Laboratory-scale freeze-dryers

Modem laboratory-scale freeze-dryers include additional devices for improved safety. Some avoid condenser overload or power outages. 

Bursae et al (2009), and more recentiy Konstantinidis et al. (2011), presented an effective method to control ice nucleation, namely the depressurization method. In this case, vials are loaded onto the freeze-dryer and pressure is increased above atmospheric level by 1.7-2 bar by the bleeding of inert gases at high pressure. The solution is then cooled to a desired temperature and pressure is decreased to induce ice nucleation simultaneously in all vials. Konstantinidis et al. (2011) showed that this method can be applied to both laboratory-scale and production-scale freeze-dryers. If the freeze-dryer can withstand pressures higher than atmospheric value, then the method can easily be implemented otherwise, it wUl be necessary to modify the equipment to support overpressure, and this can be expensive. In this situation the application of a different method for ice nucleation control is suggested. 

The various modes in which microwaves are used in the industry comprised of booster (microwave-connection) and dryers (microwave vacuum dryers and microwave freeze dryers). Microwave vacuum drying of cranberries was investigated using laboratory-scale dryer operating either in continuous or pulsed mode [38]. Pulsed application of micro-wave energy was found to be more efficient than continuous application. 

Currently, we use two production freeze-dryers, both manufactured by Serail, a CSlOO (usable capacity 20,000 ampoules or 10,000 vials) and a CS15 (capacity 4000 ampoules or 1000 vials). For development work we have a laboratory-scale Virtis Genesis. We can then further dry materials at room temperature by exposure to phosphorus pentoxide under vacuum using either an Edwards Lyomax 5 freeze-dryer or a holding tank system. 

For the preparation of co-precipitated, e.g. mixed metal oxide, catalysts, the drying step cannot be carried out satisfactorily in the preparation robot. Usually a spray drying step is applied in the production of this kind of catalyst, because the liquid phase of the precipitate suspension still contains dissolved salts that are essential for the catalytic performance. Hence, the suspension must not be filtered off nor can be dried by evaporation due to crystallization reasons. Since there are no laboratory spray-dryers available for that sample size, another method had to be implemented and was found in the freeze drying of these materials [4]. With this method almost the same is done like in spray diying but on another time-scale. Where a spray drier evaporates the water very quickly and thereby prevents the crystallization of the still dissolved salts, Ihe freeze drier literally at first freezes the solution and no crystallization can occur while the water is sublimated. Hence, an identical product is obtained. 

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