Spray drying materials

Most spray-dried instant coffees have been marketed in a granular form, rather than the small spherical spray-dried form, since the mid-1960s. The granular appearance is achieved by steam fusing the spray-dried material in towers similar to the spray drier. Belt agglomerators are also common. 

The physical properties of spray-dried materials are subject to considerable variation, depending on the direction of flow of the inlet gas and its temperature, the degree and uniformity of atomization, the solids content of the feed, the temperature of the feed, and the degree of aeration of the feed. The properties of the product usually of greatest interest are (1) particle size, (2) bulk density, and (3) dustiness. The particle size is a function of atomizer-operating conditions and also of the solids content, liquid viscosity, liquid density, and feed rate. In general, particle size increases with solids content, viscosity, density, and feed rate. 

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. 

Microencapsulation using extrusion is mainly described for glassy carbohydrate matrices [14-16, 28-29]. The glassy carbohydrates, such as starch and maltodextrins, are melted at elevated temperature and low water contents and are intensively mixed with the active in the extrusion barrel. Extrusion has been used for volatile and unstable flavours. The shelf life of flavour oils could be extended from several months to 5 years, compared with 1 year for spray-dried materials. The main drawbacks of the technology are the high investments costs and the formation of rather large particles (500-1,000 pm). 

The Maillard reaction is more susceptible with amorphous lactose than with crystalline lactose therefore, this reaction is expected to be more of a concern for spray-dried material (80). Since the reaction is acid/base catalyzed, it is ideal to maintain a neutral pH environment with lactose-based products. 

Dense gas IM samples were precipitated from dimethylsulfoxide solutions using carbon dioxide as an antisolvent, while spray dried products were generated from insulin suspensions in mannitol aqueous solutions. Dense gas and spray dried IMC samples were produced from aqueous solutions in the DG antisolvent process carbon dioxide modified with ethanol was used as an antisolvent. The particle size of DG processed formulations was substantially larger than the corresponding spray dried material for both IM and IMC samples 21.8 vs. 5.71pm and 11.9 vs. 7.24pm, respectively, as measured by laser diffraction of the dry powders. The aerosol performance of DG processed IMC formulations, however, was superior to the spray dried counterpart, as measured by impactor studies. In fact, the RF of the DG processed IMC was 47.6%, while spray dried IMC had an RF of 30.0%. The aerosol performance of IM samples followed an opposite trend with the DG product exhibiting an RF of 26.6% and the spray dried of 30.6%. ... 

Duflie JA, Marshall WR, Jr. Factors influencing the properties of spray-dried materials. Part I. Vol. 49. Chem Eng Proc, 1953 8 417 23. 

Sebhatu et al. studied the tableting characteristics of spray-dried lactose [52], which typically contains 15% amorphous material. The spray-dried material is known to absorb moisture when exposed to high... 

Figure 2.8. Emulsion PVC. A particles dried by a flow of hot air, 3750x B nozzle sprayed material, 140x C spray-dried material, 3750x. [Courtesy of Wacker-Chemie GmbH, Buighausen, Germany.]...

Operating Parameters for Some Spray-Dried Materials... 

Raehse, W. and Bauer, V., Process for spray drying materials and mixtures thereof using superheated steam, US Patent 5431780, 1995 Maa, Y.F., Nguyen, P.A., Sweeney, T., Shire, S.J., and Hsu, C.C., Protein inhalation powders Spray drying versus spray freeze drying. Pharm. Res., 1999,16, 249-254. 

Lankinen, T., Haijunen, R, Jarvinen, K., Paronen, R, and Lehto, V., Conversion of amorphous material to a corresponding crystalline material hy spray drying and utilization of the crystalline spray dried material in dmg formulations, 2003, PCT publication number WO 03/094892. 

Fluffy spray-dried material can be compacted into articles having a larger particle size and higher bulk density by the application of mechanical pressure or force. The compaction can be accomplished by known means such as tabletting presses and briquetting machines, but preferably by passing the powder between rotating rolls. 

The sucroglycerides also have an anticaking effect as well as an antioxidant effect, thus helping to increase the storage time of the spray dried material. 

Spray drying As an extraction solvent, SCF can be used to extract residual solvents from spray-dried material. 

Downstream considerations will be similar to spray-dried material. 

Particle properties are related to the drying kinetics of the droplets inside the drying chamber and are primarily dependent on the mechanical and chemical properties of the spray-dried material. These interactions are very complex to model, and therefore, process development is typically ruled by some general trends, as described below (see Fig. 8.17). The parameters that most influence particle morphology are Tout (or RSout) and Cfeed- Note that by adjusting the droplet size produced during the atomization process, one can control the particle size in such a way that size and morphology become almost independent of each other. 

Phenytoin ASD prepared with PVP K 30 using compressed antisolvent process was compared to ASD produced by spray drying process (Muhrer et al. 2006). After ensuring that both were amorphous, dissolution profile of both were compared. Based on in vitro dissolution, the performance of the SAS- based material was at least 25 % better than the spray-dried material which can be attributed to better control of particulate properties such as morphology and particle size distribution, in SCF. 

The crystallinity of spray dried SBS particles was examined according to the method described above (Sect. 2.2.13). Spray dried material was compared to micronised SBS. Bud data is not shown here. 

Keeping materials of any sort absolutely dry is very difficult given that most materials absorb moisture from the atmosphere, and this is particularly true of amorphous materials where water molecules can more easily penetrate and surround the host molecules than in a crystalline material. Furthermore freeze-dried or spray-dried materials are not completely dry when produced, and contain variable amounts of moisture depending upon the production conditions. This directly affects the stability of these materials, and it is important to measure the Tg, plasticised by the moisture content, to determine the actual value as it would be found in storage. 

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