Assessment of coverage degree during particulate material encapsulation in fluidized bed

Abstract

By encapsulating granular materials, it is possible to eliminate caking, to provide a delayed release of the active substance. In this work the encapsulation is carried out by spraying the polymer emulsion onto the particles of the fluidized bed by means of pneumatic nozzles. Drops of the polymer emulsion, having faced with the particles are spread on their surface, forming a liquid film. Solvent removing by drying causes solidification of the film. The quality of the encapsulation process was evaluated by the degree of coverage, which is equal to the fraction of the total surface area of the particles coated with a protective coating. When thin polymer shells are applied, it is very important to determine the process parameters that ensure the continuity of the protective coating. A mathematical model, which allows to predict the particles coverage degree in the fluidized bed apparatus, is given. It is assumed that the growth rate of the degree of coverage is proportional to the fraction of the uncoated surface and the consumption of the film-forming material. To identify the parameters of the developed mathematical model and verify of its adequacy, a physical experiment was exercised on a laboratory scale installation. During the experiment, samples of particles were taken from the apparatus at intervals of one minute to determine their degree of coverage. The method for determining the degree of coverage is based on a comparative analysis of the dissolution curves of the initial and processed pellets. Graphic dependencies characterizing the evolution of coverage degree of granules in time at different flow rates of the film-forming substance are given. The comparison of the calculated and experimental data, which showed their good agreement, was performed. Thus, it is shown that the proposed mathematical model of the formation of a protective coating on particles in the apparatus of the fluidized bed allows to predict reliably the degree of coverage of particles and to choose the rational parameters of the encapsulation process.