Recycling plastics through dissolution

Thema:
Dissolution

Currently, only 30% of plastic waste is recycled, of which only half in high-value applications. But the Netherlands wants to be 100% circular by 2050. To close the chain of plastics, we need new recycling technologies. That is why we developed the TNO Möbius dissolution process, a selective dissolution process used for recycling polymers and additives from plastic waste in a resource-efficient, environmentally friendly way.

Recycling plastic

What is the best, sustainable solution for waste management and recycling? Companies initially choose to recycle plastic to plastic, i.e. mechanical recycling. If that is not possible? Or when the recycled plastic can only be applied in low-value applications, also known as ‘downcycling’? other technologies are available to purify the plastics. For example chemical recycling. Chemical recycling splits the various polymers into components that companies can use to make new plastics. In between mechanical and chemical recycling there is a third technology: dissolution

Dissolution

Dissolution is based on using a solvent that dissolves one polymer and not another or additives. By means of dissolution, we separate different polymers and carry out one or more purification steps. Together, these steps form a process for waste plastic recycling into high-value applications. However,  the challenge is that the combination of plastics and additives is always different in different waste streams. Therefore, we are looking, were needed, for new, unique combinations of solvent and polymer type for a waste stream.

Requirements for new recycling technologies

We are developing technologies for physically recycling polymer and additives from waste plastics using dissolution. In addition, we are building sensors that monitor the purity of the process. This process must also:

  • be continuous, inexpensive, and efficient
  • operate on a large scale
  • deal with variations in raw materials
  • deliver consistent quality

Closing the plastic cycle

The new policy goal is to be circular by 2050. There are various recycling technologies available to close the plastic cycle. Today, we recycle about 15% of our plastics in high-value applications. These are mono flows (flows consisting of one type of material or product) that are sorted from  plastic waste from:

  • packaging, e.g., bottles, trays, and bags
  • discarded electronics, e.g., refrigerator interiors, computers
  • construction waste, e.g., window frames

New physical and thermochemical recycling technologies

These waste flows mentioned above are mechanically recycled into plastic granulate. Companies reuse this to make small rigid plastic objects and packaging for non-food. Large objects, such as garden furniture, are made from mixed plastics. At TNO, we invest in new mechanical, physical and thermochemical recycling technologies, increasing the share of recycled materials. With these new technologies, we can process more complex waste flows. We also produce raw materials for high-quality applications.

Image of a TNO employee
Image of a TNO employee behind the controls of the Möbius1.0 set-up for researching new recycling technologies

Recycling plastics into purified polymers

We have developed a physical recycling technique for the selective dissolution of certain polymers from a plastic mixture under superheated conditions. We combine this technique with the removal of impurities from the polymer solution, after which we recover the purified polymer. This technology is based on the use of a low-boiling solvent at an elevated temperature and pressure, facilitating the dissolution of the polymers.

Technology for purifying plastics

The viscosity of the polymer solution is low enough to allow the use of conventional separation techniques such as filtration and adsorption. This allows us to remove the additives and impurities present in the plastics, including small particles, such as pigments, and molecular compounds, such as softening agents and flame retardants. These were originally added to improve the properties of the plastics. After removing the additives and purification, the polymers are recovered to be re-used. We call this TNO technology the TNO Möbius dissolution process. It is suitable for the recovery of cleaned polymers from multi-material plastics and the valorization of the recovered additives.

More about the Möbius dissolution process

This technology and equipment are named after the symbol of circularity: the Möbius strip. An l advantage of this technology, compared to current state-of-the-art dissolution processes, is that it is potentially an energy-efficient proces. This is because the solvent can be evaporated at a low temperature (typically below 120 °C). Moreover, the use of a low-boiling solvent makes it possible to recover polymers with a low solvent content.

Development and scaling up

In recent years, a small team of scientists, engineers, and technicians developed the Möbius dissolution process. They began by dissolving polymers in a small batch setup. They scaled up the process to a throughput from a few gram per batch to tens of grams in a semo-batchin the current Möbius 1.0 setup. With each scale-up step, not only waste throughput is increased, but functionalities such as specific separation steps are added as well as making the process more continuous..

Möbius 2.0

The next phase is to further develop the technology and build an even more scaled-up and semi-continuous setup. This Möbius2.0 set-up is planned for 2023 and is for instance able to  recover and recycle the solvent. We design this setup to process polyolefins from packaging waste and ABS from for instance automotive waste. We will use the Möbius2.0 to determine key parameters for further upscaling towards commercialization. Moreover, it allows us to produce kilogram-scale samples for our partners. This allows them to validate the properties of the recycled polymer for their products. Another goal is to extend the scope of the technology to the recovery of clean polymers from other plastic waste flows. For example, from household applications such as carpets, electronics, and discarded building materials.

Dissolutie_beeld_in_tekst_website_shutterstock_2113536797_afgekocht_digital_media_(2)

The entire value chain for plastics

Untill now, the Möbius technology was developed and applied in national and European projects involving research institutes and industrial partners as well as commercial projects for clients. The larger projects often span the entire value chain for plastics, such as discarded electronics, automotive and multilayer packaging films. Examples of projects include PLAST2bCLEANED, ALMA, Impres, Pack-CE, CIMPA and ABSoIEU. In many of these projects we sought synergy with TNO groups whose expertise include:

  • thermochemical recycling (Petten)
  • mechanical recycling and redesign of plastic products (Eindhoven/Geleen)
  • impact assessments (Utrecht)

An example of process development by TNO is the European consortium PLAST2bCLEANED. We have set this up this project to recover not only polymers but also additives such as brominated and antimony-based flame retardants from WEEE to be recycled in high-performance engineering plastics. In the first part of the project, the process development was executed on laboratory scale. We are now scaling up the process to pilot scale and we are researching with partners such as Electrolux and Fraunhofer how we can execute the process at kg scale and demonstrate the re-use of the recovered polymer.

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