WKU Consulting — SOP Template
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Standard Operating Procedure: BHO Closed Loop Extraction

SOP Number:

Version: 1.0

Effective Date:

Prepared By:

Approved By:

Review Date:

1. Purpose

This SOP defines the procedure for butane hash oil (BHO) extraction using a closed loop hydrocarbon system. The procedure covers pre-run safety checks, material loading, extraction, collection, and initial purging. All operations must comply with local fire code, C1D1/C1D2 classification requirements, and applicable state cannabis regulations.

2. Scope

Applies to all closed loop hydrocarbon extraction runs using n-butane, isobutane, or butane/propane blends. Covers extraction from dried cannabis flower, trim, or fresh frozen material. Does not cover open blasting (prohibited in all licensed facilities).

CRITICAL SAFETY: Butane is an extremely flammable gas (NFPA 704: Health 1, Flammability 4, Instability 0). All extraction must occur in a C1D1 or C1D2 classified room with appropriate ventilation, gas detection, and explosion-proof equipment. Never operate a closed loop system outside a compliant extraction room. LEL monitors must be active and calibrated before every run.

3. Equipment & Materials

Item	Specification	Notes
Closed loop extraction system	ASME-rated, pressure-tested	Must have current pressure test certification. Inspect all clamps and gaskets before every run.
N-butane (instrument grade)	99.5%+ purity, <50 ppm moisture	Always use instrument or research grade. Mystery oil contamination in canned butane is common.
Propane (optional blend)	99.5%+ purity	10-30% propane blend increases terpene extraction and lowers viscosity.
Solvent tank / recovery tank	DOT-rated, sized to system	Never exceed rated fill capacity (80% liquid by volume).
Recovery pump	Explosion-proof, hydrocarbon-rated	CMEP-OL, Haskel, or equivalent. Non-sparking.
Vacuum oven	Capable of -29.9 inHg at 90-120F	For initial purge. Must hold stable vacuum.
Chiller / dry ice	Capable of -40C to -80C	Colder solvent = more selective extraction (less fats/waxes).
Scale	0.01g resolution for collection, 1g for material	For yield tracking and batch records.
LEL gas detector	Calibrated for butane, alarm at 10% LEL	Must be active before, during, and after every run. Non-negotiable.
PPE	Safety glasses, nitrile gloves, anti-static lab coat, closed-toe shoes	No synthetic fabrics. Ground yourself before handling solvent.

4. Pre-Run Safety Checklist

DO NOT PROCEED if any item below is not confirmed. A single leak or equipment failure during a pressurized hydrocarbon run is a catastrophic event.

☐	Check	Criteria
☐	LEL monitor powered on and calibrated	Reading 0% LEL at room ambient. Alarm set at 10% LEL.
☐	Ventilation system running	Minimum 12 air changes per hour confirmed. Negative pressure verified.
☐	Fire suppression system armed	Visual inspection of extinguisher and suppression system status.
☐	All clamps torqued and gaskets inspected	Tri-clamp connections hand-tight plus quarter turn. No cracked or worn gaskets.
☐	Pressure test (nitrogen)	System holds at 150% max operating pressure for 10 minutes with no drop.
☐	Vacuum test	System holds -28 inHg for 10 minutes with no rise. Indicates no leaks.
☐	Recovery pump operational	Pump starts, runs smooth, no unusual noise.
☐	Solvent supply valve closed	Confirm closed before loading material column.
☐	Collection vessel clean and dry	No residual solvent or extract from previous run.
☐	Batch record started	Material weight, strain, solvent lot, operator, date logged.

5. Material Preparation

1 Weigh material. Record weight in batch log. Typical column loading: 80-90% of column volume (do not overpack).

2 Grind or break down material to consistent particle size. Do not powder. Target roughly nickel-sized pieces for flower, broken but not ground for trim.

For fresh frozen material: Keep material frozen until immediately before loading. Do not let material thaw. Load column quickly and begin chilling immediately. Thawed material releases water into the solvent, creating emulsions and reducing quality.

3 Pack the material column. Even packing density throughout. No air channels. Use filter screens (25-50 micron) on both ends of the column to prevent particulate migration.

4 Seal the column. Torque all clamps. Confirm gasket seated properly with no visible gaps.

6. Extraction Procedure

6a. Solvent Chilling

5 Chill the solvent tank to target temperature before beginning the run.

Solvent Temp	Selectivity	Best For
-40C to -80C	High selectivity: cannabinoids + terpenes, minimal fats/waxes	Live resin, high-terpene extracts, material that will not be winterized
-20C to -40C	Moderate selectivity	Standard shatter/wax production with post-extraction winterization
0C to ambient	Low selectivity: pulls everything including fats, lipids, chlorophyll	Crude for distillation (winterization required downstream)

QC Note: Colder solvent = cleaner extract but potentially lower yield. The tradeoff is selectivity vs. throughput. For shatter, -40C to -60C is the sweet spot. For crude destined for distillation, ambient is acceptable since winterization removes the co-extracted lipids.

6b. Running the Extraction

6 Open the solvent supply valve slowly. Allow liquid butane to flood the material column from top to bottom. Monitor pressure gauges throughout.

7 Soak time: Allow solvent to contact material for the target duration.

Soak Duration	Effect	When to Use
3-5 minutes (quick wash)	Primarily cannabinoids + monoterpenes. Minimal wax/lipid co-extraction.	Live resin, high-terpene shatter, single-pass runs.
10-20 minutes (standard)	Full cannabinoid extraction. Some wax/lipid pickup.	Standard production runs. May require winterization.
20-45 minutes (extended)	Maximum yield. Significant wax, lipid, and chlorophyll co-extraction.	Crude for distillation only. Always winterize afterward.

8 Drain to collection vessel. Open the bottom valve and allow the butane solution to flow into the collection pot. Apply gentle nitrogen pressure (5-10 PSI) to push residual solution through the column if needed.

6c. Solvent Recovery

9 Begin solvent recovery. Heat the collection vessel gently (80-100F water bath) while running the recovery pump. Recovered butane returns to the solvent tank for reuse.

Temperature control is critical. Collection pot temperature should not exceed 110F (43C). Higher temps degrade terpenes (monoterpenes begin volatilizing above 70F/21C) and can cause thermal degradation of sensitive cannabinoids. Monitor continuously.

10 Continue recovery until no visible liquid butane remains in the collection vessel and the recovery pump flow stops. Residual butane in the extract will be removed during vacuum purging.

7. Collection and Initial Purge

11 Remove the extract from the collection vessel onto parchment paper or a PTFE sheet. Weigh the crude extract and record in the batch log.

12 Transfer to vacuum oven for residual solvent purge.

Parameter	Shatter	Badder/Budder	Crude (for distillation)
Oven temperature	90-100F (32-38C)	100-115F (38-46C)	110-130F (43-54C)
Vacuum depth	-29.5 to -29.9 inHg	-29.5 to -29.9 inHg	-29.5 to -29.9 inHg
Duration	24-72 hours	12-48 hours (whip periodically)	12-24 hours
Target residual solvent	<500 ppm (most states)	<500 ppm	<5000 ppm (will be further refined)

QC Checkpoint: Before releasing any finished product, submit a sample for residual solvent testing. Most state regulations require <500 ppm total residual hydrocarbons for consumer products. Do not skip this step.

8. Post-Run Procedure

13 Confirm LEL monitor reads 0%. If any reading above 0, continue ventilation until clear.

14 Disassemble and clean the material column. Remove spent biomass. Clean all contact surfaces with isopropanol. Inspect gaskets for wear or damage. Replace any compromised gaskets.

15 Complete the batch record. Record: input weight, output weight, yield percentage, solvent used (volume), extraction temperature, soak time, any deviations from this SOP.

9. Yield Reference

Material	Expected Yield Range	Notes
Premium flower (25%+ THC)	15-25%	Strain, freshness, and moisture content are primary variables.
Standard flower (15-25% THC)	10-18%	Typical production range for dried flower.
Trim / small buds	5-12%	Lower trichome density. Higher plant material ratio.
Fresh frozen flower	8-15% (live resin)	Water weight inflates input mass. Yield appears lower but quality is higher.

10. Troubleshooting

Symptom	Likely Cause	Corrective Action
Dark extract (green/brown)	Solvent too warm, soak too long, material too dry/old	Reduce solvent temp. Shorten soak. Verify material freshness.
Low yield (<10% from quality flower)	Insufficient solvent, column packed too tight, solvent channeling	Increase solvent ratio. Repack column evenly. Check for channels.
Residual solvent fails testing	Insufficient purge time or temp	Extend vacuum purge. Verify oven calibration. Thin out slabs for better off-gassing.
Buttery/nucleated texture (wanted shatter)	High terpene content or lipid content causing nucleation	Lower extraction temp. Winterize before purging. Use fresh, high-THCa material.
System pressure drop during run	Leak at clamp, gasket failure, cracked fitting	STOP extraction immediately. Evacuate room if LEL alarm triggers. Find and fix leak before resuming.

11. Revision History

Version	Date	Change Description	Author
1.0		Initial release