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This is due to good mixing of solids and intensive heat and mass fluidiwed between the solid and hot gas phases in the system. Generally, high energy input is required during this process to provide the latent heat of water evaporation, and thus on-line measurements become important to determine the optimal operation conditions in order to minimize energy usage.
In the pharmaceutical industry, the drying step in many pharmaceutical production lines is often a bottleneck because this process is affected by many parameters and it is difficult to determine the time required to dry the materials as well as analytically verify that a predetermined end point has been reached.
If the active pharmaceutical ingredient has a low melting point, controlling the drying process becomes more critical due to the sensitivity of the formulation to the temperature and the risk of compromising product quality and performance during drying.
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The pore volume and the surface area of the DCPA material are 0. The experimental procedure includes a wetting stage and a drying stage.
During the drying stage, hot air flows fluidieed the bed at a predetermined air flux and drying temperature to evaporate the moisture from the materials. The pressure drops across the bed, the inlet and outlet air temperatures, the bed temperature and the outlet air humidity are measured as a function of time.
Cluidised impacts of air flow and air temperature on the drying process were also investigated. The moisture content in the product during drying was measured using two approaches: Figure 2 a illustrates that the intensity of the spectra of the water bands was declined steadily during drying.
This indicates that the NIR method can be used to accurately measure the product moisture content and to determine the end point of the drying process.
The drying process for fine particles was dryef examined in this work. However during drying, the holes in the bed distributer were easily clogged by fine particles causing an unstable fluidization state.
Therefore the results for fine particles are not shown in this article. The drying profiles shown in Figure 3 indicate that this fluidized bed drying process is a three stage process, including a short pre-heating stage, a constant rate stage and a falling rate stage. The constant rate stage corresponds to a constant bed flkidised.
The fryer in the voids is evaporated first and this occurs during the constant rate stage. Once all the water in the bed voids is removed, convection drives the water inside the powder pores to flow towards the powder surface, and then water is evaporated at the surface.
This surface evaporation also occurs at the constant rate stage. With further dryre, the effect of convection reduces due to the loss fluidiesd water and the drying front starts to penetrate inside the pores.
The drying process transits from the constant rate stage to the falling rate stage, and the bed temperature goes up. Once all the water is removed from the materials, a plateau can be observed for the bed temperature indicating that the system reaches an equilibrium state. This plateau temperature is less than the inlet air temperature due to the heat loss at the equipment walls.
It is important to note that fluidlsed profiles of the moisture content and the bed temperature were quite similar for large particles, moderate particles and mixtures. This indicates that if drying is dominated by the constant rate stage, the impact of powder size on drying is beed significant.
Whether the constant rate stage dominates the drying process or the falling rate stage dominates the drying process is determined by the competition of the capillary flow rate inside the pores and the evaporation rate at the powder surface . In a drryer drying regime, where the vapor removal is faster than the capillary flow, the drying front moves quickly towards the particle center and the drying process is dominated by the falling rate stage.
Under this situation, the effect of powder size on the drying time becomes significant and previous work has shown that drying of small particles is much faster than large particles .
In a slow drying regime, where capillary flow is faster than evaporation, water evaporation mainly occurs at the powder dgyer and the drying process is mainly dominated by the constant rate stage. Under this situation, the effect of particle size on the drying time is not significant.
In pharmaceutical drying processes, if the API has a low melting point or is sensitive to heat, drying is generally carried out in a slow drying regime.
During the constant drying rate stage, the water content in the bed linearly decreases with time indicating a zero order kinetics see Figures 3a and 4a. Under this situation, the drying profiles for three cases were overlapped and the effect of particle size on the drying process could be neglected. In this work, moist dibasic calcium phosphate anhydrous DCPA has been dried using a commercial fl uidized bed dryer.
The moisture content was measured using two approaches: We also classifi ed the DCPA materials into fi nes, medium, coarse, and examined the drying process for each size cut as well as mixtures. Our results indicate that if drying is carried out in a slow drying regime, where capillary flow is faster than evaporation, drying is dominated by the constant rate stage and the impact of particle size on drying is not signifi cant.
Xue LiuPh. Fernando MuzzioPh. For more than 20 years, Professor Muzzio has focused upon pharmaceutical product and process design.
In this capacity, Dr. Muzzio directs research involving the U. FDA and more than 40 global companies. He has more than peer-reviewed scientifi c articles, book chapters, and patents.
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Keep up with our latest articles, news and events. Plus, get special offers and more delivered to your inbox. Fluidized Bed Drying of Pharmaceutical Materials: Moisture Measurement and Effects of Particle Size. Tuesday, April 2, Particle size distribution of the dry DPCA materials. Moisture measurements during the drying process. Fluiddised moisture content vs.