Evolution of Aromatic Structures during the Low-Temperature Electrochemical Upgrading of Bio-oil

The electrochemical upgrading of bio-oil is a potential renewable approach toward generating liquid biofuels or industrial chemicals under mild reaction conditions (≤80 °C and ambient pressure). The aromatic structural evolution in bio-oil is a key consideration in bio-oil application. In this study, a bio-oil sample produced from the fast pyrolysis of rice husk at 500 °C and its lignin-derived oligomers were electrolyzed in an electrolytic cell with platinum electrodes. The samples at discrete time intervals were extracted and analyzed using ultraviolet fluorescence spectroscopy, gas chromatography–mass spectrometry, and Fourier transform ion cyclotron resonance–mass spectrometry (FT-ICR MS). Results showed that aromatic compounds with one and two benzene rings decreased with a prolonged processing time. The unsaturated aromatic compounds were hydrogenated and converted into saturated compounds. Species with more than two aromatic rings were the main compounds detected by FT-ICR MS. The lignin-derived oligomers contained the most phenolic compounds with more than two aromatic rings of the bio-oil. However, the evolution of these phenolic compounds showed different trends between the electrolysis of bio-oil and the lignin-derived oligomer fraction. This phenomenon was attributed to the presence of the light components derived from cellulose/hemicellulose species in the bio-oil. These species were reactive and able to produce radicals that enhanced the hydrogenation reactions. Accordingly, interactions among bio-oil compounds occurred during electrochemical treatment.