The BP/Lummus styrene polymerization technology for the manufacture of regular and flame-retardant grades of Expandable Polystyrene (EPS) is a one-step batch suspension reaction followed by continuous dewatering, drying and size classification.
The following diagram describes the flow of material and major equipment involved in the manufacturing process:
Styrene monomer, water, initiators, suspending agents, nucleating agents and other minor ingredients are added to the reactor (101). The contents are then subjected to a time-temperature profile under agitation. The suspending agent and agitation disperse the monomer to form beads. At the appropriate time, a pre-measured quantity of pentane is introduced into the reactor. Polymerization is then continued to essentially 100% conversion. After cooling, the EPS beads and water are discharged to a holding tank (102).
From this point, the process becomes continuous. The bead/water slurry is centrifuged (103) where most of the “mother liquor” is removed. The beads are conveyed to a pneumatic dryer (104) where the remaining moisture is removed.
The dry beads are then screened (105), yielding as many as four product cuts. External lubricants are added in a proprietary blending operation (106) and the finished product is conveyed to shipping containers.
Raw materials and utilities, based on one metric ton of EPS: