Advantage and disadvantage of common granulation machine I
Writer： admin Time：2020-03-19 15:03 Browse：℃
In pharmaceutical production, granulation is a necessary process in production almost all solid preparation. Current widely-used granulation techniques are wet granulation, dry granulation(roller compaction), spraying granulation, melting granulation and centrifugal granulation. Among them, wet granulation (including fluid bed granulation and high shear wet granulation) and dry granulation(roller compactor) are the commonest.
Wet granulation – fluid bed granulation
In fluid bed granulation, particles are enlarged through two methods: coating and agglomeration. Coating refers to that adhesive in mist is distributed on the surface of particles, coats them and enlarges them, while agglomeration is a process in which two or more particles bind to each other through the liquid or solid bridge formed by adhesive. During granulation, common problems and disadvantages are:
1.Wide granule size distribution and too much fine powders after granulation
1)High frequency of fan or high position of spraying gun speed up volatilization of adhesive. Materials cannot be wet completely and no stable solid bridge is formed between particles. All in all, the dried mist will hinder agglomeration of particles.
2)Adhesive is not enough. Dosage of adhesive should be increased to form solid bridge between more particles and facilitate growth of particles.
3)Inappropriate type of concentration of adhesive cannot form stable solid bridge between particles. It is suggested to use adhesive of strong viscosity but control its viscosity in case of blockage.
4)The spraying area is smaller than the area of material bed. Central materials will contact more adhesive and form larger granules, while peripheral materials are smaller due to less contact with adhesive. In this case, the spraying area of spraying gun should be adjusted to be the same with the area of material bed (if the former is larger, wet materials will stick to wall). Material fluidity can also be adjusted. Good material fluidity can narrow granule size distribution.
2.Large granules and even collapsed bed
Granules might be large when adhesive is not dried timely after contacting particles. Undried adhesive will form liquid bridge among a number of powders and agglomerate them into large granules. To avoid larger granules or collapsed bed, the following solution may be helpful:
1)Increase atomizing pressure or reduce liquid feeding speed to reduce the droplets. Dry timely after contact of adhesive with materials in case of their agglomeration.
2)Increase fan frequency and improve material fluidity to avoid material binding and blocking.
3)Increase intake air temperature to dry materials timely after their contact with adhesive mist and to avoid continuing growth of materials.
4)Control air humidity. Large humidity will affect material drying efficiency. Therefore, liquid feeding speed should be reduced or air temperature increased.
5)Control intake air temperature and material fluidity when some materials can melt in low temperature. Partial high temperature should be avoided in case that materials melt and chock in distribution plate, which will even lead to material blocking or bed collapsing.
3.Medicine powders chocking in spraying gun during granulation
1)High frequency of fan or low position of spraying gun will narrow the distance between boiling materials and spraying gun. Some wet materials stick to the gun and cause chocking.
2)Wet materials cannot be dried timely due to high liquid feeding speed. In this case, more and more powders stick to the gun and chock it.
3)High viscosity of adhesive and insoluble particles inside will cause gun chocking. Therefore, if it is suspension, adhesive should be filtered before use.
4.Low granule output
1)In common granulation, the collecting bag of fluid can only collect materials whose size is over 20μm. If material size is small, fine powders will be blown away easily by airflow, or attach to the bags due to static electricity. In this case, even shaking bags cannot collect all medicines. Therefore, material size should be controlled to reduce material loss.
2)At the beginning of granulation, airflow rate should be small, because high-rate airflow will blow away powders before granules are formed, which causes low output. As granulation continues, granules are formed and material density increases, air speed can be increased accordingly. After spraying, adhesive will be dried and granule density increases. Then, air speed should be reduced gradually.
3)Sometimes medicines are in a small proportion, so during granulation, they will be added into and sprayed to materials together. Fan frequency can liquid feeding speed should be controlled to avoid prematurely dried mist and reduce material loss.
5.Granules being dry externally but wet internally
1)Too high temperature of the intake air will evaporate adhesive quickly so that inner adhesive cannot expand outwards. So solve this problem, material temperature can be reduced properly.
2)Materials of low melting point will melt and agglomerate. Granules containing such materials are found to be wet internally but dry externally. Therefore, conditions should be controlled in case that those materials melt.
6.Severe material static during production
At the beginning of fluid bed granulation, problem of static electricity is the most severe. In this case, liquid can be fed more quickly, air humidity increased or some micro powdery silica gel added. These methods are helpful. Except them, static electricity is related to material size. The smaller the size is, the more severe the problem is. Therefore, material size can be increased in a proper limitation.
