Showing papers in "Industrial & Engineering Chemistry Research in 1989"

Model of vapor-liquid equilibria for aqueous acid gas-alkanolamine systems using the electrolyte-NRTL equation

Abstract: Un modele important du point de vue thermodynamique est developpe pour representer les equilibres liquide vapeur dans des systemes ternaires constitues d'un gaz acide, H 2 S ou CO 2 , d'un alcanolamine, monoethanolamine ou diethanolamine et d'eau

Calcium oxide sintering in atmospheres containing water and carbon dioxide

Abstract: Etude de la cinetique du frittage de CaO en fonction de la temperature et de la pression partielle, influence de l'addition de vapeur d'eau et de dioxyde de carbone.On etudie l'evolution de la porosite et de l'aire superficielle au cours du processus

Advanced oxidation processes. Description of a kinetic model for the oxidation of hazardous materials in aqueous media with ozone and hydrogen peroxide in a semibatch reactor

Abstract: Presentation d'un modele decrivant la cinetique de l'oxydation de micropolluants dans l'eau par de l'ozone et de l'eau oxygenee dans un reacteur fonctionnant en discontinu. Ce modele est base sur les reactions connues du systeme O 3 /H 2 O 2 et des caracteristiques de transfert de masse du reacteur. Les especes cinetiques principales pour l'oxydation de micropolluants sont les radicaux hydroxyles. Le modele est teste et valide dans de l'eau distillee dans laquelle a ete ajoute du bicarbonate de sodium (agent d'elimination de OH - )

A new methodology for the optimal design and production schedule of multipurpose batch plants.

Abstract: Presentation d'une procedure algorithmique determinant simultanement le programme optimal de production et les tailles des equipements. Il s'agit de la formulation NLP (Non Linear mathematical Programming). Des modifications mineures permettent la maintenance d'options comme l'utilisation d'unites paralleles de meme taille pour la fabrication de produits distincts ou la production de produits intermediaires

Accurate solution of differential-algebraic optimization problems

Abstract: Differential algebraic optimization problems arise often in chemical engineerting processes. Current numerical methods for differential algebraic optimization problems rely on some form of approximation in order to pose die problem as a nonlinear program. Here we explore an appropriate discretization and formulation of this optimization problem by considering stability and error properties of implicit Runge * Kutta (IRK) methods for differential • algebraic equation (DAE) systems. From these properties we are able to enforce appropriate error constraints and method orders in a collocation based nonlinear programming (NLP) formulation. After demonstrating the IRK properties on a small DAE system, we show from variational conditions that optimal control problems can have the same difficulties as higher index DAE systems. This is illustrated for a number of small chemical engineering optimization examples that exhibit higher index characteristics. For these cases the NLP formulation in this paper yields efficient and accurate solutions. L Introduction The determination of optimal control profiles is of major importance for process applications. Examples within chemical engineering include problems in reactor design, process startup, batch process operation, etc. However, solution of optimization problems with differential and algebraic equation modehstiD remains a diflBcniltproble optimization problems with T n ^n algebraic equations can be solved in a straightforward way as nonlinear programs. On die other hand, unconstrained problems with differential equation models can be handled through die calculus of variations. However, models that combine both of these features are currently optimized by imposing some level of approximation to the problem. The purpose of this paper is to develop and discuss a nonlinear programming formulation that leads to the accurate solution ( within an e tolerance) of the general differential-algebraic optimal control problem. Current methods for handling these problems either apply an approximation to the_ control variable profile or to both the state and control profiles. A straightforward approach adopted by Sargent and Sullivan (1977) is to parameterize the control profile (e.g. piecewise constant) over variable-length finite elements and to solve the differential equations with this parameterization. A nonlinear programming algorithm is then applied to the control parameters in an outer calculation loop. Similar strategies have been proposed by Ray (1981) and Morshedi (1986). This "feasible path" approach requires the repeated and expensive solution of the differential-algebraic eqautions. Also, state variable inequality constraints cannot be handled in a straightforward way. Finally, the quality of the solution is strongly dependent on die parameterization of the control profile. Early studies with the second approach, parameterization of both the state and control profiles, were reported by Neuman and Sen (1972), Tsang et al (1974) and Lynn et al (1971). Here state and control profiles and die differential equations were parameterized using some method of weighted residuals (eg. orthogonal collocation). This leads to a large nonlinear program (NLP) with algebraic equality constraints. However, since NLP algorithms were less developed at that time, this approach was either inefficient when compared to feasible path methods, or was restricted to specialized (e.g. linear) problems. With advances in NLP methods through the development of Successive Quadratic Programming (SQP) and MINOS, these NLP's could be solved more efficiently and could handle nonlinear state and control profile constraints in a straightforward manner. Biegler (1984) demonstrated this approach on a small batch reactor problem. Renfro et al (1987) solved much larger problems with orthogonal collocation on finite elements and piecewise constant approximations to the control profile. In order to obtain accurate finite element solutions, however, Cuthrell and Biegler (1986,1989) imposed additional constraints in the NLP formulation in Older to enforce accurate state profiles. They classified the role of finite elements in terms of knot locations (over which die error was equidistributed, hence minimiTfri) and breakpoints that allowed for control profile discontinuities. This led to a formulation that enforced the accurate solution of the differential equations and allowed for a general description of the control profile. In this paper we explore the theoretical development of these finite element constraints and present a formulation that leads to arbitrarily accurate state variable and control variable profiles. Here finite elements serve as decision variables in the optimization problem and are simultaneously required to satisfy approximation error constraints and to locate control profile discontinuities. This formulation will be considered from the perspective of a discretized Differential-Algebraic Equation (DAE) system. Recent approximation error and stability results by Petzold and coworkers will be tailored to optimal control problems and incorporated into the NLP. The next section will review the equivalence between the variatibnal conditions for general optimal control problems and die Kuhn-Tucker conditions for the corresponding NLP formulation. Section 3 then discusses recent stability and approximation error results for Runge-Kutta methods (including collocation methods) ipplied to DAE systems. In particular we will discuss the appropriate selection of collocation methods for higher index (i.e., more difficult) DAE systems. The following section then discusses how these higher index DAE systems arise in optimal control problems with path constraints and singular arcs. Section 5 presents the solution of a number of higher index optimal control examples with our approach. Here it is shown that arbitrarily accurate solutions can be found with our NLP formulation. Finally, section 6 summarizes die paper and discusses approaches to dealing with large-scale optimal control problems. 2. Analysis of the Opdmalhy CotKlitwns for Optimal Control ProW In this section we briefly review the equivalence between the calculus of variations and the math programming approach. Special cases for optimal control problems such as singular arcs and path constraints will be discussed after this section. Consider the following general problem: Min ¥ ( z ( b ) ) + J *( z ( t ) , i i ( t ) ) dt u(t).x(t) S.L 2(0 g(u(t),: « F(z(t), e(t)) ^ 0 gf(z(b)) £ 0 z(a) •= z(t) u(t) z0 £ z(t) ^ ^ u(t) £ u(t)) z(t) u(t) where: Y( z(b)) * component of objective function due to final conditions I ( z ( t ) f u ( t ) ) d t = component of objective function due to integral of state and control vectors g « inequality design constraint vectors z(t) « state profile vector u(t) « control profiles gj « final conditions inequality constraints ZA K frwtifti condition for ttfttf vector z(t)f z(t) U « sate profile bounds u(t) , u(t) * control profile bounds The variational conditions for Ais problem are: du du du (b) (c) (d) (c) d

A mathematical model for the flash calcination of dispersed calcium carbonate and calcium hydroxide particles

Abstract: A mathematical model for the flash calcination of Ca(OH)/sub 2/ and CaCO/sub 3/ is presented. The model describes the decomposition of the parent material at the reactant-product interface, the diffusion of CO/sub 2/ or H/sub 2/O through the growing CaO layer, and the sintering of the CaO layer. The model is qualitative, but it provides useful estimates of peak CO/sub 2/ pressures on the CaO layer, relative rates of surface area development and loss for Ca(OH)/sub 2/ and CaCO/sub 3/, the effect of particle size, and the effects of time and temperature.

Advanced oxidation processes. Test of a kinetic model for the oxidation of organic compounds with ozone and hydrogen peroxide in a semibatch reactor

Abstract: Experimental data are presented to test a kinetic model of the OE/H{sub 2}O{sub 2} process in a semibatch reactor. The effect of bicarbonate and carbonate ions is measured and found to be in concurrence with model predictions. The effect of pH in the ozone mass-transfer-limited region was examined in bicarbonate-spiked distilled water. Since the reaction is mass transfer limited, the primary effect above pH 7 is the result of changes in the distribution of inorganic carbon species which are OH-radical scavengers. Below pH 7, there is a lag period during which ozone and peroxide increase until the chain reaction begins. The effects of chloride ion and the concentration of radical scavengers other than carbonate species in ground waters are also measured. The mass-transfer/reaction rate model has been used to estimate rate constants for the reaction of hydroxyl radicals with trichloroethylene, 1,2-dibromoethane, 1,2-dibromo-3-chloropropane, carbon tetrachloride, and two bicyclic alcohols, 2-methylisoborneol and geosmin. While the model developed for the distilled water system was successful in predicting the rate of tetrachloroethylene (PCE) oxidation and the concentration of residual ozone and peroxide in regions I and III, respectively, there are several features of the model that remain unresolved when the matrix is changed tomore » a real surface or ground water. This and subsequent papers will investigate these effects.« less

Fundamental kinetic modeling of hydroisomerization and hydrocracking on noble metal-loaded faujasites. 1. Rate parameters for hydroisomerization

Abstract: The hydroisomerization and hydrocracking of paraffins on zeolites is modeled in terms of fundamental reaction steps involving carbenium ions. This fundamental kinetic modeling is discussed in detail and applied to the hydroisomerization of n-octane into monomethylheptanes on a Pt/US-Y zeolite. The reaction network, involving more than 100 reactions written in terms of elementary steps, was generated by computer, and the kinetic parameters were estimated by Marquardt's minimization procedure, accounting for thermodynamic constraints

Liquid film in Taylor flow through a capillary

Abstract: On mesure l'epaisseur d'un film liquide entre une bulle de gaz et la paroi du tube dans un ecoulement de Taylor pour des systemes air/eau, air/ethanol et air/glycerol Calcul de l'epaisseur du film et de la forme des bulles par les equations de Navier et Stokes et par les equations de tension superficielle

Modeling supercritical mixtures: how predictive is it?

Abstract: Etude de plusieurs modeles thermodynamiques pour des sytemes multiphasiques, fluide solide, fluide liquide

Temperature control of exothermic batch reactors using generic model control

Abstract: Presentation d'un nouveau systeme de controle (base sur le modele de Lee et Sullivan (1988)) de l'echauffement et de la regulation de la temperature. Simulation d'un reacteur illustrant les performances de ce systeme. Comparaison de ce systeme a un systeme de controle a mode double

Multistep nonlinear predictive controller

Abstract: Presentation d'un nouvel algorithme pour le controle de systemes non lineaires et illustration de ces performances pour le controle d'un bioreacteur et d'un reacteur parfaitement agite catalytique

Temperature-heat diagrams for complex columns. 3. Underwood's method for the Petlyuk configuration

Abstract: Developpement d'une approche generalisee a l'analyse de la configuration de Petlyuk avec aucune restriction sur le nombre de composes moyens

Temperature-heat diagrams for complex columns. 2. Underwood's method for side strippers and enrichers

Abstract: The authors present insight into complex column heat flow which facilitates extension of Underwood's method to columns with side-stream strippers and side-stream enrichers. This presentation is much simpler than previous ones. The same insights show that, even though less configurations are more energy efficient, they require a larger temperature range for operation than analogous simple column sequences.

Structural models for catalytic cracking. 1. Model compound reactions

Abstract: Data on the catalytic cracking reactions of model compounds over an amorphous silica-alumina-zirconia catalyst are organized into a general framework based on carbon centers. Each hydrocarbon in a petroleum mixture consists of a collection of carbon centers, and the reaction behavior of individual compounds can be described by the reaction behavior of the carbon centers. The cracking behavior of the carbon centers has been deduced from pure compound studies available in the literature. The carbon center approach results in predictions that are in reasonbable agreement with the experimental data. The models of pure components are used as a basis for modeling the cataytic cracking reactions of hydrocarbon mixtures.

Axial dispersion of supercritical carbon dioxide in packed beds

Abstract: Mesure des coefficients de dispersion axiale dans un lit a garnissage sous des conditions supercritiques par injection de methane dans du dioxyde de carbone. Ce coefficient augmente avec la vitesse intersticielle, le diametre des particules du garnissage, la pression et la temperature; ceci est du a l'augmentation de la densite et de la vitesse du dioxyde de carbone supercritique. L'influence de la longueur du lit est negligeable

Decomposition of 1,2-dichloroethane on titanium dioxide/silica

Abstract: Etude des sites acides du systeme catalytique compose d'oxyde de titane et de silice pour la decomposition du dichloro-1,2ethane

Activation studies with a promoted precipitated iron Fischer-Tropsch catalyst

Abstract: The authors discuss the effect of reductant type (CO, H/sub 2/, or H/sub 2//CO = 0.68), activation temperature (250, 280, and 310{sup 0}C) duration (8 and 24 h), and pressure (0.1 and 1.48 MPa) on the activity and selectivity of a promoted precipitated iron catalyst (100Fe/3Cu/0.2{Kappa}) studied in a fixed bed reactor. It was found that activation parameters have a strong effect on the catalyst behavior during Fischer-Tropsch (FT) synthesis at 250{sup 0}C, 1.48 MPa, 2 nL/g of catalyst/h, and H/sub 2//CO = 1. Activations in CO led to catalysts that had higher initial activity and better selectivity (less methane and other light hydrocarbons) than H/sub 2/ activated catalysts. However, the activity of CO-reduced catalysts declined with time on stream, whereas the activity of H/sub 2/-reduced catalysts remained constant or increased during 120 h of testing. Activation in CO at 280{sup 0}C and 0.1 MPa for 24 h was the most desirable on the basis of overall catalyst activity, selectivity, and stability.

Generalized model for prediction of the steady-state drop size distributions in batch stirred vessels

Abstract: Calcul, par le modele d'interaction homogene developpe par Valentas et Admunson (1966), des distributions de taille de goutte d'une dispersion styrene/eau dans un appareil agite en discontinu

Hydrolysis in supercritical water: identification and implications of a polar transition state

Abstract: Reaction of guaiacol (o-methoxyphenol) in supercritical water and with added salts showed its hydrolysis to catechol (o-hydroxyphenol) and methanol to be through a polar transition state. Correlation of the reaction kinetics following a modified Herbrandson analysis provided a quantitative summary of the greater polarity of the hydrolysis transition state relative to the hydrolysis reactants. Salt addition further shifted the transition-state equilibrium toward the transition-state species.

Structural models for catalytic cracking. 2. Reactions of simulated oil mixtures

Abstract: The model developed in this work uses reactions of pseudocomponents to describe the catalytic cracking reactions of a typical oil. As input, the model requires analytical data on oils available from compound class separations, mass spectrometry, and NMR spectra. The analytical data are used as constraints in selecting a distribution of pseudocomponents suitable for modeling the oil. The products of the cracking reactions of the pseudocomponents are determined using an extensive model compound data base and the methods described in the first part of this work. Simulations were performed to assess the sensitivity of the model to the choice of pseudocomponents, the number of pseudocomponents, and the type of analytical data available. The simulations indicated that the model becomes insensitive to the number of pseudocomponents when the number of pseudocomponents exceeds 100. More significantly, the model was relatively insensitive to the carbon center distribution of the oil but was quite sensitive to the level of detail in the carbon number distribution. Thus, mass spectra may be more valuable in determining the cracking behavior of oils than NMR spectra.

Extension of UNIFAC to high pressures and temperatures by the use of a cubic equation of state

Abstract: Estimation de parametres pour un equilibre liquide vapeur a partir de parametres UNIFAC a de hautes pressions et temperatures

Gas-liquid phase-transfer catalysis: a new continuous-flow method in organic synthesis

Abstract: A synthetic method, gas-liquid phase-transfer catalysis (GL-PTC0), is described. GL-PTC is a continuous-flow procedure where gaseous reagents flow through a molten phase-transfer (PT) catalyst supported on a solid; no solvent is used. Reactions may develop through new mechanistic pathways compared with those of classical conditions; moreover, the reactions often occur in very selective ways. Some typical syntheses carried out under GL-PTC conditions are described in detail. They include syntheses of 2-alkylmalonic acid esters from the corresponding malonic acid esters and primary alkyl halides from primary alkyl alcohols and the reactions of dimethyl carbonate, which give N-methylanilines from anilines, anisoles from phenols, and 2-arylpropionitriles from aryl-acetonitriles.

Optimal design and synthesis of homogeneous azeotropic distillation sequences

Abstract: A systematic procedure for optimizing homogeneous azeotropic separation sequences has been developed. The procedure uses an explicit design technique which eliminates the need for recycle convergence schemes. The separation of ethanol from water using ethylene glycol as the entrainer is used to illustrate the optimization procedure. Comparisons are made with competing designs from the literature, illustrating the need to properly optimize flow sheets before drawing conclusions on the relative merits of various separation technologies.

Analysis and construction of multilayer composite membranes for the separation of gas mixtures

Abstract: Etude de trois types de membranes composites: membranes a deux couches [PAS(Poly(AminoSiloxane))/PS(PolySulfone) et PPO(Poly(dimethyl-2,6 p-phenylene oxyde))/PS] et membranes a trois couches [PPO/PAS/PS]

Mild hydrocracking of bitumen-derived coker and hydrocracker heavy gas oils: kinetics, product yields, and product properties

Abstract: Conversion des gas oils lourds en gas oils legers et en essence lourde par hydrocraquage en presence d'un catalyseur mixte NiMo/Al 2 O 3 a une temperature comprise entre 350 et 400 o C et sous pression de 7 a 11 MPa. Mesure du taux de conversion par chromatographie en phase gazeuse. Etude de la cinetique de l'hydrocraquage, de l'hydrodesulfuration et de l'hydrodesazotation

Supercritical regeneration of activated carbon loaded with benzene and toluene

Abstract: La capacite d'adsorption du benzene et du toluene sur le charbon actif regenere est determinee