Granulation technology: complete guide to wet granulation, dry granulation and fluid bed
Granulation: from powder to processable granulate
Granulation is the process in which fine powder particles are combined into larger, stable agglomerates (granules). The goal is to improve the processing properties of the powder: better flowability for dosing systems and tablet presses, higher bulk density for more compact storage and transport, improved compressibility for tableting, and reduced dust formation with hazardous substances. Granulation is a central step in pharmaceutical solid dosage form production and is also applied in food, chemistry and fertiliser production.
Wet granulation: the most widely used granulation technique
In wet granulation, powder particles are combined by adding a binder solution (granulation liquid). The binder (gelatine, PVP, HPMC, hydroxypropyl cellulose) forms bridges between particles that yield stable granules after drying. Wet granulation takes place in:
- High-shear mixer-granulator: intensive mixing and granulation in a single vessel; short process time (10–20 min); suitable for APIs requiring robust granulation
- Fluid bed granulator: powder is suspended in a fluidised bed while binder solution is sprayed on; gentler process; simultaneous granulation and drying
- Twin-screw granulator: continuous processing; high formulation flexibility; suitable for continuous manufacturing lines
Wet granulation is not suitable for moisture-sensitive or thermolabile APIs.
Dry granulation: for moisture-sensitive products
In dry granulation, powder particles are compressed together without adding liquid. The two most commonly used methods are:
- Roller compaction: powder is compressed between two counter-rotating rollers into compact ribbons, which are then milled into granulate. Scalable, continuous processing, broadly applicable
- Slugging: powder is first compressed into large tablets (slugs) and then milled. Less efficient than roller compaction; increasingly less used
Fluid bed technology: granulating and drying in one step
Fluid bed processors can granulate, coat and dry in the same equipment. An upward airflow keeps the material suspended while a spray nozzle applies binder or coating. Fluid bed technology offers high process flexibility but requires precise control of air volume flow, temperature and spray rate.
Selection criteria for granulation technology
- Moisture sensitivity of the API: moisture-sensitive → dry granulation or fluid bed
- Thermolability: thermolabile → low-temperature fluid bed or dry granulation
- Batch vs. continuous production: continuous production → twin-screw or roller compaction
- Desired granule properties: particle size, density, porosity
- Scale: from gram-scale lab to ton-scale production
Hecht Technology supplies bulk handling systems for granulate processing lines: contained transfer, dosing and transport of granulates for pharma and food. More information: hecht-technology.nl.
Hecht Technology: downstream processing after granulation
After granulation, the granulate often still needs to be dried and brought to the correct particle size. Hecht Technology supplies Nutsche filter dryers for drying moist granulates in a closed, GMP-compliant environment, and the Jett Mill for fine milling or adjusting the particle size distribution after granulation.