Adsorption behavior of sugars versus their activity in single and multicomponent liquid solutions

The importance of carbohydrate solutions in many industrial processes is well recognized nowadays. Carbohydrates are produced as mixtures of different types of sugars; therefore further separation is required for most applications. The successful prediction of separation process performance rests on the ability to describe the relevant thermodynamic and rate parameters. The accurate prediction of activity coefficients in solutions is essential for the process design. In this work the activity of carbohydrates: sucrose, glucose and fructose in high-concentrated aqueous solutions was studied for both single and binary mixtures. The solubility properties of sugars for different temperatures were correlated basing on the Schröder-van-Laar-equation with the NRTL (Non-Random-Two-Liquid) model of activity coefficient formulation. The activity of individual sugars was quantified from the solubility properties and incorporated into the isotherm model, which reproduced accurately convex shape of the isotherm courses obtained in a previous work [1]. Based on the phase equilibria for binary systems of sugars with water, the sugar activity in mixtures was established. The determined activity along with the calculated single component isotherms was used to predict competitive adsorption isotherms by applying the Real Adsorbed Solution theory [2]. The isotherms were compared to the data of competitive adsorption from the former study [1]; the experimental results were found to be fully predictable. The results obtained will be presented and discussed. [1] J. Nowak et.al., J.Chromatogr. A 1164 (2007) 224 [2] A.L. Myers, AIChE J. 29 (1983) 6