The production of general purpose polystyrenes (GPPS) and high impact polystyrenes (HIPS) is essentially the same with the exception of the initial, rubber-dissolution step for HIPS.
The following diagram describes the flow of material and major equipment involved in the manufacturing process:
The production of HIPS begins with the granulating and dissolving of rubber and other additives in styrene monomer (101) and then transferring the rubber solution to a storage tank (102). For general- purpose product, controlled amounts of ingredients are fed directly to the feed preheater (103).
From this point on, the production steps for GPPS and HIPS are the same. The feed mixture is preheated (103) and continuously fed to the pre polymerizer (104) where the rubber morphology is established.
Following pre polymerization, the polymer mixture is pumped to the polymerization reactor (105) of proprietary design. At the exit of the reactor, the polymerization is essentially complete. The mixture is then preheated (106) in preparation for devolatization.
The devolatilizer (107) is held under a very high vacuum to remove unreacted monomer and solvent from the polymer melt. The monomer is distilled in the styrene recovery unit (108) and recycled back to the prepolymizer. The polymer melt is then pumped through a die head (109) to form strands, a water bath (110) to cool the strands, a pelletizer (111) to form pellets and is screened to remove large pellets and fines. The resultant product is air-conveyed to bulk storage and packaging facilities.
The BP/Lummus process offers one of the most modern technologies for GPPS and HIPS production. A broad product line is available with a consistently high product quality. BP provides ongoing process research for product improvement and new product potential.
Plants in France, Germany, and Sweden are in operation with a total capacity of approximately 450,000 MTPY of GPPS and HIPS. Another 300,000 MTPY GPPS and HIPS unit will start up in China in 2005.
ABB Lummus Global/BP Chemicals.