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Drying

The purpose of the drying operation is to produce a dry powder to use in the dry product manufacturing process. The type of dryer used depends on the pharmaceutical being produced. The most common dryers used in this step are fluid bed dryers, tray dryers, rotary dryers, and filter dryers.

Fluid Bed Dryers

In a fluid bed dryer , a heated gas is blown through a filter cake, evaporating the solvent. This gas stream has to be passed through a filter to prevent contamination of the solid. The dryer uses a perforated basket to hold the filter cake and to allow gas to pass through. While the basket can be filled by hand, gravity-fed process are preferred to reduce the chance of product contamination.

fbd.JPG

(Copyright GEA Process Engineering Inc., Columbia, MD)

Tray Dryers

Thin layers of filter cake are placed atop trays inside a tray dryer to evaporate the solvent. Heat is provided by a single fluid system inside of a jacket that operates at temperatures of 40°C-100°C. Liquid ring pumps or dry vacuum pumps generate a vacuum inside of the tray dryer. In most pharmaceutical plants a dust filter is fitted on the dryer to prevent contamination from the outside. The problem with this type of dryer for many active pharmaceutical ingredients is low efficiency, messy loading, and that hard lumps of the API can form on the trays.

tray.JPG

(Copyright of Powder Systems Limited, registered in England no. 2233044)

Rotary Dryers

Rotary dryer are the most widely used in manufacturing of the API because of their high efficiency, resulting in low drying times. These dryers consists of a horizontal cylindrical chamber and are often fitted with a heating and cooling jacket. They have a slow paddle that rotates the solid continuously to enhance heat exchange. The heating jacket also has to have high surface area to volume ratio for most efficient heat exchange.

rotary.JPG

(Copyright R. Simon (Dryers) Ltd., Nottingham, UK)

Spray Dryers

All spray dryers used in pharmaceutical processes pass the gas through a filter to ensure that it is clean when it comes in contact with the drug. The outlet gas is also passed through a filter so that the rest of the plant is not contaminated. Nitrogen or air is used as the drying gas when the drug is recovered using inorganic solvents. Nitrogen is used to dry organic solvents in a closed configuration. The temperature, pressure, and other operational parameters depend on the solvent being dried.

spray.JPG

(Copyright GEA Process Engineering Inc., Columbia, MD)

Filter Dryers

A filter dryer combines a nutsche filter with a tray dryer to combine the filtering and drying steps. So the nutche filter operates as usual but is fitted with a heating jacket and vacuum pump to dry the material.

filter.JPG

(Copyright of Powder Systems Limited, registered in England no. 2233044)

Acknowledgements

GEA Process Engineering Inc. , Columbia, MD

Powder Systems Limited. , England no. 2233044

Pfaudler, Inc. , Rochester, NY

R. Simon (Dryers) Ltd. , Nottingham, UK

Water Technologies Business Unit of Siemens Industry, Inc. , Warrendale, PA

References

Bennett, Bill and Cole, Graham. Pharmaceutical Production: An Engineering Guide. United      Kingdom: The Institution of Chemical Engineers, 2002. Print.

"Pharmaceutical Spray Dryers - PHARMASD™." GEA Pharma Systems. GEA Process Engineering,      Web. www.gea-ps.com.

Developers

Thomas Plegue

Howard Hsu