Adsorption properties of BEA zeolites and their aluminum phosphate extrudates for purification of isomaltose

Abstract

The disaccharide isomaltose is produced via an enzymatic reaction and is adsorbed to BEA zeolite. This reaction integrated adsorption can be achieved as fluidized bed as well as fixed bed. We investigated isotherms, adsorption enthalpies and sorption kinetics of BEA zeolite and extrudates with a novel aluminum phosphate sintermatrix. These extrudates contain 50% (w/w) of BEA 150 zeolites (Si/Al = 75) as primary crystals. BET-surface for extrudates is 245 m2⋅g−1 and 487 m2⋅g−1 for zeolite. Extrudates show a monomodal macropore structure with a maximum at 90 nm. All isotherms show a type I shape. For lower equilibrium concentrations, which occur during the enzymatic reaction, Henry’s law is applied and compared to a Langmuir model. Adsorption equilibrium constant Ki,L calculated from Langmuir for extrudates at 4 °C is 64.7 mL⋅g−1 and more than twice as high as obtained from Henry’s law with Ki is 26.8 mL⋅g−1. Adsorption on extrudates at 4 °C is much stronger than on zeolite crystals where the Henry coefficient Ki is 17.1 mL⋅g−1. Adsorption enthalpy ΔhAd calculated from van’t Hoff plot with the Henry equation is −44.3 kJ⋅mol−1 for extrudates and −29.6 kJ⋅mol−1 for zeolite crystals. Finally, the kinetics for ad- and desorption were calculated from the initial slope. The diffusion rate for ad- and desorption on extrudates were in the same range while adsorption on zeolites is three orders of magnitudes faster than desorption.