Why Isn't My Endothermic Crystallization Working?

[paradoxlost]

TL;DR Summary

processes that use heat to create crystals

I'm using a process that uses heat to catalyze crystallization. I don't have to equipment to really understand what's going on, it could just be incomplete nucleation from a super saturated solution, but when I cool it, it doesn't crystallize. Now, I am in an acid solution (pH between 4-5) so if i get too cold the water will contaminate the crystals, so I can't get too cold. but i'm thinking about trying it. I'm just trying to get an idea of the kinetics of what is going on. the pKa of the molecule is 8.08.

 

[Tom.G]

Perhaps you have heard the phrase "The devil is in the details."
You have not supplied any.
Therefore, there is nothing for us to evaluate or comment on.

 

[jedishrfu]

Welcome to PF!

As @Tom.G has said we need details and what your goal and/or question is.

 

[Nik_2213]

Supersaturation is a nuisance. There are ways and means to initiate crystallisation, ranging from 'seeding' to gently scratching interior of flask with a freshly-broken glass rod. Specific triggers vary unto 'legendary'...

As mentioned, OP supplied insufficient detail to advance solution (sic) beyond generalities...

May I suggest 'Crystals and Crystal Growing' by Alan Holden and Phylis Morrison ( MIT Press) ??
A bit retro, but informative, enduring and, thankfully, still inexpensive from eg Amazon...

 

[paradoxlost]

The molecule I am trying to crystallize is an indole based alkaloid that I used a liquid-liquid extraction process to extract. The organic solvent that I use is d-limonene, so there is a lot of non-alkaloid "stuff" in solution. I am not exactly using a reactor vessel, I have steel buckets that are seal in 130F temps. I have used a sonicator probe to induce crystallization before. The solution was 172F and the precipitate was 55F. The liquid is seeded with a 99% pure crystal that I have crystallized in the past and it was confirmed by HPLC from a 3rd party lab. I do not have control of the crystallization vessel as far as temp, pressure, etc. We're working on getting a reactor, as well as a particle viewer. The alkaloid is poorly water soluble, but is acid soluble (labile at pH below 2 and temps above 80C for a longer period of time). The solubility of the acid is due to the a hydrogen addition on a nitrogen that exists in one of the rings (this I am getting from MD software and Avogadro. I am assuming it is correct).

As far as "the devil is in the details" what else would you like? I provided the pKa of the alkaloid in question, I can't really go into the non alkaloid components of the solution as I have not been able to get an exploratory test run to know exactly what they are. However, I am fairly sure they are common plant starches/waxes/carbohydrates/polymers. Polymers can be used to prevent crystallization, and I've done some experiments in the past to be relatively sure that this is the case (I took a solution that normally would crystalize well, reduced the volume with evaporation, no crystallization, replaced the volume with water, got it to crystallize. to me this indicates the concentration of non-alkaloid constituent is important). The volumes of liquids I am dealing with vary between 3 liters and 50 gallons.

The alkaloid has 3 diasteromers, as well as 3 or 4 other closely related indole-based alkaloids that tend to be present. The acid I'm using is acetic acid, and the base I use to increase the pH of the solution is calcium, sodium, potassium, or ammonium hydroxide.

I guess my main question, isn't so much to do with my process, and more the fact that there are crystallization/precipitations that are heat catalyzed, which I was always taught to be the opposite, however, as i've recently learned, calcium hydroxide is less soluble with warmer temperatures. So there are some substances that

 

[jedishrfu]

Perhaps @Borek has some insight to your posts.

 

[paradoxlost]

I'd prefer something more contemporary. From my understanding up until like 5 years ago, crystal growing was an art, not a science