Why Antioxidants Are Critical in Modern Fuels
Oxidation is one of the primary degradation mechanisms in liquid fuels. When dissolved oxygen reacts with hydrocarbon molecules, which can be accelerated by heat, light, and trace metals, a chain reaction produces hydroperoxides that break down into gums, varnishes, and acidic by-products. These deposits coat injectors, clog filters, darken fuel, and reduce engine efficiency.
The challenge is particularly acute in high-olefin streams from catalytic cracking (FCC naphtha, light cycle oil), biodiesel blends (FAME), and fuels subjected to long storage or elevated temperature. Antioxidants interrupt the free-radical chain at an early stage, dramatically extending induction periods and shelf life.
Refinery use: Antioxidants stabilize highly olefinic cracked streams in diesel blends, mitigating short induction periods, fuel darkening, and gum formation. This enables refiners to increase the proportion of lower-cost FCC-derived components in the finished pool.
Application Across Fuel Types
| Fuel Type | Key Challenge | Antioxidant Role |
|---|---|---|
| Diesel (ULSD) | Desulfurization removes natural antioxidants | Restore oxidation stability; meet EN 590 gum limit (25 g/m³ max) |
| Biodiesel / FAME Blends | High unsaturation; rapid oxidation | Extend FAME Rancimat stability (>6 h); protect blended pool |
| Gasoline / E10–E85 | High-olefin FCC naphtha; ethanol hygroscopicity | Stabilize cracked components; prevent injector and valve deposits |
| Aviation Turbine (Jet-A/A-1) | Thermal stress at altitude; JFTOT requirements | Control thermal oxidative deposits; required by DEF STAN 91-091, ASTM D1655 |
| Marine HFO / VLSFO | Asphaltene instability from blending operations | Slow oxidative sludge and sediment formation post-blending |
Storage Stability
Fuels in storage for power generation backup, military reserves, or seasonal demand are particularly vulnerable. Antioxidants at correct treat rates (typically 10–200 mg/kg depending on fuel type and storage duration) maintain required oxidation stability through extended periods and temperature cycling, reducing the need for fuel reconditioning.