bluuebunny/crossref_metadata_2025 huggingface dataset:
Kinetics of separating multicomponent mixtures by nondispersive solvent extraction: Ni and Cd
Authors: Ortiz Inmaculada , Galán Berta , Román Fresnedo San , Ibáñez Raquel
Published: April 2004

A model for nonsteady metals separation using nondispersive solvent extraction presented explicitly accounts for selective separation of multicomponent solutions and concentration of separated components in a back‐extraction phase. The separation process comprises extraction and back‐extraction steps carried out in two different hollow‐fiber modules, connected through the organic phase, together with three homogenization tanks. The model is based on a set of coupled differential equations describing mass balances of metallic solutes in the fluid phases. To be applied in its simplest form, it requires the knowledge of three characteristic parameters, two parameters related to the chemical reactions, and one mass‐transport parameter. The latter describes the mass‐transport rate through pores of the hollow‐fiber membrane filled with the organic phase. The mathematical model was checked against the kinetic results of the separation of Cd/Ni mixtures working with high‐concentration solutions and obtaining the characteristic parameters of this system.
Design procedure for safe operations in agitated batch reactors
Authors: Fortuin Jan M. H. , Heiszwolf Johan J. , Bildea Costin S.
Published: April 2004

An application‐oriented design procedure is presented for completely mixed liquid reacting systems in batch reactors. These systems can safely be operated by neglecting the heat capacity of the vessel and attributing suitable values to three scale‐independent control parameters: the initial concentration (c0); the inlet coolant temperature (Tc,i); and the Newtonian cooling time (tN). For given dimensionless values of the reaction order n, heat‐transfer capacity βn, and inlet coolant temperature ϵ, the design value α* of the dimensionless adiabatic temperature rise must satisfy α > α* < αm,a. This can help avoid both runaways (α* < αc) and oversteps of the maximum allowable temperature rise (α* < αm,a). A model is derived to calculate αc and αm,a for three different reaction orders. Simulated relationships are verified with experimental results concerning the hydration of 2,3‐epoxypropanol in a 0.27‐L agitated batch reactor.
Analysis of a gap dryer used to produce polymer films and coatings
Authors: Ramesh Narayan , Duda J. L.
Published: April 2004

The ability to predict the drying behavior of thin films and coatings is of great importance to the coating industry and governs the economical production of various polymeric products. In conventional drying processes, a continuous layer of polymer solution is deposited onto a substrate, which is dried in an oven with forced air convection. Recently, a gap dryer was developed that eliminates the need for forced gas flow and provides direct solvent recovery. A model that incorporates simultaneous heat and mass transfer in the bulk polymer and gas phases and jump conditions across the interface is utilized to describe the drying of a binary polymer–solvent system in a gap dryer. Solvent self‐diffusion in the polymer phase is described by the free‐volume theory, and the Flory‐Huggins theory is used to describe polymer–solvent thermodynamics. Simulations indicate the possibility of condensation in the gas phase that can decrease both drying efficiency and coating quality. A method to resolve this problem is proposed, as well as a comparison between the performance of a gap dryer and a conventional convection‐oven dryer.
Particle motion in packed/ebullated beds by CT and CARPT
Authors: Chen Jinwen , Rados Novica , Al‐Dahhan Muthanna H. , Duduković Milorad P. , Nguyen Duyen , Parimi Krishniah
Published: April 2004

Computed tomography (CT) and computer‐automated radioactive particle tracking (CARPT) were used to study the gas distribution and incipient particle motion in a packed/ebullated bed in which gas and liquid are in cocurrent upflow. CT scans were performed to evaluate the gas–liquid distributor and gas sparger for the experiments. Using a perforated plate gas–liquid distributor (with 96 1‐mm holes, open area of 0.1%) and a gas sparger (cross‐shaped, with 16 3‐mm holes), the cross‐sectional gas holdup distribution in the packed/ebullated bed was relatively uniform, with gas holdup of about 0.11 in the center and 0.09 near the wall of the bed at superficial gas and liquid velocities of 2 and 0.3 cm/s, respectively. The cross‐sectional averaged gas holdup was 0.095. CARPT experiments were utilized in an air–water–ethanol– (10 wt. %) solids system to identify the operating conditions at which solid particles first start to move in the bed. At a superficial gas velocity of 1.7 cm/s and superficial liquid velocity of 0.3 cm/s, solids particles in the bed started to move and travel long distances in the axial direction. CARPT experiments in the same system at superficial gas velocity of 2.0 cm/s and superficial liquid velocity of 0.3 cm/s showed that the solid particles in the bed were moving significantly throughout the column, generating a recirculation pattern with upflow in the center and downflow near the wall of the column. The time‐averaged maximum upward and downward velocity of the tracer particle was about 0.47 and 0.57 mm/s, respectively.
Review: Developments in distillation and separation technology
Authors: Porter Kenneth E.
Published: April 2004

With the focus on the power of theoretical concepts to enable the creation of new technologies, separation technology is discussed in terms of “intellectual tools” derived from ideas in diffusion accompanied by reaction and from “pinch point” techniques. Ideas are the intellectual tools shaping the changing world (we live not in the information age, but in the intellectual age). Developments in distillation equipment during the last 20 years reveal the importance of business drivers for stimulating change, and why the 1980s was the decade of structured packing and the 1990s of high throughput trays. Because of out inadequate understanding of phase equilibrium (no molecular theory of liquids) and of two‐phase flow (except for when one phase is very dilute), process and equipment design is still essentially empirical. In conclusion it is noted that more might be done to encourage the development of young intellectual tool‐makers. Research in this field might help speed up technical innovation.
Catalytic distillation in structured packings: Methyl acetate synthesis
Authors: Górak Andrzej , Hoffmann Achim
Published: April 2004

Catalytic Distillation can improve process design, the design of column internals requires special attention. The catalytic packing MULTIPAK facilitates effective catalysis, high separation efficiency, and a wide loading range simultaneously. In this work the main characteristics of MULTIPAK—pressure drop, loading range, and separation efficiency—are determined experimentally. The developed nonequilibrium stage model developed reflects the complexity of catalytic distillation processes and comprises correlations describing pressure drop and separation efficiency of MULTIPAK as a function of the operating conditions. The model has been implemented in the simulation environment Aspen Custom Modeler, and the simulation results are compared with experimental data for the synthesis of methyl acetate. This model reflects the process behavior, but differences between simulated results and experimental data can still be observed.
Recovery of VOCs from high‐volume, low‐VOC‐concentration air streams
Authors: Wang X. , Daniels R. , Baker R. W.
Published: April 2004

High‐volume, low‐VOC‐concentration air streams are produced by a broad range of industries. The most widely used treatment technology is carbon adsorption, which produces dilute aqueous waste streams as a secondary waste, is difficult to adapt to particulate‐containing streams, and is too expensive to be applied by some industries. Scrubbing the air with an absorbent liquid is economical, but limited to scrubbing with water due to the expense and difficulty of regenerating nonaqueous scrubbing liquids. A low‐volatility organic scrubbing liquid regenerated by a stripper/membrane vapor‐separation unit was used to remove VOCs from the dilute air stream. The technical and economic feasibility of the scrubbing/stripping/membrane separation hybrid process was evaluated in laboratory tests with a pilot‐scale system. The unit, operated with model‐contaminated gas streams containing 100 to 2,000 ppm methylene/chloride, removed 95% of the methylene chloride in the feed air as a condensed liquid. The experimental data show that the process offers significant cost and operating benefits over other technologies for streams in the 500 to 2,000 ppm VOC concentration range. It can be applied to treating effluent air streams from painting, degreasing, and printing operations.
Millisecond catalytic wall reactors: I. Radiant burner
Authors: Redenius J. M. , Schmidt L. D. , Deutschmann O.
Published: April 2004

Short‐contact‐time reactors have potential for high throughput in reactors much smaller than their traditional counterparts. While they operate adiabatically, heat can be exchanged at short contact time by integrating heat exchange into the reactor. Hot effluent of exothermic reaction systems can be redirected over feed gases to recuperate a portion of the sensible heat. Placing catalyst directly on reactor walls eliminates the resistance to heat transfer in the thermal boundary layer so that heat released by combustion can be effectively coupled to an emitter, such as in a radiant burner. A radiant heater was constructed, operated, and simulated incorporating short contact time, energy recuperation, and a catalytic wall. This burner operated stably for many hours at a firing rate from ∼50 to > 160 kW/m2 at a radiant temperature of 950 to 1,150 K at a radiant efficiency of ∼60% with a residence time in the reacting zone of ∼10 ms. This reactor was modeled using 2‐D Navier‐Stokes equations including detailed models for chemistry and heat transport. Temperature and compositions predicted agreed well with experimental measurements.
Intensification of phase transition on multiphase reactions
Authors: Cheng Zhen‐Min , Anter Abdulhakeim M. , Yuan Wei‐Kang
Published: April 2004

Chemical reactions, generally conducted under full gas or liquid phases, are problematic for volatile liquid reactants. For such reactants, the presence of phase transition can be favorable, since evaporation of the liquid could not only balance the reaction heat but improve the effectiveness factor of the porous catalyst. This principle was applied to engineering applications. Experiment was carried out to investigate effects of catalyst activities, flow directions, operation pressures, gas and liquid flow rates, and reactant concentrations on the reactor behavior. Quench operation with a cold‐injection side stream was initiated to prevent an excessive temperature rise, which was shown to be effective and flexible. With this novel optimizing method, the reactor temperature could be kept around 270°C under 1.0 MPa, even with a benzene concentration of 35%. Research on phase transition of benzene hydrogenation proved successful and could be extended to reaction systems with a similar range of process intensification.
NO/NOx removal with C2 H2 as additive via dielectric barrier discharges
Authors: Chang Moo Been , Yang Shyh Chaur
Published: April 2004

Effective reduction and removal of NOx from gas streams by dielectric barrier discharge (DBD) was studied. A laboratory‐scale experimental system was designed and constructed to evaluate the removal efficiency of NO and NOx. Particularly, C2 H2 was added as a reducing agent in the DeNOx plasma process via DBD. Experimental results indicated that the removal efficiency of NO/NOx increased with increasing applied voltage, gas temperature, and H2 O(g) content. As the oxygen content in the gas stream is increased, more CHi radicals will be further oxidized to CO2, thus reducing the removal efficiency of NOx. When sufficient C2 H2 was added to the DBD process, as high as 91.2% of NO and 68.2% of NOx were removed at 140°C for the gas stream containing 500 ppm NO, 1,500 ppm C2 H2, 3.2% H2 O(g), and 5% O2, with N2 as the carrier gas. In addition to N2 and H2 O, the major products found in this process included NO2, N2 O, HNO3, CO2, CO, and HCOOH, depending on H2 O(g) and O2 contents of the gas stream.
New approach for quantifying process feasibility: Convex and 1‐D quasi‐convex regions
Authors: Ierapetritou Marianthi G.
Published: April 2004

Uncertainities in chemical plants come from numerous sources: internal like fluctuated values of reaction constants and physical properties or external such as quality and flow rates of feedstreams. Accounting for uncertainty in various stages of plant operations was identified as one of the most important problems in chemical plant design and operations. A new approach proposed describes process's feasible region and a new metric for evaluating process flexibility based on the convex hull that is inscribed within the feasible region and determines its volume based on Delaunay Triangulation. The two steps involved are: 1. a series of simple optimization problems are solved to determine points at the boundary of the feasible region; 2. given the set of points at the boundary of the feasible region, the convex hull inscribed within the feasible region is determined. This is achieved by implementing the Quickhull algorithm, an incremental procedure for evaluating the convex hull, and then by computing a Delaunay Triangulation to determine the volume of the convex hull providing a new metric for process flexibility. This approach not only provides another feasibility measure, but an accurate description of the feasible space of the process. It was applied to 1‐D convex problems, and work is in progress to extend it to nonconvex systems.
Designing a commercial ion‐exchange carousel to treat DOE wastes using CST granules
Authors: Huckman M. E. , Latheef I. M. , Anthony R. G.
Published: April 2004

A column carousel system was designed to treat nuclear waste at the Savannah River Site. A carousel model was used to simulate cesium removal in an ion‐exchange carousel loaded with crystalline silicotitanate (CST) granules. The model accounts for axial dispersion and resistance to film and intraparticle diffusion. The effect of resistance to intraparticle diffusion on the required column volumes is significant. Values of the effective diffusivity of 0.25 to 0.6×10−10 m2/s were estimated from bench‐scale column experiments. This range of values resulted in a variation of column volumes by a factor of 3. The Zheng‐Anthony‐Miller equilibrium model was used to estimate Cs isotherms. The largest carousel volume did not result from waste with the lowest equilibrium loading. For wastes with low equilibrium loadings, the switching interval increased, which increases the volume of CST required to treat the same volume of waste.
Modeling for simulation of fluidized‐bed incineration process
Authors: Marias F. , Puiggali J. R. , Flamant G.
Published: April 2004

A mathematical model for the fluidized‐bed incineration process was developed using the waste composed of wood, cardboard and polyvinyl chloride. It is based on heat and mass balances of the gas held within the five zones representing both the bubbling bed and freeboard and including heat transfer with sand and reacting particles of char (pyrolysis residue). The mixture fraction concept and assumption of chemical equilibrium are used to compute temperature and species concentration fields resulting from volatile combustion. These fields are affected by char combustion, which relies, in turn, on a model based on surface reaction and a full population balance. The formation of pollutants (NOx, SOx ) was also taken into account. The main steps involved by the numerical resolution of the model are discussed, and some results are shown for a 1 MW unit.
Predictive model and deterministic mechanism in a bubbling fluidized bed
Authors: Zhao Gui‐Bing , Chen Ji‐Zhong , Yang Yong‐Rong
Published: April 2004

A predictive model based on the theory of phase space reconstruction was proposed to study the determinism and predictability of dynamics underlying pressure fluctuations by measuring and analyzing the time series of pressure signals at different locations in a bubble bed with 0.3 m in dia. and 3 m in height. Chaotic invariants (correlation dimension, K2 entropy, and Lyapunov exponent spectrum) of measured and model‐generated time series of pressure signals were nearly the same. The model captured some important nonlinear characteristics of the real system, which can be used to study the dynamics of fluidizing system. Deterministic dynamics underlying pressure signals were confirmed to exist. A new characteristic index defined as the determining level of dynamics was used to analyze deterministic degrees at different gas velocities and locations of the wall in the bed. Since prediction errors of pressure fluctuations grow exponentially with time at short time scales and the exponent separation rate between predicted and measured values is proportional to the maximal Lyapunov exponent, the long‐term predictability of pressure fluctuations is impossible. This verified chaotic properties of fluctuation dynamics in the fluidized bed with deterministic mechanism and sensitive dependence on initial conditions.
Synthesis of silica‐carbon particles in a turbulent H2‐air flame aerosol reactor
Authors: Kammler Hendrik K. , Mueller Roger , Senn Omri , Pratsinis Sotiris E.
Published: April 2004

Synthesis of flame‐made nanostructured powders was studied, for the first time, at high production rates (up to 700 g/h) in a turbulent diffusion flame reactor, addressing also the required safety concerns. A commercial hydrogen‐air burner was used for synthesis of pure silica and composite silica‐carbon particles by oxidation of hexamethyldisiloxane. The product powder was collected continuously in a baghouse filter unit and cleaned periodically by air‐pressure shocks. The effect of the fuel (hydrogen) flow rate, powder production rate and total oxidant flow rate on product particle size, morphology, and composition was also investigated. Nitrogen adsorption, transmission electron microscopy and thermogravimetric analysis coupled with a mass spectrometer, and a CO2 ‐analyzer were employed to characterize specific surface area and powder composition. Typically, aggregates of silica‐carbon composite particles (0 to 1.4 wt. % carbon) were made on specific surface areas of 75 to 250 m2/g at production rates of 125 to 700 g/h, which correspond to particle concentrations of 17 to 93 g/m3 (2–10% solid fraction by weight).
Protein ion‐exchange adsorption kinetics
Authors: Wesselingh J. A. , Bosma J. C.
Published: April 2004

The kinetics of the adsorption of the protein BSA on the ion exchanger Q‐Sepharose FF were measured for several values of the pH and ionic strength, using several techniques. The measurements were best described with a model incorporating both surface and pore diffusion and with the chemical potential gradient as the driving force for diffusion. The surface‐diffusion coefficients from this model show an inverse exponential dependency on the binding strength. This dependency can be explained by an activated jump mechanism. The pore‐diffusion coefficient is much lower than that in free solution, which is probably caused by a combination of steric and electric exclusion.
Mass‐transport dynamics, activity, and structure of sulfate‐reducing biofilms
Authors: Beyenal Haluk , Lewandowski Zbigniew
Published: April 2004

Factors limiting hydrogen sulfide production were identified in a two‐species biofilm containing sulfate‐reducing bacteria (Desulfovibrio desulfuricans) and nonsulfate‐reducing bacteria (Pseudomonas fluorescens). Profiles of hydrogen sulfide (H2S) concentration, pH, local mass‐transport coefficient, local flow velocity, and local relative effective diffusivity in the biofilm were measured using microelectrodes. Biofilms had a heterogeneous structure consisting of cell clusters separated by voids. Typically, the H2S concentration was lower in the voids than in the adjacent cell clusters, demonstrating that the voids acted as transport channels for removing H2S from cell clusters. The extent of biofilm heterogeneity was directly correlated with the flux of H2S from cell clusters. At flow velocities below 2 cm/s, the flux of H2S from cell clusters depended on the flow velocity. We concluded that at these flow velocities the H2S production rate was limited by the delivery rate of sulfate ions to the biofilm. At flow velocities above 2 cm/s, the H2S production rate was nearly constant and did not depend on the flow velocity. At high flow velocities (>2 cm/s) the H2S production rate was limited by metabolic reactions in the biofilm. Local intrabiofilm flow velocity profiles were influenced strongly by biofilm heterogeneity without significant pH variation within biofilms. Surprisingly, profiles of local relative effective diffusivity indicated that the biofilm was made up of two layers, which could be related to the specimen with a two‐species biofilm.
Effects of reactant concentrations on reactive miscible viscous fingering
Authors: Nagatsu Yuichiro , Ueda Toshihisa
Published: April 2004

Effects of reactant concentrations on the characteristics of reactive miscible viscous fingering in a Hele‐Shaw cell at low finger‐growth velocity were studied both experimentally and theoretically. The product distribution varies with the variations in the initial reactant concentrations and depends on the location of a reaction zone. When the reaction zone is located in the more‐viscous‐liquid region the product concentrates at the fingertips, but when it is located in the less‐viscous‐liquid region, the product spreads in a relatively broad area inside the fingers. This significant difference in the reaction pattern resulting from variations in the reactant concentrations is caused by the large difference of molecular diffusivity in the two liquids, that is, of viscosity which is one of the important factors for viscous fingering. These results are confirmed theoretically by one‐dimensional diffusive–reactive analysis.
Simple stochastic model of spontaneous imbibition in Hele‐Shaw cells
Authors: Rodríguez R. F. , Salinas‐Rodríguez E. , Hayashi J. A. , Soria A. , Zamora J. M.
Published: April 2004

The imbibition of water in oil in Hele‐Shaw cells is described as an asymmetric random walk of water in a globally disordered medium. The disorder is modeled by an external, nonwhite, dichotomic noise, and the resulting random walk is described in terms of an effective Markovian master equation. The solution to this equation is given, and the mean‐squared‐displacement (MSD) of fluid particles in an effective ordered medium is calculated. This same quantity was also measured in squared cells with a fixed separation, where Soltrol 170 was displaced by twice‐distilled water. The flow generated by spontaneous displacement of oil presented three sequential stages, each with a characteristic speed and advancing front structure. In the first and third stages viscous fingering was not detected, but in the intermediate development stage it was observed. From the recorded time evolution of the front, its average displacement speed and the MSD of water in oil as a function of time were determined. Imbibition of water shows an enhanced diffusion regime in the first stage where MSD varies with t2, without any external noise effect. This is followed by a simple diffusion behavior in an effective medium in the second stage, where the external noise effect is large. In the third stage Gaussian diffusion prevails again. Numerical regression techniques were used to determine the best values of model parameters that fit experimental values for different stages, so that the sum of squared errors between theoretical predictions and experimental measurements is minimized. Good agreement was found with average errors of 14.3%, 5.9% and 0.6%, respectively.
Effect of mixing on product quality in semibatch stirred tank reactors
Authors: Verschuren Iris L. M. , Wijers Johan G. , Keurentjes Jos T. F.
Published: April 2004

Semibatch stirred tank reactors with a turbulent flow field are used frequently in the chemical process industry to accomplish mixing tasks. Mixing in a turbulent flow consists of several processes. Descriptions for these processes from literature are used to construct a model to calculate the selectivity of a mixing‐sensitive reaction in a semibatch stirred tank reactor. The model is validated by determining the effects of various process parameters on the selectivity of the third Bourne reaction. Calculation of the selectivity requires information on the hydrodynamic parameters of the stirred vessel studied. The essential detailed description of these hydrodynamic parameters to obtain a good agreement between measured and calculated selectivities was determined. The model proved to be successful in predicting the product distribution of a competitive reaction, making it useful for the design and scale‐up of stirred‐tank reactors.
Liquid‐liquid extraction of aroma compounds with hollow fiber contactor
Authors: Baudot Arnaud , Floury Juliane , Smorenburg Herbert E.
Published: April 2004

The extraction of aroma compounds through a commercial hollow‐fiber contactor from model aqueous feeds to sunflower oil was tested. The stripping efficiency of this membrane‐based solvent extraction operation was systematically studied as a function of the oil/water partition coefficient of the permeants, and the flow and location of the feeds in the contactor (in the shell side or in the lumen of the fibers). The mass transfer between the two phases was modeled based on the resistances‐in‐series approach. In particular, a correlation describing the mass transfer with a transverse flow in the shell is proposed. With similar operating conditions, the stripping of the aroma compounds was more efficient when flowing the aqueous feed phase in the shell side than inside the fibers.
Mass transfer in low‐density xerogel catalysts
Authors: Heinrichs Benoît , Pirard Jean‐Paul , Schoebrechts Jean‐Paul
Published: April 2004

Texture and morphology of a Pd‐Ag/SiO2 hydrodechlorination low‐density xerogel catalyst prepared by a cogelation sol‐gel process were characterized in detail to examine mass transfer in such catalysts. The catalyst consists of active Pd‐Ag nanocrystallites trapped inside elementary 20 nm microporous silica particles arranged in larger aggregates, which constitute the macroscopic pellet. To reach active sites, reactants must first diffuse through large pores located between aggregates of SiO2 particles and then through smaller pores located between those elementary particles inside the aggregates. Finally, they diffuse through micropores located inside silica particles. Diffusion in such a “funnel” structure cannot be described assimilating the pellet to a pseudo‐continuum. Diffusion should be examined carefully at three levels of decreasing size: the macroscopic pellet, the aggregate of silica particles, and the elementary silica particle. This approach shows that cogelled xerogel catalysts have remarkable mass‐transfer properties.
Reliable density‐functional‐theory calculations of adsorption in nanoscale pores
Authors: Maier Robert W. , Stadtherr Mark A.
Published: April 2004

A popular approach for the modeling of adsorption phenomena is density‐functional theory (DFT). A new methodology described here is the first completely reliable technique for finding all solutions to the nonlinear equation systems arising in the lattice‐DFT modeling of adsorption in porous materials. The method is based on interval analysis, in particular on an interval Newton/generalized bisection algorithm, which provides a mathematical and computational guarantee that all solutions are enclosed. The method is demonstrated using a model, formulated using DFT for a confined lattice, of adsorption in slit‐like nanoscale pores. In addition to confirming solutions found previously, the method also found on several test problems a number of additional, previously unreported solutions.
Electromagnetics, heat transfer, and thermokinetics in microwave sterilization
Authors: Zhang H. , Datta A. K. , Taub I. A. , Doona C.
Published: April 2004

Sterilization of solid foods using microwave power was studied using numerical modeling and specialized experimental verification. Maxwell's equations and the heat conduction equation were coupled using two separate finite‐element programs and specially written modules to couple the programs. Spatial distributions of thermal‐time, representing sterilization, were calculated from time‐temperature history and first‐order kinetics. Experimentally, concentrations of marker compounds formed during heating were measured and taken as indices of thermal‐time. Experimental data on marker formation combined with numerical calculations provide an accurate and comprehensive picture of the sterilization process and represent a major step in establishing the efficacy of microwave sterilization processing. Unlike conventional sterilization, heating patterns can change qualitatively with geometry (shape and size) and properties (composition) of the food material, but optimal heating is possible by choosing suitable combinations of these factors. Combined with marker yield measurements, the numerical model can give comprehensive descriptions of the spatial time‐temperature history, and thus can be used to verify the sterilization process.
Controlling particle size during anatase precipitation
Authors: Sathyamoorthy Sekhar , Moggridge Geoff D. , Hounslow Michael J.
Published: April 2004

Titanium dioxide particles in the form of anatase are precipitated from concentrated titanyl sulfate solution in the sulfate process, which are then recovered by a filtration process downstream of the precipitation stage. A previous study by Sathyamoorthy et al. showed that the final anatase particles are aggregates (1‐2 μm) consisting of numerous crystals (7–8 nm) arranged in primary agglomerates (60–100 nm). Pigment quality is determined by crystal and primary agglomerate size. One way of improving filtration rate is by the formation of larger aggregates, while maintaining the crystal and primary agglomerate size at optimum values. In a new seeding procedure proposed, the controlled inoculation of seeds used in industry is combined with a new type of seed (Large Seeds). The new seeding procedure has the potential to increase downstream filtration efficiency by increasing aggregate size, while maintaining crystal and primary agglomerate sizes close to the values correctly obtained in industry. High yield in the precipitation process is also maintained.
Experimental studies of gas permeation through microporous silica membranes
Authors: Yoshioka Tomohisa , Nakanishi Eisuke , Tsuru Toshinori , Asaeda Masashi
Published: April 2004

Permeation mechanism of inorganic gases was studied experimentally and theoretically through microporous silica membranes prepared by the sol–gel method. Inorganic gas permeation was measured using the membranes with subnano pores in diameter. The permeance of He increased with increasing temperature for various cases, while that of CO2, O2 and N2 decreased. In particular, the observed temperature dependency of CO2 was greater than those of other gases. In such small pores, the interaction energy between a permeant molecule and the pore wall can affect gas‐permeation properties. A simple gas‐permeation model is used considering the effect of the attractive or repulsive pore‐wall potential field, which deviates from the ambient gas phase of the gas molecule concentration (pressure) in a pore. The model can explain the experimental gas‐permeation properties successfully. Potential curves of CO2 and N2 in a silica pore were also calculated to predict the permeation ratio of CO2/N2. This model can help understand further the gas‐permeation mechanism in micropores.
Extended PLS approach for enhanced condition monitoring of industrial processes
Authors: Kruger U. , Chen Q. , Sandoz D. J. , McFarlane R. C.
Published: April 2004

An extended partial‐least squares (EPLS) algorithm is introduced to correct a deficiency of conventional partial least squares (PLS) when used as a tool to detect abnormal operating conditions in industrial processes. In the absence of feedback control, an abnormal operating condition that affects only process response variables will not be propagated back to the process predictor (or input) variables. Thus monitoring tools developed under the conventional PLS framework and based only on the predictor matrix will fail to detect the abnormal condition. The EPLS algorithm described removes this deficiency by defining new scores that are based on both predictor and response variables. The EPLS approach provides two monitoring charts to detect abnormal process behavior, as well as contribution charts to diagnose this behavior. To demonstrate the utility of the new approach, the extended algorithm and monitoring tools are applied to a realistic simulation of a fluid catalytic cracking unit and to a real industrial process that involves a complex chemical reaction.
Viscoplastic fluid flow through a sudden axisymmetric expansion
Authors: Jay Pascal , Magnin Albert , Piau Jean Michel
Published: April 2004

Numerical experiments were carried out for yield‐stress fluid flows through a 1:4 sudden axisymmetric expansion using the Herschel‐Bulkley and Bingham models with a two‐viscosity approximation. The influence of shear thinning, inertia and yield‐stress values on the structure of the flow and on pressure and head losses was studied. The detailed structure of flow in the expansion shows an initial vortex. The yield stress generates two toroidal rigid dead zones, one located in the corner of the expansion and one located close to the stagnation point that appears between the vortex and the downstream flow. Inertia and yield stress act in opposite ways. When inertia increases, the vortex increases in size and the rigid dead zone decreases. Conversely, when yield stress increases, the vortex decreases in size and the rigid dead zone increases. Shear thinning reduces the dimensions of both vortices and dead zones. Pressure loss increases with yield stress. In addition, the numerical results are consistently compared with experimental ones.
A simulation‐optimization framework for research and development pipeline management
Authors: Subramanian Dharmashankar , Pekny Joseph F. , Reklaitis Gintaras V.
Published: April 2004

The Research and Development Pipeline management problem has far‐reaching economic implications for new‐product‐development‐driven industries, such as pharmaceutical, biotechnology and agrochemical industries. Effective decision‐making is required with respect to portfolio selection and project task scheduling in the face of significant uncertainty and an ever‐constrained resource pool. The here‐and‐now stochastic optimization problem inherent to the management of an R&D Pipeline is described in its most general form, as well as a computing architecture, Sim‐Opt, that combines mathematical programming and discrete event system simulation to assess the uncertainty and control the risk present in the pipeline. The R&D Pipeline management problem is viewed in Sim‐Opt as the control problem of a performance‐oriented, resource‐constrained, stochastic, discrete‐event, dynamic system. The concept of time lines is used to study multiple unique realizations of the controlled evolution of the discrete‐event pipeline system. Four approaches using various degrees of rigor were investigated for the optimization module in Sim‐Opt, and their relative performance is explored through an industrially motivated case study. Methods are presented to efficiently integrate information across the time lines from this framework. This integration of information demonstrated in a case study was used to infer a creative operational policy for the corresponding here‐and‐now stochastic optimization problem.
Operational envelopes for batch processes
Authors: Samsatli Nouri J. , Sharif Mona , Shah Nilay , Papageorgiou Lazaros G.
Published: April 2004

Batch processes are often subjected to a number of sources of variability, which are frequently overlooked due to operating policy implementation. In many pharmaceutical and speciality chemical processes, which are predominantly batch in nature, a high proportion of the operating procedure is implemented manually, which can lead to significant variability. The effect of this variability is typically neglected at all stages in process development and even when full‐scale production begins. The result of any variability can have a dramatic effect on some process stages (particularly sensitive ones such as crystallization), and it is therefore important to understand how variability in any of the operating variables affects the overall process. Ideally, one would like to design processes that are less sensitive to variability and specify precisely the limits of any allowable variability. A method for designing batch processes using “operating envelopes” that specify process operation in terms of a region within which the operating variables should be maintained to guarantee feasible and profitable operation of the process is presented. The problem is formulated as a multiscenario dynamic optimization problem, and an efficient hierarchical solution procedure is presented. Finally, the applicability of the procedure is demonstrated by using two example problems.
Dehydration of sodium carbonate decahydrate to monohydrate in a fluidized bed
Authors: Hartman M. , Veselý V. , Svoboda K. , Trnka O. , Beran Z.
Published: April 2004

Kinetics of the thermal dehydration of sodium carbonate decahydrate to monohydrate is investigated at temperatures between 15 and 30°C in a batch, fluidized‐bed, 140‐mm‐ID reactor. Effects of particle size, mass of bed, and gas velocity on the dehydration rate are also explored. A simple correlation based on the collected experimental data is developed. The proposed rate law formula makes it possible to estimate the dehydration rate that would be needed to design the performance of a fluidized‐bed drying unit. The produced monohydrate is subjected to textural analysis, and pore volume and surface‐area data are presented.
Mathematical model for the nonsteady decomposition of intumescent coatings
Authors: Di Blasi Colomba , Branca Carmen
Published: April 2004

A 1‐D transient mathematical model was studied for a composite system consisting of a substrate (steel) and an intumescent coating exposed to radiative heating. By applying a simple heat conduction equation for the first material, a general model proposes the coating consisting of three components, which degrade according to independent finite‐rate reactions. Mass and heat transfer take place across a variable volume medium, including a simplified mechanism for bubble dynamics and material swelling. A parametric analysis clarifies the role of several parameters on the fire retardancy performance of the coating. Good agreement is obtained between predictions and measurements of the substrate temperature profiles.
Prediction of phase equilibria for binary mixtures by molecular modeling
Authors: Fermeglia Maurizio , Pricl Sabrina
Published: April 2004

Two new procedures based on quantum/COSMO calculations and on molecular mechanics/dynamics simulations, respectively, for estimating the PHSCT EOS parameters and to predict VLE behavior for binary mixtures are presented. The quality of the predictions achieved with both methods, in conjunction with the confined computational time aspects involved, can be considered satisfactory so that these strategies can be judged as promising routes toward an on‐line coupling between molecular and process simulation.
Internal annular wall jets: Radial flow in a stirred tank
Authors: Kresta Suzanne M. , Bittorf Kevin J. , Wilson David J.
Published: April 2004

Similarity solutions are derived for internal annular wall jets and compared with experimentally determined velocity profiles at the wall of a stirred tank with radial flow. The first similarity solution considers a geometry where the thickness of the wall jet is small relative to the diameter of the cylinder and the fluid flows relative to a free stream velocity of zero. In the second solution, the free stream velocity opposes the direction of the jet flow, as is observed in the recirculating flow in a stirred tank. The internal annular wall jet model agrees very well with the flow at the wall of a stirred tank agitated with a Rushton turbine. The free stream counter flow is driven by the wall jet, and a single velocity and length scale define the self‐similar velocity profiles for the flow in the jet and in the recirculating flow. Both the analytical model and experimentally observed expansion rates are linear and the maximum velocity in the jet decays as [U ∝ (z/T)−0.5], where (z/T) is the dimensionless streamwise distance. This decay can be contrasted with the faster decay [U ∝ (z/T)−1] observed in the 3‐D wall jets produced by axial impellers. These results provide a basis for validating computational fluid dynamic simulations in stirred tanks and for estimating the largest length scales of turbulence in the bulk of the tank.
Synthesis of ZnO particles in a quench‐cooled flame reactor
Authors: Hansen Jens P. , Jensen Joakim R. , Livbjerg Hans , Johannessen Tue
Published: April 2004

The quench cooling of a flame by injection of cold air was studied in a flame reactor for the formation of ZnO particles in a premixed flame with a precursor jet. A rapid temperature drop downstream from the temperature peak is advantageous for the attainment of a large specific surface area. Computational fluid dynamics simulations were used to design a quench ring with nozzles directed slightly upward and at a small tangential angle from the direct line to the center. This novel design avoids distortion of the flow pattern below the quenching plane and effectively cools the flame immediately above. At the highest tested production rate, the specific surface area of the ZnO particles increases from 20 to 60 m2/g when quenching is employed. The particles are characterized by BET surface area measurements, TEM images, and the size distributions of particle aggregates are measured by a scanning mobility particle sizer.
Influence of functional group on the electrification of organic pigments
Authors: Tanoue Ken‐ichiro , Morita Kenshi , Maruyama Hiroyuki , Masuda Hiroaki
Published: April 2004

Electrification of phthalocyaninatocopper derivative‐powders was investigated based on the measurement of contact potential difference (CPD) between the powder and reference gold electrode. The powder‐introduced halogen substituents in the end group show negative CPD values. The value of CPD increases negatively as the number of chlorine substituents increases, while the value increases negatively as the number of bromine substituents increases. Powders having hydrogens in the end groups are initially positively electrified and tend to their respective CPD values as time elapses, while powders fully substituted by halogens are negatively electrified. It is found that the charge decay data are well represented by a sum of two exponential functions. Charge‐decay speed depends greatly on the number of substituents. Molecular orbital calculation has showed that the measured contact potential difference changes linearly with the calculated Fermi level.
Numerical scale‐up study for orthokinetic agglomeration in stirred vessels
Authors: Hollander E. D. , Derksen J. J. , Portela L. M. , Van den Akker H. E. A.
Published: April 2004

Scale‐up of orthokinetic agglomeration in stirred‐tank reactors was studied numerically. A computer code based on the lattice‐Boltzmann method was used to perform large eddy simulations. To account for the dependence of agglomeration on hydrodynamics, the kinetic relation proposed by Mumtaz et al. was applied locally. The convection‐reaction equation governing the evolution of the particle‐number concentration was solved at the same resolution as the flow field. Three scale‐up rules were studied: scale‐up at constant Re‐number, constant specific power input, and constant impeller tip speed. Vessel sizes varying from 1 to 10,000 L were simulated. The use of two types of impellers (Rushton turbine and Pitched Blade turbine) allowed for investigating the dependence of agglomeration on the macroscopic flow pattern in a reactor. Inhomogeneities in stirred‐tank flow caused unpredictable scale‐up behavior. Scale‐up at constant power input yielded the most constant reactor performance. Impeller geometry had a drastic impact on the observed agglomeration rate, even if the difference in Po number was taken into account.
Advantages and risks in increasing cyclone separator length
Authors: Hoffmann A. C. , de Groot M. , Peng W. , Dries H. W. A. , Kater J.
Published: April 2004

The effect of cyclone length on separation efficiency and pressure drop has been investigated experimentally and theoretically by varying the length of the cylindrical segment of a cylinder‐on‐cone cyclone. Experimental results based on cyclone lengths from 2.65 to 6.15 cyclone diameters showed a marked improvement in cyclone performance with increasing length up to 5.5 cyclone diameters; beyond this length the separation efficiency was dramatically reduced. Experimental data agreed well with the predictions of a range of models and CFD simulations. This helps to assess the benefit of prolonging a given cyclone. The physical mechanisms behind the observed trends are elucidated. The dramatic fall in separation performance for the longest length was caused by the “natural turning” phenomenon.
Dynamics of molecular weight distributions for polymer scission
Authors: Mehta Khamir , Madras Giridhar
Published: April 2004

The dynamics of molecular weight distributions (MWDs) for polymer degradation is of interest to various applications. The time evolutions of MWDs can be determined by solving the governing population balance equations, which are generally solved by moment techniques wherein the initial distribution is represented by a gamma distribution. The evolution of MWD is determined by the time dependence of the gamma distribution parameters. The population balance equations (PBEs) can also be solved numerically by converting them to partial differential equations (PDEs). The degradation rate coefficient in the PBE depends on the molecular weight x as (x − xo)λ or as a quadratic polynomial in x. The solutions obtained with the moment technique, which are inaccurate for certain cases, are compared with the solutions determined by solving the PDEs. The utility of the numerical scheme is also discussed for cases where the initial distribution cannot be represented satisfactorily by a gamma distribution.
Removal of surface adhered particles by surfactants and fluid motions
Authors: Batra Ashish , Paria Santanu , Manohar C. , Khilar Kartic C.
Published: April 2004

Removing or detaching particles from a surface is of interest in filter bed regeneration, cleaning of semiconductor surfaces, migration of fines in underground reservoirs, and detergency. A two‐stage removal process proposed involves penetration of the surfactant solution, diffusion and adsorption of surfactant molecules, followed by the particle removal by hydrodynamic force. The particle‐substrate system, considered here as a plate‐plate system, takes into account the surface roughness of the substrate in the form of asperities. The concept of critical hydrodynamic force required to remove or detach a particle adhering to a substrate in the presence of surfactant solution is discussed, as well as its calculation of typical values. The critical hydrodynamic force depends on the surface roughness, particle size, and other parameters of the system. When asperity size is comparable to the equilibrium distance of separation, the critical hydrodynamic force becomes very large in magnitude, indicating that particle removal is very difficult. Higher critical hydrodynamic force is required for the removal of particles of small size.