Freeze-drying based on fine-spray produces uniform microspheres
By Scott Jenkins |
A freeze-drying system recently commercialized by ULVAC, Inc. (Chigasaki, Japan; www.ulvac.co.jp) produces spherical particles by spraying a solution into a vacuum chamber. The approach has numerous advantages over conventional freeze-drying, and can be used for generating dry powders in the pharmaceutical, food and electronics industries.
The system works by spraying a solution through a specialized nozzle into a vacuum chamber (diagram) with pressures in the range of 5–30 Pa. As the raw material enters the chamber, it disperses to form droplets of uniform size, since air resistance is virtually zero inside the vacuum chamber. As water evaporates from the droplets, latent heat is removed, and the particles self-freeze into a powder whose size can be controlled within the range of 100–400 µm. The frozen particles settle onto a heated shelf, where the remaining water is removed and product collected. The patented vacuum chamber and heated collection apparatus is designed to reduce drying times and collect over 95% of the dry material.
Among the major advantages of the fine-spray technology is the direct production of a uniform powder, eliminating the need to crush dried material before final packaging. Conventional…