(569f) Modelling of Fluid Bed Drying At Different Production Scales in Pharmaceutical Drug Manufacture

Fluid bed drying is commonly used to dry material subsequent to wet granulation in pharmaceutical drug product manufacture. The key decision variables in the fluid bed drying process are the flowrate and temperature of the drying air. A constraint is usually imposed limiting the temperature of the solid material in order to prevent undesirable physical and chemical changes. In operating batches, the goal is to achieve a desired solid moisture content as quickly as possible.

In this presentation, a model is developed of a fluid bed drying process based on one published in the literature (Burgschweiger et al, 1999; Burgschweiger and Tsotsas, 2002). The model is validated against data obtained using placebo material at the lab scale. The model is able to predict batch drying profiles (solid temperatures and moisture contents) for different initial moisture contents and particle sizes. It is observed that depending on the nature of the material being dried, externally limited drying (the drying rate is limited by mass transfer to the vapour phase), internally limited drying (the drying rate is limited by mass transfer from inside the particle to the surface) or both may occur.

After validating the model using data on the lab scale, the model is applied to data obtained from production of real drug material at the production scale. It is observed that the model is able to predict batch drying profiles at the larger scale as well. This mechanism based model could be used to gain process understanding and control in scaling up the fluid bed drying process.

References

• Burgschweiger J, Groenewold H, Hirschmann C, Tsotsas E (1999) From hygroscopic single particle to batch fluidized bed drying kinetics. The Canadian Journal of Chemical Engineering 77, 333-341
• Burgschweiger J, Tsotsas E (2002) Experimental investigation and modelling of continuous fluidized bed drying under steady-state and dynamic conditions. Chemical Engineering Science 57, 5021 – 5038