Fluidized bed microencapsulation: Thermodynamics of aqueous and ethanolic coating processes

Abstract

This paper aims to provide the fluidized bed scientist with appropriate and simple tools for the elaboration of efficient experimental designs of microencapsulation processes by fluidized bed using any combination of solvent and gas. Psychometric charts are used to predict and optimize experimental parameters in microencapsulation by fluidized bed evaporative cooling processes. This paper shows that theoretical psychrometric charts for water–air, ethanol–air and, by extrapolation, and solvent–gas mixtures can be developed from simple thermodynamic equations. The psychometric charts are constructed from readily available or calculable physical data such as the heat capacities of the gas and the solvent, the latent heat of vapourization of the solvent and the saturation concentration of the solvent in the fluidization gas. The calculated psychometric chart for water–air mixtures presented in this paper is shown to agree very well with the generally accepted charts found in the literature. An ethanol–air psychometric chart is built using the same equations and compared to experimental data of evaporative cooling processes using ethanol as the solvent. The paper shows a very good agreement between the calculated psychometric charts and the empirical data obtained from both ethanol-based and water-based evaporative cooling experiments. The results show the soundness and the relevance of the theoretical development behind the construction of the calculated psychometric charts; the accuracy of any other solvent–gas psychometric charts built using the equations proposed in this paper can be rightly extrapolated.

Key Words: :

• Microencapsulation
• fluid bed
• coating
• psychometric charts