Ageing of spherulites of an industrial relevant aromatic amine derivative

Polycrystalline spherulites of an aromatic amine derivative have been precipitated in a batch process by pHshift with hydrochloric acid from stirred aqueous solutions. The time dependent behaviour of the spherulites has been studied during crystallization in the temperature range from 5 °C to 60 °C. Cake resistance values have been obtained from batch filtration tests performed at 2 bar pressure difference at different stages of the crystallization process. The FBRM mean chord length of the crystals decreases with time as a result of crystal ageing into plate-like crystals. The rate of the ageing process increases with temperature. XRD-studies show no significant differences in the crystal structure during the ageing process, and the mechanism of the transformation was not established. The filterability of aromatic amine crystals deteriorates as the crystallization progresses. The decrease in the filterability is attributed to the appearance of small plate-like crystals and a change in the interaction between the crystal surface and the solution, during the ageing of the particles.