Manufacturing processes of expandable Polystyrene

Process Description

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: 

Styrene and pentane, kg 
1000 - 1015
Process chemicals, kg 
Demineralized water, kg
Electricity, kWh 
Steam, mt 
Water cooling, m


The BP/Lummus process is one of the most modern technologies for EPS production. Computer control is used to produce product uniformity while minimizing plant energy requirements. BP provides ongoing process research for product improvement and new product potential. 

Commercial plants

Three commercial production units are in operation: one in France, one in Germany, and one in China for a total capacity of 200,000 metric tons.


ABB Lummus Global/BP Chemicals.


  1. Expanded Polystyrene (EPS) A lightweight closed-cell insulation with endless applications
  2. EPS Safety datasheet
Tags: Polystyrene eps flame-retardant