A Continuous Bulk Polymerization Process for Crystal Polystyrene

A proposed styrene polymerization process for the production of crystal polystyrene is evaluated. The present process consists of an autorefrigerated stirred tank, followed by a tubular reactor. A flash tank devolatilizer is then used to remove volatiles from the reactor effluent. A mathematical model has been developed to include three different types of polymerization reactors: (i) polymerization in a stirred tank, (ii) polymerization in a plug flow reactor, and (iii) polymerization in a real tubular reactor. The styrene conversion and polystyrene quality were determined as a function of temperature and residence time in a reactor. It was found that an ideal process would be prepolymerization in a stirred tank to a 70–75% conversion, followed by postpolymerization in a tubular static mixer to 90% conversion. The pipe has an internal diameter of 0.254 m. Equilibrium considerations were used to estimate the content of residual volatiles in the devolatilized polystyrene melt. The results show that a lower vacuum pressure would be more helpful than a higher devolatilization temperature in reducing the volatile content.