bluuebunny/crossref_metadata_2025 huggingface dataset:
Integrated membrane process for gold recovery from hydrometallurgical solutions
Authors: Kumar Anil , Haddad R. , Sastre A. M.
Published: April 2004

This work reports the nondispersive solvent extraction (NDSX) of gold cyanide from aqueous alkaline cyanide media with LIX79 and stripping of gold from the organic complex simultaneousty using two microporous hydrophobic polypropylene hollow‐fiber contactors for extraction and stripping, respectively. Extraction was studied under different hydrodynamic conditions and mass‐transfer correlations for shell and tube sides. The mass‐transfer process was compared with experimental results. The HFNDSX was operated with 12–18% LIX 79 in n‐heptane by contacting alkaline cyanide feed containing gold through the tube side and organic extractant through the shell side, which was recirculated between extraction and stripping hollow‐fiber modules through the shell side countercurrently. In the second HF contactor, the stripping solution, 1M NaOH flowed through the tube side countercurrently. Modeling of the system identified rate‐controlling steps under different experimental conditions. The interfacial chemical reaction rate at the dominant surface, and mass‐transfer resistance caused by this reaction controlled the entire extraction process. Several experiments with synthetic solutions of different compositions of gold hydrometallurgical solutions established optimum conditions to achieve a clean separation of Au(I). It was possible to separate Au(I) in the presence of other metal cyanide salts, such us Fe(II), Cu(II), Ni(II), Ag(I), and Zn(II) (NaCN = 1,000–5,000 ppm), which was concentrated in the stripping phase containing NaOH.
Propylene/propane separation by vacuum swing adsorption using 13X zeolite
Authors: Silva Francisco A. Da , Rodrigues Alírio E.
Published: April 2004

A vacuum swing adsorption process using 13X zeolite pellets with five steps was designed to split an equimolar mixture of propylene/propane: pressurization with feed; high‐pressure feed; high‐pressure purge with product; cocurrent blowdown; and counter‐current vacuum blowdown, where the enriched propylene product is withdrawn. In the process, the partial pressure of the C3‐mixture is controlled with nitrogen, which is used as inert gas. With an equimolar feed of C3 diluted to 50% with nitrogen, the column is fed at 5 bar and 423 K, and the product is obtained when the total pressure is lowered to 0.1 bar. After 15–20 cycles, the cyclic steady‐state condition is achieved, a propylene‐enriched stream of 98% mol relative to propylene/propane mixture, with 3.2% of nitrogen, a recovery of 19% (molar basis), and a productivity of 0.785 mol/kg·h is obtained. The experimental work was complemented with numerical simulations, and the effect of different operating parameters on the performance of the VSA was considered.
Three‐dimensional flow patterns in cracking furnaces with long‐flame burners
Authors: Heynderickx Geraldine J. , Oprins Arno J. M. , Marin Guy B. , Dick Erik
Published: April 2004

A 3‐D computational fluid‐dynamics model containing equations for mass, heat and momentum transfer and using a k‐ϵ closure model, was used to calculate the 3‐D flue‐gas flow pattern and the corresponding 3‐D temperature field for a pyrolysis furnace. The computational fluid dynamics model is combined with a reactor model for the cracking tubes and a radiation model for the radiative heat transfer in the furnace box. Detailed reaction kinetics for the naphtha cracking reactions in the tubes nnd a five‐step reaction mechanism for the combustion qf methane in the flames were used. This complete model reveals asymmetric flow patterns in a naphtha‐cracking furnace with 4/2/1 split‐coil reactors and fired with long‐flame burners.
Antisolvent crystallization of anhydrous sodium carbonate at atmospherical conditions
Authors: Oosterhof Harald , Witkamp Geert‐Jan , van Rosmalen Gerda M.
Published: April 2004

When antisolvents are applied to crystallize sodium carbonate from aqueous solutions, the transition temperature at which the hydrates are in equilibrium is decreased. Two models proposed can predict the influence of the amount and type of antisolvent on the transition temperature. Only binary data of the water/sodium carbonate system and measured vapor pressures over ternary soda‐saturated mixtures of water and antisolvent are needed. To validate the two models, continuous crystallization experiments were carried out at various temperatures using ethylene glycol (EG) and diethylene glycol (DEG) as antisolvent, in varying concentrations. Both models predict the influence of the antisolvent on the transition temperature with good accuracy. Anhydrous soda with bulk densities of up to 950 kg/m3 was crystallized at temperatures as low as 80°C.
Thermodynamic activity‐based enzyme kinetics: Efficient tool for nonaqueous enzymology
Authors: Sandoval Georgina C. , Marty Alain , Condoret Jean‐Stéphane
Published: April 2004

Lipase‐catalyzed synthesis reactions must be performed in nonaqueous media (organic solvents or solvent‐free systems). The choice of the optimal solvent is usually a fastidious task that necessitates the determination of kinetic parameters in each solvent. The approach used here, to overcome the lack of a model that can predict the kinetics whatever the solvent, consists in the use of thermodynamic activities instead of concentrations of components, and assumes that activity‐based kinetic parameters are the same in all solvents. This assumption is discussed, and a solution is proposed which takes into account some observed residual solvent effects. The reaction chosen to test this approach was the esterification of oleic acid with ethanol catalyzed by an immobilized lipase, Lipozyme. For this reaction, the kinetics predicted in various organic solvents and in solvent‐free systems is in agreement with the experimental data.
Evaluation of sol‐gel processed BaO·nAl2O3 materials as NOx traps
Authors: Narula Chaitanya K. , Nakouzi Sabine R. , Wu Ruowen , Goralski Christian T. , Allard Lawrence F.
Published: April 2004

Among various strategies to treat NOx, trapping is considered an economical, consumer transparent approach for gasoline engines. The conventional NOx traps are based on alkaline‐earth metal impregnated alumina. These traps work well, but cannot sustain their NOx trapping efficiency after repeated exposure to high temperatures during regeneration. In search of thermally stable materials, a series of sol‐gel processed BaO·nAl2O3 (n = 1, 4, 6) materials including BaO·6Al2O3 molecular sieves were synthesized and evaluated as NOx traps using simulated exhaust at a 25,000 h−1 space velocity. Changes in structure and surface properties occurring on thermal treatment of sol‐gel processed BaO·nAl2O3 materials significantly affect the NOx trapping efficiency of these materials. Among these materials, sol‐gel processed and precious metal impregnated BaO·6Al2O3 powder offers the optimum combination of thermal stability and NOx trapping efficiency. We deposited this powder on a honeycomb substrate, impregnated it with 2% Pt and 0.4% Rh, and reevaluated it. The NOx trapping efficiency of this catalyst is 95% (cf. 75% for the powder) at 310°C. Our data on Pt/BaO·6Al2O3 also suggest that the optimum lean cycle length for this class of NOx traps is 1 min. The efficiency of NOx traps decreases rapidly and falls in 10–20% range with an alternating 5 min lean cycle and 1 min rich cycle.
Numerical simulations of pool‐boiling heat transfer
Authors: Dhir Vijay K.
Published: April 2004

Boiling has been studied extensively during the last half of the 20th century. Many correlations and semimechanistic models have also been developed for various modes of boiling. However, due to the complexity involved in modeling continuously evolving vapor–liquid interfaces, unrealistic assumptions are often made in developing various models. With the advances of recent years in the area of computational science and engineering, it is now possible to solve, completely, the conservation equations of mass, momentum, and energy for liquid and vapor phases simultaneously when an interface is continuously evolving at and near a heated surface. The solutions provide not only detailed physics of associated thermal and hydrodynamic processes, but also the shape of the evolving interface. In demonstrating the application of numerical simulations as an effective tool, both pool nucleate and film boiling at normal earth gravity, and nucleate boiling under microgravity conditions are considered. Although these simulations have been computationally intensive, in the future calculations of this type are expected to become routine.
Simulation of the dynamics of depth filtration of non‐Brownian particles
Authors: Burganos V. N. , Skouras E. D. , Paraskeva C. A. , Payatakes A. C.
Published: April 2004

A new simulator for flow of aqueous suspensions and deposition of non‐Brownian particles in granular media can predict the pattern of deposition and concomitant reduction in permeability as functions of depth, time and system parameters. The porous structure of the granular medium represented as a 3‐D network of constricted pores considers the converging–diverging character of flow within pores. Using Lagrangian‐type simulation the particle deposition rate was calculated. Gravity and drag, as well as hydrodynamic and physicochemical interactions between suspended particles and pore walls, were considered in calculating 3‐D particle trajectories. Deposit configurations were computed, and the evolution of the pore structure was simulated at discrete time steps. Changes in the pore geometry and nature of the collector surface affect flow and trajectory computations directly. Clusters of deposited particles were allowed to become reentrained if exposed to shear stress higher than a critical value. Reentrained clusters, which moved through downstream pores, might redeposit downstream at suitable sites and cause clogging of sufficiently narrow pores. Particle clusters clogging pores have a finite permeability, which significantly affects the system's transient behavior. Clogged pores act as collectors of solitary particles and of reentrained clusters, and substantially affect the transient behavior of the filter. The loss of permeability was monitored by calculating pore and network hydraulic conductance at each time step. Numerical results for the loss of permeability, temporal evolution of filter efficiency, and specific deposit profiles are based on suspension flow simulations in a typical granular porous medium.
Qualitative/quantitative simulation of process temporal behavior using clustered fuzzy digraphs
Authors: Li R. F. , Wang X. Z.
Published: April 2004

A methodology is presented for qualitative modeling and simulation of the temporal behavior of individual variables and the composite process. The temporal behavior of a variable in a windowed time scale is captured categorically using principal‐component analysis, while the process is modeled as a causal digraph with interacting and recycle nodes. Rigorous, rather than ad hoc, reasoning rules can be devised for the causal digraph using a learning mechanism. Quantitative information can also be incorporated into the method with the introduction of fuzzy c‐means clustering without compromising the cognitive level of information embedded in the nodes and the digraph.
Analyzing mixing in periodic flows by distribution matrices: Mapping method
Authors: Kruijt Peter G. M. , Galaktionov Oleksiy S. , Anderson Patrick D. , Peters Gerrit W. M. , Meijer Han E. H.
Published: April 2004

A novel mapping method presented analyzes the long‐term efficiency of distributive mixing in Stokes flows. It uses the results of an accurate front tracking technique to calculate a distribution or mapping matrix. For the first time, it is possible to efficiently investigate the influence of geometric configurations and operating conditions on overall mixing quality. The technique was tested using the mixing dynamics of a model time periodic prototype flow; namely Stokes flow in a 2‐D, lid‐driven cavity. The method however, can also be extended to examine more realistic spatially periodic flows such as static mixers or twin screw extruders.
Comparative analysis of CFD models of dense gas–solid systems
Authors: van Wachem B. G. M. , Schouten J. C. , van den Bleek C. M. , Krishna R. , Sinclair J. L.
Published: April 2004

Many gas–solid CFD models have been put forth by academic researchers, government laboratories, and commercial vendors. These models often differ in terms of both the form of the governing equations and the closure relations, resulting in much confusion in the literature. These various forms in the literature and in commercial codes are reviewed and the resulting hydrodynamics through CFD simulations of fluidized beds compared. Experimental data on fluidized beds of Hilligardt and Werther (1986), Kehoe and Davidson (1971), Darton et al.(1977), and Kuipers (1990) are used to quantitatively assess the various treatments. Predictions based on the commonly used governing equations of Ishii (1975) do not differ from those of Anderson and Jackson (1967) in terms of macroscopic flow behavior, but differ on a local scale. Flow predictions are not sensitive to the use of different solid stress models or radial distribution functions, as different approaches are very similar in dense flow regimes. The application of a different drag model, however, significantly impacts the flow of the solids phase. A simplified algebraic granular energy‐balance equation is proposed for determining the granular temperature, instead of solving the full granular energy balance. This simplification does not lead to significantly different results, but it does reduce the computational effort of the simulations by about 20%.
Heat conduction in granular materials
Authors: Vargas Watson L. , McCarthy J. J.
Published: April 2004

Heat transfer in particulate systems is important to a vast array of industries, yet is poorly understood even in the simplest case—conduction through the solid phase. This is due in part to the stress and contact heterogeneities inherent to these systems. Heat conduction in a packet bed of cylinders is investigated both experimentally and computationally. A novel model is developed based on the Discrete Element Method, which not only sheds light on fundamental issues in heat conduction in particles, but also provides a valuable test bed for existing theories. By explicitly modeling individual particles within the bulk material, bed heterogeneities are directly included, and dynamic temperature distributions are obtained at the particle level. Comparison with experiments shows that this model yields a quantitatively accurate temperature field without the need for adjustable parameters or detailed microstructural information. This simple system may also provide insight into such phenomena as reactor hot spot formation and spontaneous combustion of bulk reactive materials.
Membrane separation processes: Current relevance and future opportunities
Authors: Strathmann H.
Published: April 2004

During the last 35 years membranes have evolved from a laboratory tool to industrial products with significant technical and commercial impact. Today, membranes are used for desalination of sea and brackish water and for treating industrial effluents. They are efficient tools for the concentration and purification of food and pharmaceutical products and the production of base chemicals. Furthermore, membranes are key components in artificial organs, drug delivery devices, and energy conversion systems. In combination with conventional techniques membranes often provide cleaner and more energy‐efficient production routes for high‐quality products. Fundamental aspects of membranes and membrane processes are discussed, as well as technically and economically effective applications. The present and future membrane market is assessed and new developments and future research needs are discussed.
Molecular simulation of adsorption: Gibbs dividing surface and comparison with experiment
Authors: Talu Orhan , Myers Alan L.
Published: April 2004

At low temperature near the normal boiling point, computer simulations of adsorption of gases can be compared directly with experiment. However, for adsorptive gas separations in which the gas is adsorbed near or above its critical temperature, absolute simulation variables must be converted to excess variables for comparison with experiment. The conversion of absolute to excess variables requires the helium pore volume of the adsorbent. Lennard‐Jones potential parameters for helium gas molecules interacting with the oxygen atoms of silicalite are ϵ/k = 28.0 K and σ = 2.952 Å. The helium pore volume of silicalite is 0.175 cm3/g. Lennard‐Jones potential parameters derived for Ar‐O interactions in silicalite are ϵ/k = 93.0 K and σ = 3.335 Å. Density profiles for adsorption of argon in silicalite at 300 K show that the local density is highest in the middle of the channels where the gas‐solid potentials overlap.
Measurement of gibbsian surface excess
Authors: Sircar S.
Published: April 2004

The Gibbsian Surface Excesses (GSE) are the true experimental variables for measurement of equilibria and kinetics for pure and multicomponent gas‐solid adsorption. The gravimetric and volumetric methods, which are the most commonly used experimental procedures, are revisited. The common practice of ignoring helium adsorption during measurement of adsorbent density by helium pycnometry and measurement of void volumes in adsorption apparatus by helium expansion can lead to large errors in estimating GSE at high pressures and for less selectivity adsorbed components of a gas mixture. Methods to overcome these problems are described.
Quartz capillary microreactor for studies of oxidation in supercritical water
Authors: Maharrey Sean P. , Miller David R.
Published: April 2004

An inexpensive, low‐power quartz capillary flow reactor was designed to investigate the global reaction rate for the supercritical water oxidation of acetic acid. The effluent from the ∼0.1 cm dia. quartz microreactor is such that it is easily incorporated into an online spectroscopic or vacuum mass spectrometer detection system. The reactor is capable of operating up to 28 MPa and 530°C. Standard HPLC sample injection valves permit the rapid change of reactant composition. This reactor is a nonisothermal design and requires a heat‐transfer calculation that involves coupling the transport equations for momentum, mass, and heat with the chemical kinetics equations. A numerical calculation presented includes a rigorous treatment of the equation of state and the transport properties of pure water. With this design, the global rate data was fitted to the following form: rA = −9.3 ± 0.7 × 1010e−(172.2 ± 1.7)/RT [CHOAc ]0.89 ± 0.07 [CPeroxide ]0.2 ± 0.1 (M/s).
CO2 sorption of a thin silica layer determined by spectroscopic ellipsometry
Authors: Benes Nieck E. , Spijksma Gerald , Verweij Henk , Wormeester Herbert , Poelsema Bene
Published: April 2004

Optical properties of a thin amorphous silica membrane and the supported γ‐alumina layer on which it was coated were obtained from spectroscopic ellipsometry. The thicknesses of γ‐alumina and silica layers from ellipsometric spectra were 1.654 μm and 73 nm, respectively. The porosity of the γ‐alumina layer was 51%. The porosity of the silica layer (15–25%), appeared to be smaller than that of unsupported silica material prepared by a similar method. Determination of the porosity of the silica layer, however, was quite inaccurate, because optical properties of the pure material were not exactly known. Ellipsometry was also used to determine the sorption behavior of CO2 in the γ‐alumina and silica layers. For both layers the observed sorption behavior could be described by a Langmuir isotherm (c = 0.84 and 2.8–3.0 mmol·g−1, respectively), with Arrhenius‐type temperature dependence (sorption heat 24.6±1.0 and 27.0±1.3 kJ·mol−1, respectively). The adsorption behavior of supported and unsupported γ‐alumina appeared to be similar. The heat of sorption was larger for supported thin silica layers than for unsupported bulk silica, suggesting smaller pores in the thin layer.
Phase boundary calculations for solutions of a polydisperse polymer
Authors: Koak Naveen , Heidemann Robert A.
Published: April 2004

A technique is described for performing phase boundary calculations (cloud‐point calculations) for solutions of a polydisperse polymer in a solvent component. The polymer is characterized as a potentially large number of individual components. The technique employs the Newton method for solving the nonlinear equilibrium equations. The independent variables in the equations are logarithms of the equilibrium ratios, temperature and pressure, and the mass ratio of polymer to solvent. A number of cloud‐point curves were calculated using the Sanchez–Lacombe equation as the thermodynamic model. The calculations were compared with experimental data for polyethylene (MW = 177,000 and MN = 8,000) with n‐hexane and polyethylene (MW = 99,000 and MN = 56,000) with ethylene. As expected, the disperse nature of the polymer significantly affected the calculated phase behavior of the polymer–solvent mixtures. Complicating features in the calculations are discussed.
Hydrodynamics of countercurrent two‐phase flow in a centrifugal field
Authors: Bisschops M. A. T. , Luyben K. Ch. A. M. , van der Wielen L. A. M.
Published: April 2004

Centrifugal adsorption technology (CAT) is a new method for continuous adsorption and ion exchange involving countercurrent flow of liquid and micrometer‐range adsorbent particles under the influence of a centrifugal force. Due to the fast adsorption kinetics associated with very small particles, CAT leads to extremely compact separation equipment with high capacities and excellent mass‐transfer efficiencies. Experimental results on the hydrodynamics of countercurrent flow of solids and liquid in a centrifugal field are discussed in terms of flooding conditions, pressure drops and holdup of the adsorbent particles in the contactor. A model developed based on the relations for homogeneous fluidization under gravity correctly describes countercurrent flow under gravity, but does not correctly describe countercurrent flow in a centrifugal field. In general, observed capacities of this model are higher than estimated. Although the centrifugal force magnifies the apparent density difference between the two phases, the two‐phase flow did not seem to exhibit heterogeneous behavior, such as observed in gas‐fluidized beds.
Three‐dimensional wall jets: Axial flow in a stirred tank
Authors: Bittorf Kevin J. , Kresta Suzanne M.
Published: April 2004

In this article, the flow at the wall of a stirred tank is compared with turbulent wall jet behavior. Agreement is shown to be very good. For all three axial impellers studied, the wall jet is three dimensional along the wall and baffle of the tank. The expansion of the jet is linear, and the maximum velocity decays with 1/z, where z is the dimensionless axial distance. These wall‐jet characteristics help further the fundamental understanding and modeling of the bulk flow in a stirred tank and provide meaningful test data for CFD validation.
Process fundamentals of membrane emulsification: Simulation with CFD
Authors: Abrahamse A. J. , van der Padt A. , Boom R. M. , de Heij W. B. C.
Published: April 2004

Membrane emulsification is a process in which a to‐be‐dispersed phase is pressed through a membrane; the droplets formed are carried away with the continuous phase. To design a suitable membrane setup, more insight into the formation of the droplets at the membrane surface is needed. Therefore, the formation of one droplet from a cylindrical pore was calculated using computational fluid dynamics. From the resulting droplet diameter (33 μm; pore diameter, 5 μm) and the calculated droplet shape, the maximum membrane porosity was calculated to be 1.5%, to prevent coalescence of droplets growing on neighboring pores. Due to the deformation of the droplet and the formation of the neck, the pressure drop over the pore and the velocity of oil in the pore varied in time. During necking, the velocity in the pore decreased sharply. After detachment of the first droplet, no satellite droplets were formed, but a small oil volume remained attached at the pore, forming a new droplet.
Detailed modeling of stationary and transient mass transfer across pervaporation membranes
Authors: Bausa Jürgen , Marquardt Wolfgang
Published: April 2004

The slow dynamic behavior of mass transfer in pervaporation has been reported by different authors. Until now, however, only a little experimental data and no model capable to describe this phenomenon have been available. A new detailed model for mass transfer in pervaporation, based on the dual‐sorption theory, Maxwell‐Stefan diffusion, and the UNIQUAC model, is proposed. This model is capable of properly describing mass transfer at steady state and during transients. Model parameters for two different PVA/PAN membranes for ethanol/water separation are given. The model shows good agreement with both steady state and dynamic experimental data.
Graphical design applied to MTBE and methyl acetate reactive distillation processes
Authors: Lee Jae W. , Westerberg Arthur W.
Published: April 2004

Graphical tray‐by‐tray methods for reactive distillation columns we developed previously are extended to study two industrial processes: MTBE production and methyl acetate production. As both processes involve four components, projection was used to obtain ternary diagrams by ignoring the inert (n‐butane) for MTBE production and by projecting onto planes of constant acetic acid concentrations for methyl acetate production. These projected methods clearly explain the placing that industry uses for the reaction zones in these processes. Further, it can be visualized why there is an optimum reflux ratio for the methyl acetate process and a value can be quantitatively predicted for it that lies within the range the literature reports.
Predictive membrane transport model for nanofiltration processes in water treatment
Authors: Tu Shih‐Chieh , Ravindran Varadarajan , Den Walter , Pirbazari Massoud
Published: April 2004

A membrane transport model was developed for prediction and simulation of membrane filtration (nanofiltration) dynamics with reference to permeate flux. It incorporates important phenomenological aspects of membrane transport, such as concentration polarization and gel layer formation, and illustrates the concentration of solutes as foulants in the mass‐transfer boundary layer on the membrane surface. Membrane filtration tests using tannic acid as a model organic compound were designed for investigating permeate fluxes, as well as solute concentration profiles for permeates and concentrates. Membrane performance experiments were conducted under various operation conditions by varying several parameters including solute concentrations, transmembrane pressures, and reject flow rates. The tests showed that the NF‐45 membrane composed of polypiperazine amide was more susceptible to organic fouling by tannic acid than the NF‐70 membrane made of cross‐linked aromatic polyamide. These observations were supported by surface‐potential measurements that demonstrated higher negative surface charges and greater hydrophilicity for the NF‐70 membrane in the presence of tannic acid. The predictive capability of the membrane transport model was evaluated using the results from membrane filtration tests. Model sensitivity studies were conducted to obtain information on effects of various input parameters pertaining to operating conditions and fluid‐dynamic regimes.
Spatiotemporal patterns during CO oxidation on Pt(100) at elevated pressures
Authors: Lele Tanmay P. , Pletcher Timothy D. , Lauterbach Jochen
Published: April 2004

CO oxidation on Pt(100) was investigated at reactant pressures of 8 Pa using ellipsomicroscopy for surface imaging to monitor spatiotemporal pattern formation on the catalyst surface and mass spectroscopy to monitor the integral reaction rate. Three distinct temperature regions showing nonlinear phenomena were found. The first region, at 540–615 K, is characterized by macroscopic, regular reaction‐rate oscillations with spatially uniform, instantaneous transitions between CO and oxygen covered states. Regular, periodic oscillations were not observed on Pt(100) before. The second region, 480–540 K, exhibited continuous dynamic pattern formation with no visible macroscopic kinetic oscillations. Front speeds measured indicated a decrease in oxygen front velocity and an increase in CO front velocity with an increasing CO/O2 partial pressure ratio. The third region, 390–430 K, is characterized by macroscopic rate oscillations, which continued for several oscillation periods and then ceased with the onset of pattern formation.
Inversion algorithms for particle sizing with photon migration measurement
Authors: Sun Zhigang , Sevick‐Muraca Eva M.
Published: April 2004

A new linear inverse method is demonstrated for recovery of particle‐size distribution (PSD) and volume fraction of opaque colloidal suspensions from frequency domain photon migration (FDPM) measurement of multiply scattered light. To deal with the ill posedness of PSD retrieving problem, the size distribution is approximated by the B‐spline expansion. Tikhonov regularization, along with both nonnegativity and smoothing constraints, in which the L‐curve method is employed to choose a regularization parameter, are also used to ensure the stable and realistic solution. The algorithm is tested using synthetic FDPM measurements at a variety of size distributions, and results are compared using other inverse methods. The influences of model and measurement error are investigated. To demonstrate our inversion approach, PSD and volume fraction of opaque titanium dioxide suspensions are recovered from actual FDPM measurements. This work demonstrates the ability of FDPM method to characterize colloidal suspensions.
Heat and mass transport in microwave drying of porous materials in a spouted bed
Authors: Feng H. , Tang J. , Cavalieri R. P. , Plumb O. A.
Published: April 2004

A heat‐ and mass‐transfer model was developed to simulate microwave and spouted‐bed combined (MWSB) drying of diced apples, a hygroscopic porous material. A total gas‐pressure equation was introduced to take into account internal vapor generation during microwave drying. The governing equations for heat and mass transfer were simplified using a scaling technique and numerically solved with the finite difference method. The physical, thermodynamic, thermal, transport and dielectric properties used in the simulation were either from our measurements or from the literature. Model predictions agreed well with experimental results. The pressure‐driven moisture migration during MWSB drying resulted in a high drying rate. The numerical analysis predicted a temperature‐leveling effect that was confirmed by experimental results. The unique temperature leveling in MWSB drying helps to control product temperature and improves product quality as compared to microwave‐assisted fixed‐bed hot‐air drying methods.
Spontaneous imbibition processes in Hele‐Shaw cells
Authors: Hayashi José A. , Soria Alberto
Published: April 2004

Experiments on spontaneous imbibition processes in Hele‐Shaw cells were carried out in squared cells (20 cm × 20 cm) with separations of 0.005, 0.015 and 0.075 cm using twice‐distilled water and Soltrol 170 as the displacing and displaced fluids, respectively. The experiments indicated that it was possible to repeat the main features of the spontaneous imbibition process using a procedure for wettability restoration of the glass sheets. The best sweep efficiency was achieved for the 0.015 cm cell gap. Two or three consecutive stages occurred depended on the cell gap, as evidenced by a characteristic speed and a characteristic advancing front structure. The initial stage speed/development stage speed ratio and the oil total area/water‐oil total interfacial length ratio as functions of time were gap‐dependent. The capillary number and interfacial power density estimations indicated that at about 0.033 cm gap there was a flow pattern transition from slightly uniform displacement to fingering flow.
Reaction crystallization kinetics of benzoic acid
Authors: Ståhl Marie , Åslund Bengt L. , Rasmuson Åke C.
Published: April 2004

Benzoic acid was crystallized in a T‐mixer by mixing hydrochloric acid and an aqueous sodium benzoate solution. Crystallization kinetics were determined by population balance modeling and parameter estimation by nonlinear optimization. The evaluation of several models showed that the model has to be carefully designed. The objective function is highly nonconvex, and the results have to be scrutinized to identify the appropriate optimum. Growth‐rate dispersion needs to be accounted for to obtain a reasonable description of experimental product‐size distributions. Six parameters of nucleation and growth kinetics were determined simultaneously in an optimization that includes experimental product‐size distributions from 14 experiments at 8 different initial supersaturations. The interfacial energy calculated from the corresponding nucleation parameter is 0.015 J/m2. The exponent of the normal power law growth‐rate equation receives a value of 2.1, suggesting that growth is controlled by surface integration. The value becomes 2.9 if the logarithm of the supersaturation ratio is used as the driving force. The coefficient of variation of the growth‐rate distribution depends only weakly on supersaturation and receives a value of 0.23 if this dependence is neglected. The final model describes experimental data well. The estimated parameters are physically reasonable and provide a physically reasonable description of the entire experiment.
Simultaneous control of copolymer composition and MWD in emulsion copolymerization
Authors: Vicente M. , Leiza J. R. , Asua J. M.
Published: April 2004

Copolymer composition and molecular‐weight distribution of linear copolymers were controlled simultaneously by maintaining concentrations of the monomers and chain‐transfer agent (CTA) at calculated values. The unreacted amounts of monomers and CTA were inferred by on‐line measurements of the reaction heat. Styrene/n‐butylacrylate emulsion copolymers of predefined constant compositions and MWDs (narrow and broad monomodal, and bimodal with different polydispersities index in each mode) were obtained by this control approach using tertdodecyl mercaptan as CTA.
Impact of common salts on oxidation of alcohols and chlorinated hydrocarbons
Authors: Suppes G. J. , Roy S. , Ruckman J.
Published: April 2004

Aqueous oxidations of phenol, methanol, ethanol, n‐propanol, n‐butanol, chloroethanol, chloropropane and chlorobutane were conducted to evaluate the impact of common salts and bases on oxidation with hydrogen peroxide. Oxidation rates increased up to greater than two orders of magnitude, depending on the electrolytes. Sodium and potassium electrolytes generally promoted oxidation at temperatures near 100°C with sodium promoting oxidation better than potassium. Ionic interactions among electrolytes change the nature of their catalytic activity. In the presence of nitric acid, calcium was the most effective of these metals for promoting oxidation. Using soluble salts is proposed for wet‐air oxidation and contaminated soil treatment.
Steam and oxysteam reforming of methane to syngas over Cox Ni1−x O supported on MgO precoated SA‐5205
Authors: Choudhary Vasant R. , Mamman Ajit S. , Uphade Balu S.
Published: April 2004

Catalytic steam and oxysteam reforming of methane to syngas studied involves coupling of exothermic oxidative conversion and endothermic steam‐reforming processes over Cox Ni1−x O (x = 0.0–0.5) supported on MgO precoated commercial low surface area (<0.01 m2 g−1) macroporous silica‐alumina SA‐5205 catalyst carrier. The influence of the Co/Ni ratio of the catalyst on its performance in steam and oxysteam reforming processes (at 800 and 850°C) was studied. For the steam reforming process, the Co/Ni ratio influences strongly on the methane and steam conversion and CO selectivity and product H2/CO ratio, particularly at lower temperature. When the Co/Ni ratio is increased, the methane and H2 O conversion and CO selectivity are decreased markedly. For the oxysteam reforming process, the influence of the Co/Ni ratio on the performance is smaller and depends on process conditions. When the Co/Ni is increased, the methane conversion passes through a maximum at the Co/Ni ratio of 0.17. The influence of the reaction temperature (800 and 850°C) and CH4/O2 and CH4/H2 O ratios on the conversion, selectivity, H2/CO product ratio, and net reaction heat (ΔHr ) was studied in the oxysteam reforming (at space velocity of 47,000 cm3·g−1·h−1) over the catalyst with an optimum Co/Ni ratio (0.17) and a higher Co/Ni ratio (1.0). The oxysteam reforming process involves coupling the exothermic oxidative conversion of methane and the endothermic methane steam reforming reactions, making the process highly energy‐efficient and nonhazardous. This process can be made thermoneutral, mildly exothermic, and mildly endothermic by manipulating process conditions.
Molecular simulation of complete phase diagrams for binary mixtures
Authors: Lamm Monica H. , Hall Carol K.
Published: April 2004

Vapor‐liquid, vapor‐solid and liquid‐solid coexistence lines are calculated for binary mixtures of Lennard‐Jones spheres using Monte Carlo simulation and the Gibbs‐Duhem integration technique. Complete phase diagrams showing equilibrium between vapor, liquid and solid phases are constructed for binary Lennard‐Jones mixtures with diameter ratios ranging from σ11 /σ22 = 0.85–1.0 and attractive well‐depth ratios ranging from ϵ11/ϵ22 = 0.625−1.6, at a reduced pressure P*≡Pσ/ϵ11 = 0.002. The Lorentz‐Berthelot combining rules are used to calculate the cross‐species interaction parameters σ12 and ϵ12. The variation in the shape of the complete phase diagrams change as a function of the diameter ratio σ11 /σ22 and well‐depth ratio ϵ11 /ϵ22 is systematically explored. The phase diagrams found here resemble those found experimentally for argon‐methane, iodine‐sulfur, water‐sodium chloride, water‐silver nitrate, water‐potassium nitrate, and p‐dichlorobenzene‐p‐dibromobenzene.
Hydrate phase equilibria of a near critical fluid: Effect of inhibition and separation
Authors: Østergaard Kasper K. , Tohidi Bahman , Burgass Rod W. , Danesh Ali , Todd Adrian C.
Published: April 2004

The hydrate phase boundary of a near critical fluid (NCF) was measured at 275–289 K in the presence of distilled water, synthetic formation water, and synthetic formation water with 10.41 wt. % methanol. The results agreed well with the predictions of an in‐house model, based on a cubic equation of state and statistical thermodynamics. To simulate a typical oil/gas production scenario, the NCF was flashed at 298.1 K and 17.189 MPa, and the resulting liquid was subsequently flashed at 298.0 K and 4.089 MPa. Hydrate free zones of the resulting liquid fractions were measured to investigate the physical separation effect on the hydrate phase boundary. The in‐house thermodynamic model was used to simulate the separators conditions and to predict the hydrate free zone of the resulting liquid and the vapor fractions. The predictions agreed closely with the experimental data, demonstrating reliability of the thermodynamic model. The results also showed that the hydrate phase boundaries of the vapor and liquid phases, which resulted from physical separation, are similar to that of the NCF.
Suspension polymerization of acrylamide in an oscillatory baffled reactor: From drops to particles
Authors: Ni X. , Johnstone J. C. , Symes K. C. , Grey B. D. , Bennett D. C.
Published: April 2004

Droplet and particle‐size distribution of inverse phase suspension polymerization of acrylamide was studied in an oscillatory baffled reactor (OBR). A discretized population balance model developed estimates the coalescence droplet rate and the type of droplet interactions contributing to the coalescence process in the system. In an OBR, fluid mixing is achieved by eddies generated when a set of prespecified orifice baffles moves periodically through liquid. These vortices can be controlled by a combination of geometrical and operational parameters, such as orifice diameter, baffle spacing, oscillation frequency, and oscillation amplitude. This type of mixing, combining with a close‐to‐constant level of turbulence intensity in the reactor, has led to a high degree of controllability and repeatability for both droplet and particle size, and a fine particle level significantly lower than a conventional stirred‐tank reactor. Generic correlation is established linking the final bead size and Sauter mean droplet size with power dissipation.
Design for model parameter uncertainty using nonlinear confidence regions
Authors: Rooney William C. , Biegler Lorenz T.
Published: April 2004

An accurate method presented accounts for uncertain model parameters in nonlinear process optimization problems. The model representation is considered in terms of algebraic equations. Uncertain quantity parameters are often discretized into a number of finite values that are then used in multiperiod optimization problems. These discrete values usually range between some lower and upper bound that can be derived from individual confidence intervals. Frequently, more than one uncertain parameter is estimated at a time from a single set of experiments. Thus, using simple lower and upper bounds to describe these parameters may not be accurate, since it assumes the parameters are uncorrelated. In 1999 Rooney and Biegler showed the importance of including parameter correlation in design problems by using elliptical joint confidence regions to describe the correlation among the uncertain model parameters. In chemical engineering systems, however, the parameter estimation problem is often highly nonlinear, and the elliptical confidence regions derived from these problems may not be accurate enough to capture the actual model parameter uncertainty. In this work, the description of model parameter uncertainty is improved by using confidence regions derived from the likelihood ratio test. It captures the nonlinearities efficiently and accurately in the parameter estimation problem. Several examples solved show the importance of accurately capturing the actual model parameter uncertainty at the design stage.
Experimental study of gas‐induced liquid‐flow structures in bubble columns
Authors: Degaleesan S. , Dudukovic M. , Pan Y.
Published: April 2004

The computer‐automated radioactive‐particle tracking (CARPT) technique is used to investigate liquid recirculation and turbulence in bubble columns. Experiments are conducted in air–water bubble columns of different sizes, with various gas distributors, and operated over a range of superficial gas velocities. This study covers gas–liquid flows from the bubbly regime to the churn turbulent regime. The time‐averaged spatial flow structure, axial liquid velocity profiles, Reynolds shear stress, and turbulence intensities profiles are analyzed for different columns and flow conditions. Supplementary experiments, using the hot‐probe anemometry technique, are performed at selected flow conditions, and the results are compared with the corresponding ones from CARPT measurements. The Reynolds stress determined by CARPT was compared with that obtained by hot‐film anemometry in an independent investigation by Menzel et al. (1990).
Analysis of temperature and pressure fields in molten carbonate fuel cell stacks
Authors: Koh Joon‐Ho , Kang Byoung Sam , Lim Hee Chun
Published: April 2004

A mathematical model based on fluid dynamics and heat‐transfer theories was applied to predict gas dynamic pressure and temperature distribution in a coflow molten carbonate fuel cell (MCFC) stack. The mass balance was simplified to obtain exact solutions with an assumption of uniform current density in the cell. The simulations were compared with data from a pilot‐scale MCFC stack. The effect of internal geometry of gas channels was simulated to accurately predict the gas‐pressure drop. A close prediction of pressure drop was possible from a partially blocked gas channel model that approximates the significant flow resistance. The effect of external boundary conditions on stack temperature profile was also analyzed. Temperatures were accurately predicted from a boundary heat conduction model with a reasonable assumption of wet seal temperatures. The 2‐D boundary conditions could be extended to 3‐D simulations to predict temperature distribution with the same accuracy. The model was applied to see the effect of scale‐up on the maximum temperature rise and average cell potential. The result verified a significant effect of cell size on the maximum stack temperature.
Tracer studies of high‐shear granulation: II. Population balance modeling
Authors: Hounslow M. J. , Pearson J. M. K. , Instone T.
Published: April 2004

A population balance framework developed describes the tracer studies in Part I. A two internal coordinate population balance equation (PBE) links the evolution with time of granule‐size and tracer‐mass distributions to underlying rate processes. A new analytical PBE was developed for the tracer distribution and novel numerical techniques, including a new discretized population balance equation for breakage or grinding. Also developed is a general differential technique for extracting rate constants from measurements of particle‐size distributions. Granulation in a high‐shear mixer proceeds after nucleation, not studied here, with very high initial breakage rates but a relatively unchanging aggregation rate constant. The breakage function is bimodal on a mass basis and the selection rate decays exponentially over about 20 s. A heterogeneous strength hypothesis was used to account for this time dependence. Aggregation rates are the highest for interactions between small and large granules and may be quantitatively given by the Equipartition of kinetic energy kernel developed from the theory of collisions between gas molecules. The model can describe granule‐size and tracer‐mass distributions simultaneously with great accuracy. The need to replace time as a driving force variable in the kinetics for these systems is identified.
Local phase holdups in gas‐solids fluidization and transport
Authors: Bi Hsiaotao T. , Su Peng‐Cheng
Published: April 2004

A two‐phase structural model consisting of a dense phase and a dilute phase with allowance for the dense‐phase expansion and the solids holdup in the dilute phase was developed and successfully applied to the analysis of local voidage fluctuation signals. Such a model can be used to derive local‐phase holdups and voidage in each phase in both bubbling/slugging/turbulent fluidized beds and circulating fluidized‐bed risers without ambiguity in defining criteria for dividing phases used by previous researchers. Such a model can also explain the existence of a maximum standard deviation at a local voidage around 0.7, and why a maximum peak is observed in the radial profiles of standard deviation of local voidage fluctuations in high‐velocity fluidized‐bed columns.