Selective Conversion of Biomass Hemicellulose to Furfural Using Maleic Acid with Microwave Heating

Abstract

Maleic acid has interesting properties versus other organic and mineral acids in furfural formation. The use of maleic acid as a catalyst in biomass conversion has the benefit in comparison to the use of other acids (mineral/organic) due to the efficient conversion of solid xylans to xylose at high yields in aqueous solution at the reasonably mild temperature of 160 °C. This manuscript reports the kinetics of xylose dehydration to furfural using maleic acid over the temperature range 180–210 °C. These kinetics were used to determine the optimal temperatures and times for a two-step process to first hydrolyze plant hemicellulose to furfural and then to subsequently dehydrate the resulting xylose to furfural. High selectivity in furfural formation was observed when maleic acid was in equimolar or higher concentrations compared to the initial xylose concentration. High selectivity for furfural, 67%, was observed for xylose derived from corn stover, switch grass, and poplar, in comparison to modest selectivity, 39%, for pine wood. In all instances, xylose from biomass was found to be more reactive toward furfural formation than pure xylose. Maximum furfural concentrations were observed in shorter times than required for pure xylose. The rate increase is attributed to chloride salts extracted concurrently into condensed phase with hemicellulose-derived xylose.