[工程科技]化反.ppt

Chapter 03 Ideal Reactors 3 ideal reactors Stirred tanks turbular or packed-bed reactors the criterion for ideality in tank reactors is that the liquid be perfectly mixed,which mans no gradients in temperature or concentration in the vessel. in plug-flow reactors,or PFRs,there are axial gradients of concentration and perhaps also axial gradients of temperature and pressure,but in the ideal PFR there is no axial diffusion or conduction. Batch Reactor Design First-order reactions For an irreversible first-order reation of the type First-order reactions The result is often given in terms of the fraction converted: Second-order reactions for a unimolecular second-order reation, Second-order reactions Second-order reactions Consecutive Reactions Consecutive Reactions Consecutive Reactions The material balance for product C is Consecutive Reactions If no C is present at the start, integration of Eq. (3.15) gives Consecutive Reactions Consecutive Reactions Parallel Reactions Selectivity effects can also be important with parallel reactions having different reaction orders. Consider the case where the main reaction is first order to both reactants and the byproduct reaction is second order to one of the reactants: Parallel Reactions The local or instantaneous selectivity is the ratio of to the total rate of consumption of A: Parallel Reactions Semibatch Reactions The reactor might be two-thirds to three-quarters full at the start, and the fluid volume increases as A is added and no product withdrawn. Figure 3.4 shows the calculated concentration curves for the same kinetics and as for Figure 3.3, with the feed of A at a slow, constant rate for 14 hours Semibatch Reactions CONTINUOUS-FLOW REACTORS CONTINUOUS-FLOW REACTORS Operating a stirred-tank reactor with continuous-flow of reactants and products (a CSTR) has some advantages over batch operation. The reactor can make products 24 hours a day for weeks at a time, whereas for a typical cycle, the ba