Characterization of crude and ethanol-stabilized bio-oils before and after accelerated aging treatment by comprehensive two-dimensional gas-chromatography with time-of-flight mass spectrometry

To explain how ethanol additive improves storage stability of pyrolysis bio-oil, comprehensive two-dimensional gas-chromatography with time-of-flight mass spectrometry (GC x GC-TOFMS) was applied on crude and ethanol-stabilized bio-oils before and after accelerated aging treatment for qualitative and quantitative analysis. About 2728, 2212, 2674, and 2781 peaks were identified in crude bio-oil before aging (CBA), crude bio-oil after aging (CAA), ethanol-stabilized bio-oil before aging (ESBA), and ethanol-stabilized bio-oil after aging (ESAA), respectively, which indicated that the addition of ethanol and accelerated aging treatment could both slightly change chemical composition of bio-oils. Many kinds of chemical compounds including acids, alcohols, aldehydes, esters, ethers, furans, furanones, ketones, phenols, aromatics, sugars, etc. were detected by GC x GC-TOFMS. For ethanol-stabilized bio-oil, total relative content and number of compounds were 50.78% +/- 0.33% and 313 +/- 8, respectively, after aging treatment while those values were 54.21% +/- 0.39% and 363 +/- 3, respectively, before aging treatment. On one hand, the reduced number of compounds after aging treatment may attribute to substantial organic chemical reactions, especially polymerization reactions, which could consume small molecular substances and generate macromolecular substances. Another reason for reduced number of compounds may be that some chemicals could undergo cracking and become gases. Analysis of two-dimensional plots for each classification group of compounds in bio-oils indicated that ethanol addition and accelerated aging treatment could both change chemical components of bio-oils to some extent. Specifically, adding ethanol into bio-oil could lead to slight decrease of aldehydes, which because of aldol reactions. Also, during accelerated aging period, many significant substances were changed such as decrease of acids, ketones, aldehydes, phenols, etc., and increase of some esters and aromatics, etc. This study may provide some technical guidance for further study on stable storage and industrial application of bio-oil. (C) 2016 Energy Institute. Published by Elsevier Ltd. All rights reserved.