bluuebunny/crossref_metadata_2025_split huggingface dataset:
Protein partitioning and transport in supported cationic acrylamide‐based hydrogels
Authors: Russell Shawn M. , Belcher Emily B. , Carta Giorgio 
Published: April 2004

AbstractThe partitioning and transport of myoglobin in cationic, acrylamide‐based hydrogels are studied by a microscopic visualization method. Homogeneous cationic gels are synthesized inside fused‐silica capillaries with a square section, which allow a direct determination of protein concentration profiles during transient adsorption and desorption. Diffuse, self‐similar profiles are observed and used to determine the equilibrium protein binding capacity and the protein diffusivity in the gel. Mass‐transfer rates are found to be essentially independent of the external solution concentration, but to vary dramatically with the gel polymer concentration. A Fickian diffusion model with a flux based on the adsorbed‐phase concentration gradient is consistent with the experimentally determined concentration profiles for both positive and negative protein concentration steps. The equilibrium and rate parameters determined for the capillary‐supported gels also compare favorably with those obtained from macroscopic measurements using composite ion‐exchange media comprising similar gels held within the pores of porous silica particles.
Stationary spatially complex solutions in cross‐flow reactors with two reactions
Authors: Sheintuch Moshe , Nekhamkina Olga 
Published: April 2004

AbstractFormation of stationary spatially multiperiodic or even chaotic patterns is analyzed for a simple model of a cross‐flow reactor with two consecutive reactions and realistically high Le and Pe. Spatial patterns emerge much like dynamic temporal patterns in a mixed system of the same kinetics. The sequence of period doubling bifurcations is determined for the corresponding ODE system and is completely confirmed by direct numerical simulations of the full PDE model. The incorporation of a slow nondiffusing inhibitor led to chaotic spatiotemporal patterns.
Photolytic reactors: Similitude in Taylor–Couette and channel flows
Authors: Forney L. J. , Pierson J. A. 
Published: April 2004

AbstractA similarity law is proposed for the yield from laminar photolytic reactors. In particular, the yield from a fast photolytic reaction is considered in the following three distinctly different reactor geometries: a square channel, an annular gap between concentric cylinders, and Taylor–Couette flow. The similarity law, based on the assumption of a self‐similar product concentration profile, demonstrates that the reaction rate can best be described with either zero (small λ) or first‐order (large λ) kinetics. Here, the distinction between both cases is determined by the radiation penetration depth, λ. Other geometric parameters affecting scale‐up are also discussed.
Leaching model for a cement mortar exposed to intermittent wetting and drying
Authors: Garrabrants Andrew C. , Sanchez Florence , Kosson David S. 
Published: April 2004

AbstractNumerical simulations of inorganic species release from an intermittently wetted cement material without carbonation effects are presented. The intermittent mass‐transport (IMT) model combines previously developed approaches describing constituent diffusion coupled with solid‐phase dissolution/precipitation and two‐regime drying of a cement matrix stored at constant relative humidity. Model simulations were validated using experimental data showing the effects of intermittent wetting on release of major matrix species (Ca, Na, K, Cl, OH) and pH‐dependent trace metals (Cd, Pb). The IMT model successfully describes constituent release flux for intermittent wetting cases with storage in an inert atmosphere (100% N2) at three levels of relative humidity (23%, 48%, 98% RH). Leachate pH simulation accounted for the release of soluble alkaline salts in conjunction with the dissolution of calcium hydroxide. The release simulations for pH‐dependent species were subsequently improved over pH determination based solely on calcium hydroxide dissolution.
Liquid‐phase hydrogenation kinetics of isooctenes on Ni/Al2O3
Authors: Lylykangas M. S. , Rautanen P. A. , Krause A. O. I. 
Published: April 2004

AbstractThe kinetics of the hydrogenation of isooctenes [2,4,4‐trimethyl‐1‐pentene (TMP‐1), and 2,4,4‐trimethyl‐2‐pentene (TMP‐2)] to isooctane (2,2,4‐trimethylpentane) was studied on a commercial Ni/Al2O3 catalyst in a three‐phase reactor. Experiments showed that nickel is a highly active catalyst for the reactions. In addition to the hydrogenation reactions, slow isomerization occurred between TMP‐1 and TMP‐2. Kinetic equations were derived based on the Horiuti–Polanyi mechanism, involving a half‐hydrogenated surface intermediate and rate limitation in the first hydrogen addition. Isomerization was assumed to take place via the partly hydrogenated intermediate, since no isomerization products were observed in the absence of hydrogen. The dynamic reactor model consisted of material balances for the gas and liquid phases, as well as for the porous catalyst particles. The estimated activation energies for the hydrogenation of TMP‐1 and TMP‐2 were 34 and 49 kJ/mol, respectively. The model described the experimentally recorded data accurately.
Synthesis of methylacetate in a simulated moving‐bed reactor: Experiments and modeling
Authors: Lode Florian , Francesconi Gianmario , Mazzotti Marco , Morbidelli Massimo 
Published: April 2004

AbstractSimulated moving‐bed reactors (SMBR) combine chemical reaction and adsorptive separation within one single unit. Toward the design of this rather complex unit, guidelines for the proper choice of the operating parameters, that is, the flow‐rate ratios and the Damköhler numbers within the different sections, have recently been devised based on a mathematical analysis of a linear‐model system. For nonlinear systems, though, the influence of the operating parameters on the unit performance is less well understood. In this work, the interplay between the operating conditions and unit performance is investigated through numerical simulations and experiments, focusing on the influence of the feed stream composition. As a model system, the synthesis of methylacetate from methanol and acetic acid, catalyzed by a sulfonated ion‐exchange resin, is considered. The experiments were carried out in an SMB reactor of miniplant scale. In addition, the reliability of the model predictions is evaluated by comparing the numerical simulation results with experimental data. It is shown through simulations that optimal performance is achieved where the feed to the SMBR is constituted of an equimolar mixture of the two reactants. Simulations and experimental results allow for an understanding of such a result.
Volume‐translated equations of state: Empirical approach and physical relevance
Authors: Yelash Leonid V. , Kraska Thomas 
Published: April 2004

AbstractThe volume translation technique is widely applied in chemical engineering modeling of phase behavior and thermodynamic properties. This empirical correction of the molar volume improves the correlation of liquid densities when cubic equations of state are employed. Based on a recently proposed method of analyzing equations of state, the influence of the volume translation on the properties obtained from an equation of state, such as virial coefficients, as well as on the phase behavior, critical properties, the isobaric thermal expansion coefficient, and the heat capacities of pure substances is investigated. The influence of different kinds of temperature‐dependent volume translations is investigated and compared to approaches that originate from theoretical considerations. The investigation shows that empirical as well as theoretical approaches for the development of equations of state can exhibit nonphysical behavior. However, the understanding of the reasons for such problems can help to develop reliable equations of state based on both kinds of method.
Coupled macromolecular transport and gel mechanics: Poroviscoelastic approach
Authors: Netti P. A. , Travascio F. , Jain R. K. 
Published: April 2004

AbstractDesigning drug delivery devices or drug delivery protocols poses problems because they are considered to operate in a mechanically static environment. It should consider, however, transport processes in these cases occur in a mechanically dynamic environment since mechanical stimuli may strongly influence transport within soft hydrated materials. A general framework combines fluid and macromolecular transport with the mechanics of hydrated polymer gels or tissue. As an example, the model equations have been created for a spherical geometry to describe the distribution of macromolecules within the gel resulting from a constant pressure or a constant flow infusion source. The model describes the overall average profiles of the interstitial fluid pressure, velocity and solid matrix dilatation, displacement, and stress, as well as macromolecular distribution. The basic theory provides new insight into understanding the transport of macromolecules within mechanically stimulated polymeric gels and tissues and, therefore, represents a valuable tool for designing and engineering novel drug delivery systems, as well as optimization of drug delivery protocols to be used in detection and treatments.
Entropic characterization of distributive mixing in polymer processing equipment
Authors: Wang Winston , Manas‐Zloczower Ica , Kaufman Miron 
Published: April 2004

AbstractMixing is an integral component of most polymer processing operations as material properties are highly influenced by the quality of mixing. The degree of distributive mixing (system homogeneity) is assessed by calculating the evolution of Renyi relative entropies for the minor component along a continuous processing equipment. The Renyi entropy involves a β parameter, which represents weighting given to the concentration of the minor component in small, localized regions. Different aspects of mixing can thus be analyzed, from the amount of void spaces to the concentration of the region where mixing is the worst in terms of the minor component. This method provides a unified, rigorous and flexible way of characterizing distributive mixing. Specifically, distributive mixing is analyzed in a numerical simulation of a twin‐flight single screw extruder by using particle tracking as a method of describing the mixing process dynamics. Renyi entropies are used to examine three different processing conditions in a twin‐flight, single screw extruder. By changing the throttle ratio, the optimal extruder length varied. The relationship between the optimal length and average residence time was good.
Nozzle‐quenching process for controlled flame synthesis of titania nanoparticles
Authors: Wegner Karsten , Pratsinis Sotiris E. 
Published: April 2004

AbstractA process for precisely controlled synthesis of nanoparticles with a broad range of sizes, morphologies, and phase compositions is presented. This is achieved by a rapid quenching of the entire flame aerosol in a critical‐flow nozzle placed above and into the flame. This process is evaluated for synthesis of titania nanoparticles by oxidation of titanium‐tetra‐isopropoxide (TTIP) in a methane/oxygen coflow diffusion‐flame reactor. Precise control of phase composition from 97 to 5 wt. % anatase (and the balance rutile) and average primary particle diameter from 5 to 60 nm is possible by positioning the quenching nozzle at the desired heights above the burner and controlling gas and precursor flow rates. The nozzle quenching also reduces the degree of agglomeration of the product particles. An operation diagram shows that the primary particle diameter and the phase composition can be independently controlled, making anatase or rutile nanoparticles with high or low specific surface area.
Modeling of CO2 capture by aqueous monoethanolamine
Authors: Freguia Stefano , Rochelle Gary T. 
Published: April 2004

AbstractThe process for CO2 removal from flue gases was modeled with RateFrac. It consists of an absorber, a stripper, and a cross heat exchanger. The solvent used in the model contains about 30 wt % monoethanolamine (MEA) in water. MEA reacts with CO2 in the packed absorber. The finite reaction rate requires a kinetic characterization. The RateFrac absorber model was integrated with a FORTRAN user kinetic subroutine to make the model consistent with the interface pseudo‐first‐order model and with a regressed Electrolyte‐NRTL equilibrium model. It was adjusted with laboratory wetted wall column data and field data from a commercial plant. Sensitivity analyses were performed on process variables to find operating conditions at low steam requirement. Many variables strongly affect the process performance, but an overall optimization shows that there are no economical ways to reduce the steam requirements by more than 10%. The reboiler duty can be reduced from that of a base case representing current industrial operating conditions, by 5% if acids are added to the solvent, by 10% if the absorber height is increased by 20%, and by 4% if the absorber is intercooled with a duty of one‐third of the reboiler duty. The power plant lost work is affected by varying stripper pressure, but not significantly, so any convenient pressure can be chosen to operate the stripper.
CO2 Plasticization of polyethersulfone/polyimide gas‐separation membranes
Authors: Kapantaidakis G. C. , Koops G. H. , Wessling M. , Kaldis S. P. , Sakellaropoulos G. P. 
Published: April 2004

AbstractThis work reports the CO2 plasticization of gas‐separation hollow‐fiber membranes based on polyimide and polyethersulfone blends. The feed pressure effect on the permeance of pure gases (CO2, N2) and the separation performance of a gaseous mixture (CO2/N2, 55/45%) is examined. Contrary to dense membranes, the permeance of CO2 through ultrathin asymmetric fibers increases immediately with pressure resulting in pronounced apparent plasticization and reduction of the ideal CO2/N2 selectivity. However, no evidence of plasticization was observed when a CO2/N2, 55/45% mixture was fed to the hollow‐fiber membranes. In all cases, CO2 permeance decreased with pressure, while that of N2 remained constant. Experimental results were validated by means of mathematical modeling. Membrane‐separation performance was overestimated when pressure‐independent permeabilities were used in the model, while pressure‐dependent permeabilities, due to the overall effect of plasticization and competition phenomena, explained excellently, the obtained stage‐cut and permeate purity.
Automated retrofit design of cooling‐water systems
Authors: Kim Jin‐Kuk , Smith Robin 
Published: April 2004

AbstractAn automated approach from the systematic investigation of interactions between cooling‐tower performance and the cooling‐water network design was developed for retrofit design of cooling‐water systems. Introducing reuse of cooling water between different cooling duties enables cooling systems to be debottlenecked. The series arrangement of heat exchangers, however, results in a pressure drop increase because of the cooling water reuse. An optimization model for cooling‐water networks developed considers pressure‐drop constraints, complexity of networks, and efficient use of the cooling tower. A new node‐superstructure model is suggested to consider the intensive property of pressure and the sequence of connections simultaneously. Physical insights are used to provide a good initialization for the resulting optimization problem. Issues of retrofit analysis are also addressed to give design guidelines for debottlenecking of cooling‐water systems.
Design of separation schemes for fractional crystallization of metathetical salts
Authors: Cisternas Luis A. , Torres Mauricio A. , Godoy María J. , Swaney Ross E. 
Published: April 2004

AbstractThe synthesis method of fractional crystallization processes for the separation of salts belonging to reciprocal salt pairs is presented based on a flow network model constructed between thermodynamic states. The state nodes represented in the model include feeds, products, intermediate products, and solid–liquid equilibrium states. Flows between the states are represented by arcs within the flow model. A systematic procedure is given for identification of the solid–liquid equilibrium states that could potentially serve as operating points. This identification is essential to the construction of the flow network and reduces the problem to a simple mathematical form. The advantages of the method lie in its capability to consider general process flow pattern, handle systems forming double salt, deal with several temperatures as potential operation conditions, and handle several feeds and products. Examples are given to illustrate the procedure.
Tracking control of general nonlinear differential‐algebraic equation systems
Authors: Liu X. P. , Rohani S. , Jutan A. 
Published: April 2004

AbstractThe problem of output tracking control is considered for a general class of nonlinear differential‐algebraic systems. Regularization algorithm proposed here provides sufficient conditions for the existence of a regularizing feedback controller that renders the closed‐loop system to have an index one. Based on the regularization algorithm, another algorithm is developed for constructing a tracking controller, which guarantees that the outputs of the closed‐loop system track the desired signals asymptotically. Simulation results on a typical chemical process show that the developed design method gives a satisfactory control performance.
Robust nonlinear model predictive control of batch processes
Authors: Nagy Zoltan K. , Braatz Richard D. 
Published: April 2004

AbstractNMPC explicitly addresses constraints and nonlinearities during the feedback control of batch processes. This NMPC algorithm also explicitly takes parameter uncertainty into account in the state estimation and state feedback controller designs. An extended Kalman filter estimates the process noise covariance matrix from the parameter uncertainty description and employs a sequential integration and correction strategy to reduce biases in the state estimates due to parameter uncertainty. The shrinking horizon NMPC algorithm minimizes a weighted sum of the nominal performance objective, an estimate of the variance of the performance objective, and an integral of the deviation of the control trajectory from the nominal optimal control trajectory. The robust performance is quantified by estimates of the distribution of the performance index along the batch run obtained by a series expansion about the control trajectory. The control and analysis approaches are applied to a simulated batch crystallization process with a realistic uncertainty description. The proposed robust NMPC algorithm improves the robust performance by a factor of six compared to open loop optimal control, and a factor of two compared to nominal NMPC. Monte Carlo simulations support the results obtained by the distributional robustness analysis technique.
Two‐section reactor model for autothermal reforming of methane to synthesis gas
Authors: Biesheuvel P. Maarten , Kramer Gert Jan 
Published: April 2004

AbstractA 1‐D stationary reactor model describes the catalytic conversion of a gaseous hydrocarbon fuel with air and steam to synthesis gas by autothermal reforming and catalytic partial oxidation. The model defines two subsequent sections in the reactor: an upstream oxidation section and a downstream reforming section. In the oxidation section, all of the oxygen is converted, with partial conversion of the fuel. An empirical fuel utilization ratio is used to quantify which part of the fuel is converted in the oxidation section as a function of the relative flows of air and steam. In the oxidation section, the gas temperature rapidly increases toward the top temperature at the intersection with the reforming section. In this section the temperature decreases while the fuel is further converted with water and CO2 as oxidant. For methane as fuel, simulation results are compared with experiments. For multicomponent fuels such as natural gas and naphtha, application of the two‐section model is described.
Effect of fluid properties on dispersion in flow through packed beds
Authors: de Carvalho J. R. F. Guedes , Delgado J. M. P. Q. 
Published: April 2004

AbstractAn experimental study is described on the effect of liquid properties on axial dispersion in packed beds. Working with water between 278 and 373 K, the range 57<Sc<1,930 was covered, and this represents a significant fraction of the domain located between what is traditionally considered “gas behavior” (that is, Sc≅1) and “liquid behavior” (typically, Sc>600). A representation of PeL vs. Pem reveals the existence of a very flat minimum (typically 102<Pem<104) for each value of Sc. The value of the minimum is almost insensitive to variations in Sc, for Sc>700, but it increases significantly with a decrease in Sc, for Sc<700. The experimental data used to test available correlations for predicting DL show that they are inaccurate over considerable ranges of the variables.
Perturbation viscometer to measure the viscosity gradients of gas mixtures
Authors: Russell P. A. , Buffham B. A. , Mason G. , Heslop M. J. 
Published: April 2004

AbstractPerturbation viscometry measures the logarithmic viscosity gradient of the viscosity–composition curve for gas mixtures. The flow and composition of a gas mixture flowing through a capillary are perturbed by adding a small flow of gas, normally one of the pure components of the gas mixture. Two pressure changes are seen at the capillary, the first due to the change in flow rate and the second, a short time later, due to the change in viscosity. The logarithmic viscosity gradient can be calculated from the ratio of these two pressure changes. Integration of logarithmic viscosity gradients measured over the full composition range gives the mixture viscosity relative to the viscosity of one of the pure components of the gas mixture. This method is attractive because, for measurements of equal precision, integration of the gradients is potentially an order of magnitude more precise than conventional methods that measure viscosities directly. It can also work at high and low temperatures and perhaps high pressures. The potential of this technique was previously demonstrated with a rudimentary apparatus, but its advantages and potential flaws need to be more closely examined. Here a fully thermostatted apparatus is detailed, including all modifications incorporated from experience operating the original apparatus. Experimental data for the helium–nitrogen mixture at 360°C, the practical upper operating limit of the apparatus, are presented. Integral consistency checks performed on the measured data show that high‐quality data produced compare well (less than 1% deviation) with the best literature data available.
Axial liquid mixing in high‐pressure bubble columns
Authors: Yang G. Q. , Fan L. S. 
Published: April 2004

AbstractAxial dispersion coefficients of the liquid phase in bubble columns at high pressure are investigated using the thermal dispersion technique. Water and hydrocarbon liquids are used as the liquid phase. The system pressure varies up to 10.3 MPa and the superficial gas velocity varies up to 0.4 cm/s, which covers both the homogeneous bubbling and churn‐turbulent flow regimes. Experimental results show that flow regime, system pressure, liquid properties, liquid‐phase motion, and column size are the main factors affecting liquid mixing. The axial dispersion coefficient of the liquid phase increases with an increase in gas velocity and decreases with increasing pressure. The effects of gas velocity and pressure on liquid mixing can be explained based on the combined mechanism of global liquid internal circulation and local turbulent fluctuations. The axial liquid dispersion coefficient also increases with increasing liquid velocity due to enhanced liquid‐phase turbulence. The scale‐up effect on liquid mixing reduces as the pressure increases.