Both precipitation and crystallization depend on the supersaturation of the solution. How will you distinguish between a solution ripe for crystallization and one for precipitation?
Normally precipitation is a process where a high level of supersaturation is created by reaction, where the product has a low solubility. Crystallization normally are operated at low supersaturation. The result is that at high supersaturation nucleation prevails over growth and the product has a small size. Working with low supersaturation, crystals will grow because nucleation intensity will be lower
In most cases a precipitant is equally likely to precipitate or cause crysttsallization. The concentration determines whether it does one or the other. The rule of thumb for crystallization is to find the point at which the protein is just soluble and try around that concentration by trial and error.
Different solutions have different critical limits of supersaturation, above which spontaneous nucleation (precipitation) begins. Below this limit there is no nucleation, only crystal growth. If production of good quality crystals, meeting target crystal size (MA) and size distribution (CSD, CV) parameters is required, on-line information on the most important parameter, supersaturation and its use for automatic control of the process is required. This is already practiced in the sugar industry (see: www.kpatents.com).
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