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How can refiners overcome challenges during FCC fast pyrolysis bio-oils (FPBO) co-processing with vacuum gasoil (VGO)?

Oct-2024

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Guillaume Vincent, BASF Refinery Catalysts, Guillaume.vincent@basf.com

FPBO, most often called bio-oils, have already demonstrated crackability in FCC units but can introduce operational challenges in FCC co-processing applications, such as:
· Miscibility issues with fossil feedstocks due to high polarity molecules and free water, requiring dedicated storage, pumping, and piping metallurgy.
· Instability of bio-oils during transportation and at feed injection temperatures, requiring specific vessels and dedicated injection line delivery systems, respectively. If a dedicated injection nozzle is required, its location needs to be optimised within the FCC riser.
· High variability in alkali, earth alkaline metals, acidity, and oxygen contents.

Bio-oils differ from crude oils due to the presence of oxygen and elevated levels of alkali metals (such as Na, K), earth alkaline metals (such as Ca, Mg), chlorides, and phosphorus. Since these contaminants can cause catalyst deactivation and operational issues, such as fouling or corrosion issues, it is recommended to reduce their concentration prior to co-processing. At commercial scale, several pretreatment processes exist to remove contaminants, such as:
- Filtration
- Desalting
- Degumming
- Hydrotreating applications
- Purification adsorbents.

Particles and other solids in these bio-oils can lead to instability. Filtration has been shown to remove particulates such as char and alkali metals. Degumming is another technique that has demonstrated the ability to remove phospholipids and trace metal ions from crude vegetable oils and could be further applied to bio-oils. Water degumming is effective for phospholipid removal, while alkali salts require acid degumming. As such, the introduction of alkali and earth alkaline metals should be limited by feed management and careful catalyst selection, such as in-situ catalyst technology.

In fact, in-situ manufactured catalyst contains the lowest Na content in the FCC industry, which helps mitigate the effect of added alkali metals. Moreover, in-situ manufactured catalysts exhibit a very high surface porosity that helps mitigate added earth alkaline metals and/or added iron, which typically accumulate at the catalyst edges. In opposition, incorporated catalysts show surface densification in their fresh state due to the usage of alumina or silica chloride-based binders during the manufacturing process, resulting in a diffusion barrier limiting pore accessibility for further cracking reactions.
Bio-oils might also contain elevated chloride levels, which should be minimised prior to FCC introduction. Chemically, chlorides can result in the reactivation of nickel deposited on equilibrium catalyst, leading to unwanted dehydrogenation reactions (higher hydrogen and delta coke). Operationally, since there is often an excess of NH3 from feed cracking, any additional chlorides can lead to the formation of incremental NH4Cl deposits at the overhead of the main fractionator. As such, the introduction of chlorides should be limited by feed management and careful catalyst selection to minimise chlorides in FCC catalyst, such as with in-situ catalyst technology.

Indeed, in-situ manufactured catalysts do not use chloride-based binders during the in-situ manufacturing process, as opposed to many incorporated catalysts utilising binders containing chlorides. Feed chlorides can be reduced with purification adsorbents. A chloride guard oriented towards organic chlorides removal is preferred for maximising the dechlorination process. However, preliminary evaluation is highly recommended to assess and confirm its efficiency on a specific bio-oil.

Bio-oils also contain significant levels of oxygen-containing molecules, resulting in a polar phase immiscible with fossil feedstocks. Additionally, high oxygen levels in feed present challenges in that much of the oxygen can go through reaction pathways to become water, CO, and CO2 non-value-adding FCC products (an example is shown in Figure 1 using vegetable oil – the increase in non-value products could be even more pronounced for an FPBO). Thus, consideration should be taken for how the use of a bio-oil might impact the FCC yield slate.

The mild hydrotreatment of bio-oils could improve miscibility through oxygen removal via hydrodeoxygenation. However, the oxygen content at which miscibility is no longer an issue is variable. Catalytic pyrolysis has also been used to stabilise the bio-oil before co-processing through the FCC unit. In catalytic pyrolysis, oxygen is removed as water and carbon oxides over a zeolite-based catalyst. Catalytic pyrolysis allows for a better bio-oil quality with a reduced oxygen content and a lower acidity compared to the original bio-oil.

A solution that does not involve oxygen removal from the feed is to use dedicated feed injection technology nozzles to allow for the injection of bio-oils at low temperature through the riser. Careful consideration with an FCC technology licensor should be taken according to the type of oil, the ratio of the co-processing oil to the primary feedstock, and the location of injection. This is because operating conditions, feed zone configuration, and co-processing objectives will vary between FCC units.

Oct-2024