Feb-2025

Managing corrosion risk in SAF and renewable diesel processes

Non-intrusive, real-time monitoring solutions can help manage the unique corrosion risks associated with biofuel feedstocks and processes.

William Fazackerley
Emerson

Article Summary

As the world grapples with climate change and seeks to reduce its carbon footprint, the transportation sector has come under increasing scrutiny. Aviation and long-haul trucking, in particular, have faced challenges in transitioning away from fossil fuels. Sustainable aviation fuel (SAF) and renewable diesel have emerged as two promising alternatives that are reshaping the landscape of transportation fuels.

However, the shift to these sustainable fuels brings its own set of challenges. The production of SAF and renewable diesel involves complex processes and the use of diverse feedstocks, ranging from used cooking oils to agricultural residues. These new feedstocks and processes introduce novel corrosion risks that threaten the integrity of production facilities.

This article explores the evolution of biofuels, delves into the production processes of SAF and renewable diesel, examines the corrosion challenges faced by producers, and discusses the innovative monitoring solutions being employed to mitigate these risks.

Evolution of biofuels
To understand the significance of SAF and renewable diesel, it is essential to look at the evolution of biofuels over the past decade. Biofuels have gone through several generations, each addressing the limitations of the previous one.

First-generation biofuels, popular in the early 2000s, were primarily derived from food crops like corn, sugarcane, and other energy crops. While these fuels offered a renewable alternative to fossil fuels, they faced criticism for competing with land use for food production, consequentially driving up food prices and deforestation.

Second-generation biofuels, which gained traction in the 2010s, aimed to address these concerns by utilising non-food biomass such as agricultural and forestry residues likes wood chips. These fuels offered improved sustainability and reduced the risks of land use change and competition with food production. As these biofuels were not capable of directly replacing their hydrocarbon counterparts, blending limits were imposed, which limited their adoption.

Third-generation biofuels, emerging in recent years, focus on waste streams, including municipal solid waste (MSW), sewage sludge, and more advanced feedstocks like algae. These feedstocks promise even greater sustainability and potential for scalability and are available as a direct replacement to legacy fuels without blending limitations.

The latest development, sometimes referred to as fourth-generation biofuels, involves engineered organisms and carbon capture technologies to produce fuels with a negative carbon footprint.

Sustainable aviation fuel
SAF represents a significant leap forward in the aviation industry’s efforts to reduce its environmental impact. Unlike traditional jet fuel, SAF is produced from sustainable feedstocks such as used cooking oil, agricultural residues, and even MSW.

The International Air Transport Association (IATA) reports that in 2022, more than 300 million litres of SAF were produced (IATA, 2023). This figure is set to grow dramatically, with more than 130 renewable fuel projects announced by more than 85 producers across 30 countries globally (Thomsen, Mistry, & Block, 2023).

Government incentives are playing a crucial role in driving SAF adoption. In the US, the Sustainable Aviation Challenge sets an ambitious goal for the airline industry to use 11 billion litres of SAF by 2030, equivalent to 15% of current jet fuel demand (US DOE, 2021),  (IATA, 2022). The EU’s Fit for 55 package includes a proposed 2% SAF blending mandate by 2025 under the ReFuelEU Aviation initiative (European Commission, 2022).

One of the key advantages of SAF is its drop-in capability, meaning it can be used in existing aircraft engines without modification. This characteristic makes it an attractive option for airlines looking to reduce their carbon footprint without investing in new aircraft or engine technologies.

Renewable diesel
While SAF is focused on decarbonising aviation fuels, renewable diesel is transforming the road transportation sector, particularly for heavy-duty vehicles and long-haul trucking. Renewable diesel should not be confused with biodiesel, an earlier biofuel that gained popularity in the past decade.

Renewable diesel offers several advantages over biodiesel. It burns more cleanly and efficiently, produces lower emissions, and can be used in high concentrations without blending with traditional diesel (see Figure 1). These characteristics make it an attractive option for fleet operators looking to reduce their environmental impact without significant changes to their existing vehicles.

The International Energy Agency (IEA) projects that renewable diesel production will triple by 2026 (IEA, 2022). This growth is driven by increasing demand from road and sea haulage sectors, which have limited options for transitioning away from traditional combustion engines in the short term.

Feedstock challenges and innovations
The choice of feedstock is crucial in the production of both SAF and renewable diesel. Early biofuel production relied heavily on vegetable oils, resulting in fatty acid methyl esters (FAME) or biodiesel. However, concerns about fuel blending and engine compatibility have shifted focus to hydrotreated processes for drop-in fuels.

Hydrotreated vegetable oils (HVO) have emerged as a popular option for producing drop-in fuels. These fuels closely resemble fossil-based fuels and offer better engine compatibility than traditional biodiesel.

To avoid first-generation biofeedstocks, producers are increasingly turning to waste materials including animal fats, used cooking oils, and greases. However, potential supply limitations have resulted in extending the use of wastes to include MSW and sewage sludges. An additional benefit of using these waste products is that they minimise landfill costs and offer financial benefits. However, maintaining consistent quality and supply can be challenging.