12 ANALYTICAL AND LABORATORY EQUIPMENT
Spray drying with a three channel nozzle
Micheal Whelehan, Philipp John and Nurhan T Dunford examine the production of core-shell microcapsules by spray drying using a 3-Fluid nozzle in a single step process.
F
or more than 50 years spray drying has been successfully employed in a vast number
of scientific and/or industrial applications as a simple, efficient, reliable and scalable technique to convert aqueous or organic solutions, emulsions, dispersions and suspensions (for convenience all will be referred to as liquid /spray solutions for the rest of this article) into a dry powder.
For the process different nozzle systems can be employed and the one selected will depend on the requirements of the user. For example, at an industrial level a rotary disc nozzle is mainly employed, while for laboratory scale research and pilot scale production a 2-Fluid nozzle is commonly used1
.
Te latter nozzle system consists of an inner and outer channel (Fig. 1a) and during operation a liquid solution is pumped through the inner channel to the nozzle tip where it is atomised by compressed air/nitrogen flowing through the outer channel. Tis procedure results in the formation of fine droplets, which are subsequently dried using hot gas to form a powder.
While spray drying is mainly considered as a ‘dehydration process’, it has been demonstrated that it can
Fig. 1. Schematic of the operational principle of different nozzle configurations for a standard lab scale spray dryer, and the type of particles produced from each system. (a) Operation of conventional 2-Fluid nozzle system to convert a liquid solution into a dry powder. (b) Employment of the 2-Fluid nozzle system to encapsulate a material within the produced powder. (c) Operation of the 3-Fluid nozzle to directly produce core-shell capsules. The schematic is a representation of the lab scale spray drying system and nozzle configurations supplied by BÜCHI Labortechnik AG1
.
also be employed as a viable encapsulation technique. Spray drying is the oldest microencapsulation technique employed within the food industry1-3
. In this
operation the ‘active material(s)’ is dissolved/ suspended in the spray solution and becomes entrapped within the powder matrix during the drying process (Fig. 1b); the produced particles are commonly referred to as ‘matrix microcapsules or microbeads’3
.
Tis approach has been very successful and enabled the encapsulation of thousands of different products; from pharmaceuticals, bioactives, essential oils, aroma compounds and food additives, providing the encapsulated material with a myriad of benefits4
.
Nevertheless spray drying as an encapsulation process is not without its disadvantages, and can result in relatively low loading of the encapsulated material, as well as insufficient protection of labile
and sensitive products1,5
(due to
emulsion preparation and/or surface exposure on the dry microbead). Tese drawbacks have prevented the technology from being used to encapsulate numerous sensitive and high value products for biotechnology, medical, cosmetic and food industries.
To overcome the above problems, BÜCHI Labortechnik AG has
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