Improvements in chemical recycling technologies are creating new opportunities for recovering resources from plastic packaging waste. So says Axion’s head of circular economy Richard McKinlay. His company works with government agencies, local authorities and companies in diverse sectors on new processing and collection methods to recover value from waste resources.
McKinlay observes action is being taken through various collaborative initiatives that are bringing together businesses from across the entire plastics value chain with UK governments and NGOs to create a circular economy for plastics and to achieve key targets. By 2025, several companies have committed to making 100% of their packaging recyclable.
For waste plastic packaging, the ‘ideal recycling solution’ would be turn it back into new packaging materials. Mechanical recycling is the standard method widely used today, involving sorting, washing and extrusion to produce a pellet used as a secondary raw material. However, mechanical recycling has a number of limitations, the main one being the inherent inability to produce a virgin-comparable product.
The only way to obtain truly virgin-quality recycled material, if we are to recycle more of our packaging waste and develop new markets for recovered resources, is through non-mechanical or chemical recycling.
Primarily, three different types of technology are being developed for recycling packaging into virgin-quality polymers: pyrolysis, solvent dissolution and chemical depolymerisation. Each uses a different process and is suitable, or has been developed, for different polymers.
Pyrolysis is the breakdown of material at elevated temperatures in the absence of oxygen. This has been used successfully for many years on biomass to produce oil but has not yet been widely used on plastic waste. Significant work has been done on developing pyrolysis processes for waste plastics, with commercial installations already in place. For example, a company in Spain is successfully using pyrolysis to recycle agricultural film.
Pyrolysis is most suitable for polyolefins – polyethylene (PE) and polypropylene (PP) – as they are simple hydrocarbons. It produces a range of hydrocarbon products, some of which can be used as a precursor to new chemical products, including polymers. Often light hydrocarbon fractions are burnt on site to generate power/heat for the process.
Although researchers are trying to develop technologies that accept all kinds of mixed waste, it is likely these materials will have to be sorted and cleaned before they can undergo pyrolysis. Potentially, new virgin-quality polymer can be made from the resulting oil. The process is particularly relevant for PE because low-density polyethylene (LDPE) is so widely used in film. However, mechanical recycling of film is quite challenging and putting recycled content back into film is very difficult.
Realistically, the only long-term solution is to break it back down into an oil. While the concept of taking the oil to a new virgin polymer is quite new, large petrochemical companies such as BASF and SABIC are now investigating the possibility of producing polymers from naphtha on a commercial scale in partnership with pyrolysis technology providers.
Engagement was low in the past but the entire supply chain is beginning to work together. With a growing need to address flexibles, pyrolysis may be the most feasible option for maximum recovery.
Solvent dissolution involves selective extraction of polymers using solvents. A relatively pure feedstock, such as washed PP from margarine tubs and other packaging, is dissolved in a suitable solvent. Any colourants, additives and non-target materials are removed, and the resulting polymer can be re-formed. This differs from pyrolysis because the polymer is not broken down, making its recovery for use in new products easier.
Solvent dissolution presents some key opportunities and can result in high yields of recovered polymer with only a 3-5% loss. There are significantly fewer ‘by-products’ produced compared to pyrolysis and the process removes all additives, including pigments and inks.
A major benefit is that it can be used to create food-grade recycled rPP – for example, margarine tubs can be turned back into new ones. It can also be used to recover PE or PP from multi-layer, non-recyclable packaging such as single-use sachet products, the collection and recycling of which would help to reduce pollution issues such as plastics entering the oceans.
Solvent recycling has its challenges: solvents can be expensive and solvent recovery is key. The more non-target material present, the higher the cost of recycling owing to potential solvent loss. Feedstocks require high levels of sorting and purity before dissolution and the process is technically challenging to develop and operate.
Companies actively involved in recycling plastics through solvent dissolution include ones based in the USA, the Netherlands and Germany.
Chemical depolymerisation is the breaking down of a polymer into either monomers or intermediates using a chemical. It is being developed primarily for polyethylene terephthalate (PET), which can be broken down using either water (hydrolysis) or monoethylene glycol (glycolysis). PE and PP cannot be broken down in such a controlled way as the polymer chain does not have any distinctive ‘cutting’ points.
Similar to solvent recycling, the process removes additives and colourants while contamination is filtered out. The monomers are polymerised to produce virgin-quality PET.
‘It is essential that big companies with money, know-how, equipment and investment power are engaged and part of the search for solutions.’
As PET is used almost exclusively in fibre and packaging, chemical depolymerisation offers significant recycling advantages. It is particularly effective for PET trays, which can be difficult to recycle mechanically because of their quality.
Challenges with chemical depolymerisation include the need to prepare the feedstock to remove as much contamination as possible. It is significantly more expensive than generic mechanical processes because of adding the chemical step to collection, sorting, washing and shredding operations. Furthermore, the environmental impact of chemical recycling is not completely clear as only now are laboratory-scale trials and pilot projects being scaled up.
The right direction
Large-scale plants capable of processing at least 50,000 tonnes per year are needed for economic viability. Although the cost of scaling-up and the investment needed have previously been prohibitive, companies are beginning to see the potential of this exciting technology. Virgin polymer producer Indorama has invested in companies in the USA and the Netherlands, while Plastipak has announced plans for a processing operation in Italy.
Public awareness is prompting the plastic packaging sector into action and into investing in new recycling technologies to deal with waste materials. Huge investment is needed, as is further refinement of these processes, but we are very much moving in the right direction. If we want to recycle everything, chemical recycling is the way we must go. Mechanical recycling techniques will only take us so far.
Non-mechanical recycling can overcome the limits of mechanical recycling to produce high-quality end materials or recover value from non-recyclable materials. However, the increased cost and potential yield compromise of non-mechanical recycling means mechanical recycling still plays a vital role.
Source: Recycling International