Lecture 9 Polymer Reaction Engineering Reactor Design

1. Lecture 9Polymer Reaction EngineeringReactor Design most polymerization reactions are exothermic. Consequently, heat removal is imperative in polymerization reactions — a problem that is accentuated by the high medium viscosity that leads to low heat transfer coefficients in stirred reactors. it is vitally important to choose the most suitable reactor and operating conditions to obtain the required polymer properties from a polymerization reaction

2. Reactor Design for bulk polymerization reaction Polymerization of polystyrene Fig(1):Vertical column reactor for the continuous bulk polymerization of styrene

6. Example 1: Explain why bulk polymerization is generally more suited for step-growth polymerization than for chain-growth polymerization Solution: The major problems in bulk polymerization are heat removal and mixing. Both step-growth and chain-growth polymerization are exothermic. But the enthalpy of polymerization for chain-growth reactions is of the order of 15 to 20 kcal/g mol compared with 2 to 6 kcal/g mol for step-growth polymerization. Also, chain-growth polymerization is characterized by high viscosities even at low conversions due to the generation of polymers early in the reaction, whereas viscosities are generally low in step-growth polymerization until the later stages of the reaction (high conversions). Thus the much higher exothermic nature of chain-growth polymerization, coupled with the difficulty of mixing the reaction mixture due to high viscosities, leads to much lower heat transfer efficiencies in chain growthpolymerization than in step-growth polymerization.