SELECTIVE ISOMERIZATION OF GLUCOSE INTO FRUCTOSE OVER MgO-ZrO2/Al2O3 CATALYST

Fructose is the sweetest natural sugar that widely used in the food industry as a dietary sweetener. It is also a key starting compound for the synthesis of wide variety biobased va­lue-added intermediates. Isomerisation of glucose into fructose is already a large-scale industrial process performed with about 1500 tof immobilized enzymes producing more than 10 million (dry matter) a glucose – fructose syrup per year. But this process requires considerable costs therefore the development of fast, cheap and reusable catalyst systems seems essential. Known solid catalysts are still significantly inferior to enzymes in process selectivity, so the search for effective cata­lysts for glucose isomerization remains relevant. The process of isomerization of 10–30% aqueous glucose solutions over alumina-supported mixed MgO-ZrO2 oxides in batch and flow mode at 90°C and atmospheric pressure was investigated. The supported mixed oxide MgO-ZrO2/Al2O3 was synthesized by a simple impregnation method which is important for the development of a simple and cheap catalyst for the target reaction. MgO-ZrO2/Al2O3 sample with a molar ratio of Mg/Zr= 4 and the deposited oxide phase content of 20 wt.% was synthesized by impregnation of commercial granular aluminum oxide with a compatible solution of magnesium and zirconium nitrates and subsequent heat treatment at 600 C for 2 h. It was found that the MgO-ZrO2/Al2O3 catalyst provides glucose conversion up to 19%, with maximum fructose selectivity up to 100% in the flow mode. The possibility of processing of concentrated (30%) glucose solutions at 90 °Cwith catalyst productivity of 0,44–0.67 mmol fructose/gcat/h was shown. After 30 h processing MgO-ZrO2/Al2O3 catalyst has been rege­nerated by calcination in air for 2 hours at 600 °C without loss of activity and selectivity.