Wet granulation is defined to be a process in which a liquid solution is added to powders and involves the use of a granulating fluid in massing a mix of primary particles that are dry (Dhenge et al., 2012). The fluid that is used for granulation contains a solvent that must be volatile so that drying can be used to remove it and also be non-toxic (Dhenge et al., 2012). Examples of fluids that are often used as granulating fluids include water and alcohol. It is the most popular method for tablet production since it is possible to apply it to almost any dosage of a drug. The key to the popularity of wet granulation is the fact that it improves the flow and compatibility of the compression mix (Li et al., 2011). There are different processes of granulation that use different technologies. The paper provides a discussion on wet granulation and the technologies that are used for it.
High Shear Granulation.
At an industrial scale, high shear granulation is the most common and is used in the production of pharmaceutical granules. High shear granulation is said to be the most effective way of turning powders into granules that are dense for coating or tableting. In a nutshell, powders are always added to the mixing bowl and the bowl is sealed so as to create the granules. A larger impeller is made to rotate at low speeds so as to spin the powders into a vortex. A liquid such as water or alcohol that is always used as the granulating liquid is always added to the product using a pump after the powders are well blended. The air in the bowl is then removed by a high-speed chopper by shearing the granules. The safety of a high shear granulator is due to its top-drive design. Below is an image of a high shear granulator:
The integration of upstream and downstream equipment is allowed by this system, and there is also an inclusion of a good mil between the dryer and the granulator. In the high shear granulator, loading, mixing and granulating a second batch of the granulator that has high shear is easy while drying the batch that was there previously is done in the fluid before they are discharged(SEVILLE, 2010). All the equipment that are used in this process must be CIP in a single process that is automated. It is a twin shaker or a blowback filter design that is recommended to be used for the graduation process. Examples of high shear granulation include melt granulation and effervescence products. There are many companies that produce and sell high shear granulators. Examples of such companies include Glatt Solutions, Freud Vector, and Dynami. The market price of high shear granulators is between $5000 to $52000 depending on the quality and the power of the high shear granulator.
Fluid bed spray granulation
In this granulation technology, fluid beds that are fitted with spray nozzles are used. The spray nozzle location is the main advantage of this granulation technology since it is an area whose shear forces are significantly higher thus making it possible to process those formulations that only high shear processors could previously granulate. Moreover, FlexStream which are a range of fluid beds is introduced thus making it possible to eliminate the difficulty of scale up. In the recent years, there has been an improvement in the fluid beds since the single pot technology offer competition. For this reason, using a closed link that has an up and downstream equipment to contain material handling is now possible.
Fluidized Spray Drying
From a one-step process, granules are produced from a liquid by the fluidized spray. It has an option in which case in the primary production, it produces the active as granules and it is for this reason that only blending is required with excipients that are seen to be suitable during subsequent processing for direct compression (Li et al., 2011). This is possible with wet actives since when the actives are not wet, then a binder must be added.
The granulation technologies should always comply with the local authorities to ensure that the process is safe and not harmful to the environment. As such equipment used for granulation can be supplied so that they meet the required explosion-proof and pressure shock. A company should choose a granulation process based on its experience.
Dhenge, R., Cartwright, J., Hounslow, M. and Salman, A. 2012. Twin screw wet granulation: Effects of properties of granulation liquid. Powder Technology, 229, pp.126-136.
Li, J., Tao, L., Dali, M., Buckley, D., Gao, J. and Hubert, M. 2011. The Effect of the Physical States of Binders on High-Shear Wet Granulation and Granule Properties: A Mechanistic Approach Toward Understanding High-Shear Wet Granulation Process. Part II. Granulation and Granule Properties. Journal of Pharmaceutical Sciences, 100(1), pp.294-310.
SEVILLE, 2010. Continuous Pharmaceutical Manufacture Using a Novel Wet Granulation Technique. Scientia Pharmaceutica, 78(3), pp.543-543.