Effect of process variables on fluiddynamics and adhesion efficiency during spouted bed coating of hard gelatine capsules

This article presents an evaluation of the effects of the spouted bed design and operating conditions on system fluiddynamics and process performance during enteric coating of hard gelatine capsules. The design parameters studied were the column diameter (150 mm and 200 mm), the included angle of the conical base, γ (60° or 40°) and the presence or absence of a Venturi inserted before the inlet air orifice. The process variables studied were the ratio between the feed flow rate of the coating suspension to the spouting gas flow rate (Ws/Wg), the mass of capsules loaded to the equipment (M0), and the ratio between the spouting gas flow rate to the gas flow rate at minimum spouting condition (Q/Qms). The response variables were the rate of increase of the capsules mass (K1), and the adhesion efficiency (η). The linear regression equation for the dependent variable K1 in terms of the independent variables adequately described the process with an r2 value of 0.872. Analysis of variance (ANOVA) revealed that increasing of Ws/Wg, Q/Qms and γ significantly increased the adhesion efficiency. Adhesion efficiencies higher than 90% were achieved by selecting precise coating conditions, indicating the feasibility of the process for coating of hard gelatine capsules.