efficiency. Straight-run naphtha from fossil sources is typ- ically rich in naphthenes, up to 50 wt%, depending on the crude source. The naphthene content in plastic pyoil is a lot smaller and often is in a 5-15 wt% range.12 In addition, it is important to remember that catalytic reforming is the key source of hydro- gen for most of the plant’s refinery operations, and refineries rely heavily on hydrogen to keep multiple hydroprocessing units online. Hydrogen yield in the CRU is almost directly proportional to the content of naphthenes. Therefore, a substantial drop of naphthenes content in the feedstock might lead to a major reduction in the amount of hydrogen produced. Furthermore, if the target is to maximise BTX in the CRU products mixture, the light naphtha (i.e., C6-C8 boiling at 60-140°C) is the opti- mal choice. Heavy naphtha (C7-C9, IBP-FBP 90-160°C) shifts product distribution towards gasoline pool components. Those are important considerations to make while exploring plastic pyoil blending into the catalytic reformer naphtha feed. Upgrading needs (CRU) The most logical point of pyoil naphtha injection into con- ventional naphtha is upstream of the existing hydrotreater. However, this option requires a detailed assessment of the hydrotreater design to gauge if the installed unit is capable of handling higher levels of heteroatoms, which are expected to increase after blending, more specifically nitrogen and metals. In addition, if blended in substantial amounts, pyoils often need stabilisation via selective hydrogenation of diolefins, which existing hydrotreating units might or might not be able to do. In this regard, the configuration of the pyoil hydro- treater is likely to resemble those used to process cracked naphthas from processes like FCC or delayed coking, so CRUs with assets and experience processing such stocks are better positioned to treat pyoils. Even though mixing minor amounts of high-grade pyoil into conventional naphtha is likely feasible with no revamp of the hydrotreating unit, as blending ratios increase, a dedicated pyoil purification system would be required. The elements that draw immediate attention in this regard are nitrogen and metals, specifically, silicon. The content of Si in plastic pyoils is typically a lot higher compared to fossil-based naphtha. If not managed properly, Si quickly saturates catalysts in the upstream hydrotreating unit, breaking through into the reformer and poisoning the catalyst. Nitrogen control in the feed to CRU is crucial to restrict ammonium chloride formation, which readily depos- its on process equipment at lower temperatures, leading to operational and safety issues. It is important to remember that CRU technology uses con- tinuous injection of chlorides to redisperse Pt over the catalyst support, so low levels of hydrochloric acid (HCl) are expected in recycle hydrogen, LPG, and even liquid reformate.1⁰ To mit- igate these risks associated with high nitrogen and metals impurities carried into the CRU naphtha feed with the pyoil, the proprietary PuriCycle HP and HM series hydroprocessing catalysts and metal guards and PuriCycle Si adsorbents have been designed for high Si pyoil feeds, to remove Si from the pyoil before or after blending with conventional naphtha.
Fluid catalytic cracking (FCC) FCC is a core technology that makes transportation fuels such as gasoline and LPG olefins. FCC is an important source of propylene, accounting for about 30% of global production. The typical feedstock into the process is vac- uum gasoil (VGO), atmospheric residue, or a mixture thereof. Traditionally, FCC occupies an important spot in the refin- ing industry by converting crude bottoms’ generally limited value into high-value products (fuels and LPG olefins). As the process is designed to handle heavy stocks, it is a lot more tolerant towards impurities compared to steam cracking and catalytic reforming. Coprocessing through an FCC unit offers the benefit of requiring no extra hydrogen and minimal modifications to the refinery. The FCC catalyst is continuously regenerated by burning off coke in the regen- erator before recirculating the catalyst to the riser for further cracking reactions by breaking down large molecules into more valuable products, such as gasoline and LPG olefins. Furthermore, FCC catalysts are highly tunable and can be designed to adjust yields or better tolerate metal deactiva- tions. The unique positioning of the FCC allows it to process a full range of pyoils, especially the heavier cuts that would otherwise require thorough purification and hydrocracking into naphtha or diesel to be qualified as steam cracker or catalytic reformer feedstocks. The favourable positioning of pyoils as the feedstock into FCC is underlined by beneficial hydrogen-to-carbon (H/C) ratios of those feeds, mainly aliphatic, compared to typical crude oil-derived heavy stocks. Higher hydrogen content typically leads to improved yields of lighter products, includ- ing propylene, and limits coke formation. Some reports even suggest the feasibility of direct dissolution of polyethylene, polypropylene, and polystyrene in vacuum gas oil (VGO) at FCC feed conditions.14 The fundamental issue of feeding pyoils into FCC is that propylene represents only a portion of the product’s spec- trum, and an estimated 60-80% of carbon is converted into fuels that clearly does not benefit the circularity principle. In accordance, the current regulatory environment does not support coprocessing pyoils into fuels, and more definite legal guidance is required to incentivise the production of circular chemicals using FCC technology. Nevertheless, FCC is still a piece of the puzzle, offering a short- to mid-term solution as chemical recycling finds wider adoption. Upgrading needs (FCC) Unlike the cases made for steam cracking and catalytic reforming, the purification needs for pyoil as the feedstock to the FCC unit are very different, especially if heavier cuts of pyoil are processed. The high level of contaminants necessi- tates the deployment of different types of adsorbents capa- ble of retaining efficiency in higher boiling liquids. Among impurities, halogens and alkali metals are more problematic due to the multiple issues they cause in the FCC process. With a typical chloride specification of about 5 ppmw, chlorides level is likely the limiting factor to control pyoil to heavy gas oil (HGO) or VGO blending ratio if no ded- icated purification is performed. PuriCycle G and PuriCycle H-type adsorbents can help operators properly condition the
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PTQ Q2 2025
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