General purpose polystyrene GPPS process

2 General purpose polystyrene (GPPS) process 4.2.2.1 Process description 

Raw materials like styrene (potentially purified), and processing aid are fed into the reactor(s). The reactor train usually includes continuous stirred tank reactors (CSTR) and/or plug flow reactors (PFR). 

Styrene itself acts as the solvent of the reaction. Moreover, up to 10 % ethyl benzene may be added to ensure better reaction control. The reactors temperatures are controlled at between 110 and 180 °C. The reaction pressure is up to 1 MPa in the case of a PFR and at atmospheric or sub-atmospheric pressure in the case of a CSTR. 

Additional chemicals are added into the feed stream or into the reactors. At the end of the reactor train, the styrene monomer conversion reaches 60 - 90 % of solid polystyrene product. The process flow then goes through a devolatilisation section where it faces one or two flashes (one or two devolatilisation vessels) to separate the polymer from the unreacted species. The devolatilisers are operated at high temperatures (220 - 260 °C) and under high vacuums ( 40 mbar). 

Between the two devolatilisation steps, an injection of water (stripping) can be added to improve monomer removal. After condensation, unreacted styrene and ethyl benzene are recycled to the feed line, either directly using a recycle loop or through a storage tank. A purge of undesirable components is carried out on this stream. 

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Application To produce a wide range of general purpose polystyrene (GPPS) with excellent high clarity and suitable properties to process PS foam via direct injection extrusion by the continuous bulk polymerization process using Toyo Engineering Corp. (TEC)/Mitsui Chemicals Inc. technology. 

Application The INEOS polystyrene (PS) technology is based on a bulk continuous process giving access to a wide range of general purpose polystyrene (GPPS) also known as crystal polystyrene and high-impact polystyrene (HIPS), which incorporates rubber particles for high shock absorbance. 

Figure 1.11 Fossil energy requirement for petrochemical polymers and PLA. The cross-hatched area of the bars represent the fossil energy used as chemical feedstock (i.e., fossil resource to build the polymer chain). The solid part of the bars represented the gross fossil energy used for the fuels and operation supplies used to drive the production processes. PC = polycarbonate HIPS = high-impact polystyrene GPPS = general purpose polystyrene LDPE = low-density polyethylene PET SSP = polyethylene terephthalate, solid-state polymerization (bottle grade) PP = polypropylene PET AM = polyethylene terepthalate, amorphous (fiber and film grade) ...

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