Question
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What are some of the optimal strategies for processing (or co-processing) second- and third-generation renewable feedstocks?
Mar-2023
Answers
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Stefan Brandt, W.R. Grace & Co, stefan.brandt@grace.com
The terms second- and third-generation renewable feedstocks are not defined globally. In a briefing of the European Parliament in 2017, second-generation biofuels were “derived from waste and agricultural residues (such as wheat straw and municipal waste) or non-food crops (such as miscanthus and short-rotation coppice).”1 Third-generation renewable feedstocks are often referred to as being related to algal biomass, for example.
While there are several process units capable of processing second- and third-generation feedstocks, the flexibility of the FCC unit is well suited for the co-processing of unconventional feedstocks. However, challenges exist in the industry to establish a continuous supply of renewable feedstock components, especially for second- and third-generation renewable components. Availability of some of these is expected to grow over the coming years. Therefore, any strategy for co-processing these feedstocks needs to start with a reliable sourcing plan.
The optimal strategy for co-processing renewable feedstocks in an FCC unit is always related to a deep understanding of the properties of the feedstock component in terms of storage, miscibility, physical and chemical properties and its impact on the operation and yield structure of the FCC unit. Thorough characterisation and catalytic pilot plant testing are recommended to identify the opportunities and challenges.
Second-generation renewable feedstocks typically exhibit higher variation in quality compared to first-generation renewable feedstocks derived from edible oil sources. Additionally, miscibility with conventional feedstock can be challenging (see Figure 1). The FCC unit can cope with feedstock quality variation because of its flexibility in operation and catalyst design adaptability. Nevertheless, the variability of the renewable feedstock component might put additional emphasis on the regular FCC unit monitoring.
Depending on the nature of the renewable feedstock, hardware modifications might be required to prevent reliability risks from co-processing. Technology licensors have developed hardware solutions to minimise these risks and optimise the catalytic conversion of the combined feed.
The FCC unit, with its flexibility in catalyst formulation and replacement, is able to adjust to challenges coming in with various feedstock contaminants. Renewable feedstocks bring other contaminants to the FCC unit than crude-derived feedstocks. At low co-processing percentages, depending on the operation, the effect on catalyst deactivation is often unnoticed. However, increased co-processing rates will ultimately put more emphasis on the risks associated with new contaminants in the FCC unit. FCC catalyst suppliers can provide solutions and recommendations based on the individual refinery strategy, operation, and objective.
Second-generation renewable feedstocks derived from lignocellulosic biomass are often high in oxygen and water content. With high oxygen and water content, these feedstocks by their nature will reduce the yields of saleable FCC products from the FCC. Additionally, water and oxygen can impact product quality and downstream processing, and these impacts have to be carefully considered when researching co-processing opportunities. Pilot plant testing with oxygen speciation analysis capabilities is a useful tool to predict the effects of both factors on yield structure, product quality, and ex Rx product processing.
In summary, catalyst and technology providers should be consulted to evaluate the optimal strategy for co-processing second- and third-generation renewable feedstock components in the individual FCC unit. Once established in the plant, increasing the amount of renewable feedstock content should be reviewed by the respective partners as a higher proportion can create new challenges to catalyst, product quality, and operation.1 European Parliament, EPRS, Advanced biofuels: Technologies and EU policy, Briefing, 8 June 2017.
Mar-2023
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