bluuebunny/crossref_metadata_2025_split huggingface dataset:
A theoretical model for quiescent coarsening in immiscible polymer blends
Authors: Hu Guo‐Hua , Li Huxi , Feng Lian‐Fang 
Published: April 2004

AbstractThe coalescence rate in immiscible polymer blends predicted by all existing models is two or three orders of magnitude lower than that observed experimentally. The model developed in this study considers for the first time that coarsening is driven by van der Waals forces and there is slippage at the interfacial boundaries between the moving particles and the matrix. The growth rate of the average radius of the particles, R, can be approximately expressed as

where β is a function of the interfacial slippage length b, R, and the average surface distance between the particles h. The parameter b depends on the incompatibility and the degree of entanglement at the interface between the two polymers of the blend. The fact that the coarsening rate is decreased by the presence of a copolymer can be explained by a decrease in the value of b.
Correlation and prediction of crystal solubility and purity
Authors: Teja Amyn S. , Givand Jeffrey C. , Rousseau Ronald W. 
Published: April 2004

AbstractA thermodynamic model is developed for the correlation and prediction of crystal solubility and purity when lattice substitution by isomorphic or near‐isomorphic impurities is the dominant mechanism that leads to impure crystals. The model is based on earlier observation that the purity of amino acid crystals obtained from aqueous solutions is related to the relative solubilities of the product and impurity in the solvent. A simple relationship is developed that allows the prediction of the purity of crystals obtained from dilute solutions containing both product and impurity species.
Phase equilibrium engineering of supercritical hydrogenation reactors
Authors: Pereda Selva , Bottini Susana B. , Brignole Esteban A. 
Published: April 2004

AbstractThe general problem of phase equilibrium engineering of supercritical hydrogenation reactors is addressed. The conceptual design of process conditions is discussed, as well as procedures to determine the range of feasible operating conditions for two reaction problems: the hydrogenation of vegetable oils and the hydrogenolysis of fatty acid methyl esters. A group contribution equation of state is applied to predict the required phase equilibrium scenarios for solvent containing reactive mixtures.
Absorption of carbon dioxide in aqueous piperazine/methyldiethanolamine
Authors: Bishnoi Sanjay , Rochelle Gary T. 
Published: April 2004

AbstractCarbon dioxide absorption in 0.6 M piperazine (PZ)/4 M methyldiethanolamine (MDEA) was measured in a wetted wall contactor. The data were simulated using a model that accounts for chemical reactions and transport effects with the eddy diffusivity theory. PZ/MDEA blends absorb CO2 faster than monoethanolamine (MEA) or diethanolamine (DEA) blends with MDEA at similar concentrations. The reaction of PZ to form a monocarbamate is dominant at low loading (<0.14). The reaction of the monocarbamate to form dicarbamate is dominant at high loading. The absorption rate did not follow pseudo first‐order behavior except at very low loading. All carbamate and dicarbamate formation reactions approached instantaneous behavior at high loading. The series resistance due to pseudo first‐order reaction and instantaneous carbamate formation matched data throughout the entire loading range. A typical ammonia plant absorber was simulated at isothermal conditions using the rigorous model. Gas film limitations were dominant (>50%) only at the top of the absorber.
Improved PI controller with delayed or filtered integral mode
Authors: Lee Jietae , Edgar Thomas F. 
Published: April 2004

AbstractIntegral action is almost always included in process control systems to eliminate steady‐state offset without uncertain process gain. The open‐loop pole, however, at the origin of the integral term causes some problems such as integral windup. Various methods to solve these problems were studied. For better control performance and robustness, a filter was added to the integral term, which decouples the effective frequency ranges between the integral and proportional terms without degradation of the integral action. It produces a phase lead in a certain frequency range without having a derivative term, enhancing the control performances and stability robustness. Based on the internal model control method or the direct synthesis method, tuning rules for the proposed controller are given.
Multivariate SPC for startups and grade transitions
Authors: Duchesne Carl , Kourti Theodora , MacGregor John F. 
Published: April 2004

AbstractProcess transitions (grade changeovers, startups, and restarts) are very frequent in industry, and usually lead to the loss of production time, the production of off‐grade materials, and to inconsistent reproducibility of product grades. Two aspects of using multivariate statistical methods based on PCA and PLS to improve process transition performance using historical records of transition data are discussed. First, multivariate SPC approaches are proposed to determine if the process conditions for the commencement of a transition (“startup readiness”) are correct and to assess the successful completion of a transition (“production readiness for the new grade”). The latter is illustrated using a simulated fluidized‐bed process for the production of different grades of linear low‐density polyethylene. Second, analysis tools are suggested for diagnosing the reasons for past transition problems and for monitoring new transitions to ensure repeatable high quality transitions. The latter methods are aimed at reducing the amount of off‐specification materials and reducing transition time, as illustrated on industrial data from restarts of a polymerization process.
Multiplicity of steady states in the codeposition of silicon carbide and carbon
Authors: Kostjuhin Igor M. , Sotirchos Stratis V. 
Published: April 2004

AbstractPast studies have suggested that the process of chemical vapor deposition of SiC and C from mixtures of methyltrichlorosilane (CH3 SiCl3, MTS), ethylene and hydrogen may exhibit multiple steady states in some regions of its space of operating parameters and conditions. This phenomenon was studied systematically and experimentally in a hot‐wall chemical‐vapor deposition reactor, in which small substrates hung from the sample arm of a sensitive microbalance are used for continuous monitoring of the deposition rate. Multiplicity of steady states occurs in a wide region of the space of process operating parameters, which covers a considerable portion of the range of conditions where deposition of SiC from MTS usually occurs. All cases studied manifest themselves as two stable (observable) deposition states at the same condition, differing by at least one order of magnitude. Various experimental observations and results of the thermochemical equilibrium analysis in the gas phase of the deposition system prove that the appearance of multiplicity in the MTS–C2H4–H2 system manifests the heterogeneous chemistry of the deposition process, not of the homogeneous chemistry or the interactions of the transport and reaction processes. The composition analysis of the deposits reveals that sudden changes of the composition from almost pure carbon at the low deposition rate branch to SiC with excess carbon at the high deposition branch take place at the two limits of the multiplicity region. It indicates that one must operate outside the range of multiple steady states to obtain deposit compositions over the whole range from C to SiC.
Calcined calcium magnesium acetate as a superior SO2 sorbent: I. Thermal decomposition
Authors: Han Dong Hoon , Sohn Hong Yong 
Published: April 2004

AbstractThe reactivity of the calcination product of calcium magnesium acetate (CMA) as a possible dry desulfurization agent was evaluated. The first step in the dry desulfurization reaction—the thermal decomposition of CMA—was investigated by determining the decomposition reaction in three steps: 1. the evaporation of water starting at 65°C, 2. the conversion of CMA into CaCO3 and MgO starting at 275°C, and 3. the decomposition of CaCO3 to CaO starting at 580°C. The pseudo‐first‐order kinetic equation was observed for the CMA decomposition to CaCO3 + MgO, with an activation energy of 165.5 kJ/mol. The decomposition of CaCO3 to CaO also obeyed the pseudo‐first‐order kinetics, with an activation energy of 200 kJ/mol. As discussed in Part II of this series, the calcination product from CMA is quite reactive due mainly to the large porosity and internal surface area generated on the removal of the acetate group during the decomposition reaction. Furthermore, as will be shown in Parts II and III, the sulfation capacity of the calcined CMA is much greater than that of conventional sorbents because its sulfation rate does not level off until complete conversion and its MgO content is also sulfated at temperatures lower than about 900°C.
Simplified design of axial‐flow cyclone mist eliminators
Authors: Brunazzi E. , Paglianti A. , Talamelli A. 
Published: April 2004

AbstractMist eliminators have widespread application in many processes, and a large number of different types of mist eliminators are available on the market. Wire‐mesh mist eliminators, vane‐type eliminators, and cyclones are used extensively in many industrial plants. Unfortunately, these separators present some significant drawbacks when they are used in high‐pressure applications or in any application in which a reduction in the diameter of the vessel containing the separator is necessary and high separation efficiency is required. Therefore, over the last several years some important suppliers have developed new axial flow separators (such as Axiflow, Swirl Tube, or Vico‐Spin). Despite the broad range of entrainment removal applications, open literature on this topic is scarce. So far, design of these axial‐flow separators can only be performed by suppliers using proprietary design criteria or using semiempirical equations with an uncertain range of applicability. This work presents new experimental data obtained at atmospheric conditions on three different axial separators and a new design model.
Influence of exit geometry in circulating fluidized‐bed risers
Authors: Harris A. T. , Davidson J. F. , Thorpe R. B. 
Published: April 2004

AbstractThe influence of exit geometry on the riser axial pressure profile in circulating fluidized beds (CFB) is examined. Experiments were performed in an academic‐scale CFB operating at conditions chosen to give dimensional similarity with an industrial CFB combustor. The influence of riser exit geometry was investigated to compare smooth and abrupt exits in terms of three different measures: (1) a dimensionless length of influence, Ω, of the exit along the riser, where Ω = (length of influence)/(riser height); (2) the exit reflection coefficient, Rf, defined by Senior in 1992 where Rf = (downward solids flow in riser)/(upward solids flow in riser) just below the riser exit; and (3) the increase in cross‐sectionally averaged solids concentration at the riser exit. Analysis of the new data and results from the literature, lead to the description of solids flow at the exit in terms of a riser exit Froude number (FrR) where FrR = ust/gR. A correlation between the riser exit Froude number and the exit reflection coefficient is presented. A serious correlation between the dimensionless length of influence of the exit bend, measured down the riser, and operating conditions, particle properties, gas properties and riser dimensions is also presented. Both correlations predict the influence of exit geometry (the exit effect) on the riser axial pressure profile. The relationship between operating parameters and the increase in cross‐sectional averaged solids concentration at the riser exit is also examined.
Evolutionary operation and control of chromatographic processes
Authors: Nagrath Deepak , Bequette B. Wayne , Cramer S. M. 
Published: April 2004

AbstractA novel generalized run‐to‐run control (GR2R) control strategy is presented for the optimization and control of nonlinear preparative chromatographic processes. The GR2R approach synergistically employs a hybrid (both physical and empirical) model to control chromatographic processes in the presence of sporadic and autocorrelated disturbances. First, parameters of the physical model through experiments are determined, and then the physical model is used to estimate initial parameters of the nonlinear empirical model (Hammerstein) using orthogonal forward regression. Parameters of the nonlinear empirical model are updated at the end of each run using a nonlinear recursive parameter estimation method. The updated empirical model is then used in the control algorithm (model predictive control) to estimate operating conditions for the next batch. Processes operating under fixed optimal conditions are compared with those operating with GR2R control for both gradient and displacement chromatography. The GR2R outperforms the fixed conditions in the presence of various disturbances (such as bed capacity, column efficiency, and feed load) and is an effective strategy for the optimization and control of complex chromatographic processes.
Integrated framework for abnormal event management and process hazards analysis
Authors: Dash Sourabh , Venkatasubramanian Venkat 
Published: April 2004

AbstractProcess hazards analysis (PHA) and abnormal event management (AEM) are important to plant safety in chemical process industries. PHA deals with the off‐line identification, assessment and mitigation of hazards, while AEM addresses process plant malfunctions on‐line. Their inherent objectives, however, are similar, such as identifying, avoiding and mitigating hazards, and planning for emergencies. While PHA reasons from causes to consequences, AEM identifies the causes from observed symptoms or faults. The PHA results contain valuable cause and consequence information, safeguards, and other operability issues. AEM can benefit from utilizing this existing knowledge about the plant. However, in current industrial practice, PHA results are not used by operators for AEM purposes. An integrated framework combining both these tasks in a synergistic manner effectively manages and displays information searched from a possibly large number of PHA results, during on‐line operation, by using a hierarchical representation of the plant. An automated methodology is developed for this representation based on topology and functional classification of equipment. The application of the integrated framework to an industrial case study is described.
Reverse‐flow operation for application of imperfectly immobilized catalysts
Authors: Hung Kim G. W. , Papadias Dennis , Björnbom Pehr , Anderlund Magnus , Åkermark Björn 
Published: April 2004

AbstractA reverse‐flow packed‐bed reactor used to solve the problem of leaching from immobilized homogeneous catalysts was studied. Product‐to‐catalyst ratios (PCRs) for a reverse‐flow reactor (RFR) and a conventional batch reactor with catalyst reuse were compared theoretically and numerically. In the ideal case without band broadening in the RFR it is possible to completely eliminate the limit on PCR due to leaching, but in practice, band broadening, caused by kinetic and dispersion effects, cannot be avoided. Nonetheless, numerical experiments showed numerous cases with much higher PCRs for the RFR than for batch operation with catalyst reuse. Therefore, an RFR may be a successful solution in cases when catalyst leaching is too high for using batch operation with catalyst reuse. The design and operation of a suitable RFR are also discussed.
Effect of hydrodynamics on reactive mixing in laminar flows
Authors: Szalai E. S. , Kukura J. , Arratia P. E. , Muzzio F. J. 
Published: April 2004

AbstractThe effects of diffusion and convection on the evolution of reactions in chaotic flows are examined. Direct numerical simulations are applied to compute the evolution of the mixing structure, describe the stretching field, and solve the convection‐reaction‐diffusion material balance in a periodic, 2‐D chaotic flow with an instantaneous, bimolecular reaction: A + B → 2P. These computations demonstrate that the location of the reactive zones in the flow can be predicted from the stretching field. The time‐evolution of the concentration profiles approaches an invariant shape when the time scale of the convective and diffusive mixing processes are comparable. Under such conditions, exponential stretching and its consequence, asymptotic directionality, are the mechanisms controlling the evolution of chaotic reactive systems.
Propene bulk polymerization kinetics: Role of prepolymerization and hydrogen
Authors: Pater Jochem T. M. , Weickert Günter , van Swaaij Wim P. M. 
Published: April 2004

AbstractAn experimental setup for the polymerization of liquid propylene was used to carry out main polymerizations with and without a prepolymerization step. Two types of prepolymerization are introduced: at a constant temperature and at rapidly increasing reactor temperatures. With the present catalyst system, at high polymerization temperatures, a prepolymerization step will increase polymerization rate. Hydrogen was used to control the molecular weight of the product. The polymerization reactor was used in combination with a gas chromatograph to determine the vapor‐liquid equilibrium (VLE) of the propylene‐hydrogen system. Measurements are compared to predictions of different equations of state. The Peng‐Robinson equation of state is best able to describe the VLE for this binary system. A temperature‐dependent interaction parameter was derived from the fits to the measured data.
Nucleation and kinetics of mixed salts in scaling
Authors: Sheikholeslami Roya 
Published: April 2004

AbstractDuring membrane and thermal desalination, the saline solution becomes supersaturated. Once the solution becomes unstable, nucleation and crystallization of the salts occur resulting in a buildup of an unwanted deposit layer on transfer surfaces and increasing the mass‐ or heat‐transfer resistance of the system and the energy input for producing water. Due to the process complexity, research focused primarily on single salt fouling and applying the nucleation and kinetics of a single system in developing physical models for precipitation (crystallization) fouling. This article demonstrates that single salt nucleation and crystallization kinetics applied so far to crystallization fouling cannot be extended to real situations when a combination of various salts and solutes are present. Other noncrystallizing species, if present, may affect the surface energy of a crystal and alter the Gibbs free energy for homogeneous nucleation. Other crystallizing species may also act as a nucleus initiating nonhomogeneous nucleation with a lower Gibbs free energy and promoting nucleation. The presence and catalytic and inhibitory effects of dissolved and solid species on metastability of the solution should be considered in kinetic analysis of crystallization fouling. Kinetic relationships developed take into account the kinetics of coprecipitating salts with and without a common ion and in the presence of other soluble species. They can be easily extended to multiprecipitating systems, but further advances in experimental techniques are necessary to integrate the kinetic analysis and experimental data.
Fuel options for solid oxide fuel cells: A thermodynamic analysis
Authors: Douvartzides S. L. , Coutelieris F. A. , Demin A. K. , Tsiakaras P. E. 
Published: April 2004

AbstractThe eligibility of natural gas (methane), methanol, ethanol, and gasoline as fuels for the generation of electrical power in solid oxide fuel cells (SOFCs) is discussed in terms of efficiency. Each raw fuel was assumed to be processed in a steam reformer to provide a hydrogen‐rich gas mixture to the SOFC feedstream. An SOFC system, consisting of an electrochemical section and a reformer, was analyzed thermodynamically assuming initial steam/fuel feed ratios at conditions where carbon deposition is thermodynamically impossible, at atmospheric total pressure, and in the temperature range of 800–1,200 K. Results were obtained in terms of both electromotive force (emf) output and efficiency. Methane seems to be the most appropriate fuel option, with an SOFC system efficiency close to 96%. Furthermore, ethanol and methanol were very promising alternative options (94% and 91%, respectively), while gasoline (83%) utilization requires special reforming conditions.
Multicomponent diffusion theory and its applications to polymer‐solvent systems
Authors: Price Peter E. , Romdhane Ilyess Hadj 
Published: April 2004

AbstractRecent publications by Zielinski and Hanley and by Alsoy and Duda have proposed relationships between self‐ and mutual‐diffusion coefficients in multicomponent systems that can be derived from Bearman's friction‐based theory. Subsequently, Zielinski and Alsoy published an article calling into question the ability of these new theories to satisfy the Onsager reciprocal relations, and Nauman and Savoca also reported that the Zielinski and Hanley theory can, in some cases, fail to satisfy material balance constraints. Here, the existing friction‐based theories are reviewed and then previous approaches to relating self‐ and mutual‐diffusion coefficients are generalized. The result is an expression that both unifies previous results and is itself a previous result. This generalization prompts us to address the issues raised regarding the existing theories. Some example calculations are also presented, and some directions for future areas of research are suggested.
Model‐based measurement of diffusion using Raman spectroscopy
Authors: Bardow André , Marquardt Wolfgang , Göke Volker , Koss Hans‐Jürgen , Lucas Klaus 
Published: April 2004

AbstractThe measurement of diffusion coefficients in multicomponent liquid mixtures is still an open question. A new technique aimed at overcoming this deficiency is presented. It is based on Raman spectroscopy, which has been extended to obtain liquid concentration data of all components in a mixture simultaneously with high temporal and spatial resolution. The following data analysis uses model‐based methods. This provides a very flexible framework, allowing substantial reduction of experimental effort and time and the direct estimation of the diffusion coefficient as a function of concentration. Furthermore, the experimental procedure is improved using optimal experimental design techniques. This new methodology is validated for binary mixtures.
Effect of drag reducers on transport phenomena in turbulent pipe flow
Authors: Hamersma Peter J. , Fortuin Jan M. H. 
Published: April 2004

AbstractMomentum transfer in turbulent pipe flows (d = 51 mm) with and without a drag reducer was studied. Age distributions of coherent fluid structures at the pipe wall were determined at different Reynolds numbers (104<Re<6 × 104) using laser‐Doppler velocimetry (LDV) and a suitable discriminating procedure. Mean ages, mean transfer thicknesses, friction factors, and time‐averaged axial velocity profiles derived from LDV signals were compared with those from axial pressure gradients using the random surface‐renewal model. The distribution of the ages was random, and drag reducers increased the mean age and the mean transfer thickness of the fluid elements at the wall, thus decreasing momentum and heat transfer at the fluid–wall interface. The mechanism of single‐surface renewals was derived from conditionally averaged, local axial fluid velocities obtained from LDV signals.