To all thermodynamicists, engineers, chemists and physicists.
What are thoughts on a distillation vessel heating jacket temperature vs the thermal degradation or decarboxilation of an extract in the following example.
10hp boiler (98kw) @15psi, stainless steel steam jacketed reactor jacket temp at 250F. The reactor can be stirred.
Now provided the vapor condensing/collection side can keep up with the heat input, distillation side. Lets say it does in this example and equates to 0psi (ambient atmospheric pressure)
The extract/solvent solution will never exceed the temperature of it’s boiling point.
What I’m trying to determine is right at the interface of the jacket surface and solution interface will it actually be 250F? Or will the solution flash boil so fast and cool to it’s boiling point and never does hit 250F
Short answer: To a first approximation, this is correct. You can reasonably assume that if a fluid is still boiling it’s going to always be at the boiling point.
Unfortunately, though we can approximate the majority of these effects as linear and somewhat constant, that is frequently not actually the case at the extremes of any given situation.
If I had to guess, there is likely a reasonably thin film at the interface that could be somewhere between the boiling point of the solution and the temperature of the jacket.
How thin is that film?
What temperature does it get to or stabilize at? Approximating it as the midpoint between the boiling point and the jacket is probably not a terrible idea.
Does that higher temperature cause other undesirable or unintended effects?
How long can we approximate the residence time at that temperature as? (My guess says it’s short, on the order of a handful of seconds at most. You can probably guesstimate this through a bunch of thermal conductivity math.)
What is the magnitude of those effects? Aka: does it matter I’m the real world?
This is all almost certainly a function of the concentration of the solution that is being distilled, vacuum or pressure level, level of agitation (or lack thereof) in the vessel, etc.
If I had to take a guess at it, I’d say you’re probably fine.
But might not be.
Long answer: more research needed, specific to your situation and your feedstock.
Somewhere on this forum this topic is debated in a convo b/t GratefulPhil and Tech1145 which Lincoln20XX has elegantly summed up the quandary which remains.
My take, based on experience is- if there exists a thin film of liquid that goes above the expected solution temp @ given pressure its not causing detectable amounts of cannabinoid decarboxylation. (Typically run jacket fluid at 130-140F) -
Now as the solution becomes more concentrated (and more viscous with higher surface tension) - the measurable solution temp will rise (quickly) to at or near that of the heat transfer fluid temp. This is the only time I worry about over heating the product and take measures to prevent such from happening.
Leidenfrost point?
At 250F I do wonder if the deltaT b/t the BP of the dilute hydrocarbon solution and the jacket @ 250F is enough to see some leidenfrost effect come into play - which could inhibit heat transfer. (i think there is a word for this effect-to-be-avoided from the early days of steam boiler design) Im sure the thermo wizards amongst us can show us some math for this.
In short, your quickest route to an answer here is to experiment cause Im sure we could all argue theory till the cows come home.
There is defenatly a film with temp difrance
And whether or not it has effect indeed only trails will tell
The main isseu with these hot films I encounter with pid controled heating mantels or jackets for the really heat up way over the set temp and the problems start
Simple example is pfosforic acid should not be heated over 140C
In a flask on a pid controled mantel it does
And the acid turns red sign of temperature
Havoc in this film layer
Main reason on direct heating mantels or jacket s i use a VAriac
Decarb of THC doesn’t start occuring at a decent rate until about 90-100 deg C. Keep in mind this is reaction kinetics thing, meaning there isn’t a hard temp where decarb occurs. It’s more like it’s always happening really slowly but below that temp the reaction timeframe is on the order of weeks or months as opposed to minutes or hours.
Anyway any temp higher than 30 but less than about 80 deg C should be good.
This would be a problem if there was little to none pentane left in solution
As long as there is pentane left pentane is the leading temperature /pressure liquid in the solution so these are the parameters one should focus on
When oil crashes out, it’s no longer in solution. And yes this is happening when little solvent is left, but this can also occur during a redissolve in a Closed system with butane
Temperature, as well as the slope of the saturation level. You can crash an oil by going too fast when cold or hot. Jumping that line from saturated to super saturated will determine how much is falling out of solution.