Influence of salts on the dehydration of several biomass-derived polyols in sub- and supercritical water

We investigated the dehydration of several biomass-derived polyols in sub- and supercritical water, in particular m-erythritol, 1,2-propanediol and 1,3-propandiol. The resulting main products were 1,4-anhydroerythritol and propionaldehyde.The additives tested for their catalytic performance were among others zinc, nickel, copper, magnesium and sodium sulfate as well as sulfuric acid. A positive catalytic effect of bivalent transition metal salts was found.Initial educt and ZnSO4 concentration variations were carried out in order to determine the reaction orders. Further, activation energies and activation volumes were measured for zinc catalysed dehydrations of the above-mentioned polyols.Finally, a possible explanation for the reaction enhancing or inhibiting effect of different salts is given and discussed.