Addition reactions—continued exothermic nature

Winyl polymerization as a rule is sensitive to a number of reaction variables, notably temperature, initiator concentration, monomer concentration, and concentration of additives or impurities of high activity in chain transfer or inhibition. In detailed studies of a vinyl polymerization reaction, especially in the case of development of a practical process suitable for production, it is often desirable to isolate the several variables involved and ascertain the effect of each. This is difficult with the conventional batch polymerization technique, because the temperature variations due to the highly exothermic nature of vinyl polymerization frequently overshadow the effect of other variables. In a continuous polymerization process, on the other hand, the reaction can be carried out under very closely controlled conditions. The effect of an individual variable can be established accurately. In addition, compared to a batch process, a continuous process normally gives a much greater throughput per unit volume of reactor capacity and usually requires less labor. 

On the other hand, different time-temperature policies are optimal for different classes of complex reactions. These are considered in Chapter 11 for complex reactions. Although the reversible reaction is also a complex reaction in the sense that two reactions occur, it is equally true that no additional species are involved in the second (reverse) reaction. Hence the reversible reaction can also be regarded as a simple reaction. If the reaction is endothermic, its reversible nature makes no difference because both the reaction rate constant and the equilibrium constant increase with temperature, and the maximum practicable temperature continues to be the optimal temperature. But if the reaction is exothermic, an increase in temperature has opposite effects it lowers the equilibrium constant but raises the rate constant. Hence an optimum temperature exists. For any reaction such as 4 <-+ whose rate equation is = k [A] - [R]/K), this optimum can be found by integrating the expression... 

In addition to batch emulsion polymerization (which is commonly used in the laboratory to study reaction mechanisms) for preliminary development/screen-ing of new latex products and to obtain approximate kinetic data for process development and reactor scale-up, the versatile semibatch and continuous emulsion polymerization processes are widely used for the production of commercial latex products. A major reason that batch reactors are not used for commercial production is due to the very exothermic nature of free radical polymerization and rather limited heat transfer capacity in large-scale reactors. Furthermore, continuous and especially semibatch reaction systems offer the operational flexibility to produce latex products with controlled polymer composition, particle morphology, and particle size distributions. These parameters will have an important influence on the performance properties of latex products. In this chapter, we will focus on the aspects of polymerization mechanisms and kinetics involved in semibatch and continuous emulsion polymerization systems. Those who are interested in the previous studies of semibatch and continuous emulsion polymerization processes should refer to the review articles cited in references 1. ... 

Regeneration with air can be done with continuous or periodic addition of small amounts of air. Both must be done carefully because of exothermic reaction. Regeneration is never complete, so the beds must be eventually changed out. This must be done carefully because of the pyrophoric (spontaneously combustible) nature of the iron sulfide. The entire bed is wetted first. 

There are several control problems in chemical reactors. One of the most commonly studied is the temperature stabilization in exothermic monomolec-ular irreversible reaction A B in a cooled continuous-stirred tank reactor, CSTR. Main theoretical questions in control of chemical reactors address the design of control functions such that, for instance (i) feedback compensates the nonlinear nature of the chemical process to induce linear stable behavior (ii) stabilization is attained in spite of constrains in input control (e.g., bounded control or anti-reset windup) (iii) temperature is regulated in spite of uncertain kinetic model (parametric or kinetics type) or (iv) stabilization is achieved in presence of recycle streams. In addition, reactor stabilization should be achieved for set of physically realizable initial conditions, (i.e., global... 

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