How to remove impurities from products
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Our company produces 4,6-dichloropyrimidine. The product is converted into needle-shaped solids through cold crystallization followed by centrifugal drying. The current product purity is around 98.3%, with other impurities accounting for 1% and moisture at 0.08%. These other impurities are affecting customers’ production processes. I don’t know any good methods to remove impurities and increase the purity to 99%
Impurities in general chemical products are divided into endogenous and exogenous types. Endogenous impurities are generally caused by side reactions; such impurities are regular in nature and their composition remains essentially constant. Such impurities need to be suppressed by controlling process conditions to minimize side reactions. Furthermore, the solvent itself is also an endogenous impurity. Exogenous impurities arise from environmental contact during the production, separation, and purification of materials, including factors such as containers, solvents, and pipelines. The composition of these impurities is difficult to control, and it is necessary to implement controls based on the characteristics of the entire process. Recrystallization is a good method for removing impurities, but it requires high energy and its operating conditions are not easy to control.
The lazy way is to perform 2 crystallizations, but the cost might be unaffordable. The plan for the 2nd floor is the fundamental solution, but it requires careful and thorough exploration, and it’s likely impossible to implement. Possible methods include: 1. Needle-shaped crystals are generally large, so impurities may be enclosed within the crystals. It would be better to change from static crystallization to dynamic crystallization. 2. During centrifugation, the material inside the centrifuge can be washed with a solvent, provided that explosion prevention regulations permit it. By doing this, my experience can increase the efficiency of my products by around 1%. 3. It reduces the number of times that the crystallization mother liquor needs to be used. There might be more; please experts add to it.
I want to know whether the other impurities in your product were already present before cold crystallization, or whether they appeared after the product was formed If it’s already present at the beginning, considering evaporating it off could be an option
Crystallization is a physical process, and of course this impurity was already present in the mother liquor before crystallization. How to evaporate solid impurities? It must be more troublesome than recrystallization, right?
Can we not consider the material that evaporates, and leave the solid impurities behind?
It’s not possible for 4.6-dichloropyrimidine
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It is best to determine what type of impurity it is before deciding on which method to use. If the concentration is not high, the possibility of using ion exchange resins for separation can be considered; of course, this process should be carried out at low concentrations. Or try using chromatography.
Is there any physical property analysis of the impurities? The melt crystallization process can be considered. Specifically, after crystallization, the material is subjected to additional heating, which causes the surface to melt slightly and thus removes impurities, improving the purity of the product.