Powder Crystals

1. Separation Principle

The separation of powder crystals mainly relies on the differences in physical properties such as particle size, density, solubility, melting point, and wettability between crystal particles and impurities (or mother liquor). Common separation mechanisms include:

• Solid-liquid separation: Using centrifugal force, pressure difference or gravity to separate solid crystals from liquid mother liquor (e.g., centrifugation, filtration).

• Particle classification: Separating crystals and impurities by screening or cyclone classification based on particle size difference.

• Crystallization & recrystallization: Controlling temperature, concentration and solvent to make target components selectively crystallize and separate out.

• Density difference separation: Separating components with different densities under centrifugal or gravity field.

2. Advantages

• High separation purity, suitable for fine chemicals, pharmaceuticals, food and other high-purity demand fields.

• Low damage to crystal structure, maintaining product morphology and performance.

• Relatively low energy consumption compared with evaporation, drying and other processes.

• Strong process controllability, easy to realize continuous and automated production.

• Wide applicability for various inorganic and organic powder crystals.

3. Difficulties

• Small particle size and easy agglomeration, leading to slow filtration/centrifugation speed and easy clogging.

• High viscosity of mother liquor or high solid content, causing poor fluidity and incomplete separation.

• Crystals are easy to break during separation, affecting product yield and crystal morphology.

• Fine crystals easily run off with filtrate, reducing recovery rate.

• Difficult to balance separation efficiency, moisture content and purity.

4. Solutions

• Optimize crystallization process: control cooling rate, stirring speed and crystal growth time to increase crystal particle size.

• Select appropriate separation equipment: use centrifuges, filter presses or vacuum filters suitable for fine crystals.

• Add appropriate auxiliary means: proper pre-heating, dilution or flocculation to improve separation performance.

• Optimize operating parameters: control centrifugal speed, feeding rate and drying time to reduce crystal breakage.

• Adopt secondary separation or washing process: reduce impurity content and filtrate loss.

• Improve equipment structure: use anti-clogging filter media and anti-breakage lining materials.