Save your unusable raws Guaranteed.

[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.