(120b) Investigation of Acoustic Dryer for API Processing

4/29/2011

Investigation of Acoustic Dryer for API Processing

David J. Lamberto, Merck & Co., Inc., Rahway, NJ

Peter Lucon,  Dwynn Nyquist, Josh Yarrington, Resodyn, Butte, MT

The development of novel drying technologies which improve drying rates and avoid particle breakage and loss of crystallinity would be beneficial to many industries.  In particular, isolation of crystalline products in the pharmaceutical industry involves operations that frequently change the physical characteristics of the solids being isolated.  Particle size reduction, undesired agglomeration, and the generation of amorphous material as a result of applied mechanical stress have been observed.  Thus far, procedures to avoid, or minimize these issues can lead to reduced process efficiencies and increased development times. 

The use of the ResonantAcoustic(R) mixer technology has the potential to lead to advances in the drying of crystalline materials through the use of low frequency sonic energy for material fluidization with minimal mechanical stress on the particles.  The new technology avoids the negative aspects of mechanical agitation and does not have the complications associated with traditional fluidized bed systems for Geldart Group C materials.  Mixing is based on intrinsic material properties and is less dependent on extrinsic equipment parameters, and therefore scale-up development efforts can be minimized and transition to production facilities is simplified. 

In this study, the performance of a prototype acoustic dryer is compared with a conventional conical dryer using two pharmaceutically relevant compounds which have widely different drying behaviors.  Data were obtained under similar operating conditions of temperature and pressure for the two technologies.  Mixing in the acoustic dryer was conducted within a fixed acceleration range for all cases while both continuous and the more typical intermittent agitation conditions in the conical dryer were explored. 

As expected, for the compounds investigated, the use of continuous agitation in the conical dryer enhanced the drying rates as compared with the use of intermittent agitation.  In one case the rates achieved were higher than that achieved in the prototype acoustic dryer while for the other the rates were equivalent.  The acoustic dryer showed less temperature and moisture variations across the dryer as compared with the conical dryer.  In addition, placement of the temperature probe directly into cake inside the acoustic dryer versus at the wall increased the accuracy of the actual cake readings throughout the drying process.  The acoustic dryer achieved drying rates 2-3 times higher as compared with the conical dryer operated with the less aggressive intermittent agitation (commonly used to minimize particle attrition).  Particle size reduction or aggregation within the acoustic dyer was minimal and similar to that achieved with intermittent agitation in the conical dryer. 

The new acoustic dryer technology has the potential to be a platform drying technology and provide a technical competitive advantage over existing technology.  The enhanced heat and mass transport and reduced impact on physical properties will result in reduced cycle times, higher product quality and enhanced process portability.  The acoustic dryer will find wide application for products where mechanical agitation is currently limited in traditional drying equipment.  Continued optimization of the acoustic dryer should lead to improved performance, better process control, and increased applicability across a wider portfolio of compounds.