Application of a protective coating on sodium percarbonate particles in a fluidized bed apparatus

Sodium percarbonate (SPC) is used as an environmentally friendly bleaching agent in synthetic detergents. This strong oxidizing agent is incompatible with some other detergent components, such as enzymes. This problem can be solved by encapsulating SPC, whose delayed release will allow the enzymes to function with maximum efficiency before deactivation in the presence of SPC. Therefore, the selection of a coating material and the coating layer thickness seems to be a relevant research direction. In this work, SPC granules were encapsulated by spraying a sodium silicate solution through a pneumatic nozzle over a fluidized layer of granules. Encapsulated SPC samples with the coating content of 5, 8, 10 and 13% of the mass of the initial product were obtained. The dissolution kinetics of the obtained capsules under static and dynamic conditions was studied. At the relative coating mass of 5, 8, 10 and 13%, the dissolution time under dynamic conditions comprised 10, 14, 19 and 30 min, respectively. In order to predict the release of the active component from encapsulated SPC under the conditions different from those used in the conducted experiments, a mathematical model of this process was obtained. For parametric identification of the mathematical model by solving an inverse problem, the value of the effective diffusion coefficient of SPC through the capsule was found to be 1·10-10 m2/s. The calculated and experimental values of SPC release from the encapsulated granules showed good agreement.