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[gainslol]

These 2 parts from the patent stood out:

- The water content is critical—too little water results in low bulk density crystals; optimal water content yields dense, well-formed crystals.

- The critical feature is that crystallization must be performed in a mixed solvent containing 10–50% by weight (preferably 20–30% by weight) of water relative to the alcohol, at a temperature of 0°C or lower.

 

[Motojager]

It is all about controlling supersaturation. That is the point of a poor solvent. The poor solvent lowers the solubility which creates the supersaturation. The temp control does the same. Too much of either to quickly and will oil out which skips right over crystals forming and turns to oil droplets.The balance is getting the saturation to a balance that is controlled. Which will allow a controlled dense crystal to slowly form. If you don't go to full oil out but the saturation goes wild tons of micro crystals rapidly form . When they rapidly form the impurities and solvent get trapped in the lattice. When they can grow controlled and slowly you get the best purity. But the fine balance is getting the most yield from solution and good crystal formation. Both can happen but there is no magic formula. Every batch reacts differently. Might have purity or polarity differences in impurities from one batch that is different in the next batch. If you scale up or down will change process, moisture in solvent, stirring speed, exact addition rate and timing of poor solvent, cooling ramp, all shift the zone where good growth happens and where you crash or oil out.

 

[TheProdigyCode]

Any ideas if there is a positive effect for longer esters like cypionate to use IPA instead of EtOH ? The idea is that it will provide slower crystallization than EtOh with an ester like cypionate so we get a better end crystal? Also after cold filtering the mother liquor what will be the best to use for cleaning the crystal's surface assuming we use IPA? Straight IPA or a mix of IPA/WFi 80/20? I am wondering if the water even in so small amount can interfere with the crystals in some way.I am very hyped,reading all this thread from the beginning and try to understand as much as I possibly can with my current knowledge. Congratulations to everyone for the effort and the huge knowledge you provide.

 

[Motojager]

Any ideas if there is a positive effect for longer esters like cypionate to use IPA instead of EtOH ? The idea is that it will provide slower crystallization than EtOh with an ester like cypionate so we get a better end crystal? Also after cold filtering the mother liquor what will be the best to use for cleaning the crystal's surface assuming we use IPA? Straight IPA or a mix of IPA/WFi 80/20? I am wondering if the water even in so small amount can interfere with the crystals in some way.I am very hyped,reading all this thread from the beginning and try to understand as much as I possibly can with my current knowledge. Congratulations to everyone for the effort and the huge knowledge you provide.

IPA is going to have less of a window as the solubility is lower especially as it cools. So will force supersaturation quicker. I wouldn't use IPA as main solvent unless dealing with less common lower polar impurities fatty byproducts, hydrocarbons etc. Most of the impurities are going to be more polar which methanol/ethanol will keep in mother liquor better. If you did use IPA to target less polar impurities, I would just use it as a single solvent with no poor solvent(water) or very very slow addition, seed and cool very slow and controlled and let it build off seeding. For the wash just use ice cold IPA if it was used as solvent.

 

[TheProdigyCode]

IPA is going to have less of a window as the solubility is lower especially as it cools. So will force supersaturation quicker. I wouldn't use IPA as main solvent unless dealing with less common lower polar impurities fatty byproducts, hydrocarbons etc. Most of the impurities are going to be more polar which methanol/ethanol will keep in mother liquor better. If you did use IPA to target less polar impurities, I would just use it as a single solvent with no poor solvent(water) or very very slow addition, seed and cool very slow and controlled and let it build off seeding. For the wash just use ice cold IPA if it was used as solvent.

Thanks for the answer. So cypionate is much more soluble in EtOh than IPA and that's going to delay the crystallization further when we cooldown. I think I got it Right thanks a lot.