bluuebunny/crossref_metadata_2025_split huggingface dataset:
Quantitative framework for reliable safety analysis
Authors: Huang Haitao , Adjiman Claire S. , Shah Nilay 
Published: April 2004

AbstractThe effectiveness of any methodology used to identify hazards in chemical processes affects both safety and economics. To achieve maximum safety at minimum cost, a conservative, but realistic, analysis must be carried out. An approach to hazard identification is proposed based on a detailed process model which includes nonlinear dynamics and uncertainty. A new modeling framework, the region‐transition model (RTM), is developed, which enables the simulation of regions of the operating space through an extension of the hybrid state transition system formalism. The RTM is illustrated on a nonlinear batch reactor with parameter uncertainty. A safety‐verification algorithm identifies regions of the input space (initial conditions and external inputs) which guarantee safe operation. The algorithm is successfully applied to three examples: a tank with overflow and underflow, a batch reactor with an exothermic reaction, and a CSTR with feed preheating.
Hydrogenation of 1,5,9‐cyclododecatriene in fixed‐bed reactors: Down‐ vs. upflow modes
Authors: Chaudhari R. V. , Jaganathan R. , Mathew S. P. , Julcour C. , Delmas H. 
Published: April 2004

AbstractPerformance of trickle‐bed and up‐flow reactors was studied experimentally and theoretically for an exothermic multistep hydrogenation of 1,5,9‐cyclododecatriene (CDT) in n‐decane as solvent over 0.5% Pd/alumina catalyst. Intrinsic kinetics was studied in a batch stirred slurry reactor using the powdered catalyst, and a Langmuir‐Hinshelwood‐type rate model is proposed. Using this rate equation, a trickle‐bed‐reactor model was developed that incorporates contributions of partial wetting and stagnant liquid holdup, in addition to the external and intraparticle mass transfer for the gas‐phase reactant (hydrogen). It was also modified to describe the behavior of the upflow reactor. Experimental data were obtained in both upflow (trickle‐bed) and down‐flow modes at different liquid velocities, pressures, and inlet feed concentrations at 373–413 K. Reactor performance of the two modes was compared in terms of global hydrogenation rate, CDT conversion, selectivity to cyclododecene and the maximum temperature rise observed in the catalyst bed. The conversions and global hydrogenation rate were significantly higher in a trickle‐bed reactor than in the upflow reactor. Similarly, a significant temperature rise in the catalyst bed was observed for the downflow operation compared to the upflow mode, which is explained from wetting characteristics of the catalyst bed. Model predictions for both reactors agreed well with experimental data.
Trickle‐bed reactor model for desulfurization and dearomatization of diesel
Authors: Chowdhury R. , Pedernera E. , Reimert R. 
Published: April 2004

AbstractDesulfurization and hydrogenation of aromatics in diesel oil were investigated in an isothermally operated trickle‐bed reactor 500 mm long and with a 19‐mm ID, using commercial bifunctional NiMo/Al2O3catalysts. The operating temperature, pressure, liquid hourly space velocity, gas/oil ratio, and the initial concentration of H2S were 300–380°C, 2–8 MPa, 1–4 h−1, 100–500 m3(NTP)/m3and 0–8 vol %, respectively. The increase in pressure and decrease in liquid hourly space velocity lead to deeper desulfurization and hydrogenation of both aromatics. Although a higher gas‐to‐oil ratio and lower initial concentration of H2S enhance the desulfurization reaction, these parameters play almost no role for hydrogenation. Desulfurization increases sharply with increased temperature, but with the same change in temperature the conversion of aromatics increases only up to 360°C, above which it falls sharply. This behavior is explained by the approaching of chemical equilibria by the reversible hydrogenation reactions of the aromatics at higher temperatures. A mechanistic mathematical model was developed for a two‐phase flow reactor, considering both mass transfer and chemical reaction in the reactor. The kinetic equations for desulfurization and for the hydrogenation of mono‐, di‐ and polyaromatics were established. Simulated results are compared satisfactorily with the experimental observations.
Degradation kinetics of polyethylene terephthalate in supercritical methanol
Authors: Goto Motonobu , Koyamoto Hiroshi , Kodama Akio , Hirose Tsutomu , Nagaoka Shoji , McCoy Benjamin J. 
Published: April 2004

AbstractDegradation of polyethylene terephthalate (PET) in supercritical methanol was investigated to develop a chemical recycling process for waste plastics. Continuous kinetics analysis was applied to the experimental data. A batch reactor was used at 573 K under the estimated pressure of 20 MPa for a reaction time of 2–120 min. PET decomposed to its monomers, dimethyl terephthalate (DMT), and ethylene glycol (EG), by methanolysis in supercritical methanol. PET with a weight‐average molecular weight of about 47,000 was converted to oligomer with that of 3,000 in 300 s and with that of 1,000 in 600 s. The largest yield of DMT was 80 mol % at 7,200 s and that of EG was 60 mol % at 3,600 s. Reaction products were analyzed with size exclusion chromatography, gas chromatography‐mass spectrometry, and reversed phase liquid chromatography. The molecular‐weight distribution (MWD) of the products was obtained as a function of reaction time. The yields of monomer components of the decomposition products, including byproducts, were measured. Continuous kinetics theory was developed to analyze the decomposition behavior. The theory includes MWD change of polymer by random and specific scissions and secondary reactions for monomer components. Change of MWD and monomers as a function of time was simulated by the continuous kinetics.
Solubility of CO2 in H2O+N‐methyldiethanolamine +(H2SO4 or Na2SO4)
Authors: Kamps Álvaro Pérez‐Salado , Rumpf Bernd , Maurer Gerd , Anoufrikov Yuri , Kuranov George , Smirnova Natalia A. 
Published: April 2004

AbstractThe solubility of carbon dioxide in aqueous solutions of methyldiethanolamine (MDEA) sulfate (1 m), in aqueous solutions of MDEA and MDEA sulfate (2 m and 1 m, respectively), and in aqueous solutions of MDEA and sodium sulfate (2 m and 1 m, respectively) was measured at 313 K to 413 K and total pressures up to 10.6 MPa. The experimental results were used to extend and test a model for the thermodynamic equilibrium encountered in the solubility of carbon dioxide in such aqueous solutions.
Atomistic SPH and a link between diffusion and interfacial tension
Authors: Nitsche Ludwig C. , Zhang Weidong 
Published: April 2004

AbstractThe mesh‐free method of smoothed particle hydrodynamics (SPH) is interpreted atomistically to treat the local density of nodes as representing solute concentration, instead of interpolating a concentration field between function values at the nodes. We exploit the conceptual simplicity of tracking little packets (representing supermolecular aggregates) of solute, as in Brownian dynamics simulations, but replace the stochastic generation of diffusive spreading over statistically independent realizations with a purely deterministic summation for extracting the local diffusion velocity using only the instantaneous locations of nearby nodes. Four test problems demonstrate the versatility and accuracy of the atomistic SPH method (ASPH) for mass transfer. Finally, by comparing ASPH with a new Stokeslet‐swarm technique for simulating drop flows (Nitsche and Schaflinger, 2001), a fundamental analogy between diffusion and interfacial tension is exposed.
Experimental study of dynamic wetting in reverse‐roll coating
Authors: Benkreira H. 
Published: April 2004

AbstractThe movement of the dynamic wetting line in reverse‐roll coating was followed in a series of experiments that gave position, XD, angle, θD and the critical metering roller speed, VM, cascade, for the onset of cascade. The data were correlated with operating conditions and compared with plunging‐tape air‐entrainment speeds, V*plunging. It was found that there was hydrodynamic assistance of wetting similar in form but smaller in magnitude to that reported in curtain coating. The correlated data for XD and θD also provide boundary conditions, which can replace the assumptions usually made in the simulations of reverse‐roll coating flows.
Protein nanoparticles formation by supercritical antisolvent with enhanced mass transfer
Authors: Chattopadhyay Pratibhash , Gupta Ram B. 
Published: April 2004

AbstractIn recent years, the supercritical antisolvent (SAS) precipitation technique has emerged as a promising method for the formation of fine particles. Despite its numerous advantages, this technique still cannot be used to produce particles in the sub‐micron range (<300 nm) for many “soft” materials. A significantly improved SAS process can produce particles of controllable size, up to an order of magnitude smaller than those of the conventional SAS process, with a narrower size distribution. Like the conventional SAS technique, this new supercritical antisolvent with enhanced mass transfer technique utilizes supercritical carbon dioxide as the antisolvent, but the solution jet is deflected by a surface vibrating at an ultrasonic frequency atomizing the jet into much smaller droplets. Furthermore, the ultrasound field generated by the vibrating surface enhances mass transfer and prevents agglomeration through increased mixing. The particle size is controlled by varying the vibration intensity of the deflecting surface, which then can be adjusted by changing the power supplied to the attached ultrasound transducer. It is demonstrated by the formation of lysozyme nanoparticles and microparticles. The biological activity of the protein is retained during the processing.
Analytical resolution of a cyclic two‐way chromatographic binary system
Authors: Castel C. , Sardin M. , Simonnot M. O. 
Published: April 2004

AbstractThe focus is on analytical resolution of the mass‐balance relation in the case of a binary ion‐exchange system containing chloride and hydrocarbonate anions involved in a two‐way chromatographic cyclic process under critical operating conditions, that is, feed and elution solutions with the same total normality and percolation volumes. Local equilibrium theory is used to demonstrate the convergence of the system toward a periodic state and to calculate iteratively the instantaneous and asymptotic concentration profiles inside the separation column. One of the main results is that the calculated chloride composition on the inlet side of the column after the elution step is equal to the chloride composition in the feed solution.
Pd membranes formed by electroless plating with osmosis: H2 permeation studies
Authors: Souleimanova Razima S. , Mukasyan Alexander S. , Varma Arvind 
Published: April 2004

AbstractThe synthesis of fully dense Pd‐Vycor glass composite membranes by electroless plating with or without osmosis is reported. Use of osmotic flux allows one to rapidly form thin (a few microns), fully dense palladium films, which have submicron size microstructure. These features significantly enhance hydrogen permeability as compared to the conventional method. By accounting for resistance of the porous support, it is confirmed that for membranes prepared by the same technique, with gradually changing microstructural characteristics, those with smaller palladium crystallites exhibit larger hydrogen flux. Pd‐stainless steel composite membranes were also prepared using electroless plating, either with or without osmosis. Membranes synthesized using osmosis exhibit superior thermal stability.
ZSM‐11 membranes: Characterization and pervaporation performance
Authors: Li Shiguang , Tuan Vu A. , Noble Richard D. , Falconer John L. 
Published: April 2004

AbstractHigh‐quality boron and aluminium‐substituted ZSM‐11 membranes were prepared on porous tubular supports to separate alcohols from water by pervaporation. The C1–C3 alcohols were preferentially separated from aqueous solutions through the B‐ZSM‐11 membrane, and the maximum flux was 1.7 kg/m2·h for a 5 wt.% methanol/water mixture. The alcohol fluxes decreased as the carbon number increased. The methanol/water separation selectivity decreased with pervaporation temperature, but other alcohol/water selectivities increased. All selectivities increased with decreasing alcohol feed concentration. In a range of 1 to 50 wt. % alcohol, the separation selectivities at 333 K for the C1–C3 linear alcohols were higher than vapor/liquid equilibrium selectivities. The highest selectivities observed for methanol/water, ethanol/water, 1‐propanol/water, and 2‐propanol/water were 28, 97, 34, and 26, respectively, at 1 wt. % alcohol feed concentrations. The separation selectivities were based on both preferential adsorption of alcohols and differences in diffusion rates.
Optimal temperature control of a steady‐state exothermic plug‐flow reactor
Authors: Smets Ilse Y. , Dochain Denis , Van Impe Jan F. 
Published: April 2004

AbstractOptimal heat exchanger temperature profiles of exothermic tubular reactors were determined under the assumption of steady‐state and plug‐flow characteristics. The minimum principle of Pontryagin (optimal control theory) was applied in a straightforward analytical sense. To enable a trade‐off between process performance and heat loss, a combined cost criterion was defined. In the first approach of specifying only terminal costs, the optimal control input was of the bang‐bang type that keeps the heat exchanger temperature constant at its maximum or minimum value. Afterwards, the terminal cost criterion was extended with an integral part that accounts for the global heat loss during the process. This integral cost part induced a control of the bang‐singular‐bang type. The desired performance can be met by selecting appropriate weights for terminal and integral costs.
Optimal parameter estimation for the online control of ion milling etch depth
Authors: Klein Eric J. , Ramirez W. Fred 
Published: April 2004

AbstractThe use of optimal parameter estimation for the online regulation of final etch depth in an ion milling process is described. A model‐based control system utilizes a 3‐D surface evolution model to predict dynamic surface profiles and etch depth. A heterodyne laser interferometer is used to measure trench height in situ for calculation of the difference in etch rates between the photoresist layer and the exposed portion of the underlying substrate layer. Adaptive material‐specific etch rate parameters and operating parameters such as ion beam strength and angle of incidence are estimated optimally with an extended Kalman filter. Optimal estimates of the in situ etch depth are calculated from the adaptive model, allowing the stopping time of the milling process to be varied from run to run to regulate final etch depth in the presence of disturbances. The system installed on an ion milling machine shows that the controller is capable of accurately regulating final etch depth in the presence of large process faults.
Phase‐equilibria calculation by group‐contribution perturbed‐hard‐sphere‐chain equation of state
Authors: Elvassore Nicola , Bertucco Alberto , Fermeglia Maurizio 
Published: April 2004

AbstractA group‐contribution (GC) method was coupled with the perturbed‐hard‐sphere‐chain (PHSC) equation of state (EOS) to predict its characteristic parameters. This model can describe both equilibrium and volumetric properties of regular fluids and chain‐like molecules. The estimation of group contributions for the characteristic volume, surface area, and interaction energy was based only on vapor‐pressure and saturated liquid‐density values of low‐molecular‐weight compounds. It was successful in estimating the EOS parameters of high‐molecular‐weight compounds and chain‐like molecules. Some application results show its reliability but the method was not applied to all classes of compounds. Good estimation of polymer density was obtained by GC PHSC with only the knowledge of their molecular structure. For mixtures, the original model was retained; binary interaction parameters were regressed from vapor–liquid equilibria of binary systems. In most cases, only one binary interaction parameter is enough to describe binary systems in a wide range of temperatures. The same model is extended to the calculation of liquid–liquid equilibria of a system exhibiting both upper critical solution temperature (UCST) and lower critical solution temperature (LCST). In summary, the data required for calculating multicomponent phase equilibria are the molecular structure in term of functional groups and binary interaction parameter values.
Methane hydrate equilibria in silica gels with broad pore‐size distributions
Authors: Smith Duane H. , Wilder Joseph W. , Seshadri Kal 
Published: April 2004

AbstractEquilibrium pressures for the dissociation of methane hydrates confined in silica gel pores of nominal radii 7.5, 5.0 and 3.0 nm were measured over a wide temperature range, and were observed to be higher than those for bulk methane hydrate. A model is presented that allows the pore radius involved in each equilibrium to be determined from these data, so that the model exactly reproduces the experimental equilibrium pressure. Based on this model, pore volume distributions were reconstructed and found to be in good agreement with those obtained from nitrogen desorption isotherms, indicating that hydrate formed nearly uniformly in the available pores.
Modeling blowdown of cylindrical vessels under fire attack
Authors: Mahgerefteh Haroun , Falope Gboyega B. O. , Oke Adeyemi O. 
Published: April 2004

AbstractA robust numerical simulation is presented for predicting the risk of rupture during emergency depressurization or blowdown of cylindrical vessels containing high‐pressure two‐phase hydrocarbon mixtures under fire attack. Accounting for nonequilibrium effects between the constituent fluid phases, the model simulates the triaxial transient thermal and pressure stress profiles generated in both the wetted and unwetted wall sections of the vessel. A comparison of this information with the vessel material of construction temperature/yield stress data allows the precise evaluation of the risk of failure and, if applicable, the rupture mode during depressurization. Finally, based on the application of the model to a real system, the subtle differences between the failure risks associated with blowdown under fire as compared to those under ambient conditions are presented and discussed in detail.
Simulation of free‐surface flows induced by partially immersed moving body: Validation
Authors: Jongen T. , Chouikhi S. M. 
Published: April 2004

AbstractPredictive performance of a free‐surface simulation technique is assessed using the volume‐of‐fluid (VoF) method, in the context of a challenging, yet simple and well‐defined, unsteady‐flow configuration mimicking the in‐mouth kinematic processes occurring during the consumption of liquid foods. An experimental “mouth‐analog” setup consisting of a cavity initially filled with a liquid and agitated by a ram moving periodically was modeled and simulated. Experimental and computational results are compared for a range of liquid viscosities (silicon oil and water) and over a range of processing conditions (low‐ and high‐agitation frequency) that trigger important effects such as surface reconnection and breakup, wall coating, filament formation, and air inclusion. Even with the large mesh and time‐step sizes used in the computations, the main relevant bulk kinematics of this complex transient free‐surface flow can be represented with a Euler volume‐tracking method such as the VoF method.
Experimental analysis of hydrodynamics in axially agitated tank
Authors: Bugay Stephan , Escudié Renaud , Liné Alain 
Published: April 2004

AbstractParticle image velocimetry (PIV) technique was used to analyze the flow field in a stirred tank induced by a Lightnin A310 axial impeller, focusing on the hydrodynamics, with particular attention to turbulence [production, transport, and dissipation rate of turbulent kinetic energy (TKE)]. The first data of interest are the three components of the mean velocity, which give the overall circulation in the tank. Since turbulence controls mainly the mixing, the six components of the Reynolds stresses were measured. The dissipation rate of TKE was estimated after an experimental evaluation of the different terms of the TKE balance equation at different levels in the tank. A profile close to the impeller is compared to previous empirical modeling where the dissipation rate of TKE was related to the level of TKE and to a macroscale of turbulence that was assumed to be proportional to the impeller.
Screening of cosolvents for a supercritical fluid: A fully predictive approach
Authors: Abaroudi K. , Trabelsi F. , Recasens F. 
Published: April 2004

AbstractSolubility of solids was modeled in modified supercritical carbon dioxide as a predictive method. The Peng‐Robinson equation of state was used to characterize the ternary systems using the one‐fluid van der Waals rules. Ternary mixture parameters k12, k23, and k13 were obtained from the binary mixtures using Wong‐Sandler mixing rules or the linear combination of Vidal‐Michelsen mixing rules together with UNIFAC as required as a fully predictive tool for the liquid activity coefficients. When this method was applied to predict the solubility of β‐naphthol in CO2 modified with 6% and 10% toluene, values for the predicted solubility were very similar to the measured ones, with deviations of 9.6 and 26.3%, respectively. However, when the method was applied to the data of Simon et al. who examined six common cosolvents, the results were not as good in absolute terms, but the solvents were sorted in about the same order as found experimentally. The method provides quite an approximate guide to judge the most effective cosolvent from several candidates using a fully predictive methodology.
Distributed stream method for tray optimization
Authors: Lang Y‐D , Biegler L. T. 
Published: April 2004

AbstractDetermining the optimum number of trays in a distillation column has been an important process optimization problem for over 50 years, which over the past decade has been addressed successfully as a mixed‐integer nonlinear‐programming (MINLP) problem. But tools for solving MINLPs are not widespread, especially in connection with detailed simulation models. In a differentiable distribution function (DDF), all streams around a column, except top and bottom products, are directed to all of the column trays and the distributed flow rate of entry or exit streams is directed to a specific tray based on the value of its DDF at that tray. It allows the placement of feeds, sidestreams, and number of trays in the column to be continuous variables in the DDF, and in the optimization problem it eliminates the need for integer variables. Instead, the tray optimization problem is formulated as an NLP using the original MESH model. It is critical to deal with trays that have no liquid or vapor flows. To describe this phenomenon properly in the optimization, complementary constraints are formulated and added to the NLP, by taking advantage of a smoothing algorithm developed by Gopal and Biegler for phase equilibrium. Also, since pressure in each tray affects distillation calculations substantially, the pressure drops across each tray depend on the optimal number of trays and a related smoothing function formulation removes the pressure drop on dry trays. Pressure in the condenser or reboiler is then adjusted accordingly. The results of the methods applied to three distillation problems show significant cost reductions in distillation design.