Fluid Dynamics and Drying of Cohesive Particles of a Biodegradable Polymer (Poly-Hydroxybutyrate) in a Rotating Pulsed Fluidized Bed

Abstract

This article presents the results of fluid dynamics and drying of poly-hydroxybutyrate (PHB) granules in a rotating pulsed fluidized bed (RPFB) dryer. Cohesiveness of PHB results in problems when using conventional drying techniques, such as a fluidized bed dryer. The excess surface water on the particles may form agglomerates that damage the flowability of the material inside the dryer. The drying study in RPFB consisted of adjusting mathematical models for predicting the moisture evaporation during the constant drying rate period (linear fit) and the decreasing drying rate period (analytical solution of Fick's second law). The influence of temperature, rotation frequency, and velocity of the drying air on the constant drying rate (Nc), effective diffusivity (Deff), and mass of particles elutriated (me) during drying was evaluated. Particle porosity was analyzed before and after drying and scanning electronic microscopy (SEM) was employed to verify structural changes on the PHB granules after drying. The RPFB dryer proved to be appropriate to dry the PHB granules, resulting in an excellent fluid dynamics behavior of the particles inside the bed and providing uniform drying of the solids. Temperature and velocity of the air had a significant influence on the drying process, but rotation frequency did not affect the process in the ranges analyzed. Fine particle elutriation occurred during the first 10 min of drying. After drying, the porosity changed and breakage of the particles was observed due to attrition inside the bed.