Adsorption separation of raffinose from sucrose by activated carbon: Equilibrium, kinetics and dynamic breakthrough

Separation of oligosaccharides with a varied number of monosaccharides is an important issue in food chemistry. Raffinose, a functional oligosaccharide, has attracted increasing attentions due to its strong proliferative effect on bacteria. Industrially, cottonseed meal is an important resource for producing raffinose; however, raffinose extracted from the cottonseed meal contains a significant amount of sucrose that debases raffinose’s quality. In this work, an adsorptive separation of raffinose and sucrose on activated carbon was reported. Adsorption isotherms, adsorption kinetics and dynamic column adsorption–desorption were investigated. The activated carbon chosen has a significantly higher adsorption capacity of raffinose (0.60~0.65 g/g) than sucrose (0.35~0.40 g/g) at the equilibrium concentration studied (~35 g/L) and temperature from 293 K to 333 K. Adsorption isotherms and kinetics were fitted by the Freundlich isotherm model and the pseudo-second-order model, respectively. The effect of flow-rate and initial feed concentration on dynamic adsorption were investigated; meanwhile, the separation performance was further confirmed from dynamic desorption using aqueous ethanol of 20% as eluant. Remarkably, raffinose with purity over 90% and recovery of 79.2% could be obtained by the adsorption–desorption cycle using an aqueous feed solution containing 20 g/L of raffinose and 6 g/L of sucrose.