BATCH AND SEMIBATCH REACTORS MODELLING AND VALIDATION BASED ON ON-LINE pH MEASUREMENT

Based on on-line pH measurement, a comparative study between batch and semibalch reactors performance has been carried out in a glass-jacketed reactor of 51 provided with the measuring, data acquiring and controlling system. The reaction system chosen was an acid-base reaction, the concentrations of the species in the reactor were obtained simply by measuring the pH of reaction solution. Based on the conductivity profiles of the solution at different temperatures, the kinetic equation of this acid-base reaction was established. The thermal behaviors of batch reactor were investigated by heating and cooling water in the reactor. The dynamic behavior of batch reaction could be described by a set of differential equations resulting from the mass and energy balance of the reaction mixture, the energy balance of the jacket wall and the circulating fluid inside the jacket. This model has been validated with experimental results, and could be applied to the complex control situations.     

Use of the axial dispersion model to describe the O3 and O3 /H2O2 advanced oxidation of alachlor in water

Experiments on alachlor degradation by ozonation alone and combined with hydrogen peroxide using different surface waters have been conducted in a reactor bubble column and a kinetic model of the advanced oxidation process has been proposed. Variables studied were the nature of the surface water (four surface waters were treated), pH (3.5–9.7) and hydrogen peroxide to ozone mass ratio at the column inlet (0.1–1.85 g g^?1). Data on residence time distribution, rate constants and the absorption kinetic regime were considered to prepare the kinetic model, which was also based on the axial dispersion model of non‐ideal flow. The model gives good predictions of alachlor and hydrogen peroxide conversions and the fraction of dissolved ozone (deviations were lower than ±15%) although it fails, in some cases, to yield accurate estimates of the observed experimental trends of concentrations in water at the reactor column outlet. The calculated results were close to those obtained from the more classical N well‐mixed tanks‐in‐series model (deviations with this model were lower than ±20%). It is concluded that quantitative deviations from experimental observations were likely due to the lack of rate data on ozone reactions with organic matter present in the surface waters investigated. © 2002 Society of Chemical Industry     

An experimental study of oscillatory states in a stirred reactor

Instabilities of the type which lead to sustained oscillations (limit cycles) were studied experimentally in a nonadiabatic, well-stirred, continuous-flow reactor. The study included: (1) the stabilization of unstable states by means of conventional feedback control, (2) the construction of phase-plane diagrams showing experimental limit cycles and other time-dependent behavior, and (3) comparisons of experimental results with theoretical predictions.The exothermic liquid-phase reaction between sodium thiosulfate and hydrogen peroxide was employed in all experiments. An empirical reaction rate expression for use in the describing equations was obtained from batch reactor experiments.Experiments were carried out with two reactors which differed only in wall thickness. The mass of the reactor with the thicker wall was sufficiently large to cause all oscillations to be damped, but for the other reactor, the mass of the wall did not seem to affect the reactor dynamics appreciably. The agreement between theoretical predictions and experimental observations was good, though there were some noticeable quantitative discrepancies in the time-dependent state.     

The behaviour of a two-compartment stirred-tank electrochemical reactor with two anodic reactions and with continuous flows of both anolyte and catholyte

A partial mathematical model is presented for a two-compartment electrochemical reactor when there is a steady flow into and out of each compartment and when both anolyte and catholyte are well mixed. Two simultaneous anodic reactions, the fast oxidation of ferrocyanide ions and oxygen evolution, together with cathodic hydrogen evolution are considered and both migration and diffusion of hydroxyl ions across the diaphragm are taken into account. The resulting differential equations relate the concentrations of hydroxyl ions in each compartment and anolyte ferrocyanide to time in terms of,inter alia, the total reactor current and the partial current for ferrocyanide oxidation. By using the measured variation of current with time from an experimental reactor operated at a constant voltage and estimating the ferrocyanide partial current the observed concentration-time variations can be matched with those obtained by numerical integration of the model equations. Data from a series of experiments have been analysed and the assumption of a constant partial ferrocyanide current over the duration of a run gives a satisfactory representation of the behaviour of the experimental reactor. Reasons for discrepancies are discussed.     

Experimental study of the direct reduction of sinterized zinc oxide by hydrogen

The gas-solid reaction between hydrogen and sinterized zinc oxide has been studied experimentally and theoretically. The attention has been focused on the influence that the elementary chemical and physical phenomena, taking place inside the pellet, have on the overall reaction rate. The experimental results, worked out according to the mathematical model proposed, allowed both to check the validity of this model and to determine the true kinetic constant and the activation energy of the reaction. The discrepancies between experimental results and theory are well within the limits of uncertainty affecting both the independently evaluated physical parameters (such as diffusivities, internal area, etc.) and the measured parameters for low values of the reaction times. On the contrary, the larger discrepancies found for larger values of time, may be attributed to the major difficulties connected with the modelling of the internal structure of a porous solid which is consumed during a reaction, for advanced states of consumption.The method adopted for analyzing continuously with time the reaction products, made use of a thermobalance working at room temperature.     

Mathematical modeling for chemical vapor deposition in a single-wafer reactor: Application to low-pressure deposition of Tungsten

A mathematical model for low pressure chemical vapor deposition in a single-wafer reactor in stagnation point flow has been developed to investigate the reactor performance. The transient transport equations for a simulated reactor include continuity, momentum, energy, and gaseous species balances. The model equations are simultaneously solved by using a numerical technique of orthogonal collocation on finite element method. Simulation studies have been performed to gain an understanding of tungsten low pressure chemical vapor deposition process. The model is then used to optimize the deposition rate and uniformity on a wafer, and the effects of operating conditions on deposition rate are studied to examine how system responses are affected by changes in process parameters. Deposition rate and uniformity calculated at the steady state are observed to be very sensitive to both temperature and total pressure. In addition, the model predictions for tungsten deposition from hydrogen reduction of tungsten hexafluoride have been compared with available experimental data in order to demonstrate the validity of the model.     

A MATHEMATICAL MODEL FOR THE CATALYST DEACTIVATION IN A COMMERCIAL RESIDUE HYDRODESULFURIZATION REACTOR SYSTEM

A mathematical model that describes catalyst deactivation in a commercial Residue Hydrodesulfurization (RDS) system is proposed. In this model, coking, metal deposition and the decrease of effective diffusivities are all considered, so that it can predict the dynamics of catalyst activity during a long run of an RDS system. The RDS system under consideration here is a complex trickle bed reactor system with four adiabatic reactors in series, between which the oil is quenched by hydrogen to prevent the catalysts in the next reactor from being damaged by high temperature. This article shows that by incorporating a catalyst deactivation model into the overall reactor system model, the predicted catalyst aging curve assumes the “S” shape, characteristic of real RDS system. The model prediction are compared with data from an operating refinery and the agreement is pleasing. KEYWORDS Residue Hydrodesulfurization(RDS) Apparent activity Catalyst deactivation curve Pore radius.     

Direct Coal Liquefaction Using Iron Carbonyl Powder Catalyst

Direct coal liquefaction involves catalyzed interactions between molecular hydrogen and coal‐oil slurries at elevated pressure and temperature, typically in the presence of an iron‐based catalyst. Iron carbonyl powder as an alternative first‐stage catalyst was investigated. A series of experimental tests under mild liquefaction conditions were carried out with a high‐pressure batch reactor in order to compare the performance of the iron carbonyl precursor to the traditional superfine iron oxide catalyst. The carbonyl iron powder performed very well in terms of total conversion of coal as well as yield of coal oil product. The iron carbonyl powder acts as an effective precursor for the in situ generation of active iron sulfide. The simple kinetic models for coal liquefaction in the literature were found to be qualitatively consistent with the yields of preasphaltenes, asphaltenes, and oils obtained from the experiments.     

Application of coal conversion technology to tire processing

Tire recycling has been carried out using technology most commonly developed for coal conversion processes trying to take advantage of well-known reactors. Two different batch reaction systems (tubing bomb reactors and magnetically stirred autoclave) and a continuous reactor (swept fixed bed reactor) were tested. In addition, the influence of hydrogen pressure (ranging from 1 to 10 MPa) was assessed together with the influence of an inert or a hydrogenating atmosphere. Independently of the reactor used (tubing bomb reactors or magnetically stirred autoclave), the initial hydrogen pressure and the atmosphere, the 100% of the organic matter conversion was obtained in all the runs when batch reactors were used. When the semicontinuous reactor was used, slightly lower conversions were obtained, probably due to the deposition of products on the surface of the solid products. In all the experiments, conversion products were always oils and gases (comprised mainly of light hydrocarbons) plus a rich in carbon black solid residue. It was observed that the distribution between oils and gases was a function of the reactor type and in some cases a function of the hydrogen pressure. Oils were characterised by thin layer chromatography coupled to a flame ionisation detector (TLC-FID) and by simulated distillation. Different results in oils composition were obtained as a function of the reactor type and hydrogen pressure.     

Esterification of acrylic acid with methanol by reactive chromatography: Experiments and simulations

The esterification of acrylic acid with methanol using Amberlyst 15 as a stationary phase has been investigated using a chromatographic reactor. Several experimental runs at various operating conditions have been conducted on a batch column. A classical reactive chromatography model including lumped kinetics, a linear driving force transport model and a heterogeneous kinetic model for the catalytic reaction has been developed. The additional dispersion of concentration fronts due to density gradient effects has been accounted for in the model. The model parameters have been determined in a fast and reliable way by directly fitting the batch column experiments. In general, a good agreement between experimental and calculated results is obtained. The evaluation of the covariance of the fitted model parameters reveals important insights about the system behavior.Based on the detailed batch column model, a complete model of a simulated-moving-bed reactor has been implemented and its optimal point of operation for the synthesis of methyl acrylate from acrylic acid has been determined. Particularly when considering the low-operating temperature, we can regard this process as a possible competition for current technologies.     

Modeling the kinetics of a photochemical water treatment process by means of artificial neural networks

We have investigated the kinetics of the degradation of 2,4-dimethyl aniline (2,4-xylidine), chosen as a model pollutant, by the photochemically enhanced Fenton reaction. This process, which may be efficiently applied to the treatment of industrial waste waters, involves a series of complex reactions leading eventually to the mineralization of the organic pollutant. A model based on artificial neural networks has been developed for fitting the experimental data obtained in a laboratory batch reactor. The model can describe the evolution of the pollutant concentration during irradiation time under various conditions. It has been used for simulating the behavior of the reaction system in sensitivity studies aimed at optimizing the amounts of reactants employed in the process — an iron(II) salt and hydrogen peroxide. The results show that the process is much more sensitive to the iron(II) salt concentration than to the hydrogen peroxide concentration, a favorable condition in terms of economic feasibility.     

Reactive phase separation: Prediction of an occlusion morphology

Reaction-induced phase separation occurring by spinodal decomposition is simulated in this paper. A technique developed earlier [Alfarraj A, Nauman EB. Spinodal decomposition in ternary systems with significantly different component diffusivities. Macromolecular Theory and Simulations, 2007;16:627-31.] that allows component diffusivities to be dramatically different has been extended to reactive conditions. The example system is the formation of impact polystyrene. The final morphology is a continuous polystyrene phase and a discrete rubber phase where the rubber particles contain polystyrene occlusions. The morphology is modeled for an agitated batch reactor. Simulations of a quiescent batch polymerization also give a discrete rubber phase. This is contrary to reports in the early patent literature, the difference being attributed to cross-linking of the rubber that is not considered in the current model.     

Hydroconversion kinetics of Marlim vacuum residue

A kinetic model was obtained for the Marlim crude vacuum residue (VR) hydroconversion. Marlim VR mixed with FCC decant oil in an 80%/20% weight basis was put in contact with a commercial NiMo on γ-alumina catalyst in a stirred batch reactor. Several temperatures and oil/catalyst ratios were used over different times (0–240 min), at a 110 bar pressure and constant hydrogen flow. The analysis of the collected product showed residua conversions of up to 70%. Hydroconversion kinetics involving thermal and catalytic cracking contributions was proposed to represent the obtained data. The resulting system of differential equations of the kinetic model was solved within reaction time, taking into account the experimental temperature profile. The chi-square objective function was minimized to adjust model parameters. A proposed effective hybrid minimization method was used, by applying a Newton-type method between certain simulated annealing minimization steps. The proposed kinetic model allowed the representation of thermal and catalytic cracking effects, in order to take into account different catalyst concentrations. Therefore it is possible to consider distinct reactor hydrodynamics, such as expanded or bubble column reactors.     

渗透汽化-酯化反应耦联膜过程动力学模型

建立了渗透汽化 -酯化反应耦联复合膜反应器过程动力学模型及测量复合膜渗透率的方法 .该动力学模型较系统地考虑了复合膜反应器中可能影响酯化反应化学平衡移动的各种因素 .研究结果表明 ,模型的模拟结果能很好地与实验结果相吻合 .     

Palladium supported on filamentous active carbon as effective catalyst for liquid-phase hydrogenation of 2-butyne-1,4-diol to 2-butene-1,4-diol

Structured palladium catalysts suitable for three-phase reactions have been developed based on woven fabrics of active carbon fibres (ACF) as the catalytic supports. The Pd/ACF were tested in liquid-phase hydrogenation of 2-butyne-1,4-diol showing a selectivity towards 2-butene-1,4-diol up to 97% at conversions up to 80%. The catalyst multiple reuse with stable activity/selectivity in a batch reactor was also demonstrated. The reaction kinetics was studied and the main kinetic parameters were obtained. Assuming a Langmuir-Hinshelwood kinetics and a weak hydrogen adsorption a suitable kinetic model was developed consistent with the experimental data.     

A MATHEMATICAL MODEL FOR THE CATALYST DEACTIVATION IN A COMMERCIAL RESIDUE HYDRODESULFURIZATION REACTOR SYSTEM

A mathematical model that describes catalyst deactivation in a commercial Residue Hydrodesulfurization (RDS) system is proposed. In this model, coking, metal deposition and the decrease of effective diffusivities are all considered, so that it can predict the dynamics of catalyst activity during a long run of an RDS system. The RDS system under consideration here is a complex trickle bed reactor system with four adiabatic reactors in series, between which the oil is quenched by hydrogen to prevent the catalysts in the next reactor from being damaged by high temperature. This article shows that by incorporating a catalyst deactivation model into the overall reactor system model, the predicted catalyst aging curve assumes the “S” shape, characteristic of real RDS system. The model prediction are compared with data from an operating refinery and the agreement is pleasing. KEYWORDS Residue Hydrodesulfurization(RDS) Apparent activity Catalyst deactivation curve Pore radius.     

Modelling of citral hydrogenation kinetics on an Ni/Al2O3 catalyst

The kinetics of citral hydrogenation in ethanol over an Ni/Al₂O₃ catalyst was studied in a slurry reactor operating at atmospheric pressure and at a temperature range of 60–77°C. Citronellal was the primary reaction product, whereas the amounts of unsaturated alcohols were very minor. Citronellol was the dominating product, generated mainly through the hydrogenation of the carbonyl group of citronellal. Based on the experimental data, a kinetic model was developed for hydrogenation. The model comprises competitive and rapid adsorption steps as well as rate-determining hydrogenation steps. The mass transfer limitation of hydrogen was included in the mathematical model. The kinetic parameters and the mass transfer parameter of hydrogen were estimated from the experimental data. A comparison of the model predictions with the experimental data revealed that the proposed kinetic approach gave a satisfactory reproduction of the data.     

ION EXCHANGE OF SEVERAL RADIONUCLIDES ON THE HYDROUS CRYSTALLINE SILICOTITANATE,UOP IONSIV IE-911

ABSTRACT

The crystalline silicotitanate, UOP IONSIV IE-911, is a proven material for removing radionuclides from a wide variety of waste streams. It is superior for removing several radionuclides from the highly alkaline solutions typical of DOE wastes. Our laboratory previously developed an equilibrium model applicable to complex solutions for IE-910 (the powder form of the granular IE-911), and more recently, we have developed several single component ion-exchange kinetic models for predicting column breakthrough curves and batch reactor concentration histories. In this paper, we model ion-exchange column performance using effective diffusivities determined from batch kinetic experiments. This technique is preferable because the batch experiments are easier, faster, and cheaper to perform than column experiments. We also extend these ideas to multicomponent systems. Finally, we evaluate the ability of our equilibrium model to predict data for IE-911.     

Xylose hydrogenation: kinetic and NMR studies of the reaction mechanisms

Hydrogenation of xylose over Raney nickel was studied in a batch reactor. A pseudo-homogeneous kinetic model was able to prognose the xylose and xylitol concentrations rather well. The obtained fit for the activation energies suggests that external diffusion limitations are absent in our experimental conditions. The sugar equilibria studies gave new information about the temperature dependence of the –β-pyranose equilibria. It was found that the equilibria in D₂O follows an S-shaped curve, the equilibria being shifted towards the -form at higher temperatures.     

Multiple model-based controller design applied to an electrochemical batch reactor

This study demonstrates the control of an electrochemical batch reactor, that produces the desired product in a competing chemical/electrochemical reaction network, using a multiple model-based controller design. Since this type of control framework requires a process model to provide predictions of the controlled variables, and because batch reactors are highly nonlinear and nonstationary in nature, a bank of linear, dynamic, state-space models rather than a single, linear state-space or convolution model is developed to represent the nonstationary behaviour of the batch process. It is shown that the performance of this model/controller design can provide good reactor performance in the face of known disturbances.