bluuebunny/crossref_metadata_2025_split huggingface dataset:
Characterization of hydrocarbon systems by DBE concept
Authors: Korsten Hans 
Published: June 2004

AbstractThermochemical data of mineral oil fractions are scarce. Due to the complex structure of natural hydrocarbon mixture, standard heat and Gibbs free energy of formation depend on the sample. A procedure for predicting these properties is presented. Both properties depend on the hydrocarbon type and on its molecular weight. The double‐bond equivalent (DBE) and the number of olefinic double bounds are the important characterization parameters of the model. DBE can basically be calculated from molecular weight and elemental composition. Alternatively, boiling point and atomic H/C ratio can be used if the model is applied to mineral oil fractions from which boiling curves can be obtained. A criterion for testing the reliability of the estimated DBE value is available, because DBE is also a function of structural group distribution.The relevance of the DBE concept is shown with regard to hydroprocessing of mineral oil fractions. The model can be applied to total average molecules as well as to an arbitrary number of pseudocomponents and continuous mixtures. The difference between feed and product DBE is equivalent to the amount of hydrogen consumed for hydrogenation of unsaturated hydrocarbons. Further properties of the product can be predicted.
Numerical analysis and data comparison of a supercritical water oxidation reactor
Authors: Oh Chang H. , Kochan Robert J. , Beller John M. 
Published: June 2004

AbstractSupercritical water oxidation of isopropyl alcohol was investigated in a pilot‐scale reactor. A computational fluid‐dynamics model developed reveals the detailed flow field, chemical‐component distribution, temperature distribution, and salt‐particle trajectories in the reactor flow domain. The near‐wall fluid temperature from the numerical analysis was compared with experimental temperature data. The temperature comparison was within a 3% error band. The effect of the chemical kinetic rate was investigated for four different rates. Turbulent salt‐particle trajectories were also calculated to investigate the effect of particle sizes on salt deposit on the wall. Also, a method of calculating the adiabatic reaction temperature was developed to estimate reaction temperatures prior to a full numerical simulation.
Application of neural networks to mass‐transfer predictions in a fast fluidized bed of fine solids
Authors: Zamankhan Piroz , Malinen Pekka , Lepomäki Hannu 
Published: June 2004

AbstractIn this study back‐propagation, feed‐forward neural networks are applied to estimate mass‐transfer parameters in fast fluidized beds of fine solids. These networks are trained to predict mass‐transfer rates using measurements of the sublimation rate of coarse naphthalene balls in fast fluidized beds of fine glass beads at several solid‐to‐gas mass flow rates within the relevant superficial gas‐velocity range. When tested to predict the effective diffusivities from a coarse particle to the bulk of the fast bed of fine solids, trained neural networks calculated the Sherwood number with high accuracy. It is demonstrated that back‐propagation, feed‐forward neural networks provide a more accurate correlation for the mass‐transfer coefficient compared to those obtained by the currently used heuristic models.
Electrochemically modulated complexation process for ethylene/ethane separation
Authors: Terry Patricia A. , Noble Richard D. , Swanson Daniel , Koval Carl A. 
Published: June 2004

AbstractAn electrochemically modulated complexation (EMC) process was designed to selectively extract and concentrate ethylene from a feed‐phase mixture with ethane. Unlike previous EMC processes, where the separation was based on equilibrium solubility differences, this separation was based on differences in the rate of complexing with copper(I) solution between the two gases. The EMC process employed flowthrough electrolysis cells that electrochemically modulate aqueous‐phase copper chlorides between high, copper(I), and low, copper(II), affinity states. The liquid phase in the high affinity form contracts a feed gas phase in a hollow‐fiber membrane module for selective extraction and contacts the receiving gas phase in the low affinity form for concentration. Experimental results and modeling of the process are reported.
In‐situ CIR‐FTIR study of the diffusion of supercritical hydrocarbons in zeolite L
Authors: Süer Murat G. , Dardas Zissis , Lu Yaping , Moser William R. , Ma Yi H. 
Published: June 2004

AbstractCylindrical internal reflectance infrared spectroscopy (CIR‐FTIR) was used for the determination of the transport properties of hydrocarbons in zeolite L at high temperatures and pressures. This was the first time that the intracrystalline diffusivity of hydrocarbons in microporous media could be determined under supercritical conditions by using a dynamic technique. The study investigated the self‐diffusion of n‐heptane, the counterdiffusion of n‐hexane and 1‐hexene, and the codiffusion of n‐heptane and pyxlene in zeolite L under subcritical and supercritical conditions. The diffusion time constants obtained for the single and binary systems showed that the diffusion within the pore was reduced significantly under supercritical conditions (i.e., liquidlike behavior) as the hydrocarbon density within the pore was increased.
Polymerization reactor control using autoregressive‐plus Volterra‐based MPC
Authors: Maner Bryon R. , Doyle Francis J. 
Published: June 2004

AbstractA nonlinear model‐predictive control scheme based on the autoregressive‐plus Volterra model is proposed. A “plant‐friendly,” yet persistently exciting, input sequence is designed for model identification. A second feature of this work is that the control action is determined by solving a less computationally burdensome nonlinear programming problem than the optimization problems associated with Newton‐type controllers and polynomial ARMA model nonlinear MPC. A third contribution is that semiglobal closed‐loop stability conditions are derived and are shown to be less conservative than those previously published. The control scheme is shown to outperform a feedback strategy using proportional integral control and a linear model‐predictive control design for the control of two polymerization reactor case studies. The complex features of the latter case study [multivarible (3 × 3), recycle loop, high‐order (24) dynamics] motivate the applicability of this approach for industrial problems.
Characterization and permeation properties of ZSM‐5 tubular membranes
Authors: Coronas Joaquín , Falconer John L. , Noble Richard D. 
Published: June 2004

AbstractZSM‐5 zeolite membranes with reproducible properties were prepared by in‐situ synthesis on porous α‐ and γ‐alumina tubular supports and characterized by XRD, SEM and electron microprobe analysis. Single‐gas permeances for H2, CH4, N2, CO2, n‐butane, and i‐butane increase over some temperature range, but some gases exhibit maxima or minima. The highest ideal selectivities at room temperature are 299 for N2/SF6, 392 for H2/n‐butane, and 2,820 for H2/i‐butane. These membranes can separate n‐butane/i‐butane, H2/n‐butane and H2/i‐butane mixtures. All n‐butane/i‐butane separation selectivities have maxima as a function of temperature and are higher than ideal selectivities because n‐butane inhibits i‐butane permeation. Thus, separation is not by size selectivity, but is due to pore blocking. Temperature depenencies of single‐gas permeances and separation selectivities depend strongly on the location of zeolite crystals and the location is determined by preparation procedure. Ideal selectivities also depend strongly on the preparation procedure. When the zeolite forms a continuous layer on the inside surface of the support tubes, pure i‐butane permeates faster than pure n‐butane so that the single‐gas permeances are not determined just by molecular size. The i‐butane permeance also increases much more with temperature than the n‐butane permeance. The permeation behavior may be the result of permeation through nonzeolitic pores in parallel with zeolite pores. When zeolite crystals are dispersed throughout the pores of α‐alumina supports, permeances are lower and gas permeation and separation properties are quite different. Ideal selectivities are lower, pure n‐butane permeates faster than i‐butane, and the permeances increase much less with temperature. Separation selectivities are lower but can be maintained to higher temperatures.
Mechanism reduction during computer generation of compact reaction models
Authors: Klinke David J. , Broadbelt Linda J. 
Published: June 2004

AbstractOne of the challenges in building reaction mechanisms using algorithms for automated model construction is to describe the essential chemistry and enable prediction of experimental data over wide ranges of reaction conditions while maintaining a manageable model size. Two complementary methodologies for building compact reaction mechanisms were developed and combined with existing algorithms based on graph theory and bond–electron matrix operations. Each strategy was developed using pentadecylbenzene pyrolysis as an illustrative example. The first approach used a radical lumping strategy to group radicals according to their reactivity. The mechanism was reduced from 719 to 215 species and successfully predicted the experimentally observed initial reactivity. However, implementation of the radical lumping criteria alone was insufficient to allow for secondary reactions to higher‐rank products. Therefore, on‐the‐fly sensitivity analysis was incorporated to identify the important and necessary species as the mechanism was generated to guide the mechanism building process. The generic algorithms developed can be applied to generate compact reaction mechanisms for a wide array of higher molecular‐weight reactants.
Clathrate phase equilibria for the water–phenol–carbon dioxide system
Authors: Yoon Ji‐Ho , Lee Huen 
Published: June 2004

AbstractClathrate phase equilibria for the ternary water–phenol–carbon dioxide system containing one‐guest and two‐host components were studied. Three four‐phase equilibrium loci for this ternary system were determined over wide temperature and pressure ranges. A quintuple point, thermodynamically unique, and invariant condition appeared in this type of ternary system, was carefully measured, and were 293.7 K and 57.2 bar. At this quintuple point, five individual phases of water‐rich liquid, phenol‐rich liquid, carbon dioxide‐rich liquid, phenol clathrate, and vapor could coexist in equilibrium. A new experimental technique was used to determine the liquid‐phase compositions coexisting with phenol clathrates at the isobaric conditions of 30.0 bar and six temperatures ranging from 278.2 and 303.2 K. A potential applicability of the clathration process to phenol separation from aqueous solutions was demonsrated in terms of phenol concentrations based on carbon dioxide‐free concentration. In particular, phenol separation by using high‐pressure carbon dioxide as a clarthrate‐inducing agent could be applied even to multiphase aqueous solutions over an entire range of phenol concentrations.
Control of semicontinuous emulsion copolymerization reactors
Authors: Saldívar Enrique , Ray W. Harmon 
Published: June 2004

AbstractThe problem of simultaneous control of composition and molecular weight of copolymers produced in semicontinuous emulsion polymerization is addressed. A first‐principles model of emulsion copolymerization is used to produce optimal open‐loop policies, which are then experimentally tested on the system methyl methacrylate/vinyl acetate. In contrast to earlier work in the control of semicontinuous emulsion copolymerization, the control problem addressed has multiple inputs and multiple outputs, and the experimental application is free of empirical correlations and performed on an unseeded system. Optimal open‐loop policies are calculated efficiently by optimizing properties of the instantaneous polymer being formed. The experimental results confirm the feasibility of these techniques. A model‐predictive control scheme, in which optimal policies are recomputed on‐line to account for disturbances, is proposed. The scheme, which exploits the advantages of the efficient calculation of optimal policies, is tested by simulation showing good performance.
Effect of catalyst distribution in a membrane reactor: Experiments and model
Authors: Szegner John , Yeung King Lun , Varma Arvind 
Published: June 2004

AbstractInorganic membrane reactors combine reaction and separation operations in a single unit. Preferential permeation of a product species through the membrane enhances equilibrium‐limited reactions beyond the thermodynamic limit. Proper catalyst formulation and spatial distribution also enhance membrane reactor performance. To minimize reactant loss due to high gas permeation, the thickness of the γ‐alumina layer in a composite alumina membrane (Membralox) was increased to 17 μm by slip‐casting with alumina sol. Among the catalysts investigated a formulation of 1.10 wt. % Pt and 1.36 wt. % Sn supported on γ‐alumina pellets yielded the highest activity, selectivity, and stability for the dehydrogenation of ethane to ethylene. Using this catalyst composition, various nonuniform platinum distributions within the pellets were prepared by solution impregnation, while maintaining a uniform distribution of Sn. The effect of nonuniform catalyst distribution on dehydrogenation of ethane in a packed‐bed membrane reactor (PBMR) under well‐mixed, isothermal conditions was evaluated both experimentally and theoretically. Reactor performance is maximized when the catalyst is concentrated near the surface of the support. Supraequilibrium conversions, about 80% beyond equilibrium values, were obtained with the narrow surface–step catalyst pellets. Experimental results agree well with theoretical predictions, obtained without the use of any adjustable parameters. The effect of membrane thickness on reactor performance was also investigated, by comparing the 17‐μm alumina membrane with a 1.2‐mm‐thick porous Vycor glass, using pellets with the narrow surface‐step distribution. For the experimental conditions employed, relatively low permeation through the porous Vycor resulted in conversions near fixed‐bed reactor values.
Mass and thermal transport analysis of oscillating flow with absorbent polymers
Authors: Kalumuck Kenneth M. , Prabhukumar Sankar , Brown Clinton E. , Chahine Georges L. 
Published: June 2004

AbstractA new concept for removing toxic gases with respirator applications based on inhalation and exhalation through absorbent polymer‐lined tubes was studied. The two‐way oscillatory flow through the respirator element enables capture and expulsion of toxic vapors, which is not feasible with activated charcoal because of the adverse effect of moist breath on the charcoal efficiency. To study the influence of various material, design and operating parameters on the performance of such a respirator, a numerical model that solves the governing equations of mass and heat transport in an oscillatory flow through an absorbent polymer‐lined tube was developed and utilized with experimentally measured property data. Factors investigated include respirator element geometry, polymer and toxic vapor characteristics, and flowthrough speed. Results show a large delay in toxic gas penetration over that obtained by conventional one‐way flow, and define the importance of partition coefficient, flow passage size, and length and velocity. Results are compared with data from simulated breathing experiments.
Polyelectrolyte precipitate formation during miscible displacement in porous media
Authors: De Debnath , Hrymak Andrew N. , Pelton Robert 
Published: June 2004

AbstractThe miscible displacement of aqueous lignin solutions (model black liquor) by water from beds formed from glass beads was studied as a function of the presence of cationic polymer in the wash water, bed structure, lignin concentration, and superficial flow rate. The displacement behaviors in homogeneous beds formed from fine beads (121 μm) were compared with results of experiments using a channel bed consisting of a bed formed from fine beads surrounding a channel of coarse beads (638 μm) running the length of the bed in the flow direction. Washing efficiencies, defined as the fraction of lignin removed when one pore volume of eluate was collected, were 84–93% for homogeneous beds washed with water compared with 31–33% for the channel bed; the range in efficiencies reflects the influence of other variables. The presence of cationic polymer in the wash water enhanced the washing efficiency by 1.7 to 2 times with a corresponding 20 to 35% decrease in the permeability of the central channel in the channel bed. The improved washing with polymer was due to selective plugging of the central channel with precipitate formed from complex formation between anionic lignin in the black liquor and the cationic polymer. Breakthrough curves obtained from 12 microconductivity probes located throughout the bed showed that mixing of lignin in the black liquor and the cationic polymer. Breakthrough curves obtained from 12 microconductivity probes located throughout the bed showed that mixing of lignin solution (high conductivity) with wash water (low conductivity) in the displacement front, as expressed by a mixing length, was a maximum in the coarse bead channel and was decreased when the wash water contained cationic polymer.
Analysis of adsorption selectivity in a one‐dimensional model system
Authors: Talbot Julian 
Published: June 2004

AbstractThe adsorption selectivity, Si, j = (Xi/yi)/(xj/yj), is examined in a 1–D model of a mixture of hard rods adsorbing on a linear substrate. The adsorbed components are characterized by their length, li, and equilibrium constant, ki. We derive an expression for the bulk‐phase pressure Po, for which there is no separation of components i and j, S,i, j = 1, in terms of these parameters. The selectivity of the smaller component always increases with the bulk pressure, which results in a selectivity reversal if, as is usually the case, the larger component is more strongly adsorbed at low surface coverages. In a binary mixture, when P < Po, the selectivity of the smaller component decreases with increasing bulk‐phase mole fraction, y1, while for P > Po, the reverse is true. The effect of varying the molecular parameters on the selectivity is also studied.
Standing wave analysis of SMB chromatography: Linear systems
Authors: Ma Z. , Wang N.‐H. L. 
Published: June 2004

AbstractThe concept of standing concentration waves is introduced to derive design equations for continuous moving bed (CMB) processes. For linear isotherm systems, simple equations are derived from the analysis to link product purity and recovery to zone lengths, bed movement velocity, flow rates, column capacity factors, and mass‐transfer coefficients. Once product purity, recovery and feed flow rate are specified for a given system, the zone flow rates and bed movement velocity that provide the highest throughput and the lowest solvent consumption can be determined from the solutions. In a given system, there is a trade‐off between product purity and throughput. If bed volume and product purities are fixed, the longer the zone lengths, the higher the throughput. Simulations based on a linear driving force model that considers axial dispersion and lumped film and intraparticle diffusion are used to compare the column profiles and effluent histories of CMB and simulated moving bed (SMB). A numerical algorithm is introduced to allow simulation of both CMB and SMB operations using the same program. The comparison shows that the design equations derived for CMB systems are applicable to SMB systems. Finally, the standing wave solutions are used to analyze an experimental SMB system from the literature (Ching et al., 1991). Simulations agree closely with the data and the predictions of the theoretical analysis.
Study of a six‐bed pressure swing adsorption process
Authors: Malek A. , Farooq S. 
Published: June 2004

AbstractA mathematical model of a six‐bed, ten‐step PSA operation is developed. The process cycle considered resembles an industrial hydrogen recovery process from the refinery fuel gas. Three hydrocarbon impurities (methane, ethane, and propane) are considered in the feed gas. The adsorbent used is activated carbon. The nonisothenmal, bulk separation PSA model adopts the linear driving force approximation for particle uptake and the extended Langmuir isotherm to represent adsorption equilibrium. A transient pressure equation is incorporated to account for the dynamics in uariable pressure steps. The model was verified using experimental results from a computer‐controlled, laboratory‐scale PSA unit. Considering the complexity of operation, comparison of various stream flow rates, concentrations, bed pressure and temperature profiles indicates that the model provides a sufficiently accurate prediction of the PSA performance. Parametric studies further show that its product purity declines relatively quickly with increasing cycle time and decreasing high operating pressure due to the breakthrough of a relatively sharp methane front. There is no real advantage in operating the PSA unit beyond a high operating pressure of about 18.0 bar.
Gas‐filled cavity structures and local void fraction distribution in aerated stirred vessel
Authors: Bombač A. , Žun I. , Filipič B. , Žumer M. 
Published: June 2004

AbstractThe local structural function obtained by a microresistivity probe at different hydrodynamic regimes is examined. The structures, such as the vortex‐clinging structure, the appearance of one and two large cavities, small 3‐3 structure, large 3‐3 structure, and ragged cavities were recognized by frequency transformation of the time‐domain structural function. An optimized phase discrimination in signal processing was used. The distribution of the local void fraction (α) in a pilot‐size stirred tank was experimentally investigated, because almost no such data can be found in the literature. The two‐phase mixture was composed of air and water; α was measured at 190 nodes in the vertical half‐section plane of the vessel. Relative differences smaller than 9% between integrated values of α and measured gas holdups agreed reasonably well under all conditions.
Model for surface diffusion in liquid‐phase adsorption
Authors: Miyabe Kanji , Takeuchi Shigeya 
Published: June 2004

AbstractBased on the absolute‐rate theory, a consistent interpretation was provided for the dependence of surface‐diffusion coefficient, Ds, on temperature and the amount adsorbed in various liquid‐phase adsorption systems, such as the Langmuir‐, Freundlich‐and Jossens‐type adsorption. It was demonstrated that a restricted molecular diffusion model for surface diffusion was useful for the analysis of the characteristic features of Ds. A formulation of Ds was derived based on the model and was applied to the analysis of surface‐diffusion phenomena in various adsorption systems. The temperature dependence could be interpreted by assuming surface diffusion as an activated process. By taking into account the change in both the logarithmic slope of an adsorption isotherm and an adsorption potential, the concentration dependence of Ds could be interpreted irrespective of the type of the adsorption isotherms.