Advanced plastics recycling

New chemical recycling technologies will supplement existing mechanical recycling.

Marc Yagoub
Honeywell UOP

Viewed : 3459

Article Summary

Today, 6% of oil consumption is used for the production of plastics. The current consumption pattern means that this will grow to 20% by 2040. Ninety per cent of the emissions associated with plastics occur during the production of the plastics, while less than 10% of emissions are associated with end-of-life disposal.

Fossil fuels demand for fuel production is declining, with 2050 demand anticipated to be only 30% of 2022 demand. The 30% residual demand is comprised mainly of petrochemicals, but indeed, recycling of plastics will also chip away at that demand. Today the plastics economy is linear. We take crude oil, produce the plastic, then use it, often only once, and then throw it away as waste. Plastic packaging used, for example, as film for food packaging means the life of the plastic is only a few days or months, whereas structural plastics such as PVC tubing can have a usage lifetime of up to 35 years. Plastic packaging is the largest application (30%) but has the shortest life cycle. This means we generate a huge amount of waste, much of which ends up in landfill or incineration. Only 14% is currently collected for recycling, and then only 9% is effectively recycled (OECD, 2022). Ideally, the plastic waste should be collected separately, allowing for efficient re-use.

Mechanical recycling
Currently, the main way of recycling plastic is mechanical recycling (see Figure 1). The plastic has to be high quality and clean before it reaches a processing centre. It then has to be separated and sorted, which further limits the amount that can be recycled. Mechanical recycling, which requires less energy and is more carbon efficient than chemical recycling, is generally the preferred option. Mechanical recycling works well for items that can be collected separately, such as HDPE and PET. Schemes such as deposit and refund for PET drinks bottles, in place in Germany, are proving to be effective in promoting separate collections for these plastics.

However, mechanical recycling has its limitations. Plastic contaminated with organic matter, such as containers used for detergents and other chemicals, cannot be recycled for food contact uses. In Europe, you cannot add more than 5% of non-food recycled material into material for food packaging. As a result, plastic recycled from mixed plastic waste tends to be used in lower-demand applications, such as in school playgrounds and plastic benches. Mechanical recycling is, therefore, not an option for plastic waste collected as part of mixed municipal solid waste. For these reasons, mechanical recycling will not reduce the demand for virgin plastic on its own.

Unfortunately, today, a big part of this waste (22% or 80 million tonnes) is mismanaged, and as many as 22 million tonnes are leaked into the environment. The OECD Global Outlook projects that unless action is taken on plastic waste collection and recycling, the amount of plastic entering the environment will double by 2060 (OECD, 2022). Plastic leakage to the environment, including microplastics, is already a major environmental problem. The Alliance To End Plastic Waste is clear recognition that manufacturers are taking this issue seriously (Alliance To End Plastic Waste, 2022).

In a perfect world, 90% of all plastics should be recycled. For this to happen, there needs to be collaboration throughout the value chain. This starts with design and includes incentives that drive the right consumer behaviours. It then utilises best practices in waste management with the separation and collection of plastic waste in combination with both mechanical and chemical recycling.

Moreover, microplastics from cosmetics, paints, and the use of recycled PET in clothing fabrics are a significant route of plastic leakage to the environment, for which collection to recover the leaked plastics is difficult. In the case of microplastics, recycling by design, for both the original materials and the way these are handled (such as laundry washing), is essential, i.e. tackling the problem at the source.
Recycling by design makes it easier to recycle plastics by reducing the use of mixed plastic components and packaging, considering the colours and dyes used and also using labelling that is easy to remove from the used items.

Circularity requires two elements. The first is an effective waste management collection system that eliminates waste leakage. The second is that participants in the value chain invest in new business models that span collection, sorting, and recycling to drive plastic circularity (McKinsey, 2022b). In developing countries, the priority is to introduce more effective waste management systems. However, in countries with well-developed waste management systems already in place, more needs to be done to standardise practice, increase consistency, and reduce confusion on what can be recycled and how to recycle.

Consumer behaviour can include deposit/refund schemes such as the scheme in Germany. However, it also covers the availability of separate collection schemes (different bins, recycling centres) to encourage the right behaviours.

Advanced plastic recycling
However, advanced plastic recycling (or chemical recycling) is the solution. The plastic is taken back to the molecule or monomers and so tackles two problems at the same time. It helps to drive down crude oil consumption, and it reduces the problem of waste plastic.
Therefore chemical recycling is the only viable recycling option for plastics that currently go to landfill or incineration. An independent study showed that in comparison with incineration for energy, chemical recycling could reduce carbon emissions by 40% (Sphera, 2022). While mechanical recycling will still always have its role, chemical recycling is able to fill the gap for those plastics that cannot be recycled mechanically, such as mixed plastics multi-layered plastics, heavily coloured plastics, and most films and containers used for household chemicals.

The pyrolysis process converts the plastic back to pyrolysis oil or recycled polymer feedstock (RPF) (see Figure 2). The Honeywell process technology is designed specifically for advanced plastics recycling. As such, the RPF is mixed with naphtha, which then is fed to a naphtha (or steam) cracker that converts the RPF back to the monomers (ethylene and propylene). This overcomes the need to manage food-contact and non-food-contact plastics, but it also can be used for coloured plastic. Thus this can be used to manufacture virgin-quality plastic and creates a truly circular ecosystem for plastics.



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