May-2025

Can pyrolysis oil unlock greater plastic circularity?

Combining pyrolysis and vapour-phase catalytic upgrading offers lower temperature and energy requirements, higher yields, and optimised product distribution and selectivity.

Markus Hartung
Evonik Catalysts

Article Summary

Much of our society is dependent on plastics, with the first synthetic plastics manufactured more than 150 years ago. Plastics made the development of computers, cell phones, and advances in modern medicine possible. Food production, transport, and power rely on plastic for efficiency and safety, while our possessions are cheaper, lighter, stronger and safer.

It is no wonder that plastic production is increasing exponentially. Between 1950 and 2018, consumption grew about 180 times, from two million tons to 368 million tons. The UN Environment Programme (UNEP) states that 430 million tons of plastic are produced each year; production is expected to double yet again by 2050. However, the reputation of plastics has suffered in recent decades due to environmental and public health concerns.

Looking at start-of-life, approximately 98% of single-use plastic produced today comes from fossil fuels. About 4% of global oil and gas production is being used as feedstock for plastics, while 3-4% is used to provide energy for the manufacture of plastics. A 2021 report found none of the 100 largest plastic producers procure more than 2% of their feedstock from recycling sources, presenting a window for opportunity.

Criticism of plastics has largely been directed towards end-of-life management. A third of plastics are single-use; if we look specifically at the plastic used in packaging, about 95% of its material value is lost after a short first-use cycle, representing an $80-120 billion missed opportunity. The amount of plastics that end up in landfill, incinerated, or leaked into the environment stands at 72%, and the rate of successful plastic recycling sits at a reported 9%. Emissions from plastic production and disposal are expected to double in the next 35 years.

A more circular economy is needed to improve the current state of these bespoke statistics. Chemical recycling has been touted as part of the solution, with one particular method, pyrolysis, gaining interest internationally and offering a route to de-fossilising raw material streams into refineries. Organic material, including biomass, waste, tyres, and especially plastics, is transformed into pyrolysis (pyrolytic) oil or gas, which can be repurposed and utilised as reusable crude oils.

Plastic recycling status
There is no single reason behind low recycling rates; they stem from multiple factors. One significant challenge is the make-up of many individual plastic products using materials such as flexible films, multilayer materials, and coloured plastics, which cannot be recycled with conventional mechanical recycling or are entirely non-recyclable. Despite this, industries and legislators face growing public pressure to increase the collection, recycling, and reuse of all plastics. However, varied international management of the problems also presents a barrier to this. 

In European Organisation for Economic Co-operation and Development (OECD) countries, the annual plastic waste generated per person is 114 kg. In the US, annual plastic waste generation is 221 kg per person, while Australia generates 148 kg per person. In the UK, figure for 2021 was reported at 99 kg per person. The Asian continent is the largest plastic waste producer, and individual Asian countries can vary widely in plastic waste rates. Developing countries in South and Southeast Asia are major destinations for waste exports, particularly from the EU and US.

There is no dedicated international instrument in place for plastics recycling today. Some countries are taking action to reduce plastic consumption or increase recycling through campaigns and awareness-raising measures. Other countries have specific laws in place, obliging businesses to minimise waste, adopt recycling targets, and phase out single-use plastics. The EU aims to ban single-use plastics by 2030 and cut the amount of plastic packaging by 15% by 2040. Australia mandated that 100% of plastic be recycled or reused by 2040. However, the country’s largest soft-plastics recycling scheme collapsed in 2022.

Collection of waste differs between developed economies, where recyclable waste is typically collected by waste management companies and sorted and cleaned with equipment, and developing countries, which often rely on human waste pickers. The US faces difficulty because its systems for collection and management of plastics waste are organised at state and regional levels, but they are highly variable. In many Asia Pacific countries, the main drivers of plastic pollution are inadequate waste collection and processing infrastructures.

The primary existing method of plastic recycling, an industry standard, is mechanical recycling. Established on an international scale and around for decades, mechanical recycling sees plastic waste processed into secondary raw materials or products without chemically disrupting polymer chains in the process. An energy-efficient process, mechanical recycling boasts a low-carbon footprint, minimal environmental impact, and helps reduce landfill disposal. In cases of mixed and/or contaminated plastic streams, these must be sorted and cleaned thoroughly to make a product of good quality – a process that ends up being both time-intensive and costly.

However, mechanical recycling is feedstock specific, only accepting polyethylene terephthalate (PET), high-density polyethylene (HDPE), polypropylene (PP), or low-density polyethylene (LDPE) in most cases. Its impact is also limited on a global scale, as it cannot be utilised for hard-to-recycle plastics, which is where chemical recycling comes in.

Chemical recycling
Also known as advanced recycling, chemical recycling is the process of converting polymeric waste by altering its chemical structure and returning it to substances that can be used as raw materials. While introduced to industry decades ago, interest in these recycling technologies and the possibilities they present has been renewed in recent years.

Complementing existing plastic recycling methods, chemical recycling can better deal with mixed plastic waste streams, like films and laminates, that would otherwise result in incineration or landfill. Examples of these methods include gasification, depolymerisation, hydrocracking, and pyrolysis.

A transformative chemical recycling technology, pyrolysis has the potential to convert used plastic waste streams unsuitable for mechanical recycling into high-quality feedstock for even the most sensitive petrochemical industry applications.

The process sees plastics collected at the end of their product life cycle and heated to high temperatures (300- 900⁰C) in an inert atmosphere without oxygen. Thermal degradation causes these plastic materials to break down into smaller molecules, in turn, transforming plastic waste into pyrolysis (pyrolytic) oil or gas, which can be repurposed and utilised in the form of reusable crude oils.

Suitable for multiple applications, pyrolysis oil can reduce dependence on fossil fuels, presenting a lower carbon solution for hard-to-abate sectors and diversifying energy materials. In petroleum refineries, it can be used as a more sustainable and high-quality feedstock alternative to fossil naphtha, including ethylene and propylene production, which are core monomer building blocks of most plastics.