Deodorization in Plastics Recycling: An End to Unpleasant Odors

In a first step, odors are eliminated as the waste plastic undergoes mechanical pretreatment during shredding, washing and drying. Further odors can be removed from the shredded plastic in a silo using fresh air circulation.

The next, intensive devolatilization step, which markedly improves the recompound’s sensory quality, takes place during compounding in a ZSK twin screw extruder.

 

Following melting and intensive homogenization of the waste plastic in the ZSK extruder’s process section, volatile particles are degassed from the plastic melt in a highly energy efficient process. Using various technologies such vacuum devolatilizations, these dissolved gases are reliably removed from the product. This effect can be significantly intensified with the addition of liquid stripping agents.

 

Use of a ZS-EG side devolatilization unit provides a particularly effective and stable degassing process in the ZSK twin screw extruder, maximizing its deodorizing capabilities when high quantities of gas are present. 

Coperion also offers post extrusion and pelletizing deodorization systems that play a further key role in improving waste plastic to the qualitative level of new plastic. They reliably remove any residual unpleasant odors from recycled plastic compounds. Hot air flows through the pellets in silos, diffusing even particularly stubborn, long-chain molecules from the compounds. For this step, Coperion has developed two different process solutions, depending upon the desired end product quality, the temperature it requires, residence time and quantity of air. 

 

One method uses two silos – one to warm and deodorize the granulate and another to cool the granulate with cold air. In this process, comparatively little energy is needed to warm the product to the desired devolatilization temperature. Moreover, the cooler’s process heat can be used to pre-warm the pellets, increasing energy efficiency. 

 

Alternatively, warming, degassing and cooling can take place in one silo by using two Bulk-X-Change heat exchangers. This solution is much more compact, requiring only one silo.