Decarb & Degas: Avoiding SPD Boilover

The purpose is to get rid of residual solvent and other highly volatile compounds before we subject the material to ultra-deep vacuum in preparation for our cannabinoid extraction. In a sense it’s a prophylactic step which allows us quickly cut through a section of compounds which behave very violently under deep vacuum and tend to bypass the cold trap and end up in your vacuum pump. Ideally this process should be done in a reactor or on a hot-plate (with proper ventilation).

I’ve already poured my crude into the SPD flask!

Can you decarb/degas in my SPD? Absolutely. It may take a long while, but it can be done. Just be very aware of your vacuum depth and set all the condensers in the system to their absolute coldest temperature.

Start by heating your crude to 65-75C in the mantle, stir bar off! Slowly ramp your vac depth until you see a consistent boil. Increase temps 5-degree increments to 100C until there is very little to no activity in the flask. At this point you should start agitating with the stir bar very slowly but keep your hand on the vacuum bypass/breather valve (sometimes called the oh-shit valve) just in case the contents start rising too quickly and crest past the ¾ point of the flask.

If you have a separate pump other than your deep-vacuum pump to use for this process – this is the time to put it to use. We are big fans of chemical diaphragm pumps since there is no oil to change and the internals can withstand a litany of nasty vapors – just make sure you plumb the exhaust to a ventilation source to carry the nasty smells out of your immediate work environment.

Pro Tip: You can run a hose from your pump’s exhaust port to a bucket filled with soapy salt water. We have tried this with a heavy dose of dawn liquid detergent, and it seems to trap the gross smells within the water as the vapor tries to percolate through the heavy suspension.

Be careful! If you ramp your vacuum too  quickly and create too much of a bottleneck for the volatiles trapped inside the crude – the light compounds will bubble up in volcanic fashion and spill up and over into the head, condenser, and receiving flasks. This is called a boil-over and don’t worry it happens to everybody. If you see this happening (crude rising quickly), you need to lay off the vacuum pressure – sometimes so far as to let atmosphere back into the system to settle the contents of the boiling flask back down.

Summary

If (when) this happens to you and you got it under control – take a deep breath, shut everything down and carefully start taking your system apart for cleaning. It may feel defeating but take comfort in the fact that it has happened to everybody at some point. I personally had a litany of boil-overs, first from inexperience, and later from not paying enough attention!  Have some rags and a spray-bottle of solvent ready for when disaster strikes – and invest in a breather valve so to help prevent future boilovers.

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