¶ CO2 Extraction
Supercritical and subcritical carbon dioxide (CO2) extraction is a solvent-based technique that uses CO2 in a state above its critical point -- where it exhibits properties of both a gas and a liquid -- to dissolve and extract cannabinoids, terpenes, and other compounds from cannabis material. CO2 extraction is the dominant method in the legal cannabis industry for large-scale production and is widely used in the food, pharmaceutical, and essential oil industries.
¶ How It Works
Carbon dioxide becomes "supercritical" when it is held above its critical temperature (88 degrees F / 31 degrees C) and critical pressure (1,071 PSI / 73.8 bar). In this supercritical state, CO2 exhibits:
- Gas-like viscosity -- Flows easily through plant material
- Liquid-like density -- Can dissolve compounds like a liquid solvent
- Tunable solvency -- Changing temperature and pressure changes which compounds CO2 preferentially dissolves
The extraction process:
- CO2 gas is compressed and heated to the supercritical (or subcritical) state
- Supercritical CO2 is pumped through a vessel containing cannabis material
- As it flows through the material, CO2 dissolves cannabinoids, terpenes, and other target compounds
- The CO2 + dissolved compounds (miscella) enters a separator vessel
- In the separator, temperature and/or pressure are changed, causing the CO2 to lose its solvency and release the dissolved compounds
- The extract is collected from the separator
- The CO2 returns to its gaseous state, is recompressed, and recycled through the system
¶ Critical Points of CO2
| Property | Value |
|---|---|
| Critical temperature | 88 degrees F (31.1 degrees C) |
| Critical pressure | 1,071 PSI (73.8 bar) |
| Triple point | -69.9 degrees F (-56.6 degrees C) at 75.1 PSI |
| State at room temperature and pressure | Gas |
¶ Supercritical vs. Subcritical CO2
| Property | Supercritical CO2 | Subcritical CO2 |
|---|---|---|
| Pressure | Above 1,071 PSI (typically 1,500-5,000+ PSI) | Below 1,071 PSI (typically 500-1,000 PSI) |
| Temperature | Above 88 degrees F (typically 100-200 degrees F / 38-93 degrees C) | Below 88 degrees F (typically 32-80 degrees F / 0-27 degrees C) |
| Extraction efficiency | High -- extracts more material faster | Lower -- slower, less total extraction |
| Selectivity | Less selective; extracts broader range including lipids, waxes, chlorophyll | More selective; primarily extracts lighter compounds (terpenes, some cannabinoids) |
| Terpene preservation | Moderate -- higher temperatures can degrade volatile terpenes | Excellent -- lower temperatures preserve delicate terpenes |
| Yield | Higher | Lower |
| Best for | Maximum cannabinoid extraction; bulk crude oil | Terpene preservation; delicate extracts; sequential extraction first pass |
| Equipment stress | Higher pressures require more robust (expensive) equipment | Lower pressures reduce equipment demands |
¶ Fractional Extraction
Many operators use both supercritical and subcritical parameters sequentially on the same batch of material -- a technique called fractional extraction:
- First pass (subcritical): Lower temperature and pressure to selectively extract terpenes and lighter compounds. This fraction is collected separately.
- Second pass (supercritical): Higher temperature and pressure to extract cannabinoids and heavier compounds. This fraction is collected separately.
- Recombination (optional): The terpene fraction can be reintroduced to the cannabinoid fraction to create a full-spectrum extract with maximum terpene preservation.
¶ Equipment Overview
CO2 extraction systems are significantly more complex and expensive than other extraction methods.
¶ Main Components
| Component | Function | Notes |
|---|---|---|
| CO2 supply | Source of CO2 gas (bulk tank, cylinder, or reclaimed) | Food-grade or beverage-grade CO2 required |
| Compressor/pump | Pressurizes CO2 to supercritical or subcritical conditions | Most expensive single component; must handle extreme pressures |
| Extraction vessel | Contains the packed cannabis material | Rated for operating pressure (typically 5,000+ PSI); various sizes |
| Separator(s) | Where CO2 releases dissolved compounds for collection | May have multiple separators for fractional collection |
| Heating/cooling system | Controls temperature of extraction and separator vessels | Precision temperature control is essential |
| Control system | Monitors and controls pressure, temperature, and flow rate | Ranges from manual gauges to fully automated computer-controlled systems |
| Flow meter | Measures CO2 flow rate through the system | Important for process consistency |
| Safety systems | Pressure relief valves, burst discs, alarms | Essential for safe operation at extreme pressures |
¶ System Classifications
| System Type | Vessel Size | Automation | Cost | Typical Use |
|---|---|---|---|---|
| Benchtop/lab | 1-5 liters | Manual to semi-automated | $10,000-$50,000 | R&D, small-scale, testing |
| Pilot | 5-20 liters | Semi-automated to automated | $50,000-$150,000 | Small commercial, craft producers |
| Production | 20-100+ liters | Fully automated | $150,000-$500,000+ | Large-scale commercial |
¶ Process Parameters
The quality and composition of CO2 extract are controlled by adjusting several key parameters:
| Parameter | Range | Effect |
|---|---|---|
| Pressure | 500-5,500 PSI | Higher pressure increases solvent density and extraction power; also affects selectivity |
| Temperature | 32-200 degrees F (0-93 degrees C) | Higher temperature increases extraction rate but can degrade terpenes |
| Flow rate | 5-50+ kg CO2/hour | Faster flow = faster extraction but less contact time; slower flow = more thorough extraction |
| Time | 1-4+ hours per run | Longer runs extract more material but with diminishing returns |
| Moisture content | 8-15% ideal | Wet material reduces efficiency; overly dry material may extract differently |
| Grind size | Coarse to moderate | Finer grind = more surface area = faster extraction, but may restrict flow |
| CO2 density | Calculated from temperature and pressure | Determines which compounds are preferentially extracted |
¶ Parameter Selection Examples
| Target | Pressure | Temperature | Notes |
|---|---|---|---|
| Terpenes only | 800-1,200 PSI | 60-80 degrees F (16-27 degrees C) | Subcritical; preserves volatile compounds |
| Cannabinoids | 3,000-5,000 PSI | 120-160 degrees F (49-71 degrees C) | Supercritical; efficient cannabinoid extraction |
| Full spectrum | Sequential: subcritical then supercritical | Sequential: low then high | Fractional extraction |
| Lipids/waxes | 5,000+ PSI | 160-200 degrees F (71-93 degrees C) | Least selective; extracts everything |
¶ Advantages of CO2 Extraction
| Advantage | Description |
|---|---|
| No residual solvents | CO2 returns to gas state at room temperature; essentially zero residual solvent in the extract |
| Tunable selectivity | By adjusting pressure and temperature, operators can target specific compounds or compound classes |
| Scalable -- From lab bench to industrial production | Same principles apply at any scale |
| Safe | CO2 is non-flammable and non-explosive (unlike hydrocarbons) |
| GRAS status | CO2 is Generally Recognized As Safe by the FDA for food processing |
| Environmentally friendly | CO2 used is typically a byproduct of other industrial processes; no net addition to atmosphere |
| Inert atmosphere | CO2 displaces oxygen during extraction, reducing oxidation of sensitive compounds |
| Used in food/pharma | Established regulatory acceptance and safety track record |
| Consistent | Automated systems produce highly reproducible results batch to batch |
¶ Disadvantages and Challenges
| Disadvantage | Description |
|---|---|
| Very expensive equipment | CO2 extraction systems cost $10,000 to $500,000+, far more than other extraction methods |
| Steep learning curve | Understanding the relationship between pressure, temperature, flow rate, and selectivity requires significant expertise |
| High pressure dangers | Operating at 3,000-5,000+ PSI carries risks if equipment fails or is improperly maintained |
| Terpene stripping | Supercritical conditions (higher temperatures) can degrade or strip volatile terpenes; requires subcritical first pass or terpene reintroduction |
| Decarboxylation | CO2 extraction conditions often decarboxylate acidic cannabinoids (THCA to THC) during the process |
| Winterization still needed | Supercritical CO2 extracts lipids and waxes that must be removed for some applications |
| Not accessible to home users | The cost and complexity of CO2 equipment puts it out of reach for casual or home extraction |
¶ Commercial CO2 Extraction
CO2 extraction is the preferred method for many commercial cannabis processors because of its safety profile, scalability, and regulatory acceptance:
- Large-scale facilities may run multiple extraction vessels in parallel, processing hundreds of pounds of material per day
- Automated recipes allow operators to run consistent, repeatable batches with minimal manual intervention
- Integration with downstream processing (distillation, chromatography) creates a complete refining pipeline
- Quality control includes lab testing of each batch for potency, residual solvents (none expected), and contamination
¶ CO2 Extract Characteristics
CO2 extracts vary widely in appearance and consistency depending on the parameters used:
| Parameter Set | Extract Characteristics |
|---|---|
| Subcritical (low temp/pressure) | Lighter color; high terpene content; oil-like consistency; aromatic |
| Supercritical (high temp/pressure) | Darker color; higher cannabinoid content; thick oil to semi-solid; less aromatic |
| Fractional (combined) | Variable; can be engineered for specific profiles |
¶ Comparison with Other Solvent-Based Methods
| Feature | CO2 | BHO/PHO | Ethanol |
|---|---|---|---|
| Equipment cost | Very high ($10K-$500K+) | Moderate-high ($3K-$250K) | Low-high ($50-$200K+) |
| Solvent cost | Low (recycled) | Moderate (recovered) | Low-moderate (recovered) |
| Residual solvents | Essentially none | Must be purged and tested | Must be purged and tested |
| Safety | Non-flammable; high pressure | Extremely flammable; explosive | Flammable; relatively safe |
| Selectivity | Tunable | Moderate | Broad |
| Terpene preservation | Good (with subcritical) | Excellent | Moderate |
| Home accessible | No | No (should not be) | Yes (QWET) |
| Scalability | Excellent | Good | Excellent |
¶ Edible Applications
CO2 extract is widely used in commercial edible manufacturing due to its clean profile, tunable composition, and the absence of residual solvent concerns. The concentrated nature of CO2 extract makes it an efficient and potent ingredient for edible formulation.
¶ Suitability for Edibles
CO2 extract is well suited for edible use, particularly in commercial and large-scale edible production. Both supercritical and subcritical CO2 extracts can be used, though they serve different edible applications:
- Supercritical CO2 extract: Higher cannabinoid content; ideal for potency-focused edibles where precise dosing is the priority
- Subcritical CO2 extract: Higher terpene content; better for edibles where flavor contribution from the extract is desired
¶ Decarboxylation State
ℹ️ CO2 extract is already partially decarboxylated. The elevated temperatures used during supercritical CO2 extraction (often 100-200 degrees F / 38-93 degrees C) initiate decarboxylation during the extraction process itself. The extract may arrive 40-70% decarboxylated depending on the exact parameters used.
For reliable edible dosing, supplemental decarboxylation is recommended to ensure full activation:
- Place CO2 extract in a heat-safe glass container
- Heat at 220-240 degrees F (104-116 degrees C) for 25-45 minutes
- CO2 extract is typically a thick oil and may separate into layers during decarboxylation -- this is normal
- Monitor the bubbling (CO2 release) -- when it slows significantly, decarboxylation is nearing completion
See Decarboxylation for complete guidance.
¶ Dosing Guidance
CO2 extract is highly concentrated and requires precise dosing:
- Supercritical CO2 extract: Typically 60-85%+ total cannabinoids
- Subcritical CO2 extract: Typically 30-60% total cannabinoids (higher terpene content dilutes cannabinoid percentage)
Practical dosing example:
- 1 gram of supercritical CO2 extract at 75% cannabinoids contains approximately 750mg total cannabinoids
- Assuming ~60% of cannabinoids are THC after full decarboxylation, that equals approximately 450mg THC
- This yields approximately 45 servings at 10mg THC each
- Start with 5-10mg THC equivalent when consuming CO2 extract-based edibles for the first time warning
Due to the extreme concentration of CO2 extract, dosing errors are a real risk. Always use a milligram scale or pre-dilute the extract in a carrier oil (such as MCT oil) at a known ratio before incorporating into edibles.
¶ Advantages for Edible Use
- No residual solvents: CO2 returns to gas state, leaving essentially zero solvent residue
- Tunable composition: Extraction parameters can be adjusted to produce extracts optimized for edible use
- Consistent: Automated CO2 systems produce highly reproducible extracts batch to batch
- Commercially proven: The dominant extraction method for regulated edible manufacturing
- Concentrated potency: Small amounts yield many servings, making it cost-effective at scale
For detailed edible preparation techniques, infusion methods, and dosing strategies, see Edibles.
¶ Navigation
- Extraction Overview -- All extraction methods
- BHO/PHO -- Hydrocarbon extraction
- Ethanol Extraction -- Alcohol-based extraction
- Distillate -- Further refining of CO2 crude
- Live Resin -- CO2 can be used for live resin
- Cannabinoids -- Compounds extracted
- Terpenes -- Aromatic compounds
- Harm Reduction -- Safety guidelines
This page provides educational information about CO2 extraction. CO2 extraction requires specialized, high-pressure equipment and should only be performed by trained professionals. Always comply with applicable laws and regulations.