Case A Continuous Stirred-Tank Reactor

If the tank is well-mixed, the concentrations and density of the tank contents are uniform throughout. This means that the outlet stream properties are identical with the tank properties, in this case concentration Ca and density p. The balance region can therefore be taken around the whole tank (Fig. 1.5). 

The total mass in the system is given by the product of the volume of the tank contents V (m- ) multiplied by the density p (kg/m ), thus V p (kg). The mass of any component A in the tank is given in terms of actual mass or number of moles by the product of volume V times the concentration of A, Ca (kg of A/m or kmol of A/m ), thus giving V Ca in kg or kmol. 

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Case A. Continuous Stirred-Tank Reactor (CSTR)... 

The F(t) curve for a system consisting of a plug flow reactor followed by a continuous stirred tank reactor is identical to that of a system in which the CSTR precedes the PFR. Show that the overall fraction conversions obtained in these two combinations are identical for the case of an irreversible first-order reaction. Assume isothermal operation. 

An important feature of biphasic hydroformylation is the separability due to density differences. Because of the differences in density of the polar compound water (1.0 gem"1) and the hydrophobic oxo products (average 0.8), no problems occur. Additionally, the hydroformylation products are not sensitive to water. Another important question is to what extent water and the reactants are mixed. Therefore, the reactor in Figure 5.3 b), a continuously stirred tank reactor (CSTR) [22], normally contains usual installations to guarantee excellent mixing. For the lower alkenes with their significant water solubility (propene, butene) this is no problem. In these cases, the hydroformylation reaction takes place at the interfacial region [23]. 

In this chapter some effects of segregation on the kinetics of a chemical reaction between two liquid phases carried out in a continuous stirred tank reactor (CSTR) will be discussed. In the derivations of these effects it will be assumed that during the reaction the dispersed phase is maintained (e.g., in the case of extraction combined with chemical reaction) and that all dispersed drops have the same size. This means that when there is segregation it is only the age distribution which causes a concentration distribution in the dispersed phase. 

R. L. Curl was the first to work out this model for the case of a chemical process with zero-order drop conversion which is carried out in a continuous stirred tank reactor (C8). His theory, somewhat modified, is given at the end of this section. 

If the compositions vary with position in the reactor, which is the case with a tubular reactor, a differential element of volume SV, must be used, and the equation integrated at a later stage. Otherwise, if the compositions are uniform, e.g. a well-mixed batch reactor or a continuous stirred-tank reactor, then the size of the volume element is immaterial it may conveniently be unit volume (1 m3) or it may be the whole reactor. Similarly, if the compositions are changing with time as in a batch reactor, the material balance must be made over a differential element of time. Otherwise for a tubular or a continuous stirred-tank reactor operating in a steady state, where compositions do not vary with time, the time interval used is immaterial and may conveniently be unit time (1 s). Bearing in mind these considerations the general material balance may be written ... 

An initial theoretical study (Gilliland et al. 1964) established that, for a simple plant model consisting of a continuous stirred-tank reactor (CSTR) and a distillation column, the material recycle stream increases the sensitivity to disturbances together with increasing the time constant of the overall plant over those of the individual units. Moreover, it was shown that in certain cases the plant can become unstable even if the reactor itself is stable. 

All steps from the second on amount to insertion of an ethoxy block between a previously inserted block and the —OH group, and so have very similar rate coefficients. Usually, the original alcohol reacts at a slighdy lower rate. If the reaction is carried out at constant partial pressure of ethene oxide, each insertion including the first is pseudo-first order in the alcohol or ethoxy alcohol reactant. With increasing reaction time in batch, successive adducts reach maximum concentrations and then decay to form higher adducts, as shown for a calculated case in Figure 5.11. The variation in yield structure with reactor space time in a continuous stirred-tank reactor is similar, but with less pronounced concentration maxima. 

This chapter will explain the principles underlying chemical reactions, and it will go on to generalize these principles to the case of several concurrent reactions with large numbers of reagents and products. Then we shall extend to the case of chemical reaction the principles of mass balance and energy balance presented in Chapter 3. Finally we shall explain in detail how to simulate a gas reactor and a continuous stirred tank reactor (CSTR). 

For a closed chemical system with a mass action rate law satisfying detailed balance these kinetic equations have a unique stable (thermodynamic) equilibrium, lim c( )=Cgq. In general, however, we shall be concerned with chemical reactions that are maintained far from chemical equilibrium by flows of reagents intoand out of a continuously stirred tank reactor (CSTR). In this case the chemical kinetic equation (C3.6.1) must be supplemented with flow terms... 

Using the thus built kinetic model, both the dynamic and steady state cases of a continuous stirred tank reactor were simulated. We show here the simulation results concerning transient effects. The case considered is the switching of feeds with different H2S concentrations. The shapes of the trajectories and the variations of activities are generally comparable to the experiment results (20,21), although the latter were obtained under low pressure (fig. 2). It is known that the addition of H2S depresses the HDS activity. Simulation results refine the conclusion. They confirm the experimentally found phenomenon in (22) that, for catalysts with different compositions, the depression... 

A test problem comparing the analytical and numerical solutions of the same problem using a finite element model 12) is illustrated in Figure 2. The solution corresponds to the case of a continuously stirred tank reactor (CSTR) in which first-order kinetics are assumed, and the rates of reaction are comparable to those we have observed in the laboratory (5,10). 

Equation (4-51) is the basic design equation for what is popularly called a continuously stirred tank reactor (CSTR). The derivation assumes equality of volumetric flow rate of feed and effluent as in the case of the PFR, the residence-time definition must be changed if this is not so. In most applications of the CSTR, however, reactions in the liquid phase are involved and volume changes with reaction are not important. 

Vasquez-Bahena J, Montes-Horcasitas MC, Ortega-Lopez J et al. (2004) Multiple steady-states in a continuous stirred tank reactor an experimental case study for hydrolysis of sucrose by invertase. Proc Biochem 39(12) 2179-2182... 

In the third case, the residence time distribution (RTD) of the solid becomes an important factor. Though the liquid RTD will again approximate closely to the perfectly mixed condition required for a continuous stirred tank reactor model except on a very large scale, generally the solid will not. Therefore the actual solid RTD must be determined as set out in Chapter 16 for a satisfactory reactor design to be made. 

A continuous-stirred-tank reactor (CSTR) for the production of propylene glycol is analyzed in Case Study 21.1, in Section 21.4 below. Approximate linear models for the reactor are generated using the five-step procedure as follows. 

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