How Can HVO Production Processes Be Adapted to Produce SAF?
The transformation of Hydrotreated Vegetable Oil (HVO) production processes into Sustainable Aviation Fuel (SAF) production primarily involves extending and refining the process chain. While both share a similar hydrodeoxygenation foundation, SAF must meet stricter physical property standards and certification requirements for aviation fuel. Below are the key steps and technical aspects of this transition:
1. Extending the Process Chain: Adding Precision Fractionation and Aromatic Supplementation
Common Process Fundamentals:
Both HVO and SAF are produced using Hydroprocessed Esters and Fatty Acids (HEFA) technology. The core step involves hydrodeoxygenation (HDO) of feedstocks (such as waste oils and animal fats) to generate linear alkanes.
SAF-Specific Steps:
Precision Fractionation: After hydrodeoxygenation, a fractionation tower is used to precisely isolate the aviation kerosene fraction with a boiling range of 130–300°C. This ensures compliance with aviation fuel requirements such as density and freezing point (≤ -47°C).
Aromatic Supplementation: Aviation fuel must contain specific aromatics to ensure seal compatibility and combustion stability. If the HVO fraction lacks sufficient aromatics, catalytic reforming or the addition of fossil-based aromatics (such as BTX) is necessary to meet ASTM D7566 standards.
2. Feedstock Adaptability and Pretreatment Upgrades
Feedstock Compatibility with Higher Standards:
While HVO can use various oils and fats (including palm oil and used cooking oil), SAF requires stricter sustainability certifications (e.g., RSB or ISCC) and prohibits the use of food crop-based feedstocks (only waste oils and agricultural/forestry residues are allowed).
Enhanced Pretreatment:
SAF feedstocks require higher purity, necessitating:
Deep demetallization and deacidification to reduce calcium, magnesium, and other metal contents that may cause catalyst poisoning.
Impurity control: Acid value (AV) must be below 2 mg KOH/g to prevent equipment corrosion.
3. Equipment Modifications and Catalyst Optimization
Fractionation Unit Expansion: Existing HVO units need to be retrofitted or expanded with fractionation towers to enable precise separation of aviation fuel fractions.
Isomerization Adjustments: While HVO uses isomerization to improve cold flow properties, SAF requires controlled isomerization depth to avoid excessive branching that could affect the freezing point, while ensuring a balanced cetane number.
Catalyst Adaptation: Bifunctional catalysts (e.g., Pt/zeolite) are used to balance hydrodeoxygenation and selective cracking, improving aviation fuel yield.
4. Practical Cases: Co-Processing Technology and Plant Transformation
MOL Group (Slovakia): At the Bratislava refinery, co-processing technology was used to successfully produce SAF by hydrotreating a blend of used cooking oil and conventional crude oil, demonstrating compatibility with existing refining equipment.
Honeywell Ecofining™ Technology: This process can directly integrate SAF production lines into existing HVO units. For example, the Jiangsu Jiaao Environmental Protection project uses used cooking oil to produce SAF, achieving up to 80% emission reduction.
SK Energy (South Korea): The Ulsan refinery adjusted fractionation parameters in its HVO production line to achieve mass production of SAF and export it to Europe.
5. Certification and Standard Compliance
Product Certification: SAF must comply with ASTM D7566 (covering seven production pathways) and CORSIA (requiring ≥50% aviation carbon reduction), whereas HVO only needs to meet automotive fuel standards (e.g., EN 15940).
Sustainability Traceability: A mass balance traceability system must be established to verify the full-chain carbon reduction of waste oil feedstocks.
Summary: Core Differences in the Transition
| Aspect | HVO Process | SAF Transition Requirements |
|---|---|---|
| Core Product | Diesel fraction (C15–C18) | Aviation fuel fraction (130–300°C) |
| Key Additional Steps | Isomerization for cold flow | Precision fractionation + aromatics supplementation |
| Feedstock Restrictions | Allows palm oil (phasing out) | Only waste oils/non-food feedstocks (RSB certified) |
| Equipment Focus | Hydroreactor + isomerization unit | High-precision fractionation + aromatics synthesis unit |
| Certification Standards | EN 15940 / ASTM D975 | ASTM D7566 + CORSIA |
Transitioning to SAF production requires an additional 10–15% investment on top of existing HVO infrastructure, but the product offers significant premium pricing (SAF produced from waste cooking oil can fetch up to three times the price of conventional fossil-based jet fuel). By enhancing fractionation precision, adjusting aromatics, and improving sustainability certification systems, HVO production lines can efficiently pivot to the high-value SAF market.