FCC pathways to co-processing

Co-processing biogenic feedstocks offers refiners options for meeting renewable fuel standards and other regulatory requirements.


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Article Summary

With increased pressure to reduce life-cycle greenhouse gas emissions and decarbonise the energy industry, refiners are faced with expanding legislative incentives and mandates to increase renewable carbon content in fuels and chemicals. Co-processing of biogenic or waste-derived oils in existing refining assets is a pathway for refiners to introduce renewable and/or circular carbon into their finished products to meet mandates and/or improve margins through incentives. To this end, many refiners have either conducted trials or are considering conducting trials for the processing of plant or animal based oils in their units. Before co-processing, the refiner should consider the economics and consequences. This should include historical cost of Renewable Identification Number (RIN) credits. The refiner must also consider RIN credits received for co-processing and the impact that will occur in their process unit from the various co-feed options and integration strategies. Co-processing can be targeted for many units. In the past, crude distillation towers, hydroprocessing (HP), and fluidised catalytic cracking (FCC) units have been targeted for co-processing. In this article, we will discuss FCC unit co-processing, feed options, and demonstration of Ketjen’s catalyst technology in laboratory testing, demonstration scale, and FCC operations for various biogenic feedstocks.

RIN credits is a US government system. Other countries, regions, and states have their own systems to encourage the use of renewable fuels, or to prohibit the sale of fuels that do not have mandated renewable content. As an example, the European Union uses the Renewable Energy Directive (RED). Canada has a unique Clean Fuel Standard. States like California and Oregon have clean fuels programmes, while Washington, Colorado, New York, and Minnesota are considering their own directives. It is important to note that the states with their own clean fuel standards may have added benefits above the RIN credits. Our focus in this article will be on the US system (RIN) credits.

In 2005, the US government established the Renewable Fuel Standard, obligating US refiners and importers of gasoline and diesel fuels to meet target renewable fuel content. If the renewable volume content is not reached in fuel products, the refiner or importer must purchase RIN credits to be in compliance with national and/or local regulations. Part of this standard is to establish categories of biofuels and to determine quotas for each category. The categories are:
-    D3: Cellulosic biofuel. Targeted for >60% greenhouse gas (GHG) reduction. Examples include pyrolysis oils from wood chips or other gasoline or oil with cellulosic origins.
-    D4: Biomass based diesel. Targeted for >50% GHG reduction. Examples include converting vegetable oils (soybean, canola, rapeseed), animal fats, and waste oils (used cooking oils or UCO) to diesel.
-    D5: Advanced biofuels. Targeted for >50% GHG reduction. Examples include non-ethanol fuels derived from corn starch biogas or waste digesters.
-    D6: Conventional renewable fuel. Targeted for >20% GHG reduction. Examples include ethanol or other biomass to replace conventional transportation or heating fuels.

Based on the ability to make, sell, or trade RIN credits, the value of each category is determined. As an example, the D3 fuel has never met the target for volume. Because of this, the D3 credit value is high and surpasses the other categories. Figure 1 shows the trend of RIN credits (converted to $/bbl) since January 2019. Since August 2020, these credits have increased significantly. D4, D5, and D6 have increased from $5-20/bbl to $50-70/bbl. In the same period, D3 credits increased more than $50/bbl. This is a cost for RINs of roughly $59-112/bbl respectively. The monetary benefits to produce these renewable fuels have increased significantly recently.

In some cases, there are blending caps that can be due to product specifications and/or mandates based on the fuel component and RIN category. Ethanol blending in regular gasoline is limited to meet specifications required for non-flex fuel vehicles. Regulations will dictate the renewable volume obligation that can be met with the D6 category; in some countries falling under the RED II European mandates, the use of non-cellulosic ethanol or the use of palm oil to meet renewable standards will be phased out. The starting biomass and process technologies can have a significant impact on the total carbon efficiency of a fuel production pathway, hence the RIN category and value.

Co-processing feed options
When considering co-processing feed options, high diversity presents unique operational and catalytic challenges for the FCC unit. Figure 2 highlights three sub-groups for FCC co-processing. This is based on the starting biomass feed category and advantages/challenges from a co-processing viewpoint.

Waste plastics and waxes from Fischer-Tropsch (FT) liquids derived from syngas produced from the gasification of biomass and/or waste materials can be readily cracked in the FCC unit due to their highly paraffinic nature, solubility in conventional VGO/resid feeds, and low oxygen content. Challenges associated with co-processing FT-liquids in the FCC unit are largely associated with the gasification of biomass and waste materials to general chemical-grade synthesis gas. They should be free from residual tars and other contaminates. The main challenges for waste plastics and pyrolysis oils are residual chlorine from PVC, trace metals, and variable composition. The variable composition includes the elevated oxygen content (polycarbonates and PET) due to the plastics used.

Major plastics including polyethylene, polypropylene, waste tyres, and polystyrene are soluble in VGO at FCC feed conditions. In theory, since they are soluble, they can be directly blended and processed in the FCC unit. Collecting, sorting, and transportation/storage at the refinery may present significant logistical and economic challenges. Co-processing of pyrolysis oils from waste plastics, in particular the heavy residual waxes from a pyrolysis process, is also a viable co-feed for the FCC unit. Under the current regulatory environment, which does not provide credits for co-processing of waste plastics to fuels, the FCC unit’s role in the circular economy will require effective carbon tracing from waste plastics to propylene, ethylene, and BTX.

Out of the various bio based feed options, vegetable oils are mainly triglycerides from plant-derived oils (palm oil, soybean oil, rapeseed/canola oil, and distillers’ corn oil), tallow, extracted lipids algae oils, and used cooking oils. The paraffinic nature of triglycerides in vegetable oils and animal fats make the co-feed highly crackable in the FCC unit. In general, vegetable oils are soluble in conventional FCC feeds; they do not have free water and they have a relatively lower oxygen content (~10 wt%) than bio-oils. Vegetable oils are produced at industrial scale, with approximately 740000 b/d production in 2020. Regional availability and direct competition with other uses, including bio-/renewable diesel, and food products, can lead to high pricing. In the US, increased biodiesel and renewable diesel production has inflated the price of soybean oil.

RDB soybean oil is 20% higher than it was in 2020. The average price of RDB soybean oil in 2020 was already two times the average crude price, resulting in higher food costs and increased competition for land use, particularly in the case for palm oil. The increase in land clearing for cultivating palm trees has led to political and ecological ramifications, resulting in several EU countries removing palm oil as a renewable resource.

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