Chemical recycling vs.pyrolysis: The debate
In 2021, 16.13 million tonnes of plastics were used in the European Union, and only 40 per cent was recycled.
The average global situation is more critical, as only 9 per cent of plastic waste is recycled worldwide. Can this plastic waste be upcycled into circular products to be returned to the economic cycle?
Mechanical recycling methods of plastics are neither versatile enough to deal with the various types of polymers nor adequate for the volumes of waste produced. Also, the market is glutted with mechanically recycled secondary plastics.
Chemical recycling can be a viable and sustainable alternative to convert end-of-life plastics to their base chemicals and divert waste from incineration and landfills. In this article, you will learn:
- What is chemical plastic waste recycling?
- How chemical recycling differs from pyrolysis, and
- The advantages and disadvantages of these two plastic recycling methods.
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Understanding the Processes: Chemical Recycling vs Pyrolysis
Chemical recycling or advanced recycling is a set of technologies for mixed (laminated and multilayered) or contaminated plastic waste that is difficult to recycle mechanically. The process can also treat waste plastic without economic potential after mechanical recycling.
The British Plastics Federation states chemical recycling breaks end-of-life plastics into simple hydrocarbons. These hydrocarbons can be monomers or polymers used as molecular building blocks for new virgin-quality plastic production or as chemical feedstocks.
Depolymerisation and purification are two technologies used to chemically recycle plastics. Theoretically, these processes can recycle plastics multiple times without degradation of quality.
Depolymerisation
Chemolysis, or depolymerisation, reverses the polymerisation used to produce plastics and yields single individual molecules (monomers) or short chains of oligomers.
The end products’ quality is comparable to virgin monomers produced from fossil fuels, meaning the products of depolymerisation can be used to produce virgin-quality plastics that could be food-grade. Various solvents, such as water/steam, glycols, amines, and menthols are necessary for different types of plastic. The plastic waste streams that can be recycled by these various depolymerisation processes are:
- Methanolysis and glycolysis can recycle polyethylene terephthalate (PET) plastics, such as beverage bottles and food packaging.
- Hydrolysis, still in the laboratory testing stage, could recycle polyamides (PA) or nylon found in clothes, toothbrush bristles, and carpets.
- Glycolysis and hydrolysis can recycle polyurethanes (PU) or foams. Flexible foams are found in upholstery, car seats, etc.; rigid foam is used in construction and insulation; other applications are paints, adhesives, etc.
Purification
This process dissolves plastics in suitable solvents, followed by purification to remove additives and contaminants.
The dissolved plastic polymers are later recrystallised with their properties unchanged and can be used for new plastic production. This chemical recycling process is helpful for several types of plastics, such as:
- Polyvinyl chloride (PVC), used to produce medical devices, pipes, and cables.
- Polypropylene (PP), found in packaging, housewares, domestic appliances, medical, automotives, and industrial items.
- Polystrene (PS), which is used to make disposable food packaging and cups.
- There are two types of polyethylene (PE). High-density polyethylene (HDPE) is used in fresh produce bags, caps, bottles, and carrier bags. Low-density polyethylene (LDPE) is used to produce films, bags, sacks, protective sheeting, etc.
Pyrolysis
Pyrolysis and gasification are advanced recycling processes that produce chemical feedstocks. Pyrolysis, also called cracking, is a thermal process, so it is considered different from purification and depolymerisation which are purely chemical processes.
Pyrolysis recycling applies high temperatures to plastic waste in an oxygen-free environment. This decomposes complex polymers into a mixture of basic hydrocarbon gases and char. The gases are distilled to produce heavy oils, light oils, naphtha, and waxes. Any non-distillable fraction remains a gas. The product composition can be altered to shift production to the more desirable lighter oils and gas by changing the temperature and treatment time. Heavier hydrocarbons can be re-treated to get lighter products.
This process produces lower-value products and oils that can’t be directly recycled for plastic production. The pyrolysis oils are comparable in quality to some fossil oils (diesel) used as fuels.
Pyrolysis is useful for treating difficult-to-recycle plastic streams like mixed or contaminated plastics and PP to produce circular products. Pyrolysis plants treat other waste streams, notably end-of-life tires, to make oils and char. Though applying pyrolysis to recycle plastics is a recent development, pilot projects worldwide have proved it is possible.
What is the difference between chemical recycling and pyrolysis?
Though pyrolysis is a type of chemical recycling, it differs significantly from purely chemical processes, and these differences are worth highlighting.
End products and circularity
Chemical recycling’s end products are high-value monomers that can be used instead of mined fossil petrochemicals to produce virgin-quality plastics.
This secondary plastic retains its value and can be recycled several times, making it a good fit for the circular economy. In comparison, pyrolysis recycling’s end products are lower-value fuels, feedstock, and char.
Burning pyrolysis oil and gas for energy is just as polluting as burning fossil fuels. The pyrolysis oils must be refined before use as feedstocks to produce plastic.
The process is less circular, as the end products can’t be directly used in the next cycle of plastic production. However, the secondary plastic produced is comparable to virgin plastics in quality and is food grade, which makes it useful for medical items and packaging for cosmetics and food.
Energy use efficiency and carbon footprint
Depending on the technology, chemical recycling processes can consume substantial energy. However, optimised chemical recycling processes are more energy efficient and have a smaller carbon footprint than manufacturing plastic from virgin fossil fuels.
Pyrolysis recycling always needs considerable energy to attain the high temperatures necessary. Additional energy use is also necessary for refining the end products. Therefore, the carbon footprint can be large.
However, carbon emissions from pyrolysis are significantly reduced by using renewable pyrolysis gas instead of fossil fuels for heating. Overall, pyrolysis recycling has a smaller carbon footprint than chemical recycling.
Feedstock flexibility
Chemical recycling processes accept specific plastic streams, which increases their efficiency. However, the proper sorting of post-consumer products may require additional effort.
Pyrolysis recycling has feedstock flexibility and can treat mixed and contaminated plastic. Some types of co-pyrolysis treat plastic mixed with biomass. However, this versatility is offset by lower-value products from pyrolysis. Moreover, PET plastics, which contain oxygen, can comprise efficiency as pyrolysis needs oxygen-free environments to be effective.
Pyrolysis has the advantage of handling waste that mechanical recycling can’t. It offers an opportunity to go beyond mechanical recycling and increase the amount of waste diverted from landfills and incineration to meet European Union (EU) targets of 2025 and 2030.
The Circular Economy Package wants to reduce landfilling to 10% of municipal waste by 2035. The EU has set ambitious targets to reduce landfilling and incineration of plastic waste.
Contec uses a proprietary pyrolysis process to turn end-of-life tires into new commodities. Learn more about our process.
Which process is more sustainable?
Context matters.
If circular plastics are the goal, chemical recycling is better as it reduces virgin raw material use.
However, plastic waste of all kinds is mixed or contaminated by the products it contains, even in the EU. In these cases, chemical recycling technology cannot be used.
Pyrolysis recycling is the ideal solution for mixed PE, PP, and PS plastics to prevent incineration for energy recovery or landfilling, which carries the risk of plastic ending up in oceans, for example.
Pyrolysis is the dominant and most profitable technology among chemical recycling processes. Since 2021, pyrolysis recycling capacity has increased by 60 per cent globally. The pyrolysis oil yield can be as high as 70 per cent, but the yield of new plastic is low. Pyrolysis recycling has a small carbon footprint if renewable gas, one of its products, is used for heating.
All chemical recycling processes have these advantages over mechanical recycling, beyond circularity:
- Resources are abundant, especially for pyrolysis recycling (mixed and contaminated plastic waste), and there is a high demand for circular plastics.
- The process encourages plastic waste collection and treatment, makes waste treatment economical, and establishes a sustainable supply chain.
- R&D efforts by industry leaders, research institutions, and national governments are promoting innovation and attracting investments to increase capacity.
According to Plastics Europe, the planned investment in chemical recycling is expected to be 2.6 billion Euros by 2025 and 8 billion Euros by 2030. Feedstock technologies such as pyrolysis and gasification are expected to account for 60 per cent of the planned capacity of 44 projects in 13 EU nations.
This will reduce plastic waste disposal and provide recycled feedstocks that could account for two-thirds of plastics and petrochemicals by 2030, cutting the use of virgin fossil fuels and boosting the circular economy.
While chemical recycling is efficient, pyrolysis recycling provides a ready solution for the problem of some mixed plastic streams to meet EU goals of reducing landfilling, increasing plastic recycling, and producing circular products.
Pilot pyrolysis recycling projects have been tested, and investments are being earmarked for expansion. Increased capacity is possible by building many small units or a few large-scale centralised plants.
Tire Pyrolysis at Contec
Contec uses a novel molten salts pyrolysis process to recycle waste tires, a complex plastic polymer.
It is one of the few pyrolysis companies in Europe that has received investments to expand its capacity threefold. Contec aims to produce circularly recovered Carbon Black, pyrolysis oil, steel, and gas. Carbon Black is a critical raw material that can be supplied to the tire industry to support the circular economy.
At Contec, we enable tire manufacturers interested in transitioning to a circular economy by providing recovered Carbon Black (ConBlack®), recovered Tire Pyrolysis Oil (ConPyro®), and recovered Steel (ConWire®) from ELTs as sustainable alternatives to current industrial production.
Get in touch to learn more about our solutions.
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