Characterization of thermal and catalytic pyrolysis bio-oils by high-resolution techniques: 1H NMR, GC × GC-TOFMS and FT-ICR MS

Abstract

Bio-oils of pine wood and sugarcane bagasse were obtained in different conditions of thermal and catalytic pyrolysis. They were analyzed by hydrogen nuclear magnetic resonance (1H NMR), comprehensive two-dimensional gas chromatography with time-of-flight mass spectrometry (GC×GC-TOFMS), and negative-ion electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (ESI(−)-FT-ICR MS) to provide a complementary and comprehensive characterization of the bio-oils. The elucidation of bio-oils composition is essential to assign the best application of bio-oils and the type of process required for upgrading methods. In general, the results obtained by 1H NMR and GC×GC-TOFMS showed a decrease of oxygen compounds (especially acids) and an increase of aromatic compounds when catalytic pyrolysis was used. The compound classes identified in each sample by GC×GC-TOFMS were acids, ketones, cyclic ketones, phenols, O-heterocyclic, and aromatic hydrocarbons. ESI(−)-FT-ICR MS provides relative signals and the bio-oil compounds containing hydroxyl or carboxylic acid groups, such as carboxylic acids and phenols, are selectively ionized. Via ESI(−)-FT-ICR MS, the oxygen-containing compounds determined in bio-oil samples were from O2–O12 classes, with the O4 being the major class. ESI(−)-FT-ICR MS results suggest that use of the ZSM-5 catalyst provides a decrease in the class abundance of higher oxygen atom number (>O5 classes), and consequently, the increase of lower oxygen atom number classes (O2–O4). The integrated results from these three high-resolution techniques were important to comprehensively assess the molecular composition of bio-oils. The 1H NMR provided the whole bio-oils composition profile assessment; GC×GC-TOFMS and ESI(−)-FT-ICR MS results allowed a detailed speciation of the chemical composition of bio-oils.