Spray drying process temperature

For example, amorphous clarithromycin was prepared by grind and spray-drying processes, and XRPD was used to follow changes in crystallinity upon exposure to elevated temperature and relative humidity [59]. Exposure of either substance to a 40°C/82% RH environment for seven days led to the formation of the crystalline form, but the spray-dried material yielded more crystalline product than did the ground material. This finding, when supported with thermal analysis studies, led to the conclusion that the amorphous substances produced by the different processing methods were not equivalent. 

The spray drying process is a common technique for particle size enlargement [10] and was applied to create agglomerates in the micron size range from suspensions of nano-particles with different dimensions. The synthesis of the primary particles was carried out like mentioned above with temperature control between 15 and 50 °C. 

The small particle size of the silica is important not only in enabling the silica to flow to the peripheral region of the porous microsphere but also in forming the hard peripheral oxide-rich shell. Particles of silica 2-3 nm in diameter sinter together to some extent even under the temperature conditions encountered in a conventional spray drying process, whereas particles 10-100 nm do not sinter below 700-1000°C. As a result, attrition resistance of the catalyst, catalyst precursor or catalyst support particle is a function of the particle size and degree of aggreggation of the silica formed by dehydration. 

The loss of heat-sensitive material during the spray-drying process has led to a number of alternative methods for dehydration of sprayed microcapsules. Spray-cooling and spray-chilling are similar to spray-drying, where the core material is dispersed in a liquefied coating or wall material and atomized at low temperature. 

The presence of low MW carbohydrates in supports may contribute, via their amorphous state (T < Tg), to possible modification/deterioration of quality and functionality of powders linked with temperature and RH, especially during the spray-drying process and storage crystallization, stickiness, caking (Vega and Roos, 2006). The determination of Tg will be important in predicting the onset of deteriorative reactions. And the choice of supports (proteins adsorption) may help to modify the powder surface (Jayasundera et al., 2009). 

A variation of the spray drying process, known as spray pyrolysis, uses a higher temperature and a reactive (often an oxidizing) environment in the chamber. This allows the salts to be dried and decomposed directly. Figure 20.4 shows the stages in the spray pyrolysis process. In addition to producing powders this technique has been used to produce thin films and fibers. 

The feed must be concentrated as much as possible before spray drying. An example of heat consumption in a spray dryer is given in Figure 9.28, in which two spray drying processes are compared, operating at different temperature ranges and employing different heat sources. 

An addition of 0.5% lactose in a Bacillus alkaline protease spray-drying process is enough to improve the recovery of active enzyme after drying and thermal treatment at 90°C (Table 48.5). In the same way, the exhaust air temperature could be increased by 10°C reaching severe drying conditions without significant loss of protease activity (Table 48.6). The solid enzyme preparation obtained in this process was also excellent in resistance to mechanical pressure [16]. 

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