Oxygen speciation in upgraded fast pyrolysis bio-oils by comprehensive two-dimensional gas chromatography

Abstract

Biomass fast pyrolysis is considered as a promising route to produce liquid for the transportation field from a renewable resource. However, the derived bio-oils are mainly oxygenated (45-50%w/w O on a wet basis) and contain almost no hydrocarbons. Therefore, upgrading is necessary to obtain a liquid with lower oxygen content and characterization of oxygenated compounds in these products is essential to assist conversion reactions. For this purpose, comprehensive two-dimensional gas chromatography (GC × GC) can be investigated. Oxygen speciation in such matrices is hampered by the large diversity of oxygenated families and the complexity of the hydrocarbon matrix. Moreover, response factors must be taken into account for oxygenate quantification as the Flame Ionisation Detector (FID) response varies when a molecule contains heteroatoms. To conclude, no distillation cuts were accessible and the analysis had to cover a large range of boiling points (30-630 °C). To take up this analytical challenge, a thorough optimization approach was developed. In fact, four GC × GC column sets were investigated to separate oxygenated compounds from the hydrocarbon matrix. Both model mixtures and the upgraded biomass flash pyrolysis oil were injected using GC × GC-FID to reach a suitable chromatographic separation. The advantages and drawbacks of each column combination for oxygen speciation in upgraded bio-oils are highlighted in this study. Among the four sets, an original polar × semi-polar column combination was selected and enabled the identification by GC × GC-ToF/MS of more than 40 compounds belonging to eight chemical families: ketones, furans, alcohols, phenols, carboxylic acids, guaiacols, anisols, and esters. For quantification purpose, the GC × GC-FID chromatogram was divided into more than 60 blobs corresponding to the previously identified analyte and hydrocarbon zones. A database associating each blob to a molecule and its specific response factor (determined by standards injection at different concentrations) was created. A detailed molecular quantification by GC × GC-FID was therefore accessible after integration of the corrected normalized areas. This paper aims to present a detail level in terms of characterization of oxygenated compounds in upgraded bio-oils which to our knowledge has never been reached so far. It is based on an original column set selection and an extremely accurate quantification procedure.

A simple procedure for chromatographic analysis of bio-oils from pyrolysis

“…However simple GC analysis usually do not allow to identify and quantify more than 50% of the products present due to lack of chromatographic resolution and availability of compounds in MS libraries [19]. Analyses are improved using multidimensional GC (GC × GC methods) which increases the overall chromatographic resolution [20][21][22][23]. Nevertheless these methods required higher investment in the instrumentations than simple GC systems [19].…”

Two-Dimensional Gas Chromatography Characterization of Pyrolysis Bio-oils: A Review

“… a Links to references: , , , , , , , , , , , , , , , , , , , , , − , − , , , − , , , , , , , , , , , , , , , , , , , , , and . …”

“…Omais et al performed a characterization of O-compounds in HBOs using GC × GC-TOF-MS and GC × GC-FID. A total of four column combinations (normal- and reversed-phase) were tested for the separation of HBOs and model compound mixtures; see Table .…”

“…The best separation of oxygenates and hydrocarbons was achieved by using 100% PEG and 50% phenyl–50% PSPS columns. However, the weak thermal resistance (temperature limit of 280 °C) of the Solgelwax (100% PEG) polar column resulted in the stationary phase bleeding at higher temperatures …”

A Simple Protocol for Quantitative Analysis of Bio-Oils through Gas-Chromatography/Mass Spectrometry

“…Separation and identification of components may be improved using multidimensional GC (GC × GC methods) which improve the overall chromatographic resolution, [30][31][32][33][34] but this method requires higher investment cost for instru-mentation than simple GC systems 29 and does not afford quantitative data.…”