Bultmann's Roll Compaction-site
on Dry Granulation

ROLL COMPACTION VERSUS OTHER TECHNOLOGIES

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	+	+	+	+
Technology
Characteristics	Friction High energy input Heat	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
Granules
Granule characteristics	Dense granules	Porous, fragile granules	Higher amount of fines	-

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