CHEMICAL RECYCLING OF PLASTIC

The term ‘recycling’ has been subject to considerable definition creep in recent years. It may once have been understood as simply using the material in one discarded article to contribute, in part or whole, to the remanufacturing of that same type of article or a different one. Now the definition has become more elastic. Some propose that it includes turning discarded plastic and other waste into fossil fuels to burn (plastic to diesel, process engineered fuels, refuse-derived fuel, etc.), non-fossil fuel (hydrogen), construction materials (integration into road surfaces and cement) or just burning it for energy. The latter has generally been called ‘energy recovery’ though some propose this should rather be ‘thermal recycling’. In some instances, processing plastic waste into fossil fuel is proposed as ‘chemical recycling’. Clearly some of these approaches can be very polluting, support a linear economy, and do not sit easily within the concept of recycling. In nearly all cases, these phrases are created by the plastics industry or the waste management industry to project a ‘greener’ and more acceptable image of their polluting business models and activities.

Most of these applications will be discussed elsewhere in this brief. This section focuses on a technique that has been subject to significant media attention as a result of its recent promotion by corporate plastic product manufacturers and retailers – chemical recycling.

Chemical recycling of plastic waste is based on using chemical and thermal processes and techniques to break down and separate polymers to a level where they can be used again as monomers, polymers, or chemical feedstock in production of new polymers, or as feedstock for other chemical manufacture. The chemical recycling process seeks to remove impurities, contaminants, and additives from the plastic waste, resulting in ‘pure’ monomers (and sometimes polymers) for polymer feedstock. Some of the main challenges for chemical recycling to overcome are the ability to scale up to an industrial level, degradation of the polymers over time, decontamination of the feedstock, and very high energy use, as well as management of, and transparency about, emissions and residues.

There are currently many unanswered questions about the energy consumption, toxic emissions and residues, and practicality of the techniques that are considered to be chemical recycling. Chemical recycling is being heavily promoted by corporations who produce and sell plastic as part of their product line or in their packaging. The European Chemical Industry Council20 argues that it differs from mechanical recycling in that it is able to process the large fraction of mixed contaminated plastic waste, remove contaminants, and either generate petrochemicals or separate monomers from contaminants to create polymers of similar quality to virgin polymers.

These petrochemicals can then be used either as ‘feedstock’, the chemical basis for polymers, or the monomers can be converted to polymer input for new plastic. However, degradation of monomers is still a problem with solvent recycling and chemical depolymerization. Thermal depolymerization can address degradation by generation of feedstock at the molecular rather than the monomer level (by pyrolysis or gasification), but historically the bulk of the output from gasification and pyrolysis processes is a form of reconstituted fossil fuel.

As pressure grows to ban plastics, the industry is seeking to update its campaign to focus consumers on recycling rather than impacts of plastic. The Alliance to End Plastic Waste21 is a consortium of plastic production and consumer goods corporations who publicly promote chemical recycling and partner with technology start-ups and pilots using such techniques. There are many similarities between the current promotion of chemical recycling by the ‘Alliance’ as a ‘solution’ to global plastic pollution and the historical push to brand plastics as recyclable resin codes and the recycling symbol.

While chemical recycling may supplement existing mechanical recycling rates, it has to be stated that it cannot be a ‘solution’ to the global plastic waste crisis while plastic production rises exponentially (Figure 1). Unless it can be implemented with high mandatory recycled content levels in new plastic alongside significant plastic production restrictions, chemical recycling will remain little more than window dressing for corporate promotional purposes. Further, chemical recycling for the purpose of creating reconstituted fossil fuels should not be supported as burning plastic derived fuels conflicts with the circular economy concept and exacerbates climate change.