Do you see growing investor interest in processing plastic waste-derived pyrolysis oil through refinery assets, such as hydrocrackers? Against this backdrop, how prepared are refiners to invest in contaminants removal systems (for pretreatment of the pyrolysis oils)?Feb-2023
Michael Allegro, BASF - Refining Catalysts, firstname.lastname@example.org
Advanced plastic recycling is becoming an important part of many long-term refinery strategies. One key consideration is how the legislation will pan out. Will plastics-to-fuel be an economical route, or is full plastics circularity the end goal?
With many refineries configured to maximise transportation fuel products, the yield of plastic precursors on a lb-per-lb basis of waste plastics may not be high enough to meet the circularity targets likely to be mandated. However, if fuels produced from waste plastic oils can qualify for renewable credit, the conversation about utilising refinery assets becomes much more attractive.
Contaminant removal is a major challenge for refiners considering processing plastic pyrolysis oils (pyoils). Aside from the associated Capex, these systems may come with unique maintenance requirements, large plot spaces, high Opex, and new environmental impacts that refineries are not prepared to bring inside their battery limits.
Additionally, there is uncertainty about waste availability, which could require refiners to purchase from multiple sources. This can lead to increased variability in pyoil quality, which could make investing in the appropriate contaminant removal systems more complicated.
Ricky Hsu, International Innotech, email@example.com
Interest is growing in converting waste plastics, including PE, PP, PS, PET, ABS, and PVC, into pyrolysis oil through steam cracking, cat cracking, or hydrocracking. However, several problems are encountered:
Å’ Lack of pretreatment systems for removing heavy metal contaminants from the feed, such as lead, nickel, zinc, copper, chromium, antimony, and barium (from additives to the plastics), to protect cat cracking or hydrocracking catalysts.
Reactor plugging problems (we observed a commercial demo plant shut down in 30 days due to plugging).
Å½ Pyrolysis oil rich in aromatics or olefins is low in cetane number and unsuitable for diesel fuel (but for lower-grade fuel oils).
The magnetically induced Universal Filter (developed and commercially demonstrated by Shin-Chuang Technology in Taiwan) may remove heavy metals and solid particles (down to nanometer sizes) in the feed stream to protect the reactor catalysts. (Refer to US patent 9,352,331). Alternatively, instead of converting waste plastics into pyrolysis oil, Shin-Chuang Technology has commercially incorporated waste tyre rubber and waste plastics into the huge worldwide specialty cement and concrete markets with very low processing costs (no chemical reactor, no heating, no pressurising, no cooling, and no CO2 or gas emissions).
Plastics, including PE, PP, PS, as well as butyl rubber (tyres) are hydrophobic, so mixing them with hydrophilic cementitious materials forms a loose mixture with very weak strength. The strength of the cement matrix required as the construction material is from the hydrates produced through hydration of cement and water. However, typical cementitious material cannot stop water from damaging its internal structures. Over the years, people have tried all kinds of methods to incorporate polar plastics such as PVA or non-polar plastics such as PP fibre into the cement-matrix composite (CMC) to improve the hydrophobic capability of cement and concrete without satisfactory results.
The novel method disclosed in US patent 10,882,785B1 issued to Shin-Chuang Technology is to disperse the hydrophobic waste plastic or rubber particles as carriers of the hydrophobic agent uniformly throughout the cement matrix by improving the surface property of the particles. Hydration occurs in the cement matrix without disturbance. After hydration, the CMC becomes hydrophobic with minimal strength loss. For example, after hydration, the ‘hydrophobic’ cement mortar containing 4 wt% waste tyre rubber exhibits higher than 95% compression strength compared to that of ‘hydrophilic’ mortar containing no rubber. An SEM image of the hydrate of the CMC showed tight and uniform C-S-H bonding to confirm the high compression strength.
Also, gaps in the CMC are hydrophobic, and the water contact angle in the gaps is too large to allow film flow of the water, so water cannot pass through. However, moisture can get through freely, making this CMC a hydrophobic but breathable construction material. The product is successfully commercialised with references available. Furthermore, the CMC provides a much-improved sound (noise) barrier and heat insulation than regular cement or concrete.
Joris Mertens, KBC (A Yokogawa Company), joris.mertens@kbcglobal
Yes, we see a growing interest in waste plastic pyrolysis and, consequently, in processing technology for the waste plastic pyrolysis oil (WPPO) product. Refiners are better prepared to handle WPPO in that they are familiar with hydrotreating technology, which is central to WPPO cleaning technology. Besides knowing how to start, run, and shut down these units, refiners are familiar with handling catalysts and have the necessary hydrogen to run them. On the other hand, treating WPPO requires consideration of other factors.
First is unit size. Both the treating technology and pyrolysis represent emerging technologies. The first industrial units coming online are tiny by refinery standards, with feed rates lower than 10 m3/h (below 1.5 kBPD). Sizes of the treating units are set primarily by availability of the WPPO feed rather than by technical constraints. Therefore, hydrogen availability is unlikely to be a major constraint despite the high specific hydrogen consumption. Although a simplified block flow diagram will look similar to that of a hydrocracker, KBC expects most of these units will be grassroots projects rather than revamps of existing units because of their size difference. For the same reason, the possibility of repurposing existing facilities to construct a WPPO cleaning/conversion facility will be limited.
Despite the small size of the contaminant/treatment unit, the variability and (un)availability of the WPPO feedstock could pose a significant operational concern. The waste plastic source will strongly influence unit performance, with some generating olefinic paraffins and others producing aromatic products, which may be less suitable for certain applications (such as ethylene cracking). Therefore, the refiner should be well aware of both the quality of the WPPO and the risk of disruptions in supply.