Sublimation drying

Freeze-drying or dehydrating equipment for sublimation drying of ... 

FREEZE-DRYING OR DEHYDRATING EOUIPMENT FOR SUBLIMATION DRYING OF ... 

In a 1-L three-necked round-bottomed flask and under an atmosphere of nitrogen, a suspension of Os3(CO)12 (0.5 g, 0.55 mmol)4 is prepared in acetonitrile (750 mL), freshly distilled from a slurry of phosphorus pentoxide under nitrogen. To ensure dissolution of the maximum amount of Os3(CO)12, the suspension is heated under reflux for 1 h. The solution is then allowed to cool to room temperature, and under a nitrogen atmosphere, a solution of freshly sublimed, dry trimethylamine oxide (42 mg, 0.55 mmol) in acetonitrile (200 mL) is added to the stirred suspension over a period of 4h using a pressure-equalized dropping funnel. 

Kabatov, A.I., Nikonov, B.A., Sventitskii, E.N., Afanasi, E.S. Working out the means of recreating the biological activity of Saccharomyces cerevisiae yeast at sublimation drying. Biotekhnologiya (1), 45—46,1991... 

M. Roy and M. J. Pikal, Process control in freeze-drying determination of the end point of sublimation drying by an electronic moisture sensor. J. Parent. Sci. Technol. 43(2) 60-66 (March-April 1989). 

Freeze drying, i.e., sublimation drying of the ice content and desorption drying of the bound or crystal water content... 

The operation vacuum should be reached quickly (within 10 min) to avoid the risk of product melting. For the same reason, the heating plates are cooled to approximately 25°C. When the operation vacuum is achieved, the heating plate temperature is raised quickly to the maximum drying temperature restricted by the capacity of the vapor traps, to perform the sublimation drying as quickly as possible for capacity reasons. During this period, the product is kept cool by the sublimation, and approximately 75 to 80 percent of the free water is sublimated. 

At the end of the sublimation drying, the product surface temperature reaches the maximum allowable product temperature, requiring that the temperature of the heating plates be lowered gradually, and the drying will change to desorption drying. The temperature will finally be kept constant at the level of the maximum allowable product temperature until the residual moisture has been reduced to 2 to 3 percent, which is a typical level for a freeze dried product. 

Continuous freeze drying From the description of batch freeze drying, it can be seen that the utihty requirements vary considerably. During sublimation drying the requirements are 2 to 2.5 times the average requirement. To overcome this peak load and to meet the market request for high unit capacities, continuous freeze dryer designs have been developed. The special features are twofold ... 

Fig. 2 Diagram depicting the phase paths of critical point drying and freeze- sublimation drying. Note that neither of these processes involve crossing the liquid-vapor line. (View this art in color at www.dekker.com.)...

Recall from Chapter 4 that one property of carbon dioxide is that it changes directly from a solid (dry ice) to a gas. In other words, it sublimes. Can you determine some properties of gases from sublimed dry ice ... 

MiniLab 1 How might you accormt for the possible popping of the bag containing the subliming dry ice ... 

How does the entropy of a system change for each of the following processes (a) condensing water vapor, (b) forming sucrose crystals from a supersaturated solution, (c) heating hydrogen gas from 60°C to 80°C, (d) subliming dry ice... 

---