Catalytic transformations of biomass resources towards value-added fuels/materials have attracted many research groups because the utilizations of these resources can contribute to the low CO2 emission on the basis of carbon neutral concept and are sustainable/renewable. Recently, we have focused on the upgrading of biomass-based C5 furaldehydes such as furfural and furfuryl alcohol towards the corresponding C6 furaldehydes (ex. 5-hydroxymethylfurfural, 2,5-bis(hydroxymethyl)furan), through the direct hydroxymethyration reaction over various heterogeneous acid catalysts [Nishimura et al., under revision]. Previously, there are really few reports studying on similar transformations. In particular, Moreau and co-workers had undertook important discussions on this type of transformations [ex. Moreau et al., Ind. Crop. Prod. 9 (1999) 235]; e.g. approx. 10% yield for HMF production from furfural with the condition of formaldehyde/furfural = 240 was reported as the maximum value, however further improvement on the reactivity of heterogeneous catalyzed system is required.
Herein, we have examined two types of reactors with various heterogeneous acid catalysts; one is a conventional batch system and the other is a futural flow system. At present, it was observed that zeolite ??and commercial acidic resin of Amberlyst-15 gave significant performances for the hydroxymethylation of furfural to HMF with formaldehyde as a reagent; approx. 28% and 40% yields respectively were achieved in batch reactor. These values were much higher than that of previous achievements till 2017. It was worthy mentioned that the Amberlyst-15 catalyst was easily reusable over 4 runs in a batch reactor system and continuously produced HMF during 24 h in a flow reactor system. Moreover, Amberlyst-15 mediated hydroxymethyrations of other C5 furaldehydes such as furfuryl alcohol, furfurylamine and furoic acid were also proceeded.
In this presentation, I’d like to introduce the details of our recent studies and discuss the design of biomass conversions on the basis of this transformation.