bluuebunny/crossref_metadata_2025 huggingface dataset:
Analysis of single‐stage nonequilibrium separation process problems
Authors: Sridhar Lakshmi N. , Maldonado Carlos , Garcia Anamarie , de Frias Atilio
Published: April 2004

Equations constituting the nonequilibrium rate‐based separation process problem involving binary and ternary mixtures were analyzed. Multiplicity occurring in the nonequilibrium stage resulted from multiplicity taking place in the equilibrium calculations at the interface. This is achieved by demonstrating a one‐to‐one correspondence between the bulk and interface compositions in a nonequilibrium stage. The analysis of the film model for the mass‐transfer problem where the fluxes are obtained using the Maxwell‐Stefan equations showed solution uniqueness for this equation set. It also showed that the imposition of the mass‐transfer equations does nothing to cause additional multiplicities.
Nonisothermal synthesis of homogeneous and multiphase reactor networks
Authors: Mehta Vipul L. , Kokossis Antonis C.
Published: April 2004

A new optimization method for the synthesis of nonisothermal reactor networks offers major challenges concerning the lack of robustness in the existing methods and the numerous local and near‐optimal solutions that characterize these problems. The approach offers a reliable and widely tested methodology that upholds a profile‐based search. The search concentrates on targets rather than network details. The results illustrate ways to avoid unnecessarily complicated networks and develop simpler and transparent designs. The single‐phase examples explain merits over past studies and other conventional synthesis methods. Multiphase examples are presented for the first time in the literature, as well as results from an industrial example.
Selectivity effects on series reactions by reactant storage and PSA operation
Authors: Kodde Adriaan J. , Fokma Ymke S. , Bliek Alfred
Published: April 2004

This work evaluates adsorptive reactors used to improve the operation of a sequential reaction scheme,

, for the total removal of A from a stream with an excess of B. In the adsorptive‐reactor concept, the reactor is filled with a physical mixture of catalyst and an adsorbent, the latter being thermodynamically selective toward primary reactant A. In this case, the sorbent is periodically regenerated using the principles of pressure swing adsorption and purged with secondary reactant D. This concept is restricted to low temperatures to have sufficient adsorption capacity. Improved reaction selectivity arises from the accumulation of A in the unit. The reaction of A maximizes the driving force for regeneration and thus accelerates the regeneration half‐cycle. The adsorptive reactor is compared to a conventional plug‐flow reactor (PFR) and to PSA and PFR units in series. Reaction selectivity improved and pure B recovered over these alternative reactors under realistic conditions. The volume‐based productivity is lower than that of PFR, but higher than that of PSA. The purge‐gas flow rate can be manipulated to balance the sorption flux and reaction rate, thereby maximizing the conversion of A. The influence of differences in sorption kinetics is discussed and the required sorbent characteristics are identified.
Examination of stochastic dispersion theory by MRI in aperiodic porous media
Authors: Irwin N. C. , Greenkorn R. A. , Altobelli S. A. , Cushman J. H.
Published: April 2004

Magnetic resonance imaging techniques were applied to obtain concentration and velocity field measurements during flow in an aperiodic heterogeneous porous medium. These measurements were used to evaluate the applicability of a stochastic perturbation theory and the validity of the assumptions underlying its derivation. A comparison of experimental moment data to the first and second moments of simulated mean concentration distributions showed that the theory did not match the experimental data. While the results showed general agreement, the stochastic model appeared to slightly overpredict the experimentally observed mixing behavior. Discrepancies between experimental and numerical results were attributed to the assumption that triplet correlation terms involving fluctuating velocities and fluctuating concentration are insignificant relative to terms containing doublet cross‐correlations. Measured velocity covariances were compared to the velocity covariance determined from the first‐order solution to the flow equation. The first‐order relation agreed generally with the measured covariance, but did not accurately predict the detailed covariance structure in the aperiodic heterogeneous model.
Permeation of drug and swelling agent through polymeric membranes
Authors: Wang Da‐Ming , Wang Ching‐Ya , Chu Chwen‐Yen , Yeh Hsiu‐Min
Published: April 2004

The permeation of drug (benzocaine) and swelling agent (ethanol) through the polymeric [poly(ethylene‐co‐vinylacetate) and polyurethane] membranes was investigated theoretically and experimentally. Based on the Flory‐Huggins and Yasuda theories, the swelling effect on permeant diffusivity was described by expressing the permeant diffusivity in powers of the activity of the swelling agent. The experimental results suggest that the leading‐order term (first order of activity) is accurate enough to describe the diffusivities of benzocaine and ethanol in the poly(ethylene‐co‐vinylacetate) and polyurethane membranes. The linear dependence of permeant diffusivity on swelling‐agent activity was further used to analyze the drug diffusion in a membrane subject to a swelling gradient. With the knowledge of the dependence of benzocaine and ethanol diffusivities on ethanol activity, the activity profile of ethanol across the membrane can be calculated, and the effective diffusivity of benzocaine can then be predicted. Experiments carried out to determine the variation in the effective benzocaine diffusivity corresponding to different swelling gradients agreed well with the calculated results.
Mass transport in a novel two‐fluid taylor vortex extractor
Authors: Baier Gretchen , Graham Michael D. , Lightfoot Edwin N.
Published: April 2004

Flow instabilities occurring in rotating flows can be exploited as a new approach to liquid–liquid extraction. Two immiscible liquids are radially stratified by centrifugal force in the annulus between corotating coaxial cylinders. When the inner cylinder is rotated above a critical speed, Taylor vortices form in one or both of the fluids. Although the flow pattern yields a relatively small amount of interfacial surface area, the surface is highly active for interphase mass transfer due to the local vortex motion. By adding countercurrent axial flow, efficient continuous processing is also possible. This flow yields a viable extraction process, particularly for fluid pairs that are easily emulsifiable and therefore have limited processing options with the current equipment commercially available. This article demonstrates that two‐fluid Taylor‐Couette flow with countercurrent axial flow is achievable in practice and explores, experimentally and computationally, the mass‐transfer characteristics of the flow. Experimentally, when the vortices first appear, axial dispersion decreases and the interphase mass transfer starts to increase. Upon further increase in differential rotation rate, the extraction performance continues to improve, with the mass‐transfer coefficient proportional to the strength of Taylor vortices. This suggests that very high extraction efficiencies can be obtained with even larger relative rotation rates. Furthermore, mass‐transfer boundary‐layer theory, in combination with computational fluid dynamics, provides a reliable method for predicting the extraction performance.
IDEAS approach to process network synthesis: Application to multicomponent MEN
Authors: Wilson Stevan , Manousiouthakis Vasilios
Published: April 2004

A novel method for the globally optimal solution of the general process network synthesis problem is first presented and then applied to the solution of the minimum utility cost (MUC) problem for mass exchange networks (MEN) with multicomponent targets (MT). Previous approaches that address the MUC MEN MT synthesis problem are discussed, and the novel conceptual framework, Infinite DimEnsionAl State‐space (IDEAS), is then introduced. IDEAS allows the formulation of general process network synthesis problems as infinite convex (linear) programs whose local solutions are guaranteed to be globally optimal. In addition, an MUC MEN MT problem where conventional methods fail is probed. Then, the optimal network generated using IDEAS is discussed, together with the wide‐ranging potential impact and flexibility of IDEAS.
Effect of number of fractionating trays on reactive distillation performance
Authors: Al‐Arfaj Muhammad A. , Luyben William L.
Published: April 2004

Sneesby et al. recently suggested that adding trays in the stripping and rectifying sections of a reactive distillation column can degrade performance. This effect, if true, is not only counterintuitive, but very disturbing because it suggests that the design of reactive distillation columns cannot use conservative estimates of tray numbers, that is, we cannot simply add excess trays, as in conventional distillation. The problem is compounded by the uncertainty in vapor–liquid equilibrium data and tray efficiencies. This implies that developing reactive distillation columns would require extensive experimental work at the pilot‐plant and plant stages to find the numbers of stages offering the best performance. Such a scenario would mean long and expensive development programs. This article explores the effect of the number of trays in the rectifying and/or stripping sections of reactive (catalytic) distillation columns. Three reactive distillation systems are used: an ideal hypothetical system, the ETBE system, and the methyl acetate system. Contrary to the published results, it is demonstrated that additional trays do not degrade performance. Two degrees of freedom available in all cases must be carefully chosen for fair comparisons.
Recycling titanium from Ti‐waste by a low‐temperature extraction process
Authors: Yang Fenglin , Hlavacek Vladimir
Published: April 2004

In the commercial chloride process, titanium is extracted from Ti concentrates at high temperatures (800–1,500°C), and the high‐purity rutile is the primary raw material. Chlorination at high temperatures results in high‐energy consumption, rapid corrosion of equipment, pipelines and control system, and agglomeration of the solid bed by the liquid byproducts. The high‐purity rutile is expensive and its natural deposit is being depleted. Therefore, a low‐temperature Ti extraction process using Ti‐waste as the primary raw material is highly desirable. Thermodynamic equilibrium simulation of the reaction system shows that the extraction of Ti from Ti waste is feasible at a temperature as low as 200°C. In this study, a simple technology was used to remove diffusion barriers, and a low‐temperature chloride process was developed. The chlorination reaction operates at 300–350°C, and Ti‐waste can be used to replace the expensive rutile. Up to 80% of the titanium can be recycled in 5 min at 350°C. The extraction of other components has a relatively low extent, so a selective extraction of Ti can be achieved. A fluidized‐bed reactor was used for the chlorination process. The formation of an activated TiO2–C–Cl complex on the TiO2/C interface accounts for the gas‐solid‐solid reaction mechanism.
Impact of confinement on zeolite cracking selectivity via Monte Carlo integration
Authors: Macedonia Michael D. , Maginn Edward J.
Published: April 2004

Monte Carlo integration methods employing a classic molecular mechanics force field were used to probe the impact of confinement on the selectivity of the n‐hexane/3‐methylpentane test reaction in 12 different zeolites. The simulations estimated relative cracking rates and predicted the constraint index (CI) selectivity for both monomolecular and bimolecular cracking mechanisms. By comparing with experimentally measured values of the CI, information on the dominant mechanism responsible for the observed selectivity was obtained. For small‐pore zeolites, the monomolecular mechanism dominated, with the measured CI attributed to reactant selectivity based on preferential adsorption. For large‐pore zeolites, the CI selectivity was attributed to confinement effects imposed on the bimolecular transition states. For zeolite structures with intermediate‐sized pores, such as MTW and TON, the simulations indicated that both reaction mechanisms may be operative. The experimentally observed reduction in the CI with temperature in ZSM‐5 can be explained in terms of the relative importance of steric and entropic factors in the stabilization of the bimolecular transition state. A change in mechanism from bimolecular to monomolecular, as postulated in the literature, is not necessary to explain the experimentally observed temperature dependence of the CI.
RobustH∞glucose control in diabetes using a physiological model
Authors: Parker Robert S. , Doyle Francis J. , Ward Jennifer H. , Peppas Nicholas A.
Published: April 2004

A robust H∞controller was developed to deliver insulin via a mechanical pump in Type I diabetic patients. A fundamental nonlinear diabetic patient model was linearized and then reduced to a third‐order linear form for controller synthesis. Uncertainty in the nonlinear model was characterized by up to ±40% variation in eight physiological parameters. A sensitivity analysis identified the three‐parameter set having the most significant effect on glucose and insulin dynamics over the frequency range of interest ω = [0.002, 0.2] (rad/min). This uncertainty was represented in the frequency domain and incorporated in the controller design. Controller performance was assessed in terms of its ability to track a normoglycemic set point (81.1 mg/dL) in response to a 50 g meal disturbance. In the nominal continuous‐time case, the controller maintained glucose concentrations within ±3.3 mg/dL of set point. A controller tuned to accommodate uncertainty yielded a maximum deviation of 17.6 mg/dL for the worst‐case parameter variation.
Scale‐up in plug‐flow reactors: Laminar feed
Authors: Forney L. J. , Penney W. R. , Vo Hanh X.
Published: April 2004

Similarity parameters are derived to correlate the selectivity of mixing controlled paraliel reactions within plug‐flow reactors with two types of static mixing elements for both aqueous and viscous solutions. For the case of laminar reactor feed, the Kolmogoroff time is shown to correlate selectivity in turbulent reactors provided the reactor Reynolds number Re < ReC. The upper limit ReC for the reactor Reynolds number is constrained by the ratio of reactant feed‐to‐total volumetric flow rate. Moreover, for larger reactor Reynolds number Re > ReC, the inertial time scale defined in terms of a reactor feed length correlates selectivity. Scaling laws are derived for both reactor diameter and length, and suggestions are made for predicting selectivity with larger turbulent feed rates.
Generalized correlation for bubble motion
Authors: Rodrigue D.
Published: April 2004

The motion of a single gas bubble rising steadily in an uncontaminated Newtonian viscous fluid of infinite extent is reviewed. Using experimental data gathered from the literature over the past century, a data bunk is set up for bubble velocities as a function of their diameters. These data provided a very broad range of liquid properties and bubble hydrodynamic regimes as density (722–1,380 kg/m3), viscosity (2.2×10−4−18 Pa·s), surface tension (15.9–91.0 mN/m), Reynolds number (1.9×10−7−1.1 × 104), and Morton number (1.0×10−11−1.0×107). From a dimensional analysis, a single equation is proposed to predict bubble velocities. The simplicity and good precision over the whole range of parameters facilitate its use in design calculations of chemical engineering.
Evaluation of instability criterion for bidisperse sedimentation
Authors: Biesheuvel P. Maarten , Verweij Henk , Breedveld Victor
Published: April 2004

The instability criterion for bidisperse sedimentation derived by Batchelor and Janse van Rensburg was combined with two empirical models for the particle velocities that are consistent with conservation of momentum and used to construct theoretical stability diagrams. The stability boundaries were fully determined by the particle volume fractions, the particle‐size ratio, and the ratio of the density differences with the liquid. The results showed that on increasing the particle‐size ratio sufficiently, stability, always is attained. For particles of similar size, instabilities occur mainly if the liquid density is intermediate between the particle densities. The stability diagrams agree well with the limited experimental data, if so‐called “vertical columns” are excluded. This seems reasonable since similar structures observed in monodisperse suspensions are not captured by the bidisperse instability criterion either.
Structure simulation of concentrated suspensions of hard spherical particles
Authors: He D. , Ekere N. N.
Published: April 2004

A monte Carlo technique is applied to simulate the structure of concentrated suspensions of hard spherical particles that obey lognormal distribution. With this technique, the random loose packing, with packing density Φm is obtained first, and then the particles in the packing are randomly separated to achieve a specified solid‐volume fraction Φ. The simulated structure is evaluated both in the microscale, the neighboring number distribution, and the distribution of gaps between neighboring particles; and in the macroscale, the distribution of the solid‐area fractions on a series of parallel cross sections. Results show that, at the same solid‐volume fraction, the increase in the standard deviation of particle diameters leads to the decrease in the mean neighboring number and leads to the increase in the mean gap. The mean relative gap obtained from the simulation is larger than that from theoretical prediction, δ=[(Φm/Φ)1/3−1]. With particles of lognormal distribution, both the gap sizes and the neighboring numbers distributed over broader ranges than that with equal particles. Results also show that, with equal particles and particles of lognormal distribution, there is no significant differenence between the distributions of the solid‐area fractions on the cross sections. The structures obtained in this study are shown to be completely random, homogeneous, and isotropic by statistical tests.
Particle sizing in dense, rapidly flowing KCI suspensions by photon migration techniques
Authors: Bartlett Matthew , Jiang Huabei
Published: April 2004

The first experimental measurement of particle‐size distribution (PSD) from undiluted, rapidly flowing potassium chloride (KCl) suspensions using continuous‐wave photon migration techniques is presented. PSDs were obtained from a laboratory simulation of production‐line slurries used in the chemical fertilizer industry. Spectral measurements of concentrated, rapidly flowing slurry containing 25–40% KCl particles were used to calculate the suspensions' reduced scattering coefficient and PSD using inverse algorithms. Our PSD results agree excellently with sieving measurements. Refractive index is important in the calculations of the PSD and the suspensions' reduced scattering coefficient.
Synthesis and characterization of catalytic nanoporous carbon membranes
Authors: Strano Michael S. , Foley Henry C.
Published: April 2004

A method is reported for the synthesis of nobel catalyic nanoporous carbon membranes. Defect‐free, nanoporous carbon films of 12.5−μm average thickness containing a dispersion of Ptx were synthesized on macroporous stainless‐steel supports. Ideal gas selectivities for the catalytic membranes were simliar to those of inert nanoporous carbon membranes with He–N2=58.6 and O2N2=4.9. The selective hydrogenation of monoolefins (propylen, l‐buiene, isobutylene) was used to probe the shape‐selective catalytic proerties nad the transport selectivities of the membranes. The results were modeled using the linear regime of coupled sdsorption, transport and rection in the membrane. Model regression yielded 14.9, 19.7. and 18.4 kJ/mol for the activation energies of permeation for propylene, isobutylene, and l‐butene, respectively. The system demonstrated selective reaction and transport favoring propane production with selectiveity ratios of 28.9:3.2.I for propane:n‐butane:isobutane at 125°C.
Crystal temperature control in the Czochralski crystal growth process
Authors: Armaou Antonios , Christofides Panagiotis D.
Published: April 2004

This work proposes a control configuration and a nonlinear multivariable model‐based feedback controller for the reduction of thermal gradients inside the crystal in the Czochralski crystal growth process after the crystal radius has reached its final value. Initially, a mathematical model which describes the evolution of the temperature inside the crystal in the radial and axial directions and accounts for radiative heat exchange between the crystal and its surroundings and motion of the crystal boundary is derived from first principles. This model is numericully solved using Galerkin's method and the behaviour of the crystal temperature is studied to obtain valuable insights which lead to the precise formulation of the control problem, the design of a new control configuration for the reduction of thermal gradients inside the crystal and the derivation of a simplified 1‐D in a space dynamic model. Then, a model reduction procedure for partial differential equation systems with time‐dependent spatial domains (Armaou and Christofides, 1999) based on a combination of Galerkin's method with approximate inertial manifolds is used to construct a fourth‐order model that describes the dominant thermal dynamics of the Czochralski process. This low‐order model is employed for the synthesis of a fourth‐order nonlinear multivariable controller that can be readily implemented in practice. The proposed control scheme is successfully implemented on a Czochralski process used to produce a 0.7 m long silicon crystal with a radius of 0.05 m and is shown to significantly reduce the axial and radial thermal gradients inside the crystal. The robustness of the proposed controller with respect to model uncertainty is demonstrated through simulations.
Artificial neural‐network‐assisted stochastic process optimization strategies
Authors: Nandi Somnath , Ghosh Soumitra , Tambe Sanjeev S. , Kulkarni Bhaskar D.
Published: April 2004

This article presents two hybrid robust process optimization approaches integrating artificial neural networks (ANN) and stochastic optimization formalism—genetic algorithms (Gas) and simultaneous perturbation stochastic approximation (SPSA). An ANN‐based process model was developed solely from process input–output data and then its input space comprising design and operating variables was optimized by employing either the GA or the SPSA methodology. These methods possess certain advantages over widely used deterministic gradient‐based techniques. The efficacy of ANN‐GA and ANN‐SPSA formalisms in the presence of noise‐free as well as noisy process data was demonstrated for a representative system involving a nonisothermal CSTR. The case study considered a nontrivial optimization objective, which, in addition to the conventional parameter design, also addresses the issue of optimal tolerance design. Comparison of the results with those from a robust deterministic modeling/optimization strategy suggests that the hybrid methodologies can be gainfully employed for process optimization.
Experimental design and inferential modeling in pharmaceutical crystallization
Authors: Togkalidou Timokleia , Braatz Richard D. , Johnson Brian K. , Davidson Omar , Andrews Arthur
Published: April 2004

A fractional factorial experimental design was used to investigate relative effects of operating conditions on the filtration resistance of a slurry produced in a pharmaceutical semicontinuous batch crystallizer. The six operating variables were seed type, seed amount, temperature, solvent ratio, addition time, and filtration resistance was used to define the factory operating procedure, which reduced filtration time 3.7‐fold. Several chemometric techniques were used to construct inferential models between the in‐process measurement of partcle chord‐length distribution and filtration resistance to help detect operational problems before completing the batch and decide when batch crystal lization runs should end. Depending on the model quality criterion, the most popular chemometric models of partial least squares and top‐down principal‐component regression can produce lower quality models. Another chemometric approach, confidence‐interval principal‐component regression, predicted 70% more accurately than the best OLS model. The main effects and inferential models serve different but complementary roles in developing and implementing high performance crystallization process opertions. A main‐effects model constructed from statistical experimental design data determined optimal operating conditions rapidly, while the inferential model can determine opertional problems and batch end times during batch end time during batch‐process operations.
Decolorization of dyes using ozone in gas‐induced a reactor
Authors: Hsu Yung‐Chien , Chen Jia‐Tsween , Yang Hsiang‐Cheng , Chen Jyh‐Herng
Published: April 2004

Treatahility of aqueous dye solutions usirig a new gas‐induced ozonator was investigated, as well as feasihiliry of decolorizing dyes using ozone, the ozone utilization efficiency, and the chemical oxygen demand (COD) under various pH values and initialdye concentrations. Expeiimental results indicate that all of the dyes used can he decolorized within 15 min. For most of the dyes used, ozone decolorizing was more rapid in acidic media. The ozone utilization efficiency can be raised to 90% or higher with proper agitation speeds. The ozone utilization efficiency and COD removal rate increased with an increase in pH value; however, the COD removal remained nearly constant for various categories of dye regardless of the initial dye concentration. The kinetics of decolorization were also examined.
Polymerization kinetics of rodlike molecules under quiescent conditions
Authors: Gupta J. Srinivasalu , Agge Ameya , Khakhar D. V.
Published: April 2004

The kinetics of solution polymerization to synthesize poly(p‐phenylene terephthalamide), a rodlike polymer, was studied theoretically and experimentally. The reaction was conducted under quiescent conditions to eliminate effects of flow‐induced orientation that are known to affect the kinetics of the process. Experiments included determining the degree of polymerization and polydispersity index for different times of reaction. Theoretical study comprised calculating the effective rate constant for the diffusion‐controlled reaction using Smoluchowski's approach and computing the evolution of the molecular‐weight distribution using the length‐dependent effective rate constant obtained in the first part. Experiments showed significant slowing of the reaction and narrow molecular‐weight distributions due to diffusion control. The degree of polymerization and the polydispersity index variation with time is nearly the same for the two initial monomer concentrations. The Smoluchowski theory predicts the effective rate constant to be keƒƒ α ρ−0.8L−3.5 for large L, with ρ the local number concentration of rods and L the length of the reacting rodlike molecule. The model has two parameters obtained by a least‐squares fit to one set of data of degree of polymerization vs. time. Results of the population balance calculations using the computed effective rate constant matched with experimental data for degree of polymerization and polydispersity vs. time for both initial monomer concentrations. The model, augmented to account for low, end‐capping side reactions, predicted an optimal initial monomer concentration for obtaining the highest degree of polymerization for a fixed reaction time, as reported in previous experimental studies.
Control strategies for front stabilization in a tubular reactor model
Authors: Panfilov Vadim , Sheintuch Moshe
Published: April 2004

The stabilization of a front pattern in a homogeneous tubular reactor model was studied. Linear stability analysis combined with the Galerkin method is used for state feedback control of the distributed parameter system. The capabilities of the global control and point‐sensor control to stabilize the front solution were studied by manipulating various reactor parameters, including fluid flow and feed conditions. Point‐sensor control in coolant flow (heat‐loss coefficient) or coolant temperature are the most effective when the temperature sensor is located close to the front position. Global control based on a space‐averaged sensor and other strategies failed. A qualitative analysis is suggested for selection of proper control of front stabilization.
Modified syntheses of Ca‐resinates by fusion method
Authors: Sundqvist S. , Turunen S. , Paatero E. , Twigt F.
Published: April 2004

Tall oil rosin was modified with fumaric acid or maleic acid anhydride to get fortified rosin. which was used as u raw material in fusion Ca‐resinate syntheses. Two reaction step were observed in the syntheses. A fast resination reaction takes place at 235°C, and a slow decarboxylation of rosin acids forms neutral rosin oil at 265°C. A mechanistic model for the decarboxylation reaction step was derived to explain the effect of fortifying substances on the reaction kinetics. A multivariate calibration method using partial least‐spare (PLS) regression was applied to monitor the acid concentration decrease on the basis of infrared spectroscopic data during the fortified syntheses. A mixture of unmodified rosin and rosin oil (decarboxylated rosin) was used as a raw material in a novel modification of fusion syntheses to increase the mass yield of the resinate. In the modified rosin oil syntheses, decarboxylation of rosin acids is avoided, and recycling the added rosin oil considerably improves the mass yield of the resinate syntheses.
Estimate of red‐cell deformability and plasma viscosity based on flow curve
Authors: Ookawara S. , Yano A. , Ogawa K. , Taniguchi K.
Published: April 2004

A new estimation method of clinical blood indices based on the flow characteristics of unadjusted whole blood is proposed, such as red‐cell deformability and plasma viscosity. Parameter values of Bingham and power law models were calculated based on the measured flow characteristics. Red‐cell deformability was measured by the method of laser diffractometry. The clinical indices were related with the non‐Newtonian model parameters by a feedforward neural network (NN). Inputs of the NN are the parameter values and hematocrit. Outputs are red‐cell deformability and plasma viscosity. It was verified that estimated values agreed well with those measured values after sufficient learning. By applying this method to 20 healthy persons, it was confirmed that the estimated values by NN were within normal range. According to these experimental results, this estimation method can be applied to clinical use.
Calculation of Brownian particle transmission in long, wide channels
Authors: Myers Matthew R.
Published: April 2004

The transport of Brownian particles in channels which are long and wide compared to their height is addressed. The cross‐sectional shape of the channel is assumed to be slowly varying, but otherwise arbitrary. A solution to the convective‐diffusive equation with reaction‐rate boundary condition was obtained by locally incorporating the modified Graetz solution in a flat channel. The solution was evaluated asymptotically for the cases of a channel with a maximum height occurring at an endpoint and at an interior maximum. The asymptotic method was applied in two example geometries: the calibration apparatus used to determine reaction‐rate constants for virus adsorption to latex barriers, and overlapping pores in a nucleation‐track membrane. The asymptotic expressions compared well with finite‐element calculations in the examples. The utility of the asymptotic approach lies in rapid estimation of particle transmission through a channel as a function of geometric and physical parameters.
Drag reduction of non‐newtonian fluids in a circular pipe with a highly water‐repellent wall
Authors: Watanabe Keizo , Udagawa Hiroshi
Published: April 2004

With a highly water‐repellent wall pipe in the drag reduction of polymer solutions, a flow system in which drag reduction is obtained in both laminar and turbulent flow ranges was realized. Experiments were carried out to measure the pressure drop in pipes with a highly water‐repellent wall and an acrylic resin wall by a pressure transducer. The basic material of the highly water‐repellent coating is fluorine‐alkane‐modified acrylic resin with added hydrophobic silica, which was left overnight in air after it was coated to the pipe wall. The diameter of the pipe was 6 mm. The polymer solutions tested were PEO15 aqueous solutions in the concentration range of 30∼1,000 ppm. The drag‐reduction ratio for laminar flow was about 11∼15%. To understand this effect, the pressure drop was measured by using surfactant solutions and degassed water, and by pressurizing tap water in the pipeline. The laminar drag was not reduced in sufuctant solutions, although degassed water and pressurizing tap water in the pipeline had no effect on the reduction. In the laminar flow range, the friction factor of a power‐law fluid with fluid slip was analyzed by applying the modified boundary condition on fluid slip at the pipe wall, and the analytical results agreed with the experimental results in the low Reynolds number range.
Reactive barrier films
Authors: Yang Chuanfang , Nuxoll Eric E. , Cussler E. L.
Published: April 2004

Immobile reactive groups within films used as packaging materials can retard transport of solutes like oqgen and water uapor. A theoy developed for these films shows that these groups do not affect the steady‐state transport across the film, but that they do increase the time before permeability begins. The theory is verified by experiments with acid barriers made of polyvinylalcohol containing colloidal zinc oxide. These results imply that the time that barrier polymers are effectiue can be increased about two orders of magnitude. When reactive groups are combined with impermeable flakes, this time can be increased about three orders of magnitude. For example, a polymer barrier currently effective for one hour can be made effectiue for over one year.
Factorized approach to nonlinear MPC using a radial basis function model
Authors: Bhartiya Sharad , Whiteley James R.
Published: April 2004

A new computationally efficient approach for nonlinear model predictive control (NMPC) presented here uses the factorability of radial basis function (RBF) process models in a traditional model predictive control (MPC) framework. The key to the approach is to formulate the RBF process model that can make nonlinear predictions across a p‐step horizon without using future unknown process measurements. The RBF model avoids error propagation from use of model predictions us input in a recursive or iterative manner. The resulting NMPC formulation using the RBF model provides analytic expressions for the gradient and Hessian of the controller's objective function in terms of RBF network parameters. Solution of the NMPC optimization problem is simplifed significantly by factorization of the RBF model output into terms containing only known and unknown parts of the process.
Synthesis of chiral crystallization processes
Authors: Schroer Joseph W. , Wibowo Christianto , Ng Ka M.
Published: April 2004

A process synthesis procedure is presented for the resolution of racemic mixtures by crystallizaiion. The phase behaviors of racemic mixtures and of those in the presence of solvents and resolving agents are discussed. The Corresponding separation schemes are synthesized by considering the separation steps in a flowsheet as movements on a phase diagram. Separations with and without involving racemization and deracemization are considered. The procedure is illustrated with several examples, including the manufacture of ibuprofen and naproxen.
Modeling and analysis of new processes for polyester and nylon production
Authors: Yao Zhen , Ray W. Harmon
Published: April 2004

Integrated 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

Factors 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

The 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

Theoretical 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

A 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

A 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

The 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

The 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

A 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

In 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.