Here’s a detailed explanation of Pressure & Temperature Effects in Supercritical Fluid Extraction (SFE):
1. Why Pressure & Temperature Matter
In SFE, CO₂ is used above its critical point, so its density, solvating power, and selectivity are highly sensitive to pressure and temperature.
- Pressure (P): Influences CO₂ density → higher density → better solubility
- Temperature (T): Influences solute vapor pressure and CO₂ density → affects extraction kinetics and selectivity
Small changes in P or T can have large effects on yield and composition.
2. Pressure Effects
| Pressure Effect | Description |
|---|---|
| CO₂ Density Increase | Higher pressure → higher density → stronger solvating power |
| Solubility Enhancement | More solute can dissolve → higher extraction yield |
| Selectivity Adjustment | Can preferentially extract heavier compounds at higher pressure |
| Extraction Kinetics | Higher density → faster mass transfer |
Example:
- CO₂ at 100 bar, 35°C: density ≈ 0.7 g/mL → extracts light oils
- CO₂ at 300 bar, 40°C: density ≈ 0.9 g/mL → extracts heavier compounds
3. Temperature Effects
| Temperature Effect | Description |
|---|---|
| Solute Vapor Pressure | ↑ Temperature → ↑ vapor pressure → solubility may increase |
| CO₂ Density Decrease | ↑ Temperature → density decreases → solvating power may drop |
| Selectivity Tuning | Light compounds may be extracted at higher T, heavy at lower T |
| Heat-Sensitive Compound Preservation | Mild T prevents degradation of delicate compounds |
Note: Temperature and pressure effects can oppose each other, so optimization is needed:
- ↑ T increases solute vapor pressure (positive)
- ↑ T decreases CO₂ density (negative)
4. Combined Pressure & Temperature Effects
- Low P, Low T: Low solubility, slow extraction
- High P, Low T: High solubility, preserves heat-sensitive compounds
- High P, High T: High solubility, faster extraction, may degrade sensitive compounds
- Optimized P & T: Maximize yield, selectivity, and compound integrity
Graphical Concept:
- Solubility vs. pressure at constant temperature → increases with P
- Solubility vs. temperature at constant pressure → may increase or decrease depending on compound
5. Practical Implications in SFE
- Selective Extraction: Adjust P & T to extract specific compounds
- Fractionation: Multi-stage separators at different P & T for compound separation
- Process Optimization: Small adjustments improve yield and purity
- Safety Considerations: Operating within vessel’s pressure/temperature limits
6. Summary Table
| Parameter | Effect on SFE |
|---|---|
| Pressure ↑ | CO₂ density ↑ → solubility ↑ → yield ↑ |
| Temperature ↑ | Solute vapor pressure ↑ → solubility may ↑, CO₂ density ↓ → solvating power ↓ |
| Combined T & P | Must be balanced to optimize yield, selectivity, and compound stability |
✅ Bottom Line:
Pressure and temperature are the two most critical variables in SFE.
- Pressure mainly controls CO₂ density and solubility
- Temperature influences solute volatility and CO₂ density
- Careful tuning of both allows selective, high-yield, high-purity extractions
I can also create a diagram showing solubility vs. pressure & temperature, highlighting the optimal SFE operating window.
Do you want me to create that diagram?