Agglomeration in suspension of salicylic acid fine particles: Analysis of the wetting period and effect of the binder injection mode on the final agglomerate size

Agglomeration in suspension is a size enlargement method which facilitates the operations of solid processing such as filtration, transport and galenic while preserving the solubilisation properties of fine particles. A small quantity of binding liquid is added into a suspension of microparticles, directly in the stirred vessel where the precipitation or crystallisation took place. With optimised quantity of binder injected and optimised injection mode, spherical and dense agglomerates can be obtained. This paper analyses the first step of the agglomeration process, i.e. the wetting period, which corresponds to the injection of the binder liquid and its dispersion within the particle suspension. The system studied is the agglomeration of salicylic acid microparticles using chloroform as binder. A visualisation cell was developed in order to observe under optical microscope the interactions between a liquid binder droplet and the particles to be agglomerated. Clearly, an immersion mechanism was observed. Experiments were also carried out in a stirred vessel to visualise the wetting phase within the reactor using an image acquisition probe. The effect of the injection mode and quantity of binder on the agglomerate size was analysed. A fast binder injection under high stirring and an optimum quantity of binder favour the formation of small agglomerates.