Apr-2025

Advancing adoption of chemical recycling: Part I

Processing waste plastic pyrolysis oils through hydrocarbon processing assets.

Artem D Vityuk
BASF Corporation

Article Summary

Plastic waste pollution is a major global issue. As the chemical industry is increasingly focused on transitioning to more sustainable value chains, technologies emerge to advance circularity in raw materials, intermediates, and finished products. Plastics and respected derivatives have long become a key growth engine of the modern chemical industry. With a global production volume of more than 400 Mt in 2022¹ and an estimated compound annual growth rate (CAGR) of 4%, total plastics throughput will reach 590 M tons by 2050.²

While varied by country, the growth trend is mostly reflective of economic development of the region and respective consumption patterns. The high versatility of properties and functions, in conjunction with favourable costs, made most plastics virtually irreplaceable for modern society. At the same time, recycling rates have been lagging behind, trending globally at only 9%.3 About 79% of all plastics made are estimated to be landfilled or scattered across global nature ecosystems.³

Insufficient recycling combined with the absence of alternative upcycling methods that would repurpose or process plastics into other useful goods or materials resulted in a tremendous plastic waste issue. There are estimates putting the accumulated amount of plastics produced globally since 1950 at 8.3 billion tons,⁴ causing exponentially compounding environmental problems and threatening ecological domains.

Other than major potential economic downturns, there are no long-term conceivable factors that would substantially limit global plastic waste volumes unless the industry, supported by proper regulatory policies, completely re-evaluates the value chains and adopts new technologies to boost circularity. The key technologies that support this transition are mechanical and chemical recycling.

While increasing mechanical recycling rates is believed to be instrumental in reducing plastic waste, a meaningful impact would only be achieved if chemical recycling is deployed at scale.⁵ Among chemical recycling technologies, pyrolysis gained the most attention as a scalable and effective method to process waste plastics.

Pyoil purification and upgrading
Pyrolysis is a thermochemical process that converts plastics into a hydrocarbon-based oil called pyrolysis oil or pyoil. Its value is recognised as the substitute for fossil-based feedstocks across various industrial petrochemical processes contributing to new plastics production. Some of the advantages of pyrolysis include the ability to accept mixed waste plastics streams, composite plastics, and high complexity waste, such as from electronics.

Nevertheless, there are also challenges. A typical pyoil is often contaminated and features a range of impurities, severely limiting its further use as a petrochemical feedstock. Efficient purification and upgrading of raw pyoil are seen as a prerequisite to enable industry-wide adoption of chemical recycling. In general, pyoil quality is dependent on the composition and types of plastic waste fed into the process and the design of the pyrolysis technology.^6,7

It is imperative to understand that there is no standard grade of a pyoil, even with loosely defined specifications. As the chemical recycling industry continues establishing itself, such standards are yet to be agreed upon by producers and downstream off-takers. The current market offers what could be described as pyoil grades featuring a varying extent of contamination and diverse compositions. Against this backdrop, the natural question arises regarding the optimal processing strategies for petrochemical and refining industries towards value maximisation while transitioning to circularity in their manufacturing chains.

There is clearly no unified approach. What is important to understand is that a) a rapid step change in adopting the circularity principles in base petrochemicals should not be expected, and b) this transition will require close integration of traditional refining and petrochemical assets. The transition is expected to be gradual by early adopters of pyoils experimenting with a range of technologies available, including core refining assets.

Parameters
Pyoil boiling range
Pyoil boiling range is a critical parameter affecting the choice of a potential downstream processing technology. There are well-grounded reasons to refer to the naphtha cut of the pyoil as being the most valuable platform for producing the key building blocks of most plastics and composites, including ethylene, propylene, and benzene, toluene and xylenes (BTX).

Basically, increasing the portion of naphtha range boiling hydrocarbons (typically up to 140°C for light and up to 200°C for heavy naphtha) in the pyoil helps increase the amount of carbon, which is to be fully recycled. That is not to say that carbon in heavier cuts of the pyoil or pyoil- associated gas cannot be turned into brand-new plastics; it would just require additional process steps and higher energy consumption if all production steps are looked at as the whole.

In addition, it is important to note that each conversion step has a yield factor, which means there is always a loss of at least some of the original carbon upon every additional processing step. This aspect is frequently overlooked and must not be forgotten. Therefore, maximising the pyoil portion directly suitable for conversion to monomers, with the minimum number of production steps and highest possible efficiency, is the key.

What are the technology options? A typical pyoil from a non-catalytic pyrolysis process features a total naphtha cut (up to 200°C of approximately 15-35 wt%, which is balanced by heavier oils and waxes). Some of the measures to increase naphtha yields include integration of a catalyst conversion step into the pyrolysis process or performing thermal or hydrocracking of the pyoil waxes. The former is referred to as catalytic pyrolysis, which, with a suitable selective catalyst, could boost the naphtha portion of the pyoil to above 80 wt%. The latter requires a dedicated conversion unit, which, in addition to substantial capital costs, is only feasible once a certain production scale is achieved.

Leading pyrolysis cracking catalysts enable maximum naphtha yields for catalytic pyrolysis processes. These catalysts can achieve naphtha yields up to about 80 wt% and have been used commercially.8 The bottoms of the pyoil, which are waxes unsuitable for direct conversion to monomers, are still possible to process.

Pyoil purity
Substantial contamination is clearly among the major factors preventing the wider adoption of pyoils. The spectrum of heteroatoms is wide and varies a lot depending on plastic composition, technology configuration, and process conditions. It is recognised that pyrolysis plants would benefit from upstream integration with plastic waste sorting facilitates capable of rejecting non-plastic contamination such as glass, paper, and soil dirt and performing initial conditioning through washing and other processes.
Early adopters are expected to invest in such projects or even acquire commercial entities to secure a continuous supply of sorted plastic waste to pyrolysis plants that naturally improves pyoil quality and simplifies downstream purification steps. On the other hand, there is also an understanding that existing sorting capacity is limited, and the majority of waste plastics accessible at favourable cost is not sorted properly. Therefore, the industry must find pathways to purify a wide range of pyoils in the most economically suitable fashion. The major types of contaminants that must be managed are:
• Diolefins and styrene to stabilise the pyoil
• Halogens
• Metals, including heavy metals and Si
• Nitrogen, oxygen.

There are different strategies to improve pyoil quality. The technologies that are being deployed use adsorbent and/or catalyst-based steps in a configuration designed in response to correspondent impurity levels and required product specifications. For example, the PuriCycle portfolio of proprietary catalysts and adsorbents supports pyoil producers as well as pyoil users to achieve the most stringent quality specifications.