bluuebunny/crossref_metadata_2025_split huggingface dataset:
Transient fluidization and segregation of binary mixtures of particles
Authors: Marzocchella A. , Salatino P. , Di Pastena V. , Lirer L. 
Published: April 2004

AbstractFluidization of binary mixtures of particles belonging to group B of the Geldart classification of powders was studied. Beds tested were prepared by mixing in different proportions particles with almost equal density (≈2,500 kg/m3) and dissimilar size (125 μm silica sand and 500 μm glass beads). Experiments were carried out using a segmented fluidization column equipped with multiple pressure transducers. Experimental procedures included continuous monitoring of pressure drop at different locations along the bed during quasi‐steady or stepwise changes of gas superficial velocity, and characterization of particle‐size distributions in each segment of the fluidization column after fluidization of the bed for given times. Three ranges of gas superficial velocity were recognized for each solids mixture. At low velocity the bed behaves as a fixed bed. At high velocity, it is fully and steadily fluidized. In an intermediate velocity range, transient fluidization takes place: an initially uniform fluidized bed eventually undergoes segregation, giving rise to a defluidized bottom layer rich in the coarser solids and to a “supernatant” fluidized layer where finer particles prevail. The thresholds between these velocity ranges are rather sharp and were characterized as functions of initial bed composition. Rates at which the defluidized solids layer builds up from initially uniform beds, and the ultimate compositions of the defluidized bottom and fluidized top layers are characterized for beds with different compositions at variable gas superficial velocity.
Structural characterization of polyetherimide‐based carbon molecular sieve membranes
Authors: Sedigh Mehran G. , Jahangiri Maryam , Liu Paul K. T. , Sahimi Muhammad , Tsotsis Theodore T. 
Published: April 2004

AbstractSupported carbon molecular sieve membranes (CMSMs) were prepared by the pyrolysis of a polyetherimide (PEI) polymeric precursor. The membranes were characterized by scanning electron microscopy, energy dispersive spectroscopy, and micropore analysis, using gas adsorption techniques to relate their microstructure characteristics to their transport and separation characteristics. The analysis shows that preparation conditions determine whether the carbon molecular sieve layer forms within or outside the γ‐alumina layer of the substrate. Micropore CO2 and N2 adsorption analysis of both supported and unsupported CMSMs showed a sharp peak at about (3.6–3.8) × 10−10 m using the Horvath‐Kawazoe method. For the supported CMSMs it was observed that consecutive coating/carbonization steps reduced the pore volume in the micro‐ and mesoporous regions, without greatly affecting the volume of pores in the range of (3.5–6) × 10−10 m. The reduction of the pore volume in the micro‐ and mesoporous regions is accompanied by an increase in the separation factor and a decrease in the permeance after each coating/carbonization cycle. Micropore analysis of a membrane, whose performance had degraded, indicated that its volume of pores between (3.6–6) × 10−10 m had drastically decreased from the corresponding value of the as‐prepared membranes.
Experimental measurements of benzene oxidation in supercritical water
Authors: DiNaro Joanna L. , Tester Jefferson W. , Howard Jack B. , Swallow Kathleen C. 
Published: April 2004

AbstractOxidation and hydrolysis reactions of benzene in supercritical water were investigated thoroughly using experimental measurements. Little to no reaction occurred without oxygen at temperatures between 530 and 625°C for residence times up to 6 s. Oxidation reactions were studied at temperatures ranging from 479 to 587°C, pressures of 139 to 278 bar, reactor residence times from 3 to 7 s, and with varying initial benzene concentrations from 0.4 to 1.2 mmol/L and oxygen concentrations from 40% of oxygen demand to 100% excess oxygen. To a 95% level of statistical confidence, the oxidation rate was found to be of 0.04 ± 0.07 order in benzene, 0.17 ± 0.05 order in oxygen, and 1.4 ± 0.1 order in water, with an activation energy of 270 ± 10 kJ/mol. The primary oxidation product at all reaction conditions studied was carbon dioxide. Other important oxidation products were carbon monoxide, phenol, and methane. Trace levels of additional light hydrocarbon gases and single‐ and multi‐ringed aromatic species were also detected under some conditions.
Kinetics of the partial oxidation of methane to formaldehyde on silica catalyst
Authors: Arena Francesco , Frusteri Francesco , Parmaliana Adolfo 
Published: April 2004

AbstractThe kinetics of the partial oxidation of methane to formaldehyde (MPO) on a “precipitated” silica catalyst in the 500–800°C range was investigated. The influence of temperature and reaction mixture composition on the density of reduced sites of the catalyst under steady state was evaluated by in situ reaction temperature oxygen chemisorption measurements. The kinetics of the MPO on silica is pseudo first and zero‐order on P and P, respectively, while the density of reduced sites depends upon the square root of the P/P ratio. The rate‐determining step is the activation of C–H bond of CH4 molecules (Ered = 142 kJ·mol−1), while oxygen replenishment is a nonactivated reaction step (Eox≈20 kJ·mol−1). A Langmuir‐Hinshelwood kinetic model, accounting for a two‐site‐dissociative activation mechanism of both CH4 and O2, thoroughly describes the steady state of the silica surface and the reaction kinetics of the MPO in the 500–800°C range.
Structural effects on adsorption of atmospheric gases in mixed Li,Ag–X‐zeolite
Authors: Hutson Nick D. , Yang Ralph T. 
Published: April 2004

AbstractSilver is known to strongly affect the adsorptive properties of zeolites. In the synthesis of mixed Li,Ag low‐silica X‐type (LSX) zeolite, adding very small amounts of silver and specific dehydration conditions results in a sorbent with enhanced adsorptive characteristics for air separation. The location of the extraframework silver in relation to the aluminosilicate framework is of primary importance for elucidating the effect of silver cations on the adsorptive characteristics of the zeolite. In this work, mixed Li,Ag ion‐exchanged zeolites were synthesized and treated to promote the formation of intracrystalline silver clusters. These samples were structurally characterized using Rietveld refinement of neutron powder diffraction data. Structural characterization revealed the presence of cations in a novel site II* in mixed Li,Ag–LSX zeolites that were vacuum‐dehydrated at 450°C. Cations in this site II* are more interactive with the atmospheric sorbates of interest than silver at the conventional site II location. Vacuum dehydration at 450°C induced thermal migration of Ag+ from site II to site II* and gives rise to the superior properties for air separation.
Boundary effects on a thermophoretic sphere in an arbitrary direction of a plane surface
Authors: Chen Shih H. 
Published: April 2004

AbstractThe thermophoresis of a sphere in a constant applied temperature gradient in an arbitrary direction with respect to a plane surface was analytically studied. The Knudsen number was assumed small to describe the fluid flow by a continuum model with a thermal creep and a hydrodynamic slip at the particle surface. The asymptotic formulas for the temperature and velocity fields in the quasi‐steady situation were obtained by a method of reflections. The plane surface can be a solid wall or a free surface. The boundary effect on the thermophoretic motion was weaker than that on the motion driven by a body force. Even so, the interaction between the plane and particle can be very significant when the gap thickness gets small. For a particle motion normal to a solid wall, plane surface effect reduces the thermophoretic velocity of the particles; however, this solid wall may be an enhancement factor on the particle migration as it is translating parallel to the wall. On the other hand, in the case of a particle migrating close to a free surface due to thermophoresis, the particle velocity can be either greater or smaller than what would exist in the absence of the plane surface, depending on the relative thermal conductivity and surface properties of the particle and its relative distance from the plant. The thickness of the thermophoretic interacting region was also evaluated by considering the thermophoretic mobility. A free surface generally exerts less influence on the particle movement than does a solid surface.
Estimating monotonic functions and their bounds
Authors: Kay Herbert , Ungar Lyle H. 
Published: April 2004

AbstractA function estimator MSQUID is presented for fitting and bounding noisy data that are known to be monotonic. MSQUID augments a “backpropagation” neural network model with a set of constraints which restricts the model to monotonic functions. Model parameters are estimated using nonlinear, constrained optimization at little increase in computation over standard neural networks. It is proven that MSQUID can estimate any monotonic function and produces more accurate estimates than unconstrained optimization. These monotonic functions and their confidence bounds can be used in many fault detection and diagnosis systems.
On defining the partial control problem: Concepts and examples
Authors: Kothare Mayuresh V. , Shinnar Reuel , Rinard Irven , Morari Manfred 
Published: April 2004

AbstractMany complex chemical processes having a large number of process variables and poorly understood models can be controlled reasonably well by controlling only a small subset of process variables using an equally small number of manipulated variables. This is the central premise of this article and is referred to as partial control. Knowingly or unknowingly, this idea has been and continues to be applied to successfully control numerous complex industrial processes. Despite its widespread use, partial control has never been explicitly formulated. The partial control problem is defined. A number of terms is introduced such as process variable dominance, modelable responses, practical degrees of freedom, and sufficiency of partial control. The new framework allows incorporation of both engineering‐based decisions and more rigorous theoretical tools to achieve the goals of partial control. A number of practical examples illustrate the applicability of these concepts.
Comparing batch column configurations: Parametric study involving multiple objectives
Authors: Kim Ki‐Joo , Diwekar Urmila M. 
Published: April 2004

AbstractThe principal objective of this study is to advance the state of the art in batch distillation synthesis by providing insights into the behavior of various column configurations, including emerging column designs, using systematic parametric performance indices. Three competing column configurations—the rectifier, the stripper, and the middle vessel column—were compared in terms of various performance indices. Performance indices used include product purity and yield, design feasibility and flexibility, and thermodynamic efficiency. Product purity is related to profitability when yield is constant. Feasibility indices based on the number of plates and the reflux ratio show whether or not such a high‐purity configuration is flexible for changing design and operating conditions. Thermodynamic efficiency provides a measure of effectiveness of heat exchange around the specific column configuration. Trade‐offs between these performance indices are presented.
Simulation of an inert membrane reactor for the synthesis of maleic anhydride
Authors: Pedernera M. , Mallada R. , Meneéndez M. , Santamaría J. 
Published: April 2004

AbstractA simulation of an inert membrane reactor in the partial oxidation of butane to maleic anhydride in high butane concentrations (2–13%) is presented. A porous membrane was used to distribute oxygen to a fixed bed of VPO catalyst, to which butane was fed. Two different reactor configurations were simulated: a standard inert membrane reactor, in which oxygen permeates inward from the shell side and the catalyst is packed on the tube side; an outward flow inert membrane reactor, in which the catalyst bed is packed on the shell side and oxygen flows outward from the tube side. The model explains the different performances of both types of reactor in terms of the interaction between the oxygen and hydrocarbon concentration profiles and the temperature profiles that are obtained with both reactor configurations.
Influence of preheating rate on kinetics of high‐temperature gas–solid reactions
Authors: Thiers Laurent , Leitenberger Bryan J. , Mukasyan Alexander S. , Varma Arvind 
Published: April 2004

AbstractThe influence of preheating rate on kinetics of high‐temperature reactions in gas–solid systems was investigated by a computer‐assisted electrothermography technique. Two systems were investigated: Nb–N2 and Ti–N2, in the temperature ranges 2,100–2,500 K and 1,350–1,600 K, respectively. The results showed that for both systems, reaction kinetics are enhanced by increasing the preheating rate to the desired reaction temperature. Analysis of the experimental data in the context of the sharp‐interface model showed that the activation energy of the diffusion coefficient does not depend on heating rate, while the preexponential factor is affected. Additional experiments suggest that nonisothermal preheating, even though of short duration, about 10 ms, influences chemical reactivity of the solid reactant by changing its specific surface area.
Phase equilibria for chain‐fluid mixtures near to and far from the critical region
Authors: Jiang Jianwen , Prausnitz John M. 
Published: April 2004

AbstractA recently established crossover equation of state for pure chain fluids is extended to chain‐fluid mixtures. Far from the critical region, where density fluctuations are small, it reduces to the classic equation of state. Near or at the critical point, the crossover equation of state incorporates contributions form long‐wavelength density fluctuations. Using segment–segment parameters for pure components and one cross parameter k12 for every binary pair as obtained from vapor–liquid equilibrium data remote from the critical region, this crossover equation of state gives vapor–liquid equilibria in good agreement with experiment for binary asymmetric mixtures of n‐alkanes far from, near to, and at the critical point.
Morphological evolution of thick wax deposits during aging
Authors: Singh Probjot , Venkatesan Ramachandran , Fogler H. Scott , Nagarajan N. R. 
Published: April 2004

AbstractThe presence of waxes in crude oil can lead to the formation of wax deposits on the walls of cold subsea pipelines, which restricts flow and can lead to plugging of the pipelines. This problem has recently become more significant as the production wells move further offshore causing the oil to be cooled below the cloud point before reaching shore. Wax deposition was studied in the laboratory under conditions simulating the deposition in a subsea pipeline. Wax deposition is initiated by the precipitation of wax directly on the pipe wall and the formation of a network of' wax crystals (wax‐oil gel) with significant amounts of oil trapped in it. Radial diffusion of the wax molecules from the bulk solution to the gel deposit causes it to simultaneously grow and age with time. The wax molecules diffusing into the gel deposit precipitate near the interface resulting in a faster aging rate of the deposit new the interface than that near the wall. This nonuniform aging of the wax deposit causes the evolution of complex morphologies of the wax deposits. The diffusion of wax molecules into the gel matrix was analyzed theoretically during the growth of the wax deposit. This mathematical model predicted the radial variation of the morphology of the wax deposit observed in the laboratory flow loop experiments along with the deposit thickness as a function of time.
Operational issues in solids processing plants: Systems view
Authors: Wibowo Christianto , Ng Ka M. 
Published: April 2004

AbstractA systematic approach to deal with the operational issues in solids processing plants is presented. Potential problems in various equipment units are identified and classified according to continuum‐scale phenomena: breakage, adhesion and cohesion, compaction, bulk solids flow problems, fluid‐driven solids flow problems, and segregation. Analysis is performed in the continuum and particle scales so as to identify the causal and opposing effects of each problem. With appropriate mathematical models and empirical correlations, these effects can be related to equipment design, operating conditions, particle attributes, and material properties. The ratio of these competing effects shows whether a potential problem is a real concern and points the direction for taking preventive measures. The action plan may include changing operating conditions or equipment design of a particular unit, or making modifications to upstream equipment units. The method is illustrated with an industrial example: the production of potash.
Aggregated structure of flocculated asphaltenes
Authors: Savvidis Theophylaktos G. , Fenistein Denis , Barré LoïC , Béhar Emmanuel 
Published: April 2004

AbstractMany petroleum processing problems are related to asphaltene flocculation. A detailed understanding of the colloidal structure of asphaltenes in oild can play a decisive role in improving processing facilities and/or operating conditions. The structure of the flocculated part of the asphaltenes of a crude oil far above the flocculation threshold was studied to understand its links with macroscopic phase separation. Asphaltene filtrations were performed using filter pore sizes from 0.025 to 10 μm. According to small angle X‐ray scattering (SAXS) spectra and density measurements, these extracted asphaltenes in toluene solutions did not have any physical differences. Measurements of nanometric sizes for the dispersed particles after dissolution in toluene show that micron‐size flocculated asphaltenes are strongly aggregated structures. Therefore, filtration experiments separate asphaltenes corresponding powders show spherically shaped aggregates of micron size. SAXS and USAXS techniques were used to investigate the internal structure of the asphaltene powder. The aggregates are clearly a compact organization of asphaltenic material. This dense structure explains why flocculated asphaltenes are subject to sedimentation, which induces the visible macroscopic phase separation.
Laminar flow of four gases through a helical rectangular duct
Authors: Berg Robert F. , Tison Stuart A. 
Published: April 2004

AbstractMeasurements and a model of gas flow through a helical duct of rectangular cross section are reported. Observations of the rate of rise of pressure in a known volume located downstream from the duct yielded molar flow rates of helium, nitrogen, argon and sulfur hexafluoride. The model predicts flow rates from the duct's entrance pressure, exit pressure, and temperature. It accounts for the gas's nonideal equation of state, gas expansion along the duct's length, the increase of kinetic energy near duct's entrance, and slip. After adjusting only one parameter (the duct's height), the model agrees with the data to within 0.2% in the range of Reynolds number 0.08<Re<40. To extend the model to Re = 1,000, the centrifugal effects were accounted for by rescaling Targett et al.'s (1995) numerical calculations. The extended model agrees with the data to within 0.2% in the range 40 < Re < 400 and to within 1% in the range 400 < Re < 1,000.
New correlation for the capture cross section in high‐gradient magnetic separation
Authors: Ebner Armin D. , Ritter James A. 
Published: April 2004

AbstractA new correlation between the capture cross‐section parameter (λ) and principal variables involved in high‐gradient magnetic separation (HGMS) was developed. It is based on the use of an alternative dimensionless parameter, β, in lieu of the traditional Um/UO, which facilitated the estimation of λ over a much broader spectrum of variables. This new correlation is far more versatile than correlations and approximate models in the current literature, which are only applicable to specific situations in HGMS systems. Overall, this new correlation should be extremely useful in the design, development, optimization and modeling of HGMS systems.
Oxidative coupling of methane on improved bismuth oxide membrane reactors
Authors: Zeng Y. , Lin Y. S. 
Published: April 2004

AbstractFluorite‐structured yuria‐bismuth oxide membranes with improved chemical stability were prepared by doping samarium in the lattice. The samarium‐doped yuria‐bismuth oxide (BYS) membranes are in fluorite structure, with high oxygen permeability and good catalytic properties for oxidative coupling of methane (OCM). The oxygen partial pressure dependence of oxygen permeation flax shows a shift of the rate‐limiting step from the suface reaction to the hulk electron‐hole conduction as temperature increases from 750 to 950°C. OCM reactions were conducted in a membrane reactor made of the disk‐shaped BYS membrane. Merhane‐ and oxygen‐containing streams are fed into the opposite sides of the BYS membrane to allow OCM reactions to occur on the membrane surface exposed to methane. The membrane reactor gives C2, yields of 4–11% with C2, selectivity up to 74%. The performance of this membrane reactor is closely related to oxygen permeation properties of the BYS membrane. Experimental results show the effectiveness in improving the C2 yield by increasing the membrane surface area to reactor volume ratio. In this disk‐shaped membrane reactor the highest C2, yield achieved is 17%, with a C2 selectivity of about 80%.
Viscosity of liquid hydrocarbons and their mixtures
Authors: Korsten Hans 
Published: April 2004

AbstractIn the petroleum industry, the viscosity of mixtures containing thousands and millions of chemical species must be predicted over large temperature ranges. Traditional models are empirical based on bulk properties. If such models are applied to mixtures other than those for which they were developed, large errors may occur. New methods proposed calculate the viscosity of petroleum fractions over large temperature ranges, using a new mixing rule reflecting observed positive and negative mixing effects. The temperature range of equations for calculating pure component viscosity is extended to the entire liquid‐phase range. If solid components are dissolved in the liquid, the viscosity increases sharply with further temperature reduction. This effect is captured in the new model by incorporating the freeze point distribution. For converting between absolute and kinematic viscosity, a new equation is proposed for the temperature effect on density.
Critical behavior in quenched random structures: Mean‐field lattice‐gas approach
Authors: De S. , Shapir Y. , Chimowitz E. H. , Kumaran V. 
Published: April 2004

AbstractA new mean‐field equation‐of‐state model is proposed for predicting the critical behavior of fluids confined in porous, random structures. The approach is based on a lattice‐gas formalism and incorporates effects of both fluid confinement and energetically heterogeneous interactions between fluid molecules and pore surfaces. The model was used to predict a variety of thermodynamic properties in these systems, including the dependence of the confined fluid's critical properties on the porosity and relative strength of fluid–fluid and fluid–pore interaction energies. The study of suface‐energy heterogeneities show that they significantly affect the critical temperature of the confined fluid, at a given porosity, compared to the uniform energy case. Comparison of the model performance with both grand canonical Monte Carlo simulation results and a set of adsorption data in a silica gel suggest that the approach taken here provides a useful analytic method for calculating physical properties in complex systems of this kind.