bluuebunny/crossref_metadata_2025_split huggingface dataset:
Kinetic and thermodynamic analysis of liquid‐phase benzene hydrogenation
Authors: Singh Utpal K. , Vannice M. Albert 
Published: April 2004

AbstractLiquid‐phase benzene hydrogenation on Pd/η‐Al2O3 catalysts was studied between 358 and 488 K and over an H2 pressure range of 7 to 54 atm. Kinetic data were obtained under differential reaction conditions that were free of all transport limitations, thus allowing the development of a kinetic model that could be compared to that for the vapor‐phase reaction. In contrast to vapor‐phase studies at 1 atm, no activity maximum was observed during liquid‐phase hydrogenation between 358 and 493 K and at 54‐atm H2 pressure. A model that invokes dissociative, noncompetitive H2 adsorption, addition of the first H atom as the rate‐determining step, and a concurrent dehydrogenated benzene surface species was consistent with experimental observations. The fitted parameters were thermodynamically consistent and agreed with those from previous vapor‐phase studies. In addition, thermodynamic analysis of the quasi‐equilibrated hydrogen adsorption process indicates that in the presence of solvent effects, increasing hydrogen solubility in the liquid phase can increase the surface coverage of hydrogen. In the absence of any solvent effect, however, surface coverage depends only on the partial pressure of hydrogen and is independent of the nature of the solvent. Furthermore, when solvent effects exist, use of the liquid‐phase hydrogen concentration in the rate expression yields a solvent‐independent adsorption equilibrium constant, while in the absence of solvent effects, P should be used in the rate expression to acquire this parameter.
Modeling the sorption of toxic metals on chelant‐impregnated adsorbent
Authors: Ravindran Varadarajan , Stevens Mario R. , Badriyha Badri N. , Pirbazari Massoud 
Published: April 2004

AbstractThe application of a microporous adsorbent, such as activated carbon impregnated with 8‐hydroxyquinoline (oxine), a chelating agent, to remove toxic metals from the aqueous phase is studied. A pore and surface diffusion model for predicting the dynamics of fixed‐bed adsorbers using oxine‐impregnated carbon is also discussed. The model incorporates adsorption equilibrium and kinetic parameters determined from independent isotherm tests and rate experiments, as well as adsorber column flow characteristics. Three modeling scenarios were employed with reference to intraparticle transport: (a) combined pore diffusion and surface diffusion; (b) pore diffusion alone, suppressing the effect of surface diffusion; and (c) surface diffusion alone, suppressing the effect of pore diffusion. Surface diffusion alone provided reasonably good predictions of the adsorber dynamics, as reflected by results from adsorber experiments. It is postulated that the sorption mechanism could be a combination of film transport of metal ions, followed by surface diffusion into adsorbent particles, and subsequent chelation of metal ions with the oxine molecules sorbed on carbon. The sorbed metals could be completely recovered under acidic conditions during the carbon regeneration process.
Gasification of spent alkylation sulfuric acid droplets in hot environments
Authors: Wang Difei F. , Shaw Benjamin D. , Yang Albert 
Published: April 2004

AbstractExperimental results on gasification behaviors of freely‐falling spent alkylation sulfuric acid droplets in high‐temperature environments are presented, as well as baseline data on evaporation of water droplets and sulfuric acid droplets. Low evaporation constants have been measured for sulfuric acid droplets and spent acid droplets (relative to water droplets). Shape distortions and fragmentation (microexplosions) of spent acid droplets were also observed, and it has been found that initial droplet diameters are important in determining onset times and intensities of microexplosive behaviors. Simplified theory is developed, which suggests that the droplet distortion and fragmentation behaviors may be a result of SO2 bubble formation inside the droplets.
Tailor‐made asymmetric PVDF hollow fibers for soluble gas removal
Authors: Li K. , Kong J. F. , Wang Dongliang , Teo W. K. 
Published: April 2004

AbstractTailor‐made polyvinylidene fluoride (PVDF) asymmetric hollow‐fiber membranes and their membrane modules were employed for soluble gas removal, such as H2S from waste gas streams. This study focused on the techniques of fabricating and characterizing the PVDF asymmetric hollow‐fiber membranes and their membrane modules for removal of H2S using an aqueous solution containing 10% NaOH. A laminar parabolic velocity profile was used to characterize the flow of the H2S gas mixture in the hollow‐fiber lumen. Effects of operating conditions and the morphological structures of the membranes on the membrane´s coefficient, kAM, were examined both theoretically and experimentally. The capabilities of the hollow‐fiber membranes developed for removal of H2S from waste gas streams were evaluated and compared with conventional symmetric hydrophobic hollow‐fiber membranes, such as polypropylene. An analysis of H2S transfer across the more developed PVDF membranes reveals that the membrane´s coefficient, kAM, evaluated from its structure parameters, such as the effective surface porosity and mean radius, agreed well with the experimental data obtained from absorption experiments.
Gas permeation properties of ion‐exchanged faujasite‐type zeolite membranes
Authors: Kusakabe K. , Kuroda T. , Uchino K. , Hasegawa Y. , Morooka S. 
Published: April 2004

AbstractNaY‐type zeolite membranes were synthesized on a porous support tube by a hydrothermal process. The membranes were ion‐exchanged with Li+ and K+ ions, and permeances through the membranes were determined for an equimolar mixture of CO2 and N2, as well as for single‐components thereof, at a temperature range of 0–400°C. The permeance to CO2 showed a maximum at 100°C, but CO2/N2 selectivity decreased with increasing temperature. The zeolite membranes that were exchanged with K+ and Li+ ions gave higher and lower CO2/N2 selectivities, respectively, than were found for the NaY‐type membrane. The permeation properties of the ion‐exchanged zeolite membranes were analyzed using a sorption–diffusion model. The high CO2/N2 selectivity of the K‐exchanged membranes can be explained by the decrease in N2 sorptivity for the mixed feed.
Global optimization of a dryer by using neural networks and genetic algorithms
Authors: Hugget A. , Sébastian P. , Nadeau J.‐P. 
Published: April 2004

AbstractFor many optimum design problems, the objective function is the result of a complex numerical code and may not be differentiable and explicit. The first aim is to propose a way of solving such complexity on an example problem. A novel and global strategy involving artificial neural networks and a genetic algorithm is presented and validated for an industrial convective dryer. To begin with, a method to represent a drying model using artificial neural networks is defined. This method is tested and the results are compared with those obtained with classic numerical methods. This approach drastically reduces simulation times and maintains good accuracy and generalization properties. Second, the associated optimal design problem is considered. This optimization appears as a difficult combinatorial problem with a complex objective function that involves different economical criteria. The second aim is to present the methodology to solve this problem using genetic algorithms. Final results illustrate the efficiency of this global approach.
Heat exchanger network retrofit considering pressure drop and heat‐transfer enhancement
Authors: Nie X. R. , Zhu X. X. 
Published: April 2004

AbstractFor the heat‐exchanger‐network (HEN) retrofit project to be successful it should satisfy not only a specified heat‐recovery target but also pressure‐drop constraints. The problem of dealing with the pressure‐drop aspects is very complex, since there are many options that affect pressure drop. To integrate these options more systematically and solve this problem more effectively, a decomposition strategy is proposed. At the first stage, the unit‐based model is used to indicate which units require additional area. In the second stage, special attention is paid to these units, where area distribution, shell arrangements, the use of heat‐transfer enhancement, and other options are optimized for these units. At the same time, the units without additional area requirement are modeled using simple models. Thus units with and without additional area requirements are treated differently during optimization. By doing this, the pressure drop can be calculated accurately while the overall model remains simple and easy to solve. Heat‐transfer enhancement is a very attractive option for HEN retrofit, since it can effectively eliminate or reduce the additional surface area space. This will eliminate additional piping, new shells or units, and their required space, which lead to much lower modification costs and less implementation time.
Hierarchical procedure for plantwide control system synthesis
Authors: Zheng Alex , Mahajanam Rama V. , Douglas J. M. 
Published: April 2004

AbstractA hierarchical procedure for synthesizing an optimal plantwide control system is proposed for an existing continuous chemical process. Alternative plantwide control systems are synthesized and are compared based on economics. The cost associated with dynamic controllability is quantified by the controllability index ν introduced by Zheng and Mahajanam (1999). The procedure is illustrated on a simple reactor‐separator‐recycle system. Although the procedure is discussed for an existing plant, a simple modification of the approach can be used to determine the optimum surge capacities of a process, including reflux drums and column sumps—a problem of increasing interest.
Steady states and constraints in model predictive control
Authors: Rao Christopher V. , Rawlings James B. 
Published: April 2004

AbstractStudies on the theory of model predictive control include the assumption that the origin is in the interior of the feasible region (that is, the inequality constraints are not active at steady state). The reason for making this assumption is that without it one cannot guarantee feasibility of the control problem on the infinite horizon because of the finite horizon parameterization of the input with an unconstrained linear feedback law. As demonstrated in this article, however, this assumption often does not hold in practice. A strategy for handling inequality constraints active at steady state is presented by projecting the system onto the active constraints under the finite horizon parameterization of the input, as well as an algorithm for constructing the optimal linear feedback law that constrains the system to the active constraints. Feasibility is obtained using output admissible sets. For the steady‐state target calculation, we propose an algorithm utilizing exact penalties that treats systems in a unified fashion with more inputs than outputs and vice versa. Assuming the system is detectable, it is proven that the algorithm yields a unique steady‐state target.
Nonlinear control of particulate processes
Authors: Chiu Timothy , Christofides Panagiotis D. 
Published: April 2004

AbstractA general methodology is proposed for the synthesis of practically‐implementable nonlinear output feedback controllers for spatially‐homogeneous particulate processes modeled by population balance equations. Initially, a nonlinear model reduction procedure based on a combination of the method of weighted residuals and the concept of approximate inertial manifold is presented for the construction of low‐order ordinary differential equation (ODE) systems that accurately reproduce the dominant dynamics of the particulate process. These ODE systems are then used for the synthesis of nonlinear low‐order output feedback controllers that enforce exponential stability in the closed‐loop system and achieve particle‐size distributions with desired characteristics. Precise closed‐loop stability conditions are given and controller implementation issues are discussed. The proposed nonlinear control method is successfully applied to a continuous crystallizer, and is shown to outperform a proportional‐integral controller and cope effectively with model uncertainty and measurement delays.
Three‐dimensional developing flow model for photocatalytic monolith reactors
Authors: Hossain Md. Moazzem , Raupp Gregory B. , Hay Steven O. , Obee Timothy N. 
Published: April 2004

AbstractA first‐principles mathematical model describes performance of a titania‐coated honeycomb monolith photocatalytic oxidation (PCO) reactor for air purification. The single‐channel, 3‐D convection–diffusion–reaction model assumes steady‐state operation, negligible axial dispersion, and negligible homogeneous reaction. The reactor model accounts rigorously for entrance effects arising from the developing fluid‐flow field and uses a previously developed first‐principles radiation‐field submodel for the UV flux profile down the monolith length. The model requires specification of an intrinsic photocatalytic reaction rate dependent on local UV light intensity and local reactant concentration, and uses reaction‐rate expressions and kinetic parameters determined independently using a flat‐plate reactor. Model predictions matched experimental pilot‐scale formaldehyde conversion measurements for a range of inlet formaldehyde concentrations, air humidity levels, monolith lengths, and for various monolith/lamp‐bank configurations. This agreement was realized without benefit of any adjustable photocatalytic reactor model parameters, radiation‐field submodel parameters, or kinetic submodel parameters. The model tends to systematically overpredict toluene conversion data by about 33%, which falls within the accepted limits of experimental kinetic parameter accuracy. With further validation, the model could be used in PCO reactor design and to develop quantitative energy utilization metrics.
Diagnosis and optimization approach for heat exchanger network retrofit
Authors: Zhu X. X. , Asante N. D. K. 
Published: April 2004

AbstractA new modeling approach for HEN retrofit design is discussed. The design task consists of a search for topology changes, called the diagnostic stage, followed by an evaluation stage and a cost optimization stage. Promising modifications are selected from the diagnosis stage and assessed in terms of the impacts on implementation cost, operability, and safety. The options deemed impractical are removed and the remaining ones are optimized together with the existing HEN to give the final HEN retrofit design. The new approach combines mathematical optimization techniques with a better understanding of the retrofit problem, based on thermodynamic analysis and practical engineering, to produce a systematic procedure capable of efficiently solving industrial‐size retrofit problems. The network pinch concept provides new insights to the HEN retrofit problem and plays an important role in selecting promising modifications, forming the foundation of the new method. This concept, when applied to mathematical formulation, significantly simplified the mathematical models while maintaining good quality of solutions. This approach allows the design tasks to be automated with user interactions.
Monitoring and diagnosing batch processes with multiway covariates regression models
Authors: Boqué Ricard , Smilde Age K. 
Published: April 2004

AbstractMultivariate statistical procedures for monitoring the behavior of batch processes are presented. A new type of regression, called multiway covariates regression, is used to find the relationship between the process variables and the quality variables of the final product. The three‐way structure of the batch process data is modeled by means of a Tucker3 or a PARAFAC model. The only information needed is a historical data set of past successful batches. Subsequent new batches can be monitored using multivariate statistical process control charts. In this way the progress of the new batch can be tracked and possible faults can be easily detected. Further detailed information from the process can be obtained by interrogating the underlying model. Diagnostic tools, such as contribution plots of each of the variables to the observed deviation, are also developed. Finally, on‐line predictions of the final quality variables can be monitored, providing an additional tool to see whether a particular batch will produce an out‐of‐spec product. These ideas are illustrated using simulated and real data of a batch polymerization reaction.
Gas‐phase polymerization of propylene with a highly active ziegler‐natta catalyst
Authors: Samson Job Jan C. , van Middelkoop Bart , Weickert Günter , Westerterp K. Roel 
Published: April 2004

AbstractThe polymerization of propylene in the gas phase has been studied with the same high‐activity catalyst as was used for liquid‐phase polymerizations in earlier work. Catalyst injection, the influence of the support bed, and precontacting of the catalyst with the cocatalyst and the electron donor have been investigated. Furthermore, different ways of prepolymerization were tested. The kinetics can be described with the same model as was used for the liquid‐phase polymerizations. The reaction rate was proportional to the pressure at pressures above 5 bar; at lower pressures the rates are lower. Comparison of the reaction rates in the gas phase and liquid phase showed the rates in the gas phase were still lower than in the liquid phase. The fast decay observed in the gas‐phase polymerizations indicated that thermal runaway and deactivation may occur at temperatures above 40–45°C.
Gas separation properties of organosilicon plasma polymerized membranes
Authors: Roualdes Stéphanie , Van der Lee Arie , Berjoan René , Sanchez José , Durand Jean 
Published: April 2004

AbstractThin films were polymerized from different organosilicon compounds in a radio‐frequency plasma deposition process. The properties of the layers were characterized with respect to the deposition rate, the density, the refractive index, and the chemical structure determined by FTIR and XPS analysis. The qualification of the films for gas‐selective membranes was tested on different porous substrates using N2, H2, O2, CO2, and CH4. Both structure and permeation performances of the synthesized films were correlated with the composite plasma parameter V/F·M (V: input voltage; F: monomer flow rate; M: monomer molecular weight). At low V/F·M ratio, the thin layers are mainly constituted of the [(CH3
)2–Si(–O)2] environment (monomer and polydimethylsiloxane one). Increasing the V/F·M results in a more “inorganic” chemical structure, higher O/Si ratio, refractive index, and density, the materials tend toward a silicalike structure. Concurrently, the prepared membranes have solution–diffusion‐controlled or Knudsen‐like separation factors, depending on whether plasma conditions are soft or hard.
Neural‐network modeling and optimization of induced foreign protein production
Authors: Tholudur Arun , Ramirez W. Fred 
Published: April 2004

AbstractAn experimental verification and validation of the neural network parameter function approach to modeling dynamic systems is provided. The neural‐network parameter‐function modeling scheme utilizes some a priori process knowledge (usually material balances) and experimental data to develop a dynamic neural‐network model. Other models based on fundamental principles are also developed. The experimental system under consideration is the host‐vector system Escherichia coli D1210 and plasmid pSD8, which produces the foreign protein β‐galactosidase under the effect of the inducer IPTG. Optimal operational conditions are derived and the neural‐network‐based model is shown to better predict the dynamics and optimum for protein production than the proposed fundamental kinetic models.
Synthesis approach to the determination of optimal waste blends under uncertainty
Authors: Chaudhuri Prosenjit , Diwekar Urmila 
Published: April 2004

AbstractThe generalized approach to the problem of synthesis under uncertainty is to formulate it as a stochastic optimization problem that involves optimization of a probabilistic function obtained by sampling over uncertain variables. The computational burden of this approach can be extreme and depends on the sample size used for characterizing the parametric uncertainties. A new and efficient approach for stochastic process synthesis is presented. The goals are achieved through an improved understanding of the sampling phenomena based on the concepts derived from fractal geometry. A new algorithm for stochastic optimization based on these concepts to accelerate the process of synthesis under uncertainty is presented. Apart from the benchmark HDA synthesis problem, a real‐world problem of synthesizing optimal waste blends is analyzed to test the applicability of this novel approach in addressing the general problem of synthesis under uncertainty. The solution of this real‐world large‐scale synthesis problem is presented under uncertainty through the application of the new stochastic annealing algorithm, which takes into consideration novel sampling methods used in probabilistic analysis of process models.
Measurement of the filtration diffusivity D(ϕ) of a flocculated suspension
Authors: Landman Kerry A. , Stankovich J. M. , White Lee R. 
Published: April 2004

AbstractIn modeling the pressure filtration of flocculated suspensions using compressional rheology, the filtration diffusivity function D(ϕ) plays the role of a diffusion coefficient in determining the time scale of the filtration process. Its dependence on volume fraction is an important factor in filtration process design. The volume of filtrate expressed per unit membrane is V = βt1/2. The value of β depends on D(ϕ) and various relationships between the two that involve data differentiation have been discussed in the literature. These involve an unknown but bounded parameter. Here a physical approximation is made that justifies setting this parameter to zero. Further, a new approximate expression for β2 in terms of D(ϕ) that avoids data differentiation is determined. Alternatively, the hindered settling factor can be recovered from an analytic expression involving data differentiation of β data with applied pressure. The accuracy of each of these approximations is assessed.
Dynamic rate‐based model for multicomponent batch distillation
Authors: Kreul L. U. , Górak A. , Barton P. I. 
Published: April 2004

AbstractDynamic rate‐based approach for modeling and simulating batch distillation is presented. To predict separation efficiencies, mass transfer was considered explicitly using the Maxwell‐Stefan. Process dynamics were modeled by considering all relevant dynamic changes in the system, including the column periphery. The model, implemented at the large‐scale ABACUSS modeling environment, addresses implications of the dynamic and multicomponent nature of the process for its mathematical representation, the use of mass‐transfer coefficients, and the need for further experimental correlations. To validate the model, a series of separations of the highly nonideal quaternary system of methyl acetate, methanol, acetic acid, and water in a pilot‐plant batch‐distillation column with structured packings were conducted. The results show that a rate‐based approach can predict the column operation within the experimental error over the entire operation time without fitting of any kind. For the first time the use of a rate‐based approach on the ground of the Maxwell‐Stefan equations for a multicomponent batch‐distillation process was validated experimentally. Comparison of predictions of the rate‐based approach with simulations based on an equally tailored equilibrium‐stage model shows that the largest differences between the two approaches occur in short periods of very significant changes in the column profile. The additional effort of rate‐based modeling can be justified for the design of operating policies of multicomponent batch‐distillation processes.