(M1430-10-54) Designing Spray Dried Particles with a Pressure Nozzle at Small Scale

Purpose: The purpose of this study is to determine the critical process parameters that impact the spray dried particle’s characteristics by generating powders using a pressure nozzle in a small-scale spray dryer. Operating at small scale during the process development phase is very important for many ASD formulations as the APIs are often very expensive.

Methods: The formulation chosen for the spray drying trials was 10% HPMC-AS in acetone. HPMC-AS is a polymer that is compatible with multiple bio-unavailable APIs. Spray drying trials were conducted on a small spray dryer, the GSD-200, using two different nozzle sizes, 0.15mm and 0.20mm. The collected powder was analyzed to evaluate residual solvent, bulk density, and particle size distribution (PSD). For all trials, the system was operated in closed loop with a nitrogen gas purge and solvent recovery. The drying gas flow rate was set to 17 CFM and the inlet gas temperature was set to 90-100 °C. A high-pressure positive displacement pump was used to deliver the solution. The pump was operated at a range of speeds to deliver the solution at pressures ranging from 200 PSI to 500 PSI. After the GSD-200 trials were completed, the process was repeated on a pilot scale machine, the GSD-800, using the same 0.20mm nozzle and high-pressure pump. The drying gas flow rate was set to 80 CFM and the inlet temperature was set to 90 °C. The resulting powder collected was analyzed to evaluate residual solvent, bulk density, and PSD. The data was then plotted to determine trends that are useful in designing a spray drying process.

Results: For all trials, in the small-scale spray dryer and the pilot spray dryer, there were two very distinct trends. First, in the range of 200 PSI to 500 PSI of solution pressure, as the pressure was increased, the particle size decreased. The other trend was in bulk density. As solution pressure increased, the bulk density increased as well. For all trials, the residual solvent was in the range of 3% to 6%. The figures below (F1 and F2) show the PSD and bulk density trends.

Conclusion: With the proper equipment and set-up, particles can be generated at a small scale using a pressure nozzle for the purpose of designing a production process without having to use large quantities of material. Although the particle characteristics using the same pressure nozzle in each system did not exactly match, the trends were the same, so the design process is scalable.

Figure 1: Particle Size Decreases as Pressure Increases

Figure 2: Density Increases as Pressure Increases