Synthesis of 5-hydroxymethylfurfural from highly concentrated aqueous fructose solutions using activated carbon.

An efficient and environmentally friendly system for producing 5-hydroxymethylfurfural (5-HMF) from fructose has been proposed. Substrate concentration is an important factor for practical application of the process; however, use of a high concentration of fructose has rarely been tested in the reaction because the conditions accelerate intermolecular side reactions to form adhesive humins. Humin byproducts stuck on reactor surfaces can make the production of 5-HMF on an industrial scale difficult. Therefore, developing a catalytic reaction system that can promote the synthesis of 5-HMF from highly concentrated fructose without causing adhesion of humins to reactors is needed. The present study demonstrated that activated carbons are promising materials for this system. Activated carbon catalyzed the conversion of fructose to 5-HMF without adhesion of humins to reactor vessels under practical conditions of high substrate concentration up to 73.2%. The catalytic activity was determined not only by the amount of surface weakly acidic oxygenated groups but also by the adsorption of fructose. In addition, strong adsorption of 5-HMF led to low selectivity of 5-HMF and the formation of adhesive humins. This is the first report to describe the synthesis of 5-HMF from solutions containing a fructose concentration greater than 70%.