Stirred batch reactor constants

Peaking and Non-isothermal Polymerizations. Biesenberger a (3) have studied the theory of "thermal ignition" applied to chain addition polymerization and worked out computational and experimental cases for batch styrene polymerization with various catalysts. They define thermal ignition as the condition where the reaction temperature increases rapidly with time and the rate of increase in temperature also increases with time (concave upward curve). Their theory, computations, and experiments were for well stirred batch reactors with constant heat transfer coefficients. Their work is of interest for understanding the boundaries of stability for abnormal situations like catalyst mischarge or control malfunctions. In practice, however, the criterion for stability in low conversion... 

Consider a well-stirred batch reactor of constant fluid volume V in which the reactions occurring are homogeneous. As the system for our macroscopic balances, we choose the fluid in the reactor volume V then the inflows Wn and outflows Wi2 vanish and no mass-transfer surface 0 is required. The species inventories are expressed in terms of fluid concentrations as... 

The fourth model of an ideal reactor can be described as a sort of combination of CSTR and BR. It is the semi-continuously operated, ideally mixed, stirred batch reactor, SBR. This is operated by charging one or more components and auxiliary materials initially and feeding at least a second reactant, with or without further auxiliary materials, at a constant rate over a certain period. 

The preparative synthesis took place in stirred batch reactors of 200-500 mL volume, with a sintered plate at the bottom, allowing the retention of the immobilized enzyme after discharge of the reacted medium. The reactions were performed in organic solvent (ethyl acetate or acetonitrile) at controlled initial water activity (a = 0.1). For KCS reactions, only a very small amount of water is produced so that its concentration can be considered constant during the reaction. After addition of the biocatalyst (previously equilibrated) and substrates, the water content was... 

The isothermal, constant volume, well-stirred batch reactor. Equation 6.1 can be simplified if, due to good mixing conditions, temperature and concentrations are uniform. According to Figure 6.2, integrating in the liquid volume we get... 

Figure 6.2 Schematic diagram of the isothermai, constant volume, well-stirred batch reactor...

Develop an unsteady-state model for a stirred batch reactor, using the nonlinear continuous reactor model presented in Example 4.8 as a starting point. For the parameter values given below, compare the dynamics of the linearized models of the batch reactor and the continuous reactor, specifically the time constants of the open-loop transfer function between c a and T c, the concentration of A, and the jacket temperature, respectively. Assume constant physical properties and the following data ... 

Altiokka et al. (2003) obtained the kinetics data on the esterification of acetic acid with isobutanol from both homogeneously (autocatalyzed) and heterogeneously catalyzed reactions using dioxane as a solvent in a stirred batch reactor. The uncatalyzed reaction was found to be second-order reversible. In the presence of the catalyst, on the other hand, the reaction was found to occur between an adsorbed alcohol molecule and a molecule of acid in the bulk fluid (Eley-Rideal model). It was also observed that the initial reaction rate decreased with alcohol and water concentrations and linearly increased with that of acid. The temperature dependency of the constants appearing in the rate expression was also determined. 

Batch reactors often are used to develop continuous processes because of their suitabiUty and convenient use in laboratory experimentation. Industrial practice generally favors processing continuously rather than in single batches, because overall investment and operating costs usually are less. Data obtained in batch reactors, except for very rapid reactions, can be well defined and used to predict performance of larger scale, continuous-flow reactors. Almost all batch reactors are well stirred thus, ideally, compositions are uniform throughout and residence times of all contained reactants are constant. 

In this work, the characteristic "living" polymer phenomenon was utilized by preparing a seed polymer in a batch reactor. The seed polymer and styrene were then fed to a constant flow stirred tank reactor. This procedure allowed use of the lumped parameter rate expression given by Equations (5) through (8) to describe the polymerization reaction, and eliminated complications involved in describing simultaneous initiation and propagation reactions. 

The concept of a well-stirred segregated reactor which also has an exponential residence time distribution function was introduced by Dankwerts (16, 17) and was elaborated upon by Zweitering (18). In a totally segregated, stirred tank reactor, the feed stream is envisioned to enter the reactor in the form of macro-molecular capsules which do not exchange their contents with other capsules in the feed stream or in the reactor volume. The capsules act as batch reactors with reaction times equal to their residence time in the reactor. The reactor product is thus found by calculating the weighted sum of a series of batch reactor products with reaction times from zero to infinity. The weighting factor is determined by the residence time distribution function of the constant flow stirred tank reactor. 

Volume changes on reaction may be neglected. At 25 °C the reaction rate constant is equal to 9.92 x 10 3 m3/kmole sec. If one employs a well-stirred isothermal batch reactor to carry out this reaction, determine the holding time necessary to achieve 95% conversion of the limiting reagent using initial concentrations of 0.1 and 0.08 kmole/m3 for cyclopentadiene and benzoquinone, respectively. 

The general characteristics of a batch reactor (BR) are introduced in Chapter 2, in connection with its use in measuring rate of reaction. The essential picture (Figure 2.1) in a BR is that of a well-stirred, closed system that may undergo heat transfer, and be of constant or variable density. The operation is inherently unsteady-state, but at any given instant, the system is uniform in all its properties. 

For the semi-batch stirred tank reactor, the model was based on the following assumptions the reactor is well agitated, so no concentration differences appear in the bulk of the liquid gas-liquid and liquid-solid mass transfer resistances can prevail and finally, the liquid phase is in batch, while hydrogen is continuously fed into the reactor. The hydrogen pressure is maintained constant. The liquid and gas volumes inside the reactor vessel can be regarded as constant, since the changes of the fluid properties due to reaction are minor. The total pressure of the gas phase (P) as well as the reactor temperature were continuously monitored and stored on a PC. The partial pressure of hydrogen (pnz) was calculated from the vapour pressure of the solvent (pvp) obtained from Antoine s equation (pvpo) and Raoult s law ... 

For the activity tests an 8-fold batch reactor system (reactor volume 20 ml) with magnetic stirring which allows the measurement of hydrogen uptake at constant hydrogen pressure was used. Analysis of substrates and products was performed offline by GC for determining selectivity values. Activity values were derived from hydrogen up-take within a defined time interval. Hydrogenation of both cinnamic acid and dibenzylether were carried out at 10 bars and 25°C. 

Willeman et al. [26] modeled the enzyme-catalyzed cyanohydrin synthesis in a stirred batch tank reactor. Assumption of a mass transfer limitation (Figure 9.3b) is made, which results in a low concentration of substrate in the aqueous phase, thus suppressing the non-enzymatic reaction. In a well-stirred biphasic system the enzyme concentration was varied, keeping the phase ratio constant A maximum rate of conversion is reached at the concentration where mass transfer of the substrate becomes limiting. Further increase of enzyme concentration does not enhance the reaction rate [27]. The different results achieved by the two groups are explained by the different process strategies. No mass transfer limitation could be detected by Hickel et al. because the stirring rate in the aqueous phase was not varied [26]. 

For example, Beltran and Alvarez (1996) successfully applied a semi-batch agitated cell for the determination of kL k,a, and the rate constants of synthetic dyes, which react very fast with molecular ozone (direct reaction, kD = 5 105 to 1 108 L mol-1 s l). In conventional stirred tank reactors operated in the semi-batch mode the mass transfer coefficient for ozone kLa(03) was determined from an instantaneous reaction of ozone and 4-nitrophenol (Beltran et al., 1992 a) as well as ozone and resorchinol (l,3-c//hydroxybenzene) or phloroglucinol... 

Prengle et al. (1996) studied the photooxidation by UV/H202 of waterborne hazardous Q-Q compounds in drinking water. Their work was conducted in a photochemical batch stirred-tank reactor, with medium pressure mercury arc immersion lamps of 100 and 450 W, covering the visible UV range, (578.0 to 222.4 nm). Tetrachloromethane, tetrachloroethane, dichloro-ethane, dichloroethene, trichloroethane, trichloroethene, and benzene were the compounds studied. Dark oxidation rates and photooxidation rates were determined. The latter rate constants were 104 to 10s greater than those under dark conditions. 

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... 

All experiments were performed in a 20-mL open batch reactor with constant stirring and temperature control. The reaction system contained a mixture of lauric acid and glycerol and the biocatalyst Lipozyme IM-20. The reaction s progress was followed by withdrawing 20-pL aliquots at various time intervals and analyzing themby GC, as previously described. 

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