Kinetics of monosaccharide conversion in the presence of homogeneous Bronsted acids

For the utilization of biomass in the fuel and polymer industry, a wide variety of catalysts have been studied for their activity either on the dehydration reaction in particular or on the monosaccharide degradations in general. Yet, systematic data outlining the effects of acidic features is not available and a common framework for catalytic activity comparison is missing that is needed for rational catalyst design. The current work aimed to provide insight about the effect of the nature of the acid and initial acidity on degradation kinetics of C-5 and C-6 carbohydrates and thereby built a platform allowing activity comparison. Mineral and organic acids ranging in acidic strength, hydrochloric, sulfuric, phosphoric, maleic, and propane sulfonic acid, were tested for their activity in the degradation of xylose, fructose and glucose at two different pH values; 1.5 and 3.6. In the presence of weak homogeneous acids, glucose undergoes degradation with drastically different activation energies at pH of 1.5 than at pH 3.6. Such a difference does not occur in the presence of strong homogenous acids. On the other hand, xylose and fructose undergo degradation with similar activation energies of approximately 140 kJ/mol regardless of the pH or nature of the homogeneous acid. A common framework that compiles the catalytic activities and outlines the differences potentially related to underlying mechanism changes provides the basis required for rational heterogeneous catalyst design. (C) 2012 Elsevier B.V. All rights reserved.