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Stress distributions on bases of granular piles were predicted based on the constitutive relations obtained by the discrete element method (DEM) using the smoothed particle hydrodynamics to elucidate the mechanism of the central stress minimum beneath piles. The calculated stress distributions are in good agreement with the experimental data of many researchers. A stress peak and a central stress minimum are mainly formed by the granular flows in a pile construction. The location of the stress peak was the same location of the minimum granular velocity before the granular pile became stationary. This suggests that the location of the stress peak corresponds to the base of the granular arching. The stresses distributions on the bases by a homogeneous falling showed the central stress maximum. The low shear stress gradient by the homogeneous falling produces a central stress peak with a gentle slope. © 2016 American Institute of Chemical Engineers AIChE J, 62: 1417–1429, 2016

Removal of Hg0 using two homogeneous Photo-Fenton-Like reactions was first investigated in a photochemical reactor. Effects of process parameters on Hg0 removal were studied. Free radical and reaction products were analyzed. Removal pathways of Hg0 were discussed. Simultaneous removal of Hg0, NO, and SO2 is also studied briefly. The results show that UV power, wavelength, H2O2 concentration, and solution pH have great effects on Hg0 removal. Hg0, and SO2 concentrations, solution temperature, Fe3+, Cu2+, CO32−, and HCO3− concentrations also have significant effects on Hg0 removal. However, concentrations of CO2, NO, O2, Cl−, NO3−, SO42−, SiO2, Al2O3, and Fe2O3 only have slight effects on Hg0 removal. Hg0/NO/SO2 can be simultaneously removed by Photo-Fenton-Like reactions. ·OH was captured, and SO42−/ NO3−/Hg2+ were also detected. Removals of Hg0 by photochemical oxidation and ·OH oxidation play a major role, and removal of Hg0 by H2O2 oxidation only plays a secondary role in removal of Hg0. © 2015 American Institute of Chemical Engineers AIChE J, 61: 1322–1333, 2015

Significance A new generation of double dielectric barrier discharge (DDBD) reactor featured by a metal powder (MP) high voltage electrode is presented. The MP high voltage electrode not only has excellent homogeneous discharge performance but also has the advantage of without regular maintenance. Therefore, the MP-DDBD reactor was proved to be suitable for the uninterrupted and safe synthesis of high purity H2O2 aqueous solution with up to 65 wt % concentration from the H2/O2 mixture. The scale-up synthesis of H2O2 was successfully attempted in an integrated device based on the MP-DDBD reactor. The future practical H2O2 synthesizer based on the MP-DDBD reactor will be small and movable, and therefore, be convenient to supply high purity H2O2 on site for small scale users like semiconductor industry. © 2013 American Institute of Chemical Engineers AIChE J 60: 415–419, 2014

A meso oscillatory flow reactor (OFR) was successfully applied for the precipitation of hydroxyapatite (HAp) nanoparticles. Mixing efficiency of the mesoreactor operated batchwise in a vertical tube was evaluated at constant power density, by monitoring variation of hue values upon mixing both spatially and temporally. The best operating conditions for fast mixing and a more homogeneous reaction medium were verified for f = 0.83 Hz and x0 = 4.5 mm. HAp precipitation was then carried out under these conditions at 37 °C for different mixing Ca/P molar ratios. HAp nanoparticles with a mean size (d50) of about 67 nm and a narrow size distribution were obtained. Furthermore, the obtained results show the advantages of the meso-OFR over a stirred tank batch reactor due to the production, about four times faster, of smaller and more uniform HAp nanoparticles. © 2013 American Institute of Chemical Engineers AIChE J, 2013, This work was supported by the Portuguese Foundation for Science and Technology (SFRH/BD/42992/2008) through the MIT-Portugal Program, Bioengineering Systems Focus Area. The authors are thankful to Dr Jorge Ferreira from LNEG (Laboratorio Nacional de Energia e Geologia, Portugal) for carrying out the X-ray measurements and his help with the interpretation of results.

A modeling approach to identify sets of culture conditions to promote homogeneous growth of cells in perfusion bioreactors equipped with regular shape scaffolds is proposed. We identify cases in which dynamic culturing is necessary using a zero-dimensional mass transport and reaction model. Then, based on the three-dimensional (3-D) rendering of the flow field inside the bioreactor, we identify regions where cellular growth may become critical; finally, using a 1-D mass transport and reaction model, we calculate the minimal perfusion flow necessary to maintain the cellular growth rate above a target threshold. The developed approach is used to analyze culturing conditions inside an indirect perfusion bioreactor equipped with a lattice scaffold. Regions where the perfusion flow is inadequate to foster cellular growth at the desired rate are identified. The perfusion flow required to maintain the target growth rate inside the bioreactor is calculated. (c) 2013 American Institute of Chemical Engineers AIChE J, 59: 3131-3144, 2013

The enantioselective extraction of hydrophobic oxybutynin (OBN) enantiomers by hydrophilic β-cyclodextrin (β-CD) derivatives was studied. The efficiency of extraction depends strongly on a number of process variables such as types of organic solvents and β-CD derivatives, concentration of selector, pH, and temperature. The experimental data were described by a reactive extraction model with a homogeneous aqueous phase reaction of R,S-OBN with β-CD. Important parameters of this model were determined experimentally. The physical distribution coefficients for molecular and ionic OBN were 4.96 × 10−3 and 9.52, respectively. The equilibrium constants of the complexation reactions were 1770 and 1340 L/mol for S- and R-OBN, respectively. By modeling and experiment, an optimal extraction condition with pH of 5 and HP-β-CD concentration of 0.1 mol/L was obtained with enantioselectivity (α) of 1.26, which was close to the theoretical maximum of 1.32 and performance factor (pfi) of 0.036. The model was verified experimentally with excellent results. © 2011 American Institute of Chemical Engineers AIChE J, 2011

The complex mechanism by which homogeneous mixtures of two solids achieve fluidization is subjected to theoretical analysis, to elaborate relationships capable to provide their “initial” and “final fluidization velocity” uif and uff, i.e., the limits that encompass the suspension process. The article shows how the equation that describes the force equilibrium of fluidization can be rewritten in forms that account for the distribution of the components of density- or size segregating mixtures during the transition to the fluidized state. This approach leads to the theoretical expression of uif and uff of either type of system, whose differences of behavior are correctly reproduced by accounting for the voidage reduction typical of beds of particles of different size. The comparison with experimental results at varying mixture composition demonstrates that the equations give a coherent interpretation of the dependence of the fluidization velocity interval of two-solid mixtures on the principal variables of interest. © 2010 American Institute of Chemical Engineers AIChE J, 2011

This paper proposes two transformations for homogeneous reaction systems with inlet and outlet streams that allow isolating three distinct parts of the state vector, namely, the reaction variants, the reaction invariants but inlet- flow variants, and the reaction and inlet-flow invariants. In the absence of an outlet stream, as in batch and semi-batch reactors, the first transformation leads to the concepts of extents of reaction and extents of inlet flow. For reaction systems with an outlet stream, the second transformation uses key components to decouple the variables and arrive at the new concepts of generalized extents of reaction and generalized extents of inlet flow. These transformations are helpful to compute the reaction invariants for general open homogeneous reaction systems. Furthermore, the energy balance equation is shown to augment the number of reaction invariants by one. The various concepts are illustrated through the analysis of a simulated ethanolysis reaction.

When willow and water were heated rapidly (7–16°C/s) to high temperatures and high pressures, most of willow (90 vol %) dissolved in water at 341°C in 2.5 s without complete dissolution. Adding 0.8 wt % Na2CO3, complete dissolution of willow (concentration up to 35 vol %) was observed at 329–367°C and water densities of 322–787 kg/m3 (14–106 MPa) in 1.5 s. By cooling the solublized willow immediately, micron particles were obtained via precipitation. If heated further to 400°C, willow was completely hydrolyzed to sugars/sugar oligomers in 14.6 s at homogeneous conditions. A flow reactor was proposed to completely solubilize willow for the production of micron particles, sugars, bio-fuels and chemicals continuously. © 2008 American Institute of Chemical Engineers AIChE J, 2008

A population balance model is developed for the prediction of the average gas holdup and axial gas holdup profile in the bubble columns operating in the homogeneous regime. The model takes into account the effect of bubble expansion along the column height and thus it is applicable to tall columns such as flotation columns in the mineral processing industries. The model captures the effect of superficial gas and liquid velocities, bubble rise velocity, operating pressure, and column height on the gas holdup. In the case of flotation columns, because of the presence of surfactants in the liquid phase, froth is observed at the top of the column. Typically, froth shows the axial profile of gas holdup and the mean bubble size, indicating that the coalescence is an important phenomenon to describe the dynamics of the froth. A probabilistic perspective is developed to address the bubble coalescence process occurring in the froth and the bubble transition probability for coalescence is obtained from experimental data in the literature.

A new feasibility evaluation procedure for reactive mixtures is presented, where simple homogeneous reactive batch columns cannot produce pure products. Such columns are not feasible for producing pure products if no node products exist that are reachable by residue curves from the reaction equilibrium manifold. Three alternatives are presented. If an unstable node heterogenous azeotrope decants to an almost-pure product, and that azeotrope is always reachable from the reaction equilibrium manifold, then a batch reactive rectifier can produce pure products with a decanter. If a homogeneous entrainer allows extractive section profiles to connect the reaction equilibrium manifold to an entrainer-product binary edge, then a homogeneous batch reactive extractive distillation (BRED) column can produce a pure product. If these criteria are not met, then an entrainer that induces an unstable node heterogenous azeotrope between itself and one of the products should be used in a rectifier, a middle-vessel column, or a BRED column. © 2006 American Institute of Chemical Engineers AIChE J, 2006

Supercritical water oxidation (SCWO) technology presents important environmental advantages for the treatment of industrial wastes and sludges. The homogeneous reaction that takes place between the oxidizable materials and oxygen, at temperatures and pressures above the critical point of the water (647.3 K and 22.12 MPa), is well known. Specific equations of state for water and aqueous mixtures, gases, and organics have been developed. The process is not having the expected industrial development. Some new plants have been closed by corrosion and operational problems related with high temperature, high pressure, and oxidative atmosphere inside of the equipments. To overcome these technical difficulties more research focused on solving operational problems is necessary. This article presents an overview of the technical aspects of the supercritical water oxidation process. Reactors design, construction materials, corrosion, salts precipitation problems, and industrial applications are discussed. © 2006 American Institute of Chemical Engineers AIChE J, 2006

This work evaluates the ability of multiphase computational fluid dynamics (CFD) models to predict known flow regimes in air–water bubble columns. An initial grid-resolution study shows that grid spacing of 0.25 cm or smaller must be used for adequate resolution. The ability of the two-fluid model to predict homogeneous- and transitional-flow behavior is analyzed next, and the flow predictions are found to be highly dependent on the model formulation (that is, bubble-induced turbulence, drag, virtual mass, lift, rotation, and strain). At low gas velocities, homogeneous flow is observed for only a particular set of force models. At higher gas velocities, the same set of models yields reasonable predictions of transitional flow for small columns. Bubble size and liquid coflow also affect flow structures and flow stability at high gas flow rates. Scale-up to larger column diameters is studied for both the homogeneous- and transitional-flow regimes. In the homogeneous regime, the flow behavior is found to be independent of column diameter. However, because of neglect of coalescence, transition to churn-turbulent flow is not observed at high gas velocities for large column diameters. © 2005 American Institute of Chemical Engineers AIChE J, 2005

A rigorous rate-based modeling approach to reactive distillation equipment is presented in detail. This approach has succeeded from the three-year project “Reactive Distillation” initiated by SUSTECH and supported by the EU in the frame of the BRITE-EURAM program. As a result, a steady-state rate-based simulator DESIGNER has been created and tested with industrially important reactive distillations. First, a thorough description of the model development, including process hydrodynamics and kinetics, is given. The general structure of DESIGNER is highlighted. Furthermore, numerical problems, simulation issues, and validation of the developed simulator are discussed, whereas several industrially important applications are demonstrated. The main advantages of DESIGNER are the direct account of mass and heat transport (rate-based approach), multicomponent mass-transport description via the Maxwell-Stefan equations, consideration of a large spectrum of reactions (homogeneous and heterogeneous; slow, moderate, and fast; equilibrium and kinetically controlled), reaction account in both bulk and film phases, availability of different hydrodynamic models, and a large choice of hydrodynamic and mass-transfer correlations for various types of column internals (trays, random and structured packings, catalytic packings). Particular attention is devoted to the mass-transfer model, including the reaction in the film region, to the catalyst efficiency determination based on the mass transfer inside the catalyst and to the hydrodynamic models for reactive trays. © 2004 American Institute of Chemical Engineers AIChE J, 50:322–342, 2004

Local measurements of phase velocities and phase fraction in a dense liquid-liquid homogeneous flow were done based on an application of PIV with a refractive index matching technique. This technique allowed to measure simultaneously both phase velocities and phase fraction fields, as well as the drop mean diameter in a vertical cocurrent flow of n-heptane dispersed in an aqueous solution of glycerin. The evolution of the relative velocity as a function of the phase fraction (0–0.4) was studied with moderate particle Reynolds numbers (10–100) for drops behaving as spherical rigid particles. A local drag coefficient was derived from these measurements. The calculated mean relative velocity as a function of the local phase fraction with existing classical drag coefficient laws showed significant discrepancies with the measurements overestimated. Thus, the drag coefficient variation rate as a function of the phase fraction was underestimated by the models. The evolution of the normalized velocity (by the terminal velocity) as a function of the phase fraction was predicted correctly with mixture viscosity models in a creeping flow regime.

The operation of reactors with flow reversal operate similar to a reactor with internal recirculation, which the feed enters through one (say, inner) reactor and then turns around and flows out through (the outer) another, when the heat-transfer coefficient between the tubes is large. In this study, we compare the behavior of a packed-bed reactor operating in flow-reversal or internal-recirculation modes, using ethylene oxidation on Pt/Al 2 O 3 as a model reaction. The reactor was built from two concentric tubes (with 28.5 and 42.5 mm in diameter), both packed with a 20 cm catalytic bed and 10 cm inert beds (of alumina-pellets) on each side. An adjustable opening between the tubes allowed for an internal recycle mode and the whole system could be operated with periodic flow reversal. The reactor can be employed then either as a simple once-through bed or as a bed with flow reversal in the inner tube or as bed with internal recirculation flowing from the inner to outer tube, or in the opposite direction, as well as an internal-recirculation reactor with flow reversal. Due to heat losses, the latter two modes were inferior to the others. The experiments, backed by simulations using a homogeneous model with independently determined parameters, showed that the technically-simpler inner-outer internal-recycle reactor operated better at low flow rates, than that with flow reversal, but the conclusion is reversed at high flow rates. The domain where the internal-recirculation reactor is superior depends on the heat-transfer coefficient between the streams. By lowering the feed concentration, the extinction point was determined for each mode highlighting again the conclusions drawn above that inner-recirculation operation may be superior to flow reversal at low flow rates. Simulations revealed also the existence of solutions with stationary fronts or oscillatory fronts.

A reverse-flow packed-bed reactor used to solve the problem of leaching from immobilized homogeneous catalysts was studied. Product-to-catalyst ratios (PCRs) for a reverse-flow reactor (RFR) and a conventional batch reactor with catalyst reuse were compared theoretically and numerically. In the ideal case without band broadening in the RFR it is possible to completely eliminate the limit on PCR due to leaching, but in practice, band broadening, caused by kinetic and dispersion effects, cannot be avoided. Nonetheless, numerical experiments showed numerous cases with much higher PCRs for the RFR than for batch operation with catalyst reuse. Therefore, an RFR may be a successful solution in cases when catalyst leaching is too high for using batch operation with catalyst reuse. The design and operation of a suitable RFR are also discussed.

Synthesis of heterogeneous batch distillation is discussed, which aims at splitting azeotropic mixtures by adding an entrainer partially miscible with one of the initial binary mixture components. Key operational parameters are identified such as the amount of entrainer added in the ternary feed, the reflux policy, and the vapor line position by examples. Synthesis and operation are less straightforward for heterogeneous batch distillation than those for the homogeneous case, but offer many advantages: more design alternatives, simplified distillation sequences, a lower consumption of entrainer, and a crossing of distillation boundaries by the still path. Feasibility is assessed using simplified modeling and confirmed using a commercial batch process simulator package. Synthesis expectations and simulated results are verified throughout bench-plant experiments for the separation of the acetonitrile-water mixture using acrylonitrile as a light heterogeneous entrainer.

Large-scale inhomogeneities in natural porous media profoundly affect the dynamic response of conveyed tracers. It is proposed that tracer dynamics in heterogeneous porous media can be represented by temporal moments based on parallel and series unit models of homogeneous columns, stirred volumes, or mass-transfer-connected closed compartments. The rules of combining the moments for elementary volumes are based on units (1) in series, where output from the preceding units is the input to the succeeding unit, and (2) in parallel, where the splitting or joining flow paths control the response. For a network of elementary volumes in series or parallel, fate and transport of contaminants in heterogeneous media can be analyzed simply in a deterministic framework. Results for several simple series and parallel models show the wealth of responses that can be quantitatively described by this procedure.

A new optimization method for the synthesis of nonisothermal reactor networks offers major challenges concerning the lack of robustness in the existing methods and the numerous local and near-optimal solutions that characterize these problems. The approach offers a reliable and widely tested methodology that upholds a profile-based search. The search concentrates on targets rather than network details. The results illustrate ways to avoid unnecessarily complicated networks and develop simpler and transparent designs. The single-phase examples explain merits over past studies and other conventional synthesis methods. Multiphase examples are presented for the first time in the literature, as well as results from an industrial example.

It is important to determine the existence and composition of homogeneous azeotropes in the analysis of phase behavior and in the synthesis and design of separation systems, from both theoretical and practical standpoints. A new method for reliably locating any and all homogeneous azeotropes for multicomponent mixtures is presented. The method also verifies the nonexistence of homogeneous azeotropes if none are present. The method is based on interval analysis, in particular an interval-Newton/generalized-bisection-algorithm providing a mathematical and computational guarantee that all azeotropes are located. This general-purpose technique can be applied in connection with any thermodynamic models. The technique is illustrated in several example problems using the Wilson, NRTL, and UNIQUAC activity-coefficient models.

Geometric methods for the conceptual design of nonideal and azeotropic distillation systems have focused primarily on three- and four-component mixtures. A generalization of geometric methods that does not rely on visualization and gives a completely equation-based approach to determine the structure of distillation regions for homogeneous mixtures is described. This method is useful for mixtures with a large number of components, provided a vapor–liquid equilibrium model is available. The approach is applied to assess feasibility and alternative separations in several examples, including a five-component mixture with nine azeotropes and a six-component mixture with seven azeotropes. These methods can be used to rapidly generate process alternatives, and the examples demonstrate that there can be a surprising number of these alternatives for the distillation of azeotropic mixtures.

Van Ommen et al. (2000) recently developed a monitoring method that was successfully used for the early detection of agglomeration in fluidized beds. This article shows that this monitoring method is more generic and can also be applied for early detection of foam formation in bubble columns. Knowing that dilute alcohol solutions simulate reasonably well the liquid-phase behavior in bioreactors (Bukur and Patel, 1989), and can also leads to foaming (Pugh, 1996), the system water/ethanol was chosen as a model system. Experiments were carried out in the homogeneous and the heterogeneous regime.

International audience; A novel approach is proposed to model heterogeneous downward dense gas-particle flows. The homogeneous behavior of the flow is described by the mass and momentum transport equations of the gas and particulate phases solved using a mono-dimension finite volume method on staggered grids. The heterogeneous features of the flow are predicted simultaneously using the bubble-emulsion formalism. The gas compressibility is taken into consideration. The model is supplemented with a new correlation to account for the wall-particle frictional effects. The predictions are compared with the vertical profiles of pressure and the amount of gas that flows up and down two standpipes and a cyclone dipleg of an industrial fluid catalytic cracking unit and of a cold small-scale circulating fluidized bed. The trends are well predicted. The model gives further information and is thus an innovative starting point for downward dense gas-particle flow hydrodynamics investigation.

Batch, fed-batch, and single-stage CSTR bioreactors operate without external sources of biomass after they have been inoculated. However, other kinds of bioreactors, such as the second and subsequent reactors in a cascade of CSTRs, operate with continuous introduction of biomass from one or more external sources. The biomass in a bioreactor with an external source is not homogeneous with respect to past history of environmental conditions, and growth of this biomass is not balanced (steady-state) growth even when the bioreactor operates in steady state. So-called unstructured models of growth, which assume biomass to lack any internal structure or to have an invariant internal state, can give only a first approximation to the growth rate behavior of the biomass in a bioreactor with an external source of biomass. Structured models, which endow biomass with a changeable internal structure, are required to obtain more accurate predictions of growth rate behavior in such reactors. Introduction of structure is not sufficient for improved accuracy, however, and the fact that biomasses from different sources are remain segregated from one another must also be accounted for by any structured growth model used. This article presents, among others, the systems of different equations that result from application of the notions to the reactors of a cascade of CSTRs.

A direct numerical simulation (DNS) code has been modified to investigate chemically reacting flows in a stationary, homogeneous turbulence. Single and multispecies reactions as well as complicated reaction schemes such as parallel/consecutive reactions are studied. The effects of some parameters are discussed. The numerical data are used to test a simple first-order closure model, proposed by Dutta and Tarbell (1989), for turbulent reacting flows. It is shown that the DNS technique provides us with an effective tool to isolate the effects of different parameters and is likely to be useful for proposing and testing closure models.

The Bodenstein approximation for trace-level intermediates is used to reduce multistep reaction-kinetic networks of arbitrary topology and size to simpler forms with only pseudosingle steps between nodes and to derive explicit equations for formation or consumption rates of end members. Networks with nontrace intermediates or steps of higher orders in intermediates must be broken at the respective steps into portions to which the procedure can then be applied separately. A recipe is provided with which rate and yield-ratio equations are readily compiled for networks of arbitrary configuration and complexity. The method is illustrated with an example of a reaction of industrial interest.

Existing methods for synthesizing thermally-integrated distillation sequences fail frequently when applied to nonideal and azeotropic systems, because increasing the column pressures often introduces new azeotropes and distillation boundaries into the mixture, which make some separation tasks infeasible. A new thermal integration procedure is presented that combines a bifurcation and residue-curve map analysis with the methods of Andrecovich and Westerberg. The procedure is demonstrated with two commercially important separations: ethanol-water-ethylene glycol and methanol-acetone-water. Energy savings of 65% and 40%, respectively, over the optimized nonintegrated sequences are possible.

The development and performance of a bubble column photoreactor for ultrapurification of SiCl4 is described. Trichlorosilane (SiHCl3), the principle contaminant in SiCl4 commercially available for use in optical fiber manufacture, is converted to SiCl4 and HCl by UV-initiated photochlorination. Studies of the homogeneous photochlorination kinetics and of Cl2 gas absorption in a bubble column were undertaken. In addition, an extensive set of data was collected from continuous-flow bubble column reactor (BCR) runs. The rate of photochlorination in the BCR was found to be mass-transfer-limited. A simple model of BCR performance, incorporating the effect of Cl2 mass transfer rate enhancement by chemical reaction, was tested that agrees well with the experimental data. The BCR was found to be operable over a wide range of SiHCl3 concentrations and SiCl4 feed rates, and capable of lowering the concentration of SiHCl3 in product to below measurable levels (

A unified statistical mechanical treatment is developed for adsorption and surface diffusion on homogeneous surfaces. Using molecular parameters, the model accounts for all physical effects of adsorbent-adsorbate, adsorbate-adsorbate, and adsorbate-gas interactions at submonolayer coverages.

Most models for fixed bed adsorbers have used either the homogeneoussolid or pore diffusion model for the pellets. When the adsorption isotherm is linear, the two models can lead to identical breakthrough curves. The conditions for this equivalence are presented here. It is shown that one of the bulk flow factors that was included in the formulation of one pore diffusion model will be significant only for feedstreams containing a relatively high concentration of adsorbate. The prosity factor of the pore model is shown to be very important, especially as the porosity decreases. The importance of the two diffusional models with respect to the predicted breakthrough curves is demonstrated. For comparable beds, it is shown that the breakthrough curve based on the homogeneous model is delayed with respect to that based on the pore model at early times, regardless of the shape of the isotherm. Finally, the various possible solutions for an irreverisble isotherm are reviewed for each of the models, and a solution is presented for the general case of a pore model with an outside film resistance.

Pressure drop correlations for flow of slurries in pipelines were developed for each of the following four flow regimes: flow with a stationary bed, saltation flow, heterogeneous flow, and homogeneous flow. A total number of 2 848 data points, comprised of 1 912 collected from the published literature together with 936 taken using our own test pipelines and relating to ranges of the pertinent variables extensive enough to span all four flow regimes were used as the basis of these correlations. Also, these data were used in developing an associated quantitative regime delineation scheme. The correlations provide an improved predictive capability over previously available procedures and are also broader in scope. The delineation procedure developed here permits straightforward classification of the data according to the flow regime prevailing, and it is moreover inclusive of all the data and is self-consistent.

Experimental measurements for an industrial azeotropic distillation tower that dehydrates secondary butyl alcohol (SBA) show erratic operation that only approaches a steady state. These are explained with steady-state simulations which show that slight variations in the aqueous reflux rate cause many trays to shift from homogeneous to heterogeneous operation, accompanied by significant changes in the SBA purity, with water or entrainer contaminating the bottoms product. When other methods failed, an arc-length homotopy-continuation method made small adjustments in the reflux ratios to obtain close agreement with the measurements.

To study the effect of H2O2 on NO reduction with NH3, the homogeneous gas phase reaction of NH3NOH2O2O2 was investigated in a Pyrex flow reactor over the temperature range from 500°C to 600°C under one atmospheric pressure. H2O2 accelerated the NO reduction by NH3 and caused it to be induced at a temperature of 500°C. In the absence of O2, NOx reduction ratio of more than 90% was obtained for NH3/NO5 and H2O2/NO1 at 550°C. In the presence of O2 or an excess of H2O2, two side reactions, which cause the NOx reduction ratio to decrease, occur. One of the side reactions is NO oxidation with H2O2. It was found experimentally that NO2 inhibited NO reduction and that H2O2 was an NO oxidizing agent, as well as an NH3 decomposing agent. The other side reaction was the formation of NO and NO2, which resulted from the oxidation of NH3 with O2. Under the conditions of our experiments, the amount of O2 in our reaction system was extremely high compared to the amounts of NO, NH3 and H2O2 in the system. Thus NOx was assumed to be produced by the oxidation of the NO reducing radicals, which were produced by the reaction of NH3 with H2O2.

Ce modele comprend une solution analytique d'un modele de double resistance, base sur le transfert de matiere externe et sur la diffusion en phase solide homogene

Diffusional mass transfer across membranes with uniform but low pore densities was studied experimentally as a function of stirring rate and pore area fraction. The results were analyzed in terms of a stagnant film boundary-layer model specially formulated for a heterogeneous membrane containing discrete pores. The overall membrane diffusional resistance is linearly related to the inverse of the pore area fraction of the membranes for a constant stirring rate. An equivalent boundary-layer thickness can be defined which is independent of membrane properties but a unique function of stirrer speed. These experimental boundary-layer thicknesses are greater by a factor of 3 than those predicted by a published Sherwood number correlation determined for homogeneous surfaces, but the stirring rate dependence is in excellent agreement with this same correlation.

Theoretical and experimental aspects of homogeneous and heterogeneous bubble nucleation are reviewed. Recent developments in nucleation theory, which include hydrodynamic and diffusion constraints, gas phase nonidealities, and heterogeneous nucleation are discussed. A large number of the measured limits of superheat of pure components are close to 88 to 90% of the critical temperature. Where calculations can be made, these measurements are in agreement with predictions from classical nucleation theory. Measurements of the limits of superheat of mixtures are useful for understanding one proposed mechanism for the dangerous phenomena known as contact vapor explosions.

A simplified model of nitrate ion transport (and other nonadsorbing solutes) in unsteady, unsaturated flow in porous media has been developed. The model represents nitrate flow in infiltration and drainage in sand quite well and can be applied to unsaturated flow in other homogeneous media with only minimum extra experimental data needed to describe the medium.

In Part I of this paper a methodology for the synthesis of optimal isothermal serial reactor structures for complex reactions was presented. This has been extended to nonisothermal systems in this paper. A complete review of the relevant background has been included in this paper. A graphical procedure has been presented for Type II complex reactions and a computer program has been described for Type III complex reactions. Two cases for the Van de Vusse reaction scheme and a naphthalene oxidation example have been used to illustrate the synthesis approach.

In turbulent flow the equations governing the development of conversion vs. distance are not closed because of the contribution of the concentration fluctuations to the average reaction rate. Toor's hypothesis permits closure from data obtained for mixing without reaction. This paper presents a critical review of the derivation of the hypothesis and discusses its validity.

Effective reaction rates and selectivities on surfaces having active and inactive regions are calculated for systems in which diffusion of reactants and products through a boundary layer is significant. With a single reaction it is shown that rates are larger than those calculated assuming area weighted averages. The selectivity of production of an intermediate in a series of reactions on a heterogeneous surface is higher than on a homogeneous surface, and with parallel reactions selectivities may be lower or higher depending on the kinetics of the competing reaction. Numerical examples from NH3 oxidation on a Pt gauze and CO oxidation in the automotive converter indicate that these effects may be important in determining selectivities and conversions in some industrial reactors.