bluuebunny/crossref_metadata_2025_split huggingface dataset:
Nondispersive membrane solvent back extraction of Phenol
Authors: Basu R. , Prasad R. , Sirkar K. K. 
Published: June 2004

AbstractNondispersive back extraction of phenol from methyl isobutyl ketone into caustic solutions has been studied using microporous polymeric membranes in flat as well as hollow‐fiber form. Dispersion‐free reactive back extraction was successfully achieved using the correct phase pressure difference. The predictive capabilities of the mathematical models developed for such a system have been investigated. This study indicates that the overall mass transfer can be controlled by boundary layer resistance and/or the membrane transfer resistance, depending on the flow configuration, the nature of the membrane, and the regime of caustic concentration. Individual film transfer coefficients on the shell side and the tube side have been isolated for different hollow‐fiber modules. A commercially available 15 cm long module containing hydrophobic microporous hollow fibers has provided very low values of height of transfer unit (HTU) and very high phenol recoveries. The experimentally obtained HTUs of this module have been predicted with significant accuracy.
Effect of mixing on the precipitation of barium sulfate in an MSMPR reactorssss
Authors: Fitchett David E. , Tarbell John M. 
Published: June 2004

AbstractThe effect of mixing intensity (power input) on the precipitation/crystallization of barium sulfate in a two‐feedstream (sodium sulfate, barium chloride) continuous stirred‐tank crystallizer with mixed product removal was investigated through experiments and companion mathematical models. Crystal growth rate and nucleation rate were very sensitive to mixing intensity, with growth rate increasing eightfold and nucleation rate decreasing 100‐fold as power input per unit mass was increased from 0.001 to 0.73 m2/s3 (0 to 1,200 rpm stirrer speed). Experimental results at high feed concentration were accurately described by a model accounting for homogeneous nucleation and kinetic growth of particles as well as turbulent mass transfer to particles and turbulent micromixing of feedstreams. The principal mixing effect was due to particle mass transfer, not micromixing. Experiments at low feed concentration were more difficult to model because of a more complex nucleation mechanism and altered particle morphology.
Rigorous dynamics and feedforward control design for distillation processes
Authors: Rovaglio Maurizio , Ranzi Eliseo , Biardi Giuseppe , Fontana Marco , Domenichini Rosa 
Published: June 2004

AbstractFeedforward control has the theoretical potential for perfect control; therefore, research to simplify and improve the use of such a control strategy for possible industrial applications has potential value. A general model for simulation of controlled distillation columns is used to reproduce operating trends of some monitored variables for an industrial column. Comparisons between simulated and operating data show a general good agreement.When a rigorous model is available and can be proved reliable for practical purposes, the design of feedforward control schemes becomes viable and can be incorporated in the more conventional approach. A specific industrial example shows the practical implementation problems and the real economic value of a feedforward control strategy to optimize the process behavior. In particular, the feedforward control action can reduce the inherent error from changes in feed composition when a basic feedback control structure is used to infer composition.
Growth and dissolution of succinic acid crystals in a batch stirred crystallizer
Authors: Qiu Yanfeng , Rasmuson Åke C. 
Published: June 2004

AbstractGrowth and dissolution of succinic acid crystals have been studied in an isothermal stirred tank crystallizer. Seeded desupersaturation and deundersaturation experiments have been performed. Parameters of a desired growth rate equation are estimated by fitting the supersaturation balance equation directly to the supersaturation measurements. The procedure is based on nonlinear optimization techniques. Thus, uncertainties in the traditional approximation of the concentration vs. time curve are circumvented. The growth process for succinic acid crystals in an aqueous solution is found to be controlled by a significant resistance in both the volume diffusion step and in the surface integration step. An implicit equation is given to accurately represent the crystal growth rate as a function of the supersaturation. When extrapolating outside the range of experiments, this equation is shown to predict growth rates that are significantly different from those predicted by a corresponding power law expression. The dissolution rate exhibits a nonlinear dependence on undersaturation which is interpreted as changes in the crystal shape. Initial dissolution rate coefficients are in good agreement with volume diffusion coefficients obtained from growth experiments.
Lumped kinetics of many parallel nth‐order reactions
Authors: Ho T. C. , White B. S. , Hu R. 
Published: June 2004

AbstractThe kinetics of lumped nth‐order reactions are examined both asymptotically and numerically. The lumped kinetics in most cases are Mth order at large times. There exist two critical values for n, denoted by n* and n*, which are expressed explicitly as functions of the feed properties. It is shown that (1) M = n when n > n*, (2) M is linear in n when n* < n < n*, and (3) M does not exist when n = n* or n ≤ n*. Whenever the feed contains some unconvertibles, M is independent of n for −∞ < n < n*. The overall effective rate constant is not continuous at n = n* nor at n = n*. Unexpectedly, when n > n* the lump's long‐time behavior is governed by all species, not just by the most refractory species. Although the asymptotic kinetics are developed for long times, they are useful for fitting the whole‐time behavior of the lump by an mth‐order model. This is true even when M does not exist in the asymptotic regime. Numerical experiments show that M and m behave similarly in many respects. For example, as n increases, they both become closer to n and less dependent on the feed properties. Some published data are rationalized in light of the present results.
Prediction of slug frequency in horizontal two‐phase slug flow
Authors: Tronconi Enrico 
Published: June 2004

AbstractAvailable data on slug frequency in horizontal two‐phase intermittent flow are predicted with adequate accuracy by assuming that the slug frequency is one half of the frequency of the unstable waves precursors of slugs, as determined according to published analyses of finite amplitude waves in conduits. The experimental effects of gas and liquid flow rates, pipe diameter, gas density and liquid viscosity on slug frequency are explained by modifications of the wave properties due to changes in the liquid level of the stratified flow existing in the pipe inlet region prior to slug formation. Simple generalized equations are provided to estimate the slug frequency for engineering calculations.
Effect of adsorption on the optimal displacement of acidic crude oil by alkali
Authors: Ramakrishnan T. S. , Wasan D. T. 
Published: June 2004

AbstractRecovery of acidic crude oil from porous media can be enhanced by injection of alkaline agents. For this process we have analyzed the detrimental effect of alkali adsorption on the mineral surface. The model, which is an extension of our earlier inert solid model, was formulated by conserving three independent species. The previous solution procedure is shown to fail and a new analysis of composition paths is necessary. By introducing the notion of critical point, a short‐cut procedure is developed.The predicted profiles and effluent histories are discussed. A new result is that adsorption on the solid surface could change the ultimate recovery even for an infinite slug of alkali due to the reduced influence of the optimal region in displacing oil. Further, the influence of a favorable viscosity ratio in displacing oil is also shown to be reduced by adsorption.
Steady laminar round jets of a viscous liquid falling vertically in the atmosphere
Authors: Adachi K. , Tagashira K. , Banba Y. , Tatsumi H. , Machida H. , Yoshioka N. 
Published: June 2004

AbstractThe shape of a laminar, liquid jet emerging from a round vertical tube into the atmosphere and the total axial force exerted on the liquid filament at the tube exit were investigated experimentally over a wide range of flow conditions. An integral invariant of the exact solution was used to check consistency between the two kinds of data. A new equation to predict the jet shape agreed moderately well with the present experimental data as well as with various previous results. The key idea of the present work is that exact knowledge of the total axial force will be very useful to predict reasonably the jet shape at a given flow condition by means of a simplified approach or to check theoretical or empirical results on free falling jets.
Competitive hydrodesulfurization and hydrogenation in a monolithic reactor
Authors: Irandoust Said , Gahne Olof 
Published: June 2004

AbstractCompetitive liquid‐phase hydrodesulfurization of thiophene and hydrogenation of cyclohexene on a monolithic CoMo/γ‐Al2O3 catalyst were studied. The flow pattern in the monolithic catalyst reactor was segmented gas‐liquid flow (slug flow). The hydrogen pressure and the temperature were varied between 30–40 bar and 509–523 K, respectively. The experimental data are consistent with rate expressions of the Langmuir‐Hinshelwood type where the reactions proceed on two different types of active sites. This kinetic model is based on hydrogenation of the thiophene ring prior to sulfur elimination.
Selecting the best distillation control configuration
Authors: Skogestad Sigurd , Lundström Petter , Jacobsen Elling W. 
Published: June 2004

AbstractThe selection of an appropriate control configuration (structure) is the most important decision when designing distillation control systems. The steady state RGA is commonly used in industry for selecting the best structure. One counterexample to the usefulness of this measure is the DB configuration, which has infinite steady state relative gain array (RGA) values, but still good control performance is possible. This is indicated by high‐frequency RGA values close to 1. In this paper it is stressed that decisions regarding controller design should be based on the initial response (high‐frequency behavior) rather than the steady state.Based on a frequency‐dependent RGA analysis and optimal Pl controller designs of four different configurations, the (L/D) (V/B) configuration is found to be the best choice for two‐point composition control. The conventional LV configuration performs poorer than the above system, but is preferable if one‐point control is used.
Determination of flow profiles in porous media using shifts in gamma spectra
Authors: Jasti Jay K. , Fogler H. Scott 
Published: June 2004

AbstractA new technique was developed to determine the tracer location and fluid velocity in porous media nonintrusively. This technique exploits the competitive effects between the photoelectric interaction and the Compton scattering phenomenon to determine the distance between a radioactive tracer in a porous medium and an externally positioned detector. The photon energy distribution shifts toward lower photon energies as the tracer moves away from the detector. The shift in the energy distribution can be quantified by the ratio of the scattered photon intensity to the full energy photon intensity. A convective‐dispersion model was used to determine the spatial distribution of the radioactive tracer. An analog Monte Carlo method was developed to simulate photon transport in porous media. Comparison between experimental data and the model shows that in‐situ tracer velocities can be accurately predicted.
Mass transport with relaxation in polymers
Authors: Camera‐Roda Giovanni , Sarti Giulio C. 
Published: June 2004

AbstractThe non‐Fickian mass transport behavior observed in polymeric materials is here analyzed through a viscoelastic constitutive equation for the diffusive flux, endowed with concentration‐dependent relaxation time and diffusivity. The present model thus overcomes the limitations shown by Neogi's model and by the Cattaneo equation used by Camera‐Roda and Sarti. In addition to the Fickian behaviors at both small and high Deborah numbers, the model accounts for case II behavior and anomalous diffusion at intermediate Deborah number, possibly with the presence of a shock wave in the concentration profile which moves at a concentration‐dependent velocity. Weight uptake accelerations and overshoots are also accounted for at intermediate Deborah numbers. The dimensionless problem has been numerically solved and the role of the relevant dimensionless parameters is discussed for both sorption and desorption.
Development of circulating fluidized bed adsorber
Authors: Nakamura Susumu , Yoshimuta Shigeharu , Shirakashi Masataka , Kanno Masayoshi , Ito Yoshiro 
Published: June 2004

AbstractA new fludized bed which is divided in a looplike shape by a partition wall has been developed for recovering trace elements from a large quantity of industrial water. The bed, a circulating fluidized bed applicable to a liquid‐solid two‐phase flow, is called a circulating fluidized bed absorber (CFBA). Adsorbent particles are mixed and carried along with water in the CFBA. At the upper part of the bed, the absorbent particles are separated from the water flow and recycled in the bed; the depleted water flows out of a water outlet. The CFBA is operated at two to three times higher velocity than conventional liquid‐solid contacting systems. The pressure drop in the CFBA is in proportion to the amount of adsorbent suspended in the contacting section. Characteristics of the CFBA, including design considerations, are described.
Methanol synthesis in a trickle‐bed reactor
Authors: Pass Geoffrey , Holzhauser Craig , Akgerman A. , Anthony R. G. 
Published: June 2004

AbstractA novel approach to methanol production from coal‐derived synthesis gas is cocurrent gas and mineral oil feed flowing over a packed bed of catalyst in the trickle flow regime. Production rates of 0.7 to 2 kg/h · kg cat were obtained for a H2/(CO + CO2) ratio of 1 and at space velocities of 2,000 to 25,000 L/h · kg cat. Slurry reactor and bubble column productivities were substantially less for H2/(CO + CO2) ratios of 0.55 to 2.3 at similar conditions as the trickle‐bed reactor. Reaction temperature was 250°C in three types of reactors but 240°C in gas‐liquid phase Berty reactor; the pressure in the slurry and bubble column reactors was 52‐70 atm and in Berty Reactor 77.5‐100 atm, whereas 70 atm pressure was used in the trickle bed. Differences in production rates and conversions can be explained by the extent of backmixing in trickle‐bed and slurry reactors operating at the same conditions.
Microelectrode study of gallium deposition from Chlorogallate melts
Authors: Verbrugge Mark W. , Carpenter Michael K. 
Published: June 2004

AbstractMicroelectrodes are used to extract thermodynamic, transport, and kinetic data for the gallium trichloride/1‐methyl‐3‐ethylimidazolium chloride room‐temperature molten salt that has been used by the authors to form GaAs thin films. The gallium electrodeposition process, which must be understood for the analysis of the GaAs deposition process, is simulated numerically. A plausible gallium deposition mechanism is identified. Microcylinder electrodes are shown to be advantageous for the acquisition of physicochemical constants. Microdisk electrodes are employed to investigate current oscillation phenomena that appear to be related to metal crystallization processes.
The Benzylphenylether thermolysis mechanism: Insights from phase behavior
Authors: Wu Benjamin C. , Klein Michael T. , Sandler Stanley I. 
Published: June 2004

AbstractThe thermolysis of benzylphenylether (BPE) was examined at 320°C in liquid, vapor, and supercritical methanol phases as a probe of the reaction mechanism. Toluene and phenol were the major products in all cases, but observed selectivities were dependent upon the reaction phase. Isotopic labeling experiments demonstrated that methanol participated in the reaction network as a hydrogen donor through a free‐radical mechanism. These results are consistent with free‐radical steps for neat BPE primary pyrolysis that include BPE fission followed by hydrogen abstraction and radical recombination reactions. A detailed set of 21 free‐radical steps quantitatively explains the dependence of the selectivity and conversion on the phase behavior.
Heat transfer and population characteristics of dispersed evaporating droplets
Authors: Core K. L. , Mulligan J. C. 
Published: June 2004

AbstractThe direct‐contact heat transfer to a dispersed population of immiscible evaporating droplets is analyzed. Also studied is a population balance formulation for the distribution of two‐phase bubbles, which is similar to that utilized in particle and droplet dispersion analysis and is capable of including bubble coalescence and break‐up. It is shown that the method of classes is useful particularly in solving such problems when the growth functions are size‐ and time‐dependent and nonquadratic. The method is applied to a liquid cool‐down, representing the initial chilling stage of a direct‐contact batch crystallizer or cold‐storage unit wherein a vessel containing a liquid is chilled by injecting a dispersion of refrigerant droplets. Transient bubble population characteristics, volumetric heat transfer coefficient, total heat transfer, and liquid temperature are predicted, along with the liquid refrigerant holdup.
Simultaneous synthesis of mass‐exchange and regeneration networks
Authors: El‐Halwagi Mahmoud M. , Manousiouthakis Vasilios 
Published: June 2004

AbstractA systematic procedure is developed for the simultaneous synthesis of primary transfer mass‐exchange networks and their associated mass‐exchange regeneration networks. The purpose of the primary transfer network is to preferentially transfer certain species from a set of rich streams to a set of lean streams. The regeneration network aims at regenerating any recyclable lean stream. The proposed procedure deals with the problem in two stages. In the first stage, a mixed‐integer nonlinear program is solved to minimize the cost of mass‐separating and regenerating agents. The solution of this program provides the location of the pinch points as well as the optimal flow rates of all the lean and the regenerative streams without any prior commitment to the network structure. In the second stage, a mixed‐integer linear program is solved to minimize the number of exchangers in both networks. An example problem with industrial relevance is solved to elucidate the merits offered by the devised synthesis procedure.
Displacement separations by continuous annular chromatography
Authors: De Carli Joseph P. , Carta Giorgio , Byers Charles H. 
Published: June 2004

AbstractContinuous displacement chromatography separations are obtained using a continuous annular chromatograph (CAC). The apparatus consists of a rotating annular bed. At fixed positions at the top of the bed, four solutions are continuously supplied: the feed mixture to be separated, a displacer solution, a regenerant, and a rinse. The four solutions flow concurrently through the bed with little mixing. If the bed is sufficiently deep, a fully developed displacement train forms and the separated components are continuously recovered at various angular locations at the bottom of the bed. Mixtures of amino acid were separated by cation exchange displacement chromatography in a laboratory‐scale CAC. Separation and concentration of dilute mixtures was obtained with a continuous separation performance comparable with the performance of a conventional chromatograph. A mathematical model is developed to describe the separation and provide guidance in design and optimization.
Kinetic separation by pressure swing adsorption: Method of characteristics model
Authors: Ackley Mark W. , Yang Ralph T. 
Published: June 2004

AbstractA theoretical model using the method of characteristics is presented for a Skarstrom‐type pressure swing adsorption (PSA) cycle using carbon molecular sieve for the kinetic separation of nitrogen/methane mixtures. Good agreement with experimental results was obtained. The solution of the reduced nonlinear ordinary differential equations along characteristics, a variable computational grid from the changing bed velocity, and a constant product flow boundary condition are complications that prohibited using the method of characteristics in favor of finite difference or orthogonal collocation methods. These complications have been overcome in the present study to develop a theoretical model, incorporating nonlinear isotherms and a linear driving force rate for diffusion, which requires less computer time and is particularly amenable for studying transient bed dynamics. The effects of feed pressure and concentration, half‐cycle time, and product flow rate on kinetic PSA performance are also illustrated.
Homogeneous nucleation in supercritical fluids
Authors: Debenedetti Pablo G. 
Published: June 2004

AbstractWhen a supercritical solution is rapidly expanded, large solute supersaturations can be attained, and small particles are formed. The evolution of the homogeneous nucleation rate, work of nucleus formation, and critical nucleus size along different expansion paths is investigated here for the model system phenanthrene‐carbon dioxide. Nucleation rates are the result of the competition among solvent expansion, cooling due to depressurization, and high supersaturation. Although supersaturations can reach very high values (> 106), relatively flat nucleation rate profiles result due to cooling and expansion. For an interfacial tension of 0.02 N/m, computed nucleation rates never exceed 104 s−1 · cm−3. A substantial fraction of the maximum nucleation rate is attained with partial decompression to pressures above 1 bar.
Intensification of pressure swing adsorption processes
Authors: Rota Renato , Wankat Phillip C. 
Published: June 2004

AbstractScaling rules have been developed which are able to change the dimension of a pressure swing adsorption plant keeping its main performance constant. Such scaling rules result from a system of algebraic equations which arises by constraining the solution of a fairly general dimensionless mathematical model to be the same in the old and new plant configuration. Different heat and mass transfer mechanisms, purification, and multicomponent bulk separation processes, both isothermal and nonisothermal, have been considered. Furthermore, the influence of different equilibrium isotherms and the main practical limitations have been discussed. The application of these rules shows that column size can be reduced significantly by using smaller particles in shorter beds with rapid cycles.