Pyrolysis: A Game Changer in the Fight Against Plastic Waste

With global plastic production expected to nearly triple from 460 million tonnes (Mt) in 2019 to 1,231 Mt by 2060, the environmental and health risks associated with plastic continue to rise. Research has identified over 16,000 chemicals in common plastic products, 4,000 of which pose significant hazards. While governments have implemented various policies to address this issue, such as the Biden-Harris Administration's aim to phase out single-use plastics by 2035, and the UK's Plastic Packaging Tax, current recycling rates remain abysmally low at just 12-13%. Clearly, a more diverse and advanced approach is needed to combat plastic waste effectively.

Limitations of Mechanical Recycling

Mechanical recycling has been a cornerstone of plastic waste management, but it faces significant limitations. When plastic is melted and reformed, its polymer chains are often weakened, resulting in lower-quality material that may not be suitable for high-end applications. Additionally, mechanical recycling struggles to handle contaminants like food residue, multi-layer packaging, and other non-plastic materials. This leads to lower recycling rates for certain plastics, such as flexible packaging films, which see a mere 7% recycling rate in the UK, compared to 63% for plastic bottles.

Moreover, mechanically recycled plastic often has a shorter life cycle, eventually ending up in landfills or incinerators, contributing to greenhouse gas emissions and the creation of microplastics, which harm ecosystems.

Pyrolysis: A Strong Contender

In contrast, pyrolysis, a type of chemical recycling often called "advanced recycling," offers a promising solution for mixed plastic waste. By heating plastics to 400-600°C without oxygen, pyrolysis breaks down polymers into smaller molecules, producing an oil-gas mixture that can be further refined. This process yields around 80% liquid (pyrolysis oil), 15% gas, and 5% carbon black (ash), with the gas and carbon black being reused in various industries.

Unlike mechanical recycling, pyrolysis produces high-quality oil that can serve as a feedstock for producing new virgin-quality plastics. According to the U.S. Department of Energy’s Argonne National Laboratory, even using just 5% pyrolysis oil in plastic production reduces greenhouse gas emissions by up to 23% compared to traditional methods reliant on crude oil.

Addressing Contamination in Pyrolysis

Despite its promise, pyrolysis still faces technical challenges, particularly with contamination from mixed plastic waste feedstocks. Impurities such as metals, organic gels, and other particulates can compromise the quality of pyrolysis oil and damage equipment. However, advancements in filtration technologies are helping mitigate these issues. For example, depth filtration methods have been shown to reduce particle contamination, making pyrolysis oil more suitable for downstream processing in steam crackers, where it is converted into lighter olefins for plastic production.

Research from Ghent University and Pall Corporation revealed that filtering pyrolysis oils reduced coke formation by 40-60% during steam cracking, without affecting product quality. This indicates the importance of contamination control in maximizing pyrolysis efficiency.

Towards a Circular Economy

While mechanical recycling will remain a key part of plastic waste management, its limitations necessitate the inclusion of chemical recycling technologies like pyrolysis to build a truly circular economy. By addressing contamination challenges and improving operational efficiency, pyrolysis can enhance the recycling of mixed plastic waste, reduce reliance on virgin plastics, and minimize the environmental impact of plastic production.

Governments must recognize the role of chemical recycling in advancing sustainability and invest in supportive policies and infrastructure to scale pyrolysis. With the right investments, pyrolysis could play a pivotal role in driving the circular economy and helping to combat the global plastic crisis.

A greener future is within reach if we embrace the full potential of these innovative technologies.