Process characterisation of continuous ring layer wet granulation at small scale

Ring layer granulation is a wet granulation process, which can be applied for the continuous production of pharmaceutical granules as an alternative to other continuous granulation techniques like twin screw granulation or continuous fluidised bed granulation. However, the ring layer process itself has so far been the subject of only little fundamental scientific investigation. Additionally, for the few published studies, medium to large scale ring layer granulators were utilized for which large quantities of sample material was necessary. This shortfall is addressed in the present study, in which the unique lab scale ring layer granulator Granucon®1, giving the possibility of small scale experiments and production campaigns, was investigated. The ring layer process was studied for the wet granulation of microcrystalline cellulose, an insoluble primary material, with variation of the process parameters tip speed, binder supply rate and solid feed rate. Moisture content showed the most significant effect on the granulation results, while shaft speed and solid feed rate influence the residence time of the granules inside the ring layer granulator. Further, while a certain shaft speed had to be reached for the ring layer to form, it also had a strong effect on the granule morphology due to its effect on the mechanical stress acting on the granules.