bluuebunny/crossref_metadata_2025 huggingface dataset:
Prediction of the density for natural gas and liquefied natural gas mixtures
Authors: Eslami Hossein
Published: April 2004

Experimental liquid densities and compressibility factors of natural gas and liquefied natural gas mixtures were reproduced using an analytical equation of state, based on the statistical‐mechanical perturbation theory of Weeks, Chandler and Andersen. The temperature‐dependent parameters of the equation of state were calculated using our previous corresponding‐states correlation, based on the normal boiling point parameters. This article shows that the equation of state for multicomponent natural gas and liquefied natural gas mixtures would be predictable with minimal input information, namely the normal boiling temperature and the liquid density at the normal boiling point. The calculated results agreed well with the experiment. From a total of 590 data points for natural gases and 203 data points for liquefied natural gases examined in this work, the average absolute deviations were 0.33% and 2.48%, respectively, and the maximum deviations were 2.63% and 4.61%, respectively.
Segment‐based excess Gibbs energy model for aqueous organic electrolytes
Authors: Chen Chau‐Chyun , Bokis Costas P. , Mathias Paul
Published: April 2004

The aqueous electrolyte nonrandom two‐liquid (NRTL) model of Chen et al. is extended to represent the excess Gibbs energy of aqueous organic electrolytes. These organic electrolytes exhibit very different solution nonideality from typical aqueous electrolytes with elemental ions. The proposed extension is an integration of the electrolyte NRTL model for aqueous electrolytes and the polymer NRTL model (Chen, 1993) for oligomers and polymers. Organic ions are treated as oligomers that consist of hydrocarbon segments and ionic segments that each exhibit distinctive physical interactions with neighboring species. This integrated NRTL model captures the nonideal phase behavior of aqueous organic electrolytes, including micelle formation. The model further provides a versatile thermodynamic framework to correlate solution nonideality of electrolyte systems, organic or inorganic, and complex systems containing both electrolytes and polymers.
Control of vertical acceleration (effective gravity) between normal and microgravity
Authors: Wakayama Nobuko I. , Zhong Chengwen , Kiyoshi Tsukasa , Itoh Kikuo , Wada Hitoshi
Published: April 2004

When an upward magnetization force Fm is imposed on a liquid, the force acting on the liquid is the difference between the gravitational and magnetization forces. Thus, the magnitude of vertical acceleration acting on the liquid can be varied from 1 g to 0 g by changing the upward Fm. To verify this vertical acceleration‐control method, behavior of bubbles formed by injecting gas from a nozzle was examined. By decreasing the magnitude of vertical acceleration, the number of bubbles formed per unit time decreased and their size increased. These results confirm that vertical acceleration can be changed from normal gravity to near‐zero gravity. The method to generate low‐gravity conditions will find many applications over a wide range of research.
Product‐oriented process synthesis and development: Creams and pastes
Authors: Wibowo Christianto , Ng Ka M.
Published: April 2004

A systematic procedure is presented for the synthesis and development of manufacturing processes for creams and pastes. The procedure integrates the skills of a chemist and a chemical engineer to produce a product with specified properties. The desired functional and sensorial performance of the product is first identified in terms of quality factors. Then, the requisite ingredients are selected, and the process flowsheet, as well as the operating conditions, is synthesized. There are four steps in the procedure: identification of product quality factors, product formulation, flowsheet synthesis, and product and process evaluation. Design guidelines, as well as physical models describing relevant phenomena, are used to assist decision‐making at each step of the procedure.
Dynamic discharge and performance of a new adsorbent for natural gas storage
Authors: Biloe S. , Goetz V. , Mauran S.
Published: April 2004

Performance of a new highly conductive adsorbent matrix for ANG systems was evaluated. The adsorbent composite block (ACB) was a mixture of superactivated carbon, labeled MAXSORB and expanded natural graphite (ENG), followed by consolidation. ENG was used both as a very high conductive matrix and as support for adsorbents. Thermal conductivity is 30 times higher than that of activated carbon packed bed. Dynamic methane discharges were studied experimentally with a 2‐L vessel filled with ACB. The influence of both the discharge flow rate and heat‐exchange conditions at the reactor wall on the delivered methane capacity was investigated. The modeling of the discharge process, validated from experimental results, shows the efficiency of this ACB with a 100‐V/V delivered methane capacity under various working conditions.
Simultaneous adsorption of SO2NOx from flue gases in a riser configuration
Authors: Das Asit K. , De Wilde Juray , Heynderickx Geraldine J. , Marin Guy B. , Iversen Steen B. , Felsvang Karsten
Published: April 2004

Simultaneous adsorption of SO2–NOx is a new, promising process in treating industrial flue gases in a short‐contact‐time dilute phase riser with Na/γ‐Al2O3 sorbent particles of 50–100 μm diameter at 370–430 K. A major part of the sorbent is recycled for maximum utilization of the sorbent capacity before regeneration. A steady‐state model for the riser adsorber is developed by combining independently determined rate equations with a 1‐D, two‐phase hydrodynamic model of the riser. The simulation was validated with the operating data from a pilot‐scale installation of 4.2 Nm3/s flue‐gas capacity and solid fluxes between 1 and 3 kg·m−2·s−1. The riser operates in an extremely dilute phase with a solid volume fraction below 7.0 × 10−4 and a slip velocity that is constant for almost the entire riser length, indicating fully developed flow. The experimental observation that an increase in the SO2–NO ratio in the feed gas leads to a higher NO removal efficiency is explained as resulting from an increased concentration of the adsorbed SO2. The SO2 removal efficiency, however, may drop if free adsorption sites are not sufficiently available. Recycling of the sorbent has only a marginal effect on the NO removal, but helps to maximize the SO2 adsorption. For the first time, the simultaneous removal of SO2 above 95% and of NOx above 80% is reported using a dry, regenerable sorbent in a riser reactor.
In situ infrared measurements on TiO2 flames: Gas and particle concentrations
Authors: Arabi‐Katbi Osama I. , Pratsinis Sotiris E. , Morrison Philip W.
Published: April 2004

Fourier transform infrared spectroscopy was performed on premixed flames of titanium tetraisopropoxide, methane and oxygen. A combination of emission/transmission (E/T) measurements yields gas temperature, gas concentrations, soot temperature, soot concentration and absorption features of TiO2 particles. To validate the temperature measurements, a thermocouple is inserted into the IR path within the flame, and its temperature is compared to the surface temperature from E/T analysis which agrees quite well. The HITEMP and HITRAN databases are used to determine the gas mol fractions in the flame. Soot is observed in the emission spectra of the flame, and its concentration decreases with its increasing position above the burner. The soot temperature is always less than the gas temperature. The IR feature of TiO2 particles is hard to observe, because it is very small relative to H2O and CO2 features. Interfering features, however, were removed using either calculated spectra or by experimentally generating a reference flame using an acetone–methane flame.
Shortcut experimental method for designing chiral SMB separations
Authors: Migliorini Cristiano , Mazzotti Marco , Zenoni Gianmarco , Morbidelli Massimo
Published: April 2004

The simulated moving‐bed (SMB) chromatographic separation of the Tröger's base enantiomers with ethanol as eluent on microcrystalline triacetate cellulose was studied. An experimental technique to design nonlinear SMB separations with few column experiments is presented. This shortcut technique allows the rigorous solution of the Equilibrium Theory model to be approximated without knowing the adsorption equilibria, and therefore can be useful in developing new separations. The predictions of the shortcut method are compared with the experimental results of the SMB separation. The effect of the feed concentration and of the nonideal contributions, such as mass‐transfer resistance and extracolumn band broadening, are elucidated.
Model for gas hydrate equilibria using a variable reference chemical potential: Part 1
Authors: Lee Sang‐Yong , Holder Gerald D.
Published: April 2004

A new model developed for predicting the dissociation pressure of gas hydrates proposes that the host–host interaction can be affected by the guest molecules, thus requiring different values of the reference properties, Δμ and Δh, for each gas hydrate. We presume that the primary impact of the guest is to distort the lattice, although other factors, such as guest polarity, can have an impact. Experimentally based Δμ and Δh values for each gas hydrate show that these values vary from guest to guest, generally increasing with guest size. Using these experimentally determined reference values, the error between calculated and experimental dissociation pressures is reduced. A correlation between Δμ and the molecular size of the guest molecule (or the Kihara hard‐core diameter ‘a’) is also developed for estimating values of Δμ, where experimental data are absent (that is, methane in structure II hydrate with no other guests).
Investigation of postflooding conditions in countercurrent gas–liquid flow
Authors: Maharudrayya S. , Jayanti S.
Published: April 2004

Systematic experiments were conducted to study the postflooding situation in air–water countercurrent flow in a tube of 0.025 m internal diameter with smooth inlet and outlet conditions for the two phases. The downflow rate of water and the pressure gradient were measured over a range of flow rates for test‐section lengths of 0.6, 1.2 and 2.0 m. Additional experiments were conducted with increasing and decreasing water flow rates at a constant air flow rate. The length of the test section or the way the flooding point was approached did not significantly affect the onset of flooding. The data show that, as the gas flow rate is increased, the pressure gradient can fall significantly in the postflooding situation due to depleting the downflow rate of liquid. Dimensionless correlations are proposed to calculate the downflow rate and the pressure gradient given for overall flow parameters.
Influence of sieve trays on the mass transfer of single drops
Authors: Henschke Martin , Pfennig Andreas
Published: April 2004

Mass transfer on single drops was studied experimentally in a conical glass test cell on a laboratory scale. To determine the influence of internals on the mass transfer, two different sieve trays with hole diameters of 3 and 6 mm, respectively, were inserted into the cell. In the experiments the resting times the drops stayed under and above a sieve tray were varied. Through the evaluation of the experimental results with a model, it is possible to determine the influences of the flow field and the sieve‐tray passage on mass transfer separately. The mixing inside the drops while they passed through the holes is relatively small even if the drops are a little larger than the hole diameter. The influence of changes of the flow field caused by the sieve trays on mass transfer is larger, and its quantitative magnitude depends on the system used.
Continuous protein recovery with a liquid–solid circulating fluidized‐bed ion exchanger
Authors: Lan Qingdao , Bassi Amarjeet S. , Zhu Jing‐Xu (Jesse) , Margaritis Argyrios
Published: April 2004

A liquid–solid circulating fluidized‐bed (LSCFB) ion‐exchange system was developed for continuous protein recovery. It contains a downcomer for protein adsorption and a riser for protein desorption, with ion‐exchange particles circulating continuously between the two columns. Effects of the operating conditions on the hydrodynamics and the continuous ion exchange of bovine serum albumin (BSA) in the system were investigated. Under typical operating conditions, up to 98% BSA was adsorbed in the downcomer (showing a very high efficiency of protein removal from the feed), and an overall protein recovery of up to 84% was obtained in the LSCFB system, indicating that the LSCFB system was a very promising strategy for the continuous recovery of proteins.
Relative gain array analysis for uncertain process models
Authors: Chen Dan , Seborg Dale E.
Published: April 2004

Relative gain array (RGA) analysis has been widely used in process control to identify promising control structures and to characterize the degree of process interactions between controlled and manipulated variables. However, the influence of process model uncertainty on RGA analysis has received little attention. Analytical expressions for RGA uncertainty bounds are derived for 2 × 2 control problems and for general, n × n control problems. Both worst‐case bounds and statistical uncertainty bounds are derived. Several simulation examples illustrate the new results. The RGA uncertainty bounds provide useful information concerning model accuracy requirements and the robustness of decentralized control systems.
Stress development in drying coatings after solidification
Authors: Lei H. , Francis L. F. , Gerberich W. W. , Scriven L. E.
Published: April 2004

As a coating solidifies by drying, it tends to shrink. It is liquid enough in early stages that any shrinkage stress is rapidly relieved by viscous flow. It becomes solid enough in later stages to support elastic stress, which results from shrinkage inhibited by adherence to the substrate. Stress can relax by viscous creep in the coating. Thus, the stress level is an outcome of competing shrinkage and relaxation. A theoretical model of diffusion and mass transfer, large shrinkage‐induced deformation and stress, together with yielding and post‐yielding viscous deformation, was developed to predict stress evolution in drying of polymer coatings after solidification. The coupled equations of diffusion and stress development are solved by the Galerkin/finite‐element method. This model is used in polymer coatings to study the effect of a grooved substrate and embedded particles to the stress and drying, and to simulate cantilever deflection method used to measure stress experimentally.
Bivariate moment simulation of coagulating and sintering nanoparticles in flames
Authors: Rosner Daniel E. , Pyykönen Jouni J.
Published: April 2004

The design/control of particle synthesis reactors is hampered by the cumbersome nature of simulation methods (such as “sectional” representations of the particle population balance equation) to track the evolution of coagulating, restructuring populations in complex flow environments. Bivariate PBE‐methods were investigated using generalizations of a recent Gaussian quadrature‐based “moment” approach (McGraw, 1997; Wright et al., 2001). A 9‐moment method was applied to an extensive data set recently obtained using a “seeded” laminar flame reactor with laser‐based, as well as TEM‐grid thermophoretic sampling. Alumina nano‐aggregate population evolution is predicted using available rate/transport laws (for coagulation, thermophoresis and sintering) and the efficacy is predicted, and, together with the efficacy of such simulation methods for parameter estimation, is also illustrated inferring a “best fit” activation energy for nanoparticle sintering. Variants/extensions of these techniques should enable their incorporation into, say, full PDF‐methods for turbulent synthesis reactors, using improved rate laws.
Consolidation during drying of aggregated suspensions
Authors: Brown L. A. , Zukoski C. F. , White L. R.
Published: April 2004

Drying of aqueous suspensions containing aggregated particle networks is important in a wide variety of solid/liquid unit operations where, in addition to optimizing the drying rate, there is a need for dimensional control of the dried product. During drying, the bed consolidates and then dehydrates. The degree of consolidation is sensitive to the strength of particle attractions altered by solution conditions such as pH, ionic strength, and particle size. These interaction forces are characterized in terms of an independently measurable quantity, the compressive yield stress Py, and link Py to the compressive capillary forces to which the suspension is subjected during drying. Using Py and a two‐phase fluid model for drying, a dimensionless parameter Q is identified to provide a guide for conditions where interparticle forces and mass‐transfer limitations will dominate drying behavior. This model yields a quantitative measure of the shape changes that can be expected upon drying. Model predictions are tested using drying experiments on 0.65 μm alumina particles in aqueous suspensions at different pH and salt concentrations.
Design of reactive extraction systems for bioproduct recovery
Authors: Pai Rajaram A. , Doherty Michael F. , Malone Michael F.
Published: April 2004

Liquid‐liquid extraction, combined with chemical reaction, can improve overall yields of product. Reactive extraction is an alternative for separations in bioprocessing, for example, for the production of carboxylic acids such as lactic or citric acid, alcohols such as ethanol, or antibiotics such as penicillin, cephalosporin or streptomycin. A method for the design of reactive extraction cascades was used for the recovery of Penicillin G and for lactic acid from aqueous mixtures using mixtures of organic solvents with reactive amines as extractants. Effects of such variables as residence time, flow rates, pH, number of stages and amine concentration are quantified. Designs capable of essentially complete recovery are reported.
New synthesis framework for the optimization of complex distillation systems
Authors: Shah Piyush B. , Kokossis Antonis C.
Published: April 2004

A new synthesis framework screens and examines complex distillation sequences. Conventional superstructure developments are replaced in favor of a novel representation that assumes the form of a supertask model. The supertask is based on simple tasks that accommodate for basic sequences. Hybrid tasks account for complex columns and sloppy splits. Discrete instances of simple tasks are combined with hybrid transformations to optimize operating conditions. The optimization problem is formulated as a simple MILP problem that is possible to solve to global optimality. The proposed representation can develop different nonconventional and novel designs featuring fully integrated columns, parallel sequences, and multiple‐effect columns. The approach is illustrated with several literature and industrial problems. In all cases solutions are reported in the form of nonconventional designs that perform as optimal or near‐optimal schemes.
General local‐equilibrium chromatographic theory for eluents containing adsorbing buffers
Authors: Frey Douglas D. , Narahari Chittoor R. , Butler Christy D.
Published: April 2004

An efficient, general strategy was developed for numerically solving the system of equations that describe a pH gradient under local‐equilibrium conditions when the elution buffer contains arbitrary numbers of both adsorbed and unadsorbed buffering species (weak electrolytes) and for a weak‐ or strong‐base ion‐exchange column packing. Since the method involves the solution of algebraic equations, instead of partial differential equations, it can be used to rapidly determine the effluent pH profile given the adsorption equilibrium constants for the buffering species. It can also be used iteratively to determine the adsorption equilibrium constants for the buffering species from an experimentally determined effluent pH profile as well as to determine the composition of the elution buffer required to achieve a desired shape for the pH gradient given the adsorption equilibrium constants for the buffering species. The calculation method is verified experimentally and used to illustrate the behavior of chromatographic methods which employ retained pH and ionic strength gradients.
Dynamics of a fixed‐bed adsorptive reactor for synthesis of diethylacetal
Authors: Silva Viviana M. T. M. , Rodrigues Alírio E.
Published: April 2004

Diethylacetal from ethanol and acetaldehyde catalyzed by the acid resin Amberlyst 18 was synthesized. Adsorption and reaction experiments were performed in a laboratory‐scale fixed‐bed adsorptive reactor, operating isothermally at 15°C and at atmospheric pressure. Experimental results of dynamic adsorption of binary nonreactive mixtures were used to obtain multicomponent adsorption equilibrium isotherms of the Langmuir type. The reaction kinetics reported earlier were used in the model of the adsorptive reactor, which also included axial dispersion, external and internal mass‐transfer resistances, and multicomponent Langmuir isotherms. Model equations were solved by orthogonal collocation on finite elements (OCFE), implemented by the PDECOL package, using the measured model parameters, and were validated by experimental data for reaction and regeneration steps, with good accuracy.
Gas permeance measurement of hollow fiber membranes in gas‐liquid environment
Authors: Lund Laura W. , Hattler Brack G. , Federspiel William J.
Published: April 2004

An apparatus and methodology were developed to measure the oxygen and carbon dioxide permeance of hollow fiber membranes (HFMs) in a gas‐liquid environment. The gas‐liquid permeance measurements were compared with measurements made in a gas‐gas environment to validate the methodology and to determine whether the permeance of an HFM in a gas‐liquid environment differs inherently than in a gas‐gas environment. The methodology is based on measuring the overall system permeance for a range of liquid velocities and isolating the membrane resistance to gas flux from the liquid boundary layer resistance by regression of a nonlinear system model to the data. The success of the methodology in accurately estimating membrane permeance depended on the maximum liquid velocity which the system could consistently generate past the fibers.
Mechanisms of photoresist dissolution
Authors: Hunek Balazs , Cussler E. L.
Published: April 2004

The comprehensive physical picture developed describes the dissolution of a broad range of materials, including novolak‐based photoresists and can be applied to the dissolution in aqueous base of both small molecules and polymers that can ionize. The model was verified by measuring the dissolution of solute‐coated spinning discs. Key experimental variables included the flow (as a Reynolds number) and the base concentration, which was in this case of sodium hydroxide. The physical and chemical characteristics of the dissolving species determine the rate‐limiting steps, which cause different dissolution behavior. The dissolution of low molecular weight phenolic resin is controlled by a combination of solute release and solute mass transfer, without the formation of any significant intermediate gel phase. Several other dissolution mechanisms are rationalized based on a simple “strings of buoys” analogy, which can be extended to other cases as well.
Hydrodynamics of trickling flow in packed beds: Relative permeability concept
Authors: Lakota Ana , Levec Janez , Carbonell Ruben G.
Published: April 2004

Liquid holdups and pressure drops for gas and liquid concurrent flow in packed beds were measured experimentally. To calculate the Ergun type constants, pressure drops were also measured for single‐ (gas)‐phase flow through the same packings. These measurements reveal that the Ergun type inertial constant depends on the particle shape. The beds were packed with porous and nonporous spheres, cylinders, extrudates, and Raschig rings. The experimental data were analyzed using the concept of relative permeabilities. The liquid‐phase relative permeability correlated well with the reduced liquid saturation in a unique power‐law form for all particles independent of their shape. The gas‐phase relative permeability as a function of the gas‐phase saturation followed the same law, but the exponent depends on the particle shape and gas‐phase Reynolds number. Predicted and experimental values for liquid holdups for all particle shapes agreed well with mean relative deviations less than 10%. Predictions of pressure drops for spherical particles, cylinders, and extrudates are at least as accurate as other less rigorous correlations (mean relative errors between 25 and 40%). Pressure drop predictions for Raschig rings are poorer (mean relative deviations of 90%), reflecting in part the variations in pressure drops from experiment to experiment with these particles.
Elastohydrodynamics of a moving substrate over a curved plate
Authors: Carvalho M. S. , Huelsman G. L. , Kolb W. B.
Published: April 2004

Conventional drying of coated substrates usually uses air impingement to support and heat the coated web. Because of the high‐velocity air flow, most of the heat is transferred by convection and the heat transfer coefficient is not uniform, leading to drying defects. To overcome this and obtain a high uniform heat transfer coefficient, the energy is supplied to the backside of the substrate by conduction through a thin air‐layer between a heated plate and the moving substrate. To obtain heat transfer coefficients comparable to those from air impingement, the distance between the web and plate has to be very small, yet not touch the plate. It is essential to form and control a thin, uniform and stable air layer between the substrate and heating plate by wrapping the moving web over a plate with a large radius of curvature. Air‐layer thickness entrained between the web and plate is related to the air flow rate between the two surfaces. The flow between a moving flexible substrate and curved solid surface was analyzed by theory and experiments to examine this elastohydrodynamic action and changes in air‐layer thickness with the plate geometry, substrate material, and operating conditions. The theoretical model consisted of the Navier–Stokes equation to describe the air motion and cylindrical shell approximation to model the web deformation. Differential equations describing the problem were solved by the Galerkin's/finite‐element method. The nonlinear algebraic system was solved by Newton's method with initialization by pseudo‐arc‐length continuation. In experiments, the distance between the moving web and curved plate was measured at different operating conditions. The predicted air‐layer thicknesses agreed well with experimental measurements. The air‐layer thickness is controlled by the flow in the plate entrance.
Linearized transport model for nanofiltration: Development and assessment
Authors: Bowen W. Richard , Welfoot Julian S. , Williams Paul M.
Published: April 2004

Finite difference linearization of pore concentration gradient in nanofiltration membranes greatly simplifies the solution of a three‐parameter model (pore radius, membrane charge, and pore dielectric constant) for electrolyte rejection by removing the requirement for numerical integration of the extended Nernst–Planck equation. The validity of the linearized model is first experimentally tested by comparing with a rigorous characterization of the Desal‐DK nanofiltration membrane, the linearized model closely agreeing with the numerical solution of the full model. Investigation of pore concentration profiles showed the assumption of linearity to be valid over a wide range of nanofiltration conditions. The linearized model was also successfully extended to ternary electrolyte mixtures, highlighting its main advantage over analytic solutions. Overall, the model is a powerful tool for characterization of nanofiltration membranes and subsequent prediction of separation performance. Computational demands are modest in terms of time and complexity.
Feasible region for a countercurrent cascade of vapor‐liquid CSTRS
Authors: Gadewar Sagar B. , Malone Michael F. , Doherty Michael F.
Published: April 2004

The attainable region approach for reaction‐mixing systems was applied to systems with simultaneous reaction and separation. A model developed for a countercurrent cascade of two‐phase CSTRs can be considered as a surrogate for the stripping or rectifying sections of a reactive distillation column. An overall composition vector defined satisfies the same geometric properties as the reaction vector. The necessary conditions for the reaction‐mixing attainable region were applied to the cascade of two‐phase CSTRs. This article focuses only on the countercurrent cascade of two‐phase CSTRs; therefore, the region identified is a feasible region, which is a subset of the attainable region for reaction‐separation systems. For consecutive reactions, the boundary of the feasible region is given by the trajectory for a cocurrent cascade of two‐phase CSTRs. The overall composition vector for the cocurrent cascade of two‐phase CSTRs is tangent to the trajectory. For single reversible reactions, the attainable region for single‐phase reactors is significantly expanded by using a countercurrent cascade of vapor‐liquid CSTRs. Two examples used are transalkylation of toluene and the synthesis of isopropyl acetate.
A multiple microreactor system for parallel catalyst preparation and testing
Authors: Pantu Piboon , Gavalas George R.
Published: April 2004

A system containing nine catalytic microreactors for parallel preparation and testing of heterogeneous catalysts is described. The catalyst samples are prepared in the form of thin films coated on thin quartz rods by dip‐coating in solutions of different composition. Catalyst‐coated rods are placed within thin tubes housed inside a wider tube heated in an electrical furnace. A multiport valve serves to sequentially conduct the reaction products from each microreactor to a mass spectrometer for analysis. The system was tested with the reaction of methane reforming with carbon dioxide over Pt/Ce1−xGdxO2−0.5x and Pt/Ce1−xSmxO2−0.5x at 650 and 700°C. Individual catalysts were characterized by X‐ray analysis, and induction‐coupled plasma mass spectrometry for catalyst mass and elemental composition. The measurements showed that Pt/CeO2 had the highest activity among the series of catalysts tested and generally the activity increased with the cerium oxide content. After exposure to the feedstream for 2–3 h at 700°C, most catalysts suffered significant deactivation except the mixed oxides with 25–85% samarium oxide that maintained relatively stable activity.
Radiation field inside a reactor of glass‐fiber meshes coated with TiO2
Authors: Esterkin Carlos R. , Negro Antonio C. , Alfano Orlando M. , Cassano Alberto E.
Published: April 2004

A photocatalytic reactor for treating polluted gaseous streams was developed with a flat‐plate configuration and parallel, glass‐fiber meshes coated with TiO2. It was irradiated from both sides with UV light provided by tubular lamps placed at both sides of the reactor. The first step in the description of the reactor performance is the knowledge of the local values of radiation intensities. The radiation field was modeled by special adaptation of the ray‐tracing technique. The model uses two optical properties of the glass‐fiber meshes: transmittance and reflectance. To validate the mathematical description of the reactor with experiments, the exiting radiative flux from one side was measured using a precise UV detector. Predictions show a maximun error of 8.3% with respect to experimental values measured at the center of the apparatus. This description of the radiation distribution is indispensable to model the photooxidation reaction.
Transient kinetics of n‐Butane oxidation to maleic anhydride over a VPO catalyst
Authors: Huang Xiao‐Feng , Li Cheng‐Yue , Chen Biao‐Hua , Silveston P. L.
Published: April 2004

Transient reaction kinetics is usually needed to model the reactor system operated under unsteady‐state mode to improve the performance of the catalyst packed in such a reactor system and to match operating conditions of different reaction steps in this system. The transient reaction kinetics of n‐butane oxidation to maleic anhydride over a commercial VPO catalyst was systematically studied, using online MS/GC measurements, transient response, and forced periodic operation methods. A simplified scheme with respect to the reaction network is proposed based on the previous studies and the observations in this work. Combining the results on the roles of lattice and adsorbed oxygen in the reaction process with the data obtained in transient response experiments, a transient kinetic model taking account of the oxygen storage and diffusion in the bulk‐phase of the catalyst was introduced and its parameters were estimated. The model was examined by the transient response experimental data and time‐average concentrations of butane and maleic anhydride under forced unsteady‐state operation.
Calculation of densities from cubic equations of state
Authors: Deiters Ulrich K.
Published: April 2004

Some cubic equations of state can eventually have unphysical solutions for the molar volume. The conditions for this phenomenon are discussed. The computational accuracy and computing time requirements of the analytical root finding method (Cardano's formula) are investigated. A new, faster iterative root finder for cubic polynomials is proposed.
Optimal operation of extractive distillation in different batch configurations
Authors: Low K. H. , Sørensen E.
Published: April 2004

Optimal operations of extractive distillation for regular and middle‐vase1 batch columns are presented based on a profit function. Detailed models are used for the rigorous dynamic optimization considering all operational decision variables, including reflux ratio, solvent feed rate, heat duties, and possible product withdrawals during the process. Optimal feed distribution and stream configuration at the middle section of the middle‐vessel column are investigated. Separation of a minimum boiling azeotropic binary mixture (acetone and methanol using water as solvent) involving different separation duties and feed compositions is presented as a case study. The pereformanance of the middle‐vessel column is signicantly influenced by the middle‐section stream configuration, with the best profit when the stream configuration is allowed to vary during the operation. The optimal operating policy for the middle‐vessel column involved the feed being charged mainly to the reboiler still with low holdup in the middle vessel during the operation.
Homogenization of mesoscopic theories: Effective properties of model membranes
Authors: Lam R. , Vlachos D. G. , Katsoulakis M. A.
Published: April 2004

A new mathematical framework for modeling diffusion in nanoporous materials or on surfaces exhibits heterogeneity in properties over large length scales and retains molecular scale information, typically captured only by molecular simulations (kinetic Monte Carlo). It first uses newly developed mesoscopic equations derived rigorously from underlying master equations by coarse‐graining statistical mechanics techniques. Homogenization techniques are then used to derive the leading‐order effective mesoscopic models that are subsequently solved by spectral methods. These solutions are also compared to direct numerical simulations for selected 2‐D model membranes with defects, when attractive adsorbate‐adsorbate interactions affect particle difSsion. Both the density and dispersion of defects significantly alter the macroscopic behavior in terms of fluxes and concentration patterns, especially when phase transitions can occur. In the presence of adsorbate‐adsorbate interactions, permeation through a nanoporous film can depend on the face of a membrane exposed to the high‐pressure side. Homogenization techniques also could offer a promising alternative to direct numerical simulations, when complex, large‐scale heterogeneities are present.
Use of COSMO‐RS for the prediction of adsorption equilibria
Authors: Mehler C. , Klamt A. , Peukert W.
Published: April 2004

The novel method COSMO‐RS for the calculation of thermodynamic partition equilibria based on quantum chemical calculations is applied for the first time to the correlation and prediction of adsorption equilibria. In the limit of small adsorbate concentrations, very good predictions have been achieved for adsorption equilibria of activated carbon for both the phase and the aqueous phase.
Transport in heterogeneous media: Tracer dynamics in complex flow networks
Authors: Başağaoğlu Hakan , Ginn Timothy R. , Green Christopher T. , McCoy Benjamin J.
Published: April 2004

Large‐scale inhomogeneities in natural porous media profoundly affect the dynamic response of conveyed tracers. It is proposed that tracer dynamics in heterogeneous porous media can be represented by temporal moments based on parallel and series unit models of homogeneous columns, stirred volumes, or mass‐transfer‐connected closed compartments. The rules of combining the moments for elementary volumes are based on units (1) in series, where output from the preceding units is the input to the succeeding unit, and (2) in parallel, where the splitting or joining flow paths control the response. For a network of elementary volumes in series or parallel, fate and transport of contaminants in heterogeneous media can be analyzed simply in a deterministic framework. Results for several simple series and parallel models show the wealth of responses that can be quantitatively described by this procedure.
Gas–liquid mass transfer to single bubbles: Effect of surface contamination
Authors: Vasconcelos Jorge M. T. , Orvalho Sandra P. , Alves Sebastião S.
Published: April 2004

The dissolution of single bubbles of gases of low solubility kept stationary in a downward stream of water was studied. In “clean” water, two regimes are identified. Initially, the process is fast, consistent with the theory for circulating bubbles. Then, the mass‐transfer rate falls sharply to that predicted for solid spheres. Transition times and transition diameters vary widely with experimental conditions. In untreated water, only the second regime is found. Results are explained in terms of the kinetics of trace surfactant accumulation at the interface. An adaptation of the stagnant‐cap model is proposed, with surface immobilization expressed in terms of interface dynamics. The model yields good prediction of the transition point for a very large set of conditions, including different gases at various concentrations in the liquid stream and a wide range of initial bubble diameters.
Design and analysis of nonequilibrium separation processes
Authors: Sridhar L. N. , Maldonado Carlos , Garcia Ana Maria
Published: April 2004

Design and analysis of nonequilibrium separation process problem are discussed. Even though there have been published articles on the design and analysis of equilibrium separation process problems, these issues have not been addressed in great detail as far as nonequilibrium problems are concerned. Strategies are developed for drawing residue curve maps using mass‐transfer model equations. In addition the multistage nonequilibrium separation process problem is rigorously analyzed and it is shown that, as in the single‐stage case, any multiplicity that occurs is a result of the multiplicity that occurs here in the phase equilibrium calculations at the interface.
Statistical process monitoring based on dissimilarity of process data
Authors: Kano Manabu , Hasebe Shinji , Hashimoto Iori , Ohno Hiromu
Published: April 2004

Multivariate statistical process control (MSPC) has been widely used for monitoring chemical processes with highly correlated variables. In this work, a novel statistical process monitoring method is proposed based on the idea that a change of operating condition can be detected by monitoring a distribution of process data, which reflects the corresponding operating conditions. To quantitatively evaluate the difference between two data sets, a dissimilarity index is introduced. The monitoring performance of the proposed method, referred to as DISSIM, and that of the conventional MSPC method are compared with their applications to simulated data collected from a simple 2 × 2 process and the Tennessee Eastman process. The results clearly show that the monitoring performance of DISSIM, especially dynamic DISSIM, is considerably better than that of the conventional MSPC method when a time‐window size is appropriately selected.
Simulating cyclohexane millisecond oxidation: Coupled chemistry and fluid dynamics
Authors: O'Connor R. P. , Schmidt L. D. , Deutschmann O.
Published: April 2004

Cyclohexane partial oxidation over a 40‐mesh Pt–10% Rh single‐gauze catalyst can produce ∼85% selectivity to oxygenates and olefins at 25% cyclohexane conversion and 100% oxygen conversion, with cyclohexene and 5‐hexenal as the dominant products. A detailed 2‐D model of the reactor is solved using density‐functional theory (with 35 reactions among 25 species) and computational fluid dynamics. Rapid quenching in the wake of the wires allows highly nonequilibrium species to be preserved. The simulations show that the competition between cyclohexyl and cyclohexylperoxy radicals is crucial in determining product selectivities. At high temperatures and low pressures, the cyclohexyl radical is favored, leading to high selectivities to cyclohexene. At lower temperatures or high pressures, cyclohexylperoxy radicals are favored, allowing the formation of parent oxygenates to dominate. Numerical simulations suggest ways to tune reactor operation for desired product distributions and allow the investigation of dangerous or costly operating conditions, such as high pressure.
Molecular thermodynamics for fluid‐phase equilibria in aqueous two‐protein systems
Authors: von Solms Nicolas , Anderson Camille O. , Blanch Harvey W. , Prausnitz John M.
Published: April 2004

With saline water as the continuous medium, a two‐component McMillan‐Mayer equation of state is used to describe liquid–liquid phase equilibria in a two‐protein system. The equation of state is based on a hard‐sphere reference with perturbations introduced through a potential of mean force to account for electrostatic forces and for attraction between protein particles. To illustrate the thermodynamic framework, one parameter each is fitted to experimental precipitation data for aqueous saline one‐protein systems containing either lysozyme or ovalbumin. A lysozyme–ovalbumin interaction parameter is then introduced to calculate phase behavior in the aqueous two‐protein system. These calculations are remarkably similar to classic vapor–liquid equilibrium calculations using an equation of state. For the aqueous two‐protein system, calculations give the light‐phase composition as well as the lysozyme and ovalbumin partition coefficients for a given dense‐phase composition. Agreement with sparse experimental data is reasonable over a range of pH and high ionic strength provided by the common precipitant ammonium sulfate.
Mapping of sonochemical reactors: Review, analysis, and experimental verification
Authors: Gogate Parag R. , Tatake Prashant A. , Kanthale Parag M. , Pandit Aniruddha B.
Published: April 2004

The erratic behavior of cavitational activity exhibited in a sonochemical reactor poses a serious problem in its design and scale‐up. Several previous studies in the past dealt with mapping of sonochemical reactors, which have been critically analyzed and recommended for efficient scale‐up strategies. There have been no efforts to link the primary effects (local pressure field) of ultrasound activity with the observed secondary effects (such as chemical reaction). In this work an ultrasonic horn (standard immersion‐type reactor), and an ultrasonic bath (rectangular geometry with transducers located at the bottom in triangular pitch) reactors were mapped with the help of local pressure measurement (using a hydrophone), and liberated iodine was estimated using the Weissler reaction, and a quantitative relationship was established between the two. In estimating chemical reaction rates, the effect of microscopic variation in the type of microreactor used (test tube in this case) on the extent of degradation was also investigated. Measured local pressure pulses were used in theoretical simulations of bubble dynamics equations to check the type of cavitation taking place locally, and to estimate the possible collapse of the pressure pulse in terms of the maximum bubble size reached during the cavitation phenomena. A relationship also was established between observed iodine liberation rates and the maximum bubble size reached. The engineers can easily use these unique relationships in an efficient design, since the secondary effect can be directly quantified.
Supercritical fluid extraction of surfactant from Si‐MCM‐41
Authors: Kawi S. , Lai M. W.
Published: April 2004

Supercritical fluid extraction has been carried out on as‐synthesized Si‐MCM‐41 in a study to evaluate the efficiency of SFE in the recovery of the organic template cetyltrimethylammonium hydroxide (CTMAOH) from the pores of Si‐MCM‐41. Effects of different extraction parameters on the extraction efficiencies were investigated. The results show that modified CO2 is required to extract CTMAOH. High extraction efficiencies are obtained at 85°C and at both 100 and 350 bar, while the lowest efficiency is obtained at 150 bar. The extraction efficiency also increases initially on increasing the modifier concentration and reaches a limiting value when the concentration is increased further. Among a series of modifiers studied, methanol and acidic methanol (modified with acetic acid) are effective. The modifiers used in the extraction have a significant impact on the properties of the final material. The compound extracted was characterized and identified as CTMAOH.
A new image reconstruction method for tomographic investigation of fluidized beds
Authors: Liu Shi , Wang Haigang , Jiang Fan , Yang W. Q.
Published: April 2004

It is important to investigate the behavior of circulating fluidized beds (CFB) for efficient coal combustion. Electrical capacitance tomography (ECT) was applied to the measurement of gas/solids distribution in square CFBs. An iterative method was used to achieve improved image reconstruction over the commonly used linear back‐projection algorithm. The solids concentration profile, temporal variation of average solids concentration, and frequency spectra, which were obtained from the ECT data, are presented.
Equilibrium theory analysis of rectifying PSA for heavy component production
Authors: Ebner Armin D. , Ritter James A.
Published: April 2004

An isothermal equilibrium theory analysis, based on linear isotherms and a binary feed stream, was carried out to evaluate the feasibility of a rectifying PSA process for producing a pure heavy component at high recovery. Analytic expressions were derived to describe the performance of this process at the periodic state. The performance was also analyzed in terms of the different concentration and velocity profiles exhibited during various cycle steps that included the analysis of complex shock and simple wave interactions. Based on a parametric study, periodic behavior was established for a wide range of process conditions; and a design study with the PCB activated carbon–H2–CH4 system at 25°C further demonstrated the feasibility of a rectifying PSA cycle for producing a 100% CH4 stream from a dilute feed stream (y = 0.01) with a respectable recovery (80%), and reasonable process conditions. It also demonstrated the potential usefulness of an actual rectifying PSA process for bulk gas separation and purification.