bluuebunny/crossref_metadata_2025_split huggingface dataset:
Sound measurement as a means of gas‐bubble sizing in aerated agitated tanks
Authors: Boyd Jonathan W. R. , Varley Julie 
Published: April 2004

AbstractBubble size affects mass transfer and mixing hydrodynamics significantly in a gas‐liquid agitated vessel. It is important that accurate and reliable techniques are developed to measure bubble size to improve design and scale‐up of such vessels. Existing bubble‐size measurement techniques are time‐consuming (e.g., photography) or complex and expensive (e.g., ultrasound). The ideal technique, capable of on‐line measurement in any type of liquid, has yet to be developed. It is possible to size gas bubbles from sound measurement within a gas‐sparged agitated tank. A significant amount of the noise, measured close to the impeller, is made up of transient, damped, sinusoidal pressure pulses, which are heard only in the presence of gas bubbles. Analysis of the individual sound pulses in terms of magnitude, frequency and damping, combined with photographic validation, indicates that the sound is caused by bubbles oscillating at frequencies dependent on bubble size. The bubbles are excited into oscillation when formed at the impeller. Sound from other sources (e.g., turbulence) is differentiated from bubble sound. Theoretical modeling and experimental results are used to estimate the sound contribution of a single bubble to a sound spectrum and calculate the bubble‐size distribution at the impeller directly from experimentally measured soundpressure spectra.
Reaction and flow variants/invariants in chemical reaction systems with inlet and outlet streams
Authors: Srinivasan B. , Amrhein M. , Bonvin D. 
Published: April 2004

AbstractThe concept of reaction invariants is extended to include flow invariants of chemical‐reaction systems with inlet and outlet streams. A transformation to normal form is introduced that allows the separation of (1) the evolution of the independent reactions, (2) the influence of inlet streams, and (3) the behavior of the reaction and flow invariants. In the light of this transformation to normal form, model reduction, state accessibility, state reconstruction, and feedback linearizability are analyzed.
Catalytic incineration of VOC containing air streams at very short contact times
Authors: Goralski C. T. , Schmidt L. D. , Brown W. L. 
Published: April 2004

AbstractA short‐contact‐time catalytic combustor described here is capable of incinerating air streams with low concentrations of volatile organic compounds (VOCs) at conversions exceeding 99.5% for contact times on the order of 5 ms. This is accomplished by adding methane to the VOC‐containing air stream to increase the fuel stream value and then passing the mixture over a platinum‐coated foam ceramic monolith at 900 – 1,400°C. The incineration of air streams containing toluene, chlorobenzene, acetonitrile, and thiophene was examined at concentrations ranging from 500 to 2,000 PPM. Residence time and methane concentration do not affect strongly the outlet concentration of the VOC and conversion. Greater than 99.5% conversion is observed for all compounds examined for residence times ranging from 4 to 12 ms and methane concentrationsfrom 5.5 to 7.0% (80–40% excess air). The mechanism of reaction in this system is primarily heterogeneous, with some homogeneous reactions driven by the heat liberated by the heterogeneous reactions. A simple homogeneous model shows that homogeneous chemistry alone cannot account for complete conversion of the additional methane fuel at the reaction conditions described.
Roles of thermal and radical quenching in emissions of wall‐stabilized hydrogen flames
Authors: Aghalayam P. , Vlachos D. G. 
Published: April 2004

AbstractA numerical study of the combustion of H2/air mixtures impinging on surfaces has been performed, using detailed chemistry and multicomponent transport, in order to elucidate the roles of surface thermal and chemical quenching in pollutant emissions. For extinguishable fuel/air mixtures, the thermal coupling with the surface has been found to be strong, and surface thermal quenching reduces NOXemissions. However, nonextinguishable mixtures are practically unaffected by changes in surface temperature, except for an increase in NO2at low surface temperatures. It is shown that radical wall quenching can affect emissions for all flames, with H being the most important one primarily for NO2near the surface, due to the reaction NO2+ H ↔ NO + OH. A new method to elucidate the dominant paths for NO formation is also presented.
Operation regimes in catalytic combustion: H2/air mixtures near Pt
Authors: Park Young K. , Bui Pierre‐André , Vlachos Dionisios G. 
Published: April 2004

AbstractThe influence of a platinum catalyst on flammability limits and operation windows for catalytic and catalyst‐assisted homogeneous oxidation is studied, for the first time to our knowledge, as a function of H2in air composition in a stagnation‐point flow geometry. The results show that the coupling between the homogeneous and heterogeneous chemistries leads to relatively easy startup, the coexistence of catalytically (partially) and homogeneously (completely) ignited branches under certain conditions, and the expansion of the fuel‐lean and rich flammability limits. A strategy to attain virtually any desired operation regime is discussed. It is shown that synergism between homogeneous and heterogeneous chemistries leads to higher combustion efficiency and lower fuel emissions at elevated temperatures for fuel‐lean mixtures only. Analysis of the flammability limits indicates that heat generated by surface reactions is primarily responsible for expansion of the flammability limits. Finally, a direct transition to flames occurs over a wide range of composition upon catalytic ignition in the absence of surface heat loss.
Liquid distribution in trickle‐bed reactors
Authors: Saroha Anil K. , Nigam K. D. P. , Saxena Alok K. , Kapoor V. K. 
Published: April 2004

AbstractExperimental measurements on liquid distribution in a trickle‐bed reactor are presented, as well as the effect of liquid and gas flow on radial liquid distribution. The influence of liquid density and surface tension was also investigated. The model for liquid distribution proposed by Herskowitz and Smith in 1978 was modified to incorporate the effect of particle orientation. Model parameters are correlated with liquid and gas flow rates, as well as liquid surface tension.
Shortcut methods for nonideal multicomponent distillation: I. Simple columns
Authors: Bausa J. , Watzdorf R. v. , Marquardt W. 
Published: April 2004

AbstractShortcut methods are a prerequisite for the fast evaluation of alternatives in process design. The rectification body method (RBM) for calculating the minimum energy demand of homogeneous, azeotropic multicomponent distillation processes is presented. The new method incorporates both the classical Underwood technique and certain previously proposed techniques as special cases. It employs all pinch point branches of both column sections and thus requires no a priori selection of active pinch points. It is entirely general and can be applied to any type of split of nonideal and azeotropic mixtures irrespective of the number of components. Hence, it significantly extends previous results and practical applicability. Its features are highlighted through examples of nonideal separations with three, four, and five components.
Active learning from process data
Authors: Raju Gokaraju K. , Cooney Charles L. 
Published: April 2004

AbstractMuch of the prevailing connectionist machine learning research in chemical engineering assumes a one‐way passive relationship between the learner and the application domain. This article investigates a two‐way active relationship between learner and domain. An active relationship is useful and even necessary if the prevailing research is to be successfully applied to real‐world problems involving sparse and strongly biased data. A process development case study is used to illustrate the impact of data quality and quantity and to compare the performance of active learning against conventional passive learning. This study highlights on the need to assess data quality and demonstrates the improvements in the rate of active learning.
Enhancing MTBE rate equation by considering reaction medium influence
Authors: Fité Carles , Tejero Javier , Iborra Montserrat , Cunill Fidel , Izquierdo J. Felipe 
Published: April 2004

AbstractRate data are reanalyzed for MTBE synthesis in the liquid phase at 318‐363 K on the sulfonic macroporous resin Bayer K‐2631. The data were obtained in a continuous upflow packed‐bed reactor fed with isobutene (IB)‐methanol (MeOH) mixtures with an IB/MeOH molar ratio ranging from 0.5 to 2.0. Rate equations based on LHHW and ER mechanisms do not predict rate data accurately, because of the influence of the reaction medium on the catalyst activity. A factor evaluating the resin‐medium affinity has been introduced in the rate equations which, as a result, fit the data with a good agreement. Fitted parameters were the overall kinetic constant and the resin solubility parameter. The apparent activation energy agrees with the values quoted in the literature, and the resin solubility parameter and its temperature dependence are plausible.
Simultaneous thermal cracking and oxidation of propane to propylene and ethylene
Authors: Choudhary Vasant R. , Rane Vilas H. , Rajput Amarjeet M. 
Published: April 2004

AbstractPropane conversion by its simultaneous endothermic thermal cracking and exothermic noncatalytic oxidative conversion topropylene and ethylene in the presence of steam and limited oxygen was investigated at various process conditions (temperature, 635–800°C; C3H8/O2 ratio in feed, 2.0–16.0; H2O/C3H8 ratio, 0.0–2.5; space velocity, 1,170–7,150 h−1; and sulfur additive/C3 H8 ratio, 10−3−10−5). Influence of a sulfur additive (thiophene, CS2, or dimethyl sulfide) in the feed on process performance was also studied. The propylene/ethylene mole ratio in the products is decreased with increasing the temperature but increased with the C3HS/O2 and H2O/C3H8 ratios and space velocity. At all the process conditions, the selectivity for CO, a useful byproduct, is much more than that for CO2. Because the thermal cracking of propane is carried out in the presence of limited O2, not only the total conversion of propane but also the conversion of propane by its thermal cracking alone is increased greatly. Hence this process occurs at a much lower temperature or contact time than that required for achieving the same conversion in the thermal cracking process. Since the endothermic thermal cracking and exothermic oxidative conversion reactions of propane occur simultaneously, both reactions are coupled to make it highly energy‐efficient, with a drastic reduction in external energy requirement and coke formation, and safe to operate. The overall process can be made almost thermoneutral, mildly exothermic, or mildly endothermic by manipulating the temperature and C3H8/O2 ratio in the feed.
Two‐phase flow in porous media: Property identification and model validation
Authors: Kulkarni Raghavendra , Watson A. Ted , Nordtvedt Jan‐Erik , Sylte André 
Published: April 2004

AbstractThe experimental design and analysis of two‐phase dynamic displacement experiments are investigated, with particular attention to incorporating measured saturation distributions. Pressure drops and saturation distributions measured with displacement experiments using multiple flow‐rate injection rates can provide accurate estimates of relative permeability and capillary pressure functions over broad ranges of fluid saturations. Successful reconciliation of measured saturation distributions and pressure drops establishes an experimental validation of the Darcy model for two‐phase flow in porous media.
pH dependence of ion‐exchange equilibrium of proteins
Authors: Bosma J. C. , Wesselingh J. A. 
Published: April 2004

AbstractThe adsorption equilibrium of bovine serum albumin on Q‐sepharose, a strong union exchanger, was studied with batch equilibrium experiments at pH between 4 and 9 and ionic strengths between 5 and 440 mmol/L. Dependence of the adsorption equilibrium on the ionic strength was modeled as an ion exchange reaction. A simplified mechanism of this ion exchange reaction also yielded an expression for the dependence of the equilibrium on the charge of the protein. This model describes the measurements well, using fitted constants with physically realistic values.
Modeling the partial oxidation of methane in a short‐contact‐time reactor
Authors: Deutschmann Olaf , Schmidt Lanny D. 
Published: April 2004

AbstractPartial oxidation of methane in monolithic catalysts at very short contact times offers a promising route to convert natural gas into syngas (H2 and CO), which can then be converted to higher alkanes or methanol. Detailed modeling is needed to understand their complex interaction of transport and kinetics in these systems and for their industrial application. In this work, the partial oxidation of methane in noble‐metal (Rh and Pt)‐coated monoliths was studied numerically as an example of short‐contact‐time reactor modeling. A tube wall catalytic reactor was simulated as a model for a single pore of the monolithic catalyst using a 2‐D flow field description coupled with detailed reaction mechanisms for surface and gas‐phase chemistry. The catalytic surface coverages of adsorbed species are calculated vs. position. The reactor is characterized by competition between complete and partial oxidation of methane. At atmospheric pressure, CO2 and H2O are formed on the catalytic surface at the entrance of the catalytic reactor. At higher pressure, gas‐phase chemistry becomes important, forming more complete oxidation products downstream and decreasing syngas selectivity by about 2% at 10 bar. Temperature (from 300 to ∼ 1,200 K), velocity, and transport coefficients change very rapidly at the catalyst entrance. The dependence of conversion and selectivity on reactor conditions was examined.
Reactivity of chars and carbons: New insights through molecular modeling
Authors: Bhatia S. K. 
Published: April 2004

AbstractA new model proposed for the gasification of chars and carbons incorporates features of the turbostratic nanoscale structure that exists in such materials. The model also considers the effect of initial surface chemistry and different reactivities perpendicular to the edges and to the faces of the underlying crystallite planes comprising the turbostratic structure. It may be more realistic than earlier models based on pore or grain structure idealizations when the carbon contains large amounts of crystallite matter. Shrinkage of the carbon particles in the chemically controlled regime is also possible due to the random complete gasification of crystalline planes. This mechanism can explain observations in the literature of panicle size reduction. Based on the model predictions, both initial surface chemistry and the number of stacked planes in the crystallites strongly influence the reactivity and particle shrinkage. Its test results agree well with literature data on the air‐oxidation of Spherocarb and show that it accurately predicts the variation of particle size with conversion. Model parameters are determined entirely from rate measurements.
Condensation of mixed vapors and thermodynamics
Authors: Vuddagiri Srinivas R. , Eubank Philip T. 
Published: April 2004

AbstractA literal interface between thermodynamics and transport phenomena occurs in the steady‐state condensation/vaporization of mixed vapors/liquids in wetted‐wall towers. Unfortunately, several prominent transport texts assume that the ratio of molar fluxes is the same as the corresponding ratio of mole fractions at the interface for the phase being formed. This is shown to be true only at particular vertical positions corresponding to the first drop of condensate. The thermodynamics of the condensation/vaporization of mixtures is reviewed to understand why the ratio of pure‐component fluxes at the interface differs from that of corresponding equilibrium mole fractions. The dynamics of steady‐state condensation in wetted‐wall towers is also developed based on the film theory of Colburn and Drew. The temperature/composition diagram is used to trace both transport phenomena and thermodynamic variables at various tower heights. The Ackermann factor is corrected allowing more general use of the design equations when the vapor is nonideal. The usual neglect of liquid‐film resistance to heat transfer is examined. Numerical calculations show an unusual rise in the interfacial temperature in a parallel flow tower immediately below the onset of condensation. Possible and impossible sets of temperature and composition profiles are described.
Resolution of glycoproteins by affinity‐based reversed micellar extraction and separation
Authors: Choe Jaehoon , Vandernoot Victoria A. , Linhardt Robert J. , Dordick Jonathan S. 
Published: April 2004

AbstractAffinity‐based reversed micellar extraction and separation (ARMES) has proven effective in separating glycoproteins from nonglycosylated proteins from natural sources. The ability of ARMES to resolve closely related glycoproteins is of paramount importance if ARMES is to be used in glycoform resolution. It is demonstrated that ARMES can resolve the structurally similar soybean peroxidase (SBP; MW 37 kDa, pI 4.1) and αt‐acid glycoprotein (AGP; MW 43 kDa, pI 3.7), both of which have affinity for Concanavalin A (Con A) (the affinity ligand). SBP was almost exclusively extracted at pH 8 and above, with a separation factor greater than 50 (resolution ∼ 20), far better than was possible using Con A affinity chromatography (R ∼ 0.25, separation factor ∼ 2). Model calculations suggest that differences in affinity measured by an equilibrium‐building assay cannot account for the favorable extraction of SBP over AGP at higher pH. Hydrophobic interactions and/or charge shielding appear to affect partitioning of the lectin ‐ glycoprotein complexes and add greatly to the selectivity of extraction in ARMES, especially at higher pH values.
NMR imaging of pulp suspension flowing through an abrupt pipe expansion
Authors: Arola Darren F. , Powell Robert L. , McCarthy Michael J. , Li Tie‐Qiang , Ödberg Lars 
Published: April 2004

AbstractNuclear magnetic resonance imaging was used to measure velocity profiles of water and an aqueous, 0.5 wt. % (consistency) wood pulp suspension flowing through a circular pipe in the vicinity of a 1:1.7 tubular expansion. Flow images are provided for various flow rates and axial positions with respect to the expansion plane. For water, both laminar and turbulent flows were investigated. Pulp suspension flows were investigated upstream and downstream from the expansion plane. The expansion plane imparts shear layer instabilities that disrupt the fiber floe network. The fiber reflocculation length is proportional to the bulk flow rate. We determined a mean reflocculation time of approximately 510 ms for this pulp fiber consistency.
Rational transfer function models for biofilm reactors
Authors: Wik Torsten , Breitholtz Claes 
Published: April 2004

AbstractDesign of controllers and optimization of plants using biofilm reactors often require dynamic models and efficient simulation methods. Standard model assumptions were used to derive nonrational transfer functions describing the fast dynamics of stirred‐tank reactors with zero‐ or first‐order reactions inside the biofilm. A method based on the location of the singularities was used to derive rational transfer functions that approximate nonrational ones. These transfer functions can be used in efficient simulation routines and in standard methods of controller design. The order of the transfer functions can be chosen in a natural way, and changes in physical parameters may directly be related to changes in the transfer functions. Further, the mass balances used and, hence, the transfer functions, are applicable to catalytic reactors with porous catalysts as well. By applying the methods to a nitrifying trickling filter, reactor parameters are estimated from residence‐time distributions and low‐order rational transfer functions are achieved. Simulated effluent dynamics, using these transfer functions, agree closely with measurements.
Dynamically scheduled MPC of nonlinear processes using hinging hyperplane models
Authors: Chikkula Yugender , Lee Jay H. , Ogunnaike B. A. 
Published: April 2004

AbstractThis article deals with the issues associated with designing scheduled model predictive controllers for nonlinear systems within the multiple‐linear‐model‐based control framework. The issues of model set generation from empirical data and closed‐loop application of the generated model set are considered. A method of hinging hyperplanes is proposed as a way to construct a piecewise linear dynamic model, conducive to dynamic scheduling of linear MFC controllers. The design and implementation of dynamically scheduled MFC using a hinge function model are discussed, as well as its advantages. Alternate MFC formulations considered here require more computation, but utilize the hinge function model as a global model. Simulated examples of isothermal CSTRs and a batch fermenter are also presented to illustrate the proposed methodologies.
Design of multistage extractive reaction processes
Authors: Samant Ketan D. , Ng Ka M. 
Published: April 2004

AbstractMultistage extractive reaction (MSER) processes can successfully improve the yield of and selectivity to the desired product, as well as separation of byproducts. A general and efficient design procedure for stand‐alone countercurrent MSER cascades and process flowsheets presented here determines the range of feasible operation for the MSER process, the number of stages in the MSER cascade, compositions and molar flow rates at each stage, and the yield or product distribution of the reaction system. It is based on the geometric properties of the phase and reaction equilibrium surfaces and the composition profiles of the MSER cascade. First, a key design variable is identified and the fixed points or pinches of the composition profiles are tracked as a function of this variable by using arc‐length continuation, without performing stage‐to‐stage calculations. The location of the fixed points gives the upper or lower bound on the window of the MSER operation. The other bound is determined by the equilibrium behavior of the system. Within the window of operation MSER profiles are guaranteed to be feasible. Then, stage‐to‐stage calculations are performed as an initial‐value problem to complete the design. The results of these calculations provide a comprehensive picture of the trade‐offs in the design of MSER processes and can be used as a basis for screening flowsheet alternatives. The procedure is illustrated with several design examples.
Rapid estimation of rate constants of batch processes using on‐line SW‐NIR
Authors: Bijlsma Sabina , Louwerse D. J. , Smilde Age K. 
Published: April 2004

AbstractA method is presented for estimating reaction rate constants very rapidly from on‐line short‐wavelength near‐infrared measurements. It can deal with a strong spectral overlap between the individual spectra of the species in the reacting system. For this an iterative curve‐resolution method is combined with a nonlinear fitting procedure. This procedure also makes it possible to assess the quality of the estimated reaction rate constants. Simulations show that the method can be applied in cases with extreme spectral overlap of the individual spectra of the species. The procedure is applied in practice to an example with a strong spectral overlap. Reaction rate constants of the two‐step epoxidation of 2,5‐di‐tert‐butyl‐1,4‐benzoquinone were estimated. This method can lead to the application to on‐line monitoring reaction rate constants.