FFE Ethanol Vapor Carry over

Our falling film evaporator periodically allows excessive uncondensed ethanol vapor to reach our vacuum pump. There’s a drop out pot before the pump, but not a cold trap. Initially I assumed the chiller for the condensing columns in the FFE would be adequate to prevent vapor carry over, however, after lowering it to it’s lowest setting (40F) we’re still seeing periodic carry over. My question is: Do people typically run a cold trap in front of their vacuum pump in a FFE application?



At atmospheric pressure not really, for vacuum applications usually yes… although it can be done you will usually end up running slower. It’s kind of like when you try to get your rotovap to haul ass and you get a bunch of etoh past the condenser.


Good to know, thanks.

Edit: The system is running at 27.5 In. Hg.

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you could try decreasing vac or heat.
how consistent is your heating?

Heating is very consistent, using a tankless water heater somewhere around 30KW in a closed loop system with a centrifugal pump for circulation. Water heater is outputting somewhere around 165F at the vessels, chiller is running at 40F, Vac is 27.5 In. Hg.

I run my ffe at -20 inhg, 40 deg and 185 deg on the evap. I get some discoloration in my ethanol but no blowby
Using an AV 15 by trusteel

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How long and what diameter is your suction piping from your FFE to your tincture/menstrum/wash tank? We have quite a long run so we run our vacuum up higher to maintain about 200gal/hr throughput.

Oh. I don’t really think that matters in my case. I have a pump/vfd that pushes my tinctures through. I have about 4 - 6’ of tubing with an inline metal screen, I push it through at about 35 psi. I don’t know the size bc I’m not at work right now but it can’t be bigger than 1/2". We’re running a drum every 4-6 hours depending on material temperature.

ahh I gotcha. Our equipment from Subzero uses a pump to transfer from the extraction vessels to holding tanks, then uses vacuum to pull through the ffe.

I’ve used one before. I never ran it for long periods of time myself so i have no flow rates. Doesn’t their keg come with a condenser finger?

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If the blow by problem is intermittent I would place money on a fluctuation of some sort.

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We actually have a large knockdown pot inline with the vacuum system, but still experience some amount of carryover. We’re either: 1. moving too fast. 2. running evap too hot. or 3. Insufficiently cooling. Based on what we’ve seen the best option would probably be rate reduction, however, the cost implications of that justify the addition of a cold water trap inline with the vacuum. I actually just met with a rep from Pfeiffer who makes our vacuum, and they have an excellent division called “Nor-Cal” that high quality and very reasonably priced cold traps. If you deal with Pfeiffer, tell them you’re a “Ethanol based botanical extract company”, don’t mention hemp/cannabis.


You may have a leak somewhere in the system. Try pulling full vacuum and closing off the vacuum valve, then run the feed pump. The pressure will raise slightly but should still hold vacuum for 30-60 minutes if everything is balanced properly. You can pressure check the system when it’s dry with compressed air or N2 and use soapy water to find any potential leaks. Hope this helps.

  1. You may need two stages of condensers, first stage for tap water, second for chiller. The second stage can be called a cold trap.
  2. I think this FFE doesn’t require a very deep vacuum.
    Here is a drawing of our 320L FFE system, hope this helps.Uploading: Drawing.jpg…

Fucking heart breaking when it happens


If you are running vacuum feed, does that mean that the top of tge evaporator is ubder atmospheric pressure aka in vacuum? It must right?

You’re responding to a 2 year old thread. Vacuum feed means that they are not using a feed pump. They are using lower pressure in the evaporator to draw the solution from the feed tank.


Thank you for responding. I understand that part. Is a vacuum pumo creating the vacuum or is it caused by a condenser doing its job faster than the evaporator?

Vac or discharge pumps keep the fluid momentum going in one direction. Ethanol doesn’t recover passively very well.


Try more heat…