bluuebunny/crossref_metadata_2025_split huggingface dataset:
Performance analysis of four‐bed H2 PSA process using layered beds
Authors: Park Jong‐Ho , Kim Jong‐Nam , Cho Soon‐Haeng 
Published: April 2004

AbstractHydrogen purification from a typical cracked gas mixture (H2/CO2/CH4/CO) by the four‐bed PSA process was studied experimentally and theoretically using layered bed of activated carbon and zeolite 5A. The mathematical model accounts for the mass and heat transfer resistance using the linear driving force approximation for the particle uptake, and the ideal adsorbed solution model represents the multicomponent adsorption equilibrium. Effects of the superficial velocity, heat transfer resistance and the bed layering on the process performance were investigated. Since the recovery sharply decreases above a certain productivity at the given purity, the relation between the productivity and recovery was studied before the process design. Its performance decreased with the increase in heat transfer resistance, but increased with heat transfer resistance in some range. Both the experiment and theory showed optimum carbon‐to‐zeolite ratios. Those optimum ratios depend on such operating variables as the superficial velocity, heat transfer resistance and product purity. For higher product purity more zeolite was used. As the superficial velocity increased, the process performance has its maximum at higher carbon‐to‐zeolite ratio. Except for the adiabatic conditions, the optimum carbon‐to‐zeolite ratio increased with the increase in the heat transfer resistance. At the adiabatic conditions, however, the optimum carbon‐to‐zeolite ratio was lower than that at the nonisothermal conditions.
Scenario‐integrated modeling and optimization of dynamic systems
Authors: Abel O. , Marquardt W. 
Published: April 2004

AbstractAssessing the consequences of exceptional events, such as failures and sudden changes in product demand or raw‐material prices, is of great importance to the operation of chemical processes. Such an exceptional event and the resulting behavior of the process are called a scenario in this article. Problem formulations for their rigorous incorporation into the optimization of dynamic systems are presented. They allow the determination of operational strategies that are economically optimal and that keep the plant within a chosen regime in the state space, even for a number of possible scenarios. The formulations are based on a unifying model framework containing both continuous and discrete dynamics. For a restricted class of problems a method for the numerical solution of the resulting scenario‐integrated dynamic optimization problems is introduced. The applicability of this technique is demonstrated with two examples of different complexity.
Two‐dimensional heterogeneous model for a reticulated‐foam photocatalytic reactor
Authors: Changrani Rajnish G. , Raupp Gregory B. 
Published: April 2004

AbstractA 2‐D heterogeneous convection reaction model for a gas–solid lamp‐in‐tube annular photocatalytic reactor is presented. The catalyst (TiO2) is supported on a reticulated‐foam monolithic structure placed in the annular space between the UV lamp and the reactor wall. Mass balances for individual species are coupled through the reaction‐rate expression that appears in the boundary condition at the fluid–solid interface in heterogeneous catalytic reactor models. The heterogeneous reaction rate is modeled using semiempirical Langmuir‐Hinshelwood‐Hougen‐Watson (LHHW) kinetics with adsorption constants for various species. The local volumetric rate of energy absorption (LVREA) term in the rate expression was computed using a 3‐D polychromatic radiation‐field model. The overall system of nonlinear partial differential equations was solved using a combination of the Crank‐Nicolson method and the globally convergent Newton‐Raphson method. The apparent, average quantum yield in the LHHW kinetic rate form is the single adjustable parameter in the model. Isopropanol (IPA) was chosen as the test contaminant to conduct experimental performance measurements for model validation. Model‐predicted radial and axial profiles for bulk and surface concentration reveal that the extent to which mass transport influences the operation of a photocatalytic reactor is determined largely by the local magnitude of the LVREA. Similitude in the scale‐up of an annular lamp‐in‐tube heterogeneous photocatalytic reactor is achieved only when the dimensionless radial radiation profile, as well as corresponding magnitudes of a geometric number, the Peclet number, the Stanton number, and the photocatalytic analog of the Damköhler number, are identical.
Kinetics and product distribution of n‐hexadecane pyrolysis
Authors: Watanabe Masaru , Tsukagoshi Masayuki , Hirakoso Hideyuki , Adschiri Tadafumi , Arai Kunio 
Published: April 2004

AbstractPyrolysis experiments on n‐hexadecane (n‐C16) were conducted at 673–723 K and n‐C16 concentrations of 0.07–1.47 mol/L by using batch type reactors. The main products of n‐C16 pyrolysis were n‐alkanes and 1‐alkenes at all the reaction conditions. The 1‐alkene/n‐alkane ratio decreased with increasing n‐C16 concentration at all the reaction temperatures. The rate of n‐C16 pyrolysis increased to a maximum and then decreased with increasing n‐C16 concentration. The activation energy of the overall rate constant of n‐C16 pyrolysis was 196 kJ/mol at 0.07 mol/L of n‐C16 concentration and 263 kJ/mol at 0.22 mol/L. To describe these phenomena, a mathematical model for the pyrolysis that expresses the radical network reaction, including initiation, isomerization, β‐scission, H abstraction, and termination, was developed. The effect of radical size on the rates of bimolecular reactions (H abstraction and termination) was important for a correct quantitative description. Comparison between the experimental data and the model showed that the rates of bimolecular reactions were inversely proportional to the carbon number i of radical Ri. The model can predict product distribution and n‐C16 pyrolysis rate in a wide range of temperatures (603–893 K) and n‐C16 concentrations (6.86 × 10−3 2.48 mol/L). Furthermore, the model can describe the pyrolysis kinetics of n‐C10–n‐C25 by considering the carbon number of the hydrocarbon.
Microencapsulation of proteins by rapid expansion of supercritical solution with a nonsolvent
Authors: Mishima Kenji , Matsuyama Kiyoshi , Tanabe Daisaku , Yamauchi Satoru , Young Timothy J. , Johnston Keith P. 
Published: April 2004

AbstractA new method—rapid expansion from supercritical solution with a nonsolvent (RESS‐N)—is reported for forming polymer microparticles containing proteins such as lysozyme (from chicken egg white) and lipase (from Pseudomonas cepacia). A suspension of protein in CO2 containing a cosolvent and dissolved polymer is sprayed through a nozzle to atmospheric pressure. The polymers are poly(ethylene glycol) (PEG4000; MW = 3,000, PEG6000; MW = 7,500, PEG20000; MW = 20,000), poly(methyl methacrylate) (PMMA; MW = 15,000), poly(L‐lactic acid) (PLA; MW = 5,000), poly(DL‐lactide‐co‐glycolide) (PGLA; MW = 5,000) and PEG–poly(propylene glycol) (PPG)–PEG triblock copolymer (MW = 13,000). The solubilities of these polymers in CO2 increase significantly with low‐molecular‐weight alcohols as cosolvents. The particles do not tend to agglomerate after expansion, since the pure cosolvent is a nonsolvent for the polymer. The structure and morphology of the microcapsules were investigated by TEM, SEM, and optical microscopy. The thickness of the polymer coating about the protein, as well as the mean particle diameter and particle‐size distribution, could be controlled by changing the feed composition of the polymer.
Molecular, pressure, and thermal diffusion in nonideal multicomponent mixtures
Authors: Ghorayeb Kassem , Firoozabadi Abbas 
Published: April 2004

AbstractA formalism based on powerful concepts of the thermodynamics of irreversible processes is derived for calculating multicomponent diffusion flux both at the critical point and away from the critical point. The derivations are based on the entropy balance expression combined with the phenomenological equations and Onsager reciprocal relations. The formalism results in a clear expression of the thermal contribution in the diffusion flux for nonideal multicomponent mixtures. The diffusion flux analysis at the critical point showed that, unlike isothermal and isobaric conditions where molecular diffusion flux is zero, molecular diffusion flux is finite and nonzero at the critical point. The thermal contribution in the diffusion flux is also finite at the critical point in multicomponent mixtures. At nonisothermal conditions, as well as nonisothermal and nonisobaric conditions, the composition gradient reaches infinity at the critical point; therefore, the mol fraction plot vs. spatial coordinates has an inflection point.
Theoretical model of thermal diffusion factors in multicomponent mixtures
Authors: Firoozabadi Abbas , Ghorayeb Kassem , Shukla Keshawa 
Published: April 2004

AbstractUnlike molecular diffusion, neither measured thermal diffusion coefficients nor the theoretical framework exist for the estimation of thermal diffusion coefficients in nonideal multicomponent mixtures. This work derives a theoretical model for thermal diffusion coefficients in ideal and nonideal multicomponent mixtures, based on the thermodynamics of irreversible processes and the molecular kinetic approach incorporating explicit effects of nonequilibrium properties, such as the net heat of transport and molecular diffusion coefficients, and of equilibrium properties of the mixture, which are determined by the Peng‐Robinson equation of state. An interesting feature of this model is that in nonideal multicomponent mixtures thermal diffusion coefficients depend on molecular diffusion coefficients, while in binary mixtures they do not. The model successfully describes thermal diffusion factors of binary mixtures for which experimental data are available, even those in extreme nonideal conditions and close to the critical point. Since experimental data on thermal diffusion factors in multicomponent hydrocarbon mixtures are not available, testing the model's accuracy was not possible. The model, however, successfully predicted spatial variation of composition in a ternary mixture of nC24/nC16/nC12, providing an indirect verification. The six‐component mixture of C1/C3/nC5/nC10/nC16/C2 shows significant dependency of thermal diffusion factors on the distance to the critical point. It also demonstrates for the first time that there is no need to adopt a sign convention for thermal diffusion coefficients in binary and higher mixtures. The thermodynamic stability analysis shows that when the thermal diffusion coefficient is positive, the component should go to the cold region in a binary mixture.
Feasible products for kinetically controlled reactive distillation of ternary mixtures
Authors: Chadda Nitin , Malone Michael F. , Doherty Michael F. 
Published: April 2004

AbstractA method to determine feasible product compositions from a single‐feed reactive distillation column for finite rates of reaction is presented. Tracking of pinch points to estimate the limit at minimum reflux is combined with performance modeling for the limit at the minimum number of stages. Using two examples it is shown how the product composition regions deform from the known limit of no reaction through intermediate rates of reaction and finally collapse onto the chemical equilibrium curve at extremely fast reaction rates. However, compositions can be achieved at intermediate reaction rates that do not lie between the limits for slow (no reaction) and fast (chemical equilibrium) reactions.
“String‐of‐beads” flow of liquids on vertical wires for gas absorption
Authors: Chinju Hirofumi , Uchiyama Kazunori , Mori Yasuhiko H. 
Published: April 2004

AbstractA liquid steadily fed onto a thin wire vertically held in a gas stream may flow down the wire, taking the form of a “string of beads,” which is a composite of teardrop‐shaped beads regularly aligned on the wire and thin cylindrical films each coating the portion of the wire between two neighboring beads. The beads slide down at a constant speed, interacting with the films flowing down much more slowly, thereby inducing some mixing motion in the liquid phase. The string‐of‐beads flow exhibited by water or an aqueous monoethanolamine solution was observed, and the mass transfer of CO2 from the surrounding CO2/N2 mixture into water flowing down single wires was studied both experimentally and analytically. The results indicate the potential of on‐wire string‐of‐beads flow devices for innovating gas–liquid contact operations to be used in, for example, removing CO2 from flue gases exhausted at fossil‐fuel‐fired power plants.
Optimal design of reverse osmosis module networks
Authors: Maskan Fazilet , Wiley Dianne E. , Johnston Lloyd P. M. , Clements David J. 
Published: April 2004

AbstractThe structure of individual reverse osmosis modules, the configuration of the module network, and the operating conditions were optimized for seawater and brackish water desalination. The system model included simple mathematical equations to predict the performance of the reverse osmosis modules. The optimization problem was formulated as a constrained multivariable nonlinear optimization. The objective function was the annual profit for the system, consisting of the profit obtained from the permeate, capital cost for the process units, and operating costs associated with energy consumption and maintenance. Optimization of several dual‐stage reverse osmosis systems were investigated and compared. It was found that optimal network designs are the ones that produce the most permeate. It may be possible to achieve economic improvements by refining current membrane module designs and their operating pressures.
Modeling fluid phase transition effects on dynamic behavior of ESDV
Authors: Mahgerefteh Haroun , Saha Pratik , Economou Ioannis G. 
Published: April 2004

AbstractThe characteristics method was employed to elucidate the effects of fluid‐phase transition on the dynamic behavior of emergency shutdown valves following full bore rupture (FBR) of long pipelines containing high‐pressure hydrocarbons. The responses of both check valves and ball valves were simulated. The application of the model to the FBR of the Piper‐Alpha MCP‐01 gas riser reveals that condensation of the gaseous inventory results in a delay in valve activation times, as well as an increase in the amount of inventory released prior to pipeline isolation. However, the magnitude of the pressure surge brought about from having to bring the high‐pressure escaping fluid to rest following emergency isolation was significantly reduced.
Finite element, discrete‐fracture model for multiphase flow in porous media
Authors: Kim Jong‐Gyun , Deo Milind D. 
Published: April 2004

AbstractA new discrete‐fracture multiphase flow model developed allows incorporation of fractures in a spatially explicit fashion. It is an alternative to conventional dual‐porosity, dual‐permeability models used most often to model fractured subsurface systems. The model was applied to a water flood on a 2‐D random fracture network. A standard Galerkin finite element method was used to discretize the domain; triangular elements were used for matrix and line elements for the fractures. The finite element formulation was validated by using a commercial finite difference simulator. Results from a simple discrete‐fracture model agreed reasonably well with the explicit fracture representation of the same domain. At low permeability contrasts between the matrix and the fractures, the model, as expected, predicted approximately symmetric water advance. At high permeability contrasts, the fracture network played a critical role in determining water advance and oil recovery. Significant oil bypassing was observed, particularly at higher flow rates. The oil recovery was determined by a complex interplay of the absolute matrix permeability, permeability contrast and flow rates. Fracture capillary pressure also played a significant role in determining water penetration in the matrix.
Extractive bioconversion in a four‐phase external‐loop airlift bioreactor
Authors: Sajc Lidija , Vunjak‐Novakovic Gordana 
Published: April 2004

AbstractThe integration of biosynthesis and product separation can increase the productivity of immobilized plant cells in airlift bioreactors. Extractive bioconversion of anthraquinones was studied in an external‐loop airlift bioreactor consisting of a riser, a downcomer, and two horizontal sections, while containing alginate‐immobilized Frangula alnus cells, a continuous aqueous phase (nutrient solution), dispersed solvent phase (n‐hexadecane or silicone oil), and gas bubbles. A simple mathematical model was developed to describe the cocurrent liquid‐liquid extraction in the riser section of the bioreactor and to rationalize the measured product concentrations in the aqueous and solvent phase. The model equations were solved analytically in a dimensionless form and used to study the effects of flow conditions, solvent properties, product formation rate, droplet size, and contactor length on the extraction efficiency and product concentration profiles in the continuous and dispersed phase.
Phase stability with cubic equations of state: Global optimization approach
Authors: Harding S. T. , Floudas C. A. 
Published: April 2004

AbstractCalculation of phase and chemical equilibria is of fundamental importance for the design and simulation of chemical processes. Methods of minimizing the Gibbs free energy provide equilibrium solutions that are candidates only for the true equilibrium solution, because the number and type of phases must be assumed before the Gibbs energy minimization problem can be formulated. The tangent plane stability criterion was used to determine the stability of a candidate equilibrium solution. The Gibbs energy minimization and tangent plane stability problems are challenging due to highly nonlinear thermodynamic functions. This work develops a global optimization approach for the tangent plane stability problem that provides a theoretical guarantee about the stability of the candidate equilibrium solution with computational efficiency. Cubic equations of state were used due to their ability to accurately predict the behavior of nonideal vapor and liquid phases across a broad range of pressures. The mathematical form of the stability problem was analyzed and nonlinear functions with special structure were identified to achieve faster convergence of the algorithm. This approach, when applied to the SRK, Peng‐Robinson, and van der Waals cubic equations of state, could address a variety of mixing rules. Computational results on problems with two‐eight components are presented.
In situ determination of the viscosity of gas mixtures containing trace quantities of oxygen
Authors: Hellgardt K. , Al‐Musa A. , Cumming I. W. , Mason G. , Buffham B. A. 
Published: April 2004

AbstractAn electrochemical cell was used to add trace quantities of oxygen to a gas stream. The viscosity of these gas mixtures was determined using an established method that measures the rate of change of viscosity with oxygen concentration. Viscosity data are reported for nitrogen/oxygen and helium/oxygen mixtures at very low oxygen concentrations. The data are compared with values for the viscosity of these gas mixtures, interpolated from results reported in the literature.
Pressure drop measurements in a microchannel
Authors: Pfund David , Rector David , Shekarriz Alireza , Popescu Aristotel , Welty James 
Published: April 2004

AbstractRecent developments in micro‐energy and micro‐chemical systems have produced a need for greater understanding of flow in small channels. Several recent studies of friction factors and transition Reynolds numbers in rectangular microchannels have produced results that differ from classical theory. In this work, friction factors and laminar flow friction constants were determined for water flowing in high aspect ratio channels with depths ranging from 128 to 521 μm. Reynolds numbers were between 60 and 3,450. Pressure drops were measured within the channel itself to exclude entrance and exit losses. Transitions to turbulence were observed with flow visualization. Uncertainties in measured variables were quantified and propagated into the estimated friction constants. Friction factors were also determined in a 1,050‐μm‐deep channel that served as a control. After considering experimental uncertainties and systematic errors, significant differences remained between the results and classical theory.
Multivariable model state feedback: Computationally simple, easy‐to‐tune alternative to MPC
Authors: Mhatre Suraj , Brosilow Coleman 
Published: April 2004

AbstractMethods for the design and tuning of multivariable model state feedback (MMSF) systems for complete and triangular output decoupling of inherently stable processes are presented. MMSF is a method of implementing multivariable IMC controllers that substantially reduces the complexity of the implementation and compensates for control effort saturation. Complexity is reduced because the controls are formed as a linear combination of past and current model states. Saturation‐induced directionality problems are avoided by temporarily increasing filter time constants to bring the control vector into the constraint set. The possibility that needed future controls will be inadequate to compensate for past control actions is avoided by setting minimum values for the controller filter time constants. The feedback structure of MMSF facilitates on‐line tuning, one process variable at a time. Also, because MMSF is a form of IMC, it can be tuned off‐line to accommodate process uncertainty using H∞ methods.
Wavelet‐based adaptive robust M‐estimator for nonlinear system identification
Authors: Wang D. , Romagnoli J. A. , Safavi A. A. 
Published: April 2004

AbstractA wavelet‐based robust M‐estimation method for the identification of nonlinear systems is proposed. Because it is not based on the assumption that there is the class of error distribution, it takes a flexible, nonparametric approach and has the advantage of directly estimating the error distribution from the data. This M‐estimator is optimal over any error distribution in the sense of maximum likelihood estimation. A Monte‐Carlo study on a nonlinear chemical engineering example was used to compare the results with various previously utilized methods.
Tuning and design of single‐input, single‐output control systems for parametric uncertainty
Authors: Stryczek Karel , Laiseca Mario , Brosilow Coleman , Leitman Marshall 
Published: April 2004

AbstractFrequency domain methods, which are for the design and tuning of control systems for processes with uncertain parameters, and are easy to use and interpret, are proposed. The advantages of the proposed methods over other H∞ methods are mainly that they require substantially less expertise on the part of the designer, and that they result in control system performance that closely approximates that which was desired. Several examples illustrate the proposed methods. A stable second‐order lag and dead time process, with gain and dead time uncertainties, provides the vehicle for studying controller designs for single and two degree of freedom control systems. Application of Mp tuning to an uncertain, unstable, first‐order lag, plus dead time process, shows that there can be a significant performance penalty associated with using a simple feedback control system rather than an internally stable model‐based control system. The performance of a controller for an integrating, oscillatory process obtained by Mp synthesis also compares favorably with that of a controller obtained by other investigators using loop shaping.