bluuebunny/crossref_metadata_2025_split huggingface dataset:
Intensification of instantaneous heterogeneous reaction by simple salts and charged microphase
Authors: Hasnat Abul , Roy Sandip 
Published: April 2004

AbstractThe mass‐transfer rate for the instantaneous heterogeneous reaction between N,N‐di‐ethylaniline (organic phase) and HCl in the aqueous phase was determined in the presence of a number of supporting electrolytes, that is, NaCl, SrCl2, AlCl3, and cetyltrimethyl ammonium bromide surfactant micelle. Both the simple salts and the cationic surfactant enhance the mass transfer of the reactive H+ ion, the effectiveness being in the order of CTAB > AlCl3 > SrCl2 > NaCl. The experimentally observed enhancement factor for the reaction in the presence of the supporting electrolytes ranges from 1.3 to 6. This enhancement is explained on the basis of the “ion‐coupling” effect that augments the diffusive fluxes of the more mobile ionic species in a multi‐ion system. The film‐theory approximation is used to obtain theoretical estimates of the enhancement factor, and these are found to be in reasonably good agreement with the experimentally obtained values.
Near‐surface dynamics of sheared polymer melts using ATR/FTIR
Authors: Wise Geoffrey M. , Denn Morton M. , Bell Alexis T. 
Published: April 2004

AbstractUsing attenuated total‐reflectance infrared spectroscopy (ATR/FTIR), the concentration of deuterated polybutadiene near the surface of a flat zinc selenide crystal was followed as it was replaced by ordinary polybutadiene by flow and diffusion. Experiments were performed in the melt, both below (M ∼ 1,500) and above (M ∼ 15,000) the entanglement threshold. The decay profiles agree well with a finite‐element simulation of the system. In contrast to previous investigations of C16's, the decay profiles of both unentangled and entangled polybutadienes are consistent with a uniform diffusivity in the near‐wall region.
Nonequal reactivity model for biocatalytic polytransesterification
Authors: Chaudhary Apurva K. , Beckman Eric J. , Russell Alan J. 
Published: April 2004

AbstractThe lipase‐catalyzed polytransesterification of divinyl adipate and 1,4‐butanediol is a dynamic process controlled by the relative magnitudes of the rates of transesterification and hydrolysis as the polymerization proceeds. A mathematical model that describes the kinetics of the biocatalytic polytransesterification process is presented. Initial rate studies with model substrates in transesterification, hydrolysis, and esterification were used to provide the initial kinetic parameters that, when combined with the effect of enzyme specificity, were used to predict product compositions under different reaction conditions. A comparison of experimental data and model predictions shows that the product composition is strongly influenced by the selective nature of enzyme catalysis, and this model effectively predicts the results of a step condensation polymerization where reactivity depends on molecular weight.
Imaging stirred‐vessel macromixing using electrical resistance tomography
Authors: Holden P. J. , Wang M. , Mann R. , Dickin F. J. , Edwards R. B. 
Published: April 2004

AbstractAn 8‐plane 16‐sensor ring electrical resistance tomography (ERT) system was designed and installed within a 1.5‐m‐dia. plant‐scale stirred uessel. Results are reported for the unsteady dynamic macromixing of miscible liquids following a pulse addition of brine tracer. Acquired data, afier reconstruction, is conveniently represented as a stack of 2‐D tomograms and 3‐D solid body isosurjaces, thereby providing an equiualent of medical whole‐body scanning for a chemical process unit. The results demonstrate the ability of ERT to distinguish the different mixing patterns from two types of impeller in 3‐D and to monitor plant‐scale miscible liquid mixing processes aperimentally, with good resolution in both space and time.
Feasibility of extractive distillation in a batch rectifier
Authors: Lelkes Z. , Lang P. , Benadda B. , Moszkowicz P. 
Published: April 2004

AbstractA simple method was developed to study the feasibility of extractive distillation in a batch rectifier. By calculating feasible profiles of different column sections and figuring them in the triangular diagram, the feasibility and limiting values of the most important operational parameters (number of stages, flow rate of entrainer, and reflux ratio) were determined for different steps of the batch extractive distillation. The unusual behavior of extractive distillation was also investigated for this process. An infeasible region can be assigned to the given values of parameters; if the still composition is located within this region, the specified separation cannot be attained. By locating this infeasible region, maximum recoveries attainable in a batch rectifier and in a middle vessel column were compared. The results obtained by this method were verified by pilot‐plant expenments for the mixture acetone + methanol water.
Analysis of instability in an industrial ammonia reactor
Authors: Morud John C. , Skogestad Sigurd 
Published: April 2004

AbstractThe starting point for this study was an incident in an industrial plant, where the ammonia synthesis reactor became unstable with rapid temperature oscillations (limit‐cycles) in the range from about 300°C to 500°C. A simple dynamic model reproduces this behavior. In industry a steady‐state van Heerden analysis is often used to analyze the stability, but a more careful analysis for this reactor system reveals that instability occurs when there still is a positive steady‐state margin, namely as a pair of complex conjugate poles cross the imaginary axis (Hopf bifurcation). This is consistent with the obseruations where the instability manifests itself as oscillations rather than extinction of the reaction. This somewhat unusual behavior can be explained by the presence of an inverse response for the temperature response through the reactor beds combined with the positive feedback caused by the preheater.
Steam reforming of naphthalene on Ni–Cr/Al2O3 catalysts doped with MgO, TiO2, and La2O3
Authors: Bangala Denis N. , Abatzoglou Nicolas , Chornet Esteban 
Published: April 2004

AbstractMagnesium, lanthanum, and titanium oxide‐doped nickel–chromium/alumina catalysts were prepared and their performances assessed in the steam reforming of naphthalene (T: 1,023 K; water‐to‐naphthalene molar ratio: 16, atmospheric pressure, residence time of 0.55 s; and GHSV = 10,080 h−1). Impregnation of nickel and chromium in MgO‐ and La2O3‐doped alumina gave the most active, stable catalysts. Nickel was active in aromatic ring opening, while chromium inhibited the encapsulation of the nickel clystallites by inactive carbon filaments. The use of MgO had a signifkant effect on the robustness of catalyst due to the formation of MgAl2O4 spinelphase. La2O3 was necessaly to drive the reaction toward total gasification. The addition of TiO2 gave poor activity and a soft catalyst. Some of the catalyst preparations were characterized before and after reaction by XRD, SEM, DTA, and surface measurements. The physical and catalytic properties are discussed in light of these characterizations. The catalyst optimized during this study showed high clystallite dispersion, excellent crushing strength, and good thermal stability. When comparing the data obtained using Ni/Al2O3 with Ni–Cr/Al203·MgO·La2O3, it is clear that the improved catalyst reached higher conversion and gas yield performances.
Product sequences in azeotropic batch distillation
Authors: Ahmad Berit S. , Zhang Yong , Barton Paul I. 
Published: April 2004

AbstractThe formation of multicomponent azeotropes in waste‐solvent streams often complicates separation and recovery of solvents. The implications of applying batch distillation to such a mixture can be studied in a residue curve map. Ahmad and Barton (1996) extend and generalize the theory for ternary residue curve maps applied to batch distillation to homogeneous systems with an arbitrary number of components. These theoretical results are used to develop an algorithm for elucidating the structure of the batch distillation composition simplex for a system with an arbitrary number of components. The batch distillation regions are identified by completing unstable boundary limit sets. The completed boundary limit sets accurately represent the topological structure of the composition simplex and make it possible to extract all product sequences achievable when applying batch distillation. The algorithm is demonstrated on the five‐component system acetone, chloroform, methanol, ethanol, and benzene, which exhibits nine azeotropes. Furthermore, the set of batch distillation product sequences predicted is validated using a commercial dynamic batch distillation column model. Although the problem does not closely approach the limiting conditions of the theory, the predictions agree excellently with the simulations.
Optimizing and controlling the operation of heat‐exchanger networks
Authors: Aguilera Néstor , Marchetti Jacinto L. 
Published: April 2004

AbstractA procedure was developed for on‐line optimization and control systems of heat‐exchanger networks, which features a two‐level control structure, one for a constant configuration control system and the other for a supervisor on‐line optimizer. The coordination between levels is achieved by adjusting the formulation of the optimization problem to meet requirements of the adopted control system. The general goal is always to work without losing stream temperature targets while keeping the highest energy integration. The operation constraints used for heat‐exchanger and utility units emphasize the computation of heat‐exchanger duties rather than intermediate stream temperatures. This simplifies the modeling task and provides clear links with the limits of the manipulated variables. The optimal condition is determined using LP or NLP, depending on the final problem formulation. Degrees of freedom for optimization and equation constraints for considering simple and multiple bypasses are rigorously discussed. An example used shows how the optimization problem can be adjusted to a specific network design, its expected operating space, and the control configuration. Dynamic simulations also show benefits and limitations of this procedure.
Batch crystallization of a photochemical: Modeling, control, and filtration
Authors: Matthews H. B. , Rawlings James B. 
Published: April 2004

AbstractModel identification and control were studied for the seeded batch crystallization of an organic, industrial photochemical. The growth and nucleation kinetics are described by empirical power‐law expressions in relative supersaturation, and an additional model describing crystal shape dynamics is proposed. The parameters in the kinetic models are estimated from on‐line measurements of solute concentration and transmittance. Parameter uncertainty is assessed, and optimal experimental design techniques are used to construct experiments to diminish uncertainty. Given the identified model, optimal open‐loop temperature schedules are designed to improve the filtration of final‐time slurries. The profiles minimize the mass of nucleated crystal relative to seed crystal mass, subject to supersaturation and yield constraints. Filtration improvements are verified using constant pressure filtration tests to determine the flow resistance of the filter cake. The best control experiment gives a cake resistance 25% lower than the best identification experiment.
Sol‐gel polycondensation kinetic modeling: Methylethoxysilanes
Authors: Rankin Stephen E. , Macosko Christopher W. , McCormick Alon V. 
Published: April 2004

AbstractQuantitative kinetic modeling of the condensation of methylethoxysilanes {(CH3)4‐f Si(OC2H5)f} of varying functionality (f) is needed to engineer inorganic polymers, resins, and ceramics. To that end, a kinetic model that accounts for hydrolysis pseudoequilibrium, nearest‐neighbor substitution effects, and unimolecular cyclization reactions in homogeneous ethoxysilane polycondensation is presented. Condensation rate parameters are determined by fitting to 29Si NMR transients. Several important features become evident: (1) the success of the hydrolysis pseudoequilibrium approximation; (2) strong negative substitution effects with unusual dependence on connectivity; (3) a strong kinetic tendency for ring formation, growing with methyl substitution; (4) acceleration of condensation upon methyl substitution; and (5) destabilization of three silicon rings by methyl substitution. The first three observations are consistent with previous findings for ethylethoxysilanes, but the last two are strikingly different.
Study of EOS‐Gex mixing rules for liquid–liquid equilibria
Authors: Escobedo‐alvarado Gonzalo N. , Sandler Stanley I. 
Published: April 2004

AbstractThe performance of two Gibbs free‐energy‐based equation‐of‐state (EOS) mixing rules is tested for the correlation and prediction of liquid‐liquid equilibria (LLE). The LLE of ten binary mixtures were examined using the Peng Robinson EOS combined with the Wong Sandler and MHVl mixing rules with two excess free‐energy models (NRTL and UNIQUAC). Good agreement with low‐pressure experimental data was obtained for nonassociating and self‐associating mixtures using temperature‐independent parameters. However, in the case of aqueous mixtures that exhibit both a lower and an upper critical solution temperature, it was necessary to use temperature‐dependent parameters, as is also true when activity coefficient models are used directly to describe such systems. The Wong Sandler mixing rule was capable of predicting the high‐pressure phase behavior of the systems studied using parameters from correlation of only low‐pressure LLE data, while the MHVl model required the introduction of a binary interaction parameter. Consequently, the MHVl model was useful for the correlation, but not for the prediction of high‐pressure LLE from low‐pressure data.
Modeling of ABS latex coagulation processes
Authors: Chung Chang‐Bock , Park Soo‐Ho , Han In‐Su , Seo Young‐Hyo , Yang Byong‐Tae 
Published: April 2004

AbstractThe mathematical models of acrylonitrile–butadiene–styrene (ABS) latex coagulation processes that show the effect of major operation variables on the particle‐size distribution of recovered resins were derived to provide a guideline for process improvement to reduce the content of fine particles in the product. Kinetic equations for the coagulation and breakup of particles taking place in a turbulent flow field were incorporated into the population balance models for batch and continuous processes. A dimensional analysis for the process models leads to two dimensionless groups, ηc and ηb, that represent the relative intensity of the coagulation and breakup phenomena. The ηc/ηb ratio is designated as a design variable for controlling the particle‐size distribution in the steady‐state operation of the coagulation processes. This role is demonstrated by numerical simulation where increasing the ratio shifted the particle‐size distribution toward large particles. The estimates of ηc/ηb obtained for a set of batch experiments also confirm that fine particles can be reduced by setting the operation variables to increase the ratio.
Description of three‐phase filtration with a novel dimensionless number
Authors: Huizenga P. , Kuipers J. A. M. , van Swaaij W. P. M. 
Published: April 2004

AbstractInternal filtration in slurry bubble columns offers a possible solution to the filtration problems related to this reactor type. The applicability of the concept has already been demonstrated at full‐scale for wastewater treatment, even though a theoretical description of internal filtration is lacking. Two types of hydrodynamic models were developed for a filtering slurry reactor. Both the model of the surface renewal type and the model based on a force‐balance approach predict that the solids concentration at the axial position of the filter uniquely depends on a single novel dimensionless number. The validity of these theories was demonstrated by measuring filter‐cake resistance as an indirect measure of solids concentration for a system in batch operation with respect to solids. In the experiments the load of solids, permeate flux (J), superficial gas velocity (Ug), particle diameter (dp), kinematic liquid viscosity (vl), and molar mass of the gas were varied.
Intermediate reboiler and condenser arrangement for binary distillation columns
Authors: Agrawal Rakesh , Herron D. Michael 
Published: April 2004

AbstractThe most thermodynamically efficient configuration for adding or removing heat from an intermediate location of an ideal binary distillation column distilling pure products is derived. The optimal policy requires that preconditioning of the feed be part of the overall decision‐making process. The optimal configuration can be determined through the use of two parameters, αIR and αIC, that are solely functions of feed composition. Simple and readily usable heuristics using these parameters are developed that help instantly identify the most efficient selection among (1) totally vaporizing and returning a side‐draw liquid stream from an intermediate location of the distillation column, (2) partially or totally vaporizing a portion of the given saturated liquid feed, (3) partially or totally condensing a portion of the given saturated vapor feed, and (4) totally condensing and returning a side‐draw vapor stream from an intermediate location of the distillation column.
Adsorption of organic solvent vapors on hydrophobic Y‐type zeolite
Authors: Yun Jeong‐Ho , Choi Dae‐Ki , Kim Sung‐Hyun 
Published: April 2004

AbstractExperimental isotherms and prediction results for adsorption of benzene, toluene, dichloromethane and 1,1‐dichloro‐1‐fluoroethane on hydrophobic Y‐type zeolite are reported. Isotherm shows the type‐V shape according to the classification by Brunauer et al. A simple thermodynamic method is employed to predict the experimental equilibrium data at various temperatures simultaneously. This plain method is based on the assumption that the value of the isosteric heat of adsorption does not depend on temperature for a certain surface loading. The Clausius–Clapeyron equation was used to calculate the isosteric heat of adsorption. To apply the method, only two sets of the experimental isotherm data at two different temperatures are needed. The Clausius–Clapeyron equation with two isotherms provided simple and reliable prediction of adsorption equilibrium relationships at various temperatures. Our results with this method showed that the predicted value agrees well with the experimental data in the range of temperatures for the system tested.
Flow regimes in centrifugal partition chromatography
Authors: van Buel M. J. , van Halsema F. E. D. , van der Wielen L. A. M. , Luyben K. Ch. A. M. 
Published: April 2004

AbstractModeling pressure drop, stationary‐phase holdup and separation efficiency in centrifugal partition chromatography (CPC) are hampered by restricted knowledge concerning the flow behavior of the liquid‐liquid two‐phase system. A transparent column (type CPC‐LLN) was constructed to determine the flow behavior as a function of the flow rate, rotational frequency and the properties of the two‐phase system. Two main types of flow regimes, droplets and (broken) jets, are observed although the spraying regime hardly occurred. Droplets occur at low flow rates and low rotational frequencies. The droplet regime changes into the (broken) jet regime when either the flow rate or the rotational frequency increases above a critical value. This critical value is described reliably by a dimensionless number correlation. A flow chart showing the type of flow regime as a function of the Weber number and the centrifugal force enables rational fine‐tuning of operating conditions for given two‐phase systems and equipment.
Structure of Distillation Regions for Multicomponent Azeotropic Mixtures
Authors: Rooks Raymond E. , Julka Vivek , Doherty Michael F. , Malone Michael F. 
Published: April 2004

AbstractGeometric methods for the conceptual design of nonideal and azeotropic distillation systems have focused primarily on three‐ and four‐component mixtures. A generalization of geometric methods that does not rely on visualization and gives a completely equation‐based approach to determine the structure of distillation regions for homogeneous mixtures is described. This method is useful for mixtures with a large number of components, provided a vapor–liquid equilibrium model is available. The approach is applied to assess feasibility and alternative separations in several examples, including a five‐component mixture with nine azeotropes and a six‐component mixture with seven azeotropes. These methods can be used to rapidly generate process alternatives, and the examples demonstrate that there can be a surprising number of these alternatives for the distillation of azeotropic mixtures.
Liquid‐phase polymerization of propylene with a highly active catalyst
Authors: Samson Job Jan C. , Weickert Günter , Heerze Annelies E. , Westerterp K. Roel 
Published: April 2004

AbstractAn experimental setup and a kinetic study of the polymerization of propylene in liquid monomer with a highly active catalyst are presented. The purification system for monomer, the catalyst injection system, the temperature control system, and the polymerization procedures are described in detail. Further, reproducibility of the experiments is tested, the kinetics are described in the temperature range of 27 to 67°C, and the influence of prepolymerization in cold liquid propylene is investigated.
Desorption by ultrasound: Phenol on activated carbon and polymeric resin
Authors: Rege Salil U. , Yang Ralph T. , Cain Charles A. 
Published: April 2004

AbstractAn experimental feasibility study of using ultrasound to accomplish the dificult desorption of phenol from activated carbon and polymeric resin adsorbents is discussed. The desorption rates of activated carbon were found to significantly increase by ultrasound at 40 kHz and 1.44 MHz. Attrition of the activated carbon due to cavitation could be prevented by operating at a higher frequency and with an intensity below the threshold of the pulverization of carbon. According to the structural stability study of Amberlite XAD‐4 and Dowex Optipore L‐493 resins to withstand the abrasive cavitational effects of ultrasound at 40 kHz, the Dowex Optipore resin was stable under experimental conditions and phenol desorption rates were enhanced significantly with sonication. The ultrasonic desorption rates were favored by decreased temperature, aerated liquid medium, and increased ultrasound intensity. The desorption rates obtained without ultrasound appeared to be limited by pore diffusion, whereas those obtained in the presence of ultrasound were limited by surface reaction. The rate enhancement was due to an increase in diffusive transport within the pores caused by acoustic vortex microstreaming. The activation energy for desorption decreased with an increase in ultrasonic power density, thus making the ultrasound weaken the adsorption bond.
Constrained nonlinear MPC using hammerstein and wiener models: PLS framework
Authors: Patwardhan Rohit S. , Lakshminarayanan S. , Shah Sirish L. 
Published: April 2004

AbstractMethods of implementing an input‐constrained, nonlinear, model‐predictive controller in latent spaces using partial‐least‐squares (PLS)‐based Hammerstein and Wiener models are discussed. For multiple‐input, multiple‐output (MIMO) systems, the PLS flamework presents a viable alternative for identification and controller synthesis using Hammerstein and Wiener structures. The constraint mappings, which have to be taken into account during controller design in the PLS flamework, are highlighted. PLS‐based Wiener models are well suited for constrained control of nonlinear systems. The use of PLS‐based Hammerstein models for control involves solution of a nonlinear program as a result of the constraint mapping. The proposed approach is demonstrated on a simulated pH‐level control of an acid base neutralization process.