Semibatch reactor scale

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. 

The performance of a novel microwave-induced pyrolysis process was evaluated by studying the degradation of HDPE and aluminiutn/polymer laminates in a semibatch bench-scale apparatus. The relationship between temperature, residence time of the pyrolytic products in the reactor, and the chemical composition of the hydrocarbon fraction produced was investigated. 28 refs. 

Factors re.sponsible for the occurrence of scale-up effects can be either material factors or size/shape factors. In addition, differences in the mode of operation (batch or semibatch reactor in the laboratory and continuous reactor on the full scale), or the type of equipment (e.g. stirred-tank reactor in the laboratory and packed- or plate- column reactor in commercial unit) can be causes of unexpected scale-up effects. A simple misuse of available tools and information also can lead to wrong effects. 

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... 

Price and Schiewetz Ind Eng. Chem. 49 (807), 1957] have studied the catalytic liquid phase hydrogenation of cyclohexene in a laboratory scale semibatch reactor. A supported platinum catalyst was suspended in a cyclohexene solution of the reactant by mechanical... 

The same example was solved using MINOPT (Rojnuckarin and Floudas, 1994) by treating the PFR model as a differential model. The required input files are shown in the MINOPT manual. Kokossis and Floudas (1990) applied the presented approach for large-scale systems in which the reactor network superstructure consisted of four CSTRs and four PFR units interconnected in all possible ways. Each PFR unit was approximated by a cascade of equal volume CSTRs (up to 200-300 CSTRs in testing the approximation). Complex reactions taking place in continuous and semibatch reactors were studied. It is important to emphasize that despite the complexity of the postulated superstructure, relatively simple structure solutions were obtained with the proposed algorithmic strategy. 

In continuous processes the reactants are fed to the reactor and the products withdrawn continuously the reactor operates under steady-state conditions. Continuous production will normally give lower production costs than batch production, but it lacks the flexibility of batch production. Continuous reactors will usually be selected for large-scale production. Processes that do not fit the definition of batch or continuous are often referred to as semicontinuous or semibatch. In a semibatch reactor, some of the reactants may be added or some of the products withdrawn as the reaction proceeds. A semicontinuous process can be one which is interrupted periodically for some purpose, for instance, for the regeneration of catalyst. 

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 ... 

This problem has been adapted with permission from the late Professor C. N. Satterfield of MIT. R. H. Price and R. B. Schiewetz [Ind Eng. Chem., 49, 807 (1957)] studied the catalytic liquid-phase hydrogenation of cyclohexene in a laboratory-scale semibatch reactor. A supported platinum catalyst was suspended in a cyclohexene solution of the reactant by mechanical agitation of the solution. Hydrogen was bubbled through the solution continuously. The reactor is described in their words as follows ... 

An industrial batch reactor has neither an inflow nor an outflow of reactants or products while the reaction is being carried out. Batch reactions can be carried out in droplet microreactors, where nanoliters of fluid are individually manipulated using techniques such as electrowetting on dielectric (EWOD) and surface tension control. Semibatch reactors are used in cases where a by-product needs to be removed continuously and to cany out exothermic batch reactions where a reactant has to be added slowly. Microfluidics allows precise control of concentration and temperature, which allows batch and semibatch reactions to be carried out in a continuous manner. Figure 1 shows the general components of a simple industrial-reactor semp, compared with a laboratory-scale setup to carry out a reaction with microfluidic chips. 

Semibatch and continuous stirred-tank reactors (CSTRs) are much more commonly found in polyolefin production. Semibatch reactors are the standard choice for laboratory-scale polymerizations, while CSTRs dominate industrial production, as will be seen in Section 2.5. The equations derived above are easily translated into semibatch and CSTR operation mode by simply adding terms for the inflow and outflow streams in the reactor. For instance, consider Equation 2.49 for the zeroth moment of dead chains. The molar flow rate [mol s ] leaving the reactor is given by... 

The batch emulsion polymerization is commonly used in the laboratory to study the reaction mechanisms, to develop new latex products and to obtain kinetic data for the process development and the reactor scale-up. Most of the commercial latex products are manufactured by semibatch or continuous reaction systems due to the very exothermic nature of the free radical polymerization and the rather limited heat transfer capacity in large-scale reactors. One major difference among the above reported polymerization processes is the residence time distribution of the growing particles within the reactor. The broadness of the residence time distribution in decreasing order is continuous>semibatch>batch. As a consequence, the broadness of the resultant particle size distribution in decreasing order is continuous>semibatch>batch, and the rate of polymerization generally follows the trend batch>semibatch>continuous. Furthermore, the versatile semibatch and continuous emulsion polymerization processes offer the operational flexibility to produce latex products with controlled polymer composition and particle morphology. This may have an important influence on the application properties of latex products [270]. 

Chlorination of butanoic acid to a-monochloro- and a,a-dichlorobutanoic acid was studied on the laboratory scale in a semibatch reactor ... 

Mesomixing is mixing on a scale smaller than the bulk circulation (or the tank diameter) but larger than the micromixing scales, where molecular and viscous diffusion become important. Mesomixing is most frequently evident at the feed pipe scale of semibatch reactors. 

Results for the static mixer in both laboratory scale 0.008 m (0.8 cm) and plant scale 0.0254 m (2.54 cm) operation were excellent. No change in selectivity or product distribution occurred over this scale-up. When there are compelling reasons to use a semibatch reactor instead of a semicontinuous system, the reactor... 

In order to account for both micromixing and mesomixing effects, a mixing model for precipitation based on the SFM has been developed and applied to continuous and semibatch precipitation. Establishing a network of ideally macromixed reactors if macromixing plays a dominant role can extend the model. The methodology of how to scale up a precipitation process is depicted in Figure 8.8. 

To illustrate the complexity of process optimization, suppose that we are to scale-up a semibatch stirred-tank reactor for carrying out the following consecutive reactions ... 

Reactors can be operated either in a batch or continuous-flow mode. The combination, batch with respect to the liquid and continuous-flow with respect to the gas, is called semibatch. Often this fine distinction is ignored and it is commonly referred to as batch. The majority of ozonation experiments reported in the literature have been performed in one-stage semi-batch heterogeneous systems, with liquid phase reactor volumes in the range VL = 1-10 L. Most full-scale applications are operated in continuous-flow for both phases. 

Heterogeneously catalyzed hydrogenation reactions can be run in batch, semibatch, or continous reactors. Our catalytic studies, which were carried out in liquid, near-critical, or supercritical C02 and/or propane mixtures, were run continuously in oil-heated (200 °C, 20.0 MPa) or electrically heated flow reactors (400 °C, 40.0 MPa) using supported precious-metal fixed-bed catalysts. The laboratory-scale apparatus for catalytic reactions in supercritical fluids is shown in Figure 14.2. This laboratory-scale apparatus can perform in situ countercurrent extraction prior to the hydrogenation step in order to purify the raw materials employed in our experiments. Typically, the following reaction conditions were used in our supercritical fluid hydrogenation experiments catalyst volume, 2-30 mL total pressure, 2.5-20.0 MPa reactor temperature, 40-190 °C carbon dioxide flow, 50-200 L/h ... 

Comparative experiments are carried out between the SCISR and the STR for further verifying the good performance of the SCISR. Both the reactors are operated in semibatch mode and under the same optimized conditions as before. The structure and dimensions of the experimental reactors have been described in Section 13.2. The size distributions of the particles in the precipitates from the two reactors are illustrated in Fig. 13.2. Obviously, the product from the SCISR is finer with a narrower size distribution, i.e., more uniform in size. It should be noted that the effective volume of the experimental SCISR is six times that of the STR, suggesting the scales favor the... 

The corresponding semibatch process is a rather slow reaction at 90 °C with simultaneous exothermic decomposition of DAST. Thus, the processed volume is restricted to laboratory scale (< 11) [ 50]. The transfer to production in a stirred tank is prohibited because of these safety reasons. A micromixer-tube reactor approach was chosen using the convective-flow-driven bas-relief caterpillar micromixer and tubes with diameters of 1-5 mm and lengths up to 20 m, respectively, and tube reactor volumes up to 500 ml (see Figure 5.16). 

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