1. Overview
Supercritical CO₂ extraction is an advanced technique that uses carbon dioxide above its critical temperature and pressure to extract aromatic compounds from resinous wood.
Why CO₂?
- At supercritical conditions, CO₂ behaves as both a gas and a liquid, allowing it to penetrate wood like a gas but dissolve resin compounds like a liquid.
- Produces high-purity, solvent-free oils with minimal thermal degradation.
2. Key Principles
- Supercritical point of CO₂: ~31°C and 73 atm (approx. 1,070 psi)
- Adjustable solvating power: By changing pressure and temperature, specific compounds (e.g., sesquiterpenes, chromones) can be selectively extracted.
- No toxic solvents: Produces clean, chemical-free premium oil suitable for perfumery and luxury markets.
3. Extraction Process
Step 1: Raw Material Preparation
- Use high-grade resinous wood (sinking or super grade).
- Chips or small pieces preferred for efficient CO₂ penetration.
- Dry to ~10–12% moisture to prevent clumping or ice formation.
Step 2: Loading Extraction Vessel
- Fill high-pressure extraction chamber with resinous chips.
- Ensure uniform packing for consistent extraction.
Step 3: CO₂ Pressurization & Heating
- Pump CO₂ into the vessel and raise pressure above 73 atm.
- Heat vessel to supercritical temperature (~35–50°C).
- Maintain for several hours depending on wood grade and desired compounds.
Step 4: Separation & Collection
- CO₂ carrying extracted compounds passes through a decompression or separator chamber.
- Oil precipitates out; CO₂ returns to gas phase and can be recycled.
- Collect pure agarwood essential oil; optionally collect CO₂-extracted resin fraction separately.
4. Advantages of Supercritical CO₂ Extraction
| Feature | Benefit |
|---|---|
| Purity | No solvents; preserves natural aroma compounds |
| Selective extraction | Can target high-value sesquiterpenes & chromones |
| Thermal protection | Low temperatures prevent aroma degradation |
| Environmental | CO₂ is non-toxic, recyclable, and clean |
| Yield efficiency | Can extract more resin compounds compared to steam distillation |
5. Limitations
- High capital cost: Specialized high-pressure equipment required.
- Technical expertise: Operators must monitor pressure, temperature, and flow rates precisely.
- Throughput: Limited batch size compared to industrial steam distillation; may require scaling for commercial operations.
6. Best Practices
- Use only premium resinous wood (sinking or super grade) for maximum aroma richness.
- Control temperature & pressure carefully to preserve delicate sesquiterpenes.
- Dry wood adequately to prevent ice formation during CO₂ depressurization.
- Recycle CO₂ where possible to reduce operating costs.
- Store extracted oil in dark, airtight containers to maintain fragrance integrity.
Supercritical CO₂ extraction is considered the gold standard for luxury agarwood oils because it produces high-purity, aromatic-rich, solvent-free oils, ideal for perfumery, niche fragrances, and premium products.