Countless modern applications would not be possible without plastics. The material scores highly with properties such as lightness, durability, flexibility and corrosion resistance. However, the composition of plastic products is just as diverse as their applications and often makes mechanical recycling difficult at the end of their useful life. The result: downcycling or incineration. Many plastics manufacturers now want to change this with chemical recycling.
Various recycling technologies are summarised under the term chemical recycling. What they all have in common is that liquid resources are produced from waste containing plastic, enabling the production of recyclates in virgin material quality.
"Chemical recycling generally refers to technologies that use chemical reactions to break down long polymer chains into their basic building blocks," explains Dr Christoph Gahn, Vice President Chemical Recycling at BASF. These secondary raw materials can then be used to replace fossil raw materials in chemical production. According to Gahn, the various chemical recycling processes differ in terms of their technological maturity and the processability of the different waste streams. The best-known process at the moment is pyrolysis, in which plastics are converted into pyrolysis oils.
Processes with Advantages and Disadvantages
Another common method is the depolymerisation of plastics, also known as solvolysis or remonomerisation. In this process, the plastics are broken down into their monomers, from which the polymer can be rebuilt. The material obtained from depolymerisation therefore re-enters the chemical value chain at a later stage as pyrolysis oil or synthesis gas. "However, this also means that pure plastic waste is required for this process," explains Christoph Gahn. Suitable input materials are individual plastics such as polyethylene terephthalate (PET), polyamide (PA) or polyurethane (PUR). Gahn is convinced that all these technologies are needed to transform the linear plastics value chain into a circular economy.
Südpack relies on depolymerisation for chemical recycling with Carboliq technology. In contrast to the pyrolysis process, in which hydrocarbon chains are broken down at temperatures of usually more than 650 °C, this technology works at temperatures below 400 °C. Due to the low process temperatures and the introduction of energy into the material solely through friction, the plastic passes almost seamlessly from its solid phase into its liquid phase (oilification). "The fact that our technology works at below 400 °C means that coking and the formation of pyrolysis gases are almost completely avoided. The gaseous phase takes up less than 2 % of the process. This gas is currently utilised thermally, but can also be used in a large-scale plant to generate electricity in a combined heat and power plant, for example," explains Dirk Hardow, Chief Executive Business Unit Functional Films & Compounds at Südpack and CEO at Carboliq.
Mechanical Recycling is not to be Replaced
Chemical recycling is picking up speed and Südpack's project is one of more than 100 projects in this field worldwide. Nevertheless, the industry only sees the technology as a supplement to mechanical recycling. "Plastic waste that can be mechanically recycled in a technically, ecologically and economically sensible way should also be recycled in this way," emphasises Dr Alexander Kronimus, Managing Director of Plastics Europe Germany. "This applies to all plastic waste, including lightweight packaging. The separate collection and processing of packaging waste enables the efficient processing of plastic packaging through mechanical recycling." Innovations in circular product design, new, improved take-back systems and AI-supported sorting and processing could also significantly increase the proportion of packaging waste that can be mechanically recycled, continued Kronimus.
Nevertheless, mechanical recycling results in residual fractions that can only be processed further, for example as substitute fuel or with a significant loss of quality. "Composite plastics, multilayer films and plastic waste from mixed municipal waste are particularly problematic," says Kronimus. "Chemical recycling should therefore be seen as a complementary system to the mechanical system in order to process the waste volumes generated in a meaningful way and to keep the carbon in the cycle," says Hendrik Rasch, Director Circular Economy Programme, Evonik, adding: "In order to implement chemical recycling on a large scale, the framework conditions must be created to enable new business models." This is not about subsidies, but about a legal framework that helps the environment and the development of innovative technologies and processes.
Specific proposals include a double quota and product-specific recycled material usage quotas to incentivise investment. According to Dirk Hardow, this includes "recognising a suitable mass balance, i.e. the targeted allocation of secondary raw materials to products in the balance sheet". This is a prerequisite for the inclusion of secondary raw materials from chemical recycling in recyclate utilisation quotas.
"Legal framework conditions and standards must be adapted so that the chemical recycling industry can play to its strengths, namely the recycling of plastics and the substitution of fossil resources," emphasises Dr Christoph Gahn.
The companies agree that chemical recycling is a key success factor with regard to a functioning circular economy in the plastics industry. "This will make it possible to achieve the recycling quotas and climate protection targets that have been set and thus facilitate the transition from a linear to a circular value chain in the plastics industry," says Hardow.
