Kinetic Modelling of Fluidised Bed Drying of Enzyme Granules and Effect on Enzyme Stability

Abstract: In the production of solid enzyme products, the granules are dried in a fluidised bed dryer prior to being coated with a protective salt coating. The coating exhibits a low mass diffusivity, which essentially encapsulates any present moisture inside. During the coating process moisture is inevitably added to the granules. It has prior been shown that moisture content in the final product has a negative impact on the shelflife stability of some of the enzyme product produced by Novozymes. It has been theorised whether it is the moisture of the granules before the coating is applied, or the moisture added during the coating which accounts for this effect. The primary objective in this thesis was to determine the correlation between moisture content from the dryer and the final products shelf-life stability. From experimental data a clear correlation was observed. A considerably decrease in absolute enzyme activity was observed when the coating was performed with high moisture content granules. It is thought that high moisture content combined with a high temperature cause the enzymes to denature. Furthermore a mathematical model was implemented in Python to simulate the drying. The simulations were shown to predict the moisture content of the granules well to the experimental data. However the simulated temperatures deviates considerably from measured values.