Chemical recycling of mixed polyethylene in a reactor system

The outcome

This project developed a unique homogenising method in which the need for sorting and separation of mixed plastic waste before being used in any type of recycling process is minimised.

The homogenising method converts unsorted mixed polyethylene waste with varying characteristics (for example, melting, flow and degradation properties) into materials with a consistent behaviour. The conversion process that was tested combines innovative experimental and theoretical modellings which contributed to the development of the efficient catalyst and feedstock recycling reactor system.

A consistent polymer feedstock is the end product of the process. This will enhance the recovery of low grade, mixed plastic into emerging recycling methods such as chemical recycling.

The need

There are some barriers to closing the loop on plastic recycling for mixed polythene waste:

• the challenges involved (cost and logistics) with mechanically sorting and separating plastic polymers into single streams
• the diverse contents and characteristics in mixed polyethylene waste, particularly miscible blends with other types of plastic in multilayer packaging applications presenting further processing challenges (this is relevant when chemicals, additives, and polymers that include chlorine in their chemical structures are added to plastic packaging products, which affects the properties and reproducibility of the final product).

This project sought to address these barriers with the goal of diverting low grade, mixed plastic currently destined for landfill and improving the recovery and future recyclability of plastic waste. This research will benefit plastic recyclers, producers of polymers (in particular polyolefins), as well as polymer waste processing companies.

Developing the solution

The project addressed diverse mixes of polyethylene waste to develop a successful homogenising method and algorithm to improve the consistency of melting and degradation behaviour. This was achieved through multiple stages including:

• homogenising mixed plastic waste through a high shear melt blending method along with an assessment of products by quality control tests
• purification through a dichlorination/dehydrochlorination method based on thermal treatment along with the incorporation of chlorine absorbents to reduce the corrosive effect of chlorine content in mixed polyethylene waste during chemical recycling
• design of a 2-stage chemical recycling unit to ensure better control over the distribution of recycling products through a quick thermal screening step by coupling a high-pressure reactor vessel to a high temperature cracking unit
• various kinetic models and simulations were used to predict degradation using pyrolysis coupled with mass spectroscopy, and to optimise the chemical recycling parameters to synthesize the most suitable catalyst.

The partnership

Deakin University led the project under Professor Minoo Naebe, who has a team of researchers with knowledge and expertise in polymers, composites and fibres, along with national and international industry partnerships.

Qenos are recognised as a global leader in the production of polyethylene (PE) polymers and are the sole manufacturer of PE polymers in Australia. GT Recycling is an innovative, family owned and operated plastic and cardboard recycling company with processing operations in Geelong. GT Recycling draws its expertise from a team with over 40 years of experience.

Pathway to commercialisation

This project is considered foundational research to the field of polymer science and chemical recycling engineering. It proved that mixed polyethylene waste could potentially be directly fed into industrial chemical recycling plants as a consistent feedstock without the worry of separation and sorting. A consistent feedstock could result in consistent recycling and value-added products that may even generate a new polymer.

Deakin University have committed to further research to understand the potential of homogenised plastic waste and end product applications.

More information

For more about this project, email marketsacceleration@sustainability.vic.gov.au