Bultmann's Roll Compaction-site
on Dry Granulation


Next to direct compression, there are mainly two commonly used wet granulation methods for converting powders into tablets: High shear mixer granulation (HSMG) and fluidized bed granulation (FBG). Next to them roll compaction (RC) is to be mentioned, which represents the dry granulation method. The absence of water directly leads to the main advantages of roll compaction over the other two granulation methods:
Since no liquid (usually water, therefore referred to as water in the following paragraphs) is used, no granulation liquid has to be prepared beforehand. Also a wetting step can be neglected. Thus no additional drying step is required and investments in drying capacity (time, expenses, space) are unnecessary. This is the cause for a high throughput of the small dry granulation equipment (expressed in kg per hour per kg or m³ of overall equipment). Furthermore dry granulation is a continuous process that can be run in batch mode, while the other granulation methods usually run in batch mode and do not allow a conti-process. Scale up of dry granulators by the same manufacturer is quite easy compared to HSMG or FBG, which will be shown later. Except for electrical connections (e.g. typical power requirements for production machines are less than 10kW), no additional supplies such as hot air or pressurized air are needed to start roll compaction.
The absence of water also causes the roll compaction’s biggest problem: No capillary forces can contribute to binding forces within the granule particles. Granule formation has to take place only by means of the powder particle’s own compressibility. Therefore excipients will have to be used that assure good compactability during dry granulation and subsequent tabletting. The missing of capillary forces also contributes to the comparably higher number of fines usually found in granules produced by dry granulations in comparison to wet granulation.

Table: Comparison of different processing technologies
(HSMG: High shear mixer granulation, FBG: Fluidized bed granulation, RC: Roll compaction, DC: Direct compression)

Processing Technology HSMG FBG RC DC
Unit operations

Preblending + + + +
Preparation of granulation liquid + +    
Agglomeration / desagglomeration + + +  
Drying + +    
Tabletting + + + +

Characteristics Friction
High energy input
Requires fluidizable powder,Risk of explosion,High energy input Requires good compactibility Requires good flow,Requires good compressibility
Equipment size (including supply) Large Very large Small Small
Throughput (kg per day/machine weight) Acceptable Small (very) high  Very high
Scale up Tricky Tricky Easy Easy at low speed
Additional supply Electricity, water, evtl. drying equipment for single pot processing such as microwave, vacuum and/or nitrogen Electricity, water, pressurized air, hot air (preferrably conditioned) Electricity Electricity
Batch size Batch Batch Continuous Continuous

Granule characteristics Dense granules Porous, fragile granules Higher amount of fines -