Comparison Of Sorption Isotherms Of Mono- and Disaccharides Relevant To Oligosaccharide Separations For Na, K, And Ca Loaded Cation Exchange Resins

Author： Vente Johan

Publisher： Taylor & Francis Ltd

ISSN： 0098-6445

Source： Chemical Engineering Communications, Vol.192, Iss.1, 2005-01, pp. : 23-33

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Abstract

Oligosaccharides (OS) are applied as a functional food and feed ingredient. OS are produced as mixtures of different types of carbohydrates, and further separation is required for most applications. An example of separation is the removal of monosaccharides in order to decrease the amount of calories and the sweet taste. The work presented here focuses on finding an optimized poly(styrene-co-divinylbenzene) cation exchange resin as the sorbent for the chromatographic removal of monosaccharides, mainly glucose, from OS. The influence of Ca 2+ , Na + , and K + as the cations of Dowex 50WX4-400 was investigated by determination of isotherms under relevant industrial conditions (temperature 60°C and sugar concentrations up to 400g/L). Both the static desorption method and the dynamic frontal analysis method were used for isotherm measurement. The two methods mentioned give slightly different isotherms, which may be attributed to the assumption of no shrinking of the resin. It was shown experimentally that K + loaded resin has a stronger adsorption of sugars than the Na + loaded resin. The observed isotherm order is: fructose≈galactose>glucose>lactose>sucrose. The lower isotherms of the disaccharides are explained by the size exclusion mechanism. The order of the monosaccharide isotherms is in line with the number of equatorial-axial oriented sugar OH groups for complexation with the cation. The observed selectivity for glucose/lactose is independent of the cations considered and about 1.3, but capacity is highest for K + loaded resin. The selectivity for fructose over sucrose is 2.4 for Ca 2+ loaded resin and is clearly higher than for Na + and K + . Therefore, based on selectivity and capacity, the K + ion seems the most suitable cation for separation of glucose from OS and the Ca 2+ cation is the best choice for removal of fructose from OS. No mass transfer effects were included in the comparison.