bluuebunny/crossref_metadata_2025 huggingface dataset:
Liquid–liquid extraction with chemical reaction in a novel impinging‐jets reactor
Authors: Dehkordi Asghar Molaei
Published: April 2004

The theory of mass transfer accompanied by chemical reaction for the pseudo‐first‐order heterogeneous liquid–liquid reactions was used to measure the effective interfacial area in a novel two‐impinging‐jets reactor (TIJR), which is characterized by a small reactor volume equipped with two simple nozzles directed toward each other. Aqueous and organic streams were jetted through the nozzles into rotating and stationary disks, resulting in a highly turbulent mixture of aqueous and organic phases. Experiments were also conducted on the physical extraction of n‐Butyl formate into distilled water to measure the overall volumetric mass‐transfer coefficients. Due to both the impinging process and high rate shear forces acting on the phases, the overall volumetric mass‐transfer coefficients and volumetric extraction rates obtained by the physical and chemical method, respectively, increased dramatically compared to those obtained by conventional reaction systems and an air‐driven two‐impinging‐streams reactor developed by the present author. The enhancing effect of impinging jets on the conversion of aqueous NaOH solution was tested by another nonimpinging‐jets reactor.
Real‐time, nonlinear control of a constrained, nonminimum‐phase process
Authors: Kanter Joshua M. , Seider Warren D. , Soroush Masoud
Published: April 2004

This article presents the first real‐time implementation of a recently‐developed model‐based control method on a pilot‐scale, multivariable, liquid‐level process that exhibits inverse response and whose actuators can be saturated. Issues in real‐time implementation of the control method are discussed, as well as a controller tuning procedure. Two model‐based controllers are implemented: one is derived using the process outputs; the other is derived using auxiliary outputs. Servo and regulatory responses presented show the differences in the performance of the two controllers. In real time, one of the model‐based controllers eliminates inverse response in one controlled output at the expense of yielding a larger inverse response in the other controlled output. This inverse‐response elimination is a real‐time validation of the linear and nonlinear theoretical results reported in the systems literature.
Multiple plant heat integration in a total site
Authors: Bagajewicz Miguel , Rodera Hernán
Published: April 2004

Heat integration across plants can be accomplished either directly using process streams or indirectly using intermediate fluids. Extensions to many plants of LP and MILP models previously developed for the two‐plant case are presented. The targeting procedure first identifies the maximum possible savings for the whole system, and, subsequently, the minimum number of connections between the two‐plant combinations required to obtain maximum savings is established. The location of intermediate fluid circuits to indirectly integrate the system is then found. Alternative solutions exist, which allow flexibility when the design of a multipurpose heat exchanger network is pursued. Finally, the optimal location of the circuits for cases of restricted operation is discussed.
Kinetic model for the pyrolysis of polysiloxane polymers to ceramic composites
Authors: Plawsky Joel L. , Wang Feng , Gill William N.
Published: April 2004

A model describing the pyrolysis of an organo‐silicate polymer (Blackglas polymer) to form a silicon oxycarbide glass was developed based on the known chemistry and architecture of the polysiloxane precursor. The objectives were to develop a plausible reaction pathway to explain the pyrolysis process, rate, and product spectrum, and to study the effect of various heating protocols on the pyrolysis process. The model successfully predicted the evolution rates of the major gases as a function of process temperature and the overall pressures reached during the process. The effects of various heating protocols on the outgassing kinetics were studied to develop an optimum protocol for a rapid pyrolysis process that gives a composite with desirable mechanical properties. Overall, the model appears to capture the essential characteristics of the process and is in good agreement with experimental results.
COSMOSPACE: Alternative to conventional activity‐coefficient models
Authors: Klamt Andreas , Krooshof Gerard J. P. , Taylor Ross
Published: April 2004

An analytical solution, COSMOSPACE, to the statistical thermodynamics of a model of pairwise interacting surfaces, is presented. This solution was initially developed for the a priori prediction model COSMO‐RS in an implicit form. A comparison of COSMOSPACE with UNIQUAC and with the quasi‐chemical theory of Guggenheim reveals the conditions under which the models yield similar results and when they differ very considerably. It is shown that COSMOSPACE is in extremely good agreement with Monte‐Carlo simulations for some lattice fluids (where UNIQUAC is particularly poor). The ability of COSMOSPACE to provide good fits to experimental data is shown for three binary mixtures including ethanol‐cyclohexane, where UNIQUAC incorrectly predicts a liquid–liquid phase separation.
Thermal conversion of biomass: Comprehensive reactor and particle modeling
Authors: Wurzenberger Johann C. , Wallner Susanne , Raupenstrauch Harald , Khinast Johannes G.
Published: April 2004

Thermal conversion of biomass is often carried out in packed‐bed furnaces. Optimization of thermal efficiency and furnace emissions is an important goal, which requires accurate understanding of all physical and chemical effects in the reactor. A combined transient single particle and fuel‐bed model is presented. The fuel‐bed model is discretized, and a representative particle is chosen and discretized in a radial direction at each grid point. Mass, momentum and energy balances are solved for the entire system. Drying is modeled using an equilibrium approach, and primary pyrolysis is described by independent parallel‐reactions. Secondary tar cracking, homogeneous gas reactions, and heterogeneous char reactions are modeled using kinetic data from literature. Simulations validated for single particles agree well with experimental studies. Simulation results for the combustion of a biomass bed are presented for one set of furnace conditions.
Enhancement of the methane storage on activated carbon by preadsorbed water
Authors: Zhou Li , Sun Yan , Zhou Yaping
Published: April 2004

The enhancement effect of preadsorbed water on methane storage on activated carbon was experimentally proven. Adsorption isotherms of methane on dry and wet activated carbon with different water content were measured at 275–283 K and pressures up to 11 MPa. A sudden change in the methane uptake mechanism that was indicated by the inflection point of isotherms was observed. The measured amount adsorbed always decreased with the increasing water content of carbon before the inflection point. However, a step rise in the isotherm to as much as 63.3% was observed when the pressure reached the inflexion point locating at 4–5 MPa. The significant enhancement of water on the methane‐storage capacity of activated carbon is expected to considerably improve the adsorbed natural gas (ANG) technology.
Bubble‐Size distributions and flow fields in bubble columns
Authors: Lehr F. , Millies M. , Mewes D.
Published: April 2004

Bubble‐size distributions and flow fields in bubble columns are calculated numerically. The population balance is simplified and reduced to a balance equation for the average bubble volume. Models developed predict the rate of bubble breakup and coalescence based on physical principles. The flow fields are numerically calculated for bubble columns with cylindrical cross sections using the Euler‐Euler method. The newly derived balance equations for the average bubble volumes are implemented into a commercial CFD code. The solutions of the balance equation for high superficial gas velocities result mainly in two fractions: one for the fraction with small and the other for the fraction with large bubble diameters. Both are considered pseudocontinuous phases, in addition to the liquid phase. The calculated flow fields are characterized by several large‐scale vortices. The local volume fractions of gas and liquid are locally inhomogeneous and highly time‐dependent. The time‐averaged flow field is axisymmetric and stationary. The calculated volume fractions, velocities, and bubble‐size distributions agree well with existing and previously published experimental results for bubble columns up to 0.3 m in diameter.
Non‐Fickian nonisothermal model for drying of polymer coatings
Authors: Vinjamur Madhu , Cairncross Richard A.
Published: April 2004

As a sequel to our study on experimental measurements of trapping skinning in a poly(methyl methacrylate)/acetone coating, a mathematical model of non‐Fickian diffusion that predicts trapping skinning is reported here including solvent transport due to a stress gradient that develops because of coating shrinkage. The predicted solvent concentration profile shows a sigmoidal shape and a front that moves into the coating. In the nearly constant rate period, the stress relaxes near the coating surface due to short relaxation times at high coating temperature. The stress relaxation causes negative non‐Fickian flux. At higher gas flow rates, the negative non‐Fickian flux causes the development of a thinner layer of low solvent concentration near the coating surface and a thicker layer of high solvent concentration inside the coating. Thus, more solvent remains in the coating dried at higher flows and trapping skinning occurs.
Modeling hydrodynamics of trickle‐bed reactors at high pressure
Authors: Narasimhan C. S. L. , Verma R. P. , Kundu Arunabha , Nigam K. D. P.
Published: April 2004

A phenomenological hydrodynamic model of a trickle‐bed reactor developed predicts pressure gradient and liquid holdup at high pressures. The model consists of 1‐D force balance equations incorporating particle–gas drag, particle–liquid drag and gas–liquid interactions. The deviation between the measured and theoretical pressure drop is explained in terms of tortuosity and axial dispersion effects. Tortuosity encountered by the flowing liquid and gas phases has two components: (1) tortuosity angle (θ), the measure of the tortuous path the fluid would take; (2) an excess friction factor, which would approximate for resulting excess drag while the tortuous path is taken. These parameters were observed to play a major role in modeling the hydrodynamics in the trickle‐bed reactor. The model takes into account the tortousity effects in a unique way. The axial dispersion effect comes into the picture due to the back‐mixing, modeled in terms of the Peclet number (Pe) in a novel way. The overall model was tested with major experimental data for the high‐pressure concerning various types of gas–liquid systems, including hydrocarbons, aqueous solutions, coalescence inhibiting liquids, and so on, that are available in the literature, and the prediction has been found to be excellent.
Neural network particle sizing in slurries by reflectance spectroscopy
Authors: Li Mingzhong , Wilkinson Derek , Schrödl Markus
Published: April 2004

Measuring concentration and size of solids in suspension is important in many industries. Even though techniques based on optical transmission measurements have been well developed, they are not always successful in practical applications because low concentration suspensions are needed. A method developed determines particle‐size distribution and concentration from reflection measurements in concentrated suspensions using neural networks with particle concentrations up to 10% volume fraction. Based on measured optical reflectance spectra of suspensions with known particle‐size distributions and concentrations, a neural network was trained to identify particle‐size distribution and volume fraction of suspensions. Training is a time‐consuming process requiring presentation of many spectra and their corresponding particle‐size distributions and volume fractions to the neural network, but once concluded satisfactorily, the neural network can be used to predict the particle‐size distribution and volume fraction of high concentration suspensions rapidly in‐situ.
Dynamic measurement for the stiffness of loosely packed powder beds
Authors: Yanagida T. , Matchett A. J. , Coulthard J. M. , Asmar B. N. , Langston P. A. , Walters J. K.
Published: April 2004

An experimental methodology to measure the stiffness of loosely packed powder beds was developed, which had not been possible using previous methods. Experiments were performed on a range of sample powders including polyethylene, rubber, glass, sand, and clay powders. Powders were placed in a vertical, open, cylindrical vessel, and subject to sweep vibration at low accelerations. Base force and acceleration were measured using an impedance head and accelerometer. Apparent mass, defined as a ratio of base force to base acceleration, measured showed a significant peak frequency. The longitudinal elastic modulus of the bed was calculated from the data. For shallow beds in which the wall friction is negligible, the peak frequency is independent of the cross‐sectional area of the bed and sweep rate, but dependent on the bed height and acceleration. Data generated by the top‐cap method agreed reasonably for cases in which the packing state was not sensitive to external force. A substantial change in elasticity was detected with changes of packing states. Furthermore, the elasticity of packed beds conforms to Kendall's fourth‐order relationship with solid volume fraction over a range of packing conditions.
Novel pervaporation technology using absorption refrigeration for vapor removal
Authors: Fahmy Alaa , Mewes Dieter , Ohlrogge Klaus
Published: April 2004

A novel process configuration for pervaporation and vapor permeation realizes the permeation driving force by absorbing the permeate vapor into a suitable solution with a very low vapor pressure. Although the suggested process design lacks an experimental demonstration, by using two well‐established technologies—the separation by pervaporation and the absorption refrigeration—it can achieve technical and economic advantages over the conventional condensation technology. Vacuum pressures as low as 8 mbar can be obtained at ambient temperatures without refrigeration, as well as low vacuum ranges that are not possible by condensation without freezing. Process simulations and feasibility investigations for the suggested process are discussed.
Combinatorial framework for effective scheduling of multipurpose batch plants
Authors: Sanmartí E. , Puigjaner L. , Holczinger T. , Friedler F.
Published: April 2004

The production scheduling of multipurpose batch plants is considered. A novel graph representation that looks at the specific characteristics of production scheduling in chemical processes is proposed. In these graphs, the nodes represent the production tasks, the arcs of the precedence relationships among them. The representation is flexible enough to consider a wide variety of production structures, including complex recipes. Both nonintermediate storage (NIS) and unlimited intermediate storage (UIS) transfer policies can be considered simply by choosing the appropriate precedence relationships. This representation provides the opportunity of incorporating highly efficient graph algorithms together with an appropriate branch‐and‐bound algorithm for solving multipurpose scheduling problems. The efficiency of the proposed method is established by solving examples and a complex case study.
Two‐mode models for describing mixing effects in homogeneous reactors
Authors: Chakraborty Saikat , Balakotaiah Vemuri
Published: April 2004

The Liapunov–Schmidt technique of bifurcation theory is used to spatially average the convection–diffusion–reaction equation over smaller time/length scales to obtain two‐mode models (TMMs) for describing mixing effects in homogeneous tubular, loop/recycle and tank reactors. For the isothermal case, these TMMs are described by a pair of coupled balance equations involving the mixing‐cup (Cm) and the spatially averaged (〈C〉) concentrations. One equation traces the evolution of Cm with (residence) time, while the other is a local equation that describes mixing resulting from coupling between diffusion, velocity gradients, and reaction at the local scales, in terms of an exchange between the two modes, Cm and 〈C〉. The TMMs have many similarities with the two‐phase models of catalytic reactors, with concept of transfer between phases being replaced by that of exchange between the two modes. Examples are presented to illustrate the usefulness of these TMMs in predicting micromixing effects on homogeneous reactions.
Measuring asphaltenes and resins, and dipole moment in petroleum fluids
Authors: Goual Lamia , Firoozabadi Abbas
Published: April 2004

A petroleum fluid can be divided into three types of species: asphaltenes, resins, and oils. Asphaltenes and resins are polar, while the rest of the so‐called oils are either nonpolar or mildly polar. The interaction among these species strongly affect asphaltene precipitation from petroleum fluids. Different measuring methods for asphaltenes in a petroleum fluid give similar results, but different results for the resin content of a petroleum fluid. In addition to the amount affecting precipitation, the polarity of asphaltenes and resins affects precipitation strongly. The Onsager formulation of dipolar moments was used to measure the dipole moment of asphaltenes, resins and the oil species from eight different petroleum fluids from various parts of the world. The dipole moment, a measure of polarity, for resins was measured in this work for the first time. Results showed that resin separated from a petroleum fluid by propane is part of the total resin. Adsorption methods, however, give the total amount of resins. For a given petroleum fluid, asphaltenes had a higher dipole moment than resins. However, resins from one petroleum fluid can have a higher dipole moment than asphaltenes from another petroleum fluid.
Modeling of heavy metal salt solubility using the extended UNIQUAC model
Authors: Iliuta Maria C. , Thomsen Kaj , Rasmussen Peter
Published: April 2004

Solid–liquid equilibria in complex aqueous systems involving a heavy metal cation (Mn2+, Fe2+, Co2+, Ni2+, Cu2+, or Zn2+) and one or more ions for which Extended UNIQUAC parameters have been published previously are modeled using the Extended UNIQUAC model. Model parameters are determined on the basis of a data bank with more than 4,000 experimental data points for binary and ternary aqueous systems. The parameters are generally valid in the temperature range from the freezing point to the boiling point of the respective solutions.
Model for the gas evolution in a porous medium driven by solute diffusion
Authors: Tsimpanogiannis Ioannis N. , Yortsos Yannis C.
Published: April 2004

An effective continuum model is derived to describe the nucleation and subsequent growth of a gas phase from a supersaturated, slightly compressible binary liquid in a porous medium, driven by solute diffusion. The evolution of the gas results from reducing the system pressure at a constant rate or withdrawing the liquid at a constant rate. The model addresses two stages before the onset of bulk gas flow, nucleation and gas‐phase growth. Negligible gradients due to gravity or viscous forces are assumed, so the critical gas saturation signaling the onset of bulk gas flow is only a function of the nucleation fraction. Important quantities characterizing the process, such as the pore number fraction hosting activated sites, deviation from thermodynamic equilibrium, maximum supersaturation, and critical gas saturation, depend crucially on the nucleation characteristics of the medium. Heterogeneous nucleation models using preexisting gas trapped in hydrophobic cavities or in terms of a rate‐dependent nucleation are used to investigate the nucleation behavior. Using a simpler analytical model the relevant quantities during nucleation can be expressed in terms of a simple combination of dimensionless parameters. The theory predicts that the maximum supersaturation is a weakly increasing function of rate, which in the region of typical experimental parameters can be approximated as a power law. It depends sensitively on the probability density function of nucleation cavity sizes. The final nucleation fraction (thus, the critical gas saturation) is predicted to be a power law of the decline rate. The theoretical exponents agree well with experimental data. The subsequent evolution of the gas phase and the approach to the critical gas saturation is also described.
Feasibility and synthesis of hybrid reactive distillation systems
Authors: Chadda Nitin , Malone Michael F. , Doherty Michael F.
Published: April 2004

A systematic method to synthesize hybrid reactive distillation configurations described here uses three building blocks. These building blocks are a cocurrent rectifying cascade, a cocurrent stripping cascade, and a countercurrent cascade. A feasibility diagram and a product purity diagram provide a global view of the “direct” and “indirect” sharp split products that can be obtained as a function of the reaction rate from single–feed and double–feed hybrid columns, respectively. These diagrams are used as a basis for quickly and systematically generating feasible column configurations (if any) that produce the desired product. Three esterification examples are used to illustrate the method. In spite of the fact that the examples form a homologous series, the feasible designs are quite different. The results compare well with column simulations.
Multiobjective optimization of SMB and varicol process for chiral separation
Authors: Zhang Ziyang , Hidajat K. , Ray Ajay K. , Morbidelli M.
Published: April 2004

The multiobjective optimization of continuous countercurrent chromatography separation units, such as simulated moving bed (SMB) and Varicol, is considered. The Varicol system is based on a nonsynchronous shift of the inlet and outlet ports instead of the synchronous one used in the SMB technology. The optimization problem is complicated by the relative large number of decision variables, including continuous variables, such as flow rates and lengths, as well as discontinuous ones, such as column number and configuration. It is also important to reformulate the optimization problem as multiobjective, since the factors affecting the cost of a given separation process are multiple and often in conflict with each other. A typical example is simultaneous maximization of the productivity of the process and the purity of the corresponding products. A new optimization procedure based on a genetic algorithm allows handling these complex optimization problems. An existing literature chiral separation model was used to illustrate the potential of this optimization procedure. This work also offered a unique opportunity to compare the optimal separation performance achievable with the SMB and Varicol technologies.
Simulation of five‐step one‐bed sorption‐enhanced reaction process
Authors: Xiu Guo‐hua , Soares Jose Luciano , Li Ping , Rodrigues Alirio E.
Published: April 2004

A five‐step, one‐bed, sorption‐enhanced reaction process proposed by Carvill et al. in 1996 for hydrogen production by steam–methane reforming was analyzed. For the simulated results of the first step, data from Hufton et al. (1999) and Ding and Alpay (2000) for a fixed‐bed column of an admixture of a catalyst and a sorbent that selectively removes CO2 from the reaction zone were used. The sorbent is periodically regenerated by using the principles of pressure‐swing adsorption. The process steps allow direct production of hydrogen with high purity and high methane conversion. A model considering multicomponent and overall mass balance, Ergun relation for pressure drop, energy balance for the bed‐volume element, and nonlinear adsorption equilibrium isotherm coupled with three main reactions was derived to describe the sorption‐enhanced reaction cyclic process. Two different isotherms were used under wet and dry conditions. The LDF model adopted describes the mass‐transfer rate of CO2 in the adsorbent. Numerical solution of model equations for the cyclic process was obtained by the orthogonal collocation method. The operating conditions allow the combination of a sufficiently high purity of hydrogen (average purity over 80%) with traces of CO and CO2, high methane conversion, fast adsorbent regeneration, and cyclic steady‐state operation. The model predictions agree reasonably with the literature data. The package is suitable for the design and analysis of sorption‐enhanced reaction process.
Surface modification of polyvinylidene fluoride pervaporation membranes
Authors: Khayet Mohamed , Chowdhury Geeta , Matsuura Takeshi
Published: April 2004

Polyvinylidene fluoride (PVDF) membranes were surface‐modified using fluorinated surface‐modifying macromolecules (SMMs) additives. The membranes were prepared using the phase‐inversion method. Two novel SMM formulations were used. The effect of some relevant parameters, such as the solvent evaporation time, evaporation temperature, and concentration of SMM in the PVDF casting solution, was considered. The prepared membranes were characterized in terms of the contact angle analysis, the liquid entry pressure of water measurements, and the scanning electron microscopy. Pervaporation experiments were conducted for dilute chloroform/water binary mixtures. Based on the contact angle analysis, the incorporation of SMM into the PVDF casting solution produced membranes with higher surface hydrophobicity. The pervaporative performance of the prepared membranes was investigated, and the relationship between the surface characteristics of the modified PVDF membranes and the chloroform separation discussed.
Flexibility analysis and design using a parametric programming framework
Authors: Bansal Vikrant , Perkins John D. , Pistikopoulos Efstratios N.
Published: April 2004

This article presents a new framework, based on parametric programming, that unifies the solution of the various flexibility analysis and design optimization problems that arise for linear, convex, and nonconvex, nonlinear systems with deterministic or stochastic uncertainties. This approach generalizes earlier work by Bansal et al. It allows (1) explicit information to be obtained on the dependence of the flexibility characteristics of a nonlinear system on the values of the uncertain parameters and design variables; (2) the critical uncertain parameter points to be identified a priori so that design optimization problems that do not require iteration between a design step and a flexibility analysis step can be solved; and (3) the nonlinearity to be removed from the optimization subproblems that need to be solved when evaluating the flexibility of systems with stochastic uncertainties.
Determination of operability limits using simplicial approximation
Authors: Goyal Vishal , Ierapetritou Marianthi G.
Published: April 2004

Determining the boundaries of any process/design where feasible and safe operation is guaranteed has long been recognized as a major concern in process industries. Of additional value is identifying the range of operating conditions where the design is most profitable. Although there is a lot of discussion in the open literature regarding design feasibility in terms of uncertainty of process variables, these techniques are rather limited due to the underestimation of the feasible space. A new approach is presented based on the ideas of inner and outer approximation of the feasible region to identify the operating envelopes where process operation is feasible, safe, and profitable. A number of example problems are presented including two case studies to illustrate the applicability of this approach.
CFD simulation of reactive flows: Catalytic combustion in a monolith
Authors: Canu P. , Vecchi S.
Published: April 2004

Catalytic combustion in a structured catalyst was used to test advantages of computational fluid dynamics (CFD) codes with respect to simpler approaches to simulation of actual data and kinetic studies. Published experimental data on square channels and segmented monoliths were compared and used as a basis for parametric studies. The relevance of temperature‐dependent transport properties was quantified. A comparison of 2‐D approximations with a full 3‐D model, which predicts a different ignition behavior, shows that the latter is needed to properly describe actual data. The segmentation of the monolith shows some influence on the overall combustion rate. The sensitivity analysis of the importance of chemical kinetics relative to mass transport suggests a need for a better description of surface mechanism, even if the simulated data are not uniquely under chemical control. A parameter‐fitting procedure for kinetic studies based on the detailed 3‐D, segmented CFD model was developed and successfully tested for modeling inhibition by water. Results show that more detailed surface and gas‐phase reactions mechanisms must be included, but only after developing and validating a comparably detailed model of the momentum and heat transport in the actual geometry of the real process.
Group contribution method for Henry's Law constant of aqueous hydrocarbons
Authors: Sedlbauer Josef , Bergin Gaëtan , Majer Vladimir
Published: April 2004

A functional group contribution scheme based on a hydration model predicts Henry's Law constant of aqueous hydrocarbons as a function of temperature and pressure. It uses the direct link of Henry's Law constant with the Gibbs free energy of hydration, as well as its temperature and pressure derivatives accessible from calorimetric and volumetric data. A semitheoretic model inspired by the fluctuation solution theory with five adjustable parameters was used for expressing the temperature and pressure dependence of ten functional contributions. A consistent group contribution scheme for hydration properties at 298 K and 0.1 MPa was taken from literature to constrain the model at reference conditions. Parameters for hydrocarbon functional groups were adjusted by simultaneous correlation of over 1,000 data points on Henry's Law constant and about 550 values on derivative hydration properties (enthalpy, heat capacity, and volume) available in a wide range of temperature and pressure. The resulting group additivity scheme can be used for predicting Henry's Law constant for alkanes, alkenes, alkylcycloalkanes, and alkylbenzenes up to 570 K and up to 100 MPa. Average accuracy of the predictions varies from 20 to 40% at ambient to high temperatures, respectively, and semiquantitative estimates are possible up to the critical point of water.
Ca‐Mg acetate as dry SO2 sorbent: II. Sulfation of CaO in calcination product
Authors: Sohn Hong Yong , Han Dong Hoon
Published: April 2004

The sulfation rate of CaO contained in calcined calcium magnesium acetate CMA by SO2 and O2 was measured. Although calcined CMA contains CaO and MgO, only CaO reacts with SO2 above 950°C. The reaction occurs at a much greater rate than with other conventional desulfurization agents like calcined limestone, dolomite, or Ca(OH)2, the last of which yields one of the most reactive forms of CaO. The remarkable enhancement of sulfation rate of CaO in calcined CMA is due to its much larger pore size and porosity than those of other agents. Another consequence of this structure of calcined CMA is that the sulfation reaction proceeds to completion without the rate leveling off, unlike in the sulfation of most oxides.
Ca‐Mg acetate as dry SO2 sorbent: III. Sulfation of MgO+CaO
Authors: Sohn Hong Yong , Han Dong Hoon
Published: April 2004

The separate sulfation rate of MgO contained in calcined calcium magnesium acetate (CMA) by SO2 and O2 was measured, as well as the simultaneous sulfation of MgO and CaO in the temperature range where the sulfates of both oxides are stable. In the temperature range below 830°C in which MgO sulfation is thermodynamically possible the reaction produced CaSO4·3MgSO4, rather than MgSO4. The formation of the CaSO4·3MgSO4 phase at a reasonable rate during the sulfation of calcined CMA has a significant implication in that it allows the utilization of MgO for SO2 removal, whereas the sulfation of MgO from conventional sources is so slow that it is of no practical interest. Thus, the calcined CMA can remove SO2 at lower temperatures than conventional SO2 absorbent and at a greater capacity and rate, which presents a substantial competitive advantage of this material.
Inertial flow structures in a simple‐packed bed of spheres
Authors: Suekane Tetsuya , Yokouchi Yasuo , Hirai Shuichiro
Published: April 2004

The detailed characteristics of the interstitial velocity distributions in pores are critical to understanding heat and mass transfer in a Packed bed of granular material. The velocity distributions in a pore that models a simple‐packed bed were measured directly by a magnetic resonance imaging technique. With an increase in the Reynolds number from 12.17 to 59.78–204.74, the increase and decrease in main flow velocity did not correspond to the local pore geometry, as is the case with a creeping flow. This indicated that inertial forces dominate over viscous forces. For example, at the Reynolds number of 204.74, the fluid penetrated through the center of the pores like a jet with negligible change of velocity. Circulation in the surrounding stagnant spaces generated eight symmetrical eddies in the plane perpendicular to the main flow direction.
Mixing of power‐law fluids using anchors: Metzner‐Otto concept revisited
Authors: Shekhar S. Murthy , Jayanti S.
Published: April 2004

In 1957 Metzner and Otto proposed a simplified way of calculating the power consumption in impeller‐driven systems for power‐law type of fluids. Assuming a proportionality between the shear rate and rotational speed of the impeller, they reported that the proportionality constant was independent of the geometric and fluid properties of the mixing system. This was later contested by a number of researchers, and different correlations have been given to evaluate the proportionality constant. An in‐depth investigation of the Metzner–Otto concept is discussed with the help of computational fluid dynamics (CFD) techniques to calculate the flow field created by an anchor impeller. Fundamentally, both of the assumptions are broadly valid for typical operating parameters used in anchor‐driven impeller systems. A new correlation, based on the Metzner–Otto concept and making use of the present CFD simulations, was developed to calculate power consumption in anchor‐driven mixing systems.
Adaptive extremum seeking control of continuous stirred‐tank bioreactors
Authors: Zhang T. , Guay M. , Dochain D.
Published: April 2004

An adaptive extremum‐seeking control scheme for continuous stirred‐tank bioreactors is proposed which utilizes the structure information of the kinetics of bioreactors to construct a seeking algorithm that drives the system states to the desired setpoints that optimize the value of an objective function. Lyapunov's stability theorem is used in the design of the extremum‐seeking controller stucture and the development of the parameter learning laws. Numerical simulations illustrate the effectiveness of this approach.
Detecting abnormal process trends by wavelet‐domain hidden Markov models
Authors: Sun Wei , Palazoğlu Ahmet , Romagnoli Jose A.
Published: April 2004

A novel method for detection of abnormal conditions during plant operation uses wavelet‐domain hidden Markov models (HMMs) as a powerful tool for statistical modeling of wavelet coefficients. By capturing the interdependence of wavelet coefficients of a measured process variable, a classification strategy is developed that can detect abnormal conditions and classify the process behavior on‐line. The method is extended to include multiple measured variables in detection and classification. Two case studies illustrate the potential of this method.
Hydroamination on homogeneous and heterogeneous catalysts: Kinetic study
Authors: Müller Thomas E. , Lercher Johannes A. , Van Nhu Nguyen
Published: April 2004

This kinetic analysis compares homogeneous and heterogeneous catalysts for the cyclization of 6‐aminohex‐1‐yne. The reaction was studied as a model for the direct addition of amine NH bonds to CC multiple bonds (hydroamination). Kinetic modeling showed that the metal‐catalyzed hydroamination reaction is followed by a proton‐catalyzed isomerization of the primary reaction product, 2‐methylene‐piperidine, to the thermodynamically more stable 2‐methyl‐1,2‐dehydropiperidine.
Dryout phenomena in a three‐phase fixed‐bed reactor
Authors: Cheng Zhen‐Min , Anter Abdulhakeim M. , Fang Xiang‐Chen , Xiao Qiong , Yuan Wei‐Kang , Bhatia Suresh K.
Published: April 2004

Understanding the mechanism of liquid‐phase evaporation in a three‐phase fixed‐bed reactor is of practical importance, because the reaction heat is usually 7–10 times the vaporization heat of the liquid components. Evaporation, especially the liquid dryout, can largely influence the reactor performance and even safety. To predict the vanishing condition of the liquid phase, Raoult's law was applied as a preliminary approach, with the liquid vanishing temperature defined based on a liquid flow rate of zero. While providing correct trends, Raoult's law exhibits some limitation in explaining the temperature profile in the reactor. To comprehensively understand the whole process of liquid evaporation, a set of experiments on inlet temperature, catalyst activity, liquid flow rate, gas flow rate, and operation pressure were carried out. A liquid‐region length‐predicting equation is suggested based on these experiments and the principle of heat balance.
Nitrobenzene adsorption in activated carbon as observed by NMR
Authors: Pel L. , Valckenborg R. M. E. , Kopinga K. , Aarden F. B. , Kerkhof P. J. A. M.
Published: April 2004

The adsorption of nitrobenzene in activated carbon was investigated by nuclear magnetic resonance (NMR). Because of the short relaxation times and carbon is an electrically conducting material, a specially adapted NMR setup was used. It was found that during the adsorption process the nitrobenzene profiles can be scaled using the Boltzmann transformation and the overall effective diffusivity can be approximated by an exponential function of the nitrobenzene content.
Synthesis of silicalite tubular membranes by in situ crystallization
Authors: Lin Xiao , Chen Xiangshu , Kita Hidetoshi , Okamoto Kenichi
Published: April 2004

Silicalite membrane preparation conditions related to membrane separation properties were studied focusing on in situ crystallization to prepare highly selective silicalite membranes on porous tubular supports by a single hydrothermal treatment. The membranes morphologies prepared under typical synthesis conditions were characterized by scanning electron microscopy. The silicalite membrane, well‐oriented with c axis normal to the support surface, could be prepared by in situ crystallization and a seeding method. The membrane separation properties were controlled by synthesis conditions such as seeding, temperatures, supports, and silica sources. Under certain conditions, such factors as tube pore size, played an important role. Silicalite membranes would be prepared better by in situ crystallization than by a seeding method under the same conditions. For example, the highest ethanol/water separation factor of 106 with a flux of 0.9 kg/m2·h for a feed concentration of 5 wt. % ethanol at 60°C was obtained for the silicalite membrane prepared on an unseeded mullite tube at 175°C for 16 h with colloidal silica, whereas the membranes prepared on the silicalite‐seeded tubes had separation factors up to 70. The higher separation selectivity for ethanol over water would be attributed to reduction in nonzeolitic pores, supported by gas permeations of n‐butane and i‐butane.
Multicomponent flash algorithm for mixtures containing polydisperse polymers
Authors: Behme Stefan , Sadowski Gabriele , Song Yuhua , Chen Chau‐Chyun
Published: April 2004

An algorithm called POLYMIX is introduced for flash calculations of multicomponent systems containing polydisperse polymers. The polydispersity of polymers is taken into account through the concept of pseudocomponents. In industrial practice, a relatively high number of pseudocomponents are often required to represent multimodal polymer molecular‐weight distributions. The algorithm formulation is independent of use of specific segment‐based polymer equations of state for computing thermodynamic properties of polymer mixtures. The algorithm further offers the advantage that the computing time for polymer flash calculations is independent of the number of pseudocomponents used to represent the polydisperse polymer. Applications to polymer mixtures containing polyethylene and polypropylene are presented.
Morphology of methane and carbon dioxide hydrates formed from water droplets
Authors: Servio Phillip , Englezos Peter
Published: April 2004

Methane and carbon dioxide hydrate crystals were formed on nearly spherical water droplets at 274.6 K and 2,150 kPa or 1,000 kPa above the corresponding three‐phase hydrate equilibrium pressure. Each experiment was performed with two droplets 5 mm and 2.5 mm in diameter or three droplets with a diameter of 2.5 mm. At the higher pressure the water droplets quickly became jagged and exhibited many needlelike or hairlike crystals extruding from the droplet, whereas at the lower pressure the surface was smooth. In almost all experiments, a depression or collapse of the hydrate layer was observed to occur. This collapse was interpreted as evidence of a continuing hydrate formation after the droplet surface was covered by the hydrate layer. The type of hydrate‐forming gas and the size of the droplet was observed not to influence the macroscopic hydrate crystal morphology. The decomposition of the methane and carbon dioxide hydrate layers was also observed. Reformation was also experimented, and the effect of memory on the morphology of hydrate crystal growth was determined.
Mechanism for N2O formation from NO at ambient temperature
Authors: Wang Jinsheng , Jia Lufei , Anthony Edward J.
Published: April 2004

N2O was reported to form in sample containers of flue gases containing NO and SO2. This could have significant implications for the evaluation of N2O buildup in the atmosphere. Existing models are based either on liquid‐phase reactions, which cannot account for N2O formation at low humidity, or on termolecular reactions, which are not likely to occur at low concentrations. In this work, we propose mechanisms for N2O formation based on gas‐phase reactions, which address the effect of SO2, O2, and moisture. Analytical expressions of the formation rate were derived and compared to reported rates, and rate constants were estimated for limiting cases. The current analyses suggest that N2O2 could be an important precursor for N2O formation from NO, and the mechanism may be important for N2O formation in power‐plant plumes.
Modeling heat and mass transfer in osmotic evaporation process
Authors: Romero J. , Rios G. M. , Sanchez J. , Bocquet S. , Savedra A.
Published: April 2004

A model for the mass‐ and heat‐transfer phenomena in an osmotic evaporation process was developed based on the transfer of solvent from one aqueous solution to be concentrated to a second one separated by a macroporous hydrophobic membrane. The transfer is realized in vapor phase through the membrane porosity as a consequence of the gradient on water activity between both solutions. This technique has the major advantage to work at relatively low temperature and in nearly isothermal conditions, which is very useful to treat thermosensitive products such as fruits and vegetable juices, or other solutions from biotech industries. A series‐resistance model for mass and heat transfer was developed considering four regions, which include the membrane layers and different boundary regions at interfaces. The high values of flow measured in a previous experimental work are compared with those obtained by simulation. In addition, the relative importance of various resistances to overall process performance is established. Basic mechanisms that help optimize membrane structural characteristics, plant design and scale‐up are also discussed.
On‐line monitoring of a crystallization process
Authors: Mougin Patricia , Thomas Alistair , Wilkinson Derek , White Graeme , Roberts Kevin J. , Herrmann Norbert , Jack Robert , Tweedie Richard
Published: April 2004

The application of ultrasonic spectroscopy for particle‐size measurements was investigated during the batch crystallization of (L)‐glutamic acid α‐polymorph from an aqueous solution. The technique, based on measurements of the attenuation of ultrasonic waves through the suspension, was applied using a prototype ultrasonic spectrometer with a flow‐through cell. High‐precision measurements of ultrasonic attenuation in the frequency range 7–110 MHz were performed, the deconvolution of which enabled in‐process measurement of crystal size distribution and solid concentration throughout the crystallization process. In addition to evincing secondary nucleation, growth and crystal breakage on‐line in real time, the experimental results were used to obtain kinetic parameters essential for process design, including secondary nucleation rate and growth rate.
Disturbance models for offset‐free model‐predictive control
Authors: Pannocchia Gabriele , Rawlings James B.
Published: April 2004

Model predictive control algorithms achieve offset‐free control objectives by adding integrating disturbances to the process model. The purpose of these additional disturbances is to lump the plant‐model mismatch and/or unmodeled disturbances. Its effectiveness has been proven for particular square cases only. For systems with a number of measured variables (p) greater than the number of manipulated variables (m), it is clear that any controller can track without offset at most m controlled variables. One may think that m integrating disturbances are sufficient to guarantee offset‐free control in the m controlled variables. We show this idea is incorrect and present general conditions that allow zero steady‐state offset. In particular, a number of integrating disturbances equal to the number of measured variables are shown to be sufficient to guarantee zero offset in the controlled variables. These results apply to square and nonsquare, open‐loop stable, integrating and unstable systems.
Optical and infrared imaging of growing polyolefin particles
Authors: Pater Jochem T. M. , Weickert Günter , van Swaaij Wim P. M.
Published: April 2004

A method was developed that observes polymer particles during a polymerization reaction using optical‐ and infrared imaging. The yielding images give good insight into catalyst‐specific properties as shape replication, distribution of activity, and the activation. The advantage of this method is the possibility to link behavior of individual particles to its own specific properties. The infrared method measures surface temperatures of growing particles. Such data are useful to feed mathematical models describing the growth of single particles. The temperature–time curves showed maximum temperature to be reached after some minutes; a simple model was used to describe this effect qualitatively. The maximum particle temperature rise was 20 K, but depended strongly on reaction rate and particle size. Temperature, prepolymerization method, catalyst recipe, and catalyst activation time were varied for a fourth‐generation Ziegler‐Natta catalyst in polymerization of propylene and ethylene.