Material balance Semi-batch reactor

Ridelhoover and Seagrave [57] studied the behaviour of these same reactions in a semi-batch reactor. Here, feed is pumped into the reactor while chemical reaction is occurring. After the reactor is filled, the reaction mixture is assumed to remain at constant volume for a period of time the reactor is then emptied to a specified level and the cycle of operation is repeated. In some respects, this can be regarded as providing mixing effects similcir to those obtained with a recycle reactor. Circumstances could be chosen so that the operational procedure could be characterised by two independent parameters the rate coefficients were specified separately. It was found that, with certain combinations of operational variables, it was possible to obtain yields of B higher than those expected from the ideal reactor types. It was necessary to use numerical procedures to solve the equations derived from material balances. 

As with the batch reactor, the semi-batch reactor operates discontinuously. The difference with true batch operation is that for the semi-batch reactor, at least one of the reactants is added as the reaction proceeds (Figure 7.1). Consequently, the material balance as well as the heat balance will be affected by the progressive addition of one of the reactants. Also, as with the batch reactor, there is no steady state. There are essentially two advantages in using a semi-batch reactor instead of a batch reactor ... 

Equations 7.4 and 7.5 form a system of differential equations for which no analytical solution is known. Thus, the description of the behavior of the semi-batch reactor with time requires the use of numerical methods for the integration of the differential equations. Usually, it is convenient to use parameters which are more process-related to describe the material balance. One is the stoichiometric ratio between the two reactants A and B ... 

It is good practice to enumerate the unknowns and applicable equations when setting up a model for the noni so thermal semi-batch reactor. As discussed in Chapter 4, for a single-phase system, the molar concentrations of the components, and the temperature and the pressure specify all Intensive variables of the reactor. If we use the reactor volume as the single extensive variable, then we have + 3 unknowns. As in Chapter 4, we have n.s equations from the material balances and one equation of state. The energy balance of this chapter provides an additional equation. Finally, we must specify the reactor pressure or some other/System. coBStraint. that. determines the reactor pressure. 

If the performance of a batch reactor is to be described by solving the differential equations for liquid phase components B, C, R, S, E and F, it is necessary to determine by solving the material balance on A across the semi-batch reactor. 

Furthermore the material mole balance equations for a semi-batch reactor can be written as 1 d(SA)... 

It becomes necessary to incorporate a total mass balance equation into the reactor model, whenever the total quantity of material in the reactor varies, as in the cases of semi-continuous or semi-batch operation or where volume changes occur, owing to density changes in flow systems. Otherwise the total mass balance equation can generally be neglected. 

In this chapter, we first consider uses of batch reactors, and their advantages and disadvantages compared with continuous-flow reactors. After considering what the essential features of process design are, we then develop design or performance equations for both isothermal and nonisothermal operation. The latter requires the energy balance, in addition to the material balance. We continue with an example of optimal performance of a batch reactor, and conclude with a discussion of semibatch and semi-continuous operation. We restrict attention to simple systems, deferring treatment of complex systems to Chapter 18. 

Another question is important for the safety assessment At which instant is the accumulation at maximum In semi-batch operations the degree of accumulation of reactants is determined by the reactant with the lowest concentration. For single irreversible second-order reactions, it is easy to determine directly the degree of accumulation by a simple material balance of the added reactant. For bimolecular elementary reactions, the maximum of accumulation is reached at the instant when the stoichiometric amount of the reactant has been added. The amount of reactant fed into the reactor (Xp) normalized to stoichiometry minus the converted fraction (A), obtained from the experimental conversion curve delivered by a reaction calorimeter (X = Xth) or by chemical analysis, gives the degree of accumulation as a function of time (Equation 7.18). Afterwards, it is easy to determine the maximum of accumulation XaCfmax and the MTSR can be obtained by Equation 7.21 calculated for the instant where the maximum accumulation occurs [7] ... 

Chapter 4. In Chapter 4 we develop the material balances for the three reactor types batch (and semi-batch), contmuous-stirred-tank,... 

Nonisothermal reactor design requires the simultaneous solution of the appropriate energy balance and the species material balances. For the batch, semi-batch, and steady-state plug-flow reactors, these balances are sets of initial-value ODEs that must be solved numerically, in very limited situations (constant thermodynamic properties, single... 

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