bluuebunny/crossref_metadata_2025_split huggingface dataset:
Electrolytic membrane recovery of bromine from waste hydrogen bromide streams
Authors: Wauters Cary N. , Winnick Jack 
Published: April 2004

AbstractA novel electrochemical process was developed for the recovery of bromine from waste gas‐phase hydrogen bromide streams. It uses a molten‐salt‐saturated membrane to electrolytically decompose hydrogen bromide into its molecular constituents, which are separated into a hydrogen‐enriched waste stream and a pure bromine product stream. Single‐cell studies were carried out in a configuration consisting of two cell housings (vitreous carbon), two gas‐diffusion electrodes (reticulated vitreous carbon or graphite felt), and a molten salt [(Li0.575K0.133Cs0.292)Br] saturated membrane (zirconia). Single‐cell results at 300°C, based on process stream concentrations ranging from 25 to 75% hydrogen bromide at 50 to 300 mL/min, demonstrated current densities exceeding 1 A/cm2 and removals as high as 95%. Water and acetone (as a light organic contaminant) addition to the process feed, as well as exposure to thermal cycling, showed no deleterious effects on cell performance. Preliminary economics indicate this to be a viable process.
Fractional crystallization by gas antisolvent technique: Theory and experiments
Authors: Bertucco Alberto , Lora Michele , Kikic Ireneo 
Published: April 2004

AbstractThe efficacy of CO2 us an antisolvent was studied experimentally for the precipitation of naphthalene and phenanthrene from their solutions in toluene at 298 and 310 K. Phenanthrene was salted out of solution at every condition investigated, whereas naphthalene was never segregated as a solid phase. These behaviors are explained by a model representing the composition of the phases and supersaturation of the solution as functions of pressure. Based on results from ternary systems, experiments were performed with the quaternary system CO2‐toluene‐naphthakne‐phenanthrene: starting from an equimolar solution of the two solids in toluene, phenanthrene with a purity higher than 98.5% can be collected in the precipitation cell, while naphthalene with about 13% of phenanthrene is recovered from the liquid phase after expansion. The simulation of the process was able to account for the experimental evidence. Although the solutes used do not have a practical application, a general method is outlined to exploit the possibility of using the supercritical antisolvent technique for separation.
Role of porosity in filtration: XIII. Behavior of highly compactible cakes
Authors: Tiller Frank M. , Kwon Jae Hyun 
Published: April 2004

AbstractCompatibility of cakes and sediments is a key factor in the behavior of thickeners, filters, centrifuges and belt presses. Stress applied to cakes decreases porosity and increases resistance to flow. Empirical models presented here represent solidosity (volume fraction of solids) εs, specific resistance α and permeability K as functions of effective pressure ps that are essential to developing mathematical models of thickening, filtration, and centrifugation. As suspensions are flocculated, the resulting aggregates become increasingly fragile and more compactible. Cake behavior undergoes substantial change, until it reaches a point at which increasing pressure unexpectedly no longer affects either % cake solids or filtrate volume vs. time. Traditional formulas for filtrate volume vs. time and average values of α, K, and εs were modified for highly compactible materials. The average value of α is proportional to the pressure drop across the cake and the average permeability is inversely proportional to Δpc.
Electrochemical membrane separation of H2S from reducing gas streams
Authors: Robinson Jeffrey S. , Smith D. Scott , Winnick Jack 
Published: April 2004

AbstractAn improved electrochemical membrane was tested with simulated coal gas having concentrations from 25 to 4,500 ppm H2S. The process produces elemental hydrogen that enriches the process gas stream at the cathode and elemental sulfur vapor that emerges from the anode. Removal efficiencies average up to 90% at any inlet level; current efficiencies are near 100% at the high inlet concentrations, decreasing significantly at lower H2S levels as the competing reduction of H2O becomes more favored. Molten carbonate fuel cell (MCFC) materials can be used exclusively at the MCFC operating temperature of 650°C, with the low concentrations of H2S, including the NiO cathode. At concentrations higher than about 60 ppm the operating temperature must be lowered approximately 50°C to avoid melting of the sulfided nickel cathode.
Effect of kinetics and mass transfer on design of extractive reaction processes
Authors: Samant Ketan D. , Ng Ka M. 
Published: April 2004

AbstractA generic model is derived for studying the effects of chemical kinetics and mass transfer on extractive reaction processes. Activity‐based models are used to describe non‐ideal liquid‐liquid phase equilibrium and reaction kinetics. Maxwell‐Stefan formulation and the film model are used to describe multicomponent mass transfer. The effects of kinetics and mass transfer are described in terms of Damköhler number matrices for reaction and for mass transfer, respectively. The elements of these matrices measure the rates of reactions and mass transfer relative to product removal. These effects are demonstrated using examples of systems with inherent phase separation and systems with solvent‐induced phase separation. The results show that it may not always be beneficial to operate extractive reaction processes near the equilibrium thermodynamic limit. Damköhler numbers have to be chosen carefully to obtain the desired performance. The use of the model in evaluating performance trade‐offs and in making judicious choices about reactor attributes is demonstrated.
State‐space nonlinear process modeling: Identification and universality
Authors: Sentoni Guillermo B. , Biegler Lorenz T. , Guiver John B. , Zhao Hong 
Published: April 2004

AbstractA practical approach was used to identify nonlinear models from available data. Knowing the true dynamics of a process allows implementation of a better and more efficient control scheme. Since this knowledge is not always available, a valid alternative to obtain a model is to identify the system. For that purpose, the DABNet (Decoupled A‐B Net) structure was used that is composed of a decoupled linear dynamic system followed by a nonlinear static map. The linear dynamic system was initially spanned by a set of discrete Laguerre systems and then cascaded with a single hidden layer Perceptron. A model reduction technique (linear balancing) used on the hidden nodes of the neural network as part of the identification process makes it possible not only to identify the main time constants, but reduce the dimensionality of the Perceptron input. It was proven that the DABNet structure can approximate every nonlinear, causal, discrete time invariant, multiple‐input single‐output system with fading memory. The final model consists of a linear state‐space system whose states, decoupled by input, are mapped by a neural network. Results concerning the application of the methodology to the approximation of a CSTR and a polymer process are presented.
Synthesis of processing system around a crystallizer
Authors: Chang Wen‐Chi , Ng Ka M. 
Published: April 2004

AbstractA systematic procedure is developed to synthesize the processing system upstream and downstream of a crystallizer. In a step‐by‐step manner, the procedure guides the user to generate alternative flow sheets for treating a given crystallizer effluent. It consists of five steps. The required unit operations are determined by comparing the product specifications (production rate, product purity, and others) with the crystallizer effluent characteristics (occlusions, inclusions, crystal size, and others). Secondly, the destinations of the reaction solvent, mother liquor, wash liquid, recrystallization solvent, and drowning‐out solvent are assigned. Third, the solvent recovery system is considered to recover the solvents and unconverted reactants and to remove the impurity from the system. Fourth, alternatives for enhancing process performance are identified. Finally, short‐cut models are used to screen process alternatives. Rules and heuristics are provided for each step, and examples for illustrating this procedure are presented.
Conversion of methane to higher hydrocarbons in AC nonequilibrium plasmas
Authors: Thanyachotpaiboon K. , Chavadej S. , Caldwell T. A. , Lobban L. L. , Mallinson R. G. 
Published: April 2004

AbstractThe effects of plasma chemistry on the conversion of methane were studied using a dielectric barrier discharge reactor at ambient temperatures. A dielectric barrier discharge reactor generates a nonequilibrium plasma when a sufficiently high voltage is applied across the reactor's electrodes. Methane molecules are activated at this temperature and coupled to form C2 hydrocarbons, higher hydrocarbons, and hydrogen. The study on the effect of voltage, residence time and third bodies on methane conversion and product selectivity shows that methane conversion initially increases with increasing voltage and residence time above the breakdown voltage, and product selectivities are essentially independent of the voltage. Production of hydrogen during the reaction limits olefin production. Methane conversion also increases when helium and ethane are in the feed stream. Helium and ethane both appear to be more easily activated than methane and enhance methane activation and conversion.
Analysis of microwave sintering of ceramics
Authors: Chatterjee Anindita , Basak Tanmay , Ayappa K. G. 
Published: April 2004

AbstractThe microwave heating of ceramic materials has been analyzed by solving the equations for grain growth and porosity (Svoboda and Riedel, 1992) during the late stages of sintering, coupled with the heat conduction equation and electric field equations for 1‐D slabs. Microwave power absorption and heating profiles have been calculated for A12O3 and SiC in the absence of sintering, and calculations have been carried out to study the effect of increasing dielectric loss ofAl2O3 as a function of temperature. A comparison of the densification and grain growth for A12O3 during microwave and conventional sintering indicates that within the framework of the present model, there is no difference between the two heating modes during the late stages of sintering.
Effect of nucleatipn profile on particle‐size distribution
Authors: Sathyagal A. N. , McCormick A. V. 
Published: April 2004

AbstractNucleation transients are important features in the reactive generation of monodisperse colloids from solution. Many previous theoretical investigations, both analytical and numerical, have addressed the roles of colloid aggregation or of direct growth from solution. Few have addressed the role of nucleation transients on the size distribution. The population balance model was used to study the effect of nucleation transients on an aggregating colloidal dispersion. (To simplify the problem, growth was neglected.) The focus was on whether, under the action of aggregation alone, extended and divided nucleation periods in some cases can lead to a very narrow particle‐size distribution. Our results support previous treatments (Look et al, 1990; Bogush and Zukoski, 1991b) suggesting this is the case. Our general approach also offers additional insights, such as strategies to manipulate the nucleation transients to independently tune the average particle size and the variance of the distribution.
Surface‐tension prediction for liquid mixtures
Authors: Escobedo Joel , Mansoori G. Ali 
Published: April 2004

AbstractEscobedo and Mansoori (1996) recently proposed a new expression, originally derived from statistical mechanics, for the surface‐tension prediction of pure fluids. The theory presented here is extended to matures of organic liquids based on the conformal solution theory of mixtures. Using the proposed equation, surface tensions of 55 binary mixtures are predicted within an overall 0.50 AAD%, which is better than other available prediction methods. The 55 binary mixtures are predicted within an overall 2.10 AAD% with a corresponding‐states version of the theory. The expressions proposed in this work are general since they have been applied to a variety of binary mixtures, and the results obtained agree well with the experimental data. The proposed model is directly applicable to multicomponent liquid mixtures.
Entrainment of air by a solid surface plunging into a non‐newtonian liquid
Authors: Cohu Olivier , Benkreira Hadj 
Published: April 2004

AbstractAn experimental investigation of the effect of fluid rheology on air entrainment in plunging tape experiments (dip coating) was carried out. The critical velocity at which the dynamic wetting line breaks up, allowing air to entrain into the liquid, was measured for a range of viscoelastic polymer solutions in glycerin/water mixtures. Variations of the critical velocities with various solutions were found to be unexpectedly small in comparison with the large viscosity variations. The results suggest that dynamic wetting failure and subsequent air entrainment are governed by nonhydrodynamic phenomena occurring at the molecular scale at the wetting line. It was also found that fluid elasticity gives rise to flow instabilities that may lead to a different, hydrodynamic mechanism of air entrainment.
Incompressive cake filtration: Mechanism, parameters, and modeling
Authors: Civan Faruk 
Published: April 2004

AbstractImproved models developed verify interpretation and prediction of incompressible filter cake thickness, filtrate volume, and rate data for linear and radial filtration cases at static and dynamic conditions. Based on the methods for determining model parameters from experimental filtration data, three sets of experimental data were analyzed, which demonstrate the diagnostic and predictive capabilities of the model. These models provide insight into the mechanism of incompressible cake filtration and offer practical means of interpreting experimental data, estimating the model parameters and simulating the linear and radial filtration processes.
Two‐dimensional model for proton exchange membrane fuel cells
Authors: Gurau Vladimir , Liu Hongtan , Kakaç Sadik 
Published: April 2004

AbstractA 2‐D mathematical model for the entire sandwich of a proton‐exchange membrane fuel cell including the gas channels was developed. The self‐consistent model for porous media was used for the equations describing transport phenomena in the membrane, catalyst layers, and gas diffusers, while standard equations of Navier‐Stokes, energy transport, continuity, and species concentrations are solved in the gas channels. A special handling of the transport equations enabled us to use the same numerical method in the unified domain consisting of the gas channels, gas diffusers, catalyst layers and membrane. It also eliminated the need to prescribe arbitrary or approximate boundary conditions at the interfaces between different parts of the fuel cell sandwich. By solving transport equations, as well as the equations for electrochemical reactions and current density with the membrane phase potential, polarization curves under various operating conditions were obtained. Modeling results compare very well with experimental results from the literature. Oxygen and water vapor mole fraction distributions in the coupled cathode gas channel‐gas diffuser were studied for various operating current densities. Liquid water velocity distributions in the membrane and influences of various parameters on the cell performance were also obtained.
Equilibrium theory for simulated moving bed adsorption processes
Authors: Chiang Anthony S. T. 
Published: April 2004

AbstractThe steady‐state operation of a simulated moving bed (8MB) process can be modeled by that of an equivalence true countercurrent (TCC) adsorption unit. An equilibrium theory based on the TCC unit is very useful for the selection of a proper condition to operate an 8MB process. The exact analysis of such an equilibrium model, however, has been limited to systems following a constant selectivity stoichiometric isotherm, which is not frequently observed. In this article, the equilibrium theory was extended to a multi‐component system that follows a constant selectivity nonstoichiometric isotherm. An exact solution is presented for the complete separation regions on the parameter space. The analysis is further applied to cases where only partial separation can be achieved.
Recursive data‐based prediction and control of batch product quality
Authors: Russell S. A. , Kesavan P. , Lee J. H. , Ogunnaike B. A. 
Published: April 2004

AbstractIn typical batch and semibatch processes, process/feedstock disturbances occur frequently and on‐line measurements of product quality variables are not available. As a result, most batch processes have not been able to achieve tight quality control. Empirical, data‐driven approaches are very attractive for dealing with this problem because of the difficulties associated with developing accurate process models from first principles. An approach for recursive on‐line quality prediction was developed around data‐based model structures. Techniques designed to incorporate the predictive models into on‐line monitoring and control of batch product quality were also examined. The proposed control approach can be viewed as shrinking‐horizon model‐predictive control based on empirical models. The effectiveness of the proposed prediction and control methods are illustrated by using an industrially relevant simulated polymerization example.
Novel monolithic stirred reactor
Authors: Albers Rolf K. Edvinsson , Houterman Marco J. J. , Vergunst Theo , Grolman Eric , Moulijn Jacob A. 
Published: April 2004

AbstractA novel reactor configuration in which blocks of monoliths are arranged in a stirrer‐like configuration was studied. A substantial liquid flow rate can be realized through the monolith blades at relatively low power input, owing to the high permeability of the monolithic structure. The inside of the monolithic channels can be coated with a thin layer of either a conventional catalyst or a biocatalyst, thereby eliminating many of the problems associated with using a suspended catalyst. The basic relationship among stirrer speed, geometry, liquid viscosity, and the resulting torque and flow through the blades were studied. Furthermore, the fast decomposition of a dilute, aqueous hydrogen peroxide solution was used to characterize the rate of external mass transfer.
A new technique for predicting the shape of solution‐grown organic crystals
Authors: Winn Daniel , Doherty Michael F. 
Published: April 2004

AbstractA method for predicting the shape of solution‐grown organic crystals is presented. The shapes depend on properties of their internal crystal structure, as well as on the processing environment. The model developed here can account for the effects of solvent and may be extended to account for the influence of certain types of additives. This method may be used as a first approach for including crystal shape in the overall design and optimization of organic solids‐processes. The technique has been used successfully to predict the shape of adipic acid grown from water, biphenyl from toluene, and ibuprofen from polar and nonpolar solvents.
Search for a model polymer blend
Authors: Balsara N. P. , Lefebvre A. A. , Lee J. H. , Lin C. C. , Hammouda B. 
Published: April 2004

AbstractThe thermodynamics of binary and multicomponent mixtures comprising polymethyl‐butylene, polyethylbutylene, andpolymethylbutylene‐block‐polyethylbutylene was studied by small‐angle neutron scattering. The Flory‐Higgins interactions parameter, deduced from these measurements, was independent of blend composition, as well as molecular weight and molecular architecture of the components, over the accessible temperature (27–201°C) and pressure (0.01–0.86 kbar) range. At temperatures above 130°C, the interaction parameter becomes independent of pressure. These findings are compared with previous experimental studies on the thermodynamics of polymer blends. To our knowledge, this level of agreement with the Flory‐Huggins theory has not been seen in any other polymer blend.
Interparticle potential and sedimentation of monodisperse colloid system
Authors: Wang H. , Wen C. S. 
Published: April 2004

AbstractThe effect of interpartide potential on the sedimentation of a colloid system has not been solved completely. A key problem is how to deal with the interpartide potential in stable systems. Based on previous works, an interpartide potential function for a stable system that cuts off the potential interaction at the position of the potential barrier (the position where interpartide potential is equal to 15 kT) is presented. Adopting this potential function, the sedimentation coefficients of monodisperse systems containing potential interacting particles are calculated, and the theoretical results are compared with those given by experiments. The potential function for the adopted stable system is more useful and reasonable than previous ones.
Estimating maximum removal efficiency in Venturi scrubbers
Authors: Ananthanarayanan N. V. , Viswanathan Shekar 
Published: April 2004

AbstractA simplified 2‐D model to predict liquid flux distribution and collection efficiency in a Venturi scrubber was tested successfully with experimental data from pilot‐ and industrial‐scale units. Establishing nonuniformity of flux distribution is the key to estimating collection efficiencies accurately. Liquid jet penetration and liquid injection velocity are critical in defining flux distribution for the entire range of conditions simulated. Increase in gas velocity makes flux distribution more uniform and enhances collection efficiencies. This effect becomes insignificant beyond a gas velocity as finer droplets get accelerated quickly to the throat gas velocity giving the collector very little interaction time. Increase or decrease in the liquid to gas (L/G) ratio beyond an optimum value made flux distribution more nonuniform and decreases collection efficiencies. Design parameters of the Venturi scrubber (aspect ratio and nozzle diameter) have an optimum that offers the most uniform flux distribution and the maximum collection efficiency. A new dimensionless group, the Venturi number, derived from the jet penetration correlation, could define both nonuniformity influx distribution and collection efficiency for changes in the L/G ratio, aspect ratio, nozzle diameter, and number of nozzles. Simulation results indicate that a maximum efficiency exists for the Venturi number between 1.0 and 1.5 × 10−3. The useful length of the scrubber throat could be determined from the L/G ratio defined by the Venturi number concept and appropriate throat gas velocity.
Recent contributions of statistical mechanics in chemical engineering
Authors: Deem Michael W. 
Published: April 2004

AbstractSome of the recent advances that have been made by chemical engineers in the field of statistical mechanics, as well as some of the new products and processes that have resulted from these advances, are reviewed. New approaches to molecular dynamics, Monte Carlo, quantum mechanics, master equations, hierarchical methods, liquid state theory, and field theory are discussed. Applications and commercial results in the microelectronics, biotechnology, pharmaceutical, and chemical process industries are highlighted.