bluuebunny/crossref_metadata_2025_split huggingface dataset:
Process analyzer location and performance assessment for optimal process monitoring
Authors: van den Berg Frans W. J. , Boelens Hans F. M. , Smilde Age K. , Hoefsloot Huub C. J. 
Published: April 2004

AbstractThe influence of process analyzer location and performance on plant‐wide process monitoring was evaluated using five uncertainty contributions to the estimation error: measurement error/uncertainty, analysis frequency, sample size/grab error, analyzer memory effect/response correlation, and delay time. The choice of both the location and performance characteristics of different process analyzers can be evaluated using a measurability factor M, ranging from zero to one, where one indicates perfect monitoring capabilities. Due to the unifying nature of the measurability factor, this factor can be used to make a rational decision between very different process analyzers. This allows for finding optimal process analyzer configurations for existing processes or for processes in the design phase. A tubular reactor simulation model was used for the partial oxidation of benzene to maleic anhydride to demonstrate the use of the measurability factor.
Surface diffusion and adsorption of hydrocarbons in activated carbon
Authors: Do H. D. , Do D. D. , Prasetyo I. 
Published: April 2004

AbstractAdsorption and diffusion in a porous media were studied theoretically and experimentally with a differential transient permeation method. The porous medium is allowed to equilibrate at some specified loading, and then the time trajectory of the permeation process is followed after a small difference between the pressures at the end faces of the porous medium is introduced at time t = 0 +. Such a trajectory vs. time would contain adsorption and diffusion characteristics of the system. By studying this for various surface loadings, pore and surface diffusions can be fully characterized. Mathematical modeling of transient permeation is detailed for pure gases or vapors diffusion and adsorption in porous media. Effects of nonlinearity of adsorption isotherm, pressure, temperature and heat effects were considered in the model. Experimental data of diffusion and adsorption of propane, n‐butane and n‐hexane in activated carbon at different temperatures and loadings show the potential of this method as a useful tool to study adsorption kinetics in porous media. Validity of the model is best tested against the transient data where the kinetics curves exhibit sigmoidal shape, which is a result of the diffusion and adsorption rate during the initial stage of permeation.
Cavitation reactors: Efficiency assessment using a model reaction
Authors: Gogate Parag R. , Shirgaonkar Irfan Z. , Sivakumar M. , Senthilkumar P. , Vichare Nilesh P. , Pandit Aniruddha B. 
Published: April 2004

AbstractAcoustic and hydrodynamic cavitation can be used for a variety of applications ranging from biological applications such as cell disruption to chemical reactions such as oxidation of organic pollutants in aqueous effluents, including biorefractory toxic chemicals. Different equipment used for cavitational effects was compared based on a model reaction (decomposition of potassium iodide resulting into iodine liberation). A correlation was developed for the prediction of the cavitational yield in terms of the cavity collapse pressure. This correlation, when used with earlier correlations for the pressure amplitude generated during the violent collapse of cavities, will help design engineers to choose particular equipment, operating conditions, and geometric parameters to achieve a desired chemical change. The developed equation relating the macroscopic reaction rates with the collapse pressure is the first of its kind reported in the literature. Pilot‐plant‐scale hydrodynamic cavitation orifice plate setup is most energy‐efficient, with significantly higher cavitational yields for the model reaction.
Enhancing performance of three‐phase catalytic packed‐bed reactors
Authors: Wilhite B. A. , Wu R. , Huang X. , McCready M. J. , Varma A. 
Published: April 2004

AbstractOur previous theoretical work predicted the possibility of enhancing three‐phase packed‐bed reactor performance by operating in the pulsing‐flow regime. This article deals with the experimental study of the beneficial effect of pulsing flow on reaction outcome. Hydrogenation of phenylacetylene, dissolved in n‐tetradecane over Pt/alumina catalyst, was chosen as the experimental reaction system. This is a triangular reaction, with styrene and ethylbenzene as the desired intermediate and final products, respectively. With properly designed experiments, the reaction performance in pulsing flow and trickling‐flow regimes was compared directly. The effects of process variables such as temperature, feed flow rates, and reactant concentration on reaction behavior were studied. A simplified model to describe the qualitative trends was also developed. Both experiments and calculations show that the yield of styrene is higher in pulsing flow than in trickling flow, which confirms the advantages of pulsing‐flow operation predicted by the theoretical work.
Spectroscopic measurement of solid solubility in supercritical fluids
Authors: Ngo Truc T. , Bush David , Eckert Charles A. , Liotta Charles L. 
Published: April 2004

AbstractDifferent in situ spectroscopic techniques, including infrared, ultraviolet, and fluorescence, were developed to measure the solubility of organic solids in supercritical carbon dioxide (scCO2). These techniques are applicable over a wide range of concentrations, as low as 10−6 or 10−7 mol fraction, where the conventional flow method is ineffective and less accurate. No separate calibration is required; in fact, the molar absorptivity is determined at the saturation point as an additional benefit. While this technique requires more time per data point, it is more accurate and unbiased than traditional methods at lower concentrations. The Patel‐Teja equation of state was used to correlate the data and expand the data for the ternary system. Data are reported for anthracene, 1,4‐naphthoquinone, and 2‐naphthol in scCO2 and CO2 with methanol cosolvent at 313 K and a pressure range from 7 to 21 MPa.
Thermodynamics of paint‐related systems with engineering models
Authors: Lindvig Thomas , Michelsen Michael L. , Kontogeorgis Georgios M. 
Published: April 2004

AbstractPaints are complex materials composed of polymers (binders) dissolved in one or more solvents, pigments, and other additives. The thermodynamics of such systems is essential, for example, for selecting improved solvents and understanding a number of phenomena related especially to adhesion to solid surfaces and drying. Many engineering models have been applied over the last decades for solutions with commoditity polymers. In this work, the performance of some of these models is investigated for paint‐related systems, focusing on those drying by the so‐called “lacquer mechanism” (evaporation of solvents). These are the Entropic‐FV, UNIFAC‐FV, GC‐Flory, and the Flory‐Huggins models using various ways for estimating the FH parameter via solubility parameters. Achievements and shortcomings of these models are discussed in conjunction with difficulties encountered in such calculations. We conclude that, despite the uncertainties involved, several models yield reasonably accurate activity coefficients, even at infinite dilution. Thus, engineering models may be useful for solvent selection via semiempirical rules of thumb, which are based on thermodynamic considerations.
Hybrid SNCR‐SCR technologies for NOx control: Modeling and experiment
Authors: Wendt Jost O. L. , Linak William P. , Groff Paul W. , Srivastava Ravi K. 
Published: April 2004

AbstractThe hybrid process of homogeneous gas‐phase selective noncatalytic reduction (SNCR) followed by selective catalytic reduction (SCR) of nitric oxide (NO) was investigated through experimentation and modeling. Measurements, using NO‐doped flue gas from a gas‐fired 29 kW test combustor, provided data that allowed a fundamentally based catalyst monolith model, adapted from the literature, to be calibrated. The SCR model, which included pore and gas film diffusion (molecular and Knudsen) and Langmuir‐Hinshelwood surface reaction kinetics, used published values for the catalyst pre‐exponential factor and activation energy, and experimental measurements to determine the previously unavailable ammonia (NH3) adsorption coefficient on the catalyst surface. Then, with no further adjustment, a combined SNCR‐SCR model was developed using literature values for the reaction rate coefficients of 112 elementary homogeneous reactions. This combined model agreed well with combined SNCR‐SCR data. The combined model was then extrapolated to practical coal combustion conditions, and the economic benefits of a combined SNCR‐SCR process were explored. With a desired total NO reduction of 95% and NH3 slip in the exhaust constrained not to exceed 5 ppm, adding SNCR led to only modest decreases in the required SCR catalyst volume. Estimated system capital and annualized costs were not economically viable unless the SNCR portion by itself reduced more than 60% of the NO.
Coalescence analysis through small‐angle light scattering
Authors: Priore Brian E. , Walker Lynn M. 
Published: April 2004

AbstractFlow‐induced coalescence in complex flow fields is studied using an in situ, real‐time small‐angle light scattering technique. Coalescence in a model polyisobutene–polydimethylsiloxane immiscible blend is triggered through step‐downs in the flow rate, creating a transition from a breakup‐controlled morphology to one controlled by coalescence. Inducing droplet breakup, by increasing the flow rate during the coalescence process, is a reliable probe of the structural changes occurring during the step‐down. The coalescence rate, duration of the transient structure, and final droplet size depend strongly on the blend viscosity ratio. Coalescence occurs at extremely dilute droplet concentrations, and an inverse relationship between concentration and time to steady state is observed. Models, developed for simple shear flow, qualitatively describe the coalescence and breakup processes, indicating their potential for predicting these phenomena in processing flows.
Experimental study of turbulent mixing in a tee mixer using PIV and PLIF
Authors: Pan Gang , Meng Hui 
Published: April 2004

AbstractTurbulent scalar mixing in the near field of a tee mixer (transverse jet in a pipe) was studied using particle image velocimetry and planar laser induced fluorescence. Two jet‐to‐pipe velocity ratios r = 3.06 and r = 5.04 were investigated for a turbulent pipe flow at a Reynolds number of 20,850. Laser measurement techniques are described, typical flow structures in the near field of tee mixer are examined, and turbulence statistics and scalar statistics are calculated. The general behavior of mixing is analyzed from the jet expansion and the concentration decay along the jet centerline, and the flow condition for jet impingement on the pipe wall is estimated. The mixing mechanism in the near field is revealed from the variation of the scalar PDF across the jet. The mixing on the upstream side of the jet is dominated by large‐scale structures and on the downstream side by small eddies and turbulent diffusion, where the β‐PDF is an excellent approximation.
Drag and stability of objects in a yield stress fluid
Authors: Jossic Laurent , Magnin Albert 
Published: April 2004

AbstractThe drag force exerted on objects in a yield stress fluid was measured when the velocities become infinitely slow. In these quasi‐static conditions, yield stress effects are predominant. Particular care was paid to determining the yield stress and checking interface conditions when characterizing these fluids from a rheometric standpoint. Drag coefficients could then be determined for interesting objects of various shapes. The important role of fluid‐object interface effects was also highlighted. On the basis of these results, a stability criterion is proposed for the object in the fluid, to estimate the yield stress needed to balance buoyancy forces.
Simple model for power consumption in aerated vessels stirred by Rushton disc turbines
Authors: Paglianti A. , Takenaka K. , Bujalski W. 
Published: April 2004

AbstractAccurate prediction of power consumption of impeller in an aerated vessel is crucial for a successful scale‐up, operation, and design of reactors in general. A mechanistic model with a correlation that can accurately predict power consumption was developed. Taking into account both geometrical parameters and physical properties of the working fluids, this model reduces the number of adjustable parameters better than published empirical relations. It has the advantage of allowing the user to easily scale up agitated vessels and to evaluate power consumption even for large‐scale equipment. It has been tested only for Rushton turbines, however, because it is simply based on mass balances, energy balances and continuity equations, it could also be implemented for use with other impellers with very few modifications.
Dispersion of fine powder agglomerates under microgravity
Authors: Pyatenko A. , Takeuchi H. , Chiba S. , Ohyama Y. 
Published: April 2004

AbstractDispersion is a very important step in powder handling. Microgravity environments were applied to study the process of powder dispersion with an orifice for low transportation gas velocities and for widely sized particle agglomerates. Particle‐size distributions were measured for particles after passing through the orifice, and the results were compared with the size distributions of primary particles. Data analysis showed that the main factor determining the dispersion efficiency is the inertial parameter. Two approaches are proposed for estimating the inertial parameter in a wide range of Reynolds numbers.
Effect of relative solubility on amino acid crystal purity
Authors: Givand Jeffrey C. , Teja Amyn S. , Rousseau Ronald W. 
Published: April 2004

AbstractThe ratio of the pure‐component solubility of a primary solute to that of an impurity in the same solvent has a dramatic impact on crystal purity when lattice substitution is the dominant mechanism of impurity incorporation in the crystal. This is demonstrated for a model system of isoleucine and leucine in which leucine is the impurity. The pure‐component solubility ratios of isoleucine to leucine in mixed solvents were measured and used to select solvents that could affect the lattice substitution of leucine in isoleucine crystals. Addition of electrolytes and/or cosolvents to aqueous solutions of the two amino acids improved the purity of isoleucine crystals obtained by cooling.
Multicomponent thermally coupled systems of distillation columns at minimum reflux
Authors: Fidkowski Zbigniew T. , Agrawal Rakesh 
Published: April 2004

AbstractA method for calculating the minimum vapor flow in a ternary fully thermally coupled system of distillation columns was developed earlier by Fidkowski and Krolikowski. This method was developed further for fully thermally coupled systems separating four or more components. For multicomponent mixtures having constant relative volatilities and equal latent heats, the method leads to the identification of all of the minimum vapor flow rates in each distillation column that provide the same overall minimum heat duty in the reboiler. The quaternary fully coupled system of columns requires less heat energy than conventional configurations. These savings are often on the order of 20–50%.
Oxygen barriers that use free radical chemistry
Authors: Yang Chuanfang , Cussler E. L. 
Published: April 2004

AbstractOxygen barriers made of linoleic acid, ethyl cellulose and a cobalt catalyst can reduce oxygen penetration over 2,000 times compared with an ethyl cellulose barrier of the same thickness. The barrier is effective only when the product of linoleic acid concentration and barrier thickness exceeds a critical value, which is apparently necessary to effectively initiate the reaction. When this condition is met, the time that the barrier is effective can be predicted using a theory that assumes oxygen consumption is diffusion‐controlled. Operating in this condition, the barrier is about 70% efficient, that is, about two‐thirds for the double bonds available in linoleic acid react with oxygen. The results provide a rationale for the design of better oxygen barriers.
Effects of catalyst activity profiles on polyethylene reactor dynamics
Authors: Wells Gary J. , Ray W. Harmon , Kosek Juraj 
Published: April 2004

AbstractThe dynamics and stability characteristics of slurry loop and tank reactors were studied using continuation analysis to examine the effects of catalyst activity profiles on reactor dynamics. The production of high‐density polyethylene through the copolymerization of ethylene with hexene was studied using catalysts of the decay type (for example, TiCl4 on silica, or other Ziegler‐Natta catalysts) and the buildup‐type (for example, chromium oxide catalysts on silica of the Phillips type). Sustained oscillations were found to exist for decay‐type catalysts in loop reactors. For both tank and loop reactors, the buildup‐type catalyst exhibited isolated solution branches (isola) and multiplicity phenomena in addition to sustained oscillations. The sigmoidal shape of the buildup‐type catalyst rate curve is postulated as the reason for the additional multiplicity and isola phenomena. The implications for industrial operating conditions are discussed.
Variables, kinetics and mechanisms of heterogeneous reburning
Authors: Chen Wei‐Yin , Tang Lin 
Published: April 2004

AbstractThe variables, kinetics, and mechanisms of heterogeneous reburning were studied in a flow reactor with a simulated flue gas. The efficiency of heterogeneous reburning depends on the origin of the char, char preparation history and the presence of oxidants, CO2 and O2, and the reducing agent CO, in reburning. Estimated intrinsic rate constants for surface NO reduction in various gaseous environments were compared with those published. In addition to its large surface area, the effectiveness of lignite char appears to be due to its ability to promote two consecutive reactions: (1) the gasification of char by CO2 and O2 for production of CO; (2) the removal of surface oxygen complexes, including those formed after adsorption of NO, by gaseous CO, for the regeneration of reactive sites. Moreover, lignite ash also catalyzes the decomposition of HCN, a major intermediate of NO conversion during gas reburning. These observations suggest that reburning by a mixed fuel containing natural gas and lignite char can be a potentially attractive route for the in–furnance control of nitrogen oxide.
Compressive yield stress from multiple‐speed centrifuge measurements
Authors: Yeow Y. Leong , Leong Yee Kwong 
Published: April 2004

AbstractMultiple‐speed centrifuge measurement is a standard technique for obtaining the compressive yield stress of concentrated suspensions. Converting the centrifuge data into a compressive yield stress vs. volume fraction curve is an inverse problem. The problem is ill posed in the sense that noise in the data is likely to be amplified if inappropriate data processing methods are used. A method based on Tikhonov regularization is applied to solve this inverse problem. An added complication of centrifuge measurement is the interface between the uncompressed and compressed layers in the centrifuge tube. This interface is not measured and has to be treated as a free boundary. A computation scheme for locating this free boundary is incorporated into the Tikhonov regularization procedure. This new way of processing centrifuge data is assessed by applying it to synthetic data and to laboratory data. Problems caused by small or noisy data sets are discussed.
Determination of the activity of H+ ions within and beyond the pH meter range
Authors: Rodil Eva , Persson Karin , Vera Juan H. , Wilczek‐Vera Grazyna 
Published: April 2004

AbstractThis work confirms that the activities of individual ions measured with ion‐selective electrodes are physically meaningful. The individual activities of the Cl−, Na+ and K+ ions in single‐electrolyte aqueous solutions of HCl, NaOH and KOH were measured at 298.2 K in the range from 0 to 2 molal. In the pH range from 1 to 13, the pH values calculated from the measured activities of the ions are in good agreement with the values obtained with a pH probe. In agreement with previous results for potassium ions, and opposite to the behavior of other cations in 1:1 electrolyte solutions, the K+ and the H+ ions were found to have smaller activities than their conjugate anions. The experimental activity coefficients of the ions were correlated with the Khoshkbarchi‐Vera equation and with the New Hydration Theory, and compared with the predictions given by the Pitzer theory.
Modeling of coalescence in polymer blends
Authors: Lyu SuPing , Bates Frank S. , Macosko Christopher W. 
Published: April 2004

AbstractCoalescence in polymer blends was modeled by combining population dynamics with three coalescence theories: Smoluchowski, trajectory, and film drainage. Modeling results are compared with our previous coalescence experiments on polystyrene/high density polyethylene blends. Comparison of the Smoluchowski theory (no hydrodynamic interactions) with our experiments reveals that ideal collisions are the main mechanism of coalescence. Coalescence efficiency, however, decreases with increasing shear rate and particle‐size difference. Most interestingly, increasing the ratio of particle to matrix viscosity causes coalescence efficiency first to increase and then to decrease. The effects of particle‐size difference on coalescence efficiency can be modeled by considering changes in trajectory due to hydrodynamic interactions between particles. By considering particle deformation, film drainage theory predicts that coalescence efficiency decreases with increasing shear rate. Comparison with the experiments was only qualitatively correct. However, the prediction that coalescence efficiency decreases with increasing the viscosity ratio by both the trajectory theory and film drainage theory is not consistent with the experimental results. The reasons for the disagreements are discussed in terms of large deformation of colliding particles.
Drying process paths of ternary polymer solution coating
Authors: Dabral Mahendra , Francis L. F. , Scriven L. E. 
Published: April 2004

AbstractDrying process paths of a ternary solution consisting of a polymer dissolved in a blend of a solvent and a nonsolvent are analyzed. A 1‐D drying model applied to a ternary solution provides composition trajectories followed at different depths in the coating as a function of time, collectively called process paths. The effects of gas‐phase mass‐transfer coefficient, relative diffusivity and relative volatility, and partial saturation of the gas phase with solvents on these process paths are presented. When the solution coating enters the two‐phase region, phase separation may take place, as illustrated by coatings prepared from ternary solutions of cellulose acetate in ketone and methanol. When acetone is the solvent, the coating phase separates. Replacing acetone with methyl ethyl ketone gives homogeneous coatings. Solution phase separation or “blush” is explained in terms of the drying‐process paths and their relationship to the two‐phase immiscible region.