Here’s a comprehensive guide on Extraction Vessel Design for Supercritical Fluid Extraction (SFE):
1. Role of the Extraction Vessel
The extraction vessel is where the raw material interacts with supercritical CO₂ under controlled temperature and pressure. Its design is critical for:
- Efficient solvent–solute contact
- Uniform flow distribution
- Safety under high pressure
- Scale-up from lab → pilot → industrial operations
2. Key Design Considerations
a. Material of Construction
- Must withstand high pressure (typically 100–600 bar) and temperature (above Tc).
- Common materials: Stainless steel (SS 316, SS 304), Hastelloy.
- Corrosion-resistant if solvents or modifiers are used.
b. Shape and Geometry
- Cylindrical vessels are most common: good pressure distribution and easy fabrication.
- Vertical orientation allows CO₂ to flow bottom-to-top or top-to-bottom.
- Aspect ratio (height/diameter) affects flow dynamics and extraction efficiency.
c. Volume / Capacity
- Lab-scale: 50–500 mL
- Pilot-scale: 1–20 L
- Industrial-scale: 50–500+ L
- Volume depends on feedstock quantity and desired throughput.
d. Flow Design
- Uniform CO₂ flow avoids channeling or bypassing of material.
- Packing material or filters at inlet/outlet prevent particle clogging.
- Distributor plates or frits can ensure even flow.
e. Temperature Control
- Jackets or internal coils for heating (to reach supercritical temperature).
- Thermocouples placed for uniform temperature monitoring.
f. Pressure Control & Safety
- Designed for max operating pressure > expected pressure (safety factor 1.5–2×).
- Equipped with:
- Pressure relief valves
- Burst disks
- Pressure sensors
3. Accessories / Additional Features
| Feature | Purpose |
|---|---|
| Sampling Ports | Take extracts during the process |
| Sight Glasses (lab-scale) | Monitor flow and packing |
| Agitation / Mixing | Optional for better contact in dense materials |
| Co-solvent Injection Port | For polar modifiers (ethanol, methanol) |
| Insulation / Jacket | Maintain uniform temperature |
4. Design Considerations for Scale-Up
- Maintain geometric similarity: height/diameter ratio consistent
- Ensure flow distribution scales proportionally
- Multi-vessel systems may be used for continuous extraction
- Materials and safety systems upgraded for higher volumes
5. Summary Table
| Aspect | Design Requirement / Consideration |
|---|---|
| Material | Stainless steel / corrosion-resistant alloy |
| Shape | Cylindrical, vertical preferred |
| Capacity | Lab: 50–500 mL, Pilot: 1–20 L, Industrial: 50–500+ L |
| Flow Distribution | Distributor plates, filters, avoid channeling |
| Temperature Control | Jackets, coils, thermocouples |
| Pressure Control | Rated for max operating pressure, relief valves, burst disks |
| Accessories | Sampling ports, agitation, co-solvent injection |
✅ Bottom Line:
A well-designed extraction vessel ensures uniform supercritical CO₂ contact, maintains process control, and provides safety under high-pressure conditions, directly impacting yield, selectivity, and reproducibility in SFE.
I can also create a visual schematic of an SFE extraction vessel, showing CO₂ inlet, flow distributor, packing, temperature jacket, and outlet to separator.
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