Atmospheric Spray Freeze Drying (ASFD): A New Approach

The ASFD process has been developed as a new method for manufacturing powder by scientists in Edmonton, Canada. The goal was to reduce drying time and operate at atmospheric conditions with reasonable collection efficiency; this work has also been patented. In contrast with other known atmospheric spray-freeze drying technologies, this new technology combines spray freezing, deposition / collection, and convective flow drying into one step employing co-current gas flow to spray-freeze the solution, convey the frozen powder towards an exit filter and in situ drying. This overcomes the difficulty of fluidizing and elutriating a cohesive frozen powder from a substrate. In this process, a powder cake with uniform thickness builds up on the exit filter after spray-freezing and conveying. The drying of the frozen powder cake follows via streaming a dry gas through the exit filter whilst keeping the temperature below the critical product temperature of the formulation. After drying, the loose free-flowing powder cake can be collected on top of the exit filter at the completion of the process. Atmospheric pressure freezedrying (ASFD) may therefore be feasible in a wide variety of materials whose solution/suspension can be sprayed, frozen, and dried into a powder cake.