Scale-Up of production of 5-hydroxymethylfurfural-rich adhesive precursors and structural features of humin side products

A batch reaction system (volume 1 L) for scaled-up production of 5-HMF-based adhesive precursor solutions from industrially available fructose syrup was developed. The stabilizing effect of sodium dithionite addition was demonstrated. With this system, no concentration steps are needed in the production of adhesive precursors for wood composite board production. The reaction system was optimized in a design of experiment approach to achieve good reaction conditions and to produce reaction solutions with 5-HMF concentrations appropriate for adhesive synthesis. Only three runs in the adjusted system are required to produce enough precursor for the synthesis of 10 kg of adhesive, thereby enabling the testing of the adhesive systems in particle board trials. Furthermore, the structure of humin side products from different reaction stages, formed from 5-HMF and byproducts by condensation, aldol-like reactions and attack on furan ring systems, was investigated. The data were compared to information from literature and possible elements of humin structures are proposed.