Investigation of the effect of gel properties on supercritical drying kinetics of ionotropic alginate gel particles

Abstract

A series of spherical ionotropic alginate gel particles with different diameters ranging from 2.8mm to 5.0mm and porosities ranging from 0.899 to 0.976 were prepared by dripping a Na-alginate solution into a solution of salts of divalent cations (Ca2+, Mn2+, Ni2+, Co2+, Cu2+ and Zn2+). After solvent exchange with ethanol, kinetics of supercritical drying of these ionotropic alginate gel particles in a packed bed was investigated at 308-338 K and 100-120 bar. Experimental data were compared with predictions of a model which considers diffusive transport inside the pores and convection in the flowing fluid stream. The model predicted drying profiles by taking into account only the changes in porosity and diameter of the gel particles. A convective mass transfer coefficient correlation that was originally developed for supercritical drying of Ca-alginate gel particles was found to be suitable for M-alginate gel particles.