Basically, increasing the portion of naphtha range boil- ing 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 por- tion 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 bal- anced by heavier oils and waxes). Some of the measures to increase naphtha yields include integration of a catalyst con- version 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 cata- lyst, 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 cat- alysts 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 mono- mers, 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 con - ditions. It is recognised that pyrolysis plants would benefit from upstream integration with plastic waste sorting facili- tates 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 sup- ply 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 pro - prietary catalysts and adsorbents supports pyoil producers as well as pyoil users to achieve the most stringent quality specifications. Composition The varying chemical composition of a typical pyoil grade produced from mixed plastic waste is evident. Common fea- tures are high olefins content of up to 50 wt%, high diolefins with a diene value of 4-8 g I 2 /g, and occasionally high aro- matics at 5-35 wt%. While elevated levels of unsaturated components are typical for most cracked feeds, aromatics speciation, and content are highly dependent on inlet plastic composition and whether a catalyst is used. A lower content of cycloalkanes (naphthene in plastic pyoils) than fossil-de- rived feedstocks is expected. While highly desired, the industry is not at the point where precise control of pyoil composition is technically feasible. Further advancement in pyrolysis technology, more specif - ically, catalytic pyrolysis, is required to tailor hydrocarbons distribution towards the needs of the targeted downstream process. Being able to tune up pyoil composition offers immense potential to boost circularity, and not only in plastics, such as when maximising aromatics content (for direct BTX recov- ery), long-chain olefins (for surfactants), or even direct C2 -C 4 olefins production in the pyrolysis step. The field of industrial catalysis has built tremendous knowledge and commercial experience in designing catalysts capable of selectively con- verting the most complex hydrocarbon-based feedstocks. Catalytic pyrolysis technology development is an active field where multiple players are engaged, from start-ups to established energy and chemical firms. Some of those pro - cesses require tailormade heterogeneous catalysts produced in large volumes. Processing pyoils Steam crackers In the petrochemical industry, the steam cracker is a key asset for producing olefins, primarily ethylene and propyl - ene, which are the building blocks for most modern plastic materials. In addition, steam crackers serve as an impor- tant source of other major platform petrochemicals such as butadiene and aromatics (relevant for liquids-fed crackers). Depending on the configuration of the furnace, there are liq - uid and gas-fed units. Naphtha is the most common feedstock for liquid-fed crackers, even though there are plants capable of taking heavier cuts. Gas crackers rely on ethane or liquefied petro - leum gas (LPG), which is a mixture of propane and butane. Naphtha or diesel range cuts from pyoil, after the proper upgrading, would be a drop-in substitute for the fossil-based feedstocks. Yet, there are peculiarities associated with at least some variations of the base olefins yields if the share of the pyoil is substantial.9
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PTQ Q2 2025
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