Kinetic semibatch reactor

The model is able to predict the influence of mixing on particle properties and kinetic rates on different scales for a continuously operated reactor and a semibatch reactor with different types of impellers and under a wide range of operational conditions. From laboratory-scale experiments, the precipitation kinetics for nucleation, growth, agglomeration and disruption have to be determined (Zauner and Jones, 2000a). The fluid dynamic parameters, i.e. the local specific energy dissipation around the feed point, can be obtained either from CFD or from FDA measurements. In the compartmental SFM, the population balance is solved and the particle properties of the final product are predicted. As the model contains only physical and no phenomenological parameters, it can be used for scale-up. 

Semibatch Model "GASPP". The kinetics for a semibatch reactor are the simpler to model, in spite of the experimental challenges of operating a semibatch gas phase polymerization. Monomer is added continuously as needed to maintain a constant operating pressure, but nothing is removed from the reactor. All catalyst particles have the same age. Equations 3-11 are solved algebraically to supply the variables in equation 5, at the desired operating conditions. The polymerization flux, N, is summed over three-minute intervals from the startup to the desired residence time, t, in hours ... 

This section is divided into three parts. The first is a comparison between the experimental data reported by Wisseroth (].)for semibatch polymerization and the calculations of the kinetic model GASPP. The comparisons are largely graphical, with data shown as point symbols and model calculations as solid curves. The second part is a comparison between some semibatch reactor results and the calculations of the continuous model C0NGAS. Finally, the third part discusses the effects of certain important process variables on catalyst yields and production rates, based on the models. 

Semibatch reactors are often used to mn highly exothermic reactions isothermally, to run gas-liquid(-solid) processes isobarically, and to prevent dangerous accumulation of some reactants in the reaction mixture. Contrary to batch of)eration, temperature and pressure in semibatch reactors can be varied independently. The liquid reaction mixture can be considered as ideally mixed, while it is assumed that the introduced gas flows up like a piston (certainly this is not entirely true). Kinetic modelling of semibatch experiments is as difficult as that of batch, non-isotherma experiments. 

S.4. Guidelines for scale-up of semibatch reactors for fast homogeneous reactions in the absence of data on chemical kinetics and on the distribution of energy dissipation in the reaction zone... 

Kinetic Model Discrimination. To discriminate between the kinetic models, semibatch reactors were set up for the measurement of reaction rates. The semi-batch terminology is used because hydrogen is fed to a batch reactor to maintain a constant hydrogen pressme. This kind of semi-batch reactor can be treated as a bateh reactor with a constant hydrogen pressme. The governing equations for a bateh reactor, using the product formation rate for three possible scenarios, were derived, as described in reference (12) with the following results ... 

Solution From the kinetic expressions given in Example 7.3, it can be concluded that n/ri = k Clca. In order to increase the selectivity of the reactions, the Clcii should be minimized. A semibatch reactor would thus be preferred, in which BA is charged at the beginning of the batch and CL fed continuously during the reaction. In any case, charging all of the chlorine at the beginning of the reaction will be impractical. 

In pulp and paper processing, anthraquinone (AQ) accelerates the delignification of wood and improves liquor selectivity. The kinetics of the liquid-phase oxidation of anthracene (AN) to AQ with NO2 in acetic acid as solvent has been studied by Rodriguez and Tijero (1989) in a semibatch reactor (batch with respect to the liquid phase), under conditions such that the kinetics of the overall gas-liquid process is controlled by the rate of the liquid-phase reaction. This reaction proceeds through the formation of the intermediate compound anthrone (ANT) ... 

We focus mainly on the advantages and disadvantages of semibatch reactors. A semicontinuous reactor may be treated in many cases as either a batch reactor or a continuous reactor, depending on the overall kinetics and/or the phase of interest. 

Glaze W H, Kang J-W (1989 a) 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, Industrial Engineering Chemical Research 28 1573-1580. 

Glaze WH, Kang JH. 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. Ind Eng Chem Res 1989 28 1573-1580. 

The preferred reactor for kinetics is the chemostat, but semibatch reactors are more often used owing to their simpler operation. 

Types of Reactor Processes Batch Reactors Semibatch Reactors Continuous Reactors Emulsion Polymerization Kinetics Other Preparation Methods... 

The influence of heat transfer on yield and selectivity in scaling up batch and semibatch reactors will be illustrated using a series reaction, taking place in an ideal jacketed stirred-tank reactor. This reaction is composed of two irreversible elementary steps, both exothermic and both with first order kinetics ... 

In this chapter we have found that a reactor type that is familiar to us and that has intuitively obvious usefulness, namely, the well-mixed semibatch reactor, is also very complex to treat—at least analytically—due to its transient behavior. It is also evident that we would never use this kind of reactor to evaluate even the most basic chemical kinetics. Thus we need a simpler type of reactor that is mathematically more tractable and experimentally more feasible to operate. We will see instances of these in the next chapter. Along the way we have now added the final element that we needed in our Mathematica toolbox, the writing of Modules. We will build on this to produce even more useful Packages in what follows. 

A kinetic investigation of the Co-catalyzed hydroformylation in a semibatch reactor [44] showed that the pseudo-first-order rate constant for the reaction is a function of pressure if the rate law known from liquid organic solvents is used for data analysis. However, a nonlinear relationship between the reaction rate and the catalyst concentration was observed and is not in agreement with the simple kinetic scheme. From a practical viewpoint, the large catalyst loadings and the relatively forcing conditions are still severe limitations of this catalytic reaction. 

Consider the process illustrated in Figure 4.17, where the second-order irreversible reaction A + B C is carried out in a semibatch reactor. Since there is a large excess of A present within the reactor, we may take the kinetics of the reaction to be pseudo-first-order in B, and since this is not a constant-volume operation let us write a molal balance on B. 

When a reactor is charged with liquid A and B is a gas that is added continuously, it becomes a semibatch reactor. The rates of reaction depend on the concentration of B in the liquid phase, which is a function of gas solubility, pressure, and agitation conditions. However, we are often concerned with the relative reaction rates and the selectivity, which do not depend on Cb if the reaction orders are the same for both reactions. The reactions are treated as pseudo-first-order, and equations are developed for an ideal batch reactor with irreversible first-order kinetics... 

Finally a fourth boundary condition shall be valid to support the worst case character of the procedure. The reaction order necessary for the formal kinetic description of a process has a severe influence on the pressure/time and respectively the tempera-ture/time-profiles to be expected. Industrial experience has shown that approximately 90% of all processes conducted in either batch or semibatch reactors can be described with a second order formal kinetic rate law. But it remains uncertain whether this statement, which is related to isothermal or isoperibolic operation with a rather limited overheating, remains valid if the reaction proceeds adiabatically and if side reactions contribute to the gross reaction rate at a much higher degree. In consequence, it shall be assumed for a credible worst case evaluation that the disturbed process follows a first order kinetics. Any reactions occurring in reality will almost certainly proceed at a much lower rate. 

Optimization can be done by proper reactor choice followed by a suitable temperature progression in the case of a batch or semibatch reactor, or by temperature profiling in the case of a tubular reactor. An even more effective way is to optimize reactant concentrations, pressure, and/or temperature by applying certain simple rules of kinetics and manipulation of the chemistry (wherever possible). Hence the combined efforts of chemist and chemical engineer are needed to optimize selectivity in a given complex reaction. 

The kinetics of reactions is specific for different reaction systems and processes and valid for isothermal and nonisothermal reactors. The effects of the kinetics on the conversion, selectivity, or yield depend on the reaction and may be quite pronounced. Liquid or gas phase reactions with high heat capacity can be performed in specific reactors, which operate isothermally or not. We will study the most common cases such as semibatch reactors, recycle reactors, fixed-bed reactors, and reactors with membranes. 

The semibatch reactor (tank or tubular) contains a large amount of liquid reactant that continuously reacts on the addition of a second reactant (liquid or gas), which is instantly consumed. The kinetics is the same, but consumption increases over reaction time as the second component is added (Figure 15.1). 

The kinetics of the esterification of levulinic acid with 2-ethylhexanol in the presence of the various catalyst has been investigated in an experimental, isothermal semibatch reactor. The kinetic equations and dieir parameters have been determined. 

Since the Bart s research [1] was limited to one selected catalyst, it seemed reasonable to widen the work to other catalyst used in industry. The goal of this work was to learn about the kinetics of esterification of levulinic acid with 2-ethylhexanol using different catalysts, based on wide range of experiments in a semibatch reactor. 

Rg. 9.8. Mixed-metallocene polymerization of ethylene in a semibatch reactor branching (constrained geometry) catalyst CGC-Ti linear catalyst Et[lnd]2ZrCl2. Reactor and kinetic data initial concentration CGC-Ti 8 x 10 kmol m initial concentration Et[lnd]2ZrCl2 3.2 X 10 kmol m monomer molar feed... 

Emulsion polymerization studies reported in the scientific literature are usually based on experiments with batch or semibatch reactor systems. Since most workers in the field are familiar with such reactors, the thrust of this discussion will be to compare continuous reactors with batch and semi-batch operations. The particular areas to be reviewed include (i) inhibitor effects, (ii) particle age distributions, (iii) particle nucleation, (iv) copolymerization, (v) particle morphology, (vi) temperature control and heat removal and (vii) polymerization kinetic models. 

The continuous analog to a semibatch reactor can be designed as a PFR with material feeds located at fixed positions along the reactor axis. Kinetic analyses for the various polymerization chemistries in a PHi are not given since they are identical to those for a BR. 

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