bluuebunny/crossref_metadata_2025_split huggingface dataset:
Modeling and analysis of new processes for polyester and nylon production
Authors: Yao Zhen , Ray W. Harmon 
Published: April 2004

AbstractIntegrated processes for nylon and polyester production were simulated. The polyester process includes four stages: esterification, prepolycondensation, finishing stage, and solid‐state polycondensation. Three stages are involved in the nylon process: prepolycondensation, melt polycondensation, and the solid‐state stage. The effect of beginning the solid‐state stage at lower DP (compared to the value of the current process) was investigated for both nylon and polyester production. Reactors with either cocurrent or countercurrent purge gas flow were applied to the finishing stage for polyester and to the melt stage for nylon. The performance of different reactors was compared. The effect of purge gas strongly depended on the mass‐transfer capacity of reactors. In the nylon process, variations in purge gas conditions had a small effect on reactor performance. However, purge gas effects on the polyester process were considerable, and countercurrent flow was more effective than cocurrent flow. The reactor operated at atmospheric pressure and, with countercurrent gas flow, can readily substitute for traditional high vacuum operation in the finishing stage of the polyester process.
Methane conversion using a high‐frequency pulsed plasma: Important factors
Authors: Yao Shuiliang , Nakayama Akira , Suzuki Eiji 
Published: April 2004

AbstractFactors influencing methane conversion in a high‐frequency pulsed plasma were studied. Pulse frequency is the most important factor influencing acetylene selectivity and methane conversion rate that represents electric energy efficiency. The high pulse‐frequency plasma promotes acetylene formation and improves methane conversion rate. With increasing pulse voltage, acetylene selectivity increases, but methane conversion rate decreases. The temperature of the background methane gas does not markedly influence methane conversion in a temperature range of 20 to 200°C. A co‐axial cylindrical reactor with a fine central anode is favorable to practical use of methane conversion.
Methane conversion using a high‐frequency pulsed plasma: Discharge features
Authors: Yao Shuiliang , Nakayama Akira , Suzuki Eiji 
Published: April 2004

AbstractThe pulsed plasma of methane was experimentally characterized using single and sequential pulse modes. At a single pulse mode, only pulsed corona and streamer discharges occurred at a low pulse voltage. A pulsed spark discharge developed afrer the pulsed streamer discharge at a high pulse voltage. An image analysis indicated that the weak luminescence could be found in the latter period of the pulsed corona discharge. The pulsed streamer and spark discharges bridged the discharge gap and emitted a relatively strong light. At a sequential pulse mode, the streamer or spark discharge developed easily and evenly at a low pulse voltage, as the pulse frequency increased in comparison with that at the single pulse mode. The high‐frequency pulsed plasma was more practical than other plasmas due to its relatively high energy efficiency at room temperature and atmospheric pressure.
Mass transfer and chemical reaction in hollow‐fiber membrane reactors
Authors: Li K. , Tan Xiaoyao 
Published: April 2004

AbstractTheoretical models developed describe hollow‐fiber memebrane reactors (modules), in which membrane functions as an efficient reactant distributor and the chemical reaction takes place either in the hollow‐fiber lumen or in the shell side. Effects of various design and operating parameters, and physical properties on the performance of the reactors were studied. Simulation results indicated that the axial dispersion has to be considered when the chemical reaction tukes place in the shell side. It, however, may be neglected when Pe > 40. Theoretical results further revealed that the mass‐transfer direction of the reactant through the membrane might be reuersed when the chemical reaction in the iiquid is extremely fast. Experimental data in the literature obtained from water‐treatment processes agreed satisfactorily with the theoretical solutions. Based on thc developed solution method, the reaction kinetic parameters can also be obtained conveniently.
Phase equilibria for water–methanol mixtures in perfluorosulfonic‐acid membranes
Authors: Geiger Arne B. , Newman John , Prausnitz John M. 
Published: April 2004

AbstractA new apparatus was constructed for precise measurements of water–methanol up‐take compositions in a membrane. Uptake concentrations of methanol and water in a Nafion 117 membrane were measured as a function of methanol mole fraction in a liquid‐methanol–water mixture for the temperature range 298 to 333 K. Also, uptake concentrations of methanol and water were determined for a second‐cycle uptake run. All methanol–water compositions were determined by gas chromatography. The results were quantitatively described by either one of two thermodynamically consistent equations derived from models for the Gibbs energy of the system.
Modeling mass transfer and hydrodynamics in fluidized‐bed adsorption of proteins
Authors: Wright Pamela R. , Glasser Benjamin J. 
Published: April 2004

AbstractA model was developed and solved to describe protein adsorption in a fluidized bed. Liquid‐solid mass transfer, adsorption and hydrodynamic effects were taken into account. The model was examined for both pore and homogeneous diffusion. The simulation results showed close agreement with experimental breakthrough curves obtained for lysozyme adsorption on Streamline SP and S‐HyperD LS resins at expansions of 2, 3 and 4 times the settled‐bed height. Parametric sensitivity analysis showed that superficial velocity and particle radius had the largest effects on breakthrough behavior for all conditions. The effect of axial dispersion, film mass transfer and solid diffusion coefficients were less significant contributors to breakthrough at all expansions and bulk phase viscosities. The simulation results for pore diffusion were affected more significantly by changes in superficial velocity and particle radius than the simulution results for homogeneous diffusion. The performance of the fluidized‐bed adsorption unit was limited by intraparticle mass‐transfer effects, especially at high degrees of bed expansion.
Role of diffusion in biocatalytic polytransesterification
Authors: Kline Billie J. , Lele Smita S. , Beckman Eric J. , Russell Alan J. 
Published: April 2004

AbstractThe solvent‐free enzyme‐catalyzed polytransesterification of divinyl adipate and 1,4‐butanediol yielding high molecular‐weight polyesters was studied. This heterogeneous system is characterized by initial exothermicity, a 104‐fold increase in viscosity, and complex kinetics involving parallel reactions and variable reaction volumes. Herein a semitheoretical analysis of solvent‐free polytransesterification was developed to further refine understanding of the role of diffusion, especially how molecular weight and poly‐dispersity evolve during solvent‐free biocatalytic polytransesterification. The evolution of polydispersity observed during the polymerization was attributed to diffusion, and there‐fore internal diffusion limitations were assessed experimentals. The analysis denzon‐strated that the system is initially under weak diffusional control, which is strengthened by the initial exothermicity of the reaction. At molecular weights over 5,000 Da, the system experienced severe mass‐transfer resistance due to chain entanglements. Reduced erizyme specificity with increasing chain length, enzyme deactivation, and vinyl hydrolysis dampen the diffusional constraints toward the end of the polymerization such that the system could return to slight diffusional or kinetic control on exceeding molecular weights of 20,000 Da.
Scale‐up of enzymatic solid‐to‐solid peptide synthesis and enzyme recovery
Authors: Erbeldinger Markus , Halling Peter J. , Ni Xiongwei 
Published: April 2004

AbstractThe feasibility of scale‐up for applicutions of enzymatic solid‐to‐solid synthesis of dipeptides Was investigated by using Thermouse catalyzed synthesis of Z‐Asp‐Phe‐OMe as a model reaction. The reaction system involves typically only 10% (w/w) enzyme syspension added to dry solid substrates. Enzymatic solid‐to solid biocatalysis combines the main advantages of aqueous media, high catalytic acitivity, low water media, and high yields. A flow sheet for the whole process is described, as well as the use of a jacketed reactor with an anchor stirrer for various steps of the process, including the neutralization reaction to adjust the acid‐base condition of the reaction mixture. A solution for enzyme recycling, an important issue for scale‐up applications, is also suggested.
Pore network simulation of imbibition into paper during coating: I. Model development
Authors: Ghassemzadeh Jaleh , Hashemi Mehrdad , Sartor Luigi , Sahimi Muhammad 
Published: April 2004

AbstractA novel imbibition model of a coating fluid in a paper was developed. The microstructure of the paper was represented by a network of interconnected channels or throats formed between the paper's fibers. Geometrical characteristics of the channels, such as effective radius and length, were selected from representative statistical distributions. The interconnectivity of the channels was characterized by an average coordination number treated as a parameter of the model, and its effect on the imbibition process was studied. The study dealt with a dynamic (time‐dependent) boundary condition, in which a convection‐driven pressure was applied to the coating fluid on the external surface of the paper or driven only by capillary forces. The flow parameters used in the model represent a high‐speed coating process. Extensive computer simulations were carried out to study the effect on the imbibition process of three distinct sets of parameters: microstructural parameters of the paper; the fluid's properties; and the dynamic boundary condition. The mean coordination number and average throat size of the paper's pore space, the coating fluid's viscosity, and the dynamic boundary condition all strongly influenced imbibition of the coating fluid.
Simultaneous grinding and dissolution of TNT solids in an agitated slurry
Authors: Gilcrease Patrick C. , Murphy Vincent G. , Reardon Kenneth F. 
Published: April 2004

AbstractIn the slurry‐phase bioremediation of soils contaminated with 2,4,6‐trinitrotoluene (TNT) solids, TNT dissolution can be the rate‐limiting step in the biodegradation process. To determine the effects of slurry concentration on solids dissolution, TNT particles were dissolved in a stirred vessel containing water and inert Teflon (PTFE) chips. For a constant agitator speed, the solid–liquid mass‐transfer coefficient (kL) decreased as the percentage of PTFE solids was increased. However, observed dissolution rates for TNT beads in agitated slurries were much higher than anticipated due to the grinding effect of PTFE chips. A size–mass balance was used to account for the grinding of TNT beads in these slurries; this same balance was then used to predict TNT dissolution rates. Slurry grinding was shown to be an important mechanism for enhancing the dissolution of TNT solids, and the size–mass balance was demonstrated to be an effective tool for modeling this process. These results have important implications for the bioremediation of TNT solids in soil slurry reactors.
Novel scaling parameter for circulating fluidized beds
Authors: Kehlenbeck Ralf , Yates John , Di Felice Renzo , Hofbauer Hermann , Rauch Reinhard 
Published: April 2004

AbstractExperimental results of a one‐fifth scale cold laboratory model of a circulating fluidized‐bed pilot plant for biomass gasification are reported here. Measurements revealed that the solid circulation rate is a function of the superficial gas velocity in the riser and the total mass load in the system. A novel dimensionless scaling parameter introduced describes the dimensionless mass turnover. Experiments were carried out varying both particle diameter, 170 μm ≤ d ≤ 860 μm, and density, 1,480 kg/m3 ≤ ρs ≤ 8,900 kg/m3. An excellent prediction for the mass turnover was obtained for mass loads varying from 1 to 15 kg and throughout the whole particle size and density range using the equations derived. Furthermore, the particle‐size distribution is a scaling parameter to be matched between a model and an industrial plant.
Effect of chemical kinetics on feasible splits for reactive distillation
Authors: Chadda Nitin , Malone Michael F. , Doherty Michael F. 
Published: April 2004

AbstractFeasible direct and indirect sharp splits for multicomponent single‐feed continuous reactive distillation are predicted with a model, in which each column section is represented by a series of cocurrent isobaric flashes. In the limits of no reaction and equilibrium chemical reaction, the model reduces to conventional models for distillation lines, and each column section can be represented by the same equations. At intermediate reaction rates, however, the models for the column sections differ, and new results for fixed points and feasible products are obtained. A bifurcation study shows the limits of feasibility, including the influence of flow rate, catalyst level and holdup. Unlike distillation without reaction, limited ranges of feasibility in all of these variables are found. The method has been applied to five examples, one of which is described in detail. Feasibility predictions are validated by column simulations.
Modular synthesis framework for combined separation/reaction systems
Authors: Ismail Soraya Rahim , Proios Petros , Pistikopoulos Efstratios N. 
Published: April 2004

AbstractAs an extension to our earlier work (1999a), this article presents a systematic approach for the synthesis of combined separation/reaction systems which involves a phenomena‐based representation formulated within a superstructure optimization framework. A multifunctional, mass‐/heat‐transfer‐based process module is utilized as the building block of process alternatives. Within this module, Gibbs‐free‐energy‐based “driving‐force” constraints are introduced to describe the physiochemical phenomena and to ensure feasibility of pure separation, reaction or combined separation/reaction (such as reactive distillation). A superstructure of these multipurpose modules is then systematically constructed to represent process alternatives, which are not explicitly prepostulated, but investigated, as mass and heat exchange network possibilities.
Designing a fast‐igniting catalytic converter system
Authors: Keith Jason M. , Chang Hsueh‐Chia , Leighton David T. 
Published: April 2004

AbstractThrough analysis and numerical simulation, the late lightoff (∼ 3 min) of the current automobile catalytic converter is attributed to a downstream ignition phenomenon that is unstable to flow‐rate fluctuations. A design is proposed which incorporates a stable and thermally efficient leading‐edge ignition. The key feature involves diverting a small portion of exhaust gas through a bypass stream, which contains an electric preheater and a preigniter, during startup. This allows the preheater to utilize a low power input using the existing battery and yet raise the gas temperature beyond a precise minimum that rapidly lights off the entire preigniter. The hot preigniter is then used to light off the main catalytic converter. Removal of the bypass after complete ignition preserves the preigniter catalyst, a major advantage. The optimal design is shown to lightoff within 10 s and reduce pollution by almost 90% over current designs and thus meet ultra low emission vehicle (ULEV) standards.
Simulation of turbulent precipitation in a semi‐batch Taylor‐Couette reactor using CFD
Authors: Marchisio D. L. , Barresi A. A. , Fox R. O. 
Published: April 2004

AbstractA finite‐mode probability density function method was used with a computational fluid dynamics code to model the semibatch precipitation of barium sulfate from aqueous solutions of barium chloride and sodium sulfate in a Taylor‐Couette reactor. It was simulated in turbulent flow at high Taylor numbers under the assumption of axial symmetry. The flow field was modeled using two different turbulence models, and flow predictions were validated using experimental tracer dispersion measurements. The crystal‐size distribution (CSD) was calculated in terms of the first five moments considering both nucleation and growth, while neglecting the effect of aggregation. The effect of the operating conditions on the CSD was studied, and code predictions were compared with experimental data.
Simulations of gas‐liquid‐solid 3‐phase flow and reaction in FCC riser reactors
Authors: Gao Jinsen , Xu Chunming , Lin Shixiong , Yang Guanghua , Guo Yincheng 
Published: April 2004

AbstractA 3‐D, three‐phase flow‐reaction model was developed to predict the performance of FCC riser reactors. This model incorporates the effect of feed vaporization into an earlier 3‐D, two‐phase flow‐reaction model (Gao et al., 1999). The synergistic effects of hydrodynamics, heat transfer, and feed vaporization on FCC reactions are elucidated. The results show that a complex phenomenon occurs in the zone up to 4m above the point at the bottom of the riser reactor where feed is injected. The changes in the spray droplet diameter, volumetric concentration and temperature of the feed in the feed injection zone are illustrated. The model was used as a design tool for an operation modification study. Results indicate that FCC reaction selectivity for the desired products (gasoline and light fuel oil) can be improved by reducing initial droplet diameter in the feed spray from 80 to 40 μm.
Mixed hydrates of methane and water‐soluble hydrocarbons modeling of empirical results
Authors: de Deugd R. M. , Jager M. D. , de Swaan Arons J. 
Published: April 2004

AbstractThe hydrate disappearance conditions (H − Lw − V → Lw − V transition) in the water–methane–water‐soluble hydrocarbon system were measured and modeled. The hydrocarbons in the experiments are tetrahydrofuran (THF), 1,3‐dioxolane and tetrahydropyran, and THF, 1,3‐dioxolane and acetone in the modeling study. Experiments and calculations, which correspond qualitatively and quantitatively very well, show a large reduction in the equilibrium pressure upon addition of the hydrocarbons. The minimum pressure is about 5–6 mol % hydrocarbon relative to water, independent of temperature and applied hydrocarbon, with the composition almost equal to the ratio between the number of large cages and water molecules in structure II hydrates (5.88%). Based on this observation, the hydrates are assumed to be structure II methane–hydrocarbon mixed hydrates. The model is also used to calculate the occupancies of the hydrate cavities. No experimental data are available to compare the predicted values, but the results help understand observed phenomena better.
Optimal carbon source switching strategy for the production of PHA copolymers
Authors: Mantzaris Nikolaos V. , Kelley Aaron S. , Srienc Friedrich , Daoutidis Prodromos 
Published: April 2004

AbstractDuring polymerization in a nongrowing cell population of Ralstonia eutropha, alternating between two different carbon sources (fructose and fructose/valeric acid) could lead to the production of block copolymers consisting of blocks of homo‐poly‐3‐hydroxybutyrate (PHB) and polyhydroxybutyrate‐co‐valerate (PHBV) copolymer. The problem of finding the optimal number of carbon source switches and corresponding switching times that maximize the final concentration of diblock copolymers (PHB‐PHBV and PHBV‐PHB) was addressed. It was mathematically formulated in the mixed‐integer nonlinear programming (MINLP) framework, which allows the decomposition of the original problem into the primal and master problems. The primal problem corresponds to the original problem for a fixed number of carbon source switches, whereas the master problem consists of finding the number of carbon source switches that maximizes the optimum solutions of all possible primal problems. The global optimum was obtained for 39 carbon source switches. It corresponds to a mass fraction of 50.6% of final diblock copolymer concentration over the final total polymer concentration.
PIV study of small‐scale flow structure around a Rushton turbine
Authors: Sharp K. V. , Adrian R. J. 
Published: April 2004

AbstractThe structure of turbulent motions was measured in a region surrounding the blade tips of a Rushton turbine mixer. The tip vortices responsible for micromixing were created in this region, as was the radial jet that drives the large‐scale circulation responsible for macromixing. Measurements of instantaneous velocity fields in axial–radial planes showed large cycle‐to‐cycle variability relative to the mean. The average measurements of the azimuthal vorticity and the Reynolds stresses in the radial–axial plane showed the growth and motion of the tip vortices as they drift away from the blades. Radial and axial spatial derivatives were measured to assess various methods of computing the turbulent viscous dissipation. The small scales were significantly anisotropic at the Reynolds numbers studied.
Computational analysis of surface‐tension‐driven coating‐defect flow
Authors: Blunk Richard H. J. , Wilkes James O. 
Published: April 2004

AbstractBondline readout (BLRO) is a coating defect frequently exhibited on adhesively‐bonded, polymeric automotive body panels painted with high‐glamor/flow clearcoats. BLRO or telegraphing results from Marangoni‐type, surface‐tension‐driven flows. An efficient numerical code was developed to predict temperature‐ and concentration‐induced BLRO flows to use it as an effective tool for screening and developing potential clearcoat systems. Two numerical codes were developed: a 1‐D code based on the lubrication approximation; a 2‐D code based on the SIMPLER (Semiimplicit method for pressure‐linked equations revised) algorithm. The 1‐D code produced BLRO profiles in agreement with those predicted from the 2‐D code and those measured from BLRO flow experiments, thus confirming a proposed BLRO mechanism. Moreover, the 1‐D code was vastly more time‐efficient than the 2‐D code due to a severe time‐step stability limitation found with the latter.
Mass transfer across dilated interfaces
Authors: Tokarz Alexander , Millies Marco , Mewes Dieter 
Published: April 2004

AbstractThe mutual dependence of mass and momentum transport at fluid interfaces was studied theoretically and experimentally. Applying thermodynamics of irreversible processes to systems with interfaces showed, on a theoretical basis, that the dilation of the interface acts as a thermodynamic driving force for the mass transfer across the interface. Mass‐transfer rates and concentration profiles at the dilated interface between toluene and water were measured using holographic interferometry for various transfer components. Experimental study showed that mass‐transfer rates increase with increasing dilational rate, due solely to an enhanced convective transport in the continuous phases. The dilation does not affect the concentrations at the interface. It was demonstrated theoretically that the maximum possible alteration in the interfacial concentrations due to dilation was in the order of magnitude of the experimental accuracy of the interferometer. It was concluded that the thermodynamic driving force due to dilation is—if present—too small to be relevant to technical applications.