Mini FFE for purging

In my ongoing war on glassware in my lab, not even my small equipment is safe. Specifically my 5L rotovap, whos’ vapor duct I broke while cleaning it, bricking it. I had one machined out of 316 since the vendor no longer carries the 5L unit and looked at the possibility of an all SS rotovap. The thing that particularly bothers me is actually the rotary flask. Not only do I have a rotating vacuum joint, I end up with the pesky residue that cannot be removed despite heat gunning, as well as being unwieldy (bad for me and clumsy employees).

My 5L rotovap, I have a 2x48" TC shotgun condenser since I broke the glass one. Notice a pattern?

While FFEs get a lot of crap for not purging properly and typically aren’t able to decarb (especially useful if you can do this in you’re rotovap), I’d hazard a guess that if tuned to the task, an FFE could accomplish all of these tasks.

These are some speculative parameters that could make this a viable idea (at least for me). For reference, I use a membrane system to do bulk recovery (~400L), a small FFE to do the secondary bulk recovery (50L) and the rotovap to handle the rest (5L)

Evaporator Length: This obviously controls residence time and a longer evaporator may be necessary if preheating is infeasible. I was thinking a 2x24" could be sufficient for my purposes.

Temperature: I’m planning on going hot, especially for a dual purge/decarb functionality; 150C seems like it’s where I want to be for a good purge and to decarb with a short residence time. I suspect that dehydration and charring is still subject to happen here, so lower temps before that step will be necessary. I plan on having a heater that is 1.5X the kw of my chiller.

On purging, the higher temp will likely be important for removing residuals as well.

Vacuum: Full vac, all the time, obviously.

Feed Viscosity & Solvent Content: Another important one, since we are trying to purge residual, the less solvent the better. The other seemingly important factor is keeping the surface area thin to allow the thin film to do what it does.

Does anyone have reason to think this is a bad thing to attempt or something I’m overlooking? Has anyone attempted this?


The way the ball flask is sitting on its neck like that is giving me ptsd

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If you need a beefy UL listed oil heater hit me up.

In theory this is all possible, you should be able to decarb rather quickly but one issue is boiling and spattering. Youll need a vapor shield similar to @AlexSiegel 's spd head design so youre not sucking airborne droplets of crude oil into your collection vessel or vapor trap.

If your final catch pan was also heated thatd be a benefit.

I think @IrondogAllen is running some FFE specials if you end up saying fuggit

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Why? Besides attached to the roto that is one of the safest places for a flask.


I may have explored this area a time or two.

There’s no reason a FFE can’t handle purge+decarb duties.

More surface area means more throughput.

High-efficiency heat exchangers will probably make your life easier.

Full vac may or may not be necessary or helpful, depending on your feedstock and goals.

A FFE is going to be more sensitive to operator error or negligence and to feed consistency than a Roto. If you’re the only one putting hands on it, or it’s properly automated, you’re probably fine. If not, there’s a nonzero chance you’re gonna have a not-so-great time, at least once.

An all-stainless flash evaporator/roto combination seems to me like the right way to do this. Somewhat less trivial to implement though, depending on your extraction solvent choice and upstream processes.

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It’s got water under it so if roto or table gets bumped it makes a wave and if waves is from enough energy then flask leaves lip of water bath then comes clanking back down

Best place for the ball is in the holder. Ball holder.

Ball. Holder.

This is extraction guy, :point_up_2: lol


Idk why you would invest the time, money and energy to revamp a rotovap for decarb and purge duties to still have a rotovap, complete with all its flaws, when a dedicated jacketed vessel with a mixer, heater for the jacket and a hx with a small chiller for recondensing evaporated solvents would do the job better and with more and better control over heat duration and temperature. Plus no water bath to be constantly replenishing and making a mess.

If anyone needs some 150L decarb reactors I have a pair in Oklahoma for sale, $7500, set on casters and blocks to be able to drain into 5 gal buckets, with VFDs for speed control on Mixer Direct/MXD Process dual prop mixers, with circ pumps, oil heaters and tube and shell HXs for condensers.

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It’s not extraction lol.

That’s a rotary evaporator

@greenbuggy The main reason is lower residence times and the flexibility of feed, residue, and distillate vessels because triclamp parts have much more variety and are interchangeable unlike all of the parts on my rotovap. The main reason I’m doing this is because I can implement this for ~$600, and for 10L, not that I mind the shameless plug

There’s glycerin in the bath so it can go to higher temps without losing volume, plus its water soluble and doesn’t generate oil mist causing lipoid pneumonia. I usually hit 120C before I even notice evaporation, which is nice. Also, the cabinets are fixed in place, you’d need to hit the table with a sledgehammer, and the rotovap is very heavy so it’s not going anywhere.


This is the only problem with my larger FFE; I just used parts I had lying around baring the evaporator. A ball valve is a terrible choice for throttling flow with any precision. I figure I’ll be a pain to dial in, but what isn’t :person_shrugging:, my FFE was like that, but now I can walk away for 3hrs with no issue.

Full vac is likely a good idea for purging, not required for decarbing. I also use vac as my feed method to eliminate the need for a pump.

My only concern with high efficiency heat exchangers is with viscous feed and holdup volume, since this will be a relatively small piece of equipment.

Now I feel stupid for posting that.

I’m curious what size you small FFE is.
If your FFE was large enough to match the needs of volume and efficiency, you could simply link the collection under the hot side of the FFE to the inject port on the roto to finish the decarb. I would suggest a SS decarb vessel with an overhead stirrer personally.


My current one is 3x36" shell and tube heat exchanger. The top part is a filter plate that is slightly rotated to cover the holes to distribute the thin film. Slightly obstructed by the 100L keg in front is a 50L keg behind it.


I see, that’ll get some evaporation done but looks to be really inefficient, I’d recommend going with a larger S&T condenser but then you’d need more heating KW and chilling KW to make it fast and efficient

Stripping and Decarbing at once is going to create a lot of oil mist if you’re shooting for 1 pass. You’ll need a good separator to keep your vapor path clean. I think a batch decarb reactor or big SPD would be better suited for your scale.


It’s just what I had on hand. It works well enough and is actually reasonably well matched, just don’t want to drop money on another piece until I likely break the condenser. That is also my large one for secondary recovery, the one I want to make will be smaller. I’d like to test it, but I can’t really afford a high temp heat exchange fluid at that scale (just DI water RN).

@highestzen, I don’t necessarily need to do it in one pass, I figured there will be both decarb and devol occuring at the same time hence similar temps. I suppose reducing vacuum would prefer decarb. I may just buy a small s&t heat exchanger and share the condenser when necessary since I’m a cheap bastard on a budget.

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I think this is a cool project!

Reminds me of @goldleaf_scientific 's epic glass FFE roto they were prototyping a few years ago!

Excited to see this project progress!

Got any videos of it recovering?


It doesn’t exist yet, I’m determining if its feasible or not.