Refiners are challenged to respond to continually changing market economics, which has led to them processing heavier feeds in their fluid catalytic cracking units (FCCUs) with more contaminants. This has been proven through the analysis of equilibrium catalyst and operating data from over 200 FCCUs globally.1 Furthermore, a survey conducted at a recent event for the downstream industry revealed that the top priorities for most refiners include improving FCC bottoms upgrading, distillate production, conversion and olefins production.2 Consequently, there is strong demand for improved bottoms cracking and metals passivation technologies, which unlock the operational flexibility to achieve a range of FCC targets.
The needs of each FCCU are unique. Close inspection reveals important differences in feed quality, unit configuration, objectives, and constraint, meaning that tailor-made solutions are required for each refinery. New catalysts have recently been introduced to address these individual challenges; including units processing moderate to heavy resid feedstock, refiners wanting lower hydrogen and coke yields, or those that desire deep bottoms conversion and higher overall product yields. When designing a catalyst, it is important to consider that heavy feeds bring in more contaminant metals.
Contaminant metals in heavy feeds primarily comprise of iron (Fe), nickel (Ni), and vanadium (V). Sodium (Na) can also be deposited from the feed. In this article, the three key features in managing contaminant metals are outlined. These are: pore architecture for iron contamination, activity retention for sodium, as well as nickel and vanadium passivation.
Pore architecture for iron contamination
Destruction of slurry and maximisation of liquid yields remain top priorities for the FCCU. To minimise slurry and improve FCC yields, the importance of engineered catalyst pore architecture cannot be underestimated.3 Features of a highly-engineered pore architecture include suitable pore dimensions, pore volume distribution and connectivity between pores. A catalyst with high surface porosity and engineered pore architecture is typically best equipped to mitigate the effects of iron. Added iron (i.e. organic iron deposited on the catalyst by the feedstock) can block catalyst pores, which hinders access to and from the catalyst sites. In severe cases of iron poisoning, the catalyst activity significantly decreases.
Examination of catalysts exposed to high added iron shows iron nodules on the surface. Thus, a catalyst with high surface porosity is necessary to provide iron tolerance. Other effects of iron poisoning include dehydrogenation reactions, carbon monoxide combustion promotion and increased sulfur oxide emissions….
- POPE, J., CLOUGH, M. and SHACKLEFORD, A., ‘Lessons from FCC History’, PTQ Catalysis, pp. 37 – 45, (2017).
- ERTC, 22nd Annual Meeting, Athens, Greece, (13 – 15 November 2017).
- KOMVOKIS, V., TAN, L., CLOUGH, M., PAN, S. and YILMAZ, B., ‘Zeolites in Sustainable Chemistry’, Springer, pp. 271 – 296, (2016).
Written by Carl Keeley, Vasilis Komvokis, Fernando Sánchez Arandilla and Modesto Miranda, BASF, Europe.
Read the article online at: https://www.hydrocarbonengineering.com/special-reports/05072018/metals-management/