Difference Between Dry and Wet Granulation

Main Difference – Dry vs Wet Granulation

Granulation is the process of producing grains or granules. The size of a granule is typically in the range 0.2 – 4.0 mm. This term is often used in pharmaceutical industry since granulation is the process used in the production of tablets. There are three types of granulations as dry granulation, wet granulation, and direct blending. The main difference between dry and wet granulation is that dry granulation is the formation of granules without using any liquid solution whereas wet granulation is the formation of granules by adding a granulating liquid.

Key Areas Covered

1. What is Dry Granulation
     – Definition, Process
2. What is Wet Granulation
     – Definition, Process
3. What is the Difference Between Dry and Wet Granulation
     – Comparison of Key Differences

Key Terms: Dry Granulation, Ethanol, Granulation, Granule, Isopropanol, Pharmaceutical, Roll Compactor, Tablet, Tablet Press, Wet Granulation

What is Dry Granulation

Dry granulation is a process where no liquid component is used in the granule formation. This is done for compounds that are extremely sensitive to moisture and heat. Since no liquid is used, the process requires compacting and densifying the finely powdered compound to convert it into granules.

In dry granulation, granules are formed under a high pressure. The powder of the compound is aggregated using a high pressure. Dry granulation is done with a tablet press (swaying/high shear mixer-granulators) or roll compactors. The dry granulation can be done in two different ways:

1. Formation of a large tablet
2. Formation of a continuous sheet

Figure 1: Tablet Pressing Operation

Large tablets are made via dry granulation, using a heavy duty tableting press. Continuous sheets are produced using roll compactors, by squeezing the powder through two rollers. However, the tablet press may not give tablets with uniform density; this is because the powder has doesn’t have sufficient natural flow since there is no solvent. But in producing continuous sheets, the roller compactors use specific systems that can consistently feed the powder through two rollers. This gives a uniform sheet. When the sheet is compact enough, it can be used for tablet compression after going through proper milling and final blending.

What is Wet Granulation

Wet granulation is the process in which formation of granules is done by adding a granulating liquid. Here, a granulating fluid is used for the massing of powder particles. However, the fluid used here is essentially volatile and non-toxic. It should be volatile because only a volatile fluid can easily be removed by drying the final product. It should be non-toxic because this granulation is used in the production of tablets that are used to treat certain diseases.

The liquids that are often used as granulating fluid include water, ethanol, and isopropanol. Sometimes these solutions are used in combination as well. When water is used in this process, water can be mixed with the powder, forming bonds between powder particles. But if the granule falls apart when dried, water is not a suitable granulation fluid. Therefore, a bonder is also used along with water.

In the traditional method, the wet mass is forced through a sieve to produce granules which are then dried. When water-sensitive drugs are produced, an organic solvent is used in the place of water. Wet granulation is preferred than direct compression into tablets since direct compression can cause the destruction of active components in the powder.

Difference Between Dry and Wet Granulation

Definition

Dry Granulation: Dry granulation is the process of forming granules without using any liquid solution. 

Wet Granulation: Wet granulation is the process of forming granules by adding a granulating liquid.

Process

Dry Granulation: Dry granulation involves the direct compression of a finely ground powder.

Wet Granulation: Wet granulation involves mixing the powder with a granulating fluid, followed by forcing through a sieve to make tablets.

Components

Dry Granulation: Dry granulation requires finely powdered compound and tablet pressers or roll compactors.

Wet Granulation: Wet granulation requires powder particles, a granulating fluid, and a sieve.

Importance

Dry Granulation: Dry granulation is required when producing tablets from highly moisture and heat sensitive compounds.

Wet Granulation: Wet granulation is required to avoid the destruction of active components in the powder.

Conclusion

Granulation is a major process used in the production of tablets in the pharmaceutical industry. There are three major types of granulations used. Dry granulation and wet granulation are two of them. The main difference between dry granulation and wet granulation is that dry granulation is the process of forming granules without using any liquid solution whereas wet granulation is the process of forming granules by adding a granulating liquid.

Reference:

1. “Granulation (Process).” Wikipedia, Wikimedia Foundation, 9 Jan. 2018, Available here.
2. “Wet Granulation Advantages And Disadvantages Biology Essay.” UKEssays, Available here.

Image Courtesy:

1. “Tablet press animation” By Jeff Dahl – Own work (GFDL) via Commons Wikimedia
2. “Four colors of pills” By Ragesoss – Own work (CC BY-SA 3.0) via Commons Wikimedia