bluuebunny/crossref_metadata_2025_split huggingface dataset:
Gradient formation in membrane unit for differential precipitation of proteins
Authors: Sookkumnerd Terasut , Hsu James T. , Ito Yoichiro 
Published: April 2004

AbstractA new protein fractionation technique presented transfers ammonium sulfate to create a gradient of ammonium sulfate inside a membrane unit for differential precipitation of proteins called “centrifugal precipitation chromatography.” Because it does not require any solid support, it should provide a better alternative to the conventional chromatography with solid stationary phase. To understand the phenomena and achieve a better separation, a mathematical model explaining the ammonium sulfate gradient formation inside the stationary membrane unit is investigated. The model is extended with empirical correlation to the centrifugal membrane unit—a new approach for protein purification. The model agreed well with the experiments for both stationary and centrifugal units. Upon using the model to calculate the ammonium sulfate gradient formation in a membrane unit, this new technique can be useful in separating a mixture of proteins whose solubility in ammonium sulfate solution differs. To demonstrate the technique experimentally, mixtures of proteins are loaded into the column; the partial resolution between proteins is achieved with the step concentration switch of the inlet ammonium sulfate solution.
Closed operation of multivessel batch distillation: Experimental verification
Authors: Wittgens Bernd , Skogestad Sigurd 
Published: April 2004

AbstractThe multivessel batch distillation column, as well as conventional batch distillation, can be operated in a closed (total reflux) mode where the products are collected in vessels along the column. A previously proposed and simulated feedback control strategy for the closed operation is to indirectly adjust the vessel holdups by using the reflux flow out of the vessel to control the termperature at some location in the column section below. The feasibility of this scheme is demonstrated here experimentally on a laboratory‐scale multivessel column. The experimental column consists of a reboiler, two intermediate vessels, and an accumulator, where a mixture of methanol–ethanol–propanol–butanol is separated into almost pure components. The first published experimental work on the closed operation of batch distillation is presented, as well as its results on the operation of a multivessel column.
Monte‐Carlo simulation of branching distribution in Ni‐diimine catalyzed polyethylene
Authors: Simon Leonardo C. , Soares Joao B. P. , de Souza Roberto F. 
Published: April 2004

AbstractMonte‐Carlo simulation was used to study the short‐chain branch formation of polyethylene made with a Ni‐diimine catalyst. Branches are formed through the chain‐walking mechanism without any comonomer addition. The model describes the type of branch, that is, methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octly, nonyl, and decyl (or longer branches) and the distribution of these branches in the backbone, showing information that cannot be accessed by 13C NMR. The branching structure of these polymers seems to be determined by two major kinetic steps described by the following model parameters: a beta transfer parameter describing the ratio of monomer insertion to beta hydrogen transfer and an isomerization barrier parameter controlling the ratio among different types of branches. The model showed that methyl branches are favored on the other branches in the chain‐walking mechanism. The branch distribution obtained with the model developed herein agrees well with 13C NMR experimental results.
Calcium carbonate precipitation using new segmented flow tubular reactor
Authors: Vacassy R. , Lemaître J. , Hofmann H. , Gerlings J. H. 
Published: April 2004

AbstractA new segmented flow tubular reactor for the continuous production of powders was used to synthesize calcium carbonate by precipitation. This new reactor uses a nonmiscible phase (air in most cases) to create individual microvolumes of the reacting mixture or suspension ensuring that a plug‐flow regime is maintained. In a microvolume, poor micromixing can be avoided and the homogeneity in reaction conditions is increased better than in larger volumes, leading to a better control of powder characteristics. Calcium carbonate with controlled characteristics could be precipitated continuously using this new segmented flow tubular reactor. Pure calcite could be obtained in the tubular reactor by segmenting a Ca2+ solution with a reactive CO2/NH3 gas mixture. This synthesis process is very promising for industrial production since the scale‐up should easily be achieved by multiplying the number of tubes working in parallel.
Inverse method to obtain reaction surface area during gas‐solid reactions
Authors: Krammer Gernot F. 
Published: April 2004

AbstractDuring noncatalytic gas‐solid reactions, both the chemical composition, and the size and texture of the particle change simultaneously. A new inverse method allows to determine the influence of the reaction parameters (such as temperature) and changes in the specific reaction surface area with conversion. It can also establish the range of conversion, where constant reaction conditions are present at the reaction surface. This method is based on the mathematical treatment of experimental results which include the conversion vs. time together with the corresponding reaction parameters. This method consists of several well established mathematical procedures applicable to the specific situation at gas‐solid reactions: variable conversion and reaction time are separated and inverted, respectively. The ratio of two reaction rates (of different experiments) at the same conversion provides information about the (only time‐dependent) influence of the reaction parameter on the reaction rate. Finally, also the specific reaction surface area as a function of conversion is derived.
Kinetic model of the partial oxidation of methane to synthesis gas over Ru/TiO2 catalyst
Authors: Elmasides Costas , Ioannides Theophilos , Verykios Xenophon E. 
Published: April 2004

AbstractThe kinetic behavior of the Ru/TiO2 catalyst in the partial oxidation of methane to synthesis gas was investigated as a function of temperature and partial pressures of CH4 and O2. It was found that the catalyst promotes, to a large extent the direct formation of CO and H2 from the reaction of methane and oxygen, while the reforming and water–gas shift reactions are negligible under these conditions. A kinetic model, based on formation of CO and H2 as primary products and of CO2 and H2O as secondary oxidation products, describes satisfactorily the observed kinetic behavior. Values of model parameters satisfy thermodynamic constraints and agree well with data derived from surface science techniques and kinetic studies of elementary surface processes that are in the literature.
Dissolution kinetics of polymer powders
Authors: Parker Alan , Vigouroux Florence , Reed Wayne F. 
Published: April 2004

AbstractThe dissolution kinetics of polymer powders as isolated grains or in beds were studied theoretically and experimentally. A simple model developed for the dissolution of a dispersion of isolated grains with an arbitrary size distribution was confirmed experimentally using polysaccharides in water. Based on experimental data for the dissolution of lump‐forming powder beds, modeled using a bimodal population of grains and lumps, a robust technique was developed for analyzing experimental data, which is independent of the details of lump formation. A qualitative picture of lump formation is described, based on the idea that during the initial hydration of a powder bed a “pore blocking” condition quickly develops due to the formation of a gel layer around the dry grains. Once formed, lumps dissolved the same way and with the same kinetic description, as individual, dispersed grains.
Experimental study of wave occlusion on falling films in a vertical pipe
Authors: Dao Eric K. , Balakotaiah Vemuri 
Published: April 2004

AbstractExperiments were conducted to study wave occlusion on falling films in a vertical pipe with aqueous solutions of glycerine with viscosities from 0.022 to 1.25 kg/(m·s). Pipe diameters were varied from 0.00635 to 0.015875 m. For each case, the critical liquid flow rate was determined at which the free falling wavy annular flow transforms into slug flow due to wave occlusion. The experimental results are correlated in terms of the liquid Reynolds number at occlusion (ReLS = 4q/πνD) and two dimensionless groups influencing the transition: the Kapitza number Ka = σ/[(νg)1/3 μ], and the Bond number Bo = ρgD2/σ. The annular‐slug transition correlation was ReLS = 0.062 Ka4/3 Bo2/3 and valid in the range 0.1<ReLS <200, 0.2<Ka<55 and 7<Bo<50. Experimental results were compared to related published results, and the experimental correlation is explained qualitatively.
Effect of solute concentration on hindered diffusion in porous membranes
Authors: Shao Jiahui , Baltus Ruth E. 
Published: April 2004

AbstractThe effect of solute concentration on hindered diffusion was investigated by measuring diffusion rates of dextran and polyethylene glycol (PEG) in track‐etched polycarbonate membranes at concentrations up to 60 mg/mL. Results were interpreted using a model that incorporates a first‐order virial coefficient to describe the concentration dependence of the equilibrium partition coefficient, as well as the intrapore diffusivity. For dextran, both virial coefficients were positive, indicating that the effective diffusivity increases with solute concentration. Measured values of the virial coefficient for equilibrium partitioning agreed with a model that includes attractive van der Waals interactions between dextran and the pore wall. For PEG, both virial coefficients were negative, indicating that the diffusivity decreases as solute concentration increases. These observations may be due to chain entanglement or aggregation that occurs with increasing PEG concentration.
Simulation of vortex core precession in a reverse‐flow cyclone
Authors: Derksen J. J. , Van den Akker H. E. A. 
Published: April 2004

AbstractA large‐eddy simulation of the single‐phase turbulent flow in a model cyclone geometry on a uniform, cubic computational grid consisting of 4.9×106 cells was performed. The Navier‐Stokes equations were discretized according to a lattice‐Boltzmann scheme. The Reynolds number, based on the inlet velocity and the cyclone body diameter, was 14,000. A standard Smagorinsky subgrid‐scale model with cs = 0.1, including wall‐damping functions, was applied. The 3‐D, average flow field was predicted with a high level of accuracy. Furthermore, the simulations exhibit vortex‐core precession, that is, the core of the main vortex is observed to move about the geometrical axis of the cyclone in a quasi‐periodic manner. The Strouhal number associated with the simulated vortex‐core precession was 0.53, whereas 0.49 was experimentally observed in a similar geometry at approximately the same Reynolds number.
Numerical simulation of transient flow of two immiscible liquids in pipeline
Authors: Fairuzov Yuri V. 
Published: April 2004

AbstractA two‐fluid model for transient flow of two immiscible liquids in a pipeline was formulated based on two transient continuity equations and a combined momentum equation in a quasi‐steady form. It can be used for simulating both stratified and dispersed flow. Numerical simulations were performed to investigate the behavior of oil–water flow during transients caused by an increase or decrease in the water volume fraction at the entrance to the pipeline. An increase in the water flow rate within the stratified flow regime may result in the formation of a shock (an abrupt change in the water holdup). In transients produced by a decrease in the input water volume fraction, the smoothening of the water holdup wavefront occurs. This behavior is explained by a strong dependence of the speed of the holdup wave propagation in stratified flow on the water holdup. The results obtained for inclined pipelines show that the slope of the pipe affects the flow behavior significantly. The liquid–liquid flow model was used to simulate the transport of corrosion inhibitor in a pipeline conveying an oil–water mixture.
Local bubble‐size distribution in fluidized beds
Authors: Santana D. , Macías‐Machín A. 
Published: April 2004

AbstractThe importance of the rise angle of bubbles on the influence of local bubble‐size distribution in fluidized beds was studied. A new method is proposed for transforming chord‐length distribution to a local bubble‐size distribution, including the effect of the velocity vector direction on the transformation. Monte‐Carlo simulation was used to generate bubbles synthetically with several rise angles, based on the fact that the velocity vector direction distribution of bubbles was a Bingham distribution. The transformation of chord‐length data obtained by an imaginary probe, using the Parzen window as an estimation of the probability density function, gives a good estimation of the local bubble‐size distribution for different rise angles and the new approach offered here, knowing that the direction of the velocity vector direction for any orientation of the bubbles in the fluidized bed gives a superior agreement than the approach where the local bubble‐size distribution is estimated from bubbles with vertical rises.
Robust design of countercurrent adsorption separation processes: 5. Nonconstant selectivity
Authors: Migliorini Cristiano , Mazzotti Marco , Morbidelli Massimo 
Published: April 2004

AbstractOperating conditions for the separation of a binary mixture using a nonadsorbable eluent through simulated moving‐bed technology were designed. The results obtained using equilibrium theory for adsorption described by Langmuir models lead to the definition of explicit constraints on the operating parameters to operate the unit in the desired regime of separation. A more general approach was able to produce the same result for a larger class of isotherms. The physical and mathematical conditions defining this larger class of isotherms are discussed, as well as the algorithms necessary to calculate the region of complete separation. Applications to the bi‐Langmuir isotherm and the ideal adsorbed solution model, which are more flexible than the Langmuir model and can describe systems where selectivity changes with composition, are discussed. A shortcut method to get an explicit, though approximate, solution is proposed and its accuracy is discussed.
Unified approach for synthesizing crystallization‐based separation processes
Authors: Wibowo Christianto , Ng Ka M. 
Published: April 2004

AbstractA procedure for synthesizing crystallization‐based separation processes is presented. In an evolutionary manner and without being restricted to a particular crystallization technique, flowsheet alternatives are generated to meet the separation objectives for a given system. This is achieved by recognizing the fact that four basic crystallization‐related movements in composition space are sufficient to represent a variety of crystallization processes. Suitable movements are selected based on relevant features of the phase diagram to construct feasible flowsheets. The procedure consists of six steps. First, separation objectives are defined. Second, a separation core structure is generated. Third, the separation sequence and unit operations are selected, followed by adding other units to the structure for proper plant operations. Fifth, appropriate crystallizer type is selected. Finally, economic evaluation and feasibility checks are performed for the generated alternatives. Rules are provided to aid decision‐making at each step. The procedure is illustrated with various examples including separation of amino acids, p‐ and m‐cresols, chlorobenzoic acids, calcium carbonate and magnesium oxide from dolomite, and the production of salt.
Rigorous modeling of UV absorption by TiO2 films in a photocatalytic reactor
Authors: Zhang Z. , Anderson W. A. , Moo‐Young M. 
Published: April 2004

AbstractThe radiation absorption profiles on the surfaces of TiO2 films in a corrugated‐plate photocatalytic reactor were modeled based on first principles. A new term, the local‐area‐specific rate of energy absorption (LASREA), was adopted to describe the catalyst surface radiation in heterogeneous photoreactors. The LASREA and the energy absorption efficiency were both quite sensitive to the dimensions of the corrugated plates. Due to the multiple photon reflections between the opposing surfaces, corrugated plates possess a superior capability for recapturing longer wavelength photons that would otherwise be reflected out of some reactor designs. This results in higher energy absorption efficiency and more uniform LASREA on the catalyst films. Compared to a flat plate, corrugations are predicted to enhance the energy absorption efficiency by up to 50% for UV‐A fluorescent‐lamp‐powered systems and more than 100% for solar‐powered systems.
Acid‐neutralizing of marine cylinder lubricants: Measurements and effects of dispersants
Authors: Wu Rong Chang , Papadopoulos Kyriakos D. , Campbell Curt B. 
Published: April 2004

AbstractConsiderable amounts of sulfuric acid are produced in marine diesel engines during the combustion of high‐level sulfur fuels, thus causing corrosive wear. The acid‐neutralizing ability of marine cylinder lubricants (MCLs) is therefore a “measuring stick” of their quality. A new experimental protocol was previously published to qualitatively test the acid‐neutralizing ability of marine cylinder lubricants. Using a capillary video‐microscopy technique and measuring the shrinking rate of the size of nitric‐acid drops in MCL, the acid‐neutralizing ability of commercial MCLs, as well as model lubricants, can be determined quantitatively. The shrinking rate of the nitric‐acid drop size in MCL was constant during the reaction period and independent of the initial drop size. Analysis of the experimental results, following an interfacial neutralization reaction mechanism, suggests that the adsorption of overbased reverse micelles on acid‐oil interface is the controlling step in the reaction process. The presence of small amounts of dispersant (1 wt. %) in a model MCL on the neutralization reaction decreased the reaction rate for both nitric and sulfuric acid, while further increase in dispersant concentration (up to about 4%) did not reduce the acid‐neutralizing ability further. For sulfuric acid, dispersants act also to effectively disperse the hydrated calcium sulfate crystals produced by the neutralization reaction with sulfuric acid.
Theoretic information approach to protein stabilization by solvent engineering
Authors: Di Domenico Roberto , Lavecchia Roberto , Ottavi Alessandro 
Published: April 2004

AbstractA novel approach based on molecular thermodynamics and the information theory is proposed to quantify the influence of water‐miscible additives on protein stability. According to the two‐state mechanism of inactivation, solvent effects are described in terms of perturbation of the equilibrium between the folded and unfolded protein forms. The model provides the dependence of the protein's melting temperature on the additive concentration. Effects of the latter are accounted for by an empirical parameter related to the free energy of transfer of the protein from the pure to the mixed solvent. The model was tested using experimental data relative to the influence of hydroxylic and aminoacidic additives on the thermal unfolding of hen egg lysozyme and erythrocyte carbonic anhydrase. Fitting parameters were correlated in terms of a theoretic information index characterizing the additive's molecule and incorporating an atomic‐composition term and a topological contribution. Model calculations agreed very well with experimental data, suggesting that the molecular information content of the additive can be used effectively to correlate solvent‐induced perturbations of stability. The procedure was also used to predict melting temperatures in systems containing binary mixtures of additives and to reconstruct thermal unfolding curves in the different media.
Semicontinuous, middle‐vessel distillation of ternary mixtures
Authors: Phimister James R. , Seider Warren D. 
Published: April 2004

AbstractThe operation of a semicontinuous, middle‐vessel column (SCMVC) that separates a nearly‐ideal ternary mixture is analyzed. MVCs have a large vessel between the rectification and stripping sections. In traditional batch rectification or stripping, a still is charged and distillate or bottoms products are removed, leaving heavy or light concentrates in the still, respectively. In contrast, the middle vessel of an MVC is charged, and, similar to a continuous process, both distillate and bottoms products are withdrawn. The process separates nearly‐ideal ternary mixtures into three nearly‐pure species, with the intermediate‐boiling species concentrating in the middle vessel, and the light and heavy species concentrating in the distillate and bottoms products, respectively. Shortcut methods are adapted to determine the minimum number of trays and minimum reflux ratio. Alternative control configurations are considered to achieve suitable performance throughout the campaign. Two DB configurations are shown to be suitable for this process, with the middle vessel decoupling the composition control loops and permitting dual‐composition control with little interaction. Simulations confirm that difficulties encountered when using a DB configuration for the dual‐composition control of a continuous column do not occur for a SCMVC.
Synthesis and oxygen‐permeation properties of thin YSZ/Pd composite membranes
Authors: Kim Jinsoo , Lin Y. S. 
Published: April 2004

AbstractThin dense yttria‐stabilized‐zirconia (YSZ)/Pd composite (dual‐phase) membranes were fabricated on porous YSZ membranes by a new approach that combines the reservoir method and chemical vapor deposition (CVD) technique. A thin porous YSZ layer was coated on a porous alumina support by dip coating the YSZ suspension. A continuous Pd phase was formed inside pores of the YSZ layer by the reservoir method. The residual pores of the YSZ/Pd layer were plugged with yttria/zirconia by CVD to ensure the gas tightness of the membranes. The oxygen‐permeation fluxes through these composite (dual‐phase) membranes, measured in situ in the CVD reactor, are 2.0×10−8 and 4.8×10−8 mol/cm2·s at 1,050°C when air and oxygen are used as the permeate gases, respectively. These oxygen‐permeation values are about 1 order of magnitude higher than those of pure YSZ membranes prepared under similar conditions. The apparent activation energies for oxygen permeation at 900–1,050°C are 193 kJ/mol for thin YSZ/Pd composite (dual‐phase) membranes and 124 kJ/mol for pure YSZ membranes. These results are explained in terms of relative importance of various mass‐transfer steps for oxygen permeation and microstructure of the YSZ/Pd composite membranes prepared by this technique.
Modeling chromatographic chiral separations under nonlinear competitive conditions
Authors: Migliorini Cristiano , Mazzotti Marco , Zenoni Gianmarco , Pedeferri MariaPia , Morbidelli Massimo 
Published: April 2004

AbstractThe chromatographic separation of Tröger's base enantiomers with ethanol as eluent on microcrystalline triacetate cellulose (CTA) was studied. Binary competitive adsorption equilibrium data measured were interpreted using ideal adsorbed solution and real adsorbed solution (RAS) theory. Both models were used to simulate a set of column breakthrough experiments. The competitive behavior of the two enantiomers is quantitatively discussed and the reliability of the two models is assessed. The results show that the RAS model can describe with good accuracy the complex competitive adsorption behavior exhibited by the CTA/Tröger's base model system. This conclusion is expected to apply to the adsorption of the other enantiomeric mixtures on chiral stationary phases.