Comparison of lignocellulosic-based biomass pyrolysis processes by multi-scale molecular characterization

Abstract

Nowadays, biomass is considered one of the key solutions for the energy transition as a renewable energy source. It can be converted by pyrolysis into bio-oil, which can be used for producing biofuels or valuable chemicals. However, bio-oils produced from pyrolysis present high oxygen content and it is necessary to use advanced pyrolysis processes to improve the quality of the bio-oils. In this study, three bio-oils produced by different pyrolysis processes: fast pyrolysis (FP), catalytic fast pyrolysis (CFP), and reactive catalytic fast pyrolysis (RCFP) were analyzed using different analytical techniques. A first bulk analysis was performed using proximate and ultimate analysis and gel permeation chromatography with refractive index and UV detection (GPC-RI and GPCUV), which provided crucial information on the elemental composition and mass distribution of the bio-oil components. A deeper investigation at the molecular level was performed using Fourier Transform Ion Cyclotron Resonance Mass Spectrometry (FTICR MS) and High-Performance Thin Layer Chromatography (HPTLC) to determine detailed molecular classification of the bio-oil components. Finally, a fractionation method using flash chromatography (FC) was used to provide a more accurate chemical description. The obtained fractions were analyzed by two-dimensional "comprehensive" gas chromatography (GCxGC) coupled with mass spectrometry (MS) and flame ionization detector (FID), HPTLC, and FTICR MS. The results show that the bio-oils produced from FP and CFP are very similar chemically spoken. The bio-oil from RCFP has less oxygenated products and more unsaturated hydrocarbon species. Therefore, RCFP process was found to be the best process for producing oils with a low O/C ratio.