bluuebunny/crossref_metadata_2025_split huggingface dataset:
Cocurrent downflow circulating fluidized bed (downer) reactors — A state of the art review
Authors: Zhu J.‐X. , Yu Z.‐Q. , Jin Y. , Grace J. R. , Issangya A. 
Published: March 2009

AbstractIn the last decade, cocurrent downflow circulating fluidized bed reactors, called “downer” reactors, have been proposed as an alternative to upflow circulating fluidized bed, or “riser”, reactors. In this paper, published results on downer studies are summarized and future directions of research are recommended. Downer reactors are shown to have several distinct advantages over upflow circulating fluidized bed reactors and can potentially be used in many industrial processes, mainly due to a more uniform gas and solids flow structure compared with risers.
A generic algorithm for optimization of CFSTRs in series with any biokinetic equation
Authors: Baheri H. R. , Hill G. A. , Roesler W. J. 
Published: March 2009

AbstractA simple generic code for optimization of CFSTRs in series with any biokinetic equation (structured, unstructured, segregated or distributed) has been developed. The program accepts biokinetic equations without any preliminary mathematical manipulation, does necessary material balances, solves material balance equations and optimizes the system under a given objective function. The program was tested with four different optimization problems (different biokinetics of unstructured, segregated and a structured model) and the results were compared to published data. In all cases, good agreement was found. Finally, the model has been applied to multiple CFSTRs with a cybernetic biokinetic model, and the effect of model parameters on the optimum total residence time is demonstrated.
Fine particle deposition in laminar and turbulent flows
Authors: Vašaacute;k F. , Kaštánek F. , Bowen B. D. , Chen C. Y. , Epstein N. 
Published: March 2009

AbstractThe deposition of fine silica and polystyrene spheres was measured for conditions of laminar and turbulent flow (960 ≤ Re ≤ 16040) in a rectangular channel using image analysis. The plate glass deposition surfaces were rendered positively charged by coating them with a cationic copolymer while, under the water chemistry conditions employed, both types of particles were negatively charged. It was found that, contrary to the results for laminar flow, the initial depositon rates in turbulent flow decreased with increasing Re, indicating that deposition was no longer mass‐transfer controlled and that particle attachment played an increasingly important role as Re was raised. Attachment was modelled as a rate process in series with mass transfer in which the attachment rate varies inversely as the square of the friction velocity. Under the conditions of the present experiments, no particle re‐entrainment was observed, so that the declining rate of particle accumulation on the wall recorded in each run could only be attributed to a declining deposition rate. Even where asymptotic accumulations were reached, particle coverages never exceeded 3.5%.
Permeate pressure build‐up in shellside‐fed hollow fiber pervaporation membranes
Authors: Feng Xianshe , Huang Robert Y. M. 
Published: March 2009

AbstractPervaporation of water, ethanol and isopropanol through polydimethylsiloxane hollow fiber membranes was studied, with emphasis on elucidating the significance of permeate pressure build‐up inside the fibers when the shell‐feed mode of operation was used. The differential form of the Hagen‐Poiseuille equation was used to describe the permeate pressure profile, and the theoretical predictions of permeate productivity were confirmed by experimental data. A parametric analysis showed that the dimensions of the hollow fiber (inside and outside diameters, and length) significantly affected the overall pervaporation performance of a hollow fiber membrane module, and the fiber dimensions must be optimized in order to achieve high productivity.
Kinetic study of fructose‐glucose isomerization in a recirculation reactor
Authors: Camacho‐Rubio F. , Jurado‐Alameda E. , González‐Tello P. , Luzón‐González G. 
Published: March 2009

AbstractWe have studied the equilibrium and kinetics of fructose‐to‐glucose isomerization using a commercial immobilized glucose isomerase, Sweetzyme T® (from NOVO), in a packed‐bed recirculation reactor which enabled us to eliminate the influence of external‐mass transfer and which could function as a differential reactor when a sufficient flow rate was used. The results obtained have also been corrected with regard to the influence of internal transport in the immobilized enzyme particles.Isomerization kinetics is a pseudo first‐order reversible reaction in the ranges studied: 303–333 K, pH 7.5 and 0.5 to 2.0 mol/L hexose concentrations. We compare our results with those found in the literature, and propose equations for the influence of temperature on the equilibrium and on the kinetic constants.
Diffusion limitation effects in the washcoat of a catalytic monolith reactor
Authors: Leung D. , Hayes R. E. , Kolaczkowski S. T. 
Published: March 2009

AbstractIn monolith reactors with catalytic washcoat, intraphase diffusion effects have often been underestimated. This paper presents numerical simulations of diffusion/reaction in the washcoat of a catalytic monolith reactor. The problem is solved in two dimensions for the washcoat geometry obtained in a 1‐mm square monolith channel, as revealed by scanning electron microscopy. For the oxidation of carbon monoxide, propane or methane diffusion limitation can be substantial at typical operating conditions. The two‐dimensional solution is compared to a one‐dimensional approximation. The latter approximation for the real washcoat is valid provided that the characteristic length is selected carefully. This value is different from the characteristic length of the two‐dimensional washcoat. The characteristic length of a two‐dimensional geometry is not sufficient in itself to describe all washcoat geometries. It is predicted that the application of a diffusion barrier of 4–6 μm of inactive washcoat may be used to lower the rate of reaction in the inlet region of the monolith reactor.
The influence of temperature and the concentration of MNSO4 on the simultaneous absorption and reaction of mixtures of SO2 and O2
Authors: Bravo V. R. , Camacho F. R. , Moya M. V. 
Published: March 2009

AbstractWe have studied the simultaneous absorption of gaseous mixtures of SO2 and O2 in solutions of MnSO4 up to 0.75 mol/L and at temperatures between 10 and 40°C. The reactor used was operated continuously for the gas phase and batchwise for the liquid. The liquid phase was saturated in SO2 at the first sampling after one hour. The absorption of O2 was the controlling step in the process, with reaction order of 0 and 1 for SO2 and O2, respectively, and a fast reaction regime for MnSO4 at concentrations of more than 0.025 mol/L.As far as manganese is concerned, our results show that the reaction order varies according to its concentration and we have obtained an equation which relates the kinetic constant to temperature and the concentration of the catalyst.
Using ultrafiltration to analyze the molar mass distribution of kraft lignin at ph 13
Authors: Li J. , O'Hagan T. , MacLeod J. M. 
Published: March 2009

AbstractWe used deliberately calibrated ultrafiltration membranes to analyze the molar mass distribution (MMD) of kraft lignin in alkaline solution. The membranes were first tested with probe macromolecules to obtain sieving curves at the same conditions as the lignin analysis. Using a restricted transport model, we calculated the average effective membrane pore sizes. The results were different from the nominal cut‐off values. The MMD of a lignin sample at pH 13 was analyzed by separating the lignin solution into five fractions; the MMD using the calibrated cut‐off values was confirmed by gel permeation chromatography.
Sequential identification: A procedure for insuring internal consistency of steady‐state gains for multivariable systems
Authors: Shen Shih‐Haur , Yu Cheng‐Ching 
Published: March 2009

AbstractThe importance of obtaining consistent steady‐state gains increases as the expected level of performance increases. A new consistency relationship is derived to ensure that the steady‐state gains identified are physically correct. In addition to the consistency relationship, an identification procedure is also proposed to achieve the internal consistency. Unlike the typical identification‐reconciliation procedure, the proposed approach meets the internal consisency via the identification procedure (no reconciliation is necessary). Two nonlinear distillation examples, a 2 × 2 system and a 3 × 3 system, are used to illustrate the effectiveness of the proposed approach. The results show that physically correct description of the columns can be achieved using the proposed approach for a range of changes in the manipulated variables.
Microfiltration of apple juice using inorganic membranes: Process optimization and juice stability
Authors: Alvarez V. , Andres L. J. , Riera F. A. , Alvarez R. 
Published: March 2009

AbstractCrossflow membrane microfiltration of low‐pectine raw apple juice was studied using inorganic membranes (TECH SEP Carbosep®, Lyon, France) having a nominal pore size of 0.2 μm. Permeate flux was measured at different operation conditions (trans‐membrane pressure between 100 and 500 kPa, feed velocities between 1 and 6 m/s, and temperatures of 293, 298 and 323 K). Some concentration experiments were made in order to study the rejection of pectins and polyphenols at different VCR (volume concentration ratio) values. Final stabilization tests were carried out to analyze the long‐term clarified juice behaviour.
On the reported attempts to radically improve the performance of the steam methane reforming reactor
Authors: Adris A. M. , Pruden B. B. , Lim C. J. , Grace J. R. 
Published: March 2009

AbstractSteam reforming of light hydrocarbons is a key step for producing hydrogen and syngas for important processes in the petroleum and petrochemical industries. Since the establishment of the SMR process in 1930, research and development have led to improved catalyst performance and improved reactor tube materials. Since about 1970, new reactor configurations have been considered. The authors critically review recent attempts to radically improve the SMR reactor performance, analyze the areas of improvement and the suitability of proposed configurations for different reforming applications.
Influence du dodecyl sulfate de sodium sur la tension interfaciale du système biphasé butanol‐eau
Authors: Mollet Céline , Touhami Youssef , Hornof Vladimir 
Published: March 2009

AbstractLe présent article a pour objet l'étude expérimentale de la tension interfaciale entre les deux phases formées par le système partiellement miscible composé du butanol‐1 et de l'eau. En utilisant la méthode du volume de la goutte, l'effet d'un agent tensioactif, le dodécyl sulfate de sodium, sur la tension interfaciale fut étudié. On a trouvé que l'addition de l'agent tensioactif à la phase riche en butanol (la phase de goutte) cause une baisse légère de la tension dont la magnitude est influencée par le temps de contact. Lorsque l'agent tensioactif est mis dans la phase aqueuse (la phase externe), la baisse de la tension est plus importante et égale à celle observée quand ce dernier est présent dans les deux phases. On peut conclure que l'orientation des phases dans l'appareil de mesure produit un effet important sur la tension interfaciale apparente mesurée.
Absorption of sulfur dioxide in aqueous dispersions of dimethyl aniline
Authors: Bhattacharya Suman , Dutta Binay K. , Shyamal Manoranjan , Basu Ranjan K. 
Published: March 2009

AbstractAbsorption of sulfur dioxide in aqueous dispersions of dimethyl aniline has been carried out in a laboratory stirred cell with a flat gas—liquid interface. The effects of liquid loading, gas concentrations and other parameters have been studied. The absorption rate is linear in gas concentration, and increases with increasing dispersed phase concentration. Substantial enhancement of absorption compared to that in water occurs. Emulsification of the liquid by addition of a surfactant does not increase the absorption rate. The rate of desorption of sulfur dioxide from a loaded solution at 60°C remains essentially constant. A theoretical model for absorption has been developed assuming each droplet in the film to be enclosed by a spherical shell of the aqueous phase through which the solute diffuses at steady state. Comparison of the calculated enhancement factors with the experimental values confirms the validity of the model.
Dynamic modelling and performance optimization of an extractive fermentation
Authors: Arnold Sabine G. , McLellan P. James , Daugulis Andrew J. 
Published: March 2009

AbstractA dynamic model for a continuous extractive fermentation process is proposed. Using this model and the Iterative Dynamic Programming algorithm, optimal operating profiles are identified for process start‐up from conventional fermentation operation. Under the optimal operating profile, profit during the transient operation accumulates at a rate approaching that of steady state operation. A sensitivity analysis investigating the effect of economic variations on the overall profit function shows that optimization of manipulated variable profiles primarily reduces the impact of substrate cost, so that the profit function approaches a linear function of the product value.
Scalar mixing in turbulent concentric round jets
Authors: Grandmaison E. W. , Becker H. A. , Zettler N. L. 
Published: March 2009

AbstractThe scalar mixing field of a free, turbulent concentric round jet has been examined using marker nephelometry. The flow conditions included velocity ratios between the centre and annular jet of 0.188, 0.519 and 0.911. The correlation function between the concentration fluctuations in the two jet streams increased from –1.0 near the nozzle to + 1.0 further downstream indicating a tendency to complete mixing between the jets. The initial mixing behaviour between the jets was better for the lower velocity ratio between the jets (Ui/Uo = 0.188) although further downstream there was better transverse mixing between the jets with the higher velocity ratio (Ui/Uo = 0.911).
Inertia Effects on the Flow of Bingham Plastics Through Sudden Contractions in a Pipe
Authors: Vradis George C. , Hammad Khaled J. 
Published: March 2009

AbstractThe present numerical study concentrates on the effects of moderate and high Reynolds numbers on the laminar flow of a non‐Newtonian rigid viscoplastic (Bingham) fluid through a sudden contraction in a pipe. The flow is assumed to be steady, incompressible, and isothermal. Results are presented for a wide range of the governing Reynolds and yield numbers and the significant effects of these two parameters both on the integral and local kinematic properties of the flow field are established. Low yield numbers result in the disappearance of the recirculating flow region at the corner replacing it with a region of very low rates of deformation. The evolution of the centerline velocity in the vicinity of the contraction plane is shown to be independent of the yield number and dependent on the Reynolds number, while the concavities in the streamwise velocity profiles appearing at high Reynolds numbers are independent of the yield number. The pressure losses through the contraction increase with yield number with the effect being more pronounced at lower Reynolds numbers.
The Effect Of the dust collection system on the flowpattern and separation efficiency of a gas cyclone
Authors: Hoffmann A. C. , Groot M. De , Hospers A. 
Published: March 2009

AbstractThe influence of the presence of a hopper section, consisting of a dust hopper and swirl attenuator, under gas–solid cyclones has been investigated by numerical simulation. Inclusion of this configuration in the simulations was found to have a significant influence on both flowpattern and separation efficiency. Moreover, predicted axial gas velocity profiles agreed better with independent experimental measurements. The cyclone separation was predicted to be better with the hopper section included than without, a physical reason is proposed. Comparison of simulated grade‐efficiency curves with experimental data indicates improved agreement, in some cases substantially so.
Solubility of N2O and CO2 in n‐Dodecane
Authors: Henni Amr , Jaffer Shaffiq , Mather Alan E. 
Published: March 2009

AbstractThe solubility of CO2 and N2O in a physical solvent, n‐dodecane [C.A. Registry N° 124–18–5], has been measured at 40, 80 and 120°C at pressures up to 9.6 MPa. The experimental results were correlated by the Peng‐Robinson (1976) equation of state, and the interaction parameters, the Henry's constants and the N2O analogy parameters were obtained.
Pulse experiments over catalyst beds: A window of measurable reaction rate coefficients
Authors: Huinink J. P. , Hoebink J. H. B. J. , Marin G. B. 
Published: March 2009

AbstractThe elimination of concentration profiles in porous catalyst pellets is not straightforward for transient kinetic experiments since profiles may arise from limited diffusion rates, but also from accumulation in the pellets. For TAP pulse experiments, dominated by Knudsen diffusion on the reactor scale, intrapellet diffusion is typically instantaneous for industrial catalysts. The Knudsen diffusivity for beds of porous pellets can be calculated from its value for non‐porous pellets by accounting for the intrapellet porosity. The window of measurable rate coefficients is governed by a Damköhler number of the first type. A criterion is derived for experimental conditions, that allow intrinsic kinetic measurements with porous catalysts. The size of the admitted pulse should be sufficiently large to avoid pulse depletion by adsorption.
Influence of various metal oxides in the bistability observed in the oxidative dehydrogenation of 2 — Propanol over copper catalysts
Authors: Gil A. , Ruiz P. , Delmon B. 
Published: March 2009

AbstractThis article presents new results concerning a bistability phenomenon observed recently in the oxidative dehydrogenation of 2 ‐ propanol over copper catalysts. In this system, an activity hysteresis loop is observed when the partial oxygen pressure is varied. This bistability has been explained by the oxidation of metallic copper when the partial oxygen pressure increases and copper oxide reduction when the partial oxygen pressure decreases. In the experiments reported here, an external second phase (α‐Sb2O4, SnO2, Cr2O3, CeO2, Co3O4, MoO3, PbO2, NiO, Bi2O3 and MnO2) has been mixed with the copper catalysts. This modifies the hysteresis loop. The possible role played by the oxygen spillover at low temperature (150°C) on this modification is discussed.
Synthesis gas production from natural gas in a fixed bed reactor with reversed flow
Authors: De Groote A. M. , Froment G. F. , Kobylinski Th. 
Published: March 2009

AbstractThe feasibility of producing synthesis gas by partial oxidation of natural gas on a Ni‐catalyst in a fixed bed reactor with reversed flow was investigated by means of simulation. A one dimensional reactor model of the non‐steady state heterogeneous type, accounting for internal diffusional limitations, was applied. A double temperature peak is observed just after flow reversal, influencing the selectivities at the exit through enhanced steam reforming reactions. The second peak gradually decreases in importance with time during the semi‐cycle. The influence of several operating conditions on the reactor performance was studied. Most of the coke deposited in a semi‐cycle can be removed after flow reversal. This observation opens new perspectives for the reversed flow operation.
Annular wall layer thickness in circulating fluidized bed risers
Authors: Bi H. T. , Zhou J. , Qin S.Z. , Grace J. R. 
Published: March 2009

AbstractThe thickness of downward‐flowing annular wall layers in circulating fluidized bed risers has been determined in the literature based on measured radial profiles of both local particle velocity and solids flux. The thickness of the wall layer is shown to be larger based on solids flux profiles than when based on particle velocity profiles, because fluctuations in local instantaneous particle velocity are correlated with fluctuations in local solids concentration. A new correlation is developed to predict the time‐average thickness of the downflowing particle streamer layer based on solids flux measurements as a function of the cross‐sectional average voidage. It successfully accounts for the variation of the wall layer thickness with axial location and solids circulation rate.
Contrôle hydrodynamique de l'evaporation d'un film liquide ruisselant sur une paroi isotherme à symétrie de révolution dans un courant d'air humide
Authors: Kaoua M. , Cherif A. Ali , Daïf A. , Daguenet M. 
Published: March 2009

AbstractLes auteurs étudient numériquement, à l'aide d'une méthode aux différences finies associée à l'algorithme de Thomas, l'évaporation, dans un courant d'air humide, d'un film mince d'eau s'écoulant sur la paroi, supposée isotherme, de corps à symétrie de révolution, la variabilité des propriétés physiques des fluides étant prise en compte et le régime supposé laminaire et permanent. L'influence des principaux paramètres du système sur l'évaporation est précisée, notamment celle du profil de la paroi du corps axisymétrique. Les auteurs montrent que, pour des conditions de calcul fixées, il est possible de trouver un ellipsoïde de révolution aplati offrant une paroi uniformément accessible sur une grande étendue entre le pǒle et l'équateur.
Supercritical carbon dioxide extraction of spearmint oil from mint‐plant leaves
Authors: Özer Eli̇f Ö , İin Sevan Plat , Akman Uǧur , Hortaçsu Öner 
Published: March 2009

AbstractSpearmint oil (essential oil of Mentha spicata) was extracted from Turkish mint‐plant leaves using supercritical CO2 in a basket‐type extractor. Effects of temperature, pressure, extraction time, amount of CO2, and entrainer (ethanol) concentration on composition of essential‐oil extracts and oil yield, relative to hydro‐distillation, were investigated. Relative yields were as high as 80%. Monoterpenes fraction in extracts was inversely correlated with relative oil yields. Monoterpenes were preferentially extracted by CO2 due to their high vapor pressure, low molar mass and low polarity. Supercritical extraction presented advantages over the conventional hydro‐distillation by yielding extracts lower in monoterpenes fraction and by enabling high yields at temperatures safe for the heat‐sensitive essential oil.
Prediction of the azeotropic behavior of binary mixtures from gas—Liquid P‐T‐x critical data with cubic equations of state
Authors: García‐Sánchez Fernando , Hernández‐Garduza Otilio , García‐Flores Blanca E. , Eliosa‐Jiménez Gaudencio 
Published: March 2009

AbstractA computational procedure is described to predict homogeneous azeotropic loci of binary mixtures with cubic equations of state and gas—liquid P‐T‐x critical information. The performance of the method is demonstrated on three binary systems exhibiting either negative or positive azeotropic behavior which persists up to the critical region. The method of Heidemann and Khalil was used for correlating the critical data while that of Wang and Whiting was used to predict the azeotropic lines together with a stability test applied on each estimated point. Good agreement between calculated and measured azeotropic data was obtained for the systems studied.