HydroCycling: Chemical recycling of plastic waste into petrochemical base and raw materials

Raw material utilization of plastic waste

In the mechanical recycling of plastics materials, polymer damage, the combination of several polymers into "blends" and composite materials such as multi-layer films, or non-polymer substances including fillers, dyes, plasticizers and product adhesives limit the number of recycling cycles.

An innovative addition is, thus, feedstock or chemical recycling – the chemical decomposition into small molecules and their subsequent conversion into new polymer products. Chemically recycled used plastics can be utilized as raw materials to produce new plastic articles. The combination and complementarity of raw material and mechanical processes can significantly increase the quantity of recycled used plastics and the quality of the recyclates. 

Chemical recycling processes can be applied to e.g. by-products of scrap metal recycling, so-called shredder light fractions. Waste plastics from the construction sector, e.g. bromine-containing expanded polystyrene, or fractions from the recovery of waste electrical and electronic equipment may also be chemically recycled. For these and other fractions, the "HydroCycling" project is developing concepts for their mechanical processing and subsequent catalytic conversion into petrochemical raw materials and basic chemicals.

HydroCycling - from laboratory to demonstrator

The industry currently favors two chemical recycling routes: One is via the pyrolysis of used plastics and the use of the pyrolysis oils as petrochemical raw materials. The second route is gasification and the production of petrochemical polymer building blocks from synthesis gas. "HydroCycling" also attempts to largely preserve the molecular structures of used plastics and use hydrogenation to obtain petrochemical raw materials and basic chemicals. Catalytic hydrogenation of polymers has been scientifically described many times. Depending on the catalysts used and the operating conditions, different polymers have been converted in pure form or in mixtures, e.g. with refinery streams. In "HydroCycling", the influence of the composition of available, real plastic waste on hydrogenation will also be investigated. Pre-processing steps will be developed experimentally. The aim is to remove interfering foreign substances from the plastic waste to obtain usable input materials for the “HydroCycling” process. These will be converted into hydrocarbon mixtures by catalytic hydrogenation on a laboratory scale. Product work-up and utilization will be simulated in combination with a commercial “HydroCycling” plant at a refinery or petrochemical site. An important objective is to develop a concept for a demonstrator in a follow-up project. The process developed in individual steps at laboratory scale could be combined, its operation could be demonstrated and first product samples be produced.

Realization and holistic assessment

In addition to this work, a comprehensive assessment of the “HydroCycling” concept from a techno-economic, ecological, regulatory, and patent law perspective is being carried out as part of the project. This is a prerequisite for industrial implementation of the new process.

Progress and Results of the First Project Phase (Status April 2025)

• Identification of access points to existing post-consumer plastics from various waste streams and development of a logistics concept for supplying feedstock to the site of a commercial HydroCycling facility. Through mechanical processing of waste source streams, the polymer content must be concentrated and the fluctuating compositions balanced. Only with a consistent, specification-compliant quality will post-consumer plastics be reliably recyclable in industrial HydroCycling plants.

• Successful extrusion and subsequent hydrogenation of various post-consumer plastics into petrochemical products using suitable catalysts. The design of an industrial reactor is challenging: within the reaction volume, multiple liquid, gaseous, and solid phases coexist. Differences in density and the fluid dynamic properties of these phases could cause mechanical instabilities and impair catalysis. These relationships are investigated using a cold flow model in conjunction with simulations. A "hot" demonstrator will be designed in the current project and could potentially be implemented at the start of a follow-up project.

• Simulation of the HydroCycling process for the conversion of a representative mixed plastic. Specification-compliant product streams can be processed at petrochemical sites into various chemical products and, in particular, new polymer materials.

• Proven environmental relief: Industrial HydroCycling can relieve both the environment and infrastructure. A life cycle analysis from the concept phase will be gradually refined to realistically demonstrate these benefits.

• Regulatory requirements: In addition to a favorable economic environment, successful commercialization of HydroCycling requires an appropriate regulatory framework, such as suitable waste legislation and recognition of HydroCycling as a chemical recycling process with regard to future recycling quotas.