Fluidized bed coating and granulation: influence of process-related variables and physicochemical properties on the growth kinetics

Abstract

This study, which deals with the coating and granulation of solid particles by aqueous solutions of polymers or inorganic salts, aims to understand the effect of: – process-related variables such as the excess gas velocity, atomizer location, liquid flow rate and concentration, and atomizing air flow rate, – physicochemical-related variables such as the viscosity of solutions, wettability of the granulating liquid on solid particle surfaces, initial particle mean size, and porosity of the particles on the agglomeration kinetics of solid particles in a fluidized bed. The results showed that for a given particle size, the fluidizing air velocity was the most important factor affecting the growth kinetics and the stability of the operation. An increase of the relative humidity, depending on the liquid flow rate as well as the air flow rate, favor agglomeration mechanism especially for values greater than 0.4. An increase in the particle initial size leads to an enhancement of the layering mechanism, especially for values greater than 300 μm. The effect of the interfacial tension is investigated by adding different concentrations of a non-ionic surfactant to the binding solution. The effect of the contact angle is then studied using non-hydrophobic, partly hydrophobic, or totally hydrophobic particles. The growth of agglomerates appears to be favoured when the interfacial tension increases and the contact angle decreases. The viscosity of the solution has less effect than the interfacial parameters. The results show that the dominant forces in the granulation process are the capillary forces.