ABS Emulsion process by Technip Stone & Webster Process Technology

Acrylonitrile butadiene styrene (ABS) is used in the electronics, appliances, building, construction and transportation industries. A wide range of ABS thermoplastic resin products can be produced by SABlC’s ABS emulsion process. Composites of styrene acrylonitrile (SAN) copolymer and high butadiene acrylonitrile styrene graft [high rubber graft (HRG)1 yield ABS products with exceptional impact strength. The properties of ABS can be widely varied by using different concentrations of butadiene rubber and acrylonitrile in the copolymer.

The ABS process requires the production of four distinct products: SAN copolymer; polybutadiene latex (PBL), an emulsion of polybutadiene rubber in water; HRG resin; and finished ABS product via compounding. The SAN production area includes feed filtration, bulk reaction, devolatization, unreacted monomer recovery and product pelletizing. Styrene, acrylonitrile and additives are continuously charged to the reactor. The SAN polymer is produced in a single stirred reactor that provides sufficient residence time at the controlled reactor conditions to achieve the required monomer conversion, typically operated at 55% to 70% solids. Unreacted volatile materials in the polymer melt are devolatilized by using a flash system operating at controlled vacuum. Recovered monomers are recycled to the reactor. Features of the SAN reactor configuration allow straightforward control of product composition and molecular weight. Waste vapors are scrubbed for recovery. Following devolatization, the polymer melt is pelletized, cooled and sent to storage. A typical design is capable of producing multiple unique SAN grades. Separately but in parallel with SAN production, PBL is manufactured as a raw material to make resin in the HRG process area. The four main steps to produce PBL are feed preparation, reaction, flash removal of unreacted butadiene, and particle size control. The reactor is charged with demineralized water, emulsifier and butadiene. After heat-up and polymerization, additional butadiene, initiator and chain transfer agent are added on a continuous basis. This unique semi-batch process significantly improves reactor cycle time while minimizing the risk of runaway reaction that is normally present in traditional batch PBL reactors. Butadiene is polymerized to near completion. Reactor contents (crude PBL) are directed to a flash chamber operating under vacuum to remove unreacted butadiene monomer which is recycled to the feed system. Prior to storage and feeding, in the HRG resin production area, crude PBL is sent to a proprietary particle size control step.

The HRG reaction process, a semi-batch emulsion reaction of styrene and acrylonitrile with PBL, is followed by a continuous coagulation to form resin particles, water removal and drying. Initially, PBL latex solution and demineralized water are added to the reactor. After heating, styrene, acrylonitrile and additives are charged to the reactor. Application of semi-batch operation results in lower monomer inventory and reduced runaway polymerization potential. Prior to transfer from the reactor, to increase monomer conversion, a small amount of methyl methacrylate is added. The HRG latex is next directed to a coagulation system where particle size is controlled by agitation speed and acid addition. The proprietary coagulation process is designed to separate the latex emulsion by creating an HRG resin slurry. The coagulated slurry is then washed and dewatered in a series of proprietary process steps. Finally. the wet resin is dried to less than 1% moisture content in a rotary dryer.

Finished ABS product is formulated in the compounding area using a twin-screw extruder. An automated feed system delivers HRG resin, SAN pellets and pre-blended additives to the extruder. The extruder system includes a screen changer, strand die, water slide pelletizer, pellet dryer, water recirculation system and screener. After screening, the pellet material is transferred to product surge hoppers and packaging.

A broad range of ABS products, including plating, extrusion and fire-retardant grades, are available for license. Emulsion ABS products are well suited for high-gloss automotive, high-heat automotive, refrigeration, medical, food and pipe applications. Cycolac* ABS resins provide an excellent balance of processability, impact, dimensional stability, and high-temperature resistance with a stable light base color.

Key features:
– inherently safe reaction processes, low reaction viscosities
– Competitive capital and operating costs
– High reactor productivity
– Single HRG product results in simplified operation
– Exceptional product quality
– A broad family of products meeting the most demanding application requirements
– Optimized impact-flow performance with low organic volatiles and non-polymer impurities
– Additive flexibility enables specialty products from natural/black/white and custom colors

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