Coating of cohesive particles in a fluidized bed reactor by chemical vapor deposition

Fluidized beds are known to offer high heat and mass transfer rates as well as good solids mixing, which are used in classical particle forming processes such as coating, agglomeration, and granulation. In these processes, liquids containing solid materials are sprayed onto the particle bed, leading to a coating of the fluidized particles by drying of the liquid phase.
This paper presents a novel coating process based on chemical vapor deposition (CVD). In this process, fine, cohesive pigment powders are coated with thin carbon layers. These materials are used in the cosmetics industry and show superior visual properties. The coating process was developed by Merck KGaA Darmstadt on a laboratory scale and transferred to production scale with the help of Glatt Ingenieurtechnik GmbH Weimar. In close cooperation, the process was successfully transferred to regular operation. In addition to the development of the project, special challenges in scale transfer and their solutions are presented.