Using the local adsorption equilibrium distribution based on a Langmuir type adsorption model to investigate liquid phase adsorption of sugars on zeolite BEA

Adsorption isotherms generated by the Elution by Characteristic Point Method were used to determine the local adsorption equilibrium distribution (AEqD) on commercial zeolite BEA 150 extrudate pellets at room temperature. The linear sugar alcohol sorbitol and the circular sugar fructose were used as sensor molecules since both showed a rather strong adsorption with a typical type I isotherm. The expectation maximization method was transferred into a MATLAB code to calculate the most probable AEqD explaining the experimental data. The resulting distribution favors a bi-site Langmuir model that is in good agreement with the pore sizes of this zeolite, the critical diameters of the adsorptive molecules and gas phase experiments conducted previously. In summary, both molecules are too big to enter the zigzag channels of the zeolite. Instead they occupy two different binding sites in the straight channels and at the intersections between the straight and the zigzag channels. Therefore, sugars and sugar alcohol can be a good sensor to investigate the interaction between a zeolite crystal and adsorptive molecules in the liquid phase.