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

Abstract

Copyright © 2019 American Chemical Society. 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.