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

摘要

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 (H-1 NMR), comprehensive two-dimensional gas chromatography with time-of-flight mass spectrometry (GC x 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 H-1 NMR and GC x 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 x 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 ESIH-FT-ICR MS, the oxygen-containing compounds determined in bio-oil samples were from O-2-O-12 classes, with the O-4 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 (>O-5 classes), and consequently, the increase of lower oxygen atom number classes (O-2-O-4). The integrated results from these three high-resolution techniques were important to comprehensively assess the molecular composition of bio-oils. The H-1 NMR provided the whole bio-oils composition profile assessment; GC x GC-TOFMS and ESI(-)-FT-ICR MS results allowed a detailed speciation of the chemical composition of bio-oils. (C) 2015 Elsevier B.V. All rights reserved.