Reactor isothermal polystyrene

Timm, Gilbert, Ko, and Simmons O) presented a dynamic model for an isothermal, continuous, well-mixed polystyrene reactor. This model was in turn based upon the kinetic model developed by Timm and co-workers (2-4) based on steady state data. The process was simulated using the model and a simple steady state optimization and decoupling algorithm was tested. The results showed that steady state decoupling was adequate for molecular weight control, but not for the control of production rate. In the latter case the transient fluctuations were excessive. 

Problem 6-15 (Level 1) Xu et al. ° have studied the hydrogenation of polystyrene to poly(cyclohexylethylene) using a Pd/ BaS04 catalyst in an isothermal batch reactor. The reaction is as given below. 

The various differential equations of Table 6.1 are nonlinear and eoupled, and, in principle, they must be solved numerically, which takes exeessive computational time. For isothermal reactors for time-invariant rate constants, it is possible to derive a complete analytical solution, which is given in Appendix 6.1. However, actual reactor performance is always nonisothermal in addition, rate constants (particularly kp and k ) are dependent on reaction parameters in a very complex way. Tables 6.2 and 6.3 show the physical properties and rate constants for polystyrene and polymethyl methacrylate systems. Several researchers have attempted to solve for the reactor performance for these systems, and all of them have reported that the differential equations of Table 6.1 (along with the energy balance relation) take excessive computational time. The following discussion minimizes this problem by using the isothermal solution presented in Appendix 6.1. 

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