Energy-Efficient Separation for High Purity
Melt crystallization is an economic and efficient alternative to distillation for the separation of chemicals. It is typically used in purification applications where distillation becomes difficult.
Applications of Melt Crystallization
For example, melt crystallization can be used to separate:
· Isomers with close boiling points
· Azeotropic systems
· Temperature sensitive substances
· Components that tend to polymerize
· Explosive substances
Typically, crude product is cooled in scraped surface crystallizers, which might be exchanger type or vessel type crystallizers, depending on the specific application. The crystallizer produces pure product crystals and concentrates the impurities in the remaining liquid mother liquor. The crystals are then separated from the impurity rich mother liquor producing a pure product stream and a reject stream. The reject contains the concentrated impurities but also valuable product which may be recovered, depending on the specific application.
Each individual crystal is suspended in the mother liquor and is allowed to grow free flowing in the liquid. With billions of crystals per cubic meter the growth surface can reach 5,000 to 10,000 m² per m³ of volume. This massive growth surface allows near ideal growth rates that result in the characteristic pure crystals expected from the eutectic crystallization process. The crystallizer suspension is pumped into a wash column where the pure crystals are separated and then washed to remove any remaining mother liquor. Suspension based crystallizers produce pure crystals. Wash columns can effectively remove all of the mother liquor and thereby produce ultra-high purity product.