bluuebunny/crossref_metadata_2025_split huggingface dataset:
Effect of mass transfer and catalyst layer thickness on photocatalytic reaction
Authors: Chen Dingwang , Li Fengmei , Ray Ajay K. 
Published: April 2004

AbstractSemiconductor photocatalytic processes have been studied for nearly 20 years due to their intriguing advantages in environmental remediation. A rational approach in determining the effect of mass transfer and catalyst layer thickness during photocatalytic reactions is proposed. The reaction occurs at the liquid–catalyst interface, and therefore when the catalyst is immobilized, both external and internal mass transfer plays significant roles in overall photocatalytic processes. Several model parameters—external mass‐transfer coefficient, dynamic adsorption equilibrium constant, adsorption rate constant, internal mass‐transfer coefficient, and effective diffusivity—were determined either experimentally or by fitting realistic models to experimental results using benzoic acid as a model component. Even though all these parameters are critical to the design and development of photocatalytic processes, they are not available in the literature. The effect of the internal mass transfer on the photocatalytic degradation rate over different catalyst layer thicknesses under two different operating configurations was analyzed theoretically and experimentally verified. It was observed that an optimal catalyst layer thickness exists for substrate‐to‐catalyst illumination.
Multiobjective optimization of an industrial wiped‐film pet reactor
Authors: Bhaskar V. , Gupta Santosh K. , Ray Ajay K. 
Published: April 2004

AbstractMultiobjective optimization of a third‐stage, wiped‐film polyester reactor was carried out using a model that describes an industrial poly(ethylene terephthalate) reactor quite well. The two objective functions minimized are the the acid and vinyl end group concentrations in the product. These are two of the undesirable side products produced in the reactor. The optimization problem incorporates an endpoint constraint to produce a polymer with a desired value of the degree of polymerization. In addition, the concentration of the di‐ethylene glycol end group in the product is constrained to lie within a certain range of values. Adaptations of the nondominated sorting genetic algorithm have been developed to obtain optimal values of the five decision variables: reactor pressure, temperature, catalyst concentration, residence time of the polymer inside the reactor, and the speed of the agitator. The optimal solution was a unique point (no Pareto set obtained). Problems of multiplicity and premature convergence were encountered. A “smoothening” procedure is suggested to generate near‐optimal operating conditions. The optimal solution corresponds simultaneously to minimum values of the residence time of the polymeric reaction mass in the reactor.
Formation and aging of incipient thin film wax‐oil gels
Authors: Singh Probjot , Venkatesan Ramachandran , Fogler H. Scott , Nagarajan Nagi 
Published: April 2004

AbstractA fundamental study of the deposition and aging of a thin incipient wax‐oil gel that is formed during the flow of waxy oils in cooled pipes was performed. The solubility of high molecular weight paraffins in naphthenic, aromatic or paraffinic solvents is very low and decreases rapidly with decreasing temperature. This property of the paraffins leads to the formation of gels of complex morphology that deposit on the cold walls of the subsea pipelines during the flow of waxy crudes. This deposition reduces the pipe diameter and decreases the flow capacity of the pipe. These wax‐oil gels contain a large fraction of oil trapped in a 3‐D network structure of the wax crystals that behaves as a porous medium. After the incipient gel is formed, wax molecules continue to diffuse into this structure, thereby increasing its wax content. A model system of wax and oil mixture was used to understand the aging process of the wax‐oil gels, which hardens the wax deposit with time. To understand the physics of the aging process for incipient thin‐film deposits, a series of laboratory flow loop experiments was performed. The aging process was a counterdiffusion phenomenon with a critical carbon number above which wax molecules diffuse into the gel deposit and below which oil molecules diffuse out of the deposit. The aging rate of the gel deposit depends on the oil flow rate and the wall temperature. A mathematical model developed predicted the growth and wax content of the gel deposit on externally cooled pipe walls. The theory agreed with experiments excellently for thin gels.
Novel method for preparing palladium membranes by photocatalytic deposition
Authors: Wu Li‐Qun , Xu Nanping , Shi Jun 
Published: April 2004

AbstractAn ultrathin palladium film on a porous TiO2ceramic membrane was successfully synthesized by a novel photocatalytic deposition (PCD) method. The mechanism was interpreted by the photocatalytic reaction between the surface of the TiO2semiconductor and the Pd(II) solution. Energy dispersive (EDS) analysis and argon permeability of the membrane were used to characterize the deposited Pd. During the PCD process, photoreaction took place with higher efficiency when the pH value of the solution was controlled at the 3—3.5 range. A short irradiation time of 18 min was enough for PCD at a normal reaction temperature. A methanol additive in the solution of about 40 vol. % was optimum for the deposition of Pd. XRD and SEM results on the Pd‐based membrane prepared by PCD indicated that the metal existed in the form of a pure palladium element, with a layer thickness of about 0.1 μm. The gas permeation experiment was conducted in a high‐temperature permeator from 623 to 723 K. The results indicated that there were contributions to the hydrogen flux attributable to both dense and microholes parts of the resulting Pd/TiO2membrane.
Multicomponent space‐charge transport model for ion‐exchange membranes
Authors: Yang Yahan , Pintauro Peter N. 
Published: April 2004

AbstractA multicomponent space‐charge transport model for ion‐exchange membranes was developed, where the membrane structure was modeled as an array of cylindrical pores with a uniform distribution of fixed‐charge sites on the pore walls. Ion/fixed‐charge site electrostatic interactions, electric‐field‐induced water dipole orientation, ion‐hydration free‐energy changes during ion partitioning, and concentration‐dependent transport parameters were considered in the analysis. The model predicted experimental concentration vs. time data accurately for Donnan dialysis separations with a DuPont Nafion 117 cation‐exchange membrane, where the membrane separated a dilute H2SO4 solution from an aqueous mixture of either Cs2SO4 + Li2SO4 or Cs2SO4 + Na2SO4. Both computer predictions and experimental measurements showed that the alkali metal cation with the larger hard‐sphere radius (lower surface charge density) was selectively absorbed in and transported across the membrane during a multicomponent separation. The cation/cation transport permselectivity was less than the selectivity for equilibrium uptake due to slow ion transport near the pore wall, where discrimination between like‐charge cations was greatest.
Boron‐substituted ZSM‐5 membranes: Preparation and separation performance
Authors: Tuan Vu A. , Noble Richard D. , Falconer John L. 
Published: April 2004

AbstractZSM‐5 zeolite membranes with boron substituted into the framework for silicon were prepared on porous stainless‐steel and α‐alumina tubular supports. These membranes had higher n‐C4H10/i‐C4H10 separation selectivities, and effectively separated these isomer mixtures to higher temperatures than membranes with aluminum substituted into the framework. Membranes were prepared with Si/B ratios as low as 12, and the best membranes were prepared from alkali‐free gels. The highest n‐C4H10/i‐C4H10 permselectivity at 473 K was 60, and the highest at 527 K was 24. For most alkali‐free membranes, the n‐C4H10/i‐C4H10 permselectivities and separation selectivities increased with boron content, and membranes on α‐alumina supports had both higher permeances and separation selectivities. Membranes with the same permeances and selectivities can be reproducibly prepared, and they are stable at elevated temperatures.
Graphical methods for reaction distribution in a reactive distillation column
Authors: Lee Jae W. , Hauan Steinar , Westerberg Arthur W. 
Published: April 2004

AbstractVisual methods of determining how to distribute reaction zones within a binary reactive distillation column were studied using both the Ponchon–Savarit and McCabe–Thiele methods modified to account for the reaction. Two types of reactions are compatible with a totally binary system: isomerization and dimerization. For isomerization with a heavy reactant and a light product, both diagrams indicate the potential for a pinch point if the reaction zone is in the stripping section and no such potential if the zone is in the rectifying section. These same diagrams show that the column will have fewer stages and less usage of utility to yield the same final top and bottom products with the reaction in the rectifying section. The situation reverses if the reactant is the light species for isomerization, suggesting reaction should then take place in the stripping section. The heat effect from the isomerization reaction is considered for four cases depending on whether the reaction is endothermic or exothermic. Even if the heat of the isomerization is dominant, the results do not change: with a heavy reactant and a light product, the separation performance is better when the reaction takes place in the rectifying section. In the dimerization reaction, where two light reactants form a heavy product, the light reactant enriches as we go down the column and the composition profile is reversed in a Ponchon–Savarit diagram with the reaction in the rectifying section even if there is no pinch point. Results on the location of reaction zones are confirmed by rigorous simulations.
Modeling crystal shapes of organic materials grown from solution
Authors: Winn Daniel , Doherty Michael F. 
Published: April 2004

AbstractThe shape of a crystalline organic solid has a major impact on its downstream processing and on its end‐product quality, issues that are becoming increasingly important in the specialty and fine chemical, as well as the pharmaceutical and life science, industries. Though it is widely known that improved crystal shapes can be achieved by varying the conditions of crystallization (such as solvent type and impurity levels), there is far less understanding of how to effect such a change. Until recently, most methods for predicting crystal shapes were based exclusively on the internal crystal structure, and hence could not account for solvent or impurity effects. New approaches, however, offer the possibility of accurately predicting the effects of solvents. Models for predicting crystal shape are reviewed, as well as their utility for process and product design.
Particle‐size analysis in mass crystallization from solutions
Authors: Zelmanov G. , Semiat R. 
Published: April 2004

AbstractThe problem of product‐size distribution exiting a crystallizer is addressed theoretically and experimentally. The distribution function of the particle size is solved and demonstrated experimentally as a function of fines destruction, solids content of feed, particle circulation ratio, feed particle sizes, particle concentration. Theoretical tools are given for estimation of various important parameters such as distribution moments, rate of growth, rate of nuclei production and particle‐size distribution. A good agreement is shown between the theoretical model and the experimental results.
Establishing independence of continuous process product samples
Authors: Christiansen Reed L. 
Published: April 2004

AbstractNew product qualification frequently requires that a manufacturer provide customers with several independent samples for evaluation. For continuous manufacturing processes, equipment residence time distributions (RTDs) introduce serial dependence among the samples. Determining RTD by pulse or step modulation of a tracer or process variable can produce off‐spec material and add costs by limiting the opportunity to conduct other product or process development experiments. A novel method of determining a continuous process' RTD does not risk production of off‐spec material. Through analysis of serial component analytical data, the process' washout curve can be inferred. The theoretical basis for the method is presented and experimental requirements enumerated. Applicability to well‐mixed, laminar flow and convective‐dispersive processes is demonstrated. Experimental validation in a specialty polymer pilot plant resulted in an error of about 5% in mean residence time, when compared to estimates from pulse tests and calibrated level measurements.
Wall effects of laminar hydrogen flames over platinum and inert surfaces
Authors: Andrae Johan C. G. , Björnbom Pehr H. 
Published: April 2004

AbstractDifferent aspects of wall effects in the combustion of lean, laminar and stationary hydrogen flames in an axisymmetric boundary‐layer flow were studied using numerical simulations with the program CRESLAF. The importance of the chemical wall effects compared to thermal wall effects caused by heat transfer to a cold wall was investigated in the reaction zone by using different combustion systems at atmospheric pressure. Surface mechanisms include a catalytic surface, an inert surface that promotes radical recombinations, and a completely inert wall used as reference was the simplest possible boundary condition. The analysis of the results show that for the richer combustion case (ϕ = 0.5) the surface chemistry gives significant wall effects, while the thermal and velocity boundary layer gives rather small effects. But for the leaner combustion case (ϕ = 0.1) the thermal and velocity boundary layer gives more significant wall effects, while surface chemistry gives less significant wall effects compared to the other case. As expected, the overall wall effects were more pronounced for the leaner combustion case.
Vapor–liquid equilibrium of aqueous solutions of formaldehyde and methanol
Authors: Albert Michael , Coto García Baudilio , Kuhnert Christian , Peschla Roger , Maurer Gerd 
Published: April 2004

AbstractA thermodynamic model for phase and chemical equilibrium in formaldehyde–water mixtures was extended to describe vapor–liquid and chemical equilibrium in the binary formaldehyde–methanol system and in the ternary formaldehyde–water–methanol system. Ternary mixtures were extended using new experimental vapor–liquid equilibrium data for the influence of especially small amounts of methanol on the volatility (of small amounts) of formaldehyde in aqueous solutions. New experimental data for the range 333 to 383 K are reported. Some model parameters were fitted to ternary phase equilibrium data, because of cross‐reactions between poly(oxymethylene) glycols and poly(oxymethylene) hemiformals, and strong influence of interactions between those species on the phase equilibrium of the ternary mixture. The new model presents a reliable method for calculating vapor–liquid equilibrium and the conversion of formaldehyde to reaction products [poly(oxymethylene) glycols and poly(oxymethylene) hemiformals] over the whole range of temperature and composition where reliable experimental data are available.
Fluid dynamics in coal liquefaction reactors using neutron absorption tracer technique
Authors: Sakai Naohide , Onozaki Masaki , Saegusa Hitoshi , Ishibashi Hirohito , Hayashi Takashi , Kobayashi Masatoshi , Tachikawa Noboru , Ishikawa Isamu , Morooka Shigeharu 
Published: April 2004

AbstractHydrodynamic properties in the coal liquefaction reactors at the Kashima pilot plant, which was constructed based on the NEDOL process, were investigated using the neutron absorption tracer technique. The reactor system is composed of three vessels, each with 1.0 m ID and 11.8 m in height. The gas velocity in the reactors under coal liquefaction conditions was estimated using a reaction simulator that contained reaction rates and vapor–liquid equilibrium. The axial dispersion coefficients in the first and third reactors at superficial gas velocities of 0.06–0.07 m/s were much smaller than those reported for air–water systems under ambient conditions. This suggests that the pilot‐plant reactors operated fundamentally in the homogeneous bubble flow regime.
Direct simulation Monte Carlo method for particle coagulation and aggregation
Authors: Kruis F. Einar , Maisels Arkadi , Fissan Heinz 
Published: April 2004

AbstractA Monte Carlo simulation technique developed describes dispersed‐phase systems with emphasis on coagulation and aggregation. The method does not use particle trajectories, but is based on the transformation of known collision frequencies into collision probabilities of particle pairs. The particle evolution was computed as a stochastic game, computing the time step after each collision. The simulations were validated by comparing with exact mathematical solutions for aggregation of solid particles and with numerical solutions based on sectional methods for coagulation of droplets. The direct simulation Monte Carlo (DSMC) method is advantageous, because the simulation of complex, multidimensional systems results in very elaborate models when using sectional models and is implemented very easily. Two examples of industrial importance are chemical reaction in coagulating droplets and coating of particles with small solid particles.
Use IAST with MPSD to predict binary adsorption kinetics on activated carbon
Authors: Qiao Shizhang , Hu Xijun 
Published: April 2004

AbstractA model using the ideal adsorbed solution theory (IAST) coupled with the micropore‐size distribution (MPSD) concept is proposed to describe the multicomponent adsorption equilibrium and kinetics of gases in activated carbon. To overcome the thermodynamic violation, the IAST instead of the extended Langmuir equation was used to calculate the local multicomponent adsorption equilibrium. The micropore size is related to the adsorbate–adsorbent interaction energy by the Lennard‐Jones potential. The overall adsorption isotherm and the diffusion flux of the adsorbed species are the integrals of their corresponding local values over all micropore‐size distribution range accessible by the adsorbate molecules. The size exclusion effect was taken into account in the competition of different sized molecules for a given pore. The model predictions were tested with the adsorption kinetics data of binary gases on Ajax and Norit activated carbon. The results were better than predictions of a previous multicomponent adsorption kinetics model also using the MPSD concept, but with the local multicomponent adsorption isotherm described by the extended Langmuir equation.
Kinetics for the partial oxidation of methane on a Pt gauze at low conversions
Authors: de Smet Carlo R. H. , de Croon Mart H. J. M. , Berger Rob J. , Marin Guy B. , Schouten Jaap C. 
Published: April 2004

AbstractIntrinsic kinetics of the catalytic partial oxidation of methane were studied at atmospheric pressure in the presence of transport limitations using a single Pt gauze. Catalyst temperature and gas‐phase temperatures were measured directly. CO, CO2, and H2O were the main products at catalyst temperatures between 1,030 and 1,200 K, residence times of 0.02 to 0.2 ms, CH4/O2 ratios between 1.8 and 5.0, and O2 conversions between 9 and 46%. A kinetic model was developed that consists of six reaction steps. Methane adsorption had to be considered as oxygen‐assisted to describe the experimental data, in particular the decrease of the selectivity for CO with increasing space times. Corresponding intrinsic kinetic parameters were obtained from the literature and from regression of the experimental CO selectivities. The calculated conversions and selectivities were obtained using the intrinsic kinetic model, together with a reactor model accounting for no transport limitations quantitatively without any adjustable parameter. Simulations indicate initial CO selectivities between 86 and 96% over the investigated range of conditions, and illustrate the relevance of both surface kinetics and mass transport in CO formation.
Multicomponent hydrogen/hydrocarbon separation by MFI‐type zeolite membranes
Authors: Dong Junhang , Lin Y. S. , Liu Wei 
Published: April 2004

AbstractSeparation of an eight‐component simulated refinery gas mixture including hydrogen (∼84 mol %) and light hydrocarbons (C1–C4, 7.5∼0.3 mol %) by α‐alumina‐supported polycrystalline MFI zeolite membranes was studied at 25–500°C and feed pressures of 0.1–0.4 MPa. The zeolite membrane showed excellent separation properties for rejection of hydrogen from the hydrogen/hydrocarbon mixture at <100°C. At room temperature and atmospheric pressure on both feed and permeate sides, hydrogen permeation rate is almost zero, while the hydrocarbon permeation rate is 2–4×10−4 mol·m−2·s−1. The zeolite membrane outperforms the microporous carbon membrane in terms of both selectivity and permeance for hydrocarbons over hydrogen. At 500°C the zeolite membrane becomes permselective for hydrogen over hydrogen (C1–C4). In the whole temperature range iso‐butane is nonpermeable (with a permeance below the GC analysis limit) through the zeolite membrane. Separation results of the zeolite membrane can be characterized by a solution‐diffusion model considering competitive adsorption of hydrocarbons over hydrogen and configurational diffusion in the zeolite pores. The MFI‐type zeolite membranes showed promise for applications in separation processes for hydrogen concentration/purification from various hydrogen/hydrocarbon mixtures (at lower temperatures) and in membrane reactors for dehydrogenation reactions (at high temperatures).
Characterization of batch mixers using numerical flow simulations
Authors: Jongen T. 
Published: April 2004

AbstractThe objective of this work is to characterize various deformations to which viscous pastes are subjected during their batch mixing and to investigate the influence of mixer configurations and operating conditions. For this, several mixer geometries were modeled in a way representative of the mixing mechanisms taking place. The twin‐blade arrangement, which is typical in batch mixing, was used in this study, as well as planetary mixers. The equations governing the deformation of the fluid were solved in the various mixer geometries, using numerical solution techniques (finite‐element discretization on a fixed mesh, with a fictitious domain method accounting for the internally moving blades). Based on the time‐dependence velocity fields obtained, the type of deformation taking place in various mixers was characterized using relevant kinematic flow classification parameters. These parameters were then related to the mechanical action of the mixer.