bluuebunny/crossref_metadata_2025_split huggingface dataset:
Deterministic global optimization for error‐in‐variables parameter estimation
Authors: Gau Chao‐Yang , Stadtherr Mark A. 
Published: April 2004

AbstractStandard techniques for solving the optimization problem arising in parameter estimation by the error‐in‐variables (EIV) approach offer no guarantee that the global optimum has been found. It is demonstrated here that the interval‐Newton approach can provide a powerful, deterministic global optimization methodology for the reliable solution of EIV parameter estimation problems in chemical process modeling, offering mathematical and computational guarantees that the global optimum has been found. Although this methodology is typically regarded as being applicable only to very small problems, it is successfully applied here to problems with over 200 variables. It is a general‐purpose technique and is applied here to a diverse group of problems, including examples in reactor modeling, in modeling vapor‐liquid equilibrium, and in modeling a heat exchanger network.
Optimal operation of distillation processes under uncertain inflows accumulated in a feed tank
Authors: Li Pu , Wendt Moritz , Arellano‐Garcia H. , Wozny Günter 
Published: April 2004

AbstractA new method of optimizing the operation of distillation processes with uncertain inflow streams from upstream plants is discussed. The case considered is the streams that will be first accumulated in a tank before feeding to the column. To minimize the total amount of operating energy while keeping a stable column operation under these inflows, a novel decomposed optimization strategy consisting of two steps was used. For an optimal planning of the dynamic operation, a smooth feed flow policy to the column is developed in the first step by stochastic optimization under chance constraints by ensuring a predefined probability of holding the tank level inside the desired range. An easy‐to‐use method developed computes the maximum reachable probability of holding the constraints so that a feasible solution of the chance constrained problem can be guaranteed. Since the uncertainty in the inflow stream variability is absorbed in the stochastic optimization over the tank, the operation of the dowstream distillation column is deterministic. Therefore, in the second step, the reflux and reboiler duty policies of the column are developed by deterministic dynamic optimization. The optimal overall strategy is obtained by the maximized smoothness of the feed flow to the distillation column. The approach is applied to a pilot column, and the developed operating policies are implemented on the real plant by experiment.
Selective hydrogenation of acetylene through a short contact time reactor
Authors: Vincent Matthew J. , Gonzalez Richard D. 
Published: April 2004

AbstractA novel approach to the selective hydrogenation of acetylene involves a short contact time reactor. A thin Pd/γ‐Al2O3 catalytic membrane (about 5 μm thick) was observed to be void of minor defects. Forcing a dilute C2H2/H2/Ar mixture through the layer produced high conversions coupled with high selectivity at high temperatures. The selectivity was observed to increase with temperature. A gas‐dispersion model with derived kinetics was employed to explain the results. A solution to the corresponding coupled nonlinear differential equations resulted in a Peclet number of 64.5 and a contact time of 9.5 × 10−3 s through the reactor at 100°C. A critical thickness is predicted to exist for a maximum in ethylene concentration. A value of 2.5 μm at 200°C is representative. Lastly, permeability experiments agree with modeling results to show that Knudsen diffusion is absent despite a narrow pore‐size distribution.
FBR for catalytic propylene polymerization: Controlled mixing and reactor modeling
Authors: Meier G. B. , Weickert G. , van Swaaij W. P. M. 
Published: April 2004

AbstractParticle mixing and segregation have been studied in a small‐scale fluidized‐bed reactor (FBR) under pressure. The solids mixing is relatively faster than the residence time of catalyst particles in the case of a polymerization process, but smaller particles accumulate in the upper zone. Semibatch propylene polymerization experiments showed that the vertical temperature gradients are caused mainly by catalyst segregation. At low gas velocities, segregation and mixing can differ under reacting conditions compared to nonreacting conditions due to particle–particle interactions. Catalyst concentration gradients caused by incomplete mixing are strengthened remarkably by the exothermic reaction even at low polymerization rates. These observations do not represent an industrial situation. The FBR has therefore been equipped with a draft tube and cone to control vertical solids mixing. The internal solids circulation rate is a nonlinear function of the gas velocity. Strongly reduced segregation, elutriation, and entrainment observed were compared to experiments without a draft tube. Temperature profiles observed during polymerization can be controlled by the solids circulation rate. Hydrogen injections led to an instantaneously increased polymerization rate, probably due to the reactivation of dormant sites. Irreversible deactivation rates of dormant and active sites seem to be the same. Moreover, hydrogen appeared to be very effective for widening the molecular‐weight distribution. A compartment model developed describes the temperature profile in the reactor and related molecular‐weight distribution of the polymer.
Monolayer hydration governs nonideality in osmotic pressure of protein solutions
Authors: Yousef M. A. , Datta R. , Rodgers V. G. J. 
Published: April 2004

AbstractStrong nonideality observed in the osmotic pressure of concentrated globular proteins in aqueous media of moderate salt concentrations has long been associated with protein–protein interaction. As a consequence, virial expansions, based on the McMillan–Mayer theory, have been used to extract the physical phenomena observed. Our recent articles showed that a free‐solvent model assuming hydration and salt binding are dominate factors for nonlinearity, successfully modeled BSA (67 kDa) and IgG (155 kDa) protein aqueous solutions at moderate salt concentrations. Similar findings for lysozyme (HEL, 14 kDa) and ovalbumin (45 kDa) are reported here. More significantly, the independently calculated hydration values regressed from the osmotic pressure data were compared with the solvent accessible surface areas of each protein investigated. The results showed that the hydration values determined from the free‐solvent model are remarkably a monolayer equivalent of water.
Hygroscopic properties of mixed ammonium sulfate and carboxylic acids particles
Authors: Hämeri Kaarle , Charlson Robert , Hansson Hans‐Christen 
Published: April 2004

AbstractThe hygroscopic growth of internally mixed ammonium sulfate and carboxylic acid particles was measured as a function of relative humidity by using a tandem differential mobility analyzer (TDMA). In TDMA experiments the organic compounds with different solubilities act in several ways, ranging from the behavior of totally insoluble substance to that of soluble compounds. The hygroscopic properties for mixtures containing either adipic acid or phthalic acid together with ammonium sulfate indicate that the organic fraction of the particles behaves as an inert mass and does not contribute to water uptake. The mixtures involving malonic acid or succinic acid increased the water uptake of the ammonium sulfate part only. The results indicate that the solubility of the organic fraction in individual aerosol particles clearly influences the aerosol–water interaction.
Thermodynamic equilibrium of organic‐electrolyte mixtures in aerosol particles
Authors: Ming Yi , Russell Lynn M. 
Published: April 2004

AbstractThis thermodynamic model describes the phase equilibria of mixtures of electrolytes and organic species in aqueous solutions existing as aerosol particles. The activity coefficient of each species in solution is explicitly related to the chemical composition by treating the (inorganic) ion–water, organic–water and ion‐organic interactions with a combined Pitzer–UNIFAC thermodynamic approach. It was parameterized with a new type of multifunctional “meta‐group” to better represent measured properties of long‐chain monofunctional compounds and short‐chain multifunctional compounds. Interactions between dissolved electrolytes and organic species are modeled using the “salting‐out” effect of NaCl with organic compounds to predict the hygroscopic growth of particles composed of a salt and diacid. The predicted growth agrees well with laboratory measurements. The presence of 50% malonic acid decreases the growth of pure (NH4)2SO4 by 20% at high relative humidities, while mixtures with 50% succinic acid and 50% glutaric acid cause decreases of 35% and 38%, respectively. The mixing of organic compounds with solubility higher than 4 mol·L−1 with salt can decrease the observed DRH. The mixture of malonic acid and (NH4)2SO4 is predicted to start taking up water at 58%, much lower than the DRH of pure (NH4)2SO4 (80%). Insoluble compounds do not change the observed DRH, while reducing the amount of water taken up. The predicted water contents for internal and external mixtures are largely similar, with small differences predicted for mixtures of soluble organic species. The largest deviation of 10% between the water contents of internal and external mixtures occurs for 50% malonic acid with 50% (NH4)2SO4. For less soluble compounds such as succinic acid and glutaric acid, the two types of growth generally agree within 3%.
Mean concentrations and concentration fluctuations in a stirred‐tank reactor
Authors: Verschuren Iris L. M. , Wijers Johan G. , Keurentjes Jos T. F. 
Published: April 2004

AbstractMixing has a major influence on the product ratio of fast competitive reactions, as the product ratio of these reactions is determined by local concentrations. To integrate models from literature for the description of the mean and fluctuating concentration of a continuous reactant flow fed to a stirred‐tank reactor, the models are validated against detailed experimental data for a stirred‐tank reactor equipped with a Rushton turbine impeller. Application of these models requires information on local hydrodynamic parameters, which are determined by laser Doppler velocimetry. Model calculations are validated by determining the mean concentration and concentration variance of an inert tracer fed with planar laser‐induced fluorescence to the studied stirred‐tank reactor. To calculate the mean concentration, a combination of a theoretical model, measured mean concentrations and LDV measurements is used to determine the turbulent diffusion coefficient. The turbulent mixer model is used to calculate the concentration variance. Compared to the literature, this model requires adjustment of the constant in the production of the concentration variance to fit the measured concentration variances correctly. For the mean concentration and its variance, measurements agreed reasonably with simulations.
Fluidized‐bed pyrolysis of polyolefins wastes: Predictive defluidization model
Authors: Mastellone Maria Laura , Arena Umberto 
Published: April 2004

AbstractThe risk of defluidization during the low‐temperature pyrolytic processes of polyolefins is one of the major constraints to a wider utilization of fluidized beds for the pyrolysis of plastic wastes. A predictive model can estimate the occurrence of defluidization under different operating conditions, taking into account the role of physical properties of the polymers and hydrodynamic variables of the reactor, together with that of the main operating parameters, like the process temperature and the plastic waste feed rate. The results agree well with the experimental data obtained by feeding recycled polypropylene and polyethylene in a laboratory‐scale bubbling fluidized‐bed pyrolyzer. An operating map allows to distinguish the region of reactor stable operation from that of defluidization.
Effect of compressibility on performance of hydraulic wash columns
Authors: van Oord‐Knol L. , Bruinsma O. S. L. , Jansens P. J. 
Published: April 2004

AbstractIn a hydraulic wash column the solid crystals are separated from the mother liquor by filtration in the top section of the column. Remaining impurities are removed via countercurrent washing of the crystals in the bottom section. Since compressibility limits the capacity of a wash column, this phenomenon needs to be quantified and modeled rigorously. The compressibility of the bed was determined from the porosity profile and the liquid‐pressure profile inside the wash column. The porosity of the bed decreases from 0.65 to 0.3 during transport of the bed. This is associated with a decrease in local bed permeability by a factor of 10. The compressibility of the bed, therefore, partly explains the large ratio between the average permeability above and below the wash front. Compressibility coefficients make it possible to relate the compressive stress to the porosity and permeability in the top section of the bed. These coefficients are, therefore, incorporated in a model to successfully predict the capacity of a wash column with a compressible bed.
Thermal boundary layers in sweeping gas membrane distillation processes
Authors: Khayet M. , Godino M. P. , Mengual J. I. 
Published: April 2004

AbstractThe sweeping gas membrane distillation process was analyzed in a plate and frame membrane module, and a method clarifying the contribution of each boundary layer separately was developed. The temperature polarization coefficients of the fluid phases as well as the overall one have been defined, and their effects on the permeate flux were studied. Also studied is the influence of experimentally relevant parameters, such as the inlet temperatures or circulation velocities of the fluids. Results from two porous and hydrophobic membranes in different experimental conditions were interpreted on the basis of a combined Knudsen/molecular diffusion flow model. The theory agreed well with the experiment.
Ministructured catalyst bed for gas‐liquid‐solid multiphase catalytic reaction
Authors: Liu Wei 
Published: April 2004

AbstractA ministructured reactor concept improves the performance of multiphase gas‐liquid‐solid reactions over conventional packed‐bed and trickle‐bed reactors. In the mini‐structured reactor, the catalyst bed is structured at the particle level by dividing the bed into a number of identical, parallel flow channels with the channel walls being catalyzed. The hydraulic diameter of each channel opening is from 0.2 to 2 mm, comparable to the conventional particle size. The mini‐structured reactor can be assembled using monolith catalyst modules that have been a proven material technology for gas‐phase reactions. Two types of gas‐liquid‐solid reactions, olefin hydrogenation and toluene saturation, are used to test the fundamental feasibility of the mini‐structured reactor under steady‐state reaction conditions in a cocurrent down flow mode. The new reactor shows an order of magnitude increase in the activity compared to a trickle‐bed operation for reaction conditions of practical interest. This degree of activity improvement is larger than estimates based on conventional analyses of catalyst geometric surface area and/or characteristic pore diffusion lengths. Individual catalyst particles are significantly underutilized in a trickle‐bed reactor. More ideal contacting of gas, liquid and catalyst, as well as the enhancement of overall mass‐transfer processes in the mini‐structured reactor, makes it possible to dramatically improve the gas/liquid multiphase reaction performance over solid catalysts.
Role of water in the kinetic modeling of catalyst deactivation in the MTG process
Authors: Gayubo Ana G. , Aguayo Andrés T. , Morán Angel L. , Olazar Martín , Bilbao Javier 
Published: April 2004

AbstractA kinetic model is proposed for deactivation by coke of a HZSM‐5 zeolite catalyst used in the transformation of methanol into hydrocarbons in the 573–723 K range. The attenuating effect on coke deposition due to the presence of water in the reaction medium was quantified by a parameter that increases with reaction temperature. The slower deactivaton of the methanol dehydration step compared to the formation steps of olefin and gasoline lumps is taken into account. In view of the results, water content in the reaction medium is an efficient variable for controlling the results of activity–selectivity–deactivation. This model is not applicable for a temperature of 723 K when water content in the reaction medium is high, due to the fact that under these conditions the zeolite is subjected to irreversible deactivation.
CFD modeling and simulation of clogging in packed beds with nonaqueous media
Authors: Ortiz‐Arroyo Arturo , Larachi Faïçal , Grandjean Bernard P. A. , Roy Shantanu 
Published: April 2004

AbstractWhen liquids containing low concentrations of fine solid impurities are treated in packed‐bed reactors, clogging develops and starts hampering the flow severely. This phenomenon, called deep‐bed filtration, constitutes serious concern over hydrotreating or hydrocracking of bituminous sands in packed‐bed reactors, in which such nonfilterable fines as native clay or incipient coke cause reactor dysfunction by clogging. A detailed k‐fluid Eulerian 2‐D transient computational‐fluid dynamic (CFD) model was formulated to describe the space‐time evolution of clogging patterns developing in deep‐bed filtration of the liquids. A local formulation of the macroscopic logarithmic filtration law is proposed, as well as a geometrical model for the effective specific surface area of momentum exchange. Both mono‐ and multiple‐layer deposition mechanisms were accounted for by including appropriate filter coefficient formulations. Transient, 2‐D axisymmetrical simulations were benchmarked using experimental results and observations of Narayan et al. (1997) of the carbon‐black contaminated kerosene flow through packed beds. Comparing the simulations and experiments showed that CFD is useful for the quantitative description of packed‐bed clogging.
Multicomponent diffusion of hydrogen‐bonding solutes in a polymer
Authors: Elabd Yossef A. , Barbari Timothy A. 
Published: April 2004

AbstractThe diffusion of methyl ethyl ketone (MEK)/1‐butanol (BOH) mixtures in polyisobutylene (PIB) was studied using time‐resolved FTIR‐ATR spectroscopy at varying mixture compositions. Diffusion coefficients and hydrogen‐bonding interactions were quantitatively measured using this technique. In the MEK/BOH/PIB system, three species were identified from the infrared spectra, free MEK, an MEK‐BOH complex, and a self‐associated BOH cluster. The diffusion coefficient for the MEK‐BOH complex was less than that for free MEK, but larger than the values determined for the BOH cluster. These results were compared to a numerical solution of a multicomponent transport model that explicitly accounts for solute–solute interactions to determine individual diffusion coefficients for all the species identified. In addition, the MEK/BOH/PIB results were compared to those for an MEK/acetonitrile (ACN) mixture, a nonhydrogen‐bonding system, in PIB, to elucidate the differences between interacting and noninteracting systems.
Dynamic behavior of hydraulic wash columns
Authors: van Oord‐Knol L. , Bruinsma O. S. L. , Jansens P. J. 
Published: April 2004

AbstractHydraulic wash columns are well suited for solid–liquid separation and ultrapurification in melt‐suspension crystallization. For steady operation of a hydraulic wash column and proper purification, the length of the crystal bed and position of the wash front should stay within safe limits, which requires a well‐defined control system. To understand the interactions between slurry properties, column dimensions, and process conditions, a dynamic model was developed. The model was validated with help of experiments in a pilot‐plant wash column, fed from a continuous crystallizer. P‐Xylene was used as the model compound. It satisfactorily predicted the trends in the length of the crystal bed and the wash front height, and the interactions in the wash column are largely understood. With the help of the model a feedback control system with two control loops was designed and simulated. For a wide range of crystal fractions (0.05 to 0.3 v/v) in the feed stream, both the length of the bed and the wash front were kept at the desired setpoint values, indicating the flexibility of a controlled wash column.
Backstepping design of composition cascade control for distillation columns
Authors: Alvarez‐Ramirez Jose , Alvarez Jesus , Monroy‐Loperena Rosendo 
Published: April 2004

AbstractAlthough the cascade control of distillation columns had been extensively studied, some aspects still remain unexplored or unresolved. For instance, a unifying approach is needed to systematize the existing ad hoc controller constructions, to rigorously explain their remarkably robust property in using rather simple input‐output linear models, and to explore the possibility of improving their construction and functioning. Some of these problems are addressed by the recently developed backstepping‐passivation approach in constructive nonlinear control, yielding a systematic controller construction coupled to a simple tuning scheme that can be executed with standard tuning rules, a closed‐loop stability criterion, an explanation of the closed‐loop dynamics behavior, and controllers that perform better than existing ones. The applicability of the theoretical results and their controller construction‐tuning schemes are illustrated by considering the single‐ and dual‐point control cases of a binary acetone‐ethanol distillation column.
Absorption with instantaneous reaction in a droplet with sparingly soluble fines
Authors: Scala Fabrizio , D'Ascenzo Michele 
Published: April 2004

AbstractThe problem of gas absorption followed by an instantaneous irreversible chemical reaction in a rigid droplet containing sparingly soluble fine reactant particles is discussed. A model was developed for the general case when the reactant particle dissolution near the gas–liquid interface is nonnegligible. Solids dissolution is treated taking into account the average spacing between the suspended particles. A simple analytical expression for the rate of gas absorption is derived under the assumption of slow particle dissolution, and conditions are given for applicability of the model. A numerical example, relevant for the spray‐dry desulfurization process, for the system SO2‐Ca(OH)2 in water is discussed.
Hybrid framework for hazard identification and assessment in batch processes
Authors: Viswanathan S. , Shah N. , Venkatasubramanian V. 
Published: April 2004

AbstractA framework presented addresses the three main parts of a process hazards analysis study: hazard identification, hazard evaluation, and hazard mitigation. The framework utilizes a hybrid methodology that effectively combines a qualitative digraph model‐based technique for performing hazard identification and a quantitative optimization‐based technique for performing hazard evaluation and hazard mitigation. The combined framework circumvents the local minima problems faced by mathematical optimization algorithms, as well as the qualitative ambiguities that plague digraph models. The systems used to implement the framework are BatchHAZOPExpert, gPROMS, and gOPT. BatchHAZOPExpert is used for hazard identification, while gPROMS and gOPT are used for hazard evaluation and hazard mitigation. The application of the integrated framework is illustrated by implementing it on two industrial case studies.