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Co-processing of renewable or recycled hydrocarbon molecules (biocrude) alongside petroleum crude oil is gaining traction as a near-term solution for introducing renewable material into the aviation fuel system.  This method allows existing refineries to produce partially renewable fuel without requiring extensive infrastructure changes or investments, making it a cost-effective and efficient solution for increasing the renewable content of the fuel.  Co-processing is seen as an additional  approach to large-scale SAF production, allowing the aviation industry to incrementally reduce emissions as dedicated (or ‘stand-alone’) SAF production facilities are developed, and other production concepts mature.

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Currently, the global fuel specifications permit the incorporation of renewable feedstocks up to 30% into aviation fuel coprocessing production processes, depending on the approach.  It is important to distinguish co-processing from blending: while blending involves the physical mixing of separately produced SAF and petroleum fuels, co-processing occurs within refinery production processes, refining a biocrude alongside conventional petroleum crude.  Renewable crude feedstocks currently include fats, oils, and greases, Fischer-Tropsch process generated hydrocarbons and already hydroprocessed biomass, among others, and in the future may potentially include pyrolysis oil, hydrothermal liquefaction oils, and others. Different renewable feedstocks may be co-fed at different points in refinery operations depending on their prior processing and suitability for particular units.  Several refineries in Europe are currently utilizing co-processing to produce SAF in order to meet the obligations of EU policy.

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Co-processing offers several advantages, primarily leveraging existing refinery infrastructure to facilitate rapid integration of renewable content into aviation fuels.  By integrating renewable feedstocks into the refining process, co-processing reduces upstream emissions.  This approach allows for a range of feedstocks to be used, thereby improving energy security, lowering investment costs, and enabling quicker deployment while still meeting the rising demand for aviation fuel.  Additionally, because fuel produced via co-processing adheres to global fuel standards, fuel quality, and therefore safety, is ensured.  Additionally, it is likely that any refiner who might produce co-processed SAF is already producing petroleum-based jet fuel and already has a supply chain established for efficient (low cost/low carbon) delivery of such fuel to the airports, suppliers and end users.  This also obviates the need for blending (as defined in ASTM D7566), which has proven to be a challenge for stand-alone SAF producers.

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Despite its benefits, co-processing faces challenges, particularly in terms of carbon reduction and feedstock limitations.  Since it blends renewable feedstocks with petroleum crude, the overall emissions savings may be lower on a per fuel unit basis compared to stand-alone SAF production facilities that can produce a higher content of renewable molecules in the final fuel blend).  Furthermore, introducing renewable feedstocks can introduce trace impurities (e.g., metals) necessitating additional processing and controls within the refinery.  The renewable content in the final fuel is typically a small percentage, limiting the fuel’s ability to achieve long-term sustainability targets.  However, the potential for rapid near-term scale-up of co-processing may enhance near-term emissions reductions through large volumes of fuel even if the incremental emissions of a unit of fuel are relatively small. Furthermore, it should also be noted that efforts are underway to evaluate and qualify higher levels of renewable feedstocks or biocrudes for co-processing.  Additionally, some within the industry are considering the longer-term benefits of enabling biocrudes to be produced in hub-and-spoke types of supply chains.  This concept enables feedstocks to be converted to a more energy-dense biocrude in close proximity to the feedstock production/collection point, lowering shipping costs and carbon impact, prior to delivering biocrudes to a refinery for final processing to fit-for-use jet fuel molecules.  This may also allow for expanded production capacity at lower overall cost by alleviating the need for each biocrude producer to invest in fuel finishing infrastructure (hydrotreating, hydrocracking, hydroisomerization, polymerization, fractionations/distillation) at each location.

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In summary, co-processing offers an efficient, cost-effective way to integrate renewable feedstocks into traditional petroleum refineries, providing a practical near-term solution for expanding renewable fuel availability.  By leveraging co-processing now, airlines can begin with small emissions reductions on a relatively large volume of fuel while dedicated SAF plants and/or hub-and-spoke concepts are built and scaled to support long-term goals with deeper reductions per unit of SAF.  This method serves as an immediate bridge to full-scale SAF commercialization from a continually expanding breadth of opportunities in the future.