Chromatographic Separation of Carbohydrates

Abstract

The general theories of chromatography are reviewed. Also the theories concerning the chromatographic separation of sugar mixtures are presented and examples of industrial applications reported. The general performance of zeolites, anion and cation exchange resins for the separation of carbohydrate mixtures using batch analytical techniques have been evaluated. A Semi-Continuous Counter-current Chromatographic Refiner (SCCR4) unit which has twelve 25.4 mm internal diameter stainless steel columns each of 750 mm length was used to separate feedstocks of either synthetic equimolar mixtures of fructose and glucose or inverted sucrose. The unit was packed with a cation cross-linked polystyrene resin in the calcium form. Fructose products of 93% purity and 2.0% w/v solids concentration were achieved. An intercolumn hold-up of 7% prevented higher purities from being obtained. An unexpected and significant shift in the location of the average column concentration profiles was found depending on which feedstock was used. A larger SCCR7 unit with twelve 54 mm internal diameter stainless steel columns each of 750 mm length was constructed and packed with an anion exchange resin in the bisulphite form. The unit was used to separate either fructose and glucose mixtures or inverted sucrose at different operating conditions. Fructose and glucose products of 99% purity were achieved. Also, for the first time with an SCCR unit, fructose products with up to 12% w/v solids concentration were obtained. It was also found that there was no shift in the location of the concentration profiles depending on whether fructose and glucose or inverted sucrose mixtures were separated. Unlike the cation resin which was found to be very stable, the anion resin required frequent regeneration. A theoretical model based on the plate equilibrium concept has been adapted to simulate the performance of the SCCR7 unit. Equilibrium data obtained at infinite dilution were used in the simulation. An approximate agreement between the experimental results and the model predictions was found.