Purification potential of melt crystallisation

A heated filter centrifuge was used to purify crystals grown in an organic melt. The centrifugation proved as a very efficient method to separate the mother liquor from the crystals in respect to filtration and draining. Crystals of a mixture of diphenyl and naphthalene are produced by different crystallization techniques (suspension, layer, solidification) in order to vary the process conditions (cooling rate) in a wide range. The purity of cystals depends on thermodynamics, on the equilibrium distribution of impurities, kinetics (e.g. growth rate), and the quantity and concentration of the impurities. plication of centrifugation in combination with sweating and washing processes leads to high purities. The purity of a melt containing an initial concentration of 80 mass% could be improved in one step to >99 mass%. Further on the growth conditions have a minor influence on the purity, in case the centrifuging and sweating process is used. ese purpose a new type of purification technology (combination of a high speed solidification unit and a heated filter centrifuge) is presented.