Discontinuous stirred tank reactor

The discontinuous stirred tank reactor represents one of the most traditional reactor configurations for enzymatic reactions. It consists of a stirred tank where the enzyme, substrates, and cofactors are added at the beginning of the operation with no inlet and/or outlet stream during the reaction time. This type of reactor is usually considered to present an ideal hydrodynamic behavior therefore, the reactor is supposed to be completely mixed and the concentration of all... 

Selective hardening of edible oils in discontinuous stirred tank reactors (STR), continuous trickle bed reactors and in continuous flow reactors operating with supercritical CO2... 

The main difference between parameter estimates based on continuous (micro-trickle bed reactor) and discontinuous (stirred tank reactor) experiments is the preexponential factor which is somewhat smaller for continuous operation. The parameter values reported in Eq. 1 and 2 correspond to continuous operations. This problem is analyzed elsewhere in more detail (6 ). 

Figure 3.8. Measurement (a) and evaluation (b) of the mixing time, of the liquid phase in a discontinuous stirred tank reactor using the degree-of-mixing parameter m, Equ. 3.17. In reactors with constant recirculation, the circulation time, t, may also be determined as indicated. The degree of inhomogeneity J is also shown. (From Dechema, 1982).

A discontinuous stirred tank reactor (DCSTR) with ideal mixing conditions has no concentration profile in space. The process is, however, time dependent and thus has a concentration/time profile (c/t). 

Figure 3.30. Basic reactor concept and concentration-versus>time and concentration-versus-space profiles. DCSTR, discontinuous stirred tank reactor SCSTR, semicon-tinuous stirred tank reactor CSTR, continuous stirred tank reactor CPFR, continuous plug flow reactor NCSTR, a cascade of N stirred vessels.

Model 1 The Ideal Discontinuous Stirred Tank Reactor (DCSTR)... 

During the manufacturing process, if the grafting increases during early stages of the reaction, the phase volume will also increase, but the size of the particles will remain constant [146-148]. Furthermore, reactor choice plays a decisive role. If the continuous stirred tank reactor (CSTR) is used, little grafting takes place and the occlusion is poor and, consequently, the rubber efficiency is poor. However, in processes akin to the discontinuous system(e.g., tower/cascade reactors), the dispersed phase contains a large number of big inclusions. 

Discontinuous (batch) processes are carried out in pressure vessels (autoclaves) where DMC is maintained as liquid by autogenous pressure. Instead, CF reactions at atmospheric pressure require that both DMC and the reagent(s) in the vapor phase come into contact with a catalytic bed a constraint that has spurred the development of new applications and alternative reaction engineering, namely, GL-PTC and the continuously fed stirred-tank reactor (CSTR). 

We have demonstrated that vegetable oils and fatty acid esters can be selectively hardened in liquid, near-critical, or supercritical C02 or propane and in mixtures thereof at temperatures between 60 °C and 120 °C and at a total pressure up to 20.0 MPa. Table 14.2 summarizes the results for the selective hydrogenation of vegetable oils in supercritical C02 in comparison with hydrogenation reactions performed in a discontinuous (i.e., batch or semibatch) stirred-tank reactor and in a continuous trickle-bed reactor. 

This expression enhances the fact that the heat release rate is a function of the conversion and will therefore vary with time in discontinuous reactors or during storage. In a batch reaction, there is no steady state. It is constant in the Continuous Stirred Tank Reactor (CSTR) and is a function of the location in the tubular reactor (see Chapter 8). The heat release rate is... 

The discontinuous stirred reactor (Batch Reactor, BR, Fig. 2.1(a)) corresponds to a closed thermodynamic system, whereas the two continuous reactors (Continuous Stirred Tank Reactor, CSTR, Fig. 2.1(b), and Plug Flow Reactor, PFR, Fig. 2.1(c))... 

Catalytic tests in sc CO2 were run continuously in an oil heated flow reactor (200°C, 20 MPa) with supported precious metal fixed bed catalysts on activated carbon and polysiloxane (DELOXAN ). We also investigated immobilized metal complex fixed bed catalysts supported on DELOXAN . DELOXAN is used because of its unique chemical and physical properties (e. g. high pore volume and specific surface area in combination with a meso- and macro-pore-size distribution, which is especially attractive for catalytic reactions). The effects of reaction conditions (temperature, pressure, H2 flow, CO2 flow, LHSV) and catalyst design on reaction rates and selectivites were determined. Comparative studies were performed either continuously with precious metal fixed bed catalysts in a trickle bed reactor, or discontinuously in stirred tank reactors with powdered nickel on kieselguhr or precious metal on activated carbon catalysts. Reaction products were analyzed off-line with capillary gas chromatography. 

The intrinsic reaction rate has been measured in a discontinuous slurry stirred tank reactor and in a continuous microtrickle bed reactor (6 ). This last one is represented in Figure 1 Both methods lead to rather similar expressions for the intrin-sid rate equation r(mol/kg Pd. s)... 

Classical chemical reaction engineering provides mathematical concepts to describe the ideal (and real) mass balances and reaction kinetics of commonly used reactor types that include discontinuous batch, mixed flow, plug flow, batch recirculation systems and staged or cascade reactor configurations (Levenspiel, 1996). Mixed flow reactors are sometimes referred to as continuously stirred tank reactors (CSTRs). The different reactor types are shown schematically in Fig. 8-1. All these reactor types and configurations are amenable to photochemical reaction engineering. 

The fermentations were carried out in stirred tank reactors with 10 L woiidng volume in discontinuous fed-batch mode which means that carbon and nitrogen sources were fed to the media in several portions but not continuously. The temperature was maintained at 30 C. The pH was regulated automatically to maintain 7 0.1 by addition of 20 wt% NaOH and 20 wt% H3PO4 respectively. Agitation and aeration were controlled manually. 

Mechanically agitated stirred tank reactors are preferentially used in food- and bio-technology or with smaller chemical productions where they are operated very often discontinuously. The gas phase is supplied either under pressure through a static gas feeder, by self-suction agitators or by surface aeration, sometimes assisted by an additional stirrer fitted just below the gas-liquid interface. Paddles with inclined or straight blades and turbines are the most common types of agitators. They are very effective with viscose liquids at low gas flow rates and large liquid volumes. 

Simple reactions In closed (discontinuous stirred tank) or steady-state open (continuous stirred tank or plug flow) reactor systems... 

Chapter 2 presents calorimeters for measuring accurately the rate of heat release during discontinuous and continuous reactions versus time under isothermal and nonisothermal conditions. In addition, the chapter contains a description of an apparatus that can be used to record online the rate of heat release within a stirred tank reactor during a reaction. 

Leading characteristics of five main kinds of reactors are described following. Stirred tanks, fixed beds, slurries, and three-phase fluidized beds are used. Catalyst particle sizes are a compromise between pressure drop, ease of separation from the fluids, and ease of fluidization. For particles above about 0.04 mm dia, diffusion of liquid into the pores and, consequently, accessibility of the internal surface of the catalyst have a minor effect on the overall conversion rate, so that catalysts with small specific surfaces, of the order of 1 m2/g, are adequate with liquid systems. Except in trickle beds the gas phase is the discontinuous one. Except in some operations of bubble towers, the catalyst remains in the vessel, although minor amounts of catalyst entrainment may occur. 

Characteristically this equation contains again the time t as a process variable. This term with the time t disappears and can be neglected in the case of stationarity (if t t) and when Cj q = c , that is, in a batch reactor. Therefore the stoichiometric balance equation of a discontinuous system can be formally applied to a nonstationary continuous stirred tank. Similarly, the stoichiometric equations of heterogeneous reactor systems with interfacial mass transfer can be derived (Budde, Bulle, and Riickauf, 1981). 

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