Photo sequence of a DCVC run. The color bands are well known to me and the crude always seperates out in this sequence. One photo is image enhanced to highlight bands. These were just archived lab notes pix I took but thought this would be a good start for a topic.
This is what a DCVC sep looks like, time stamped with starting dewaxed dark brown crude testing nominally at 60% THC. Test tubes only show fractions up to but excluding the green band. Dark brown test tubes have target compound. Evaporated those tubes and purged with vacuum. Shown after dabbing in a Petri dish.
Time stamp shows it goes pretty fast. Silica gel 60 is packed in first. Then a layer of sand. Then a dry load of Celite containing the dark brown crude dissolved onto it. Then another layer of sand. Solvent gradient was Hexane/ethyl acetate.
When you begin a DCVC run you have to stay focused because it goes fast and each addition of solvent has a changing ratio of hexane to ethyl acetate. The top pink layer normally won’t budged off the column without ethyle acetate and methanol at 10% methanol. All cannabinoids elute well before the green band and on this run I just tossed the gel after the cannabinoid band eluted. There is always a bright yellow/orange band that precedes the cannabinoids. It is just trace when evaporated and is a bright color but unwanted.
Here is a link that shows final solvent purge of Celite after dark brown crude was loaded onto it. The crude is dissolved first into hexane at room temp. Then the white Celite is dumped it to absorb the hexane. Then the hexane is evaporated off. Final purge is done over gentle heat and a vacuum is pulled on the glass mixing bowl which is the bottom half of my small vac chamber. Then the dry powder is loaded onto a DCDV column to run.
Here are some more archived photos. I often combine and evaporate solvent in Petri dishes from 20 ml fractions collected. One photo shows the order the compound eluted from the column. In this instance it took a methanol/ethyl acetate to get the last 6 fractions shown. The last 6 fractions have no appreciable cannabinoid content and are discarded. Dish 1 has brightly colored yellow/orange compounds that lend an off taste when vaped and this is discarded as well. Dish 2-5 have D9 THC. Dish 2 or 3 contains the THCa. After overnight of evaporation either dish 2 or 3 will have bubbles all through the compound which I judge to be decarboxylation.
This was a bulk run and really loaded the column. Great for prepping before distillation or just good refinement after solvent purge. I show Celite loaded with compound and dry powder. It gets loaded onto the silica gel. Note in the column that the Celite is white after releasing the compound from the solvent wash.
is there a specific range of vac you aim for? I’m assuming its a pretty gentle pull to not detract from contact time on the media? or can you pretty much rip it through ?
I pull it through pretty fast but the deal is that solvents boil under too much vacuum. When the solvent gets strong enough to start moving the cannabinoid onto the gel in such a bulk mode then it is tougher to pull through. The vacuum will rise at that point so an eye is set on the regulator to watch for this and I often open the regulator up a bit to lower the vacuum when the main body hits the gel. If the solvent boils in the column it messes it up. There is no reason to have it go too fast because I have to stop anyway to collect fractions as they elute and mix the next solvent gradient.
My diaphragm pump regulator usually reads between 5 and 10 psi off of zero and it works well.
I haven’t measured the Celite to crude ratio. It depends a bit on what is in the crude first. More terps and such will alter it, but don’t worry. Just estimate how much to dump into your solvent. After you stir it if it is caked up just estimate how much more to add and stir it in. Then If you stir it into caked up stuff and it isn’t mixing well, simply add back enough solvent to the mix to redisolve everything again but now there will be more Celite and evap to a powder. After one or two batches it is easy to judge plus you really cannot put too much Celite in.
I am limited by column size so too much Celite means two runs because it won’t all pack into my small column.
I prefer also to run this as the SOP between first and second run. Purity skyrockets on the second run after a clean and well prepped DCVC run on first run material. It also means I can run slightly lower temps so the effects down the line add up. What I plan to do this month is use my saved but flushed column from last month. It is too nicely packed and working to toss just yet (silica gel 60 and now flushed Celite with a sand layer on top). I want a new column for the run after first pass but will wet load my medicine this month on top of the sand and Celite layer already loaded and run it prior to first pass too.
I am not production so can be picky about using a clean column. My goal this month, foolishly, is to attempt to achieve lab standard purity. No reason but the challenge and I am pretty sure I can nail it. I have a few tricks to really knock out the tenacious contaminates too and am gonna bring it all into one lab. A production lab would likely be better to dedicate a column for just pre-distillation and a seperate one for post distillation. this way reusing a column would not drag already seperated compounds into a finished product. There is always residual hold up on the silica gel 60 I use.
I have no experience scaling up. My suggestion is the same as for distillation really if you plan to attempt it. I suggest first succeeding on a micro scale like one ounce. Figure out how to correctly and repeatable run an ounce of crude through the process. For DCVC the investment in a column(s) like mine sets you back a few hundred dollars and you need a suitable vacuum. Dual vane pumps and pumps that do not like solvent fume should never be used. Hexane and ethyl acetate fume VERY quickly destroyed the seals and thusly the first vacuum pump I owned lolz. I left ethyl acetate in my sublimator overnight once and sealed into it. The Viton o-ring expanded by about 10% overnight! Major fail lolz. New o-ring $15 from Amazon.
Once you figure out on just one ounce where the pitfalls are and how it looks when it is running right then you will have an idea how to scale it.
There is one video that I watched over again several times and each time it seems I spot something else that helps. This is the video that started me on this and if you take the time to really listen to what he says, every word, then you will have the best info out there by far. I altered the procedure because I am seperating for preparing a compound (not analyzing) and I know when the target has eluted so I never have more than about a dozen fractions if flushing the column and even less when I stop the run after collecting cannabinoids.
The ratio is a gradient. It starts at 100% hexane. Then I pull through a 10% ethyl acetate to hexane gradient. This gets the flavonoids and color agents like carotenoids and terps moving and cannabinoids will just start to move. Then up to 20% EA to hexane which gets the cannabinoid profile moving great.
Once the cannabinoids are mostly through I switch to 50/50 EA/hexane which gets the chlorophyls off the column if wanted. Then to flush the column clean I switch to 90% EA to 10% methanol. This gets the really tough parts to wash through. Usually a light pink band is last this way. If the column has already been used a bit I often just leave the green on the column and toss the gel. The cost trade off is no solvent used to flush the column which can take a lot of solvent. The gel on average costs about $15 per column and I can use it nicely a few times before I toss it. There is always residual traces of hold up on the column so a fresh packed one is preferred when running it for final refinement.
Last month I switched to acetone instead of Ethyl Acetate. I did this on accident once when I grabbed the wrong can! It works a bit more aggressively it seems than EA and got a much better seperation on the first terp/caratanoid (bright yellows and oranges) fraction and from just two runs it looks like the acetone ratio is best at slightly reduced ratios. However just two runs with acetone instead of EA is hardly enough to be more precise with ratios but it did a great job at nailing the cannabinoid profile running just slightly less than I would EA.
With Dry Column Vacuum Chromatography you pull the entire gradient through until the column is dry(ish).This is unheard of in flash chromatography or any other method. Each flask of solvent dumped in gets progressively better at washing the compound through the gel and each flask is vacuumed through the gel. Then the next flask is added with the stronger mix (EA is stronger at washing stuff through silica gel than hexane) and washes through the next fraction. The compound sticks to the gel like a stain and the trick is to wash the stain through a little at a time by making the solvent stronger.
Before I knew the ratio the protocol was simply to increase the strong solvent (EA or acetone) compared to the weak solvent (hexane) in 5% steps. So it goes from pure hexane to pure EA in 5% steps and each fraction is vacuumed through the gel before the next fraction is added. At each fraction a new part of the compound will have moved through. It is incredible how effective and economical this method is. I use 20 ml test tubes. I rarely use more than 12 to collect all fractions this way when I stop collecting after the cannabinoids elute. It is a powerful and fast seperation method.
That is very little solvent use compared to other forms of chromatography and the run through the column takes about 15 minutes or less. It is very fast with the constant solvent gradient.
There are really two considerations I use when selecting a solvent for utility. Safety issues or personal preferences aside.
First the solvent system must provide good seperations. Second the solvent must be easily removed with the gear that I have.
All the solvents I use from methanol to acetone, ethyl acetate, hexane, and a few others can be easily evaporated with a minimal of gear. Limonene might work great as a solvent for seperation, but removing it would require vacuum distillation just to remove the solvent. Without trying it I have no idea no how well it would seperate but if limonene associates even a little with silicon gel… who knows? My hunch is you would have a lemon fresh mess of silicon gel .
This is the column I use for small experiments. I push a vacuum hose onto the end of it which is plumbed to a double neck boiling flask in a way that catches the fraction in the flask while the vacuum is running. It goes way fast and is for small scale ideas. Sort of spendy for a small tube but it works.
Yes I can use a column several times. I flush it and save a good column to run crude as a crude seperation column. If all I ever did was a “roughing” pass on the crude then I could use the column many times just for that really. For me since I run one small batch per month it isn’t necessary to have one column packed running just for crude and then a column say for running the higher refinement. It takes ten minutes or less if the column is already packed.
So my SOP reallly is a fresh pack column to run the final DCVC run on crude that had been distilled or run through the sublimator. Then I can seperate trace compounds without worrying about trace contamination from used gel. Then I flush the column well and pull it dry. It could be run again too for fine refinement but I save it for the crude run for next month. That green and really polar stuff that hates to elute on top of the green takes a lot of polar solvent to flush from the column from the crude so it works out to just toss it then.
At these prices it sure gets economical to just run the crude no matter what for me. At maybe 120 grams per column for me that brings the price WAY down. Of course 500 grams lasts me several months but mostly because I hold back to save gel. It is a trade off for me. If I DCVC the crude then most of the terpenes can be removed that way and I can skip (mostly) the horizontal rig to remove terpenes before the sublimator. Plus first run through the sublimator looks like second run this way.
On the other hand I save gel and some solvent by distilling out everything I do not want but there are more passes through the rig for high purity. The advantage is no consumables. I am thinking the gel seps are gonna become much more standard. This could also replace the dewaxing phase at the expense of silica gel but who cares at barrel prices lolz.
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