(133c) Bio-Oil Upgrading By Combining Chemical Pre-Reduction with Electrocatalytic Hydrogenation

Fast pyrolysis of lignocellulosic biomass produces bio-oil, a mixture of several hundred compounds containing different oxygenated functionalities including alcohols, aldehydes, ketones, and carboxylic acids. Electrocatalytic hydrogenation (ECH) may be applied to produce fuels and chemicals from bio-oil under fairly mild conditions (ambient pressure and temperature < 80 ℃). Promising results have been obtained for ECH of singular model compounds (e.g. furfural, 4-alkylguaiacols, di-p-tolyl ether) using noble metal electrocatalysts (ruthenium-platinum supported on an activated carbon cloth). However, ECH of multi-compound mixtures and bio-oil fractions remains a challenging prospect. It was observed during preliminary trials on whole bio-oil ECH that presence of compounds with an aldehyde functionality (e.g., furfural) inhibited the reduction of other compounds such as phenols and guaiacols. Therefore, ECH of a binary mixture containing a phenolic compound (4-propylphenol) and a heteroaromatic aldehyde (furfural) was investigated in the present study. Reagent-based reduction of the aldehyde group to an alcohol using sodium borohydride prior to ECH suppressed the inhibitory effect of the aldehyde group and improved reactivity of the phenolic compound during ECH. A similar approach involving chemical pre-reduction and ECH was subsequently extended to bio-oil fractions wherein it was observed that reduction of the aldehyde moieties to alcohols enabled conversion of the phenolic compounds present in the bio-oil fractions to cycloalkanols and cycloalkanes.