastic film‐drainage analysis is developed. The coalescence model accounts for previously considered factors, such as turbulence intensity, drop size, and drop deformability, while additionally describing the dual effects of drop surface potential and system electrolyte concentration. Model results indicate that electrostatic repulsion may strongly inhibit small drop coalescence, as well as coalescence between larger deformable drops. Comparison of model predictions to data from several transient coalescence experiments shows good agreement in most cases.
Esterification of ethenyl benzene and its derivatives with acetic acid in the presence of perchloric acid as a catalyst
Authors: Martínez de la Cuesta Pedro J. , Martínez Eloísa Rus , Palomino Pérez Fuensanta I. , Sarria Francisca Romero
Published: March 2009

The esterification process of ethenyl benzene and its derivative compounds (p‐methyl, p‐methoxy, p‐chloro, m‐methyl, m‐nitro and m‐chloro, respectively) was carried out with acetic acid and using perchloric acid as a catalyst. From the effects of the variables studied it could be concluded that: the temperature and the catalyst concentration influence positively over the olefin conversion, whereas the initial olefin concentration exert no effect over the same; and that the presence of perchloric salts exerts a different influence, depending on the temperature and on the catalyst concentration. It has been proven that the substituted radicals in the m‐ or p‐ positions exert an important influence over the conversion of the studied olefins, presenting growing reactivity in the following order: m‐nitro ethenyl benzene, m‐chloro ethenyl benzene, p‐chloro ethenyl benzene, m‐methyl ethenyl benzene, ethenyl benzene, p‐methyl ethenyl benzene and p‐methoxy ethenyl benzene. Finally, a kinetic and thermodynamic study has been done and the corresponding parameters have been calculated, with an adequate fitting.
Microstructural aspects of the flow behaviour in a liquid—solids circulating fluidized bed
Authors: Zheng Ying , Zhu Jing‐Xu (Jesse)
Published: March 2009

The local instantaneous and time‐average suspension densities were determined in a 76 mm diameter by 3 m tall liquid‐solids circulating fluidized bed riser using a fibre‐optic probe. Attempts were made to qualify the microflow structure through statistical analysis of the local bed voidage fluctuations obtained under different operating conditions for the first time. The results show that local microflow structure is uniform in the axial direction but non‐uniform in the radial direction with more flow fluctuation near the wall than in the core of the column for a given axial position. The standard deviation and intermittency index tend to increase with increasing solids circulating rates. Comparing with the gas—solids CFB, the liquid—solids CFB shows much more homogeneous flow structure in both the axial and radial microscopic flow behaviours. The microflow behaviours in the conventional liquid—solids fluidization, liquid—solids circulating fluidization and dilute‐phase liquid transport regimes are also characterized by examining the probability distribution and the intermittency index of the solids holdup.
Modelling FCC units under steady and unsteady state conditions
Authors: Arandes José M. , Azkoiti Miren J. , Bilbao José , de Lasa Hugo I.
Published: March 2009

A FCC phenomenological‐based model is presented in this study. This model accounts for the behaviour of the riser, the stripper and the regenerator. Both the reactor and the regenerator are incorporated in the model using detailed reaction kinetics. Catalyst regeneration allows for both catalytic and non‐catalyzed combustion of CO to CO2. Overall, the model is constituted by a set of ordinary differential equations, relatively easy to solve and suitable for steady and unsteady state simulation of FCC units. The proposed model avoids, as much as possible, empirical expressions being suitable for simulation of industrial FCC units and process control studies.
Three‐stage well‐mixed reactor model for a pressurized coal gasifier
Authors: Song B. H. , Watkinson A. Paul
Published: March 2009

Three Canadian coals of different rank were gasified with air‐steam mixtures in a 0.1 m diameter spouted bed reactor at pressures to 292 kPa, average bed temperatures varying between 840 and 960°C, and steam‐to‐coal feed ratios between 0.0 and 2.88. In order to analyze gasifier performance and correlate data, a three‐stage model has been developed incorporating instantaneous devolatilization of coal, instantaneous combustion of carbon at the bottom of the bed, and steam/carbon gasification and water gas shift reaction in a single well mixed isothermal stage. The capture of H2S by limestone sorbent injection is also treated. The effects of various assumptions and model parameters on the predictions were investigated. The present model indicates that gasifier performance is mainly controlled by the fast coal devolatilization and char combustion reactions, and the contribution to carbon conversion of the slow char gasification reactions is comparatively small. The incorporation of tar decomposition into the model provides significantly closer predictions of experimental gas composition than is obtained otherwise.
Fractionation of nylon fibres using a vertical settler
Authors: Chen Joyce X. , Masliyah Jacob H.
Published: March 2009

Based on theoretical analysis, a continuous vertical settler was found capable of fractionating fibres according to their length. Fractionation experiments confirm the theoretical predictions. Under the extreme dilution used in this study, there was no effect of feed consistency. The performance of fibre fractionation decreased with an increase in the overflow stream flow rate. Fibre fractionation performance improved for a larger fibre diameter. A theoretical model was developed to simulate fractionation in the continuous vertical settler and it agrees fairly well with the experimental results.
Comparaison de deux types d'écoulements (tangentiel plan et tourbillonnaire) dans des modules d'ultrafiltration. Influence de la contrainte pariétale
Authors: Morineau‐Thomas Odile , Lelièvre Caroline , Rossignol Nathalie , Jaouen Pascal , Legentilhomme Patrick
Published: March 2009

Cette étude est consacrée à l'évaluation des performances d'un nouveau procédé de séparation par membrane constitué d'une cellule annulaire munie d'une entrée tangentielle unique à sa base. Pour cela, nous avons comparé les flux de perméation de ce module, siège d'un écoulement tourbillonnaire non entretenu, à ceux obtenus avec un module à écoulement tangentiel plan classique. L'ultrafiltration de suspensions modèles de bentonite nous a permis de comparer les performances des deux modules pour différentes conditions opératoires. Les influences du débit, du nombre de Reynolds et du gradient pariétal de vitesse à la surface de la membrane ont été étudiées; ce dernier paramètre apparaǐt comme le critère le plus approprié pour mettre en parallèle les deux géométries. En effet, il prend en considération la nature de l'ecoulement et plus particullèrement la contrainte de cisaillement à la surface měme de la membrane qui régit le transfert de solvant au travers de cette dernière. Dans certaines conditions, le module à écoulement tourbillonnaire permet d'atteindre des flux de perméation augmentés de plus de 30% par rapport à ceux obtenus avec un module tangentiel plan classique. L'étude de la consommation énergétique de ces deux cellules permet de confirmer l'intérět des écoulements tourbillonnaires pour la conception de nouvelles géométries de modules de séparation par membrane.
Piloting of anionic polymerization of styrene in tetrahydrofurant
Authors: Saban Marko , Liebermann George , Jay Alex , Shi An‐Chang , Ro Nam , Dale William , Forgione Pat
Published: March 2009

Anionic polymerization of styrene in THF with n‐butyllithium/alpha‐methylstyrene initiator is described as a first step in preparation of a styrenic block copoly‐mer. In order to suppress rapid decay of living alpha‐methylstyrene unimers, which occurred at room temperature, the initiation reaction was carried out at −20(+5)°C. The kinetic parameters of this decay reaction were determined and used for process optimization. By combining experiments with modelling of styrene propagation reaction all key process parameters were defined for l‐L, 38‐L, and 189‐L reactors. A good match was demonstrated between the model and experimental propagation exotherm for semibatch reaction conditions. Overall, it was demonstrated that technical grade THF and styrene could be used at pilot plant scale to prepare well‐defined polymers up to Mn 22 000 via the “living” polymerization mechanism. The resulting polymers had narrow molecular weight distributions (1.06 < Mw/Mn < 1.30).
The role of the vapour phase in fluid coker cyclone fouling: Part 1. Coke yields
Authors: Mallory Donald G. , Mehta S. A. (Raj) , Moore R. Gordon , Richardson Susan
Published: March 2009

The cyclone sections of fluid coking reactors at oil sand upgrading facilities have been observed to undergo severe coke fouling during each operational cycle. This work was conducted to determine if vapour phase deposition mechanisms could be responsible for the formations observed in the cyclones. The effects of vapour phase temperature (from 490°C to 560°C) and residence time (from 0.4 to 4.4 s) were studied. Raising the vapour phase temperature above the temperature at which the vapours were derived was found to significantly increase both the yield and rate of production of vapour phase coke.
On the control of an unstable periodic state in the repeated fed‐batch operation of a biochemical system
Authors: Jayant Alok , Subramaniam Pushpavanam
Published: March 2009

In this paper we discuss the proportional feedback control of a repeated fed‐batch reactor around a desired but unstable periodic state. The flow rate in each cycle is assumed to be a constant. The unstable periodic state is determined using a shooting method technique and its stability is found using the Floquet theory. The control action is based on the performance, i.e., biomass concentration, at the end of the cycle. Two choices of the manipulated variable are investigated, i.e., the cycle time and the flow rate. The concentration of the substrate in the feed is assumed to be a constant.
The viscoelastic properties of polymer‐modified asphalts
Authors: Carreau Pierre J. , Bousmina Mosto , Bonniot Frank
Published: March 2009

The linear viscoelastic properties of one family of base asphalts, unmodified or modified by the simple addition of an elastomer or by further in‐situ crosslinking, have been investigated. The time‐temperature superposition principle was shown to be valid for the base as well as for the modified asphalts. The addition of the elastomer styrene‐butadiene (SB) copolymer increased drastically the storage modulus and the elastic character of the asphalts. The thermal susceptibility of the polymer modified asphalts was considerably reduced and this combined with an increased resistance to deformation (larger complex modulus) suggests much better performances for road applications. The chemically modified asphalt containing 3% SB showed similar viscoelastic properties as the physical blend containing 6% SB.
Enrichment of heavy water in flat‐plate thermal diffusion columns of the frazier scheme with the optimal plate aspect ratio for best performance
Authors: Yeh Ho‐Ming
Published: March 2009

The solutions of the optimum plate aspect ratio as well as the corresponding maximum separation, maximum production rate and minimum plate surface area in thermal diffusion columns of the Frazier scheme for enrichment of heavy water have been obtained, analogous to those obtained in the previous work for separation of a binary system. It was found that all the optimum plate aspect ratios do not depend on feed concentration, while the corresponding best performances do. It is found that considerable improvement in performance is obtained when the operation is carried out with the optimal plate aspect ratio.
Deposition of magnetite particles from flowing suspensions under flow‐boiling and single‐phase forced‐convective heat transfer
Authors: Turner Carl W. , Klimas Stan J.
Published: March 2009

The deposition rate of colloidal magnetite particles was measured under both single‐phase forced‐convective and flow‐boiling conditions. All measurements were made at alkaline pH where both the heat transfer surface and the surface of the magnetite particles appear to be negatively charged. For single‐phase forced convection, the deposition rate constant is lower than the mass transfer coefficient for colloidal particles, and the difference is attributed to the force of repulsion between the negatively charged surfaces of the particle and substrate. The deposition rate measured under flow‐boiling conditions is lower than that reported for the deposition of colloidal particles at neutral pH. The difference is, again, attributed to the force of repulsion between the particle and substrate. Particle removal rates were significantly lower than deposition rates; analysis using the theory of turbulent bursts suggests a removal efficiency of only 10−9% for each turbulent burst. The low removal efficiency is consistent with the particle diameter being significantly smaller than the thickness of the laminar sublayer in these tests.
Integral equation study of the residual chemical potential in infinite‐dilution supercritical solutions
Authors: Lotfollahi Mohammad Nader , Modarress Hamid , Mansoori G. Ali
Published: March 2009

A new method for solving the integral equation based on the Ornstein‐Zernike equation for binary mixture is proposed. Then the radial distribution function obtained for both the Percus‐Yevick and the hypernetted chain closure equations are used to calculate the residual chemical potential at infinite‐dilution and at reduced temperatures T* = 2, 1.5 (supercritical isotherms) over a varying range of reduced densities ρ* = 0.1 to 0.6 for various types of the Lennard‐Jones mixture in terms of size ratios D and energy ratios C. To examine the ability of the integral equation approach for the residual chemical potential calculations, the results are compared with the Monte‐Carlo simulation data and the van der Waals I results (Shing et al., 1988). It is seen that at ρ* = 0.1 to 0.5, the deviation of the integral equation results from the MC simulation data is less than the reported statistical fluctuation.
The effect of adsorption on mass transfer in fluidized bed catalytic reactors
Authors: Akşahin Inci , Eroĝlu Inci , Yücel Hayrettin
Published: March 2009

Tracer gas residence time distributions (RTD) in a laboratory scale fluidized bed system have been measured for pulses of three different tracer gases (methane, ethane and propane) at different temperatures in the range 323 to 435 K. The fluidized solid was a commercial zeolite based FCC catalyst (CBZ‐2), and measurements were carried out in a superficial air velocity range of 0.01 to 0.04 m/s. The data were interpreted with two‐phase dense phase dispersion models for adsorptive tracers, available in the literature. In addition, modified models were considered by assuming a stationary dense phase and neglecting axial dispersion in this phase. Mean residence time, μ1, and the variance of the residence time, σ2, of RTD data were calculated for each experimental run. Applying the moment technique in the Laplace domain, the differential equations for all models considered were analytically solved.

Mass transfer coefficients obtained from dynamic experiments were compared with the values estimated from the relations available in the literature. It was found that methods considering convective flux alone between the bubble and emulsion phases give closer values to the experimental ones than the methods also including the diffusive flux.
Drag coefficient—reynolds number transition for gas bubbles rising steadily in viscous fluids
Authors: Rodrigue Denis
Published: March 2009

Recently, the author (Rodrigue, 2001) developed a generalized correlation for the motion of gas bubbles rising steadily in uncontaminated viscous Newtonian fluids of infinite extent. It is the purpose of this note to show that this model can be written in an explicit form for the drag coefficient as a function of the Reynolds and Morton numbers. This new correlation is then used to predict the position of the minimum in a graphical representation of CD versus Re. It is shown that the model can predict quite nicely this hydrodynamic transition for viscous fluids.
Alkaline hydrolysis of isoamylformate: Effect of dissolved electrolytes on kinetics
Authors: Ghosh Bhaswati , Bhattacharjee Sekhar , Chaudhuri Basab , Mukherjee Dulal C.
Published: March 2009

The kinetics of alkaline hydrolysis of isoamylformate with aqueous solutions of sodium hydroxide and pottassium hydroxide has been determined by using the theory of mass transfer with chemical reaction; the effect of presence of electrolyte salts such as sodium chloride and sodium sulfate in aqueous alkaline solution has been assessed. Experiments have been conducted in a stirred cell having a flat liquid—liquid interface. For the different aqueous phases employed, the alkaline hydrolysis conforms to the fast pseudo‐first order reaction regime. The system is of considerable practical importance and has been successfully employed for the measurement of the interracial area of a flooded packed bed contactor that contained cation exchange resin particles having a diameter of approximately 0.5 mm as packing particles.
Bang‐Bang solution of nonlinear time‐optimal control problems using a semi‐exhaustivesearch
Authors: Gupta Yash P.
Published: March 2009

At times, the objective is to seek a bang‐bang control policy for nonlinear time‐optimal control problems. The usefulness of iterative dynamic programming (IDP) has been shown in the literature for solving such problems. However, the convergence to the optimal solution has been obtained from about 50% of the guessed values near the optimum. In this paper, we present a semiexhaustive search method for seeking such solutions and a comparison is made with the IDP. The results show that the convergence can be obtained from a significantly higher number of guessed values chosen over a much wider region around the optimum.
Experimental study of a reverse flow catalytic converter for a dual fuel engine
Authors: Liu Benlin , Checkel M. David , Hayes Robert E.
Published: March 2009

Theperformance of a reverse flow catalytic converter for a methane/diesel dual fuel engine, a monolith honeycomb converter with palladium catalyst washcoat, was evaluated under steady and transient engine conditions. The reverse flow converter provided superior performance (that is, higher conversion of pollutants) for several steady engine operations, compared with unidirectional flow operation. For transient operation following a step change in engine operating conditions, reverse flow is better than unidirectional flow when the change in engine operation results in a reduction in exhaust gas temperature. For an increasing exhaust gas temperature, reverse flow decreased the rate of increase of reactor temperature. The reverse flow converter was tested using the transient Japanese 6‐Mode tests. Reverse flow operation gave higher conversions than unidirectional flow for this test, with a switch time of 5 s giving the best results.
Lateral flux and velocity of FCC particles in a CFB riser
Authors: Malcus Stefan , Pugsley Todd
Published: March 2009

The radial profiles of the lateral solids mass flux and the lateral solids velocity were determined for FCC particles in a 7 m tall circulating fluidtzed bed riser 0.14 m in diameter by applying a lateral flux probe and electrical capacitance tomography. The external solids mass flux was varied between 148 and 302 kg/(m2.s), while the superficial gas velocity was varied between 3.7 and 4.7 m/s. Under these conditions, a dense bottom region and an upper dilute region coexisted in the riser. Lateral fluxes in the dense bottom region reached 100 kg/(m2.s) at the wall, but fell to 14 kg/(m2.s) at the wall in the upper dilute region. At both axial locations, a net deposition of solids from the core to the annulus occurred, indicating that fully developed flow was never established under these conditions. The lateral fluxes in the bottom region were significantly larger than those found in previous studies. It was further concluded that considering the lateral solids flux to be only a function of solids concentration is an over‐simplification.