Yep. Doing the math first is highly advised. Surprised it’s not in this thread yet. It has been posted several times.
This version is most useful imo
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The prv is supposed to be there as a safety.
If it releases, you’re loosing terpenes.
This one was overloaded.
Yes. Stays well below 250psi.
This thread is soo juices!!
You can also gauge the completeness of the conversion of thca into thc by seeing how much pressure you’re producing.
Example: 1000g extract @65% thca = 650g of thca. 650*~13%=~85g CO2.
What pressure does 85g (full decarb)of CO2 produce at a given volume and temperature? Is that figure below the rating of your process vessel? What about 42.5g? (50%decarb)
Accurate estimates are important, but knowing your concentration of thca prior to decarb (IE in house analytics)will allow you to tune it for the desired conversion rate.
Okay, I assume you are using relatively higher temperatures? Using low temperatures, I have found that the pressure can actually inhibit decarboxylation if there is too much input weight. Thats why I was curious 
As per @Photon_noir , decarb is a psuedo first order reaction so the pressures we work with shouldn’t have any effect on liberation of CO2 and will proceed as if there was no pressure.
But yes, we use relatively high temps. Above 100C.
For anyone curious here is the method I use to solve ppCO2
PV = nRT
(using Danny’s example above) 85g CO2 = approximately 1.93 moles of CO2
decarb temp is in Kelvin (add 273 to the temperature in Celsius; gotta use standard units)
R = 8.314 (when using kPa for your pressure units and litres for your volume)
solve for pressure or volume as required
Remember volume is not the entire container’s volume; just the headspace. So if you have an 11L container with 2L taken up by liquid, your headspace volume is 9L.
Right, so its not the pressure, its probably a reactant concentration issue which means I need to be looking into the kinetics.
Okay, lets see if I can figure the kinetics out then.
k
[A] + [B] —> [C] + [D] … A = THCa, B = ?, and C = THC, D = CO2
[B] >>> [A]
k[B]
so [A] -----> [C] + [D]
k[B] = k’
k'
[A] -----> [C] + [D]
If this is what Decarboxylation follows, then what is B? @Photon_noir
Are we assuming its O2?
According to [Decarboxylation of Δ <SUP>9</SUP>-tetrahydrocannabinol: Kinetics and molecular modeling - NASA/ADS]
Upon heating, Δ9-tetrahydrocannabinolic acid decarboxylates to give the psychoactive compound Δ9-Tetrahydrocannabinol.[8] When cannabis is heated in vacuum, the decarboxylation of tetrahydrocannabinolic acid (THCA) appears to follow first order kinetics. The log fraction of THCA present decreases steadily over time, and the rate of decrease varies according to temperature. At 10-degree increments from 100 to 140 °C, half of the THCA is consumed in 30, 11, 6, 3, and 2 minutes; hence the rate constant follows Arrhenius’ law, ranging between 10−8 and 10−5 in a linear log-log relationship with inverse temperature. However, modelling of decarboxylation of salicylic acid with a water molecule had suggested an activation barrier of 150 kJ/mol for a single molecule in solvent, much too high for the observed rate. Therefore, it was concluded that this reaction, conducted in the solid phase in plant material with a high fraction of carboxylic acids, follows a pseudo first order kinetics in which a nearby carboxylic acid precipitates without affecting the observed rate constant.
What I am reading here is that decarboxylation can be first order reaction or pseudo first order. THCa to THC being first order reaction, what do you all think?
About 13% of THCa is composed of CO2 so all you need to do is figure how much CO2 you have, and apply it to the volume and temp and boom, there’s your pressure.
Absolutely, but I do not have any specific data to share, just generalizations.
Heat degrades and isomerizes terpenes really easily, so the less heat they are subjected to, the better. When we decarb with the terps, the scent is heavier, if that makes sense. Not sure how else to describe it. While it retains much of the same character as the non-decarbed version, it is definitely not the same.
Does decarbing with the terps make the greatest product ever? No, but it is more than sufficient for the input material we’re currently running. We’re also modifying our prototype decarb units, and I’m sure we’ll be sharing with the class before too long.
You guys are the coolest. Thanks for always sharing with the group.
This is where (and only where after a bit of research) pressure plays a role in kinetic rate reactions. Increase pressure with oxygen present will increase those undesired side reactions of the Terpenes. This is why the head space flushed with an inert gas or a vacuum to remove the oxygen is so important at high decarb temperatures.
The o2 is the strictic cause of oxidation when heat is apply? ocurr oxidation without o2 when apply heat ?
Yes, @406_Chemabis & @Dannywarbucks !
I have found a few minutia for decarboxylation processes to consider, as well…
Decarboxylation prefers to occur AT the heated interface with the resin (e.g. the glass or metal wall and/or floor of the decarb vessel)… so the greater your heated surface area to volume ratio, the faster it will proceed. In fact, this may be ONE way metal oxide particles in suspension catalyze decarboxylation: by providing hot solid surfaces throughout the resin volume! (After all, the surfaces of glass, steel or aluminum heating vessels are technically oxides, too…)
MgO, ZnO, TiO2 and other metal oxides all seem to work similarly for this catalysis, and using them pushes the rxn to have a well-defined 1st Order mechanism and rate (pressure has even less bearing on rate, for example).
Isomerization rxns can be instigated by heating alone, but even 10 psi of head pressure can increase isomerization rate… less than, but similar to the way some weaker acids might catalyze such rxns. Therefore, it is IMPERATIVE to use MgO or another alkali metal oxide (decarboxylation catalyst) to inhibit isomerization during (especially pressurized) decarboxylation. It mitigates any acid effects and it also lowers the heat required for a decent rate of decarb.
So if all o2 is removeed from a sistem and apply heat, let says 95 celcius , terpens will broke or oxidate? Independet if is presure or not.
I double vac purge and backfill with uhp nitrogen to mitigate oxidation. Would crashing thca and spinning taste better? Maybe, but how much and whose cart/device? And how much time and labor do you spend doing that at scale?
I really think a solid mgo catalyst ( possibly rotating?) element would be an excellent augmentation to an existing system. Something made to fit a 6" lid with a 1.5" triclamp fitting like this? Adjustable length shaft.
Sounds like a good idea, @Dannywarbucks ! Just have to be careful not to break it! 
For that reason, I would just recommend MgO ceramic boiling chips.
@Vegeta , the terpenes and other molecules can thermally decompose (break down into other molecules) with long exposure to heat. Some of them are sensitive to light; some to heat; some to pressure. The best way to find out is to analyze the material for terpenes before and after your processes.
I run decarb with MgO under full vac at 70C and collect terps on a cold trap with dry ice.
You want to avoid oxygene while heating your extract as heat and oxygene will start degrading terpenes, promoting side reactions and what not.
I found the 70C to be the sweet spot. With 0.5g of powder MgO per kg of crude and 2h run time I get about 50% decarboxylation. Full decarb after another hour.
Going over 75C will introduce enough energy to start breaking more fragile terpenes and a well know “satan’s fart” notes will start to take over.
But ideally one would want to remove terpenes from freshly harvested biomass first. 35C under vac is perfect. It’s like stream distillation using water present in the plant but gentlier. And it takes 5-10 minutes to get most of the terpenes out.
Any fuckery with extracts, especially where high temp is required will affect the terpens. Remove them upfront and reintroduce later.
Make sure there is no water before adding MgO as this sucker will suck it and create very hard to remove turbocharged “limescale”.
Strip terps in 5 to 10 min from biomas?? That is glorious