Direct Production of Vanillin from Wood Particles by Copper Oxide-Peroxide Reaction Promoted by Electric and Magnetic Fields of Microwaves

Production of biobased functional polymers from woody biomass is becoming increasingly important for biorefineries. We studied the direct production of vanillin and vanillic acid, which are key monomer components for thermostable polymers, from a softwood Japanese cedar by an alkaline copper oxide peroxide reaction using microwave (MW) and conventional heating (CH) reactors. MW heating at 180 degrees C for 10 min produced vanillin and vanillic acid in yields nearly three times higher than those produced by conventional heating (10.1% vs 3.4%). The MW and CH experiments were precisely compared using the same heating conditions and the same reaction vessel. A cavity resonator (single-mode microwave) which can separate electric (E) and magnetic (H) fields were used for wood degradation. The results revealed that the reactions were accelerated by both fields with a slightly more prominent effect of electric fields (E-max). The activation energy of experiments under CH, MW-E-max, and MW-H-max was calculated. The yield enhancement and decrease of activation energy unequivocally indicate the MW-sensitive character of this reaction. When hardwood (Eucalyptus globulus) was used as a feedstock, syringaldehyde and syringic acid were produced together with vanillin and vanillic acid, and the maximum yield of the monomers reached 11.4% based on the original wood weight under MW heating. This method was successfully scaled up by using a 1-L scale MW reactor to give vanillin and vanillic acid at a total yield of 8.5%.