Recycling plastics through dissolution

Thema:
Dissolution

Currently, only 30% of plastic waste is recycled. 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 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, or mechanical recycling. If that is not possible, other technologies are available to purify the plastics. For example, an additional step of chemical recycling. This splits the various polymers into components that companies can recycle.

Dissolution

We use a solvent that dissolves one polymer or additive and not another. This is called dissolution. By means of dissolution, we separate different polymers in order to carry out the next purification step. But the combination of plastics and additives is always different. Therefore, we are always looking for new, unique combinations of solvent and polymer types.

Requirements for new recycling technologies

We are developing technologies to chemically recycle polymer additives. 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. These are mono flows (flows consisting of one type of material or product) of plastic waste from:

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

New physical and thermochemical recycling technologies

These waste flows are mechanically recycled into plastic granulate. Companies reuse this to make small objects and packaging for non-food. Large objects, such as garden furniture, are made from mixed plastics. At TNO, we invest in new 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 researching new recycling technologies on a computer in a TNO lab

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, 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, we purify and restore the polymers. This TNO technology is called the Möbius dissolution process. It is suitable for the recovery of cleaned polymers from multi-material plastics and the valorisation of the recovered additives.

Möbius dissolution process

This technology and equipment are named after the symbol of circularity: the Möbius strip. A potential advantage of this technology, compared to current state-of-the-art dissolution processes, is that it is a potentially energy-efficient operation. This is because the solvent can be evaporated at a low temperature. 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 semi-batch setup. They scaled up this setup from a working volume of tens of millilitres to two litres. This made the first production of samples of a few grams possible. In the current Möbius 1.0 setup, this has been increased to a scale of hundreds of grams. By adding separation and recovery steps for both the additives and the cleaned polymers, the setup has also been made more functional.

Möbius 2.0

The next phase is to further develop the technology and build an even more scaled-up and semi-continuous setup, where the solvent can be recovered, analysed, and possibly recycled (Möbius 2.0). We will be using this setup to produce kilo-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, end-of-life vehicles, and discarded building materials.

The entire value chain for plastics

So far, the joint projects in which the Möbius technology was developed and applied consist of national and European projects involving research institutes and industrial partners. Theprojects span the entire value chain for plastics, including discarded electronics and multilayer packaging films. Example of projects include Plast2bCleaned, Impres, Pack-CE CIMPA, and ABSoIEU. At the same time, we sought synergy with TNO groups dealing with:

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

Recycling plastics from electronic waste with PLAST2bCLEANED

PLAST2bCLEANED

An example of process development by TNO is the European consortium PLAST2bCLEANED. We set this up to recover additives such as brominated and antimony-based flame retardants from high-performance engineering plastics in electronics. Initially, we set this up on a laboratory and pilot scale. We are now researching with partners such as Electrolux and Fraunhofer how we can develop the process to demonstration scale.

Economic importance of additive recovery

It is of economic importance to recover additives because they are valuable. Moreover, additives can disrupt the recycling process. Because the techniques are expensive, they are particularly suitable for high-performance plastics and composites in the electronics and automotive industries. Our expertise also includes the techno-economic analysis of processes required for this purpose.

Electronic waste

The goal of PLAST2bCLEANED is to develop a recycling solution for plastics from Waste Electrical and Electronic Equipment (WEEE), including computers, TVs, refrigerators, and phones. WEEE is the fastest growing stream of municipal waste. The reason for this is that the number of electronic products is increasing, while their lifespan is decreasing. The processing of WEEE in Europe yields 1.2 million tonnes of mixed plastics annually.

WEEE plastics

WEEE plastics often contain unwanted contaminants that impede recycling. Currently, 75% of WEEE plastics from Europe are exported to Asia. There, these products are recycled into new plastics containing hazardous substances. Or they may end up in a landfill, resulting in the leaking of hazardous substances. As a result, there is an urgent need for an economically viable technological solution for recycling WEEE plastics. With PLAST2bCLEANED, we are developing such a recycling solution. To achieve this goal, we are focussing on recycling the most common WEEE plastics, namely ABS (Acrylonitrile Butadiene Styrene) and HIPS (High-Impact Polystyrene).

Want to know more about PLAST2bCLEANED?

Read more about the key technologies that we are developing in the PLAST2bCLEANED project, as well as their application and a demonstration of the solution.

Key technologies

With PLAST2bCLEANED, we are developing the following key technologies:

  • Pre-treatment to sort and separate HIPS and ABS containing flame retardants from other plastic components.
  • Dissolving WEEE plastics in superheated solvents.
  • Removing additives to collect the brominated and antimony-based components and remove other unwanted additives from the polymer.
  • Recovering polymer and solvent. In this way, three cycles are closed: polymer, bromine, and antimony trioxide.

Demonstration of the solution

We will integrate the developed technologies into a pilot plant at TRL 5 that can produce polymer samples on a kilogram scale. In addition, we will evaluate the composition and properties of the recycled polymer, which are relevant for reuse in electronic goods. We will demonstrate the recovered ABS by using it in an electrical product, such as a refrigerator or a vacuum cleaner. We will then make a comprehensive assessment of the economic viability and sustainability of the solution. We will compare these with current processing methods.

Application of technologies

We can easily translate the developed technology to similar waste flows from other sectors, for example, the automotive industry, construction and infrastructure, and the packaging industry. The combination of pre-sorting and the use of superheated solvents offers an economic and ecological advantage.

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