EXPERIMENTATION AND MODELING OF PHARMACEUTICAL LYOPHILIZATION USING A PILOT-PLANT

Freeze-drying is the process whereby a solvent (usually water) is removed from a frozen solution or a frozen foodstuff by sublimation. Since freeze-drying is a low-temperature process during which the chemical alteration of the products is minimized, it has several advantages over competitive desiccation processes, especially when used for biological materials, pharmaceuticals and temperature-sensitive products. In this study, the lyophilization process was carried out on a frozen solution of cloxacillin monosodium salt using a pilot plant. Experimental drying rate values are presented; the variables considered include solute concentration, product thickness, temperature of the heating plate and pressure in the drying chamber. The primary drying rate is strongly influenced by the concentration, the heating plate temperature and pressure, but only slightly influenced by the product thickness. The secondary drying rate can be interpreted using a first-order lumped model, whose kinetic constant seems to be independent of the variables examined. A physical model is proposed for heat transfer between the heating plate and the tray containing the product, based on Knudsen conduction in a thin layer and is compared successfully with the experimental data.