Chemical characterization and water content determination of bio-oils obtained from various biomass species using ³¹P NMR spectroscopy

Abstract

Background: Pyrolysis is a promising approach to utilize biomass for biofuels. One of the key challenges for this conversion is how to analyze complicated components in the pyrolysis oils. Water contents of pyrolysis oils are normally analyzed by Karl Fischer titration. The use of 2-chloro-4,4,5,5,-tetramethyl-1,3,2-dioxaphospholane followed by ³¹P NMR analysis has been used to quantitatively analyze the structure of hydroxyl groups in lignin and whole biomass. Results:³¹P NMR analysis of pyrolysis oils is a novel technique to simultaneously characterize components and analyze water contents in pyrolysis oils produced from various biomasses. The water contents of various pyrolysis oils range from 16 to 40 wt%. The pyrolysis oils obtained from Loblolly pine had higher guaiacyl content, while that from oak had a higher syringyl content. Conclusion: The comparison with Karl Fischer titration shows that ³¹P NMR could also reliably be used to measure the water content of pyrolysis oils. Simultaneously with analysis of water content, quantitative characterization of hydroxyl groups, including aliphatic, C-5 substituted/syringyl, guaiacyl, p-hydroxyl phenyl and carboxylic hydroxyl groups, could also be provided by ³¹P NMR analysis.

Financial & competing interests disclosure

Financial assistance from the Chevron Corp. to conduct this study is greatly appreciated and acknowledged. Part of this work was also supported by the US DoE under Contract No. DE-AC36–08-GO28308 with the National Renewable Energy Laboratory. The authors have no other relevant affiliations or financial involvement with any organization or entity with a financial interest in or financial conflict with the subject matter or materials discussed in the manuscript apart from those disclosed.

No writing assistance was utilized in the production of this manuscript.