Question
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A wider range of feedstocks are considered for refinery processing, including bio-based feedstocks and polymeric compounds from waste plastics. Are there new types of corrosion control chemistries that can help prevent corrosion and fouling of process assets from feedstocks with harmful components (such as high TAN, chlorides)?
Dec-2022
Answers
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Jon Strohm, Albemarle Corporation, jon.strohm@albemarle.com
Various solutions to address corrosion and fouling in FCC unit feed systems have been developed by companies such as Nalco/EcoLab, including de-emulsifiers, antioxidants/dispersants, antifoulants, and metal passivation coatings. While such solutions can protect the FCC unit’s upstream assets, many contaminants will ultimately be deposited on the catalyst within the reactor.
A holistic approach to control process equipment and catalyst fouling is critical to the successful co-processing of alternative feedstocks. Both biogenic and waste plastic oils contain much higher contaminants (Ca, Na, Fe), but also the introduction of new contaminants (Mg, K, P) that are known to increase the catalyst deactivation rate. Encapsulation and vitrification of FCC catalysts’ external surface through the reaction of silica with these bespoke contaminants under FCC conditions result in reduced catalyst accessibility.
Lack of accessibility leads to reduced profitability through loss of activity and bottoms upgrading ability while also increasing the coke and dry gas make in the unit. Hence, catalysts with enhanced metals tolerance and high accessibility are required to maintain catalyst activity to profitably process these unconventional feedstocks. Against this backdrop, innovative FCC catalyst technologies address the specific challenges associated with these unconventional feeds. The proprietary SaFeGuard and ReNewFCC families of catalysts can deliver outstanding performance benefits for both conventional and unconventional feeds.
The SaFeGuard and ReNewFCC catalyst technologies arrest or delay the surface sintering and vitrification process, resulting in higher accessibility retention even at high levels of metal contaminants. The metals tolerance benefits using this new technology have been proven at lab scale in terms of higher accessibility retention, open surface pores, and upgrading the heavier bottoms fraction with significantly less coke and dry gas make.
With the high oxygen content of biogenic oils, the formation of CO, CO2, and other light oxygenates, including aldehydes and ketones, can have a significant impact on downstream scrubbers and gas separation units. Increased carbonates and oxygenates can result in fouling. Furthermore, by controlling the deoxygenation pathways, the ReNewFCC technologies can significantly reduce delta coke and dry gas volume and maximise deoxygenation to provide increased operational flexibility to reliably and profitably co-process renewable feedstocks in the FCC.
With the onus on developing tailored solutions for new feedstock challenges, the catalyst technology supplier, in collaboration with process corrosion experts, can better deliver value when working closely with FCC unit engineers in safely navigating the exciting transition towards conversion of a wider combination of conventional and unconventional feedstocks.
Dec-2022
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Chad Perrott, Albemarle Corporation, chad.perrott@albemarle.com
There are an increasing number of feedstocks being considered for potential refinery processing. Bio-based feedstocks are a broad group of potential feeds to refineries. They consist of two major groups: fats, oils, and grease (FOG) and bio-oils. FOG comes from various grades such as tallow, vegetable oil, and used cooking oil that are easily liquefied, but not all streams are ‘refined’ before introducing hydroprocessing to remove halides and manage TAN levels. The non-refined FOG feeds have varying levels of alkali metals (>50x), Si, P (>200x), and ~10 wt% oxygen when compared to fossil oils.
The refined FOG feeds have lower levels but, in most cases, will still require special consideration for the prevention of reactor fouling. In contrast, bio-oils can be made by thermal pyrolysis or hydrothermal liquefaction (HTL) of lignocellulosic materials like woody biomass or similar non-liquid bio waste products. Bio-oils from these processes have increased variability in alkali metals (up to 500x), high TAN (up to 100x), Si (up to 5x), phosphorus (>>50x), and very high oxygen content >30% when compared to typical refinery feeds.
In addition to bio-based feedstocks, various polymeric compounds are considered for feeds, including durable waste plastics, used tyres, or electronic waste. These types of waste can be fed to thermal pyrolysis or HTL processes to produce waste plastic oils with different compositions from their respective origins, therefore consisting of varying levels of di- and mono-olefins (~2x), halides (>>50x), Si (up to 60x), and N (up to 2-3x) when compared to fossil oils.
So, these new feeds contain various contaminants known to foul or corrode hydroprocessing units. Like the processing of them, handling these contaminants to avoid corrosion and fouling is a developing area. For FOG feeds, the alkali metals and acidity can be managed through feed ‘refining’ technologies for bio-based feeds, here referred to as pretreatment to avoid confusion with the refining of fossil oils. However, the Si and P remain after the pretreatment step. For the various pyrolysis and HTL oils, the disposition of the alkali metals is still being studied.
For bio-oils, free water content can carry various salts of Ca, Na, K, P, and Mg as well as Fe to the reactor. In high concentrations, these will cause reactor bed fouling. In lower concentrations, catalyst deactivation is likely.
Increased Si and/or P levels from any of these new feeds will result in rapid reactor bed fouling and catalyst deactivation. Guard bed technologies can be utilised to combat these problems. Albemarle has recently introduced the proprietary ReNewFine product line to address increased P issues. Development of enhanced grades is ongoing in these new fields.
Dec-2022
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