Flow chart of the PET TPA process

The amorphous, low viscosity PET chips are first crystallised to a crystallisation degree of approximately 40 % to reduce their tendency to stick. Besides crystallisation, the content of water and acetaldehyde is reduced as well. There are several configurations possible for this crystallisation phase  

For all configurations, temperatures range from 120 - 170 °C. The gas phase (nitrogen or air) is used to heat up the product and to remove the water, acetaldehyde and pol5mier dust. 

In the next stage, the product is heated up to the desired temperature for solid state polymerisation (e g. 215-240 °C), commonly with a large countercurrent nitrogen flow (fluidised bed or not) and the pol5mierisation is initiated. 

When the ehips leave the solid state polymerisation (SSP) reactor they are cooled and stored in a silo. The product is usually stored under nitrogen or dried air, as the PET chips are very hygroseopie and the presence of small traces of water would decrease the degree of polymerisation, especially during subsequent proeessing at elevated temperatures. 

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