(285f) CFD Modelling of Spray Drying of Biopharmaceuticals

Spray Drying (SD) has attracted lots of interest in pharmaceutical industry as an efficient one-step drying and formulation process of biopharmaceuticals. The complexity of the influential factors on final product properties make its optimization process a costly, time consuming procedure. Also, use of temperatures higher than 100° C is another concern in processing of thermally unstable drugs with spray drying technique.

Modelling techniques have shown a huge promise in defining predictive models of SD process. Although modelling of SD is still in its infancy, it has now become an inevitable part of continuous manufacturing process.^1,2 Computational Fluid Mechanics (CFD) simulations is a powerful method of modelling air flow of SD. Also, it is capable of predicting particle size, outlet temperature and interparticle interactions. However this is all pertinent that the model is defined and interpreted correctly.

In this research CFD modelling was employed to investigate the air flow in a co-current laboratory scale Buchi B-295 spray dryer. A mixed Eulerian/Lagrangian approach, in which the single phase Reynolds Averaged Navier Stokes (RANS) equations are solved were used to determine the flow field. Also, the effect of different type of nozzle and the swirl angle (ultrasonic vs. two fluid nozzle) on air flow pattern was examined.

Particle tracking of hundreds of particles was used to check the temperature variance between the particles at different stages of drying process in drying chamber. Using the Lagrangian approach the fate of individual representative droplets was determined when they reach the walls. By having the knowledge on moisture content and temperature the expected contact regime, i.e. sticking or bouncing could be defined.

Finally, the design of experiment approach on a ternary system of API(Acetaminophen)/excipient(HPMCP) was used to validate the modelling approach results. A good agreement between the inlet-outlet temperatures was found between modelling and experimental results. Also, particle size distribution validated the outcome of the CFD modelling approach.

References

(1) Oakley, D. E. Spray Dryer Modeling in Theory and Practice. Drying Technology 2004, 22 (6), 1371â??1402. DOI: 10.1081/DRT-120038734.

(2) Spray Drying Technology (2); M.W.Woo, A.S. Mujumdar, W.R.W. Daud, Ed. 1; Singapore, 2010.