KARLSRUHE, Germany—Chemical recycling of mixed plastic waste is both technically feasible and environmentally and financially promising, according to new research from Audi and Karlsruhe Institute of Technology (KIT).
The researchers have invented a way to turn mixed plastic waste from automotive manufacturing into pyrolysis oil, which could replace petroleum as a raw material for the production of new plastic parts for cars. Together with partners from the chemical industry and KIT, Audi is now researching ways to industrialize the recycling process.
Many car parts are made of plastics, including fuel tanks, air bag covers or radiator grilles. These parts must meet stringent requirements for safety, heat resistance and quality. As a result, plastic parts that are subject to high levels of stress are typically made from “virgin” materials; mechanically recycled plastics usually cannot meet performance requirements. Additionally, mixed plastic waste is often not available for mechanical recycling.
To solve this problem, KIT and Audi launched a pilot project for chemical recycling in 2020. Tests were carried out to determine the extent to which mixed automotive plastic could be fed back into a resource-friendly cycle via chemical recycling.
The project was led by Dieter Stapf, Ph.D., of the KIT Institute of Technical Chemistry, and Rebekka Volk, Ph.D., of the KIT Institute of Industrial Management and Industrial Production. The researchers looked at the technical feasibility, cost-effectiveness and environmental impact. The results show that chemical recycling can be used to process mixed plastic waste from automotive manufacturing into pyrolysis oil that, in turn, could be used to create new plastic with the same high quality as virgin materials.
Audi is one of the first automakers to test this recycling process. The next step is to determine if the process can be done at an industrial scale.
“An initial assessment shows that chemical recycling may be superior to energy recovery from both a financial and environmental perspective,” says Volk. “We are comparing this process with energy recovery [i.e., burning plastic waste for heat]. An initial comparison of the figures shows that the costs for chemical recycling are on par with…energy recovery.
“Furthermore, chemical recycling offers the opportunity to recycle much of the carbon and reuse it in the production of new plastic components. As a result, carbon dioxide emissions from chemical recycling are significantly lower than those from the energy recovery process, which benefits the climate.”
Complementing mechanical recycling, pyrolysis converts mixed waste plastics and composites into a liquid chemical feedstock while separating out unwanted constituents. After a purification step, this pyrolysis oil can be processed into new plastic using conventional industrial processes, thus replacing primary raw materials from fossil energy sources, such as petroleum.
For Philipp Eder, project manager for chemical recycling in the supply chain at Audi, chemical recycling is not just about meeting the legal recycling requirements stipulated by German and European waste legislation.
“Audi wants to use intelligent methods to proactively shape the market for secondary raw materials and take responsibility in line with our mission of achieving a competitive edge through the use of innovative technologies,” he says.
As such, Audi has identified chemical recycling as an opportunity and has set out to successively increase the amount of recycled plastic in its models. Up to now, Audi has primarily used recycled single-variety plastics. A current example is the use of PET in the Audi A3. PET is a plastic that consists of a single-variety chemical compound, which is easier to process than mixed plastics. The A3 is available with three different fabric covers for the car seats that contain up to 89 percent recycled material. The new Audi Q4 e-tron electric SUV also contains components with recycled content, including mounting brackets, wheel arch liners, fender covers, floor paneling and wheel spoilers. A total of 27 components contain recycled material.
In the future, mixed high-performance plastics produced via chemical recycling could also be added.
Audi’s recycling efforts are part of a companywide environmental program, “Mission: Zero,” that focuses on resource conservation, waste avoidance and closed recycling loops in production. For example, plastic waste from A6 and A7 assembly at the Neckarsulm plant is sorted, shredded and then processed into 3D printing filament. This plastic thread is then used to produce precision-fit assembly aids for production with the help of 3D printers. Audi’s 3D printing team is working closely on this with the Dutch start-up 3devo, which supplied the technology for making and using the filaments.
In another recycling project, plastic sheets are being recycled into trash bags. The carmaker is also working with suppliers to optimize packaging for parts. This has already enabled Audi to eliminate almost 23 tons of nonrecyclable packaging at its Neckarsulm assembly plant alone.