Selectivity stirred tank

Specific reactor characteristics depend on the particular use of the reactor as a laboratory, pilot plant, or industrial unit. AH reactors have in common selected characteristics of four basic reactor types the weH-stirred batch reactor, the semibatch reactor, the continuous-flow stirred-tank reactor, and the tubular reactor (Fig. 1). A reactor may be represented by or modeled after one or a combination of these. SuitabHity of a model depends on the extent to which the impacts of the reactions, and thermal and transport processes, are predicted for conditions outside of the database used in developing the model (1-4). 

Continuous-Flow Stirred-Tank Reactor. In a continuous-flow stirred-tank reactor (CSTR), reactants and products are continuously added and withdrawn. In practice, mechanical or hydrauHc agitation is required to achieve uniform composition and temperature, a choice strongly influenced by process considerations, ie, multiple specialty product requirements and mechanical seal pressure limitations. The CSTR is the idealized opposite of the weU-stirred batch and tubular plug-flow reactors. Analysis of selected combinations of these reactor types can be useful in quantitatively evaluating more complex gas-, Hquid-, and soHd-flow behaviors. 

Continuous-flow stirred-tank reactors ia series are simpler and easier to design for isothermal operation than are tubular reactors. Reactions with narrow operating temperature ranges or those requiring close control of reactant concentrations for optimum selectivity benefit from series arrangements. 

FIG. 23-30 Basic stirred tank design and selected lands of impellers, (h) Propeller, (c) Turbine, (d) Hollow, (e) Anchor,... 

There are a variety of ways of accomplishing a particular unit operation. Alternative types of process equipment have different inherently safer characteristics such as inventory, operating conditions, operating techniques, mechanical complexity, and forgiveness (i.e., the process/unit operation is inclined to move itself toward a safe region, rather than unsafe). For example, to complete a reaction step, the designer could select a continuous stirred tank reactor (CSTR), a small tubular reactor, or a distillation tower to process the reaction. 

In this short initial communication we wish to describe a general purpose continuous-flow stirred-tank reactor (CSTR) system which incorporates a digital computer for supervisory control purposes and which has been constructed for use with radical and other polymerization processes. The performance of the system has been tested by attempting to control the MWD of the product from free-radically initiated solution polymerizations of methyl methacrylate (MMA) using oscillatory feed-forward control strategies for the reagent feeds. This reaction has been selected for study because of the ease of experimentation which it affords and because the theoretical aspects of the control of MWD in radical polymerizations has attracted much attention in the scientific literature. 

There are two important types of ideal, continuous-flow reactors the piston flow reactor or PFR, and the continuous-flow stirred tank reactor or CSTR. They behave very diflerently with respect to conversion and selectivity. The piston flow reactor behaves exactly like a batch reactor. It is usually visualized as a long tube as illustrated in Figure 1.3. Suppose a small clump of material enters the reactor at time t = 0 and flows from the inlet to the outlet. We suppose that there is no mixing between this particular clump and other clumps that entered at different times. The clump stays together and ages and reacts as it flows down the tube. After it has been in the piston flow reactor for t seconds, the clump will have the same composition as if it had been in a batch reactor for t seconds. The composition of a batch reactor varies with time. The composition of a small clump flowing through a piston flow reactor varies with time in the same way. It also varies with position down the tube. The relationship between time and position is... 

The main part of the report describes the results of systematic investigations into the hydrodynamic stress on particles in stirred tanks, reactors with dominating boundary-layer flow, shake flasks, viscosimeters, bubble columns and gas-operated loop reactors. These results for model and biological particle systems permit fundamental conclusions on particle stress and the dimensions and selection of suitable bioreactors according to the criterion of particle stress. 

Even in the case of standard reactors such as stirred tanks and bubble columns, lack of knowledge in this area limits our ability to use particle stress as a selection criterion. The reasons for this lack of knowledge are, on the one hand, that the velocity fields in the reactors, which would allow a certain prediction, can only be obtained by sophisticated measurements and measurement techniques, and on the other hand, the stress on particles becomes evident only as an integral result of a long term process. 

While in Fig. 16 selected results are plotted against the average energy density e = P/V9, in Fig. 17 all of the essential results for stirred tanks and bubble... 

Such improvements in conversion were reported for the oxidation of ethanol by hydrogen peroxide to acetic acid. This is a well-studied reaction, carried out in a continuous stirred-tank reactor (CSTR). Near-complete conversion (> 99%) at near-complete selectivity (> 99%) was found in a micro-reaction system [150]. Processing in a CSTR resulted in 30-95% conversion at > 99% selectivity. 

If the process is carried out in a stirred batch reactor (SBR) or in a plug-flow reactor (PFR) the final product will always be the mixture of both products, i.e. the selectivity will be less than one. Contrary to this, the selectivity in a continuous stirred-tank reactor (CSTR) can approach one. A selectivity equal to one, however, can only be achieved in an infinite time. In order to reach a high selectivity the mean residence time must be very long, and, consequently, the productivity of the reactor will be very low. A compromise must be made between selectivity and productivity. This is always a choice based upon economics. 

In a typical test 750 mg of catalyst was added to a continuous stirred tank reactor containing the nitrate ions in 1 L of phosphate buffer solution. This suspension contained 85% H3PO4 (331 g), NaNOs (198 g), NaOH (84g), and Ge02 dissolved in water and was stirred under a H2 flow of 150 L/h. The amonnt of hyam formed and selectivity after 90 min at 30°C were measured by titration [2-3]. Catalysts A and C were also chosen for stndying the effect of Pd loading and Pt addition. 

Drawing heavily from prior experience in hydrogenation of nitriles (7-10) and of ADN to ACN and/or HMD (11), in particular, we decided to restrict the scope of this investigation to Raney Ni 2400 and Raney Co 2724 catalysts. The hydrogenation reactions were initially carried out in a semi-batch reactor, followed by continuous stirred tank reactor to study the activity, selectivity, and life of the catalyst. 

Selectivity considerations may also dictate the use of stirred tank reactors. They are preferred if undesirable side reactions predominate at high reactant concentrations, and they are also useful when one desires to skip certain concentration or temperature ranges where byproduct formation may be excessive. 

Figure 4.15 Selective adsorption synthesis of a-cyclodextrin from starch applying a hatch process using a sequence of stirred-tank reactor, heat exchanger modules and adsorption step...

Many correlations allow estimation of the gas-liquid volumetric mass transfer coefficient kLa in mechanically stirred tank reactors. The following intends not to provide a comprehensive review but rather a critical evaluation of selected correlations adapted to hydrogenations [Eqs. (40) to (43)] [25, 51-53]. 

Many wastewater flows in industry can not be treated by standard aerobic or anaerobic treatment methods due to the presence of relatively low concentration of toxic pollutants. Ozone can be used as a pretreatment step for the selective oxidation of these toxic pollutants. Due to the high costs of ozone it is important to minimise the loss of ozone due to reaction of ozone with non-toxic easily biodegradable compounds, ozone decay and discharge of ozone with the effluent from the ozone reactor. By means of a mathematical model, set up for a plug flow reactor and a continuos flow stirred tank reactor, it is possible to calculate more quantitatively the efficiency of the ozone use, independent of reaction kinetics, mass transfer rates of ozone and reactor type. The model predicts that the oxidation process is most efficiently realised by application of a plug flow reactor instead of a continuous flow stirred tank reactor. 

P. Albertos and M. Perez Polo. Selected Topics in Dynamics and Control of Chemical and Biochemical Processes, chapter Nonisothermal stirred-tank reactor with irreversible exothermic reaction A B. 1.Modelling and local control. LNCIS. Springer-Verlag, 2005 (in this volume). 

The types of equipment used, which range from stirred tanks and mixer-settlers to centrifugal contactors and various types of columns, affect both capital and operating costs [9]. In the decision to build a plant, the choice of the most suitable contactor for the specific situation is most important. In some systems, because of the chemistry and mass transfer rates involved, several alternative designs of contacting equipment are available. In the selection of a contactor, one must consider the capacity and stage requirements solvent type and residence time phase flow ratio physical properties direction of mass transfer phase dispersion and coalescence holdup kinetics equilibrium presence of solids overall performance and maintenance as a function of contactor complexity. This may appear very complicated, but with some experience, the choice is relatively simple. 

Reductive alkylation is an efficient method to synthesize secondary amines from primary amines. The aim of this study is to optimize sulfur-promoted platinum catalysts for the reductive alkylation of p-aminodiphenylamine (ADPA) with methyl isobutyl ketone (MIBK) to improve the productivity of N-(l,3-dimethylbutyl)-N-phenyl-p-phenylenediamine (6-PPD). In this study, we focus on Pt loading, the amount of sulfur, and the pH as the variables. The reaction was conducted in the liquid phase under kinetically limited conditions in a continuously stirred tank reactor at a constant hydrogen pressure. Use of the two-factorial design minimized the number of experiments needed to arrive at the optimal solution. The activity and selectivity of the reaction was followed using the hydrogen-uptake and chromatographic analysis of products. The most optimal catalyst was identified to be l%Pt-0.1%S/C prepared at a pH of 6. 

Whole cells are used in stirred tanks with pH control, producing fS )-2-chloropropanoic acid in 50% yield from the racemate (0.3 M) with an enantiomeric excess of over 95%. This approach was selected in preference to other methods of resolution such as acylation of the racemate and then stereoselective hydrolysis. The dehalogenase enzyme is specific for substrates with a carboxyl group and a 2-chloro or bromo substituent. No cofactor or metal ion is required and reaction involves an inversion of configuration. 

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