bluuebunny/crossref_metadata_2025_split huggingface dataset:
Membrane separation processes: Current relevance and future opportunities
Authors: Strathmann H. 
Published: April 2004

AbstractDuring 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

AbstractAt 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

AbstractThe 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

AbstractAn 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

AbstractOptical 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

AbstractA 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

AbstractCentrifugal 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

AbstractIn 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

AbstractMembrane 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

AbstractThe 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

AbstractGraphical 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

AbstractA 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

AbstractCO 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

AbstractA 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

AbstractA 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

AbstractExperiments 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

AbstractBenzoic 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

AbstractCopolymer 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

AbstractAqueous 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

AbstractCatalytic 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

AbstractVapor‐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.