High-impact polystyrene plant

Figure 3.13 High-impact polystyrene plant (CSTR=continuous stirred tank veactor LFR = linear flow reactor)...

The concept is similar to the grafting of plants in botany. To form a styrene-butadiene graft polymer, already polymerized butadiene is dissolved in monomeric styrene and an initiator is added. Because polybutadiene readily undergoes chain transfer at the allylic sites, polystyrene chains grow on the polybutadiene backbone. This forms high impact polystyrene, a low cost plastic that is otherwise too brittle without the grafting. 

Figure 3.13 illustrates what one might build today for a high-impact polystyrene (HIPS) plant today. The individual companies involved have patented a number of specialized reactor configurations. These are illustrated in Figure 27 in a review by Echte [36]. One common configuration is shown here in Figure 3.13 with two backmixed reactors (CSTR) followed by two linear flow... 

The Canadian Polystyrene Recycling Association (CPRA), with a plant in Mississauga, ON, accepts polystyrene from all over Canada. Over 95 percent of its revenue comes from the sale of recycled resins, mostly black high-impact polystyrene (HIPS). The remainder comes from member companies, representing manufacturers, distributors, and end users of polystyrene products. The plant, which has a capacity of 5000 tonnes of PS per year, accepts both food-service PS and cushioning materials. While it uses mostly postconsumer materials as feedstock, it also accepts obsolete PS materials from manufacturers, such as scrap from sign manufacturing. ... 

The second large-scale process was the batch mass suspension process. Monsanto did the pioneer work on this (41). In this process, prepolymerization is carried out in bulk and main polymerization in suspension the latter is taken to conversions of over 99%. In contrast to the continuous mass process, peroxide starters are used in order to achieve a high conversion at tolerable reaction times. Figure 3 shows a basic flow diagram of such a plant. A detailed discussion of advantages and disadvantages of the two processes can be found in R. Bishop s monograph published in 1971 (42), and it is continued in a paper by Simon and Chappelear in 1979 (43). It was a decisive factor for the economic success of impact polystyrene that these processes had been completely developed and mastered in theory and practice. 

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