From Waste to New Product: When Will Chemical Recycling Come?

Mr Hofmann, what exactly is chemical recycling? Can you explain the process in a little more detail?
Chemical recycling breaks down the plastic into smaller components, such as basic chemicals or monomers. This can be done by solvolysis, for example, which is based on solvents. In contrast to solvent-based mechanical recycling, where the plastic is dissolved as a whole and recovered again, the solvent breaks down the plastic into its basic components in solvolysis. This process works very well with PET and polyurethane.

However, polyolefins, which are often used in food packaging, cannot be processed in this way. Another process, pyrolysis, is suitable for this. This is a thermochemical process in which high temperatures of up to around 650°C are used in the absence of oxygen to break down the plastic into smaller molecules. The result is an oil that is similar in composition to fossil oil and from which the chemical industry can produce plastics again. Finally, there is gasification, which can also thermochemically break down the plastic into the smallest possible components, synthesis gas, from which methanol and other basic chemicals can be produced.

What is the current technological status of chemical recycling? Are the relevant technologies already fully developed?
As far as I know, there is currently no technology that has reached market maturity. However, some suppliers have made great progress and are on the verge of commercialising plants with relevant capacities. However, most plants have not yet reached the necessary scale for stable continuous operation.

What are the advantages of chemical recycling in the utilisation of packaging waste?
Chemical recycling has the advantage that it can also handle highly mixed materials or multi-material packaging where mechanical recycling reaches its limits. For example, multilayer films consist of different layers bonded together, while other packaging often contains plastic additives. In such cases, mechanical recycling becomes difficult as very energy-intensive processes such as hot washing or solvent-based separation processes are required. Chemical recycling can offer advantages here, as it can convert these complex materials into an intermediate product, which can then be used to produce virgin-quality plastic that is also suitable for use in the food sector. Chemical recycling can therefore also prevent mechanically non-recyclable waste from being incinerated.

However, it should be noted that chemical recycling does not recycle the entire volume. In pyrolysis, for example, the oil yield is a maximum of 80 percent. With solvolysis, on the other hand, only specific polymers such as PET or PA can be recycled. And then, of course, there is the energy required for the process and the subsequent treatment of the oils.

What steps are necessary to implement chemical recycling on a large scale?
When setting up large capacities, i.e. upscaling, the energy input into the reactors during pyrolysis must be taken into account. The plants need to be larger and at the same time more efficient in order to reduce energy consumption. The issue of operational stability is also important. This is because such a plant should be able to operate continuously, i.e. around the clock and seven days a week. Even if the input material, which can vary with waste, changes, frequent cleaning should not be necessary, for example.

Two other aspects are important when upscaling: firstly, to avoid having to transport the waste over long distances, the plants should be located where higher volumes of waste are produced. Then only the oil needs to be transported to the crackers in the chemical plants. On the other hand, it makes economic sense to set up the plant in a chemical park, for example, where the infrastructure for treatment facilities and purification systems for flue and process gases are already in place.

This oil is then fed into a conventional cracker in the form of a drop-in?
Exactly. From an economic point of view, it is currently not possible to build a cracker that is only operated with pyrolysis oil, as the quantities are not yet sufficient and will probably never be sufficient in the near future to operate a cracker economically. Drop-in solutions therefore make more sense for the time being.

How can it be determined which granulate consists of recycled material when the pyrolysis oil is fed into a conventional cracker?
This is done using the so-called energy and mass balance approach. This approach is currently being discussed in the EU Commission. Until now, the amount of oil used could be classified as recyclate. You can think of it like electricity: you can't say that one electron is green and another is not. It's similar here too. However, there is a discussion about how the parts of the oil that become fuels and thus CO₂ can be deducted in order to achieve a more precise balance and thus avoid greenwashing. 

Thank you very much for the interview Mr Hofmann.