Agglomeration Advisor: To spray or not to spray: What controls wetting in wet granulation processes?
A key decision you must make in granulation is whether solvent or binder liquid should be sprayed or simply pumped onto the powder bed. To make this decision, you must consider how wetting and nucleation contribute to overall agglomerate growth.
Agglomeration processes can be loosely broken down into agitation and compression methods. Although terminology is industry-specific, I'll refer to agglomeration by agitation as granulation. This month's column will focus on wet granulation.
In this process, a particulate feed is introduced to a process vessel, either in batches or continuously, to form granules. (The term granulation as used here includes pelletization or balling as found in the iron ore industry, but doesn't include using screening to break down compacts as is found in some tableting industries.) Granulation equipment includes fluid-bed, disc, drum, and mixer granulators as well as many hybrid designs. The feed typically consists of a mixture of solid ingredients (the formulation), including a key ingredient (called the active product ingredient, API, or technical ingredient), binders, diluents, flow aids, surfactants, wetting agents, lubricants, fillers, or end-use aids (such as sintering aids, colors or dyes, and taste modifiers).