CHEMICAL RECYCLING | PYROLYSIS PROJECTS


Within PRISM, TNO is looking at different


approaches to chemical recycling. “Detail on different technologies is relatively low, so direct comparison is not easy,” says Imhof. “From a high level perspective, most pyrolysis technologies are similar in terms of efficiency and carbon footprint. Adaptation of current pyrolysis units is not very high. Current units are very small, 10-20 000 tonnes, which is peanuts. But you need to develop on the small scale first before you can move up to higher volumes.” He says: “At TNO, I would love all the parties involved in pyrolysis to work together to broaden the applicability of feedstocks as much as possible. The commonality of issues should be investigated on an independent level and each technology can be applied to specific streams.”


TNO has been focusing on development of a


high-temperature pyrolysis platform technology called Milena, which was originally developed for producing energy from biomass, but which is now being further developed for chemical recycling of plastics. Imhof says this has a process set-up compa- rable with FCC (fluidic catalytic cracking). It can be coupled to a gas cleaning process called Olga. Milena and Olga technology is licensed by Netherlands-based Synova. It is also likely to produce units itself either on its own or in joint ventures. In March, it entered into a joint develop- ment and cooperation agreement with Technip Energies to commercialize Synova’s advanced plastic waste-to-olefins technology, in conjunction with Technip Energies’ steam cracking technology. Another major independent company in the chemical recycling field is Plastic Energy. It currently has two commercial chemical recycling


Coperion supports Ghent University in chemical recycling research


Coperion has supplied an extrusion system to Ghent University in Belgium for research and develop- ment tasks in chemical recycling of mixed plastic waste. Chemical reaction engineering in general and the kinetics of chemical reactions are major areas of research at the Laboratory for Chemical Technology (LCT) at Ghent University. Coperion designed this laboratory


system, built upon a ZSK 18 MEGAlab twin-screw extruder, specifically for chemical recycling of post-consumer waste within a throughput range of 1-10 kg per hour. Along with the extruder, it includes a feeder from Coperion K-Tron, as well as a vacuum unit. Coperion says that its twin-screw


extruder technology is particularly well suited for chemical recycling of plastics. After post-consumer waste, either shredded or compacted, is added to the extruder’s process section by the Coperion K-Tron feeder, significant mechanical energy is introduced into the material in a short time due to the continuous surface renewal, as well as intensive dispersion and shearing along the twin-screws.


18


Chemical recycling using twin-screw extruder, reactor and distillation unit Within about 30 s, a homogene-


ous, highly devolatilised melt with a temperature of up to 350°C is produced. Further materials, such as catalysts, can be added and mixed in as needed. In some cases, residual water or chlorides from PVC are introduced into the extruder in minute quantities along with the plastic waste. Both are extracted via vacuum devolatilisation in the extruder’s process section. Within the reactor, the melt is


further heated. Pyrolysis of the polymers at up to 500°C takes place, splitting the polymer chains into shorter units in an oxygen-free


PLASTICS RECYCLING WORLD | November/December 2021


environment. At the same time, chain reactions are initiated which lead to cracking polymers into a broad mixture of hydrocarbons. They are transformed into mono-


mers, petrochemical raw materials, or synthesis gases and then processed further through distillation into marketable products such as oil, heavy fuel or waxes. The Coperion ZSK twin-screw


extruder is part of a new setup for chemical recycling at Ghent Univer- sity. It will be among others coupled to a vortex reactor, where the molten plastic will flow directly into the reactor.


www.plasticsrecyclingworld.com


IMAGE: COPERION


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