Batch reactor isoperibolic

Figure 6.8 Substitution reaction in the isoperibolic batch reactor for different switching temperatures for the cooling system. Upper plot reactor temperature as a function of time. Lower plot yield (NP/NA0) as a function of time. The parameter is the temperature at which the cooling system is switched on.

Figure 6.10 Example substitution reaction in the Isoperibolic batch reactor starting from 25°C with a constant cooling system temperature (Tc) at 25 °C. Reactor temperature (T,°C) and conversion as a function of time (h).

Thus, the equations describing the thermal stability of batch reactors are written, and the relevant dimensionless groups are singled out. These equations have been used in different forms to discuss different stability criteria proposed in the literature for adiabatic and isoperibolic reactors. The Semenov criterion is valid for zero-order kinetics, i.e., under the simplifying assumption that the explosion occurs with a negligible consumption of reactants. Other classical approaches remove this simplifying assumption and are based on some geometric features of the temperature-time or temperature-concentration curves, such as the existence of points of inflection and/or of maximum, or on the parametric sensitivity of these curves. 

For a safe operation, the runaway boundaries of the phenol-formaldehyde reaction must be determined. This is done here with reference to an isoperibolic batch reactor (while the temperature-controlled case is addressed in Sect. 5.8). As shown in Sect. 2.4, the complex kinetics of this system is described by 89 reactions involving 13 different chemical species. The model of the system consists of the already introduced mass (2.27) and energy (2.30) balances in the reactor. Given the system complexity, dimensionless variables are not introduced. 

The safety technical assessment of cooled batch reactors is based among other things on a recognition which is best understood by a schematic comparison of today s most common modes of operation. These are, as presented in Figure 4-38, isothermal, isoperibolic and partially controlled operation. 

Having completed the safety assessment for the isoperibolic batch processes, isothermal batch reactors now shall be considered. The most critical point in the course of process, which is the point of occurrence of the maximum driving temperature difference, is mathematically characterized in this case ... 

Bosch, J., Strozzi, F., Zbilut, J.P. and Zaldivar, J.M. (2004) On-line runaway detection in isoperibolic batch and semibatch reactors using the divergence criterion. Computers and Chemical Engineering, 28 (4), 527-44. 

Finally a fourth boundary condition shall be valid to support the worst case character of the procedure. The reaction order necessary for the formal kinetic description of a process has a severe influence on the pressure/time and respectively the tempera-ture/time-profiles to be expected. Industrial experience has shown that approximately 90% of all processes conducted in either batch or semibatch reactors can be described with a second order formal kinetic rate law. But it remains uncertain whether this statement, which is related to isothermal or isoperibolic operation with a rather limited overheating, remains valid if the reaction proceeds adiabatically and if side reactions contribute to the gross reaction rate at a much higher degree. In consequence, it shall be assumed for a credible worst case evaluation that the disturbed process follows a first order kinetics. Any reactions occurring in reality will almost certainly proceed at a much lower rate. 

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