Catalysis 2025 Issue

Renewables Part 2: A focus on SAF Review of HEFA technologies as well as alcohol-to-jet and Fischer-Tropsch synthetic paraffinic kerosene processes and the impact of feedstock and process choices

Woody Shiflett Blue Ridge Consulting LLC

I n Part 1 of this article published in PTQ Q1 2025, 1 the potential for renewable diesel (RD) and sustainable avi- ation fuel (SAF) was reviewed, with a particular focus on SAF. The chemistry of hydrotreated esters and fatty acids (HEFA) processes, the current predominant technology employed for RD and SAF, was overviewed along with the types of catalysts used. Co-processing opportunities were explained as a lower barrier means to entering SAF produc- tion with existing fossil fuel assets. In this article, a detailed look is taken at existing HEFA technologies as well as alcohol-to-jet (ATJ) and Fischer- Tropsch synthetic paraffinic kerosene (FT-SPK) processes. A brief, high-level assessment is made of the dependence of carbon intensity (CI) and greenhouse gas (GHG) emissions on feedstock and process choices. Additionally, the impact of the complexity of governmental regulations and incen- tives on production economics is shown by example. RD and SAF hydroprocessing processes All technology providers of renewables hydroprocessing offer two-stage systems, and some also offer single-stage systems. Single-stage systems have lower capital expense (Capex) but less flexibility and yield. As noted in the co- processing discussion, such systems are also limited in their ability to produce SAF and primarily produce RD. Triglycerides typically yield C16 , C 18 , C 20 , and C 22 normal alkanes via strict hydrodeoxygenation (HDO) mechanisms, and C 15 , C 17 , C 19 , and C 21 via decarboxylation, placing the compounds in the diesel boiling range. The jet fuel boiling range is in the carbon range of C₈ to C16 alkanes, dictating that the hydrotreated vegetable oil (HVO) product will need to be hydrocracked into the range appro- priate for SAF. In a two-stage unit, this is readily facilitated by incorporating hydrocracking functionality into the dewax- ing catalyst or employing hydrocracking catalyst along with dewaxing catalyst in the second-stage reactor. Otherwise, HVO will need to be directed to a separate hydrocracking unit in order to produce SAF. In maximum SAF production mode, these processes can yield about 75-80% SAF. Neste developed its own proprietary process, NExBTL, for the production of renewable fuels. It received a patent for it in 1997 and subsequently commercialised its first plant in its Porvoo, Finland refinery in 2007. NExBTL technology allows Neste to convert a wide range of renewable raw materials into premium-quality renewable products, including fuels for road transport and aviation, as well as for renewable prod- ucts for chemicals and plastics feedstocks.

Since 2007, Neste has added production capacity in Rotterdam (2010) and Singapore (2011) using its propri- etary MY Renewable Diesel and MY Sustainable Aviation Fuel brands, making it one of the largest global renewable fuels producers. After a planned expansion at the Singapore refinery, completed in 2023, the total global renewable product capacity will be close to 4.5 million ton/annum (1,500 million US gal/year, 100,000 bbl/day). Approximately one-third of this is estimated to be SAF. In addition, Neste has formed a joint venture with Marathon to produce renew- able fuels at Marathon’s Martinez, California refinery, adding a nameplate capacity of 2.1 million tons per annum (700 million US gal/year, 45,000bbl/day) at the end of 2023. This is expected to be largely RD at the time of writing. The jet fuel boiling range is in the carbon range of C₈ to C16 alkanes, dictating that the HVO product will need to be hydrocracked into the range appropriate for SAF Neste’s proprietary NExBTL technology is closely held and is stated to contain both an HDO step and an isom- erisation step after preliminary pretreatment to remove contaminants. Patent activity shows that a counter-current flow isomerisation step could be an innovative part of the process. Ketjen supplies catalyst for the NExBTL process. Of note are SAF offtake or supply agreements with more than a dozen airlines, including Singapore Airlines, Air New Zealand, Air France-KLM, JAL, DHL, VivaAerobus, Boeing, Avfuel (US West Coast), American, Alaska, Air Canada, Emirates, United, and Ryanair. Technology supplier approaches There is a plethora of information regarding technology sup - pliers and licensors available on their respective websites and in industry publications. Most use similar approaches to HEFA processing and employ catalyst systems based fundamentally on hydroprocessing catalyst technology. Hence, only overview and summary information will be covered in this article. Honeywell UOP collaborated with Eni SpA in the early 2000s to address evolving EU renewable fuels require- ments, with subsequent patent activity in 2007 and 2008

Catalysis 2025