Heptane recovery vs ethanol recovery

Recently we started water washing our crude but when we’re done and it’s time to recover back out heptane we’re experiencing a tremendous amount of loss.

What are the proper specs to recover heptane? If anyone has any pointers on how to recover as much heptane back as possible it would be much appreciated.

less vacuum more cold trap


Right now we are using a cooling tower to use our cooling column; water is only circulating through the column around 80f, I’m assuming that’s to warm.

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Yes, too warm!


You need to pull less vacuum to make up for the warm water.

How is your vacuum pump routed and what type of vacuum pump is it? You are pulling heptane vapors through your vacuum pump and pumping it out of the outlet possibly into your room if the outlet isn’t plumbed elsewhere.


A good rule of thumb is having a Delta (difference) of 50c between your vapor and condenser. This is inclusive of vacuum, so if you’re dropping yout BP from vacuum your condenser needs to go colder too


@tweedledew It’s the Delta 20 Rule. 20C between vapor and condenser. and 20C between the vapor and heating source.

50C is too much of a difference, you’ll lose efficiency.

EDIT: Widely applied to applications in evaporation and HVAC in general.



Don’t assume.

Go look it up :thinking:

You can calculate the boiling point of your solvent at any given vacuum level using the Antoine equation and a couple of data points.

Is all I could find in 90sec

Eg, what is the vapor pressure at 27C? How does that compare to the vac level you’re pulling?

So what state is your heptane in?

Edit: useful data here https://nvlpubs.nist.gov/nistpubs/jres/24/jresv24n3p229_A1b.pdf might take a second or twelve to wrap your head around it.

There is also a paywalled publication that probably has exactly what you need… https://pubs.acs.org/doi/10.1021/je990230x

(Sci-Hub | Vapor Pressure of Heptane from the Triple Point to the Critical Point | 10.1021/je990230x)

Although with 27C “cooling”, even shutting off the vac entirely is still gonna leave you with vapor bypassing your condenser imo

edit: for reasons that probably involve lack of caffeine I was using the BP of pentane (37C rather than 98C) here.


I’d agree with you to a point, much of it depends on the surface area and efficiency of the condenser itself, and the relative vapor pressure at hand.

Many people use rotovaps, and the glass is just terribly inefficient, so in the cannabis space with glass In mind, I’ve found a “delta 20” to be inadequate for solvent recovery in general.

I suppose we should ask for more info from OP on how he’s recovering to see what makes the most sense.

Provided we’ve got efficient surface area to condense with you’re definitely right, but across a bunch of real world applications I find I’ve needed to get minimum 30c delta, if not higher.

I tend to also set things at a 40+ degree delta, and by the time it’s actually running it’s tighter too once the chiller is under load.


Of Course! I was just pointing out that it’s generally known as the Delta 20 rule, not 50.

A bunch of cannabis applications throw this rule right out the door (IE condenser at an extremely low temp; dry ice condensers, -80 Cold traps, etc), which tends to work quite well. You’re definitely right that the delta 20 rule can sometimes be inadequate for solvent recovery — keep in mind the definition of “rule of thumb”…


Hah, I believe it was the legally allowed width of cane you could beat your wife with :stuck_out_tongue_winking_eye: etymologically speaking


lmfaooo. totally forgot about that

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We have a liquid ring vaccum pump so all vapors are getting pulled into the water. We’re currently running it around .025 MPa

We are using a 500L ball reactor , pulling .025MPa on the Vaccum. We have a cooling tower hooked up the jacket that has 108000 kcal:hr of cooling power but our water never really gets below 80.

Was thinking of hooking up our -30/80 touch science recirculating chiller. Would that work and if so what temp would you recommend setting the chiller temp.

I mean, could probably just mostly ditch the vacuum and add more heat if you’re not too concerned with keeping temps low.

If you’re going to put a chiller in line, but use water, I’d recommend not having it go below 0c, cuz water tends to stop flowing around there. Add some glycol to your reservoir to lower the BP if you need to condense colder than that.

but I’d say you’re ok with either less vacuum more heat on the evap end if you wanna run 80f water for cooling.


Great, thanks for the advice!

found it…


at 300K (the temp of your “cooling” water) the vapor pressure of heptane is ~50mmHg

assuming you’re not actually regulating that vac, and are just sucking as hard as you can; with a vac level of 0.025MPa (0.25bar), one might guesstimate that your solvent was only getting down to 330k (57C) as it is leaving your condenser.

you could give yourself another 30C in head room if you regulated the vacuum at 0.7MPa

do you have a thermoprobe in your boiling “flask”?

what temp are you currently driving the boiler?
what is the actual temp of the boiler? the head?

Antoine link for Ethanol: Ethanol


you’re suggesting putting the chiller after the cooling tower, but before the condenser right? Which seems like the correct way to play that game.

I don’t think that chiller alone would be up for the task, and I’m not certain OP got that you were suggesting supplementing the cooling tower rather than replacing it.

I suspect ditching the vac entirely, even without adding more heat is the easiest/cheapest way to recover more solvent. if more heat is available, that will speed things up, if it’s not, who cares, they’re no longer loosing most of their solvent to atmosphere.


how does the volume of that water compare to the (tremendous) amount of solvent you’re loosing every run?

you sure you’ve still got water in that pump? (I’ve seen ethanol replace vac oil more times than I can count).

where is the heptane going then?

is that on a controller?

It we got rid of the vaccum completely would we not just build up pressure inside the reactor?

Also not sure how much heptane was diluted into
The water, we just went ahead and replaced with fresh water. We lost about 25 gallons of heptane so I’d imagine most of that went into the water.

The .025 MPa is on our gauge on the vessel.

Not if you are condensing the vapor appropriately. ie balancing condensation with evaporation.

Think about a CLS being run passively…

So how are you heating this contraption?
(Temp, power, implementation)

Is it adjustable?

So that is a “yes” to “just sucking as hard as possible”?

If it’s on your boiler, that suggests you’re boiling at 57C, rather than condensing at 57C, which might mean you’ll need to add a few more ergs to run at atmospheric