Spray drying
Air is most commonly used as the heated drying medium; however, nitrogen may be used if the liquid is flammable (such as ethanol) or if the product is oxygen-sensitive.
[citation needed] The fine powders generated by the first stage drying can be recycled in continuous flow either at the top of the chamber (around the sprayed liquid) or at the bottom, inside the integrated fluidized bed.
A spray dryer takes a liquid stream and separates the solute or suspension as a solid and the solvent into a vapor.
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.
They also turn a solution (or slurry) into a dried powder in a single step, which simplifies the process and improves profit margins.
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.
The small size of the drops (averaging 100 micrometers in diameter) results in a relatively large surface area which dries quickly.
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.
Thermal degradation of products can be overcome by using lower operating temperatures and larger chamber sizes for increased residence times.
[8] 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.
[9][10] The spray drying process contains a variety of input parameters that can alter the shape and size of yielded particles.
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.
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.
A ) Solution or suspension to be dried in; B ) Atomization gas in; 1 ) Drying gas in; 2 ) Heating of drying gas; 3 ) Spraying of solution or suspension; 4 ) Drying chamber; 5 ) Part between drying chamber and cyclone; 6 ) Cyclone ; 7 ) Drying gas is taken away; 8 ) Collection vessel of product.
The arrows indicate that this is co-current lab-spraydryer.
