Mar-2025

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

Article Summary

In Part 1 of this article published in PTQ Q1 2025,1 the potential for renewable diesel (RD) and sustainable aviation 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 production 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 incentives 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, C18, C20, and C22 normal alkanes via strict hydrodeoxygenation (HDO) mechanisms, and C15, C17, C19, and C21 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 appropriate for SAF. In a two-stage unit, this is readily facilitated by incorporating hydrocracking functionality into the dewaxing 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 products for chemicals and plastics feedstocks.

Since 2007, Neste has added production capacity in Rotterdam (2010) and Singapore (2011) using its proprietary 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 renewable 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.

Neste’s proprietary NExBTL technology is closely held and is stated to contain both an HDO step and an isomerisation 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 suppliers 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 requirements, with subsequent patent activity in 2007 and 2008 forming the foundation for its proprietary Ecofining process for the production of RD and jet fuels. The first process licence ensued in 2013, and commercialisation followed at Eni’s Venice refinery in 2014. Since that time, more than 150,000 barrels per stream day (BPSD) of Ecofining capacity has been placed into operation across 13 individual units that range in size up to 35,000 barrels per day (BPD) as of January 2025. Five of those are repurposed assets, according to Honeywell UOP sources.

Ecofining is offered in two options: a lower Capex single-stage design to produce Honeywell’s proprietary RD, and a two-stage option to optimise the production of UOP’s proprietary Green Jet Fuel, a SAF blend component. The two-stage option includes the flexibility to produce RD with changing market needs.

There are more than 50 Ecofining licences as of January 2025. One of Diamond Green Diesel’s Port Arthur, Texas, Ecofining units was modified to produce 235 million gal/year (900 million litres/year or 15,000 bbl/day) by the end of 2024. Diamond Green Diesel announced a supply agreement with JetBlue. World Energy Paramount, one of the larger SAF producers at 240 million gal/year (900 million litres/year or 16,000 bbl/day), licensed the Ecofining process. World Energy has offtake agreements with United, Air France-KLM, JetBlue, SAS, and DHL.

UOP also offers co-processing revamps of existing hydrotreating units, particularly distillate hydrotreating units. Other UOP routes to SAF include eFuels with methanol-to-jet (eFining), ethanol-to-jet, and FT routes with FT Unicracking to be covered later.

Topsoe’s proprietary HydroFlex process addresses the production of RD and SAF with both single-stage and two-stage units. Commercial application of the process began in 2010, and 20+ co-processing units plus some 60+ fully renewable units have been licensed, of which some 75% are two-stage units according to industry sources. Topsoe uses a graded catalyst activity and selectivity approach with a variety of catalysts. Topsoe uses formulations other than the standard NiMo/alumina catalysts employed in general hydroprocessing to achieve improved selectivity towards HDO, up to 97%. Patent literature points to a Mo/alumina formulation for such high HDO selectivity.

Montana Renewables employs HydroFlex technology to produce some 30 million gal/year (110 million litres/year or 2,000 bbl/day) SAF, as does Phillips 66 Rodeo, California to produce some 800 million gal/year (3 billion litres/year or 53,000 bbl/day) of RD and SAF, of which about 20-25% will be SAF at the time of writing. Montana Renewables has announced a multiyear SAF offtake agreement with Shell, and Phillips has a supply agreement with British Airways.