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History

The spray drying technique was first described in 1860 with the first spray dryer instrument patented by Samuel Percy in 1872. With time, the spray drying method grew in popularity, at first mainly for milk production in the 1920s and during World War II, when there was a need to reduce the weight and volume of food and other materials. In the second half of the 20th century, commercialization of spray dryers increased, as did the number of spray drying applications.

Spray dryer

A spray dryer takes a liquid stream and separates the solute or suspension as a solid and the solvent into a vapor. The solid is usually collected in a drum or cyclone. The liquid input stream is sprayed through a nozzle into a hot vapor stream and vaporized. Solids form as moisture quickly leaves the droplets. A nozzle is usually used to make the droplets as small as possible, maximizing surface area hence heat transfer and the rate of water vaporization. Droplet sizes can range from 20 to 180 μm depending on the nozzle.⁶ There are two main types of nozzles: high pressure single fluid nozzle (50 to 300 bars) and two-fluid nozzles: one fluid is the liquid to dry and the second is compressed gas (generally air at 1 to 7 bars).

Spray dryers can dry a product very quickly compared to other methods of drying. They also turn a solution (or slurry) into a dried powder in a single step, which simplifies the process and improves profit margins.

In pharmaceutical manufacturing, spray drying is employed to manufacture Amorphous Solid Dispersions, by uniformly dispersing Active Pharmaceutical Ingredients into a polymer matrix. This state will put the active compounds (drug) in a higher state of energy which in turn facilitates diffusion of drug species in patient body.⁷

Micro-encapsulation

Spray drying often is used as an encapsulation technique by the food and other industries. A substance to be encapsulated (the load) and an amphipathic carrier (usually some sort of modified starch) are homogenized as a suspension in water (the slurry). The slurry is then fed into a spray drier, usually a tower heated to temperatures above the boiling point of water.

As the slurry enters the tower, it is atomized. Partly because of the high surface tension of water and partly because of the hydrophobic/hydrophilic interactions between the amphipathic carrier, the water, and the load, the atomized slurry forms micelles. The small size of the drops (averaging 100 micrometers in diameter) results in a relatively large surface area which dries quickly. As the water dries, the carrier forms a hardened shell around the load.⁸

Load loss is usually a function of molecular weight. That is, lighter molecules tend to boil off in larger quantities at the processing temperatures. Loss is minimized industrially by spraying into taller towers. A larger volume of air has a lower average humidity as the process proceeds. By the osmosis principle, water will be encouraged by its difference in fugacities in the vapor and liquid phases to leave the micelles and enter the air. Therefore, the same percentage of water can be dried out of the particles at lower temperatures if larger towers are used. Alternatively, the slurry can be sprayed into a partial vacuum. Since the boiling point of a solvent is the temperature at which the vapor pressure of the solvent is equal to the ambient pressure, reducing pressure in the tower has the effect of lowering the boiling point of the solvent.

The application of the spray drying encapsulation technique is to prepare "dehydrated" powders of substances which do not have any water to dehydrate. For example, instant drink mixes are spray dries of the various chemicals which make up the beverage. The technique was once used to remove water from food products. One example is the preparation of dehydrated milk. Because the milk was not being encapsulated and because spray drying causes thermal degradation, milk dehydration and similar processes have been replaced by other dehydration techniques. Skim milk powders are still widely produced using spray drying technology, typically at high solids concentration for maximum drying efficiency. Thermal degradation of products can be overcome by using lower operating temperatures and larger chamber sizes for increased residence times.⁹

Recent research is now suggesting that the use of spray-drying techniques may be an alternative method for crystallization of amorphous powders during the drying process since the temperature effects on the amorphous powders may be significant depending on drying residence times.¹⁰¹¹

Designing particle shape and size

The spray drying process contains a variety of input parameters that can alter the shape and size of yielded particles.

Common input parameters:

1. Solution Concentration
2. Drying Gas Flow
3. Inlet Temperature
4. Spraying Gas Flow
5. Feed Rate

From the following input parameters comes a series of pathways a particle can take towards its yielded shape and size. Certain parameters like spraying gas flow, feed rate, and the solution concentration heavily influence the yielded particle size, whereas the inlet temperature plays a significant role into the shape of the particle at the end. Particle size has a great correlation with the original size of the solution droplet from the atomizer, so the greatest way to control particle size can be done by heavily saturating the solution and making the initial droplet larger or smaller. Once the initial droplet enters the drying chamber, the droplet can continue to crust formation, or no particle will be formed. From the crust formation, the temperature of the drying process and duration of the particle in the drying process can lead the particle toward a dry shell or a deformed particle. The dry shell can proceed into a solid particle or a shattered particle. The crust formation can also forgo the dry shell or deformed particle if the drying conditions are not correct and undergo an internal bubble nucleation with another series of pathways.

The current understanding of the drying conditions varies between different spray drying configurations and solution contents, but more research is being completed into the determination of what drives each particle shape pathways as future applications in pharmaceutical and industrial areas require better control over specific particle shapes and sizes of their products.

Applications

Food milk powder, coffee, tea, eggs, cereal, spices, flavorings, blood,¹² starch and starch derivatives, vitamins, enzymes, stevia, nutraceutical, colourings, animal feed, etc. Pharmaceutical antibiotics, medical ingredients,¹³¹⁴ additives. Industrial paint pigments, ceramic materials, catalyst supports, microalgae.

Bibliography

• Charles Onwulata (2005). Encapsulated and powdered foods. CRC Press. p. 268. ISBN 978-0-8247-5327-6.

Further reading

• Cook, E.M, and DuMont, H.D. (1991) Process Drying Practice, McGraw-Hill, Inc., ISBN 0-07-012462-0
• Keey, R.B., (1992). Drying of Loose and Particulate Materials 1st ed., Taylor & Francis, ISBN 0-89116-878-8
• Nutritional evaluation of food processing second edition (1975), Robert S. Harris, Ph.D. and Endel Karmas Ph.D. (eds)
• Filková, I., & Mujumdar, A. S. (2020). Industrial spray drying systems. In Handbook of industrial drying (pp. 263-307). CRC Press.
• Jafari, S. M., Arpagaus, C., Cerqueira, M. A., & Samborska, K. (2021). Nano spray drying of food ingredients; materials, processing and applications. Trends in Food Science & Technology, 109, 632-646.
• Klimša, V., Ruphuy, G., Jonáš, J., Mašková, L., Kašpar, O., Žvátora, P., & Štěpánek, F. (2023). Spray drying robot for high-throughput combinatorial fabrication of multicomponent solid dispersions. Powder Technology, 428, 118872.

External links

• Animation of standard Spray Drying Concept
• Spray Drying trainings paper

References

1. Campbell, Heather R.; Alsharif, Fahd M.; Marsac, Patrick J.; Lodder, Robert A. (2020). "The Development of a Novel Pharmaceutical Formulation of D-Tagatose for Spray-Drying". Journal of Pharmaceutical Innovation. 17: 1–13. doi:10.1007/s12247-020-09507-4. /wiki/Doi_(identifier) ↩

2. A. S. Mujumdar (2007). Handbook of industrial drying. CRC Press. p. 710. ISBN 978-1-57444-668-5. 978-1-57444-668-5 ↩

3. "Contract Spray Dryer & Spray Drying Services | Elan". http://www.elantechnology.com/spray-drying/ ↩

4. Walter R. Niessen (2002). Combustion and incineration processes. CRC Press. p. 588. ISBN 978-0-8247-0629-6. 978-0-8247-0629-6 ↩

5. Onwulata p.66 ↩

6. Walter R. Niessen (2002). Combustion and incineration processes. CRC Press. p. 588. ISBN 978-0-8247-0629-6. 978-0-8247-0629-6 ↩

7. Poozesh, Sadegh; Lu, Kun; Marsac, Patrick J. (July 2018). "On the particle formation in spray drying process for bio-pharmaceutical applications: Interrogating a new model via computational fluid dynamics". International Journal of Heat and Mass Transfer. 122: 863–876. Bibcode:2018IJHMT.122..863P. doi:10.1016/j.ijheatmasstransfer.2018.02.043. /wiki/Bibcode_(identifier) ↩

8. Ajay Kumar (2009). Bioseparation Engineering. I. K. International. p. 179. ISBN 978-93-8002-608-4. 978-93-8002-608-4 ↩

9. Onwulata pp.389–430 ↩

10. Onwulata p.268 ↩

11. Chiou, D.; Langrish, T. A. G. (2007). "Crystallization of Amorphous Components in Spray-Dried Powders". Drying Technology. 25 (9): 1427–1435. doi:10.1080/07373930701536718. /wiki/Doi_(identifier) ↩

12. Heuzé V.; Tran G. (2016) [Last updated on March 31, 2016, 10:31]. "Blood meal". Feedipedia. a programme by INRA, CIRAD, AFZ and FAO. https://www.feedipedia.org/node/221 ↩

13. Ting, Jeffrey M.; Porter, William W.; Mecca, Jodi M.; Bates, Frank S.; Reineke, Theresa M. (2018-01-10). "Advances in Polymer Design for Enhancing Oral Drug Solubility and Delivery". Bioconjugate Chemistry. 29 (4): 939–952. doi:10.1021/acs.bioconjchem.7b00646. ISSN 1043-1802. PMID 29319295. /wiki/Theresa_M._Reineke ↩

14. Ricarte, Ralm G.; Van Zee, Nicholas J.; Li, Ziang; Johnson, Lindsay M.; Lodge, Timothy P.; Hillmyer, Marc A. (2019-09-05). "Recent Advances in Understanding the Micro- and Nanoscale Phenomena of Amorphous Solid Dispersions". Molecular Pharmaceutics. 16 (10): 4089–4103. doi:10.1021/acs.molpharmaceut.9b00601. ISSN 1543-8384. PMID 31487183. /wiki/Doi_(identifier) ↩