bluuebunny/crossref_metadata_2025_split huggingface dataset:
Thermodynamics of adsorption in porous materials
Authors: Myers A. L. 
Published: April 2004

AbstractThermodynamic equations are developed for adsorption of multicomponent gas mixtures in microporous adsorbents based on the principles of solution thermodynamics. The conventional spreading pressure and surface area variables, which describe 2‐D films, must be abandoned for adsorption in micropores, in which spreading pressure cannot be measured experimentally or calculated from intermolecular forces. Adsorption is divided into two steps: (1) isothermal compression of the gas, (2) isothermal immersion of clean adsorbent in the compressed gas. Thermodynamic functions (Gibbs free energy, enthalpy, and entropy) from solution thermodynamics provide a complete thermodynamic description of the system. Applications are described for characterization of adsorbents, gas storage at high pressure, mixture adsorption, enthalpy balances, molecular simulation, adsorption calorimetry, and shape selectivity in catalysis.
Ionic strength dependence of protein adsorption to dye‐ligand adsorbents
Authors: Zhang Songping , Sun Yan 
Published: April 2004

AbstractThe adsorption equilibria and kinetics of bovine serum albumin (BSA) and lysozyme to two Cibacron Blue 3GA (CB) modified agarose gels, that is, 6% agarose‐coated steel (6AS) and Sepharose CL‐6B, in 0.01 kmol·m−3 tris‐HCl buffer (pH 7.5) were studied. Effects of aqueous‐phase ionic strength on both the adsorption equilibrium and uptake rate of the proteins were significant and distinctly different between BSA and lysozyme. The adsorption of lysozyme decreased monotonically with increasing ionic strength. Ionic strengths, however, maximized BSA adsorption capacities of the two CB‐modified agarose gels in the tris‐HCl buffer (about 0.2 kmol·m−3 for CB‐6AS and 0.05 kmol·m−3 for CB‐Sepharose), when the pore‐size difference of the two matrixes and electrostatic interactions between the BSA and CB molecules of like charge were considered. The effective diffusivity of BSA, derived from a pore‐diffusion model, to both the CB‐modified agarose gels increased significantly with the increasing ionic strength at the ionic strength range of 0.01 to 0.3 kmol·m−3, due to the electrostatic interactions between the BSA and CB molecules of like charge. In contrast, the effective diffusivities of lysozyme to CB‐Sepharose in the buffer containing 0.1 and 0.3 kmol·m−3 NaCl were nearly the same.
Maximum order tree algorithm for optimal scheduling of product distribution lines
Authors: Mokashi S. D. , Kokossis A. C. 
Published: April 2004

AbstractResearch on scheduling and planning in the chemical engineering community subscribes to one of two schools of thought. A general‐purpose optimization approach resorts to using conventional mathematical programming techniques on generic models of a scheduling problem, which has a limitation in its application to large‐scale industrial problems in terms of the computational time involved. The other extreme of heuristic methods lacks guarantees on the quality of the solution. A philosophy is proposed of contextual optimization that exploits problem‐specific knowledge to develop efficient algorithms. This concept is applied to a delivery scheduling problem to generate a tailored graph‐based method called the maximum order tree algorithm, which reduces the CPU time dramatically compared to conventional methods without compromising on the quality of the solution. When applied to a single‐site distribution case study, it resulted in savings of over a quarter of a million dollars per year over the existing heuristic‐rule‐based system.
Enhancing model predictive control using dynamic data reconciliation
Authors: Abu‐el‐zeet Z. H. , Roberts P. D. , Becerra V. M. 
Published: April 2004

AbstractThe use of data reconciliation techniques can considerably reduce the inaccuracy of process data due to measurement errors. This in turn results in improved control system performance and process knowledge. Dynamic data reconciliation techniques are applied to a model‐based predictive control scheme. It is shown through simulations on a chemical reactor system that the overall performance of the model‐based predictive controller is enhanced considerably when data reconciliation is applied. The dynamic data reconciliation techniques used include a combined strategy for the simultaneous identification of outliers and systematic bias.
Influence of product adsorption on the operation of a reverse‐flow reactor
Authors: Garg Rohit , Garayhi Abdul , Luss Dan 
Published: April 2004

AbstractThe adsorption on the catalyst surface of the product of an exothermic reaction in a reverse‐flow reactor (RFR) may lead to large variations in the temporal effluent product concentration. Using a dilute reactant feed, the adsorbed product effluent concentration is low following each flow reversal, but it eventually exceeds the feed reactant concentration. The product adsorption may decrease the range of operating conditions (parameter values) for which the RFR can attain an ignited state. A cooled RFR may attain, for certain parameter values, complex dynamic states such as quasi‐periodic and chaotic states. An increase in the adsorption capacity of the catalyst decreases the range of parameter values for which complex dynamic states exist. The desired period‐1 operation of the RFR is more robust in the presence of product adsorption. Product adsorption may lead to surprising dynamic features, such as the coexistence of up to three stable quasi‐periodic states for the same operating conditions.
Optimal design for flow uniformity in microchannel reactors
Authors: Commenge J. M. , Falk L. , Corriou J. P. , Matlosz M. 
Published: April 2004

AbstractVelocity and residence time distributions play a crucial role in the performance of microreactors for chemical synthesis. The specific features of fluid flow through multiplate microchannel reactors are examined by an approximate pressure drop model whose validity is confirmed through comparison with more detailed finite‐volume calculations. The model results allow for determination of the influence of the geometrical characteristics of the microchannel structures on the flow distributions and are used to optimize the reactor design for maximum flow uniformity.
Fast solvent screening via quantum chemistry: COSMO‐RS approach
Authors: Eckert Frank , Klamt Andreas 
Published: April 2004

AbstractCOSMO‐RS, a general and fast methodology for the a priori prediction of thermophysical data of liquids is presented. It is based on cheap unimolecular quantum chemical calculations, which, combined with exact statistical thermodynamics, provide the information necessary for the evaluation of molecular interactions in liquids. COSMO‐RS is an alternative to structure interpolating group contribution methods. The method is independent of experimental data and generally applicable. A methodological comparison with group contribution methods is given. The applicability of the COSMO‐RS method to the goal of solvent screening is demonstrated at various examples of vapor–liquid‐, liquid–liquid‐, solid–liquid‐equilibria and vapor‐pressure predictions.
Lattice‐fluid equation of state with hydrogen‐bond cooperativity
Authors: Muthukumaran Poongunran , Brinkley Ray L. , Gupta Ram B. 
Published: April 2004

AbstractHydrogen bonding plays an important role in thermodynamic properties of polar fluids. Existing equations of state that include h‐bonding cannot accurately predict the phase behavior for polar fluids. In the theories for h‐bond‐chain forming molecules, h‐bonding strength is considered a constant at a given temperature and pressure. Infrared spectroscopy and ab initio calculations show that the h‐bonding strength depends on whether or not the molecule was previously h‐bonded at other sites. When an h‐bond is formed between an already hydrogen‐bonded species and a free species, the second h‐bond has different energetic characteristics from the primary h‐bond. In the case of l‐alkanol self‐h‐bonding, the equilibrium constant for the second h‐bond is ten times that for the primary h‐bond. This phenomenon called h‐bond cooperativity was incorporated in a lattice‐fluid‐hydrogen‐bonding equation of state. Calculations for pure l‐alkanols, show that the theory can be improved significantly by the incorporation of h‐bond cooperativity. Agreement with the phase behavior and spectroscopic h‐bonding data improves using cooperativity, without any additional adjustable parameters. Heat of mixing calculations agree well with the experimental data.
Characterization of flow and mixing in an SMX static mixer
Authors: Zalc J. M. , Szalai E. S. , Muzzio F. J. , Jaffer S. 
Published: April 2004

AbstractLaminar flow and mixing of a Newtonian fluid are characterized in a four‐element Koch‐Glitsch SMX static mixer. The computational analysis on a fine, unstructured mesh containing more than 3.5 million tetrahedral elements led to high‐resolution numerical data for velocity and pressure. Computed pressure drops agreed excellently with those in the literature. The flow in this static mixer is essentially independent of the flow rate up to Re = 1, thereby causing the flow characteristics to deviate substantially from those observed when Re < 1. Furthermore, mixing behavior is examined using Lagrangian particle tracking simulations, as well as statistical methods to facilitate comparisons with experimental data. The mixing rate calculated from the simulations agreed closely with experimentally measured values. Both exponential decrease in the variation coefficient as a function of downstream length and the evolution of a self‐similar mixing structure are both evidence of chaotic mixing in the SMX mixer.
Characteristics of acoustic standing waves in fluidized beds
Authors: Herrera C. A. , Levy E. K. , Ochs J. 
Published: April 2004

AbstractFine particles are typically difficult to fluidize with gas, due to interparticle forces that cause the bed material to be cohesive. The use of acoustic waves, generated by a loudspeaker positioned above the bed, to agitate the bed material and enhance fluidization, has been investigated. The bed was fluidized with air at conditions near minimum bubbling. Sound‐pressure measurements within the bed showed the presence of acoustic standing waves throughout the bed. Acoustic standing‐wave theory, which assumes that the bed behaves as a 1‐D, quasi fluid with constant speed of sound, was used to model the sound‐pressure‐level data. It was found that the parameter kh, where k is the wave number and h is the bed depth, determines the sound‐pressure amplitude throughout the bed. The system reaches its highest sound pressure at resonance conditions for kh = (2n − 1)π/2. A comparison indicates good agreement between the theory and the experimental data.
Mass‐Transfer modeling in the pervaporation of VOCs from diluted solutions
Authors: Urtiaga Ane , Gorri Daniel , Ortiz Inmaculada 
Published: April 2004

AbstractA generic model is derived for studying the mass‐transfer kinetics of the pervaporation of multicomponent mixtures of volatile organochloride compounds. Applying it to the pervaporation of dilute mixtures of trichloromethane, dichloromethane and trichloroethylene using tubular polydimethylsiloxane (PDMS) membranes permits: (1) estimation of the representative mass‐transfer parameters, that is, solute diffusivity in the aqueous phase and membrane permeability of the individual components; (2) discrimination of the relative importance of the mass‐transport resistances to the pervaporation flux as a function of operation variables; and (3) determination of the selectivity in multicomponent pervaporation. Diffusivity values calculated with the model agree well with predictions by the Wilke–Chang correlation for nonelectrolyte solutes. Permeability values of PDMS membranes change in the trichloroethylene > trichloromethane > dichloromethane direction. The relative importance of mass‐transfer resistances for the considered volatile organic compounds depends on the operation variables, that is, flow rate of the feed solution and membrane thickness. Furthermore, for trichloroethylene the main resistance is located in the feed solution, whereas for dichloromethane for high values of feed flow rate the resistance in the membrane could exert a major influence on kinetic control, and the behavior of trichloromethane is intermediate between both compounds.
Formation and dynamics of a hot zone in radial flow reactor
Authors: Marwaha B. , Luss D. 
Published: April 2004

AbstractAn infrared camera was used to study the formation and dynamics of hot zones normal to the flow direction on the surface of a radial‐flow reactor, placed horizontally, inside a vessel. The test reaction—the atmospheric oxidation of carbon monoxide—exhibited steady‐state multiplicity. Slow cooling of the vessel caused a shift from a fully‐ignited state to one with a hot zone in the center of the reactor bounded by cold zones at both reactor ends. The hot zone was separated by sharp temperature fronts from the adjacent cold zones. It shrank upon further cooling of the vessel and eventually extinguished. In certain cases, two stable states existed for the same operating conditions with qualitatively different hot zones and reaction rates. A slow back‐and‐forth motion of the temperature fronts (breathing) caused complex oscillations in the overall reaction rate. The dynamic features of the two fronts were different in some cases due to nonuniform catalytic activity and inefficient thermal dispersion. The amplitude and frequency of the temperature breathing motion increased upon cooling of the vessel containing the reactor. Experiments suggest that transversal hot zones are likely to form in packed‐bed reactors close to the extinction temperature.
Population balance modeling of aerated stirred vessels based on CFD
Authors: Venneker Bart C. H. , Derksen Jos J. , Van den Akker Harrie E. A. 
Published: April 2004

AbstractA developed model predicts local gas fraction and bubble‐size distributions for turbulent gas dispersion in a stirred vessel, based on the population balance equations (PBE), with relations taken from literature for bubble coalescence and breakup derived from isotropic turbulence theory. The transport of bubbles throughout the vessel is simulated by a scaled single‐phase flow field obtained by CFD simulations. Model predictions for the gas fractions in pseudoplastic Xanthan solutions are compared with local measurements and agree well qualitatively. This formulation overcomes the necessity of choosing a constant bubble size throughout the domain, as is done in two‐fluid models and is, therefore, more reliable in mass‐transfer calculations.
Adaptive process monitoring via multichannel EIV lattice filters
Authors: Li Weihua , Bhargava Abhishek , Shah Sirish L. 
Published: April 2004

AbstractOnline monitoring of multivariable processes is crucial to operational safety and product quality. For this, multivariable statistical analysis methods, such as principal‐component analysis (PCA), partial least squares, and canonical variate analysis have been widely applied. However, few recursive monitoring techniques have been developed for fully dynamic and time‐varying processes. Recursive PCA has been successfully applied to monitor static time‐varying processes, but does not work for fully dynamic processes. Dynamic PCA has been developed, but its recursive variant is not available. Many processes operate in dynamic states and are often time‐varying, and the time‐varying property includes the variation of parameters and of process structure, e.g., the change of model order. A novel approach to the adaptive monitoring of multivariate dynamic and time‐varying processes by the recursive multichannel instrumental variable (IV) lattice filters was developed using the errors‐in‐variables (EIV) state space model to represent a dynamic process. To show the relationship between EIV state‐space representation of the process and a multichannel IV lattice filter, the lattice filter was used to generate a residual vector for process monitoring. By using lattice filter's ability of recursively updating the process model both in time and order, a real time, on‐line algorithm was used to update the residual vector with newly sampled process data, including a practical approach to recursive determination of the process model order. Based on the residual vector, the Hotelling T2 statistic and the associated confidence limits are used as the monitoring index. The proposed scheme was evaluated on a simulation example and a pilot plant to support the theoretical results.
Solubility of H2S and CO2 in N‐octyl‐2‐pyrrolidone and of H2S in methanol and benzene
Authors: Fischer Kai , Chen Jian , Petri Martin , Gmehling Jürgen 
Published: April 2004

AbstractThe solubility of hydrogen sulfide and carbon dioxide in N‐octyl‐2‐pyrrolidone (NOP) was measured up to 1.4 MPa at 303 and 324 K using the static synthetic method. Experimental results were compared to those of the predictive Soave–Redlich–Kwong (PSRK) model, wherein the group interaction parameters for the NMP‐group (N‐methyl‐2‐pyrrolidone) were applied to the NOP systems. The reliability of the apparatus used and the applied data treatment were checked by comparing new experimental data for the system hydrogen sulfide+benzene at 304 and 324 K and pressures up to 1.2 MPa, and for the system hydrogen sulfide+methanol at 298 K and up to 0.4 MPa, with published data measured with the analytical method.
Prediction of fully developed turbulent convection with minimal explicit empiricism
Authors: Churchill Stuart W. , Zajic Stefan C. 
Published: April 2004

AbstractFrom a purely theoretical analogy between energy and momentum transfer in fully developed turbulent Convection, an expression without explicit empiricism, and which appears to be applicable for all channels, all modes of heating on the surface(s), all values of Re in the turbulent regime, and all moderate and large values of Pr, was deduced for Nu. An analogous complementaly expression for small values of Pr has the same generality, but incorporates one explicit empirical exponent. The numerical implementation of these two expressions for Nu for specific values of Re and Pr introduces some empiricism, but the resulting uncertainty in Nu, including that associated with the aforementioned exponent, is truly negligible. Because of their accuracy and generality, these two expressions, together with several supplementaly relationships, appear to be superior to all existing ones for design calculations. Because of their simple and fundamental structure, they appear to be equally superior for educational purposes.
Velocity of isolated particles along a pipe in stratified gas–liquid flow
Authors: Stevenson P. , Thorpe R. B. 
Published: April 2004

AbstractThe average velocity of isolated grains of sand was experimentally measured in smooth stratified flow in slightly declined pipes. Isolated particles in smooth stratified flow behave similarly to isolated particles propelled by both hydraulic conveying and intermittent gas/liquid flow. In all three cases, particle velocity is linear with respect to the average liquid velocity of the flow (or the average fluid velocity in the slug body for intermittent flow) and has a gradient of approximately one. The data in stratified flow are successfully correlated dimensionlessly (Eq. 7). The correlation is extrapolated to zero particle velocity to estimate the conditions required to ensure sand transport in a flowline in smooth stratified flow. The experimental results suggest that particle velocity is strongly governed by the size of a particle relative to the depth of the viscous sublayer at the pipe wall. If a particle is larger than the viscous sublayer, it is exposed to more coherent turbulent structures and therefore experiences a greater drag.
Cycle detection and characterization in chemical engineering
Authors: Briens L. A. , Briens C. L. 
Published: April 2004

AbstractNonperiodic cycles occur in times series obtained in many chemical engineering applications. Variations in the cycle characteristics provide valuable information about the system in which the time series was measured. New methods are developed to detect cycles and determine their characteristics such as the cycle time, its regularity, the cycle strength, and the regularity of the cycle amplitude. These methods are thoroughly validated with both mathematically generated and experimental time series. The best detection method for nonperiodic cycles uses either the V statistic or, if it fails, the new, more sensitive, but more complex, P statistic. Cycle characteristics can be used to detect flow regime transitions in multiphase systems such as risers, gas‐solid, and gas‐liquid‐solid fluidized beds using signals from a variety of simple probes.
Real‐time multirate state estimation in a pilot‐scale polymerization reactor
Authors: Zambare Neeraj , Soroush Masoud , Grady Michael C. 
Published: April 2004

AbstractReal‐time implementation of a robust multirate state estimator on a continuous stirred‐tank, free‐radical, styrene polymerization reactor is presented. The estimator is designed based on a first‐principles model of the process. It has integral action that allows for robust estimation of the process states. The estimator calculates frequent robust estimates of polymer weight‐average and number‐average molecular weights and monomer concentration. These are estimated from frequent online measurements of the reactor temperature, and infrequent offline and delayed measurements of polymer weight‐average and number‐average molecular weights and monomer concentration. In‐frequent measurements of monomer concentration are obtained by gas chromatography and gravimetry, and those of weight‐average and number‐average molecular weights by gel permeation chromatography.
Simulation of microalgae growth in limiting light conditions: Flow effect
Authors: Pruvost J. , Legrand J. , Legentilhomme P. , Muller‐Feuga A. 
Published: April 2004

AbstractEffect of hydrodynamical conditions on a microalgae culture growth was investigated in a photobioreactor with annular light chambers, with the focus on the relation between the cell displacement and the amount of light received by microorganisms, by comparing two different flow conditions in light chambers: an axial flow generating a poor radial mixing and a 3‐D swirling motion. To determine microorganism trajectories, a Lagrangian approach was retained, allowing light received to be considered from a single microalga point of view. The light distribution was calculated using Beer–Lambert law, and a biological modeling of the culture growth was proposed, with consideration of light/dark cycle effects induced by cell displacement in the depth of the culture. Finally, batch cultures of Porphyridium purpureum were simulated for both hydrodynamical conditions in light chambers. The advantage of applying a three‐dimensional motion to generate cell renewal in front of the light source, allowing microorganisms to use light more efficiently, is clearly shown.
Feasibility of heterogeneous batch distillation processes
Authors: Rodríguez Donis Ivonne , Gerbaud Vincent , Joulia Xavier 
Published: April 2004

AbstractSynthesis of heterogeneous batch distillation is discussed, which aims at splitting azeotropic mixtures by adding an entrainer partially miscible with one of the initial binary mixture components. Key operational parameters are identified such as the amount of entrainer added in the ternary feed, the reflux policy, and the vapor line position by examples. Synthesis and operation are less straightforward for heterogeneous batch distillation than those for the homogeneous case, but offer many advantages: more design alternatives, simplified distillation sequences, a lower consumption of entrainer, and a crossing of distillation boundaries by the still path. Feasibility is assessed using simplified modeling and confirmed using a commercial batch process simulator package. Synthesis expectations and simulated results are verified throughout bench‐plant experiments for the separation of the acetonitrile—water mixture using acrylonitrile as a light heterogeneous entrainer.