bluuebunny/crossref_metadata_2025_split huggingface dataset:
Extraction of nitric acid from aqueous media with Oϕ D(iB)CMPO–n‐dodecane
Authors: Spencer Barry B. , Counce Robert M. , Egan B. Zane 
Published: June 2004

AbstractA study of the extraction characteristics of nitric acid with octyl(phenyl)‐N,N‐diisobutylcarbamoylmethyl phosphine oxide [OϕD(iB)CMPO or, simply, CMPO] was conducted. In the experimental program, CMPO was dissolved in n‐dodecane to produce the organic extracting medium. The objectives of the project were to infer extraction stoichiometry and to estimate equilibrium constants for the extraction of nitric acid with the CMPO extractant.Experiments were performed over a limited range of concentrations to avoid conditions favoring formation of a third phase. Aqueous nitric acid concentrations were limited to 0.30 M at 25°C, 1.0 M at 40°C, and 3.0 M at 50°C. The data indicate that CMPO extracts nitric acid with a 1:1 stoichiometry. The value of the equilibrium constant is estimated at 2.66 ± 0.09 at 25°C. The enthalpy of the extraction is estimated to be ‐ 5.46 ± 0.46 kcal/mol.
Oxidative dehydrogenation of butane using membrane reactors
Authors: Téllez C. , Menéndez M. , Santamaría J. 
Published: June 2004

AbstractThe oxidative dehydrogenation of butane was studied at temperatures between 450 and 550°C using a conventional fixed‐bed reactor and inert membrane catalytic reactors with different feed arrangements. When inert membrane reactors were employed, a ceramic membrane was used to distribute oxygen to a fixed bed of V‐Mg‐O catalyst. The membrane reactor was found to be more efficient than a fixed‐bed reactor under most of the conditions investigated. In addition, in the membrane reactor the formation of hot spots decreased considerably, leading to a more stable and safer operation.
Macro‐ and microscopic fluid transport in living tissues: Application to solid tumors
Authors: Netti Paolo A. , Baxter Laurence T. , Boucher Yves , Skalak Richard , Jain Rakesh K. 
Published: June 2004

AbstractTransvascular and interstitial fluid movements are involved in many important biological processes such as convective macromolecular transport and contribute to the mechanical behavior of tissue. Although intimately coupled, there is a tendency in the literature to regard these two fluid‐transport mechanisms separately; if the interaction is considered, the description is usually confined to the local level (e.g., transvascular or interstitial perivascular). A general framework presented here combines transvascular and interstitial fluid movement with the mechanics of soft tissue and integrates macro‐and microscopic views of the phenomena. On the macroscopic level, interstitial fluid transport is described by adapting the field equations of the poroelastic theory using average field variables defined on a scale of several blood vessel diameters (∼ 1 mm), while transvascular transport is described by a generalized Starling's law. As an example, the model equations have been specialized for a spherical solid tumor and an analytical solution is presented for the transient redistribution of interstitial fluid following a rapid change in vascular pressure or flow. The model describes the overall average profiles of the interstitial fluid pressure and velocity, as well as the dilatation, displacement and stress of the solid matrix. Moreover, on a smaller length scale the model can describe the local fluid movement (perivascular) using the average field variables as boundary conditions. The basic theory provides new insight into understanding the fluid transport in biological tissues and a valuable tool for determining relevant fluid‐transport parameters. Implications for improving drug delivery to solid tumors are also discussed.
On‐line control of a semibatch emulsion polymerization reactor based on calorimetry
Authors: de Buruaga Isabel Sáenz , Echevarría Antonio , Armitage Philip D. , de la Cal José C. , Leiza José R. , Asua José M. 
Published: June 2004

AbstractIn this work, on‐line calorimetry was used to estimate the conversion and the copolymer composition in emulsion polymerization systems. Real‐time feedback control of the polymer composition during the semibatch emulsion copolymerization of vinyl acetate and butyl acrylate was carried out. Both homogeneous copolymers and copolymers with previous defined composition profiles were obtained. It was shown that the feedback control was able to avoid monomer accumulation in the reactor, and hence potentially dangerous thermal runaways, without any deleterious effect on the polymer composition, when a sudden inhibition was caused by deliberately adding a solution of hydroquinone. The use of feedback control for the maximization of the production rate under safe conditions in the unseeded emulsion copolymerization of vinyl acetate and VeoVa10 (an alkyl vinyl ester from Shell) is also presented.
Yield stress of suspensions loaded with size distributed particles
Authors: Kapur Prakash C. , Scales Peter J. , Boger David V. , Healy Thomas W. 
Published: June 2004

AbstractA new theoretical approach is proposed for the yield stress of concentrated, flocculated particulate suspensions. Explicit cognizance is taken for the three‐dimensional, mechanically rigid particle network held together by interparticle forces wherein the mean coordination number in the assemblage increases and the separation between the particles decreases with an increase in the volume fraction of the solid phase. The Rump‐Molerus model relting isotropic normal stress and isotropic normal interparticle force in a bed of single‐sized spheres is modified to incorporate the size distribution of particles and extended to the suspension network. The model estimates the yield stress as a function of solids loading for various kinds of size distribution and is in reasonable agreement with experimental data when the surface properties of the particle are held constant.
Fugacity coefficients for free radicals in dense fluids: HO2 in supercritical water
Authors: Mizan Tahmid I. , Savage Phillip E. , Ziff Robert M. 
Published: June 2004

AbstractThe fugacity coefficients of the hydroperoxyl radical in supercritical water are estimated through molecular simulations. A potential function for the radical is first derived from ab initio self‐consistent field molecular orbital calculations at the unrestricted Hartree‐Fock level and from data in the literature. Molecular dynamics simulations of the hydroperoxyl radical are then performed in supercritical water and the fugacity coefficient of the radical is calculated by the free‐energy perturbation method using the dynamic coupling parameter window‐modification technique. The values of the fugacity coefficients at 773 K differ from unity. This methodology facilitates the incorporation of thermodynamic nonidealities in mechanism‐based kinetic models for free‐radical reactions in supercritical water.
Modeling and experimental study of a sequential phosphazene reaction by phase‐transfer catalysis
Authors: Wu Ho‐Shing , Meng Shang‐Shin 
Published: June 2004

AbstractThe substitution reaction of hexachlorocyclotriphosphazene, N3P3Cl6, with phenol was performed to synthesize the partially substituted (phenoxy) chlorocyclotriphosphazenes, N3P3Cl6 − i(OC6H5)i, i = 1 – 6 by phase‐transfer catalysis (PTC) in an organic phase/alkaline solution. The steric hindrance effect plays a crucial role in this reaction. The reaction system was controlled by both chemical kinetics and mass‐transfer effects. The mass transfer of the catalyst between two phases was investigated by a pseudosteady‐state liquid–liquid PTC (LLPTC) model. Also, the intrinsic reaction‐rate constants of the series substitution and the overall mass‐transfer coefficient of the catalyst from the organic phase to the aqueous phase were determined by a combined model. In addition, the corresponding energies, enthalpies, and entropies of activation of the series substitution were also estimated.
Gas‐holdup measurements in bubble columns using computed tomography
Authors: Kumar Sailesh B. , Moslemian Davood , Duduković Milorad P. 
Published: June 2004

AbstractA computed tomographic scanner was developed for imaging gas‐holdup distributions in two‐phase flow systems such as bubble columns and fluidized beds. The scanner has been used to study the effects of various operating parameters (such as column diameter, superficial gas velocity, and distributor type) on the gas holdup and its distribution in an air–water bubble column. The experimental investigation shows that the column dimensions have no significant effect on the void fraction when the column diameter is greater than 0.15 m. Differences in the holdup distribution due to the kind of distributor used are significant only at low gas flow rates. Surface tension of the liquid has a profound influence on the gas holdup and its distribution.
Chaotic behavior of gas‐solids flow in the riser of a laboratory‐scale circulating fluidized bed
Authors: Marzocchella Antonio , Zijerveld Robert C. , Schouten Jaap C. , van den Bleek Cor M. 
Published: June 2004

AbstractA cold model of a circulating fluidized bed with a 0.030‐m‐ID, 2.77‐m‐high riser was operated in a wide range of operating conditions. Several solids were tested, from 57 μm to 1,830 μm in size and from 1,100 kg/m3 to 2,540 kg/m3 in density. Pressure fluctuations were measured at several points along the riser, and time series were processed to evaluate chaotic invariants (Kolmogorov entropy and correlation dimesion). Axial profiles of average values of pressure and voidage were also evaluated. At fixed operating conditions, the Kolmogorov entropy changed along the riser, which appeared to be a fuction of the local voidage and showed a minimum when voidage decreases from 1.00 until about 0.90. Changes of the Kolmogorov entropy with local voidage were interpreted based on interactions among solids and gas turbulence structure. Three regions were identified in the voidage range investigated: particles‐controlled region, clusters‐controlled region, and bottom‐bed‐controlled region.
Structural stability of chemical process plants
Authors: Hangos Katalin M. , Perkins John D. 
Published: June 2004

AbstractThe problem of analyzing the stability of chemical process plants is considered. The idea of exchange plants has been extended with more general binary transfer terms and binary equilibrium, resulting in the idea of binary exchange‐equilibrium plants. Their structural stability is analyzed using results on conservation matrices. It was found that binary exchange‐equilibrium plants with no azeotropes are stable irrespective of the connections of their operating units. The general results are illustrated in examples of practical importance: heat‐exchanger networks and binary distillation columns with constant molar flows.
Oscillating temperature pulses during CO oxidation on a Pd/Al2O3 ring
Authors: Liauw M. A. , Somani M. , Annamalai J. , Luss D. 
Published: June 2004

AbstractBack‐and‐forth‐moving temperature fronts separating regions with high and low temperatures (amplitudes up to 100 K) formed on a Pd on alumina ring during the atmospheric oxidation of carbon monoxide. The back‐and‐forth front movement reflects the intrinsic nonuniformity of the catalytic system and the impact of global coupling. The ignition and extinction fronts usually moved at different velocities, in agreement with theoretical predictions. Complex spatiotemporal patterns were observed due to small‐amplitude temperature fronts that moved on the high‐temperature region at a much higher velocity than the high‐amplitude fronts. The qualitative motion features were affected by changes in the excess oxygen concentration. The nonuniform states existed mainly for feed conditions for which the only uniform state was an extinguished one.
Reactivation of the HZSM‐5 zeolite‐based catalyst used in the MTG process
Authors: Gayubo Ana G. , Aguayo Andrés T. , Benito Pedro L. , Landeta Alberto , Castilla Marta , Bilbao Javier 
Published: June 2004

AbstractThe recovery of the acidic structure and activity during the regeneration step by coke combustion of an HZSM‐5 zeolite‐based catalyst used in the methanol‐to‐gasoline (MTG) process in reaction–regeneration cycles was studied. The reactivation kinetics (activity us. coke combustion time) was determined as a function of temperature and time on stream of the reaction step. The validity of the reactivation kinetic model was proven by using it for the simulation of the cyclic operation under conditions of catalyst partial reactivation, together with the kinetic model for the MTG process.
Analysis of microwave thawing of slabs with effective heat capacity method
Authors: Basak Tanmay , Ayappa K. G. 
Published: June 2004

AbstractMicrowave thawing of materials, which melt over a finite temperature range, are analyzed using the effective heat capacity method. The state of the material, solid, liquid or mush is deduced from the equilibrium liquid volume fraction vs. temperature relationship for the substance, and the microwave power is calculated from Maxwell's equations. Using Galerkin finite elements, the microwave power, temperature and liquid volume fractions were obtained for microwave thawing of tylose slabs. Thawing progresses from the inside and/or outside depending on the slab thickness. For slabs ⩾ 5 cm, thawing progresses predominantly from the surface of the sample. Resonances, during which the microwave power absorption is high, causes the 2‐cm slab to thaw quicker than 1‐cm slabs. A power law for the thawing time vs. sample thickness yields an exponent of 1.56 for microwave thawing and 2 for conventional thawing. To control the temperature rise in the liquid regions, simulations were carried out with an on‐off control on the microwave power. On‐off control results in greater power savings for thick samples.
Shear and compressive rheology of aggregated alumina suspensions
Authors: Channell Glenn M. , Zukoski Charles F. 
Published: June 2004

AbstractThe shear and compressive properties of aggregated alumina particles are determined as functions of volume fraction and the strength of the interparticle attraction. Over a range of volume fractions, yield stresses, τy, elastic moduli, the strain delimiting the extent of the linear elastic response, and compressive yield stress, Py, are well described by power‐law functions of volume fraction, while the role of interparticle attractions can be accounted for by expressing these mechanical properties as (ϕ/ϕg − 1)n, where ϕg captures the strength of particle attractions and n the microstructure. The links between compressive and shear properties are well described by linear elastic models where the Py and τy are a function of Poisson's ratio which, for the suspensions investigated, has a value near 0.49.
Measurement of ultrasonic forces for particle–liquid separations
Authors: Woodside Steven M. , Bowen Bruce D. , Piret James M. 
Published: June 2004

AbstractThe magnitude and direction of the ultrasonic radiation forces that act on individual particles in a standing‐wave field were determined using a microscope‐based imaging system. The forces are calculated from measured particle velocities assuming that the drag force, given by Stokes' law, is exactly counterbalanced by the imposed ultrasonic forces. The axial primary radiation force was found to vary sinusoidally with axial position and to be proportional to the local acoustic energy density, as predicted by theory. The magnitude of the transverse primary force was determined by two independent methods to be about 100‐fold weaker than the axial force. Separation concepts exploiting the transverse force for cell retention have been successful despite the great disparity in magnitude between the axial and transvers‐force components. This may be explained by the reduced hydrodynamic forces on aggregated particles in transverse flow due to their alignment in the sound field.
Synthesis of reactive crystallization processes
Authors: Berry David A. , Ng Ka M. 
Published: June 2004

AbstractA systematic method is presented to synthesize reactive crystallization processes. It shows how to selectively crystallize a desired solid product(s) after a reaction step and how to use compound formation to effect separation of a mixture. The method is based on the generation of phase diagrams with liquid‐phase reactions. Using transformed coordinates, systems with three or fewer degrees of freedom can be conveniently analyzed, regardless of the number of components and reactions. Features of the solid–liquid phase diagram that are relevant to process synthesis are identified. The method is illustrated with systems with multiple components, complex reactions, and multiple phases.
Polymer trace devolatilization: II. Case study and experimental verification
Authors: Yang Chi‐Tai , Smith Theodore G. , Bigio David I. , Anolick Colin 
Published: June 2004

AbstractIn this work, the bimodal/film model is compared with the cell model based on a case study using polystyrene/styrene devolatilization. It shows improvements over the cell model: (1) it requires a lower initial number of bubbles, which is more physically realistic and (2) it takes into account the observation of a limiting foam volume growth for a specific polymer in devolatilization. A stripper dispersion experiment was designed to investigate the effect of dispersed nitrogen stripper bubbles on the foam dynamics and devolatilization efficiency. The variables examined include polymer viscosity, initial volatile concentration, and the initial number and size of dispersed stripper bubbles. Polymer viscosity was the dominant factor in limiting the maximum foam volume expansion. The number and size of dispersed stripper bubbles show positive and negative effects (which are only secondary) on the maximum foam volume expansion, respectively. The initial volatile concentration has no effect on limiting the maximum foam volume expansion.
Effect of inlet conditions on scalar statistics in pipe mixing
Authors: Guilkey James E. , McMurtry Patrick A. , Klewicki Joseph C. 
Published: June 2004

AbstractRecent experimental validation of theoretical and numerical predictions regarding scalar variance decay in a pipe have revealed that the traditional plug‐flow reactor picture of pipe flow omits key physical mechanisms. In particular, the far‐field decay exhibits a power law rather than exponential decay. These observations are examined by performing a set of experiments where the manner in which the scalar constituents are introduced into the pipe is varied. Significant differences are noted in the behavior of the variance decay until the very far field is reached, where an invariant power‐law form emerges.
Radial distribution of the flow velocity, efficiency and concentration in a wide HPLC column
Authors: Farkas Tivadar , Sepaniak Michael J. , Guiochon Georges 
Published: June 2004

AbstractThe use of optical fibers in a fluorescence–detection scheme permits the accurate determination of the radial distribution of the transit time, the column efficiency, and the analyte concentration at the exit of a chromatographic axial–compression column (50 mmID). The results obtained demonstrate that the column is not homogeneous, but suggest a nearly cylindrical distribution of the packing density. The average velocity close to the column wall is 7% lower than along its axis and the HETP 25% higher. The lack of homogeneity of the column packing is another source of band broadening not taken into account in chromatography so far. It causes the apparent HETP derived from the conventional elution chromatogram recorded on the bulk eluent to be larger than the local HETP and the band profile to be unsymmetrical with a slight tail reminiscent of kinetic tailing.
Statistical monitoring of multivariable dynamic processes with state‐space models
Authors: Negiz Antoine , Çlinar Ali 
Published: June 2004

AbstractIndustrial continuous processes may have a large number of process variables and are usually operated for extended periods at fixed operating points under closed‐loop control, yielding process measurements that are autocorrelated, cross‐correlated, and collinear. A statistical process monitoring (SPM) method based on multivariate statistics and system theory is introduced to monitor the variability of such processes. The statistical model that describes the in‐control variability is based on a canonical‐variate (CV) state‐space model that is an equivalent representation of a vector autoregressive moving‐average time‐series model. The CV state variables obtained from the state‐space model are linear combinations of the past process measurements that explain the variability of the future measurements the most. Because of this distinctive feature, the CV state variables are regarded as the principal dynamic directions A T2statistic based on the CV state variables is used for developing an SPM procedure. Simple examples based on simulated data and an experimental application based on a high‐temperature short‐time milk pasteurization process illustrate advantages of the proposed SPM method.
Nitrile reaction in high‐temperature water: Kinetics and mechanism
Authors: Izzo Bill , Harrell Cynthia L. , Klein Michael T. 
Published: June 2004

AbstractThe reaction pathways, kinetics and mechanisms underlying the hydrolysis of aliphatic and aromatic nitriles in high‐temperature water (HTW) were investigated. The reaction products were the associated amides and carboxylic acids. Autocatalytic kinetics were observed and confirmed by experiment and analysis of the physical chemistry of the HTW reaction environment. A model incorporating two autocatalytic steps captured the observed kinetics well, and the associated optimized rate constants highlighted the key differences in the reaction chemistry of aliphatic and aromatic nitriles. The rate behavior of nitrile hydrolysis at these conditions has tangible consequences regarding optimal processing strategies.
Moisture transport in shrinking gels during saturated drying
Authors: Achanta Srinivas , Okos Martin R. , Cushman John H. , Kessler David P. 
Published: June 2004

AbstractThe transport of moisture in shrinking food gels during drying is studied based on a novel thermomechanical theory accounting for a structural transition in the material—from the rubbery to the galssy state—during drying. The proposed theory is applied to the drying of a model cylindrical starch–gluten gel system. The predicted drying characteristics depend on the Deborah number, a ratio of the characteristic relaxation time to the characteristic diffusion time. At low Deborah numbers, drying is Fickian. At intermediate and high Deborah numbers, however, drying is non‐Fickian, leading to an apparent mass‐transfer shutdown, which is a result of surface dryout and skin/shell formation. Based on a time‐dependent surface boundary condition, the model proposes that surface drying is not only a function of the Biot number but also a function of the “Shell” number, a ratio of the Deborah and Biot numbers. The model is verified by comparing its predictions with experimental data from drying of starch–gluten gels at 22.5 and 40°C. The model predictions agree with experimental data and capture the observed sigmoidal shape of the experimental drying curves in the saturated flow regime. The predicted moisture profiles show shell formation and growth during drying, compatible with the experimental moisture profiles from the literature.