Subcritical water as eluent for chromatographic separation of carbohydrates using cation-exchange resins

The separation of sugars and sugar alcohols with a strong cation-exchange poly(styrene-co-divinylbenzene) (PS-DVB) resin in the Na + form using subcritical (superheated) water as an eluent was studied in order to elucidate the potential of the technology in the recovery of carbohydrates from hemicelluloses hydrolysates. The separations were carried out on a column having inner diameter 2.2 cm and a bed length of 26 cm. The flow rate was typically 1 ml/min and pressure 1 MPa. The effect of temperature increase on chromatographic performance was studied up to 423 K. In addition, the stability of the aqueous carbohydrates and cation-exchange resin was studied. Results indicate that increasing temperature affects the separation by decreasing the retention volume and peak width rather than by improving the selectivity. The strong cation-exchanger withstands the subcritical conditions well but some carbohydrates start to degrade at 373 K in water. Depending on the compound, the upper separation temperature limit for the sugars is around 398 K, whereas the sugar alcohols studied are able to tolerate even 423 K. Thus, the elevated temperature is favorable for separation and technically advantageous, especially if the treated feed is already at elevated temperature, e.g. following a hydrolysis process.