25. January 2021
In order to be able to extract high-quality feedstock from mixed plastic waste using mechanical methods this waste is sorted, cleaned, shredded, melted in an extruder and filtered in the process. One attractive alternative seems to be breaking down plastics from unsorted material flows with little preparation into their chemical components, meaning extracting feedstock of the highest purity from which polymers of new merchandise quality can be synthesised again.
In addition to its complexity, the big disadvantage of this approach has proven to the high energy requirements. For example, manufacturing pyrolysis oils and gases out of plastic waste requires temperatures of between 300 °C and 700 °C, and the oils subsequently have to be broken down in a cracker at about 850 °C. Such facilities can only be operated profitably at all if the throughput is much higher than that required for cost-effective mechanical recycling. It has to be taken into account that chemical recycling also produces waste in the form of waste water and residues.
Consequently, chemical recycling seems to be a supplement to energetic recovery in particular. This technology can be helpful wherever large quantities of unsorted plastic waste are generated in close proximity and no extra energy has to be generated for the process. The eco-balance always has to be the decisive factor. Ultimately, chemical recycling proves to be practicable if it results in energy savings and the emissions are lower than those caused by incineration. The proportion of chemical plastics recycling worldwide is currently less than one per cent, and under the circumstances detailed here it seems to be a long way away from reaching a higher figure – even if the procedure is classified as recycling in Germany and is thus preferred to incineration in the waste hierarchy.
Chair of the Management Board